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GNAT User’s Guide
GNAT, The GNU Ada Compiler
GCC version 4.8.3
AdaCore
Next: Getting Started with GNAT, Up: Top [Contents][Index]
This guide describes the use of GNAT, a compiler and software development toolset for the full Ada programming language. It documents the features of the compiler and tools, and explains how to use them to build Ada applications.
GNAT implements Ada 95 and Ada 2005, and it may also be invoked in Ada 83 compatibility mode. By default, GNAT assumes Ada 2005, but you can override with a compiler switch (see Compiling Different Versions of Ada) to explicitly specify the language version. Throughout this manual, references to “Ada” without a year suffix apply to both the Ada 95 and Ada 2005 versions of the language.
| • What This Guide Contains: | ||
| • What You Should Know before Reading This Guide: | ||
| • Related Information: | ||
| • Conventions: |
Next: What You Should Know before Reading This Guide, Previous: Index, Up: About This Guide [Contents][Index]
This guide contains the following chapters:
gcc, the Ada compiler.
gnatbind, the GNAT binding
utility.
gnatlink, a
program that provides for linking using the GNAT run-time library to
construct a program. gnatlink can also incorporate foreign language
object units into the executable.
gnatmake, a
utility that automatically determines the set of sources
needed by an Ada compilation unit, and executes the necessary compilations
binding and link.
gnatelim tool and unused subprogram/data
elimination.
gnatchop, a utility that allows you to preprocess a file that
contains Ada source code, and split it into one or more new files, one
for each compilation unit.
gnatxref and gnatfind, two tools that provide an easy
way to navigate through sources.
gnatkr
file name krunching utility, used to handle shortened
file names on operating systems with a limit on the length of names.
gnatprep, a
preprocessor utility that allows a single source file to be used to
generate multiple or parameterized source files by means of macro
substitution.
gnatls, a
utility that displays information about compiled units, including dependences
on the corresponding sources files, and consistency of compilations.
gnatclean, a utility
to delete files that are produced by the compiler, binder and linker.
gnatmem, a utility that monitors dynamic
allocation and deallocation and helps detect “memory leaks”.
gnatcheck,
a utility that checks Ada code against a set of rules.
gnatstub,
a utility that generates empty but compilable bodies for library units.
gnattest,
a utility that generates unit testing templates for library units.
gnathtml.
Next: Related Information, Previous: What This Guide Contains, Up: About This Guide [Contents][Index]
This guide assumes a basic familiarity with the Ada 95 language, as described in the International Standard ANSI/ISO/IEC-8652:1995, January 1995. It does not require knowledge of the new features introduced by Ada 2005, (officially known as ISO/IEC 8652:1995 with Technical Corrigendum 1 and Amendment 1). Both reference manuals are included in the GNAT documentation package.
Next: Conventions, Previous: What You Should Know before Reading This Guide, Up: About This Guide [Contents][Index]
For further information about related tools, refer to the following documents:
Next: Running GNAT, Previous: Related Information, Up: About This Guide [Contents][Index]
Following are examples of the typographical and graphic conventions used in this guide:
Functions, utility program names, standard names,
and classes.
Variables, environment variables, and metasyntactic
variables.
and then shown this way.
Commands that are entered by the user are preceded in this manual by the
characters “$ ” (dollar sign followed by space). If your system
uses this sequence as a prompt, then the commands will appear exactly as
you see them in the manual. If your system uses some other prompt, then
the command will appear with the $ replaced by whatever prompt
character you are using.
Full file names are shown with the “/” character
as the directory separator; e.g., parent-dir/subdir/myfile.adb.
If you are using GNAT on a Windows platform, please note that
the “\” character should be used instead.
Next: The GNAT Compilation Model, Previous: About This Guide, Up: Top [Contents][Index]
This chapter describes some simple ways of using GNAT to build executable Ada programs. Running GNAT, through Using the gnatmake Utility, show how to use the command line environment. Introduction to GPS, provides a brief introduction to the GNAT Programming Studio, a visually-oriented Integrated Development Environment for GNAT. GPS offers a graphical “look and feel”, support for development in other programming languages, comprehensive browsing features, and many other capabilities. For information on GPS please refer to Using the GNAT Programming Studio.
| • Running GNAT: | ||
| • Running a Simple Ada Program: | ||
| • Running a Program with Multiple Units: | ||
| • Using the gnatmake Utility: | ||
| • Introduction to GPS: |
Next: Running a Simple Ada Program, Previous: Conventions, Up: Getting Started with GNAT [Contents][Index]
Three steps are needed to create an executable file from an Ada source file:
All three steps are most commonly handled by using the gnatmake
utility program that, given the name of the main program, automatically
performs the necessary compilation, binding and linking steps.
Next: Running a Program with Multiple Units, Previous: Running GNAT, Up: Getting Started with GNAT [Contents][Index]
Any text editor may be used to prepare an Ada program.
(If Emacs is
used, the optional Ada mode may be helpful in laying out the program.)
The
program text is a normal text file. We will assume in our initial
example that you have used your editor to prepare the following
standard format text file:
with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
Put_Line ("Hello WORLD!");
end Hello;
|
This file should be named hello.adb.
With the normal default file naming conventions, GNAT requires
that each file
contain a single compilation unit whose file name is the
unit name,
with periods replaced by hyphens; the
extension is ads for a
spec and adb for a body.
You can override this default file naming convention by use of the
special pragma Source_File_Name (see Using Other File Names).
Alternatively, if you want to rename your files according to this default
convention, which is probably more convenient if you will be using GNAT
for all your compilations, then the gnatchop utility
can be used to generate correctly-named source files
(see Renaming Files Using gnatchop).
You can compile the program using the following command ($ is used
as the command prompt in the examples in this document):
$ gcc -c hello.adb
gcc is the command used to run the compiler. This compiler is
capable of compiling programs in several languages, including Ada and
C. It assumes that you have given it an Ada program if the file extension is
either .ads or .adb, and it will then call
the GNAT compiler to compile the specified file.
The -c switch is required. It tells gcc to only do a
compilation. (For C programs, gcc can also do linking, but this
capability is not used directly for Ada programs, so the -c
switch must always be present.)
This compile command generates a file
hello.o, which is the object
file corresponding to your Ada program. It also generates
an “Ada Library Information” file hello.ali,
which contains additional information used to check
that an Ada program is consistent.
To build an executable file,
use gnatbind to bind the program
and gnatlink to link it. The
argument to both gnatbind and gnatlink is the name of the
ALI file, but the default extension of .ali can
be omitted. This means that in the most common case, the argument
is simply the name of the main program:
$ gnatbind hello $ gnatlink hello
A simpler method of carrying out these steps is to use
gnatmake,
a master program that invokes all the required
compilation, binding and linking tools in the correct order. In particular,
gnatmake automatically recompiles any sources that have been
modified since they were last compiled, or sources that depend
on such modified sources, so that “version skew” is avoided.
$ gnatmake hello.adb
The result is an executable program called hello, which can be run by entering:
$ hello
assuming that the current directory is on the search path for executable programs.
and, if all has gone well, you will see
Hello WORLD!
appear in response to this command.
Next: Using the gnatmake Utility, Previous: Running a Simple Ada Program, Up: Getting Started with GNAT [Contents][Index]
Consider a slightly more complicated example that has three files: a main program, and the spec and body of a package:
package Greetings is
procedure Hello;
procedure Goodbye;
end Greetings;
with Ada.Text_IO; use Ada.Text_IO;
package body Greetings is
procedure Hello is
begin
Put_Line ("Hello WORLD!");
end Hello;
procedure Goodbye is
begin
Put_Line ("Goodbye WORLD!");
end Goodbye;
end Greetings;
with Greetings; procedure Gmain is begin Greetings.Hello; Greetings.Goodbye; end Gmain; |
Following the one-unit-per-file rule, place this program in the following three separate files:
spec of package Greetings
body of package Greetings
body of main program
To build an executable version of this program, we could use four separate steps to compile, bind, and link the program, as follows:
$ gcc -c gmain.adb $ gcc -c greetings.adb $ gnatbind gmain $ gnatlink gmain
Note that there is no required order of compilation when using GNAT. In particular it is perfectly fine to compile the main program first. Also, it is not necessary to compile package specs in the case where there is an accompanying body; you only need to compile the body. If you want to submit these files to the compiler for semantic checking and not code generation, then use the -gnatc switch:
$ gcc -c greetings.ads -gnatc
Although the compilation can be done in separate steps as in the
above example, in practice it is almost always more convenient
to use the gnatmake tool. All you need to know in this case
is the name of the main program’s source file. The effect of the above four
commands can be achieved with a single one:
$ gnatmake gmain.adb
In the next section we discuss the advantages of using gnatmake in
more detail.
Next: Introduction to GPS, Previous: Running a Program with Multiple Units, Up: Getting Started with GNAT [Contents][Index]
gnatmake UtilityIf you work on a program by compiling single components at a time using
gcc, you typically keep track of the units you modify. In order to
build a consistent system, you compile not only these units, but also any
units that depend on the units you have modified.
For example, in the preceding case,
if you edit gmain.adb, you only need to recompile that file. But if
you edit greetings.ads, you must recompile both
greetings.adb and gmain.adb, because both files contain
units that depend on greetings.ads.
gnatbind will warn you if you forget one of these compilation
steps, so that it is impossible to generate an inconsistent program as a
result of forgetting to do a compilation. Nevertheless it is tedious and
error-prone to keep track of dependencies among units.
One approach to handle the dependency-bookkeeping is to use a
makefile. However, makefiles present maintenance problems of their own:
if the dependencies change as you change the program, you must make
sure that the makefile is kept up-to-date manually, which is also an
error-prone process.
The gnatmake utility takes care of these details automatically.
Invoke it using either one of the following forms:
$ gnatmake gmain.adb $ gnatmake gmain
The argument is the name of the file containing the main program;
you may omit the extension. gnatmake
examines the environment, automatically recompiles any files that need
recompiling, and binds and links the resulting set of object files,
generating the executable file, gmain.
In a large program, it
can be extremely helpful to use gnatmake, because working out by hand
what needs to be recompiled can be difficult.
Note that gnatmake
takes into account all the Ada rules that
establish dependencies among units. These include dependencies that result
from inlining subprogram bodies, and from
generic instantiation. Unlike some other
Ada make tools, gnatmake does not rely on the dependencies that were
found by the compiler on a previous compilation, which may possibly
be wrong when sources change. gnatmake determines the exact set of
dependencies from scratch each time it is run.
Next: Source Representation, Previous: Using the gnatmake Utility, Up: Getting Started with GNAT [Contents][Index]
Although the command line interface (gnatmake, etc.) alone
is sufficient, a graphical Interactive Development
Environment can make it easier for you to compose, navigate, and debug
programs. This section describes the main features of GPS
(“GNAT Programming Studio”), the GNAT graphical IDE.
You will see how to use GPS to build and debug an executable, and
you will also learn some of the basics of the GNAT “project” facility.
GPS enables you to do much more than is presented here; e.g., you can produce a call graph, interface to a third-party Version Control System, and inspect the generated assembly language for a program. Indeed, GPS also supports languages other than Ada. Such additional information, and an explanation of all of the GPS menu items. may be found in the on-line help, which includes a user’s guide and a tutorial (these are also accessible from the GNAT startup menu).
| • Building a New Program with GPS: | ||
| • Simple Debugging with GPS: |
Next: Simple Debugging with GPS, Up: Introduction to GPS [Contents][Index]
GPS invokes the GNAT compilation tools using information contained in a project (also known as a project file): a collection of properties such as source directories, identities of main subprograms, tool switches, etc., and their associated values. See GNAT Project Manager for details. In order to run GPS, you will need to either create a new project or else open an existing one.
This section will explain how you can use GPS to create a project, to associate Ada source files with a project, and to build and run programs.
Invoke GPS, either from the command line or the platform’s IDE. After it starts, GPS will display a “Welcome” screen with three radio buttons:
Start with default project in directory
Create new project with wizard
Open existing project
Select Create new project with wizard and press OK.
A new window will appear. In the text box labeled with
Enter the name of the project to create, type sample
as the project name.
In the next box, browse to choose the directory in which you
would like to create the project file.
After selecting an appropriate directory, press Forward.
A window will appear with the title
Version Control System Configuration.
Simply press Forward.
A window will appear with the title
Please select the source directories for this project.
The directory that you specified for the project file will be selected
by default as the one to use for sources; simply press Forward.
A window will appear with the title
Please select the build directory for this project.
The directory that you specified for the project file will be selected
by default for object files and executables;
simply press Forward.
A window will appear with the title
Please select the main units for this project.
You will supply this information later, after creating the source file.
Simply press Forward for now.
A window will appear with the title
Please select the switches to build the project.
Press Apply. This will create a project file named
sample.prj in the directory that you had specified.
After you create the new project, a GPS window will appear, which is partitioned into two main sections:
Select File on the menu bar, and then the New command.
The Workspace area will become white, and you can now
enter the source program explicitly.
Type the following text
with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
Put_Line("Hello from GPS!");
end Hello;
Select File, then Save As, and enter the source file name
hello.adb.
The file will be saved in the same directory you specified as the
location of the default project file.
You need to add the new source file to the project.
To do this, select
the Project menu and then Edit project properties.
Click the Main files tab on the left, and then the
Add button.
Choose hello.adb from the list, and press Open.
The project settings window will reflect this action.
Click OK.
In the main GPS window, now choose the Build menu, then Make,
and select hello.adb.
The Messages window will display the resulting invocations of gcc,
gnatbind, and gnatlink
(reflecting the default switch settings from the
project file that you created) and then a “successful compilation/build”
message.
To run the program, choose the Build menu, then Run, and
select hello.
An Arguments Selection window will appear.
There are no command line arguments, so just click OK.
The Messages window will now display the program’s output (the string
Hello from GPS), and at the bottom of the GPS window a status
update is displayed (Run: hello).
Close the GPS window (or select File, then Exit) to
terminate this GPS session.
Previous: Building a New Program with GPS, Up: Introduction to GPS [Contents][Index]
This section illustrates basic debugging techniques (setting breakpoints, examining/modifying variables, single stepping).
Start GPS and select Open existing project; browse to
specify the project file sample.prj that you had created in the
earlier example.
Select File, then New, and type in the following program:
with Ada.Text_IO; use Ada.Text_IO;
procedure Example is
Line : String (1..80);
N : Natural;
begin
Put_Line("Type a line of text at each prompt; an empty line to exit");
loop
Put(": ");
Get_Line (Line, N);
Put_Line (Line (1..N) );
exit when N=0;
end loop;
end Example;
Select File, then Save as, and enter the file name
example.adb.
Add Example as a new main unit for the project:
Project, then Edit Project Properties.
Main files tab, click Add, then
select the file example.adb from the list, and
click Open.
You will see the file name appear in the list of main units
OK
To build the executable
select Build, then Make, and then choose example.adb.
Run the program to see its effect (in the Messages area). Each line that you enter is displayed; an empty line will cause the loop to exit and the program to terminate.
Note that the -g switches to gcc and gnatlink,
which are required for debugging, are on by default when you create
a new project.
Thus unless you intentionally remove these settings, you will be able
to debug any program that you develop using GPS.
Select Debug, then Initialize, then example
After performing the initialization step, you will observe a small icon to the right of each line number. This serves as a toggle for breakpoints; clicking the icon will set a breakpoint at the corresponding line (the icon will change to a red circle with an “x”), and clicking it again will remove the breakpoint / reset the icon.
For purposes of this example, set a breakpoint at line 10 (the
statement Put_Line (Line (1..N));
Select Debug, then Run. When the
Program Arguments window appears, click OK.
A console window will appear; enter some line of text,
e.g. abcde, at the prompt.
The program will pause execution when it gets to the
breakpoint, and the corresponding line is highlighted.
Move the mouse over one of the occurrences of the variable N.
You will see the value (5) displayed, in “tool tip” fashion.
Right click on N, select Debug, then select Display N.
You will see information about N appear in the Debugger Data
pane, showing the value as 5.
Right click on the N in the Debugger Data pane, and
select Set value of N.
When the input window appears, enter the value 4 and click
OK.
This value does not automatically appear in the Debugger Data
pane; to see it, right click again on the N in the
Debugger Data pane and select Update value.
The new value, 4, will appear in red.
Select Debug, then Next.
This will cause the next statement to be executed, in this case the
call of Put_Line with the string slice.
Notice in the console window that the displayed string is simply
abcd and not abcde which you had entered.
This is because the upper bound of the slice is now 4 rather than 5.
Toggle the breakpoint icon at line 10.
Select Debug, then Continue.
The program will reach the next iteration of the loop, and
wait for input after displaying the prompt.
This time, just hit the Enter key.
The value of N will be 0, and the program will terminate.
The console window will disappear.
Next: Compiling Using gcc, Previous: Getting Started with GNAT, Up: Top [Contents][Index]
This chapter describes the compilation model used by GNAT. Although similar to that used by other languages, such as C and C++, this model is substantially different from the traditional Ada compilation models, which are based on a library. The model is initially described without reference to the library-based model. If you have not previously used an Ada compiler, you need only read the first part of this chapter. The last section describes and discusses the differences between the GNAT model and the traditional Ada compiler models. If you have used other Ada compilers, this section will help you to understand those differences, and the advantages of the GNAT model.
Next: Foreign Language Representation, Previous: Introduction to GPS, Up: The GNAT Compilation Model [Contents][Index]
Ada source programs are represented in standard text files, using Latin-1 coding. Latin-1 is an 8-bit code that includes the familiar 7-bit ASCII set, plus additional characters used for representing foreign languages (see Foreign Language Representation for support of non-USA character sets). The format effector characters are represented using their standard ASCII encodings, as follows:
VTVertical tab, 16#0B#
HTHorizontal tab, 16#09#
CRCarriage return, 16#0D#
LFLine feed, 16#0A#
FFForm feed, 16#0C#
Source files are in standard text file format. In addition, GNAT will
recognize a wide variety of stream formats, in which the end of
physical lines is marked by any of the following sequences:
LF, CR, CR-LF, or LF-CR. This is useful
in accommodating files that are imported from other operating systems.
The end of a source file is normally represented by the physical end of
file. However, the control character 16#1A# (SUB) is also
recognized as signalling the end of the source file. Again, this is
provided for compatibility with other operating systems where this
code is used to represent the end of file.
Each file contains a single Ada compilation unit, including any pragmas associated with the unit. For example, this means you must place a package declaration (a package spec) and the corresponding body in separate files. An Ada compilation (which is a sequence of compilation units) is represented using a sequence of files. Similarly, you will place each subunit or child unit in a separate file.
Next: File Naming Rules, Previous: Source Representation, Up: The GNAT Compilation Model [Contents][Index]
GNAT supports the standard character sets defined in Ada as well as several other non-standard character sets for use in localized versions of the compiler (see Character Set Control).
| • Latin-1: | ||
| • Other 8-Bit Codes: | ||
| • Wide Character Encodings: |
Next: Other 8-Bit Codes, Previous: Comparison between GNAT and Conventional Ada Library Models, Up: Foreign Language Representation [Contents][Index]
The basic character set is Latin-1. This character set is defined by ISO
standard 8859, part 1. The lower half (character codes 16#00#
… 16#7F#) is identical to standard ASCII coding, but the upper
half is used to represent additional characters. These include extended letters
used by European languages, such as French accents, the vowels with umlauts
used in German, and the extra letter A-ring used in Swedish.
For a complete list of Latin-1 codes and their encodings, see the source
file of library unit Ada.Characters.Latin_1 in file
a-chlat1.ads.
You may use any of these extended characters freely in character or
string literals. In addition, the extended characters that represent
letters can be used in identifiers.
Next: Wide Character Encodings, Previous: Latin-1, Up: Foreign Language Representation [Contents][Index]
GNAT also supports several other 8-bit coding schemes:
Latin-2 letters allowed in identifiers, with uppercase and lowercase equivalence.
Latin-3 letters allowed in identifiers, with uppercase and lowercase equivalence.
Latin-4 letters allowed in identifiers, with uppercase and lowercase equivalence.
ISO 8859-5 letters (Cyrillic) allowed in identifiers, with uppercase and lowercase equivalence.
ISO 8859-15 (Latin-9) letters allowed in identifiers, with uppercase and lowercase equivalence
This code page is the normal default for PCs in the U.S. It corresponds to the original IBM PC character set. This set has some, but not all, of the extended Latin-1 letters, but these letters do not have the same encoding as Latin-1. In this mode, these letters are allowed in identifiers with uppercase and lowercase equivalence.
This code page is a modification of 437 extended to include all the Latin-1 letters, but still not with the usual Latin-1 encoding. In this mode, all these letters are allowed in identifiers with uppercase and lowercase equivalence.
Any character in the range 80-FF allowed in identifiers, and all are considered distinct. In other words, there are no uppercase and lowercase equivalences in this range. This is useful in conjunction with certain encoding schemes used for some foreign character sets (e.g., the typical method of representing Chinese characters on the PC).
No upper-half characters in the range 80-FF are allowed in identifiers. This gives Ada 83 compatibility for identifier names.
For precise data on the encodings permitted, and the uppercase and lowercase equivalences that are recognized, see the file csets.adb in the GNAT compiler sources. You will need to obtain a full source release of GNAT to obtain this file.
Next: Compiling Programs, Previous: Other 8-Bit Codes, Up: Foreign Language Representation [Contents][Index]
GNAT allows wide character codes to appear in character and string literals, and also optionally in identifiers, by means of the following possible encoding schemes:
In this encoding, a wide character is represented by the following five character sequence:
ESC a b c d
Where a, b, c, d are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ESC A345 is used to represent the wide character with code
16#A345#.
This scheme is compatible with use of the full Wide_Character set.
The wide character with encoding 16#abcd# where the upper bit is on
(in other words, “a” is in the range 8-F) is represented as two bytes,
16#ab# and 16#cd#. The second byte cannot be a format control
character, but is not required to be in the upper half. This method can
be also used for shift-JIS or EUC, where the internal coding matches the
external coding.
A wide character is represented by a two-character sequence,
16#ab# and
16#cd#, with the restrictions described for upper-half encoding as
described above. The internal character code is the corresponding JIS
character according to the standard algorithm for Shift-JIS
conversion. Only characters defined in the JIS code set table can be
used with this encoding method.
A wide character is represented by a two-character sequence
16#ab# and
16#cd#, with both characters being in the upper half. The internal
character code is the corresponding JIS character according to the EUC
encoding algorithm. Only characters defined in the JIS code set table
can be used with this encoding method.
A wide character is represented using UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO 10646-1/Am.2. Depending on the character value, the representation is a one, two, or three byte sequence:
16#0000#-16#007f#: 2#0xxxxxxx# 16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx# 16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
where the xxx bits correspond to the left-padded bits of the 16-bit character value. Note that all lower half ASCII characters are represented as ASCII bytes and all upper half characters and other wide characters are represented as sequences of upper-half (The full UTF-8 scheme allows for encoding 31-bit characters as 6-byte sequences, but in this implementation, all UTF-8 sequences of four or more bytes length will be treated as illegal).
In this encoding, a wide character is represented by the following eight character sequence:
[ " a b c d " ]
Where a, b, c, d are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, [“A345”] is used to represent the wide character with code
16#A345#. It is also possible (though not required) to use the
Brackets coding for upper half characters. For example, the code
16#A3# can be represented as [``A3''].
This scheme is compatible with use of the full Wide_Character set, and is also the method used for wide character encoding in the standard ACVC (Ada Compiler Validation Capability) test suite distributions.
Note: Some of these coding schemes do not permit the full use of the Ada character set. For example, neither Shift JIS, nor EUC allow the use of the upper half of the Latin-1 set.
Next: Using Other File Names, Previous: Foreign Language Representation, Up: The GNAT Compilation Model [Contents][Index]
The default file name is determined by the name of the unit that the file contains. The name is formed by taking the full expanded name of the unit and replacing the separating dots with hyphens and using lowercase for all letters.
An exception arises if the file name generated by the above rules starts with one of the characters ‘a’, ‘g’, ‘i’, or ‘s’, and the second character is a minus. In this case, the character tilde is used in place of the minus. The reason for this special rule is to avoid clashes with the standard names for child units of the packages System, Ada, Interfaces, and GNAT, which use the prefixes ‘s-’, ‘a-’, ‘i-’, and ‘g-’, respectively.
The file extension is .ads for a spec and .adb for a body. The following list shows some examples of these rules.
Main (spec)
Main (body)
Arith_Functions (package spec)
Arith_Functions (package body)
Func.Spec (child package spec)
Func.Spec (child package body)
Sub (subunit of Main)
A.Bad (child package body)
Following these rules can result in excessively long file names if corresponding unit names are long (for example, if child units or subunits are heavily nested). An option is available to shorten such long file names (called file name “krunching”). This may be particularly useful when programs being developed with GNAT are to be used on operating systems with limited file name lengths. See Using gnatkr.
Of course, no file shortening algorithm can guarantee uniqueness over all possible unit names; if file name krunching is used, it is your responsibility to ensure no name clashes occur. Alternatively you can specify the exact file names that you want used, as described in the next section. Finally, if your Ada programs are migrating from a compiler with a different naming convention, you can use the gnatchop utility to produce source files that follow the GNAT naming conventions. (For details see Renaming Files Using gnatchop.)
Note: in the case of Windows NT/XP or OpenVMS operating
systems, case is not significant. So for example on Windows XP
if the canonical name is main-sub.adb, you can use the file name
Main-Sub.adb instead. However, case is significant for other
operating systems, so for example, if you want to use other than
canonically cased file names on a Unix system, you need to follow
the procedures described in the next section.
Next: Alternative File Naming Schemes, Previous: File Naming Rules, Up: The GNAT Compilation Model [Contents][Index]
In the previous section, we have described the default rules used by GNAT to determine the file name in which a given unit resides. It is often convenient to follow these default rules, and if you follow them, the compiler knows without being explicitly told where to find all the files it needs.
However, in some cases, particularly when a program is imported from another Ada compiler environment, it may be more convenient for the programmer to specify which file names contain which units. GNAT allows arbitrary file names to be used by means of the Source_File_Name pragma. The form of this pragma is as shown in the following examples:
pragma Source_File_Name (My_Utilities.Stacks, Spec_File_Name => "myutilst_a.ada"); pragma Source_File_name (My_Utilities.Stacks, Body_File_Name => "myutilst.ada"); |
As shown in this example, the first argument for the pragma is the unit name (in this example a child unit). The second argument has the form of a named association. The identifier indicates whether the file name is for a spec or a body; the file name itself is given by a string literal.
The source file name pragma is a configuration pragma, which means that normally it will be placed in the gnat.adc file used to hold configuration pragmas that apply to a complete compilation environment. For more details on how the gnat.adc file is created and used see Handling of Configuration Pragmas.
GNAT allows completely arbitrary file names to be specified using the
source file name pragma. However, if the file name specified has an
extension other than .ads or .adb it is necessary to use
a special syntax when compiling the file. The name in this case must be
preceded by the special sequence -x followed by a space and the name
of the language, here ada, as in:
$ gcc -c -x ada peculiar_file_name.sim
gnatmake handles non-standard file names in the usual manner (the
non-standard file name for the main program is simply used as the
argument to gnatmake). Note that if the extension is also non-standard,
then it must be included in the gnatmake command, it may not
be omitted.
Next: Generating Object Files, Previous: Using Other File Names, Up: The GNAT Compilation Model [Contents][Index]
In the previous section, we described the use of the Source_File_Name
pragma to allow arbitrary names to be assigned to individual source files.
However, this approach requires one pragma for each file, and especially in
large systems can result in very long gnat.adc files, and also create
a maintenance problem.
GNAT also provides a facility for specifying systematic file naming schemes
other than the standard default naming scheme previously described. An
alternative scheme for naming is specified by the use of
Source_File_Name pragmas having the following format:
pragma Source_File_Name ( Spec_File_Name => FILE_NAME_PATTERN [,Casing => CASING_SPEC] [,Dot_Replacement => STRING_LITERAL]); pragma Source_File_Name ( Body_File_Name => FILE_NAME_PATTERN [,Casing => CASING_SPEC] [,Dot_Replacement => STRING_LITERAL]); pragma Source_File_Name ( Subunit_File_Name => FILE_NAME_PATTERN [,Casing => CASING_SPEC] [,Dot_Replacement => STRING_LITERAL]); FILE_NAME_PATTERN ::= STRING_LITERAL CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
The FILE_NAME_PATTERN string shows how the file name is constructed.
It contains a single asterisk character, and the unit name is substituted
systematically for this asterisk. The optional parameter
Casing indicates
whether the unit name is to be all upper-case letters, all lower-case letters,
or mixed-case. If no
Casing parameter is used, then the default is all
lower-case.
The optional Dot_Replacement string is used to replace any periods
that occur in subunit or child unit names. If no Dot_Replacement
argument is used then separating dots appear unchanged in the resulting
file name.
Although the above syntax indicates that the
Casing argument must appear
before the Dot_Replacement argument, but it
is also permissible to write these arguments in the opposite order.
As indicated, it is possible to specify different naming schemes for
bodies, specs, and subunits. Quite often the rule for subunits is the
same as the rule for bodies, in which case, there is no need to give
a separate Subunit_File_Name rule, and in this case the
Body_File_name rule is used for subunits as well.
The separate rule for subunits can also be used to implement the rather unusual case of a compilation environment (e.g. a single directory) which contains a subunit and a child unit with the same unit name. Although both units cannot appear in the same partition, the Ada Reference Manual allows (but does not require) the possibility of the two units coexisting in the same environment.
The file name translation works in the following steps:
Source_File_Name pragma for the given unit,
then this is always used, and any general pattern rules are ignored.
Source_File_Name pragma that applies to
the unit, then the resulting file name will be used if the file exists. If
more than one pattern matches, the latest one will be tried first, and the
first attempt resulting in a reference to a file that exists will be used.
Source_File_Name pragma that applies to the unit
for which the corresponding file exists, then the standard GNAT default
naming rules are used.
As an example of the use of this mechanism, consider a commonly used scheme in which file names are all lower case, with separating periods copied unchanged to the resulting file name, and specs end with .1.ada, and bodies end with .2.ada. GNAT will follow this scheme if the following two pragmas appear:
pragma Source_File_Name (Spec_File_Name => "*.1.ada"); pragma Source_File_Name (Body_File_Name => "*.2.ada");
The default GNAT scheme is actually implemented by providing the following default pragmas internally:
pragma Source_File_Name (Spec_File_Name => "*.ads", Dot_Replacement => "-"); pragma Source_File_Name (Body_File_Name => "*.adb", Dot_Replacement => "-");
Our final example implements a scheme typically used with one of the Ada 83 compilers, where the separator character for subunits was “__” (two underscores), specs were identified by adding _.ADA, bodies by adding .ADA, and subunits by adding .SEP. All file names were upper case. Child units were not present of course since this was an Ada 83 compiler, but it seems reasonable to extend this scheme to use the same double underscore separator for child units.
pragma Source_File_Name (Spec_File_Name => "*_.ADA", Dot_Replacement => "__", Casing = Uppercase); pragma Source_File_Name (Body_File_Name => "*.ADA", Dot_Replacement => "__", Casing = Uppercase); pragma Source_File_Name (Subunit_File_Name => "*.SEP", Dot_Replacement => "__", Casing = Uppercase);
Next: Source Dependencies, Previous: Alternative File Naming Schemes, Up: The GNAT Compilation Model [Contents][Index]
An Ada program consists of a set of source files, and the first step in compiling the program is to generate the corresponding object files. These are generated by compiling a subset of these source files. The files you need to compile are the following:
The preceding rules describe the set of files that must be compiled to generate the object files for a program. Each object file has the same name as the corresponding source file, except that the extension is .o as usual.
You may wish to compile other files for the purpose of checking their syntactic and semantic correctness. For example, in the case where a package has a separate spec and body, you would not normally compile the spec. However, it is convenient in practice to compile the spec to make sure it is error-free before compiling clients of this spec, because such compilations will fail if there is an error in the spec.
GNAT provides an option for compiling such files purely for the purposes of checking correctness; such compilations are not required as part of the process of building a program. To compile a file in this checking mode, use the -gnatc switch.
Next: The Ada Library Information Files, Previous: Generating Object Files, Up: The GNAT Compilation Model [Contents][Index]
A given object file clearly depends on the source file which is compiled
to produce it. Here we are using depends in the sense of a typical
make utility; in other words, an object file depends on a source
file if changes to the source file require the object file to be
recompiled.
In addition to this basic dependency, a given object may depend on
additional source files as follows:
with’s a unit X, the object file
depends on the file containing the spec of unit X. This includes
files that are with’ed implicitly either because they are parents
of with’ed child units or they are run-time units required by the
language constructs used in a particular unit.
Inline applies and inlining is activated with the
-gnatn switch, the object file depends on the file containing the
body of this subprogram as well as on the file containing the spec. Note
that for inlining to actually occur as a result of the use of this switch,
it is necessary to compile in optimizing mode.
The use of -gnatN activates inlining optimization that is performed by the front end of the compiler. This inlining does not require that the code generation be optimized. Like -gnatn, the use of this switch generates additional dependencies.
When using a gcc-based back end (in practice this means using any version of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of -gnatN is deprecated, and the use of -gnatn is preferred. Historically front end inlining was more extensive than the gcc back end inlining, but that is no longer the case.
These rules are applied transitively: if unit A with’s
unit B, whose elaboration calls an inlined procedure in package
C, the object file for unit A will depend on the body of
C, in file c.adb.
The set of dependent files described by these rules includes all the files on which the unit is semantically dependent, as dictated by the Ada language standard. However, it is a superset of what the standard describes, because it includes generic, inline, and subunit dependencies.
An object file must be recreated by recompiling the corresponding source
file if any of the source files on which it depends are modified. For
example, if the make utility is used to control compilation,
the rule for an Ada object file must mention all the source files on
which the object file depends, according to the above definition.
The determination of the necessary
recompilations is done automatically when one uses gnatmake.
Next: Binding an Ada Program, Previous: Source Dependencies, Up: The GNAT Compilation Model [Contents][Index]
Each compilation actually generates two output files. The first of these is the normal object file that has a .o extension. The second is a text file containing full dependency information. It has the same name as the source file, but an .ali extension. This file is known as the Ada Library Information (ALI) file. The following information is contained in the ALI file.
gcc command for the compilation
Pure).
with’ed units, including presence of
Elaborate or Elaborate_All pragmas.
Linker_Options pragmas used in the unit
Body_Version or Version
attributes in the unit.
gnatxref and gnatfind to
provide cross-reference information.
For a full detailed description of the format of the ALI file,
see the source of the body of unit Lib.Writ, contained in file
lib-writ.adb in the GNAT compiler sources.
Next: Mixed Language Programming, Previous: The Ada Library Information Files, Up: The GNAT Compilation Model [Contents][Index]
When using languages such as C and C++, once the source files have been compiled the only remaining step in building an executable program is linking the object modules together. This means that it is possible to link an inconsistent version of a program, in which two units have included different versions of the same header.
The rules of Ada do not permit such an inconsistent program to be built. For example, if two clients have different versions of the same package, it is illegal to build a program containing these two clients. These rules are enforced by the GNAT binder, which also determines an elaboration order consistent with the Ada rules.
The GNAT binder is run after all the object files for a program have been created. It is given the name of the main program unit, and from this it determines the set of units required by the program, by reading the corresponding ALI files. It generates error messages if the program is inconsistent or if no valid order of elaboration exists.
If no errors are detected, the binder produces a main program, in Ada by default, that contains calls to the elaboration procedures of those compilation unit that require them, followed by a call to the main program. This Ada program is compiled to generate the object file for the main program. The name of the Ada file is b~xxx.adb (with the corresponding spec b~xxx.ads) where xxx is the name of the main program unit.
Finally, the linker is used to build the resulting executable program, using the object from the main program from the bind step as well as the object files for the Ada units of the program.
Next: Building Mixed Ada & C++ Programs, Previous: Binding an Ada Program, Up: The GNAT Compilation Model [Contents][Index]
This section describes how to develop a mixed-language program, specifically one that comprises units in both Ada and C.
| • Interfacing to C: | ||
| • Calling Conventions: |
Next: Calling Conventions, Up: Mixed Language Programming [Contents][Index]
Interfacing Ada with a foreign language such as C involves using
compiler directives to import and/or export entity definitions in each
language—using extern statements in C, for instance, and the
Import, Export, and Convention pragmas in Ada.
A full treatment of these topics is provided in Appendix B, section 1
of the Ada Reference Manual.
There are two ways to build a program using GNAT that contains some Ada sources and some foreign language sources, depending on whether or not the main subprogram is written in Ada. Here is a source example with the main subprogram in Ada:
/* file1.c */
#include <stdio.h>
void print_num (int num)
{
printf ("num is %d.\n", num);
return;
}
/* file2.c */
/* num_from_Ada is declared in my_main.adb */
extern int num_from_Ada;
int get_num (void)
{
return num_from_Ada;
}
-- my_main.adb procedure My_Main is -- Declare then export an Integer entity called num_from_Ada My_Num : Integer := 10; pragma Export (C, My_Num, "num_from_Ada"); -- Declare an Ada function spec for Get_Num, then use -- C function get_num for the implementation. function Get_Num return Integer; pragma Import (C, Get_Num, "get_num"); -- Declare an Ada procedure spec for Print_Num, then use -- C function print_num for the implementation. procedure Print_Num (Num : Integer); pragma Import (C, Print_Num, "print_num"); begin Print_Num (Get_Num); end My_Main;
gcc -c file1.c gcc -c file2.c
gnatmake -c my_main.adb
gnatbind my_main.ali
gnatlink my_main.ali file1.o file2.o
The last three steps can be grouped in a single command:
gnatmake my_main.adb -largs file1.o file2.o
If the main program is in a language other than Ada, then you may have more than one entry point into the Ada subsystem. You must use a special binder option to generate callable routines that initialize and finalize the Ada units (see Binding with Non-Ada Main Programs). Calls to the initialization and finalization routines must be inserted in the main program, or some other appropriate point in the code. The call to initialize the Ada units must occur before the first Ada subprogram is called, and the call to finalize the Ada units must occur after the last Ada subprogram returns. The binder will place the initialization and finalization subprograms into the b~xxx.adb file where they can be accessed by your C sources. To illustrate, we have the following example:
/* main.c */
extern void adainit (void);
extern void adafinal (void);
extern int add (int, int);
extern int sub (int, int);
int main (int argc, char *argv[])
{
int a = 21, b = 7;
adainit();
/* Should print "21 + 7 = 28" */
printf ("%d + %d = %d\n", a, b, add (a, b));
/* Should print "21 - 7 = 14" */
printf ("%d - %d = %d\n", a, b, sub (a, b));
adafinal();
}
-- unit1.ads
package Unit1 is
function Add (A, B : Integer) return Integer;
pragma Export (C, Add, "add");
end Unit1;
-- unit1.adb
package body Unit1 is
function Add (A, B : Integer) return Integer is
begin
return A + B;
end Add;
end Unit1;
-- unit2.ads
package Unit2 is
function Sub (A, B : Integer) return Integer;
pragma Export (C, Sub, "sub");
end Unit2;
-- unit2.adb
package body Unit2 is
function Sub (A, B : Integer) return Integer is
begin
return A - B;
end Sub;
end Unit2;
gcc -c main.c
gnatmake -c unit1.adb gnatmake -c unit2.adb
gnatbind -n unit1.ali unit2.ali
gnatlink unit2.ali main.o -o exec_file
This procedure yields a binary executable called exec_file.
Depending on the circumstances (for example when your non-Ada main object
does not provide symbol main), you may also need to instruct the
GNAT linker not to include the standard startup objects by passing the
-nostartfiles switch to gnatlink.
Previous: Interfacing to C, Up: Mixed Language Programming [Contents][Index]
GNAT follows standard calling sequence conventions and will thus interface to any other language that also follows these conventions. The following Convention identifiers are recognized by GNAT:
AdaThis indicates that the standard Ada calling sequence will be used and all Ada data items may be passed without any limitations in the case where GNAT is used to generate both the caller and callee. It is also possible to mix GNAT generated code and code generated by another Ada compiler. In this case, the data types should be restricted to simple cases, including primitive types. Whether complex data types can be passed depends on the situation. Probably it is safe to pass simple arrays, such as arrays of integers or floats. Records may or may not work, depending on whether both compilers lay them out identically. Complex structures involving variant records, access parameters, tasks, or protected types, are unlikely to be able to be passed.
Note that in the case of GNAT running on a platform that supports HP Ada 83, a higher degree of compatibility can be guaranteed, and in particular records are layed out in an identical manner in the two compilers. Note also that if output from two different compilers is mixed, the program is responsible for dealing with elaboration issues. Probably the safest approach is to write the main program in the version of Ada other than GNAT, so that it takes care of its own elaboration requirements, and then call the GNAT-generated adainit procedure to ensure elaboration of the GNAT components. Consult the documentation of the other Ada compiler for further details on elaboration.
However, it is not possible to mix the tasking run time of GNAT and HP Ada 83, All the tasking operations must either be entirely within GNAT compiled sections of the program, or entirely within HP Ada 83 compiled sections of the program.
AssemblerSpecifies assembler as the convention. In practice this has the same effect as convention Ada (but is not equivalent in the sense of being considered the same convention).
AsmEquivalent to Assembler.
COBOLData will be passed according to the conventions described in section B.4 of the Ada Reference Manual.
CData will be passed according to the conventions described in section B.3 of the Ada Reference Manual.
A note on interfacing to a C “varargs” function:
varargs allows a function to take a variable number of
arguments. There is no direct equivalent in this to Ada. One
approach that can be used is to create a C wrapper for each
different profile and then interface to this C wrapper. For
example, to print an int value using printf,
create a C function printfi that takes two arguments, a
pointer to a string and an int, and calls printf.
Then in the Ada program, use pragma Import to
interface to printfi.
varargs function by providing a specific Ada profile
for a particular call. However, this does not work on
all platforms, since there is no guarantee that the
calling sequence for a two argument normal C function
is the same as for calling a varargs C function with
the same two arguments.
DefaultEquivalent to C.
ExternalEquivalent to C.
C_Plus_Plus (or CPP)This stands for C++. For most purposes this is identical to C. See the separate description of the specialized GNAT pragmas relating to C++ interfacing for further details.
FortranData will be passed according to the conventions described in section B.5 of the Ada Reference Manual.
IntrinsicThis applies to an intrinsic operation, as defined in the Ada Reference Manual. If a pragma Import (Intrinsic) applies to a subprogram, this means that the body of the subprogram is provided by the compiler itself, usually by means of an efficient code sequence, and that the user does not supply an explicit body for it. In an application program, the pragma may be applied to the following sets of names:
type Distance is new Long_Float; type Time is new Long_Float; type Velocity is new Long_Float; function "/" (D : Distance; T : Time) return Velocity; pragma Import (Intrinsic, "/");
This common idiom is often programmed with a generic definition and an explicit body. The pragma makes it simpler to introduce such declarations. It incurs no overhead in compilation time or code size, because it is implemented as a single machine instruction.
function builtin_sqrt (F : Float) return Float; pragma Import (Intrinsic, builtin_sqrt, "__builtin_sqrtf");
Most of the GCC builtins are accessible this way, and as for other import conventions (e.g. C), it is the user’s responsibility to ensure that the Ada subprogram profile matches the underlying builtin expectations.
StdcallThis is relevant only to Windows XP/2000/NT implementations of GNAT,
and specifies that the Stdcall calling sequence will be used,
as defined by the NT API. Nevertheless, to ease building
cross-platform bindings this convention will be handled as a C calling
convention on non-Windows platforms.
DLLThis is equivalent to Stdcall.
Win32This is equivalent to Stdcall.
StubbedThis is a special convention that indicates that the compiler
should provide a stub body that raises Program_Error.
GNAT additionally provides a useful pragma Convention_Identifier
that can be used to parameterize conventions and allow additional synonyms
to be specified. For example if you have legacy code in which the convention
identifier Fortran77 was used for Fortran, you can use the configuration
pragma:
pragma Convention_Identifier (Fortran77, Fortran);
And from now on the identifier Fortran77 may be used as a convention
identifier (for example in an Import pragma) with the same
meaning as Fortran.
Next: Comparison between GNAT and C/C++ Compilation Models, Previous: Mixed Language Programming, Up: The GNAT Compilation Model [Contents][Index]
A programmer inexperienced with mixed-language development may find that building an application containing both Ada and C++ code can be a challenge. This section gives a few hints that should make this task easier. The first section addresses the differences between interfacing with C and interfacing with C++. The second section looks into the delicate problem of linking the complete application from its Ada and C++ parts. The last section gives some hints on how the GNAT run-time library can be adapted in order to allow inter-language dispatching with a new C++ compiler.
| • Interfacing to C++: | ||
| • Linking a Mixed C++ & Ada Program: | ||
| • A Simple Example: | ||
| • Interfacing with C++ constructors: | ||
| • Interfacing with C++ at the Class Level: |
GNAT supports interfacing with the G++ compiler (or any C++ compiler generating code that is compatible with the G++ Application Binary Interface —see http://www.codesourcery.com/archives/cxx-abi).
Interfacing can be done at 3 levels: simple data, subprograms, and
classes. In the first two cases, GNAT offers a specific Convention
C_Plus_Plus (or CPP) that behaves exactly like Convention C.
Usually, C++ mangles the names of subprograms. To generate proper mangled
names automatically, see Generating Ada Bindings for C and C++ headers).
This problem can also be addressed manually in two ways:
extern "C" syntax.
nm) and using it as the
Link_Name argument of the pragma import.
Interfacing at the class level can be achieved by using the GNAT specific
pragmas such as CPP_Constructor. See Interfacing to C++ in GNAT Reference Manual, for additional information.
Next: A Simple Example, Previous: Interfacing to C++, Up: Building Mixed Ada & C++ Programs [Contents][Index]
Usually the linker of the C++ development system must be used to link mixed applications because most C++ systems will resolve elaboration issues (such as calling constructors on global class instances) transparently during the link phase. GNAT has been adapted to ease the use of a foreign linker for the last phase. Three cases can be considered:
g++.
Note that if the C++ code uses inline functions, you will need to
compile your C++ code with the -fkeep-inline-functions switch in
order to provide an existing function implementation that the Ada code can
link with.
$ g++ -c -fkeep-inline-functions file1.C $ g++ -c -fkeep-inline-functions file2.C $ gnatmake ada_unit -largs file1.o file2.o --LINK=g++
PATH, the previous method may be used. It is
important to note that environment variables such as
C_INCLUDE_PATH, GCC_EXEC_PREFIX, BINUTILS_ROOT, and
GCC_ROOT will affect both compilers
at the same time and may make one of the two compilers operate
improperly if set during invocation of the wrong compiler. It is also
very important that the linker uses the proper libgcc.a GCC
library – that is, the one from the C++ compiler installation. The
implicit link command as suggested in the gnatmake command
from the former example can be replaced by an explicit link command with
the full-verbosity option in order to verify which library is used:
$ gnatbind ada_unit $ gnatlink -v -v ada_unit file1.o file2.o --LINK=c++
If there is a problem due to interfering environment variables, it can be worked around by using an intermediate script. The following example shows the proper script to use when GNAT has not been installed at its default location and g++ has been installed at its default location:
$ cat ./my_script #!/bin/sh unset BINUTILS_ROOT unset GCC_ROOT c++ $* $ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script
If the setjmp/longjmp exception mechanism is used, only the paths
to the libgcc libraries are required:
$ cat ./my_script #!/bin/sh CC $* `gcc -print-file-name=libgcc.a` `gcc -print-file-name=libgcc_eh.a` $ gnatlink ada_unit file1.o file2.o --LINK=./my_script
Where CC is the name of the non-GNU C++ compiler.
If the zero cost exception mechanism is used, and the platform
supports automatic registration of exception tables (e.g. Solaris),
paths to more objects are required:
$ cat ./my_script #!/bin/sh CC `gcc -print-file-name=crtbegin.o` $* \ `gcc -print-file-name=libgcc.a` `gcc -print-file-name=libgcc_eh.a` \ `gcc -print-file-name=crtend.o` $ gnatlink ada_unit file1.o file2.o --LINK=./my_script
If the zero cost exception mechanism is used, and the platform
doesn’t support automatic registration of exception tables (e.g. HP-UX
or AIX), the simple approach described above will not work and
a pre-linking phase using GNAT will be necessary.
Another alternative is to use the gprbuild multi-language builder
which has a large knowledge base and knows how to link Ada and C++ code
together automatically in most cases.
Next: Interfacing with C++ constructors, Previous: Linking a Mixed C++ & Ada Program, Up: Building Mixed Ada & C++ Programs [Contents][Index]
The following example, provided as part of the GNAT examples, shows how to achieve procedural interfacing between Ada and C++ in both directions. The C++ class A has two methods. The first method is exported to Ada by the means of an extern C wrapper function. The second method calls an Ada subprogram. On the Ada side, The C++ calls are modelled by a limited record with a layout comparable to the C++ class. The Ada subprogram, in turn, calls the C++ method. So, starting from the C++ main program, the process passes back and forth between the two languages.
Here are the compilation commands:
$ gnatmake -c simple_cpp_interface
$ g++ -c cpp_main.C
$ g++ -c ex7.C
$ gnatbind -n simple_cpp_interface
$ gnatlink simple_cpp_interface -o cpp_main --LINK=g++
-lstdc++ ex7.o cpp_main.o
Here are the corresponding sources:
//cpp_main.C
#include "ex7.h"
extern "C" {
void adainit (void);
void adafinal (void);
void method1 (A *t);
}
void method1 (A *t)
{
t->method1 ();
}
int main ()
{
A obj;
adainit ();
obj.method2 (3030);
adafinal ();
}
//ex7.h
class Origin {
public:
int o_value;
};
class A : public Origin {
public:
void method1 (void);
void method2 (int v);
A();
int a_value;
};
//ex7.C
#include "ex7.h"
#include <stdio.h>
extern "C" { void ada_method2 (A *t, int v);}
void A::method1 (void)
{
a_value = 2020;
printf ("in A::method1, a_value = %d \n",a_value);
}
void A::method2 (int v)
{
ada_method2 (this, v);
printf ("in A::method2, a_value = %d \n",a_value);
}
A::A(void)
{
a_value = 1010;
printf ("in A::A, a_value = %d \n",a_value);
}
-- Ada sources
package body Simple_Cpp_Interface is
procedure Ada_Method2 (This : in out A; V : Integer) is
begin
Method1 (This);
This.A_Value := V;
end Ada_Method2;
end Simple_Cpp_Interface;
with System;
package Simple_Cpp_Interface is
type A is limited
record
Vptr : System.Address;
O_Value : Integer;
A_Value : Integer;
end record;
pragma Convention (C, A);
procedure Method1 (This : in out A);
pragma Import (C, Method1);
procedure Ada_Method2 (This : in out A; V : Integer);
pragma Export (C, Ada_Method2);
end Simple_Cpp_Interface;
Next: Interfacing with C++ at the Class Level, Previous: A Simple Example, Up: Building Mixed Ada & C++ Programs [Contents][Index]
In order to interface with C++ constructors GNAT provides the
pragma CPP_Constructor (See Interfacing to C++ in GNAT Reference Manual, for additional information).
In this section we present some common uses of C++ constructors
in mixed-languages programs in GNAT.
Let us assume that we need to interface with the following C++ class:
class Root {
public:
int a_value;
int b_value;
virtual int Get_Value ();
Root(); // Default constructor
Root(int v); // 1st non-default constructor
Root(int v, int w); // 2nd non-default constructor
};
For this purpose we can write the following package spec (further information on how to build this spec is available in Interfacing with C++ at the Class Level and Generating Ada Bindings for C and C++ headers).
with Interfaces.C; use Interfaces.C;
package Pkg_Root is
type Root is tagged limited record
A_Value : int;
B_Value : int;
end record;
pragma Import (CPP, Root);
function Get_Value (Obj : Root) return int;
pragma Import (CPP, Get_Value);
function Constructor return Root;
pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ev");
function Constructor (v : Integer) return Root;
pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ei");
function Constructor (v, w : Integer) return Root;
pragma Cpp_Constructor (Constructor, "_ZN4RootC1Eii");
end Pkg_Root;
On the Ada side the constructor is represented by a function (whose name is arbitrary) that returns the classwide type corresponding to the imported C++ class. Although the constructor is described as a function, it is typically a procedure with an extra implicit argument (the object being initialized) at the implementation level. GNAT issues the appropriate call, whatever it is, to get the object properly initialized.
Constructors can only appear in the following contexts:
In a declaration of an object whose type is a class imported from C++, either the default C++ constructor is implicitly called by GNAT, or else the required C++ constructor must be explicitly called in the expression that initializes the object. For example:
Obj1 : Root; Obj2 : Root := Constructor; Obj3 : Root := Constructor (v => 10); Obj4 : Root := Constructor (30, 40);
The first two declarations are equivalent: in both cases the default C++
constructor is invoked (in the former case the call to the constructor is
implicit, and in the latter case the call is explicit in the object
declaration). Obj3 is initialized by the C++ non-default constructor
that takes an integer argument, and Obj4 is initialized by the
non-default C++ constructor that takes two integers.
Let us derive the imported C++ class in the Ada side. For example:
type DT is new Root with record
C_Value : Natural := 2009;
end record;
In this case the components DT inherited from the C++ side must be initialized by a C++ constructor, and the additional Ada components of type DT are initialized by GNAT. The initialization of such an object is done either by default, or by means of a function returning an aggregate of type DT, or by means of an extension aggregate.
Obj5 : DT; Obj6 : DT := Function_Returning_DT (50); Obj7 : DT := (Constructor (30,40) with C_Value => 50);
The declaration of Obj5 invokes the default constructors: the
C++ default constructor of the parent type takes care of the initialization
of the components inherited from Root, and GNAT takes care of the default
initialization of the additional Ada components of type DT (that is,
C_Value is initialized to value 2009). The order of invocation of
the constructors is consistent with the order of elaboration required by
Ada and C++. That is, the constructor of the parent type is always called
before the constructor of the derived type.
Let us now consider a record that has components whose type is imported from C++. For example:
type Rec1 is limited record
Data1 : Root := Constructor (10);
Value : Natural := 1000;
end record;
type Rec2 (D : Integer := 20) is limited record
Rec : Rec1;
Data2 : Root := Constructor (D, 30);
end record;
The initialization of an object of type Rec2 will call the
non-default C++ constructors specified for the imported components.
For example:
Obj8 : Rec2 (40);
Using Ada 2005 we can use limited aggregates to initialize an object invoking C++ constructors that differ from those specified in the type declarations. For example:
Obj9 : Rec2 := (Rec => (Data1 => Constructor (15, 16),
others => <>),
others => <>);
The above declaration uses an Ada 2005 limited aggregate to
initialize Obj9, and the C++ constructor that has two integer
arguments is invoked to initialize the Data1 component instead
of the constructor specified in the declaration of type Rec1. In
Ada 2005 the box in the aggregate indicates that unspecified components
are initialized using the expression (if any) available in the component
declaration. That is, in this case discriminant D is initialized
to value 20, Value is initialized to value 1000, and the
non-default C++ constructor that handles two integers takes care of
initializing component Data2 with values 20,30.
In Ada 2005 we can use the extended return statement to build the Ada equivalent to C++ non-default constructors. For example:
function Constructor (V : Integer) return Rec2 is
begin
return Obj : Rec2 := (Rec => (Data1 => Constructor (V, 20),
others => <>),
others => <>) do
-- Further actions required for construction of
-- objects of type Rec2
...
end record;
end Constructor;
In this example the extended return statement construct is used to build in place the returned object whose components are initialized by means of a limited aggregate. Any further action associated with the constructor can be placed inside the construct.
Previous: Interfacing with C++ constructors, Up: Building Mixed Ada & C++ Programs [Contents][Index]
In this section we demonstrate the GNAT features for interfacing with C++ by means of an example making use of Ada 2005 abstract interface types. This example consists of a classification of animals; classes have been used to model our main classification of animals, and interfaces provide support for the management of secondary classifications. We first demonstrate a case in which the types and constructors are defined on the C++ side and imported from the Ada side, and latter the reverse case.
The root of our derivation will be the Animal class, with a
single private attribute (the Age of the animal) and two public
primitives to set and get the value of this attribute.
class Animal {
public:
virtual void Set_Age (int New_Age);
virtual int Age ();
private:
int Age_Count;
};
Abstract interface types are defined in C++ by means of classes with pure
virtual functions and no data members. In our example we will use two
interfaces that provide support for the common management of Carnivore
and Domestic animals:
class Carnivore {
public:
virtual int Number_Of_Teeth () = 0;
};
class Domestic {
public:
virtual void Set_Owner (char* Name) = 0;
};
Using these declarations, we can now say that a Dog is an animal that is
both Carnivore and Domestic, that is:
class Dog : Animal, Carnivore, Domestic {
public:
virtual int Number_Of_Teeth ();
virtual void Set_Owner (char* Name);
Dog(); // Constructor
private:
int Tooth_Count;
char *Owner;
};
In the following examples we will assume that the previous declarations are
located in a file named animals.h. The following package demonstrates
how to import these C++ declarations from the Ada side:
with Interfaces.C.Strings; use Interfaces.C.Strings;
package Animals is
type Carnivore is interface;
pragma Convention (C_Plus_Plus, Carnivore);
function Number_Of_Teeth (X : Carnivore)
return Natural is abstract;
type Domestic is interface;
pragma Convention (C_Plus_Plus, Set_Owner);
procedure Set_Owner
(X : in out Domestic;
Name : Chars_Ptr) is abstract;
type Animal is tagged record
Age : Natural := 0;
end record;
pragma Import (C_Plus_Plus, Animal);
procedure Set_Age (X : in out Animal; Age : Integer);
pragma Import (C_Plus_Plus, Set_Age);
function Age (X : Animal) return Integer;
pragma Import (C_Plus_Plus, Age);
type Dog is new Animal and Carnivore and Domestic with record
Tooth_Count : Natural;
Owner : String (1 .. 30);
end record;
pragma Import (C_Plus_Plus, Dog);
function Number_Of_Teeth (A : Dog) return Integer;
pragma Import (C_Plus_Plus, Number_Of_Teeth);
procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
pragma Import (C_Plus_Plus, Set_Owner);
function New_Dog return Dog;
pragma CPP_Constructor (New_Dog);
pragma Import (CPP, New_Dog, "_ZN3DogC2Ev");
end Animals;
Thanks to the compatibility between GNAT run-time structures and the C++ ABI, interfacing with these C++ classes is easy. The only requirement is that all the primitives and components must be declared exactly in the same order in the two languages.
Regarding the abstract interfaces, we must indicate to the GNAT compiler by
means of a pragma Convention (C_Plus_Plus), the convention used to pass
the arguments to the called primitives will be the same as for C++. For the
imported classes we use pragma Import with convention C_Plus_Plus
to indicate that they have been defined on the C++ side; this is required
because the dispatch table associated with these tagged types will be built
in the C++ side and therefore will not contain the predefined Ada primitives
which Ada would otherwise expect.
As the reader can see there is no need to indicate the C++ mangled names
associated with each subprogram because it is assumed that all the calls to
these primitives will be dispatching calls. The only exception is the
constructor, which must be registered with the compiler by means of
pragma CPP_Constructor and needs to provide its associated C++
mangled name because the Ada compiler generates direct calls to it.
With the above packages we can now declare objects of type Dog on the Ada side and dispatch calls to the corresponding subprograms on the C++ side. We can also extend the tagged type Dog with further fields and primitives, and override some of its C++ primitives on the Ada side. For example, here we have a type derivation defined on the Ada side that inherits all the dispatching primitives of the ancestor from the C++ side.
with Animals; use Animals; package Vaccinated_Animals is type Vaccinated_Dog is new Dog with null record; function Vaccination_Expired (A : Vaccinated_Dog) return Boolean; end Vaccinated_Animals;
It is important to note that, because of the ABI compatibility, the programmer does not need to add any further information to indicate either the object layout or the dispatch table entry associated with each dispatching operation.
Now let us define all the types and constructors on the Ada side and export them to C++, using the same hierarchy of our previous example:
with Interfaces.C.Strings;
use Interfaces.C.Strings;
package Animals is
type Carnivore is interface;
pragma Convention (C_Plus_Plus, Carnivore);
function Number_Of_Teeth (X : Carnivore)
return Natural is abstract;
type Domestic is interface;
pragma Convention (C_Plus_Plus, Set_Owner);
procedure Set_Owner
(X : in out Domestic;
Name : Chars_Ptr) is abstract;
type Animal is tagged record
Age : Natural := 0;
end record;
pragma Convention (C_Plus_Plus, Animal);
procedure Set_Age (X : in out Animal; Age : Integer);
pragma Export (C_Plus_Plus, Set_Age);
function Age (X : Animal) return Integer;
pragma Export (C_Plus_Plus, Age);
type Dog is new Animal and Carnivore and Domestic with record
Tooth_Count : Natural;
Owner : String (1 .. 30);
end record;
pragma Convention (C_Plus_Plus, Dog);
function Number_Of_Teeth (A : Dog) return Integer;
pragma Export (C_Plus_Plus, Number_Of_Teeth);
procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
pragma Export (C_Plus_Plus, Set_Owner);
function New_Dog return Dog'Class;
pragma Export (C_Plus_Plus, New_Dog);
end Animals;
Compared with our previous example the only difference is the use of
pragma Export to indicate to the GNAT compiler that the primitives will
be available to C++. Thanks to the ABI compatibility, on the C++ side there is
nothing else to be done; as explained above, the only requirement is that all
the primitives and components are declared in exactly the same order.
For completeness, let us see a brief C++ main program that uses the
declarations available in animals.h (presented in our first example) to
import and use the declarations from the Ada side, properly initializing and
finalizing the Ada run-time system along the way:
#include "animals.h"
#include <iostream>
using namespace std;
void Check_Carnivore (Carnivore *obj) {…}
void Check_Domestic (Domestic *obj) {…}
void Check_Animal (Animal *obj) {…}
void Check_Dog (Dog *obj) {…}
extern "C" {
void adainit (void);
void adafinal (void);
Dog* new_dog ();
}
void test ()
{
Dog *obj = new_dog(); // Ada constructor
Check_Carnivore (obj); // Check secondary DT
Check_Domestic (obj); // Check secondary DT
Check_Animal (obj); // Check primary DT
Check_Dog (obj); // Check primary DT
}
int main ()
{
adainit (); test(); adafinal ();
return 0;
}
Next: Comparison between GNAT and Conventional Ada Library Models, Previous: Building Mixed Ada & C++ Programs, Up: The GNAT Compilation Model [Contents][Index]
The GNAT model of compilation is close to the C and C++ models. You can
think of Ada specs as corresponding to header files in C. As in C, you
don’t need to compile specs; they are compiled when they are used. The
Ada with is similar in effect to the #include of a C
header.
One notable difference is that, in Ada, you may compile specs separately to check them for semantic and syntactic accuracy. This is not always possible with C headers because they are fragments of programs that have less specific syntactic or semantic rules.
The other major difference is the requirement for running the binder, which performs two important functions. First, it checks for consistency. In C or C++, the only defense against assembling inconsistent programs lies outside the compiler, in a makefile, for example. The binder satisfies the Ada requirement that it be impossible to construct an inconsistent program when the compiler is used in normal mode.
The other important function of the binder is to deal with elaboration
issues. There are also elaboration issues in C++ that are handled
automatically. This automatic handling has the advantage of being
simpler to use, but the C++ programmer has no control over elaboration.
Where gnatbind might complain there was no valid order of
elaboration, a C++ compiler would simply construct a program that
malfunctioned at run time.
Next: Latin-1, Previous: Comparison between GNAT and C/C++ Compilation Models, Up: The GNAT Compilation Model [Contents][Index]
This section is intended for Ada programmers who have used an Ada compiler implementing the traditional Ada library model, as described in the Ada Reference Manual.
In GNAT, there is no “library” in the normal sense. Instead, the set of source files themselves acts as the library. Compiling Ada programs does not generate any centralized information, but rather an object file and a ALI file, which are of interest only to the binder and linker. In a traditional system, the compiler reads information not only from the source file being compiled, but also from the centralized library. This means that the effect of a compilation depends on what has been previously compiled. In particular:
with’ed, the unit seen by the compiler corresponds
to the version of the unit most recently compiled into the library.
In GNAT, compiling one unit never affects the compilation of any other units because the compiler reads only source files. Only changes to source files can affect the results of a compilation. In particular:
with’ed, the unit seen by the compiler corresponds
to the source version of the unit that is currently accessible to the
compiler.
The most important result of these differences is that order of compilation is never significant in GNAT. There is no situation in which one is required to do one compilation before another. What shows up as order of compilation requirements in the traditional Ada library becomes, in GNAT, simple source dependencies; in other words, there is only a set of rules saying what source files must be present when a file is compiled.
Next: Binding Using gnatbind, Previous: The GNAT Compilation Model, Up: Top [Contents][Index]
gccThis chapter discusses how to compile Ada programs using the gcc
command. It also describes the set of switches
that can be used to control the behavior of the compiler.
| • Compiling Programs: | ||
| • Switches for gcc: | ||
| • Search Paths and the Run-Time Library (RTL): | ||
| • Order of Compilation Issues: | ||
| • Examples: |
Next: Switches for gcc, Previous: Wide Character Encodings, Up: Compiling Using gcc [Contents][Index]
The first step in creating an executable program is to compile the units
of the program using the gcc command. You must compile the
following files:
You need not compile the following files
because they are compiled as part of compiling related units. GNAT package specs when the corresponding body is compiled, and subunits when the parent is compiled.
If you attempt to compile any of these files, you will get one of the following error messages (where fff is the name of the file you compiled):
cannot generate code for file fff (package spec) to check package spec, use -gnatc cannot generate code for file fff (missing subunits) to check parent unit, use -gnatc cannot generate code for file fff (subprogram spec) to check subprogram spec, use -gnatc cannot generate code for file fff (subunit) to check subunit, use -gnatc
As indicated by the above error messages, if you want to submit one of these files to the compiler to check for correct semantics without generating code, then use the -gnatc switch.
The basic command for compiling a file containing an Ada unit is
$ gcc -c [switches] file name
where file name is the name of the Ada file (usually
having an extension
.ads for a spec or .adb for a body).
You specify the
-c switch to tell gcc to compile, but not link, the file.
The result of a successful compilation is an object file, which has the
same name as the source file but an extension of .o and an Ada
Library Information (ALI) file, which also has the same name as the
source file, but with .ali as the extension. GNAT creates these
two output files in the current directory, but you may specify a source
file in any directory using an absolute or relative path specification
containing the directory information.
gcc is actually a driver program that looks at the extensions of
the file arguments and loads the appropriate compiler. For example, the
GNU C compiler is cc1, and the Ada compiler is gnat1.
These programs are in directories known to the driver program (in some
configurations via environment variables you set), but need not be in
your path. The gcc driver also calls the assembler and any other
utilities needed to complete the generation of the required object
files.
It is possible to supply several file names on the same gcc
command. This causes gcc to call the appropriate compiler for
each file. For example, the following command lists three separate
files to be compiled:
$ gcc -c x.adb y.adb z.c
calls gnat1 (the Ada compiler) twice to compile x.adb and
y.adb, and cc1 (the C compiler) once to compile z.c.
The compiler generates three object files x.o, y.o and
z.o and the two ALI files x.ali and y.ali from the
Ada compilations. Any switches apply to all the files listed,
except for
-gnatx switches, which apply only to Ada compilations.
Next: Search Paths and the Run-Time Library (RTL), Previous: Compiling Programs, Up: Compiling Using gcc [Contents][Index]
gccThe gcc command accepts switches that control the
compilation process. These switches are fully described in this section.
First we briefly list all the switches, in alphabetical order, then we
describe the switches in more detail in functionally grouped sections.
More switches exist for GCC than those documented here, especially for specific targets. However, their use is not recommended as they may change code generation in ways that are incompatible with the Ada run-time library, or can cause inconsistencies between compilation units.
Compile your program to run on target, which is the name of a system configuration. You must have a GNAT cross-compiler built if target is not the same as your host system.
Load compiler executables (for example, gnat1, the Ada compiler)
from dir instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See Options for Directory Search in Using the
GNU Compiler Collection (GCC), for further details. You would normally
use the -b or -V switch instead.
Compile. Always use this switch when compiling Ada programs.
Note: for some other languages when using gcc, notably in
the case of C and C++, it is possible to use
use gcc without a -c switch to
compile and link in one step. In the case of GNAT, you
cannot use this approach, because the binder must be run
and gcc cannot be used to run the GNAT binder.
Makes the compiler output callgraph information for the program, on a per-file basis. The information is generated in the VCG format. It can be decorated with additional, per-node and/or per-edge information, if a list of comma-separated markers is additionally specified. When the su marker is specified, the callgraph is decorated with stack usage information; it is equivalent to -fstack-usage. When the da marker is specified, the callgraph is decorated with information about dynamically allocated objects.
Generates SCO (Source Coverage Obligation) information in the ALI file. This information is used by advanced coverage tools. See unit SCOs in the compiler sources for details in files scos.ads and scos.adb.
Enables Link Time Optimization. This switch must be used in conjunction
with the traditional -Ox switches and instructs the compiler to
defer most optimizations until the link stage. The advantage of this
approach is that the compiler can do a whole-program analysis and choose
the best interprocedural optimization strategy based on a complete view
of the program, instead of a fragmentary view with the usual approach.
This can also speed up the compilation of huge programs and reduce the
size of the final executable, compared with a per-unit compilation with
full inlining across modules enabled with the -gnatn2 switch.
The drawback of this approach is that it may require much more memory.
The switch, as well as the accompanying -Ox switches, must be
specified both for the compilation and the link phases.
If the n parameter is specified, the optimization and final code
generation at link time are executed using n parallel jobs by
means of an installed make program.
Suppresses all inlining, even if other optimization or inlining
switches are set. This includes suppression of inlining that
results from the use of the pragma Inline_Always.
Any occurrences of pragma Inline or Inline_Always
are ignored, and -gnatn and -gnatN have no
effects if this switch is present. Note that inlining can also
be suppressed on a finer-grained basis with pragma No_Inline.
Suppresses automatic inlining of subprograms, which is enabled if -O3 is used.
Suppresses automatic inlining of small subprograms, which is enabled if -O2 is used.
Suppresses inlining of subprograms local to the unit and called once from within it, which is enabled if -O1 is used.
Suppresses high-level loop induction variable optimizations, which are enabled if -O1 is used. These optimizations are generally profitable but, for some specific cases of loops with numerous uses of the iteration variable that follow a common pattern, they may end up destroying the regularity that could be exploited at a lower level and thus producing inferior code.
Causes the compiler to avoid assumptions regarding non-aliasing of objects of different types. See Optimization and Strict Aliasing for details.
Activates stack checking. See Stack Overflow Checking for details.
Makes the compiler output stack usage information for the program, on a per-subprogram basis. See Static Stack Usage Analysis for details.
Generate debugging information. This information is stored in the object file and copied from there to the final executable file by the linker, where it can be read by the debugger. You must use the -g switch if you plan on using the debugger.
Enforce Ada 83 restrictions.
Enforce Ada 95 restrictions.
Allow full Ada 2005 features.
Allow full Ada 2005 features (same as -gnat05)
Allow full Ada 2012 features (same as -gnat12)
Assertions enabled. Pragma Assert and pragma Debug to be
activated. Note that these pragmas can also be controlled using the
configuration pragmas Assertion_Policy and Debug_Policy.
It also activates pragmas Check, Precondition, and
Postcondition. Note that these pragmas can also be controlled
using the configuration pragma Check_Policy. In Ada 2012, it
also activates all assertions defined in the RM as aspects: preconditions,
postconditions, type invariants and (sub)type predicates. In all Ada modes,
corresponding pragmas for type invariants and (sub)type predicates are
also activated.
Avoid processing gnat.adc. If a gnat.adc file is present, it will be ignored.
Generate brief messages to stderr even if verbose mode set.
Assume no invalid (bad) values except for ’Valid attribute use (see Validity Checking).
Check syntax and semantics only (no code generation attempted).
Generate CodePeer information (no code generation attempted). This switch will generate an intermediate representation suitable for use by CodePeer (.scil files). This switch is not compatible with code generation (it will, among other things, disable some switches such as -gnatn, and enable others such as -gnata).
Specify debug options for the compiler. The string of characters after the -gnatd specify the specific debug options. The possible characters are 0-9, a-z, A-Z, optionally preceded by a dot. See compiler source file debug.adb for details of the implemented debug options. Certain debug options are relevant to applications programmers, and these are documented at appropriate points in this users guide.
Create expanded source files for source level debugging. This switch also suppress generation of cross-reference information (see -gnatx).
Check that there is no aliasing between two parameters of the same subprogram.
Specify a configuration pragma file (the equal sign is optional) (see The Configuration Pragmas Files).
Disable atomic synchronization
Defines a symbol, associated with value, for preprocessing. (see Integrated Preprocessing).
Generate extra information in exception messages. In particular, display extra column information and the value and range associated with index and range check failures, and extra column information for access checks. In cases where the compiler is able to determine at compile time that a check will fail, it gives a warning, and the extra information is not produced at run time.
Display full source path name in brief error messages.
Check for overflow on all floating-point operations, including those
for unconstrained predefined types. See description of pragma
Check_Float_Overflow in GNAT RM.
Save result of preprocessing in a text file.
Set maximum number of instantiations during compilation of a single unit to nnn. This may be useful in increasing the default maximum of 8000 for the rare case when a single unit legitimately exceeds this limit.
Indicates that the source is a multi-unit source and that the index of the unit to compile is nnn. nnn needs to be a positive number and need to be a valid index in the multi-unit source.
Specify a mapping file (the equal sign is optional) (see Units to Sources Mapping Files).
Specify a preprocessing data file (the equal sign is optional) (see Integrated Preprocessing).
Turn categorization dependency errors into warnings. Ada requires that units that WITH one another have compatible categories, for example a Pure unit cannot WITH a Preelaborate unit. If this switch is used, these errors become warnings (which can be ignored, or suppressed in the usual manner). This can be useful in some specialized circumstances such as the temporary use of special test software.
Synonym of -fdump-scos, kept for backards compatibility.
Generate target dependent information.
Check validity of subprogram parameters.
Ignore all STYLE_CHECKS pragmas. Full legality checks are still carried out, but the pragmas have no effect on what style checks are active. This allows all style checking options to be controlled from the command line.
Full dynamic elaboration checks.
Full errors. Multiple errors per line, all undefined references, do not attempt to suppress cascaded errors.
Externals names are folded to all uppercase.
Internal GNAT implementation mode. This should not be used for applications programs, it is intended only for use by the compiler and its run-time library. For documentation, see the GNAT sources. Note that -gnatg implies -gnatwae and -gnatyg so that all standard warnings and all standard style options are turned on. All warnings and style messages are treated as errors.
List generated expanded code in source form.
Output usage information. The output is written to stdout.
Identifier character set (c=1/2/3/4/8/9/p/f/n/w). For details of the possible selections for c, see Character Set Control.
Ignore representation clauses. When this switch is used, representation clauses are treated as comments. This is useful when initially porting code where you want to ignore rep clause problems, and also for compiling foreign code (particularly for use with ASIS). The representation clauses that are ignored are: enumeration_representation_clause, record_representation_clause, and attribute_definition_clause for the following attributes: Address, Alignment, Bit_Order, Component_Size, Machine_Radix, Object_Size, Size, Small, Stream_Size, and Value_Size. Note that this option should be used only for compiling – the code is likely to malfunction at run time.
Reformat error messages to fit on nn character lines
Limit file names to n (1-999) characters (k = krunch).
Output full source listing with embedded error messages.
Used in conjunction with -gnatG or -gnatD to intersperse original source lines (as comment lines with line numbers) in the expanded source output.
Limit number of detected error or warning messages to n where n is in the range 1..999999. The default setting if no switch is given is 9999. If the number of warnings reaches this limit, then a message is output and further warnings are suppressed, but the compilation is continued. If the number of error messages reaches this limit, then a message is output and the compilation is abandoned. The equal sign here is optional. A value of zero means that no limit applies.
Activate inlining for subprograms for which pragma Inline is
specified. This inlining is performed by the GCC back-end. An optional
digit sets the inlining level: 1 for moderate inlining across modules
or 2 for full inlining across modules. If no inlining level is specified,
the compiler will pick it based on the optimization level.
Activate front end inlining for subprograms for which
pragma Inline is specified. This inlining is performed
by the front end and will be visible in the
-gnatG output.
When using a gcc-based back end (in practice this means using any version of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of -gnatN is deprecated, and the use of -gnatn is preferred. Historically front end inlining was more extensive than the gcc back end inlining, but that is no longer the case.
Set default mode for handling generation of code to avoid intermediate
arithmetic overflow. Here ‘??’ is two digits, a
single digit, or nothing. Each digit is one of the digits ‘1’
through ‘3’:
1:
all intermediate overflows checked against base type (STRICT)
2:
minimize intermediate overflows (MINIMIZED)
3:
eliminate intermediate overflows (ELIMINATED)
If only one digit appears then it applies to all cases; if two digits are given, then the first applies outside assertions, and the second within assertions.
If no digits follow the -gnato, then it is equivalent to -gnato11, causing all intermediate overflows to be handled in strict mode.
This switch also causes arithmetic overflow checking to be performed
(as though pragma Unsuppress (Overflow_Mode) has been specified.
The default if no option -gnato is given is that overflow handling
is in STRICT mode (computations done using the base type), and that
overflow checking is suppressed.
Note that division by zero is a separate check that is not controlled by this switch (division by zero checking is on by default).
See also Specifying the Desired Mode.
Suppress all checks. See Run-Time Checks for details. This switch has no effect if cancelled by a subsequent -gnat-p switch.
Cancel effect of previous -gnatp switch.
Enable polling. This is required on some systems (notably Windows NT) to obtain asynchronous abort and asynchronous transfer of control capability. See Pragma Polling in GNAT Reference Manual, for full details.
Don’t quit. Try semantics, even if parse errors.
Don’t quit. Generate ALI and tree files even if illegalities.
Treat pragma Restrictions as Restriction_Warnings.
Output representation information for declared types and objects.
Syntax check only.
Print package Standard.
Generate tree output file.
All compiler tables start at nnn times usual starting size.
List units for this compilation.
Tag all error messages with the unique string “error:”
Verbose mode. Full error output with source lines to stdout.
Control level of validity checking (see Validity Checking).
Warning mode where xxx is a string of option letters that denotes the exact warnings that are enabled or disabled (see Warning Message Control).
Wide character encoding method (e=n/h/u/s/e/8).
Suppress generation of cross-reference information.
Enable GNAT implementation extensions and latest Ada version.
Enable built-in style checks (see Style Checking).
Distribution stub generation and compilation (m=r/c for receiver/caller stubs).
Direct GNAT to search the dir directory for source files needed by the current compilation (see Search Paths and the Run-Time Library (RTL)).
Except for the source file named in the command line, do not look for source files in the directory containing the source file named in the command line (see Search Paths and the Run-Time Library (RTL)).
This standard gcc switch causes the compiler to use larger offsets in its
jump table representation for case statements.
This may result in less efficient code, but is sometimes necessary
(for example on HP-UX targets)
in order to compile large and/or nested case statements.
This switch is used in gcc to redirect the generated object file
and its associated ALI file. Beware of this switch with GNAT, because it may
cause the object file and ALI file to have different names which in turn
may confuse the binder and the linker.
Inhibit the search of the default location for the GNAT Run Time Library (RTL) source files.
Inhibit the search of the default location for the GNAT Run Time Library (RTL) ALI files.
n controls the optimization level.
No optimization, the default setting if no -O appears
Normal optimization, the default if you specify -O without an operand. A good compromise between code quality and compilation time.
Extensive optimization, may improve execution time, possibly at the cost of substantially increased compilation time.
Same as -O2, and also includes inline expansion for small subprograms in the same unit.
Optimize space usage
See also Optimization Levels.
Catch exit codes from the compiler and use the most meaningful as exit status.
Specifies the default location of the runtime library. Same meaning as the
equivalent gnatmake flag (see Switches for gnatmake).
Used in place of -c to cause the assembler source file to be generated, using .s as the extension, instead of the object file. This may be useful if you need to examine the generated assembly code.
Used in conjunction with -S to cause the generated assembly code file to be annotated with variable names, making it significantly easier to follow.
Show commands generated by the gcc driver. Normally used only for
debugging purposes or if you need to be sure what version of the
compiler you are executing.
Execute ver version of the compiler. This is the gcc
version, not the GNAT version.
Turn off warnings generated by the back end of the compiler. Use of this switch also causes the default for front end warnings to be set to suppress (as though -gnatws had appeared at the start of the options).
You may combine a sequence of GNAT switches into a single switch. For example, the combined switch
-gnatofi3
is equivalent to specifying the following sequence of switches:
-gnato -gnatf -gnati3
The following restrictions apply to the combination of switches in this manner:
-gnatzc and -gnatzr may not be combined with any other switches, and only one of them may appear in the command line.
Next: Warning Message Control, Previous: Examples, Up: Switches for gcc [Contents][Index]
The standard default format for error messages is called “brief format”. Brief format messages are written to stderr (the standard error file) and have the following form:
e.adb:3:04: Incorrect spelling of keyword "function" e.adb:4:20: ";" should be "is"
The first integer after the file name is the line number in the file,
and the second integer is the column number within the line.
GPS can parse the error messages
and point to the referenced character.
The following switches provide control over the error message
format:
The v stands for verbose. The effect of this setting is to write long-format error messages to stdout (the standard output file. The same program compiled with the -gnatv switch would generate:
3. funcion X (Q : Integer)
|
>>> Incorrect spelling of keyword "function"
4. return Integer;
|
>>> ";" should be "is"
|
The vertical bar indicates the location of the error, and the ‘>>>’ prefix can be used to search for error messages. When this switch is used the only source lines output are those with errors.
The l stands for list.
This switch causes a full listing of
the file to be generated. In the case where a body is
compiled, the corresponding spec is also listed, along
with any subunits. Typical output from compiling a package
body p.adb might look like:
Compiling: p.adb
1. package body p is
2. procedure a;
3. procedure a is separate;
4. begin
5. null
|
>>> missing ";"
6. end;
Compiling: p.ads
1. package p is
2. pragma Elaborate_Body
|
>>> missing ";"
3. end p;
Compiling: p-a.adb
1. separate p
|
>>> missing "("
2. procedure a is
3. begin
4. null
|
>>> missing ";"
5. end;
|
When you specify the -gnatv or -gnatl switches and standard output is redirected, a brief summary is written to stderr (standard error) giving the number of error messages and warning messages generated.
This has the same effect as -gnatl except that the output is written to a file instead of to standard output. If the given name fname does not start with a period, then it is the full name of the file to be written. If fname is an extension, it is appended to the name of the file being compiled. For example, if file xyz.adb is compiled with -gnatl=.lst, then the output is written to file xyz.adb.lst.
This switch forces all error messages to be preceded by the unique string “error:”. This means that error messages take a few more characters in space, but allows easy searching for and identification of error messages.
The b stands for brief.
This switch causes GNAT to generate the
brief format error messages to stderr (the standard error
file) as well as the verbose
format message or full listing (which as usual is written to
stdout (the standard output file).
The m stands for maximum.
n is a decimal integer in the
range of 1 to 999999 and limits the number of error or warning
messages to be generated. For example, using
-gnatm2 might yield
e.adb:3:04: Incorrect spelling of keyword "function" e.adb:5:35: missing ".." fatal error: maximum number of errors detected compilation abandoned
The default setting if no switch is given is 9999. If the number of warnings reaches this limit, then a message is output and further warnings are suppressed, but the compilation is continued. If the number of error messages reaches this limit, then a message is output and the compilation is abandoned. A value of zero means that no limit applies.
Note that the equal sign is optional, so the switches -gnatm2 and -gnatm=2 are equivalent.
The f stands for full.
Normally, the compiler suppresses error messages that are likely to be
redundant. This switch causes all error
messages to be generated. In particular, in the case of
references to undefined variables. If a given variable is referenced
several times, the normal format of messages is
e.adb:7:07: "V" is undefined (more references follow)
where the parenthetical comment warns that there are additional
references to the variable V. Compiling the same program with the
-gnatf switch yields
e.adb:7:07: "V" is undefined e.adb:8:07: "V" is undefined e.adb:8:12: "V" is undefined e.adb:8:16: "V" is undefined e.adb:9:07: "V" is undefined e.adb:9:12: "V" is undefined
The -gnatf switch also generates additional information for some error messages. Some examples are:
In normal operation mode (or if -gnatj0 is used, then error messages with continuation lines are treated as though the continuation lines were separate messages (and so a warning with two continuation lines counts as three warnings, and is listed as three separate messages).
If the -gnatjnn switch is used with a positive value for nn, then messages are output in a different manner. A message and all its continuation lines are treated as a unit, and count as only one warning or message in the statistics totals. Furthermore, the message is reformatted so that no line is longer than nn characters.
The q stands for quit (really “don’t quit”).
In normal operation mode, the compiler first parses the program and
determines if there are any syntax errors. If there are, appropriate
error messages are generated and compilation is immediately terminated.
This switch tells
GNAT to continue with semantic analysis even if syntax errors have been
found. This may enable the detection of more errors in a single run. On
the other hand, the semantic analyzer is more likely to encounter some
internal fatal error when given a syntactically invalid tree.
In normal operation mode, the ALI file is not generated if any illegalities are detected in the program. The use of -gnatQ forces generation of the ALI file. This file is marked as being in error, so it cannot be used for binding purposes, but it does contain reasonably complete cross-reference information, and thus may be useful for use by tools (e.g., semantic browsing tools or integrated development environments) that are driven from the ALI file. This switch implies -gnatq, since the semantic phase must be run to get a meaningful ALI file.
In addition, if -gnatt is also specified, then the tree file is generated even if there are illegalities. It may be useful in this case to also specify -gnatq to ensure that full semantic processing occurs. The resulting tree file can be processed by ASIS, for the purpose of providing partial information about illegal units, but if the error causes the tree to be badly malformed, then ASIS may crash during the analysis.
When -gnatQ is used and the generated ALI file is marked as
being in error, gnatmake will attempt to recompile the source when it
finds such an ALI file, including with switch -gnatc.
Note that -gnatQ has no effect if -gnats is specified, since ALI files are never generated if -gnats is set.
Next: Debugging and Assertion Control, Previous: Output and Error Message Control, Up: Switches for gcc [Contents][Index]
In addition to error messages, which correspond to illegalities as defined in the Ada Reference Manual, the compiler detects two kinds of warning situations.
First, the compiler considers some constructs suspicious and generates a warning message to alert you to a possible error. Second, if the compiler detects a situation that is sure to raise an exception at run time, it generates a warning message. The following shows an example of warning messages:
e.adb:4:24: warning: creation of object may raise Storage_Error e.adb:10:17: warning: static value out of range e.adb:10:17: warning: "Constraint_Error" will be raised at run time
GNAT considers a large number of situations as appropriate
for the generation of warning messages. As always, warnings are not
definite indications of errors. For example, if you do an out-of-range
assignment with the deliberate intention of raising a
Constraint_Error exception, then the warning that may be
issued does not indicate an error. Some of the situations for which GNAT
issues warnings (at least some of the time) are given in the following
list. This list is not complete, and new warnings are often added to
subsequent versions of GNAT. The list is intended to give a general idea
of the kinds of warnings that are generated.
accept statement
select
return statement along some execution path in a function
with clauses
Bit_Order usage that does not have any effect
Standard.Duration used to resolve universal fixed expression
with’ed by application unit
for loop that is known to be null or might be null
The following section lists compiler switches that are available to control the handling of warning messages. It is also possible to exercise much finer control over what warnings are issued and suppressed using the GNAT pragma Warnings, See Pragma Warnings in GNAT Reference manual.
Activate most optional warnings. This switch activates most optional warning messages. See the remaining list in this section for details on optional warning messages that can be individually controlled. The warnings that are not turned on by this switch are -gnatwd (implicit dereferencing), -gnatwh (hiding), -gnatw.d (tag warnings with -gnatw switch) -gnatw.h (holes (gaps) in record layouts) -gnatw.i (overlapping actuals), -gnatw.k (redefinition of names in standard), -gnatwl (elaboration warnings), -gnatw.l (inherited aspects), -gnatw.o (warn on values set by out parameters ignored), -gnatwt (tracking of deleted conditional code) and -gnatw.u (unordered enumeration), All other optional warnings are turned on.
Suppress all optional errors. This switch suppresses all optional warning messages, see remaining list in this section for details on optional warning messages that can be individually controlled. Note that unlike switch -gnatws, the use of switch -gnatwA does not suppress warnings that are normally given unconditionally and cannot be individually controlled (for example, the warning about a missing exit path in a function). Also, again unlike switch -gnatws, warnings suppressed by the use of switch -gnatwA can be individually turned back on. For example the use of switch -gnatwA followed by switch -gnatwd will suppress all optional warnings except the warnings for implicit dereferencing.
Activate warnings on failing assertions. This switch activates warnings for assertions where the compiler can tell at compile time that the assertion will fail. Note that this warning is given even if assertions are disabled. The default is that such warnings are generated.
Suppress warnings on failing assertions. This switch suppresses warnings for assertions where the compiler can tell at compile time that the assertion will fail.
Activate warnings on bad fixed values. This switch activates warnings for static fixed-point expressions whose value is not an exact multiple of Small. Such values are implementation dependent, since an implementation is free to choose either of the multiples that surround the value. GNAT always chooses the closer one, but this is not required behavior, and it is better to specify a value that is an exact multiple, ensuring predictable execution. The default is that such warnings are not generated.
Suppress warnings on bad fixed values. This switch suppresses warnings for static fixed-point expressions whose value is not an exact multiple of Small.
Activate warnings on biased representation. This switch activates warnings when a size clause, value size clause, component clause, or component size clause forces the use of biased representation for an integer type (e.g. representing a range of 10..11 in a single bit by using 0/1 to represent 10/11). The default is that such warnings are generated.
Suppress warnings on biased representation. This switch suppresses warnings for representation clauses that force the use of biased representation.
Activate warnings on conditionals. This switch activates warnings for conditional expressions used in tests that are known to be True or False at compile time. The default is that such warnings are not generated. Note that this warning does not get issued for the use of boolean variables or constants whose values are known at compile time, since this is a standard technique for conditional compilation in Ada, and this would generate too many false positive warnings.
This warning option also activates a special test for comparisons using
the operators “>=” and“ <=”.
If the compiler can tell that only the equality condition is possible,
then it will warn that the “>” or “<” part of the test
is useless and that the operator could be replaced by “=”.
An example would be comparing a Natural variable <= 0.
This warning option also generates warnings if one or both tests is optimized away in a membership test for integer values if the result can be determined at compile time. Range tests on enumeration types are not included, since it is common for such tests to include an end point.
This warning can also be turned on using -gnatwa.
Suppress warnings on conditionals. This switch suppresses warnings for conditional expressions used in tests that are known to be True or False at compile time.
Activate warnings on missing component clauses. This switch activates warnings for record components where a record representation clause is present and has component clauses for the majority, but not all, of the components. A warning is given for each component for which no component clause is present.
This warning can also be turned on using -gnatwa.
Suppress warnings on missing component clauses. This switch suppresses warnings for record components that are missing a component clause in the situation described above.
Activate warnings on implicit dereferencing.
If this switch is set, then the use of a prefix of an access type
in an indexed component, slice, or selected component without an
explicit .all will generate a warning. With this warning
enabled, access checks occur only at points where an explicit
.all appears in the source code (assuming no warnings are
generated as a result of this switch). The default is that such
warnings are not generated.
Note that -gnatwa does not affect the setting of
this warning option.
Suppress warnings on implicit dereferencing. This switch suppresses warnings for implicit dereferences in indexed components, slices, and selected components.
Activate tagging of warning messages.
If this switch is set, then warning messages are tagged, either with
the string “-gnatw?” showing which switch controls the warning,
or with “[enabled by default]” if the warning is not under control of a
specific -gnatw? switch. This mode is off by default, and is not
affected by the use of -gnatwa.
Deactivate tagging of warning messages.
If this switch is set, then warning messages return to the default
mode in which warnings are not tagged as described above for
-gnatw.d.
Treat warnings and style checks as errors. This switch causes warning messages and style check messages to be treated as errors. The warning string still appears, but the warning messages are counted as errors, and prevent the generation of an object file. Note that this is the only -gnatw switch that affects the handling of style check messages.
Activate every optional warning
This switch activates all optional warnings, including those which
are not activated by -gnatwa. The use of this switch is not
recommended for normal use. If you turn this switch on, it is almost
certain that you will get large numbers of useless warnings. The
warnings that are excluded from -gnatwa are typically highly
specialized warnings that are suitable for use only in code that has
been specifically designed according to specialized coding rules.
Activate warnings on unreferenced formals. This switch causes a warning to be generated if a formal parameter is not referenced in the body of the subprogram. This warning can also be turned on using -gnatwa or -gnatwu. The default is that these warnings are not generated.
Suppress warnings on unreferenced formals. This switch suppresses warnings for unreferenced formal parameters. Note that the combination -gnatwu followed by -gnatwF has the effect of warning on unreferenced entities other than subprogram formals.
Activate warnings on unrecognized pragmas. This switch causes a warning to be generated if an unrecognized pragma is encountered. Apart from issuing this warning, the pragma is ignored and has no effect. This warning can also be turned on using -gnatwa. The default is that such warnings are issued (satisfying the Ada Reference Manual requirement that such warnings appear).
Suppress warnings on unrecognized pragmas. This switch suppresses warnings for unrecognized pragmas.
Activate warnings on hiding. This switch activates warnings on hiding declarations. A declaration is considered hiding if it is for a non-overloadable entity, and it declares an entity with the same name as some other entity that is directly or use-visible. The default is that such warnings are not generated. Note that -gnatwa does not affect the setting of this warning option.
Suppress warnings on hiding. This switch suppresses warnings on hiding declarations.
Activate warnings on holes/gaps in records. This switch activates warnings on component clauses in record representation clauses that leave holes (gaps) in the record layout. If this warning option is active, then record representation clauses should specify a contiguous layout, adding unused fill fields if needed. Note that -gnatwa does not affect the setting of this warning option.
Suppress warnings on holes/gaps in records. This switch suppresses warnings on component clauses in record representation clauses that leave holes (haps) in the record layout.
Activate warnings on implementation units.
This switch activates warnings for a with of an internal GNAT
implementation unit, defined as any unit from the Ada,
Interfaces, GNAT,
or System
hierarchies that is not
documented in either the Ada Reference Manual or the GNAT
Programmer’s Reference Manual. Such units are intended only
for internal implementation purposes and should not be with’ed
by user programs. The default is that such warnings are generated
This warning can also be turned on using -gnatwa.
Disable warnings on implementation units.
This switch disables warnings for a with of an internal GNAT
implementation unit.
Activate warnings on overlapping actuals. This switch enables a warning on statically detectable overlapping actuals in a subprogram call, when one of the actuals is an in-out parameter, and the types of the actuals are not by-copy types. The warning is off by default, and is not included under -gnatwa.
Disable warnings on overlapping actuals. This switch disables warnings on overlapping actuals in a call..
Activate warnings on obsolescent features (Annex J).
If this warning option is activated, then warnings are generated for
calls to subprograms marked with pragma Obsolescent and
for use of features in Annex J of the Ada Reference Manual. In the
case of Annex J, not all features are flagged. In particular use
of the renamed packages (like Text_IO) and use of package
ASCII are not flagged, since these are very common and
would generate many annoying positive warnings. The default is that
such warnings are not generated. This warning is also turned on by
the use of -gnatwa.
In addition to the above cases, warnings are also generated for
GNAT features that have been provided in past versions but which
have been superseded (typically by features in the new Ada standard).
For example, pragma Ravenscar will be flagged since its
function is replaced by pragma Profile(Ravenscar), and
pragma Interface_Name will be flagged since its function
is replaced by pragma Import.
Note that this warning option functions differently from the
restriction No_Obsolescent_Features in two respects.
First, the restriction applies only to annex J features.
Second, the restriction does flag uses of package ASCII.
Suppress warnings on obsolescent features (Annex J). This switch disables warnings on use of obsolescent features.
Activate warnings on variables that could be constants. This switch activates warnings for variables that are initialized but never modified, and then could be declared constants. The default is that such warnings are not given. This warning can also be turned on using -gnatwa.
Suppress warnings on variables that could be constants. This switch disables warnings on variables that could be declared constants.
Activate warnings on redefinition of names in standard. This switch activates warnings for declarations that declare a name that is defined in package Standard. Such declarations can be confusing, especially since the names in package Standard continue to be directly visible, meaning that use visibiliy on such redeclared names does not work as expected. Names of discriminants and components in records are not included in this check. This warning is not part of the warnings activated by -gnatwa. It must be explicitly activated.
Suppress warnings on variables that could be constants. This switch activates warnings for declarations that declare a name that is defined in package Standard.
Activate warnings for elaboration pragmas.
This switch activates warnings on missing
Elaborate_All and Elaborate pragmas.
See the section in this guide on elaboration checking for details on
when such pragmas should be used. In dynamic elaboration mode, this switch
generations warnings about the need to add elaboration pragmas. Note however,
that if you blindly follow these warnings, and add Elaborate_All
warnings wherever they are recommended, you basically end up with the
equivalent of the static elaboration model, which may not be what you want for
legacy code for which the static model does not work.
For the static model, the messages generated are labeled "info:" (for information messages). They are not warnings to add elaboration pragmas, merely informational messages showing what implicit elaboration pragmas have been added, for use in analyzing elaboration circularity problems.
Warnings are also generated if you
are using the static mode of elaboration, and a pragma Elaborate
is encountered. The default is that such warnings
are not generated.
This warning is not automatically turned on by the use of -gnatwa.
Suppress warnings for elaboration pragmas. This switch suppresses warnings on missing Elaborate and Elaborate_All pragmas. See the section in this guide on elaboration checking for details on when such pragmas should be used.
List inherited aspects. This switch causes the compiler to list inherited invariants, preconditions, and postconditions from Type_Invariant’Class, Invariant’Class, Pre’Class, and Post’Class aspects. Also list inherited subtype predicates. These messages are not automatically turned on by the use of -gnatwa.
Suppress listing of inherited aspects. This switch suppresses listing of inherited aspects.
Activate warnings on modified but unreferenced variables. This switch activates warnings for variables that are assigned (using an initialization value or with one or more assignment statements) but whose value is never read. The warning is suppressed for volatile variables and also for variables that are renamings of other variables or for which an address clause is given. This warning can also be turned on using -gnatwa. The default is that these warnings are not given.
Disable warnings on modified but unreferenced variables. This switch disables warnings for variables that are assigned or initialized, but never read.
Activate warnings on suspicious modulus values. This switch activates warnings for modulus values that seem suspicious. The cases caught are where the size is the same as the modulus (e.g. a modulus of 7 with a size of 7 bits), and modulus values of 32 or 64 with no size clause. The guess in both cases is that 2**x was intended rather than x. In addition expressions of the form 2*x for small x generate a warning (the almost certainly accurate guess being that 2**x was intended). The default is that these warnings are given.
Disable warnings on suspicious modulus values. This switch disables warnings for suspicious modulus values.
Set normal warnings mode. This switch sets normal warning mode, in which enabled warnings are issued and treated as warnings rather than errors. This is the default mode. the switch -gnatwn can be used to cancel the effect of an explicit -gnatws or -gnatwe. It also cancels the effect of the implicit -gnatwe that is activated by the use of -gnatg.
Activate warnings on address clause overlays. This switch activates warnings for possibly unintended initialization effects of defining address clauses that cause one variable to overlap another. The default is that such warnings are generated. This warning can also be turned on using -gnatwa.
Suppress warnings on address clause overlays. This switch suppresses warnings on possibly unintended initialization effects of defining address clauses that cause one variable to overlap another.
Activate warnings on modified but unreferenced out parameters. This switch activates warnings for variables that are modified by using them as actuals for a call to a procedure with an out mode formal, where the resulting assigned value is never read. It is applicable in the case where there is more than one out mode formal. If there is only one out mode formal, the warning is issued by default (controlled by -gnatwu). The warning is suppressed for volatile variables and also for variables that are renamings of other variables or for which an address clause is given. The default is that these warnings are not given. Note that this warning is not included in -gnatwa, it must be activated explicitly.
Disable warnings on modified but unreferenced out parameters. This switch suppresses warnings for variables that are modified by using them as actuals for a call to a procedure with an out mode formal, where the resulting assigned value is never read.
Activate warnings on ineffective pragma Inlines. This switch activates warnings for failure of front end inlining (activated by -gnatN) to inline a particular call. There are many reasons for not being able to inline a call, including most commonly that the call is too complex to inline. The default is that such warnings are not given. This warning can also be turned on using -gnatwa. Warnings on ineffective inlining by the gcc back-end can be activated separately, using the gcc switch -Winline.
Suppress warnings on ineffective pragma Inlines. This switch suppresses warnings on ineffective pragma Inlines. If the inlining mechanism cannot inline a call, it will simply ignore the request silently.
Activate warnings on parameter ordering. This switch activates warnings for cases of suspicious parameter ordering when the list of arguments are all simple identifiers that match the names of the formals, but are in a different order. The warning is suppressed if any use of named parameter notation is used, so this is the appropriate way to suppress a false positive (and serves to emphasize that the "misordering" is deliberate). The default is that such warnings are not given. This warning can also be turned on using -gnatwa.
Suppress warnings on parameter ordering. This switch suppresses warnings on cases of suspicious parameter ordering.
Activate warnings on questionable missing parentheses. This switch activates warnings for cases where parentheses are not used and the result is potential ambiguity from a readers point of view. For example (not a > b) when a and b are modular means ((not a) > b) and very likely the programmer intended (not (a > b)). Similarly (-x mod 5) means (-(x mod 5)) and quite likely ((-x) mod 5) was intended. In such situations it seems best to follow the rule of always parenthesizing to make the association clear, and this warning switch warns if such parentheses are not present. The default is that these warnings are given. This warning can also be turned on using -gnatwa.
Suppress warnings on questionable missing parentheses. This switch suppresses warnings for cases where the association is not clear and the use of parentheses is preferred.
Activate warnings on redundant constructs. This switch activates warnings for redundant constructs. The following is the current list of constructs regarded as redundant:
Base where typ'Base is the same
as typ.
Pack when all components are placed by a record
representation clause.
This warning can also be turned on using -gnatwa. The default is that warnings for redundant constructs are not given.
Suppress warnings on redundant constructs. This switch suppresses warnings for redundant constructs.
Activate warnings for object renaming function. This switch activates warnings for an object renaming that renames a function call, which is equivalent to a constant declaration (as opposed to renaming the function itself). The default is that these warnings are given. This warning can also be turned on using -gnatwa.
Suppress warnings for object renaming function. This switch suppresses warnings for object renaming function.
Suppress all warnings. This switch completely suppresses the output of all warning messages from the GNAT front end, including both warnings that can be controlled by switches described in this section, and those that are normally given unconditionally. The effect of this suppress action can only be cancelled by a subsequent use of the switch -gnatwn.
Note that switch -gnatws does not suppress
warnings from the gcc back end.
To suppress these back end warnings as well, use the switch -w
in addition to -gnatws. Also this switch has no effect on the
handling of style check messages.
Activate warnings on overridden size clauses. This switch activates warnings on component clauses in record representation clauses where the length given overrides that specified by an explicit size clause for the component type. A warning is similarly given in the array case if a specified component size overrides an explicit size clause for the array component type. Note that -gnatwa does not affect the setting of this warning option.
Suppress warnings on overridden size clauses. This switch suppresses warnings on component clauses in record representation clauses that override size clauses, and similar warnings when an array component size overrides a size clause.
Activate warnings for tracking of deleted conditional code. This switch activates warnings for tracking of code in conditionals (IF and CASE statements) that is detected to be dead code which cannot be executed, and which is removed by the front end. This warning is off by default, and is not turned on by -gnatwa, it has to be turned on explicitly. This may be useful for detecting deactivated code in certified applications.
Suppress warnings for tracking of deleted conditional code. This switch suppresses warnings for tracking of deleted conditional code.
Activate warnings on suspicious contracts.
This switch activates warnings on suspicious postconditions (whether a
pragma Postcondition or a Post aspect in Ada 2012)
and suspicious contract cases (pragma Contract_Case). A
function postcondition or contract case is suspicious when no postcondition
or contract case for this function mentions the result of the function.
A procedure postcondition or contract case is suspicious when it only
refers to the pre-state of the procedure, because in that case it should
rather be expressed as a precondition. The default is that such warnings
are not generated. This warning can also be turned on using -gnatwa.
Suppress warnings on suspicious contracts. This switch suppresses warnings on suspicious postconditions.
Activate warnings on unused entities.
This switch activates warnings to be generated for entities that
are declared but not referenced, and for units that are with’ed
and not
referenced. In the case of packages, a warning is also generated if
no entities in the package are referenced. This means that if a with’ed
package is referenced but the only references are in use
clauses or renames
declarations, a warning is still generated. A warning is also generated
for a generic package that is with’ed but never instantiated.
In the case where a package or subprogram body is compiled, and there
is a with on the corresponding spec
that is only referenced in the body,
a warning is also generated, noting that the
with can be moved to the body. The default is that
such warnings are not generated.
This switch also activates warnings on unreferenced formals
(it includes the effect of -gnatwf).
This warning can also be turned on using -gnatwa.
Suppress warnings on unused entities. This switch suppresses warnings for unused entities and packages. It also turns off warnings on unreferenced formals (and thus includes the effect of -gnatwF).
Activate warnings on unordered enumeration types.
This switch causes enumeration types to be considered as conceptually
unordered, unless an explicit pragma Ordered is given for the type.
The effect is to generate warnings in clients that use explicit comparisons
or subranges, since these constructs both treat objects of the type as
ordered. (A client is defined as a unit that is other than the unit in
which the type is declared, or its body or subunits.) Please refer to
the description of pragma Ordered in the
GNAT Reference Manual for further details.
The default is that such warnings are not generated.
This warning is not automatically turned on by the use of -gnatwa.
Deactivate warnings on unordered enumeration types. This switch causes all enumeration types to be considered as ordered, so that no warnings are given for comparisons or subranges for any type.
Activate warnings on unassigned variables. This switch activates warnings for access to variables which may not be properly initialized. The default is that such warnings are generated. This warning can also be turned on using -gnatwa.
Suppress warnings on unassigned variables. This switch suppresses warnings for access to variables which may not be properly initialized. For variables of a composite type, the warning can also be suppressed in Ada 2005 by using a default initialization with a box. For example, if Table is an array of records whose components are only partially uninitialized, then the following code:
Tab : Table := (others => <>);
will suppress warnings on subsequent statements that access components of variable Tab.
Activate info messages for non-default bit order. This switch activates messages (labeled "info", they are not warnings, just informational messages) about the effects of non-default bit-order on records to which a component clause is applied. The effect of specifying non-default bit ordering is a bit subtle (and changed with Ada 2005), so these messages, which are given by default, are useful in understanding the exact consequences of using this feature. These messages can also be turned on using -gnatwa
Suppress info messages for non-default bit order. This switch suppresses information messages for the effects of specifying non-default bit order on record components with component clauses.
Activate warnings on wrong low bound assumption. This switch activates warnings for indexing an unconstrained string parameter with a literal or S’Length. This is a case where the code is assuming that the low bound is one, which is in general not true (for example when a slice is passed). The default is that such warnings are generated. This warning can also be turned on using -gnatwa.
Suppress warnings on wrong low bound assumption. This switch suppresses warnings for indexing an unconstrained string parameter with a literal or S’Length. Note that this warning can also be suppressed in a particular case by adding an assertion that the lower bound is 1, as shown in the following example.
procedure K (S : String) is
pragma Assert (S'First = 1);
…
Activate warnings on unnecessary Warnings Off pragmas
This switch activates warnings for use of pragma Warnings (Off, entity)
where either the pragma is entirely useless (because it suppresses no
warnings), or it could be replaced by pragma Unreferenced or
pragma Unmodified. The default is that these warnings are not given.
Note that this warning is not included in -gnatwa, it must be
activated explicitly.
Suppress warnings on unnecessary Warnings Off pragmas
This switch suppresses warnings for use of pragma Warnings (Off, entity).
Activate warnings on Export/Import pragmas. This switch activates warnings on Export/Import pragmas when the compiler detects a possible conflict between the Ada and foreign language calling sequences. For example, the use of default parameters in a convention C procedure is dubious because the C compiler cannot supply the proper default, so a warning is issued. The default is that such warnings are generated. This warning can also be turned on using -gnatwa.
Suppress warnings on Export/Import pragmas. This switch suppresses warnings on Export/Import pragmas. The sense of this is that you are telling the compiler that you know what you are doing in writing the pragma, and it should not complain at you.
Activate warnings for No_Exception_Propagation mode. This switch activates warnings for exception usage when pragma Restrictions (No_Exception_Propagation) is in effect. Warnings are given for implicit or explicit exception raises which are not covered by a local handler, and for exception handlers which do not cover a local raise. The default is that these warnings are not given.
Disable warnings for No_Exception_Propagation mode. This switch disables warnings for exception usage when pragma Restrictions (No_Exception_Propagation) is in effect.
Activate warnings for Ada compatibility issues.
For the most part, newer versions of Ada are upwards compatible
with older versions. For example, Ada 2005 programs will almost
always work when compiled as Ada 2012.
However there are some exceptions (for example the fact that
some is now a reserved word in Ada 2012). This
switch activates several warnings to help in identifying
and correcting such incompatibilities. The default is that
these warnings are generated. Note that at one point Ada 2005
was called Ada 0Y, hence the choice of character.
This warning can also be turned on using -gnatwa.
Disable warnings for Ada compatibility issues. This switch suppresses the warnings intended to help in identifying incompatibilities between Ada language versions.
Activate warnings on unchecked conversions. This switch activates warnings for unchecked conversions where the types are known at compile time to have different sizes. The default is that such warnings are generated. Warnings are also generated for subprogram pointers with different conventions, and, on VMS only, for data pointers with different conventions. This warning can also be turned on using -gnatwa.
Suppress warnings on unchecked conversions. This switch suppresses warnings for unchecked conversions where the types are known at compile time to have different sizes or conventions.
The warnings controlled by the -gnatw switch are generated by the front end of the compiler. The GCC back end can provide additional warnings and they are controlled by the -W switch. For example, -Wunused activates back end warnings for entities that are declared but not referenced.
Similarly, -Wuninitialized activates the back end warning for uninitialized variables. This switch must be used in conjunction with an optimization level greater than zero.
Warn if the stack usage of a subprogram might be larger than len bytes. See Static Stack Usage Analysis for details.
This switch enables most warnings from the GCC back end. The code generator detects a number of warning situations that are missed by the GNAT front end, and this switch can be used to activate them. The use of this switch also sets the default front end warning mode to -gnatwa, that is, most front end warnings activated as well.
Conversely, this switch suppresses warnings from the GCC back end. The use of this switch also sets the default front end warning mode to -gnatws, that is, front end warnings suppressed as well.
A string of warning parameters can be used in the same parameter. For example:
-gnatwaGe
will turn on all optional warnings except for unrecognized pragma warnings, and also specify that warnings should be treated as errors.
When no switch -gnatw is used, this is equivalent to:
Next: Validity Checking, Previous: Warning Message Control, Up: Switches for gcc [Contents][Index]
The pragmas Assert and Debug normally have no effect and
are ignored. This switch, where ‘a’ stands for assert, causes
Assert and Debug pragmas to be activated.
The pragmas have the form:
pragma Assert (Boolean-expression [, static-string-expression]) pragma Debug (procedure call) |
The Assert pragma causes Boolean-expression to be tested.
If the result is True, the pragma has no effect (other than
possible side effects from evaluating the expression). If the result is
False, the exception Assert_Failure declared in the package
System.Assertions is
raised (passing static-string-expression, if present, as the
message associated with the exception). If no string expression is
given the default is a string giving the file name and line number
of the pragma.
The Debug pragma causes procedure to be called. Note that
pragma Debug may appear within a declaration sequence, allowing
debugging procedures to be called between declarations.
Next: Style Checking, Previous: Debugging and Assertion Control, Up: Switches for gcc [Contents][Index]
The Ada Reference Manual defines the concept of invalid values (see RM 13.9.1). The primary source of invalid values is uninitialized variables. A scalar variable that is left uninitialized may contain an invalid value; the concept of invalid does not apply to access or composite types.
It is an error to read an invalid value, but the RM does not require run-time checks to detect such errors, except for some minimal checking to prevent erroneous execution (i.e. unpredictable behavior). This corresponds to the -gnatVd switch below, which is the default. For example, by default, if the expression of a case statement is invalid, it will raise Constraint_Error rather than causing a wild jump, and if an array index on the left-hand side of an assignment is invalid, it will raise Constraint_Error rather than overwriting an arbitrary memory location.
The -gnatVa may be used to enable additional validity checks, which are not required by the RM. These checks are often very expensive (which is why the RM does not require them). These checks are useful in tracking down uninitialized variables, but they are not usually recommended for production builds.
The other -gnatVx switches below allow finer-grained control; you can enable whichever validity checks you desire. However, for most debugging purposes, -gnatVa is sufficient, and the default -gnatVd (i.e. standard Ada behavior) is usually sufficient for non-debugging use.
The -gnatB switch tells the compiler to assume that all values are valid (that is, within their declared subtype range) except in the context of a use of the Valid attribute. This means the compiler can generate more efficient code, since the range of values is better known at compile time. However, an uninitialized variable can cause wild jumps and memory corruption in this mode.
The -gnatVx switch allows control over the validity
checking mode as described below.
The x argument is a string of letters that
indicate validity checks that are performed or not performed in addition
to the default checks required by Ada as described above.
All validity checks. All validity checks are turned on. That is, -gnatVa is equivalent to gnatVcdfimorst.
Validity checks for copies. The right hand side of assignments, and the initializing values of object declarations are validity checked.
Default (RM) validity checks. Some validity checks are done by default following normal Ada semantics (RM 13.9.1 (9-11)). A check is done in case statements that the expression is within the range of the subtype. If it is not, Constraint_Error is raised. For assignments to array components, a check is done that the expression used as index is within the range. If it is not, Constraint_Error is raised. Both these validity checks may be turned off using switch -gnatVD. They are turned on by default. If -gnatVD is specified, a subsequent switch -gnatVd will leave the checks turned on. Switch -gnatVD should be used only if you are sure that all such expressions have valid values. If you use this switch and invalid values are present, then the program is erroneous, and wild jumps or memory overwriting may occur.
Validity checks for elementary components. In the absence of this switch, assignments to record or array components are not validity checked, even if validity checks for assignments generally (-gnatVc) are turned on. In Ada, assignment of composite values do not require valid data, but assignment of individual components does. So for example, there is a difference between copying the elements of an array with a slice assignment, compared to assigning element by element in a loop. This switch allows you to turn off validity checking for components, even when they are assigned component by component.
Validity checks for floating-point values.
In the absence of this switch, validity checking occurs only for discrete
values. If -gnatVf is specified, then validity checking also applies
for floating-point values, and NaNs and infinities are considered invalid,
as well as out of range values for constrained types. Note that this means
that standard IEEE infinity mode is not allowed. The exact contexts
in which floating-point values are checked depends on the setting of other
options. For example,
-gnatVif or
-gnatVfi
(the order does not matter) specifies that floating-point parameters of mode
in should be validity checked.
Validity checks for in mode parameters
Arguments for parameters of mode in are validity checked in function
and procedure calls at the point of call.
Validity checks for in out mode parameters.
Arguments for parameters of mode in out are validity checked in
procedure calls at the point of call. The 'm' here stands for
modify, since this concerns parameters that can be modified by the call.
Note that there is no specific option to test out parameters,
but any reference within the subprogram will be tested in the usual
manner, and if an invalid value is copied back, any reference to it
will be subject to validity checking.
No validity checks. This switch turns off all validity checking, including the default checking for case statements and left hand side subscripts. Note that the use of the switch -gnatp suppresses all run-time checks, including validity checks, and thus implies -gnatVn. When this switch is used, it cancels any other -gnatV previously issued.
Validity checks for operator and attribute operands.
Arguments for predefined operators and attributes are validity checked.
This includes all operators in package Standard,
the shift operators defined as intrinsic in package Interfaces
and operands for attributes such as Pos. Checks are also made
on individual component values for composite comparisons, and on the
expressions in type conversions and qualified expressions. Checks are
also made on explicit ranges using ‘..’ (e.g. slices, loops etc).
Validity checks for parameters. This controls the treatment of parameters within a subprogram (as opposed to -gnatVi and -gnatVm which control validity testing of parameters on a call. If either of these call options is used, then normally an assumption is made within a subprogram that the input arguments have been validity checking at the point of call, and do not need checking again within a subprogram). If -gnatVp is set, then this assumption is not made, and parameters are not assumed to be valid, so their validity will be checked (or rechecked) within the subprogram.
Validity checks for function returns.
The expression in return statements in functions is validity
checked.
Validity checks for subscripts. All subscripts expressions are checked for validity, whether they appear on the right side or left side (in default mode only left side subscripts are validity checked).
Validity checks for tests.
Expressions used as conditions in if, while or exit
statements are checked, as well as guard expressions in entry calls.
The -gnatV switch may be followed by
a string of letters
to turn on a series of validity checking options.
For example,
-gnatVcr
specifies that in addition to the default validity checking, copies and
function return expressions are to be validity checked.
In order to make it easier
to specify the desired combination of effects,
the upper case letters CDFIMORST may
be used to turn off the corresponding lower case option.
Thus
-gnatVaM
turns on all validity checking options except for
checking of in out procedure arguments.
The specification of additional validity checking generates extra code (and
in the case of -gnatVa the code expansion can be substantial).
However, these additional checks can be very useful in detecting
uninitialized variables, incorrect use of unchecked conversion, and other
errors leading to invalid values. The use of pragma Initialize_Scalars
is useful in conjunction with the extra validity checking, since this
ensures that wherever possible uninitialized variables have invalid values.
See also the pragma Validity_Checks which allows modification of
the validity checking mode at the program source level, and also allows for
temporary disabling of validity checks.
Next: Run-Time Checks, Previous: Validity Checking, Up: Switches for gcc [Contents][Index]
The -gnatyx switch causes the compiler to enforce specified style rules. A limited set of style rules has been used in writing the GNAT sources themselves. This switch allows user programs to activate all or some of these checks. If the source program fails a specified style check, an appropriate message is given, preceded by the character sequence “(style)”. This message does not prevent successful compilation (unless the -gnatwe switch is used).
Note that this is by no means intended to be a general facility for checking arbitrary coding standards. It is simply an embedding of the style rules we have chosen for the GNAT sources. If you are starting a project which does not have established style standards, you may find it useful to adopt the entire set of GNAT coding standards, or some subset of them. If you already have an established set of coding standards, then it may be that selected style checking options do indeed correspond to choices you have made, but for general checking of an existing set of coding rules, you should look to the gnatcheck tool, which is designed for that purpose.
The string x is a sequence of letters or digits indicating the particular style checks to be performed. The following checks are defined:
Specify indentation level.
If a digit from 1-9 appears
in the string after -gnaty
then proper indentation is checked, with the digit indicating the
indentation level required. A value of zero turns off this style check.
The general style of required indentation is as specified by
the examples in the Ada Reference Manual. Full line comments must be
aligned with the -- starting on a column that is a multiple of
the alignment level, or they may be aligned the same way as the following
non-blank line (this is useful when full line comments appear in the middle
of a statement.
Check attribute casing.
Attribute names, including the case of keywords such as digits
used as attributes names, must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase.
Use of array index numbers in array attributes. When using the array attributes First, Last, Range, or Length, the index number must be omitted for one-dimensional arrays and is required for multi-dimensional arrays.
Blanks not allowed at statement end. Trailing blanks are not allowed at the end of statements. The purpose of this rule, together with h (no horizontal tabs), is to enforce a canonical format for the use of blanks to separate source tokens.
Check Boolean operators.
The use of AND/OR operators is not permitted except in the cases of modular
operands, array operands, and simple stand-alone boolean variables or
boolean constants. In all other cases and then/or else are
required.
Check comments, double space. Comments must meet the following set of rules:
--” that starts the column must either start in column one,
or else at least one blank must precede this sequence.
--” at the start of the comment.
--” that starts the comment, with the following exceptions.
--” characters, possibly preceded
by blanks is permitted.
--x” where x is a special character
is permitted.
This allows proper processing of the output generated by specialized tools
including gnatprep (where “--!” is used) and the SPARK
annotation
language (where “--#” is used). For the purposes of this rule, a
special character is defined as being in one of the ASCII ranges
16#21#…16#2F# or 16#3A#…16#3F#.
Note that this usage is not permitted
in GNAT implementation units (i.e., when -gnatg is used).
--” is permitted as long as at
least one blank follows the initial “--”. Together with the preceding
rule, this allows the construction of box comments, as shown in the following
example:
--------------------------- -- This is a box comment -- -- with two text lines. -- ---------------------------
Check comments, single space.
This is identical to c except that only one space
is required following the -- of a comment instead of two.
Check no DOS line terminators present. All lines must be terminated by a single ASCII.LF character (in particular the DOS line terminator sequence CR/LF is not allowed).
Check end/exit labels.
Optional labels on end statements ending subprograms and on
exit statements exiting named loops, are required to be present.
No form feeds or vertical tabs. Neither form feeds nor vertical tab characters are permitted in the source text.
GNAT style mode. The set of style check switches is set to match that used by the GNAT sources. This may be useful when developing code that is eventually intended to be incorporated into GNAT. For further details, see GNAT sources.
No horizontal tabs. Horizontal tab characters are not permitted in the source text. Together with the b (no blanks at end of line) check, this enforces a canonical form for the use of blanks to separate source tokens.
Check if-then layout.
The keyword then must appear either on the same
line as corresponding if, or on a line on its own, lined
up under the if with at least one non-blank line in between
containing all or part of the condition to be tested.
check mode IN keywords.
Mode in (the default mode) is not
allowed to be given explicitly. in out is fine,
but not in on its own.
Check keyword casing.
All keywords must be in lower case (with the exception of keywords
such as digits used as attribute names to which this check
does not apply).
Check layout.
Layout of statement and declaration constructs must follow the
recommendations in the Ada Reference Manual, as indicated by the
form of the syntax rules. For example an else keyword must
be lined up with the corresponding if keyword.
There are two respects in which the style rule enforced by this check
option are more liberal than those in the Ada Reference Manual. First
in the case of record declarations, it is permissible to put the
record keyword on the same line as the type keyword, and
then the end in end record must line up under type.
This is also permitted when the type declaration is split on two lines.
For example, any of the following three layouts is acceptable:
type q is record
a : integer;
b : integer;
end record;
type q is
record
a : integer;
b : integer;
end record;
type q is
record
a : integer;
b : integer;
end record;
|
Second, in the case of a block statement, a permitted alternative
is to put the block label on the same line as the declare or
begin keyword, and then line the end keyword up under
the block label. For example both the following are permitted:
Block : declare
A : Integer := 3;
begin
Proc (A, A);
end Block;
Block :
declare
A : Integer := 3;
begin
Proc (A, A);
end Block;
|
The same alternative format is allowed for loops. For example, both of the following are permitted:
Clear : while J < 10 loop
A (J) := 0;
end loop Clear;
Clear :
while J < 10 loop
A (J) := 0;
end loop Clear;
|
Set maximum nesting level. The maximum level of nesting of constructs (including subprograms, loops, blocks, packages, and conditionals) may not exceed the given value nnn. A value of zero disconnects this style check.
Check maximum line length. The length of source lines must not exceed 79 characters, including any trailing blanks. The value of 79 allows convenient display on an 80 character wide device or window, allowing for possible special treatment of 80 character lines. Note that this count is of characters in the source text. This means that a tab character counts as one character in this count and a wide character sequence counts as a single character (however many bytes are needed in the encoding).
Set maximum line length. The length of lines must not exceed the given value nnn. The maximum value that can be specified is 32767. If neither style option for setting the line length is used, then the default is 255. This also controls the maximum length of lexical elements, where the only restriction is that they must fit on a single line.
Check casing of entities in Standard.
Any identifier from Standard must be cased
to match the presentation in the Ada Reference Manual (for example,
Integer and ASCII.NUL).
Turn off all style checks. All style check options are turned off.
Check order of subprogram bodies. All subprogram bodies in a given scope (e.g. a package body) must be in alphabetical order. The ordering rule uses normal Ada rules for comparing strings, ignoring casing of letters, except that if there is a trailing numeric suffix, then the value of this suffix is used in the ordering (e.g. Junk2 comes before Junk10).
Check that overriding subprograms are explicitly marked as such. The declaration of a primitive operation of a type extension that overrides an inherited operation must carry an overriding indicator.
Check pragma casing. Pragma names must be written in mixed case, that is, the initial letter and any letter following an underscore must be uppercase. All other letters must be lowercase.
Check references. All identifier references must be cased in the same way as the corresponding declaration. No specific casing style is imposed on identifiers. The only requirement is for consistency of references with declarations.
Check separate specs. Separate declarations (“specs”) are required for subprograms (a body is not allowed to serve as its own declaration). The only exception is that parameterless library level procedures are not required to have a separate declaration. This exception covers the most frequent form of main program procedures.
Check no statements after then/else.
No statements are allowed
on the same line as a then or else keyword following the
keyword in an if statement. or else and and then are not
affected, and a special exception allows a pragma to appear after else.
Check token spacing. The following token spacing rules are enforced:
abs and not must be followed by a space.
=> must be surrounded by spaces.
<> must be preceded by a space or a left parenthesis.
** must be surrounded by spaces.
There is no restriction on the layout of the ** binary operator.
Exactly one blank (and no other white space) must appear between
a not token and a following in token.
Check unnecessary blank lines. Unnecessary blank lines are not allowed. A blank line is considered unnecessary if it appears at the end of the file, or if more than one blank line occurs in sequence.
Check extra parentheses.
Unnecessary extra level of parentheses (C-style) are not allowed
around conditions in if statements, while statements and
exit statements.
Set all standard style check options
This is equivalent to gnaty3aAbcefhiklmnprst, that is all checking
options enabled with the exception of -gnatyB, -gnatyd,
-gnatyI, -gnatyLnnn, -gnatyo, -gnatyO,
-gnatyS, -gnatyu, and -gnatyx.
Remove style check options This causes any subsequent options in the string to act as canceling the corresponding style check option. To cancel maximum nesting level control, use L parameter witout any integer value after that, because any digit following - in the parameter string of the -gnaty option will be threated as canceling indentation check. The same is true for M parameter. y and N parameters are not allowed after -.
This causes any subsequent options in the string to enable the corresponding style check option. That is, it cancels the effect of a previous -, if any.
In the above rules, appearing in column one is always permitted, that is, counts as meeting either a requirement for a required preceding space, or as meeting a requirement for no preceding space.
Appearing at the end of a line is also always permitted, that is, counts as meeting either a requirement for a following space, or as meeting a requirement for no following space.
If any of these style rules is violated, a message is generated giving
details on the violation. The initial characters of such messages are
always “(style)”. Note that these messages are treated as warning
messages, so they normally do not prevent the generation of an object
file. The -gnatwe switch can be used to treat warning messages,
including style messages, as fatal errors.
The switch -gnaty on its own (that is not followed by any letters or digits) is equivalent to the use of -gnatyy as described above, that is all built-in standard style check options are enabled.
The switch -gnatyN clears any previously set style checks.
Next: Using gcc for Syntax Checking, Previous: Style Checking, Up: Switches for gcc [Contents][Index]
By default, the following checks are suppressed: integer overflow
checks, stack overflow checks, and checks for access before
elaboration on subprogram calls. All other checks, including range
checks and array bounds checks, are turned on by default. The
following gcc switches refine this default behavior.
This switch causes the unit to be compiled
as though pragma Suppress (All_checks)
had been present in the source. Validity checks are also eliminated (in
other words -gnatp also implies -gnatVn.
Use this switch to improve the performance
of the code at the expense of safety in the presence of invalid data or
program bugs.
Note that when checks are suppressed, the compiler is allowed, but not required, to omit the checking code. If the run-time cost of the checking code is zero or near-zero, the compiler will generate it even if checks are suppressed. In particular, if the compiler can prove that a certain check will necessarily fail, it will generate code to do an unconditional “raise”, even if checks are suppressed. The compiler warns in this case. Another case in which checks may not be eliminated is when they are embedded in certain run time routines such as math library routines.
Of course, run-time checks are omitted whenever the compiler can prove that they will not fail, whether or not checks are suppressed.
Note that if you suppress a check that would have failed, program execution is erroneous, which means the behavior is totally unpredictable. The program might crash, or print wrong answers, or do anything else. It might even do exactly what you wanted it to do (and then it might start failing mysteriously next week or next year). The compiler will generate code based on the assumption that the condition being checked is true, which can result in disaster if that assumption is wrong.
The -gnatp switch has no effect if a subsequent -gnat-p switch appears.
This switch cancels the effect of a previous gnatp switch.
This switch controls the mode used for computing intermediate arithmetic integer operations, and also enables overflow checking. For a full description of overflow mode and checking control, see the “Overflow Check Handling in GNAT” appendix in this User’s Guide.
Overflow checks are always enabled by this switch. The argument controls the mode, using the codes
Long_Long_Integer). Overflow checking ensures that
the result fits in this larger integer type.
If two digits are present after -gnato then the first digit sets the mode for expressions outside assertions, and the second digit sets the mode for expressions within assertions. Here assertions is used in the technical sense (which includes for example precondition and postcondition expressions).
If one digit is present, the corresponding mode is applicable to both expressions within and outside assertion expressions.
If no digits are present, the default is to enable overflow checks and set STRICT mode for both kinds of expressions. This is compatible with the use of -gnato in previous versions of GNAT.
Note that the -gnato?? switch does not affect the code generated
for any floating-point operations; it applies only to integer
semantics.
For floating-point, GNAT has the Machine_Overflows
attribute set to False and the normal mode of operation is to
generate IEEE NaN and infinite values on overflow or invalid operations
(such as dividing 0.0 by 0.0).
The reason that we distinguish overflow checking from other kinds of range constraint checking is that a failure of an overflow check, unlike for example the failure of a range check, can result in an incorrect value, but cannot cause random memory destruction (like an out of range subscript), or a wild jump (from an out of range case value). Overflow checking is also quite expensive in time and space, since in general it requires the use of double length arithmetic.
Note again that the default is -gnato00, so overflow checking is
not performed in default mode. This means that out of the box, with the
default settings, GNAT does not do all the checks expected from the
language description in the Ada Reference Manual. If you want all constraint
checks to be performed, as described in this Manual, then you must
explicitly use the -gnato?? switch either on the gnatmake or
gcc command.
Enables dynamic checks for access-before-elaboration on subprogram calls and generic instantiations. Note that -gnatE is not necessary for safety, because in the default mode, GNAT ensures statically that the checks would not fail. For full details of the effect and use of this switch, See Compiling Using gcc.
Activates stack overflow checking. For full details of the effect and use of this switch see Stack Overflow Checking.
The setting of these switches only controls the default setting of the
checks. You may modify them using either Suppress (to remove
checks) or Unsuppress (to add back suppressed checks) pragmas in
the program source.
Next: Using gcc for Semantic Checking, Previous: Run-Time Checks, Up: Switches for gcc [Contents][Index]
gcc for Syntax CheckingThe s stands for “syntax”.
Run GNAT in syntax checking only mode. For example, the command
$ gcc -c -gnats x.adb
compiles file x.adb in syntax-check-only mode. You can check a series of files in a single command , and can use wild cards to specify such a group of files. Note that you must specify the -c (compile only) flag in addition to the -gnats flag. . You may use other switches in conjunction with -gnats. In particular, -gnatl and -gnatv are useful to control the format of any generated error messages.
When the source file is empty or contains only empty lines and/or comments, the output is a warning:
$ gcc -c -gnats -x ada toto.txt toto.txt:1:01: warning: empty file, contains no compilation units $
Otherwise, the output is simply the error messages, if any. No object file or
ALI file is generated by a syntax-only compilation. Also, no units other
than the one specified are accessed. For example, if a unit X
with’s a unit Y, compiling unit X in syntax
check only mode does not access the source file containing unit
Y.
Normally, GNAT allows only a single unit in a source file. However, this
restriction does not apply in syntax-check-only mode, and it is possible
to check a file containing multiple compilation units concatenated
together. This is primarily used by the gnatchop utility
(see Renaming Files Using gnatchop).
Next: Compiling Different Versions of Ada, Previous: Using gcc for Syntax Checking, Up: Switches for gcc [Contents][Index]
gcc for Semantic CheckingThe c stands for “check”.
Causes the compiler to operate in semantic check mode,
with full checking for all illegalities specified in the
Ada Reference Manual, but without generation of any object code
(no object file is generated).
Because dependent files must be accessed, you must follow the GNAT semantic restrictions on file structuring to operate in this mode:
The output consists of error messages as appropriate. No object file is generated. An ALI file is generated for use in the context of cross-reference tools, but this file is marked as not being suitable for binding (since no object file is generated). The checking corresponds exactly to the notion of legality in the Ada Reference Manual.
Any unit can be compiled in semantics-checking-only mode, including units that would not normally be compiled (subunits, and specifications where a separate body is present).
Next: Character Set Control, Previous: Using gcc for Semantic Checking, Up: Switches for gcc [Contents][Index]
The switches described in this section allow you to explicitly specify the version of the Ada language that your programs are written in. By default GNAT assumes Ada 2005, but you can also specify Ada 95 or indicate Ada 83 compatibility mode.
Although GNAT is primarily an Ada 95 / Ada 2005 compiler, this switch specifies that the program is to be compiled in Ada 83 mode. With -gnat83, GNAT rejects most post-Ada 83 extensions and applies Ada 83 semantics where this can be done easily. It is not possible to guarantee this switch does a perfect job; some subtle tests, such as are found in earlier ACVC tests (and that have been removed from the ACATS suite for Ada 95), might not compile correctly. Nevertheless, this switch may be useful in some circumstances, for example where, due to contractual reasons, existing code needs to be maintained using only Ada 83 features.
With few exceptions (most notably the need to use <> on
unconstrained generic formal parameters, the use of the new Ada 95 / Ada 2005
reserved words, and the use of packages
with optional bodies), it is not necessary to specify the
-gnat83 switch when compiling Ada 83 programs, because, with rare
exceptions, Ada 95 and Ada 2005 are upwardly compatible with Ada 83. Thus
a correct Ada 83 program is usually also a correct program
in these later versions of the language standard.
For further information, please refer to Compatibility and Porting Guide.
This switch directs the compiler to implement the Ada 95 version of the language. Since Ada 95 is almost completely upwards compatible with Ada 83, Ada 83 programs may generally be compiled using this switch (see the description of the -gnat83 switch for further information about Ada 83 mode). If an Ada 2005 program is compiled in Ada 95 mode, uses of the new Ada 2005 features will cause error messages or warnings.
This switch also can be used to cancel the effect of a previous -gnat83, -gnat05/2005, or -gnat12/2012 switch earlier in the command line.
This switch directs the compiler to implement the Ada 2005 version of the language, as documented in the official Ada standards document. Since Ada 2005 is almost completely upwards compatible with Ada 95 (and thus also with Ada 83), Ada 83 and Ada 95 programs may generally be compiled using this switch (see the description of the -gnat83 and -gnat95 switches for further information).
This switch directs the compiler to implement the Ada 2012 version of the language. Since Ada 2012 is almost completely upwards compatible with Ada 2005 (and thus also with Ada 83, and Ada 95), Ada 83 and Ada 95 programs may generally be compiled using this switch (see the description of the -gnat83, -gnat95, and -gnat05/2005 switches for further information).
For information about the approved “Ada Issues” that have been incorporated into Ada 2012, see http://www.ada-auth.org/ais.html. Included with GNAT releases is a file features-ada12 that describes the set of implemented Ada 2012 features.
This switch directs the compiler to implement the latest version of the language (currently Ada 2012) and also to enable certain GNAT implementation extensions that are not part of any Ada standard. For a full list of these extensions, see the GNAT reference manual.
Next: File Naming Control, Previous: Compiling Different Versions of Ada, Up: Switches for gcc [Contents][Index]
Normally GNAT recognizes the Latin-1 character set in source program identifiers, as described in the Ada Reference Manual. This switch causes GNAT to recognize alternate character sets in identifiers. c is a single character indicating the character set, as follows:
1ISO 8859-1 (Latin-1) identifiers
2ISO 8859-2 (Latin-2) letters allowed in identifiers
3ISO 8859-3 (Latin-3) letters allowed in identifiers
4ISO 8859-4 (Latin-4) letters allowed in identifiers
5ISO 8859-5 (Cyrillic) letters allowed in identifiers
9ISO 8859-15 (Latin-9) letters allowed in identifiers
pIBM PC letters (code page 437) allowed in identifiers
8IBM PC letters (code page 850) allowed in identifiers
fFull upper-half codes allowed in identifiers
nNo upper-half codes allowed in identifiers
wWide-character codes (that is, codes greater than 255) allowed in identifiers
See Foreign Language Representation, for full details on the implementation of these character sets.
Specify the method of encoding for wide characters. e is one of the following:
hHex encoding (brackets coding also recognized)
uUpper half encoding (brackets encoding also recognized)
sShift/JIS encoding (brackets encoding also recognized)
eEUC encoding (brackets encoding also recognized)
8UTF-8 encoding (brackets encoding also recognized)
bBrackets encoding only (default value)
For full details on these encoding methods see Wide Character Encodings. Note that brackets coding is always accepted, even if one of the other options is specified, so for example -gnatW8 specifies that both brackets and UTF-8 encodings will be recognized. The units that are with’ed directly or indirectly will be scanned using the specified representation scheme, and so if one of the non-brackets scheme is used, it must be used consistently throughout the program. However, since brackets encoding is always recognized, it may be conveniently used in standard libraries, allowing these libraries to be used with any of the available coding schemes.
Note that brackets encoding only applies to program text. Within comments, brackets are considered to be normal graphic characters, and bracket sequences are never recognized as wide characters.
If no -gnatW? parameter is present, then the default representation is normally Brackets encoding only. However, if the first three characters of the file are 16#EF# 16#BB# 16#BF# (the standard byte order mark or BOM for UTF-8), then these three characters are skipped and the default representation for the file is set to UTF-8.
Note that the wide character representation that is specified (explicitly or by default) for the main program also acts as the default encoding used for Wide_Text_IO files if not specifically overridden by a WCEM form parameter.
When no -gnatW? is specified, then characters (other than wide characters represented using brackets notation) are treated as 8-bit Latin-1 codes. The codes recognized are the Latin-1 graphic characters, and ASCII format effectors (CR, LF, HT, VT). Other lower half control characters in the range 16#00#..16#1F# are not accepted in program text or in comments. Upper half control characters (16#80#..16#9F#) are rejected in program text, but allowed and ignored in comments. Note in particular that the Next Line (NEL) character whose encoding is 16#85# is not recognized as an end of line in this default mode. If your source program contains instances of the NEL character used as a line terminator, you must use UTF-8 encoding for the whole source program. In default mode, all lines must be ended by a standard end of line sequence (CR, CR/LF, or LF).
Note that the convention of simply accepting all upper half characters in comments means that programs that use standard ASCII for program text, but UTF-8 encoding for comments are accepted in default mode, providing that the comments are ended by an appropriate (CR, or CR/LF, or LF) line terminator. This is a common mode for many programs with foreign language comments.
Next: Subprogram Inlining Control, Previous: Character Set Control, Up: Switches for gcc [Contents][Index]
Activates file name “krunching”. n, a decimal integer in the range 1-999, indicates the maximum allowable length of a file name (not including the .ads or .adb extension). The default is not to enable file name krunching.
For the source file naming rules, See File Naming Rules.
Next: Auxiliary Output Control, Previous: File Naming Control, Up: Switches for gcc [Contents][Index]
The n here is intended to suggest the first syllable of the
word “inline”.
GNAT recognizes and processes Inline pragmas. However, for the
inlining to actually occur, optimization must be enabled and, in order
to enable inlining of subprograms specified by pragma Inline,
you must also specify this switch.
In the absence of this switch, GNAT does not attempt
inlining and does not need to access the bodies of
subprograms for which pragma Inline is specified if they are not
in the current unit.
You can optionally specify the inlining level: 1 for moderate inlining across modules, which is a good compromise between compilation times and performances at run time, or 2 for full inlining across modules, which may bring about longer compilation times. If no inlining level is specified, the compiler will pick it based on the optimization level: 1 for -O1, -O2 or -Os and 2 for -O3.
If you specify this switch the compiler will access these bodies, creating an extra source dependency for the resulting object file, and where possible, the call will be inlined. For further details on when inlining is possible see Inlining of Subprograms.
This switch activates front-end inlining which also generates additional dependencies.
When using a gcc-based back end (in practice this means using any version of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of -gnatN is deprecated, and the use of -gnatn is preferred. Historically front end inlining was more extensive than the gcc back end inlining, but that is no longer the case.
Next: Debugging Control, Previous: Subprogram Inlining Control, Up: Switches for gcc [Contents][Index]
Causes GNAT to write the internal tree for a unit to a file (with the extension .adt. This not normally required, but is used by separate analysis tools. Typically these tools do the necessary compilations automatically, so you should not have to specify this switch in normal operation. Note that the combination of switches -gnatct generates a tree in the form required by ASIS applications.
Print a list of units required by this compilation on stdout. The listing includes all units on which the unit being compiled depends either directly or indirectly.
If this switch is not used, the exit code returned by gcc when
compiling multiple files indicates whether all source files have
been successfully used to generate object files or not.
When -pass-exit-codes is used, gcc exits with an extended
exit status and allows an integrated development environment to better
react to a compilation failure. Those exit status are:
There was an error in at least one source file.
At least one source file did not generate an object file.
The compiler died unexpectedly (internal error for example).
An object file has been generated for every source file.
Next: Exception Handling Control, Previous: Auxiliary Output Control, Up: Switches for gcc [Contents][Index]
Activate internal debugging switches. x is a letter or digit, or
string of letters or digits, which specifies the type of debugging
outputs desired. Normally these are used only for internal development
or system debugging purposes. You can find full documentation for these
switches in the body of the Debug unit in the compiler source
file debug.adb.
This switch causes the compiler to generate auxiliary output containing a pseudo-source listing of the generated expanded code. Like most Ada compilers, GNAT works by first transforming the high level Ada code into lower level constructs. For example, tasking operations are transformed into calls to the tasking run-time routines. A unique capability of GNAT is to list this expanded code in a form very close to normal Ada source. This is very useful in understanding the implications of various Ada usage on the efficiency of the generated code. There are many cases in Ada (e.g. the use of controlled types), where simple Ada statements can generate a lot of run-time code. By using -gnatG you can identify these cases, and consider whether it may be desirable to modify the coding approach to improve efficiency.
The optional parameter nn if present after -gnatG specifies an
alternative maximum line length that overrides the normal default of 72.
This value is in the range 40-999999, values less than 40 being silently
reset to 40. The equal sign is optional.
The format of the output is very similar to standard Ada source, and is
easily understood by an Ada programmer. The following special syntactic
additions correspond to low level features used in the generated code that
do not have any exact analogies in pure Ada source form. The following
is a partial list of these special constructions. See the spec
of package Sprint in file sprint.ads for a full list.
If the switch -gnatL is used in conjunction with -gnatG, then the original source lines are interspersed in the expanded source (as comment lines with the original line number).
new xxx [storage_pool = yyy]Shows the storage pool being used for an allocator.
at end procedure-name;Shows the finalization (cleanup) procedure for a scope.
(if expr then expr else expr)Conditional expression equivalent to the x?y:z construction in C.
target^(source)A conversion with floating-point truncation instead of rounding.
target?(source)A conversion that bypasses normal Ada semantic checking. In particular enumeration types and fixed-point types are treated simply as integers.
target?^(source)Combines the above two cases.
x #/ yx #mod yx #* yx #rem yA division or multiplication of fixed-point values which are treated as integers without any kind of scaling.
free expr [storage_pool = xxx]Shows the storage pool associated with a free statement.
[subtype or type declaration]Used to list an equivalent declaration for an internally generated type that is referenced elsewhere in the listing.
freeze type-name [actions]Shows the point at which type-name is frozen, with possible associated actions to be performed at the freeze point.
reference itypeReference (and hence definition) to internal type itype.
function-name! (arg, arg, arg)Intrinsic function call.
label-name : labelDeclaration of label labelname.
#$ subprogram-nameAn implicit call to a run-time support routine (to meet the requirement of H.3.1(9) in a convenient manner).
expr && expr && expr … && exprA multiple concatenation (same effect as expr & expr & expr, but handled more efficiently).
[constraint_error]Raise the Constraint_Error exception.
expression'referenceA pointer to the result of evaluating expression.
target-type!(source-expression)An unchecked conversion of source-expression to target-type.
[numerator/denominator]Used to represent internal real literals (that) have no exact representation in base 2-16 (for example, the result of compile time evaluation of the expression 1.0/27.0).
When used in conjunction with -gnatG, this switch causes
the expanded source, as described above for
-gnatG to be written to files with names
xxx.dg, where xxx is the normal file name,
instead of to the standard output file. For
example, if the source file name is hello.adb, then a file
hello.adb.dg will be written. The debugging
information generated by the gcc -g switch
will refer to the generated xxx.dg file. This allows
you to do source level debugging using the generated code which is
sometimes useful for complex code, for example to find out exactly
which part of a complex construction raised an exception. This switch
also suppress generation of cross-reference information (see
-gnatx) since otherwise the cross-reference information
would refer to the .dg file, which would cause
confusion since this is not the original source file.
Note that -gnatD actually implies -gnatG automatically, so it is not necessary to give both options. In other words -gnatD is equivalent to -gnatDG).
If the switch -gnatL is used in conjunction with -gnatDG, then the original source lines are interspersed in the expanded source (as comment lines with the original line number).
The optional parameter nn if present after -gnatD specifies an
alternative maximum line length that overrides the normal default of 72.
This value is in the range 40-999999, values less than 40 being silently
reset to 40. The equal sign is optional.
This switch causes pragma Restrictions to be treated as Restriction_Warnings so that violation of restrictions causes warnings rather than illegalities. This is useful during the development process when new restrictions are added or investigated. The switch also causes pragma Profile to be treated as Profile_Warnings, and pragma Restricted_Run_Time and pragma Ravenscar set restriction warnings rather than restrictions.
This switch controls output from the compiler of a listing showing
representation information for declared types and objects. For
-gnatR0, no information is output (equivalent to omitting
the -gnatR switch). For -gnatR1 (which is the default,
so -gnatR with no parameter has the same effect), size and alignment
information is listed for declared array and record types. For
-gnatR2, size and alignment information is listed for all
declared types and objects. Finally -gnatR3 includes symbolic
expressions for values that are computed at run time for
variant records. These symbolic expressions have a mostly obvious
format with #n being used to represent the value of the n’th
discriminant. See source files repinfo.ads/adb in the
GNAT sources for full details on the format of -gnatR3
output. If the switch is followed by an s (e.g. -gnatR2s), then
the output is to a file with the name file.rep where
file is the name of the corresponding source file.
Note that it is possible for record components to have zero size. In
this case, the component clause uses an obvious extension of permitted
Ada syntax, for example at 0 range 0 .. -1.
Representation information requires that code be generated (since it is the code generator that lays out complex data structures). If an attempt is made to output representation information when no code is generated, for example when a subunit is compiled on its own, then no information can be generated and the compiler outputs a message to this effect.
The use of the switch -gnatS for an Ada compilation will cause the compiler to output a representation of package Standard in a form very close to standard Ada. It is not quite possible to do this entirely in standard Ada (since new numeric base types cannot be created in standard Ada), but the output is easily readable to any Ada programmer, and is useful to determine the characteristics of target dependent types in package Standard.
Normally the compiler generates full cross-referencing information in
the ALI file. This information is used by a number of tools,
including gnatfind and gnatxref. The -gnatx switch
suppresses this information. This saves some space and may slightly
speed up compilation, but means that these tools cannot be used.
Next: Units to Sources Mapping Files, Previous: Debugging Control, Up: Switches for gcc [Contents][Index]
GNAT uses two methods for handling exceptions at run-time. The
setjmp/longjmp method saves the context when entering
a frame with an exception handler. Then when an exception is
raised, the context can be restored immediately, without the
need for tracing stack frames. This method provides very fast
exception propagation, but introduces significant overhead for
the use of exception handlers, even if no exception is raised.
The other approach is called “zero cost” exception handling. With this method, the compiler builds static tables to describe the exception ranges. No dynamic code is required when entering a frame containing an exception handler. When an exception is raised, the tables are used to control a back trace of the subprogram invocation stack to locate the required exception handler. This method has considerably poorer performance for the propagation of exceptions, but there is no overhead for exception handlers if no exception is raised. Note that in this mode and in the context of mixed Ada and C/C++ programming, to propagate an exception through a C/C++ code, the C/C++ code must be compiled with the -funwind-tables GCC’s option.
The following switches may be used to control which of the two exception handling methods is used.
This switch causes the setjmp/longjmp run-time (when available) to be used for exception handling. If the default mechanism for the target is zero cost exceptions, then this switch can be used to modify this default, and must be used for all units in the partition. This option is rarely used. One case in which it may be advantageous is if you have an application where exception raising is common and the overall performance of the application is improved by favoring exception propagation.
This switch causes the zero cost approach to be used for exception handling. If this is the default mechanism for the target (see below), then this switch is unneeded. If the default mechanism for the target is setjmp/longjmp exceptions, then this switch can be used to modify this default, and must be used for all units in the partition. This option can only be used if the zero cost approach is available for the target in use, otherwise it will generate an error.
The same option --RTS must be used both for gcc
and gnatbind. Passing this option to gnatmake
(see Switches for gnatmake) will ensure the required consistency
through the compilation and binding steps.
Next: Integrated Preprocessing, Previous: Exception Handling Control, Up: Switches for gcc [Contents][Index]
A mapping file is a way to communicate to the compiler two mappings: from unit names to file names (without any directory information) and from file names to path names (with full directory information). These mappings are used by the compiler to short-circuit the path search.
The use of mapping files is not required for correct operation of the
compiler, but mapping files can improve efficiency, particularly when
sources are read over a slow network connection. In normal operation,
you need not be concerned with the format or use of mapping files,
and the -gnatem switch is not a switch that you would use
explicitly. It is intended primarily for use by automatic tools such as
gnatmake running under the project file facility. The
description here of the format of mapping files is provided
for completeness and for possible use by other tools.
A mapping file is a sequence of sets of three lines. In each set, the
first line is the unit name, in lower case, with %s appended
for specs and %b appended for bodies; the second line is the
file name; and the third line is the path name.
Example:
main%b main.2.ada /gnat/project1/sources/main.2.ada
When the switch -gnatem is specified, the compiler will create in memory the two mappings from the specified file. If there is any problem (nonexistent file, truncated file or duplicate entries), no mapping will be created.
Several -gnatem switches may be specified; however, only the last one on the command line will be taken into account.
When using a project file, gnatmake creates a temporary
mapping file and communicates it to the compiler using this switch.
Next: Code Generation Control, Previous: Units to Sources Mapping Files, Up: Switches for gcc [Contents][Index]
GNAT sources may be preprocessed immediately before compilation. In this case, the actual text of the source is not the text of the source file, but is derived from it through a process called preprocessing. Integrated preprocessing is specified through switches -gnatep and/or -gnateD. -gnatep indicates, through a text file, the preprocessing data to be used. -gnateD specifies or modifies the values of preprocessing symbol.
Note that when integrated preprocessing is used, the output from the
preprocessor is not written to any external file. Instead it is passed
internally to the compiler. If you need to preserve the result of
preprocessing in a file, then you should use gnatprep
to perform the desired preprocessing in stand-alone mode.
It is recommended that gnatmake switch -s should be
used when Integrated Preprocessing is used. The reason is that preprocessing
with another Preprocessing Data file without changing the sources will
not trigger recompilation without this switch.
Note that gnatmake switch -m will almost
always trigger recompilation for sources that are preprocessed,
because gnatmake cannot compute the checksum of the source after
preprocessing.
The actual preprocessing function is described in details in section Preprocessing Using gnatprep. This section only describes how integrated preprocessing is triggered and parameterized.
-gnatep=fileThis switch indicates to the compiler the file name (without directory
information) of the preprocessor data file to use. The preprocessor data file
should be found in the source directories. Note that when the compiler is
called by a builder (gnatmake or gprbuild) with a project
file, if the object directory is not also a source directory, the builder needs
to be called with -x.
A preprocessing data file is a text file with significant lines indicating how should be preprocessed either a specific source or all sources not mentioned in other lines. A significant line is a nonempty, non-comment line. Comments are similar to Ada comments.
Each significant line starts with either a literal string or the character ’*’. A literal string is the file name (without directory information) of the source to preprocess. A character ’*’ indicates the preprocessing for all the sources that are not specified explicitly on other lines (order of the lines is not significant). It is an error to have two lines with the same file name or two lines starting with the character ’*’.
After the file name or the character ’*’, another optional literal string indicating the file name of the definition file to be used for preprocessing (see Form of Definitions File). The definition files are found by the compiler in one of the source directories. In some cases, when compiling a source in a directory other than the current directory, if the definition file is in the current directory, it may be necessary to add the current directory as a source directory through switch -I., otherwise the compiler would not find the definition file.
Then, optionally, switches similar to those of gnatprep may
be found. Those switches are:
-bCauses both preprocessor lines and the lines deleted by preprocessing to be replaced by blank lines, preserving the line number. This switch is always implied; however, if specified after -c it cancels the effect of -c.
-cCauses both preprocessor lines and the lines deleted
by preprocessing to be retained as comments marked
with the special string “--! ”.
-Dsymbol=valueDefine or redefine a symbol, associated with value. A symbol is an Ada
identifier, or an Ada reserved word, with the exception of if,
else, elsif, end, and, or and then.
value is either a literal string, an Ada identifier or any Ada reserved
word. A symbol declared with this switch replaces a symbol with the
same name defined in a definition file.
-sCauses a sorted list of symbol names and values to be listed on the standard output file.
-uCauses undefined symbols to be treated as having the value FALSE
in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a #if or #elsif test will be treated as an error.
Examples of valid lines in a preprocessor data file:
"toto.adb" "prep.def" -u -- preprocess "toto.adb", using definition file "prep.def", -- undefined symbol are False. * -c -DVERSION=V101 -- preprocess all other sources without a definition file; -- suppressed lined are commented; symbol VERSION has the value V101. "titi.adb" "prep2.def" -s -- preprocess "titi.adb", using definition file "prep2.def"; -- list all symbols with their values.
-gnateDsymbol[=value]Define or redefine a preprocessing symbol, associated with value. If no value
is given on the command line, then the value of the symbol is True.
A symbol is an identifier, following normal Ada (case-insensitive)
rules for its syntax, and value is any sequence (including an empty sequence)
of characters from the set (letters, digits, period, underline).
Ada reserved words may be used as symbols, with the exceptions of if,
else, elsif, end, and, or and then.
A symbol declared with this switch on the command line replaces a symbol with the same name either in a definition file or specified with a switch -D in the preprocessor data file.
This switch is similar to switch -D of gnatprep.
-gnateGWhen integrated preprocessing is performed and the preprocessor modifies the source text, write the result of this preprocessing into a file <source>.prep.
Previous: Integrated Preprocessing, Up: Switches for gcc [Contents][Index]
The GCC technology provides a wide range of target dependent -m switches for controlling details of code generation with respect to different versions of architectures. This includes variations in instruction sets (e.g. different members of the power pc family), and different requirements for optimal arrangement of instructions (e.g. different members of the x86 family). The list of available -m switches may be found in the GCC documentation.
Use of these -m switches may in some cases result in improved code performance.
The GNAT technology is tested and qualified without any -m switches, so generally the most reliable approach is to avoid the use of these switches. However, we generally expect most of these switches to work successfully with GNAT, and many customers have reported successful use of these options.
Our general advice is to avoid the use of -m switches unless special needs lead to requirements in this area. In particular, there is no point in using -m switches to improve performance unless you actually see a performance improvement.
Next: Order of Compilation Issues, Previous: Switches for gcc, Up: Compiling Using gcc [Contents][Index]
With the GNAT source-based library system, the compiler must be able to find source files for units that are needed by the unit being compiled. Search paths are used to guide this process.
The compiler compiles one source file whose name must be given explicitly on the command line. In other words, no searching is done for this file. To find all other source files that are needed (the most common being the specs of units), the compiler examines the following directories, in the following order:
gcc command line, in the order given.
ADA_PRJ_INCLUDE_FILE environment variable.
ADA_PRJ_INCLUDE_FILE is normally set by gnatmake or by the gnat
driver when project files are used. It should not normally be set
by other means.
ADA_INCLUDE_PATH environment variable.
Construct this value
exactly as the PATH environment variable: a list of directory
names separated by colons (semicolons when working with the NT version).
Specifying the switch -I- inhibits the use of the directory containing the source file named in the command line. You can still have this directory on your search path, but in this case it must be explicitly requested with a -I switch.
Specifying the switch -nostdinc inhibits the search of the default location for the GNAT Run Time Library (RTL) source files.
The compiler outputs its object files and ALI files in the current
working directory.
Caution: The object file can be redirected with the -o switch;
however, gcc and gnat1 have not been coordinated on this
so the ALI file will not go to the right place. Therefore, you should
avoid using the -o switch.
The packages Ada, System, and Interfaces and their
children make up the GNAT RTL, together with the simple System.IO
package used in the "Hello World" example. The sources for these units
are needed by the compiler and are kept together in one directory. Not
all of the bodies are needed, but all of the sources are kept together
anyway. In a normal installation, you need not specify these directory
names when compiling or binding. Either the environment variables or
the built-in defaults cause these files to be found.
In addition to the language-defined hierarchies (System, Ada and
Interfaces), the GNAT distribution provides a fourth hierarchy,
consisting of child units of GNAT. This is a collection of generally
useful types, subprograms, etc. See About
This Guid in GNAT Reference Manual, for further details.
Besides simplifying access to the RTL, a major use of search paths is in compiling sources from multiple directories. This can make development environments much more flexible.
Next: Examples, Previous: Search Paths and the Run-Time Library (RTL), Up: Compiling Using gcc [Contents][Index]
If, in our earlier example, there was a spec for the hello
procedure, it would be contained in the file hello.ads; yet this
file would not have to be explicitly compiled. This is the result of the
model we chose to implement library management. Some of the consequences
of this model are as follows:
with’s, all its subunits, and the bodies of any generics it
instantiates must be available (reachable by the search-paths mechanism
described above), or you will receive a fatal error message.
Next: Output and Error Message Control, Previous: Order of Compilation Issues, Up: Compiling Using gcc [Contents][Index]
The following are some typical Ada compilation command line examples:
$ gcc -c xyz.adbCompile body in file xyz.adb with all default options.
$ gcc -c -O2 -gnata xyz-def.adbCompile the child unit package in file xyz-def.adb with extensive
optimizations, and pragma Assert/Debug statements
enabled.
$ gcc -c -gnatc abc-def.adbCompile the subunit in file abc-def.adb in semantic-checking-only mode.
Next: Linking Using gnatlink, Previous: Compiling Using gcc, Up: Top [Contents][Index]
gnatbind| • Running gnatbind: | ||
| • Switches for gnatbind: | ||
| • Command-Line Access: | ||
| • Search Paths for gnatbind: | ||
| • Examples of gnatbind Usage: |
This chapter describes the GNAT binder, gnatbind, which is used
to bind compiled GNAT objects.
Note: to invoke gnatbind with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
The gnatbind program performs four separate functions:
gnatlink. The two most important
functions of this program
are to call the elaboration routines of units in an appropriate order
and to call the main program.
gnatlink utility used to link the Ada application.
Next: Switches for gnatbind, Previous: Integrated Preprocessing, Up: Binding Using gnatbind [Contents][Index]
gnatbindThe form of the gnatbind command is
$ gnatbind [switches] mainprog[.ali] [switches]
where mainprog.adb is the Ada file containing the main program
unit body. gnatbind constructs an Ada
package in two files whose names are
b~mainprog.ads, and b~mainprog.adb.
For example, if given the
parameter hello.ali, for a main program contained in file
hello.adb, the binder output files would be b~hello.ads
and b~hello.adb.
When doing consistency checking, the binder takes into consideration
any source files it can locate. For example, if the binder determines
that the given main program requires the package Pack, whose
.ALI
file is pack.ali and whose corresponding source spec file is
pack.ads, it attempts to locate the source file pack.ads
(using the same search path conventions as previously described for the
gcc command). If it can locate this source file, it checks that
the time stamps
or source checksums of the source and its references to in ALI files
match. In other words, any ALI files that mentions this spec must have
resulted from compiling this version of the source file (or in the case
where the source checksums match, a version close enough that the
difference does not matter).
The effect of this consistency checking, which includes source files, is that the binder ensures that the program is consistent with the latest version of the source files that can be located at bind time. Editing a source file without compiling files that depend on the source file cause error messages to be generated by the binder.
For example, suppose you have a main program hello.adb and a
package P, from file p.ads and you perform the following
steps:
gcc -c hello.adb to compile the main program.
gcc -c p.ads to compile package P.
gnatbind hello.
At this point, the file p.ali contains an out-of-date time stamp because the file p.ads has been edited. The attempt at binding fails, and the binder generates the following error messages:
error: "hello.adb" must be recompiled ("p.ads" has been modified)
error: "p.ads" has been modified and must be recompiled
Now both files must be recompiled as indicated, and then the bind can succeed, generating a main program. You need not normally be concerned with the contents of this file, but for reference purposes a sample binder output file is given in Example of Binder Output File.
In most normal usage, the default mode of gnatbind which is to
generate the main package in Ada, as described in the previous section.
In particular, this means that any Ada programmer can read and understand
the generated main program. It can also be debugged just like any other
Ada code provided the -g switch is used for
gnatbind and gnatlink.
Next: Command-Line Access, Previous: Running gnatbind, Up: Binding Using gnatbind [Contents][Index]
gnatbindThe following switches are available with gnatbind; details will
be presented in subsequent sections.
Display Copyright and version, then exit disregarding all other options.
If --version was not used, display usage, then exit disregarding all other options.
Indicates that, if supported by the platform, the adainit procedure should be treated as an initialisation routine by the linker (a constructor). This is intended to be used by the Project Manager to automatically initialize shared Stand-Alone Libraries.
Specify directory to be searched for ALI files.
Specify directory to be searched for source file.
Output ALI list (to standard output or to the named file).
Generate brief messages to stderr even if verbose mode set.
Check only, no generation of binder output file.
This switch can be used to change the default task stack size value to a specified size nn, which is expressed in bytes by default, or in kilobytes when suffixed with k or in megabytes when suffixed with m. In the absence of a ‘[k|m]’ suffix, this switch is equivalent, in effect, to completing all task specs with
pragma Storage_Size (nn);
When they do not already have such a pragma.
This switch can be used to change the default secondary stack size value to a specified size nn, which is expressed in bytes by default, or in kilobytes when suffixed with k or in megabytes when suffixed with m.
The secondary stack is used to deal with functions that return a variable sized result, for example a function returning an unconstrained String. There are two ways in which this secondary stack is allocated.
For most targets, the secondary stack is growing on demand and is allocated as a chain of blocks in the heap. The -D option is not very relevant. It only give some control over the size of the allocated blocks (whose size is the minimum of the default secondary stack size value, and the actual size needed for the current allocation request).
For certain targets, notably VxWorks 653, the secondary stack is allocated by carving off a fixed ratio chunk of the primary task stack. The -D option is used to define the size of the environment task’s secondary stack.
Output complete list of elaboration-order dependencies.
Store tracebacks in exception occurrences when the target supports it.
See also the packages GNAT.Traceback and
GNAT.Traceback.Symbolic for more information.
Note that on x86 ports, you must not use -fomit-frame-pointer
gcc option.
Force the checks of elaboration flags. gnatbind does not normally
generate checks of elaboration flags for the main executable, except when
a Stand-Alone Library is used. However, there are cases when this cannot be
detected by gnatbind. An example is importing an interface of a Stand-Alone
Library through a pragma Import and only specifying through a linker switch
this Stand-Alone Library. This switch is used to guarantee that elaboration
flag checks are generated.
Output usage (help) information
Use 32-bit allocations for __gnat_malloc (and thus for access types).
For further details see Dynamic Allocation Control.
Use 64-bit allocations for __gnat_malloc (and thus for access types).
For further details see Dynamic Allocation Control.
Specify directory to be searched for source and ALI files.
Do not look for sources in the current directory where gnatbind was
invoked, and do not look for ALI files in the directory containing the
ALI file named in the gnatbind command line.
Output chosen elaboration order.
Bind the units for library building. In this case the adainit and adafinal procedures (see Binding with Non-Ada Main Programs) are renamed to xxxinit and xxxfinal. Implies -n. (See GNAT and Libraries, for more details.)
Rename generated main program from main to xyz. This option is supported on cross environments only.
Limit number of detected errors or warnings to n, where n is in the range 1..999999. The default value if no switch is given is 9999. If the number of warnings reaches this limit, then a message is output and further warnings are suppressed, the bind continues in this case. If the number of errors reaches this limit, then a message is output and the bind is abandoned. A value of zero means that no limit is enforced. The equal sign is optional.
Furthermore, under Windows, the sources pointed to by the libraries path set in the registry are not searched for.
No main program.
Do not look for sources in the system default directory.
Do not look for library files in the system default directory.
Specifies the default location of the runtime library. Same meaning as the
equivalent gnatmake flag (see Switches for gnatmake).
Name the output file file (default is b~xxx.adb). Note that if this option is used, then linking must be done manually, gnatlink cannot be used.
Output object list (to standard output or to the named file).
Pessimistic (worst-case) elaboration order
Generate binder file suitable for CodePeer.
Output closure source list.
Require all source files to be present.
Specifies the value to be used when detecting uninitialized scalar objects with pragma Initialize_Scalars. The xxx string specified with the switch may be either
16#xx# (i.e., xx is a string of two hexadecimal digits).
In addition, you can specify -Sev to indicate that the value is
to be set at run time. In this case, the program will look for an environment
variable of the form GNAT_INIT_SCALARS=xx, where xx is one
of in/lo/hi/xx with the same meanings as above.
If no environment variable is found, or if it does not have a valid value,
then the default is in (invalid values).
Link against a static GNAT run time.
Link against a shared GNAT run time when available.
Tolerate time stamp and other consistency errors
Set the time slice value to n milliseconds. If the system supports the specification of a specific time slice value, then the indicated value is used. If the system does not support specific time slice values, but does support some general notion of round-robin scheduling, then any nonzero value will activate round-robin scheduling.
A value of zero is treated specially. It turns off time
slicing, and in addition, indicates to the tasking run time that the
semantics should match as closely as possible the Annex D
requirements of the Ada RM, and in particular sets the default
scheduling policy to FIFO_Within_Priorities.
Enable dynamic stack usage, with n results stored and displayed at program termination. A result is generated when a task terminates. Results that can’t be stored are displayed on the fly, at task termination. This option is currently not supported on Itanium platforms. (See Dynamic Stack Usage Analysis for details.)
Verbose mode. Write error messages, header, summary output to stdout.
Warning mode (x=s/e for suppress/treat as error)
Override default wide character encoding for standard Text_IO files.
Exclude source files (check object consistency only).
Enable leap seconds support in Ada.Calendar and its children.
No main subprogram.
You may obtain this listing of switches by running gnatbind with
no arguments.
Next: Binder Error Message Control, Previous: Examples of gnatbind Usage, Up: Switches for gnatbind [Contents][Index]
As described earlier, by default gnatbind checks
that object files are consistent with one another and are consistent
with any source files it can locate. The following switches control binder
access to sources.
Require source files to be present. In this mode, the binder must be able to locate all source files that are referenced, in order to check their consistency. In normal mode, if a source file cannot be located it is simply ignored. If you specify this switch, a missing source file is an error.
Override default wide character encoding for standard Text_IO files. Normally the default wide character encoding method used for standard [Wide_[Wide_]]Text_IO files is taken from the encoding specified for the main source input (see description of switch -gnatWx for the compiler). The use of this switch for the binder (which has the same set of possible arguments) overrides this default as specified.
Exclude source files. In this mode, the binder only checks that ALI
files are consistent with one another. Source files are not accessed.
The binder runs faster in this mode, and there is still a guarantee that
the resulting program is self-consistent.
If a source file has been edited since it was last compiled, and you
specify this switch, the binder will not detect that the object
file is out of date with respect to the source file. Note that this is the
mode that is automatically used by gnatmake because in this
case the checking against sources has already been performed by
gnatmake in the course of compilation (i.e. before binding).
Next: Elaboration Control, Previous: Consistency-Checking Modes, Up: Switches for gnatbind [Contents][Index]
The following switches provide control over the generation of error messages from the binder:
Verbose mode. In the normal mode, brief error messages are generated to stderr. If this switch is present, a header is written to stdout and any error messages are directed to stdout. All that is written to stderr is a brief summary message.
Generate brief error messages to stderr even if verbose mode is specified. This is relevant only when used with the -v switch.
Limits the number of error messages to n, a decimal integer in the range 1-999. The binder terminates immediately if this limit is reached.
Renames the generated main program from main to xxx.
This is useful in the case of some cross-building environments, where
the actual main program is separate from the one generated
by gnatbind.
Suppress all warning messages.
Treat any warning messages as fatal errors.
The binder performs a number of consistency checks including:
GNAT were used for compilation
Normally failure of such checks, in accordance with the consistency requirements of the Ada Reference Manual, causes error messages to be generated which abort the binder and prevent the output of a binder file and subsequent link to obtain an executable.
The -t switch converts these error messages into warnings, so that binding and linking can continue to completion even in the presence of such errors. The result may be a failed link (due to missing symbols), or a non-functional executable which has undefined semantics. This means that -t should be used only in unusual situations, with extreme care.
Next: Output Control, Previous: Binder Error Message Control, Up: Switches for gnatbind [Contents][Index]
The following switches provide additional control over the elaboration order. For full details see Elaboration Order Handling in GNAT.
Normally the binder attempts to choose an elaboration order that is
likely to minimize the likelihood of an elaboration order error resulting
in raising a Program_Error exception. This switch reverses the
action of the binder, and requests that it deliberately choose an order
that is likely to maximize the likelihood of an elaboration error.
This is useful in ensuring portability and avoiding dependence on
accidental fortuitous elaboration ordering.
Normally it only makes sense to use the -p
switch if dynamic
elaboration checking is used (-gnatE switch used for compilation).
This is because in the default static elaboration mode, all necessary
Elaborate and Elaborate_All pragmas are implicitly inserted.
These implicit pragmas are still respected by the binder in
-p mode, so a
safe elaboration order is assured.
Note that -p is not intended for production use; it is more for debugging/experimental use.
Next: Dynamic Allocation Control, Previous: Elaboration Control, Up: Switches for gnatbind [Contents][Index]
The following switches allow additional control over the output generated by the binder.
Check only. Do not generate the binder output file. In this mode the binder performs all error checks but does not generate an output file.
Output complete list of elaboration-order dependencies, showing the reason for each dependency. This output can be rather extensive but may be useful in diagnosing problems with elaboration order. The output is written to stdout.
Output usage information. The output is written to stdout.
Output linker options to stdout. Includes library search paths,
contents of pragmas Ident and Linker_Options, and libraries added
by gnatbind.
Output chosen elaboration order. The output is written to stdout.
Output full names of all the object files that must be linked to provide the Ada component of the program. The output is written to stdout. This list includes the files explicitly supplied and referenced by the user as well as implicitly referenced run-time unit files. The latter are omitted if the corresponding units reside in shared libraries. The directory names for the run-time units depend on the system configuration.
Set name of output file to file instead of the normal b~mainprog.adb default. Note that file denote the Ada binder generated body filename. Note that if this option is used, then linking must be done manually. It is not possible to use gnatlink in this case, since it cannot locate the binder file.
Generate list of pragma Restrictions that could be applied to
the current unit. This is useful for code audit purposes, and also may
be used to improve code generation in some cases.
Next: Binding with Non-Ada Main Programs, Previous: Output Control, Up: Switches for gnatbind [Contents][Index]
The heap control switches – -H32 and -H64 –
determine whether dynamic allocation uses 32-bit or 64-bit memory.
They only affect compiler-generated allocations via __gnat_malloc;
explicit calls to malloc and related functions from the C
run-time library are unaffected.
Allocate memory on 32-bit heap
Allocate memory on 64-bit heap. This is the default
unless explicitly overridden by a 'Size clause on the access type.
These switches are only effective on VMS platforms.
Next: Binding Programs with No Main Subprogram, Previous: Dynamic Allocation Control, Up: Switches for gnatbind [Contents][Index]
In our description so far we have assumed that the main
program is in Ada, and that the task of the binder is to generate a
corresponding function main that invokes this Ada main
program. GNAT also supports the building of executable programs where
the main program is not in Ada, but some of the called routines are
written in Ada and compiled using GNAT (see Mixed Language Programming).
The following switch is used in this situation:
No main program. The main program is not in Ada.
In this case, most of the functions of the binder are still required, but instead of generating a main program, the binder generates a file containing the following callable routines:
adainitYou must call this routine to initialize the Ada part of the program by
calling the necessary elaboration routines. A call to adainit is
required before the first call to an Ada subprogram.
Note that it is assumed that the basic execution environment must be setup to be appropriate for Ada execution at the point where the first Ada subprogram is called. In particular, if the Ada code will do any floating-point operations, then the FPU must be setup in an appropriate manner. For the case of the x86, for example, full precision mode is required. The procedure GNAT.Float_Control.Reset may be used to ensure that the FPU is in the right state.
adafinalYou must call this routine to perform any library-level finalization
required by the Ada subprograms. A call to adafinal is required
after the last call to an Ada subprogram, and before the program
terminates.
If the -n switch
is given, more than one ALI file may appear on
the command line for gnatbind. The normal closure
calculation is performed for each of the specified units. Calculating
the closure means finding out the set of units involved by tracing
with references. The reason it is necessary to be able to
specify more than one ALI file is that a given program may invoke two or
more quite separate groups of Ada units.
The binder takes the name of its output file from the last specified ALI
file, unless overridden by the use of the -o file.
The output is an Ada unit in source form that can be compiled with GNAT.
This compilation occurs automatically as part of the gnatlink
processing.
Currently the GNAT run time requires a FPU using 80 bits mode precision. Under targets where this is not the default it is required to call GNAT.Float_Control.Reset before using floating point numbers (this include float computation, float input and output) in the Ada code. A side effect is that this could be the wrong mode for the foreign code where floating point computation could be broken after this call.
Next: Running gnatlink, Previous: Binding with Non-Ada Main Programs, Up: Switches for gnatbind [Contents][Index]
It is possible to have an Ada program which does not have a main subprogram. This program will call the elaboration routines of all the packages, then the finalization routines.
The following switch is used to bind programs organized in this manner:
Normally the binder checks that the unit name given on the command line corresponds to a suitable main subprogram. When this switch is used, a list of ALI files can be given, and the execution of the program consists of elaboration of these units in an appropriate order. Note that the default wide character encoding method for standard Text_IO files is always set to Brackets if this switch is set (you can use the binder switch -Wx to override this default).
Next: Search Paths for gnatbind, Previous: Switches for gnatbind, Up: Binding Using gnatbind [Contents][Index]
The package Ada.Command_Line provides access to the command-line
arguments and program name. In order for this interface to operate
correctly, the two variables
int gnat_argc; char **gnat_argv;
are declared in one of the GNAT library routines. These variables must
be set from the actual argc and argv values passed to the
main program. With no n present, gnatbind
generates the C main program to automatically set these variables.
If the n switch is used, there is no automatic way to
set these variables. If they are not set, the procedures in
Ada.Command_Line will not be available, and any attempt to use
them will raise Constraint_Error. If command line access is
required, your main program must set gnat_argc and
gnat_argv from the argc and argv values passed to
it.
Next: Examples of gnatbind Usage, Previous: Command-Line Access, Up: Binding Using gnatbind [Contents][Index]
gnatbindThe binder takes the name of an ALI file as its argument and needs to locate source files as well as other ALI files to verify object consistency.
For source files, it follows exactly the same search rules as gcc
(see Search Paths and the Run-Time Library (RTL)). For ALI files the
directories searched are:
gnatbind
command line, in the order given.
ADA_PRJ_OBJECTS_FILE environment variable.
ADA_PRJ_OBJECTS_FILE is normally set by gnatmake or by the gnat
driver when project files are used. It should not normally be set
by other means.
ADA_OBJECTS_PATH environment variable.
Construct this value
exactly as the PATH environment variable: a list of directory
names separated by colons (semicolons when working with the NT version
of GNAT).
In the binder the switch -I is used to specify both source and library file paths. Use -aI instead if you want to specify source paths only, and -aO if you want to specify library paths only. This means that for the binder -Idir is equivalent to -aIdir -aOdir. The binder generates the bind file (a C language source file) in the current working directory.
The packages Ada, System, and Interfaces and their
children make up the GNAT Run-Time Library, together with the package
GNAT and its children, which contain a set of useful additional
library functions provided by GNAT. The sources for these units are
needed by the compiler and are kept together in one directory. The ALI
files and object files generated by compiling the RTL are needed by the
binder and the linker and are kept together in one directory, typically
different from the directory containing the sources. In a normal
installation, you need not specify these directory names when compiling
or binding. Either the environment variables or the built-in defaults
cause these files to be found.
Besides simplifying access to the RTL, a major use of search paths is in compiling sources from multiple directories. This can make development environments much more flexible.
Next: Consistency-Checking Modes, Previous: Search Paths for gnatbind, Up: Binding Using gnatbind [Contents][Index]
gnatbind UsageThis section contains a number of examples of using the GNAT binding
utility gnatbind.
gnatbind helloThe main program Hello (source program in hello.adb) is
bound using the standard switch settings. The generated main program is
b~hello.adb. This is the normal, default use of the binder.
gnatbind hello -o mainprog.adbThe main program Hello (source program in hello.adb) is
bound using the standard switch settings. The generated main program is
mainprog.adb with the associated spec in
mainprog.ads. Note that you must specify the body here not the
spec. Note that if this option is used, then linking must be done manually,
since gnatlink will not be able to find the generated file.
Next: The GNAT Make Program gnatmake, Previous: Binding Using gnatbind, Up: Top [Contents][Index]
gnatlinkThis chapter discusses gnatlink, a tool that links
an Ada program and builds an executable file. This utility
invokes the system linker (via the gcc command)
with a correct list of object files and library references.
gnatlink automatically determines the list of files and
references for the Ada part of a program. It uses the binder file
generated by the gnatbind to determine this list.
Note: to invoke gnatlink with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
| • Running gnatlink: | ||
| • Switches for gnatlink: |
Next: Switches for gnatlink, Previous: Binding Programs with No Main Subprogram, Up: Linking Using gnatlink [Contents][Index]
gnatlinkThe form of the gnatlink command is
$ gnatlink [switches] mainprog[.ali] [non-Ada objects] [linker options]
The arguments of gnatlink (switches, main ALI file,
non-Ada objects
or linker options) may be in any order, provided that no non-Ada object may
be mistaken for a main ALI file.
Any file name F without the .ali
extension will be taken as the main ALI file if a file exists
whose name is the concatenation of F and .ali.
mainprog.ali references the ALI file of the main program.
The .ali extension of this file can be omitted. From this
reference, gnatlink locates the corresponding binder file
b~mainprog.adb and, using the information in this file along
with the list of non-Ada objects and linker options, constructs a
linker command file to create the executable.
The arguments other than the gnatlink switches and the main
ALI file are passed to the linker uninterpreted.
They typically include the names of
object files for units written in other languages than Ada and any library
references required to resolve references in any of these foreign language
units, or in Import pragmas in any Ada units.
linker options is an optional list of linker specific
switches.
The default linker called by gnatlink is gcc which in
turn calls the appropriate system linker.
One useful option for the linker is -s: it reduces the size of the executable by removing all symbol table and relocation information from the executable.
Standard options for the linker such as -lmy_lib or
-Ldir can be added as is.
For options that are not recognized by
gcc as linker options, use the gcc switches
-Xlinker or -Wl,.
Refer to the GCC documentation for details.
Here is an example showing how to generate a linker map:
$ gnatlink my_prog -Wl,-Map,MAPFILE
Using linker options it is possible to set the program stack and heap size. See Setting Stack Size from gnatlink and Setting Heap Size from gnatlink.
gnatlink determines the list of objects required by the Ada
program and prepends them to the list of objects passed to the linker.
gnatlink also gathers any arguments set by the use of
pragma Linker_Options and adds them to the list of arguments
presented to the linker.
Next: Running gnatmake, Previous: Running gnatlink, Up: Linking Using gnatlink [Contents][Index]
gnatlinkThe following switches are available with the gnatlink utility:
Display Copyright and version, then exit disregarding all other options.
If --version was not used, display usage, then exit disregarding all other options.
On some targets, the command line length is limited, and gnatlink
will generate a separate file for the linker if the list of object files
is too long.
The -f switch forces this file
to be generated even if
the limit is not exceeded. This is useful in some cases to deal with
special situations where the command line length is exceeded.
The option to include debugging information causes the Ada bind file (in
other words, b~mainprog.adb) to be compiled with
-g.
In addition, the binder does not delete the b~mainprog.adb,
b~mainprog.o and b~mainprog.ali files.
Without -g, the binder removes these files by
default. The same procedure apply if a C bind file was generated using
-C gnatbind option, in this case the filenames
are b_mainprog.c and b_mainprog.o.
Do not compile the file generated by the binder. This may be used when a link is rerun with different options, but there is no need to recompile the binder file.
Causes additional information to be output, including a full list of the included object files. This switch option is most useful when you want to see what set of object files are being used in the link step.
Very verbose mode. Requests that the compiler operate in verbose mode when it compiles the binder file, and that the system linker run in verbose mode.
exec-name specifies an alternate name for the generated
executable program. If this switch is omitted, the executable has the same
name as the main unit. For example, gnatlink try.ali creates
an executable called try.
Compile your program to run on target, which is the name of a system configuration. You must have a GNAT cross-compiler built if target is not the same as your host system.
Load compiler executables (for example, gnat1, the Ada compiler)
from dir instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See Directory Options in The GNU Compiler Collection,
for further details. You would normally use the -b or
-V switch instead.
When linking an executable, create a map file. The name of the map file has the same name as the executable with extension ".map".
When linking an executable, create a map file. The name of the map file is "mapfile".
Program used for compiling the binder file. The default is
gcc. You need to use quotes around compiler_name if
compiler_name contains spaces or other separator characters.
As an example --GCC="foo -x -y" will instruct gnatlink to
use foo -x -y as your compiler. Note that switch -c is always
inserted after your command name. Thus in the above example the compiler
command that will be used by gnatlink will be foo -c -x -y.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces. If the compiler executable is
different from the default one (gcc or <prefix>-gcc), then the back-end
switches in the ALI file are not used to compile the binder generated source.
For example, this is the case with --GCC="foo -x -y". But the back end
switches will be used for --GCC="gcc -gnatv". If several
--GCC=compiler_name are used, only the last compiler_name
is taken into account. However, all the additional switches are also taken
into account. Thus,
--GCC="foo -x -y" --GCC="bar -z -t" is equivalent to
--GCC="bar -x -y -z -t".
name is the name of the linker to be invoked. This is especially
useful in mixed language programs since languages such as C++ require
their own linker to be used. When this switch is omitted, the default
name for the linker is gcc. When this switch is used, the
specified linker is called instead of gcc with exactly the same
parameters that would have been passed to gcc so if the desired
linker requires different parameters it is necessary to use a wrapper
script that massages the parameters before invoking the real linker. It
may be useful to control the exact invocation by using the verbose
switch.
Next: Improving Performance, Previous: Linking Using gnatlink, Up: Top [Contents][Index]
gnatmake| • Running gnatmake: | ||
| • Switches for gnatmake: | ||
| • Mode Switches for gnatmake: | ||
| • Notes on the Command Line: | ||
| • How gnatmake Works: | ||
| • Examples of gnatmake Usage: |
A typical development cycle when working on an Ada program consists of the following steps:
The third step can be tricky, because not only do the modified files
have to be compiled, but any files depending on these files must also be
recompiled. The dependency rules in Ada can be quite complex, especially
in the presence of overloading, use clauses, generics and inlined
subprograms.
gnatmake automatically takes care of the third and fourth steps
of this process. It determines which sources need to be compiled,
compiles them, and binds and links the resulting object files.
Unlike some other Ada make programs, the dependencies are always
accurately recomputed from the new sources. The source based approach of
the GNAT compilation model makes this possible. This means that if
changes to the source program cause corresponding changes in
dependencies, they will always be tracked exactly correctly by
gnatmake.
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gnatmakeThe usual form of the gnatmake command is
$ gnatmake [switches] file_name [file_names] [mode_switches]
The only required argument is one file_name, which specifies
a compilation unit that is a main program. Several file_names can be
specified: this will result in several executables being built.
If switches are present, they can be placed before the first
file_name, between file_names or after the last file_name.
If mode_switches are present, they must always be placed after
the last file_name and all switches.
If you are using standard file extensions (.adb and .ads), then the
extension may be omitted from the file_name arguments. However, if
you are using non-standard extensions, then it is required that the
extension be given. A relative or absolute directory path can be
specified in a file_name, in which case, the input source file will
be searched for in the specified directory only. Otherwise, the input
source file will first be searched in the directory where
gnatmake was invoked and if it is not found, it will be search on
the source path of the compiler as described in
Search Paths and the Run-Time Library (RTL).
All gnatmake output (except when you specify
-M) is to
stderr. The output produced by the
-M switch is send to
stdout.
Next: Mode Switches for gnatmake, Previous: Running gnatmake, Up: The GNAT Make Program gnatmake [Contents][Index]
gnatmakeYou may specify any of the following switches to gnatmake:
Display Copyright and version, then exit disregarding all other options.
If --version was not used, display usage, then exit disregarding all other options.
Program used for compiling. The default is ‘gcc’. You need to use
quotes around compiler_name if compiler_name contains
spaces or other separator characters. As an example --GCC="foo -x
-y" will instruct gnatmake to use foo -x -y as your
compiler. A limitation of this syntax is that the name and path name of
the executable itself must not include any embedded spaces. Note that
switch -c is always inserted after your command name. Thus in the
above example the compiler command that will be used by gnatmake
will be foo -c -x -y. If several --GCC=compiler_name are
used, only the last compiler_name is taken into account. However,
all the additional switches are also taken into account. Thus,
--GCC="foo -x -y" --GCC="bar -z -t" is equivalent to
--GCC="bar -x -y -z -t".
Program used for binding. The default is ‘gnatbind’. You need to
use quotes around binder_name if binder_name contains spaces
or other separator characters. As an example --GNATBIND="bar -x
-y" will instruct gnatmake to use bar -x -y as your
binder. Binder switches that are normally appended by gnatmake
to ‘gnatbind’ are now appended to the end of bar -x -y.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.
Program used for linking. The default is ‘gnatlink’. You need to
use quotes around linker_name if linker_name contains spaces
or other separator characters. As an example --GNATLINK="lan -x
-y" will instruct gnatmake to use lan -x -y as your
linker. Linker switches that are normally appended by gnatmake to
‘gnatlink’ are now appended to the end of lan -x -y.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.
Actual object directory of each project file is the subdirectory subdir of the object directory specified or defaulted in the project file.
Disallow simultaneous compilations in the same object directory when project files are used.
By default, shared library projects are not allowed to import static library projects. When this switch is used on the command line, this restriction is relaxed.
Specify a source info file. This switch is active only when project files
are used. If the source info file is specified as a relative path, then it is
relative to the object directory of the main project. If the source info file
does not exist, then after the Project Manager has successfully parsed and
processed the project files and found the sources, it creates the source info
file. If the source info file already exists and can be read successfully,
then the Project Manager will get all the needed information about the sources
from the source info file and will not look for them. This reduces the time
to process the project files, especially when looking for sources that take a
long time. If the source info file exists but cannot be parsed successfully,
the Project Manager will attempt to recreate it. If the Project Manager fails
to create the source info file, a message is issued, but gnatmake does not
fail. gnatmake "trusts" the source info file. This means that
if the source files have changed (addition, deletion, moving to a different
source directory), then the source info file need to be deleted and recreated.
When linking an executable, create a map file. The name of the map file has the same name as the executable with extension ".map".
When linking an executable, create a map file. The name of the map file is "mapfile".
Consider all files in the make process, even the GNAT internal system
files (for example, the predefined Ada library files), as well as any
locked files. Locked files are files whose ALI file is write-protected.
By default,
gnatmake does not check these files,
because the assumption is that the GNAT internal files are properly up
to date, and also that any write protected ALI files have been properly
installed. Note that if there is an installation problem, such that one
of these files is not up to date, it will be properly caught by the
binder.
You may have to specify this switch if you are working on GNAT
itself. The switch -a is also useful
in conjunction with -f
if you need to recompile an entire application,
including run-time files, using special configuration pragmas,
such as a Normalize_Scalars pragma.
By default
gnatmake -a compiles all GNAT
internal files with
gcc -c -gnatpg rather than gcc -c.
Bind only. Can be combined with -c to do compilation and binding, but no link. Can be combined with -l to do binding and linking. When not combined with -c all the units in the closure of the main program must have been previously compiled and must be up to date. The root unit specified by file_name may be given without extension, with the source extension or, if no GNAT Project File is specified, with the ALI file extension.
Compile only. Do not perform binding, except when -b
is also specified. Do not perform linking, except if both
-b and
-l are also specified.
If the root unit specified by file_name is not a main unit, this is the
default. Otherwise gnatmake will attempt binding and linking
unless all objects are up to date and the executable is more recent than
the objects.
Use a temporary mapping file. A mapping file is a way to communicate to the compiler two mappings: from unit names to file names (without any directory information) and from file names to path names (with full directory information). A mapping file can make the compiler’s file searches faster, especially if there are many source directories, or the sources are read over a slow network connection. If -P is used, a mapping file is always used, so -C is unnecessary; in this case the mapping file is initially populated based on the project file. If -C is used without -P, the mapping file is initially empty. Each invocation of the compiler will add any newly accessed sources to the mapping file.
Use a specific mapping file. The file, specified as a path name (absolute or relative) by this switch, should already exist, otherwise the switch is ineffective. The specified mapping file will be communicated to the compiler. This switch is not compatible with a project file (-Pfile) or with multiple compiling processes (-jnnn, when nnn is greater than 1).
Display progress for each source, up to date or not, as a single line
completed x out of y (zz%)
If the file needs to be compiled this is displayed after the invocation of the compiler. These lines are displayed even in quiet output mode.
Put all object files and ALI file in directory dir. If the -D switch is not used, all object files and ALI files go in the current working directory.
This switch cannot be used when using a project file.
Indicates that the main source is a multi-unit source and the rank of the unit
in the source file is nnn. nnn needs to be a positive number and a valid
index in the source. This switch cannot be used when gnatmake is
invoked for several mains.
Follow all symbolic links when processing project files. This should be used if your project uses symbolic links for files or directories, but is not needed in other cases.
This also assumes that no directory matches the naming scheme for files (for instance that you do not have a directory called "sources.ads" when using the default GNAT naming scheme).
When you do not have to use this switch (i.e. by default), gnatmake is able to save a lot of system calls (several per source file and object file), which can result in a significant speed up to load and manipulate a project file, especially when using source files from a remote system.
Output the commands for the compiler, the binder and the linker on standard output, instead of standard error.
Force recompilations. Recompile all sources, even though some object files may be up to date, but don’t recompile predefined or GNAT internal files or locked files (files with a write-protected ALI file), unless the -a switch is also specified.
When using project files, if some errors or warnings are detected during parsing and verbose mode is not in effect (no use of switch -v), then error lines start with the full path name of the project file, rather than its simple file name.
Enable debugging. This switch is simply passed to the compiler and to the linker.
In normal mode, gnatmake compiles all object files and ALI files
into the current directory. If the -i switch is used,
then instead object files and ALI files that already exist are overwritten
in place. This means that once a large project is organized into separate
directories in the desired manner, then gnatmake will automatically
maintain and update this organization. If no ALI files are found on the
Ada object path (Search Paths and the Run-Time Library (RTL)),
the new object and ALI files are created in the
directory containing the source being compiled. If another organization
is desired, where objects and sources are kept in different directories,
a useful technique is to create dummy ALI files in the desired directories.
When detecting such a dummy file, gnatmake will be forced to
recompile the corresponding source file, and it will be put the resulting
object and ALI files in the directory where it found the dummy file.
Use n processes to carry out the (re)compilations. On a
multiprocessor machine compilations will occur in parallel. In the
event of compilation errors, messages from various compilations might
get interspersed (but gnatmake will give you the full ordered
list of failing compiles at the end). If this is problematic, rerun
the make process with n set to 1 to get a clean list of messages.
Keep going. Continue as much as possible after a compilation error. To
ease the programmer’s task in case of compilation errors, the list of
sources for which the compile fails is given when gnatmake
terminates.
If gnatmake is invoked with several file_names and with this
switch, if there are compilation errors when building an executable,
gnatmake will not attempt to build the following executables.
Link only. Can be combined with -b to binding and linking. Linking will not be performed if combined with -c but not with -b. When not combined with -b all the units in the closure of the main program must have been previously compiled and must be up to date, and the main program needs to have been bound. The root unit specified by file_name may be given without extension, with the source extension or, if no GNAT Project File is specified, with the ALI file extension.
Specify that the minimum necessary amount of recompilations
be performed. In this mode gnatmake ignores time
stamp differences when the only
modifications to a source file consist in adding/removing comments,
empty lines, spaces or tabs. This means that if you have changed the
comments in a source file or have simply reformatted it, using this
switch will tell gnatmake not to recompile files that depend on it
(provided other sources on which these files depend have undergone no
semantic modifications). Note that the debugging information may be
out of date with respect to the sources if the -m switch causes
a compilation to be switched, so the use of this switch represents a
trade-off between compilation time and accurate debugging information.
Check if all objects are up to date. If they are, output the object
dependences to stdout in a form that can be directly exploited in
a Makefile. By default, each source file is prefixed with its
(relative or absolute) directory name. This name is whatever you
specified in the various -aI
and -I switches. If you use
gnatmake -M
-q
(see below), only the source file names,
without relative paths, are output. If you just specify the
-M
switch, dependencies of the GNAT internal system files are omitted. This
is typically what you want. If you also specify
the -a switch,
dependencies of the GNAT internal files are also listed. Note that
dependencies of the objects in external Ada libraries (see switch
-aLdir in the following list)
are never reported.
Don’t compile, bind, or link. Checks if all objects are up to date. If they are not, the full name of the first file that needs to be recompiled is printed. Repeated use of this option, followed by compiling the indicated source file, will eventually result in recompiling all required units.
Output executable name. The name of the final executable program will be exec_name. If the -o switch is omitted the default name for the executable will be the name of the input file in appropriate form for an executable file on the host system.
This switch cannot be used when invoking gnatmake with several
file_names.
When using project files (-Pproject), create automatically missing object directories, library directories and exec directories.
Use project file project. Only one such switch can be used. See gnatmake and Project Files.
Quiet. When this flag is not set, the commands carried out by
gnatmake are displayed.
Recompile if compiler switches have changed since last compilation. All compiler switches but -I and -o are taken into account in the following way: orders between different “first letter” switches are ignored, but orders between same switches are taken into account. For example, -O -O2 is different than -O2 -O, but -g -O is equivalent to -O -g.
This switch is recommended when Integrated Preprocessing is used.
Unique. Recompile at most the main files. It implies -c. Combined with -f, it is equivalent to calling the compiler directly. Note that using -u with a project file and no main has a special meaning (see Project Files and Main Subprograms).
When used without a project file or with one or several mains on the command line, is equivalent to -u. When used with a project file and no main on the command line, all sources of all project files are checked and compiled if not up to date, and libraries are rebuilt, if necessary.
Verbose. Display the reason for all recompilations gnatmake
decides are necessary, with the highest verbosity level.
Verbosity level Low. Display fewer lines than in verbosity Medium.
Verbosity level Medium. Potentially display fewer lines than in verbosity High.
Verbosity level High. Equivalent to -v.
Indicate the verbosity of the parsing of GNAT project files. See Switches Related to Project Files.
Indicate that sources that are not part of any Project File may be compiled. Normally, when using Project Files, only sources that are part of a Project File may be compile. When this switch is used, a source outside of all Project Files may be compiled. The ALI file and the object file will be put in the object directory of the main Project. The compilation switches used will only be those specified on the command line. Even when -x is used, mains specified on the command line need to be sources of a project file.
Indicate that external variable name has the value value.
The Project Manager will use this value for occurrences of
external(name) when parsing the project file.
See Switches Related to Project Files.
No main subprogram. Bind and link the program even if the unit name given on the command line is a package name. The resulting executable will execute the elaboration routines of the package and its closure, then the finalization routines.
gcc switchesAny uppercase or multi-character switch that is not a gnatmake switch
is passed to gcc (e.g. -O, -gnato, etc.)
Source and library search path switches:
When looking for source files also look in directory dir. The order in which source files search is undertaken is described in Search Paths and the Run-Time Library (RTL).
Consider dir as being an externally provided Ada library.
Instructs gnatmake to skip compilation units whose .ALI
files have been located in directory dir. This allows you to have
missing bodies for the units in dir and to ignore out of date bodies
for the same units. You still need to specify
the location of the specs for these units by using the switches
-aIdir
or -Idir.
Note: this switch is provided for compatibility with previous versions
of gnatmake. The easier method of causing standard libraries
to be excluded from consideration is to write-protect the corresponding
ALI files.
When searching for library and object files, look in directory dir. The order in which library files are searched is described in Search Paths for gnatbind.
Equivalent to -aLdir -aIdir.
Equivalent to -aOdir -aIdir.
Do not look for source files in the directory containing the source
file named in the command line.
Do not look for ALI or object files in the directory
where gnatmake was invoked.
Add directory dir to the list of directories in which the linker will search for libraries. This is equivalent to -largs -Ldir. Furthermore, under Windows, the sources pointed to by the libraries path set in the registry are not searched for.
Do not look for source files in the system default directory.
Do not look for library files in the system default directory.
Specifies the default location of the runtime library. GNAT looks for the runtime in the following directories, and stops as soon as a valid runtime is found (adainclude or ada_source_path, and adalib or ada_object_path present):
The selected path is handled like a normal RTS path.
Next: Notes on the Command Line, Previous: Switches for gnatmake, Up: The GNAT Make Program gnatmake [Contents][Index]
gnatmakeThe mode switches (referred to as mode_switches) allow the
inclusion of switches that are to be passed to the compiler itself, the
binder or the linker. The effect of a mode switch is to cause all
subsequent switches up to the end of the switch list, or up to the next
mode switch, to be interpreted as switches to be passed on to the
designated component of GNAT.
Compiler switches. Here switches is a list of switches
that are valid switches for gcc. They will be passed on to
all compile steps performed by gnatmake.
Binder switches. Here switches is a list of switches
that are valid switches for gnatbind. They will be passed on to
all bind steps performed by gnatmake.
Linker switches. Here switches is a list of switches
that are valid switches for gnatlink. They will be passed on to
all link steps performed by gnatmake.
Make switches. The switches are directly interpreted by gnatmake,
regardless of any previous occurrence of -cargs, -bargs
or -largs.
Next: How gnatmake Works, Previous: Mode Switches for gnatmake, Up: The GNAT Make Program gnatmake [Contents][Index]
This section contains some additional useful notes on the operation
of the gnatmake command.
gnatmake finds no ALI files, it recompiles the main program
and all other units required by the main program.
This means that gnatmake
can be used for the initial compile, as well as during subsequent steps of
the development cycle.
gnatmake file.adb, where file.adb
is a subunit or body of a generic unit, gnatmake recompiles
file.adb (because it finds no ALI) and stops, issuing a
warning.
gnatmake the switch -I
is used to specify both source and
library file paths. Use -aI
instead if you just want to specify
source paths only and -aO
if you want to specify library paths
only.
gnatmake will ignore any files whose ALI file is write-protected.
This may conveniently be used to exclude standard libraries from
consideration and in particular it means that the use of the
-f switch will not recompile these files
unless -a is also specified.
gnatmake has been designed to make the use of Ada libraries
particularly convenient. Assume you have an Ada library organized
as follows: obj-dir contains the objects and ALI files for
of your Ada compilation units,
whereas include-dir contains the
specs of these units, but no bodies. Then to compile a unit
stored in main.adb, which uses this Ada library you would just type
$ gnatmake -aIinclude-dir -aLobj-dir main
gnatmake along with the
-m (minimal recompilation)
switch provides a mechanism for avoiding unnecessary recompilations. Using
this switch,
you can update the comments/format of your
source files without having to recompile everything. Note, however, that
adding or deleting lines in a source files may render its debugging
info obsolete. If the file in question is a spec, the impact is rather
limited, as that debugging info will only be useful during the
elaboration phase of your program. For bodies the impact can be more
significant. In all events, your debugger will warn you if a source file
is more recent than the corresponding object, and alert you to the fact
that the debugging information may be out of date.
Next: Examples of gnatmake Usage, Previous: Notes on the Command Line, Up: The GNAT Make Program gnatmake [Contents][Index]
gnatmake WorksGenerally gnatmake automatically performs all necessary
recompilations and you don’t need to worry about how it works. However,
it may be useful to have some basic understanding of the gnatmake
approach and in particular to understand how it uses the results of
previous compilations without incorrectly depending on them.
First a definition: an object file is considered up to date if the corresponding ALI file exists and if all the source files listed in the dependency section of this ALI file have time stamps matching those in the ALI file. This means that neither the source file itself nor any files that it depends on have been modified, and hence there is no need to recompile this file.
gnatmake works by first checking if the specified main unit is up
to date. If so, no compilations are required for the main unit. If not,
gnatmake compiles the main program to build a new ALI file that
reflects the latest sources. Then the ALI file of the main unit is
examined to find all the source files on which the main program depends,
and gnatmake recursively applies the above procedure on all these
files.
This process ensures that gnatmake only trusts the dependencies
in an existing ALI file if they are known to be correct. Otherwise it
always recompiles to determine a new, guaranteed accurate set of
dependencies. As a result the program is compiled “upside down” from what may
be more familiar as the required order of compilation in some other Ada
systems. In particular, clients are compiled before the units on which
they depend. The ability of GNAT to compile in any order is critical in
allowing an order of compilation to be chosen that guarantees that
gnatmake will recompute a correct set of new dependencies if
necessary.
When invoking gnatmake with several file_names, if a unit is
imported by several of the executables, it will be recompiled at most once.
Note: when using non-standard naming conventions
(see Using Other File Names), changing through a configuration pragmas
file the version of a source and invoking gnatmake to recompile may
have no effect, if the previous version of the source is still accessible
by gnatmake. It may be necessary to use the switch
-f.
Next: Performance Considerations, Previous: How gnatmake Works, Up: The GNAT Make Program gnatmake [Contents][Index]
gnatmake Usagegnatmake hello.adbCompile all files necessary to bind and link the main program
hello.adb (containing unit Hello) and bind and link the
resulting object files to generate an executable file hello.
gnatmake main1 main2 main3Compile all files necessary to bind and link the main programs
main1.adb (containing unit Main1), main2.adb
(containing unit Main2) and main3.adb
(containing unit Main3) and bind and link the resulting object files
to generate three executable files main1,
main2
and main3.
gnatmake -q Main_Unit -cargs -O2 -bargs -lCompile all files necessary to bind and link the main program unit
Main_Unit (from file main_unit.adb). All compilations will
be done with optimization level 2 and the order of elaboration will be
listed by the binder. gnatmake will operate in quiet mode, not
displaying commands it is executing.
Next: Renaming Files Using gnatchop, Previous: The GNAT Make Program gnatmake, Up: Top [Contents][Index]
This chapter presents several topics related to program performance.
It first describes some of the tradeoffs that need to be considered
and some of the techniques for making your program run faster.
It then documents the gnatelim tool and unused subprogram/data
elimination feature, which can reduce the size of program executables.
| • Performance Considerations: | ||
| • Text_IO Suggestions: | ||
| • Reducing Size of Ada Executables with gnatelim: | ||
| • Reducing Size of Executables with unused subprogram/data elimination: |
Next: Text_IO Suggestions, Previous: Examples of gnatmake Usage, Up: Improving Performance [Contents][Index]
The GNAT system provides a number of options that allow a trade-off between
The defaults (if no options are selected) aim at improving the speed of compilation and minimizing dependences, at the expense of performance of the generated code:
These options are suitable for most program development purposes. This chapter describes how you can modify these choices, and also provides some guidelines on debugging optimized code.
Next: Use of Restrictions, Previous: Reducing Size of Executables with unused subprogram/data elimination, Up: Performance Considerations [Contents][Index]
By default, GNAT generates all run-time checks, except integer overflow checks, stack overflow checks, and checks for access before elaboration on subprogram calls. The latter are not required in default mode, because all necessary checking is done at compile time. Two gnat switches, -gnatp and -gnato allow this default to be modified. See Run-Time Checks.
Our experience is that the default is suitable for most development purposes.
We treat integer overflow specially because these are quite expensive and in our experience are not as important as other run-time checks in the development process. Note that division by zero is not considered an overflow check, and divide by zero checks are generated where required by default.
Elaboration checks are off by default, and also not needed by default, since GNAT uses a static elaboration analysis approach that avoids the need for run-time checking. This manual contains a full chapter discussing the issue of elaboration checks, and if the default is not satisfactory for your use, you should read this chapter.
For validity checks, the minimal checks required by the Ada Reference Manual (for case statements and assignments to array elements) are on by default. These can be suppressed by use of the -gnatVn switch. Note that in Ada 83, there were no validity checks, so if the Ada 83 mode is acceptable (or when comparing GNAT performance with an Ada 83 compiler), it may be reasonable to routinely use -gnatVn. Validity checks are also suppressed entirely if -gnatp is used.
Note that the setting of the switches controls the default setting of
the checks. They may be modified using either pragma Suppress (to
remove checks) or pragma Unsuppress (to add back suppressed
checks) in the program source.
Next: Optimization Levels, Previous: Controlling Run-Time Checks, Up: Performance Considerations [Contents][Index]
The use of pragma Restrictions allows you to control which features are permitted in your program. Apart from the obvious point that if you avoid relatively expensive features like finalization (enforceable by the use of pragma Restrictions (No_Finalization), the use of this pragma does not affect the generated code in most cases.
One notable exception to this rule is that the possibility of task abort results in some distributed overhead, particularly if finalization or exception handlers are used. The reason is that certain sections of code have to be marked as non-abortable.
If you use neither the abort statement, nor asynchronous transfer
of control (select … then abort), then this distributed overhead
is removed, which may have a general positive effect in improving
overall performance. Especially code involving frequent use of tasking
constructs and controlled types will show much improved performance.
The relevant restrictions pragmas are
pragma Restrictions (No_Abort_Statements); pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
It is recommended that these restriction pragmas be used if possible. Note that this also means that you can write code without worrying about the possibility of an immediate abort at any point.
Next: Debugging Optimized Code, Previous: Use of Restrictions, Up: Performance Considerations [Contents][Index]
Without any optimization option, the compiler’s goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the subprogram and get exactly the results you would expect from the source code.
Turning on optimization makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program.
If you use multiple -O options, with or without level numbers, the last such option is the one that is effective.
The default is optimization off. This results in the fastest compile
times, but GNAT makes absolutely no attempt to optimize, and the
generated programs are considerably larger and slower than when
optimization is enabled. You can use the
-O switch (the permitted forms are -O0, -O1
-O2, -O3, and -Os)
to gcc to control the optimization level:
No optimization (the default); generates unoptimized code but has the fastest compilation time.
Note that many other compilers do fairly extensive optimization even if “no optimization” is specified. With gcc, it is very unusual to use -O0 for production if execution time is of any concern, since -O0 really does mean no optimization at all. This difference between gcc and other compilers should be kept in mind when doing performance comparisons.
Moderate optimization; optimizes reasonably well but does not degrade compilation time significantly.
Full optimization; generates highly optimized code and has the slowest compilation time.
Full optimization as in -O2; also uses more aggressive automatic inlining of subprograms within a unit (see Inlining of Subprograms) and attempts to vectorize loops.
Optimize space usage (code and data) of resulting program.
Higher optimization levels perform more global transformations on the program and apply more expensive analysis algorithms in order to generate faster and more compact code. The price in compilation time, and the resulting improvement in execution time, both depend on the particular application and the hardware environment. You should experiment to find the best level for your application.
Since the precise set of optimizations done at each level will vary from release to release (and sometime from target to target), it is best to think of the optimization settings in general terms. See Options That Control Optimization in Using the GNU Compiler Collection (GCC), for details about the -O settings and a number of -f options that individually enable or disable specific optimizations.
Unlike some other compilation systems, gcc has
been tested extensively at all optimization levels. There are some bugs
which appear only with optimization turned on, but there have also been
bugs which show up only in unoptimized code. Selecting a lower
level of optimization does not improve the reliability of the code
generator, which in practice is highly reliable at all optimization
levels.
Note regarding the use of -O3: The use of this optimization level is generally discouraged with GNAT, since it often results in larger executables which may run more slowly. See further discussion of this point in Inlining of Subprograms.
Next: Inlining of Subprograms, Previous: Optimization Levels, Up: Performance Considerations [Contents][Index]
Although it is possible to do a reasonable amount of debugging at nonzero optimization levels, the higher the level the more likely that source-level constructs will have been eliminated by optimization. For example, if a loop is strength-reduced, the loop control variable may be completely eliminated and thus cannot be displayed in the debugger. This can only happen at -O2 or -O3. Explicit temporary variables that you code might be eliminated at level -O1 or higher.
The use of the -g switch, which is needed for source-level debugging, affects the size of the program executable on disk, and indeed the debugging information can be quite large. However, it has no effect on the generated code (and thus does not degrade performance)
Since the compiler generates debugging tables for a compilation unit before it performs optimizations, the optimizing transformations may invalidate some of the debugging data. You therefore need to anticipate certain anomalous situations that may arise while debugging optimized code. These are the most common cases:
step or next
commands show
the PC bouncing back and forth in the code. This may result from any of
the following optimizations:
goto, a return, or
a break in a C switch statement.
In general, when an unexpected value appears for a local variable or parameter you should first ascertain if that value was actually computed by your program, as opposed to being incorrectly reported by the debugger. Record fields or array elements in an object designated by an access value are generally less of a problem, once you have ascertained that the access value is sensible. Typically, this means checking variables in the preceding code and in the calling subprogram to verify that the value observed is explainable from other values (one must apply the procedure recursively to those other values); or re-running the code and stopping a little earlier (perhaps before the call) and stepping to better see how the variable obtained the value in question; or continuing to step from the point of the strange value to see if code motion had simply moved the variable’s assignments later.
In light of such anomalies, a recommended technique is to use -O0
early in the software development cycle, when extensive debugging capabilities
are most needed, and then move to -O1 and later -O2 as
the debugger becomes less critical.
Whether to use the -g switch in the release version is
a release management issue.
Note that if you use -g you can then use the strip program
on the resulting executable,
which removes both debugging information and global symbols.
Next: Vectorization of loops, Previous: Debugging Optimized Code, Up: Performance Considerations [Contents][Index]
A call to a subprogram in the current unit is inlined if all the following conditions are met:
gcc cannot support in inlined
subprograms.
pragma Inline is applied to the
subprogram and the -gnatn switch is specified; the
subprogram is local to the unit and called once from within it; the
subprogram is small and optimization level -O2 is specified;
optimization level -O3 is specified.
Calls to subprograms in with’ed units are normally not inlined.
To achieve actual inlining (that is, replacement of the call by the code
in the body of the subprogram), the following conditions must all be true:
gcc cannot support in inlined
subprograms.
pragma Inline for the subprogram.
Even if all these conditions are met, it may not be possible for the compiler to inline the call, due to the length of the body, or features in the body that make it impossible for the compiler to do the inlining.
Note that specifying the -gnatn switch causes additional compilation dependencies. Consider the following:
package R is procedure Q; pragma Inline (Q); end R; package body R is … end R; with R; procedure Main is begin … R.Q; end Main; |
With the default behavior (no -gnatn switch specified), the
compilation of the Main procedure depends only on its own source,
main.adb, and the spec of the package in file r.ads. This
means that editing the body of R does not require recompiling
Main.
On the other hand, the call R.Q is not inlined under these
circumstances. If the -gnatn switch is present when Main
is compiled, the call will be inlined if the body of Q is small
enough, but now Main depends on the body of R in
r.adb as well as on the spec. This means that if this body is edited,
the main program must be recompiled. Note that this extra dependency
occurs whether or not the call is in fact inlined by gcc.
The use of front end inlining with -gnatN generates similar additional dependencies.
Note: The -fno-inline switch can be used to prevent all inlining. This switch overrides all other conditions and ensures that no inlining occurs. The extra dependences resulting from -gnatn will still be active, even if this switch is used to suppress the resulting inlining actions.
Note: The -fno-inline-functions switch can be used to prevent automatic inlining of subprograms if -O3 is used.
Note: The -fno-inline-small-functions switch can be used to prevent automatic inlining of small subprograms if -O2 is used.
Note: The -fno-inline-functions-called-once switch can be used to prevent inlining of subprograms local to the unit and called once from within it if -O1 is used.
Note regarding the use of -O3: -gnatn is made up of two
sub-switches -gnatn1 and -gnatn2 that can be directly
specified in lieu of it, -gnatn being translated into one of them
based on the optimization level. With -O2 or below, -gnatn
is equivalent to -gnatn1 which activates pragma Inline with
moderate inlining across modules. With -O3, -gnatn is
equivalent to -gnatn2 which activates pragma Inline with
full inlining across modules. If you have used pragma Inline in appropriate cases, then it is usually much better to use -O2 and -gnatn and avoid the use of -O3 which has the additional
effect of inlining subprograms you did not think should be inlined. We have
found that the use of -O3 may slow down the compilation and increase
the code size by performing excessive inlining, leading to increased
instruction cache pressure from the increased code size and thus minor
performance improvements. So the bottom line here is that you should not
automatically assume that -O3 is better than -O2, and
indeed you should use -O3 only if tests show that it actually
improves performance for your program.
Next: Other Optimization Switches, Previous: Inlining of Subprograms, Up: Performance Considerations [Contents][Index]
You can take advantage of the auto-vectorizer present in the gcc
back end to vectorize loops with GNAT. The corresponding command line switch
is -ftree-vectorize but, as it is enabled by default at -O3
and other aggressive optimizations helpful for vectorization also are enabled
by default at this level, using -O3 directly is recommended.
You also need to make sure that the target architecture features a supported SIMD instruction set. For example, for the x86 architecture, you should at least specify -msse2 to get significant vectorization (but you don’t need to specify it for x86-64 as it is part of the base 64-bit architecture). Similarly, for the PowerPC architecture, you should specify -maltivec.
The preferred loop form for vectorization is the for iteration scheme.
Loops with a while iteration scheme can also be vectorized if they are
very simple, but the vectorizer will quickly give up otherwise. With either
iteration scheme, the flow of control must be straight, in particular no
exit statement may appear in the loop body. The loop may however
contain a single nested loop, if it can be vectorized when considered alone:
A : array (1..4, 1..4) of Long_Float;
S : array (1..4) of Long_Float;
procedure Sum is
begin
for I in A'Range(1) loop
for J in A'Range(2) loop
S (I) := S (I) + A (I, J);
end loop;
end loop;
end Sum;
|
The vectorizable operations depend on the targeted SIMD instruction set, but the adding and some of the multiplying operators are generally supported, as well as the logical operators for modular types. Note that, in the former case, enabling overflow checks, for example with -gnato, totally disables vectorization. The other checks are not supposed to have the same definitive effect, although compiling with -gnatp might well reveal cases where some checks do thwart vectorization.
Type conversions may also prevent vectorization if they involve semantics that are not directly supported by the code generator or the SIMD instruction set. A typical example is direct conversion from floating-point to integer types. The solution in this case is to use the following idiom:
Integer (S'Truncation (F))
if S is the subtype of floating-point object F.
In most cases, the vectorizable loops are loops that iterate over arrays. All kinds of array types are supported, i.e. constrained array types with static bounds:
type Array_Type is array (1 .. 4) of Long_Float;
constrained array types with dynamic bounds:
type Array_Type is array (1 .. Q.N) of Long_Float; type Array_Type is array (Q.K .. 4) of Long_Float; type Array_Type is array (Q.K .. Q.N) of Long_Float;
or unconstrained array types:
type Array_Type is array (Positive range <>) of Long_Float;
The quality of the generated code decreases when the dynamic aspect of the array type increases, the worst code being generated for unconstrained array types. This is so because, the less information the compiler has about the bounds of the array, the more fallback code it needs to generate in order to fix things up at run time.
It is possible to specify that a given loop should be subject to vectorization
preferably to other optimizations by means of pragma Loop_Optimize:
pragma Loop_Optimize (Vector);
placed immediately within the loop will convey the appropriate hint to the compiler for this loop.
You can obtain information about the vectorization performed by the compiler by specifying -ftree-vectorizer-verbose=N. For more details of this switch, see Options for Debugging Your Program or GCC in Using the GNU Compiler Collection (GCC).
Next: Optimization and Strict Aliasing, Previous: Vectorization of loops, Up: Performance Considerations [Contents][Index]
Since GNAT uses the gcc back end, all the specialized
gcc optimization switches are potentially usable. These switches
have not been extensively tested with GNAT but can generally be expected
to work. Examples of switches in this category are -funroll-loops
and the various target-specific -m options (in particular, it has
been observed that -march=xxx can significantly improve performance
on appropriate machines). For full details of these switches, see
Hardware Models and Configurations in Using
the GNU Compiler Collection (GCC).
Next: About gnatelim, Previous: Other Optimization Switches, Up: Performance Considerations [Contents][Index]
The strong typing capabilities of Ada allow an optimizer to generate efficient code in situations where other languages would be forced to make worst case assumptions preventing such optimizations. Consider the following example:
procedure R is
type Int1 is new Integer;
type Int2 is new Integer;
type Int1A is access Int1;
type Int2A is access Int2;
Int1V : Int1A;
Int2V : Int2A;
…
begin
…
for J in Data'Range loop
if Data (J) = Int1V.all then
Int2V.all := Int2V.all + 1;
end if;
end loop;
…
end R;
|
In this example, since the variable Int1V can only access objects
of type Int1, and Int2V can only access objects of type
Int2, there is no possibility that the assignment to
Int2V.all affects the value of Int1V.all. This means that
the compiler optimizer can "know" that the value Int1V.all is constant
for all iterations of the loop and avoid the extra memory reference
required to dereference it each time through the loop.
This kind of optimization, called strict aliasing analysis, is
triggered by specifying an optimization level of -O2 or
higher or -Os and allows GNAT to generate more efficient code
when access values are involved.
However, although this optimization is always correct in terms of
the formal semantics of the Ada Reference Manual, difficulties can
arise if features like Unchecked_Conversion are used to break
the typing system. Consider the following complete program example:
package p1 is
type int1 is new integer;
type int2 is new integer;
type a1 is access int1;
type a2 is access int2;
end p1;
with p1; use p1;
package p2 is
function to_a2 (Input : a1) return a2;
end p2;
with Unchecked_Conversion;
package body p2 is
function to_a2 (Input : a1) return a2 is
function to_a2u is
new Unchecked_Conversion (a1, a2);
begin
return to_a2u (Input);
end to_a2;
end p2;
with p2; use p2;
with p1; use p1;
with Text_IO; use Text_IO;
procedure m is
v1 : a1 := new int1;
v2 : a2 := to_a2 (v1);
begin
v1.all := 1;
v2.all := 0;
put_line (int1'image (v1.all));
end;
|
This program prints out 0 in -O0 or -O1
mode, but it prints out 1 in -O2 mode. That’s
because in strict aliasing mode, the compiler can and
does assume that the assignment to v2.all could not
affect the value of v1.all, since different types
are involved.
This behavior is not a case of non-conformance with the standard, since
the Ada RM specifies that an unchecked conversion where the resulting
bit pattern is not a correct value of the target type can result in an
abnormal value and attempting to reference an abnormal value makes the
execution of a program erroneous. That’s the case here since the result
does not point to an object of type int2. This means that the
effect is entirely unpredictable.
However, although that explanation may satisfy a language lawyer, in practice an applications programmer expects an unchecked conversion involving pointers to create true aliases and the behavior of printing 1 seems plain wrong. In this case, the strict aliasing optimization is unwelcome.
Indeed the compiler recognizes this possibility, and the unchecked conversion generates a warning:
p2.adb:5:07: warning: possible aliasing problem with type "a2" p2.adb:5:07: warning: use -fno-strict-aliasing switch for references p2.adb:5:07: warning: or use "pragma No_Strict_Aliasing (a2);"
Unfortunately the problem is recognized when compiling the body of
package p2, but the actual "bad" code is generated while
compiling the body of m and this latter compilation does not see
the suspicious Unchecked_Conversion.
As implied by the warning message, there are approaches you can use to avoid the unwanted strict aliasing optimization in a case like this.
One possibility is to simply avoid the use of -O2, but that is a bit drastic, since it throws away a number of useful optimizations that do not involve strict aliasing assumptions.
A less drastic approach is to compile the program using the
option -fno-strict-aliasing. Actually it is only the
unit containing the dereferencing of the suspicious pointer
that needs to be compiled. So in this case, if we compile
unit m with this switch, then we get the expected
value of zero printed. Analyzing which units might need
the switch can be painful, so a more reasonable approach
is to compile the entire program with options -O2
and -fno-strict-aliasing. If the performance is
satisfactory with this combination of options, then the
advantage is that the entire issue of possible "wrong"
optimization due to strict aliasing is avoided.
To avoid the use of compiler switches, the configuration
pragma No_Strict_Aliasing with no parameters may be
used to specify that for all access types, the strict
aliasing optimization should be suppressed.
However, these approaches are still overkill, in that they causes all manipulations of all access values to be deoptimized. A more refined approach is to concentrate attention on the specific access type identified as problematic.
First, if a careful analysis of uses of the pointer shows
that there are no possible problematic references, then
the warning can be suppressed by bracketing the
instantiation of Unchecked_Conversion to turn
the warning off:
pragma Warnings (Off);
function to_a2u is
new Unchecked_Conversion (a1, a2);
pragma Warnings (On);
Of course that approach is not appropriate for this particular example, since indeed there is a problematic reference. In this case we can take one of two other approaches.
The first possibility is to move the instantiation of unchecked
conversion to the unit in which the type is declared. In
this example, we would move the instantiation of
Unchecked_Conversion from the body of package
p2 to the spec of package p1. Now the
warning disappears. That’s because any use of the
access type knows there is a suspicious unchecked
conversion, and the strict aliasing optimization
is automatically suppressed for the type.
If it is not practical to move the unchecked conversion to the same unit
in which the destination access type is declared (perhaps because the
source type is not visible in that unit), you may use pragma
No_Strict_Aliasing for the type. This pragma must occur in the
same declarative sequence as the declaration of the access type:
type a2 is access int2; pragma No_Strict_Aliasing (a2);
Here again, the compiler now knows that the strict aliasing optimization
should be suppressed for any reference to type a2 and the
expected behavior is obtained.
Finally, note that although the compiler can generate warnings for simple cases of unchecked conversions, there are tricker and more indirect ways of creating type incorrect aliases which the compiler cannot detect. Examples are the use of address overlays and unchecked conversions involving composite types containing access types as components. In such cases, no warnings are generated, but there can still be aliasing problems. One safe coding practice is to forbid the use of address clauses for type overlaying, and to allow unchecked conversion only for primitive types. This is not really a significant restriction since any possible desired effect can be achieved by unchecked conversion of access values.
The aliasing analysis done in strict aliasing mode can certainly have significant benefits. We have seen cases of large scale application code where the time is increased by up to 5% by turning this optimization off. If you have code that includes significant usage of unchecked conversion, you might want to just stick with -O1 and avoid the entire issue. If you get adequate performance at this level of optimization level, that’s probably the safest approach. If tests show that you really need higher levels of optimization, then you can experiment with -O2 and -O2 -fno-strict-aliasing to see how much effect this has on size and speed of the code. If you really need to use -O2 with strict aliasing in effect, then you should review any uses of unchecked conversion of access types, particularly if you are getting the warnings described above.
Next: Reducing Size of Ada Executables with gnatelim, Previous: Performance Considerations, Up: Improving Performance [Contents][Index]
Text_IO SuggestionsThe Ada.Text_IO package has fairly high overheads due in part to
the requirement of maintaining page and line counts. If performance
is critical, a recommendation is to use Stream_IO instead of
Text_IO for volume output, since this package has less overhead.
If Text_IO must be used, note that by default output to the standard
output and standard error files is unbuffered (this provides better
behavior when output statements are used for debugging, or if the
progress of a program is observed by tracking the output, e.g. by
using the Unix tail -f command to watch redirected output.
If you are generating large volumes of output with Text_IO and
performance is an important factor, use a designated file instead
of the standard output file, or change the standard output file to
be buffered using Interfaces.C_Streams.setvbuf.
Next: Reducing Size of Executables with unused subprogram/data elimination, Previous: Text_IO Suggestions, Up: Improving Performance [Contents][Index]
gnatelimThis section describes gnatelim, a tool which detects unused
subprograms and helps the compiler to create a smaller executable for your
program.
| • About gnatelim: | ||
| • Running gnatelim: | ||
| • Processing Precompiled Libraries: | ||
| • Correcting the List of Eliminate Pragmas: | ||
| • Making Your Executables Smaller: | ||
| • Summary of the gnatelim Usage Cycle: |
Next: Running gnatelim, Previous: Optimization and Strict Aliasing, Up: Reducing Size of Ada Executables with gnatelim [Contents][Index]
gnatelimWhen a program shares a set of Ada packages with other programs, it may happen that this program uses only a fraction of the subprograms defined in these packages. The code created for these unused subprograms increases the size of the executable.
gnatelim tracks unused subprograms in an Ada program and
outputs a list of GNAT-specific pragmas Eliminate marking all the
subprograms that are declared but never called. By placing the list of
Eliminate pragmas in the GNAT configuration file gnat.adc and
recompiling your program, you may decrease the size of its executable,
because the compiler will not generate the code for ’eliminated’ subprograms.
See Pragma Eliminate in GNAT Reference Manual, for more
information about this pragma.
gnatelim needs as its input data the name of the main subprogram.
If a set of source files is specified as gnatelim arguments, it
treats these files as a complete set of sources making up a program to
analyse, and analyses only these sources.
After a full successful build of the main subprogram gnatelim can be
called without specifying sources to analyse, in this case it computes
the source closure of the main unit from the ALI files.
The following command will create the set of ALI files needed for
gnatelim:
$ gnatmake -c Main_Prog
Note that gnatelim does not need object files.
Next: Processing Precompiled Libraries, Previous: About gnatelim, Up: Reducing Size of Ada Executables with gnatelim [Contents][Index]
gnatelimgnatelim has the following command-line interface:
$ gnatelim [switches] -main=main_unit_name {filename} [-cargs gcc_switches]
main_unit_name should be a name of a source file that contains the main subprogram of a program (partition).
Each filename is the name (including the extension) of a source file to process. “Wildcards” are allowed, and the file name may contain path information.
‘gcc_switches’ is a list of switches for
gcc. They will be passed on to all compiler invocations made by
gnatelim to generate the ASIS trees. Here you can provide
-I switches to form the source search path,
use the -gnatec switch to set the configuration file,
use the -gnat05 switch if sources should be compiled in
Ada 2005 mode etc.
gnatelim has the following switches:
Take the argument source files from the specified file. This file should be an
ordinary text file containing file names separated by spaces or
line breaks. You can use this switch more than once in the same call to
gnatelim. You also can combine this switch with
an explicit list of files.
Duplicate all the output sent to stderr into a log file. The log file is named gnatelim.log and is located in the current directory.
Duplicate all the output sent to stderr into a specified log file.
Do not generate pragmas for dispatching operations.
Do not generate pragmas for subprograms declared in the sources listed in a specified file
Put gnatelim output into a specified file. If this file already exists,
it is overridden. If this switch is not used, gnatelim outputs its results
into stderr
Quiet mode: by default gnatelim outputs to the standard error
stream the number of program units left to be processed. This option turns
this trace off.
Print out execution time.
Verbose mode: gnatelim version information is printed as Ada
comments to the standard output stream. Also, in addition to the number of
program units left gnatelim will output the name of the current unit
being processed.
Quiet warning mode - some warnings are suppressed. In particular warnings that indicate that the analysed set of sources is incomplete to make up a partition and that some subprogram bodies are missing are not generated.
Note: to invoke gnatelim with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
Next: Correcting the List of Eliminate Pragmas, Previous: Running gnatelim, Up: Reducing Size of Ada Executables with gnatelim [Contents][Index]
If some program uses a precompiled Ada library, it can be processed by
gnatelim in a usual way. gnatelim will newer generate an
Eliminate pragma for a subprogram if the body of this subprogram has not
been analysed, this is a typical case for subprograms from precompiled
libraries. Switch -wq may be used to suppress
warnings about missing source files and non-analyzed subprogram bodies
that can be generated when processing precompiled Ada libraries.
Next: Making Your Executables Smaller, Previous: Processing Precompiled Libraries, Up: Reducing Size of Ada Executables with gnatelim [Contents][Index]
In some rare cases gnatelim may try to eliminate
subprograms that are actually called in the program. In this case, the
compiler will generate an error message of the form:
main.adb:4:08: cannot reference subprogram "P" eliminated at elim.out:5
You will need to manually remove the wrong Eliminate pragmas from
the configuration file indicated in the error message. You should recompile
your program from scratch after that, because you need a consistent
configuration file(s) during the entire compilation.
Next: Summary of the gnatelim Usage Cycle, Previous: Correcting the List of Eliminate Pragmas, Up: Reducing Size of Ada Executables with gnatelim [Contents][Index]
In order to get a smaller executable for your program you now have to recompile the program completely with the configuration file containing pragmas Eliminate generated by gnatelim. If these pragmas are placed in gnat.adc file located in your current directory, just do:
$ gnatmake -f main_prog
(Use the -f option for gnatmake to
recompile everything
with the set of pragmas Eliminate that you have obtained with
gnatelim).
Be aware that the set of Eliminate pragmas is specific to each
program. It is not recommended to merge sets of Eliminate
pragmas created for different programs in one configuration file.
Next: About unused subprogram/data elimination, Previous: Making Your Executables Smaller, Up: Reducing Size of Ada Executables with gnatelim [Contents][Index]
gnatelim Usage CycleHere is a quick summary of the steps to be taken in order to reduce
the size of your executables with gnatelim. You may use
other GNAT options to control the optimization level,
to produce the debugging information, to set search path, etc.
$ gnatmake -c main_prog
Eliminate pragmas in default configuration file
gnat.adc in the current directory
$ gnatelim main_prog >[>] gnat.adc
$ gnatmake -f main_prog
Next: Controlling Run-Time Checks, Previous: Reducing Size of Ada Executables with gnatelim, Up: Improving Performance [Contents][Index]
This section describes how you can eliminate unused subprograms and data from your executable just by setting options at compilation time.
| • About unused subprogram/data elimination: | ||
| • Compilation options: | ||
| • Example of unused subprogram/data elimination: |
Next: Compilation options, Previous: Summary of the gnatelim Usage Cycle, Up: Reducing Size of Executables with unused subprogram/data elimination [Contents][Index]
By default, an executable contains all code and data of its composing objects (directly linked or coming from statically linked libraries), even data or code never used by this executable.
This feature will allow you to eliminate such unused code from your executable, making it smaller (in disk and in memory).
This functionality is available on all Linux platforms except for the IA-64 architecture and on all cross platforms using the ELF binary file format. In both cases GNU binutils version 2.16 or later are required to enable it.
Next: Example of unused subprogram/data elimination, Previous: About unused subprogram/data elimination, Up: Reducing Size of Executables with unused subprogram/data elimination [Contents][Index]
The operation of eliminating the unused code and data from the final executable is directly performed by the linker.
In order to do this, it has to work with objects compiled with the following options: -ffunction-sections -fdata-sections. These options are usable with C and Ada files. They will place respectively each function or data in a separate section in the resulting object file.
Once the objects and static libraries are created with these options, the
linker can perform the dead code elimination. You can do this by setting
the -Wl,--gc-sections option to gcc command or in the
-largs section of gnatmake. This will perform a
garbage collection of code and data never referenced.
If the linker performs a partial link (-r ld linker option), then you will need to provide one or several entry point using the -e / --entry ld option.
Note that objects compiled without the -ffunction-sections and -fdata-sections options can still be linked with the executable. However, no dead code elimination will be performed on those objects (they will be linked as is).
The GNAT static library is now compiled with -ffunction-sections and -fdata-sections on some platforms. This allows you to eliminate the unused code and data of the GNAT library from your executable.
Previous: Compilation options, Up: Reducing Size of Executables with unused subprogram/data elimination [Contents][Index]
Here is a simple example:
with Aux;
procedure Test is
begin
Aux.Used (10);
end Test;
package Aux is
Used_Data : Integer;
Unused_Data : Integer;
procedure Used (Data : Integer);
procedure Unused (Data : Integer);
end Aux;
package body Aux is
procedure Used (Data : Integer) is
begin
Used_Data := Data;
end Used;
procedure Unused (Data : Integer) is
begin
Unused_Data := Data;
end Unused;
end Aux;
Unused and Unused_Data are never referenced in this code
excerpt, and hence they may be safely removed from the final executable.
$ gnatmake test
$ nm test | grep used
020015f0 T aux__unused
02005d88 B aux__unused_data
020015cc T aux__used
02005d84 B aux__used_data
$ gnatmake test -cargs -fdata-sections -ffunction-sections \
-largs -Wl,--gc-sections
$ nm test | grep used
02005350 T aux__used
0201ffe0 B aux__used_data
It can be observed that the procedure Unused and the object
Unused_Data are removed by the linker when using the
appropriate options.
Next: Configuration Pragmas, Previous: Improving Performance, Up: Top [Contents][Index]
gnatchopThis chapter discusses how to handle files with multiple units by using
the gnatchop utility. This utility is also useful in renaming
files to meet the standard GNAT default file naming conventions.
| • Handling Files with Multiple Units: | ||
| • Operating gnatchop in Compilation Mode: | ||
| • Command Line for gnatchop: | ||
| • Switches for gnatchop: | ||
| • Examples of gnatchop Usage: |
Next: Operating gnatchop in Compilation Mode, Previous: Compilation options, Up: Renaming Files Using gnatchop [Contents][Index]
The basic compilation model of GNAT requires that a file submitted to the compiler have only one unit and there be a strict correspondence between the file name and the unit name.
The gnatchop utility allows both of these rules to be relaxed,
allowing GNAT to process files which contain multiple compilation units
and files with arbitrary file names. gnatchop
reads the specified file and generates one or more output files,
containing one unit per file. The unit and the file name correspond,
as required by GNAT.
If you want to permanently restructure a set of “foreign” files so that
they match the GNAT rules, and do the remaining development using the
GNAT structure, you can simply use gnatchop once, generate the
new set of files and work with them from that point on.
Alternatively, if you want to keep your files in the “foreign” format,
perhaps to maintain compatibility with some other Ada compilation
system, you can set up a procedure where you use gnatchop each
time you compile, regarding the source files that it writes as temporary
files that you throw away.
Note that if your file containing multiple units starts with a byte order mark (BOM) specifying UTF-8 encoding, then the files generated by gnatchop will each start with a copy of this BOM, meaning that they can be compiled automatically in UTF-8 mode without needing to specify an explicit encoding.
Next: Command Line for gnatchop, Previous: Handling Files with Multiple Units, Up: Renaming Files Using gnatchop [Contents][Index]
The basic function of gnatchop is to take a file with multiple units
and split it into separate files. The boundary between files is reasonably
clear, except for the issue of comments and pragmas. In default mode, the
rule is that any pragmas between units belong to the previous unit, except
that configuration pragmas always belong to the following unit. Any comments
belong to the following unit. These rules
almost always result in the right choice of
the split point without needing to mark it explicitly and most users will
find this default to be what they want. In this default mode it is incorrect to
submit a file containing only configuration pragmas, or one that ends in
configuration pragmas, to gnatchop.
However, using a special option to activate “compilation mode”,
gnatchop
can perform another function, which is to provide exactly the semantics
required by the RM for handling of configuration pragmas in a compilation.
In the absence of configuration pragmas (at the main file level), this
option has no effect, but it causes such configuration pragmas to be handled
in a quite different manner.
First, in compilation mode, if gnatchop is given a file that consists of
only configuration pragmas, then this file is appended to the
gnat.adc file in the current directory. This behavior provides
the required behavior described in the RM for the actions to be taken
on submitting such a file to the compiler, namely that these pragmas
should apply to all subsequent compilations in the same compilation
environment. Using GNAT, the current directory, possibly containing a
gnat.adc file is the representation
of a compilation environment. For more information on the
gnat.adc file, see Handling of Configuration Pragmas.
Second, in compilation mode, if gnatchop
is given a file that starts with
configuration pragmas, and contains one or more units, then these
configuration pragmas are prepended to each of the chopped files. This
behavior provides the required behavior described in the RM for the
actions to be taken on compiling such a file, namely that the pragmas
apply to all units in the compilation, but not to subsequently compiled
units.
Finally, if configuration pragmas appear between units, they are appended to the previous unit. This results in the previous unit being illegal, since the compiler does not accept configuration pragmas that follow a unit. This provides the required RM behavior that forbids configuration pragmas other than those preceding the first compilation unit of a compilation.
For most purposes, gnatchop will be used in default mode. The
compilation mode described above is used only if you need exactly
accurate behavior with respect to compilations, and you have files
that contain multiple units and configuration pragmas. In this
circumstance the use of gnatchop with the compilation mode
switch provides the required behavior, and is for example the mode
in which GNAT processes the ACVC tests.
Next: Switches for gnatchop, Previous: Operating gnatchop in Compilation Mode, Up: Renaming Files Using gnatchop [Contents][Index]
gnatchopThe gnatchop command has the form:
$ gnatchop switches file name [file name …] [directory]
The only required argument is the file name of the file to be chopped. There are no restrictions on the form of this file name. The file itself contains one or more Ada units, in normal GNAT format, concatenated together. As shown, more than one file may be presented to be chopped.
When run in default mode, gnatchop generates one output file in
the current directory for each unit in each of the files.
directory, if specified, gives the name of the directory to which the output files will be written. If it is not specified, all files are written to the current directory.
For example, given a file called hellofiles containing
procedure hello;
with Text_IO; use Text_IO;
procedure hello is
begin
Put_Line ("Hello");
end hello;
|
the command
$ gnatchop hellofiles
generates two files in the current directory, one called hello.ads containing the single line that is the procedure spec, and the other called hello.adb containing the remaining text. The original file is not affected. The generated files can be compiled in the normal manner.
When gnatchop is invoked on a file that is empty or that contains only empty lines and/or comments, gnatchop will not fail, but will not produce any new sources.
For example, given a file called toto.txt containing
-- Just a comment |
the command
$ gnatchop toto.txt
will not produce any new file and will result in the following warnings:
toto.txt:1:01: warning: empty file, contains no compilation units no compilation units found no source files written
Next: Examples of gnatchop Usage, Previous: Command Line for gnatchop, Up: Renaming Files Using gnatchop [Contents][Index]
gnatchopgnatchop recognizes the following switches:
Display Copyright and version, then exit disregarding all other options.
If --version was not used, display usage, then exit disregarding all other options.
Causes gnatchop to operate in compilation mode, in which
configuration pragmas are handled according to strict RM rules. See
previous section for a full description of this mode.
This passes the given -gnatxxx switch to gnat which is
used to parse the given file. Not all xxx options make sense,
but for example, the use of -gnati2 allows gnatchop to
process a source file that uses Latin-2 coding for identifiers.
Causes gnatchop to generate a brief help summary to the standard
output file showing usage information.
Limit generated file names to the specified number mm
of characters.
This is useful if the
resulting set of files is required to be interoperable with systems
which limit the length of file names.
No space is allowed between the -k and the numeric value. The numeric
value may be omitted in which case a default of -k8,
suitable for use
with DOS-like file systems, is used. If no -k switch
is present then
there is no limit on the length of file names.
Causes the file modification time stamp of the input file to be
preserved and used for the time stamp of the output file(s). This may be
useful for preserving coherency of time stamps in an environment where
gnatchop is used as part of a standard build process.
Causes output of informational messages indicating the set of generated files to be suppressed. Warnings and error messages are unaffected.
Generate Source_Reference pragmas. Use this switch if the output
files are regarded as temporary and development is to be done in terms
of the original unchopped file. This switch causes
Source_Reference pragmas to be inserted into each of the
generated files to refers back to the original file name and line number.
The result is that all error messages refer back to the original
unchopped file.
In addition, the debugging information placed into the object file (when
the -g switch of gcc or gnatmake is
specified)
also refers back to this original file so that tools like profilers and
debuggers will give information in terms of the original unchopped file.
If the original file to be chopped itself contains
a Source_Reference
pragma referencing a third file, then gnatchop respects
this pragma, and the generated Source_Reference pragmas
in the chopped file refer to the original file, with appropriate
line numbers. This is particularly useful when gnatchop
is used in conjunction with gnatprep to compile files that
contain preprocessing statements and multiple units.
Causes gnatchop to operate in verbose mode. The version
number and copyright notice are output, as well as exact copies of
the gnat1 commands spawned to obtain the chop control information.
Overwrite existing file names. Normally gnatchop regards it as a
fatal error if there is already a file with the same name as a
file it would otherwise output, in other words if the files to be
chopped contain duplicated units. This switch bypasses this
check, and causes all but the last instance of such duplicated
units to be skipped.
Specify the path of the GNAT parser to be used. When this switch is used, no attempt is made to add the prefix to the GNAT parser executable.
Next: Handling of Configuration Pragmas, Previous: Switches for gnatchop, Up: Renaming Files Using gnatchop [Contents][Index]
gnatchop Usagegnatchop -w hello_s.ada prerelease/filesChops the source file hello_s.ada. The output files will be placed in the directory prerelease/files, overwriting any files with matching names in that directory (no files in the current directory are modified).
gnatchop archiveChops the source file archive
into the current directory. One
useful application of gnatchop is in sending sets of sources
around, for example in email messages. The required sources are simply
concatenated (for example, using a Unix cat
command), and then
gnatchop is used at the other end to reconstitute the original
file names.
gnatchop file1 file2 file3 direcChops all units in files file1, file2, file3, placing the resulting files in the directory direc. Note that if any units occur more than once anywhere within this set of files, an error message is generated, and no files are written. To override this check, use the -w switch, in which case the last occurrence in the last file will be the one that is output, and earlier duplicate occurrences for a given unit will be skipped.
Next: Handling Arbitrary File Naming Conventions Using gnatname, Previous: Renaming Files Using gnatchop, Up: Top [Contents][Index]
Configuration pragmas include those pragmas described as
such in the Ada Reference Manual, as well as
implementation-dependent pragmas that are configuration pragmas.
See Implementation Defined Pragmas in GNAT Reference Manual,
for details on these additional GNAT-specific configuration pragmas.
Most notably, the pragma Source_File_Name, which allows
specifying non-default names for source files, is a configuration
pragma. The following is a complete list of configuration pragmas
recognized by GNAT:
Ada_83 Ada_95 Ada_05 Ada_2005 Ada_12 Ada_2012 Annotate Assertion_Policy Assume_No_Invalid_Values C_Pass_By_Copy Check_Name Check_Policy Compile_Time_Error Compile_Time_Warning Compiler_Unit Component_Alignment Convention_Identifier Debug_Policy Detect_Blocking Default_Storage_Pool Discard_Names Elaboration_Checks Eliminate Extend_System Extensions_Allowed External_Name_Casing Fast_Math Favor_Top_Level Float_Representation Implicit_Packing Initialize_Scalars Interrupt_State License Locking_Policy Long_Float No_Run_Time No_Strict_Aliasing Normalize_Scalars Optimize_Alignment Persistent_BSS Polling Priority_Specific_Dispatching Profile Profile_Warnings Propagate_Exceptions Queuing_Policy Ravenscar Restricted_Run_Time Restrictions Restrictions_Warnings Reviewable Short_Circuit_And_Or Source_File_Name Source_File_Name_Project Style_Checks Suppress Suppress_Exception_Locations Task_Dispatching_Policy Universal_Data Unsuppress Use_VADS_Size Validity_Checks Warnings Wide_Character_Encoding
| • Handling of Configuration Pragmas: | ||
| • The Configuration Pragmas Files: |
Next: The Configuration Pragmas Files, Previous: Examples of gnatchop Usage, Up: Configuration Pragmas [Contents][Index]
Configuration pragmas may either appear at the start of a compilation unit, or they can appear in a configuration pragma file to apply to all compilations performed in a given compilation environment.
GNAT also provides the gnatchop utility to provide an automatic
way to handle configuration pragmas following the semantics for
compilations (that is, files with multiple units), described in the RM.
See Operating gnatchop in Compilation Mode for details.
However, for most purposes, it will be more convenient to edit the
gnat.adc file that contains configuration pragmas directly,
as described in the following section.
In the case of Restrictions pragmas appearing as configuration
pragmas in individual compilation units, the exact handling depends on
the type of restriction.
Restrictions that require partition-wide consistency (like
No_Tasking) are
recognized wherever they appear
and can be freely inherited, e.g. from a with’ed unit to the with’ing
unit. This makes sense since the binder will in any case insist on seeing
consistent use, so any unit not conforming to any restrictions that are
anywhere in the partition will be rejected, and you might as well find
that out at compile time rather than at bind time.
For restrictions that do not require partition-wide consistency, e.g. SPARK or No_Implementation_Attributes, in general the restriction applies only to the unit in which the pragma appears, and not to any other units.
The exception is No_Elaboration_Code which always applies to the entire object file from a compilation, i.e. to the body, spec, and all subunits. This restriction can be specified in a configuration pragma file, or it can be on the body and/or the spec (in eithe case it applies to all the relevant units). It can appear on a subunit only if it has previously appeared in the body of spec.
Next: Arbitrary File Naming Conventions, Previous: Handling of Configuration Pragmas, Up: Configuration Pragmas [Contents][Index]
In GNAT a compilation environment is defined by the current directory at the time that a compile command is given. This current directory is searched for a file whose name is gnat.adc. If this file is present, it is expected to contain one or more configuration pragmas that will be applied to the current compilation. However, if the switch -gnatA is used, gnat.adc is not considered.
Configuration pragmas may be entered into the gnat.adc file
either by running gnatchop on a source file that consists only of
configuration pragmas, or more conveniently by
direct editing of the gnat.adc file, which is a standard format
source file.
In addition to gnat.adc, additional files containing configuration pragmas may be applied to the current compilation using the switch -gnatecpath. path must designate an existing file that contains only configuration pragmas. These configuration pragmas are in addition to those found in gnat.adc (provided gnat.adc is present and switch -gnatA is not used).
It is allowed to specify several switches -gnatec, all of which will be taken into account.
If you are using project file, a separate mechanism is provided using project attributes, see Specifying Configuration Pragmas for more details.
Next: GNAT Project Manager, Previous: Configuration Pragmas, Up: Top [Contents][Index]
gnatname| • Arbitrary File Naming Conventions: | ||
| • Running gnatname: | ||
| • Switches for gnatname: | ||
| • Examples of gnatname Usage: |
Next: Running gnatname, Previous: The Configuration Pragmas Files, Up: Handling Arbitrary File Naming Conventions Using gnatname [Contents][Index]
The GNAT compiler must be able to know the source file name of a compilation
unit. When using the standard GNAT default file naming conventions
(.ads for specs, .adb for bodies), the GNAT compiler
does not need additional information.
When the source file names do not follow the standard GNAT default file naming
conventions, the GNAT compiler must be given additional information through
a configuration pragmas file (see Configuration Pragmas)
or a project file.
When the non-standard file naming conventions are well-defined,
a small number of pragmas Source_File_Name specifying a naming pattern
(see Alternative File Naming Schemes) may be sufficient. However,
if the file naming conventions are irregular or arbitrary, a number
of pragma Source_File_Name for individual compilation units
must be defined.
To help maintain the correspondence between compilation unit names and
source file names within the compiler,
GNAT provides a tool gnatname to generate the required pragmas for a
set of files.
Next: Switches for gnatname, Previous: Arbitrary File Naming Conventions, Up: Handling Arbitrary File Naming Conventions Using gnatname [Contents][Index]
gnatnameThe usual form of the gnatname command is
$ gnatname [switches] naming_pattern [naming_patterns] [--and [switches] naming_pattern [naming_patterns]]
All of the arguments are optional. If invoked without any argument,
gnatname will display its usage.
When used with at least one naming pattern, gnatname will attempt to
find all the compilation units in files that follow at least one of the
naming patterns. To find these compilation units,
gnatname will use the GNAT compiler in syntax-check-only mode on all
regular files.
One or several Naming Patterns may be given as arguments to gnatname.
Each Naming Pattern is enclosed between double quotes (or single
quotes on Windows).
A Naming Pattern is a regular expression similar to the wildcard patterns
used in file names by the Unix shells or the DOS prompt.
gnatname may be called with several sections of directories/patterns.
Sections are separated by switch --and. In each section, there must be
at least one pattern. If no directory is specified in a section, the current
directory (or the project directory is -P is used) is implied.
The options other that the directory switches and the patterns apply globally
even if they are in different sections.
Examples of Naming Patterns are
"*.[12].ada" "*.ad[sb]*" "body_*" "spec_*"
For a more complete description of the syntax of Naming Patterns, see the second kind of regular expressions described in g-regexp.ads (the “Glob” regular expressions).
When invoked with no switch -P, gnatname will create a
configuration pragmas file gnat.adc in the current working directory,
with pragmas Source_File_Name for each file that contains a valid Ada
unit.
Next: Examples of gnatname Usage, Previous: Running gnatname, Up: Handling Arbitrary File Naming Conventions Using gnatname [Contents][Index]
gnatnameSwitches for gnatname must precede any specified Naming Pattern.
You may specify any of the following switches to gnatname:
Display Copyright and version, then exit disregarding all other options.
If --version was not used, display usage, then exit disregarding all other options.
Start another section of directories/patterns.
Create a configuration pragmas file file (instead of the default gnat.adc). There may be zero, one or more space between -c and file. file may include directory information. file must be writable. There may be only one switch -c. When a switch -c is specified, no switch -P may be specified (see below).
Look for source files in directory dir. There may be zero, one or more spaces between -d and dir. When a switch -d is specified, the current working directory will not be searched for source files, unless it is explicitly specified with a -d or -D switch. Several switches -d may be specified. If dir is a relative path, it is relative to the directory of the configuration pragmas file specified with switch -c, or to the directory of the project file specified with switch -P or, if neither switch -c nor switch -P are specified, it is relative to the current working directory. The directory specified with switch -d must exist and be readable.
Look for source files in all directories listed in text file file. There may be zero, one or more spaces between -D and file. file must be an existing, readable text file. Each nonempty line in file must be a directory. Specifying switch -D is equivalent to specifying as many switches -d as there are nonempty lines in file.
Foreign patterns. Using this switch, it is possible to add sources of languages other than Ada to the list of sources of a project file. It is only useful if a -P switch is used. For example,
gnatname -Pprj -f"*.c" "*.ada"
will look for Ada units in all files with the .ada extension, and will add to the list of file for project prj.gpr the C files with extension .c.
Output usage (help) information. The output is written to stdout.
Create or update project file proj. There may be zero, one or more space between -P and proj. proj may include directory information. proj must be writable. There may be only one switch -P. When a switch -P is specified, no switch -c may be specified.
Verbose mode. Output detailed explanation of behavior to stdout. This includes name of the file written, the name of the directories to search and, for each file in those directories whose name matches at least one of the Naming Patterns, an indication of whether the file contains a unit, and if so the name of the unit.
Very Verbose mode. In addition to the output produced in verbose mode, for each file in the searched directories whose name matches none of the Naming Patterns, an indication is given that there is no match.
Excluded patterns. Using this switch, it is possible to exclude some files that would match the name patterns. For example,
gnatname -x "*_nt.ada" "*.ada"
will look for Ada units in all files with the .ada extension, except those whose names end with _nt.ada.
Next: Switches for gnatxref, Previous: Switches for gnatname, Up: Handling Arbitrary File Naming Conventions Using gnatname [Contents][Index]
gnatname Usage$ gnatname -c /home/me/names.adc -d sources "[a-z]*.ada*"
In this example, the directory /home/me must already exist and be writable. In addition, the directory /home/me/sources (specified by -d sources) must exist and be readable.
Note the optional spaces after -c and -d.
$ gnatname -P/home/me/proj -x "*_nt_body.ada" -dsources -dsources/plus -Dcommon_dirs.txt "body_*" "spec_*"
Note that several switches -d may be used, even in conjunction with one or several switches -D. Several Naming Patterns and one excluded pattern are used in this example.
Next: Tools Supporting Project Files, Previous: Handling Arbitrary File Naming Conventions Using gnatname, Up: Top [Contents][Index]
Next: Building With Projects, Up: GNAT Project Manager [Contents][Index]
This chapter describes GNAT’s Project Manager, a facility that allows you to manage complex builds involving a number of source files, directories, and options for different system configurations. In particular, project files allow you to specify:
Project files are written in a syntax close to that of Ada, using familiar notions such as packages, context clauses, declarations, default values, assignments, and inheritance (see Project File Reference).
Project files can be built hierarchically from other project files, simplifying complex system integration and project reuse (see Organizing Projects into Subsystems).
Several tools support project files, generally in addition to specifying the information on the command line itself). They share common switches to control the loading of the project (in particular -Pprojectfile and -Xvbl=value). See Switches Related to Project Files.
The Project Manager supports a wide range of development strategies, for systems of all sizes. Here are some typical practices that are easily handled:
all OS dependencies in a small number of implementation units.
Project files can be used to achieve some of the effects of a source versioning system (for example, defining separate projects for the different sets of sources that comprise different releases) but the Project Manager is independent of any source configuration management tool that might be used by the developers.
The various sections below introduce the different concepts related to projects. Each section starts with examples and use cases, and then goes into the details of related project file capabilities.
Next: Organizing Projects into Subsystems, Previous: Introduction, Up: GNAT Project Manager [Contents][Index]
In its simplest form, a unique project is used to build a single executable. This section concentrates on such a simple setup. Later sections will extend this basic model to more complex setups.
The following concepts are the foundation of project files, and will be further detailed later in this documentation. They are summarized here as a reference.
A text file using an Ada-like syntax, generally using the .gpr extension. It defines build-related characteristics of an application. The characteristics include the list of sources, the location of those sources, the location for the generated object files, the name of the main program, and the options for the various tools involved in the build process.
A specific project characteristic is defined by an attribute clause. Its value is a string or a sequence of strings. All settings in a project are defined through a list of predefined attributes with precise semantics. See Attributes.
Global attributes are defined at the top level of a project.
Attributes affecting specific tools are grouped in a
package whose name is related to tool’s function. The most common
packages are Builder, Compiler, Binder,
and Linker. See Packages.
In addition to attributes, a project can use variables to store intermediate values and avoid duplication in complex expressions. It can be initialized with a value coming from the environment. A frequent use of variables is to define scenarios. See External Values, See Scenarios in Projects, and See Variables.
A source file is associated with a language through a naming convention. For
instance, foo.c is typically the name of a C source file;
bar.ads or bar.1.ada are two common naming conventions for a
file containing an Ada spec. A compilation unit is often composed of a main
source file and potentially several auxiliary ones, such as header files in C.
The naming conventions can be user defined See Naming Schemes, and will
drive the builder to call the appropriate compiler for the given source file.
Source files are searched for in the source directories associated with the
project through the Source_Dirs attribute. By default, all the files (in
these source directories) following the naming conventions associated with the
declared languages are considered to be part of the project. It is also
possible to limit the list of source files using the Source_Files or
Source_List_File attributes. Note that those last two attributes only
accept basenames with no directory information.
An object file is an intermediate file produced by the compiler from a compilation unit. It is used by post-compilation tools to produce final executables or libraries. Object files produced in the context of a given project are stored in a single directory that can be specified by the Object_Dir attribute. In order to store objects in two or more object directories, the system must be split into distinct subsystems with their own project file.
The following subsections introduce gradually all the attributes of interest for simple build needs. Here is the simple setup that will be used in the following examples.
The Ada source files pack.ads, pack.adb, and proc.adb are in
the common/ directory. The file proc.adb contains an Ada main
subprogram Proc that withs package Pack. We want to compile
these source files with the switch -O2, and put the resulting files in
the directory obj/.
common/ pack.ads pack.adb proc.adb
common/release/ proc.ali, proc.o pack.ali, pack.o
Our project is to be called Build. The name of the file is the name of the project (case-insensitive) with the .gpr extension, therefore the project file name is build.gpr. This is not mandatory, but a warning is issued when this convention is not followed.
This is a very simple example, and as stated above, a single project file is enough for it. We will thus create a new file, that for now should contain the following code:
project Build is end Build;
Next: Object and Exec Directory, Up: Building With Projects [Contents][Index]
When you create a new project, the first thing to describe is how to find the corresponding source files. This is the only settings that are needed by all the tools that will use this project (builder, compiler, binder and linker for the compilation, IDEs to edit the source files,…).
First step is to declare the source directories, which are the directories to be searched to find source files. In the case of the example, the common directory is the only source directory.
There are several ways of defining source directories:
The syntax for directories is platform specific. For portability, however, the project manager will always properly translate UNIX-like path names to the native format of specific platform. For instance, when the same project file is to be used both on Unix and Windows, "/" should be used as the directory separator rather than "\".
When using that construct, it can sometimes be convenient to also use the attribute Excluded_Source_Dirs, which is also a list of paths. Each entry specifies a directory whose immediate content, not including subdirs, is to be excluded. It is also possible to exclude a complete directory subtree using the "**" notation.
It is often desirable to remove, from the source directories, directory subtrees rooted at some subdirectories. An example is the subdirectories created by a Version Control System such as Subversion that creates directory subtrees rooted at subdirectories ".svn". To do that, attribute Ignore_Source_Sub_Dirs can be used. It specifies the list of simple file names for the roots of these undesirable directory subtrees.
for Source_Dirs use ("./**");
for Ignore_Source_Sub_Dirs use (".svn");
When applied to the simple example, and because we generally prefer to have the project file at the toplevel directory rather than mixed with the sources, we will create the following file
build.gpr
project Build is
for Source_Dirs use ("common"); -- <<<<
end Build;
Once source directories have been specified, one may need to indicate source files of interest. By default, all source files present in the source directories are considered by the project manager. When this is not desired, it is possible to specify the list of sources to consider explicitly. In such a case, only source file base names are indicated and not their absolute or relative path names. The project manager is in charge of locating the specified source files in the specified source directories.
Since the project manager was initially developed for Ada environments, the default language is usually Ada and the above project file is complete: it defines without ambiguity the sources composing the project: that is to say, all the sources in subdirectory "common" for the default language (Ada) using the default naming convention.
However, when compiling a multi-language application, or a pure C
application, the project manager must be told which languages are of
interest, which is done by setting the Languages attribute to a list of
strings, each of which is the name of a language. Tools like
gnatmake only know about Ada, while other tools like
gprbuild know about many more languages such as C, C++, Fortran,
assembly and others can be added dynamically.
Even when using only Ada, the default naming might not be suitable. Indeed, how does the project manager recognizes an "Ada file" from any other file? Project files can describe the naming scheme used for source files, and override the default (see Naming Schemes). The default is the standard GNAT extension (.adb for bodies and .ads for specs), which is what is used in our example, explaining why no naming scheme is explicitly specified. See Naming Schemes.
Source_Files
In some cases, source directories might contain files that should not be
included in a project. One can specify the explicit list of file names to
be considered through the Source_Files attribute.
When this attribute is defined, instead of looking at every file in the
source directories, the project manager takes only those names into
consideration reports errors if they cannot be found in the source
directories or does not correspond to the naming scheme.
(). Alternatively,
Source_Dirs can be set to the empty list, with the same
result.
Source_List_File
If there is a great number of files, it might be more convenient to use
the attribute Source_List_File, which specifies the full path of a file.
This file must contain a list of source file names (one per line, no
directory information) that are searched as if they had been defined
through Source_Files. Such a file can easily be created through
external tools.
A warning is issued if both attributes Source_Files and
Source_List_File are given explicit values. In this case, the
attribute Source_Files prevails.
Excluded_Source_Files
Specifying an explicit list of files is not always convenient.It might be
more convenient to use the default search rules with specific exceptions.
This can be done thanks to the attribute Excluded_Source_Files
(or its synonym Locally_Removed_Files).
Its value is the list of file names that should not be taken into account.
This attribute is often used when extending a project,
See Project Extension. A similar attribute
Excluded_Source_List_File plays the same
role but takes the name of file containing file names similarly to
Source_List_File.
In most simple cases, such as the above example, the default source file search
behavior provides the expected result, and we do not need to add anything after
setting Source_Dirs. The project manager automatically finds
pack.ads, pack.adb and proc.adb as source files of the
project.
Note that it is considered an error for a project file to have no sources attached to it unless explicitly declared as mentioned above.
If the order of the source directories is known statically, that is if
"**" is not used in the string list Source_Dirs, then there may
be several files with the same source file name sitting in different
directories of the project. In this case, only the file in the first directory
is considered as a source of the project and the others are hidden. If
"**" is used in the string list Source_Dirs, it is an error
to have several files with the same source file name in the same directory
"**" subtree, since there would be an ambiguity as to which one should
be used. However, two files with the same source file name may exist in two
single directories or directory subtrees. In this case, the one in the first
directory or directory subtree is a source of the project.
Next: Main Subprograms, Previous: Source Files and Directories, Up: Building With Projects [Contents][Index]
The next step when writing a project is to indicate where the compiler should put the object files. In fact, the compiler and other tools might create several different kind of files (for GNAT, there is the object file and the ALI file for instance). One of the important concepts in projects is that most tools may consider source directories as read-only and do not attempt to create new or temporary files there. Instead, all files are created in the object directory. It is of course not true for project-aware IDEs, whose purpose it is to create the source files.
The object directory is specified through the Object_Dir attribute.
Its value is the path to the object directory, either absolute or
relative to the directory containing the project file. This
directory must already exist and be readable and writable, although
some tools have a switch to create the directory if needed (See
the switch -p for gnatmake and gprbuild).
If the attribute Object_Dir is not specified, it defaults to
the project directory, that is the directory containing the project file.
For our example, we can specify the object dir in this way:
project Build is
for Source_Dirs use ("common");
for Object_Dir use "obj"; -- <<<<
end Build;
As mentioned earlier, there is a single object directory per project. As a result, if you have an existing system where the object files are spread in several directories, you can either move all of them into the same directory if you want to build it with a single project file, or study the section on subsystems (see Organizing Projects into Subsystems) to see how each separate object directory can be associated with one of the subsystem constituting the application.
When the linker is called, it usually creates an executable. By
default, this executable is placed in the object directory of the project. It
might be convenient to store it in its own directory.
This can be done through the Exec_Dir attribute, which, like
Object_Dir contains a single absolute or relative path and must point to
an existing and writable directory, unless you ask the tool to create it on
your behalf. When not specified, It defaults to the object directory and
therefore to the project file’s directory if neither Object_Dir nor
Exec_Dir was specified.
In the case of the example, let’s place the executable in the root of the hierarchy, ie the same directory as build.gpr. Hence the project file is now
project Build is
for Source_Dirs use ("common");
for Object_Dir use "obj";
for Exec_Dir use "."; -- <<<<
end Build;
Next: Tools Options in Project Files, Previous: Object and Exec Directory, Up: Building With Projects [Contents][Index]
In the previous section, executables were mentioned. The project manager needs
to be taught what they are. In a project file, an executable is indicated by
pointing to source file of the main subprogram. In C this is the file that
contains the main function, and in Ada the file that contains the main
unit.
There can be any number of such main files within a given project, and thus
several executables can be built in the context of a single project file. Of
course, one given executable might not (and in fact will not) need all the
source files referenced by the project. As opposed to other build environments
such as makefile, one does not need to specify the list of
dependencies of each executable, the project-aware builders knows enough of the
semantics of the languages to build ands link only the necessary elements.
The list of main files is specified via the Main attribute. It contains
a list of file names (no directories). If a project defines this
attribute, it is not necessary to identify main files on the
command line when invoking a builder, and editors like
GPS will be able to create extra menus to spawn or debug the
corresponding executables.
project Build is
for Source_Dirs use ("common");
for Object_Dir use "obj";
for Exec_Dir use ".";
for Main use ("proc.adb"); -- <<<<
end Build;
If this attribute is defined in the project, then spawning the builder with a command such as
gnatmake -Pbuild
automatically builds all the executables corresponding to the files listed in the Main attribute. It is possible to specify one or more executables on the command line to build a subset of them.
Next: Compiling with Project Files, Previous: Main Subprograms, Up: Building With Projects [Contents][Index]
We now have a project file that fully describes our environment, and can be
used to build the application with a simple gnatmake command as seen
in the previous section. In fact, the empty project we showed immediately at
the beginning (with no attribute at all) could already fulfill that need if it
was put in the common directory.
Of course, we always want more control. This section will show you how to specify the compilation switches that the various tools involved in the building of the executable should use.
Since source names and locations are described into the project file, it is not necessary to use switches on the command line for this purpose (switches such as -I for gcc). This removes a major source of command line length overflow. Clearly, the builders will have to communicate this information one way or another to the underlying compilers and tools they call but they usually use response files for this and thus should not be subject to command line overflows.
Several tools are participating to the creation of an executable: the compiler produces object files from the source files; the binder (in the Ada case) creates an source file that takes care, among other things, of elaboration issues and global variables initialization; and the linker gathers everything into a single executable that users can execute. All these tools are known by the project manager and will be called with user defined switches from the project files. However, we need to introduce a new project file concept to express which switches to be used for any of the tools involved in the build.
A project file is subdivided into zero or more packages, each of which contains the attributes specific to one tool (or one set of tools). Project files use an Ada-like syntax for packages. Package names permitted in project files are restricted to a predefined set (see Packages), and the contents of packages are limited to a small set of constructs and attributes (see Attributes).
Our example project file can be extended with the following empty packages. At this stage, they could all be omitted since they are empty, but they show which packages would be involved in the build process.
project Build is
for Source_Dirs use ("common");
for Object_Dir use "obj";
for Exec_Dir use ".";
for Main use ("proc.adb");
package Builder is --<<< for gnatmake and gprbuild
end Builder;
package Compiler is --<<< for the compiler
end Compiler;
package Binder is --<<< for the binder
end Binder;
package Linker is --<<< for the linker
end Linker;
end Build;
Let’s first examine the compiler switches. As stated in the initial description of the example, we want to compile all files with -O2. This is a compiler switch, although it is usual, on the command line, to pass it to the builder which then passes it to the compiler. It is recommended to use directly the right package, which will make the setup easier to understand for other people.
Several attributes can be used to specify the switches:
This is the first mention in this manual of an indexed attribute. When this attribute is defined, one must supply an index in the form of a literal string. In the case of Default_Switches, the index is the name of the language to which the switches apply (since a different compiler will likely be used for each language, and each compiler has its own set of switches). The value of the attribute is a list of switches.
In this example, we want to compile all Ada source files with the
-O2 switch, and the resulting project file is as follows
(only the Compiler package is shown):
package Compiler is
for Default_Switches ("Ada") use ("-O2");
end Compiler;
in some cases, we might want to use specific switches for one or more files. For instance, compiling proc.adb might not be possible at high level of optimization because of a compiler issue. In such a case, the Switches attribute (indexed on the file name) can be used and will override the switches defined by Default_Switches. Our project file would become:
package Compiler is
for Default_Switches ("Ada") use ("-O2");
for Switches ("proc.adb") use ("-O0");
end Compiler;
Switches may take a pattern as an index, such as in:
package Compiler is
for Default_Switches ("Ada") use ("-O2");
for Switches ("pkg*") use ("-O0");
end Compiler;
Sources pkg.adb and pkg-child.adb would be compiled with -O0, not -O2.
Switches can also be given a language name as index instead of a file
name in which case it has the same semantics as Default_Switches.
However, indexes with wild cards are never valid for language name.
this attribute may specify the path
of a file containing configuration pragmas for use by the Ada compiler,
such as pragma Restrictions (No_Tasking). These pragmas will be
used for all the sources of the project.
The switches for the other tools are defined in a similar manner through the
Default_Switches and Switches attributes, respectively in the
Builder package (for gnatmake and gprbuild),
the Binder package (binding Ada executables) and the Linker
package (for linking executables).
Next: Executable File Names, Previous: Tools Options in Project Files, Up: Building With Projects [Contents][Index]
Now that our project files are written, let’s build our executable. Here is the command we would use from the command line:
gnatmake -Pbuild
This will automatically build the executables specified through the Main attribute: for each, it will compile or recompile the sources for which the object file does not exist or is not up-to-date; it will then run the binder; and finally run the linker to create the executable itself.
gnatmake only knows how to handle Ada files. By using
gprbuild as a builder, you could automatically manage C files the
same way: create the file utils.c in the common directory,
set the attribute Languages to "(Ada, C)", and run
gprbuild -Pbuild
Gprbuild knows how to recompile the C files and will
recompile them only if one of their dependencies has changed. No direct
indication on how to build the various elements is given in the
project file, which describes the project properties rather than a
set of actions to be executed. Here is the invocation of
gprbuild when building a multi-language program:
$ gprbuild -Pbuild gcc -c proc.adb gcc -c pack.adb gcc -c utils.c gprbind proc ... gcc proc.o -o proc
Notice the three steps described earlier:
The default output of GPRbuild’s execution is kept reasonably simple and easy
to understand. In particular, some of the less frequently used commands are not
shown, and some parameters are abbreviated. So it is not possible to rerun the
effect of the gprbuild command by cut-and-pasting its output.
GPRbuild’s option -v provides a much more verbose output which includes,
among other information, more complete compilation, post-compilation and link
commands.
Next: Avoid Duplication With Variables, Previous: Compiling with Project Files, Up: Building With Projects [Contents][Index]
By default, the executable name corresponding to a main file is computed from the main source file name. Through the attribute Builder.Executable, it is possible to change this default.
For instance, instead of building proc (or proc.exe
on Windows), we could configure our project file to build "proc1"
(resp proc1.exe) with the following addition:
project Build is
... -- same as before
package Builder is
for Executable ("proc.adb") use "proc1";
end Builder
end Build;
Attribute Executable_Suffix, when specified, may change the suffix
of the executable files, when no attribute Executable applies:
its value replace the platform-specific executable suffix.
The default executable suffix is empty on UNIX and ".exe" on Windows.
It is also possible to change the name of the produced executable by using the
command line switch -o. When several mains are defined in the project,
it is not possible to use the -o switch and the only way to change the
names of the executable is provided by Attributes Executable and
Executable_Suffix.
Next: Naming Schemes, Previous: Executable File Names, Up: Building With Projects [Contents][Index]
To illustrate some other project capabilities, here is a slightly more complex project using similar sources and a main program in C:
project C_Main is
for Languages use ("Ada", "C");
for Source_Dirs use ("common");
for Object_Dir use "obj";
for Main use ("main.c");
package Compiler is
C_Switches := ("-pedantic");
for Default_Switches ("C") use C_Switches;
for Default_Switches ("Ada") use ("-gnaty");
for Switches ("main.c") use C_Switches & ("-g");
end Compiler;
end C_Main;
This project has many similarities with the previous one.
As expected, its Main attribute now refers to a C source.
The attribute Exec_Dir is now omitted, thus the resulting
executable will be put in the directory obj.
The most noticeable difference is the use of a variable in the Compiler package to store settings used in several attributes. This avoids text duplication, and eases maintenance (a single place to modify if we want to add new switches for C files). We will revisit the use of variables in the context of scenarios (see Scenarios in Projects).
In this example, we see how the file main.c can be compiled with
the switches used for all the other C files, plus -g.
In this specific situation the use of a variable could have been
replaced by a reference to the Default_Switches attribute:
for Switches ("c_main.c") use Compiler'Default_Switches ("C") & ("-g");
Note the tick (’) used to refer to attributes defined in a package.
Here is the output of the GPRbuild command using this project:
$gprbuild -Pc_main gcc -c -pedantic -g main.c gcc -c -gnaty proc.adb gcc -c -gnaty pack.adb gcc -c -pedantic utils.c gprbind main.bexch ... gcc main.o -o main
The default switches for Ada sources, the default switches for C sources (in the compilation of lib.c), and the specific switches for main.c have all been taken into account.
Next: Installation, Previous: Avoid Duplication With Variables, Up: Building With Projects [Contents][Index]
Sometimes an Ada software system is ported from one compilation environment to another (say GNAT), and the file are not named using the default GNAT conventions. Instead of changing all the file names, which for a variety of reasons might not be possible, you can define the relevant file naming scheme in the Naming package of your project file.
The naming scheme has two distinct goals for the project manager: it allows finding of source files when searching in the source directories, and given a source file name it makes it possible to guess the associated language, and thus the compiler to use.
Note that the use by the Ada compiler of pragmas Source_File_Name is not supported when using project files. You must use the features described in this paragraph. You can however specify other configuration pragmas (see Specifying Configuration Pragmas).
The following attributes can be defined in package Naming:
Its value must be one of "lowercase" (the default if
unspecified), "uppercase" or "mixedcase". It describes the
casing of file names with regards to the Ada unit name. Given an Ada unit
My_Unit, the file name will respectively be my_unit.adb (lowercase),
MY_UNIT.ADB (uppercase) or My_Unit.adb (mixedcase).
On Windows, file names are case insensitive, so this attribute is
irrelevant.
This attribute specifies the string that should replace the "." in unit
names. Its default value is "-" so that a unit
Parent.Child is expected to be found in the file
parent-child.adb. The replacement string must satisfy the following
requirements to avoid ambiguities in the naming scheme:
'.' except if the entire string
is "."
For Ada, these attributes give the suffix used in file names that contain
specifications. For other languages, they give the extension for files
that contain declaration (header files in C for instance). The attribute
is indexed on the language.
The two attributes are equivalent, but the latter is obsolescent.
If Spec_Suffix ("Ada") is not specified, then the default is
".ads".
The value must satisfy the following requirements:
These attributes give the extension used for file names that contain code (bodies in Ada). They are indexed on the language. The second version is obsolescent and fully replaced by the first attribute.
These attributes must satisfy the same requirements as Spec_Suffix.
In addition, they must be different from any of the values in
Spec_Suffix.
If Body_Suffix ("Ada") is not specified, then the default is
".adb".
If Body_Suffix ("Ada") and Spec_Suffix ("Ada") end with the
same string, then a file name that ends with the longest of these two
suffixes will be a body if the longest suffix is Body_Suffix ("Ada")
or a spec if the longest suffix is Spec_Suffix ("Ada").
If the suffix does not start with a ’.’, a file with a name exactly equal
to the suffix will also be part of the project (for instance if you define
the suffix as Makefile, a file called Makefile will be part
of the project. This capability is usually not interesting when building.
However, it might become useful when a project is also used to
find the list of source files in an editor, like the GNAT Programming System
(GPS).
This attribute is specific to Ada. It denotes the suffix used in file names
that contain separate bodies. If it is not specified, then it defaults to
same value as Body_Suffix ("Ada"). The same rules apply as for the
Body_Suffix attribute. The only accepted index is "Ada".
This attribute Spec can be used to define the source file name for a
given Ada compilation unit’s spec. The index is the literal name of the Ada
unit (case insensitive). The value is the literal base name of the file that
contains this unit’s spec (case sensitive or insensitive depending on the
operating system). This attribute allows the definition of exceptions to the
general naming scheme, in case some files do not follow the usual
convention.
When a source file contains several units, the relative position of the unit can be indicated. The first unit in the file is at position 1
for Spec ("MyPack.MyChild") use "mypack.mychild.spec";
for Spec ("top") use "foo.a" at 1;
for Spec ("foo") use "foo.a" at 2;
These attribute play the same role as Spec for Ada bodies.
These attributes define exceptions to the naming scheme for languages other than Ada. They are indexed on the language name, and contain a list of file names respectively for headers and source code.
For example, the following package models the Apex file naming rules:
package Naming is
for Casing use "lowercase";
for Dot_Replacement use ".";
for Spec_Suffix ("Ada") use ".1.ada";
for Body_Suffix ("Ada") use ".2.ada";
end Naming;
Next: Distributed support, Previous: Naming Schemes, Up: Building With Projects [Contents][Index]
After building an application or a library it is often required to
install it into the development environment. For instance this step is
required if the library is to be used by another application.
The gprinstall tool provides an easy way to install
libraries, executable or object code generated during the build. The
Install package can be used to change the default locations.
The following attributes can be defined in package Install:
Whether the project is to be installed, values are true
(default) or false.
Root directory for the installation.
Subdirectory of Prefix where executables are to be installed. Default is bin.
Subdirectory of Prefix where directory with the library or object files is to be installed. Default is lib.
Subdirectory of Prefix where directory with sources is to be installed. Default is include.
Subdirectory of Prefix where the generated project file is to be installed. Default is share/gpr.
Previous: Installation, Up: Building With Projects [Contents][Index]
For large projects the compilation time can become a limitation in the development cycle. To cope with that, GPRbuild supports distributed compilation.
The following attributes can be defined in package Remote:
A list of string referencing the remote build slaves to use for the
compilation phase. The format is:
[protocol://]name.domain[:port].
Where protocol is one of:
The sources are copied using the external rsync tool.
The sources are accessed via a shared directory or mount point.
The default port used to communicate with gprslave is
8484.
Root directory of the project’s sources. The default value is the project’s directory.
Next: Scenarios in Projects, Previous: Building With Projects, Up: GNAT Project Manager [Contents][Index]
A subsystem is a coherent part of the complete system to be built. It is represented by a set of sources and one single object directory. A system can be composed of a single subsystem when it is simple as we have seen in the first section. Complex systems are usually composed of several interdependent subsystems. A subsystem is dependent on another subsystem if knowledge of the other one is required to build it, and in particular if visibility on some of the sources of this other subsystem is required. Each subsystem is usually represented by its own project file.
In this section, the previous example is being extended. Let’s assume some
sources of our Build project depend on other sources.
For instance, when building a graphical interface, it is usual to depend upon
a graphical library toolkit such as GtkAda. Furthermore, we also need
sources from a logging module we had previously written.
| • Project Dependencies: | ||
| • Cyclic Project Dependencies: | ||
| • Sharing Between Projects: | ||
| • Global Attributes: |
GtkAda comes with its own project file (appropriately called gtkada.gpr), and we will assume we have already built a project called logging.gpr for the logging module. With the information provided so far in build.gpr, building the application would fail with an error indicating that the gtkada and logging units that are relied upon by the sources of this project cannot be found.
This is easily solved by adding the following with clauses at the beginning of our project:
with "gtkada.gpr";
with "a/b/logging.gpr";
project Build is
... -- as before
end Build;
When such a project is compiled, gnatmake will automatically
check the other projects and recompile their sources when needed. It will also
recompile the sources from Build when needed, and finally create the
executable. In some cases, the implementation units needed to recompile a
project are not available, or come from some third-party and you do not want to
recompile it yourself. In this case, the attribute Externally_Built to
"true" can be set, indicating to the builder that this project can be assumed
to be up-to-date, and should not be considered for recompilation. In Ada, if
the sources of this externally built project were compiled with another version
of the compiler or with incompatible options, the binder will issue an error.
The project’s with clause has several effects. It provides source
visibility between projects during the compilation process. It also guarantees
that the necessary object files from Logging and GtkAda are
available when linking Build.
As can be seen in this example, the syntax for importing projects is similar
to the syntax for importing compilation units in Ada. However, project files
use literal strings instead of names, and the with clause identifies
project files rather than packages.
Each literal string after with is the path
(absolute or relative) to a project file. The .gpr extension is
optional, although we recommend adding it. If no extension is specified,
and no project file with the .gpr extension is found, then
the file is searched for exactly as written in the with clause,
that is with no extension.
As mentioned above, the path after a with has to be a literal
string, and you cannot use concatenation, or lookup the value of external
variables to change the directories from which a project is loaded.
A solution if you need something like this is to use aggregate projects
(see Aggregate Projects).
When a relative path or a base name is used, the project files are searched relative to each of the directories in the project path. This path includes all the directories found with the following algorithm, in that order, as soon as a matching file is found, the search stops:
gnatmake in all cases, and for gprbuild if option
--target is specified)
gnatmake and gprbuild)
gnatmake and gprbuild)
In our example, gtkada.gpr is found in the predefined directory if it was installed at the same root as GNAT.
Some tools also support extending the project path from the command line,
generally through the -aP. You can see the value of the project
path by using the gnatls -v command.
Any symbolic link will be fully resolved in the directory of the importing project file before the imported project file is examined.
Any source file in the imported project can be used by the sources of the
importing project, transitively.
Thus if A imports B, which imports C, the sources of
A may depend on the sources of C, even if A does not
import C explicitly. However, this is not recommended, because if
and when B ceases to import C, some sources in A will
no longer compile. gprbuild has a switch --no-indirect-imports
that will report such indirect dependencies.
One very important aspect of a project hierarchy is that
a given source can only belong to one project (otherwise the project manager
would not know which settings apply to it and when to recompile it). It means
that different project files do not usually share source directories or
when they do, they need to specify precisely which project owns which sources
using attribute Source_Files or equivalent. By contrast, 2 projects
can each own a source with the same base file name as long as they live in
different directories. The latter is not true for Ada Sources because of the
correlation between source files and Ada units.
Next: Sharing Between Projects, Previous: Project Dependencies, Up: Organizing Projects into Subsystems [Contents][Index]
Cyclic dependencies are mostly forbidden:
if A imports B (directly or indirectly) then B
is not allowed to import A. However, there are cases when cyclic
dependencies would be beneficial. For these cases, another form of import
between projects exists: the limited with. A project A that
imports a project B with a straight with may also be imported,
directly or indirectly, by B through a limited with.
The difference between straight with and limited with is that
the name of a project imported with a limited with cannot be used in the
project importing it. In particular, its packages cannot be renamed and
its variables cannot be referred to.
with "b.gpr";
with "c.gpr";
project A is
For Exec_Dir use B'Exec_Dir; -- ok
end A;
limited with "a.gpr"; -- Cyclic dependency: A -> B -> A
project B is
For Exec_Dir use A'Exec_Dir; -- not ok
end B;
with "d.gpr";
project C is
end C;
limited with "a.gpr"; -- Cyclic dependency: A -> C -> D -> A
project D is
For Exec_Dir use A'Exec_Dir; -- not ok
end D;
Next: Global Attributes, Previous: Cyclic Project Dependencies, Up: Organizing Projects into Subsystems [Contents][Index]
When building an application, it is common to have similar needs in several of the projects corresponding to the subsystems under construction. For instance, they will all have the same compilation switches.
As seen before (see Tools Options in Project Files), setting compilation
switches for all sources of a subsystem is simple: it is just a matter of
adding a Compiler.Default_Switches attribute to each project files with
the same value. Of course, that means duplication of data, and both places need
to be changed in order to recompile the whole application with different
switches. It can become a real problem if there are many subsystems and thus
many project files to edit.
There are two main approaches to avoiding this duplication:
project Logging is
package Compiler is
for Switches ("Ada") use ("-O2");
end Compiler;
package Binder is
for Switches ("Ada") use ("-E");
end Binder;
end Logging;
with "logging.gpr";
project Build is
package Compiler renames Logging.Compiler;
package Binder is
for Switches ("Ada") use Logging.Binder'Switches ("Ada");
end Binder;
end Build;
The solution used for Compiler gets the same value for all
attributes of the package, but you cannot modify anything from the
package (adding extra switches or some exceptions). The second
version is more flexible, but more verbose.
If you need to refer to the value of a variable in an imported project, rather than an attribute, the syntax is similar but uses a "." rather than an apostrophe. For instance:
with "imported";
project Main is
Var1 := Imported.Var;
end Main;
abstract project Shared is
for Source_Files use (); -- no project
package Compiler is
for Switches ("Ada") use ("-O2");
end Compiler;
end Shared;
with "shared.gpr";
project Logging is
package Compiler renames Shared.Compiler;
end Logging;
with "shared.gpr";
project Build is
package Compiler renames Shared.Compiler;
end Build;
As for the first example, we could have chosen to set the attributes
one by one rather than to rename a package. The reason we explicitly
indicate that Shared has no sources is so that it can be created
in any directory and we are sure it shares no sources with Build
or Logging, which of course would be invalid.
Note the additional use of the abstract qualifier in shared.gpr. This qualifier is optional, but helps convey the message that we do not intend this project to have sources (see Qualified Projects for more qualifiers).
Previous: Sharing Between Projects, Up: Organizing Projects into Subsystems [Contents][Index]
We have already seen many examples of attributes used to specify a special option of one of the tools involved in the build process. Most of those attributes are project specific. That it to say, they only affect the invocation of tools on the sources of the project where they are defined.
There are a few additional attributes that apply to all projects in a hierarchy as long as they are defined on the "main" project. The main project is the project explicitly mentioned on the command-line. The project hierarchy is the "with"-closure of the main project.
Here is a list of commonly used global attributes:
This attribute points to a file that contains configuration pragmas
to use when building executables. These pragmas apply for all
executables built from this project hierarchy. As we have seen before,
additional pragmas can be specified on a per-project basis by setting the
Compiler.Local_Configuration_Pragmas attribute.
This attribute is a list of compiler switches to use when compiling any
source file in the project hierarchy. These switches are used in addition
to the ones defined in the Compiler package, which only apply to
the sources of the corresponding project. This attribute is indexed on
the name of the language.
Using such global capabilities is convenient. It can also lead to unexpected behavior. Especially when several subsystems are shared among different main projects and the different global attributes are not compatible. Note that using aggregate projects can be a safer and more powerful replacement to global attributes.
Next: Library Projects, Previous: Organizing Projects into Subsystems, Up: GNAT Project Manager [Contents][Index]
Various aspects of the projects can be modified based on scenarios. These are user-defined modes that change the behavior of a project. Typical examples are the setup of platform-specific compiler options, or the use of a debug and a release mode (the former would activate the generation of debug information, when the second will focus on improving code optimization).
Let’s enhance our example to support a debug and a release modes.The issue is to let the user choose what kind of system he is building: use -g as compiler switches in debug mode and -O2 in release mode. We will also setup the projects so that we do not share the same object directory in both modes, otherwise switching from one to the other might trigger more recompilations than needed or mix objects from the 2 modes.
One naive approach is to create two different project files, say build_debug.gpr and build_release.gpr, that set the appropriate attributes as explained in previous sections. This solution does not scale well, because in presence of multiple projects depending on each other, you will also have to duplicate the complete hierarchy and adapt the project files to point to the right copies.
Instead, project files support the notion of scenarios controlled by external values. Such values can come from several sources (in decreasing order of priority):
When launching gnatmake or gprbuild, the user can pass
extra -X switches to define the external value. In
our case, the command line might look like
gnatmake -Pbuild.gpr -Xmode=debug or gnatmake -Pbuild.gpr -Xmode=release
When the external value does not come from the command line, it can come from the value of environment variables of the appropriate name. In our case, if an environment variable called "mode" exist, its value will be taken into account.
We now need to get that value in the project. The general form is to use the predefined function external which returns the current value of the external. For instance, we could setup the object directory to point to either obj/debug or obj/release by changing our project to
project Build is
for Object_Dir use "obj/" & external ("mode", "debug");
... -- as before
end Build;
The second parameter to external is optional, and is the default
value to use if "mode" is not set from the command line or the environment.
In order to set the switches according to the different scenarios, other constructs have to be introduced such as typed variables and case statements.
A typed variable is a variable that can take only a limited number of values, similar to an enumeration in Ada. Such a variable can then be used in a case statement and create conditional sections in the project. The following example shows how this can be done:
project Build is
type Mode_Type is ("debug", "release"); -- all possible values
Mode : Mode_Type := external ("mode", "debug"); -- a typed variable
package Compiler is
case Mode is
when "debug" =>
for Switches ("Ada") use ("-g");
when "release" =>
for Switches ("Ada") use ("-O2");
end case;
end Compiler;
end Build;
The project has suddenly grown in size, but has become much more flexible.
Mode_Type defines the only valid values for the mode variable. If
any other value is read from the environment, an error is reported and the
project is considered as invalid.
The Mode variable is initialized with an external value
defaulting to "debug". This default could be omitted and that would
force the user to define the value. Finally, we can use a case statement to set the
switches depending on the scenario the user has chosen.
Most aspects of the projects can depend on scenarios. The notable exception
are project dependencies (with clauses), which may not depend on a scenario.
Scenarios work the same way with project hierarchies: you can either
duplicate a variable similar to Mode in each of the project (as long
as the first argument to external is always the same and the type is
the same), or simply set the variable in the shared.gpr project
(see Sharing Between Projects).
Next: Project Extension, Previous: Scenarios in Projects, Up: GNAT Project Manager [Contents][Index]
So far, we have seen examples of projects that create executables. However, it is also possible to create libraries instead. A library is a specific type of subsystem where, for convenience, objects are grouped together using system-specific means such as archives or windows DLLs.
Library projects provide a system- and language-independent way of building both static and dynamic libraries. They also support the concept of standalone libraries (SAL) which offers two significant properties: the elaboration (e.g. initialization) of the library is either automatic or very simple; a change in the implementation part of the library implies minimal post-compilation actions on the complete system and potentially no action at all for the rest of the system in the case of dynamic SALs.
The GNAT Project Manager takes complete care of the library build, rebuild and installation tasks, including recompilation of the source files for which objects do not exist or are not up to date, assembly of the library archive, and installation of the library (i.e., copying associated source, object and ALI files to the specified location).
| • Building Libraries: | ||
| • Using Library Projects: | ||
| • Stand-alone Library Projects: | ||
| • Installing a library with project files: |
Next: Using Library Projects, Up: Library Projects [Contents][Index]
Let’s enhance our example and transform the logging subsystem into a
library. In order to do so, a few changes need to be made to logging.gpr.
A number of specific attributes needs to be defined: at least Library_Name
and Library_Dir; in addition, a number of other attributes can be used
to specify specific aspects of the library. For readability, it is also
recommended (although not mandatory), to use the qualifier library in
front of the project keyword.
This attribute is the name of the library to be built. There is no restriction on the name of a library imposed by the project manager, except for stand-alone libraries whose names must follow the syntax of Ada identifiers; however, there may be system specific restrictions on the name. In general, it is recommended to stick to alphanumeric characters (and possibly single underscores) to help portability.
This attribute is the path (absolute or relative) of the directory where
the library is to be installed. In the process of building a library,
the sources are compiled, the object files end up in the explicit or
implicit Object_Dir directory. When all sources of a library
are compiled, some of the compilation artifacts, including the library itself,
are copied to the library_dir directory. This directory must exists and be
writable. It must also be different from the object directory so that cleanup
activities in the Library_Dir do not affect recompilation needs.
Here is the new version of logging.gpr that makes it a library:
library project Logging is -- "library" is optional for Library_Name use "logging"; -- will create "liblogging.a" on Unix for Object_Dir use "obj"; for Library_Dir use "lib"; -- different from object_dir end Logging;
Once the above two attributes are defined, the library project is valid and is enough for building a library with default characteristics. Other library-related attributes can be used to change the defaults:
The value of this attribute must be either "static", "dynamic" or
"relocatable" (the latter is a synonym for dynamic). It indicates
which kind of library should be built (the default is to build a
static library, that is an archive of object files that can potentially
be linked into a static executable). When the library is set to be dynamic,
a separate image is created that will be loaded independently, usually
at the start of the main program execution. Support for dynamic libraries is
very platform specific, for instance on Windows it takes the form of a DLL
while on GNU/Linux, it is a dynamic elf image whose suffix is usually
.so. Library project files, on the other hand, can be written in
a platform independent way so that the same project file can be used to build
a library on different operating systems.
If you need to build both a static and a dynamic library, it is recommended use two different object directories, since in some cases some extra code needs to be generated for the latter. For such cases, one can either define two different project files, or a single one which uses scenarios to indicate the various kinds of library to be built and their corresponding object_dir.
This attribute may be specified to indicate the directory where the ALI
files of the library are installed. By default, they are copied into the
Library_Dir directory, but as for the executables where we have a
separate Exec_Dir attribute, you might want to put them in a separate
directory since there can be hundreds of them. The same restrictions as for
the Library_Dir attribute apply.
This attribute is platform dependent, and has no effect on VMS and Windows.
On Unix, it is used only for dynamic libraries as the internal
name of the library (the "soname"). If the library file name (built
from the Library_Name) is different from the Library_Version,
then the library file will be a symbolic link to the actual file whose name
will be Library_Version. This follows the usual installation schemes
for dynamic libraries on many Unix systems.
project Logging is
Version := "1";
for Library_Dir use "lib";
for Library_Name use "logging";
for Library_Kind use "dynamic";
for Library_Version use "liblogging.so." & Version;
end Logging;
After the compilation, the directory lib will contain both a libdummy.so.1 library and a symbolic link to it called libdummy.so.
This attribute is the name of the tool to use instead of "gcc" to link shared libraries. A common use of this attribute is to define a wrapper script that accomplishes specific actions before calling gcc (which itself is calling the linker to build the library image).
This attribute may be used to specify additional switches (last switches) when linking a shared library.
This attribute, that is taken into account only by gprbuild, may be
used to specified leading options (first switches) when linking a shared
library.
This attribute specifies additional switches to be given to the linker when
linking an executable. It is ignored when defined in the main project and
taken into account in all other projects that are imported directly or
indirectly. These switches complement the Linker.Switches
defined in the main project. This is useful when a particular subsystem
depends on an external library: adding this dependency as a
Linker_Options in the project of the subsystem is more convenient than
adding it to all the Linker.Switches of the main projects that depend
upon this subsystem.
Next: Stand-alone Library Projects, Previous: Building Libraries, Up: Library Projects [Contents][Index]
When the builder detects that a project file is a library project file, it recompiles all sources of the project that need recompilation and rebuild the library if any of the sources have been recompiled. It then groups all object files into a single file, which is a shared or a static library. This library can later on be linked with multiple executables. Note that the use of shard libraries reduces the size of the final executable and can also reduce the memory footprint at execution time when the library is shared among several executables.
It is also possible to build multi-language libraries. When using
gprbuild as a builder, multi-language library projects allow naturally
the creation of multi-language libraries . gnatmake, does not try to
compile non Ada sources. However, when the project is multi-language, it will
automatically link all object files found in the object directory, whether or
not they were compiled from an Ada source file. This specific behavior does not
apply to Ada-only projects which only take into account the objects
corresponding to the sources of the project.
A non-library project can import a library project. When the builder is invoked
on the former, the library of the latter is only rebuilt when absolutely
necessary. For instance, if a unit of the
library is not up-to-date but non of the executables need this unit, then the
unit is not recompiled and the library is not reassembled.
For instance, let’s assume in our example that logging has the following
sources: log1.ads, log1.adb, log2.ads and
log2.adb. If log1.adb has been modified, then the library
liblogging will be rebuilt when compiling all the sources of
Build only if proc.ads, pack.ads or pack.adb
include a "with Log1".
To ensure that all the sources in the Logging library are
up to date, and that all the sources of Build are also up to date,
the following two commands needs to be used:
gnatmake -Plogging.gpr gnatmake -Pbuild.gpr
All ALI files will also be copied from the object directory to the
library directory. To build executables, gnatmake will use the
library rather than the individual object files.
Library projects can also be useful to describe a library that need to be used
but, for some reason, cannot be rebuilt. For instance, it is the case when some
of the library sources are not available. Such library projects need simply to
use the Externally_Built attribute as in the example below:
library project Extern_Lib is
for Languages use ("Ada", "C");
for Source_Dirs use ("lib_src");
for Library_Dir use "lib2";
for Library_Kind use "dynamic";
for Library_Name use "l2";
for Externally_Built use "true"; -- <<<<
end Extern_Lib;
In the case of externally built libraries, the Object_Dir
attribute does not need to be specified because it will never be
used.
The main effect of using such an externally built library project is mostly to
affect the linker command in order to reference the desired library. It can
also be achieved by using Linker.Linker_Options or Linker.Switches
in the project corresponding to the subsystem needing this external library.
This latter method is more straightforward in simple cases but when several
subsystems depend upon the same external library, finding the proper place
for the Linker.Linker_Options might not be easy and if it is
not placed properly, the final link command is likely to present ordering issues.
In such a situation, it is better to use the externally built library project
so that all other subsystems depending on it can declare this dependency thanks
to a project with clause, which in turn will trigger the builder to find
the proper order of libraries in the final link command.
Next: Installing a library with project files, Previous: Using Library Projects, Up: Library Projects [Contents][Index]
A stand-alone library is a library that contains the necessary code to elaborate the Ada units that are included in the library. A stand-alone library is a convenient way to add an Ada subsystem to a more global system whose main is not in Ada since it makes the elaboration of the Ada part mostly transparent. However, stand-alone libraries are also useful when the main is in Ada: they provide a means for minimizing relinking & redeployment of complex systems when localized changes are made.
The name of a stand-alone library, specified with attribute
Library_Name, must have the syntax of an Ada identifier.
The most prominent characteristic of a stand-alone library is that it offers a
distinction between interface units and implementation units. Only the former
are visible to units outside the library. A stand-alone library project is thus
characterised by a third attribute, usually Library_Interface, in addition
to the two attributes that make a project a Library Project
(Library_Name and Library_Dir). This third attribute may also be
Interfaces. Library_Interface only works when the interface is in Ada
and takes a list of units as parameter. Interfaces works for any supported
language and takes a list of sources as parameter.
This attribute defines an explicit subset of the units of the project. Units
from projects importing this library project may only "with" units whose
sources are listed in the Library_Interface. Other sources are
considered implementation units.
for Library_Dir use "lib";
for Library_Name use "loggin";
for Library_Interface use ("lib1", "lib2"); -- unit names
This attribute defines an explicit subset of the source files of a project.
Sources from projects importing this project, can only depend on sources from
this subset. This attribute can be used on non library projects. It can also
be used as a replacement for attribute Library_Interface, in which
case, units have to be replaced by source files. For multi-language library
projects, it is the only way to make the project a Stand-Alone Library project
whose interface is not purely Ada.
This attribute defines the kind of standalone library to
build. Values are either standard (the default), no or
encapsulated. When standard is used the code to elaborate and
finalize the library is embedded, when encapsulated is used the
library can furthermore only depends on static libraries (including
the GNAT runtime). This attribute can be set to no to make it clear
that the library should not be standalone in which case the
Library_Interface should not defined.
for Library_Dir use "lib";
for Library_Name use "loggin";
for Library_Interface use ("lib1", "lib2"); -- unit names
for Library_Standalone use "encapsulated";
In order to include the elaboration code in the stand-alone library, the binder
is invoked on the closure of the library units creating a package whose name
depends on the library name (b~logging.ads/b in the example).
This binder-generated package includes initialization and finalization
procedures whose names depend on the library name (logginginit and
loggingfinal in the example). The object corresponding to this package is
included in the library.
A dynamic stand-alone Library is automatically initialized if automatic initialization of Stand-alone Libraries is supported on the platform and if attribute Library_Auto_Init is not specified or is specified with the value "true". A static Stand-alone Library is never automatically initialized. Specifying "false" for this attribute prevent automatic initialization.
When a non-automatically initialized stand-alone library is used in an executable, its initialization procedure must be called before any service of the library is used. When the main subprogram is in Ada, it may mean that the initialization procedure has to be called during elaboration of another package.
For a stand-alone library, only the ALI files of the interface units
(those that are listed in attribute Library_Interface) are copied to
the library directory. As a consequence, only the interface units may be
imported from Ada units outside of the library. If other units are imported,
the binding phase will fail.
When a stand-alone library is bound, the switches that are specified in
the attribute Binder.Default_Switches ("Ada") are
used in the call to gnatbind.
This attribute defines the location (absolute or relative to the project
directory) where the sources of the interface units are copied at
installation time.
These sources includes the specs of the interface units along with the closure
of sources necessary to compile them successfully. That may include bodies and
subunits, when pragmas Inline are used, or when there is a generic
units in the spec. This directory cannot point to the object directory or
one of the source directories, but it can point to the library directory,
which is the default value for this attribute.
This attribute controls the export of symbols and, on some platforms (like VMS) that have the notions of major and minor IDs built in the library files, it controls the setting of these IDs. It is not supported on all platforms (where it will just have no effect). It may have one of the following values:
"autonomous" or "default": exported symbols are not controlled
"compliant": if attribute Library_Reference_Symbol_File
is not defined, then it is equivalent to policy "autonomous". If there
are exported symbols in the reference symbol file that are not in the
object files of the interfaces, the major ID of the library is increased.
If there are symbols in the object files of the interfaces that are not
in the reference symbol file, these symbols are put at the end of the list
in the newly created symbol file and the minor ID is increased.
"controlled": the attribute Library_Reference_Symbol_File must be
defined. The library will fail to build if the exported symbols in the
object files of the interfaces do not match exactly the symbol in the
symbol file.
"restricted": The attribute Library_Symbol_File must be defined.
The library will fail to build if there are symbols in the symbol file that
are not in the exported symbols of the object files of the interfaces.
Additional symbols in the object files are not added to the symbol file.
"direct": The attribute Library_Symbol_File must be defined and
must designate an existing file in the object directory. This symbol file
is passed directly to the underlying linker without any symbol processing.
This attribute may define the path name of a reference symbol file that is read when the symbol policy is either "compliant" or "controlled", on platforms that support symbol control, such as VMS, when building a stand-alone library. The path may be an absolute path or a path relative to the project directory.
This attribute may define the name of the symbol file to be created when building a stand-alone library when the symbol policy is either "compliant", "controlled" or "restricted", on platforms that support symbol control, such as VMS. When symbol policy is "direct", then a file with this name must exist in the object directory.
Previous: Stand-alone Library Projects, Up: Library Projects [Contents][Index]
When using project files, a usable version of the library is created in the
directory specified by the Library_Dir attribute of the library
project file. Thus no further action is needed in order to make use of
the libraries that are built as part of the general application build.
You may want to install a library in a context different from where the library
is built. This situation arises with third party suppliers, who may want
to distribute a library in binary form where the user is not expected to be
able to recompile the library. The simplest option in this case is to provide
a project file slightly different from the one used to build the library, by
using the externally_built attribute. Using Library Projects
Another option is to use gprinstall to install the library in a
different context than the build location. A project to use this library is
generated automatically by gprinstall which also copy, in the install
location, the minimum set of sources needed to use the library.
Installation
Next: Aggregate Projects, Previous: Library Projects, Up: GNAT Project Manager [Contents][Index]
During development of a large system, it is sometimes necessary to use modified versions of some of the source files, without changing the original sources. This can be achieved through the project extension facility.
Suppose for instance that our example Build project is built every night
for the whole team, in some shared directory. A developer usually need to work
on a small part of the system, and might not want to have a copy of all the
sources and all the object files (mostly because that would require too much
disk space, time to recompile everything). He prefers to be able to override
some of the source files in his directory, while taking advantage of all the
object files generated at night.
Another example can be taken from large software systems, where it is common to have multiple implementations of a common interface; in Ada terms, multiple versions of a package body for the same spec. For example, one implementation might be safe for use in tasking programs, while another might only be used in sequential applications. This can be modeled in GNAT using the concept of project extension. If one project (the “child”) extends another project (the “parent”) then by default all source files of the parent project are inherited by the child, but the child project can override any of the parent’s source files with new versions, and can also add new files or remove unnecessary ones. This facility is the project analog of a type extension in object-oriented programming. Project hierarchies are permitted (an extending project may itself be extended), and a project that extends a project can also import other projects.
A third example is that of using project extensions to provide different
versions of the same system. For instance, assume that a Common
project is used by two development branches. One of the branches has now
been frozen, and no further change can be done to it or to Common.
However, the other development branch still needs evolution of Common.
Project extensions provide a flexible solution to create a new version
of a subsystem while sharing and reusing as much as possible from the original
one.
A project extension inherits implicitly all the sources and objects from the
project it extends. It is possible to create a new version of some of the
sources in one of the additional source dirs of the extending project. Those new
versions hide the original versions. Adding new sources or removing existing
ones is also possible. Here is an example on how to extend the project
Build from previous examples:
project Work extends "../bld/build.gpr" is end Work;
The project after extends is the one being extended. As usual, it can be
specified using an absolute path, or a path relative to any of the directories
in the project path (see Project Dependencies). This project does not
specify source or object directories, so the default value for these attribute
will be used that is to say the current directory (where project Work is
placed). We can already compile that project with
gnatmake -Pwork
If no sources have been placed in the current directory, this command
won’t do anything, since this project does not change the
sources it inherited from Build, therefore all the object files
in Build and its dependencies are still valid and are reused
automatically.
Suppose we now want to supply an alternate version of pack.adb
but use the existing versions of pack.ads and proc.adb.
We can create the new file Work’s current directory (likely
by copying the one from the Build project and making changes to
it. If new packages are needed at the same time, we simply create
new files in the source directory of the extending project.
When we recompile, gnatmake will now automatically recompile
this file (thus creating pack.o in the current directory) and
any file that depends on it (thus creating proc.o). Finally, the
executable is also linked locally.
Note that we could have obtained the desired behavior using project import
rather than project inheritance. A base project would contain the
sources for pack.ads and proc.adb, and Work would
import base and add pack.adb. In this scenario, base
cannot contain the original version of pack.adb otherwise there would be
2 versions of the same unit in the closure of the project and this is not
allowed. Generally speaking, it is not recommended to put the spec and the
body of a unit in different projects since this affects their autonomy and
reusability.
In a project file that extends another project, it is possible to indicate that an inherited source is not part of the sources of the extending project. This is necessary sometimes when a package spec has been overridden and no longer requires a body: in this case, it is necessary to indicate that the inherited body is not part of the sources of the project, otherwise there will be a compilation error when compiling the spec.
For that purpose, the attribute Excluded_Source_Files is used.
Its value is a list of file names.
It is also possible to use attribute Excluded_Source_List_File.
Its value is the path of a text file containing one file name per
line.
project Work extends "../bld/build.gpr" is
for Source_Files use ("pack.ads");
-- New spec of Pkg does not need a completion
for Excluded_Source_Files use ("pack.adb");
end Work;
All packages that are not declared in the extending project are inherited from
the project being extended, with their attributes, with the exception of
Linker'Linker_Options which is never inherited. In particular, an
extending project retains all the switches specified in the project being
extended.
At the project level, if they are not declared in the extending project, some
attributes are inherited from the project being extended. They are:
Languages, Main (for a root non library project) and
Library_Name (for a project extending a library project)
| • Project Hierarchy Extension: |
Up: Project Extension [Contents][Index]
One of the fundamental restrictions in project extension is the following: A project is not allowed to import directly or indirectly at the same time an extending project and one of its ancestors.
By means of example, consider the following hierarchy of projects.
a.gpr contains package A1 b.gpr, imports a.gpr and contains B1, which depends on A1 c.gpr, imports b.gpr and contains C1, which depends on B1
If we want to locally extend the packages A1 and C1, we need to
create several extending projects:
a_ext.gpr which extends a.gpr, and overrides A1 b_ext.gpr which extends b.gpr and imports a_ext.gpr c_ext.gpr which extends c.gpr, imports b_ext.gpr and overrides C1
project A_Ext extends "a.gpr" is
for Source_Files use ("a1.adb", "a1.ads");
end A_Ext;
with "a_ext.gpr";
project B_Ext extends "b.gpr" is
end B_Ext;
with "b_ext.gpr";
project C_Ext extends "c.gpr" is
for Source_Files use ("c1.adb");
end C_Ext;
The extension b_ext.gpr is required, even though we are not overriding any of the sources of b.gpr because otherwise c_expr.gpr would import b.gpr which itself knows nothing about a_ext.gpr.
When extending a large system spanning multiple projects, it is often inconvenient to extend every project in the hierarchy that is impacted by a small change introduced in a low layer. In such cases, it is possible to create an implicit extension of entire hierarchy using extends all relationship.
When the project is extended using extends all inheritance, all projects
that are imported by it, both directly and indirectly, are considered virtually
extended. That is, the project manager creates implicit projects
that extend every project in the hierarchy; all these implicit projects do not
control sources on their own and use the object directory of
the "extending all" project.
It is possible to explicitly extend one or more projects in the hierarchy in order to modify the sources. These extending projects must be imported by the "extending all" project, which will replace the corresponding virtual projects with the explicit ones.
When building such a project hierarchy extension, the project manager will ensure that both modified sources and sources in implicit extending projects that depend on them, are recompiled.
Thus, in our example we could create the following projects instead:
a_ext.gpr, extends a.gpr and overrides A1 c_ext.gpr, "extends all" c.gpr, imports a_ext.gpr and overrides C1
project A_Ext extends "a.gpr" is
for Source_Files use ("a1.adb", "a1.ads");
end A_Ext;
with "a_ext.gpr";
project C_Ext extends all "c.gpr" is
for Source_Files use ("c1.adb");
end C_Ext;
When building project c_ext.gpr, the entire modified project space is
considered for recompilation, including the sources of b.gpr that are
impacted by the changes in A1 and C1.
Next: Aggregate Library Projects, Previous: Project Extension, Up: GNAT Project Manager [Contents][Index]
Aggregate projects are an extension of the project paradigm, and are meant to solve a few specific use cases that cannot be solved directly using standard projects. This section will go over a few of these use cases to try to explain what you can use aggregate projects for.
Most often, an application is organized into modules and submodules,
which are very conveniently represented as a project tree or graph
(the root project A withs the projects for each modules (say B and C),
which in turn with projects for submodules.
Very often, modules will build their own executables (for testing purposes for instance), or libraries (for easier reuse in various contexts).
However, if you build your project through gnatmake or
gprbuild, using a syntax similar to
gprbuild -PA.gpr
this will only rebuild the main programs of project A, not those of the
imported projects B and C. Therefore you have to spawn several
gnatmake commands, one per project, to build all executables.
This is a little inconvenient, but more importantly is inefficient
because gnatmake needs to do duplicate work to ensure that sources are
up-to-date, and cannot easily compile things in parallel when using
the -j switch.
Also libraries are always rebuilt when building a project.
You could therefore define an aggregate project Agg that groups A, B and C. Then, when you build with
gprbuild -PAgg.gpr
this will build all mains from A, B and C.
aggregate project Agg is
for Project_Files use ("a.gpr", "b.gpr", "c.gpr");
end Agg;
If B or C do not define any main program (through their Main attribute), all their sources are built. When you do not group them in the aggregate project, only those sources that are needed by A will be built.
If you add a main to a project P not already explicitly referenced in the aggregate project, you will need to add "p.gpr" in the list of project files for the aggregate project, or the main will not be built when building the aggregate project.
Next: Define a build environment, Previous: Building all main programs from a single project tree, Up: Aggregate Projects [Contents][Index]
One other case is when you have multiple applications and libraries that are built independently from each other (but can be built in parallel). For instance, you have a project tree rooted at A, and another one (which might share some subprojects) rooted at B.
Using only gprbuild, you could do
gprbuild -PA.gpr gprbuild -PB.gpr
to build both. But again, gprbuild has to do some duplicate work for
those files that are shared between the two, and cannot truly build
things in parallel efficiently.
If the two projects are really independent, share no sources other than through a common subproject, and have no source files with a common basename, you could create a project C that imports A and B. But these restrictions are often too strong, and one has to build them independently. An aggregate project does not have these limitations and can aggregate two project trees that have common sources.
This scenario is particularly useful in environments like VxWorks 653
where the applications running in the multiple partitions can be built
in parallel through a single gprbuild command. This also works nicely
with Annex E.
Next: Performance improvements in builder, Previous: Building a set of projects with a single command, Up: Aggregate Projects [Contents][Index]
The environment variables at the time you launch gprbuild or
gnatmake will influence the view these tools have of the project
(PATH to find the compiler, ADA_PROJECT_PATH or GPR_PROJECT_PATH to find the
projects, environment variables that are referenced in project files
through the "external" statement,...). Several command line switches
can be used to override those (-X or -aP), but on some systems and
with some projects, this might make the command line too long, and on
all systems often make it hard to read.
An aggregate project can be used to set the environment for all projects built through that aggregate. One of the nice aspects is that you can put the aggregate project under configuration management, and make sure all your user have a consistent environment when building. The syntax looks like
aggregate project Agg is
for Project_Files use ("A.gpr", "B.gpr");
for Project_Path use ("../dir1", "../dir1/dir2");
for External ("BUILD") use "PRODUCTION";
package Builder is
for Switches ("Ada") use ("-q");
end Builder;
end Agg;
One of the often requested features in projects is to be able to
reference external variables in with statements, as in
with external("SETUP") & "path/prj.gpr"; -- ILLEGAL
project MyProject is
...
end MyProject;
For various reasons, this isn’t authorized. But using aggregate projects provide an elegant solution. For instance, you could use a project file like:
aggregate project Agg is
for Project_Path use (external("SETUP") % "path");
for Project_Files use ("myproject.gpr");
end Agg;
with "prj.gpr"; -- searched on Agg'Project_Path
project MyProject is
...
end MyProject;
Next: Syntax of aggregate projects, Previous: Define a build environment, Up: Aggregate Projects [Contents][Index]
The loading of aggregate projects is optimized in gprbuild and
gnatmake, so that all files are searched for only once on the disk
(thus reducing the number of system calls and contributing to faster
compilation times especially on systems with sources on remote
servers). As part of the loading, gprbuild and gnatmake
compute how and where a source file should be compiled, and even if it is found
several times in the aggregated projects it will be compiled only
once.
Since there is no ambiguity as to which switches should be used, files
can be compiled in parallel (through the usual -j switch) and this can
be done while maximizing the use of CPUs (compared to launching
multiple gprbuild and gnatmake commands in parallel).
Next: package Builder in aggregate projects, Previous: Performance improvements in builder, Up: Aggregate Projects [Contents][Index]
An aggregate project follows the general syntax of project files. The
recommended extension is still .gpr. However, a special
aggregate qualifier must be put before the keyword
project.
An aggregate project cannot with any other project (standard or
aggregate), except an abstract project which can be used to share
attribute values. Building other aggregate projects from an aggregate
project is done through the Project_Files attribute (see below).
An aggregate project does not have any source files directly (only through other standard projects). Therefore a number of the standard attributes and packages are forbidden in an aggregate project. Here is the (non exhaustive) list:
The only package that is authorized (albeit optional) is Builder. Other packages (in particular Compiler, Binder and Linker) are forbidden. It is an error to have any of these (and such an error prevents the proper loading of the aggregate project).
Three new attributes have been created, which can only be used in the context of aggregate projects:
This attribute is compulsory (or else we are not aggregating any project, and thus not doing anything). It specifies a list of .gpr files that are grouped in the aggregate. The list may be empty. The project files can be either other aggregate projects, or standard projects. When grouping standard projects, you can have both the root of a project tree (and you do not need to specify all its imported projects), and any project within the tree.
Basically, the idea is to specify all those projects that have
main programs you want to build and link, or libraries you want to
build. You can even specify projects that do not use the Main
attribute nor the Library_* attributes, and the result will be to
build all their source files (not just the ones needed by other
projects).
The file can include paths (absolute or relative). Paths are relative to the location of the aggregate project file itself (if you use a base name, we expect to find the .gpr file in the same directory as the aggregate project file). The extension .gpr is mandatory, since this attribute contains file names, not project names.
Paths can also include the "*" and "**" globbing patterns. The
latter indicates that any subdirectory (recursively) will be
searched for matching files. The latter ("**") can only occur at the
last position in the directory part (ie "a/**/*.gpr" is supported, but
not "**/a/*.gpr"). Starting the pattern with "**" is equivalent
to starting with "./**".
For now, the pattern "*" is only allowed in the filename part, not
in the directory part. This is mostly for efficiency reasons to limit the
number of system calls that are needed.
Here are a few valid examples:
for Project_Files use ("a.gpr", "subdir/b.gpr");
-- two specific projects relative to the directory of agg.gpr
for Project_Files use ("**/*.gpr");
-- all projects recursively
This attribute can be used to specify a list of directories in
which to look for project files in with statements.
When you specify a project in Project_Files
say "x/y/a.gpr"), and this projects imports a project "b.gpr", only
b.gpr is searched in the project path. a.gpr must be exactly at
<dir of the aggregate>/x/y/a.gpr.
This attribute, however, does not affect the search for the aggregated
project files specified with Project_Files.
Each aggregate project has its own (that is if agg1.gpr includes agg2.gpr, they can potentially both have a different project path).
This project path is defined as the concatenation, in that order, of:
In the example above, agg2.gpr’s project path is not influenced by the attribute agg1’Project_Path, nor is agg1 influenced by agg2’Project_Path.
This can potentially lead to errors. In the following example:
+---------------+ +----------------+
| Agg1.gpr |-=--includes--=-->| Agg2.gpr |
| 'project_path| | 'project_path |
| | | |
+---------------+ +----------------+
: :
includes includes
: :
v v
+-------+ +---------+
| P.gpr |<---------- withs --------| Q.gpr |
+-------+---------\ +---------+
| |
withs |
| |
v v
+-------+ +---------+
| R.gpr | | R'.gpr |
+-------+ +---------+
When looking for p.gpr, both aggregates find the same physical file on the disk. However, it might happen that with their different project paths, both aggregate projects would in fact find a different r.gpr. Since we have a common project (p.gpr) "with"ing two different r.gpr, this will be reported as an error by the builder.
Directories are relative to the location of the aggregate project file.
Here are a few valid examples:
for Project_Path use ("/usr/local/gpr", "gpr/");
This attribute can be used to set the value of environment
variables as retrieved through the external statement
in projects. It does not affect the environment variables
themselves (so for instance you cannot use it to change the value
of your PATH as seen from the spawned compiler).
This attribute affects the external values as seen in the rest of the aggreate projects, and in the aggregated projects.
The exact value of external a variable comes from one of three sources (each level overrides the previous levels):
for External ("BUILD_MODE") use "DEBUG";
These override the value given by the attribute, so that users can override the value set in the (presumably shared with others in his team) aggregate project.
gprbuild and gnatmake
This always takes precedence.
This attribute is only taken into account in the main aggregate
project (i.e. the one specified on the command line to gprbuild or
gnatmake), and ignored in other aggregate projects. It is invalid
in standard projects.
The goal is to have a consistent value in all
projects that are built through the aggregate, which would not
be the case in the diamond case: A groups the aggregate
projects B and C, which both (either directly or indirectly)
build the project P. If B and C could set different values for
the environment variables, we would have two different views of
P, which in particular might impact the list of source files in P.
Previous: Syntax of aggregate projects, Up: Aggregate Projects [Contents][Index]
As we mentioned before, only the package Builder can be specified in an aggregate project. In this package, only the following attributes are valid:
This attribute gives the list of switches to use for the builder
(gprbuild or gnatmake), depending on the language of the
main file. For instance,
for Switches ("Ada") use ("-d", "-p");
for Switches ("C") use ("-p");
These switches are only read from the main aggregate project (the one passed on the command line), and ignored in all other aggregate projects or projects.
It can only contain builder switches, not compiler switches.
This attribute gives the list of compiler switches for the various languages. For instance,
for Global_Compilation_Switches ("Ada") use ("-O1", "-g");
for Global_Compilation_Switches ("C") use ("-O2");
This attribute is only taken into account in the aggregate project specified on the command line, not in other aggregate projects.
In the projects grouped by that aggregate, the attribute Builder.Global_Compilation_Switches is also ignored. However, the attribute Compiler.Default_Switches will be taken into account (but that of the aggregate have higher priority). The attribute Compiler.Switches is also taken into account and can be used to override the switches for a specific file. As a result, it always has priority.
The rules are meant to avoid ambiguities when compiling. For instance, aggregate project Agg groups the projects A and B, that both depend on C. Here is an extra for all of these projects:
aggregate project Agg is
for Project_Files use ("a.gpr", "b.gpr");
package Builder is
for Global_Compilation_Switches ("Ada") use ("-O2");
end Builder;
end Agg;
with "c.gpr";
project A is
package Builder is
for Global_Compilation_Switches ("Ada") use ("-O1");
-- ignored
end Builder;
package Compiler is
for Default_Switches ("Ada") use ("-O1", "-g");
for Switches ("a_file1.adb") use ("-O0");
end Compiler;
end A;
with "c.gpr";
project B is
package Compiler is
for Default_Switches ("Ada") use ("-O0");
end Compiler;
end B;
project C is
package Compiler is
for Default_Switches ("Ada") use ("-O3", "-gnatn");
for Switches ("c_file1.adb") use ("-O0", "-g");
end Compiler;
end C;
then the following switches are used:
Even though C is seen through two paths (through A and through B), the switches used by the compiler are unambiguous.
This attribute can be used to specify a file containing configuration pragmas, to be passed to the compiler. Since we ignore the package Builder in other aggregate projects and projects, only those pragmas defined in the main aggregate project will be taken into account.
Projects can locally add to those by using the
Compiler.Local_Configuration_Pragmas attribute if they need.
For projects that are built through the aggregate, the package Builder is ignored, except for the Executable attribute which specifies the name of the executables resulting from the link of the main programs, and for the Executable_Suffix.
Next: Project File Reference, Previous: Aggregate Projects, Up: GNAT Project Manager [Contents][Index]
Aggregate library projects make it possible to build a single library using object files built using other standard or library projects. This gives the flexibility to describe an application as having multiple modules (a GUI, database access, ...) using different project files (so possibly built with different compiler options) and yet create a single library (static or relocatable) out of the corresponding object files.
| • Building aggregate library projects: | ||
| • Syntax of aggregate library projects: |
For example, we can define an aggregate project Agg that groups A, B and C:
aggregate library project Agg is
for Project_Files use ("a.gpr", "b.gpr", "c.gpr");
for Library_Name use ("agg");
for Library_Dir use ("lagg");
end Agg;
Then, when you build with:
gprbuild agg.gpr
This will build all units from projects A, B and C and will create a static library named libagg.a into the lagg directory. An aggregate library project has the same set of restriction as a standard library project.
Note that a shared aggregate library project cannot aggregates a static library project. In platforms where a compiler option is required to create relocatable object files, a Builder package in the aggregate library project may be used:
aggregate library project Agg is
for Project_Files use ("a.gpr", "b.gpr", "c.gpr");
for Library_Name use ("agg");
for Library_Dir use ("lagg");
for Library_Kind use "relocatable";
package Builder is
for Global_Compilation_Switches ("Ada") use ("-fPIC");
end Builder;
end Agg;
With the above aggregate library Builder package, the -fPIC
option will be passed to the compiler when building any source code
from projects a.gpr, b.gpr and c.gpr.
Previous: Building aggregate library projects, Up: Aggregate Library Projects [Contents][Index]
An aggregate library project follows the general syntax of project
files. The recommended extension is still .gpr. However, a special
aggregate library qualifier must be put before the keyword
project.
An aggregate library project cannot with any other project
(standard or aggregate), except an abstract project which can be used
to share attribute values.
An aggregate library project does not have any source files directly (only through other standard projects). Therefore a number of the standard attributes and packages are forbidden in an aggregate library project. Here is the (non exhaustive) list:
The only package that is authorized (albeit optional) is Builder.
The Project_Files attribute (See see Aggregate Projects) is used to described the aggregated projects whose object files have to be included into the aggregate library.
Previous: Aggregate Library Projects, Up: GNAT Project Manager [Contents][Index]
This section describes the syntactic structure of project files, the various constructs that can be used. Finally, it ends with a summary of all available attributes.
| • Project Declaration: | ||
| • Qualified Projects: | ||
| • Declarations: | ||
| • Packages: | ||
| • Expressions: | ||
| • External Values: | ||
| • Typed String Declaration: | ||
| • Variables: | ||
| • Attributes: | ||
| • Case Statements: |
Next: Qualified Projects, Up: Project File Reference [Contents][Index]
Project files have an Ada-like syntax. The minimal project file is:
project Empty is end Empty;
The identifier Empty is the name of the project.
This project name must be present after the reserved
word end at the end of the project file, followed by a semi-colon.
Identifiers (i.e. the user-defined names such as project or variable names) have the same syntax as Ada identifiers: they must start with a letter, and be followed by zero or more letters, digits or underscore characters; it is also illegal to have two underscores next to each other. Identifiers are always case-insensitive ("Name" is the same as "name").
simple_name ::= identifier
name ::= simple_name { . simple_name }
Strings are used for values of attributes or as indexes for these attributes. They are in general case sensitive, except when noted otherwise (in particular, strings representing file names will be case insensitive on some systems, so that "file.adb" and "File.adb" both represent the same file).
Reserved words are the same as for standard Ada 95, and cannot
be used for identifiers. In particular, the following words are currently
used in project files, but others could be added later on. In bold are the
extra reserved words in project files: all, at, case, end, for, is,
limited, null, others, package, renames, type, use, when, with, extends,
external, project.
Comments in project files have the same syntax as in Ada, two consecutive hyphens through the end of the line.
A project may be an independent project, entirely defined by a single project file. Any source file in an independent project depends only on the predefined library and other source files in the same project. But a project may also depend on other projects, either by importing them through with clauses, or by extending at most one other project. Both types of dependency can be used in the same project.
A path name denotes a project file. It can be absolute or relative. An absolute path name includes a sequence of directories, in the syntax of the host operating system, that identifies uniquely the project file in the file system. A relative path name identifies the project file, relative to the directory that contains the current project, or relative to a directory listed in the environment variables ADA_PROJECT_PATH and GPR_PROJECT_PATH. Path names are case sensitive if file names in the host operating system are case sensitive. As a special case, the directory separator can always be "/" even on Windows systems, so that project files can be made portable across architectures. The syntax of the environment variable ADA_PROJECT_PATH and GPR_PROJECT_PATH is a list of directory names separated by colons on UNIX and semicolons on Windows.
A given project name can appear only once in a context clause.
It is illegal for a project imported by a context clause to refer, directly or indirectly, to the project in which this context clause appears (the dependency graph cannot contain cycles), except when one of the with clause in the cycle is a limited with.
with "other_project.gpr"; project My_Project extends "extended.gpr" is end My_Project;
These dependencies form a directed graph, potentially cyclic when using limited with. The subprogram reflecting the extends relations is a tree.
A project’s immediate sources are the source files directly defined by that project, either implicitly by residing in the project source directories, or explicitly through any of the source-related attributes. More generally, a project sources are the immediate sources of the project together with the immediate sources (unless overridden) of any project on which it depends directly or indirectly.
A project hierarchy can be created, where projects are children of
other projects. The name of such a child project must be Parent.Child,
where Parent is the name of the parent project. In particular, this
makes all with clauses of the parent project automatically visible
in the child project.
project ::= context_clause project_declaration
context_clause ::= {with_clause}
with_clause ::= with path_name { , path_name } ;
path_name ::= string_literal
project_declaration ::= simple_project_declaration | project_extension
simple_project_declaration ::=
project <project_>name is
{declarative_item}
end <project_>simple_name;
Next: Declarations, Previous: Project Declaration, Up: Project File Reference [Contents][Index]
Before the reserved project, there may be one or two qualifiers, that
is identifiers or reserved words, to qualify the project.
The current list of qualifiers is:
project must either have no declaration of attributes Source_Dirs,
Source_Files, Languages or Source_List_File, or one of
Source_Dirs, Source_Files, or Languages must be declared
as empty. If it extends another project, the project it extends must also be a
qualified abstract project.
This is the default (implicit) qualifier.
project files.
from other project or library project files.
Library_Name and Library_Dir.
It describes compilers and other tools to gprbuild.
Next: Packages, Previous: Qualified Projects, Up: Project File Reference [Contents][Index]
Declarations introduce new entities that denote types, variables, attributes, and packages. Some declarations can only appear immediately within a project declaration. Others can appear within a project or within a package.
declarative_item ::= simple_declarative_item | typed_string_declaration | package_declaration simple_declarative_item ::= variable_declaration | typed_variable_declaration | attribute_declaration | case_construction | empty_declaration empty_declaration ::= null ;
An empty declaration is allowed anywhere a declaration is allowed. It has no effect.
Next: Expressions, Previous: Declarations, Up: Project File Reference [Contents][Index]
A project file may contain packages, that group attributes (typically all the attributes that are used by one of the GNAT tools).
A package with a given name may only appear once in a project file. The following packages are currently supported in project files (See see Attributes for the list of attributes that each can contain).
BinderThis package specifies characteristics useful when invoking the binder either
directly via the gnat driver or when using a builder such as
gnatmake or gprbuild. See Main Subprograms.
BuilderThis package specifies the compilation options used when building an
executable or a library for a project. Most of the options should be
set in one of Compiler, Binder or Linker packages,
but there are some general options that should be defined in this
package. See Main Subprograms, and see Executable File Names in
particular.
CheckThis package specifies the options used when calling the checking tool
gnatcheck via the gnat driver. Its attribute
Default_Switches has the same semantics as for the package
Builder. The first string should always be -rules to specify
that all the other options belong to the -rules section of the
parameters to gnatcheck.
CompilerThis package specifies the compilation options used by the compiler for each languages. See Tools Options in Project Files.
Cross_ReferenceThis package specifies the options used when calling the library tool
gnatxref via the gnat driver. Its attributes
Default_Switches and Switches have the same semantics as for the
package Builder.
EliminateThis package specifies the options used when calling the tool
gnatelim via the gnat driver. Its attributes
Default_Switches and Switches have the same semantics as for the
package Builder.
FinderThis package specifies the options used when calling the search tool
gnatfind via the gnat driver. Its attributes
Default_Switches and Switches have the same semantics as for the
package Builder.
GnatlsThis package the options to use when invoking gnatls via the
gnat driver.
GnatstubThis package specifies the options used when calling the tool
gnatstub via the gnat driver. Its attributes
Default_Switches and Switches have the same semantics as for the
package Builder.
IDEThis package specifies the options used when starting an integrated
development environment, for instance GPS or Gnatbench.
See The Development Environments.
InstallThis package specifies the options used when installing a project
with gprinstall. See Installation.
LinkerThis package specifies the options used by the linker. See Main Subprograms.
MakefileThis package is used by the GPS plugin Makefile.py. See the documentation in that plugin (from GPS: /Tools/Plug-ins).
MetricsThis package specifies the options used when calling the tool
gnatmetric via the gnat driver. Its attributes
Default_Switches and Switches have the same semantics as for the
package Builder.
NamingThis package specifies the naming conventions that apply to the source files in a project. In particular, these conventions are used to automatically find all source files in the source directories, or given a file name to find out its language for proper processing. See Naming Schemes.
Pretty_PrinterThis package specifies the options used when calling the formatting tool
gnatpp via the gnat driver. Its attributes
Default_Switches and Switches have the same semantics as for the
package Builder.
StackThis package specifies the options used when calling the tool
gnatstack via the gnat driver. Its attributes
Default_Switches and Switches have the same semantics as for the
package Builder.
SynchronizeThis package specifies the options used when calling the tool
gnatsync via the gnat driver.
In its simplest form, a package may be empty:
project Simple is package Builder is end Builder; end Simple;
A package may contain attribute declarations, variable declarations and case constructions, as will be described below.
When there is ambiguity between a project name and a package name,
the name always designates the project. To avoid possible confusion, it is
always a good idea to avoid naming a project with one of the
names allowed for packages or any name that starts with gnat.
A package can also be defined by a renaming declaration. The new package renames a package declared in a different project file, and has the same attributes as the package it renames. The name of the renamed package must be the same as the name of the renaming package. The project must contain a package declaration with this name, and the project must appear in the context clause of the current project, or be its parent project. It is not possible to add or override attributes to the renaming project. If you need to do so, you should use an extending declaration (see below).
Packages that are renamed in other project files often come from project files that have no sources: they are just used as templates. Any modification in the template will be reflected automatically in all the project files that rename a package from the template. This is a very common way to share settings between projects.
Finally, a package can also be defined by an extending declaration. This is similar to a renaming declaration, except that it is possible to add or override attributes.
package_declaration ::= package_spec | package_renaming | package_extension
package_spec ::=
package <package_>simple_name is
{simple_declarative_item}
end package_identifier ;
package_renaming ::==
package <package_>simple_name renames <project_>simple_name.package_identifier ;
package_extension ::==
package <package_>simple_name extends <project_>simple_name.package_identifier is
{simple_declarative_item}
end package_identifier ;
Next: External Values, Previous: Packages, Up: Project File Reference [Contents][Index]
An expression is any value that can be assigned to an attribute or a variable. It is either a literal value, or a construct requiring runtime computation by the project manager. In a project file, the computed value of an expression is either a string or a list of strings.
A string value is one of:
"comm/my_proj.gpr"
"prefix_" & Var.
A list of strings is one of the following:
(File_Name, "gnat.adc", File_Name & ".orig") or ().
("A", "B") & "C"
The following is the grammar for expressions
string_literal ::= "{string_element}" -- Same as Ada
string_expression ::= string_literal
| variable_name
| external_value
| attribute_reference
| ( string_expression { & string_expression } )
string_list ::= ( string_expression { , string_expression } )
| string_variable_name
| string_attribute_reference
term ::= string_expression | string_list
expression ::= term { & term } -- Concatenation
Concatenation involves strings and list of strings. As soon as a list of strings is involved, the result of the concatenation is a list of strings. The following Ada declarations show the existing operators:
function "&" (X : String; Y : String) return String; function "&" (X : String_List; Y : String) return String_List; function "&" (X : String_List; Y : String_List) return String_List;
Here are some specific examples:
List := () & File_Name; -- One string in this list List2 := List & (File_Name & ".orig"); -- Two strings Big_List := List & Lists2; -- Three strings Illegal := "gnat.adc" & List2; -- Illegal, must start with list
Next: Typed String Declaration, Previous: Expressions, Up: Project File Reference [Contents][Index]
An external value is an expression whose value is obtained from the command
that invoked the processing of the current project file (typically a
gnatmake or gprbuild command).
There are two kinds of external values, one that returns a single string, and one that returns a string list.
The syntax of a single string external value is:
external_value ::= external ( string_literal [, string_literal] )
The first string_literal is the string to be used on the command line or in the environment to specify the external value. The second string_literal, if present, is the default to use if there is no specification for this external value either on the command line or in the environment.
Typically, the external value will either exist in the environment variables or be specified on the command line through the -Xvbl=value switch. If both are specified, then the command line value is used, so that a user can more easily override the value.
The function external always returns a string. It is an error if the
value was not found in the environment and no default was specified in the
call to external.
An external reference may be part of a string expression or of a string list expression, and can therefore appear in a variable declaration or an attribute declaration.
Most of the time, this construct is used to initialize typed variables, which are then used in case statements to control the value assigned to attributes in various scenarios. Thus such variables are often called scenario variables.
The syntax for a string list external value is:
external_value ::= external_as_list ( string_literal , string_literal )
The first string_literal is the string to be used on the command line or in the environment to specify the external value. The second string_literal is the separator between each component of the string list.
If the external value does not exist in the environment or on the command line, the result is an empty list. This is also the case, if the separator is an empty string or if the external value is only one separator.
Any separator at the beginning or at the end of the external value is discarded. Then, if there is no separator in the external value, the result is a string list with only one string. Otherwise, any string between the beginning and the first separator, between two consecutive separators and between the last separator and the end are components of the string list.
external_as_list ("SWITCHES", ",")
If the external value is "-O2,-g", the result is ("-O2", "-g").
If the external value is ",-O2,-g,", the result is also ("-O2", "-g").
if the external value is "-gnav", the result is ("-gnatv").
If the external value is ",,", the result is ("").
If the external value is ",", the result is (), the empty string list.
Next: Variables, Previous: External Values, Up: Project File Reference [Contents][Index]
A type declaration introduces a discrete set of string literals. If a string variable is declared to have this type, its value is restricted to the given set of literals. These are the only named types in project files. A string type may only be declared at the project level, not inside a package.
typed_string_declaration ::=
type <typed_string_>_simple_name is ( string_literal {, string_literal} );
The string literals in the list are case sensitive and must all be different. They may include any graphic characters allowed in Ada, including spaces. Here is an example of a string type declaration:
type OS is ("NT", "nt", "Unix", "GNU/Linux", "other OS");
Variables of a string type are called typed variables; all other
variables are called untyped variables. Typed variables are
particularly useful in case constructions, to support conditional
attribute declarations. (see Case Statements).
A string type may be referenced by its name if it has been declared in the same project file, or by an expanded name whose prefix is the name of the project in which it is declared.
Next: Attributes, Previous: Typed String Declaration, Up: Project File Reference [Contents][Index]
Variables store values (strings or list of strings) and can appear as part of an expression. The declaration of a variable creates the variable and assigns the value of the expression to it. The name of the variable is available immediately after the assignment symbol, if you need to reuse its old value to compute the new value. Before the completion of its first declaration, the value of a variable defaults to the empty string ("").
A typed variable can be used as part of a case expression to compute the value, but it can only be declared once in the project file, so that all case statements see the same value for the variable. This provides more consistency and makes the project easier to understand. The syntax for its declaration is identical to the Ada syntax for an object declaration. In effect, a typed variable acts as a constant.
An untyped variable can be declared and overridden multiple times within the same project. It is declared implicitly through an Ada assignment. The first declaration establishes the kind of the variable (string or list of strings) and successive declarations must respect the initial kind. Assignments are executed in the order in which they appear, so the new value replaces the old one and any subsequent reference to the variable uses the new value.
A variable may be declared at the project file level, or within a package.
typed_variable_declaration ::= <typed_variable_>simple_name : <typed_string_>name := string_expression; variable_declaration ::= <variable_>simple_name := expression;
Here are some examples of variable declarations:
This_OS : OS := external ("OS"); -- a typed variable declaration
That_OS := "GNU/Linux"; -- an untyped variable declaration
Name := "readme.txt";
Save_Name := Name & ".saved";
Empty_List := ();
List_With_One_Element := ("-gnaty");
List_With_Two_Elements := List_With_One_Element & "-gnatg";
Long_List := ("main.ada", "pack1_.ada", "pack1.ada", "pack2_.ada");
A variable reference may take several forms:
A context may be one of the following:
Next: Case Statements, Previous: Variables, Up: Project File Reference [Contents][Index]
A project (and its packages) may have attributes that define the project’s properties. Some attributes have values that are strings; others have values that are string lists.
attribute_declaration ::= simple_attribute_declaration | indexed_attribute_declaration simple_attribute_declaration ::= for attribute_designator use expression ; indexed_attribute_declaration ::= for <indexed_attribute_>simple_name ( string_literal) use expression ; attribute_designator ::= <simple_attribute_>simple_name | <indexed_attribute_>simple_name ( string_literal )
There are two categories of attributes: simple attributes and indexed attributes. Each simple attribute has a default value: the empty string (for string attributes) and the empty list (for string list attributes). An attribute declaration defines a new value for an attribute, and overrides the previous value. The syntax of a simple attribute declaration is similar to that of an attribute definition clause in Ada.
Some attributes are indexed. These attributes are mappings whose domain is a set of strings. They are declared one association at a time, by specifying a point in the domain and the corresponding image of the attribute. Like untyped variables and simple attributes, indexed attributes may be declared several times. Each declaration supplies a new value for the attribute, and replaces the previous setting.
Here are some examples of attribute declarations:
-- simple attributes
for Object_Dir use "objects";
for Source_Dirs use ("units", "test/drivers");
-- indexed attributes
for Body ("main") use "Main.ada";
for Switches ("main.ada") use ("-v", "-gnatv");
for Switches ("main.ada") use Builder'Switches ("main.ada") & "-g";
-- indexed attributes copy (from package Builder in project Default)
-- The package name must always be specified, even if it is the current
-- package.
for Default_Switches use Default.Builder'Default_Switches;
Attributes references may be appear anywhere in expressions, and are used to retrieve the value previously assigned to the attribute. If an attribute has not been set in a given package or project, its value defaults to the empty string or the empty list.
attribute_reference ::= attribute_prefix ' <simple_attribute>_simple_name [ (string_literal) ] attribute_prefix ::= project | <project_>simple_name | package_identifier | <project_>simple_name . package_identifier
Examples are:
project'Object_Dir
Naming'Dot_Replacement
Imported_Project'Source_Dirs
Imported_Project.Naming'Casing
Builder'Default_Switches ("Ada")
The prefix of an attribute may be:
project for an attribute of the current project
Legal attribute names are listed below, including the package in which they must be declared. These names are case-insensitive. The semantics for the attributes is explained in great details in other sections.
The column index indicates whether the attribute is an indexed attribute, and when it is whether its index is case sensitive (sensitive) or not (insensitive), or if case sensitivity depends is the same as file names sensitivity on the system (file). The text is between brackets ([]) if the index is optional.
| Attribute Name | Value | Package | Index |
|---|---|---|---|
| General attributes | see Building With Projects | ||
| Name | string | - | (Read-only, name of project) |
| Project_Dir | string | - | (Read-only, directory of project) |
| Source_Files | list | - | - |
| Source_Dirs | list | - | - |
| Source_List_File | string | - | - |
| Locally_Removed_Files | list | - | - |
| Excluded_Source_Files | list | - | - |
| Object_Dir | string | - | - |
| Exec_Dir | string | - | - |
| Excluded_Source_Dirs | list | - | - |
| Excluded_Source_Files | list | - | - |
| Excluded_Source_List_File | list | - | - |
| Inherit_Source_Path | list | - | insensitive |
| Languages | list | - | - |
| Main | list | - | - |
| Main_Language | string | - | - |
| Externally_Built | string | - | - |
| Roots | list | - | file |
| Library-related attributes | see Library Projects | ||
| Library_Dir | string | - | - |
| Library_Name | string | - | - |
| Library_Kind | string | - | - |
| Library_Version | string | - | - |
| Library_Interface | string | - | - |
| Library_Auto_Init | string | - | - |
| Library_Options | list | - | - |
| Leading_Library_Options | list | - | - |
| Library_Src_Dir | string | - | - |
| Library_ALI_Dir | string | - | - |
| Library_GCC | string | - | - |
| Library_Symbol_File | string | - | - |
| Library_Symbol_Policy | string | - | - |
| Library_Reference_Symbol_File | string | - | - |
| Interfaces | list | - | - |
| Naming | see Naming Schemes | ||
| Spec_Suffix | string | Naming | insensitive (language) |
| Body_Suffix | string | Naming | insensitive (language) |
| Separate_Suffix | string | Naming | - |
| Casing | string | Naming | - |
| Dot_Replacement | string | Naming | - |
| Spec | string | Naming | insensitive (Ada unit) |
| Body | string | Naming | insensitive (Ada unit) |
| Specification_Exceptions | list | Naming | insensitive (language) |
| Implementation_Exceptions | list | Naming | insensitive (language) |
| Building | see Switches and Project Files | ||
| Default_Switches | list | Builder, Compiler, Binder, Linker, Cross_Reference, Finder, Pretty_Printer, gnatstub, Check, Synchronize, Eliminate, Metrics, IDE | insensitive (language name) |
| Switches | list | Builder, Compiler, Binder, Linker, Cross_Reference, Finder, gnatls, Pretty_Printer, gnatstub, Check, Synchronize, Eliminate, Metrics, Stack | [file] (file name) |
| Local_Configuration_Pragmas | string | Compiler | - |
| Local_Config_File | string | insensitive | - |
| Global_Configuration_Pragmas | list | Builder | - |
| Global_Compilation_Switches | list | Builder | language |
| Executable | string | Builder | [file] |
| Executable_Suffix | string | Builder | - |
| Global_Config_File | string | Builder | insensitive (language) |
| IDE (used and created by GPS) | |||
| Remote_Host | string | IDE | - |
| Program_Host | string | IDE | - |
| Communication_Protocol | string | IDE | - |
| Compiler_Command | string | IDE | insensitive (language) |
| Debugger_Command | string | IDE | - |
| Gnatlist | string | IDE | - |
| Gnat | string | IDE | - |
| VCS_Kind | string | IDE | - |
| VCS_File_Check | string | IDE | - |
| VCS_Log_Check | string | IDE | - |
| Documentation_Dir | string | IDE | - |
| Configuration files | See gprbuild manual | ||
| Default_Language | string | - | - |
| Run_Path_Option | list | - | - |
| Run_Path_Origin | string | - | - |
| Separate_Run_Path_Options | string | - | - |
| Toolchain_Version | string | - | insensitive |
| Toolchain_Description | string | - | insensitive |
| Object_Generated | string | - | insensitive |
| Objects_Linked | string | - | insensitive |
| Target | string | - | - |
| Library_Builder | string | - | - |
| Library_Support | string | - | - |
| Archive_Builder | list | - | - |
| Archive_Builder_Append_Option | list | - | - |
| Archive_Indexer | list | - | - |
| Archive_Suffix | string | - | - |
| Library_Partial_Linker | list | - | - |
| Shared_Library_Prefix | string | - | - |
| Shared_Library_Suffix | string | - | - |
| Symbolic_Link_Supported | string | - | - |
| Library_Major_Minor_Id_Supported | string | - | - |
| Library_Auto_Init_Supported | string | - | - |
| Shared_Library_Minimum_Switches | list | - | - |
| Library_Version_Switches | list | - | - |
| Library_Install_Name_Option | string | - | - |
| Runtime_Library_Dir | string | - | insensitive |
| Runtime_Source_Dir | string | - | insensitive |
| Driver | string | Compiler,Binder,Linker | insensitive (language) |
| Required_Switches | list | Compiler,Binder,Linker | insensitive (language) |
| Leading_Required_Switches | list | Compiler | insensitive (language) |
| Trailing_Required_Switches | list | Compiler | insensitive (language) |
| Pic_Options | list | Compiler | insensitive (language) |
| Path_Syntax | string | Compiler | insensitive (language) |
| Object_File_Suffix | string | Compiler | insensitive (language) |
| Object_File_Switches | list | Compiler | insensitive (language) |
| Multi_Unit_Switches | list | Compiler | insensitive (language) |
| Multi_Unit_Object_Separator | string | Compiler | insensitive (language) |
| Mapping_File_Switches | list | Compiler | insensitive (language) |
| Mapping_Spec_Suffix | string | Compiler | insensitive (language) |
| Mapping_body_Suffix | string | Compiler | insensitive (language) |
| Config_File_Switches | list | Compiler | insensitive (language) |
| Config_Body_File_Name | string | Compiler | insensitive (language) |
| Config_Body_File_Name_Index | string | Compiler | insensitive (language) |
| Config_Body_File_Name_Pattern | string | Compiler | insensitive (language) |
| Config_Spec_File_Name | string | Compiler | insensitive (language) |
| Config_Spec_File_Name_Index | string | Compiler | insensitive (language) |
| Config_Spec_File_Name_Pattern | string | Compiler | insensitive (language) |
| Config_File_Unique | string | Compiler | insensitive (language) |
| Dependency_Switches | list | Compiler | insensitive (language) |
| Dependency_Driver | list | Compiler | insensitive (language) |
| Include_Switches | list | Compiler | insensitive (language) |
| Include_Path | string | Compiler | insensitive (language) |
| Include_Path_File | string | Compiler | insensitive (language) |
| Prefix | string | Binder | insensitive (language) |
| Objects_Path | string | Binder | insensitive (language) |
| Objects_Path_File | string | Binder | insensitive (language) |
| Linker_Options | list | Linker | - |
| Leading_Switches | list | Linker | - |
| Map_File_Options | string | Linker | - |
| Executable_Switches | list | Linker | - |
| Lib_Dir_Switch | string | Linker | - |
| Lib_Name_Switch | string | Linker | - |
| Max_Command_Line_Length | string | Linker | - |
| Response_File_Format | string | Linker | - |
| Response_File_Switches | list | Linker | - |
Previous: Attributes, Up: Project File Reference [Contents][Index]
A case statement is used in a project file to effect conditional behavior. Through this statement, you can set the value of attributes and variables depending on the value previously assigned to a typed variable.
All choices in a choice list must be distinct. Unlike Ada, the choice
lists of all alternatives do not need to include all values of the type.
An others choice must appear last in the list of alternatives.
The syntax of a case construction is based on the Ada case statement
(although the null statement for empty alternatives is optional).
The case expression must be a typed string variable, whose value is often given by an external reference (see External Values).
Each alternative starts with the reserved word when, either a list of
literal strings separated by the "|" character or the reserved word
others, and the "=>" token.
Each literal string must belong to the string type that is the type of the
case variable.
After each =>, there are zero or more statements. The only
statements allowed in a case construction are other case statements,
attribute declarations and variable declarations. String type declarations and
package declarations are not allowed. Variable declarations are restricted to
variables that have already been declared before the case construction.
case_statement ::=
case <typed_variable_>name is {case_item} end case ;
case_item ::=
when discrete_choice_list =>
{case_statement
| attribute_declaration
| variable_declaration
| empty_declaration}
discrete_choice_list ::= string_literal {| string_literal} | others
Here is a typical example:
project MyProj is
type OS_Type is ("GNU/Linux", "Unix", "NT", "VMS");
OS : OS_Type := external ("OS", "GNU/Linux");
package Compiler is
case OS is
when "GNU/Linux" | "Unix" =>
for Switches ("Ada") use ("-gnath");
when "NT" =>
for Switches ("Ada") use ("-gnatP");
when others =>
null;
end case;
end Compiler;
end MyProj;
Next: The Cross-Referencing Tools gnatxref and gnatfind, Previous: GNAT Project Manager, Up: Top [Contents][Index]
| • gnatmake and Project Files: | ||
| • The GNAT Driver and Project Files: | ||
| • The Development Environments: |
This section covers several topics related to gnatmake and
project files: defining switches for gnatmake
and for the tools that it invokes; specifying configuration pragmas;
the use of the Main attribute; building and rebuilding library project
files.
| • Switches Related to Project Files: | ||
| • Switches and Project Files: | ||
| • Specifying Configuration Pragmas: | ||
| • Project Files and Main Subprograms: | ||
| • Library Project Files: |
Next: Switches and Project Files, Up: gnatmake and Project Files [Contents][Index]
The following switches are used by GNAT tools that support project files:
Indicates the name of a project file. This project file will be parsed with the verbosity indicated by -vPx, if any, and using the external references indicated by -X switches, if any. There may zero, one or more spaces between -P and project.
There must be only one -P switch on the command line.
Since the Project Manager parses the project file only after all the switches on the command line are checked, the order of the switches -P, -vPx or -X is not significant.
Indicates that external variable name has the value value.
The Project Manager will use this value for occurrences of
external(name) when parsing the project file.
If name or value includes a space, then name=value should be put between quotes.
-XOS=NT -X"user=John Doe"
Several -X switches can be used simultaneously. If several -X switches specify the same name, only the last one is used.
An external variable specified with a -X switch takes precedence over the value of the same name in the environment.
Indicates the verbosity of the parsing of GNAT project files.
-vP0 means Default; -vP1 means Medium; -vP2 means High.
The default is Default: no output for syntactically correct project files. If several -vPx switches are present, only the last one is used.
Add directory <dir> at the beginning of the project search path, in order, after the current working directory.
Follow all symbolic links when processing project files.
This switch is recognized by gnatmake and gnatclean. It
indicate that the real directories (except the source directories) are the
subdirectories <subdir> of the directories specified in the project files.
This applies in particular to object directories, library directories and
exec directories. If the subdirectories do not exist, they are created
automatically.
Next: Specifying Configuration Pragmas, Previous: Switches Related to Project Files, Up: gnatmake and Project Files [Contents][Index]
For each of the packages Builder, Compiler, Binder, and
Linker, you can specify a Default_Switches
attribute, a Switches attribute, or both;
as their names imply, these switch-related
attributes affect the switches that are used for each of these GNAT
components when
gnatmake is invoked. As will be explained below, these
component-specific switches precede
the switches provided on the gnatmake command line.
The Default_Switches attribute is an attribute
indexed by language name (case insensitive) whose value is a string list.
For example:
package Compiler is
for Default_Switches ("Ada")
use ("-gnaty",
"-v");
end Compiler;
The Switches attribute is indexed on a file name (which may or may
not be case sensitive, depending
on the operating system) whose value is a string list. For example:
package Builder is
for Switches ("main1.adb")
use ("-O2");
for Switches ("main2.adb")
use ("-g");
end Builder;
For the Builder package, the file names must designate source files
for main subprograms. For the Binder and Linker packages, the
file names must designate ALI or source files for main subprograms.
In each case just the file name without an explicit extension is acceptable.
For each tool used in a program build (gnatmake, the compiler, the
binder, and the linker), the corresponding package contributes a set of
switches for each file on which the tool is invoked, based on the
switch-related attributes defined in the package.
In particular, the switches
that each of these packages contributes for a given file f comprise:
Switches (f),
if it is specified in the package for the given file,
Default_Switches ("Ada"),
if it is specified in the package.
If neither of these attributes is defined in the package, then the package does not contribute any switches for the given file.
When gnatmake is invoked on a file, the switches comprise
two sets, in the following order: those contributed for the file
by the Builder package;
and the switches passed on the command line.
When gnatmake invokes a tool (compiler, binder, linker) on a file,
the switches passed to the tool comprise three sets,
in the following order:
Builder package in the project file supplied on the command line;
The term applicable switches reflects the fact that
gnatmake switches may or may not be passed to individual
tools, depending on the individual switch.
gnatmake may invoke the compiler on source files from different
projects. The Project Manager will use the appropriate project file to
determine the Compiler package for each source file being compiled.
Likewise for the Binder and Linker packages.
As an example, consider the following package in a project file:
project Proj1 is
package Compiler is
for Default_Switches ("Ada")
use ("-g");
for Switches ("a.adb")
use ("-O1");
for Switches ("b.adb")
use ("-O2",
"-gnaty");
end Compiler;
end Proj1;
If gnatmake is invoked with this project file, and it needs to
compile, say, the files a.adb, b.adb, and c.adb, then
a.adb will be compiled with the switch
-O1,
b.adb with switches
-O2
and -gnaty,
and c.adb with -g.
The following example illustrates the ordering of the switches contributed by different packages:
project Proj2 is
package Builder is
for Switches ("main.adb")
use ("-g",
"-O1",
"-f");
end Builder;
package Compiler is
for Switches ("main.adb")
use ("-O2");
end Compiler;
end Proj2;
If you issue the command:
gnatmake -Pproj2 -O0 main
then the compiler will be invoked on main.adb with the following sequence of switches
-g -O1 -O2 -O0
with the last -O switch having precedence over the earlier ones; several other switches (such as -c) are added implicitly.
The switches
-g
and -O1 are contributed by package
Builder, -O2 is contributed
by the package Compiler
and -O0 comes from the command line.
The -g
switch will also be passed in the invocation of
Gnatlink.
A final example illustrates switch contributions from packages in different project files:
project Proj3 is
for Source_Files use ("pack.ads", "pack.adb");
package Compiler is
for Default_Switches ("Ada")
use ("-gnata");
end Compiler;
end Proj3;
with "Proj3";
project Proj4 is
for Source_Files use ("foo_main.adb", "bar_main.adb");
package Builder is
for Switches ("foo_main.adb")
use ("-s",
"-g");
end Builder;
end Proj4;
-- Ada source file: with Pack; procedure Foo_Main is … end Foo_Main;
If the command is
gnatmake -PProj4 foo_main.adb -cargs -gnato
then the switches passed to the compiler for foo_main.adb are
-g (contributed by the package Proj4.Builder) and
-gnato (passed on the command line).
When the imported package Pack is compiled, the switches used
are -g from Proj4.Builder,
-gnata (contributed from package Proj3.Compiler,
and -gnato from the command line.
When using gnatmake with project files, some switches or
arguments may be expressed as relative paths. As the working directory where
compilation occurs may change, these relative paths are converted to absolute
paths. For the switches found in a project file, the relative paths
are relative to the project file directory, for the switches on the command
line, they are relative to the directory where gnatmake is invoked.
The switches for which this occurs are:
-I,
-A,
-L,
-aO,
-aL,
-aI, as well as all arguments that are not switches (arguments to
switch
-o, object files specified in package Linker or after
-largs on the command line). The exception to this rule is the switch
–RTS= for which a relative path argument is never converted.
Next: Project Files and Main Subprograms, Previous: Switches and Project Files, Up: gnatmake and Project Files [Contents][Index]
When using gnatmake with project files, if there exists a file
gnat.adc that contains configuration pragmas, this file will be
ignored.
Configuration pragmas can be defined by means of the following attributes in
project files: Global_Configuration_Pragmas in package Builder
and Local_Configuration_Pragmas in package Compiler.
Both these attributes are single string attributes. Their values is the path name of a file containing configuration pragmas. If a path name is relative, then it is relative to the project directory of the project file where the attribute is defined.
When compiling a source, the configuration pragmas used are, in order,
those listed in the file designated by attribute
Global_Configuration_Pragmas in package Builder of the main
project file, if it is specified, and those listed in the file designated by
attribute Local_Configuration_Pragmas in package Compiler of
the project file of the source, if it exists.
Next: Library Project Files, Previous: Specifying Configuration Pragmas, Up: gnatmake and Project Files [Contents][Index]
When using a project file, you can invoke gnatmake
with one or several main subprograms, by specifying their source files on the
command line.
gnatmake -Pprj main1.adb main2.adb main3.adb
Each of these needs to be a source file of the same project, except when the switch -u is used.
When -u is not used, all the mains need to be sources of the
same project, one of the project in the tree rooted at the project specified
on the command line. The package Builder of this common project, the
"main project" is the one that is considered by gnatmake.
When -u is used, the specified source files may be in projects
imported directly or indirectly by the project specified on the command line.
Note that if such a source file is not part of the project specified on the
command line, the switches found in package Builder of the
project specified on the command line, if any, that are transmitted
to the compiler will still be used, not those found in the project file of
the source file.
When using a project file, you can also invoke gnatmake without
explicitly specifying any main, and the effect depends on whether you have
defined the Main attribute. This attribute has a string list value,
where each element in the list is the name of a source file (the file
extension is optional) that contains a unit that can be a main subprogram.
If the Main attribute is defined in a project file as a non-empty
string list and the switch -u is not used on the command
line, then invoking gnatmake with this project file but without any
main on the command line is equivalent to invoking gnatmake with all
the file names in the Main attribute on the command line.
Example:
project Prj is
for Main use ("main1.adb", "main2.adb", "main3.adb");
end Prj;
With this project file, "gnatmake -Pprj"
is equivalent to
"gnatmake -Pprj main1.adb main2.adb main3.adb".
When the project attribute Main is not specified, or is specified
as an empty string list, or when the switch -u is used on the command
line, then invoking gnatmake with no main on the command line will
result in all immediate sources of the project file being checked, and
potentially recompiled. Depending on the presence of the switch -u,
sources from other project files on which the immediate sources of the main
project file depend are also checked and potentially recompiled. In other
words, the -u switch is applied to all of the immediate sources of the
main project file.
When no main is specified on the command line and attribute Main exists
and includes several mains, or when several mains are specified on the
command line, the default switches in package Builder will
be used for all mains, even if there are specific switches
specified for one or several mains.
But the switches from package Binder or Linker will be
the specific switches for each main, if they are specified.
Previous: Project Files and Main Subprograms, Up: gnatmake and Project Files [Contents][Index]
When gnatmake is invoked with a main project file that is a library
project file, it is not allowed to specify one or more mains on the command
line.
When a library project file is specified, switches -b and -l have special meanings.
gnatmake that gnatbind should be invoked for the
library.
gnatmake that the binder generated file should be compiled
(in the case of a stand-alone library) and that the library should be built.
Next: The Development Environments, Previous: gnatmake and Project Files, Up: Tools Supporting Project Files [Contents][Index]
A number of GNAT tools, other than gnatmake
can benefit from project files:
(gnatbind,
gnatcheck,
gnatclean,
gnatelim,
gnatfind,
gnatlink,
gnatls,
gnatmetric,
gnatpp,
gnatstub,
and gnatxref). However, none of these tools can be invoked
directly with a project file switch (-P).
They must be invoked through the gnat driver.
The gnat driver is a wrapper that accepts a number of commands and
calls the corresponding tool. It was designed initially for VMS platforms (to
convert VMS qualifiers to Unix-style switches), but it is now available on all
GNAT platforms.
On non-VMS platforms, the gnat driver accepts the following commands
(case insensitive):
gnatbind
gnatchop
gnatclean
gnatelim
gnatfind
gnatkr
gnatlink
gnatls
gnatmake
gnatname
gnatprep
gnatpp
gnatmetric
gnatstub
gnatxref
(note that the compiler is invoked using the command
gnatmake -f -u -c).
On non-VMS platforms, between gnat and the command, two
special switches may be used:
-v to display the invocation of the tool.
-dn to prevent the gnat driver from removing
the temporary files it has created. These temporary files are
configuration files and temporary file list files.
The command may be followed by switches and arguments for the invoked tool.
gnat bind -C main.ali gnat ls -a main gnat chop foo.txt
Switches may also be put in text files, one switch per line, and the text files may be specified with their path name preceded by ’@’.
gnat bind @args.txt main.ali
In addition, for commands BIND, COMP or COMPILE, FIND, ELIM, LS or LIST, LINK, METRIC, PP or PRETTY, STUB and XREF, the project file related switches (-P, -X and -vPx) may be used in addition to the switches of the invoking tool.
When GNAT PP or GNAT PRETTY is used with a project file, but with no source
specified on the command line, it invokes gnatpp with all
the immediate sources of the specified project file.
When GNAT METRIC is used with a project file, but with no source
specified on the command line, it invokes gnatmetric
with all the immediate sources of the specified project file and with
-d with the parameter pointing to the object directory
of the project.
In addition, when GNAT PP, GNAT PRETTY or GNAT METRIC is used with a project file, no source is specified on the command line and switch -U is specified on the command line, then the underlying tool (gnatpp or gnatmetric) is invoked for all sources of all projects, not only for the immediate sources of the main project. (-U stands for Universal or Union of the project files of the project tree)
For each of the following commands, there is optionally a corresponding package in the main project.
Binder for command BIND (invoking gnatbind)
Check for command CHECK (invoking
gnatcheck)
Compiler for command COMP or COMPILE (invoking the compiler)
Cross_Reference for command XREF (invoking
gnatxref)
Eliminate for command ELIM (invoking
gnatelim)
Finder for command FIND (invoking gnatfind)
Gnatls for command LS or LIST (invoking gnatls)
Gnatstub for command STUB
(invoking gnatstub)
Linker for command LINK (invoking gnatlink)
Check for command CHECK
(invoking gnatcheck)
Metrics for command METRIC
(invoking gnatmetric)
Pretty_Printer for command PP or PRETTY
(invoking gnatpp)
Package Gnatls has a unique attribute Switches,
a simple variable with a string list value. It contains switches
for the invocation of gnatls.
project Proj1 is
package gnatls is
for Switches
use ("-a",
"-v");
end gnatls;
end Proj1;
All other packages have two attribute Switches and
Default_Switches.
Switches is an indexed attribute, indexed by the
source file name, that has a string list value: the switches to be
used when the tool corresponding to the package is invoked for the specific
source file.
Default_Switches is an attribute,
indexed by the programming language that has a string list value.
Default_Switches ("Ada") contains the
switches for the invocation of the tool corresponding
to the package, except if a specific Switches attribute
is specified for the source file.
project Proj is
for Source_Dirs use ("**");
package gnatls is
for Switches use
("-a",
"-v");
end gnatls;
package Compiler is
for Default_Switches ("Ada")
use ("-gnatv",
"-gnatwa");
end Binder;
package Binder is
for Default_Switches ("Ada")
use ("-C",
"-e");
end Binder;
package Linker is
for Default_Switches ("Ada")
use ("-C");
for Switches ("main.adb")
use ("-C",
"-v",
"-v");
end Linker;
package Finder is
for Default_Switches ("Ada")
use ("-a",
"-f");
end Finder;
package Cross_Reference is
for Default_Switches ("Ada")
use ("-a",
"-f",
"-d",
"-u");
end Cross_Reference;
end Proj;
With the above project file, commands such as
gnat comp -Pproj main gnat ls -Pproj main gnat xref -Pproj main gnat bind -Pproj main.ali gnat link -Pproj main.ali
will set up the environment properly and invoke the tool with the switches
found in the package corresponding to the tool:
Default_Switches ("Ada") for all tools,
except Switches ("main.adb")
for gnatlink.
It is also possible to invoke some of the tools,
(gnatcheck,
gnatmetric,
and gnatpp)
on a set of project units thanks to the combination of the switches
-P, -U and possibly the main unit when one is interested
in its closure. For instance,
gnat metric -Pproj
will compute the metrics for all the immediate units of project
proj.
gnat metric -Pproj -U
will compute the metrics for all the units of the closure of projects
rooted at proj.
gnat metric -Pproj -U main_unit
will compute the metrics for the closure of units rooted at
main_unit. This last possibility relies implicitly
on gnatbind’s option -R. But if the argument files for the
tool invoked by the gnat driver are explicitly specified
either directly or through the tool -files option, then the tool
is called only for these explicitly specified files.
Previous: The GNAT Driver and Project Files, Up: Tools Supporting Project Files [Contents][Index]
See the appropriate manuals for more details. These environments will store a number of settings in the project itself, when they are meant to be shared by the whole team working on the project. Here are the attributes defined in the package IDE in projects.
Remote_HostThis is a simple attribute. Its value is a string that designates the remote host in a cross-compilation environment, to be used for remote compilation and debugging. This field should not be specified when running on the local machine.
Program_HostThis is a simple attribute. Its value is a string that specifies the name of IP address of the embedded target in a cross-compilation environment, on which the program should execute.
Communication_ProtocolThis is a simple string attribute. Its value is the name of the protocol
to use to communicate with the target in a cross-compilation environment,
e.g. "wtx" or "vxworks".
Compiler_CommandThis is an associative array attribute, whose domain is a language name. Its
value is string that denotes the command to be used to invoke the compiler.
The value of Compiler_Command ("Ada") is expected to be compatible with
gnatmake, in particular in the handling of switches.
Debugger_CommandThis is simple attribute, Its value is a string that specifies the name of the debugger to be used, such as gdb, powerpc-wrs-vxworks-gdb or gdb-4.
Default_SwitchesThis is an associative array attribute. Its indexes are the name of the external tools that the GNAT Programming System (GPS) is supporting. Its value is a list of switches to use when invoking that tool.
GnatlistThis is a simple attribute. Its value is a string that specifies the name
of the gnatls utility to be used to retrieve information about the
predefined path; e.g., "gnatls", "powerpc-wrs-vxworks-gnatls".
VCS_KindThis is a simple attribute. Its value is a string used to specify the Version Control System (VCS) to be used for this project, e.g. CVS, RCS ClearCase or Perforce.
GnatThis is a simple attribute. Its value is a string that specifies the name
of the gnat utility to be used when executing various tools from
GPS, in particular "gnat pp", "gnat stub",…
VCS_File_CheckThis is a simple attribute. Its value is a string that specifies the command used by the VCS to check the validity of a file, either when the user explicitly asks for a check, or as a sanity check before doing the check-in.
VCS_Log_CheckThis is a simple attribute. Its value is a string that specifies the command used by the VCS to check the validity of a log file.
VCS_Repository_RootThe VCS repository root path. This is used to create tags or branches
of the repository. For subversion the value should be the URL
as specified to check-out the working copy of the repository.
VCS_Patch_RootThe local root directory to use for building patch file. All patch chunks will be relative to this path. The root project directory is used if this value is not defined.
Next: The GNAT Pretty-Printer gnatpp, Previous: Tools Supporting Project Files, Up: Top [Contents][Index]
gnatxref and gnatfindThe compiler generates cross-referencing information (unless you set the ‘-gnatx’ switch), which are saved in the .ali files. This information indicates where in the source each entity is declared and referenced. Note that entities in package Standard are not included, but entities in all other predefined units are included in the output.
Before using any of these two tools, you need to compile successfully your application, so that GNAT gets a chance to generate the cross-referencing information.
The two tools gnatxref and gnatfind take advantage of this
information to provide the user with the capability to easily locate the
declaration and references to an entity. These tools are quite similar,
the difference being that gnatfind is intended for locating
definitions and/or references to a specified entity or entities, whereas
gnatxref is oriented to generating a full report of all
cross-references.
To use these tools, you must not compile your application using the
-gnatx switch on the gnatmake command line
(see The GNAT Make Program gnatmake). Otherwise, cross-referencing
information will not be generated.
Note: to invoke gnatxref or gnatfind with a project file,
use the gnat driver (see The GNAT Driver and Project Files).
Next: Switches for gnatfind, Previous: Examples of gnatname Usage, Up: The Cross-Referencing Tools gnatxref and gnatfind [Contents][Index]
gnatxref SwitchesThe command invocation for gnatxref is:
$ gnatxref [switches] sourcefile1 [sourcefile2 …]
where
identifies the source files for which a report is to be generated. The “with”ed units will be processed too. You must provide at least one file.
These file names are considered to be regular expressions, so for instance specifying source*.adb is the same as giving every file in the current directory whose name starts with source and whose extension is adb.
You shouldn’t specify any directory name, just base names. gnatxref
and gnatfind will be able to locate these files by themselves using
the source path. If you specify directories, no result is produced.
The switches can be:
Display Copyright and version, then exit disregarding all other options.
If --version was not used, display usage, then exit disregarding all other options.
If this switch is present, gnatfind and gnatxref will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making gnatfind and gnatxref
much faster, and their output much smaller. Read-only here refers to access
or permissions status in the file system for the current user.
When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for gnatmake.
When searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
gnatmake.
Do not look for sources in the system default directory.
Do not look for library files in the system default directory.
Specify an alternate ali file extension. The default is ali and other
extensions (e.g. sli for SPARK library files) may be specified via this
switch. Note that if this switch overrides the default, which means that only
the new extension will be considered.
Specifies the default location of the runtime library. Same meaning as the
equivalent gnatmake flag (see Switches for gnatmake).
If this switch is set gnatxref will output the parent type
reference for each matching derived types.
If this switch is set, the output file names will be preceded by their directory (if the file was found in the search path). If this switch is not set, the directory will not be printed.
If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
gnatfind and gnatxref.
Equivalent to ‘-aODIR -aIDIR’.
Specify a project file to use See GNAT Project Manager.
If you need to use the .gpr
project files, you should use gnatxref through the GNAT driver
(gnat xref -Pproject).
By default, gnatxref and gnatfind will try to locate a
project file in the current directory.
If a project file is either specified or found by the tools, then the content of the source directory and object directory lines are added as if they had been specified respectively by ‘-aI’ and ‘-aO’.
Output only unused symbols. This may be really useful if you give your
main compilation unit on the command line, as gnatxref will then
display every unused entity and ’with’ed package.
Instead of producing the default output, gnatxref will generate a
tags file that can be used by vi. For examples how to use this
feature, see Examples of gnatxref Usage. The tags file is output
to the standard output, thus you will have to redirect it to a file.
All these switches may be in any order on the command line, and may even appear after the file names. They need not be separated by spaces, thus you can say ‘gnatxref -ag’ instead of ‘gnatxref -a -g’.
Next: Project Files for gnatxref and gnatfind, Previous: Switches for gnatxref, Up: The Cross-Referencing Tools gnatxref and gnatfind [Contents][Index]
gnatfind SwitchesThe command line for gnatfind is:
$ gnatfind [switches] pattern[:sourcefile[:line[:column]]] [file1 file2 …]
where
An entity will be output only if it matches the regular expression found in pattern, see Regular Expressions in gnatfind and gnatxref.
Omitting the pattern is equivalent to specifying ‘*’, which will match any entity. Note that if you do not provide a pattern, you have to provide both a sourcefile and a line.
Entity names are given in Latin-1, with uppercase/lowercase equivalence for matching purposes. At the current time there is no support for 8-bit codes other than Latin-1, or for wide characters in identifiers.
gnatfind will look for references, bodies or declarations
of symbols referenced in sourcefile, at line line
and column column. See Examples of gnatfind Usage
for syntax examples.
is a decimal integer identifying the line number containing the reference to the entity (or entities) to be located.
is a decimal integer identifying the exact location on the line of the first character of the identifier for the entity reference. Columns are numbered from 1.
The search will be restricted to these source files. If none are given, then the search will be done for every library file in the search path. These file must appear only after the pattern or sourcefile.
These file names are considered to be regular expressions, so for instance specifying source*.adb is the same as giving every file in the current directory whose name starts with source and whose extension is adb.
The location of the spec of the entity will always be displayed, even if it isn’t in one of file1, file2,... The occurrences of the entity in the separate units of the ones given on the command line will also be displayed.
Note that if you specify at least one file in this part, gnatfind may
sometimes not be able to find the body of the subprograms.
At least one of ’sourcefile’ or ’pattern’ has to be present on the command line.
The following switches are available:
Display Copyright and version, then exit disregarding all other options.
If --version was not used, display usage, then exit disregarding all other options.
If this switch is present, gnatfind and gnatxref will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making gnatfind and gnatxref
much faster, and their output much smaller. Read-only here refers to access
or permission status in the file system for the current user.
When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for gnatmake.
When searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
gnatmake.
Do not look for sources in the system default directory.
Do not look for library files in the system default directory.
Specify an alternate ali file extension. The default is ali and other
extensions (e.g. sli for SPARK library files) may be specified via this
switch. Note that if this switch overrides the default, which means that only
the new extension will be considered.
Specifies the default location of the runtime library. Same meaning as the
equivalent gnatmake flag (see Switches for gnatmake).
If this switch is set, then gnatfind will output the parent type
reference for each matching derived types.
By default, gnatfind accept the simple regular expression set for
‘pattern’. If this switch is set, then the pattern will be
considered as full Unix-style regular expression.
If this switch is set, the output file names will be preceded by their directory (if the file was found in the search path). If this switch is not set, the directory will not be printed.
If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
gnatfind and gnatxref.
Equivalent to ‘-aODIR -aIDIR’.
Specify a project file (see GNAT Project Manager) to use.
By default, gnatxref and gnatfind will try to locate a
project file in the current directory.
If a project file is either specified or found by the tools, then the content of the source directory and object directory lines are added as if they had been specified respectively by ‘-aI’ and ‘-aO’.
By default, gnatfind will output only the information about the
declaration, body or type completion of the entities. If this switch is
set, the gnatfind will locate every reference to the entities in
the files specified on the command line (or in every file in the search
path if no file is given on the command line).
If this switch is set, then gnatfind will output the content
of the Ada source file lines were the entity was found.
If this switch is set, then gnatfind will output the type hierarchy for
the specified type. It act like -d option but recursively from parent
type to parent type. When this switch is set it is not possible to
specify more than one file.
All these switches may be in any order on the command line, and may even appear after the file names. They need not be separated by spaces, thus you can say ‘gnatxref -ag’ instead of ‘gnatxref -a -g’.
As stated previously, gnatfind will search in every directory in the
search path. You can force it to look only in the current directory if
you specify * at the end of the command line.
Next: Regular Expressions in gnatfind and gnatxref, Previous: Switches for gnatfind, Up: The Cross-Referencing Tools gnatxref and gnatfind [Contents][Index]
gnatxref and gnatfindProject files allow a programmer to specify how to compile its
application, where to find sources, etc. These files are used
primarily by GPS, but they can also be used
by the two tools
gnatxref and gnatfind.
A project file name must end with .gpr. If a single one is
present in the current directory, then gnatxref and gnatfind will
extract the information from it. If multiple project files are found, none of
them is read, and you have to use the ‘-p’ switch to specify the one
you want to use.
The following lines can be included, even though most of them have default values which can be used in most cases. The lines can be entered in any order in the file. Except for src_dir and obj_dir, you can only have one instance of each line. If you have multiple instances, only the last one is taken into account.
src_dir=DIR[default: "./"]
specifies a directory where to look for source files. Multiple src_dir
lines can be specified and they will be searched in the order they
are specified.
obj_dir=DIR[default: "./"]
specifies a directory where to look for object and library files. Multiple
obj_dir lines can be specified, and they will be searched in the order
they are specified
comp_opt=SWITCHES[default: ""]
creates a variable which can be referred to subsequently by using
the ${comp_opt} notation. This is intended to store the default
switches given to gnatmake and gcc.
bind_opt=SWITCHES[default: ""]
creates a variable which can be referred to subsequently by using
the ‘${bind_opt}’ notation. This is intended to store the default
switches given to gnatbind.
link_opt=SWITCHES[default: ""]
creates a variable which can be referred to subsequently by using
the ‘${link_opt}’ notation. This is intended to store the default
switches given to gnatlink.
main=EXECUTABLE[default: ""]
specifies the name of the executable for the application. This variable can
be referred to in the following lines by using the ‘${main}’ notation.
comp_cmd=COMMAND[default: "gcc -c -I${src_dir} -g -gnatq"]
specifies the command used to compile a single file in the application.
make_cmd=COMMAND[default: "gnatmake ${main} -aI${src_dir}
-aO${obj_dir} -g -gnatq -cargs ${comp_opt}
-bargs ${bind_opt} -largs ${link_opt}"]
specifies the command used to recompile the whole application.
run_cmd=COMMAND[default: "${main}"]
specifies the command used to run the application.
debug_cmd=COMMAND[default: "gdb ${main}"]
specifies the command used to debug the application
gnatxref and gnatfind only take into account the
src_dir and obj_dir lines, and ignore the others.
Next: Examples of gnatxref Usage, Previous: Project Files for gnatxref and gnatfind, Up: The Cross-Referencing Tools gnatxref and gnatfind [Contents][Index]
gnatfind and gnatxrefAs specified in the section about gnatfind, the pattern can be a
regular expression. Actually, there are to set of regular expressions
which are recognized by the program:
globbing patternsThese are the most usual regular expression. They are the same that you generally used in a Unix shell command line, or in a DOS session.
Here is a more formal grammar:
regexp ::= term
term ::= elmt -- matches elmt
term ::= elmt elmt -- concatenation (elmt then elmt)
term ::= * -- any string of 0 or more characters
term ::= ? -- matches any character
term ::= [char {char}] -- matches any character listed
term ::= [char - char] -- matches any character in range
full regular expressionThe second set of regular expressions is much more powerful. This is the type of regular expressions recognized by utilities such a grep.
The following is the form of a regular expression, expressed in Ada reference manual style BNF is as follows
regexp ::= term {| term} -- alternation (term or term …)
term ::= item {item} -- concatenation (item then item)
item ::= elmt -- match elmt
item ::= elmt * -- zero or more elmt's
item ::= elmt + -- one or more elmt's
item ::= elmt ? -- matches elmt or nothing
elmt ::= nschar -- matches given character
elmt ::= [nschar {nschar}] -- matches any character listed
elmt ::= [^ nschar {nschar}] -- matches any character not listed
elmt ::= [char - char] -- matches chars in given range
elmt ::= \ char -- matches given character
elmt ::= . -- matches any single character
elmt ::= ( regexp ) -- parens used for grouping
char ::= any character, including special characters
nschar ::= any character except ()[].*+?^
Following are a few examples:
will match any of the two strings ‘abcde’ and ‘fghi’,
will match any string like ‘abd’, ‘abcd’, ‘abccd’, ‘abcccd’, and so on,
will match any string which has only lowercase characters in it (and at least one character.
Next: Examples of gnatfind Usage, Previous: Regular Expressions in gnatfind and gnatxref, Up: The Cross-Referencing Tools gnatxref and gnatfind [Contents][Index]
gnatxref UsageFor the following examples, we will consider the following units:
main.ads: 1: with Bar; 2: package Main is 3: procedure Foo (B : in Integer); 4: C : Integer; 5: private 6: D : Integer; 7: end Main; main.adb: 1: package body Main is 2: procedure Foo (B : in Integer) is 3: begin 4: C := B; 5: D := B; 6: Bar.Print (B); 7: Bar.Print (C); 8: end Foo; 9: end Main; bar.ads: 1: package Bar is 2: procedure Print (B : Integer); 3: end bar; |
The first thing to do is to recompile your application (for instance, in that case just by doing a ‘gnatmake main’, so that GNAT generates the cross-referencing information. You can then issue any of the following commands:
gnatxref main.adbgnatxref generates cross-reference information for main.adb
and every unit ’with’ed by main.adb.
The output would be:
B Type: Integer
Decl: bar.ads 2:22
B Type: Integer
Decl: main.ads 3:20
Body: main.adb 2:20
Ref: main.adb 4:13 5:13 6:19
Bar Type: Unit
Decl: bar.ads 1:9
Ref: main.adb 6:8 7:8
main.ads 1:6
C Type: Integer
Decl: main.ads 4:5
Modi: main.adb 4:8
Ref: main.adb 7:19
D Type: Integer
Decl: main.ads 6:5
Modi: main.adb 5:8
Foo Type: Unit
Decl: main.ads 3:15
Body: main.adb 2:15
Main Type: Unit
Decl: main.ads 2:9
Body: main.adb 1:14
Print Type: Unit
Decl: bar.ads 2:15
Ref: main.adb 6:12 7:12
that is the entity Main is declared in main.ads, line 2, column 9,
its body is in main.adb, line 1, column 14 and is not referenced any where.
The entity Print is declared in bar.ads, line 2, column 15 and it
is referenced in main.adb, line 6 column 12 and line 7 column 12.
gnatxref package1.adb package2.adsgnatxref will generates cross-reference information for
package1.adb, package2.ads and any other package ’with’ed by any
of these.
gnatxref can generate a tags file output, which can be used
directly from vi. Note that the standard version of vi
will not work properly with overloaded symbols. Consider using another
free implementation of vi, such as vim.
$ gnatxref -v gnatfind.adb > tags
will generate the tags file for gnatfind itself (if the sources
are in the search path!).
From vi, you can then use the command ‘:tag entity’
(replacing entity by whatever you are looking for), and vi will
display a new file with the corresponding declaration of entity.
Next: Switches for gnatpp, Previous: Examples of gnatxref Usage, Up: The Cross-Referencing Tools gnatxref and gnatfind [Contents][Index]
gnatfind Usagegnatfind -f xyz:main.adbFind declarations for all entities xyz referenced at least once in main.adb. The references are search in every library file in the search path.
The directories will be printed as well (as the ‘-f’ switch is set)
The output will look like:
directory/main.ads:106:14: xyz <= declaration directory/main.adb:24:10: xyz <= body directory/foo.ads:45:23: xyz <= declaration
that is to say, one of the entities xyz found in main.adb is declared at line 12 of main.ads (and its body is in main.adb), and another one is declared at line 45 of foo.ads
gnatfind -fs xyz:main.adbThis is the same command as the previous one, instead gnatfind will
display the content of the Ada source file lines.
The output will look like:
directory/main.ads:106:14: xyz <= declaration procedure xyz; directory/main.adb:24:10: xyz <= body procedure xyz is directory/foo.ads:45:23: xyz <= declaration xyz : Integer;
This can make it easier to find exactly the location your are looking for.
gnatfind -r "*x*":main.ads:123 foo.adbFind references to all entities containing an x that are referenced on line 123 of main.ads. The references will be searched only in main.ads and foo.adb.
gnatfind main.ads:123Find declarations and bodies for all entities that are referenced on line 123 of main.ads.
This is the same as gnatfind "*":main.adb:123.
gnatfind mydir/main.adb:123:45Find the declaration for the entity referenced at column 45 in line 123 of file main.adb in directory mydir. Note that it is usual to omit the identifier name when the column is given, since the column position identifies a unique reference.
The column has to be the beginning of the identifier, and should not point to any character in the middle of the identifier.
Next: The GNAT Metric Tool gnatmetric, Previous: The Cross-Referencing Tools gnatxref and gnatfind, Up: Top [Contents][Index]
gnatppThe gnatpp tool is an ASIS-based utility
for source reformatting / pretty-printing.
It takes an Ada source file as input and generates a reformatted
version as output.
You can specify various style directives via switches; e.g.,
identifier case conventions, rules of indentation, and comment layout.
To produce a reformatted file, gnatpp generates and uses the ASIS
tree for the input source and thus requires the input to be syntactically and
semantically legal.
If this condition is not met, gnatpp will terminate with an
error message; no output file will be generated.
gnatpp cannot process sources that contain
preprocessing directives.
If the compilation unit
contained in the input source depends semantically upon units located
outside the current directory, you have to provide the source search path
when invoking gnatpp, if these units are contained in files with
names that do not follow the GNAT file naming rules, you have to provide
the configuration file describing the corresponding naming scheme;
see the description of the gnatpp
switches below. Another possibility is to use a project file and to
call gnatpp through the gnat driver
(see The GNAT Driver and Project Files).
The gnatpp command has the form
$ gnatpp [switches] filename [-cargs gcc_switches]
where
gcc. They will be passed on to all compiler invocations made by
gnatelim to generate the ASIS trees. Here you can provide
-I switches to form the source search path,
use the -gnatec switch to set the configuration file,
use the -gnat05 switch if sources should be compiled in
Ada 2005 mode etc.
| • Switches for gnatpp: | ||
| • Formatting Rules: |
Next: Formatting Rules, Previous: Examples of gnatfind Usage, Up: The GNAT Pretty-Printer gnatpp [Contents][Index]
gnatppThe following subsections describe the various switches accepted by
gnatpp, organized by category.
You specify a switch by supplying a name and generally also a value.
In many cases the values for a switch with a given name are incompatible with
each other
(for example the switch that controls the casing of a reserved word may have
exactly one value: upper case, lower case, or
mixed case) and thus exactly one such switch can be in effect for an
invocation of gnatpp.
If more than one is supplied, the last one is used.
However, some values for the same switch are mutually compatible.
You may supply several such switches to gnatpp, but then
each must be specified in full, with both the name and the value.
Abbreviated forms (the name appearing once, followed by each value) are
not permitted.
For example, to set
the alignment of the assignment delimiter both in declarations and in
assignment statements, you must write -A2A3
(or -A2 -A3), but not -A23.
In most cases, it is obvious whether or not the values for a switch with a given name are compatible with each other. When the semantics might not be evident, the summaries below explicitly indicate the effect.
Next: Casing Control, Up: Switches for gnatpp [Contents][Index]
Programs can be easier to read if certain constructs are vertically aligned. By default all alignments are set ON. Through the -A0 switch you may reset the default to OFF, and then use one or more of the other -An switches to activate alignment for specific constructs.
Set all alignments to OFF
Align : in declarations
Align := in initializations in declarations
Align := in assignment statements
Align => in associations
Align at keywords in the component clauses in record
representation clauses
The -A switches are mutually compatible; any combination is allowed.
Next: Construct Layout Control, Previous: Alignment Control, Up: Switches for gnatpp [Contents][Index]
gnatpp allows you to specify the casing for reserved words,
pragma names, attribute designators and identifiers.
For identifiers you may define a
general rule for name casing but also override this rule
via a set of dictionary files.
Three types of casing are supported: lower case, upper case, and mixed case. Lower and upper case are self-explanatory (but since some letters in Latin1 and other GNAT-supported character sets exist only in lower-case form, an upper case conversion will have no effect on them.) “Mixed case” means that the first letter, and also each letter immediately following an underscore, are converted to their uppercase forms; all the other letters are converted to their lowercase forms.
Attribute designators are lower case
Attribute designators are upper case
Attribute designators are mixed case (this is the default)
Keywords (technically, these are known in Ada as reserved words) are lower case (this is the default)
Keywords are upper case
Name casing for defining occurrences are as they appear in the source file (this is the default)
Names are in upper case
Names are in lower case
Names are in mixed case
Enumeration literal casing for defining occurrences are as they appear in the source file. Overrides -n casing setting.
Enumeration literals are in upper case. Overrides -n casing setting.
Enumeration literals are in lower case. Overrides -n casing setting.
Enumeration literals are in mixed case. Overrides -n casing setting.
Names introduced by type and subtype declarations are always cased as they appear in the declaration in the source file. Overrides -n casing setting.
Names introduced by type and subtype declarations are always in upper case. Overrides -n casing setting.
Names introduced by type and subtype declarations are always in lower case. Overrides -n casing setting.
Names introduced by type and subtype declarations are always in mixed case. Overrides -n casing setting.
Names introduced by number declarations are always in upper case. Overrides -n casing setting.
Names introduced by number declarations are always in lower case. Overrides -n casing setting.
Names introduced by number declarations are always in mixed case. Overrides -n casing setting.
Pragma names are lower case
Pragma names are upper case
Pragma names are mixed case (this is the default)
Use file as a dictionary file that defines the casing for a set of specified names, thereby overriding the effect on these names by any explicit or implicit -n switch. To supply more than one dictionary file, use several -D switches.
gnatpp implicitly uses a default dictionary file to define the casing for the Ada predefined names and the names declared in the GNAT libraries.
Do not use the default dictionary file; instead, use the casing defined by a -n switch and any explicit dictionary file(s)
The structure of a dictionary file, and details on the conventions used in the default dictionary file, are defined in Name Casing.
The -D- and -Dfile switches are mutually compatible.
Next: General Text Layout Control, Previous: Casing Control, Up: Switches for gnatpp [Contents][Index]
This group of gnatpp switches controls the layout of comments and
complex syntactic constructs. See Formatting Comments for details
on their effect.
All the comments remain unchanged
GNAT-style comment line indentation (this is the default).
Reference-manual comment line indentation.
GNAT-style comment beginning
Reformat comment blocks
Keep unchanged special form comments
GNAT-style layout (this is the default)
Compact layout
Uncompact layout
All the VT characters are removed from the comment text. All the HT characters are expanded with the sequences of space characters to get to the next tab stops.
Do not place the keyword is on a separate line in a subprogram body in
case if the spec occupies more than one line.
Place statement label(s) on a separate line, with the following statement on the next line.
Place the keyword loop in FOR and WHILE loop statements and the
keyword then in IF statements on a separate line.
Do not place the keyword loop in FOR and WHILE loop statements and the
keyword then in IF statements on a separate line. This option is
incompatible with --separate-loop-then option.
Start each USE clause in a context clause from a separate line.
Use a separate line for a loop or block statement name, but do not use an extra indentation level for the statement itself.
The -c1 and -c2 switches are incompatible. The -c3 and -c4 switches are compatible with each other and also with -c1 and -c2. The -c0 switch disables all the other comment formatting switches.
The -l1, -l2, and -l3 switches are incompatible.
Next: Other Formatting Options, Previous: Construct Layout Control, Up: Switches for gnatpp [Contents][Index]
These switches allow control over line length and indentation.
Maximum line length, nnn from 32…256, the default value is 79
Indentation level, nnn from 1…9, the default value is 3
Indentation level for continuation lines (relative to the line being continued), nnn from 1…9. The default value is one less than the (normal) indentation level, unless the indentation is set to 1 (in which case the default value for continuation line indentation is also 1)
Next: Setting the Source Search Path, Previous: General Text Layout Control, Up: Switches for gnatpp [Contents][Index]
These switches control the inclusion of missing end/exit labels, and the indentation level in case statements.
Do not insert missing end/exit labels. An end label is the name of
a construct that may optionally be repeated at the end of the
construct’s declaration;
e.g., the names of packages, subprograms, and tasks.
An exit label is the name of a loop that may appear as target
of an exit statement within the loop.
By default, gnatpp inserts these end/exit labels when
they are absent from the original source. This option suppresses such
insertion, so that the formatted source reflects the original.
Insert a Form Feed character after a pragma Page.
Do not use an additional indentation level for case alternatives and variants if there are nnn or more (the default value is 10). If nnn is 0, an additional indentation level is used for case alternatives and variants regardless of their number.
If the number of parameter associations is greater than nnn and if at least one association uses named notation, start each association from a new line. If nnn is 0, no check for the number of associations is made, this is the default.
If the number of parameter specifications is greater than nnn (or equal to nnn in case of a function), start each specification from a new line. The default for nnn is 3.
Next: Output File Control, Previous: Other Formatting Options, Up: Switches for gnatpp [Contents][Index]
To define the search path for the input source file, gnatpp
uses the same switches as the GNAT compiler, with the same effects.
The same as the corresponding gcc switch
The same as the corresponding gcc switch
The same as the corresponding gcc switch
The same as the corresponding gcc switch
Next: Other gnatpp Switches, Previous: Setting the Source Search Path, Up: Switches for gnatpp [Contents][Index]
By default the output is sent to the file whose name is obtained by appending
the .pp suffix to the name of the input file
(if the file with this name already exists, it is unconditionally overwritten).
Thus if the input file is my_ada_proc.adb then
gnatpp will produce my_ada_proc.adb.pp
as output file.
The output may be redirected by the following switches:
Send the output to Standard_Output
Write the output into output_file.
If output_file already exists, gnatpp terminates without
reading or processing the input file.
Write the output into output_file, overwriting the existing file (if one is present).
Replace the input source file with the reformatted output, and copy the
original input source into the file whose name is obtained by appending the
.npp suffix to the name of the input file.
If a file with this name already exists, gnatpp terminates without
reading or processing the input file.
Like -r except that if the file with the specified name already exists, it is overwritten.
Replace the input source file with the reformatted output without creating any backup copy of the input source.
Specifies the format of the reformatted output file. The xxx string specified with the switch may be either
Specify the wide character encoding method used to write the code in the result file e is one of the following:
Options -pipe, -o and -of are allowed only if the call to gnatpp contains only one file to reformat. Option --eol and -W cannot be used together with -pipe option.
Previous: Output File Control, Up: Switches for gnatpp [Contents][Index]
gnatpp SwitchesThe additional gnatpp switches are defined in this subsection.
Take the argument source files from the specified file. This file should be an
ordinary text file containing file names separated by spaces or
line breaks. You can use this switch more than once in the same call to
gnatpp. You also can combine this switch with an explicit list of
files.
Verbose mode;
gnatpp generates version information and then
a trace of the actions it takes to produce or obtain the ASIS tree.
Warning mode;
gnatpp generates a warning whenever it cannot provide
a required layout in the result source.
Next: Switches for gnatmetric, Previous: Switches for gnatpp, Up: The GNAT Pretty-Printer gnatpp [Contents][Index]
The following subsections show how gnatpp treats “white space”,
comments, program layout, and name casing.
They provide the detailed descriptions of the switches shown above.
| • White Space and Empty Lines: | ||
| • Formatting Comments: | ||
| • Construct Layout: | ||
| • Name Casing: |
Next: Formatting Comments, Up: Formatting Rules [Contents][Index]
gnatpp does not have an option to control space characters.
It will add or remove spaces according to the style illustrated by the
examples in the Ada Reference Manual.
The only format effectors
(see Ada Reference Manual, paragraph 2.1(13))
that will appear in the output file are platform-specific line breaks,
and also format effectors within (but not at the end of) comments.
In particular, each horizontal tab character that is not inside
a comment will be treated as a space and thus will appear in the
output file as zero or more spaces depending on
the reformatting of the line in which it appears.
The only exception is a Form Feed character, which is inserted after a
pragma Page when -ff is set.
The output file will contain no lines with trailing “white space” (spaces, format effectors).
Empty lines in the original source are preserved only if they separate declarations or statements. In such contexts, a sequence of two or more empty lines is replaced by exactly one empty line. Note that a blank line will be removed if it separates two “comment blocks” (a comment block is a sequence of whole-line comments). In order to preserve a visual separation between comment blocks, use an “empty comment” (a line comprising only hyphens) rather than an empty line. Likewise, if for some reason you wish to have a sequence of empty lines, use a sequence of empty comments instead.
Next: Construct Layout, Previous: White Space and Empty Lines, Up: Formatting Rules [Contents][Index]
Comments in Ada code are of two kinds:
The indentation of a whole-line comment is that of either the preceding or following line in the formatted source, depending on switch settings as will be described below.
For an end-of-line comment, gnatpp leaves the same number of spaces
between the end of the preceding Ada lexical element and the beginning
of the comment as appear in the original source,
unless either the comment has to be split to
satisfy the line length limitation, or else the next line contains a
whole line comment that is considered a continuation of this end-of-line
comment (because it starts at the same position).
In the latter two
cases, the start of the end-of-line comment is moved right to the nearest
multiple of the indentation level.
This may result in a “line overflow” (the right-shifted comment extending
beyond the maximum line length), in which case the comment is split as
described below.
There is a difference between -c1 (GNAT-style comment line indentation) and -c2 (reference-manual comment line indentation). With reference-manual style, a whole-line comment is indented as if it were a declaration or statement at the same place (i.e., according to the indentation of the preceding line(s)). With GNAT style, a whole-line comment that is immediately followed by an if or case statement alternative, a record variant, or the reserved word begin, is indented based on the construct that follows it.
For example:
if A then
null;
-- some comment
else
null;
end if;
|
Reference-manual indentation produces:
if A then null; -- some comment else null; end if; |
while GNAT-style indentation produces:
if A then null; -- some comment else null; end if; |
The -c3 switch (GNAT style comment beginning) has the following effect:
gnatpp inserts spaces if necessary after the starting two hyphens
to ensure that there are at least two spaces between these hyphens and the
first non-blank character of the comment.
For an end-of-line comment, if in the original source the next line is a whole-line comment that starts at the same position as the end-of-line comment, then the whole-line comment (and all whole-line comments that follow it and that start at the same position) will start at this position in the output file.
That is, if in the original source we have:
begin
A := B + C; -- B must be in the range Low1..High1
-- C must be in the range Low2..High2
--B+C will be in the range Low1+Low2..High1+High2
X := X + 1;
|
Then in the formatted source we get
begin
A := B + C; -- B must be in the range Low1..High1
-- C must be in the range Low2..High2
-- B+C will be in the range Low1+Low2..High1+High2
X := X + 1;
|
A comment that exceeds the line length limit will be split.
Unless switch
-c4 (reformat comment blocks) is set and
the line belongs to a reformattable block, splitting the line generates a
gnatpp warning.
The -c4 switch specifies that whole-line
comments may be reformatted in typical
word processor style (that is, moving words between lines and putting as
many words in a line as possible).
The -c5 switch specifies, that comments
that has a special format (that is, a character that is neither a letter nor digit
not white space nor line break immediately following the leading -- of
the comment) should be without any change moved from the argument source
into reformatted source. This switch allows to preserve comments that are used
as a special marks in the code (e.g. SPARK annotation).
Next: Name Casing, Previous: Formatting Comments, Up: Formatting Rules [Contents][Index]
In several cases the suggested layout in the Ada Reference Manual includes an extra level of indentation that many programmers prefer to avoid. The affected cases include:
In compact mode (when GNAT style layout or compact layout is set),
the pretty printer uses one level of indentation instead
of two. This is achieved in the record definition and record representation
clause cases by putting the record keyword on the same line as the
start of the declaration or representation clause, and in the block and loop
case by putting the block or loop header on the same line as the statement
identifier.
The difference between GNAT style -l1 and compact -l2 layout on the one hand, and uncompact layout -l3 on the other hand, can be illustrated by the following examples:
GNAT style, compact layout Uncompact layout
type q is record type q is
a : integer; record
b : integer; a : integer;
end record; b : integer;
end record;
for q use record for q use
a at 0 range 0 .. 31; record
b at 4 range 0 .. 31; a at 0 range 0 .. 31;
end record; b at 4 range 0 .. 31;
end record;
Block : declare Block :
A : Integer := 3; declare
begin A : Integer := 3;
Proc (A, A); begin
end Block; Proc (A, A);
end Block;
Clear : for J in 1 .. 10 loop Clear :
A (J) := 0; for J in 1 .. 10 loop
end loop Clear; A (J) := 0;
end loop Clear;
|
A further difference between GNAT style layout and compact layout is that GNAT style layout inserts empty lines as separation for compound statements, return statements and bodies.
Note that the layout specified by --separate-stmt-name for named block and loop statements overrides the layout defined by these constructs by -l1, -l2 or -l3 option.
Previous: Construct Layout, Up: Formatting Rules [Contents][Index]
gnatpp always converts the usage occurrence of a (simple) name to
the same casing as the corresponding defining identifier.
You control the casing for defining occurrences via the
-n switch.
With -nD (“as declared”, which is the default),
defining occurrences appear exactly as in the source file
where they are declared.
The other values for this switch —
-nU,
-nL,
-nM —
result in
upper, lower, or mixed case, respectively.
If gnatpp changes the casing of a defining
occurrence, it analogously changes the casing of all the
usage occurrences of this name.
If the defining occurrence of a name is not in the source compilation unit
currently being processed by gnatpp, the casing of each reference to
this name is changed according to the value of the -n
switch (subject to the dictionary file mechanism described below).
Thus gnatpp acts as though the -n switch
had affected the
casing for the defining occurrence of the name.
Some names may need to be spelled with casing conventions that are not covered by the upper-, lower-, and mixed-case transformations. You can arrange correct casing by placing such names in a dictionary file, and then supplying a -D switch. The casing of names from dictionary files overrides any -n switch.
To handle the casing of Ada predefined names and the names from GNAT libraries,
gnatpp assumes a default dictionary file.
The name of each predefined entity is spelled with the same casing as is used
for the entity in the Ada Reference Manual.
The name of each entity in the GNAT libraries is spelled with the same casing
as is used in the declaration of that entity.
The -D- switch suppresses the use of the
default dictionary file.
Instead, the casing for predefined and GNAT-defined names will be established
by the -n switch or explicit dictionary files.
For example, by default the names Ada.Text_IO and GNAT.OS_Lib
will appear as just shown,
even in the presence of a -nU switch.
To ensure that even such names are rendered in uppercase,
additionally supply the -D- switch
(or else, less conveniently, place these names in upper case in a dictionary
file).
A dictionary file is a plain text file; each line in this file can be either a blank line (containing only space characters and ASCII.HT characters), an Ada comment line, or the specification of exactly one casing schema.
A casing schema is a string that has the following syntax:
casing_schema ::= identifier | *simple_identifier*
simple_identifier ::= letter{letter_or_digit}
|
(See Ada Reference Manual, Section 2.3) for the definition of the identifier lexical element and the letter_or_digit category.)
The casing schema string can be followed by white space and/or an Ada-style comment; any amount of white space is allowed before the string.
If a dictionary file is passed as
the value of a -Dfile switch
then for every
simple name and every identifier, gnatpp checks if the dictionary
defines the casing for the name or for some of its parts (the term “subword”
is used below to denote the part of a name which is delimited by “_” or by
the beginning or end of the word and which does not contain any “_” inside):
gnatpp uses for this name
the casing defined by the dictionary; no subwords are checked for this word
gnatpp checks if the dictionary contains the
corresponding string of the form *simple_identifier*,
and if it does, the casing of this simple_identifier is used
for this subword
gnatpp switches, each
dictionary adds new casing exceptions and overrides all the existing casing
exceptions set by the previous dictionaries
gnatpp checks if the word or subword is in the dictionary,
this check is not case sensitive
For example, suppose we have the following source to reformat:
procedure test is name1 : integer := 1; name4_name3_name2 : integer := 2; name2_name3_name4 : Boolean; name1_var : Float; begin name2_name3_name4 := name4_name3_name2 > name1; end; |
And suppose we have two dictionaries:
dict1: NAME1 *NaMe3* *Name1* |
dict2: *NAME3* |
If gnatpp is called with the following switches:
gnatpp -nM -D dict1 -D dict2 test.adb
then we will get the following name casing in the gnatpp output:
procedure Test is NAME1 : Integer := 1; Name4_NAME3_Name2 : Integer := 2; Name2_NAME3_Name4 : Boolean; Name1_Var : Float; begin Name2_NAME3_Name4 := Name4_NAME3_Name2 > NAME1; end Test; |
Next: File Name Krunching Using gnatkr, Previous: The GNAT Pretty-Printer gnatpp, Up: Top [Contents][Index]
gnatmetricThe gnatmetric tool is an ASIS-based utility
for computing various program metrics.
It takes an Ada source file as input and generates a file containing the
metrics data as output. Various switches control which
metrics are computed and output.
gnatmetric generates and uses the ASIS
tree for the input source and thus requires the input to be syntactically and
semantically legal.
If this condition is not met, gnatmetric will generate
an error message; no metric information for this file will be
computed and reported.
If the compilation unit contained in the input source depends semantically
upon units in files located outside the current directory, you have to provide
the source search path when invoking gnatmetric.
If it depends semantically upon units that are contained
in files with names that do not follow the GNAT file naming rules, you have to
provide the configuration file describing the corresponding naming scheme (see
the description of the gnatmetric switches below.)
Alternatively, you may use a project file and invoke gnatmetric
through the gnat driver (see The GNAT Driver and Project Files).
The gnatmetric command has the form
$ gnatmetric [switches] {filename} [-cargs gcc_switches]
where
gcc. They will be passed on to all compiler invocations made by
gnatmetric to generate the ASIS trees. Here you can provide
-I switches to form the source search path,
and use the -gnatec switch to set the configuration file,
use the -gnat05 switch if sources should be compiled in
Ada 2005 mode etc.
| • Switches for gnatmetric: |
Next: About gnatkr, Previous: Formatting Rules, Up: The GNAT Metric Tool gnatmetric [Contents][Index]
gnatmetricThe following subsections describe the various switches accepted by
gnatmetric, organized by category.
| • Output Files Control: | ||
| • Disable Metrics For Local Units: | ||
| • Specifying a set of metrics to compute: | ||
| • Other gnatmetric Switches: | ||
| • Generate project-wide metrics: |
Next: Disable Metrics For Local Units, Up: Switches for gnatmetric [Contents][Index]
gnatmetric has two output formats. It can generate a
textual (human-readable) form, and also XML. By default only textual
output is generated.
When generating the output in textual form, gnatmetric creates
for each Ada source file a corresponding text file
containing the computed metrics, except for the case when the set of metrics
specified by gnatmetric parameters consists only of metrics that are computed
for the whole set of analyzed sources, but not for each Ada source.
By default, this file is placed in the same directory as where the source
file is located, and its name is obtained
by appending the .metrix suffix to the name of the
input file.
All the output information generated in XML format is placed in a single file. By default this file is placed in the current directory and has the name metrix.xml.
Some of the computed metrics are summed over the units passed to
gnatmetric; for example, the total number of lines of code.
By default this information is sent to stdout, but a file
can be specified with the -og switch.
The following switches control the gnatmetric output:
Generate the XML output
Generate the XML output and the XML schema file that describes the structure of the XML metric report, this schema is assigned to the XML file. The schema file has the same name as the XML output file with .xml suffix replaced with .xsd
Do not generate the output in text form (implies -x)
Put text files with detailed metrics into output_dir
Use file_suffix, instead of .metrix in the name of the output file.
Put global metrics into file_name
Put the XML output into file_name (also implies -x)
Use “short” source file names in the output. (The gnatmetric
output includes the name(s) of the Ada source file(s) from which the metrics
are computed. By default each name includes the absolute path. The
-sfn switch causes gnatmetric
to exclude all directory information from the file names that are output.)
Next: Specifying a set of metrics to compute, Previous: Output Files Control, Up: Switches for gnatmetric [Contents][Index]
gnatmetric relies on the GNAT compilation model -
one compilation
unit per one source file. It computes line metrics for the whole source
file, and it also computes syntax
and complexity metrics for the file’s outermost unit.
By default, gnatmetric will also compute all metrics for certain
kinds of locally declared program units:
These kinds of entities will be referred to as eligible local program units, or simply eligible local units, in the discussion below.
Note that a subprogram declaration, generic instantiation, or renaming declaration only receives metrics computation when it appear as the outermost entity in a source file.
Suppression of metrics computation for eligible local units can be obtained via the following switch:
Do not compute detailed metrics for eligible local program units
Next: Other gnatmetric Switches, Previous: Disable Metrics For Local Units, Up: Switches for gnatmetric [Contents][Index]
By default all the metrics are computed and reported. The switches described in this subsection allow you to control, on an individual basis, whether metrics are computed and reported. If at least one positive metric switch is specified (that is, a switch that defines that a given metric or set of metrics is to be computed), then only explicitly specified metrics are reported.
| • Line Metrics Control: | ||
| • Syntax Metrics Control: | ||
| • Complexity Metrics Control: | ||
| • Coupling Metrics Control: |
For any (legal) source file, and for each of its
eligible local program units, gnatmetric computes the following
metrics:
gnatmetric sums the values of the line metrics for all the
files being processed and then generates the cumulative results. The tool
also computes for all the files being processed the average number of code
lines in bodies.
You can use the following switches to select the specific line metrics to be computed and reported.
Report all the line metrics
Do not report any of line metrics
Report the number of all lines
Do not report the number of all lines
Report the number of code lines
Do not report the number of code lines
Report the number of comment lines
Do not report the number of comment lines
Report the number of code lines containing end-of-line comments
Do not report the number of code lines containing end-of-line comments
Report the comment percentage in the program text
Do not report the comment percentage in the program text
Report the number of blank lines
Do not report the number of blank lines
Report the average number of code lines in subprogram bodies, task bodies, entry bodies and statement sequences in package bodies. The metric is computed and reported for the whole set of processed Ada sources only.
Do not report the average number of code lines in subprogram bodies, task bodies, entry bodies and statement sequences in package bodies.
Next: Complexity Metrics Control, Previous: Line Metrics Control, Up: Specifying a set of metrics to compute [Contents][Index]
gnatmetric computes various syntactic metrics for the
outermost unit and for each eligible local unit:
The total number of declarations and the total number of statements. Note that the definition of declarations is the one given in the reference manual:
“Each of the following is defined to be a declaration: any basic_declaration; an enumeration_literal_specification; a discriminant_specification; a component_declaration; a loop_parameter_specification; a parameter_specification; a subprogram_body; an entry_declaration; an entry_index_specification; a choice_parameter_specification; a generic_formal_parameter_declaration.”
This means for example that each enumeration literal adds one to the count, as well as each subprogram parameter.
Thus the results from this metric will be significantly greater than might be expected from a naive view of counting semicolons.
According to Ada Reference Manual, 10.1(1), “A program unit is either a package, a task unit, a protected unit, a protected entry, a generic unit, or an explicitly declared subprogram other than an enumeration literal.”
This corresponds to the notion of the maximum nesting level in the GNAT built-in style checks (see Style Checking)
For the outermost unit in the file, gnatmetric additionally computes
the following metrics:
This metric is computed for package specs. It is the number of subprograms and generic subprograms declared in the visible part (including the visible part of nested packages, protected objects, and protected types).
This metric is computed for bodies and subunits. The metric is equal to a total number of subprogram bodies in the compilation unit. Neither generic instantiations nor renamings-as-a-body nor body stubs are counted. Any subprogram body is counted, independently of its nesting level and enclosing constructs. Generic bodies and bodies of protected subprograms are counted in the same way as “usual” subprogram bodies.
This metric is computed for package specs and generic package declarations. It is the total number of types that can be referenced from outside this compilation unit, plus the number of types from all the visible parts of all the visible generic packages. Generic formal types are not counted. Only types, not subtypes, are included.
Along with the total number of public types, the following types are counted and reported separately:
This metric is computed for any compilation unit. It is equal to the total number of the declarations of different types given in the compilation unit. The private and the corresponding full type declaration are counted as one type declaration. Incomplete type declarations and generic formal types are not counted. No distinction is made among different kinds of types (abstract, private etc.); the total number of types is computed and reported.
By default, all the syntax metrics are computed and reported. You can use the following switches to select specific syntax metrics.
Report all the syntax metrics
Do not report any of syntax metrics
Report the total number of declarations
Do not report the total number of declarations
Report the total number of statements
Do not report the total number of statements
Report the number of public subprograms in a compilation unit
Do not report the number of public subprograms in a compilation unit
Report the number of all the subprograms in a compilation unit
Do not report the number of all the subprograms in a compilation unit
Report the number of public types in a compilation unit
Do not report the number of public types in a compilation unit
Report the number of all the types in a compilation unit
Do not report the number of all the types in a compilation unit
Report the maximal program unit nesting level
Do not report the maximal program unit nesting level
Report the maximal construct nesting level
Do not report the maximal construct nesting level
Next: Coupling Metrics Control, Previous: Syntax Metrics Control, Up: Specifying a set of metrics to compute [Contents][Index]
For a program unit that is an executable body (a subprogram body (including
generic bodies), task body, entry body or a package body containing
its own statement sequence) gnatmetric computes the following
complexity metrics:
The McCabe cyclomatic complexity metric is defined in http://www.mccabe.com/pdf/mccabe-nist235r.pdf
According to McCabe, both control statements and short-circuit control forms should be taken into account when computing cyclomatic complexity. For Ada 2012 we have also take into account conditional expressions and quantified expressions. For each body, we compute three metric values:
The cyclomatic complexity is also computed for Ada 2012 expression functions. An expression function cannot have statements as its components, so only one metric value is computed as a cyclomatic complexity of an expression function.
The origin of cyclomatic complexity metric is the need to estimate the number
of independent paths in the control flow graph that in turn gives the number
of tests needed to satisfy paths coverage testing completeness criterion.
Considered from the testing point of view, a static Ada loop (that is,
the loop statement having static subtype in loop parameter
specification) does not add to cyclomatic complexity. By providing
--no-static-loop option a user
may specify that such loops should not be counted when computing the
cyclomatic complexity metric
The Ada essential complexity metric is a McCabe cyclomatic complexity metric
counted for the code that is reduced by excluding all the pure structural Ada
control statements. An compound statement is considered as a non-structural
if it contains a raise or return statement as it subcomponent,
or if it contains a goto statement that transfers the control outside
the operator. A selective accept statement with terminate alternative
is considered as non-structural statement. When computing this metric,
exit statements are treated in the same way as goto
statements unless -ne option is specified.
The Ada essential complexity metric defined here is intended to quantify the extent to which the software is unstructured. It is adapted from the McCabe essential complexity metric defined in http://www.mccabe.com/pdf/mccabe-nist235r.pdf but is modified to be more suitable for typical Ada usage. For example, short circuit forms are not penalized as unstructured in the Ada essential complexity metric.
When computing cyclomatic and essential complexity, gnatmetric skips
the code in the exception handlers and in all the nested program units. The
code of assertions and predicates (that is, subprogram preconditions and
postconditions, subtype predicates and type invariants) is also skipped.
By default, all the complexity metrics are computed and reported. For more fine-grained control you can use the following switches:
Report all the complexity metrics
Do not report any of complexity metrics
Report the McCabe Cyclomatic Complexity
Do not report the McCabe Cyclomatic Complexity
Report the Essential Complexity
Do not report the Essential Complexity
Report maximal loop nesting level
Do not report maximal loop nesting level
Report the average McCabe Cyclomatic Complexity for all the subprogram bodies, task bodies, entry bodies and statement sequences in package bodies. The metric is computed and reported for whole set of processed Ada sources only.
Do not report the average McCabe Cyclomatic Complexity for all the subprogram bodies, task bodies, entry bodies and statement sequences in package bodies
Do not consider exit statements as gotos when
computing Essential Complexity
Do not consider static loops when computing cyclomatic complexity
Report the extra exit points for subprogram bodies. As an exit point, this
metric counts return statements and raise statements in case when the
raised exception is not handled in the same body. In case of a function this
metric subtracts 1 from the number of exit points, because a function body
must contain at least one return statement.
Do not report the extra exit points for subprogram bodies
Previous: Complexity Metrics Control, Up: Specifying a set of metrics to compute [Contents][Index]
Coupling metrics measure the dependencies between a given entity and other entities the program consists of. The goal of these metrics is to estimate the stability of the whole program considered as the collection of entities (modules, classes etc.).
Gnatmetric computes the following coupling metrics:
Two kinds of coupling metrics are computed:
the number of entities the given entity depends upon. It estimates in what extent the given entity depends on the changes in “external world”
the number of entities that depend on a given entity. It estimates in what extent the “external world” depends on the changes in a given entity
Object-oriented coupling metrics are metrics that measure the dependencies between a given class (or a group of classes) and the other classes in the program. In this subsection the term “class” is used in its traditional object-oriented programming sense (an instantiable module that contains data and/or method members). A category (of classes) is a group of closely related classes that are reused and/or modified together.
A class K’s fan-out coupling is the number of classes
that K depends upon.
A category’s fan-out coupling is the number of classes outside the
category that the classes inside the category depend upon.
A class K’s fan-in coupling is the number of classes
that depend upon K.
A category’s fan-in coupling is the number of classes outside the
category that depend on classes belonging to the category.
Ada’s implementation of the object-oriented paradigm does not use the traditional class notion, so the definition of the coupling metrics for Ada maps the class and class category notions onto Ada constructs.
For the coupling metrics, several kinds of modules – a library package, a library generic package, and a library generic package instantiation – that define a tagged type or an interface type are considered to be a class. A category consists of a library package (or a library generic package) that defines a tagged or an interface type, together with all its descendant (generic) packages that define tagged or interface types. That is a category is an Ada hierarchy of library-level program units. So class coupling in case of Ada is called as tagged coupling, and category coupling - as hierarchy coupling.
For any package counted as a class, its body and subunits (if any) are considered together with its spec when counting the dependencies, and coupling metrics are reported for spec units only. For dependencies between classes, the Ada semantic dependencies are considered. For object-oriented coupling metrics, only dependencies on units that are considered as classes, are considered.
For unit and control coupling also not compilation units but program units are counted. That is, for a package, its spec, its body and its subunits (if any) are considered as making up one unit, and the dependencies that are counted are the dependencies of all these compilation units collected together as the dependencies as a (whole) unit. And metrics are reported for spec compilation units only (or for a subprogram body unit in case if there is no separate spec for the given subprogram).
For unit coupling, dependencies between all kinds of program units are considered. For control coupling, for each unit the dependencies of this unit upon units that define subprograms are counted, so control fan-out coupling is reported for all units, but control fan-in coupling - only for the units that define subprograms.
The following simple example illustrates the difference between unit coupling and control coupling metrics:
package Lib_1 is
function F_1 (I : Integer) return Integer;
end Lib_1;
package Lib_2 is
type T_2 is new Integer;
end Lib_2;
package body Lib_1 is
function F_1 (I : Integer) return Integer is
begin
return I + 1;
end F_1;
end Lib_1;
with Lib_2; use Lib_2;
package Pack is
Var : T_2;
function Fun (I : Integer) return Integer;
end Pack;
with Lib_1; use Lib_1;
package body Pack is
function Fun (I : Integer) return Integer is
begin
return F_1 (I);
end Fun;
end Pack;
if we apply gnatmetric with --coupling-all option to these
units, the result will be:
Coupling metrics:
=================
Unit Lib_1 (C:\customers\662\L406-007\lib_1.ads)
control fan-out coupling : 0
control fan-in coupling : 1
unit fan-out coupling : 0
unit fan-in coupling : 1
Unit Pack (C:\customers\662\L406-007\pack.ads)
control fan-out coupling : 1
control fan-in coupling : 0
unit fan-out coupling : 2
unit fan-in coupling : 0
Unit Lib_2 (C:\customers\662\L406-007\lib_2.ads)
control fan-out coupling : 0
unit fan-out coupling : 0
unit fan-in coupling : 1
The result does not contain values for object-oriented coupling because none of the argument unit contains a tagged type and therefore none of these units can be treated as a class.
Pack (considered as a program unit, that is spec+body) depends on two
units - Lib_1 and Lib_2, therefore it has unit fan-out coupling
equals to 2. And nothing depend on it, so its unit fan-in coupling is 0 as
well as control fan-in coupling. Only one of the units Pack depends
upon defines a subprogram, so its control fan-out coupling is 1.
Lib_2 depends on nothing, so fan-out metrics for it are 0. It does
not define a subprogram, so control fan-in metric cannot be applied to it,
and there is one unit that depends on it (Pack), so it has
unit fan-in coupling equals to 1.
Lib_1 is similar to Lib_2, but it does define a subprogram.
So it has control fan-in coupling equals to 1 (because there is a unit
depending on it).
When computing coupling metrics, gnatmetric counts only
dependencies between units that are arguments of the gnatmetric
call. Coupling metrics are program-wide (or project-wide) metrics, so to
get a valid result, you should call gnatmetric for
the whole set of sources that make up your program. It can be done
by calling gnatmetric from the GNAT driver with -U
option (see The GNAT Driver and Project Files for details).
By default, all the coupling metrics are disabled. You can use the following switches to specify the coupling metrics to be computed and reported:
Report all the coupling metrics
Report tagged (class) fan-out coupling
Report tagged (class) fan-in coupling
Report hierarchy (category) fan-out coupling
Report hierarchy (category) fan-in coupling
Report unit fan-out coupling
Report unit fan-in coupling
Report control fan-out coupling
Report control fan-in coupling
Next: Generate project-wide metrics, Previous: Specifying a set of metrics to compute, Up: Switches for gnatmetric [Contents][Index]
gnatmetric SwitchesAdditional gnatmetric switches are as follows:
Take the argument source files from the specified file. This file should be an
ordinary text file containing file names separated by spaces or
line breaks. You can use this switch more than once in the same call to
gnatmetric. You also can combine this switch with
an explicit list of files.
Verbose mode;
gnatmetric generates version information and then
a trace of sources being processed.
Quiet mode.
Previous: Other gnatmetric Switches, Up: Switches for gnatmetric [Contents][Index]
In order to compute metrics on all units of a given project, you can use
the gnat driver along with the -P option:
gnat metric -Pproj
If the project proj depends upon other projects, you can compute
the metrics on the project closure using the -U option:
gnat metric -Pproj -U
Finally, if not all the units are relevant to a particular main program in the project closure, you can generate metrics for the set of units needed to create a given main program (unit closure) using the -U option followed by the name of the main unit:
gnat metric -Pproj -U main
Next: Preprocessing Using gnatprep, Previous: The GNAT Metric Tool gnatmetric, Up: Top [Contents][Index]
gnatkrThis chapter discusses the method used by the compiler to shorten
the default file names chosen for Ada units so that they do not
exceed the maximum length permitted. It also describes the
gnatkr utility that can be used to determine the result of
applying this shortening.
| • About gnatkr: | ||
| • Using gnatkr: | ||
| • Krunching Method: | ||
| • Examples of gnatkr Usage: |
Next: Using gnatkr, Previous: Switches for gnatmetric, Up: File Name Krunching Using gnatkr [Contents][Index]
gnatkrThe default file naming rule in GNAT is that the file name must be derived from the unit name. The exact default rule is as follows:
The reason for this exception is to avoid clashes with the standard names for children of System, Ada, Interfaces, and GNAT, which use the prefixes ‘s-’, ‘a-’, ‘i-’, and ‘g-’, respectively.
The -gnatknn switch of the compiler activates a “krunching” circuit that limits file names to nn characters (where nn is a decimal integer). For example, using OpenVMS, where the maximum file name length is 39, the value of nn is usually set to 39, but if you want to generate a set of files that would be usable if ported to a system with some different maximum file length, then a different value can be specified. The default value of 39 for OpenVMS need not be specified.
The gnatkr utility can be used to determine the krunched name for
a given file, when krunched to a specified maximum length.
Next: Krunching Method, Previous: About gnatkr, Up: File Name Krunching Using gnatkr [Contents][Index]
gnatkrThe gnatkr command has the form
$ gnatkr name [length]
name is the uncrunched file name, derived from the name of the unit in the standard manner described in the previous section (i.e., in particular all dots are replaced by hyphens). The file name may or may not have an extension (defined as a suffix of the form period followed by arbitrary characters other than period). If an extension is present then it will be preserved in the output. For example, when krunching hellofile.ads to eight characters, the result will be hellofil.ads.
Note: for compatibility with previous versions of gnatkr dots may
appear in the name instead of hyphens, but the last dot will always be
taken as the start of an extension. So if gnatkr is given an argument
such as Hello.World.adb it will be treated exactly as if the first
period had been a hyphen, and for example krunching to eight characters
gives the result hellworl.adb.
Note that the result is always all lower case (except on OpenVMS where it is all upper case). Characters of the other case are folded as required.
length represents the length of the krunched name. The default when no argument is given is 8 characters. A length of zero stands for unlimited, in other words do not chop except for system files where the implied crunching length is always eight characters.
The output is the krunched name. The output has an extension only if the original argument was a file name with an extension.
Next: Examples of gnatkr Usage, Previous: Using gnatkr, Up: File Name Krunching Using gnatkr [Contents][Index]
The initial file name is determined by the name of the unit that the file
contains. The name is formed by taking the full expanded name of the
unit and replacing the separating dots with hyphens and
using lowercase
for all letters, except that a hyphen in the second character position is
replaced by a tilde if the first character is
‘a’, ‘i’, ‘g’, or ‘s’.
The extension is .ads for a
spec and .adb for a body.
Krunching does not affect the extension, but the file name is shortened to
the specified length by following these rules:
As an example, consider the krunching of
our-strings-wide_fixed.adb
to fit the name into 8 characters as required by some operating systems.
our-strings-wide_fixed 22 our strings wide fixed 19 our string wide fixed 18 our strin wide fixed 17 our stri wide fixed 16 our stri wide fixe 15 our str wide fixe 14 our str wid fixe 13 our str wid fix 12 ou str wid fix 11 ou st wid fix 10 ou st wi fix 9 ou st wi fi 8 Final file name: oustwifi.adb
replaced by a-
replaced by g-
replaced by i-
replaced by s-
These system files have a hyphen in the second character position. That is why normal user files replace such a character with a tilde, to avoid confusion with system file names.
As an example of this special rule, consider
ada-strings-wide_fixed.adb, which gets krunched as follows:
ada-strings-wide_fixed 22 a- strings wide fixed 18 a- string wide fixed 17 a- strin wide fixed 16 a- stri wide fixed 15 a- stri wide fixe 14 a- str wide fixe 13 a- str wid fixe 12 a- str wid fix 11 a- st wid fix 10 a- st wi fix 9 a- st wi fi 8 Final file name: a-stwifi.adb
Of course no file shortening algorithm can guarantee uniqueness over all
possible unit names, and if file name krunching is used then it is your
responsibility to ensure that no name clashes occur. The utility
program gnatkr is supplied for conveniently determining the
krunched name of a file.
Next: Preprocessing Symbols, Previous: Krunching Method, Up: File Name Krunching Using gnatkr [Contents][Index]
gnatkr Usage$ gnatkr very_long_unit_name.ads --> velounna.ads $ gnatkr grandparent-parent-child.ads --> grparchi.ads $ gnatkr Grandparent.Parent.Child.ads --> grparchi.ads $ gnatkr grandparent-parent-child --> grparchi $ gnatkr very_long_unit_name.ads/count=6 --> vlunna.ads $ gnatkr very_long_unit_name.ads/count=0 --> very_long_unit_name.ads
Next: The GNAT Library Browser gnatls, Previous: File Name Krunching Using gnatkr, Up: Top [Contents][Index]
gnatprepThis chapter discusses how to use GNAT’s gnatprep utility for simple
preprocessing.
Although designed for use with GNAT, gnatprep does not depend on any
special GNAT features.
For further discussion of conditional compilation in general, see
Conditional Compilation.
| • Preprocessing Symbols: | ||
| • Using gnatprep: | ||
| • Switches for gnatprep: | ||
| • Form of Definitions File: | ||
| • Form of Input Text for gnatprep: |
Next: Using gnatprep, Previous: Examples of gnatkr Usage, Up: Preprocessing Using gnatprep [Contents][Index]
Preprocessing symbols are defined in definition files and referred to in sources to be preprocessed. A Preprocessing symbol is an identifier, following normal Ada (case-insensitive) rules for its syntax, with the restriction that all characters need to be in the ASCII set (no accented letters).
Next: Switches for gnatprep, Previous: Preprocessing Symbols, Up: Preprocessing Using gnatprep [Contents][Index]
gnatprepTo call gnatprep use
$ gnatprep [switches] infile outfile [deffile]
where
is an optional sequence of switches as described in the next section.
is the full name of the input file, which is an Ada source file containing preprocessor directives.
is the full name of the output file, which is an Ada source in standard Ada form. When used with GNAT, this file name will normally have an ads or adb suffix.
is the full name of a text file containing definitions of preprocessing symbols to be referenced by the preprocessor. This argument is optional, and can be replaced by the use of the -D switch.
Next: Form of Definitions File, Previous: Using gnatprep, Up: Preprocessing Using gnatprep [Contents][Index]
gnatprepCauses both preprocessor lines and the lines deleted by preprocessing to be replaced by blank lines in the output source file, preserving line numbers in the output file.
Causes both preprocessor lines and the lines deleted
by preprocessing to be retained in the output source as comments marked
with the special string "--! ". This option will result in line numbers
being preserved in the output file.
Causes comments to be scanned. Normally comments are ignored by gnatprep. If this option is specified, then comments are scanned and any $symbol substitutions performed as in program text. This is particularly useful when structured comments are used (e.g., when writing programs in the SPARK dialect of Ada). Note that this switch is not available when doing integrated preprocessing (it would be useless in this context since comments are ignored by the compiler in any case).
Defines a new preprocessing symbol, associated with value. If no value is given
on the command line, then symbol is considered to be True. This switch
can be used in place of a definition file.
Causes a Source_Reference pragma to be generated that
references the original input file, so that error messages will use
the file name of this original file. The use of this switch implies
that preprocessor lines are not to be removed from the file, so its
use will force -b mode if
-c
has not been specified explicitly.
Note that if the file to be preprocessed contains multiple units, then
it will be necessary to gnatchop the output file from
gnatprep. If a Source_Reference pragma is present
in the preprocessed file, it will be respected by
gnatchop -r
so that the final chopped files will correctly refer to the original
input source file for gnatprep.
Causes a sorted list of symbol names and values to be listed on the standard output file.
Causes undefined symbols to be treated as having the value FALSE in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a #if or #elsif test will be treated as an error.
Note: if neither -b nor -c is present, then preprocessor lines and deleted lines are completely removed from the output, unless -r is specified, in which case -b is assumed.
Next: Form of Input Text for gnatprep, Previous: Switches for gnatprep, Up: Preprocessing Using gnatprep [Contents][Index]
The definitions file contains lines of the form
symbol := value
where symbol is a preprocessing symbol, and value is one of the following:
Comment lines may also appear in the definitions file, starting with
the usual --,
and comments may be added to the definitions lines.
Next: Running gnatls, Previous: Form of Definitions File, Up: Preprocessing Using gnatprep [Contents][Index]
gnatprepThe input text may contain preprocessor conditional inclusion lines, as well as general symbol substitution sequences.
The preprocessor conditional inclusion commands have the form
#if expression [then] lines #elsif expression [then] lines #elsif expression [then] lines … #else lines #end if; |
In this example, expression is defined by the following grammar:
expression ::= <symbol> expression ::= <symbol> = "<value>" expression ::= <symbol> = <symbol> expression ::= <symbol> 'Defined expression ::= not expression expression ::= expression and expression expression ::= expression or expression expression ::= expression and then expression expression ::= expression or else expression expression ::= ( expression )
The following restriction exists: it is not allowed to have "and" or "or" following "not" in the same expression without parentheses. For example, this is not allowed:
not X or Y
This should be one of the following:
(not X) or Y not (X or Y)
For the first test (expression ::= <symbol>) the symbol must have
either the value true or false, that is to say the right-hand of the
symbol definition must be one of the (case-insensitive) literals
True or False. If the value is true, then the
corresponding lines are included, and if the value is false, they are
excluded.
The test (expression ::= <symbol> 'Defined) is true only if
the symbol has been defined in the definition file or by a -D
switch on the command line. Otherwise, the test is false.
The equality tests are case insensitive, as are all the preprocessor lines.
If the symbol referenced is not defined in the symbol definitions file,
then the effect depends on whether or not switch -u
is specified. If so, then the symbol is treated as if it had the value
false and the test fails. If this switch is not specified, then
it is an error to reference an undefined symbol. It is also an error to
reference a symbol that is defined with a value other than True
or False.
The use of the not operator inverts the sense of this logical test.
The not operator cannot be combined with the or or and
operators, without parentheses. For example, "if not X or Y then" is not
allowed, but "if (not X) or Y then" and "if not (X or Y) then" are.
The then keyword is optional as shown
The # must be the first non-blank character on a line, but
otherwise the format is free form. Spaces or tabs may appear between
the # and the keyword. The keywords and the symbols are case
insensitive as in normal Ada code. Comments may be used on a
preprocessor line, but other than that, no other tokens may appear on a
preprocessor line. Any number of elsif clauses can be present,
including none at all. The else is optional, as in Ada.
The # marking the start of a preprocessor line must be the first
non-blank character on the line, i.e., it must be preceded only by
spaces or horizontal tabs.
Symbol substitution outside of preprocessor lines is obtained by using the sequence
$symbol
anywhere within a source line, except in a comment or within a
string literal. The identifier
following the $ must match one of the symbols defined in the symbol
definition file, and the result is to substitute the value of the
symbol in place of $symbol in the output file.
Note that although the substitution of strings within a string literal
is not possible, it is possible to have a symbol whose defined value is
a string literal. So instead of setting XYZ to hello and writing:
Header : String := "$XYZ";
you should set XYZ to "hello" and write:
Header : String := $XYZ;
and then the substitution will occur as desired.
Next: Cleaning Up Using gnatclean, Previous: Preprocessing Using gnatprep, Up: Top [Contents][Index]
gnatlsgnatls is a tool that outputs information about compiled
units. It gives the relationship between objects, unit names and source
files. It can also be used to check the source dependencies of a unit
as well as various characteristics.
Note: to invoke gnatls with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
| • Running gnatls: | ||
| • Switches for gnatls: | ||
| • Examples of gnatls Usage: |
Next: Switches for gnatls, Previous: Form of Input Text for gnatprep, Up: The GNAT Library Browser gnatls [Contents][Index]
gnatlsThe gnatls command has the form
$ gnatls switches object_or_ali_file
The main argument is the list of object or ali files (see The Ada Library Information Files) for which information is requested.
In normal mode, without additional option, gnatls produces a
four-column listing. Each line represents information for a specific
object. The first column gives the full path of the object, the second
column gives the name of the principal unit in this object, the third
column gives the status of the source and the fourth column gives the
full path of the source representing this unit.
Here is a simple example of use:
$ gnatls *.o ./demo1.o demo1 DIF demo1.adb ./demo2.o demo2 OK demo2.adb ./hello.o h1 OK hello.adb ./instr-child.o instr.child MOK instr-child.adb ./instr.o instr OK instr.adb ./tef.o tef DIF tef.adb ./text_io_example.o text_io_example OK text_io_example.adb ./tgef.o tgef DIF tgef.adb
The first line can be interpreted as follows: the main unit which is contained in object file demo1.o is demo1, whose main source is in demo1.adb. Furthermore, the version of the source used for the compilation of demo1 has been modified (DIF). Each source file has a status qualifier which can be:
OK (unchanged)The version of the source file used for the compilation of the specified unit corresponds exactly to the actual source file.
MOK (slightly modified)The version of the source file used for the compilation of the specified unit differs from the actual source file but not enough to require recompilation. If you use gnatmake with the qualifier -m (minimal recompilation), a file marked MOK will not be recompiled.
DIF (modified)No version of the source found on the path corresponds to the source used to build this object.
??? (file not found)No source file was found for this unit.
HID (hidden, unchanged version not first on PATH)The version of the source that corresponds exactly to the source used for compilation has been found on the path but it is hidden by another version of the same source that has been modified.
Next: Examples of gnatls Usage, Previous: Running gnatls, Up: The GNAT Library Browser gnatls [Contents][Index]
gnatlsgnatls recognizes the following switches:
Display Copyright and version, then exit disregarding all other options.
If --version was not used, display usage, then exit disregarding all other options.
Consider all units, including those of the predefined Ada library. Especially useful with -d.
List sources from which specified units depend on.
Output the list of options.
Only output information about object files.
Only output information about source files.
Only output information about compilation units.
Take as arguments the files listed in text file file. Text file file may contain empty lines that are ignored. Each nonempty line should contain the name of an existing file. Several such switches may be specified simultaneously.
Source path manipulation. Same meaning as the equivalent gnatmake
flags (see Switches for gnatmake).
Specifies the default location of the runtime library. Same meaning as the
equivalent gnatmake flag (see Switches for gnatmake).
Verbose mode. Output the complete source, object and project paths. Do not use the default column layout but instead use long format giving as much as information possible on each requested units, including special characteristics such as:
PreelaborableThe unit is preelaborable in the Ada sense.
No_Elab_CodeNo elaboration code has been produced by the compiler for this unit.
PureThe unit is pure in the Ada sense.
Elaborate_BodyThe unit contains a pragma Elaborate_Body.
Remote_TypesThe unit contains a pragma Remote_Types.
Shared_PassiveThe unit contains a pragma Shared_Passive.
PredefinedThis unit is part of the predefined environment and cannot be modified by the user.
Remote_Call_InterfaceThe unit contains a pragma Remote_Call_Interface.
Next: Running gnatclean, Previous: Switches for gnatls, Up: The GNAT Library Browser gnatls [Contents][Index]
gnatls UsageExample of using the verbose switch. Note how the source and object paths are affected by the -I switch.
$ gnatls -v -I.. demo1.o
GNATLS 5.03w (20041123-34)
Copyright 1997-2004 Free Software Foundation, Inc.
Source Search Path:
<Current_Directory>
../
/home/comar/local/adainclude/
Object Search Path:
<Current_Directory>
../
/home/comar/local/lib/gcc-lib/x86-linux/3.4.3/adalib/
Project Search Path:
<Current_Directory>
/home/comar/local/lib/gnat/
./demo1.o
Unit =>
Name => demo1
Kind => subprogram body
Flags => No_Elab_Code
Source => demo1.adb modified
The following is an example of use of the dependency list. Note the use of the -s switch which gives a straight list of source files. This can be useful for building specialized scripts.
$ gnatls -d demo2.o
./demo2.o demo2 OK demo2.adb
OK gen_list.ads
OK gen_list.adb
OK instr.ads
OK instr-child.ads
$ gnatls -d -s -a demo1.o
demo1.adb
/home/comar/local/adainclude/ada.ads
/home/comar/local/adainclude/a-finali.ads
/home/comar/local/adainclude/a-filico.ads
/home/comar/local/adainclude/a-stream.ads
/home/comar/local/adainclude/a-tags.ads
gen_list.ads
gen_list.adb
/home/comar/local/adainclude/gnat.ads
/home/comar/local/adainclude/g-io.ads
instr.ads
/home/comar/local/adainclude/system.ads
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Next: GNAT and Libraries, Previous: The GNAT Library Browser gnatls, Up: Top [Contents][Index]
gnatcleangnatclean is a tool that allows the deletion of files produced by the
compiler, binder and linker, including ALI files, object files, tree files,
expanded source files, library files, interface copy source files, binder
generated files and executable files.
| • Running gnatclean: | ||
| • Switches for gnatclean: |
Next: Switches for gnatclean, Previous: Examples of gnatls Usage, Up: Cleaning Up Using gnatclean [Contents][Index]
gnatcleanThe gnatclean command has the form:
$ gnatclean switches names
names is a list of source file names. Suffixes .ads and
adb may be omitted. If a project file is specified using switch
-P, then names may be completely omitted.
In normal mode, gnatclean delete the files produced by the compiler and,
if switch -c is not specified, by the binder and
the linker. In informative-only mode, specified by switch
-n, the list of files that would have been deleted in
normal mode is listed, but no file is actually deleted.
Next: Introduction to Libraries in GNAT, Previous: Running gnatclean, Up: Cleaning Up Using gnatclean [Contents][Index]
gnatcleangnatclean recognizes the following switches:
Display Copyright and version, then exit disregarding all other options.
If --version was not used, display usage, then exit disregarding all other options.
Actual object directory of each project file is the subdirectory subdir of the object directory specified or defaulted in the project file.
By default, shared library projects are not allowed to import static library projects. When this switch is used on the command line, this restriction is relaxed.
Only attempt to delete the files produced by the compiler, not those produced by the binder or the linker. The files that are not to be deleted are library files, interface copy files, binder generated files and executable files.
Indicate that ALI and object files should normally be found in directory dir.
When using project files, if some errors or warnings are detected during parsing and verbose mode is not in effect (no use of switch -v), then error lines start with the full path name of the project file, rather than its simple file name.
Output a message explaining the usage of gnatclean.
Informative-only mode. Do not delete any files. Output the list of the files that would have been deleted if this switch was not specified.
Use project file project. Only one such switch can be used. When cleaning a project file, the files produced by the compilation of the immediate sources or inherited sources of the project files are to be deleted. This is not depending on the presence or not of executable names on the command line.
Quiet output. If there are no errors, do not output anything, except in verbose mode (switch -v) or in informative-only mode (switch -n).
When a project file is specified (using switch -P), clean all imported and extended project files, recursively. If this switch is not specified, only the files related to the main project file are to be deleted. This switch has no effect if no project file is specified.
Verbose mode.
Indicates the verbosity of the parsing of GNAT project files. See Switches Related to Project Files.
Indicates that external variable name has the value value.
The Project Manager will use this value for occurrences of
external(name) when parsing the project file.
See Switches Related to Project Files.
When searching for ALI and object files, look in directory dir.
Equivalent to -aOdir.
Do not look for ALI or object files in the directory
where gnatclean was invoked.
Next: Using the GNU make Utility, Previous: Cleaning Up Using gnatclean, Up: Top [Contents][Index]
This chapter describes how to build and use libraries with GNAT, and also shows how to recompile the GNAT run-time library. You should be familiar with the Project Manager facility (see GNAT Project Manager) before reading this chapter.
| • Introduction to Libraries in GNAT: | ||
| • General Ada Libraries: | ||
| • Stand-alone Ada Libraries: | ||
| • Rebuilding the GNAT Run-Time Library: |
Next: General Ada Libraries, Previous: Switches for gnatclean, Up: GNAT and Libraries [Contents][Index]
A library is, conceptually, a collection of objects which does not have its own main thread of execution, but rather provides certain services to the applications that use it. A library can be either statically linked with the application, in which case its code is directly included in the application, or, on platforms that support it, be dynamically linked, in which case its code is shared by all applications making use of this library.
GNAT supports both types of libraries. In the static case, the compiled code can be provided in different ways. The simplest approach is to provide directly the set of objects resulting from compilation of the library source files. Alternatively, you can group the objects into an archive using whatever commands are provided by the operating system. For the latter case, the objects are grouped into a shared library.
In the GNAT environment, a library has three types of components:
A GNAT library may expose all its source files, which is useful for documentation purposes. Alternatively, it may expose only the units needed by an external user to make use of the library. That is to say, the specs reflecting the library services along with all the units needed to compile those specs, which can include generic bodies or any body implementing an inlined routine. In the case of stand-alone libraries those exposed units are called interface units (see Stand-alone Ada Libraries).
All compilation units comprising an application, including those in a library, need to be elaborated in an order partially defined by Ada’s semantics. GNAT computes the elaboration order from the ALI files and this is why they constitute a mandatory part of GNAT libraries. Stand-alone libraries are the exception to this rule because a specific library elaboration routine is produced independently of the application(s) using the library.
Next: Stand-alone Ada Libraries, Previous: Introduction to Libraries in GNAT, Up: GNAT and Libraries [Contents][Index]
| • Building a library: | ||
| • Installing a library: | ||
| • Using a library: |
Next: Installing a library, Up: General Ada Libraries [Contents][Index]
The easiest way to build a library is to use the Project Manager, which supports a special type of project called a Library Project (see Library Projects).
A project is considered a library project, when two project-level attributes
are defined in it: Library_Name and Library_Dir. In order to
control different aspects of library configuration, additional optional
project-level attributes can be specified:
Library_KindThis attribute controls whether the library is to be static or dynamic
Library_VersionThis attribute specifies the library version; this value is used during dynamic linking of shared libraries to determine if the currently installed versions of the binaries are compatible.
Library_OptionsLibrary_GCCThese attributes specify additional low-level options to be used during library generation, and redefine the actual application used to generate library.
The GNAT Project Manager takes full care of the library maintenance task, including recompilation of the source files for which objects do not exist or are not up to date, assembly of the library archive, and installation of the library (i.e., copying associated source, object and ALI files to the specified location).
Here is a simple library project file:
project My_Lib is
for Source_Dirs use ("src1", "src2");
for Object_Dir use "obj";
for Library_Name use "mylib";
for Library_Dir use "lib";
for Library_Kind use "dynamic";
end My_lib;
and the compilation command to build and install the library:
$ gnatmake -Pmy_lib
It is not entirely trivial to perform manually all the steps required to produce a library. We recommend that you use the GNAT Project Manager for this task. In special cases where this is not desired, the necessary steps are discussed below.
There are various possibilities for compiling the units that make up the
library: for example with a Makefile (see Using the GNU make Utility) or
with a conventional script. For simple libraries, it is also possible to create
a dummy main program which depends upon all the packages that comprise the
interface of the library. This dummy main program can then be given to
gnatmake, which will ensure that all necessary objects are built.
After this task is accomplished, you should follow the standard procedure of the underlying operating system to produce the static or shared library.
Here is an example of such a dummy program:
with My_Lib.Service1; with My_Lib.Service2; with My_Lib.Service3; procedure My_Lib_Dummy is begin null; end;
Here are the generic commands that will build an archive or a shared library.
# compiling the library $ gnatmake -c my_lib_dummy.adb # we don't need the dummy object itself $ rm my_lib_dummy.o my_lib_dummy.ali # create an archive with the remaining objects $ ar rc libmy_lib.a *.o # some systems may require "ranlib" to be run as well # or create a shared library $ gcc -shared -o libmy_lib.so *.o # some systems may require the code to have been compiled with -fPIC # remove the object files that are now in the library $ rm *.o # Make the ALI files read-only so that gnatmake will not try to # regenerate the objects that are in the library $ chmod -w *.ali
Please note that the library must have a name of the form libxxx.a or libxxx.so (or libxxx.dll on Windows) in order to be accessed by the directive -lxxx at link time.
Next: Using a library, Previous: Building a library, Up: General Ada Libraries [Contents][Index]
If you use project files, library installation is part of the library build process (see Installing a library with project files).
When project files are not an option, it is also possible, but not recommended, to install the library so that the sources needed to use the library are on the Ada source path and the ALI files & libraries be on the Ada Object path (see Search Paths and the Run-Time Library (RTL). Alternatively, the system administrator can place general-purpose libraries in the default compiler paths, by specifying the libraries’ location in the configuration files ada_source_path and ada_object_path. These configuration files must be located in the GNAT installation tree at the same place as the gcc spec file. The location of the gcc spec file can be determined as follows:
$ gcc -v
The configuration files mentioned above have a simple format: each line must contain one unique directory name. Those names are added to the corresponding path in their order of appearance in the file. The names can be either absolute or relative; in the latter case, they are relative to where theses files are located.
The files ada_source_path and ada_object_path might not be present in a GNAT installation, in which case, GNAT will look for its run-time library in the directories adainclude (for the sources) and adalib (for the objects and ALI files). When the files exist, the compiler does not look in adainclude and adalib, and thus the ada_source_path file must contain the location for the GNAT run-time sources (which can simply be adainclude). In the same way, the ada_object_path file must contain the location for the GNAT run-time objects (which can simply be adalib).
You can also specify a new default path to the run-time library at compilation
time with the switch --RTS=rts-path. You can thus choose / change
the run-time library you want your program to be compiled with. This switch is
recognized by gcc, gnatmake, gnatbind,
gnatls, gnatfind and gnatxref.
It is possible to install a library before or after the standard GNAT library, by reordering the lines in the configuration files. In general, a library must be installed before the GNAT library if it redefines any part of it.
Previous: Installing a library, Up: General Ada Libraries [Contents][Index]
Once again, the project facility greatly simplifies the use of
libraries. In this context, using a library is just a matter of adding a
with clause in the user project. For instance, to make use of the
library My_Lib shown in examples in earlier sections, you can
write:
with "my_lib"; project My_Proj is … end My_Proj;
Even if you have a third-party, non-Ada library, you can still use GNAT’s
Project Manager facility to provide a wrapper for it. For example, the
following project, when withed by your main project, will link with the
third-party library liba.a:
project Liba is for Externally_Built use "true"; for Source_Files use (); for Library_Dir use "lib"; for Library_Name use "a"; for Library_Kind use "static"; end Liba;
This is an alternative to the use of pragma Linker_Options. It is
especially interesting in the context of systems with several interdependent
static libraries where finding a proper linker order is not easy and best be
left to the tools having visibility over project dependence information.
In order to use an Ada library manually, you need to make sure that this library is on both your source and object path (see Search Paths and the Run-Time Library (RTL) and Search Paths for gnatbind). Furthermore, when the objects are grouped in an archive or a shared library, you need to specify the desired library at link time.
For example, you can use the library mylib installed in /dir/my_lib_src and /dir/my_lib_obj with the following commands:
$ gnatmake -aI/dir/my_lib_src -aO/dir/my_lib_obj my_appl \ -largs -lmy_lib
This can be expressed more simply:
$ gnatmake my_appl
when the following conditions are met:
ADA_INCLUDE_PATH, or by the administrator to the file
ada_source_path
ADA_OBJECTS_PATH, or by the administrator to the file
ada_object_path
Linker_Options has been added to one of the sources.
For example:
pragma Linker_Options ("-lmy_lib");
Next: Rebuilding the GNAT Run-Time Library, Previous: General Ada Libraries, Up: GNAT and Libraries [Contents][Index]
| • Introduction to Stand-alone Libraries: | ||
| • Building a Stand-alone Library: | ||
| • Creating a Stand-alone Library to be used in a non-Ada context: | ||
| • Restrictions in Stand-alone Libraries: |
Next: Building a Stand-alone Library, Up: Stand-alone Ada Libraries [Contents][Index]
A Stand-alone Library (abbreviated “SAL”) is a library that contains the necessary code to elaborate the Ada units that are included in the library. In contrast with an ordinary library, which consists of all sources, objects and ALI files of the library, a SAL may specify a restricted subset of compilation units to serve as a library interface. In this case, the fully self-sufficient set of files will normally consist of an objects archive, the sources of interface units’ specs, and the ALI files of interface units. If an interface spec contains a generic unit or an inlined subprogram, the body’s source must also be provided; if the units that must be provided in the source form depend on other units, the source and ALI files of those must also be provided.
The main purpose of a SAL is to minimize the recompilation overhead of client
applications when a new version of the library is installed. Specifically,
if the interface sources have not changed, client applications do not need to
be recompiled. If, furthermore, a SAL is provided in the shared form and its
version, controlled by Library_Version attribute, is not changed,
then the clients do not need to be relinked.
SALs also allow the library providers to minimize the amount of library source text exposed to the clients. Such “information hiding” might be useful or necessary for various reasons.
Stand-alone libraries are also well suited to be used in an executable whose main routine is not written in Ada.
Next: Creating a Stand-alone Library to be used in a non-Ada context, Previous: Introduction to Stand-alone Libraries, Up: Stand-alone Ada Libraries [Contents][Index]
GNAT’s Project facility provides a simple way of building and installing
stand-alone libraries; see Stand-alone Library Projects.
To be a Stand-alone Library Project, in addition to the two attributes
that make a project a Library Project (Library_Name and
Library_Dir; see Library Projects), the attribute
Library_Interface must be defined. For example:
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Interface use ("int1", "int1.child");
Attribute Library_Interface has a non-empty string list value,
each string in the list designating a unit contained in an immediate source
of the project file.
When a Stand-alone Library is built, first the binder is invoked to build
a package whose name depends on the library name
(b~dummy.ads/b in the example above).
This binder-generated package includes initialization and
finalization procedures whose
names depend on the library name (dummyinit and dummyfinal
in the example
above). The object corresponding to this package is included in the library.
You must ensure timely (e.g., prior to any use of interfaces in the SAL)
calling of these procedures if a static SAL is built, or if a shared SAL
is built
with the project-level attribute Library_Auto_Init set to
"false".
For a Stand-Alone Library, only the ALI files of the Interface Units
(those that are listed in attribute Library_Interface) are copied to
the Library Directory. As a consequence, only the Interface Units may be
imported from Ada units outside of the library. If other units are imported,
the binding phase will fail.
It is also possible to build an encapsulated library where not only
the code to elaborate and finalize the library is embedded but also
ensuring that the library is linked only against static
libraries. So an encapsulated library only depends on system
libraries, all other code, including the GNAT runtime, is embedded. To
build an encapsulated library the attribute
Library_Standalone must be set to encapsulated:
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Interface use ("int1", "int1.child");
for Library_Standalone use "encapsulated";
The default value for this attribute is standard in which case
a stand-alone library is built.
The attribute Library_Src_Dir may be specified for a
Stand-Alone Library. Library_Src_Dir is a simple attribute that has a
single string value. Its value must be the path (absolute or relative to the
project directory) of an existing directory. This directory cannot be the
object directory or one of the source directories, but it can be the same as
the library directory. The sources of the Interface
Units of the library that are needed by an Ada client of the library will be
copied to the designated directory, called the Interface Copy directory.
These sources include the specs of the Interface Units, but they may also
include bodies and subunits, when pragmas Inline or Inline_Always
are used, or when there is a generic unit in the spec. Before the sources
are copied to the Interface Copy directory, an attempt is made to delete all
files in the Interface Copy directory.
Building stand-alone libraries by hand is somewhat tedious, but for those occasions when it is necessary here are the steps that you need to perform:
init
and final procedures. For example:
gnatbind -n int1.ali int2.ali -Lsal1
gcc -c b~int2.adb
init (and possibly
final) procedures for automatic initialization (and finalization).
The built library should be placed in a directory different from
the object directory.
ALI files of the interface to the library directory,
add in this copy an indication that it is an interface to a SAL
(i.e., add a word SL on the line in the ALI file that starts
with letter “P”) and make the modified copy of the ALI file
read-only.
Using SALs is not different from using other libraries (see Using a library).
Next: Restrictions in Stand-alone Libraries, Previous: Building a Stand-alone Library, Up: Stand-alone Ada Libraries [Contents][Index]
It is easy to adapt the SAL build procedure discussed above for use of a SAL in a non-Ada context.
The only extra step required is to ensure that library interface subprograms
are compatible with the main program, by means of pragma Export
or pragma Convention.
Here is an example of simple library interface for use with C main program:
package My_Package is procedure Do_Something; pragma Export (C, Do_Something, "do_something"); procedure Do_Something_Else; pragma Export (C, Do_Something_Else, "do_something_else"); end My_Package;
On the foreign language side, you must provide a “foreign” view of the library interface; remember that it should contain elaboration routines in addition to interface subprograms.
The example below shows the content of mylib_interface.h (note
that there is no rule for the naming of this file, any name can be used)
/* the library elaboration procedure */ extern void mylibinit (void); /* the library finalization procedure */ extern void mylibfinal (void); /* the interface exported by the library */ extern void do_something (void); extern void do_something_else (void);
Libraries built as explained above can be used from any program, provided
that the elaboration procedures (named mylibinit in the previous
example) are called before the library services are used. Any number of
libraries can be used simultaneously, as long as the elaboration
procedure of each library is called.
Below is an example of a C program that uses the mylib library.
#include "mylib_interface.h"
int
main (void)
{
/* First, elaborate the library before using it */
mylibinit ();
/* Main program, using the library exported entities */
do_something ();
do_something_else ();
/* Library finalization at the end of the program */
mylibfinal ();
return 0;
}
Note that invoking any library finalization procedure generated by
gnatbind shuts down the Ada run-time environment.
Consequently, the
finalization of all Ada libraries must be performed at the end of the program.
No call to these libraries or to the Ada run-time library should be made
after the finalization phase.
Previous: Creating a Stand-alone Library to be used in a non-Ada context, Up: Stand-alone Ada Libraries [Contents][Index]
The pragmas listed below should be used with caution inside libraries, as they can create incompatibilities with other Ada libraries:
Locking_Policy
Queuing_Policy
Task_Dispatching_Policy
Unreserve_All_Interrupts
When using a library that contains such pragmas, the user must make sure
that all libraries use the same pragmas with the same values. Otherwise,
Program_Error will
be raised during the elaboration of the conflicting
libraries. The usage of these pragmas and its consequences for the user
should therefore be well documented.
Similarly, the traceback in the exception occurrence mechanism should be enabled or disabled in a consistent manner across all libraries. Otherwise, Program_Error will be raised during the elaboration of the conflicting libraries.
If the Version or Body_Version
attributes are used inside a library, then you need to
perform a gnatbind step that specifies all ALI files in all
libraries, so that version identifiers can be properly computed.
In practice these attributes are rarely used, so this is unlikely
to be a consideration.
Next: Using gnatmake in a Makefile, Previous: Stand-alone Ada Libraries, Up: GNAT and Libraries [Contents][Index]
It may be useful to recompile the GNAT library in various contexts, the
most important one being the use of partition-wide configuration pragmas
such as Normalize_Scalars. A special Makefile called
Makefile.adalib is provided to that effect and can be found in
the directory containing the GNAT library. The location of this
directory depends on the way the GNAT environment has been installed and can
be determined by means of the command:
$ gnatls -v
The last entry in the object search path usually contains the gnat library. This Makefile contains its own documentation and in particular the set of instructions needed to rebuild a new library and to use it.
Next: Memory Management Issues, Previous: GNAT and Libraries, Up: Top [Contents][Index]
make UtilityThis chapter offers some examples of makefiles that solve specific
problems. It does not explain how to write a makefile (see GNU
make in GNU make), nor does it try to replace the
gnatmake utility (see The GNAT Make Program gnatmake).
All the examples in this section are specific to the GNU version of
make. Although make is a standard utility, and the basic language
is the same, these examples use some advanced features found only in
GNU make.
| • Using gnatmake in a Makefile: | ||
| • Automatically Creating a List of Directories: | ||
| • Generating the Command Line Switches: | ||
| • Overcoming Command Line Length Limits: |
Next: Automatically Creating a List of Directories, Previous: Rebuilding the GNAT Run-Time Library, Up: Using the GNU make Utility [Contents][Index]
Complex project organizations can be handled in a very powerful way by using GNU make combined with gnatmake. For instance, here is a Makefile which allows you to build each subsystem of a big project into a separate shared library. Such a makefile allows you to significantly reduce the link time of very big applications while maintaining full coherence at each step of the build process.
The list of dependencies are handled automatically by
gnatmake. The Makefile is simply used to call gnatmake in each of
the appropriate directories.
Note that you should also read the example on how to automatically create the list of directories (see Automatically Creating a List of Directories) which might help you in case your project has a lot of subdirectories.
## This Makefile is intended to be used with the following directory
## configuration:
## - The sources are split into a series of csc (computer software components)
## Each of these csc is put in its own directory.
## Their name are referenced by the directory names.
## They will be compiled into shared library (although this would also work
## with static libraries
## - The main program (and possibly other packages that do not belong to any
## csc is put in the top level directory (where the Makefile is).
## toplevel_dir __ first_csc (sources) __ lib (will contain the library)
## \_ second_csc (sources) __ lib (will contain the library)
## \_ …
## Although this Makefile is build for shared library, it is easy to modify
## to build partial link objects instead (modify the lines with -shared and
## gnatlink below)
##
## With this makefile, you can change any file in the system or add any new
## file, and everything will be recompiled correctly (only the relevant shared
## objects will be recompiled, and the main program will be re-linked).
# The list of computer software component for your project. This might be
# generated automatically.
CSC_LIST=aa bb cc
# Name of the main program (no extension)
MAIN=main
# If we need to build objects with -fPIC, uncomment the following line
#NEED_FPIC=-fPIC
# The following variable should give the directory containing libgnat.so
# You can get this directory through 'gnatls -v'. This is usually the last
# directory in the Object_Path.
GLIB=…
# The directories for the libraries
# (This macro expands the list of CSC to the list of shared libraries, you
# could simply use the expanded form:
# LIB_DIR=aa/lib/libaa.so bb/lib/libbb.so cc/lib/libcc.so
LIB_DIR=${foreach dir,${CSC_LIST},${dir}/lib/lib${dir}.so}
${MAIN}: objects ${LIB_DIR}
gnatbind ${MAIN} ${CSC_LIST:%=-aO%/lib} -shared
gnatlink ${MAIN} ${CSC_LIST:%=-l%}
objects::
# recompile the sources
gnatmake -c -i ${MAIN}.adb ${NEED_FPIC} ${CSC_LIST:%=-I%}
# Note: In a future version of GNAT, the following commands will be simplified
# by a new tool, gnatmlib
${LIB_DIR}:
mkdir -p ${dir $@ }
cd ${dir $@ } && gcc -shared -o ${notdir $@ } ../*.o -L${GLIB} -lgnat
cd ${dir $@ } && cp -f ../*.ali .
# The dependencies for the modules
# Note that we have to force the expansion of *.o, since in some cases
# make won't be able to do it itself.
aa/lib/libaa.so: ${wildcard aa/*.o}
bb/lib/libbb.so: ${wildcard bb/*.o}
cc/lib/libcc.so: ${wildcard cc/*.o}
# Make sure all of the shared libraries are in the path before starting the
# program
run::
LD_LIBRARY_PATH=`pwd`/aa/lib:`pwd`/bb/lib:`pwd`/cc/lib ./${MAIN}
clean::
${RM} -rf ${CSC_LIST:%=%/lib}
${RM} ${CSC_LIST:%=%/*.ali}
${RM} ${CSC_LIST:%=%/*.o}
${RM} *.o *.ali ${MAIN}
Next: Generating the Command Line Switches, Previous: Using gnatmake in a Makefile, Up: Using the GNU make Utility [Contents][Index]
In most makefiles, you will have to specify a list of directories, and store it in a variable. For small projects, it is often easier to specify each of them by hand, since you then have full control over what is the proper order for these directories, which ones should be included.
However, in larger projects, which might involve hundreds of subdirectories, it might be more convenient to generate this list automatically.
The example below presents two methods. The first one, although less
general, gives you more control over the list. It involves wildcard
characters, that are automatically expanded by make. Its
shortcoming is that you need to explicitly specify some of the
organization of your project, such as for instance the directory tree
depth, whether some directories are found in a separate tree, ...
The second method is the most general one. It requires an external
program, called find, which is standard on all Unix systems. All
the directories found under a given root directory will be added to the
list.
# The examples below are based on the following directory hierarchy: # All the directories can contain any number of files # ROOT_DIRECTORY -> a -> aa -> aaa # -> ab # -> ac # -> b -> ba -> baa # -> bb # -> bc # This Makefile creates a variable called DIRS, that can be reused any time # you need this list (see the other examples in this section) # The root of your project's directory hierarchy ROOT_DIRECTORY=. #### # First method: specify explicitly the list of directories # This allows you to specify any subset of all the directories you need. #### DIRS := a/aa/ a/ab/ b/ba/ #### # Second method: use wildcards # Note that the argument(s) to wildcard below should end with a '/'. # Since wildcards also return file names, we have to filter them out # to avoid duplicate directory names. # We thus use make'sdirandsortfunctions. # It sets DIRs to the following value (note that the directories aaa and baa # are not given, unless you change the arguments to wildcard). # DIRS= ./a/a/ ./b/ ./a/aa/ ./a/ab/ ./a/ac/ ./b/ba/ ./b/bb/ ./b/bc/ #### DIRS := ${sort ${dir ${wildcard ${ROOT_DIRECTORY}/*/ ${ROOT_DIRECTORY}/*/*/}}} #### # Third method: use an external program # This command is much faster if run on local disks, avoiding NFS slowdowns. # This is the most complete command: it sets DIRs to the following value: # DIRS= ./a ./a/aa ./a/aa/aaa ./a/ab ./a/ac ./b ./b/ba ./b/ba/baa ./b/bb ./b/bc #### DIRS := ${shell find ${ROOT_DIRECTORY} -type d -print}
Next: Overcoming Command Line Length Limits, Previous: Automatically Creating a List of Directories, Up: Using the GNU make Utility [Contents][Index]
Once you have created the list of directories as explained in the previous section (see Automatically Creating a List of Directories), you can easily generate the command line arguments to pass to gnatmake.
For the sake of completeness, this example assumes that the source path is not the same as the object path, and that you have two separate lists of directories.
# see "Automatically creating a list of directories" to create
# these variables
SOURCE_DIRS=
OBJECT_DIRS=
GNATMAKE_SWITCHES := ${patsubst %,-aI%,${SOURCE_DIRS}}
GNATMAKE_SWITCHES += ${patsubst %,-aO%,${OBJECT_DIRS}}
all:
gnatmake ${GNATMAKE_SWITCHES} main_unit
Next: Some Useful Memory Pools, Previous: Generating the Command Line Switches, Up: Using the GNU make Utility [Contents][Index]
One problem that might be encountered on big projects is that many operating systems limit the length of the command line. It is thus hard to give gnatmake the list of source and object directories.
This example shows how you can set up environment variables, which will
make gnatmake behave exactly as if the directories had been
specified on the command line, but have a much higher length limit (or
even none on most systems).
It assumes that you have created a list of directories in your Makefile, using one of the methods presented in Automatically Creating a List of Directories. For the sake of completeness, we assume that the object path (where the ALI files are found) is different from the sources patch.
Note a small trick in the Makefile below: for efficiency reasons, we
create two temporary variables (SOURCE_LIST and OBJECT_LIST), that are
expanded immediately by make. This way we overcome the standard
make behavior which is to expand the variables only when they are
actually used.
On Windows, if you are using the standard Windows command shell, you must replace colons with semicolons in the assignments to these variables.
# In this example, we create both ADA_INCLUDE_PATH and ADA_OBJECTS_PATH.
# This is the same thing as putting the -I arguments on the command line.
# (the equivalent of using -aI on the command line would be to define
# only ADA_INCLUDE_PATH, the equivalent of -aO is ADA_OBJECTS_PATH).
# You can of course have different values for these variables.
#
# Note also that we need to keep the previous values of these variables, since
# they might have been set before running 'make' to specify where the GNAT
# library is installed.
# see "Automatically creating a list of directories" to create these
# variables
SOURCE_DIRS=
OBJECT_DIRS=
empty:=
space:=${empty} ${empty}
SOURCE_LIST := ${subst ${space},:,${SOURCE_DIRS}}
OBJECT_LIST := ${subst ${space},:,${OBJECT_DIRS}}
ADA_INCLUDE_PATH += ${SOURCE_LIST}
ADA_OBJECTS_PATH += ${OBJECT_LIST}
export ADA_INCLUDE_PATH
export ADA_OBJECTS_PATH
all:
gnatmake main_unit
Next: Stack Related Facilities, Previous: Using the GNU make Utility, Up: Top [Contents][Index]
This chapter describes some useful memory pools provided in the GNAT library
and in particular the GNAT Debug Pool facility, which can be used to detect
incorrect uses of access values (including “dangling references”).
It also describes the gnatmem tool, which can be used to track down
“memory leaks”.
| • Some Useful Memory Pools: | ||
| • The GNAT Debug Pool Facility: | ||
| • The gnatmem Tool: |
Next: The GNAT Debug Pool Facility, Previous: Overcoming Command Line Length Limits, Up: Memory Management Issues [Contents][Index]
The System.Pool_Global package offers the Unbounded_No_Reclaim_Pool
storage pool. Allocations use the standard system call malloc while
deallocations use the standard system call free. No reclamation is
performed when the pool goes out of scope. For performance reasons, the
standard default Ada allocators/deallocators do not use any explicit storage
pools but if they did, they could use this storage pool without any change in
behavior. That is why this storage pool is used when the user
manages to make the default implicit allocator explicit as in this example:
type T1 is access Something;
-- no Storage pool is defined for T2
type T2 is access Something_Else;
for T2'Storage_Pool use T1'Storage_Pool;
-- the above is equivalent to
for T2'Storage_Pool use System.Pool_Global.Global_Pool_Object;
The System.Pool_Local package offers the Unbounded_Reclaim_Pool storage
pool. The allocation strategy is similar to Pool_Local’s
except that the all
storage allocated with this pool is reclaimed when the pool object goes out of
scope. This pool provides a explicit mechanism similar to the implicit one
provided by several Ada 83 compilers for allocations performed through a local
access type and whose purpose was to reclaim memory when exiting the
scope of a given local access. As an example, the following program does not
leak memory even though it does not perform explicit deallocation:
with System.Pool_Local;
procedure Pooloc1 is
procedure Internal is
type A is access Integer;
X : System.Pool_Local.Unbounded_Reclaim_Pool;
for A'Storage_Pool use X;
v : A;
begin
for I in 1 .. 50 loop
v := new Integer;
end loop;
end Internal;
begin
for I in 1 .. 100 loop
Internal;
end loop;
end Pooloc1;
The System.Pool_Size package implements the Stack_Bounded_Pool used when
Storage_Size is specified for an access type.
The whole storage for the pool is
allocated at once, usually on the stack at the point where the access type is
elaborated. It is automatically reclaimed when exiting the scope where the
access type is defined. This package is not intended to be used directly by the
user and it is implicitly used for each such declaration:
type T1 is access Something; for T1'Storage_Size use 10_000;
Next: The gnatmem Tool, Previous: Some Useful Memory Pools, Up: Memory Management Issues [Contents][Index]
The use of unchecked deallocation and unchecked conversion can easily
lead to incorrect memory references. The problems generated by such
references are usually difficult to tackle because the symptoms can be
very remote from the origin of the problem. In such cases, it is
very helpful to detect the problem as early as possible. This is the
purpose of the Storage Pool provided by GNAT.Debug_Pools.
In order to use the GNAT specific debugging pool, the user must associate a debug pool object with each of the access types that may be related to suspected memory problems. See Ada Reference Manual 13.11.
type Ptr is access Some_Type; Pool : GNAT.Debug_Pools.Debug_Pool; for Ptr'Storage_Pool use Pool;
GNAT.Debug_Pools is derived from a GNAT-specific kind of
pool: the Checked_Pool. Such pools, like standard Ada storage pools,
allow the user to redefine allocation and deallocation strategies. They
also provide a checkpoint for each dereference, through the use of
the primitive operation Dereference which is implicitly called at
each dereference of an access value.
Once an access type has been associated with a debug pool, operations on values of the type may raise four distinct exceptions, which correspond to four potential kinds of memory corruption:
GNAT.Debug_Pools.Accessing_Not_Allocated_Storage
GNAT.Debug_Pools.Accessing_Deallocated_Storage
GNAT.Debug_Pools.Freeing_Not_Allocated_Storage
GNAT.Debug_Pools.Freeing_Deallocated_Storage
For types associated with a Debug_Pool, dynamic allocation is performed using
the standard GNAT allocation routine. References to all allocated chunks of
memory are kept in an internal dictionary. Several deallocation strategies are
provided, whereupon the user can choose to release the memory to the system,
keep it allocated for further invalid access checks, or fill it with an easily
recognizable pattern for debug sessions. The memory pattern is the old IBM
hexadecimal convention: 16#DEADBEEF#.
See the documentation in the file g-debpoo.ads for more information on the various strategies.
Upon each dereference, a check is made that the access value denotes a
properly allocated memory location. Here is a complete example of use of
Debug_Pools, that includes typical instances of memory corruption:
with Gnat.Io; use Gnat.Io;
with Unchecked_Deallocation;
with Unchecked_Conversion;
with GNAT.Debug_Pools;
with System.Storage_Elements;
with Ada.Exceptions; use Ada.Exceptions;
procedure Debug_Pool_Test is
type T is access Integer;
type U is access all T;
P : GNAT.Debug_Pools.Debug_Pool;
for T'Storage_Pool use P;
procedure Free is new Unchecked_Deallocation (Integer, T);
function UC is new Unchecked_Conversion (U, T);
A, B : aliased T;
procedure Info is new GNAT.Debug_Pools.Print_Info(Put_Line);
begin
Info (P);
A := new Integer;
B := new Integer;
B := A;
Info (P);
Free (A);
begin
Put_Line (Integer'Image(B.all));
exception
when E : others => Put_Line ("raised: " & Exception_Name (E));
end;
begin
Free (B);
exception
when E : others => Put_Line ("raised: " & Exception_Name (E));
end;
B := UC(A'Access);
begin
Put_Line (Integer'Image(B.all));
exception
when E : others => Put_Line ("raised: " & Exception_Name (E));
end;
begin
Free (B);
exception
when E : others => Put_Line ("raised: " & Exception_Name (E));
end;
Info (P);
end Debug_Pool_Test;
The debug pool mechanism provides the following precise diagnostics on the execution of this erroneous program:
Debug Pool info: Total allocated bytes : 0 Total deallocated bytes : 0 Current Water Mark: 0 High Water Mark: 0 Debug Pool info: Total allocated bytes : 8 Total deallocated bytes : 0 Current Water Mark: 8 High Water Mark: 8 raised: GNAT.DEBUG_POOLS.ACCESSING_DEALLOCATED_STORAGE raised: GNAT.DEBUG_POOLS.FREEING_DEALLOCATED_STORAGE raised: GNAT.DEBUG_POOLS.ACCESSING_NOT_ALLOCATED_STORAGE raised: GNAT.DEBUG_POOLS.FREEING_NOT_ALLOCATED_STORAGE Debug Pool info: Total allocated bytes : 8 Total deallocated bytes : 4 Current Water Mark: 4 High Water Mark: 8
Next: Stack Overflow Checking, Previous: The GNAT Debug Pool Facility, Up: Memory Management Issues [Contents][Index]
gnatmem ToolThe gnatmem utility monitors dynamic allocation and
deallocation activity in a program, and displays information about
incorrect deallocations and possible sources of memory leaks.
It is designed to work in association with a static runtime library
only and in this context provides three types of information:
| • Running gnatmem: | ||
| • Switches for gnatmem: | ||
| • Example of gnatmem Usage: |
Next: Switches for gnatmem, Previous: Dynamic Stack Usage Analysis, Up: The gnatmem Tool [Contents][Index]
gnatmemgnatmem makes use of the output created by the special version of
allocation and deallocation routines that record call information. This
allows to obtain accurate dynamic memory usage history at a minimal cost to
the execution speed. Note however, that gnatmem is not supported on
all platforms (currently, it is supported on AIX, HP-UX, GNU/Linux,
Solaris and Windows NT/2000/XP (x86).
The gnatmem command has the form
$ gnatmem [switches] user_program
The program must have been linked with the instrumented version of the allocation and deallocation routines. This is done by linking with the libgmem.a library. For correct symbolic backtrace information, the user program should be compiled with debugging options (see Switches for gcc). For example to build my_program:
$ gnatmake -g my_program -largs -lgmem
As library libgmem.a contains an alternate body for package
System.Memory, s-memory.adb should not be compiled and linked
when an executable is linked with library libgmem.a. It is then not
recommended to use gnatmake with switch -a.
When my_program is executed, the file gmem.out is produced.
This file contains information about all allocations and deallocations
performed by the program. It is produced by the instrumented allocations and
deallocations routines and will be used by gnatmem.
In order to produce symbolic backtrace information for allocations and deallocations performed by the GNAT run-time library, you need to use a version of that library that has been compiled with the -g switch (see Rebuilding the GNAT Run-Time Library).
Gnatmem must be supplied with the gmem.out file and the executable to
examine. If the location of gmem.out file was not explicitly supplied by
-i switch, gnatmem will assume that this file can be found in the
current directory. For example, after you have executed my_program,
gmem.out can be analyzed by gnatmem using the command:
$ gnatmem my_program
This will produce the output with the following format:
*************** debut cc
$ gnatmem my_program Global information ------------------ Total number of allocations : 45 Total number of deallocations : 6 Final Water Mark (non freed mem) : 11.29 Kilobytes High Water Mark : 11.40 Kilobytes . . . Allocation Root # 2 ------------------- Number of non freed allocations : 11 Final Water Mark (non freed mem) : 1.16 Kilobytes High Water Mark : 1.27 Kilobytes Backtrace : my_program.adb:23 my_program.alloc . . .
The first block of output gives general information. In this case, the
Ada construct “new” was executed 45 times, and only 6 calls to an
Unchecked_Deallocation routine occurred.
Subsequent paragraphs display information on all allocation roots.
An allocation root is a specific point in the execution of the program
that generates some dynamic allocation, such as a “new”
construct. This root is represented by an execution backtrace (or subprogram
call stack). By default the backtrace depth for allocations roots is 1, so
that a root corresponds exactly to a source location. The backtrace can
be made deeper, to make the root more specific.
Next: Example of gnatmem Usage, Previous: Running gnatmem, Up: The gnatmem Tool [Contents][Index]
gnatmemgnatmem recognizes the following switches:
Quiet. Gives the minimum output needed to identify the origin of the memory leaks. Omits statistical information.
N is an integer literal (usually between 1 and 10) which controls the depth of the backtraces defining allocation root. The default value for N is 1. The deeper the backtrace, the more precise the localization of the root. Note that the total number of roots can depend on this parameter. This parameter must be specified before the name of the executable to be analyzed, to avoid ambiguity.
This switch has the same effect as just depth parameter.
Do the gnatmem processing starting from file, rather than
gmem.out in the current directory.
This switch causes gnatmem to mask the allocation roots that have less
than n leaks. The default value is 1. Specifying the value of 0 will allow to
examine even the roots that didn’t result in leaks.
This switch causes gnatmem to sort the allocation roots according to the
specified order of sort criteria, each identified by a single letter. The
currently supported criteria are n, h, w standing respectively for
number of unfreed allocations, high watermark, and final watermark
corresponding to a specific root. The default order is nwh.
Next: Running gnatstub, Previous: Switches for gnatmem, Up: The gnatmem Tool [Contents][Index]
gnatmem UsageThe following example shows the use of gnatmem
on a simple memory-leaking program.
Suppose that we have the following Ada program:
with Unchecked_Deallocation;
procedure Test_Gm is
type T is array (1..1000) of Integer;
type Ptr is access T;
procedure Free is new Unchecked_Deallocation (T, Ptr);
A : Ptr;
procedure My_Alloc is
begin
A := new T;
end My_Alloc;
procedure My_DeAlloc is
B : Ptr := A;
begin
Free (B);
end My_DeAlloc;
begin
My_Alloc;
for I in 1 .. 5 loop
for J in I .. 5 loop
My_Alloc;
end loop;
My_Dealloc;
end loop;
end;
|
The program needs to be compiled with debugging option and linked with
gmem library:
$ gnatmake -g test_gm -largs -lgmem
Then we execute the program as usual:
$ test_gm
Then gnatmem is invoked simply with
$ gnatmem test_gm
which produces the following output (result may vary on different platforms):
Global information ------------------ Total number of allocations : 18 Total number of deallocations : 5 Final Water Mark (non freed mem) : 53.00 Kilobytes High Water Mark : 56.90 Kilobytes Allocation Root # 1 ------------------- Number of non freed allocations : 11 Final Water Mark (non freed mem) : 42.97 Kilobytes High Water Mark : 46.88 Kilobytes Backtrace : test_gm.adb:11 test_gm.my_alloc Allocation Root # 2 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 10.02 Kilobytes High Water Mark : 10.02 Kilobytes Backtrace : s-secsta.adb:81 system.secondary_stack.ss_init Allocation Root # 3 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 12 Bytes High Water Mark : 12 Bytes Backtrace : s-secsta.adb:181 system.secondary_stack.ss_init
Note that the GNAT run time contains itself a certain number of allocations that have no corresponding deallocation, as shown here for root #2 and root #3. This is a normal behavior when the number of non-freed allocations is one, it allocates dynamic data structures that the run time needs for the complete lifetime of the program. Note also that there is only one allocation root in the user program with a single line back trace: test_gm.adb:11 test_gm.my_alloc, whereas a careful analysis of the program shows that ’My_Alloc’ is called at 2 different points in the source (line 21 and line 24). If those two allocation roots need to be distinguished, the backtrace depth parameter can be used:
$ gnatmem 3 test_gm
which will give the following output:
Global information ------------------ Total number of allocations : 18 Total number of deallocations : 5 Final Water Mark (non freed mem) : 53.00 Kilobytes High Water Mark : 56.90 Kilobytes Allocation Root # 1 ------------------- Number of non freed allocations : 10 Final Water Mark (non freed mem) : 39.06 Kilobytes High Water Mark : 42.97 Kilobytes Backtrace : test_gm.adb:11 test_gm.my_alloc test_gm.adb:24 test_gm b_test_gm.c:52 main Allocation Root # 2 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 10.02 Kilobytes High Water Mark : 10.02 Kilobytes Backtrace : s-secsta.adb:81 system.secondary_stack.ss_init s-secsta.adb:283 <system__secondary_stack___elabb> b_test_gm.c:33 adainit Allocation Root # 3 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 3.91 Kilobytes High Water Mark : 3.91 Kilobytes Backtrace : test_gm.adb:11 test_gm.my_alloc test_gm.adb:21 test_gm b_test_gm.c:52 main Allocation Root # 4 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 12 Bytes High Water Mark : 12 Bytes Backtrace : s-secsta.adb:181 system.secondary_stack.ss_init s-secsta.adb:283 <system__secondary_stack___elabb> b_test_gm.c:33 adainit
The allocation root #1 of the first example has been split in 2 roots #1 and #3 thanks to the more precise associated backtrace.
Next: Verifying Properties Using gnatcheck, Previous: Memory Management Issues, Up: Top [Contents][Index]
This chapter describes some useful tools associated with stack checking and analysis. In particular, it deals with dynamic and static stack usage measurements.
| • Stack Overflow Checking: | ||
| • Static Stack Usage Analysis: | ||
| • Dynamic Stack Usage Analysis: |
Next: Static Stack Usage Analysis, Previous: The gnatmem Tool, Up: Stack Related Facilities [Contents][Index]
For most operating systems, gcc does not perform stack overflow
checking by default. This means that if the main environment task or
some other task exceeds the available stack space, then unpredictable
behavior will occur. Most native systems offer some level of protection by
adding a guard page at the end of each task stack. This mechanism is usually
not enough for dealing properly with stack overflow situations because
a large local variable could “jump” above the guard page.
Furthermore, when the
guard page is hit, there may not be any space left on the stack for executing
the exception propagation code. Enabling stack checking avoids
such situations.
To activate stack checking, compile all units with the gcc option -fstack-check. For example:
gcc -c -fstack-check package1.adb
Units compiled with this option will generate extra instructions to check
that any use of the stack (for procedure calls or for declaring local
variables in declare blocks) does not exceed the available stack space.
If the space is exceeded, then a Storage_Error exception is raised.
For declared tasks, the stack size is controlled by the size
given in an applicable Storage_Size pragma or by the value specified
at bind time with -d (see Switches for gnatbind) or is set to
the default size as defined in the GNAT runtime otherwise.
For the environment task, the stack size depends on
system defaults and is unknown to the compiler. Stack checking
may still work correctly if a fixed
size stack is allocated, but this cannot be guaranteed.
To ensure that a clean exception is signalled for stack
overflow, set the environment variable
GNAT_STACK_LIMIT to indicate the maximum
stack area that can be used, as in:
SET GNAT_STACK_LIMIT 1600
The limit is given in kilobytes, so the above declaration would set the stack limit of the environment task to 1.6 megabytes. Note that the only purpose of this usage is to limit the amount of stack used by the environment task. If it is necessary to increase the amount of stack for the environment task, then this is an operating systems issue, and must be addressed with the appropriate operating systems commands.
Next: Dynamic Stack Usage Analysis, Previous: Stack Overflow Checking, Up: Stack Related Facilities [Contents][Index]
A unit compiled with -fstack-usage will generate an extra file that specifies the maximum amount of stack used, on a per-function basis. The file has the same basename as the target object file with a .su extension. Each line of this file is made up of three fields:
static, dynamic, bounded.
The second field corresponds to the size of the known part of the function frame.
The qualifier static means that the function frame size
is purely static.
It usually means that all local variables have a static size.
In this case, the second field is a reliable measure of the function stack
utilization.
The qualifier dynamic means that the function frame size is not static.
It happens mainly when some local variables have a dynamic size. When this
qualifier appears alone, the second field is not a reliable measure
of the function stack analysis. When it is qualified with bounded, it
means that the second field is a reliable maximum of the function stack
utilization.
A unit compiled with -Wstack-usage will issue a warning for each subprogram whose stack usage might be larger than the specified amount of bytes. The wording is in keeping with the qualifier documented above.
Next: Running gnatmem, Previous: Static Stack Usage Analysis, Up: Stack Related Facilities [Contents][Index]
It is possible to measure the maximum amount of stack used by a task, by
adding a switch to gnatbind, as:
$ gnatbind -u0 file
With this option, at each task termination, its stack usage is output on stderr. It is not always convenient to output the stack usage when the program is still running. Hence, it is possible to delay this output until program termination. for a given number of tasks specified as the argument of the -u option. For instance:
$ gnatbind -u100 file
will buffer the stack usage information of the first 100 tasks to terminate and output this info at program termination. Results are displayed in four columns:
Index | Task Name | Stack Size | Stack Usage
where:
is a number associated with each task.
is the name of the task analyzed.
is the maximum size for the stack.
is the measure done by the stack analyzer. In order to prevent overflow, the stack is not entirely analyzed, and it’s not possible to know exactly how much has actually been used.
The environment task stack, e.g., the stack that contains the main unit, is only processed when the environment variable GNAT_STACK_LIMIT is set.
The package GNAT.Task_Stack_Usage provides facilities to get
stack usage reports at run-time. See its body for the details.
Next: Creating Sample Bodies Using gnatstub, Previous: Stack Related Facilities, Up: Top [Contents][Index]
gnatcheckThe gnatcheck tool is an ASIS-based utility that checks properties
of Ada source files according to a given set of semantic rules.
In order to check compliance with a given rule, gnatcheck has to
semantically analyze the Ada sources.
Therefore, checks can only be performed on
legal Ada units. Moreover, when a unit depends semantically upon units located
outside the current directory, the source search path has to be provided when
calling gnatcheck, either through a specified project file or
through gnatcheck switches.
For full details, refer to GNATcheck Reference Manual document.
Next: Creating Unit Tests Using gnattest, Previous: Verifying Properties Using gnatcheck, Up: Top [Contents][Index]
gnatstubgnatstub creates body stubs, that is, empty but compilable bodies
for library unit declarations.
Note: to invoke gnatstub with a project file, use the gnat
driver (see The GNAT Driver and Project Files).
To create a body stub, gnatstub has to compile the library
unit declaration. Therefore, bodies can be created only for legal
library units. Moreover, if a library unit depends semantically upon
units located outside the current directory, you have to provide
the source search path when calling gnatstub, see the description
of gnatstub switches below.
By default, all the program unit body stubs generated by gnatstub
raise the predefined Program_Error exception, which will catch
accidental calls of generated stubs. This behavior can be changed with
option --no-exception (see below).
| • Running gnatstub: | ||
| • Switches for gnatstub: |
Next: Switches for gnatstub, Previous: Example of gnatmem Usage, Up: Creating Sample Bodies Using gnatstub [Contents][Index]
gnatstubgnatstub has a command-line interface of the form:
$ gnatstub [switches] filename [directory] [-cargs gcc_switches]
where
is the name of the source file that contains a library unit declaration
for which a body must be created. The file name may contain the path
information.
The file name does not have to follow the GNAT file name conventions. If the
name
does not follow GNAT file naming conventions, the name of the body file must
be provided
explicitly as the value of the -obody-name option.
If the file name follows the GNAT file naming
conventions and the name of the body file is not provided,
gnatstub
creates the name
of the body file from the argument file name by replacing the .ads
suffix
with the .adb suffix.
indicates the directory in which the body stub is to be placed (the default is the current directory)
gcc. They will be passed on to all compiler invocations made by
gnatstub to generate the ASIS trees. Here you can provide
-I switches to form the source search path,
use the -gnatec switch to set the configuration file,
use the -gnat05 switch if sources should be compiled in
Ada 2005 mode etc.
is an optional sequence of switches as described in the next section
Next: Running gnattest, Previous: Running gnatstub, Up: Creating Sample Bodies Using gnatstub [Contents][Index]
gnatstubIf the destination directory already contains a file with the name of the body file for the argument spec file, replace it with the generated body stub.
Put the comment header (i.e., all the comments preceding the compilation unit) from the source of the library unit declaration into the body stub.
Put a sample comment header into the body stub.
Use the content of the file as the comment header for a generated body stub.
These switches have the same meaning as in calls to
gcc.
They define the source search path in the call to
gcc issued
by gnatstub to compile an argument source file.
This switch has the same meaning as in calls to gcc.
It defines the additional configuration file to be passed to the call to
gcc issued
by gnatstub to compile an argument source file.
(n is a non-negative integer). Set the maximum line length in the body stub to n; the default is 79. The maximum value that can be specified is 32767. Note that in the special case of configuration pragma files, the maximum is always 32767 regardless of whether or not this switch appears.
(n is a non-negative integer from 1 to 9). Set the indentation level in the generated body sample to n. The default indentation is 3.
Order local bodies alphabetically. (By default local bodies are ordered in the same way as the corresponding local specs in the argument spec file.)
Same as -gnatyn
Do not remove the tree file (i.e., the snapshot of the compiler internal
structures used by gnatstub) after creating the body stub.
Same as -gnatyMn
Avoid raising PROGRAM_ERROR in the generated bodies of program unit stubs. This is not always possible for function stubs.
Do not place local comment header with unit name before body stub for a unit.
Body file name. This should be set if the argument file name does not follow the GNAT file naming conventions. If this switch is omitted the default name for the body will be obtained from the argument file name according to the GNAT file naming conventions.
Quiet mode: do not generate a confirmation when a body is successfully created, and do not generate a message when a body is not required for an argument unit.
Reuse the tree file (if it exists) instead of creating it. Instead of
creating the tree file for the library unit declaration, gnatstub
tries to find it in the current directory and use it for creating
a body. If the tree file is not found, no body is created. This option
also implies -k, whether or not
the latter is set explicitly.
Overwrite the existing tree file. If the current directory already
contains the file which, according to the GNAT file naming rules should
be considered as a tree file for the argument source file,
gnatstub
will refuse to create the tree file needed to create a sample body
unless this option is set.
Verbose mode: generate version information.
Next: Performing Dimensionality Analysis in GNAT, Previous: Creating Sample Bodies Using gnatstub, Up: Top [Contents][Index]
gnattestgnattest is an ASIS-based utility that creates unit-test skeletons
as well as a test driver infrastructure (harness). gnattest creates
a skeleton for each visible subprogram in the packages under consideration when
they do not exist already.
In order to process source files from a project, gnattest has to
semantically analyze the sources. Therefore, test skeletons can only be
generated for legal Ada units. If a unit is dependent on other units,
those units should be among the source files of the project or of other projects
imported by this one.
Generated skeletons and harnesses are based on the AUnit testing framework.
AUnit is an Ada adaptation of the xxxUnit testing frameworks, similar to JUnit
for Java or CppUnit for C++. While it is advised that gnattest users read
the AUnit manual, deep knowledge of AUnit is not necessary for using gnattest.
For correct operation of gnattest, AUnit should be installed and
aunit.gpr must be on the project path. This happens automatically when Aunit
is installed at its default location.
Next: Switches for gnattest, Previous: Switches for gnatstub, Up: Creating Unit Tests Using gnattest [Contents][Index]
gnattestgnattest has a command-line interface of the form
$ gnattest -Pprojname [--harness-dir=dirname] [switches] [filename] [-cargs gcc_switches]
where
specifies the project defining the location of source files. When no file names are provided on the command line, all sources in the project are used as input. This switch is required.
is the name of the source file containing the library unit package declaration for which a test package will be created. The file name may be given with a path.
is a list of switches for
gcc. These switches will be passed on to all compiler invocations
made by gnattest to generate a set of ASIS trees. Here you can provide
-I switches to form the source search path,
use the -gnatec switch to set the configuration file,
use the -gnat05 switch if sources should be compiled in
Ada 2005 mode, etc.
is an optional sequence of switches as described in the next section.
gnattest results can be found in two different places.
test_driver.gpr. Tests can be compiled and run
using a command such as:
gnatmake -P<harness-dir>/test_driver test_runner
Note that you might need to specify the necessary values of scenario variables when you are not using the AUnit defaults.
Note that if the project already has both my_unit.ads and my_unit-test_data.ads, this will cause a name conflict with the generated test package.
Next: Project Attributes for gnattest, Previous: Running gnattest, Up: Creating Unit Tests Using gnattest [Contents][Index]
gnattestWhen this option is given, gnattest creates a harness for all
sources, treating them as test packages.
Sources described in projname are considered potential additional manual tests to be added to the test suite.
Recursively consider all sources from all projects.
Indicate that external variable name has the value value.
Suppresses noncritical output messages.
Verbose mode: generates version information.
Enables substitution check: run all tests from all parents in order to check substitutability.
Specifies the default behavior of generated skeletons. val can be either "fail" or "pass", "fail" being the default.
The directory hierarchy of tested sources is recreated in the dirname directory, and test packages are placed in corresponding directories. If the dirname is a relative path, it is considered relative to the object directory of the project file. When all sources from all projects are taken recursively from all projects, directory hierarchies of tested sources are recreated for each project in their object directories and test packages are placed accordingly.
Test packages are placed in subdirectories.
All test packages are placed in the dirname directory. If the dirname is a relative path, it is considered relative to the object directory of the project file. When all sources from all projects are taken recursively from all projects, dirname directories are created for each project in their object directories and test packages are placed accordingly.
specifies the directory that will hold the harness packages and project file for the test driver. If the dirname is a relative path, it is considered relative to the object directory of the project file.
Bodies of all test routines are generated as separates. Note that this mode is kept for compatibility reasons only and it is not advised to use it due to possible problems with hash in names of test skeletons when using an inconsistent casing. Separate test skeletons can be incorporated to monolith test package with improved hash being used by using --transition switch.
This allows transition from separate test routines to monolith test packages. All matching test routines are overwritten with contents of corresponding separates. Note that if separate test routines had any manually added with clauses they will be moved to the test package body as is and have to be moved by hand.
--tests_root, --subdir and --tests-dir switches are mutually exclusive.
Next: Simple Example, Previous: Switches for gnattest, Up: Creating Unit Tests Using gnattest [Contents][Index]
gnattestMost of the command-line options can also be passed to the tool by adding special attributes to the project file. Those attributes should be put in package gnattest. Here is the list of attributes:
Each of those attributes can be overridden from the command line if needed.
Other gnattest switches can also be passed via the project
file as an attribute list called GNATtest_Switches.
Next: Setting Up and Tearing Down the Testing Environment, Previous: Project Attributes for gnattest, Up: Creating Unit Tests Using gnattest [Contents][Index]
Let’s take a very simple example using the first gnattest example
located in:
<install_prefix>/share/examples/gnattest/simple
This project contains a simple package containing one subprogram. By running gnattest:
$ gnattest --harness-dir=driver -Psimple.gpr
a test driver is created in directory "driver". It can be compiled and run:
$ cd driver $ gprbuild -Ptest_driver $ test_runner
One failed test with diagnosis "test not implemented" is reported. Since no special output option was specified, the test package Simple.Tests is located in:
<install_prefix>/share/examples/gnattest/simple/obj/gnattest/tests
For each package containing visible subprograms, a child test package is generated. It contains one test routine per tested subprogram. Each declaration of a test subprogram has a comment specifying which tested subprogram it corresponds to. Bodies of test routines are placed in test package bodies and are surrounded by special comment sections. Those comment sections should not be removed or modified in order for gnattest to be able to regenerate test packages and keep already written tests in place. The test routine Test_Inc_5eaee3 located at simple-test_data-tests.adb contains a single statement: a call to procedure Assert. It has two arguments: the Boolean expression we want to check and the diagnosis message to display if the condition is false.
That is where actual testing code should be written after a proper setup. An actual check can be performed by replacing the Assert call with:
Assert (Inc (1) = 2, "wrong incrementation");
After recompiling and running the test driver, one successfully passed test is reported.
Next: Regenerating Tests, Previous: Simple Example, Up: Creating Unit Tests Using gnattest [Contents][Index]
Besides test routines themselves, each test package has a parent package Test_Data that has two procedures: Set_Up and Tear_Down. This package is never overwritten by the tool. Set_Up is called before each test routine of the package and Tear_Down is called after each test routine. Those two procedures can be used to perform necessary initialization and finalization, memory allocation, etc. Test type declared in Test_Data package is parent type for the test type of test package and can have user-defined components whose values can be set by Set_Up routine and used in test routines afterwards.
Next: Default Test Behavior, Previous: Setting Up and Tearing Down the Testing Environment, Up: Creating Unit Tests Using gnattest [Contents][Index]
Bodies of test routines and test_data packages are never overridden after they have been created once. As long as the name of the subprogram, full expanded Ada names, and the order of its parameters is the same, and comment sections are intact the old test routine will fit in its place and no test skeleton will be generated for the subprogram.
This can be demonstrated with the previous example. By uncommenting declaration
and body of function Dec in simple.ads and simple.adb, running
gnattest on the project, and then running the test driver:
gnattest --harness-dir=driver -Psimple.gpr cd driver gprbuild -Ptest_driver test_runner
the old test is not replaced with a stub, nor is it lost, but a new test skeleton is created for function Dec.
The only way of regenerating tests skeletons is to remove the previously created tests together with corresponding comment sections.
Next: Testing Primitive Operations of Tagged Types, Previous: Regenerating Tests, Up: Creating Unit Tests Using gnattest [Contents][Index]
The generated test driver can treat unimplemented tests in two ways: either count them all as failed (this is useful to see which tests are still left to implement) or as passed (to sort out unimplemented ones from those actually failing).
The test driver accepts a switch to specify this behavior:
–skeleton-default=val, where val is either "pass" or "fail" (exactly as for
gnattest).
The default behavior of the test driver is set with the same switch as passed to gnattest when generating the test driver.
Passing it to the driver generated on the first example:
test_runner --skeleton-default=pass
makes both tests pass, even the unimplemented one.
Next: Testing Inheritance, Previous: Default Test Behavior, Up: Creating Unit Tests Using gnattest [Contents][Index]
Creation of test skeletons for primitive operations of tagged types entails a number of features. Test routines for all primitives of a given tagged type are placed in a separate child package named according to the tagged type. For example, if you have tagged type T in package P, all tests for primitives of T will be in P.T_Test_Data.T_Tests.
Consider running gnattest on the second example (note: actual tests for this example already exist, so there’s no need to worry if the tool reports that no new stubs were generated):
cd <install_prefix>/share/examples/gnattest/tagged_rec gnattest --harness-dir=driver -Ptagged_rec.gpr
Taking a closer look at the test type declared in the test package Speed1.Controller_Test_Data is necessary. It is declared in:
<install_prefix>/share/examples/gnattest/tagged_rec/obj/gnattest/tests
Test types are direct or indirect descendants of AUnit.Test_Fixtures.Test_Fixture type. In the case of nonprimitive tested subprograms, the user doesn’t need to be concerned with them. However, when generating test packages for primitive operations, there are some things the user needs to know.
Type Test_Controller has components that allow assignment of various derivations of type Controller. And if you look at the specification of package Speed2.Auto_Controller, you will see that Test_Auto_Controller actually derives from Test_Controller rather than AUnit type Test_Fixture. Thus, test types mirror the hierarchy of tested types.
The Set_Up procedure of Test_Data package corresponding to a test package of primitive operations of type T assigns to Fixture a reference to an object of that exact type T. Notice, however, that if the tagged type has discriminants, the Set_Up only has a commented template for setting up the fixture, since filling the discriminant with actual value is up to the user.
The knowledge of the structure of test types allows additional testing without additional effort. Those possibilities are described below.
Next: Tagged Types Substitutability Testing, Previous: Testing Primitive Operations of Tagged Types, Up: Creating Unit Tests Using gnattest [Contents][Index]
Since the test type hierarchy mimics the hierarchy of tested types, the inheritance of tests takes place. An example of such inheritance can be seen by running the test driver generated for the second example. As previously mentioned, actual tests are already written for this example.
cd driver gprbuild -Ptest_driver test_runner
There are 6 passed tests while there are only 5 testable subprograms. The test routine for function Speed has been inherited and run against objects of the derived type.
Next: Testing with Contracts, Previous: Testing Inheritance, Up: Creating Unit Tests Using gnattest [Contents][Index]
Tagged Types Substitutability Testing is a way of verifying the global type consistency by testing. Global type consistency is a principle stating that if S is a subtype of T (in Ada, S is a derived type of tagged type T), then objects of type T may be replaced with objects of type S (that is, objects of type S may be substituted for objects of type T), without altering any of the desirable properties of the program. When the properties of the program are expressed in the form of subprogram preconditions and postconditions (let’s call them pre and post), the principle is formulated as relations between the pre and post of primitive operations and the pre and post of their derived operations. The pre of a derived operation should not be stronger than the original pre, and the post of the derived operation should not be weaker than the original post. Those relations ensure that verifying if a dispatching call is safe can be done just by using the pre and post of the root operation.
Verifying global type consistency by testing consists of running all the unit tests associated with the primitives of a given tagged type with objects of its derived types.
In the example used in the previous section, there was clearly a violation of type consistency. The overriding primitive Adjust_Speed in package Speed2 removes the functionality of the overridden primitive and thus doesn’t respect the consistency principle. Gnattest has a special option to run overridden parent tests against objects of the type which have overriding primitives:
gnattest --harness-dir=driver --validate-type-extensions -Ptagged_rec.gpr cd driver gprbuild -Ptest_driver test_runner
While all the tests pass by themselves, the parent test for Adjust_Speed fails against objects of the derived type.
Non-overridden tests are already inherited for derived test types, so the –validate-type-extensions enables the application of overriden tests to objects of derived types.
Next: Additional Tests, Previous: Tagged Types Substitutability Testing, Up: Creating Unit Tests Using gnattest [Contents][Index]
gnattest supports pragmas Precondition, Postcondition, and Test_Case,
as well as corresponding aspects.
Test routines are generated, one per each Test_Case associated with a tested
subprogram. Those test routines have special wrappers for tested functions
that have composition of pre- and postcondition of the subprogram with
"requires" and "ensures" of the Test_Case (depending on the mode, pre and post
either count for Nominal mode or do not count for Robustness mode).
The third example demonstrates how this works:
cd <install_prefix>/share/examples/gnattest/contracts gnattest --harness-dir=driver -Pcontracts.gpr
Putting actual checks within the range of the contract does not cause any error reports. For example, for the test routine which corresponds to test case 1:
Assert (Sqrt (9.0) = 3.0, "wrong sqrt");
and for the test routine corresponding to test case 2:
Assert (Sqrt (-5.0) = -1.0, "wrong error indication");
are acceptable:
cd driver gprbuild -Ptest_driver test_runner
However, by changing 9.0 to 25.0 and 3.0 to 5.0, for example, you can get a precondition violation for test case one. Also, by using any otherwise correct but positive pair of numbers in the second test routine, you can also get a precondition violation. Postconditions are checked and reported the same way.
Next: Support for other platforms/run-times, Previous: Testing with Contracts, Up: Creating Unit Tests Using gnattest [Contents][Index]
gnattest can add user-written tests to the main suite of the test
driver. gnattest traverses the given packages and searches for test
routines. All procedures with a single in out parameter of a type which is
derived from AUnit.Test_Fixtures.Test_Fixture and that are declared in package
specifications are added to the suites and are then executed by the test driver.
(Set_Up and Tear_Down are filtered out.)
An example illustrates two ways of creating test harnesses for user-written tests. Directory additional_tests contains an AUnit-based test driver written by hand.
<install_prefix>/share/examples/gnattest/additional_tests/
To create a test driver for already-written tests, use the –harness-only option:
gnattest -Padditional/harness/harness.gpr --harness-dir=harness_only \ --harness-only gnatmake -Pharness_only/test_driver.gpr harness_only/test_runner
Additional tests can also be executed together with generated tests:
gnattest -Psimple.gpr --additional-tests=additional/harness/harness.gpr \ --harness-dir=mixing gnatmake -Pmixing/test_driver.gpr mixing/test_runner
Next: Current Limitations, Previous: Additional Tests, Up: Creating Unit Tests Using gnattest [Contents][Index]
gnattest can be used to generate the test harness for platforms
and run-time libraries others than the default native target with the
default full run-time. For example, when using a limited run-time library
such as Zero FootPrint (ZFP), a simplified harness is generated.
Two variables are used to tell the underlying AUnit framework how to generate
the test harness: PLATFORM, which identifies the target, and
RUNTIME, used to determine the run-time library for which the harness
is generated. Corresponding prefix should also be used when calling
gnattest for non-native targets. For example, the following options
are used to generate the AUnit test harness for a PowerPC ELF target using
the ZFP run-time library:
powerpc-elf-gnattest -Psimple.gpr -XPLATFORM=powerpc-elf -XRUNTIME=zfp
Next: Using Other Utility Programs with GNAT, Previous: Support for other platforms/run-times, Up: Creating Unit Tests Using gnattest [Contents][Index]
The tool currently does not support following features:
Next: Generating Ada Bindings for C and C++ headers, Previous: Creating Unit Tests Using gnattest, Up: Top [Contents][Index]
The GNAT compiler now supports dimensionality checking. The user can specify physical units for objects, and the compiler will verify that uses of these objects are compatible with their dimensions, in a fashion that is familiar to engineering practice. The dimensions of algebraic expressions (including powers with static exponents) are computed from their consistuents.
This feature depends on Ada 2012 aspect specifications, and is available from version 7.0.1 of GNAT onwards. The GNAT-specific aspect Dimension_System allows the user to define a system of units; the aspect Dimension then allows the user to declare dimensioned quantities within a given system.
The major advantage of this model is that it does not require the declaration of multiple operators for all possible combinations of types: it is only necessary to use the proper subtypes in object declarations.
The simplest way to impose dimensionality checking on a computation is to make use of the package System.Dim.Mks, which is part of the GNAT library. This package defines a floating-point type MKS_Type, for which a sequence of dimension names are specified, together with their conventional abbreviations. The following should be read together with the full specification of the package, in file s-dimmks.ads.
type Mks_Type is new Long_Long_Float
with
Dimension_System => (
(Unit_Name => Meter, Unit_Symbol => 'm', Dim_Symbol => 'L'),
(Unit_Name => Kilogram, Unit_Symbol => "kg", Dim_Symbol => 'M'),
(Unit_Name => Second, Unit_Symbol => 's', Dim_Symbol => 'T'),
(Unit_Name => Ampere, Unit_Symbol => 'A', Dim_Symbol => 'I'),
(Unit_Name => Kelvin, Unit_Symbol => 'K', Dim_Symbol => "Theta"),
(Unit_Name => Mole, Unit_Symbol => "mol", Dim_Symbol => 'N'),
(Unit_Name => Candela, Unit_Symbol => "cd", Dim_Symbol => 'J'));
The package then defines a series of subtypes that correspond to these conventional units. For example:
subtype Length is Mks_Type
with
Dimension => (Symbol => 'm',
Meter => 1,
others => 0);
and similarly for Mass, Time, Electric_Current, Thermodynamic_Temperature, Amount_Of_Substance, and Luminous_Intensity (the standard set of units of the SI system).
The package also defines conventional names for values of each unit, for example:
m : constant Length := 1.0; kg : constant Mass := 1.0; s : constant Time := 1.0; A : constant Electric_Current := 1.0;
as well as useful multiples of these units:
cm : constant Length := 1.0E-02; g : constant Mass := 1.0E-03; min : constant Time := 60.0; day : constant TIme := 60.0 * 24.0 * min; ...
The user can then define a derived unit by providing the aspect that specifies its dimensions within the MKS system, as well as the string to be used for output of a value of that unit:
subtype Acceleration is Mks_Type
with Dimension => ("m/sec^2", Meter => 1, Second => -2, others => 0);
Here is a complete example of use:
with System.Dim.MKS; use System.Dim.Mks;
with System.Dim.Mks_IO; use System.Dim.Mks_IO;
with Text_IO; use Text_IO;
procedure Free_Fall is
subtype Acceleration is Mks_Type
with Dimension => ("m/sec^2", 1, 0, -2, others => 0);
G : constant acceleration := 9.81 * m / (s ** 2);
T : Time := 10.0*s;
Distance : Length;
begin
Put ("Gravitational constant: ");
Put (G, Aft => 2, Exp => 0); Put_Line ("");
Distance := 0.5 * G * T ** 2;
Put ("distance travelled in 10 seconds of free fall ");
Put (Distance, Aft => 2, Exp => 0);
Put_Line ("");
end Free_Fall;
Execution of this program yields:
Gravitational constant: 9.81 m/sec^2 distance travelled in 10 seconds of free fall 490.50 m
However, incorrect assignments such as:
Distance := 5.0; Distance := 5.0 * kg:
are rejected with the following diagnoses:
Distance := 5.0;
>>> dimensions mismatch in assignment
>>> left-hand side has dimension [L]
>>> right-hand side is dimensionless
Distance := 5.0 * kg:
>>> dimensions mismatch in assignment
>>> left-hand side has dimension [L]
>>> right-hand side has dimension [M]
The dimensions of an expression are properly displayed, even if there is no explicit subtype for it. If we add to the program:
Put ("Final velocity: ");
Put (G * T, Aft =>2, Exp =>0);
Put_Line ("");
then the output includes:
Final velocity: 98.10 m.s**(-1)
Next: Other Utility Programs, Previous: Performing Dimensionality Analysis in GNAT, Up: Top [Contents][Index]
GNAT now comes with a binding generator for C and C++ headers which is intended to do 95% of the tedious work of generating Ada specs from C or C++ header files.
Note that this capability is not intended to generate 100% correct Ada specs, and will is some cases require manual adjustments, although it can often be used out of the box in practice.
Some of the known limitations include:
shm_get vs SHM_GET).
The code generated is using the Ada 2005 syntax, which makes it easier to interface with other languages than previous versions of Ada.
| • Running the binding generator: | ||
| • Generating bindings for C++ headers: | ||
| • Switches: |
Next: Generating bindings for C++ headers, Up: Generating Ada Bindings for C and C++ headers [Contents][Index]
The binding generator is part of the gcc compiler and can be
invoked via the -fdump-ada-spec switch, which will generate Ada
spec files for the header files specified on the command line, and all
header files needed by these files transitively. For example:
$ g++ -c -fdump-ada-spec -C /usr/include/time.h $ gcc -c -gnat05 *.ads
will generate, under GNU/Linux, the following files: time_h.ads, bits_time_h.ads, stddef_h.ads, bits_types_h.ads which correspond to the files /usr/include/time.h, /usr/include/bits/time.h, etc…, and will then compile in Ada 2005 mode these Ada specs.
The -C switch tells gcc to extract comments from headers,
and will attempt to generate corresponding Ada comments.
If you want to generate a single Ada file and not the transitive closure, you can use instead the -fdump-ada-spec-slim switch.
You can optionally specify a parent unit, of which all generated units will
be children, using -fada-spec-parent=unit.
Note that we recommend when possible to use the g++ driver to
generate bindings, even for most C headers, since this will in general
generate better Ada specs. For generating bindings for C++ headers, it is
mandatory to use the g++ command, or gcc -x c++ which
is equivalent in this case. If g++ cannot work on your C headers
because of incompatibilities between C and C++, then you can fallback to
gcc instead.
For an example of better bindings generated from the C++ front-end, the name of the parameters (when available) are actually ignored by the C front-end. Consider the following C header:
extern void foo (int variable);
with the C front-end, variable is ignored, and the above is handled as:
extern void foo (int);
generating a generic:
procedure foo (param1 : int);
with the C++ front-end, the name is available, and we generate:
procedure foo (variable : int);
In some cases, the generated bindings will be more complete or more meaningful when defining some macros, which you can do via the -D switch. This is for example the case with Xlib.h under GNU/Linux:
g++ -c -fdump-ada-spec -DXLIB_ILLEGAL_ACCESS -C /usr/include/X11/Xlib.h
The above will generate more complete bindings than a straight call without the -DXLIB_ILLEGAL_ACCESS switch.
In other cases, it is not possible to parse a header file in a stand-alone
manner, because other include files need to be included first. In this
case, the solution is to create a small header file including the needed
#include and possible #define directives. For example, to
generate Ada bindings for readline/readline.h, you need to first
include stdio.h, so you can create a file with the following two
lines in e.g. readline1.h:
#include <stdio.h> #include <readline/readline.h>
and then generate Ada bindings from this file:
$ g++ -c -fdump-ada-spec readline1.h
Next: Switches, Previous: Running the binding generator, Up: Generating Ada Bindings for C and C++ headers [Contents][Index]
Generating bindings for C++ headers is done using the same options, always
with the g++ compiler.
In this mode, C++ classes will be mapped to Ada tagged types, constructors
will be mapped using the CPP_Constructor pragma, and when possible,
multiple inheritance of abstract classes will be mapped to Ada interfaces
(See Interfacing to C++ in GNAT Reference Manual, for additional
information on interfacing to C++).
For example, given the following C++ header file:
class Carnivore {
public:
virtual int Number_Of_Teeth () = 0;
};
class Domestic {
public:
virtual void Set_Owner (char* Name) = 0;
};
class Animal {
public:
int Age_Count;
virtual void Set_Age (int New_Age);
};
class Dog : Animal, Carnivore, Domestic {
public:
int Tooth_Count;
char *Owner;
virtual int Number_Of_Teeth ();
virtual void Set_Owner (char* Name);
Dog();
};
|
The corresponding Ada code is generated:
package Class_Carnivore is
type Carnivore is limited interface;
pragma Import (CPP, Carnivore);
function Number_Of_Teeth (this : access Carnivore) return int is abstract;
end;
use Class_Carnivore;
package Class_Domestic is
type Domestic is limited interface;
pragma Import (CPP, Domestic);
procedure Set_Owner
(this : access Domestic;
Name : Interfaces.C.Strings.chars_ptr) is abstract;
end;
use Class_Domestic;
package Class_Animal is
type Animal is tagged limited record
Age_Count : aliased int;
end record;
pragma Import (CPP, Animal);
procedure Set_Age (this : access Animal; New_Age : int);
pragma Import (CPP, Set_Age, "_ZN6Animal7Set_AgeEi");
end;
use Class_Animal;
package Class_Dog is
type Dog is new Animal and Carnivore and Domestic with record
Tooth_Count : aliased int;
Owner : Interfaces.C.Strings.chars_ptr;
end record;
pragma Import (CPP, Dog);
function Number_Of_Teeth (this : access Dog) return int;
pragma Import (CPP, Number_Of_Teeth, "_ZN3Dog15Number_Of_TeethEv");
procedure Set_Owner
(this : access Dog; Name : Interfaces.C.Strings.chars_ptr);
pragma Import (CPP, Set_Owner, "_ZN3Dog9Set_OwnerEPc");
function New_Dog return Dog;
pragma CPP_Constructor (New_Dog);
pragma Import (CPP, New_Dog, "_ZN3DogC1Ev");
end;
use Class_Dog;
|
Previous: Generating bindings for C++ headers, Up: Generating Ada Bindings for C and C++ headers [Contents][Index]
Generate Ada spec files for the given header files transitively (including all header files that these headers depend upon).
Generate Ada spec files for the header files specified on the command line only.
Specifies that all files generated by -fdump-ada-spec* are to be child units of the specified parent unit.
Extract comments from headers and generate Ada comments in the Ada spec files.
Next: Code Coverage and Profiling, Previous: Generating Ada Bindings for C and C++ headers, Up: Top [Contents][Index]
This chapter discusses some other utility programs available in the Ada environment.
| • Using Other Utility Programs with GNAT: | ||
| • The External Symbol Naming Scheme of GNAT: | ||
| • Converting Ada Files to html with gnathtml: | ||
| • Installing gnathtml: |
Next: The External Symbol Naming Scheme of GNAT, Previous: Current Limitations, Up: Other Utility Programs [Contents][Index]
The object files generated by GNAT are in standard system format and in particular the debugging information uses this format. This means programs generated by GNAT can be used with existing utilities that depend on these formats.
In general, any utility program that works with C will also often work with
Ada programs generated by GNAT. This includes software utilities such as
gprof (a profiling program), gdb (the FSF debugger), and utilities such
as Purify.
Next: Converting Ada Files to html with gnathtml, Previous: Using Other Utility Programs with GNAT, Up: Other Utility Programs [Contents][Index]
In order to interpret the output from GNAT, when using tools that are originally intended for use with other languages, it is useful to understand the conventions used to generate link names from the Ada entity names.
All link names are in all lowercase letters. With the exception of library procedure names, the mechanism used is simply to use the full expanded Ada name with dots replaced by double underscores. For example, suppose we have the following package spec:
package QRS is MN : Integer; end QRS; |
The variable MN has a full expanded Ada name of QRS.MN, so
the corresponding link name is qrs__mn.
Of course if a pragma Export is used this may be overridden:
package Exports is Var1 : Integer; pragma Export (Var1, C, External_Name => "var1_name"); Var2 : Integer; pragma Export (Var2, C, Link_Name => "var2_link_name"); end Exports; |
In this case, the link name for Var1 is whatever link name the C compiler would assign for the C function var1_name. This typically would be either var1_name or _var1_name, depending on operating system conventions, but other possibilities exist. The link name for Var2 is var2_link_name, and this is not operating system dependent.
One exception occurs for library level procedures. A potential ambiguity
arises between the required name _main for the C main program,
and the name we would otherwise assign to an Ada library level procedure
called Main (which might well not be the main program).
To avoid this ambiguity, we attach the prefix _ada_ to such
names. So if we have a library level procedure such as
procedure Hello (S : String); |
the external name of this procedure will be _ada_hello.
Next: Installing gnathtml, Previous: The External Symbol Naming Scheme of GNAT, Up: Other Utility Programs [Contents][Index]
gnathtmlThis Perl script allows Ada source files to be browsed using
standard Web browsers. For installation procedure, see the section
See Installing gnathtml.
Ada reserved keywords are highlighted in a bold font and Ada comments in a blue font. Unless your program was compiled with the gcc -gnatx switch to suppress the generation of cross-referencing information, user defined variables and types will appear in a different color; you will be able to click on any identifier and go to its declaration.
The command line is as follow:
$ perl gnathtml.pl [switches] ada-files
You can pass it as many Ada files as you want. gnathtml will generate
an html file for every ada file, and a global file called index.htm.
This file is an index of every identifier defined in the files.
The available switches are the following ones:
Only the Ada 83 subset of keywords will be highlighted.
This option allows you to change the color used for comments. The default value is green. The color argument can be any name accepted by html.
If the Ada files depend on some other files (for instance through
with clauses, the latter files will also be converted to html.
Only the files in the user project will be converted to html, not the files
in the run-time library itself.
This command is the same as -d above, but gnathtml will
also look for files in the run-time library, and generate html files for them.
This option allows you to change the extension of the generated HTML files. If you do not specify an extension, it will default to htm.
By default, gnathtml will generate html links only for global entities (’with’ed units, global variables and types,…). If you specify -f on the command line, then links will be generated for local entities too.
If this switch is provided and number is not 0, then
gnathtml will number the html files every number line.
Specify a directory to search for library files (.ALI files) and source files. You can provide several -I switches on the command line, and the directories will be parsed in the order of the command line.
Specify the output directory for html files. By default, gnathtml will saved the generated html files in a subdirectory named html/.
If you are using Emacs and the most recent Emacs Ada mode, which provides a full Integrated Development Environment for compiling, checking, running and debugging applications, you may use .gpr files to give the directories where Emacs can find sources and object files.
Using this switch, you can tell gnathtml to use these files. This allows you to get an html version of your application, even if it is spread over multiple directories.
This switch allows you to change the color used for symbol definitions. The default value is red. The color argument can be any name accepted by html.
This switch provides the name of a file. This file contains a list of file names to be converted, and the effect is exactly as though they had appeared explicitly on the command line. This is the recommended way to work around the command line length limit on some systems.
Previous: Converting Ada Files to html with gnathtml, Up: Other Utility Programs [Contents][Index]
gnathtmlPerl needs to be installed on your machine to run this script.
Perl is freely available for almost every architecture and
Operating System via the Internet.
On Unix systems, you may want to modify the first line of the script
gnathtml, to explicitly tell the Operating system where Perl
is. The syntax of this line is:
#!full_path_name_to_perl
Alternatively, you may run the script using the following command line:
$ perl gnathtml.pl [switches] files
Next: Running and Debugging Ada Programs, Previous: Other Utility Programs, Up: Top [Contents][Index]
This chapter describes how to use gcov - coverage testing tool - and
gprof - profiler tool - on your Ada programs.
| • Code Coverage of Ada Programs using gcov: | ||
| • Profiling an Ada Program using gprof: |
Next: Profiling an Ada Program using gprof, Previous: Converting Ada Files to html with gnathtml, Up: Code Coverage and Profiling [Contents][Index]
gcov is a test coverage program: it analyzes the execution of a given
program on selected tests, to help you determine the portions of the program
that are still untested.
gcov is part of the GCC suite, and is described in detail in the GCC
User’s Guide. You can refer to this documentation for a more complete
description.
This chapter provides a quick startup guide, and details some Gnat-specific features.
| • Quick startup guide: | ||
| • Gnat specifics: |
Next: Gnat specifics, Up: Code Coverage of Ada Programs using gcov [Contents][Index]
In order to perform coverage analysis of a program using gcov, 3
steps are needed:
gcov tool to generate the result.
The code instrumentation needed by gcov is created at the object level:
The source code is not modified in any way, because the instrumentation code is
inserted by gcc during the compilation process. To compile your code with code
coverage activated, you need to recompile your whole project using the
switches
-fprofile-arcs and -ftest-coverage, and link it using
-fprofile-arcs.
$ gnatmake -P my_project.gpr -f -cargs -fprofile-arcs -ftest-coverage \ -largs -fprofile-arcs
This compilation process will create .gcno files together with the usual object files.
Once the program is compiled with coverage instrumentation, you can run it as many times as needed - on portions of a test suite for example. The first execution will produce .gcda files at the same location as the .gcno files. The following executions will update those files, so that a cumulative result of the covered portions of the program is generated.
Finally, you need to call the gcov tool. The different options of
gcov are available in the GCC User’s Guide, section ’Invoking gcov’.
This will create annotated source files with a .gcov extension: my_main.adb file will be analysed in my_main.adb.gcov.
Previous: Quick startup guide, Up: Code Coverage of Ada Programs using gcov [Contents][Index]
Because Ada semantics, portions of the source code may be shared among
several object files. This is the case for example when generics are
involved, when inlining is active or when declarations generate initialisation
calls. In order to take
into account this shared code, you need to call gcov on all
source files of the tested program at once.
The list of source files might exceed the system’s maximum command line
length. In order to bypass this limitation, a new mechanism has been
implemented in gcov: you can now list all your project’s files into a
text file, and provide this file to gcov as a parameter, preceded by a @
(e.g. ‘gcov @mysrclist.txt’).
Note that on AIX compiling a static library with -fprofile-arcs is
not supported as there can be unresolved symbols during the final link.
Next: The GNAT Debugger GDB, Previous: Code Coverage of Ada Programs using gcov, Up: Code Coverage and Profiling [Contents][Index]
This section is not meant to be an exhaustive documentation of gprof.
Full documentation for it can be found in the GNU Profiler User’s Guide
documentation that is part of this GNAT distribution.
Profiling a program helps determine the parts of a program that are executed most often, and are therefore the most time-consuming.
gprof is the standard GNU profiling tool; it has been enhanced to
better handle Ada programs and multitasking.
It is currently supported on the following platforms
In order to profile a program using gprof, 3 steps are needed:
gprof tool.
The following sections detail the different steps, and indicate how to interpret the results:
| • Compilation for profiling: | ||
| • Program execution: | ||
| • Running gprof: | ||
| • Interpretation of profiling results: |
Next: Program execution, Up: Profiling an Ada Program using gprof [Contents][Index]
In order to profile a program the first step is to tell the compiler
to generate the necessary profiling information. The compiler switch to be used
is -pg, which must be added to other compilation switches. This
switch needs to be specified both during compilation and link stages, and can
be specified once when using gnatmake:
gnatmake -f -pg -P my_project
Note that only the objects that were compiled with the ‘-pg’ switch will be profiled; if you need to profile your whole project, use the ‘-f’ gnatmake switch to force full recompilation.
Next: Running gprof, Previous: Compilation for profiling, Up: Profiling an Ada Program using gprof [Contents][Index]
Once the program has been compiled for profiling, you can run it as usual.
The only constraint imposed by profiling is that the program must terminate normally. An interrupted program (via a Ctrl-C, kill, etc.) will not be properly analyzed.
Once the program completes execution, a data file called gmon.out is generated in the directory where the program was launched from. If this file already exists, it will be overwritten.
Next: Interpretation of profiling results, Previous: Program execution, Up: Profiling an Ada Program using gprof [Contents][Index]
The gprof tool is called as follow:
gprof my_prog gmon.out
or simpler:
gprof my_prog
The complete form of the gprof command line is the following:
gprof [switches] [executable [data-file]]
gprof supports numerous switch. The order of these
switch does not matter. The full list of options can be found in
the GNU Profiler User’s Guide documentation that comes with this documentation.
The following is the subset of those switches that is most relevant:
These options control whether symbol names should be demangled when
printing output. The default is to demangle C++ symbols. The
--no-demangle option may be used to turn off demangling. Different
compilers have different mangling styles. The optional demangling style
argument can be used to choose an appropriate demangling style for your
compiler, in particular Ada symbols generated by GNAT can be demangled using
--demangle=gnat.
The ‘-e function’ option tells gprof not to print
information about the function function_name (and its
children…) in the call graph. The function will still be listed
as a child of any functions that call it, but its index number will be
shown as ‘[not printed]’. More than one ‘-e’ option may be
given; only one function_name may be indicated with each ‘-e’
option.
The -E function option works like the -e option, but
execution time spent in the function (and children who were not called from
anywhere else), will not be used to compute the percentages-of-time for
the call graph. More than one ‘-E’ option may be given; only one
function_name may be indicated with each ‘-E’ option.
The ‘-f function’ option causes gprof to limit the
call graph to the function function_name and its children (and
their children…). More than one ‘-f’ option may be given;
only one function_name may be indicated with each ‘-f’
option.
The ‘-F function’ option works like the -f option, but
only time spent in the function and its children (and their
children…) will be used to determine total-time and
percentages-of-time for the call graph. More than one ‘-F’ option
may be given; only one function_name may be indicated with each
‘-F’ option. The ‘-F’ option overrides the ‘-E’ option.
Previous: Running gprof, Up: Profiling an Ada Program using gprof [Contents][Index]
The results of the profiling analysis are represented by two arrays: the ’flat profile’ and the ’call graph’. Full documentation of those outputs can be found in the GNU Profiler User’s Guide.
The flat profile shows the time spent in each function of the program, and how many time it has been called. This allows you to locate easily the most time-consuming functions.
The call graph shows, for each subprogram, the subprograms that call it, and the subprograms that it calls. It also provides an estimate of the time spent in each of those callers/called subprograms.
Next: Platform-Specific Information for the Run-Time Libraries, Previous: Code Coverage and Profiling, Up: Top [Contents][Index]
This chapter discusses how to debug Ada programs.
An incorrect Ada program may be handled in three ways by the GNAT compiler:
Next: Running GDB, Previous: Profiling an Ada Program using gprof, Up: Running and Debugging Ada Programs [Contents][Index]
GDB is a general purpose, platform-independent debugger that
can be used to debug mixed-language programs compiled with gcc,
and in particular is capable of debugging Ada programs compiled with
GNAT. The latest versions of GDB are Ada-aware and can handle
complex Ada data structures.
See Debugging with GDB in Debugging with GDB,
for full details on the usage of GDB, including a section on
its usage on programs. This manual should be consulted for full
details. The section that follows is a brief introduction to the
philosophy and use of GDB.
When GNAT programs are compiled, the compiler optionally writes debugging
information into the generated object file, including information on
line numbers, and on declared types and variables. This information is
separate from the generated code. It makes the object files considerably
larger, but it does not add to the size of the actual executable that
will be loaded into memory, and has no impact on run-time performance. The
generation of debug information is triggered by the use of the
-g switch in the gcc or gnatmake command
used to carry out the compilations. It is important to emphasize that
the use of these options does not change the generated code.
The debugging information is written in standard system formats that
are used by many tools, including debuggers and profilers. The format
of the information is typically designed to describe C types and
semantics, but GNAT implements a translation scheme which allows full
details about Ada types and variables to be encoded into these
standard C formats. Details of this encoding scheme may be found in
the file exp_dbug.ads in the GNAT source distribution. However, the
details of this encoding are, in general, of no interest to a user,
since GDB automatically performs the necessary decoding.
When a program is bound and linked, the debugging information is collected from the object files, and stored in the executable image of the program. Again, this process significantly increases the size of the generated executable file, but it does not increase the size of the executable program itself. Furthermore, if this program is run in the normal manner, it runs exactly as if the debug information were not present, and takes no more actual memory.
However, if the program is run under control of GDB, the
debugger is activated. The image of the program is loaded, at which
point it is ready to run. If a run command is given, then the program
will run exactly as it would have if GDB were not present. This
is a crucial part of the GDB design philosophy. GDB is
entirely non-intrusive until a breakpoint is encountered. If no
breakpoint is ever hit, the program will run exactly as it would if no
debugger were present. When a breakpoint is hit, GDB accesses
the debugging information and can respond to user commands to inspect
variables, and more generally to report on the state of execution.
Next: Introduction to GDB Commands, Previous: The GNAT Debugger GDB, Up: Running and Debugging Ada Programs [Contents][Index]
This section describes how to initiate the debugger.
The debugger can be launched from a GPS menu or
directly from the command line. The description below covers the latter use.
All the commands shown can be used in the GPS debug console window,
but there are usually more GUI-based ways to achieve the same effect.
The command to run GDB is
$ gdb program
where program is the name of the executable file. This
activates the debugger and results in a prompt for debugger commands.
The simplest command is simply run, which causes the program to run
exactly as if the debugger were not present. The following section
describes some of the additional commands that can be given to GDB.
Next: Using Ada Expressions, Previous: Running GDB, Up: Running and Debugging Ada Programs [Contents][Index]
GDB contains a large repertoire of commands. See Debugging with GDB in Debugging with GDB,
for extensive documentation on the use
of these commands, together with examples of their use. Furthermore,
the command help invoked from within GDB activates a simple help
facility which summarizes the available commands and their options.
In this section we summarize a few of the most commonly
used commands to give an idea of what GDB is about. You should create
a simple program with debugging information and experiment with the use of
these GDB commands on the program as you read through the
following section.
set args argumentsThe arguments list above is a list of arguments to be passed to
the program on a subsequent run command, just as though the arguments
had been entered on a normal invocation of the program. The set args
command is not needed if the program does not require arguments.
runThe run command causes execution of the program to start from
the beginning. If the program is already running, that is to say if
you are currently positioned at a breakpoint, then a prompt will ask
for confirmation that you want to abandon the current execution and
restart.
breakpoint locationThe breakpoint command sets a breakpoint, that is to say a point at which
execution will halt and GDB will await further
commands. location is
either a line number within a file, given in the format file:linenumber,
or it is the name of a subprogram. If you request that a breakpoint be set on
a subprogram that is overloaded, a prompt will ask you to specify on which of
those subprograms you want to breakpoint. You can also
specify that all of them should be breakpointed. If the program is run
and execution encounters the breakpoint, then the program
stops and GDB signals that the breakpoint was encountered by
printing the line of code before which the program is halted.
catch exception nameThis command causes the program execution to stop whenever exception name is raised. If name is omitted, then the execution is suspended when any exception is raised.
print expressionThis will print the value of the given expression. Most simple
Ada expression formats are properly handled by GDB, so the expression
can contain function calls, variables, operators, and attribute references.
continueContinues execution following a breakpoint, until the next breakpoint or the termination of the program.
stepExecutes a single line after a breakpoint. If the next statement is a subprogram call, execution continues into (the first statement of) the called subprogram.
nextExecutes a single line. If this line is a subprogram call, executes and returns from the call.
listLists a few lines around the current source location. In practice, it is usually more convenient to have a separate edit window open with the relevant source file displayed. Successive applications of this command print subsequent lines. The command can be given an argument which is a line number, in which case it displays a few lines around the specified one.
backtraceDisplays a backtrace of the call chain. This command is typically used after a breakpoint has occurred, to examine the sequence of calls that leads to the current breakpoint. The display includes one line for each activation record (frame) corresponding to an active subprogram.
upAt a breakpoint, GDB can display the values of variables local
to the current frame. The command up can be used to
examine the contents of other active frames, by moving the focus up
the stack, that is to say from callee to caller, one frame at a time.
downMoves the focus of GDB down from the frame currently being
examined to the frame of its callee (the reverse of the previous command),
frame nInspect the frame with the given number. The value 0 denotes the frame of the current breakpoint, that is to say the top of the call stack.
The above list is a very short introduction to the commands that
GDB provides. Important additional capabilities, including conditional
breakpoints, the ability to execute command sequences on a breakpoint,
the ability to debug at the machine instruction level and many other
features are described in detail in Debugging with GDB in Debugging with GDB. Note that most commands can be abbreviated
(for example, c for continue, bt for backtrace).
Next: Calling User-Defined Subprograms, Previous: Introduction to GDB Commands, Up: Running and Debugging Ada Programs [Contents][Index]
GDB supports a fairly large subset of Ada expression syntax, with some
extensions. The philosophy behind the design of this subset is
GDB should provide basic literals and access to operations for
arithmetic, dereferencing, field selection, indexing, and subprogram calls,
leaving more sophisticated computations to subprograms written into the
program (which therefore may be called from GDB).
GDB user.
GDB user.
Thus, for brevity, the debugger acts as if there were
implicit with and use clauses in effect for all user-written
packages, thus making it unnecessary to fully qualify most names with
their packages, regardless of context. Where this causes ambiguity,
GDB asks the user’s intent.
For details on the supported Ada syntax, see Debugging with GDB in Debugging with GDB.
Next: Using the Next Command in a Function, Previous: Using Ada Expressions, Up: Running and Debugging Ada Programs [Contents][Index]
An important capability of GDB is the ability to call user-defined
subprograms while debugging. This is achieved simply by entering
a subprogram call statement in the form:
call subprogram-name (parameters)
The keyword call can be omitted in the normal case where the
subprogram-name does not coincide with any of the predefined
GDB commands.
The effect is to invoke the given subprogram, passing it the
list of parameters that is supplied. The parameters can be expressions and
can include variables from the program being debugged. The
subprogram must be defined
at the library level within your program, and GDB will call the
subprogram within the environment of your program execution (which
means that the subprogram is free to access or even modify variables
within your program).
The most important use of this facility is in allowing the inclusion of
debugging routines that are tailored to particular data structures
in your program. Such debugging routines can be written to provide a suitably
high-level description of an abstract type, rather than a low-level dump
of its physical layout. After all, the standard
GDB print command only knows the physical layout of your
types, not their abstract meaning. Debugging routines can provide information
at the desired semantic level and are thus enormously useful.
For example, when debugging GNAT itself, it is crucial to have access to
the contents of the tree nodes used to represent the program internally.
But tree nodes are represented simply by an integer value (which in turn
is an index into a table of nodes).
Using the print command on a tree node would simply print this integer
value, which is not very useful. But the PN routine (defined in file
treepr.adb in the GNAT sources) takes a tree node as input, and displays
a useful high level representation of the tree node, which includes the
syntactic category of the node, its position in the source, the integers
that denote descendant nodes and parent node, as well as varied
semantic information. To study this example in more detail, you might want to
look at the body of the PN procedure in the stated file.
Next: Ada Exceptions, Previous: Calling User-Defined Subprograms, Up: Running and Debugging Ada Programs [Contents][Index]
When you use the next command in a function, the current source
location will advance to the next statement as usual. A special case
arises in the case of a return statement.
Part of the code for a return statement is the “epilog” of the function. This is the code that returns to the caller. There is only one copy of this epilog code, and it is typically associated with the last return statement in the function if there is more than one return. In some implementations, this epilog is associated with the first statement of the function.
The result is that if you use the next command from a return
statement that is not the last return statement of the function you
may see a strange apparent jump to the last return statement or to
the start of the function. You should simply ignore this odd jump.
The value returned is always that from the first return statement
that was stepped through.
Next: Ada Tasks, Previous: Using the Next Command in a Function, Up: Running and Debugging Ada Programs [Contents][Index]
You can set catchpoints that stop the program execution when your program raises selected exceptions.
catch exceptionSet a catchpoint that stops execution whenever (any task in the) program raises any exception.
catch exception nameSet a catchpoint that stops execution whenever (any task in the) program raises the exception name.
catch exception unhandledSet a catchpoint that stops executing whenever (any task in the) program raises an exception for which there is no handler.
info exceptionsinfo exceptions regexpThe info exceptions command permits the user to examine all defined
exceptions within Ada programs. With a regular expression, regexp, as
argument, prints out only those exceptions whose name matches regexp.
Next: Debugging Generic Units, Previous: Ada Exceptions, Up: Running and Debugging Ada Programs [Contents][Index]
GDB allows the following task-related commands:
info tasksThis command shows a list of current Ada tasks, as in the following example:
(gdb) info tasks ID TID P-ID Thread Pri State Name 1 8088000 0 807e000 15 Child Activation Wait main_task 2 80a4000 1 80ae000 15 Accept/Select Wait b 3 809a800 1 80a4800 15 Child Activation Wait a * 4 80ae800 3 80b8000 15 Running c
In this listing, the asterisk before the first task indicates it to be the currently running task. The first column lists the task ID that is used to refer to tasks in the following commands.
break linespec task taskidbreak linespec task taskid if …These commands are like the break … thread ….
linespec specifies source lines.
Use the qualifier ‘task taskid’ with a breakpoint command
to specify that you only want GDB to stop the program when a
particular Ada task reaches this breakpoint. taskid is one of the
numeric task identifiers assigned by GDB, shown in the first
column of the ‘info tasks’ display.
If you do not specify ‘task taskid’ when you set a breakpoint, the breakpoint applies to all tasks of your program.
You can use the task qualifier on conditional breakpoints as
well; in this case, place ‘task taskid’ before the
breakpoint condition (before the if).
task tasknoThis command allows to switch to the task referred by taskno. In particular, This allows to browse the backtrace of the specified task. It is advised to switch back to the original task before continuing execution otherwise the scheduling of the program may be perturbed.
For more detailed information on the tasking support, see Debugging with GDB in Debugging with GDB.
Next: Remote Debugging using gdbserver, Previous: Ada Tasks, Up: Running and Debugging Ada Programs [Contents][Index]
GNAT always uses code expansion for generic instantiation. This means that each time an instantiation occurs, a complete copy of the original code is made, with appropriate substitutions of formals by actuals.
It is not possible to refer to the original generic entities in
GDB, but it is always possible to debug a particular instance of
a generic, by using the appropriate expanded names. For example, if we have
procedure g is
generic package k is
procedure kp (v1 : in out integer);
end k;
package body k is
procedure kp (v1 : in out integer) is
begin
v1 := v1 + 1;
end kp;
end k;
package k1 is new k;
package k2 is new k;
var : integer := 1;
begin
k1.kp (var);
k2.kp (var);
k1.kp (var);
k2.kp (var);
end;
|
Then to break on a call to procedure kp in the k2 instance, simply use the command:
(gdb) break g.k2.kp
When the breakpoint occurs, you can step through the code of the instance in the normal manner and examine the values of local variables, as for other units.
Next: GNAT Abnormal Termination or Failure to Terminate, Previous: Debugging Generic Units, Up: Running and Debugging Ada Programs [Contents][Index]
On platforms where gdbserver is supported, it is possible to use this tool to debug your application remotely. This can be useful in situations where the program needs to be run on a target host that is different from the host used for development, particularly when the target has a limited amount of resources (either CPU and/or memory).
To do so, start your program using gdbserver on the target machine. gdbserver then automatically suspends the execution of your program at its entry point, waiting for a debugger to connect to it. The following commands starts an application and tells gdbserver to wait for a connection with the debugger on localhost port 4444.
$ gdbserver localhost:4444 program Process program created; pid = 5685 Listening on port 4444
Once gdbserver has started listening, we can tell the debugger to establish a connection with this gdbserver, and then start the same debugging session as if the program was being debugged on the same host, directly under the control of GDB.
$ gdb program (gdb) target remote targethost:4444 Remote debugging using targethost:4444 0x00007f29936d0af0 in ?? () from /lib64/ld-linux-x86-64.so. (gdb) b foo.adb:3 Breakpoint 1 at 0x401f0c: file foo.adb, line 3. (gdb) continue Continuing. Breakpoint 1, foo () at foo.adb:4 4 end foo;
It is also possible to use gdbserver to attach to an already running program, in which case the execution of that program is simply suspended until the connection between the debugger and gdbserver is established.
For more information on how to use gdbserver, Using the gdbserver Program in Debugging with GDB. GNAT provides support for gdbserver on x86-linux, x86-windows and x86_64-linux.
Next: Naming Conventions for GNAT Source Files, Previous: Remote Debugging using gdbserver, Up: Running and Debugging Ada Programs [Contents][Index]
When presented with programs that contain serious errors in syntax or semantics, GNAT may on rare occasions experience problems in operation, such as aborting with a segmentation fault or illegal memory access, raising an internal exception, terminating abnormally, or failing to terminate at all. In such cases, you can activate various features of GNAT that can help you pinpoint the construct in your program that is the likely source of the problem.
The following strategies are presented in increasing order of difficulty, corresponding to your experience in using GNAT and your familiarity with compiler internals.
gcc with the -gnatf. This first
switch causes all errors on a given line to be reported. In its absence,
only the first error on a line is displayed.
The -gnatdO switch causes errors to be displayed as soon as they are encountered, rather than after compilation is terminated. If GNAT terminates prematurely or goes into an infinite loop, the last error message displayed may help to pinpoint the culprit.
gcc with the -v (verbose) switch. In this
mode, gcc produces ongoing information about the progress of the
compilation and provides the name of each procedure as code is
generated. This switch allows you to find which Ada procedure was being
compiled when it encountered a code generation problem.
gcc with the -gnatdc switch. This is a GNAT specific
switch that does for the front-end what -v does
for the back end. The system prints the name of each unit,
either a compilation unit or nested unit, as it is being analyzed.
gdb directly on the gnat1 executable. gnat1 is the
front-end of GNAT, and can be run independently (normally it is just
called from gcc). You can use gdb on gnat1 as you
would on a C program (but see The GNAT Debugger GDB for caveats). The
where command is the first line of attack; the variable
lineno (seen by print lineno), used by the second phase of
gnat1 and by the gcc backend, indicates the source line at
which the execution stopped, and input_file name indicates the name of
the source file.
Next: Getting Internal Debugging Information, Previous: GNAT Abnormal Termination or Failure to Terminate, Up: Running and Debugging Ada Programs [Contents][Index]
In order to examine the workings of the GNAT system, the following brief description of its organization may be helpful:
Ada, as
defined in Annex A.
Interfaces, as
defined in Annex B.
System. This includes
both language-defined children and GNAT run-time routines.
GNAT. These are useful
general-purpose packages, fully documented in their specs. All
the other .c files are modifications of common gcc files.
Next: Stack Traceback, Previous: Naming Conventions for GNAT Source Files, Up: Running and Debugging Ada Programs [Contents][Index]
Most compilers have internal debugging switches and modes. GNAT does also, except GNAT internal debugging switches and modes are not secret. A summary and full description of all the compiler and binder debug flags are in the file debug.adb. You must obtain the sources of the compiler to see the full detailed effects of these flags.
The switches that print the source of the program (reconstructed from the internal tree) are of general interest for user programs, as are the options to print the full internal tree, and the entity table (the symbol table information). The reconstructed source provides a readable version of the program after the front-end has completed analysis and expansion, and is useful when studying the performance of specific constructs. For example, constraint checks are indicated, complex aggregates are replaced with loops and assignments, and tasking primitives are replaced with run-time calls.
Next: Summary of Run-Time Configurations, Previous: Getting Internal Debugging Information, Up: Running and Debugging Ada Programs [Contents][Index]
Traceback is a mechanism to display the sequence of subprogram calls that leads to a specified execution point in a program. Often (but not always) the execution point is an instruction at which an exception has been raised. This mechanism is also known as stack unwinding because it obtains its information by scanning the run-time stack and recovering the activation records of all active subprograms. Stack unwinding is one of the most important tools for program debugging.
The first entry stored in traceback corresponds to the deepest calling level, that is to say the subprogram currently executing the instruction from which we want to obtain the traceback.
Note that there is no runtime performance penalty when stack traceback is enabled, and no exception is raised during program execution.
| • Non-Symbolic Traceback: | ||
| • Symbolic Traceback: |
Next: Symbolic Traceback, Up: Stack Traceback [Contents][Index]
Note: this feature is not supported on all platforms. See GNAT.Traceback spec in g-traceb.ads for a complete list of supported platforms.
| • Tracebacks From an Unhandled Exception: | ||
| • Tracebacks From Exception Occurrences (non-symbolic): | ||
| • Tracebacks From Anywhere in a Program (non-symbolic): |
Next: Tracebacks From Exception Occurrences (non-symbolic), Up: Non-Symbolic Traceback [Contents][Index]
A runtime non-symbolic traceback is a list of addresses of call instructions.
To enable this feature you must use the -E
gnatbind’s option. With this option a stack traceback is stored as part
of exception information. You can retrieve this information using the
addr2line tool.
Here is a simple example:
procedure STB is
procedure P1 is
begin
raise Constraint_Error;
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
|
$ gnatmake stb -bargs -E $ stb Execution terminated by unhandled exception Exception name: CONSTRAINT_ERROR Message: stb.adb:5 Call stack traceback locations: 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4
As we see the traceback lists a sequence of addresses for the unhandled
exception CONSTRAINT_ERROR raised in procedure P1. It is easy to
guess that this exception come from procedure P1. To translate these
addresses into the source lines where the calls appear, the
addr2line tool, described below, is invaluable. The use of this tool
requires the program to be compiled with debug information.
$ gnatmake -g stb -bargs -E $ stb Execution terminated by unhandled exception Exception name: CONSTRAINT_ERROR Message: stb.adb:5 Call stack traceback locations: 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 $ addr2line --exe=stb 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 00401373 at d:/stb/stb.adb:5 0040138B at d:/stb/stb.adb:10 0040139C at d:/stb/stb.adb:14 00401335 at d:/stb/b~stb.adb:104 004011C4 at /build/…/crt1.c:200 004011F1 at /build/…/crt1.c:222 77E892A4 in ?? at ??:0
The addr2line tool has several other useful options:
--functionsto get the function name corresponding to any location
--demangle=gnatto use the gnat decoding mode for the function names. Note that for binutils version 2.9.x the option is simply --demangle.
$ addr2line --exe=stb --functions --demangle=gnat 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 00401373 in stb.p1 at d:/stb/stb.adb:5 0040138B in stb.p2 at d:/stb/stb.adb:10 0040139C in stb at d:/stb/stb.adb:14 00401335 in main at d:/stb/b~stb.adb:104 004011C4 in <__mingw_CRTStartup> at /build/…/crt1.c:200 004011F1 in <mainCRTStartup> at /build/…/crt1.c:222
From this traceback we can see that the exception was raised in stb.adb at line 5, which was reached from a procedure call in stb.adb at line 10, and so on. The b~std.adb is the binder file, which contains the call to the main program. See Running gnatbind. The remaining entries are assorted runtime routines, and the output will vary from platform to platform.
It is also possible to use GDB with these traceback addresses to debug
the program. For example, we can break at a given code location, as reported
in the stack traceback:
$ gdb -nw stb Furthermore, this feature is not implemented inside Windows DLL. Only the non-symbolic traceback is reported in this case. (gdb) break *0x401373 Breakpoint 1 at 0x401373: file stb.adb, line 5.
It is important to note that the stack traceback addresses do not change when debug information is included. This is particularly useful because it makes it possible to release software without debug information (to minimize object size), get a field report that includes a stack traceback whenever an internal bug occurs, and then be able to retrieve the sequence of calls with the same program compiled with debug information.
Next: Tracebacks From Anywhere in a Program (non-symbolic), Previous: Tracebacks From an Unhandled Exception, Up: Non-Symbolic Traceback [Contents][Index]
Non-symbolic tracebacks are obtained by using the -E binder argument.
The stack traceback is attached to the exception information string, and can
be retrieved in an exception handler within the Ada program, by means of the
Ada facilities defined in Ada.Exceptions. Here is a simple example:
with Ada.Text_IO;
with Ada.Exceptions;
procedure STB is
use Ada;
use Ada.Exceptions;
procedure P1 is
K : Positive := 1;
begin
K := K - 1;
exception
when E : others =>
Text_IO.Put_Line (Exception_Information (E));
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
This program will output:
$ stb Exception name: CONSTRAINT_ERROR Message: stb.adb:12 Call stack traceback locations: 0x4015e4 0x401633 0x401644 0x401461 0x4011c4 0x4011f1 0x77e892a4
Previous: Tracebacks From Exception Occurrences (non-symbolic), Up: Non-Symbolic Traceback [Contents][Index]
It is also possible to retrieve a stack traceback from anywhere in a
program. For this you need to
use the GNAT.Traceback API. This package includes a procedure called
Call_Chain that computes a complete stack traceback, as well as useful
display procedures described below. It is not necessary to use the
-E gnatbind option in this case, because the stack traceback mechanism
is invoked explicitly.
In the following example we compute a traceback at a specific location in
the program, and we display it using GNAT.Debug_Utilities.Image to
convert addresses to strings:
with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Debug_Utilities;
procedure STB is
use Ada;
use GNAT;
use GNAT.Traceback;
procedure P1 is
TB : Tracebacks_Array (1 .. 10);
-- We are asking for a maximum of 10 stack frames.
Len : Natural;
-- Len will receive the actual number of stack frames returned.
begin
Call_Chain (TB, Len);
Text_IO.Put ("In STB.P1 : ");
for K in 1 .. Len loop
Text_IO.Put (Debug_Utilities.Image (TB (K)));
Text_IO.Put (' ');
end loop;
Text_IO.New_Line;
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
$ gnatmake -g stb $ stb In STB.P1 : 16#0040_F1E4# 16#0040_14F2# 16#0040_170B# 16#0040_171C# 16#0040_1461# 16#0040_11C4# 16#0040_11F1# 16#77E8_92A4#
You can then get further information by invoking the addr2line
tool as described earlier (note that the hexadecimal addresses
need to be specified in C format, with a leading “0x”).
Previous: Non-Symbolic Traceback, Up: Stack Traceback [Contents][Index]
A symbolic traceback is a stack traceback in which procedure names are associated with each code location.
Note that this feature is not supported on all platforms. See GNAT.Traceback.Symbolic spec in g-trasym.ads for a complete list of currently supported platforms.
Note that the symbolic traceback requires that the program be compiled with debug information. If it is not compiled with debug information only the non-symbolic information will be valid.
| • Tracebacks From Exception Occurrences (symbolic): | ||
| • Tracebacks From Anywhere in a Program (symbolic): |
with Ada.Text_IO;
with GNAT.Traceback.Symbolic;
procedure STB is
procedure P1 is
begin
raise Constraint_Error;
end P1;
procedure P2 is
begin
P1;
end P2;
procedure P3 is
begin
P2;
end P3;
begin
P3;
exception
when E : others =>
Ada.Text_IO.Put_Line (GNAT.Traceback.Symbolic.Symbolic_Traceback (E));
end STB;
$ gnatmake -g .\stb -bargs -E -largs -lgnat -laddr2line -lintl $ stb 0040149F in stb.p1 at stb.adb:8 004014B7 in stb.p2 at stb.adb:13 004014CF in stb.p3 at stb.adb:18 004015DD in ada.stb at stb.adb:22 00401461 in main at b~stb.adb:168 004011C4 in __mingw_CRTStartup at crt1.c:200 004011F1 in mainCRTStartup at crt1.c:222 77E892A4 in ?? at ??:0
In the above example the “.\” syntax in the gnatmake command
is currently required by addr2line for files that are in
the current working directory.
Moreover, the exact sequence of linker options may vary from platform
to platform.
The above -largs section is for Windows platforms. By contrast,
under Unix there is no need for the -largs section.
Differences across platforms are due to details of linker implementation.
Previous: Tracebacks From Exception Occurrences (symbolic), Up: Symbolic Traceback [Contents][Index]
It is possible to get a symbolic stack traceback
from anywhere in a program, just as for non-symbolic tracebacks.
The first step is to obtain a non-symbolic
traceback, and then call Symbolic_Traceback to compute the symbolic
information. Here is an example:
with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Traceback.Symbolic;
procedure STB is
use Ada;
use GNAT.Traceback;
use GNAT.Traceback.Symbolic;
procedure P1 is
TB : Tracebacks_Array (1 .. 10);
-- We are asking for a maximum of 10 stack frames.
Len : Natural;
-- Len will receive the actual number of stack frames returned.
begin
Call_Chain (TB, Len);
Text_IO.Put_Line (Symbolic_Traceback (TB (1 .. Len)));
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
Next: Example of Binder Output File, Previous: Running and Debugging Ada Programs, Up: Top [Contents][Index]
The GNAT run-time implementation may vary with respect to both the underlying threads library and the exception handling scheme. For threads support, one or more of the following are supplied:
For exception handling, either or both of two models are supplied:
This appendix summarizes which combinations of threads and exception support are supplied on various GNAT platforms. It then shows how to select a particular library either permanently or temporarily, explains the properties of (and tradeoffs among) the various threads libraries, and provides some additional information about several specific platforms.
Next: Specifying a Run-Time Library, Previous: Stack Traceback, Up: Platform-Specific Information for the Run-Time Libraries [Contents][Index]
| alpha-openvms | |
rts-native (default) | |
Tasking | native VMS threads |
Exceptions | ZCX
|
rts-sjlj | |
Tasking | native TRU64 threads |
Exceptions | SJLJ
|
| ia64-hp_linux | |
rts-native (default) | |
Tasking | pthread library |
Exceptions | ZCX
|
| ia64-hpux | |
rts-native (default) | |
Tasking | native HP-UX threads |
Exceptions | SJLJ
|
| ia64-openvms | |
rts-native (default) | |
Tasking | native VMS threads |
Exceptions | ZCX
|
| ia64-sgi_linux | |
rts-native (default) | |
Tasking | pthread library |
Exceptions | ZCX
|
| pa-hpux | |
rts-native (default) | |
Tasking | native HP-UX threads |
Exceptions | ZCX
|
rts-sjlj | |
Tasking | native HP-UX threads |
Exceptions | SJLJ
|
| ppc-aix | |
rts-native (default) | |
Tasking | native AIX threads |
Exceptions | ZCX
|
rts-sjlj | |
Tasking | native AIX threads |
Exceptions | SJLJ
|
| ppc-darwin | |
rts-native (default) | |
Tasking | native MacOS threads |
Exceptions | ZCX
|
| sparc-solaris | |
rts-native (default) | |
Tasking | native Solaris threads library |
Exceptions | ZCX
|
rts-pthread | |
Tasking | pthread library |
Exceptions | ZCX
|
rts-sjlj | |
Tasking | native Solaris threads library |
Exceptions | SJLJ
|
| sparc64-solaris | |
rts-native (default) | |
Tasking | native Solaris threads library |
Exceptions | ZCX
|
| x86-linux | |
rts-native (default) | |
Tasking | pthread library |
Exceptions | ZCX
|
rts-sjlj | |
Tasking | pthread library |
Exceptions | SJLJ
|
| x86-lynx | |
rts-native (default) | |
Tasking | native LynxOS threads |
Exceptions | SJLJ
|
| x86-solaris | |
rts-native (default) | |
Tasking | native Solaris threads |
Exceptions | ZCX
|
rts-sjlj | |
Tasking | native Solaris threads library |
Exceptions | SJLJ
|
| x86-windows | |
rts-native (default) | |
Tasking | native Win32 threads |
Exceptions | ZCX
|
rts-sjlj | |
Tasking | native Win32 threads |
Exceptions | SJLJ
|
| x86-windows-rtx | |
rts-rtx-rtss (default) | |
Tasking | RTX real-time subsystem RTSS threads (kernel mode) |
Exceptions | SJLJ
|
rts-rtx-w32 | |
Tasking | RTX Win32 threads (user mode) |
Exceptions | ZCX
|
| x86_64-linux | |
rts-native (default) | |
Tasking | pthread library |
Exceptions | ZCX
|
rts-sjlj | |
Tasking | pthread library |
Exceptions | SJLJ
|
Next: Choosing the Scheduling Policy, Previous: Summary of Run-Time Configurations, Up: Platform-Specific Information for the Run-Time Libraries [Contents][Index]
The adainclude subdirectory containing the sources of the GNAT run-time library, and the adalib subdirectory containing the ALI files and the static and/or shared GNAT library, are located in the gcc target-dependent area:
target=$prefix/lib/gcc/gcc-dumpmachine/gcc-dumpversion/
As indicated above, on some platforms several run-time libraries are supplied. These libraries are installed in the target dependent area and contain a complete source and binary subdirectory. The detailed description below explains the differences between the different libraries in terms of their thread support.
The default run-time library (when GNAT is installed) is rts-native. This default run time is selected by the means of soft links. For example on x86-linux:
$(target-dir)
|
+--- adainclude----------+
| |
+--- adalib-----------+ |
| | |
+--- rts-native | |
| | | |
| +--- adainclude <---+
| | |
| +--- adalib <----+
|
+--- rts-sjlj
|
+--- adainclude
|
+--- adalib
If the rts-sjlj library is to be selected on a permanent basis, these soft links can be modified with the following commands:
$ cd $target $ rm -f adainclude adalib $ ln -s rts-sjlj/adainclude adainclude $ ln -s rts-sjlj/adalib adalib
Alternatively, you can specify rts-sjlj/adainclude in the file $target/ada_source_path and rts-sjlj/adalib in $target/ada_object_path.
Selecting another run-time library temporarily can be achieved by using the --RTS switch, e.g., --RTS=sjlj
Next: Solaris-Specific Considerations, Previous: Specifying a Run-Time Library, Up: Platform-Specific Information for the Run-Time Libraries [Contents][Index]
When using a POSIX threads implementation, you have a choice of several
scheduling policies: SCHED_FIFO,
SCHED_RR
and SCHED_OTHER.
Typically, the default is SCHED_OTHER, while using SCHED_FIFO
or SCHED_RR requires special (e.g., root) privileges.
By default, GNAT uses the SCHED_OTHER policy. To specify
SCHED_FIFO,
you can use one of the following:
pragma Time_Slice (0.0)
pragma Task_Dispatching_Policy (FIFO_Within_Priorities)
To specify SCHED_RR,
you should use pragma Time_Slice with a
value greater than 0.0, or else use the corresponding -T
binder option.
Next: Linux-Specific Considerations, Previous: Choosing the Scheduling Policy, Up: Platform-Specific Information for the Run-Time Libraries [Contents][Index]
This section addresses some topics related to the various threads libraries on Sparc Solaris.
| • Solaris Threads Issues: |
GNAT under Solaris/Sparc 32 bits comes with an alternate tasking run-time
library based on POSIX threads — rts-pthread.
This run-time library has the advantage of being mostly shared across all
POSIX-compliant thread implementations, and it also provides under
Solaris 8 the PTHREAD_PRIO_INHERIT
and PTHREAD_PRIO_PROTECT
semantics that can be selected using the predefined pragma
Locking_Policy
with respectively
Inheritance_Locking and Ceiling_Locking as the policy.
As explained above, the native run-time library is based on the Solaris thread
library (libthread) and is the default library.
When the Solaris threads library is used (this is the default), programs
compiled with GNAT can automatically take advantage of
and can thus execute on multiple processors.
The user can alternatively specify a processor on which the program should run
to emulate a single-processor system. The multiprocessor / uniprocessor choice
is made by
setting the environment variable GNAT_PROCESSOR
to one of the following:
-2Use the default configuration (run the program on all
available processors) - this is the same as having GNAT_PROCESSOR
unset
-1Let the run-time implementation choose one processor and run the program on that processor
0 .. Last_ProcRun the program on the specified processor.
Last_Proc is equal to _SC_NPROCESSORS_CONF - 1
(where _SC_NPROCESSORS_CONF is a system variable).
Next: AIX-Specific Considerations, Previous: Solaris-Specific Considerations, Up: Platform-Specific Information for the Run-Time Libraries [Contents][Index]
On GNU/Linux without NPTL support (usually system with GNU C Library
older than 2.3), the signal model is not POSIX compliant, which means
that to send a signal to the process, you need to send the signal to all
threads, e.g. by using killpg().
Next: RTX-Specific Considerations, Previous: Linux-Specific Considerations, Up: Platform-Specific Information for the Run-Time Libraries [Contents][Index]
On AIX, the resolver library initializes some internal structure on
the first call to get*by* functions, which are used to implement
GNAT.Sockets.Get_Host_By_Name and
GNAT.Sockets.Get_Host_By_Address.
If such initialization occurs within an Ada task, and the stack size for
the task is the default size, a stack overflow may occur.
To avoid this overflow, the user should either ensure that the first call
to GNAT.Sockets.Get_Host_By_Name or
GNAT.Sockets.Get_Host_By_Addrss
occurs in the environment task, or use pragma Storage_Size to
specify a sufficiently large size for the stack of the task that contains
this call.
Next: HP-UX-Specific Considerations, Previous: AIX-Specific Considerations, Up: Platform-Specific Information for the Run-Time Libraries [Contents][Index]
The Real-time Extension (RTX) to Windows is based on the Windows Win32 API. Applications can be built to work in two different modes:
Next: Elaboration Code, Previous: RTX-Specific Considerations, Up: Platform-Specific Information for the Run-Time Libraries [Contents][Index]
On HP-UX, appropriate privileges are required to change the scheduling
parameters of a task. The calling process must have appropriate
privileges or be a member of a group having PRIV_RTSCHED access to
successfully change the scheduling parameters.
By default, GNAT uses the SCHED_HPUX policy. To have access to the
priority range 0-31 either the FIFO_Within_Priorities or the
Round_Robin_Within_Priorities scheduling policies need to be set.
To specify the FIFO_Within_Priorities scheduling policy you can use
one of the following:
pragma Time_Slice (0.0)
pragma Task_Dispatching_Policy (FIFO_Within_Priorities)
To specify the Round_Robin_Within_Priorities, scheduling policy
you should use pragma Time_Slice with a
value greater than 0.0, or use the corresponding -T
binder option, or set the pragma Task_Dispatching_Policy
(Round_Robin_Within_Priorities).
Next: Elaboration Order Handling in GNAT, Previous: Platform-Specific Information for the Run-Time Libraries, Up: Top [Contents][Index]
This Appendix displays the source code for gnatbind’s output
file generated for a simple “Hello World” program.
Comments have been added for clarification purposes.
-- The package is called Ada_Main unless this name is actually used
-- as a unit name in the partition, in which case some other unique
-- name is used.
with System;
package ada_main is
Elab_Final_Code : Integer;
pragma Import (C, Elab_Final_Code, "__gnat_inside_elab_final_code");
-- The main program saves the parameters (argument count,
-- argument values, environment pointer) in global variables
-- for later access by other units including
-- Ada.Command_Line.
gnat_argc : Integer;
gnat_argv : System.Address;
gnat_envp : System.Address;
-- The actual variables are stored in a library routine. This
-- is useful for some shared library situations, where there
-- are problems if variables are not in the library.
pragma Import (C, gnat_argc);
pragma Import (C, gnat_argv);
pragma Import (C, gnat_envp);
-- The exit status is similarly an external location
gnat_exit_status : Integer;
pragma Import (C, gnat_exit_status);
GNAT_Version : constant String :=
"GNAT Version: 6.0.0w (20061115)";
pragma Export (C, GNAT_Version, "__gnat_version");
-- This is the generated adafinal routine that performs
-- finalization at the end of execution. In the case where
-- Ada is the main program, this main program makes a call
-- to adafinal at program termination.
procedure adafinal;
pragma Export (C, adafinal, "adafinal");
-- This is the generated adainit routine that performs
-- initialization at the start of execution. In the case
-- where Ada is the main program, this main program makes
-- a call to adainit at program startup.
procedure adainit;
pragma Export (C, adainit, "adainit");
-- This routine is called at the start of execution. It is
-- a dummy routine that is used by the debugger to breakpoint
-- at the start of execution.
procedure Break_Start;
pragma Import (C, Break_Start, "__gnat_break_start");
-- This is the actual generated main program (it would be
-- suppressed if the no main program switch were used). As
-- required by standard system conventions, this program has
-- the external name main.
function main
(argc : Integer;
argv : System.Address;
envp : System.Address)
return Integer;
pragma Export (C, main, "main");
-- The following set of constants give the version
-- identification values for every unit in the bound
-- partition. This identification is computed from all
-- dependent semantic units, and corresponds to the
-- string that would be returned by use of the
-- Body_Version or Version attributes.
type Version_32 is mod 2 ** 32;
u00001 : constant Version_32 := 16#7880BEB3#;
u00002 : constant Version_32 := 16#0D24CBD0#;
u00003 : constant Version_32 := 16#3283DBEB#;
u00004 : constant Version_32 := 16#2359F9ED#;
u00005 : constant Version_32 := 16#664FB847#;
u00006 : constant Version_32 := 16#68E803DF#;
u00007 : constant Version_32 := 16#5572E604#;
u00008 : constant Version_32 := 16#46B173D8#;
u00009 : constant Version_32 := 16#156A40CF#;
u00010 : constant Version_32 := 16#033DABE0#;
u00011 : constant Version_32 := 16#6AB38FEA#;
u00012 : constant Version_32 := 16#22B6217D#;
u00013 : constant Version_32 := 16#68A22947#;
u00014 : constant Version_32 := 16#18CC4A56#;
u00015 : constant Version_32 := 16#08258E1B#;
u00016 : constant Version_32 := 16#367D5222#;
u00017 : constant Version_32 := 16#20C9ECA4#;
u00018 : constant Version_32 := 16#50D32CB6#;
u00019 : constant Version_32 := 16#39A8BB77#;
u00020 : constant Version_32 := 16#5CF8FA2B#;
u00021 : constant Version_32 := 16#2F1EB794#;
u00022 : constant Version_32 := 16#31AB6444#;
u00023 : constant Version_32 := 16#1574B6E9#;
u00024 : constant Version_32 := 16#5109C189#;
u00025 : constant Version_32 := 16#56D770CD#;
u00026 : constant Version_32 := 16#02F9DE3D#;
u00027 : constant Version_32 := 16#08AB6B2C#;
u00028 : constant Version_32 := 16#3FA37670#;
u00029 : constant Version_32 := 16#476457A0#;
u00030 : constant Version_32 := 16#731E1B6E#;
u00031 : constant Version_32 := 16#23C2E789#;
u00032 : constant Version_32 := 16#0F1BD6A1#;
u00033 : constant Version_32 := 16#7C25DE96#;
u00034 : constant Version_32 := 16#39ADFFA2#;
u00035 : constant Version_32 := 16#571DE3E7#;
u00036 : constant Version_32 := 16#5EB646AB#;
u00037 : constant Version_32 := 16#4249379B#;
u00038 : constant Version_32 := 16#0357E00A#;
u00039 : constant Version_32 := 16#3784FB72#;
u00040 : constant Version_32 := 16#2E723019#;
u00041 : constant Version_32 := 16#623358EA#;
u00042 : constant Version_32 := 16#107F9465#;
u00043 : constant Version_32 := 16#6843F68A#;
u00044 : constant Version_32 := 16#63305874#;
u00045 : constant Version_32 := 16#31E56CE1#;
u00046 : constant Version_32 := 16#02917970#;
u00047 : constant Version_32 := 16#6CCBA70E#;
u00048 : constant Version_32 := 16#41CD4204#;
u00049 : constant Version_32 := 16#572E3F58#;
u00050 : constant Version_32 := 16#20729FF5#;
u00051 : constant Version_32 := 16#1D4F93E8#;
u00052 : constant Version_32 := 16#30B2EC3D#;
u00053 : constant Version_32 := 16#34054F96#;
u00054 : constant Version_32 := 16#5A199860#;
u00055 : constant Version_32 := 16#0E7F912B#;
u00056 : constant Version_32 := 16#5760634A#;
u00057 : constant Version_32 := 16#5D851835#;
-- The following Export pragmas export the version numbers
-- with symbolic names ending in B (for body) or S
-- (for spec) so that they can be located in a link. The
-- information provided here is sufficient to track down
-- the exact versions of units used in a given build.
pragma Export (C, u00001, "helloB");
pragma Export (C, u00002, "system__standard_libraryB");
pragma Export (C, u00003, "system__standard_libraryS");
pragma Export (C, u00004, "adaS");
pragma Export (C, u00005, "ada__text_ioB");
pragma Export (C, u00006, "ada__text_ioS");
pragma Export (C, u00007, "ada__exceptionsB");
pragma Export (C, u00008, "ada__exceptionsS");
pragma Export (C, u00009, "gnatS");
pragma Export (C, u00010, "gnat__heap_sort_aB");
pragma Export (C, u00011, "gnat__heap_sort_aS");
pragma Export (C, u00012, "systemS");
pragma Export (C, u00013, "system__exception_tableB");
pragma Export (C, u00014, "system__exception_tableS");
pragma Export (C, u00015, "gnat__htableB");
pragma Export (C, u00016, "gnat__htableS");
pragma Export (C, u00017, "system__exceptionsS");
pragma Export (C, u00018, "system__machine_state_operationsB");
pragma Export (C, u00019, "system__machine_state_operationsS");
pragma Export (C, u00020, "system__machine_codeS");
pragma Export (C, u00021, "system__storage_elementsB");
pragma Export (C, u00022, "system__storage_elementsS");
pragma Export (C, u00023, "system__secondary_stackB");
pragma Export (C, u00024, "system__secondary_stackS");
pragma Export (C, u00025, "system__parametersB");
pragma Export (C, u00026, "system__parametersS");
pragma Export (C, u00027, "system__soft_linksB");
pragma Export (C, u00028, "system__soft_linksS");
pragma Export (C, u00029, "system__stack_checkingB");
pragma Export (C, u00030, "system__stack_checkingS");
pragma Export (C, u00031, "system__tracebackB");
pragma Export (C, u00032, "system__tracebackS");
pragma Export (C, u00033, "ada__streamsS");
pragma Export (C, u00034, "ada__tagsB");
pragma Export (C, u00035, "ada__tagsS");
pragma Export (C, u00036, "system__string_opsB");
pragma Export (C, u00037, "system__string_opsS");
pragma Export (C, u00038, "interfacesS");
pragma Export (C, u00039, "interfaces__c_streamsB");
pragma Export (C, u00040, "interfaces__c_streamsS");
pragma Export (C, u00041, "system__file_ioB");
pragma Export (C, u00042, "system__file_ioS");
pragma Export (C, u00043, "ada__finalizationB");
pragma Export (C, u00044, "ada__finalizationS");
pragma Export (C, u00045, "system__finalization_rootB");
pragma Export (C, u00046, "system__finalization_rootS");
pragma Export (C, u00047, "system__finalization_implementationB");
pragma Export (C, u00048, "system__finalization_implementationS");
pragma Export (C, u00049, "system__string_ops_concat_3B");
pragma Export (C, u00050, "system__string_ops_concat_3S");
pragma Export (C, u00051, "system__stream_attributesB");
pragma Export (C, u00052, "system__stream_attributesS");
pragma Export (C, u00053, "ada__io_exceptionsS");
pragma Export (C, u00054, "system__unsigned_typesS");
pragma Export (C, u00055, "system__file_control_blockS");
pragma Export (C, u00056, "ada__finalization__list_controllerB");
pragma Export (C, u00057, "ada__finalization__list_controllerS");
-- BEGIN ELABORATION ORDER
-- ada (spec)
-- gnat (spec)
-- gnat.heap_sort_a (spec)
-- gnat.heap_sort_a (body)
-- gnat.htable (spec)
-- gnat.htable (body)
-- interfaces (spec)
-- system (spec)
-- system.machine_code (spec)
-- system.parameters (spec)
-- system.parameters (body)
-- interfaces.c_streams (spec)
-- interfaces.c_streams (body)
-- system.standard_library (spec)
-- ada.exceptions (spec)
-- system.exception_table (spec)
-- system.exception_table (body)
-- ada.io_exceptions (spec)
-- system.exceptions (spec)
-- system.storage_elements (spec)
-- system.storage_elements (body)
-- system.machine_state_operations (spec)
-- system.machine_state_operations (body)
-- system.secondary_stack (spec)
-- system.stack_checking (spec)
-- system.soft_links (spec)
-- system.soft_links (body)
-- system.stack_checking (body)
-- system.secondary_stack (body)
-- system.standard_library (body)
-- system.string_ops (spec)
-- system.string_ops (body)
-- ada.tags (spec)
-- ada.tags (body)
-- ada.streams (spec)
-- system.finalization_root (spec)
-- system.finalization_root (body)
-- system.string_ops_concat_3 (spec)
-- system.string_ops_concat_3 (body)
-- system.traceback (spec)
-- system.traceback (body)
-- ada.exceptions (body)
-- system.unsigned_types (spec)
-- system.stream_attributes (spec)
-- system.stream_attributes (body)
-- system.finalization_implementation (spec)
-- system.finalization_implementation (body)
-- ada.finalization (spec)
-- ada.finalization (body)
-- ada.finalization.list_controller (spec)
-- ada.finalization.list_controller (body)
-- system.file_control_block (spec)
-- system.file_io (spec)
-- system.file_io (body)
-- ada.text_io (spec)
-- ada.text_io (body)
-- hello (body)
-- END ELABORATION ORDER
end ada_main;
-- The following source file name pragmas allow the generated file
-- names to be unique for different main programs. They are needed
-- since the package name will always be Ada_Main.
pragma Source_File_Name (ada_main, Spec_File_Name => "b~hello.ads");
pragma Source_File_Name (ada_main, Body_File_Name => "b~hello.adb");
-- Generated package body for Ada_Main starts here
package body ada_main is
-- The actual finalization is performed by calling the
-- library routine in System.Standard_Library.Adafinal
procedure Do_Finalize;
pragma Import (C, Do_Finalize, "system__standard_library__adafinal");
-------------
-- adainit --
-------------
procedure adainit is
-- These booleans are set to True once the associated unit has
-- been elaborated. It is also used to avoid elaborating the
-- same unit twice.
E040 : Boolean;
pragma Import (Ada, E040, "interfaces__c_streams_E");
E008 : Boolean;
pragma Import (Ada, E008, "ada__exceptions_E");
E014 : Boolean;
pragma Import (Ada, E014, "system__exception_table_E");
E053 : Boolean;
pragma Import (Ada, E053, "ada__io_exceptions_E");
E017 : Boolean;
pragma Import (Ada, E017, "system__exceptions_E");
E024 : Boolean;
pragma Import (Ada, E024, "system__secondary_stack_E");
E030 : Boolean;
pragma Import (Ada, E030, "system__stack_checking_E");
E028 : Boolean;
pragma Import (Ada, E028, "system__soft_links_E");
E035 : Boolean;
pragma Import (Ada, E035, "ada__tags_E");
E033 : Boolean;
pragma Import (Ada, E033, "ada__streams_E");
E046 : Boolean;
pragma Import (Ada, E046, "system__finalization_root_E");
E048 : Boolean;
pragma Import (Ada, E048, "system__finalization_implementation_E");
E044 : Boolean;
pragma Import (Ada, E044, "ada__finalization_E");
E057 : Boolean;
pragma Import (Ada, E057, "ada__finalization__list_controller_E");
E055 : Boolean;
pragma Import (Ada, E055, "system__file_control_block_E");
E042 : Boolean;
pragma Import (Ada, E042, "system__file_io_E");
E006 : Boolean;
pragma Import (Ada, E006, "ada__text_io_E");
-- Set_Globals is a library routine that stores away the
-- value of the indicated set of global values in global
-- variables within the library.
procedure Set_Globals
(Main_Priority : Integer;
Time_Slice_Value : Integer;
WC_Encoding : Character;
Locking_Policy : Character;
Queuing_Policy : Character;
Task_Dispatching_Policy : Character;
Adafinal : System.Address;
Unreserve_All_Interrupts : Integer;
Exception_Tracebacks : Integer);
pragma Import (C, Set_Globals, "__gnat_set_globals");
-- SDP_Table_Build is a library routine used to build the
-- exception tables. See unit Ada.Exceptions in files
-- a-except.ads/adb for full details of how zero cost
-- exception handling works. This procedure, the call to
-- it, and the two following tables are all omitted if the
-- build is in longjmp/setjmp exception mode.
procedure SDP_Table_Build
(SDP_Addresses : System.Address;
SDP_Count : Natural;
Elab_Addresses : System.Address;
Elab_Addr_Count : Natural);
pragma Import (C, SDP_Table_Build, "__gnat_SDP_Table_Build");
-- Table of Unit_Exception_Table addresses. Used for zero
-- cost exception handling to build the top level table.
ST : aliased constant array (1 .. 23) of System.Address := (
Hello'UET_Address,
Ada.Text_Io'UET_Address,
Ada.Exceptions'UET_Address,
Gnat.Heap_Sort_A'UET_Address,
System.Exception_Table'UET_Address,
System.Machine_State_Operations'UET_Address,
System.Secondary_Stack'UET_Address,
System.Parameters'UET_Address,
System.Soft_Links'UET_Address,
System.Stack_Checking'UET_Address,
System.Traceback'UET_Address,
Ada.Streams'UET_Address,
Ada.Tags'UET_Address,
System.String_Ops'UET_Address,
Interfaces.C_Streams'UET_Address,
System.File_Io'UET_Address,
Ada.Finalization'UET_Address,
System.Finalization_Root'UET_Address,
System.Finalization_Implementation'UET_Address,
System.String_Ops_Concat_3'UET_Address,
System.Stream_Attributes'UET_Address,
System.File_Control_Block'UET_Address,
Ada.Finalization.List_Controller'UET_Address);
-- Table of addresses of elaboration routines. Used for
-- zero cost exception handling to make sure these
-- addresses are included in the top level procedure
-- address table.
EA : aliased constant array (1 .. 23) of System.Address := (
adainit'Code_Address,
Do_Finalize'Code_Address,
Ada.Exceptions'Elab_Spec'Address,
System.Exceptions'Elab_Spec'Address,
Interfaces.C_Streams'Elab_Spec'Address,
System.Exception_Table'Elab_Body'Address,
Ada.Io_Exceptions'Elab_Spec'Address,
System.Stack_Checking'Elab_Spec'Address,
System.Soft_Links'Elab_Body'Address,
System.Secondary_Stack'Elab_Body'Address,
Ada.Tags'Elab_Spec'Address,
Ada.Tags'Elab_Body'Address,
Ada.Streams'Elab_Spec'Address,
System.Finalization_Root'Elab_Spec'Address,
Ada.Exceptions'Elab_Body'Address,
System.Finalization_Implementation'Elab_Spec'Address,
System.Finalization_Implementation'Elab_Body'Address,
Ada.Finalization'Elab_Spec'Address,
Ada.Finalization.List_Controller'Elab_Spec'Address,
System.File_Control_Block'Elab_Spec'Address,
System.File_Io'Elab_Body'Address,
Ada.Text_Io'Elab_Spec'Address,
Ada.Text_Io'Elab_Body'Address);
-- Start of processing for adainit
begin
-- Call SDP_Table_Build to build the top level procedure
-- table for zero cost exception handling (omitted in
-- longjmp/setjmp mode).
SDP_Table_Build (ST'Address, 23, EA'Address, 23);
-- Call Set_Globals to record various information for
-- this partition. The values are derived by the binder
-- from information stored in the ali files by the compiler.
Set_Globals
(Main_Priority => -1,
-- Priority of main program, -1 if no pragma Priority used
Time_Slice_Value => -1,
-- Time slice from Time_Slice pragma, -1 if none used
WC_Encoding => 'b',
-- Wide_Character encoding used, default is brackets
Locking_Policy => ' ',
-- Locking_Policy used, default of space means not
-- specified, otherwise it is the first character of
-- the policy name.
Queuing_Policy => ' ',
-- Queuing_Policy used, default of space means not
-- specified, otherwise it is the first character of
-- the policy name.
Task_Dispatching_Policy => ' ',
-- Task_Dispatching_Policy used, default of space means
-- not specified, otherwise first character of the
-- policy name.
Adafinal => System.Null_Address,
-- Address of Adafinal routine, not used anymore
Unreserve_All_Interrupts => 0,
-- Set true if pragma Unreserve_All_Interrupts was used
Exception_Tracebacks => 0);
-- Indicates if exception tracebacks are enabled
Elab_Final_Code := 1;
-- Now we have the elaboration calls for all units in the partition.
-- The Elab_Spec and Elab_Body attributes generate references to the
-- implicit elaboration procedures generated by the compiler for
-- each unit that requires elaboration.
if not E040 then
Interfaces.C_Streams'Elab_Spec;
end if;
E040 := True;
if not E008 then
Ada.Exceptions'Elab_Spec;
end if;
if not E014 then
System.Exception_Table'Elab_Body;
E014 := True;
end if;
if not E053 then
Ada.Io_Exceptions'Elab_Spec;
E053 := True;
end if;
if not E017 then
System.Exceptions'Elab_Spec;
E017 := True;
end if;
if not E030 then
System.Stack_Checking'Elab_Spec;
end if;
if not E028 then
System.Soft_Links'Elab_Body;
E028 := True;
end if;
E030 := True;
if not E024 then
System.Secondary_Stack'Elab_Body;
E024 := True;
end if;
if not E035 then
Ada.Tags'Elab_Spec;
end if;
if not E035 then
Ada.Tags'Elab_Body;
E035 := True;
end if;
if not E033 then
Ada.Streams'Elab_Spec;
E033 := True;
end if;
if not E046 then
System.Finalization_Root'Elab_Spec;
end if;
E046 := True;
if not E008 then
Ada.Exceptions'Elab_Body;
E008 := True;
end if;
if not E048 then
System.Finalization_Implementation'Elab_Spec;
end if;
if not E048 then
System.Finalization_Implementation'Elab_Body;
E048 := True;
end if;
if not E044 then
Ada.Finalization'Elab_Spec;
end if;
E044 := True;
if not E057 then
Ada.Finalization.List_Controller'Elab_Spec;
end if;
E057 := True;
if not E055 then
System.File_Control_Block'Elab_Spec;
E055 := True;
end if;
if not E042 then
System.File_Io'Elab_Body;
E042 := True;
end if;
if not E006 then
Ada.Text_Io'Elab_Spec;
end if;
if not E006 then
Ada.Text_Io'Elab_Body;
E006 := True;
end if;
Elab_Final_Code := 0;
end adainit;
--------------
-- adafinal --
--------------
procedure adafinal is
begin
Do_Finalize;
end adafinal;
----------
-- main --
----------
-- main is actually a function, as in the ANSI C standard,
-- defined to return the exit status. The three parameters
-- are the argument count, argument values and environment
-- pointer.
function main
(argc : Integer;
argv : System.Address;
envp : System.Address)
return Integer
is
-- The initialize routine performs low level system
-- initialization using a standard library routine which
-- sets up signal handling and performs any other
-- required setup. The routine can be found in file
-- a-init.c.
procedure initialize;
pragma Import (C, initialize, "__gnat_initialize");
-- The finalize routine performs low level system
-- finalization using a standard library routine. The
-- routine is found in file a-final.c and in the standard
-- distribution is a dummy routine that does nothing, so
-- really this is a hook for special user finalization.
procedure finalize;
pragma Import (C, finalize, "__gnat_finalize");
-- We get to the main program of the partition by using
-- pragma Import because if we try to with the unit and
-- call it Ada style, then not only do we waste time
-- recompiling it, but also, we don't really know the right
-- switches (e.g. identifier character set) to be used
-- to compile it.
procedure Ada_Main_Program;
pragma Import (Ada, Ada_Main_Program, "_ada_hello");
-- Start of processing for main
begin
-- Save global variables
gnat_argc := argc;
gnat_argv := argv;
gnat_envp := envp;
-- Call low level system initialization
Initialize;
-- Call our generated Ada initialization routine
adainit;
-- This is the point at which we want the debugger to get
-- control
Break_Start;
-- Now we call the main program of the partition
Ada_Main_Program;
-- Perform Ada finalization
adafinal;
-- Perform low level system finalization
Finalize;
-- Return the proper exit status
return (gnat_exit_status);
end;
-- This section is entirely comments, so it has no effect on the
-- compilation of the Ada_Main package. It provides the list of
-- object files and linker options, as well as some standard
-- libraries needed for the link. The gnatlink utility parses
-- this b~hello.adb file to read these comment lines to generate
-- the appropriate command line arguments for the call to the
-- system linker. The BEGIN/END lines are used for sentinels for
-- this parsing operation.
-- The exact file names will of course depend on the environment,
-- host/target and location of files on the host system.
-- BEGIN Object file/option list
-- ./hello.o
-- -L./
-- -L/usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/
-- /usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/libgnat.a
-- END Object file/option list
end ada_main;
The Ada code in the above example is exactly what is generated by the
binder. We have added comments to more clearly indicate the function
of each part of the generated Ada_Main package.
The code is standard Ada in all respects, and can be processed by any
tools that handle Ada. In particular, it is possible to use the debugger
in Ada mode to debug the generated Ada_Main package. For example,
suppose that for reasons that you do not understand, your program is crashing
during elaboration of the body of Ada.Text_IO. To locate this bug,
you can place a breakpoint on the call:
Ada.Text_Io'Elab_Body;
and trace the elaboration routine for this package to find out where the problem might be (more usually of course you would be debugging elaboration code in your own application).
Next: Overflow Check Handling in GNAT, Previous: Example of Binder Output File, Up: Top [Contents][Index]
This chapter describes the handling of elaboration code in Ada and in GNAT, and discusses how the order of elaboration of program units can be controlled in GNAT, either automatically or with explicit programming features.
Next: Checking the Elaboration Order, Previous: HP-UX-Specific Considerations, Up: Elaboration Order Handling in GNAT [Contents][Index]
Ada provides rather general mechanisms for executing code at elaboration time, that is to say before the main program starts executing. Such code arises in three contexts:
Variables declared at the library level, in package specs or bodies, can require initialization that is performed at elaboration time, as in:
Sqrt_Half : Float := Sqrt (0.5); |
Code in a BEGIN-END section at the outer level of a package body is
executed as part of the package body elaboration code.
Tasks that are declared using task allocators at the library level start executing immediately and hence can execute at elaboration time.
Subprogram calls are possible in any of these contexts, which means that any arbitrary part of the program may be executed as part of the elaboration code. It is even possible to write a program which does all its work at elaboration time, with a null main program, although stylistically this would usually be considered an inappropriate way to structure a program.
An important concern arises in the context of elaboration code:
we have to be sure that it is executed in an appropriate order. What we
have is a series of elaboration code sections, potentially one section
for each unit in the program. It is important that these execute
in the correct order. Correctness here means that, taking the above
example of the declaration of Sqrt_Half,
if some other piece of
elaboration code references Sqrt_Half,
then it must run after the
section of elaboration code that contains the declaration of
Sqrt_Half.
There would never be any order of elaboration problem if we made a rule
that whenever you with a unit, you must elaborate both the spec and body
of that unit before elaborating the unit doing the with’ing:
with Unit_1; package Unit_2 is … |
would require that both the body and spec of Unit_1 be elaborated
before the spec of Unit_2. However, a rule like that would be far too
restrictive. In particular, it would make it impossible to have routines
in separate packages that were mutually recursive.
You might think that a clever enough compiler could look at the actual elaboration code and determine an appropriate correct order of elaboration, but in the general case, this is not possible. Consider the following example.
In the body of Unit_1, we have a procedure Func_1
that references
the variable Sqrt_1, which is declared in the elaboration code
of the body of Unit_1:
Sqrt_1 : Float := Sqrt (0.1); |
The elaboration code of the body of Unit_1 also contains:
if expression_1 = 1 then Q := Unit_2.Func_2; end if; |
Unit_2 is exactly parallel,
it has a procedure Func_2 that references
the variable Sqrt_2, which is declared in the elaboration code of
the body Unit_2:
Sqrt_2 : Float := Sqrt (0.1); |
The elaboration code of the body of Unit_2 also contains:
if expression_2 = 2 then Q := Unit_1.Func_1; end if; |
Now the question is, which of the following orders of elaboration is acceptable:
Spec of Unit_1 Spec of Unit_2 Body of Unit_1 Body of Unit_2
or
Spec of Unit_2 Spec of Unit_1 Body of Unit_2 Body of Unit_1
If you carefully analyze the flow here, you will see that you cannot tell
at compile time the answer to this question.
If expression_1 is not equal to 1,
and expression_2 is not equal to 2,
then either order is acceptable, because neither of the function calls is
executed. If both tests evaluate to true, then neither order is acceptable
and in fact there is no correct order.
If one of the two expressions is true, and the other is false, then one
of the above orders is correct, and the other is incorrect. For example,
if expression_1 /= 1 and expression_2 = 2,
then the call to Func_1
will occur, but not the call to Func_2.
This means that it is essential
to elaborate the body of Unit_1 before
the body of Unit_2, so the first
order of elaboration is correct and the second is wrong.
By making expression_1 and expression_2
depend on input data, or perhaps
the time of day, we can make it impossible for the compiler or binder
to figure out which of these expressions will be true, and hence it
is impossible to guarantee a safe order of elaboration at run time.
Next: Controlling the Elaboration Order, Previous: Elaboration Code, Up: Elaboration Order Handling in GNAT [Contents][Index]
In some languages that involve the same kind of elaboration problems, e.g. Java and C++, the programmer is expected to worry about these ordering problems himself, and it is common to write a program in which an incorrect elaboration order gives surprising results, because it references variables before they are initialized. Ada is designed to be a safe language, and a programmer-beware approach is clearly not sufficient. Consequently, the language provides three lines of defense:
Some standard rules restrict the possible choice of elaboration
order. In particular, if you with a unit, then its spec is always
elaborated before the unit doing the with. Similarly, a parent
spec is always elaborated before the child spec, and finally
a spec is always elaborated before its corresponding body.
Dynamic checks are made at run time, so that if some entity is accessed
before it is elaborated (typically by means of a subprogram call)
then the exception (Program_Error) is raised.
Facilities are provided for the programmer to specify the desired order of elaboration.
Let’s look at these facilities in more detail. First, the rules for dynamic checking. One possible rule would be simply to say that the exception is raised if you access a variable which has not yet been elaborated. The trouble with this approach is that it could require expensive checks on every variable reference. Instead Ada has two rules which are a little more restrictive, but easier to check, and easier to state:
A subprogram can only be called at elaboration time if its body
has been elaborated. The rules for elaboration given above guarantee
that the spec of the subprogram has been elaborated before the
call, but not the body. If this rule is violated, then the
exception Program_Error is raised.
A generic unit can only be instantiated if the body of the generic
unit has been elaborated. Again, the rules for elaboration given above
guarantee that the spec of the generic unit has been elaborated
before the instantiation, but not the body. If this rule is
violated, then the exception Program_Error is raised.
The idea is that if the body has been elaborated, then any variables it references must have been elaborated; by checking for the body being elaborated we guarantee that none of its references causes any trouble. As we noted above, this is a little too restrictive, because a subprogram that has no non-local references in its body may in fact be safe to call. However, it really would be unsafe to rely on this, because it would mean that the caller was aware of details of the implementation in the body. This goes against the basic tenets of Ada.
A plausible implementation can be described as follows.
A Boolean variable is associated with each subprogram
and each generic unit. This variable is initialized to False, and is set to
True at the point body is elaborated. Every call or instantiation checks the
variable, and raises Program_Error if the variable is False.
Note that one might think that it would be good enough to have one Boolean
variable for each package, but that would not deal with cases of trying
to call a body in the same package as the call
that has not been elaborated yet.
Of course a compiler may be able to do enough analysis to optimize away
some of the Boolean variables as unnecessary, and GNAT indeed
does such optimizations, but still the easiest conceptual model is to
think of there being one variable per subprogram.
Next: Controlling Elaboration in GNAT - Internal Calls, Previous: Checking the Elaboration Order, Up: Elaboration Order Handling in GNAT [Contents][Index]
In the previous section we discussed the rules in Ada which ensure
that Program_Error is raised if an incorrect elaboration order is
chosen. This prevents erroneous executions, but we need mechanisms to
specify a correct execution and avoid the exception altogether.
To achieve this, Ada provides a number of features for controlling
the order of elaboration. We discuss these features in this section.
First, there are several ways of indicating to the compiler that a given unit has no elaboration problems:
A library package that does not require a body does not permit a body (this rule was introduced in Ada 95). Thus if we have a such a package, as in:
package Definitions is
generic
type m is new integer;
package Subp is
type a is array (1 .. 10) of m;
type b is array (1 .. 20) of m;
end Subp;
end Definitions;
|
A package that with’s Definitions may safely instantiate
Definitions.Subp because the compiler can determine that there
definitely is no package body to worry about in this case
Places sufficient restrictions on a unit to guarantee that no call to any subprogram in the unit can result in an elaboration problem. This means that the compiler does not need to worry about the point of elaboration of such units, and in particular, does not need to check any calls to any subprograms in this unit.
This pragma places slightly less stringent restrictions on a unit than does pragma Pure, but these restrictions are still sufficient to ensure that there are no elaboration problems with any calls to the unit.
This pragma requires that the body of a unit be elaborated immediately
after its spec. Suppose a unit A has such a pragma,
and unit B does
a with of unit A. Recall that the standard rules require
the spec of unit A
to be elaborated before the with’ing unit; given the pragma in
A, we also know that the body of A
will be elaborated before B, so
that calls to A are safe and do not need a check.
Note that,
unlike pragma Pure and pragma Preelaborate,
the use of
Elaborate_Body does not guarantee that the program is
free of elaboration problems, because it may not be possible
to satisfy the requested elaboration order.
Let’s go back to the example with Unit_1 and Unit_2.
If a programmer
marks Unit_1 as Elaborate_Body,
and not Unit_2, then the order of
elaboration will be:
Spec of Unit_2 Spec of Unit_1 Body of Unit_1 Body of Unit_2
Now that means that the call to Func_1 in Unit_2
need not be checked,
it must be safe. But the call to Func_2 in
Unit_1 may still fail if
Expression_1 is equal to 1,
and the programmer must still take
responsibility for this not being the case.
If all units carry a pragma Elaborate_Body, then all problems are
eliminated, except for calls entirely within a body, which are
in any case fully under programmer control. However, using the pragma
everywhere is not always possible.
In particular, for our Unit_1/Unit_2 example, if
we marked both of them as having pragma Elaborate_Body, then
clearly there would be no possible elaboration order.
The above pragmas allow a server to guarantee safe use by clients, and
clearly this is the preferable approach. Consequently a good rule
is to mark units as Pure or Preelaborate if possible,
and if this is not possible,
mark them as Elaborate_Body if possible.
As we have seen, there are situations where neither of these
three pragmas can be used.
So we also provide methods for clients to control the
order of elaboration of the servers on which they depend:
This pragma is placed in the context clause, after a with clause,
and it requires that the body of the named unit be elaborated before
the unit in which the pragma occurs. The idea is to use this pragma
if the current unit calls at elaboration time, directly or indirectly,
some subprogram in the named unit.
This is a stronger version of the Elaborate pragma. Consider the following example:
Unit Awith's unit B and calls B.Func in elab code Unit Bwith's unit C, and B.Func calls C.Func
Now if we put a pragma Elaborate (B)
in unit A, this ensures that the
body of B is elaborated before the call, but not the
body of C, so
the call to C.Func could still cause Program_Error to
be raised.
The effect of a pragma Elaborate_All is stronger, it requires
not only that the body of the named unit be elaborated before the
unit doing the with, but also the bodies of all units that the
named unit uses, following with links transitively. For example,
if we put a pragma Elaborate_All (B) in unit A,
then it requires
not only that the body of B be elaborated before A,
but also the
body of C, because B with’s C.
We are now in a position to give a usage rule in Ada for avoiding elaboration problems, at least if dynamic dispatching and access to subprogram values are not used. We will handle these cases separately later.
The rule is simple. If a unit has elaboration code that can directly or
indirectly make a call to a subprogram in a with’ed unit, or instantiate
a generic package in a with’ed unit,
then if the with’ed unit does not have
pragma Pure or Preelaborate, then the client should have
a pragma Elaborate_All
for the with’ed unit. By following this rule a client is
assured that calls can be made without risk of an exception.
For generic subprogram instantiations, the rule can be relaxed to
require only a pragma Elaborate since elaborating the body
of a subprogram cannot cause any transitive elaboration (we are
not calling the subprogram in this case, just elaborating its
declaration).
If this rule is not followed, then a program may be in one of four states:
No order of elaboration exists which follows the rules, taking into
account any Elaborate, Elaborate_All,
or Elaborate_Body pragmas. In
this case, an Ada compiler must diagnose the situation at bind
time, and refuse to build an executable program.
One or more acceptable elaboration orders exist, and all of them
generate an elaboration order problem. In this case, the binder
can build an executable program, but Program_Error will be raised
when the program is run.
One or more acceptable elaboration orders exists, and some of them work, and some do not. The programmer has not controlled the order of elaboration, so the binder may or may not pick one of the correct orders, and the program may or may not raise an exception when it is run. This is the worst case, because it means that the program may fail when moved to another compiler, or even another version of the same compiler.
One ore more acceptable elaboration orders exist, and all of them work. In this case the program runs successfully. This state of affairs can be guaranteed by following the rule we gave above, but may be true even if the rule is not followed.
Note that one additional advantage of following our rules on the use
of Elaborate and Elaborate_All
is that the program continues to stay in the ideal (all orders OK) state
even if maintenance
changes some bodies of some units. Conversely, if a program that does
not follow this rule happens to be safe at some point, this state of affairs
may deteriorate silently as a result of maintenance changes.
You may have noticed that the above discussion did not mention
the use of Elaborate_Body. This was a deliberate omission. If you
with an Elaborate_Body unit, it still may be the case that
code in the body makes calls to some other unit, so it is still necessary
to use Elaborate_All on such units.
Next: Controlling Elaboration in GNAT - External Calls, Previous: Controlling the Elaboration Order, Up: Elaboration Order Handling in GNAT [Contents][Index]
In the case of internal calls, i.e., calls within a single package, the programmer has full control over the order of elaboration, and it is up to the programmer to elaborate declarations in an appropriate order. For example writing:
function One return Float;
Q : Float := One;
function One return Float is
begin
return 1.0;
end One;
|
will obviously raise Program_Error at run time, because function
One will be called before its body is elaborated. In this case GNAT will
generate a warning that the call will raise Program_Error:
1. procedure y is
2. function One return Float;
3.
4. Q : Float := One;
|
>>> warning: cannot call "One" before body is elaborated
>>> warning: Program_Error will be raised at run time
5.
6. function One return Float is
7. begin
8. return 1.0;
9. end One;
10.
11. begin
12. null;
13. end;
|
Note that in this particular case, it is likely that the call is safe, because
the function One does not access any global variables.
Nevertheless in Ada, we do not want the validity of the check to depend on
the contents of the body (think about the separate compilation case), so this
is still wrong, as we discussed in the previous sections.
The error is easily corrected by rearranging the declarations so that the
body of One appears before the declaration containing the call
(note that in Ada 95 and Ada 2005,
declarations can appear in any order, so there is no restriction that
would prevent this reordering, and if we write:
function One return Float;
function One return Float is
begin
return 1.0;
end One;
Q : Float := One;
|
then all is well, no warning is generated, and no
Program_Error exception
will be raised.
Things are more complicated when a chain of subprograms is executed:
function A return Integer; function B return Integer; function C return Integer; function B return Integer is begin return A; end; function C return Integer is begin return B; end; X : Integer := C; function A return Integer is begin return 1; end; |
Now the call to C
at elaboration time in the declaration of X is correct, because
the body of C is already elaborated,
and the call to B within the body of
C is correct, but the call
to A within the body of B is incorrect, because the body
of A has not been elaborated, so Program_Error
will be raised on the call to A.
In this case GNAT will generate a
warning that Program_Error may be
raised at the point of the call. Let’s look at the warning:
1. procedure x is
2. function A return Integer;
3. function B return Integer;
4. function C return Integer;
5.
6. function B return Integer is begin return A; end;
|
>>> warning: call to "A" before body is elaborated may
raise Program_Error
>>> warning: "B" called at line 7
>>> warning: "C" called at line 9
7. function C return Integer is begin return B; end;
8.
9. X : Integer := C;
10.
11. function A return Integer is begin return 1; end;
12.
13. begin
14. null;
15. end;
|
Note that the message here says “may raise”, instead of the direct case,
where the message says “will be raised”. That’s because whether
A is
actually called depends in general on run-time flow of control.
For example, if the body of B said
function B return Integer is
begin
if some-condition-depending-on-input-data then
return A;
else
return 1;
end if;
end B;
|
then we could not know until run time whether the incorrect call to A would
actually occur, so Program_Error might
or might not be raised. It is possible for a compiler to
do a better job of analyzing bodies, to
determine whether or not Program_Error
might be raised, but it certainly
couldn’t do a perfect job (that would require solving the halting problem
and is provably impossible), and because this is a warning anyway, it does
not seem worth the effort to do the analysis. Cases in which it
would be relevant are rare.
In practice, warnings of either of the forms given above will usually correspond to real errors, and should be examined carefully and eliminated. In the rare case where a warning is bogus, it can be suppressed by any of the following methods:
Elaboration_Check for the called subprogram
Warnings_Off to turn warnings off for the call
For the internal elaboration check case,
GNAT by default generates the
necessary run-time checks to ensure
that Program_Error is raised if any
call fails an elaboration check. Of course this can only happen if a
warning has been issued as described above. The use of pragma
Suppress (Elaboration_Check) may (but is not guaranteed to) suppress
some of these checks, meaning that it may be possible (but is not
guaranteed) for a program to be able to call a subprogram whose body
is not yet elaborated, without raising a Program_Error exception.
Next: Default Behavior in GNAT - Ensuring Safety, Previous: Controlling Elaboration in GNAT - Internal Calls, Up: Elaboration Order Handling in GNAT [Contents][Index]
The previous section discussed the case in which the execution of a particular thread of elaboration code occurred entirely within a single unit. This is the easy case to handle, because a programmer has direct and total control over the order of elaboration, and furthermore, checks need only be generated in cases which are rare and which the compiler can easily detect. The situation is more complex when separate compilation is taken into account. Consider the following:
package Math is
function Sqrt (Arg : Float) return Float;
end Math;
package body Math is
function Sqrt (Arg : Float) return Float is
begin
…
end Sqrt;
end Math;
with Math; package Stuff is X : Float := Math.Sqrt (0.5); end Stuff; with Stuff; procedure Main is begin … end Main; |
where Main is the main program. When this program is executed, the
elaboration code must first be executed, and one of the jobs of the
binder is to determine the order in which the units of a program are
to be elaborated. In this case we have four units: the spec and body
of Math,
the spec of Stuff and the body of Main).
In what order should the four separate sections of elaboration code
be executed?
There are some restrictions in the order of elaboration that the binder
can choose. In particular, if unit U has a with
for a package X, then you
are assured that the spec of X
is elaborated before U , but you are
not assured that the body of X
is elaborated before U.
This means that in the above case, the binder is allowed to choose the
order:
spec of Math spec of Stuff body of Math body of Main
but that’s not good, because now the call to Math.Sqrt
that happens during
the elaboration of the Stuff
spec happens before the body of Math.Sqrt is
elaborated, and hence causes Program_Error exception to be raised.
At first glance, one might say that the binder is misbehaving, because
obviously you want to elaborate the body of something you with
first, but
that is not a general rule that can be followed in all cases. Consider
package X is … package Y is … with X; package body Y is … with Y; package body X is … |
This is a common arrangement, and, apart from the order of elaboration
problems that might arise in connection with elaboration code, this works fine.
A rule that says that you must first elaborate the body of anything you
with cannot work in this case:
the body of X with’s Y,
which means you would have to
elaborate the body of Y first, but that with’s X,
which means
you have to elaborate the body of X first, but … and we have a
loop that cannot be broken.
It is true that the binder can in many cases guess an order of elaboration
that is unlikely to cause a Program_Error
exception to be raised, and it tries to do so (in the
above example of Math/Stuff/Spec, the GNAT binder will
by default
elaborate the body of Math right after its spec, so all will be well).
However, a program that blindly relies on the binder to be helpful can get into trouble, as we discussed in the previous sections, so GNAT provides a number of facilities for assisting the programmer in developing programs that are robust with respect to elaboration order.
Next: Treatment of Pragma Elaborate, Previous: Controlling Elaboration in GNAT - External Calls, Up: Elaboration Order Handling in GNAT [Contents][Index]
The default behavior in GNAT ensures elaboration safety. In its default mode GNAT implements the rule we previously described as the right approach. Let’s restate it:
with’ed unit, or instantiate a generic
package in a with’ed unit, then if the with’ed unit
does not have pragma Pure or
Preelaborate, then the client should have an
Elaborate_All pragma for the with’ed unit.
In the case of instantiating a generic subprogram, it is always
sufficient to have only an Elaborate pragma for the
with’ed unit.
By following this rule a client is assured that calls and instantiations can be made without risk of an exception.
In this mode GNAT traces all calls that are potentially made from
elaboration code, and puts in any missing implicit Elaborate
and Elaborate_All pragmas.
The advantage of this approach is that no elaboration problems
are possible if the binder can find an elaboration order that is
consistent with these implicit Elaborate and
Elaborate_All pragmas. The
disadvantage of this approach is that no such order may exist.
If the binder does not generate any diagnostics, then it means that it has
found an elaboration order that is guaranteed to be safe. However, the binder
may still be relying on implicitly generated Elaborate and
Elaborate_All pragmas so portability to other compilers than GNAT is not
guaranteed.
If it is important to guarantee portability, then the compilations should
use the
-gnatwl
(warn on elaboration problems) switch. This will cause warning messages
to be generated indicating the missing Elaborate and
Elaborate_All pragmas.
Consider the following source program:
with k; package j is m : integer := k.r; end; |
where it is clear that there
should be a pragma Elaborate_All
for unit k. An implicit pragma will be generated, and it is
likely that the binder will be able to honor it. However, if you want
to port this program to some other Ada compiler than GNAT.
it is safer to include the pragma explicitly in the source. If this
unit is compiled with the
-gnatwl
switch, then the compiler outputs a warning:
1. with k;
2. package j is
3. m : integer := k.r;
|
>>> warning: call to "r" may raise Program_Error
>>> warning: missing pragma Elaborate_All for "k"
4. end;
|
and these warnings can be used as a guide for supplying manually
the missing pragmas. It is usually a bad idea to use this warning
option during development. That’s because it will warn you when
you need to put in a pragma, but cannot warn you when it is time
to take it out. So the use of pragma Elaborate_All may lead to
unnecessary dependencies and even false circularities.
This default mode is more restrictive than the Ada Reference Manual, and it is possible to construct programs which will compile using the dynamic model described there, but will run into a circularity using the safer static model we have described.
Of course any Ada compiler must be able to operate in a mode consistent with the requirements of the Ada Reference Manual, and in particular must have the capability of implementing the standard dynamic model of elaboration with run-time checks.
In GNAT, this standard mode can be achieved either by the use of
the -gnatE switch on the compiler (gcc or
gnatmake) command, or by the use of the configuration pragma:
pragma Elaboration_Checks (DYNAMIC);
Either approach will cause the unit affected to be compiled using the standard dynamic run-time elaboration checks described in the Ada Reference Manual. The static model is generally preferable, since it is clearly safer to rely on compile and link time checks rather than run-time checks. However, in the case of legacy code, it may be difficult to meet the requirements of the static model. This issue is further discussed in What to Do If the Default Elaboration Behavior Fails.
Note that the static model provides a strict subset of the allowed behavior and programs of the Ada Reference Manual, so if you do adhere to the static model and no circularities exist, then you are assured that your program will work using the dynamic model, providing that you remove any pragma Elaborate statements from the source.
Next: Elaboration Issues for Library Tasks, Previous: Default Behavior in GNAT - Ensuring Safety, Up: Elaboration Order Handling in GNAT [Contents][Index]
The use of pragma Elaborate
should generally be avoided in Ada 95 and Ada 2005 programs,
since there is no guarantee that transitive calls
will be properly handled. Indeed at one point, this pragma was placed
in Annex J (Obsolescent Features), on the grounds that it is never useful.
Now that’s a bit restrictive. In practice, the case in which
pragma Elaborate is useful is when the caller knows that there
are no transitive calls, or that the called unit contains all necessary
transitive pragma Elaborate statements, and legacy code often
contains such uses.
Strictly speaking the static mode in GNAT should ignore such pragmas,
since there is no assurance at compile time that the necessary safety
conditions are met. In practice, this would cause GNAT to be incompatible
with correctly written Ada 83 code that had all necessary
pragma Elaborate statements in place. Consequently, we made the
decision that GNAT in its default mode will believe that if it encounters
a pragma Elaborate then the programmer knows what they are doing,
and it will trust that no elaboration errors can occur.
The result of this decision is two-fold. First to be safe using the
static mode, you should remove all pragma Elaborate statements.
Second, when fixing circularities in existing code, you can selectively
use pragma Elaborate statements to convince the static mode of
GNAT that it need not generate an implicit pragma Elaborate_All
statement.
When using the static mode with -gnatwl, any use of
pragma Elaborate will generate a warning about possible
problems.
Next: Mixing Elaboration Models, Previous: Treatment of Pragma Elaborate, Up: Elaboration Order Handling in GNAT [Contents][Index]
In this section we examine special elaboration issues that arise for programs that declare library level tasks.
Generally the model of execution of an Ada program is that all units are elaborated, and then execution of the program starts. However, the declaration of library tasks definitely does not fit this model. The reason for this is that library tasks start as soon as they are declared (more precisely, as soon as the statement part of the enclosing package body is reached), that is to say before elaboration of the program is complete. This means that if such a task calls a subprogram, or an entry in another task, the callee may or may not be elaborated yet, and in the standard Reference Manual model of dynamic elaboration checks, you can even get timing dependent Program_Error exceptions, since there can be a race between the elaboration code and the task code.
The static model of elaboration in GNAT seeks to avoid all such dynamic behavior, by being conservative, and the conservative approach in this particular case is to assume that all the code in a task body is potentially executed at elaboration time if a task is declared at the library level.
This can definitely result in unexpected circularities. Consider the following example
package Decls is
task Lib_Task is
entry Start;
end Lib_Task;
type My_Int is new Integer;
function Ident (M : My_Int) return My_Int;
end Decls;
with Utils;
package body Decls is
task body Lib_Task is
begin
accept Start;
Utils.Put_Val (2);
end Lib_Task;
function Ident (M : My_Int) return My_Int is
begin
return M;
end Ident;
end Decls;
with Decls;
package Utils is
procedure Put_Val (Arg : Decls.My_Int);
end Utils;
with Text_IO;
package body Utils is
procedure Put_Val (Arg : Decls.My_Int) is
begin
Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
end Put_Val;
end Utils;
with Decls;
procedure Main is
begin
Decls.Lib_Task.Start;
end;
If the above example is compiled in the default static elaboration
mode, then a circularity occurs. The circularity comes from the call
Utils.Put_Val in the task body of Decls.Lib_Task. Since
this call occurs in elaboration code, we need an implicit pragma
Elaborate_All for Utils. This means that not only must
the spec and body of Utils be elaborated before the body
of Decls, but also the spec and body of any unit that is
with'ed by the body of Utils must also be elaborated before
the body of Decls. This is the transitive implication of
pragma Elaborate_All and it makes sense, because in general
the body of Put_Val might have a call to something in a
with'ed unit.
In this case, the body of Utils (actually its spec) with's
Decls. Unfortunately this means that the body of Decls
must be elaborated before itself, in case there is a call from the
body of Utils.
Here is the exact chain of events we are worrying about:
Decls a call is made from within the body of a library
task to a subprogram in the package Utils. Since this call may
occur at elaboration time (given that the task is activated at elaboration
time), we have to assume the worst, i.e., that the
call does happen at elaboration time.
Util must be elaborated before
the body of Decls so that this call does not cause an access before
elaboration.
Util, specifically within the body of
Util.Put_Val there may be calls to any unit with’ed
by this package.
with’ed package is package Decls, so there
might be a call to a subprogram in Decls in Put_Val.
In fact there is such a call in this example, but we would have to
assume that there was such a call even if it were not there, since
we are not supposed to write the body of Decls knowing what
is in the body of Utils; certainly in the case of the
static elaboration model, the compiler does not know what is in
other bodies and must assume the worst.
Decls must also be
elaborated before we elaborate the unit containing the call, but
that unit is Decls! This means that the body of Decls
must be elaborated before itself, and that’s a circularity.
Indeed, if you add an explicit pragma Elaborate_All for Utils in
the body of Decls you will get a true Ada Reference Manual
circularity that makes the program illegal.
In practice, we have found that problems with the static model of elaboration in existing code often arise from library tasks, so we must address this particular situation.
Note that if we compile and run the program above, using the dynamic model of elaboration (that is to say use the -gnatE switch), then it compiles, binds, links, and runs, printing the expected result of 2. Therefore in some sense the circularity here is only apparent, and we need to capture the properties of this program that distinguish it from other library-level tasks that have real elaboration problems.
We have four possible answers to this question:
If we use the -gnatE switch, then as noted above, the program works.
Why is this? If we examine the task body, it is apparent that the task cannot
proceed past the
accept statement until after elaboration has been completed, because
the corresponding entry call comes from the main program, not earlier.
This is why the dynamic model works here. But that’s really giving
up on a precise analysis, and we prefer to take this approach only if we cannot
solve the
problem in any other manner. So let us examine two ways to reorganize
the program to avoid the potential elaboration problem.
Write separate packages, so that library tasks are isolated from other declarations as much as possible. Let us look at a variation on the above program.
package Decls1 is
task Lib_Task is
entry Start;
end Lib_Task;
end Decls1;
with Utils;
package body Decls1 is
task body Lib_Task is
begin
accept Start;
Utils.Put_Val (2);
end Lib_Task;
end Decls1;
package Decls2 is
type My_Int is new Integer;
function Ident (M : My_Int) return My_Int;
end Decls2;
with Utils;
package body Decls2 is
function Ident (M : My_Int) return My_Int is
begin
return M;
end Ident;
end Decls2;
with Decls2;
package Utils is
procedure Put_Val (Arg : Decls2.My_Int);
end Utils;
with Text_IO;
package body Utils is
procedure Put_Val (Arg : Decls2.My_Int) is
begin
Text_IO.Put_Line (Decls2.My_Int'Image (Decls2.Ident (Arg)));
end Put_Val;
end Utils;
with Decls1;
procedure Main is
begin
Decls1.Lib_Task.Start;
end;
All we have done is to split Decls into two packages, one
containing the library task, and one containing everything else. Now
there is no cycle, and the program compiles, binds, links and executes
using the default static model of elaboration.
A significant part of the problem arises because of the use of the single task declaration form. This means that the elaboration of the task type, and the elaboration of the task itself (i.e. the creation of the task) happen at the same time. A good rule of style in Ada is to always create explicit task types. By following the additional step of placing task objects in separate packages from the task type declaration, many elaboration problems are avoided. Here is another modified example of the example program:
package Decls is
task type Lib_Task_Type is
entry Start;
end Lib_Task_Type;
type My_Int is new Integer;
function Ident (M : My_Int) return My_Int;
end Decls;
with Utils;
package body Decls is
task body Lib_Task_Type is
begin
accept Start;
Utils.Put_Val (2);
end Lib_Task_Type;
function Ident (M : My_Int) return My_Int is
begin
return M;
end Ident;
end Decls;
with Decls;
package Utils is
procedure Put_Val (Arg : Decls.My_Int);
end Utils;
with Text_IO;
package body Utils is
procedure Put_Val (Arg : Decls.My_Int) is
begin
Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
end Put_Val;
end Utils;
with Decls;
package Declst is
Lib_Task : Decls.Lib_Task_Type;
end Declst;
with Declst;
procedure Main is
begin
Declst.Lib_Task.Start;
end;
What we have done here is to replace the task declaration in
package Decls with a task type declaration. Then we
introduce a separate package Declst to contain the actual
task object. This separates the elaboration issues for
the task type
declaration, which causes no trouble, from the elaboration issues
of the task object, which is also unproblematic, since it is now independent
of the elaboration of Utils.
This separation of concerns also corresponds to
a generally sound engineering principle of separating declarations
from instances. This version of the program also compiles, binds, links,
and executes, generating the expected output.
The previous two approaches described how a program can be restructured to avoid the special problems caused by library task bodies. in practice, however, such restructuring may be difficult to apply to existing legacy code, so we must consider solutions that do not require massive rewriting.
Let us consider more carefully why our original sample program works
under the dynamic model of elaboration. The reason is that the code
in the task body blocks immediately on the accept
statement. Now of course there is nothing to prohibit elaboration
code from making entry calls (for example from another library level task),
so we cannot tell in isolation that
the task will not execute the accept statement during elaboration.
However, in practice it is very unusual to see elaboration code
make any entry calls, and the pattern of tasks starting
at elaboration time and then immediately blocking on accept or
select statements is very common. What this means is that
the compiler is being too pessimistic when it analyzes the
whole package body as though it might be executed at elaboration
time.
If we know that the elaboration code contains no entry calls, (a very safe assumption most of the time, that could almost be made the default behavior), then we can compile all units of the program under control of the following configuration pragma:
pragma Restrictions (No_Entry_Calls_In_Elaboration_Code);
This pragma can be placed in the gnat.adc file in the usual
manner. If we take our original unmodified program and compile it
in the presence of a gnat.adc containing the above pragma,
then once again, we can compile, bind, link, and execute, obtaining
the expected result. In the presence of this pragma, the compiler does
not trace calls in a task body, that appear after the first accept
or select statement, and therefore does not report a potential
circularity in the original program.
The compiler will check to the extent it can that the above restriction is not violated, but it is not always possible to do a complete check at compile time, so it is important to use this pragma only if the stated restriction is in fact met, that is to say no task receives an entry call before elaboration of all units is completed.
Next: What to Do If the Default Elaboration Behavior Fails, Previous: Elaboration Issues for Library Tasks, Up: Elaboration Order Handling in GNAT [Contents][Index]
So far, we have assumed that the entire program is either compiled using the dynamic model or static model, ensuring consistency. It is possible to mix the two models, but rules have to be followed if this mixing is done to ensure that elaboration checks are not omitted.
The basic rule is that a unit compiled with the static model cannot
be with'ed by a unit compiled with the dynamic model. The
reason for this is that in the static model, a unit assumes that
its clients guarantee to use (the equivalent of) pragma
Elaborate_All so that no elaboration checks are required
in inner subprograms, and this assumption is violated if the
client is compiled with dynamic checks.
The precise rule is as follows. A unit that is compiled with dynamic
checks can only with a unit that meets at least one of the
following criteria:
with'ed unit is itself compiled with dynamic elaboration
checks (that is with the -gnatE switch.
with'ed unit is an internal GNAT implementation unit from
the System, Interfaces, Ada, or GNAT hierarchies.
with'ed unit has pragma Preelaborate or pragma Pure.
with'ing unit (that is the client) has an explicit pragma
Elaborate_All for the with'ed unit.
If this rule is violated, that is if a unit with dynamic elaboration
checks with's a unit that does not meet one of the above four
criteria, then the binder (gnatbind) will issue a warning
similar to that in the following example:
warning: "x.ads" has dynamic elaboration checks and with's warning: "y.ads" which has static elaboration checks
These warnings indicate that the rule has been violated, and that as a result elaboration checks may be missed in the resulting executable file. This warning may be suppressed using the -ws binder switch in the usual manner.
One useful application of this mixing rule is in the case of a subsystem
which does not itself with units from the remainder of the
application. In this case, the entire subsystem can be compiled with
dynamic checks to resolve a circularity in the subsystem, while
allowing the main application that uses this subsystem to be compiled
using the more reliable default static model.
Next: Elaboration for Dispatching Calls, Previous: Mixing Elaboration Models, Up: Elaboration Order Handling in GNAT [Contents][Index]
If the binder cannot find an acceptable order, it outputs detailed diagnostics. For example:
error: elaboration circularity detected info: "proc (body)" must be elaborated before "pack (body)" info: reason: Elaborate_All probably needed in unit "pack (body)" info: recompile "pack (body)" with -gnatwl info: for full details info: "proc (body)" info: is needed by its spec: info: "proc (spec)" info: which is withed by: info: "pack (body)" info: "pack (body)" must be elaborated before "proc (body)" info: reason: pragma Elaborate in unit "proc (body)"
In this case we have a cycle that the binder cannot break. On the one
hand, there is an explicit pragma Elaborate in proc for
pack. This means that the body of pack must be elaborated
before the body of proc. On the other hand, there is elaboration
code in pack that calls a subprogram in proc. This means
that for maximum safety, there should really be a pragma
Elaborate_All in pack for proc which would require that
the body of proc be elaborated before the body of
pack. Clearly both requirements cannot be satisfied.
Faced with a circularity of this kind, you have three different options.
The most desirable option from the point of view of long-term maintenance is to rearrange the program so that the elaboration problems are avoided. One useful technique is to place the elaboration code into separate child packages. Another is to move some of the initialization code to explicitly called subprograms, where the program controls the order of initialization explicitly. Although this is the most desirable option, it may be impractical and involve too much modification, especially in the case of complex legacy code.
If the compilations are done using the
-gnatE
(dynamic elaboration check) switch, then GNAT behaves in a quite different
manner. Dynamic checks are generated for all calls that could possibly result
in raising an exception. With this switch, the compiler does not generate
implicit Elaborate or Elaborate_All pragmas. The behavior then is
exactly as specified in the Ada Reference Manual.
The binder will generate
an executable program that may or may not raise Program_Error, and then
it is the programmer’s job to ensure that it does not raise an exception. Note
that it is important to compile all units with the switch, it cannot be used
selectively.
The drawback of dynamic checks is that they generate a
significant overhead at run time, both in space and time. If you
are absolutely sure that your program cannot raise any elaboration
exceptions, and you still want to use the dynamic elaboration model,
then you can use the configuration pragma
Suppress (Elaboration_Check) to suppress all such checks. For
example this pragma could be placed in the gnat.adc file.
When you know that certain calls or instantiations in elaboration code cannot
possibly lead to an elaboration error, and the binder nevertheless complains
about implicit Elaborate and Elaborate_All pragmas that lead to
elaboration circularities, it is possible to remove those warnings locally and
obtain a program that will bind. Clearly this can be unsafe, and it is the
responsibility of the programmer to make sure that the resulting program has no
elaboration anomalies. The pragma Suppress (Elaboration_Check) can be
used with different granularity to suppress warnings and break elaboration
circularities:
pragma Elaborate indicates correctly
that no elaboration checks are required on calls to the designated unit.
There may be cases in which the caller knows that no transitive calls
can occur, so that a pragma Elaborate will be sufficient in a
case where pragma Elaborate_All would cause a circularity.
These five cases are listed in order of decreasing safety, and therefore require increasing programmer care in their application. Consider the following program:
package Pack1 is
function F1 return Integer;
X1 : Integer;
end Pack1;
package Pack2 is
function F2 return Integer;
function Pure (x : integer) return integer;
-- pragma Suppress (Elaboration_Check, On => Pure); -- (3)
-- pragma Suppress (Elaboration_Check); -- (4)
end Pack2;
with Pack2;
package body Pack1 is
function F1 return Integer is
begin
return 100;
end F1;
Val : integer := Pack2.Pure (11); -- Elab. call (1)
begin
declare
-- pragma Suppress(Elaboration_Check, Pack2.F2); -- (1)
-- pragma Suppress(Elaboration_Check); -- (2)
begin
X1 := Pack2.F2 + 1; -- Elab. call (2)
end;
end Pack1;
with Pack1;
package body Pack2 is
function F2 return Integer is
begin
return Pack1.F1;
end F2;
function Pure (x : integer) return integer is
begin
return x ** 3 - 3 * x;
end;
end Pack2;
with Pack1, Ada.Text_IO;
procedure Proc3 is
begin
Ada.Text_IO.Put_Line(Pack1.X1'Img); -- 101
end Proc3;
In the absence of any pragmas, an attempt to bind this program produces the following diagnostics:
error: elaboration circularity detected info: "pack1 (body)" must be elaborated before "pack1 (body)" info: reason: Elaborate_All probably needed in unit "pack1 (body)" info: recompile "pack1 (body)" with -gnatwl for full details info: "pack1 (body)" info: must be elaborated along with its spec: info: "pack1 (spec)" info: which is withed by: info: "pack2 (body)" info: which must be elaborated along with its spec: info: "pack2 (spec)" info: which is withed by: info: "pack1 (body)"
The sources of the circularity are the two calls to Pack2.Pure and
Pack2.F2 in the body of Pack1. We can see that the call to
F2 is safe, even though F2 calls F1, because the call appears after the
elaboration of the body of F1. Therefore the pragma (1) is safe, and will
remove the warning on the call. It is also possible to use pragma (2)
because there are no other potentially unsafe calls in the block.
The call to Pure is safe because this function does not depend on the
state of Pack2. Therefore any call to this function is safe, and it
is correct to place pragma (3) in the corresponding package spec.
Finally, we could place pragma (4) in the spec of Pack2 to disable
warnings on all calls to functions declared therein. Note that this is not
necessarily safe, and requires more detailed examination of the subprogram
bodies involved. In particular, a call to F2 requires that F1
be already elaborated.
It is hard to generalize on which of these four approaches should be
taken. Obviously if it is possible to fix the program so that the default
treatment works, this is preferable, but this may not always be practical.
It is certainly simple enough to use
-gnatE
but the danger in this case is that, even if the GNAT binder
finds a correct elaboration order, it may not always do so,
and certainly a binder from another Ada compiler might not. A
combination of testing and analysis (for which the warnings generated
with the
-gnatwl
switch can be useful) must be used to ensure that the program is free
of errors. One switch that is useful in this testing is the
-p (pessimistic elaboration order)
switch for
gnatbind.
Normally the binder tries to find an order that has the best chance
of avoiding elaboration problems. However, if this switch is used, the binder
plays a devil’s advocate role, and tries to choose the order that
has the best chance of failing. If your program works even with this
switch, then it has a better chance of being error free, but this is still
not a guarantee.
For an example of this approach in action, consider the C-tests (executable tests) from the ACVC suite. If these are compiled and run with the default treatment, then all but one of them succeed without generating any error diagnostics from the binder. However, there is one test that fails, and this is not surprising, because the whole point of this test is to ensure that the compiler can handle cases where it is impossible to determine a correct order statically, and it checks that an exception is indeed raised at run time.
This one test must be compiled and run using the -gnatE switch, and then it passes. Alternatively, the entire suite can be run using this switch. It is never wrong to run with the dynamic elaboration switch if your code is correct, and we assume that the C-tests are indeed correct (it is less efficient, but efficiency is not a factor in running the ACVC tests.)
Next: Summary of Procedures for Elaboration Control, Previous: What to Do If the Default Elaboration Behavior Fails, Up: Elaboration Order Handling in GNAT [Contents][Index]
In rare cases, the static elaboration model fails to prevent
dispatching calls to not-yet-elaborated subprograms. In such cases, we
fall back to run-time checks; premature calls to any primitive
operation of a tagged type before the body of the operation has been
elaborated will raise Program_Error.
Access-to-subprogram types, however, are handled conservatively, and do not require run-time checks. This was not true in earlier versions of the compiler; you can use the -gnatd.U debug switch to revert to the old behavior if the new conservative behavior causes elaboration cycles.
Next: Other Elaboration Order Considerations, Previous: Elaboration for Dispatching Calls, Up: Elaboration Order Handling in GNAT [Contents][Index]
First, compile your program with the default options, using none of
the special elaboration control switches. If the binder successfully
binds your program, then you can be confident that, apart from issues
raised by the use of access-to-subprogram types and dynamic dispatching,
the program is free of elaboration errors. If it is important that the
program be portable, then use the
-gnatwl
switch to generate warnings about missing Elaborate or
Elaborate_All pragmas, and supply the missing pragmas.
If the program fails to bind using the default static elaboration
handling, then you can fix the program to eliminate the binder
message, or recompile the entire program with the
-gnatE switch to generate dynamic elaboration checks,
and, if you are sure there really are no elaboration problems,
use a global pragma Suppress (Elaboration_Check).
Next: Background, Previous: Summary of Procedures for Elaboration Control, Up: Elaboration Order Handling in GNAT [Contents][Index]
This section has been entirely concerned with the issue of finding a valid elaboration order, as defined by the Ada Reference Manual. In a case where several elaboration orders are valid, the task is to find one of the possible valid elaboration orders (and the static model in GNAT will ensure that this is achieved).
The purpose of the elaboration rules in the Ada Reference Manual is to make sure that no entity is accessed before it has been elaborated. For a subprogram, this means that the spec and body must have been elaborated before the subprogram is called. For an object, this means that the object must have been elaborated before its value is read or written. A violation of either of these two requirements is an access before elaboration order, and this section has been all about avoiding such errors.
In the case where more than one order of elaboration is possible, in the sense that access before elaboration errors are avoided, then any one of the orders is “correct” in the sense that it meets the requirements of the Ada Reference Manual, and no such error occurs.
However, it may be the case for a given program, that there are constraints on the order of elaboration that come not from consideration of avoiding elaboration errors, but rather from extra-lingual logic requirements. Consider this example:
with Init_Constants; package Constants is X : Integer := 0; Y : Integer := 0; end Constants; package Init_Constants is procedure P; -- require a body end Init_Constants; with Constants; package body Init_Constants is procedure P is begin null; end; begin Constants.X := 3; Constants.Y := 4; end Init_Constants; with Constants; package Calc is Z : Integer := Constants.X + Constants.Y; end Calc; with Calc; with Text_IO; use Text_IO; procedure Main is begin Put_Line (Calc.Z'Img); end Main;
In this example, there is more than one valid order of elaboration. For example both the following are correct orders:
Init_Constants spec Constants spec Calc spec Init_Constants body Main body and Init_Constants spec Init_Constants body Constants spec Calc spec Main body
There is no language rule to prefer one or the other, both are correct
from an order of elaboration point of view. But the programmatic effects
of the two orders are very different. In the first, the elaboration routine
of Calc initializes Z to zero, and then the main program
runs with this value of zero. But in the second order, the elaboration
routine of Calc runs after the body of Init_Constants has set
X and Y and thus Z is set to 7 before Main
runs.
One could perhaps by applying pretty clever non-artificial intelligence to the situation guess that it is more likely that the second order of elaboration is the one desired, but there is no formal linguistic reason to prefer one over the other. In fact in this particular case, GNAT will prefer the second order, because of the rule that bodies are elaborated as soon as possible, but it’s just luck that this is what was wanted (if indeed the second order was preferred).
If the program cares about the order of elaboration routines in a case like this, it is important to specify the order required. In this particular case, that could have been achieved by adding to the spec of Calc:
pragma Elaborate_All (Constants);
which requires that the body (if any) and spec of Constants,
as well as the body and spec of any unit with’ed by
Constants be elaborated before Calc is elaborated.
Clearly no automatic method can always guess which alternative you require,
and if you are working with legacy code that had constraints of this kind
which were not properly specified by adding Elaborate or
Elaborate_All pragmas, then indeed it is possible that two different
compilers can choose different orders.
However, GNAT does attempt to diagnose the common situation where there are uninitialized variables in the visible part of a package spec, and the corresponding package body has an elaboration block that directly or indirectly initialized one or more of these variables. This is the situation in which a pragma Elaborate_Body is usually desirable, and GNAT will generate a warning that suggests this addition if it detects this situation.
The gnatbind
-p switch may be useful in smoking
out problems. This switch causes bodies to be elaborated as late as possible
instead of as early as possible. In the example above, it would have forced
the choice of the first elaboration order. If you get different results
when using this switch, and particularly if one set of results is right,
and one is wrong as far as you are concerned, it shows that you have some
missing Elaborate pragmas. For the example above, we have the
following output:
gnatmake -f -q main main 7 gnatmake -f -q main -bargs -p main 0
It is of course quite unlikely that both these results are correct, so
it is up to you in a case like this to investigate the source of the
difference, by looking at the two elaboration orders that are chosen,
and figuring out which is correct, and then adding the necessary
Elaborate or Elaborate_All pragmas to ensure the desired order.
Next: Conditional Compilation, Previous: Elaboration Order Handling in GNAT, Up: Top [Contents][Index]
| • Background: | ||
| • Overflow Checking Modes in GNAT: | ||
| • Specifying the Desired Mode: | ||
| • Default Settings: | ||
| • Implementation Notes: |
Next: Overflow Checking Modes in GNAT, Previous: Other Elaboration Order Considerations, Up: Overflow Check Handling in GNAT [Contents][Index]
Overflow checks are checks that the compiler may make to ensure that intermediate results are not out of range. For example:
A : Integer; ... A := A + 1;
if A has the value Integer'Last, then the addition may cause
overflow since the result is out of range of the type Integer.
In this case Constraint_Error will be raised if checks are
enabled.
A trickier situation arises in examples like the following:
A, C : Integer; ... A := (A + 1) + C;
where A is Integer'Last and C is -1.
Now the final result of the expression on the right hand side is
Integer'Last which is in range, but the question arises whether the
intermediate addition of (A + 1) raises an overflow error.
The (perhaps surprising) answer is that the Ada language definition does not answer this question. Instead it leaves it up to the implementation to do one of two things if overflow checks are enabled.
Constraint_Error), or
If the compiler chooses the first approach, then the assignment of this
example will indeed raise Constraint_Error if overflow checking is
enabled, or result in erroneous execution if overflow checks are suppressed.
But if the compiler chooses the second approach, then it can perform both additions yielding the correct mathematical result, which is in range, so no exception will be raised, and the right result is obtained, regardless of whether overflow checks are suppressed.
Note that in the first example an exception will be raised in either case, since if the compiler gives the correct mathematical result for the addition, it will be out of range of the target type of the assignment, and thus fails the range check.
This lack of specified behavior in the handling of overflow for intermediate results is a source of non-portability, and can thus be problematic when programs are ported. Most typically this arises in a situation where the original compiler did not raise an exception, and then the application is moved to a compiler where the check is performed on the intermediate result and an unexpected exception is raised.
Furthermore, when using Ada 2012’s preconditions and other assertion forms, another issue arises. Consider:
procedure P (A, B : Integer) with
Pre => A + B <= Integer'Last;
One often wants to regard arithmetic in a context like this from
a mathematical point of view. So for example, if the two actual parameters
for a call to P are both Integer'Last, then
the precondition should be regarded as False. If we are executing
in a mode with run-time checks enabled for preconditions, then we would
like this precondition to fail, rather than raising an exception
because of the intermediate overflow.
However, the language definition leaves the specification of
whether the above condition fails (raising Assert_Error) or
causes an intermediate overflow (raising Constraint_Error)
up to the implementation.
The situation is worse in a case such as the following:
procedure Q (A, B, C : Integer) with
Pre => A + B + C <= Integer'Last;
Consider the call
Q (A => Integer'Last, B => 1, C => -1);
From a mathematical point of view the precondition is True, but at run time we may (but are not guaranteed to) get an exception raised because of the intermediate overflow (and we really would prefer this precondition to be considered True at run time).
Next: Specifying the Desired Mode, Previous: Background, Up: Overflow Check Handling in GNAT [Contents][Index]
To deal with the portability issue, and with the problem of mathematical versus run-time intepretation of the expressions in assertions, GNAT provides comprehensive control over the handling of intermediate overflow. GNAT can operate in three modes, and furthemore, permits separate selection of operating modes for the expressions within assertions (here the term “assertions” is used in the technical sense, which includes preconditions and so forth) and for expressions appearing outside assertions.
The three modes are:
STRICT)
In this mode, all intermediate results for predefined arithmetic operators are computed using the base type, and the result must be in range of the base type. If this is not the case then either an exception is raised (if overflow checks are enabled) or the execution is erroneous (if overflow checks are suppressed). This is the normal default mode.
MINIMIZED)
In this mode, the compiler attempts to avoid intermediate overflows by
using a larger integer type, typically Long_Long_Integer,
as the type in which arithmetic is
performed for predefined arithmetic operators. This may be slightly more
expensive at
run time (compared to suppressing intermediate overflow checks), though
the cost is negligible on modern 64-bit machines. For the examples given
earlier, no intermediate overflows would have resulted in exceptions,
since the intermediate results are all in the range of
Long_Long_Integer (typically 64-bits on nearly all implementations
of GNAT). In addition, if checks are enabled, this reduces the number of
checks that must be made, so this choice may actually result in an
improvement in space and time behavior.
However, there are cases where Long_Long_Integer is not large
enough, consider the following example:
procedure R (A, B, C, D : Integer) with
Pre => (A**2 * B**2) / (C**2 * D**2) <= 10;
where A = B = C = D = Integer'Last.
Now the intermediate results are
out of the range of Long_Long_Integer even though the final result
is in range and the precondition is True (from a mathematical point
of view). In such a case, operating in this mode, an overflow occurs
for the intermediate computation (which is why this mode
says most intermediate overflows are avoided). In this case,
an exception is raised if overflow checks are enabled, and the
execution is erroneous if overflow checks are suppressed.
ELIMINATED)
In this mode, the compiler avoids all intermediate overflows
by using arbitrary precision arithmetic as required. In this
mode, the above example with A**2 * B**2 would
not cause intermediate overflow, because the intermediate result
would be evaluated using sufficient precision, and the result
of evaluating the precondition would be True.
This mode has the advantage of avoiding any intermediate overflows, but at the expense of significant run-time overhead, including the use of a library (included automatically in this mode) for multiple-precision arithmetic.
This mode provides cleaner semantics for assertions, since now the run-time behavior emulates true arithmetic behavior for the predefined arithmetic operators, meaning that there is never a conflict between the mathematical view of the assertion, and its run-time behavior.
Note that in this mode, the behavior is unaffected by whether or
not overflow checks are suppressed, since overflow does not occur.
It is possible for gigantic intermediate expressions to raise
Storage_Error as a result of attempting to compute the
results of such expressions (e.g. Integer'Last ** Integer'Last)
but overflow is impossible.
Note that these modes apply only to the evaluation of predefined arithmetic, membership, and comparison operators for signed integer aritmetic.
For fixed-point arithmetic, checks can be suppressed. But if checks
are enabled
then fixed-point values are always checked for overflow against the
base type for intermediate expressions (that is such checks always
operate in the equivalent of STRICT mode).
For floating-point, on nearly all architectures, Machine_Overflows
is False, and IEEE infinities are generated, so overflow exceptions
are never raised. If you want to avoid infinities, and check that
final results of expressions are in range, then you can declare a
constrained floating-point type, and range checks will be carried
out in the normal manner (with infinite values always failing all
range checks).
Next: Default Settings, Previous: Overflow Checking Modes in GNAT, Up: Overflow Check Handling in GNAT [Contents][Index]
The desired mode of for handling intermediate overflow can be specified using
either the Overflow_Mode pragma or an equivalent compiler switch.
The pragma has the form
pragma Overflow_Mode ([General =>] MODE [, [Assertions =>] MODE]);
where MODE is one of
STRICT: intermediate overflows checked (using base type)
MINIMIZED: minimize intermediate overflows
ELIMINATED: eliminate intermediate overflows
The case is ignored, so MINIMIZED, Minimized and
minimized all have the same effect.
If only the General parameter is present, then the given MODE
applies
to expressions both within and outside assertions. If both arguments
are present, then General applies to expressions outside assertions,
and Assertions applies to expressions within assertions. For example:
pragma Overflow_Mode
(General => Minimized, Assertions => Eliminated);
specifies that general expressions outside assertions be evaluated in “minimize intermediate overflows” mode, and expressions within assertions be evaluated in “eliminate intermediate overflows” mode. This is often a reasonable choice, avoiding excessive overhead outside assertions, but assuring a high degree of portability when importing code from another compiler, while incurring the extra overhead for assertion expressions to ensure that the behavior at run time matches the expected mathematical behavior.
The Overflow_Mode pragma has the same scoping and placement
rules as pragma Suppress, so it can occur either as a
configuration pragma, specifying a default for the whole
program, or in a declarative scope, where it applies to the
remaining declarations and statements in that scope.
Note that pragma Overflow_Mode does not affect whether
overflow checks are enabled or suppressed. It only controls the
method used to compute intermediate values. To control whether
overflow checking is enabled or suppressed, use pragma Suppress
or Unsuppress in the usual manner
Additionally, a compiler switch -gnato? or -gnato?? can be used to control the checking mode default (which can be subsequently overridden using pragmas).
Here ‘?’ is one of the digits ‘1’ through ‘3’:
1:
use base type for intermediate operations (STRICT)
2:
minimize intermediate overflows (MINIMIZED)
3:
eliminate intermediate overflows (ELIMINATED)
As with the pragma, if only one digit appears then it applies to all cases; if two digits are given, then the first applies outside assertions, and the second within assertions. Thus the equivalent of the example pragma above would be -gnato23.
If no digits follow the -gnato, then it is equivalent to
-gnato11,
causing all intermediate operations to be computed using the base
type (STRICT mode).
In addition to setting the mode used for computation of intermediate
results, the -gnato switch also enables overflow checking (which
is suppressed by default). It thus combines the effect of using
a pragma Overflow_Mode and pragma Unsuppress.
Next: Implementation Notes, Previous: Specifying the Desired Mode, Up: Overflow Check Handling in GNAT [Contents][Index]
The default mode for overflow checks is
General => Strict
which causes all computations both inside and outside assertions to use the base type. In addition overflow checks are suppressed.
This retains compatibility with previous versions of GNAT which suppressed overflow checks by default and always used the base type for computation of intermediate results.
The switch -gnato (with no digits following) is equivalent to
General => Strict
which causes overflow checking of all intermediate overflows both inside and outside assertions against the base type. This provides compatibility with this switch as implemented in previous versions of GNAT.
The pragma Suppress (Overflow_Check) disables overflow
checking, but it has no effect on the method used for computing
intermediate results.
The pragma Unsuppress (Overflow_Check) enables overflow
checking, but it has no effect on the method used for computing
intermediate results.
Next: Use of Boolean Constants, Previous: Default Settings, Up: Overflow Check Handling in GNAT [Contents][Index]
In practice on typical 64-bit machines, the MINIMIZED mode is
reasonably efficient, and can be generally used. It also helps
to ensure compatibility with code imported from some other
compiler to GNAT.
Setting all intermediate overflows checking (CHECKED mode)
makes sense if you want to
make sure that your code is compatible with any other possible
Ada implementation. This may be useful in ensuring portability
for code that is to be exported to some other compiler than GNAT.
The Ada standard allows the reassociation of expressions at
the same precedence level if no parentheses are present. For
example, A+B+C parses as though it were (A+B)+C, but
the compiler can reintepret this as A+(B+C), possibly
introducing or eliminating an overflow exception. The GNAT
compiler never takes advantage of this freedom, and the
expression A+B+C will be evaluated as (A+B)+C.
If you need the other order, you can write the parentheses
explicitly A+(B+C) and GNAT will respect this order.
The use of ELIMINATED mode will cause the compiler to
automatically include an appropriate arbitrary precision
integer arithmetic package. The compiler will make calls
to this package, though only in cases where it cannot be
sure that Long_Long_Integer is sufficient to guard against
intermediate overflows. This package does not use dynamic
alllocation, but it does use the secondary stack, so an
appropriate secondary stack package must be present (this
is always true for standard full Ada, but may require
specific steps for restricted run times such as ZFP).
Although ELIMINATED mode causes expressions to use arbitrary
precision arithmetic, avoiding overflow, the final result
must be in an appropriate range. This is true even if the
final result is of type [Long_[Long_]]Integer'Base, which
still has the same bounds as its associated constrained
type at run-time.
Currently, the ELIMINATED mode is only available on target
platforms for which Long_Long_Integer is 64-bits (nearly all GNAT
platforms).
Next: Inline Assembler, Previous: Overflow Check Handling in GNAT, Up: Top [Contents][Index]
It is often necessary to arrange for a single source program to serve multiple purposes, where it is compiled in different ways to achieve these different goals. Some examples of the need for this feature are
In C, or C++, the typical approach would be to use the preprocessor that is defined as part of the language. The Ada language does not contain such a feature. This is not an oversight, but rather a very deliberate design decision, based on the experience that overuse of the preprocessing features in C and C++ can result in programs that are extremely difficult to maintain. For example, if we have ten switches that can be on or off, this means that there are a thousand separate programs, any one of which might not even be syntactically correct, and even if syntactically correct, the resulting program might not work correctly. Testing all combinations can quickly become impossible.
Nevertheless, the need to tailor programs certainly exists, and in this Appendix we will discuss how this can be achieved using Ada in general, and GNAT in particular.
| • Use of Boolean Constants: | ||
| • Debugging - A Special Case: | ||
| • Conditionalizing Declarations: | ||
| • Use of Alternative Implementations: | ||
| • Preprocessing: |
Next: Debugging - A Special Case, Previous: Implementation Notes, Up: Conditional Compilation [Contents][Index]
In the case where the difference is simply which code sequence is executed, the cleanest solution is to use Boolean constants to control which code is executed.
FP_Initialize_Required : constant Boolean := True; … if FP_Initialize_Required then … end if;
Not only will the code inside the if statement not be executed if
the constant Boolean is False, but it will also be completely
deleted from the program.
However, the code is only deleted after the if statement
has been checked for syntactic and semantic correctness.
(In contrast, with preprocessors the code is deleted before the
compiler ever gets to see it, so it is not checked until the switch
is turned on.)
Typically the Boolean constants will be in a separate package, something like:
package Config is FP_Initialize_Required : constant Boolean := True; Reset_Available : constant Boolean := False; … end Config;
The Config package exists in multiple forms for the various targets,
with an appropriate script selecting the version of Config needed.
Then any other unit requiring conditional compilation can do a with
of Config to make the constants visible.
Next: Conditionalizing Declarations, Previous: Use of Boolean Constants, Up: Conditional Compilation [Contents][Index]
A common use of conditional code is to execute statements (for example dynamic checks, or output of intermediate results) under control of a debug switch, so that the debugging behavior can be turned on and off. This can be done using a Boolean constant to control whether the code is active:
if Debugging then
Put_Line ("got to the first stage!");
end if;
or
if Debugging and then Temperature > 999.0 then raise Temperature_Crazy; end if;
Since this is a common case, there are special features to deal with
this in a convenient manner. For the case of tests, Ada 2005 has added
a pragma Assert that can be used for such tests. This pragma is modeled
on the Assert pragma that has always been available in GNAT, so this
feature may be used with GNAT even if you are not using Ada 2005 features.
The use of pragma Assert is described in
Pragma Assert in GNAT Reference Manual, but as an
example, the last test could be written:
pragma Assert (Temperature <= 999.0, "Temperature Crazy");
or simply
pragma Assert (Temperature <= 999.0);
In both cases, if assertions are active and the temperature is excessive,
the exception Assert_Failure will be raised, with the given string in
the first case or a string indicating the location of the pragma in the second
case used as the exception message.
You can turn assertions on and off by using the Assertion_Policy
pragma.
This is an Ada 2005 pragma which is implemented in all modes by
GNAT, but only in the latest versions of GNAT which include Ada 2005
capability. Alternatively, you can use the -gnata switch
to enable assertions from the command line (this is recognized by all versions
of GNAT).
For the example above with the Put_Line, the GNAT-specific pragma
Debug can be used:
pragma Debug (Put_Line ("got to the first stage!"));
If debug pragmas are enabled, the argument, which must be of the form of
a procedure call, is executed (in this case, Put_Line will be called).
Only one call can be present, but of course a special debugging procedure
containing any code you like can be included in the program and then
called in a pragma Debug argument as needed.
One advantage of pragma Debug over the if Debugging then
construct is that pragma Debug can appear in declarative contexts,
such as at the very beginning of a procedure, before local declarations have
been elaborated.
Debug pragmas are enabled using either the -gnata switch that also
controls assertions, or with a separate Debug_Policy pragma.
The latter pragma is new in the Ada 2005 versions of GNAT (but it can be used
in Ada 95 and Ada 83 programs as well), and is analogous to
pragma Assertion_Policy to control assertions.
Assertion_Policy and Debug_Policy are configuration pragmas,
and thus they can appear in gnat.adc if you are not using a
project file, or in the file designated to contain configuration pragmas
in a project file.
They then apply to all subsequent compilations. In practice the use of
the -gnata switch is often the most convenient method of controlling
the status of these pragmas.
Note that a pragma is not a statement, so in contexts where a statement
sequence is required, you can’t just write a pragma on its own. You have
to add a null statement.
if … then … -- some statements else pragma Assert (Num_Cases < 10); null; end if;
Next: Use of Alternative Implementations, Previous: Debugging - A Special Case, Up: Conditional Compilation [Contents][Index]
In some cases, it may be necessary to conditionalize declarations to meet different requirements. For example we might want a bit string whose length is set to meet some hardware message requirement.
In some cases, it may be possible to do this using declare blocks controlled by conditional constants:
if Small_Machine then
declare
X : Bit_String (1 .. 10);
begin
…
end;
else
declare
X : Large_Bit_String (1 .. 1000);
begin
…
end;
end if;
Note that in this approach, both declarations are analyzed by the compiler so this can only be used where both declarations are legal, even though one of them will not be used.
Another approach is to define integer constants, e.g. Bits_Per_Word,
or Boolean constants, e.g. Little_Endian, and then write declarations
that are parameterized by these constants. For example
for Rec use Field1 at 0 range Boolean'Pos (Little_Endian) * 10 .. Bits_Per_Word; end record;
If Bits_Per_Word is set to 32, this generates either
for Rec use Field1 at 0 range 0 .. 32; end record;
for the big endian case, or
for Rec use record Field1 at 0 range 10 .. 32; end record;
for the little endian case. Since a powerful subset of Ada expression
notation is usable for creating static constants, clever use of this
feature can often solve quite difficult problems in conditionalizing
compilation (note incidentally that in Ada 95, the little endian
constant was introduced as System.Default_Bit_Order, so you do not
need to define this one yourself).
Next: Preprocessing, Previous: Conditionalizing Declarations, Up: Conditional Compilation [Contents][Index]
In some cases, none of the approaches described above are adequate. This can occur for example if the set of declarations required is radically different for two different configurations.
In this situation, the official Ada way of dealing with conditionalizing such code is to write separate units for the different cases. As long as this does not result in excessive duplication of code, this can be done without creating maintenance problems. The approach is to share common code as far as possible, and then isolate the code and declarations that are different. Subunits are often a convenient method for breaking out a piece of a unit that is to be conditionalized, with separate files for different versions of the subunit for different targets, where the build script selects the right one to give to the compiler.
As an example, consider a situation where a new feature in Ada 2005 allows something to be done in a really nice way. But your code must be able to compile with an Ada 95 compiler. Conceptually you want to say:
if Ada_2005 then … neat Ada 2005 code else … not quite as neat Ada 95 code end if;
where Ada_2005 is a Boolean constant.
But this won’t work when Ada_2005 is set to False,
since the then clause will be illegal for an Ada 95 compiler.
(Recall that although such unreachable code would eventually be deleted
by the compiler, it still needs to be legal. If it uses features
introduced in Ada 2005, it will be illegal in Ada 95.)
So instead we write
procedure Insert is separate;
Then we have two files for the subunit Insert, with the two sets of
code.
If the package containing this is called File_Queries, then we might
have two files
and the build script renames the appropriate file to
file_queries-insert.adb
and then carries out the compilation.
This can also be done with project files’ naming schemes. For example:
For Body ("File_Queries.Insert") use "file_queries-insert-2005.ada";
Note also that with project files it is desirable to use a different extension than ads / adb for alternative versions. Otherwise a naming conflict may arise through another commonly used feature: to declare as part of the project a set of directories containing all the sources obeying the default naming scheme.
The use of alternative units is certainly feasible in all situations, and for example the Ada part of the GNAT run-time is conditionalized based on the target architecture using this approach. As a specific example, consider the implementation of the AST feature in VMS. There is one spec:
s-asthan.ads
which is the same for all architectures, and three bodies:
used for all non-VMS operating systems
used for VMS on the Alpha
used for VMS on the ia64
The dummy version s-asthan.adb simply raises exceptions noting that this operating system feature is not available, and the two remaining versions interface with the corresponding versions of VMS to provide VMS-compatible AST handling. The GNAT build script knows the architecture and operating system, and automatically selects the right version, renaming it if necessary to s-asthan.adb before the run-time build.
Another style for arranging alternative implementations is through Ada’s
access-to-subprogram facility.
In case some functionality is to be conditionally included,
you can declare an access-to-procedure variable Ref that is initialized
to designate a “do nothing” procedure, and then invoke Ref.all
when appropriate.
In some library package, set Ref to Proc'Access for some
procedure Proc that performs the relevant processing.
The initialization only occurs if the library package is included in the
program.
The same idea can also be implemented using tagged types and dispatching
calls.
Next: Basic Assembler Syntax, Previous: Use of Alternative Implementations, Up: Conditional Compilation [Contents][Index]
Although it is quite possible to conditionalize code without the use of C-style preprocessing, as described earlier in this section, it is nevertheless convenient in some cases to use the C approach. Moreover, older Ada compilers have often provided some preprocessing capability, so legacy code may depend on this approach, even though it is not standard.
To accommodate such use, GNAT provides a preprocessor (modeled to a large extent on the various preprocessors that have been used with legacy code on other compilers, to enable easier transition).
The preprocessor may be used in two separate modes. It can be used quite
separately from the compiler, to generate a separate output source file
that is then fed to the compiler as a separate step. This is the
gnatprep utility, whose use is fully described in
Preprocessing Using gnatprep.
The preprocessing language allows such constructs as
#if DEBUG or PRIORITY > 4 then bunch of declarations #else completely different bunch of declarations #end if;
The values of the symbols DEBUG and PRIORITY can be
defined either on the command line or in a separate file.
The other way of running the preprocessor is even closer to the C style and
often more convenient. In this approach the preprocessing is integrated into
the compilation process. The compiler is fed the preprocessor input which
includes #if lines etc, and then the compiler carries out the
preprocessing internally and processes the resulting output.
For more details on this approach, see Integrated Preprocessing.
Next: Compatibility and Porting Guide, Previous: Conditional Compilation, Up: Top [Contents][Index]
If you need to write low-level software that interacts directly
with the hardware, Ada provides two ways to incorporate assembly
language code into your program. First, you can import and invoke
external routines written in assembly language, an Ada feature fully
supported by GNAT. However, for small sections of code it may be simpler
or more efficient to include assembly language statements directly
in your Ada source program, using the facilities of the implementation-defined
package System.Machine_Code, which incorporates the gcc
Inline Assembler. The Inline Assembler approach offers a number of advantages,
including the following:
This chapter presents a series of examples to show you how to use the Inline Assembler. Although it focuses on the Intel x86, the general approach applies also to other processors. It is assumed that you are familiar with Ada and with assembly language programming.
Next: A Simple Example of Inline Assembler, Previous: Preprocessing, Up: Inline Assembler [Contents][Index]
The assembler used by GNAT and gcc is based not on the Intel assembly language, but rather on a language that descends from the AT&T Unix assembler as (and which is often referred to as “AT&T syntax”). The following table summarizes the main features of as syntax and points out the differences from the Intel conventions. See the gcc as and gas (an as macro pre-processor) documentation for further information.
gcc / as: Prefix with “%”; for example %eax
Intel: No extra punctuation; for example eax
gcc / as: Prefix with “$”; for example $4
Intel: No extra punctuation; for example 4
gcc / as: Prefix with “$”; for example $loc
Intel: No extra punctuation; for example loc
gcc / as: No extra punctuation; for example loc
Intel: Square brackets; for example [loc]
gcc / as: Parentheses; for example (%eax)
Intel: Square brackets; for example [eax]
gcc / as: Leading “0x” (C language syntax); for example 0xA0
Intel: Trailing “h”; for example A0h
gcc / as: Explicit in op code; for example movw to move
a 16-bit word
Intel: Implicit, deduced by assembler; for example mov
gcc / as: Split into two lines; for example
rep
stosl
Intel: Keep on one line; for example rep stosl
gcc / as: Source first; for example movw $4, %eax
Intel: Destination first; for example mov eax, 4
Next: Output Variables in Inline Assembler, Previous: Basic Assembler Syntax, Up: Inline Assembler [Contents][Index]
The following example will generate a single assembly language statement,
nop, which does nothing. Despite its lack of run-time effect,
the example will be useful in illustrating the basics of
the Inline Assembler facility.
with System.Machine_Code; use System.Machine_Code;
procedure Nothing is
begin
Asm ("nop");
end Nothing;
Asm is a procedure declared in package System.Machine_Code;
here it takes one parameter, a template string that must be a static
expression and that will form the generated instruction.
Asm may be regarded as a compile-time procedure that parses
the template string and additional parameters (none here),
from which it generates a sequence of assembly language instructions.
The examples in this chapter will illustrate several of the forms
for invoking Asm; a complete specification of the syntax
is found in Machine Code Insertions in GNAT Reference
Manual.
Under the standard GNAT conventions, the Nothing procedure
should be in a file named nothing.adb.
You can build the executable in the usual way:
gnatmake nothing
However, the interesting aspect of this example is not its run-time behavior but rather the generated assembly code. To see this output, invoke the compiler as follows:
gcc -c -S -fomit-frame-pointer -gnatp nothing.adb
where the options are:
-ccompile only (no bind or link)
-Sgenerate assembler listing
-fomit-frame-pointerdo not set up separate stack frames
-gnatpdo not add runtime checks
This gives a human-readable assembler version of the code. The resulting
file will have the same name as the Ada source file, but with a .s
extension. In our example, the file nothing.s has the following
contents:
.file "nothing.adb" gcc2_compiled.: ___gnu_compiled_ada: .text .align 4 .globl __ada_nothing __ada_nothing: #APP nop #NO_APP jmp L1 .align 2,0x90 L1: ret
The assembly code you included is clearly indicated by
the compiler, between the #APP and #NO_APP
delimiters. The character before the ’APP’ and ’NOAPP’
can differ on different targets. For example, GNU/Linux uses ’#APP’ while
on NT you will see ’/APP’.
If you make a mistake in your assembler code (such as using the wrong size modifier, or using a wrong operand for the instruction) GNAT will report this error in a temporary file, which will be deleted when the compilation is finished. Generating an assembler file will help in such cases, since you can assemble this file separately using the as assembler that comes with gcc.
Assembling the file using the command
as nothing.s
will give you error messages whose lines correspond to the assembler input file, so you can easily find and correct any mistakes you made. If there are no errors, as will generate an object file nothing.out.
Next: Input Variables in Inline Assembler, Previous: A Simple Example of Inline Assembler, Up: Inline Assembler [Contents][Index]
The examples in this section, showing how to access the processor flags, illustrate how to specify the destination operands for assembly language statements.
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags is
Flags : Unsigned_32;
use ASCII;
begin
Asm ("pushfl" & LF & HT & -- push flags on stack
"popl %%eax" & LF & HT & -- load eax with flags
"movl %%eax, %0", -- store flags in variable
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
Put_Line ("Flags register:" & Flags'Img);
end Get_Flags;
In order to have a nicely aligned assembly listing, we have separated multiple assembler statements in the Asm template string with linefeed (ASCII.LF) and horizontal tab (ASCII.HT) characters. The resulting section of the assembly output file is:
#APP pushfl popl %eax movl %eax, -40(%ebp) #NO_APP
It would have been legal to write the Asm invocation as:
Asm ("pushfl popl %%eax movl %%eax, %0")
but in the generated assembler file, this would come out as:
#APP pushfl popl %eax movl %eax, -40(%ebp) #NO_APP
which is not so convenient for the human reader.
We use Ada comments at the end of each line to explain what the assembler instructions actually do. This is a useful convention.
When writing Inline Assembler instructions, you need to precede each register
and variable name with a percent sign. Since the assembler already requires
a percent sign at the beginning of a register name, you need two consecutive
percent signs for such names in the Asm template string, thus %%eax.
In the generated assembly code, one of the percent signs will be stripped off.
Names such as %0, %1, %2, etc., denote input or output
variables: operands you later define using Input or Output
parameters to Asm.
An output variable is illustrated in
the third statement in the Asm template string:
movl %%eax, %0
The intent is to store the contents of the eax register in a variable that can
be accessed in Ada. Simply writing movl %%eax, Flags would not
necessarily work, since the compiler might optimize by using a register
to hold Flags, and the expansion of the movl instruction would not be
aware of this optimization. The solution is not to store the result directly
but rather to advise the compiler to choose the correct operand form;
that is the purpose of the %0 output variable.
Information about the output variable is supplied in the Outputs
parameter to Asm:
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
The output is defined by the Asm_Output attribute of the target type;
the general format is
Type'Asm_Output (constraint_string, variable_name)
The constraint string directs the compiler how to store/access the associated variable. In the example
Unsigned_32'Asm_Output ("=m", Flags);
the "m" (memory) constraint tells the compiler that the variable
Flags should be stored in a memory variable, thus preventing
the optimizer from keeping it in a register. In contrast,
Unsigned_32'Asm_Output ("=r", Flags);
uses the "r" (register) constraint, telling the compiler to
store the variable in a register.
If the constraint is preceded by the equal character (=), it tells the compiler that the variable will be used to store data into it.
In the Get_Flags example, we used the "g" (global) constraint,
allowing the optimizer to choose whatever it deems best.
There are a fairly large number of constraints, but the ones that are most useful (for the Intel x86 processor) are the following:
=output constraint
gglobal (i.e. can be stored anywhere)
min memory
Ia constant
ause eax
buse ebx
cuse ecx
duse edx
Suse esi
Duse edi
ruse one of eax, ebx, ecx or edx
quse one of eax, ebx, ecx, edx, esi or edi
The full set of constraints is described in the gcc and as documentation; note that it is possible to combine certain constraints in one constraint string.
You specify the association of an output variable with an assembler operand
through the %n notation, where n is a non-negative
integer. Thus in
Asm ("pushfl" & LF & HT & -- push flags on stack
"popl %%eax" & LF & HT & -- load eax with flags
"movl %%eax, %0", -- store flags in variable
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
%0 will be replaced in the expanded code by the appropriate operand,
whatever
the compiler decided for the Flags variable.
In general, you may have any number of output variables:
%0, %1, etc.
Outputs parameter as a parenthesized comma-separated list
of Asm_Output attributes
For example:
Asm ("movl %%eax, %0" & LF & HT &
"movl %%ebx, %1" & LF & HT &
"movl %%ecx, %2",
Outputs => (Unsigned_32'Asm_Output ("=g", Var_A), -- %0 = Var_A
Unsigned_32'Asm_Output ("=g", Var_B), -- %1 = Var_B
Unsigned_32'Asm_Output ("=g", Var_C))); -- %2 = Var_C
where Var_A, Var_B, and Var_C are variables
in the Ada program.
As a variation on the Get_Flags example, we can use the constraints
string to direct the compiler to store the eax register into the Flags
variable, instead of including the store instruction explicitly in the
Asm template string:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_2 is
Flags : Unsigned_32;
use ASCII;
begin
Asm ("pushfl" & LF & HT & -- push flags on stack
"popl %%eax", -- save flags in eax
Outputs => Unsigned_32'Asm_Output ("=a", Flags));
Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_2;
The "a" constraint tells the compiler that the Flags
variable will come from the eax register. Here is the resulting code:
#APP pushfl popl %eax #NO_APP movl %eax,-40(%ebp)
The compiler generated the store of eax into Flags after expanding the assembler code.
Actually, there was no need to pop the flags into the eax register; more simply, we could just pop the flags directly into the program variable:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_3 is
Flags : Unsigned_32;
use ASCII;
begin
Asm ("pushfl" & LF & HT & -- push flags on stack
"pop %0", -- save flags in Flags
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_3;
Next: Inlining Inline Assembler Code, Previous: Output Variables in Inline Assembler, Up: Inline Assembler [Contents][Index]
The example in this section illustrates how to specify the source operands for assembly language statements. The program simply increments its input value by 1:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment is
function Incr (Value : Unsigned_32) return Unsigned_32 is
Result : Unsigned_32;
begin
Asm ("incl %0",
Outputs => Unsigned_32'Asm_Output ("=a", Result),
Inputs => Unsigned_32'Asm_Input ("a", Value));
return Result;
end Incr;
Value : Unsigned_32;
begin
Value := 5;
Put_Line ("Value before is" & Value'Img);
Value := Incr (Value);
Put_Line ("Value after is" & Value'Img);
end Increment;
The Outputs parameter to Asm specifies
that the result will be in the eax register and that it is to be stored
in the Result variable.
The Inputs parameter looks much like the Outputs parameter,
but with an Asm_Input attribute.
The "=" constraint, indicating an output value, is not present.
You can have multiple input variables, in the same way that you can have more than one output variable.
The parameter count (%0, %1) etc, still starts at the first output statement, and continues with the input statements.
Just as the Outputs parameter causes the register to be stored into the
target variable after execution of the assembler statements, so does the
Inputs parameter cause its variable to be loaded into the register
before execution of the assembler statements.
Thus the effect of the Asm invocation is:
Value into eax
incl %eax instruction
Result variable
The resulting assembler file (with -O2 optimization) contains:
_increment__incr.1: subl $4,%esp movl 8(%esp),%eax #APP incl %eax #NO_APP movl %eax,%edx movl %ecx,(%esp) addl $4,%esp ret
Next: Other Asm Functionality, Previous: Input Variables in Inline Assembler, Up: Inline Assembler [Contents][Index]
For a short subprogram such as the Incr function in the previous
section, the overhead of the call and return (creating / deleting the stack
frame) can be significant, compared to the amount of code in the subprogram
body. A solution is to apply Ada’s Inline pragma to the subprogram,
which directs the compiler to expand invocations of the subprogram at the
point(s) of call, instead of setting up a stack frame for out-of-line calls.
Here is the resulting program:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment_2 is
function Incr (Value : Unsigned_32) return Unsigned_32 is
Result : Unsigned_32;
begin
Asm ("incl %0",
Outputs => Unsigned_32'Asm_Output ("=a", Result),
Inputs => Unsigned_32'Asm_Input ("a", Value));
return Result;
end Incr;
pragma Inline (Increment);
Value : Unsigned_32;
begin
Value := 5;
Put_Line ("Value before is" & Value'Img);
Value := Increment (Value);
Put_Line ("Value after is" & Value'Img);
end Increment_2;
Compile the program with both optimization (-O2) and inlining (-gnatn) enabled.
The Incr function is still compiled as usual, but at the
point in Increment where our function used to be called:
pushl %edi call _increment__incr.1
the code for the function body directly appears:
movl %esi,%eax #APP incl %eax #NO_APP movl %eax,%edx
thus saving the overhead of stack frame setup and an out-of-line call.
Next: Compatibility with Ada 83, Previous: Inlining Inline Assembler Code, Up: Inline Assembler [Contents][Index]
Asm FunctionalityThis section describes two important parameters to the Asm
procedure: Clobber, which identifies register usage;
and Volatile, which inhibits unwanted optimizations.
| • The Clobber Parameter: | ||
| • The Volatile Parameter: |
Next: The Volatile Parameter, Up: Other Asm Functionality [Contents][Index]
Clobber ParameterOne of the dangers of intermixing assembly language and a compiled language
such as Ada is that the compiler needs to be aware of which registers are
being used by the assembly code. In some cases, such as the earlier examples,
the constraint string is sufficient to indicate register usage (e.g.,
"a" for
the eax register). But more generally, the compiler needs an explicit
identification of the registers that are used by the Inline Assembly
statements.
Using a register that the compiler doesn’t know about
could be a side effect of an instruction (like mull
storing its result in both eax and edx).
It can also arise from explicit register usage in your
assembly code; for example:
Asm ("movl %0, %%ebx" & LF & HT &
"movl %%ebx, %1",
Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
Inputs => Unsigned_32'Asm_Input ("g", Var_In));
where the compiler (since it does not analyze the Asm template string)
does not know you are using the ebx register.
In such cases you need to supply the Clobber parameter to Asm,
to identify the registers that will be used by your assembly code:
Asm ("movl %0, %%ebx" & LF & HT &
"movl %%ebx, %1",
Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
Inputs => Unsigned_32'Asm_Input ("g", Var_In),
Clobber => "ebx");
The Clobber parameter is a static string expression specifying the
register(s) you are using. Note that register names are not prefixed
by a percent sign. Also, if more than one register is used then their names
are separated by commas; e.g., "eax, ebx"
The Clobber parameter has several additional uses:
cc to indicate that flags might have changed
memory if you changed a memory location
Previous: The Clobber Parameter, Up: Other Asm Functionality [Contents][Index]
Volatile ParameterCompiler optimizations in the presence of Inline Assembler may sometimes have
unwanted effects. For example, when an Asm invocation with an input
variable is inside a loop, the compiler might move the loading of the input
variable outside the loop, regarding it as a one-time initialization.
If this effect is not desired, you can disable such optimizations by setting
the Volatile parameter to True; for example:
Asm ("movl %0, %%ebx" & LF & HT &
"movl %%ebx, %1",
Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
Inputs => Unsigned_32'Asm_Input ("g", Var_In),
Clobber => "ebx",
Volatile => True);
By default, Volatile is set to False unless there is no
Outputs parameter.
Although setting Volatile to True prevents unwanted
optimizations, it will also disable other optimizations that might be
important for efficiency. In general, you should set Volatile
to True only if the compiler’s optimizations have created
problems.
Next: Microsoft Windows Topics, Previous: Inline Assembler, Up: Top [Contents][Index]
This chapter describes the compatibility issues that may arise between GNAT and other Ada compilation systems (including those for Ada 83), and shows how GNAT can expedite porting applications developed in other Ada environments.
Next: Compatibility between Ada 95 and Ada 2005, Previous: Other Asm Functionality, Up: Compatibility and Porting Guide [Contents][Index]
Ada 95 and Ada 2005 are highly upwards compatible with Ada 83. In particular, the design intention was that the difficulties associated with moving from Ada 83 to Ada 95 or Ada 2005 should be no greater than those that occur when moving from one Ada 83 system to another.
However, there are a number of points at which there are minor incompatibilities. The Ada 95 Annotated Reference Manual contains full details of these issues, and should be consulted for a complete treatment. In practice the following subsections treat the most likely issues to be encountered.
| • Legal Ada 83 programs that are illegal in Ada 95: | ||
| • More deterministic semantics: | ||
| • Changed semantics: | ||
| • Other language compatibility issues: |
Next: More deterministic semantics, Up: Compatibility with Ada 83 [Contents][Index]
Some legal Ada 83 programs are illegal (i.e., they will fail to compile) in Ada 95 and thus also in Ada 2005:
Some uses of character literals are ambiguous. Since Ada 95 has introduced
Wide_Character as a new predefined character type, some uses of
character literals that were legal in Ada 83 are illegal in Ada 95.
For example:
for Char in 'A' .. 'Z' loop … end loop;
The problem is that 'A' and 'Z' could be from either
Character or Wide_Character. The simplest correction
is to make the type explicit; e.g.:
for Char in Character range 'A' .. 'Z' loop … end loop;
The identifiers abstract, aliased, protected,
requeue, tagged, and until are reserved in Ada 95.
Existing Ada 83 code using any of these identifiers must be edited to
use some alternative name.
The rules in Ada 95 are slightly different with regard to the point at which entities are frozen, and representation pragmas and clauses are not permitted past the freeze point. This shows up most typically in the form of an error message complaining that a representation item appears too late, and the appropriate corrective action is to move the item nearer to the declaration of the entity to which it refers.
A particular case is that representation pragmas cannot be applied to a subprogram body. If necessary, a separate subprogram declaration must be introduced to which the pragma can be applied.
In Ada 83, a package that did not require a package body was nevertheless
allowed to have one. This lead to certain surprises in compiling large
systems (situations in which the body could be unexpectedly ignored by the
binder). In Ada 95, if a package does not require a body then it is not
permitted to have a body. To fix this problem, simply remove a redundant
body if it is empty, or, if it is non-empty, introduce a dummy declaration
into the spec that makes the body required. One approach is to add a private
part to the package declaration (if necessary), and define a parameterless
procedure called Requires_Body, which must then be given a dummy
procedure body in the package body, which then becomes required.
Another approach (assuming that this does not introduce elaboration
circularities) is to add an Elaborate_Body pragma to the package spec,
since one effect of this pragma is to require the presence of a package body.
Numeric_Error is now the same as Constraint_ErrorIn Ada 95, the exception Numeric_Error is a renaming of
Constraint_Error.
This means that it is illegal to have separate exception handlers for
the two exceptions. The fix is simply to remove the handler for the
Numeric_Error case (since even in Ada 83, a compiler was free to raise
Constraint_Error in place of Numeric_Error in all cases).
In Ada 83, it was permissible to pass an indefinite type (e.g. String)
as the actual for a generic formal private type, but then the instantiation
would be illegal if there were any instances of declarations of variables
of this type in the generic body. In Ada 95, to avoid this clear violation
of the methodological principle known as the “contract model”,
the generic declaration explicitly indicates whether
or not such instantiations are permitted. If a generic formal parameter
has explicit unknown discriminants, indicated by using (<>) after the
subtype name, then it can be instantiated with indefinite types, but no
stand-alone variables can be declared of this type. Any attempt to declare
such a variable will result in an illegality at the time the generic is
declared. If the (<>) notation is not used, then it is illegal
to instantiate the generic with an indefinite type.
This is the potential incompatibility issue when porting Ada 83 code to Ada 95.
It will show up as a compile time error, and
the fix is usually simply to add the (<>) to the generic declaration.
Next: Changed semantics, Previous: Legal Ada 83 programs that are illegal in Ada 95, Up: Compatibility with Ada 83 [Contents][Index]
Conversions from real types to integer types round away from 0. In Ada 83 the conversion Integer(2.5) could deliver either 2 or 3 as its value. This implementation freedom was intended to support unbiased rounding in statistical applications, but in practice it interfered with portability. In Ada 95 the conversion semantics are unambiguous, and rounding away from 0 is required. Numeric code may be affected by this change in semantics. Note, though, that this issue is no worse than already existed in Ada 83 when porting code from one vendor to another.
The Real-Time Annex introduces a set of policies that define the behavior of features that were implementation dependent in Ada 83, such as the order in which open select branches are executed.
Next: Other language compatibility issues, Previous: More deterministic semantics, Up: Compatibility with Ada 83 [Contents][Index]
The worst kind of incompatibility is one where a program that is legal in
Ada 83 is also legal in Ada 95 but can have an effect in Ada 95 that was not
possible in Ada 83. Fortunately this is extremely rare, but the one
situation that you should be alert to is the change in the predefined type
Character from 7-bit ASCII to 8-bit Latin-1.
CharacterThe range of Standard.Character is now the full 256 characters
of Latin-1, whereas in most Ada 83 implementations it was restricted
to 128 characters. Although some of the effects of
this change will be manifest in compile-time rejection of legal
Ada 83 programs it is possible for a working Ada 83 program to have
a different effect in Ada 95, one that was not permitted in Ada 83.
As an example, the expression
Character'Pos(Character'Last) returned 127 in Ada 83 and now
delivers 255 as its value.
In general, you should look at the logic of any
character-processing Ada 83 program and see whether it needs to be adapted
to work correctly with Latin-1. Note that the predefined Ada 95 API has a
character handling package that may be relevant if code needs to be adapted
to account for the additional Latin-1 elements.
The desirable fix is to
modify the program to accommodate the full character set, but in some cases
it may be convenient to define a subtype or derived type of Character that
covers only the restricted range.
Previous: Changed semantics, Up: Compatibility with Ada 83 [Contents][Index]
All implementations of GNAT provide a switch that causes GNAT to operate in Ada 83 mode. In this mode, some but not all compatibility problems of the type described above are handled automatically. For example, the new reserved words introduced in Ada 95 and Ada 2005 are treated simply as identifiers as in Ada 83. However, in practice, it is usually advisable to make the necessary modifications to the program to remove the need for using this switch. See Compiling Different Versions of Ada.
A number of pragmas and attributes from Ada 83 were removed from Ada 95,
generally because they were replaced by other mechanisms. Ada 95 and Ada 2005
compilers are allowed, but not required, to implement these missing
elements. In contrast with some other compilers, GNAT implements all
such pragmas and attributes, eliminating this compatibility concern. These
include pragma Interface and the floating point type attributes
(Emax, Mantissa, etc.), among other items.
Next: Implementation-dependent characteristics, Previous: Compatibility with Ada 83, Up: Compatibility and Porting Guide [Contents][Index]
Although Ada 2005 was designed to be upwards compatible with Ada 95, there are a number of incompatibilities. Several are enumerated below; for a complete description please see the Annotated Ada 2005 Reference Manual, or section 9.1.1 in Rationale for Ada 2005.
The words interface, overriding and synchronized are
reserved in Ada 2005.
A pre-Ada 2005 program that uses any of these as an identifier will be
illegal.
A number of packages in the predefined environment contain new declarations:
Ada.Exceptions, Ada.Real_Time, Ada.Strings,
Ada.Strings.Fixed, Ada.Strings.Bounded,
Ada.Strings.Unbounded, Ada.Strings.Wide_Fixed,
Ada.Strings.Wide_Bounded, Ada.Strings.Wide_Unbounded,
Ada.Tags, Ada.Text_IO, and Interfaces.C.
If an Ada 95 program does a with and use of any of these
packages, the new declarations may cause name clashes.
A nondispatching subprogram with an access parameter cannot be renamed as a dispatching operation. This was permitted in Ada 95.
Rule changes in this area have led to some incompatibilities; for example, constrained subtypes of some access types are not permitted in Ada 2005.
The allowance of aggregates for limited types in Ada 2005 raises the possibility of ambiguities in legal Ada 95 programs, since additional types now need to be considered in expression resolution.
Certain expressions involving “*” or “/” for a fixed-point type, which
were legal in Ada 95 and invoked the predefined versions of these operations,
are now ambiguous.
The ambiguity may be resolved either by applying a type conversion to the
expression, or by explicitly invoking the operation from package
Standard.
The Ada 95 return-by-reference mechanism has been removed. Instead, the user can declare a function returning a value from an anonymous access type.
Next: Compatibility with Other Ada Systems, Previous: Compatibility between Ada 95 and Ada 2005, Up: Compatibility and Porting Guide [Contents][Index]
Although the Ada language defines the semantics of each construct as precisely as practical, in some situations (for example for reasons of efficiency, or where the effect is heavily dependent on the host or target platform) the implementation is allowed some freedom. In porting Ada 83 code to GNAT, you need to be aware of whether / how the existing code exercised such implementation dependencies. Such characteristics fall into several categories, and GNAT offers specific support in assisting the transition from certain Ada 83 compilers.
| • Implementation-defined pragmas: | ||
| • Implementation-defined attributes: | ||
| • Libraries: | ||
| • Elaboration order: | ||
| • Target-specific aspects: |
Next: Implementation-defined attributes, Up: Implementation-dependent characteristics [Contents][Index]
Ada compilers are allowed to supplement the language-defined pragmas, and
these are a potential source of non-portability. All GNAT-defined pragmas
are described in Implementation Defined Pragmas in GNAT
Reference Manual, and these include several that are specifically
intended to correspond to other vendors’ Ada 83 pragmas.
For migrating from VADS, the pragma Use_VADS_Size may be useful.
For compatibility with HP Ada 83, GNAT supplies the pragmas
Extend_System, Ident, Inline_Generic,
Interface_Name, Passive, Suppress_All,
and Volatile.
Other relevant pragmas include External and Link_With.
Some vendor-specific
Ada 83 pragmas (Share_Generic, Subtitle, and Title) are
recognized, thus
avoiding compiler rejection of units that contain such pragmas; they are not
relevant in a GNAT context and hence are not otherwise implemented.
Next: Libraries, Previous: Implementation-defined pragmas, Up: Implementation-dependent characteristics [Contents][Index]
Analogous to pragmas, the set of attributes may be extended by an
implementation. All GNAT-defined attributes are described in
Implementation Defined Attributes in GNAT Reference
Manual, and these include several that are specifically intended
to correspond to other vendors’ Ada 83 attributes. For migrating from VADS,
the attribute VADS_Size may be useful. For compatibility with HP
Ada 83, GNAT supplies the attributes Bit, Machine_Size and
Type_Class.
Next: Elaboration order, Previous: Implementation-defined attributes, Up: Implementation-dependent characteristics [Contents][Index]
Vendors may supply libraries to supplement the standard Ada API. If Ada 83 code uses vendor-specific libraries then there are several ways to manage this in Ada 95 or Ada 2005:
Next: Target-specific aspects, Previous: Libraries, Up: Implementation-dependent characteristics [Contents][Index]
The implementation can choose any elaboration order consistent with the unit
dependency relationship. This freedom means that some orders can result in
Program_Error being raised due to an “Access Before Elaboration”: an attempt
to invoke a subprogram its body has been elaborated, or to instantiate a
generic before the generic body has been elaborated. By default GNAT
attempts to choose a safe order (one that will not encounter access before
elaboration problems) by implicitly inserting Elaborate or
Elaborate_All pragmas where
needed. However, this can lead to the creation of elaboration circularities
and a resulting rejection of the program by gnatbind. This issue is
thoroughly described in Elaboration Order Handling in GNAT.
In brief, there are several
ways to deal with this situation:
Elaborate_Body or
Elaborate pragmas, and then inhibit the generation of implicit
Elaborate_All
pragmas either globally (as an effect of the -gnatE switch) or locally
(by selectively suppressing elaboration checks via pragma
Suppress(Elaboration_Check) when it is safe to do so).
Previous: Elaboration order, Up: Implementation-dependent characteristics [Contents][Index]
Low-level applications need to deal with machine addresses, data representations, interfacing with assembler code, and similar issues. If such an Ada 83 application is being ported to different target hardware (for example where the byte endianness has changed) then you will need to carefully examine the program logic; the porting effort will heavily depend on the robustness of the original design. Moreover, Ada 95 (and thus Ada 2005) are sometimes incompatible with typical Ada 83 compiler practices regarding implicit packing, the meaning of the Size attribute, and the size of access values. GNAT’s approach to these issues is described in Representation Clauses.
Next: Representation Clauses, Previous: Implementation-dependent characteristics, Up: Compatibility and Porting Guide [Contents][Index]
If programs avoid the use of implementation dependent and implementation defined features, as documented in the Ada Reference Manual, there should be a high degree of portability between GNAT and other Ada systems. The following are specific items which have proved troublesome in moving Ada 95 programs from GNAT to other Ada 95 compilers, but do not affect porting code to GNAT. (As of January 2007, GNAT is the only compiler available for Ada 2005; the following issues may or may not arise for Ada 2005 programs when other compilers appear.)
Ada 95 compilers are allowed, but not required, to implement the missing Ada 83 pragmas and attributes that are no longer defined in Ada 95. GNAT implements all such pragmas and attributes, eliminating this as a compatibility concern, but some other Ada 95 compilers reject these pragmas and attributes.
GNAT implements the full set of special needs annexes. At the current time, it is the only Ada 95 compiler to do so. This means that programs making use of these features may not be portable to other Ada 95 compilation systems.
Some other Ada 95 compilers implement only the minimal set of representation clauses required by the Ada 95 reference manual. GNAT goes far beyond this minimal set, as described in the next section.
Next: Compatibility with HP Ada 83, Previous: Compatibility with Other Ada Systems, Up: Compatibility and Porting Guide [Contents][Index]
The Ada 83 reference manual was quite vague in describing both the minimal required implementation of representation clauses, and also their precise effects. Ada 95 (and thus also Ada 2005) are much more explicit, but the minimal set of capabilities required is still quite limited.
GNAT implements the full required set of capabilities in Ada 95 and Ada 2005, but also goes much further, and in particular an effort has been made to be compatible with existing Ada 83 usage to the greatest extent possible.
A few cases exist in which Ada 83 compiler behavior is incompatible with the requirements in Ada 95 (and thus also Ada 2005). These are instances of intentional or accidental dependence on specific implementation dependent characteristics of these Ada 83 compilers. The following is a list of the cases most likely to arise in existing Ada 83 code.
Some Ada 83 compilers allowed a Size specification to cause implicit
packing of an array or record. This could cause expensive implicit
conversions for change of representation in the presence of derived
types, and the Ada design intends to avoid this possibility.
Subsequent AI’s were issued to make it clear that such implicit
change of representation in response to a Size clause is inadvisable,
and this recommendation is represented explicitly in the Ada 95 (and Ada 2005)
Reference Manuals as implementation advice that is followed by GNAT.
The problem will show up as an error
message rejecting the size clause. The fix is simply to provide
the explicit pragma Pack, or for more fine tuned control, provide
a Component_Size clause.
The Size attribute in Ada 95 (and Ada 2005) for discrete types is defined as
the minimal number of bits required to hold values of the type. For example,
on a 32-bit machine, the size of Natural will typically be 31 and not
32 (since no sign bit is required). Some Ada 83 compilers gave 31, and
some 32 in this situation. This problem will usually show up as a compile
time error, but not always. It is a good idea to check all uses of the
’Size attribute when porting Ada 83 code. The GNAT specific attribute
Object_Size can provide a useful way of duplicating the behavior of
some Ada 83 compiler systems.
A common assumption in Ada 83 code is that an access type is in fact a pointer, and that therefore it will be the same size as a System.Address value. This assumption is true for GNAT in most cases with one exception. For the case of a pointer to an unconstrained array type (where the bounds may vary from one value of the access type to another), the default is to use a “fat pointer”, which is represented as two separate pointers, one to the bounds, and one to the array. This representation has a number of advantages, including improved efficiency. However, it may cause some difficulties in porting existing Ada 83 code which makes the assumption that, for example, pointers fit in 32 bits on a machine with 32-bit addressing.
To get around this problem, GNAT also permits the use of “thin pointers” for access types in this case (where the designated type is an unconstrained array type). These thin pointers are indeed the same size as a System.Address value. To specify a thin pointer, use a size clause for the type, for example:
type X is access all String; for X'Size use Standard'Address_Size;
which will cause the type X to be represented using a single pointer. When using this representation, the bounds are right behind the array. This representation is slightly less efficient, and does not allow quite such flexibility in the use of foreign pointers or in using the Unrestricted_Access attribute to create pointers to non-aliased objects. But for any standard portable use of the access type it will work in a functionally correct manner and allow porting of existing code. Note that another way of forcing a thin pointer representation is to use a component size clause for the element size in an array, or a record representation clause for an access field in a record.
Next: Compatibility with Other Ada Systems, Previous: Representation Clauses, Up: Compatibility and Porting Guide [Contents][Index]
The VMS version of GNAT fully implements all the pragmas and attributes provided by HP Ada 83, as well as providing the standard HP Ada 83 libraries, including Starlet. In addition, data layouts and parameter passing conventions are highly compatible. This means that porting existing HP Ada 83 code to GNAT in VMS systems should be easier than most other porting efforts. The following are some of the most significant differences between GNAT and HP Ada 83.
In GNAT, the default floating-point format is IEEE, whereas in HP Ada 83, it is VMS format. GNAT does implement the necessary pragmas (Long_Float, Float_Representation) for changing this default.
The package System in GNAT exactly corresponds to the definition in the Ada 95 reference manual, which means that it excludes many of the HP Ada 83 extensions. However, a separate package Aux_DEC is provided that contains the additional definitions, and a special pragma, Extend_System allows this package to be treated transparently as an extension of package System.
The definitions provided by Aux_DEC are exactly compatible with those in the HP Ada 83 version of System, with one exception. HP Ada provides the following declarations:
TO_ADDRESS (INTEGER) TO_ADDRESS (UNSIGNED_LONGWORD) TO_ADDRESS (universal_integer)
The version of TO_ADDRESS taking a universal integer argument is in fact an extension to Ada 83 not strictly compatible with the reference manual. In GNAT, we are constrained to be exactly compatible with the standard, and this means we cannot provide this capability. In HP Ada 83, the point of this definition is to deal with a call like:
TO_ADDRESS (16#12777#);
Normally, according to the Ada 83 standard, one would expect this to be ambiguous, since it matches both the INTEGER and UNSIGNED_LONGWORD forms of TO_ADDRESS. However, in HP Ada 83, there is no ambiguity, since the definition using universal_integer takes precedence.
In GNAT, since the version with universal_integer cannot be supplied, it is not possible to be 100% compatible. Since there are many programs using numeric constants for the argument to TO_ADDRESS, the decision in GNAT was to change the name of the function in the UNSIGNED_LONGWORD case, so the declarations provided in the GNAT version of AUX_Dec are:
function To_Address (X : Integer) return Address; pragma Pure_Function (To_Address); function To_Address_Long (X : Unsigned_Longword) return Address; pragma Pure_Function (To_Address_Long);
This means that programs using TO_ADDRESS for UNSIGNED_LONGWORD must change the name to TO_ADDRESS_LONG.
The Task_Id values assigned will be different in the two systems, and GNAT does not provide a specified value for the Task_Id of the environment task, which in GNAT is treated like any other declared task.
For full details on these and other less significant compatibility issues, see appendix E of the HP publication entitled HP Ada, Technical Overview and Comparison on HP Platforms.
For GNAT running on other than VMS systems, all the HP Ada 83 pragmas and attributes are recognized, although only a subset of them can sensibly be implemented. The description of pragmas in Implementation Defined Pragmas in GNAT Reference Manual indicates whether or not they are applicable to non-VMS systems.
Next: Mac OS Topics, Previous: Compatibility and Porting Guide, Up: Top [Contents][Index]
This chapter describes topics that are specific to the Microsoft Windows platforms (NT, 2000, and XP Professional).
Next: Using a network installation of GNAT, Previous: Representation Clauses, Up: Microsoft Windows Topics [Contents][Index]
One of the strengths of the GNAT technology is that its tool set
(gcc, gnatbind, gnatlink, gnatmake, the
gdb debugger, etc.) is used in the same way regardless of the
platform.
On Windows this tool set is complemented by a number of Microsoft-specific tools that have been provided to facilitate interoperability with Windows when this is required. With these tools:
CONSOLE or WINDOWS
subsystems.
Immediately below are listed all known general GNAT-for-Windows restrictions. Other restrictions about specific features like Windows Resources and DLLs are listed in separate sections below.
GetLastError and SetLastError
when tasking, protected records, or exceptions are used. In these
cases, in order to implement Ada semantics, the GNAT run-time system
calls certain Win32 routines that set the last error variable to 0 upon
success. It should be possible to use GetLastError and
SetLastError when tasking, protected record, and exception
features are not used, but it is not guaranteed to work.
Next: CONSOLE and WINDOWS subsystems, Previous: Using GNAT on Windows, Up: Microsoft Windows Topics [Contents][Index]
Make sure the system on which GNAT is installed is accessible from the
current machine, i.e., the install location is shared over the network.
Shared resources are accessed on Windows by means of UNC paths, which
have the format \\server\sharename\path
In order to use such a network installation, simply add the UNC path of the bin directory of your GNAT installation in front of your PATH. For example, if GNAT is installed in \GNAT directory of a share location called c-drive on a machine LOKI, the following command will make it available:
path \\loki\c-drive\gnat\bin;%path%
Be aware that every compilation using the network installation results in the transfer of large amounts of data across the network and will likely cause serious performance penalty.
Next: Temporary Files, Previous: Using a network installation of GNAT, Up: Microsoft Windows Topics [Contents][Index]
There are two main subsystems under Windows. The CONSOLE subsystem
(which is the default subsystem) will always create a console when
launching the application. This is not something desirable when the
application has a Windows GUI. To get rid of this console the
application must be using the WINDOWS subsystem. To do so
the -mwindows linker option must be specified.
$ gnatmake winprog -largs -mwindows
Next: Mixed-Language Programming on Windows, Previous: CONSOLE and WINDOWS subsystems, Up: Microsoft Windows Topics [Contents][Index]
It is possible to control where temporary files gets created by setting
the TMP environment variable. The file will be created:
TMP environment variable if
this directory exists.
TMP environment variable is not
set (or not pointing to a directory) and if this directory exists.
This allows you to determine exactly where the temporary file will be created. This is particularly useful in networked environments where you may not have write access to some directories.
Next: Windows Calling Conventions, Previous: Temporary Files, Up: Microsoft Windows Topics [Contents][Index]
Developing pure Ada applications on Windows is no different than on other GNAT-supported platforms. However, when developing or porting an application that contains a mix of Ada and C/C++, the choice of your Windows C/C++ development environment conditions your overall interoperability strategy.
If you use gcc or Microsoft C to compile the non-Ada part of
your application, there are no Windows-specific restrictions that
affect the overall interoperability with your Ada code. If you do want
to use the Microsoft tools for your C++ code, you have two choices:
In addition to the description about C main in see Mixed Language Programming section, if the C main uses a stand-alone library it is required on x86-windows to setup the SEH context. For this the C main must looks like this:
/* main.c */
extern void adainit (void);
extern void adafinal (void);
extern void __gnat_initialize(void*);
extern void call_to_ada (void);
int main (int argc, char *argv[])
{
int SEH [2];
/* Initialize the SEH context */
__gnat_initialize (&SEH);
adainit();
/* Then call Ada services in the stand-alone library */
call_to_ada();
adafinal();
}
Note that this is not needed on x86_64-windows where the Windows native SEH support is used.
Next: Introduction to Dynamic Link Libraries (DLLs), Previous: Mixed-Language Programming on Windows, Up: Microsoft Windows Topics [Contents][Index]
This section pertain only to Win32. On Win64 there is a single native calling convention. All convention specifiers are ignored on this platform.
| • C Calling Convention: | ||
| • Stdcall Calling Convention: | ||
| • Win32 Calling Convention: | ||
| • DLL Calling Convention: |
When a subprogram F (caller) calls a subprogram G
(callee), there are several ways to push G’s parameters on the
stack and there are several possible scenarios to clean up the stack
upon G’s return. A calling convention is an agreed upon software
protocol whereby the responsibilities between the caller (F) and
the callee (G) are clearly defined. Several calling conventions
are available for Windows:
C (Microsoft defined)
Stdcall (Microsoft defined)
Win32 (GNAT specific)
DLL (GNAT specific)
Next: Stdcall Calling Convention, Up: Windows Calling Conventions [Contents][Index]
C Calling ConventionThis is the default calling convention used when interfacing to C/C++
routines compiled with either gcc or Microsoft Visual C++.
In the C calling convention subprogram parameters are pushed on the
stack by the caller from right to left. The caller itself is in charge of
cleaning up the stack after the call. In addition, the name of a routine
with C calling convention is mangled by adding a leading underscore.
The name to use on the Ada side when importing (or exporting) a routine
with C calling convention is the name of the routine. For
instance the C function:
int get_val (long);
should be imported from Ada as follows:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (C, Get_Val, External_Name => "get_val");
Note that in this particular case the External_Name parameter could
have been omitted since, when missing, this parameter is taken to be the
name of the Ada entity in lower case. When the Link_Name parameter
is missing, as in the above example, this parameter is set to be the
External_Name with a leading underscore.
When importing a variable defined in C, you should always use the C
calling convention unless the object containing the variable is part of a
DLL (in which case you should use the Stdcall calling
convention, see Stdcall Calling Convention).
Next: Win32 Calling Convention, Previous: C Calling Convention, Up: Windows Calling Conventions [Contents][Index]
Stdcall Calling ConventionThis convention, which was the calling convention used for Pascal programs, is used by Microsoft for all the routines in the Win32 API for efficiency reasons. It must be used to import any routine for which this convention was specified.
In the Stdcall calling convention subprogram parameters are pushed
on the stack by the caller from right to left. The callee (and not the
caller) is in charge of cleaning the stack on routine exit. In addition,
the name of a routine with Stdcall calling convention is mangled by
adding a leading underscore (as for the C calling convention) and a
trailing @nn, where nn is the overall size (in
bytes) of the parameters passed to the routine.
The name to use on the Ada side when importing a C routine with a
Stdcall calling convention is the name of the C routine. The leading
underscore and trailing @nn are added automatically by
the compiler. For instance the Win32 function:
APIENTRY int get_val (long);
should be imported from Ada as follows:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (Stdcall, Get_Val); -- On the x86 a long is 4 bytes, so the Link_Name is "_get_val@4"
As for the C calling convention, when the External_Name
parameter is missing, it is taken to be the name of the Ada entity in lower
case. If instead of writing the above import pragma you write:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (Stdcall, Get_Val, External_Name => "retrieve_val");
then the imported routine is _retrieve_val@4. However, if instead
of specifying the External_Name parameter you specify the
Link_Name as in the following example:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (Stdcall, Get_Val, Link_Name => "retrieve_val");
then the imported routine is retrieve_val, that is, there is no
decoration at all. No leading underscore and no Stdcall suffix
@nn.
This is especially important as in some special cases a DLL’s entry
point name lacks a trailing @nn while the exported
name generated for a call has it.
It is also possible to import variables defined in a DLL by using an import pragma for a variable. As an example, if a DLL contains a variable defined as:
int my_var;
then, to access this variable from Ada you should write:
My_Var : Interfaces.C.int; pragma Import (Stdcall, My_Var);
Note that to ease building cross-platform bindings this convention
will be handled as a C calling convention on non-Windows platforms.
Next: DLL Calling Convention, Previous: Stdcall Calling Convention, Up: Windows Calling Conventions [Contents][Index]
Win32 Calling ConventionThis convention, which is GNAT-specific is fully equivalent to the
Stdcall calling convention described above.
Previous: Win32 Calling Convention, Up: Windows Calling Conventions [Contents][Index]
DLL Calling ConventionThis convention, which is GNAT-specific is fully equivalent to the
Stdcall calling convention described above.
Next: Using DLLs with GNAT, Previous: Windows Calling Conventions, Up: Microsoft Windows Topics [Contents][Index]
A Dynamically Linked Library (DLL) is a library that can be shared by several applications running under Windows. A DLL can contain any number of routines and variables.
One advantage of DLLs is that you can change and enhance them without forcing all the applications that depend on them to be relinked or recompiled. However, you should be aware than all calls to DLL routines are slower since, as you will understand below, such calls are indirect.
To illustrate the remainder of this section, suppose that an application wants to use the services of a DLL API.dll. To use the services provided by API.dll you must statically link against the DLL or an import library which contains a jump table with an entry for each routine and variable exported by the DLL. In the Microsoft world this import library is called API.lib. When using GNAT this import library is called either libAPI.dll.a, libapi.dll.a, libAPI.a or libapi.a (names are case insensitive).
After you have linked your application with the DLL or the import library and you run your application, here is what happens:
DllMain or
DllMainCRTStartup are invoked. These routines typically contain
the initialization code needed for the well-being of the routines and
variables exported by the DLL.
There is an additional point which is worth mentioning. In the Windows world there are two kind of DLLs: relocatable and non-relocatable DLLs. Non-relocatable DLLs can only be loaded at a very specific address in the target application address space. If the addresses of two non-relocatable DLLs overlap and these happen to be used by the same application, a conflict will occur and the application will run incorrectly. Hence, when possible, it is always preferable to use and build relocatable DLLs. Both relocatable and non-relocatable DLLs are supported by GNAT. Note that the -s linker option (see GNU Linker User’s Guide) removes the debugging symbols from the DLL but the DLL can still be relocated.
As a side note, an interesting difference between Microsoft DLLs and Unix shared libraries, is the fact that on most Unix systems all public routines are exported by default in a Unix shared library, while under Windows it is possible (but not required) to list exported routines in a definition file (see The Definition File).
Next: Building DLLs with GNAT Project files, Previous: Introduction to Dynamic Link Libraries (DLLs), Up: Microsoft Windows Topics [Contents][Index]
| • Creating an Ada Spec for the DLL Services: | ||
| • Creating an Import Library: |
To use the services of a DLL, say API.dll, in your Ada application you must have:
Once you have all the above, to compile an Ada application that uses the
services of API.dll and whose main subprogram is My_Ada_App,
you simply issue the command
$ gnatmake my_ada_app -largs -lAPI
The argument -largs -lAPI at the end of the gnatmake command
tells the GNAT linker to look for an import library. The linker will
look for a library name in this specific order:
The first three are the GNU style import libraries. The third is the Microsoft style import libraries. The last two are the actual DLL names.
Note that if the Ada package spec for API.dll contains the following pragma
pragma Linker_Options ("-lAPI");
you do not have to add -largs -lAPI at the end of the
gnatmake command.
If any one of the items above is missing you will have to create it yourself. The following sections explain how to do so using as an example a fictitious DLL called API.dll.
Next: Creating an Import Library, Up: Using DLLs with GNAT [Contents][Index]
A DLL typically comes with a C/C++ header file which provides the definitions of the routines and variables exported by the DLL. The Ada equivalent of this header file is a package spec that contains definitions for the imported entities. If the DLL you intend to use does not come with an Ada spec you have to generate one such spec yourself. For example if the header file of API.dll is a file api.h containing the following two definitions:
int some_var; int get (char *); |
then the equivalent Ada spec could be:
with Interfaces.C.Strings; package API is use Interfaces; Some_Var : C.int; function Get (Str : C.Strings.Chars_Ptr) return C.int; private pragma Import (C, Get); pragma Import (DLL, Some_Var); end API; |
Note that a variable is
always imported with a DLL convention. A function
can have C or Stdcall convention.
(see Windows Calling Conventions).
Previous: Creating an Ada Spec for the DLL Services, Up: Using DLLs with GNAT [Contents][Index]
| • The Definition File: | ||
| • GNAT-Style Import Library: | ||
| • Microsoft-Style Import Library: |
If a Microsoft-style import library API.lib or a GNAT-style import library libAPI.dll.a or libAPI.a is available with API.dll you can skip this section. You can also skip this section if API.dll or libAPI.dll is built with GNU tools as in this case it is possible to link directly against the DLL. Otherwise read on.
Next: GNAT-Style Import Library, Up: Creating an Import Library [Contents][Index]
As previously mentioned, and unlike Unix systems, the list of symbols
that are exported from a DLL must be provided explicitly in Windows.
The main goal of a definition file is precisely that: list the symbols
exported by a DLL. A definition file (usually a file with a .def
suffix) has the following structure:
[LIBRARY name] [DESCRIPTION string] EXPORTS symbol1 symbol2 … |
LIBRARY nameThis section, which is optional, gives the name of the DLL.
DESCRIPTION stringThis section, which is optional, gives a description string that will be embedded in the import library.
EXPORTSThis section gives the list of exported symbols (procedures, functions or
variables). For instance in the case of API.dll the EXPORTS
section of API.def looks like:
EXPORTS some_var get |
Note that you must specify the correct suffix (@nn)
(see Windows Calling Conventions) for a Stdcall
calling convention function in the exported symbols list.
There can actually be other sections in a definition file, but these sections are not relevant to the discussion at hand.
Next: Microsoft-Style Import Library, Previous: The Definition File, Up: Creating an Import Library [Contents][Index]
To create a static import library from API.dll with the GNAT tools you should proceed as follows:
dll2def tool as follows:
$ dll2def API.dll > API.def
dll2def is a very simple tool: it takes as input a DLL and prints
to standard output the list of entry points in the DLL. Note that if
some routines in the DLL have the Stdcall convention
(see Windows Calling Conventions) with stripped @nn
suffix then you’ll have to edit api.def to add it, and specify
-k to gnatdll when creating the import library.
Here are some hints to find the right @nn suffix.
dumpbin tool (see the
corresponding Microsoft documentation for further details).
$ dumpbin /exports api.lib
libAPI.dll.a, using gnatdll
(see Using gnatdll) as follows:
$ gnatdll -e API.def -d API.dll
gnatdll takes as input a definition file API.def and the
name of the DLL containing the services listed in the definition file
API.dll. The name of the static import library generated is
computed from the name of the definition file as follows: if the
definition file name is xyz.def, the import library name will
be libxyz.a. Note that in the previous example option
-e could have been removed because the name of the definition
file (before the “.def” suffix) is the same as the name of the
DLL (see Using gnatdll for more information about gnatdll).
Previous: GNAT-Style Import Library, Up: Creating an Import Library [Contents][Index]
With GNAT you can either use a GNAT-style or Microsoft-style import library. A Microsoft import library is needed only if you plan to make an Ada DLL available to applications developed with Microsoft tools (see Mixed-Language Programming on Windows).
To create a Microsoft-style import library for API.dll you should proceed as follows:
dll2def tool as described above or the Microsoft dumpbin
tool (see the corresponding Microsoft documentation for further details).
lib utility:
$ lib -machine:IX86 -def:API.def -out:API.lib
If you use the above command the definition file API.def must contain a line giving the name of the DLL:
LIBRARY "API"
See the Microsoft documentation for further details about the usage of
lib.
Next: Building DLLs with GNAT, Previous: Using DLLs with GNAT, Up: Microsoft Windows Topics [Contents][Index]
There is nothing specific to Windows in the build process. see Library Projects.
Due to a system limitation, it is not possible under Windows to create threads
when inside the DllMain routine which is used for auto-initialization
of shared libraries, so it is not possible to have library level tasks in SALs.
Next: Building DLLs with gnatdll, Previous: Building DLLs with GNAT Project files, Up: Microsoft Windows Topics [Contents][Index]
This section explain how to build DLLs using the GNAT built-in DLL support. With the following procedure it is straight forward to build and use DLLs with GNAT.
The first step is to build all objects files that are to be included
into the DLL. This is done by using the standard gnatmake tool.
To build the DLL you must use gcc’s -shared and
-shared-libgcc options. It is quite simple to use this method:
$ gcc -shared -shared-libgcc -o api.dll obj1.o obj2.o …
It is important to note that in this case all symbols found in the
object files are automatically exported. It is possible to restrict
the set of symbols to export by passing to gcc a definition
file, see The Definition File. For example:
$ gcc -shared -shared-libgcc -o api.dll api.def obj1.o obj2.o …
If you use a definition file you must export the elaboration procedures for every package that required one. Elaboration procedures are named using the package name followed by "_E".
For the DLL to be used by client programs the bodies must be hidden from it and the .ali set with read-only attribute. This is very important otherwise GNAT will recompile all packages and will not actually use the code in the DLL. For example:
$ mkdir apilib $ copy *.ads *.ali api.dll apilib $ attrib +R apilib\*.ali
At this point it is possible to use the DLL by directly linking against it. Note that you must use the GNAT shared runtime when using GNAT shared libraries. This is achieved by using -shared binder’s option.
$ gnatmake main -Iapilib -bargs -shared -largs -Lapilib -lAPI
Next: GNAT and Windows Resources, Previous: Building DLLs with GNAT, Up: Microsoft Windows Topics [Contents][Index]
Note that it is preferred to use GNAT Project files (see Building DLLs with GNAT Project files) or the built-in GNAT DLL support (see Building DLLs with GNAT) or to build DLLs.
This section explains how to build DLLs containing Ada code using
gnatdll. These DLLs will be referred to as Ada DLLs in the
remainder of this section.
The steps required to build an Ada DLL that is to be used by Ada as well as non-Ada applications are as follows:
C or
Stdcall calling convention to avoid any Ada name mangling for the
entities exported by the DLL (see Exporting Ada Entities). You can
skip this step if you plan to use the Ada DLL only from Ada applications.
adainit generated by gnatbind to perform the elaboration of
the Ada code in the DLL (see Ada DLLs and Elaboration). The initialization
routine exported by the Ada DLL must be invoked by the clients of the DLL
to initialize the DLL.
adafinal generated by gnatbind to perform the
finalization of the Ada code in the DLL (see Ada DLLs and Finalization).
The finalization routine exported by the Ada DLL must be invoked by the
clients of the DLL when the DLL services are no further needed.
gnatdll to produce the DLL and the import
library (see Using gnatdll).
Note that a relocatable DLL stripped using the strip
binutils tool will not be relocatable anymore. To build a DLL without
debug information pass -largs -s to gnatdll. This
restriction does not apply to a DLL built using a Library Project.
see Library Projects.
Next: Exporting Ada Entities, Up: Building DLLs with gnatdll [Contents][Index]
When using Ada DLLs from Ada applications there is a limitation users should be aware of. Because on Windows the GNAT run time is not in a DLL of its own, each Ada DLL includes a part of the GNAT run time. Specifically, each Ada DLL includes the services of the GNAT run time that are necessary to the Ada code inside the DLL. As a result, when an Ada program uses an Ada DLL there are two independent GNAT run times: one in the Ada DLL and one in the main program.
It is therefore not possible to exchange GNAT run-time objects between the
Ada DLL and the main Ada program. Example of GNAT run-time objects are file
handles (e.g. Text_IO.File_Type), tasks types, protected objects
types, etc.
It is completely safe to exchange plain elementary, array or record types, Windows object handles, etc.
Next: Ada DLLs and Elaboration, Previous: Limitations When Using Ada DLLs from Ada, Up: Building DLLs with gnatdll [Contents][Index]
Building a DLL is a way to encapsulate a set of services usable from any
application. As a result, the Ada entities exported by a DLL should be
exported with the C or Stdcall calling conventions to avoid
any Ada name mangling. As an example here is an Ada package
API, spec and body, exporting two procedures, a function, and a
variable:
with Interfaces.C; use Interfaces; package API is Count : C.int := 0; function Factorial (Val : C.int) return C.int; procedure Initialize_API; procedure Finalize_API; -- Initialization & Finalization routines. More in the next section. private pragma Export (C, Initialize_API); pragma Export (C, Finalize_API); pragma Export (C, Count); pragma Export (C, Factorial); end API; |
package body API is
function Factorial (Val : C.int) return C.int is
Fact : C.int := 1;
begin
Count := Count + 1;
for K in 1 .. Val loop
Fact := Fact * K;
end loop;
return Fact;
end Factorial;
procedure Initialize_API is
procedure Adainit;
pragma Import (C, Adainit);
begin
Adainit;
end Initialize_API;
procedure Finalize_API is
procedure Adafinal;
pragma Import (C, Adafinal);
begin
Adafinal;
end Finalize_API;
end API;
|
If the Ada DLL you are building will only be used by Ada applications
you do not have to export Ada entities with a C or Stdcall
convention. As an example, the previous package could be written as
follows:
package API is Count : Integer := 0; function Factorial (Val : Integer) return Integer; procedure Initialize_API; procedure Finalize_API; -- Initialization and Finalization routines. end API; |
package body API is
function Factorial (Val : Integer) return Integer is
Fact : Integer := 1;
begin
Count := Count + 1;
for K in 1 .. Val loop
Fact := Fact * K;
end loop;
return Fact;
end Factorial;
…
-- The remainder of this package body is unchanged.
end API;
|
Note that if you do not export the Ada entities with a C or
Stdcall convention you will have to provide the mangled Ada names
in the definition file of the Ada DLL
(see Creating the Definition File).
Next: Ada DLLs and Finalization, Previous: Exporting Ada Entities, Up: Building DLLs with gnatdll [Contents][Index]
The DLL that you are building contains your Ada code as well as all the routines in the Ada library that are needed by it. The first thing a user of your DLL must do is elaborate the Ada code (see Elaboration Order Handling in GNAT).
To achieve this you must export an initialization routine
(Initialize_API in the previous example), which must be invoked
before using any of the DLL services. This elaboration routine must call
the Ada elaboration routine adainit generated by the GNAT binder
(see Binding with Non-Ada Main Programs). See the body of
Initialize_Api for an example. Note that the GNAT binder is
automatically invoked during the DLL build process by the gnatdll
tool (see Using gnatdll).
When a DLL is loaded, Windows systematically invokes a routine called
DllMain. It would therefore be possible to call adainit
directly from DllMain without having to provide an explicit
initialization routine. Unfortunately, it is not possible to call
adainit from the DllMain if your program has library level
tasks because access to the DllMain entry point is serialized by
the system (that is, only a single thread can execute “through” it at a
time), which means that the GNAT run time will deadlock waiting for the
newly created task to complete its initialization.
Next: Creating a Spec for Ada DLLs, Previous: Ada DLLs and Elaboration, Up: Building DLLs with gnatdll [Contents][Index]
When the services of an Ada DLL are no longer needed, the client code should
invoke the DLL finalization routine, if available. The DLL finalization
routine is in charge of releasing all resources acquired by the DLL. In the
case of the Ada code contained in the DLL, this is achieved by calling
routine adafinal generated by the GNAT binder
(see Binding with Non-Ada Main Programs).
See the body of Finalize_Api for an
example. As already pointed out the GNAT binder is automatically invoked
during the DLL build process by the gnatdll tool
(see Using gnatdll).
Next: Creating the Definition File, Previous: Ada DLLs and Finalization, Up: Building DLLs with gnatdll [Contents][Index]
To use the services exported by the Ada DLL from another programming
language (e.g. C), you have to translate the specs of the exported Ada
entities in that language. For instance in the case of API.dll,
the corresponding C header file could look like:
extern int *_imp__count; #define count (*_imp__count) int factorial (int); |
It is important to understand that when building an Ada DLL to be used by
other Ada applications, you need two different specs for the packages
contained in the DLL: one for building the DLL and the other for using
the DLL. This is because the DLL calling convention is needed to
use a variable defined in a DLL, but when building the DLL, the variable
must have either the Ada or C calling convention. As an
example consider a DLL comprising the following package API:
package API is Count : Integer := 0; … -- Remainder of the package omitted. end API; |
After producing a DLL containing package API, the spec that
must be used to import API.Count from Ada code outside of the
DLL is:
package API is Count : Integer; pragma Import (DLL, Count); end API; |
Next: Using gnatdll, Previous: Creating a Spec for Ada DLLs, Up: Building DLLs with gnatdll [Contents][Index]
The definition file is the last file needed to build the DLL. It lists
the exported symbols. As an example, the definition file for a DLL
containing only package API (where all the entities are exported
with a C calling convention) is:
EXPORTS
count
factorial
finalize_api
initialize_api
|
If the C calling convention is missing from package API,
then the definition file contains the mangled Ada names of the above
entities, which in this case are:
EXPORTS
api__count
api__factorial
api__finalize_api
api__initialize_api
|
Previous: Creating the Definition File, Up: Building DLLs with gnatdll [Contents][Index]
gnatdll| • gnatdll Example: | ||
| • gnatdll behind the Scenes: | ||
| • Using dlltool: |
gnatdll is a tool to automate the DLL build process once all the Ada
and non-Ada sources that make up your DLL have been compiled.
gnatdll is actually in charge of two distinct tasks: build the
static import library for the DLL and the actual DLL. The form of the
gnatdll command is
$ gnatdll [switches] list-of-files [-largs opts] |
where list-of-files is a list of ALI and object files. The object file list must be the exact list of objects corresponding to the non-Ada sources whose services are to be included in the DLL. The ALI file list must be the exact list of ALI files for the corresponding Ada sources whose services are to be included in the DLL. If list-of-files is missing, only the static import library is generated.
You may specify any of the following switches to gnatdll:
-a[address]Build a non-relocatable DLL at address. If address is not
specified the default address 0x11000000 will be used. By default,
when this switch is missing, gnatdll builds relocatable DLL. We
advise the reader to build relocatable DLL.
-b addressSet the relocatable DLL base address. By default the address is
0x11000000.
-bargs optsBinder options. Pass opts to the binder.
-d dllfiledllfile is the name of the DLL. This switch must be present for
gnatdll to do anything. The name of the generated import library is
obtained algorithmically from dllfile as shown in the following
example: if dllfile is xyz.dll, the import library name is
libxyz.dll.a. The name of the definition file to use (if not specified
by option -e) is obtained algorithmically from dllfile
as shown in the following example:
if dllfile is xyz.dll, the definition
file used is xyz.def.
-e deffiledeffile is the name of the definition file.
-gGenerate debugging information. This information is stored in the object file and copied from there to the final DLL file by the linker, where it can be read by the debugger. You must use the -g switch if you plan on using the debugger or the symbolic stack traceback.
-hHelp mode. Displays gnatdll switch usage information.
-IdirDirect gnatdll to search the dir directory for source and
object files needed to build the DLL.
(see Search Paths and the Run-Time Library (RTL)).
-kRemoves the @nn suffix from the import library’s exported
names, but keeps them for the link names. You must specify this
option if you want to use a Stdcall function in a DLL for which
the @nn suffix has been removed. This is the case for most
of the Windows NT DLL for example. This option has no effect when
-n option is specified.
-l fileThe list of ALI and object files used to build the DLL are listed in file, instead of being given in the command line. Each line in file contains the name of an ALI or object file.
-nNo Import. Do not create the import library.
-qQuiet mode. Do not display unnecessary messages.
-vVerbose mode. Display extra information.
-largs optsLinker options. Pass opts to the linker.
Next: gnatdll behind the Scenes, Up: Using gnatdll [Contents][Index]
gnatdll ExampleAs an example the command to build a relocatable DLL from api.adb once api.adb has been compiled and api.def created is
$ gnatdll -d api.dll api.ali
The above command creates two files: libapi.dll.a (the import library) and api.dll (the actual DLL). If you want to create only the DLL, just type:
$ gnatdll -d api.dll -n api.ali
Alternatively if you want to create just the import library, type:
$ gnatdll -d api.dll
Next: Using dlltool, Previous: gnatdll Example, Up: Using gnatdll [Contents][Index]
gnatdll behind the ScenesThis section details the steps involved in creating a DLL. gnatdll
does these steps for you. Unless you are interested in understanding what
goes on behind the scenes, you should skip this section.
We use the previous example of a DLL containing the Ada package API,
to illustrate the steps necessary to build a DLL. The starting point is a
set of objects that will make up the DLL and the corresponding ALI
files. In the case of this example this means that api.o and
api.ali are available. To build a relocatable DLL, gnatdll does
the following:
gnatdll builds the base file (api.base). A base file gives
the information necessary to generate relocation information for the
DLL.
$ gnatbind -n api $ gnatlink api -o api.jnk -mdll -Wl,--base-file,api.base
In addition to the base file, the gnatlink command generates an
output file api.jnk which can be discarded. The -mdll switch
asks gnatlink to generate the routines DllMain and
DllMainCRTStartup that are called by the Windows loader when the DLL
is loaded into memory.
gnatdll uses dlltool (see Using dlltool) to build the
export table (api.exp). The export table contains the relocation
information in a form which can be used during the final link to ensure
that the Windows loader is able to place the DLL anywhere in memory.
$ dlltool --dllname api.dll --def api.def --base-file api.base \
--output-exp api.exp
gnatdll builds the base file using the new export table. Note that
gnatbind must be called once again since the binder generated file
has been deleted during the previous call to gnatlink.
$ gnatbind -n api
$ gnatlink api -o api.jnk api.exp -mdll
-Wl,--base-file,api.base
gnatdll builds the new export table using the new base file and
generates the DLL import library libAPI.dll.a.
$ dlltool --dllname api.dll --def api.def --base-file api.base \
--output-exp api.exp --output-lib libAPI.a
gnatdll builds the relocatable DLL using the final export
table.
$ gnatbind -n api $ gnatlink api api.exp -o api.dll -mdll
Previous: gnatdll behind the Scenes, Up: Using gnatdll [Contents][Index]
dlltooldlltool is the low-level tool used by gnatdll to build
DLLs and static import libraries. This section summarizes the most
common dlltool switches. The form of the dlltool command
is
$ dlltool [switches]
dlltool switches include:
Read the base file basefile generated by the linker. This switch is used to create a relocatable DLL.
Read the definition file.
Gives the name of the DLL. This switch is used to embed the name of the
DLL in the static import library generated by dlltool with switch
--output-lib.
Kill @nn from exported names
(see Windows Calling Conventions
for a discussion about Stdcall-style symbols.
Prints the dlltool switches with a concise description.
Generate an export file exportfile. The export file contains the export table (list of symbols in the DLL) and is used to create the DLL.
Generate a static import library libfile.
Verbose mode.
Use assembler-name as the assembler. The default is as.
Next: Debugging a DLL, Previous: Building DLLs with gnatdll, Up: Microsoft Windows Topics [Contents][Index]
| • Building Resources: | ||
| • Compiling Resources: | ||
| • Using Resources: |
Resources are an easy way to add Windows specific objects to your application. The objects that can be added as resources include:
For example, a version information resource can be defined as follow and embedded into an executable or DLL:
A version information resource can be used to embed information into an executable or a DLL. These information can be viewed using the file properties from the Windows Explorer. Here is an example of a version information resource:
1 VERSIONINFO
FILEVERSION 1,0,0,0
PRODUCTVERSION 1,0,0,0
BEGIN
BLOCK "StringFileInfo"
BEGIN
BLOCK "080904E4"
BEGIN
VALUE "CompanyName", "My Company Name"
VALUE "FileDescription", "My application"
VALUE "FileVersion", "1.0"
VALUE "InternalName", "my_app"
VALUE "LegalCopyright", "My Name"
VALUE "OriginalFilename", "my_app.exe"
VALUE "ProductName", "My App"
VALUE "ProductVersion", "1.0"
END
END
BLOCK "VarFileInfo"
BEGIN
VALUE "Translation", 0x809, 1252
END
END
The value 0809 (langID) is for the U.K English language and
04E4 (charsetID), which is equal to 1252 decimal, for
multilingual.
This section explains how to build, compile and use resources. Note that this section does not cover all resource objects, for a complete description see the corresponding Microsoft documentation.
Next: Compiling Resources, Up: GNAT and Windows Resources [Contents][Index]
A resource file is an ASCII file. By convention resource files have an
.rc extension.
The easiest way to build a resource file is to use Microsoft tools
such as imagedit.exe to build bitmaps, icons and cursors and
dlgedit.exe to build dialogs.
It is always possible to build an .rc file yourself by writing a
resource script.
It is not our objective to explain how to write a resource file. A complete description of the resource script language can be found in the Microsoft documentation.
Next: Using Resources, Previous: Building Resources, Up: GNAT and Windows Resources [Contents][Index]
This section describes how to build a GNAT-compatible (COFF) object file
containing the resources. This is done using the Resource Compiler
windres as follows:
$ windres -i myres.rc -o myres.o
By default windres will run gcc to preprocess the .rc
file. You can specify an alternate preprocessor (usually named
cpp.exe) using the windres --preprocessor
parameter. A list of all possible options may be obtained by entering
the command windres --help.
It is also possible to use the Microsoft resource compiler rc.exe
to produce a .res file (binary resource file). See the
corresponding Microsoft documentation for further details. In this case
you need to use windres to translate the .res file to a
GNAT-compatible object file as follows:
$ windres -i myres.res -o myres.o
Previous: Compiling Resources, Up: GNAT and Windows Resources [Contents][Index]
To include the resource file in your program just add the
GNAT-compatible object file for the resource(s) to the linker
arguments. With gnatmake this is done by using the -largs
option:
$ gnatmake myprog -largs myres.o
Next: Setting Stack Size from gnatlink, Previous: GNAT and Windows Resources, Up: Microsoft Windows Topics [Contents][Index]
| • Program and DLL Both Built with GCC/GNAT: | ||
| • Program Built with Foreign Tools and DLL Built with GCC/GNAT: |
Debugging a DLL is similar to debugging a standard program. But we have to deal with two different executable parts: the DLL and the program that uses it. We have the following four possibilities:
GCC/GNAT.
GCC/GNAT.
GCC/GNAT and the DLL is built with
foreign tools.
In this section we address only cases one and two above.
There is no point in trying to debug
a DLL with GNU/GDB, if there is no GDB-compatible debugging
information in it. To do so you must use a debugger compatible with the
tools suite used to build the DLL.
Next: Program Built with Foreign Tools and DLL Built with GCC/GNAT, Up: Debugging a DLL [Contents][Index]
This is the simplest case. Both the DLL and the program have GDB
compatible debugging information. It is then possible to break anywhere in
the process. Let’s suppose here that the main procedure is named
ada_main and that in the DLL there is an entry point named
ada_dll.
The DLL (see Introduction to Dynamic Link Libraries (DLLs)) and program must have been built with the debugging information (see GNAT -g switch). Here are the step-by-step instructions for debugging it:
GDB on the main program.
$ gdb -nw ada_main
(gdb) start
This step is required to be able to set a breakpoint inside the DLL. As long as the program is not run, the DLL is not loaded. This has the consequence that the DLL debugging information is also not loaded, so it is not possible to set a breakpoint in the DLL.
(gdb) break ada_dll (gdb) cont
At this stage a breakpoint is set inside the DLL. From there on you can use the standard approach to debug the whole program (see Running and Debugging Ada Programs).
Previous: Program and DLL Both Built with GCC/GNAT, Up: Debugging a DLL [Contents][Index]
| • Debugging the DLL Directly: | ||
| • Attaching to a Running Process: |
In this case things are slightly more complex because it is not possible to
start the main program and then break at the beginning to load the DLL and the
associated DLL debugging information. It is not possible to break at the
beginning of the program because there is no GDB debugging information,
and therefore there is no direct way of getting initial control. This
section addresses this issue by describing some methods that can be used
to break somewhere in the DLL to debug it.
First suppose that the main procedure is named main (this is for
example some C code built with Microsoft Visual C) and that there is a
DLL named test.dll containing an Ada entry point named
ada_dll.
The DLL (see Introduction to Dynamic Link Libraries (DLLs)) must have been built with debugging information (see GNAT -g option).
Next: Attaching to a Running Process, Up: Program Built with Foreign Tools and DLL Built with GCC/GNAT [Contents][Index]
$ objdump --file-header main.exe
The starting address is reported on the last line. For example:
main.exe: file format pei-i386 architecture: i386, flags 0x0000010a: EXEC_P, HAS_DEBUG, D_PAGED start address 0x00401010
$ gdb main.exe
$ (gdb) break *0x00401010 $ (gdb) run
The program will stop at the given address.
(gdb) break ada_dll.adb:45
Or if you want to break using a symbol on the DLL, you need first to select the Ada language (language used by the DLL).
(gdb) set language ada (gdb) break ada_dll
(gdb) cont
This will run the program until it reaches the breakpoint that has been set. From that point you can use the standard way to debug a program as described in (see Running and Debugging Ada Programs).
It is also possible to debug the DLL by attaching to a running process.
Previous: Debugging the DLL Directly, Up: Program Built with Foreign Tools and DLL Built with GCC/GNAT [Contents][Index]
With GDB it is always possible to debug a running process by
attaching to it. It is possible to debug a DLL this way. The limitation
of this approach is that the DLL must run long enough to perform the
attach operation. It may be useful for instance to insert a time wasting
loop in the code of the DLL to meet this criterion.
$ main
$ gdb
(gdb) attach 208
(gdb) symbol-file main.exe
(gdb) break ada_dll
(gdb) cont
This last step will resume the process execution, and stop at the breakpoint we have set. From there you can use the standard approach to debug a program as described in (see Running and Debugging Ada Programs).
Next: Setting Heap Size from gnatlink, Previous: Debugging a DLL, Up: Microsoft Windows Topics [Contents][Index]
gnatlinkIt is possible to specify the program stack size at link time. On modern
versions of Windows, starting with XP, this is mostly useful to set the size of
the main stack (environment task). The other task stacks are set with pragma
Storage_Size or with the gnatbind -d command.
Since older versions of Windows (2000, NT4, etc.) do not allow setting the reserve size of individual tasks, the link-time stack size applies to all tasks, and pragma Storage_Size has no effect. In particular, Stack Overflow checks are made against this link-time specified size.
This setting can be done with
gnatlink using either:
$ gnatlink hello -Xlinker --stack=0x10000,0x1000
This sets the stack reserve size to 0x10000 bytes and the stack commit size to 0x1000 bytes.
$ gnatlink hello -Wl,--stack=0x1000000
This sets the stack reserve size to 0x1000000 bytes. Note that with -Wl option it is not possible to set the stack commit size because the coma is a separator for this option.
Next: Codesigning the Debugger, Previous: Setting Stack Size from gnatlink, Up: Microsoft Windows Topics [Contents][Index]
gnatlinkUnder Windows systems, it is possible to specify the program heap size from
gnatlink using either:
$ gnatlink hello -Xlinker --heap=0x10000,0x1000
This sets the heap reserve size to 0x10000 bytes and the heap commit size to 0x1000 bytes.
$ gnatlink hello -Wl,--heap=0x1000000
This sets the heap reserve size to 0x1000000 bytes. Note that with -Wl option it is not possible to set the heap commit size because the coma is a separator for this option.
Next: GNU Free Documentation License, Previous: Microsoft Windows Topics, Up: Top [Contents][Index]
This chapter describes topics that are specific to Apple’s OS X platform.
| • Codesigning the Debugger: |
Next: Index, Previous: Setting Heap Size from gnatlink, Up: Mac OS Topics [Contents][Index]
The Darwin Kernel requires the debugger to have special permissions before it is allowed to control other processes. These permissions are granted by codesigning the GDB executable. Without these permissions, the debugger will report error messages such as:
Starting program: /x/y/foo Unable to find Mach task port for process-id 28885: (os/kern) failure (0x5). (please check gdb is codesigned - see taskgated(8))
Codesigning requires a certificate. The following procedure explains how to create one:
Once a certificate has been created, the debugger can be codesigned as follow. In a Terminal, run the following command...
codesign -f -s "gdb-cert" <gnat_install_prefix>/bin/gdb
... where "gdb-cert" should be replaced by the actual certificate name chosen above, and <gnat_install_prefix> should be replaced by the location where you installed GNAT.
Next: Index, Previous: Mac OS Topics, Up: Top [Contents][Index]
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Previous: GNU Free Documentation License, Up: Top [Contents][Index]
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A B C D E F G H I L M N O P R S T U V W Z |
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A B C D E F G H I L M N O P R S T U V W Z |
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gcc
gcc
gcc for Syntax Checkinggcc for Semantic Checkinggnatbind
gnatlink
gnatmake
gnatchop
gnatname
gnatxref and gnatfind
gnatpp
gnatmetric
gnatkr
gnatprep
gnatls
gnatclean
make Utility
gnatcheckgnatstub
gnattest
gnattestgnattestgnattestgnatlinkgnatlinkMost programs should experience a substantial speed improvement by being compiled with a ZCX run-time. This is especially true for tasking applications or applications with many exception handlers.