\input texinfo   @c -*-texinfo-*-
@input texiplus
@c %**start of header

@c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
@c                                                                            o
@c                            GNAT DOCUMENTATION                              o
@c                                                                            o
@c                              G N A T _ U G                                 o
@c                                                                            o
@c                            1.408.2.6
@c                                                                            o
@c          Copyright (C) 1992-2001 Ada Core Technologies, Inc.               o
@c                                                                            o
@c  GNAT is free software;  you can  redistribute it  and/or modify it under  o
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@c  OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY  o
@c  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License  o
@c  for  more details.  You should have  received  a copy of the GNU General  o
@c  Public License  distributed with GNAT;  see file COPYING.  If not, write  o
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@c  MA 02111-1307, USA.                                                       o
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@c  GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com).    o
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@c                           GNAT_UG Style Guide
@c
@c  1. Always put a @noindent on the line before the first paragraph
@c     after any of these commands:
@c
@c          @chapter
@c          @section
@c          @subsection
@c          @subsubsection
@c          @subsubsubsection
@c
@c          @end smallexample
@c          @end itemize
@c          @end enumerate
@c
@c  2. DO NOT use @example. Use @smallexample instead.
@c
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@c
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@c     @itemize or @enumerate command.
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@c     or "ali".
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@setfilename gnat_ug.info
@settitle GNAT User's Guide
@setchapternewpage odd
@syncodeindex fn cp
@c %**end of header

@titlepage




@title GNAT User's Guide


@subtitle GNAT, The GNU Ada 95 Compiler
@subtitle Document revision level 1.408.2.6
@subtitle GNAT Version 3.14p
@subtitle Date: 2001/05/10 16:08:26
@author Ada Core Technologies, Inc.

@page
@vskip 0pt plus 1filll


@copyright{} Copyright 1995-2000, Ada Core Technologies, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.


Silicon Graphics and IRIS are registered trademarks
and IRIX is a trademark of Silicon Graphics, Inc.

IBM PC is a trademark of International
Business Machines Corporation.

UNIX is a registered trademark of AT&T
Bell Laboratories.

The following are trademarks of Compaq Computers:
DEC, DEC Ada, DECthreads, DIGITAL, DECset, OpenVMS, and VAX.

The following are trademarks of Microsoft Corporation:
Windows NT, Windows 95, Windows 98.

The following are trademarks of Wind River Systems:
VxWorks, Tornado.

@end titlepage
@ifinfo
@node Top, About This Guide, (dir), (dir)
@top GNAT User's Guide



GNAT User's Guide


GNAT, The GNU Ada 95 Compiler

GNAT Version 3.14p

Date: 2001/05/10 16:08:26

Ada Core Technologies, Inc.


@copyright{} Copyright 1995-2000, Ada Core Technologies, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.


Silicon Graphics and IRIS are registered trademarks
and IRIX is a trademark of Silicon Graphics, Inc.

IBM PC is a trademark of International
Business Machines Corporation.

UNIX is a registered trademark of AT&T
Bell Laboratories.

The following are trademarks of Compaq Computers:
DEC, DEC Ada, DECthreads, DIGITAL, DECset, OpenVMS, and VAX.

The following are trademarks of Microsoft Corporation:
Windows NT, Windows 95, Windows 98.

The following are trademarks of Wind River Systems:
VxWorks, Tornado.

@menu
* About This Guide::
* Getting Started with GNAT::
* The GNAT Compilation Model::
* Compiling Using gcc::
* Binding Using gnatbind::
* Linking Using gnatlink::
* The GNAT Make Program gnatmake::
* Renaming Files Using gnatchop::
* Configuration Pragmas::
* Elaboration Order Handling in GNAT::
* The Cross-Referencing Tools gnatxref and gnatfind::
* File Name Krunching Using gnatkr::
* Preprocessing Using gnatprep::
* The GNAT Library Browser gnatls::
* GNAT and Libraries::
* Using the GNU make Utility::
* Finding Memory Problems with gnatmem::
* Finding Memory Problems with GNAT Debug Pool::
* Creating Sample Bodies Using gnatstub::
* Reducing the Size of Ada Executables with gnatelim::
* Other Utility Programs::
* Running and Debugging Ada Programs::
* Performance Considerations::
* Index::

 --- The Detailed Node Listing ---

About This Guide

* What This Guide Contains::
* What You Should Know before Reading This Guide::
* Related Information::
* Conventions::


Getting Started with GNAT

* Running GNAT::
* Running a Simple Ada Program::
* Running a Program with Multiple Units::
* Using the gnatmake Utility::

The GNAT Compilation Model

* Source Representation::
* Foreign Language Representation::
* File Naming Rules::
* Using Other File Names::
* Alternative File Naming Schemes::
* Generating Object Files::
* Source Dependencies::
* The Ada Library Information Files::
* Binding an Ada Program::
* Mixed Language Programming::
* Building Mixed Ada & C++ Programs::
* Comparison between GNAT and C/C++ Compilation Models::
* Comparison between GNAT and Conventional Ada Library Models::

Foreign Language Representation

* Latin-1::
* Other 8-Bit Codes::
* Wide Character Encodings::

Compiling Ada Programs With gcc

* Compiling Programs::
* Switches for gcc::
* Search Paths and the Run-Time Library (RTL)::
* Order of Compilation Issues::
* Examples::

Switches for gcc

* Output and Error Message Control::
* Debugging and Assertion Control::
* Run-Time Checks::
* Stack Overflow Checking::
* Run-Time Control::
* Style Checking::
* Using gcc for Syntax Checking::
* Using gcc for Semantic Checking::
* Compiling Ada 83 Programs::
* Character Set Control::
* File Naming Control::
* Subprogram Inlining Control::
* Auxiliary Output Control::
* Debugging Control::

Binding Ada Programs With gnatbind

* Running gnatbind::
* Generating the Binder Program in C::
* Consistency-Checking Modes::
* Binder Error Message Control::
* Elaboration Control::
* Output Control::
* Binding with Non-Ada Main Programs::
* Binding Programs with No Main Subprogram::
* Summary of Binder Switches::
* Command-Line Access::
* Search Paths for gnatbind::
* Examples of gnatbind Usage::

Linking Using gnatlink

* Running gnatlink::
* Switches for gnatlink::
* Setting Stack Size from gnatlink::
* Setting Heap Size from gnatlink::

The GNAT Make Program gnatmake

* Running gnatmake::
* Switches for gnatmake::
* Mode Switches for gnatmake::
* Notes on the Command Line::
* How gnatmake Works::
* Examples of gnatmake Usage::

Renaming Files Using gnatchop

* Handling Files with Multiple Units::
* Operating gnatchop in Compilation Mode::
* Command Line for gnatchop::
* Switches for gnatchop::
* Examples of gnatchop Usage::

Configuration Pragmas

* Handling of Configuration Pragmas::
* The Configuration Pragmas File::

Elaboration Order Handling in GNAT

* Elaboration Code in Ada 95::
* Checking the Elaboration Order in Ada 95::
* Controlling the Elaboration Order in Ada 95::
* Controlling Elaboration in GNAT - Internal Calls::
* Controlling Elaboration in GNAT - External Calls::
* Default Behavior in GNAT - Ensuring Safety::
* Elaboration Issues for Library Tasks::
* Mixing Elaboration Models::
* What to Do If the Default Elaboration Behavior Fails::
* Elaboration for Access-to-Subprogram Values::
* Summary of Procedures for Elaboration Control::
* Other Elaboration Order Considerations::

The Cross-Referencing Tools gnatxref and gnatfind

* gnatxref Switches::
* gnatfind Switches::
* Project Files::
* Regular Expressions in gnatfind and gnatxref::
* Examples of gnatxref Usage::
* Examples of gnatfind Usage::

File Name Krunching Using gnatkr

* About gnatkr::
* Using gnatkr::
* Krunching Method::
* Examples of gnatkr Usage::

Preprocessing Using gnatprep

* Using gnatprep::
* Switches for gnatprep::
* Form of Definitions File::
* Form of Input Text for gnatprep::


The GNAT Library Browser gnatls

* Running gnatls::
* Switches for gnatls::
* Examples of gnatls Usage::


GNAT and Libraries

* Creating an Ada Library::
* Installing an Ada Library::
* Using an Ada Library::
* Rebuilding the GNAT Run-Time Library::

Using the GNU make Utility

* Using gnatmake in a Makefile::
* Automatically Creating a List of Directories::
* Generating the Command Line Switches::
* Overcoming Command Line Length Limits::

Finding Memory Problems with gnatmem

* Running gnatmem (GDB Mode)::
* Running gnatmem (GMEM Mode)::
* Switches for gnatmem::
* Examples of gnatmem Usage::
* GDB and GMEM Modes::
* Implementation Note::


Finding Memory Problems with GNAT Debug Pool

Creating Sample Bodies Using gnatstub

* Running gnatstub::
* Switches for gnatstub::

Reducing the Size of Ada Executables with gnatelim

* About gnatelim::
* Eliminate Pragma::
* Tree Files::
* Preparing Tree and Bind Files for gnatelim::
* Running gnatelim::
* Correcting the List of Eliminate Pragmas::
* Making Your Executables Smaller::
* Summary of the gnatelim Usage Cycle::

Other Utility Programs

* Using Other Utility Programs with GNAT::
* The gnatpsys Utility Program::
* The gnatpsta Utility Program::
* The External Symbol Naming Scheme of GNAT::
* Ada Mode for Glide::
* Converting Ada Files to html with gnathtml::


Running and Debugging Ada Programs

* The GNAT Debugger GDB::
* Running GDB::
* Introduction to GDB Commands::
* Using Ada Expressions::
* Calling User-Defined Subprograms::
* Ada Exceptions::
* Ada Tasks::
* Debugging Generic Units::
* GNAT Abnormal Termination or Failure to Terminate::
* Naming Conventions for GNAT Source Files::
* Getting Internal Debugging Information::





Performance Considerations

* Controlling Run-Time Checks::
* Optimization Levels::
* Debugging Optimized Code::
* Inlining of Subprograms::

* Index::
@end menu
@end ifinfo

@node About This Guide
@unnumbered About This Guide

@noindent
This guide describes the use of GNAT, a compiler and software development
toolset for the full Ada 95 programming language.
It describes the features of the compiler and tools, and details
how to use them to build Ada 95 applications.

@menu
* What This Guide Contains::
* What You Should Know before Reading This Guide::
* Related Information::
* Conventions::
@end menu

@node What This Guide Contains
@unnumberedsec What This Guide Contains

@noindent
This guide contains the following chapters:
@itemize @bullet
@item
@ref{Getting Started with GNAT}, describes how to get started compiling
and running Ada programs with the GNAT Ada programming environment.
@item
@ref{The GNAT Compilation Model}, describes the compilation model used
by GNAT.
@item
@ref{Compiling Using gcc}, describes how to compile
Ada programs with @code{gcc}, the Ada compiler.
@item
@ref{Binding Using gnatbind}, describes how to
perform binding of Ada programs with @code{gnatbind}, the GNAT binding
utility.
@item
@ref{Linking Using gnatlink},
describes @code{gnatlink}, a
program that provides for linking using the GNAT run-time library to
construct a program. @code{gnatlink} can also incorporate foreign language
object units into the executable.
@item
@ref{The GNAT Make Program gnatmake}, describes @code{gnatmake}, a
utility that automatically determines the set of sources
needed by an Ada compilation unit, and executes the necessary compilations
binding and link.
@item
@ref{Renaming Files Using gnatchop}, describes
@code{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.
@item
@ref{The Cross-Referencing Tools gnatxref and gnatfind}, discusses
@code{gnatxref} and @code{gnatfind}, two tools that provide an easy
way to navigate through sources.
@item
@ref{File Name Krunching Using gnatkr}, describes the @code{gnatkr}
file name krunching utility, used to handle shortened
file names on operating systems with a limit on the length of names.
@item
@ref{Preprocessing Using gnatprep}, describes @code{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.
@item
@ref{The GNAT Library Browser gnatls}, describes @code{gnatls}, a
utility that displays information about compiled units, including dependences
on the corresponding sources files, and consistency of compilations.
@item
@ref{GNAT and Libraries}, describes the process of creating and using
Libraries with GNAT. It also describes how to recompile the GNAT run-time
library.

@item
@ref{Using the GNU make Utility}, describes some techniques for using
the GNAT toolset in Makefiles.

@item
@ref{Finding Memory Problems with gnatmem}, describes @code{gnatmem}, a
utility that monitors dynamic allocation and deallocation activity in a
program, and displays information about incorrect deallocations and sources
of possible memory leaks.
@item
@ref{Finding Memory Problems with GNAT Debug Pool}, describes how to
use the GNAT-specific Debug Pool in order to detect as early as possible
the use of incorrect memory references.

@item
@ref{Creating Sample Bodies Using gnatstub}, discusses @code{gnatstub},
a utility that generates empty but compilable bodies for library units.
@item
@ref{Reducing the Size of Ada Executables with gnatelim}, describes
@code{gnatelim}, a tool which detects unused subprograms and helps
the compiler to create a smaller executable for the program.
@item
@ref{Other Utility Programs}, discusses several other GNAT utilities,
including @code{gnatpsta} and @code{gnatpsys}.
@item
@ref{Running and Debugging Ada Programs}, describes how to run and debug
Ada programs.

@item
@ref{Building Mixed Ada & C++ Programs}, gives hints on how to interface
with c++.

@item
@ref{Performance Considerations}, reviews the trade offs between using
defaults or options in program development.
@end itemize

@node What You Should Know before Reading This Guide
@unnumberedsec What You Should Know before Reading This Guide

@cindex Ada 95 Language Reference Manual
@noindent
This user's guide assumes that you are familiar with Ada 95 language, as
described in the International Standard ANSI/ISO/IEC-8652:1995, Jan
1995.

@node Related Information
@unnumberedsec Related Information

@noindent
For further information about related tools, refer to the following
documents:

@itemize @bullet
@item
@cite{GNAT Reference Manual}, which contains all reference
material for the GNAT implementation of Ada 95.

@item
@cite{Ada 95 Language Reference Manual}, which contains all reference
material for the Ada 95 programming language.

@item
@cite{Debugging with GDB}
contains all details on the use of the GNU source-level debugger.

@item
@cite{GNU Emacs Manual}
contains full information on the extensible editor and programming
environment Emacs.


@end itemize

@node Conventions
@unnumberedsec Conventions
@cindex Conventions
@cindex Typographical conventions

@noindent
Following are examples of the typographical and graphic conventions used
in this guide:

@itemize @bullet
@item
@code{Functions}, @code{utility program names}, @code{standard names},
and @code{classes}.

@item
@samp{Option flags}

@item
@file{File Names}, @file{button names}, and @file{field names}.

@item
@var{Variables}.

@item
@emph{Emphasis}.

@item
[optional information or parameters]

@item
Examples are described by text
@smallexample
and then shown this way.
@end smallexample
@end itemize

@noindent
Commands that are entered by the user are preceded in this manual by the
characters @w{"@code{$ }"} (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 @code{$} replaced by whatever prompt
character you are using.


@node Getting Started with GNAT
@chapter Getting Started with GNAT

@noindent
This chapter describes some simple ways of using GNAT to build executable Ada
programs.

@menu
* Running GNAT::
* Running a Simple Ada Program::
* Running a Program with Multiple Units::
* Using the gnatmake Utility::
@end menu

@node Running GNAT
@section Running GNAT

@noindent
Three steps are needed to create an executable file from an Ada source
file:

@enumerate
@item
The source file(s) must be compiled.
@item
The file(s) must be bound using the GNAT binder.
@item
All appropriate object files must be linked to produce an executable.
@end enumerate

@noindent
All three steps are most commonly handled by using the @code{gnatmake}
utility program that, given the name of the main program, automatically
performs the necessary compilation, binding and linking steps.

@node Running a Simple Ada Program
@section Running a Simple Ada Program

@noindent
Any text editor may be used to prepare an Ada program. If @code{glide} is
used, the optional Ada mode may be helpful in laying out the program. The
program text is a normal text file. We will suppose in our initial
example that you have used your editor to prepare the following
standard format text file:

@smallexample
@group
@cartouche
@b{with} Ada.Text_IO; @b{use} Ada.Text_IO;
@b{procedure} Hello @b{is}
@b{begin}
   Put_Line ("Hello WORLD!");
@b{end} Hello;
@end cartouche
@end group
@end smallexample

@noindent
This file should be named @file{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, and whose
extension is @file{.ads} for a
spec and @file{.adb} for a body.
You can override this default file naming convention by use of the
special pragma @code{Source_File_Name} (@pxref{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 @code{gnatchop} utility
can be used to generate correctly-named source files
(@pxref{Renaming Files Using gnatchop}).

You can compile the program using the following command (@code{$} is used
as the command prompt in the examples in this document):

@smallexample
$ gcc -c hello.adb
@end smallexample


@noindent
@code{gcc} is the command used to run the compiler. This compiler is
capable of compiling programs in several languages, including Ada 95 and
C. It assumes that you have given it an Ada program if the file extension is
either @file{.ads} or @file{.adb}, and it will then call the GNAT compiler to compile
the specified file.

The @code{-c} switch is required. It tells @code{gcc} to only do a
compilation. (For C programs, @code{gcc} can also do linking, but this
capability is not used directly for Ada programs, so the @code{-c}
switch must always be present.)

This compile command generates a file
@file{hello.o} which is the object
file corresponding to your Ada program. It also generates a file
@file{hello.ali}
which contains additional information used to check
that an Ada program is consistent. To build an executable file,
use @code{gnatbind} to bind the program
and @code{gnatlink} to link it. The
argument to both @code{gnatbind} and @code{gnatlink} is the name of the
@file{ali} file, but the default extension of @file{.ali} can
be omitted. This means that in the most common case, the argument
is simply the name of the main program:

@smallexample
$ gnatbind hello
$ gnatlink hello
@end smallexample


@noindent
A simpler method of carrying out these steps is to use
@code{gnatmake}, which
is a master program that invokes all of the required
compilation, binding and linking tools in the correct order. In particular,
@code{gnatmake} automatically recompiles any sources that have been modified
since they were last compiled, or sources that depend
on such modified sources, so that a consistent compilation is ensured.

@smallexample
$ gnatmake hello.adb
@end smallexample


@noindent
The result is an executable program called @file{hello}, which can be
run by entering:

@c The following should be removed (BMB 2001-01-23)
@c @smallexample
@c $ ./hello
@c @end smallexample

@smallexample
$ hello
@end smallexample

@noindent
assuming that the current directory is on the search path for executable programs.


@noindent
and, if all has gone well, you will see

@smallexample
Hello WORLD!
@end smallexample

@noindent
appear in response to this command.

@node Running a Program with Multiple Units
@section Running a Program with Multiple Units

@noindent
Consider a slightly more complicated example that has three files: a
main program, and the spec and body of a package:

@smallexample
@cartouche
@group
@b{package} Greetings @b{is}
   @b{procedure} Hello;
   @b{procedure} Goodbye;
@b{end} Greetings;

@b{with} Ada.Text_IO; @b{use} Ada.Text_IO;
@b{package} @b{body} Greetings @b{is}
   @b{procedure} Hello @b{is}
   @b{begin}
      Put_Line ("Hello WORLD!");
   @b{end} Hello;

   @b{procedure} Goodbye @b{is}
   @b{begin}
      Put_Line ("Goodbye WORLD!");
   @b{end} Goodbye;
@b{end} Greetings;
@end group

@group
@b{with} Greetings;
@b{procedure} Gmain @b{is}
@b{begin}
   Greetings.Hello;
   Greetings.Goodbye;
@b{end} Gmain;
@end group
@end cartouche
@end smallexample

@noindent
Following the one-unit-per-file rule, place this program in the
following three separate files:

@table @file
@item greetings.ads
spec of package @code{Greetings}

@item greetings.adb
body of package @code{Greetings}

@item gmain.adb
body of main program
@end table

@noindent
To build an executable version of
this program, we could use four separate steps to compile, bind, and link
the program, as follows:

@smallexample
$ gcc -c gmain.adb
$ gcc -c greetings.adb
$ gnatbind gmain
$ gnatlink gmain
@end smallexample


@noindent
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
@code{-gnatc} switch:

@smallexample
   $ gcc -c greetings.ads -gnatc
@end smallexample


@noindent
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 @code{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:

@smallexample
$ gnatmake gmain.adb
@end smallexample


@noindent

In the next section we discuss the advantages of using @code{gnatmake} in
more detail.

@node Using the gnatmake Utility
@section Using the @code{gnatmake} Utility

@noindent
If you work on a program by compiling single components at a time using
@code{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 @file{gmain.adb}, you only need to recompile that file. But if
you edit @file{greetings.ads}, you must recompile both
@file{greetings.adb} and @file{gmain.adb}, because both files contain
units that depend on @file{greetings.ads}.

@code{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 @code{gnatmake} utility takes care of these details automatically.
Invoke it using either one of the following forms:

@smallexample
$ gnatmake gmain.adb
$ gnatmake gmain
@end smallexample


@noindent
The argument is the name of the file containing the main program;
you may omit the extension. @code{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, @file{gmain}.
In a large program, it
can be extremely helpful to use @code{gnatmake}, because working out by hand
what needs to be recompiled can be difficult.

Note that @code{gnatmake}
takes into account all the Ada 95 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, @code{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. @code{gnatmake} determines the exact set of
dependencies from scratch each time it is run.


@node The GNAT Compilation Model
@chapter The GNAT Compilation Model
@cindex GNAT compilation model
@cindex Compilation model

@menu
* Source Representation::
* Foreign Language Representation::
* File Naming Rules::
* Using Other File Names::
* Alternative File Naming Schemes::
* Generating Object Files::
* Source Dependencies::
* The Ada Library Information Files::
* Binding an Ada Program::
* Mixed Language Programming::
* Building Mixed Ada & C++ Programs::
* Comparison between GNAT and C/C++ Compilation Models::
* Comparison between GNAT and Conventional Ada Library Models::
@end menu

@noindent
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.

@node Source Representation
@section Source Representation
@cindex Latin-1

@noindent
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 (@pxref{Foreign Language Representation}
for support of non-USA character sets). The format effector characters
are represented using their standard ASCII encodings, as follows:

@table @code
@item VT
@findex VT
Vertical tab, @code{16#0B#}

@item HT
@findex HT
Horizontal tab, @code{16#09#}

@item CR
@findex CR
Carriage return, @code{16#0D#}

@item LF
@findex LF
Line feed, @code{16#0A#}

@item FF
@findex FF
Form feed, @code{16#0C#}
@end table

@noindent
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
physical lines is marked by any of the following sequences:
@code{LF}, @code{CR}, @code{CR-LF}, or @code{LF-CR}. This is useful
in accommodating files that are imported from other operating systems.

@cindex End of source file
@cindex Source file, end
@findex SUB
The end of a source file is normally represented by the physical end of
file. However, the control character @code{16#1A#} (@code{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 @dfn{spec}) and the corresponding body in
separate files. An Ada @dfn{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.

@node Foreign Language Representation
@section Foreign Language Representation

@noindent
GNAT supports the standard character sets defined in Ada 95 as well as
several other non-standard character sets for use in localized versions
of the compiler (@pxref{Character Set Control}).
@menu
* Latin-1::
* Other 8-Bit Codes::
* Wide Character Encodings::
@end menu

@node Latin-1
@subsection Latin-1
@cindex Latin-1

@noindent
The basic character set is Latin-1. This character set is defined by ISO
standard 8859, part 1. The lower half (character codes @code{16#00#}
... @code{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.

@findex Ada.Characters.Latin_1
For a complete list of Latin-1 codes and their encodings, see the source
file of library unit @code{Ada.Characters.Latin_1} in file
@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.

@node Other 8-Bit Codes
@subsection Other 8-Bit Codes

@noindent
GNAT also supports several other 8-bit coding schemes:

@table @asis
@cindex Latin-2
@item Latin-2
Latin-2 letters allowed in identifiers, with uppercase and lowercase
equivalence.

@item Latin-3
@cindex Latin-3
Latin-3 letters allowed in identifiers, with uppercase and lowercase
equivalence.

@item Latin-4
@cindex Latin-4
Latin-4 letters allowed in identifiers, with uppercase and lowercase
equivalence.

@item IBM PC (code page 437)
@cindex code page 437
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.

@item IBM PC (code page 850)
@cindex code page 850
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.

@item Full Upper 8-bit
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).

@item No Upper-Half
No upper-half characters in the range 80-FF are allowed in identifiers.
This gives Ada 83 compatibility for identifier names.
@end table

@noindent
For precise data on the encodings permitted, and the uppercase and lowercase
equivalences that are recognized, see the file @file{csets.adb} in
the GNAT compiler sources. You will need to obtain a full source release
of GNAT to obtain this file.

@node Wide Character Encodings
@subsection Wide Character Encodings

@noindent
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:

@table @asis

@item Hex Coding
In this encoding, a wide character is represented by the following five
character sequence:

@smallexample
ESC a b c d
@end smallexample

@noindent
Where @code{a}, @code{b}, @code{c}, @code{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
@code{16#A345#}.
This scheme is compatible with use of the full Wide_Character set.

@item Upper-Half Coding
@cindex Upper-Half Coding
The wide character with encoding @code{16#abcd#} where the upper bit is on (in
other words, "a" is in the range 8-F) is represented as two bytes,
@code{16#ab#} and @code{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.

@item Shift JIS Coding
@cindex Shift JIS Coding
A wide character is represented by a two-character sequence,
@code{16#ab#} and
@code{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.

@item EUC Coding
@cindex EUC Coding
A wide character is represented by a two-character sequence
@code{16#ab#} and
@code{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.

@item UTF-8 Coding
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:
@smallexample
@iftex
@leftskip=.7cm
@end iftex
16#0000#-16#007f#: 2#0xxxxxxx#
16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#

@end smallexample

@noindent
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).
@item Brackets Coding
In this encoding, a wide character is represented by the following eight
character sequence:

@smallexample
[ " a b c d " ]
@end smallexample

@noindent
Where @code{a}, @code{b}, @code{c}, @code{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
@code{16#A345#}. It is also possible (though not required) to use the
Brackets coding for upper half characters. For example, the code
@code{16#A3#} can be represented as @code{["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.

@end table

@noindent
Note: Some of these coding schemes do not permit the full use of the
Ada 95 character set. For example, neither Shift JIS, nor EUC allow the
use of the upper half of the Latin-1 set.

@node File Naming Rules
@section File Naming Rules

@noindent
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 @file{.ads} for a spec and
@file{.adb} for a body. The following list shows some
examples of these rules.

@table @file
@item main.ads
Main (spec)
@item main.adb
Main (body)
@item arith_functions.ads
Arith_Functions (package spec)
@item arith_functions.adb
Arith_Functions (package body)
@item func-spec.ads
Func.Spec (child package spec)
@item func-spec.adb
Func.Spec (child package body)
@item main-sub.adb
Sub (subunit of Main)
@item a~bad.adb
A.Bad (child package body)
@end table

@noindent
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. @xref{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 @pxref{Renaming Files Using gnatchop}.)

@node Using Other File Names
@section Using Other File Names
@cindex File names

@noindent
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:
@cindex Source_File_Name pragma

@smallexample
@group
@cartouche
@b{pragma} Source_File_Name (My_Utilities.Stacks,
  Spec_File_Name => "myutilst_a.ada");
@b{pragma} Source_File_name (My_Utilities.Stacks,
  Body_File_Name => "myutilst.ada");
@end cartouche
@end group
@end smallexample

@noindent
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 @file{gnat.adc}
file used to hold configuration
pragmas that apply to a complete compilation environment.
For more details on how the @file{gnat.adc} file is created and used
@pxref{Handling of Configuration Pragmas}
@cindex @file{gnat.adc}

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 @file{.ads} or @file{.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 @code{-x} followed by a space and the name of the
language, here @code{ada}, as in:

@smallexample
$ gcc -c -x ada peculiar_file_name.sim
@end smallexample

@noindent
@code{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.

@node Alternative File Naming Schemes
@section Alternative File Naming Schemes
@cindex File naming schemes, alternative
@cindex File names

In the previous section, we described the use of the @code{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 @file{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
@code{Source_File_Name} pragmas having the following format:
@cindex Source_File_Name pragma

@smallexample
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

@end smallexample

@noindent
The @code{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
@code{Casing} indicates
whether the unit name is to be all upper-case letters, all lower-case letters,
or mixed-case. If no
@code{Casing} parameter is used, then the default is all
lower-case.

The optional @code{Dot_Replacement} string is used to replace any periods
that occur in subunit or child unit names. If no @code{Dot_Replacement}
argument is used then separating dots appear unchanged in the resulting
file name.
Although the above syntax indicates that the
@code{Casing} argument must appear
before the @code{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 @code{Subunit_File_Name} rule, and in this case the
@code{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:

@itemize @bullet

@item
If there is a specific @code{Source_File_Name} pragma for the given unit,
then this is always used, and any general pattern rules are ignored.

@item
If there is a pattern type @code{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.

@item
If no pattern type @code{Source_File_Name} pragma that applies to the unit
for which the corresponding file exists, then the standard GNAT default
naming rules are used.

@end itemize

@noindent
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:

@smallexample
pragma Source_File_Name
  (Spec_File_Name => "*.1.ada");
pragma Source_File_Name
  (Body_File_Name => "*.2.ada");
@end smallexample

@noindent
The default GNAT scheme is actually implemented by providing the following
default pragmas internally:

@smallexample
pragma Source_File_Name
  (Spec_File_Name => "*.ads", Dot_Replacement => "-");
pragma Source_File_Name
  (Body_File_Name => "*.adb", Dot_Replacement => "-");
@end smallexample

@noindent
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 @file{_.ADA}, bodies
by adding @file{.ADA}, and subunits by
adding @file{.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.

@smallexample
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);
@end smallexample

@node Generating Object Files
@section Generating Object Files

@noindent
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:

@itemize @bullet
@item
If a package spec has no body, compile the package spec to produce the
object file for the package.

@item
If a package has both a spec and a body, compile the body to produce the
object file for the package. The source file for the package spec need
not be compiled in this case because there is only one object file, which
contains the code for both the spec and body of the package.

@item
For a subprogram, compile the subprogram body to produce the object file
for the subprogram. The spec, if one is present, is as usual in a
separate file, and need not be compiled.

@item
@cindex Subunits
In the case of subunits, only compile the parent unit. A single object
file is generated for the entire subunit tree, which includes all the
subunits.

@item
Compile child units independently of their parent units
(though, of course, the spec of all the ancestor unit must be present in order
to compile a child unit).

@item
@cindex Generics
Compile generic units in the same manner as any other units. The object
files in this case are small dummy files that contain at most the
flag used for elaboration checking. This is because GNAT always handles generic
instantiation by means of macro expansion. However, it is still necessary to
compile generic units, for dependency checking and elaboration purposes.
@end itemize

@noindent
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
@file{.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 @code{-gnatc} switch.

@node Source Dependencies
@section Source Dependencies

@noindent
A given object file clearly depends on the source file which is compiled
to produce it. Here we are using @dfn{depends} in the sense of a typical
@code{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:

@itemize @bullet
@item
If a file being compiled @code{with}'s a unit @var{X}, the object file
depends on the file containing the spec of unit @var{X}. This includes
files that are @code{with}'ed implicitly either because they are parents
of @code{with}'ed child units or they are run-time units required by the
language constructs used in a particular unit.

@item
If a file being compiled instantiates a library level generic unit, the
object file depends on both the spec and body files for this generic
unit.

@item
If a file being compiled instantiates a generic unit defined within a
package, the object file depends on the body file for the package as
well as the spec file.

@item
@findex Inline
@cindex @code{-gnatn} switch
If a file being compiled contains a call to a subprogram for which
pragma @code{Inline} applies and inlining is activated with the
@code{-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.

@cindex @code{-gnatN} switch
The use of @code{-gnatN} activates a more extensive inlining optimization
that is performed by the front end of the compiler. This inlining does
not require that the code generation be optimized. Like @code{-gnatn},
the use of this switch generates additional dependencies.

@item
If an object file O  depends on the proper body of a subunit through inlining
or instantiation, it depends on the parent unit of the subunit. This means that
any modification of the parent unit or one of its subunits affects the
compilation of O.

@item
The object file for a parent unit depends on all its subunit body files.

@item
The previous two rules meant that for purposes of computing dependencies and
recompilation, a body and all its subunits are treated as an indivisible whole.

@noindent
These rules are applied transitively: if unit @code{A} @code{with}'s
unit @code{B}, whose elaboration calls an inlined procedure in package
@code{C}, the object file for unit @code{A} will depend on the body of
@code{C}, in file @file{c.adb}.

The set of dependent files described by these rules includes all the
files on which the unit is semantically dependent, as described in the
Ada 95 Language Reference Manual. However, it is a superset of what the
ARM 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 @code{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 @code{gnatmake}.
@end itemize

@node The Ada Library Information Files
@section The Ada Library Information Files
@cindex Ada Library Information files
@cindex @file{ali} files

@noindent
Each compilation actually generates two output files. The first of these
is the normal object file that has a @file{.o} extension. The second is a
text file containing full dependency information. It has the same
name as the source file, but an @file{.ali} extension.
This file is known as the Ada Library Information (@file{ali}) file.
The following information is contained in the @file{ali} file.

@itemize @bullet
@item
Version information (indicates which version of GNAT was used to compile
the unit(s) in question)

@item
Main program information (including priority and time slice settings,
as well as the wide character encoding used during compilation).

@item
List of arguments used in the @code{gcc} command for the compilation

@item
Attributes of the unit, including configuration pragmas used, an indication
of whether the compilation was successful, exception model used etc.

@item
A list of relevant restrictions applying to the unit (used for consistency)
checking.

@item
Categorization information (e.g. use of pragma @code{Pure}).

@item
Information on all @code{with}'ed units, including presence of
@code{Elaborate} or @code{Elaborate_All} pragmas.

@item
Information from any @code{Linker_Options} pragmas used in the unit

@item
Information on the use of @code{Body_Version} or @code{Version}
attributes in the unit.

@item
Dependency information. This is a list of files, together with
time stamp and checksum information. These are files on which
the unit depends in the sense that recompilation is required
if any of these units are modified.

@item
Cross-reference data. Contains information on all entities referenced
in the unit. Used by tools like @code{gnatxref} and @code{gnatfind} to
provide cross-reference information.

@end itemize

@noindent
For a full detailed description of the format of the @file{ali} file,
see the source of the body of unit @code{Lib.Writ}, contained in file
@file{lib-writ.adb} in the GNAT compiler sources.

@node Binding an Ada Program
@section Binding an Ada Program

@noindent
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 @file{b~@var{xxx}.adb} (with the corresponding spec
@file{b~@var{xxx}.ads}) where @var{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.

@node Mixed Language Programming
@section Mixed Language Programming
@cindex Mixed Language Programming

@menu
* Interfacing to C::
* Calling Conventions::
@end menu

@node Interfacing to C
@subsection Interfacing to C
@noindent
There are two ways to
build a program that contains some Ada files and some other language
files depending on whether the main program is in Ada or not.
If the main program is in Ada, you should proceed as follows:

@enumerate
@item
Compile the other language files to generate object files. For instance:
@smallexample
gcc -c file1.c
gcc -c file2.c
@end smallexample

@item
Compile the Ada units to produce a set of object files and ALI
files. For instance:
@smallexample
gnatmake -c my_main.adb
@end smallexample

@item
Run the Ada binder on the Ada main program. For instance:
@smallexample
gnatbind my_main.ali
@end smallexample

@item
Link the Ada main program, the Ada objects and the other language
objects. For instance:
@smallexample
gnatlink my_main.ali file1.o file2.o
@end smallexample
@end enumerate

The three last steps can be grouped in a single command:
@smallexample
gnatmake my_main.adb -largs file1.o file2.o
@end smallexample

@cindex Binder output file
@noindent
If the main program is in some language other than Ada, Then you may
have more than one entry point in the Ada subsystem. You must use a
special option of the binder to generate callable routines to initialize
and finalize the Ada units (@pxref{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. You use the same procedure for building the
program as described previously. In this case, however, the binder
only places the initialization and finalization subprograms into file
@file{b~@var{xxx}.adb} instead of the main program.
So, if the main program is not in Ada, you should proceed as follows:

@enumerate
@item
Compile the other language files to generate object files. For instance:
@smallexample
gcc -c file1.c
gcc -c file2.c
@end smallexample

@item
Compile the Ada units to produce a set of object files and ALI
files. For instance:
@smallexample
gnatmake -c entry_point1.adb
gnatmake -c entry_point2.adb
@end smallexample

@item
Run the Ada binder on the Ada main program. For instance:
@smallexample
gnatbind -n entry_point1.ali entry_point2.ali
@end smallexample

@item
Link the Ada main program, the Ada objects and the other language
objects. You only need to give the last entry point here. For instance:
@smallexample
gnatlink entry_point2.ali file1.o file2.o
@end smallexample
@end enumerate

@node Calling Conventions
@subsection Calling Conventions
@cindex Foreign Languages
@cindex Calling Conventions
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:

@itemize @bullet
@cindex Interfacing to Ada
@cindex Other Ada compilers
@cindex Convention Ada
@item
Ada. This 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 DEC 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
DEC Ada 83, All the tasking operations must either be entirely within
GNAT compiled sections of the program, or entirely within DEC Ada 83
compiled sections of the program.

@cindex Interfacing to Assembler
@cindex Convention Asm
@findex Asm
@item
Asm. Equivalent to Ada.

@cindex Convention Assembler
@item
Assembler. Equivalent to Ada.

@cindex Interfacing to COBOL
@cindex Convention COBOL
@findex COBOL
@item
COBOL. Data will be passed according to the conventions described
in section B.4 of the Ada 95 Reference Manual.

@findex C
@cindex Interfacing to C
@cindex Convention C
@item
C. Data will be passed according to the conventions described
in section B.3 of the Ada 95 Reference Manual.

@findex C++
@cindex Interfacing to C++
@cindex Convention C++
@item
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.

@findex Fortran
@cindex Interfacing to Fortran
@cindex Convention Fortran
@item
Fortran. Data will be passed according to the conventions described
in section B.5 of the Ada 95 Reference Manual.

@item
Intrinsic. This applies to an intrinsic operation, as defined in the Ada 95
Reference Manual. If a 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 can only
be applied to the following two sets of names, which the GNAT compiler
recognizes.
@itemize @bullet
@item
Rotate_Left, Rotate_Right, Shift_Left, Shift_Right, Shift_Right_-
Arithmetic.  The corresponding subprogram declaration must have
two formal parameters. The
first one must be a signed integer type or a modular type with a binary
modulus, and the second parameter must be of type Natural.
The return type must be the same as the type of the first argument. The size
of this type can only be 8, 16, 32, or 64.
@item binary arithmetic operators: "+", "-", "*", "/"
The corresponding operator declaration must have parameters and result type
that have the same root numeric type (for example, all three are long_float
types). This simplifies the definition of operations that use type checking
to perform dimensional checks:
@smallexample
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, "/");
@end smallexample
@noindent
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.
@end itemize
@noindent

@findex Stdcall
@cindex Convention Stdcall
@item
Stdcall. This is relevant only to NT/Win95 implementations of GNAT,
and specifies that the Stdcall calling sequence will be used, as defined
by the NT API.

@findex Stubbed
@cindex Convention Stubbed
@item
Stubbed. This is a special convention that indicates that the compiler
should provide a stub body that raises @code{Program_Error}.
@end itemize

@node Building Mixed Ada & C++ Programs
@section Building Mixed Ada & C++ Programs

@noindent
Building a mixed application containing both Ada and C++ code may be a
challenge for the unaware programmer. As a matter of fact, this
interfacing has not been standardized in the Ada 95 reference manual due
to the immaturity and lack of standard of C++ at the time. This
section gives a few hints that should make this task easier. In
particular the first section addresses the differences with
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 give some hints on how the GNAT run time can be adapted in order
to allow inter-language dispatching with a new C++ compiler.

@menu
* Interfacing to C++::
* Linking a Mixed C++ & Ada Program::
* A Simple Example::
* Adapting the Run Time to a New C++ Compiler::
@end menu

@node Interfacing to C++
@subsection Interfacing to C++

@noindent
GNAT supports interfacing with C++ compilers generating code that is
compatible with the standard Application Binary Interface of the given
platform.

@noindent
Interfacing can be done at 3 levels: simple data, subprograms and
classes. In the first 2 cases, GNAT offer a specific @var{Convention
CPP} that behaves exactly like @var{Convention C}. Usually C++ mangle
names of subprograms and currently GNAT does not provide any help to
solve the demangling problem. This problem can be addressed in 2 ways:
@itemize @bullet
@item
by modifying the C++ code in order to force a C convention using
the @var{extern "C"} syntax.

@item
by figuring out the mangled name and use it as the Link_Name argument of
the pragma import.
@end itemize

@noindent
Interfacing at the class level can be achieved by using the GNAT specific
pragmas such as @code{CPP_Class} and @code{ CPP_Virtual}. See the GNAT
Reference Manual for additional information.

@node Linking a Mixed C++ & Ada Program
@subsection Linking a Mixed C++ & Ada Program

@noindent
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:
@enumerate

@item
Using GNAT and G++ (GNU C++ compiler) from the same GCC
installation. The c++ linker can simply be called by using the c++
specific driver called @code{c++}. Note that this setup is not
very common because it may request recompiling the whole GCC
tree from sources and it does not allow to upgrade easily to a new
version of one compiler for one of the two languages without taking the
risk of destabilizing the other.

@smallexample
$ c++ -c file1.C
$ c++ -c file2.C
$ gnatmake ada_unit -largs file1.o file2.o --LINK=c++
@end smallexample

@item
Using GNAT and G++ from 2 different GCC installations. If both compilers
are on the PATH, the same method can be used. It is important to be
aware that environment variables such as C_INCLUDE_PATH,
GCC_EXEC_PREFIX, BINUTILS_ROOT or GCC_ROOT will affect both compilers at
the same time and thus may make one of the 2 compilers operate
improperly if they are set for the other. In particular it is important
that the link command has access to the proper gcc library @file{libgcc.a},
that is to say the one that is part of 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 full verbosity in order to verify which library is used:
@smallexample
$ gnatbind ada_unit
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=c++
@end smallexample
If there is a problem due to interfering environment variables, it can
be workaround 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:

@smallexample
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script
$ cat ./my_script
#!/bin/sh
unset BINUTILS_ROOT
unset GCC_ROOT
c++ $*
@end smallexample

@item
Using a non GNU C++ compiler. The same set of command as previously
described can be used to insure that the c++ linker is
used. Nonetheless, the Ada code may implicitly depend on the gcc
library. The latter can be located thanks to gnatls: it is to be found
on the last directory of the object path. It must then be explicitly
mentioned in the link command :
@smallexample
$ gnatls -v
$ Gdir=<the last directory on the object path>
$ gnatlink ada_unit file1.o file2.o -L$Gdir -lgcc
      --LINK=<cpp_linker>
@end smallexample
@end enumerate

@node A Simple Example
@subsection  A Simple Example
@noindent
The following example, provided as part of the GNAT examples, show how
to achieve procedural interfacing between Ada and C++ in both
directions. The C++ class A has 2 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++ calss is modelized by
a limited record with a layout comparable to the C++ class. The Ada
subprogram, in turn, calls the c++ method. So from the C++ main program
the code goes back and forth between the 2 languages.

@noindent
Here are the compilation commands
for native configurations:
@smallexample
$ gnatmake -c simple_cpp_interface
$ c++ -c cpp_main.C
$ c++ -c ex7.C
$ gnatbind -n simple_cpp_interface
$ gnatlink simple_cpp_interface -o cpp_main --LINK=$(CPLUSPLUS)
      -lstdc++ ex7.o cpp_main.o
@end smallexample
@noindent
Here are the corresponding sources:
@smallexample

//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);
  virtual 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
@b{package} @b{body} Simple_Cpp_Interface @b{is}

   @b{procedure} Ada_Method2 (This : @b{in} @b{out} A; V : Integer) @b{is}
   @b{begin}
      Method1 (This);
      This.A_Value := V;
   @b{end} Ada_Method2;

@b{end} Simple_Cpp_Interface;

@b{package} Simple_Cpp_Interface @b{is}
   @b{type} A @b{is} @b{limited}
      @b{record}
         O_Value : Integer;
         A_Value : Integer;
      @b{end} @b{record};
   @b{pragma} Convention (C, A);

   @b{procedure} Method1 (This : @b{in} @b{out} A);
   @b{pragma} Import (C, Method1);

   @b{procedure} Ada_Method2 (This : @b{in} @b{out} A; V : Integer);
   @b{pragma} Export (C, Ada_Method2);

@b{end} Simple_Cpp_Interface;
@end smallexample

@node Adapting the Run Time to a New C++ Compiler
@subsection Adapting the Run Time to a New C++ Compiler
@noindent
GNAT offers the capability to derive Ada 95 tagged types directly from
preexisting C++ classes and . See "Interfacing with C++" in the GNAT
reference manual. The mechanism used by GNAT for achieving such a goal
has been made user configurable through a GNAT library unit
@code{Interfaces.CPP}. The default version of this file is adapted to
the GNU c++ compiler. Internal knowledge of the virtual
table layout used by the new C++ compiler is needed to configure
properly this unit. The Interface of this unit is known by the compiler
and cannot be changed except for the value of the constants defining the
characteristics of the virtual table: CPP_DT_Prologue_Size, CPP_DT_Entry_Size,
CPP_TSD_Prologue_Size, CPP_TSD_Entry_Size. Read comments in the source
of this unit for more details.

@node Comparison between GNAT and C/C++ Compilation Models
@section Comparison between GNAT and C/C++ Compilation Models

@noindent
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 @code{with} is similar in effect to the @code{#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.

@cindex Elaboration order control
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 @code{gnatbind} might complain there was no valid order of
elaboration, a C++ compiler would simply construct a program that
malfunctioned at run time.

@node Comparison between GNAT and Conventional Ada Library Models
@section Comparison between GNAT and Conventional Ada Library Models

@noindent
This section is intended to be useful to Ada programmers who have
previously used an Ada compiler implementing the traditional Ada library
model, as described in the Ada 95 Language Reference Manual. If you
have not used such a system, please go on to the next section.

@cindex GNAT library
In GNAT, there is no @dfn{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:

@itemize @bullet
@item
When a unit is @code{with}'ed, the unit seen by the compiler corresponds
to the version of the unit most recently compiled into the library.

@item
Inlining is effective only if the necessary body has already been
compiled into the library.

@item
Compiling a unit may obsolete other units in the library.
@end itemize

@noindent
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:

@itemize @bullet
@item
When a unit is @code{with}'ed, the unit seen by the compiler corresponds
to the source version of the unit that is currently accessible to the
compiler.

@item
@cindex Inlining
Inlining requires the appropriate source files for the package or
subprogram bodies to be available to the compiler. Inlining is always
effective, independent of the order in which units are complied.

@item
Compiling a unit never affects any other compilations. The editing of
sources may cause previous compilations to be out of date if they
depended on the source file being modified.
@end itemize

@noindent
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.

@node Compiling Using gcc
@chapter Compiling Using @code{gcc}

@noindent
This chapter discusses how to compile Ada programs using the @code{gcc}
command. It also describes the set of switches
that can be used to control the behavior of the compiler.
@menu
* Compiling Programs::
* Switches for gcc::
* Search Paths and the Run-Time Library (RTL)::
* Order of Compilation Issues::
* Examples::
@end menu

@node Compiling Programs
@section Compiling Programs

@noindent
The first step in creating an executable program is to compile the units
of the program using the @code{gcc} command. You must compile the
following files:

@itemize @bullet
@item
the body file (@file{.adb}) for a library level subprogram or generic
subprogram

@item
the spec file (@file{.ads}) for a library level package or generic
package that has no body

@item
the body file (@file{.adb}) for a library level package
or generic package that has a body

@end itemize

@noindent
You need @emph{not} compile the following files

@itemize @bullet

@item
the spec of a library unit which has a body

@item
subunits
@end itemize

@noindent
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.
@cindex No code generated
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):

@smallexample
No code generated for file @var{fff} (@var{package spec})
No code generated for file @var{fff} (@var{subunit})
@end smallexample

@noindent
The basic command for compiling a file containing an Ada unit is

@smallexample
$ gcc -c [@var{switches}] @file{file name}
@end smallexample

@noindent
where @var{file name} is the name of the Ada file (usually
having an extension
@file{.ads} for a spec or @file{.adb} for a body).
You specify the
@code{-c} switch to tell @code{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 @file{.o} and an Ada
Library Information (ALI) file, which also has the same name as the
source file, but with @file{.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.

@findex gnat1
@code{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 @file{cc1}, and the Ada compiler is @file{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 @code{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 @code{gcc}
command. This causes @code{gcc} to call the appropriate compiler for
each file. For example, the following command lists three separate
files to be compiled:

@smallexample
$ gcc -c x.adb y.adb z.c
@end smallexample

@noindent
calls @code{gnat1} (the Ada compiler) twice to compile @file{x.adb} and
@file{y.adb}, and @code{cc1} (the C compiler) once to compile @file{z.c}.
The compiler generates three object files @file{x.o}, @file{y.o} and
@file{z.o} and the two ALI files @file{x.ali} and @file{y.ali} from the
Ada compilations. Any switches apply to all the files listed,
except for
@code{-gnat@var{x}} switches, which apply only to Ada compilations.

@node Switches for gcc
@section Switches for @code{gcc}

@noindent
The @code{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.

@menu
* Output and Error Message Control::
* Debugging and Assertion Control::
* Run-Time Checks::
* Stack Overflow Checking::
* Run-Time Control::
* Style Checking::
* Using gcc for Syntax Checking::
* Using gcc for Semantic Checking::
* Compiling Ada 83 Programs::
* Character Set Control::
* File Naming Control::
* Subprogram Inlining Control::
* Auxiliary Output Control::
* Debugging Control::
@end menu

@table @code
@cindex @code{-b} (@code{gcc})
@item -b @var{target}
Compile your program to run on @var{target}, which is the name of a
system configuration. You must have a GNAT cross-compiler built if
@var{target} is not the same as your host system.

@item -B@var{dir}
@cindex @code{-B} (@code{gcc})
Load compiler executables (for example, @code{gnat1}, the Ada compiler)
from @var{dir} instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available. See the
@code{gcc} manual page for further details. You would normally use the
@code{-b} or @code{-V} switch instead.

@item -c
@cindex @code{-c} (@code{gcc})
Compile. Always use this switch when compiling Ada programs.

Note: for some other languages when using @code{gcc}, notably in
the case of C and C++, it is possible to use
use @code{gcc} without a @code{-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 @code{gcc} cannot be used to run the GNAT binder.

@item -g
@cindex @code{-g} (@code{gcc})
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
@code{-g} switch if you plan on using the debugger.

@item -I@var{dir}
@cindex @code{-I} (@code{gcc})
@cindex RTL
Direct GNAT to search the @var{dir} directory for source files needed by
the current compilation
(@pxref{Search Paths and the Run-Time Library (RTL)}).

@item -I-
@cindex @code{-I-} (@code{gcc})
@cindex 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
(@pxref{Search Paths and the Run-Time Library (RTL)}).

@item -o @var{file}
@cindex @code{-o} (@code{gcc})
This switch is used in @code{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.

@item -O[@var{n}]
@cindex @code{-O} (@code{gcc})
@var{n} controls the optimization level.

@table @asis
@item n = 0
No optimization, the default setting if no @code{-O} appears

@item n = 1
Normal optimization, the default if you specify @code{-O} without
an operand.

@item n = 2
Extensive optimization

@item n = 3
Extensive optimization with automatic inlining. This applies only to
inlining within a unit. For details on control of inter-unit inlining
see @xref{Subprogram Inlining Control}.
@end table


@item -S
@cindex @code{-S} (@code{gcc})
Used in place of @code{-c} to
cause the assembler source file to be
generated, using @file{.s} as the extension,
instead of the object file.
This may be useful if you need to examine the generated assembly code.

@item -v
@cindex @code{-v} (@code{gcc})
Show commands generated by the @code{gcc} driver. Normally used only for
debugging purposes or if you need to be sure what version of the
compiler you are executing.

@item -V @var{ver}
@cindex @code{-V} (@code{gcc})
Execute @var{ver} version of the compiler. This is the @code{gcc}
version, not the GNAT version.

@item -funwind-tables
@cindex @code{-funwind-tables} (@code{gcc})
This switch causes the object files to be generated with unwind table
information. This is required for use of zero cost exception handling,
of for use of the trace capabilities in the GNAT library.

@item -gnata
Assertions enabled. @code{Pragma Assert} and @code{pragma Debug} to be
activated.

@item -gnatb
Generate brief messages to @file{stderr} even if verbose mode set.

@item -gnatc
Check syntax and semantics only (no code generation attempted).

@item -gnatC
Compress debug information and external symbol name table entries.

@item -gnatD
Output expanded source files for source level debugging. This switch
also suppress generation of cross-reference information (see -gnatx).

@item -gnatE
Full dynamic elaboration checks.

@item -gnatf
Full errors. Multiple errors per line, all undefined references.

@item -gnatF
Externals names are folded to all uppercase.

@item -gnatg
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.

@item -gnatG
List generated expanded code in source form.

@item -gnati@var{c}
Identifier character set
(@var{c}=1/2/3/4/8/p/f/n/w).

@item -gnath
Output usage information. The output is written to @file{stdout}.

@item -gnatk@var{n}
Limit file names to @var{n} (1-999) characters (@code{k} = krunch).

@item -gnatl
Output full source listing with embedded error messages.

@item -gnatm@var{n}
Limit number of detected errors to @var{n} (1-999).

@item -gnatn
Activate inlining across unit boundaries for subprograms for which
pragma @code{inline} is specified.

@item -gnatN
Activate front end inlining.

@item -fno-inline
Suppresses all inlining, even if other optimization or inlining switches
are set.

@item -fstack-check
Activates stack checking. See separate section on stack checking for
details of the use of this option.

@item -gnato
Enable numeric overflow checking (which is not normally enabled by default).

@item -gnatp
Suppress all checks.

@item -gnatq
Don't quit; try semantics, even if parse errors.

@item -gnatQ
Don't quit; generate @file{ali} and tree files even if illegalities.

@item -gnatP
Enable polling. This is required on some systems (notably Windows NT) to
obtain asynchronous abort and asynchronous transfer of control capability.
See the description of pragma Polling in the GNAT Reference Manual for
full details.

@item -gnatR0/1/2
Output representation information for declared types and objects.

@item -gnats
Syntax check only.

@item -gnatt
Tree output file to be generated.

@item -gnatT nnn
Set time slice to specified number of microseconds

@item -gnatu
List units for this compilation.

@item -gnatU
Tag all error messages with the unique string "error:"

@item -gnatv
Verbose mode. Full error output with source lines to @file{stdout}.

@item -gnatw@var{m}
Warning mode
(@var{m}=@code{s,e,l} for suppress, treat as error, elaboration
warnings).

@item -gnatW@var{e}
Wide character encoding method
(@var{e}=n/h/u/s/e/8).

@item -gnatx
Suppress generation of cross-reference information.

@item -gnatw@var{m}
Warning mode

@item -gnaty
Enable built-in style checks. See separate section describing this feature.

@item -gnatz@var{m}
Distribution stub generation and compilation
(@var{m}=r/c for receiver/caller stubs).

@item -gnat83
Enforce Ada 83 restrictions.

@item -pass-exit-codes
Catch exit codes from the compiler and use the most meaningful as
exit status.
@end table

You may combine a sequence of GNAT switches into a single switch. For
example, the combined switch

@cindex Combining GNAT switches
@smallexample
-gnatcfi3
@end smallexample

@noindent
is equivalent to specifying the following sequence of switches:

@smallexample
-gnatc -gnatf -gnati3
@end smallexample

@node Output and Error Message Control
@subsection Output and Error Message Control
@findex stderr

@noindent
The standard default format for error messages is called "brief format."
Brief format messages are written to @file{stderr} (the standard error
file) and have the following form:

@smallexample
@iftex
@leftskip=.7cm
@end iftex
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:4:20: ";" should be "is"
@end smallexample

@noindent
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.
@code{glide} can parse the error messages
and point to the referenced character.
The following switches provide control over the error message
format:

@table @code
@item -gnatv
@cindex @code{-gnatv} (@code{gcc})
@findex stdout
The v stands for verbose.
The effect of this setting is to write long-format error
messages to @file{stdout} (the standard output file.
The same program compiled with the
@code{-gnatv} switch would generate:

@smallexample
@group
@cartouche
3. funcion X (Q : Integer)
   |
>>> Incorrect spelling of keyword "function"
4. return Integer;
                 |
>>> ";" should be "is"
@end cartouche
@end group
@end smallexample

@noindent
The vertical bar indicates the location of the error, and the @samp{>>>}
prefix can be used to search for error messages. When this switch is
used the only source lines output are those with errors.

@item -gnatl
@cindex @code{-gnatl} (@code{gcc})
The @code{l} stands for list.
This switch causes a full listing of
the file to be generated. The output might look as follows:

@smallexample
@group
@cartouche
 1. procedure E is
 2.    V : Integer;
 3.    funcion X (Q : Integer)
       |
    >>> Incorrect spelling of keyword "function"
 4.     return Integer;
                      |
    >>> ";" should be "is"
 5.    begin
 6.       return Q + Q;
 7.    end;
 8. begin
 9.    V := X + X;
10.end E;
@end cartouche
@end group
@end smallexample

@noindent
@findex stderr
When you specify the @code{-gnatv} or @code{-gnatl} switches and
standard output is redirected, a brief summary is written to
@file{stderr} (standard error) giving the number of error messages and
warning messages generated.

@item -gnatU
@cindex @code{-gnatU} (@code{gcc})
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.

@item -gnatb
@cindex @code{-gnatb} (@code{gcc})
The @code{b} stands for brief.
This switch causes GNAT to generate the
brief format error messages to @file{stderr} (the standard error
file) as well as the verbose
format message or full listing (which as usual is written to
@file{stdout} (the standard output file).

@item -gnatm@var{n}
@cindex @code{-gnatm} (@code{gcc})
The @code{m} stands for maximum.
@var{n} is a decimal integer in the
range of 1 to 999 and limits the number of error messages to be
generated. For example, using @code{-gnatm2} might yield

@smallexample
@iftex
@leftskip=.7cm
@end iftex
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:5:35: missing ".."
fatal error: maximum errors reached
compilation abandoned
@end smallexample

@item -gnatf
@cindex @code{-gnatf} (@code{gcc})
@cindex Error messages, suppressing
The @code{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
@smallexample
@iftex
@leftskip=.7cm
@end iftex
e.adb:7:07: "V" is undefined (more references follow)
@end smallexample

@noindent
where the parenthetical comment warns that there are additional
references to the variable @code{V}. Compiling the same program with the
@code{-gnatf} switch yields

@smallexample
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
@end smallexample

@item -gnatq
@cindex @code{-gnatq} (@code{gcc})
The @code{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.

@item -gnatQ
In normal operation mode, the @file{ali} file is not generated if any
illegalities are detected in the program. The use of @code{-gnatQ} forces
generation of the @file{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 browing tools or integrated development
environments) that are driven from the @file{ali} file.

In addition, if @code{-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 @code{-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.

@noindent
In addition to error messages, which correspond to illegalities as defined
in the Ada 95 Reference Manual, the compiler detects two kinds of warning
situations.

@cindex Warning messages
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:
@smallexample
@iftex
@leftskip=.2cm
@end iftex
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

@end smallexample

@noindent
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
@code{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:

@itemize @bullet
@item
Possible infinitely recursive calls

@item
Out-of-range values being assigned

@item
Possible order of elaboration problems

@item
Unreachable code

@item
Variables that are never assigned a value

@item
Variables that are referenced before being initialized

@item
Task entries with no corresponding Accept statement

@item
Duplicate Accepts for the same task entry in a select

@item
Objects that take too much storage

@item
Unchecked conversion between types of differing sizes

@item
Missing return statements along some execution paths in a function

@item
Incorrect pragmas

@item
Incorrect external names

@item
Allocation from empty storage pool

@item
Potentially blocking operations in protected types

@item
Suspicious parenthesization of expressions

@item
Mismatching bounds in an aggregate

@item
Attempt to return local value by reference

@item
Unrecognized pragmas

@item
Premature instantiation of a generic body

@item
Attempt to pack aliased components

@item
Out of bounds array subscripts

@item
Wrong length on string assignment

@item
Violations of style rules if style checking is enabled
@end itemize

@noindent
The following switches are available to control the handling of
warning messages:

@table @code
@item -gnatwa (activate all optional errors)
@cindex @code{-gnatwa} (@code{gcc})
This swich activates all optional warning messages, see remaining list
in this section for details on optional warning messages that can be
individually controlled. The one exception is that @code{-gnatwa} does
not activate warnings for hiding variables (@code{-gnatwh}), so
if this warning is required, it must be explicitly set.

@item -gnatwA (suppress all optional errors)
@cindex @code{-gnatwA} (@code{gcc})
This swich suppresses all optional warning messages, see remaining list
in this section for details on optional warning messages that can be
individually controlled.

@item -gnatwb (activate warnings on biased rounding)
If a static floating-point expression has a value that is exactly half
way between two adjacent machine numbers, then the rules of Ada
(Ada Reference Manual, section 4.9(38)) require that this rounding
be done away from zero, even if the normal unbiased rounding rules
at run time would require rounding towards zero. This warning message
alerts you to such instances where compile-time rounding and run-time
rounding are not equivalent. If it is important to get proper run-time
rounding, then you can force this by making one of the operands into
a variable. The default is that such warnings are not generated.
Note that @code{-gnatwa} does not affect the setting of this warning option.

@item -gnatwB (suppress warnings on biased rounding)
This switch disables warnings on biased rounding.

@item -gnatwc (activate warnings on conditionals)
@cindex @code{-gnatwc} (@code{gcc})
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.
This warning can also be turned on using @code{-gnatwa}.

@item -gnatwC (suppress warnings on conditionals)
@cindex @code{-gnatwC} (@code{gcc})
This switch suppresses warnings for conditional expressions used in
tests that are known to be True or False at compile time.

@item -gnatwe (treat warnings as errors)
@cindex @code{-gnatwe} (@code{gcc})
This switch causes warning 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.

@item -gnatwh (activate warnings on hiding)
@cindex @code{-gnatwh} (@code{gcc})
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 @code{-gnatwa} does not affect the setting of this warning option.

@item -gnatwH (suppress warnings on hiding)
@cindex @code{-gnatwH} (@code{gcc})
This switch suppresses warnings on hiding declarations.

@item -gnatwi (activate warnings on implementation units).
@cindex @code{-gnatwi} (@code{gcc})
This switch activates warnings for a @code{with} of an internal GNAT
implementation unit, defined as any unit from the @code{Ada},
@code{Interfaces}, @code{GNAT},
 or @code{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 @code{with}'ed
by user programs. The default is that such warnings are generated
This warning can also be turned on using @code{-gnatwa}.

@item -gnatwI (disable warnings on implementation units).
@cindex @code{-gnatwI} (@code{gcc})
This switch disables warnings for a @code{with} of an internal GNAT
implementation unit.

@item -gnatwl (activate warnings on elaboration pragmas)
@cindex @code{-gnatwl} (@code{gcc})
This swich activates warnings on missing pragma Elaborate_All statements.
See the section in this guide on elaboration checking for details on
when such pragma should be used. The default is that such warnings
are not generated.
This warning can also be turned on using @code{-gnatwa}.

@item -gnatwL (suppress warnings on elaboration pragmas)
@cindex @code{-gnatwL} (@code{gcc})
This swich suppresses warnings on missing pragma Elaborate_All statements.
See the section in this guide on elaboration checking for details on
when such pragma should be used.

@item -gnatwo (activate warnings on address clause overlays)
@cindex @code{-gnatwo} (@code{gcc})
This swich 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 @code{-gnatwa}.

@item -gnatwO (suppress warnings on address clause overlays)
@cindex @code{-gnatwO} (@code{gcc})
This swich suppresses warnings on possibly unintended initialization
effects of defining address clauses that cause one variable to overlap
another.

@item -gnatwp (activate warnings on ineffective pragma Inlines)
@cindex @code{-gnatwp} (@code{gcc})
This swich activates warnings for failure of front end inlining
(activated by @code{-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.
This warning can also be turned on using @code{-gnatwa}.

@item -gnatwP (suppress warnings on ineffective pragma Inlines)
@cindex @code{-gnatwP} (@code{gcc})
This swich suppresses warnings on ineffective pragma Inlines. If the
inlining mechanism cannot inline a call, it will simply ignore the
request silently.

@item -gnatwr (activate warnings on redundant constructs)
@cindex @code{-gnatwr} (@code{gcc})
This switch activates warnings for redundant constructs. In particular
assignments of a variable to itself, and a type conversion that converts
an object to its own type. The default
is that such warnings are not generated.

@item -gnatwR (suppress warnings on redundant constructs)
@cindex @code{-gnatwR} (@code{gcc})
This switch suppresses warnings for redundant constructs.

@item -gnatws (suppress all warnings)
@cindex @code{-gnatws} (@code{gcc})
This switch completely suppresses the
output of all warning messages from the GNAT front end.
Note that it does not suppress warnings from the @code{gcc} back end.
To suppress these back end warnings as well, use the switch @code{-w}
in addition to @code{-gnatws}.

@item -gnatwu (activate warnings on unused entities)
@cindex @code{-gnatwu} (@code{gcc})
This switch activates warnings to be generated for entities that
are defined but not referenced, and for units that are @code{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 the package
is referenced but the only references are in @code{use}
clauses or @code{renames}
declarations, a warning is still generated. A warning is also generated
for a generic package that is @code{with}'ed but never instantiated.
In the case where a package or subprogram body is compiled, and there
is a @code{with} on the corresponding spec
that is only referenced in the body,
a warning is also generated, noting that the
@code{with} can be moved to the body. The default is that
such warnings are not generated.
This warning can also be turned on using @code{-gnatwa}.

@item -gnatwU (suppress warnings on unused entities)
@cindex @code{-gnatwU} (@code{gcc})
This switch suppresses warnings for unused entities and packages.

@noindent
A string of warning parameters can be used in the same parameter. For example:

@smallexample
-gnatwaLe
@end smallexample

@noindent
Would turn on all optional warnings except for elaboration pragma warnings,
and also specify that warnings should be treated as errors.

@item -w
@cindex @code{-w}
This switch suppresses warnings from the @code{gcc} backend. It may be
used in conjunction with @code{-gnatws} to ensure that all warnings
are suppressed during the entire compilation process.

@end table
@end table

@node Debugging and Assertion Control
@subsection Debugging and Assertion Control

@table @code
@item -gnata
@cindex @code{-gnata} (@code{gcc})
@findex Assert
@findex Debug
@cindex Assertions

@noindent
The pragmas @code{Assert} and @code{Debug} normally have no effect and
are ignored. This switch, where @samp{a} stands for assert, causes
@code{Assert} and @code{Debug} pragmas to be activated.

The pragmas have the form:

@smallexample
@group
@cartouche
   @b{pragma} Assert (@var{Boolean-expression} [,
                      @var{static-string-expression}])
   @b{pragma} Debug (@var{procedure call})
@end cartouche
@end group
@end smallexample

@noindent
The @code{Assert} pragma causes @var{Boolean-expression} to be tested.
If the result is @code{True}, the pragma has no effect (other than
possible side effects from evaluating the expression). If the result is
@code{False}, the exception @code{Assert_Error} declared in the package
@code{System.Assertions} is
raised (passing @var{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 @code{Debug} pragma causes @var{procedure} to be called. Note that
@code{pragma Debug} may appear within a declaration sequence, allowing
debugging procedures to be called between declarations.

@end table

@node Style Checking
@subsection Style Checking
@findex Style checking

@noindent
The -gnaty@var{x} 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 warning message is given, preceded by
the character sequence "(style)".
The string @var{x} is a sequence of letters or digits
indicating the particular style
checks to be performed. The following checks are defined:

@table @code
@item 1-9 (specify indentation level)
If a digit from 1-9 appears in the string after @code{-gnaty} then proper
indentation is checked, with the digit indicating the indentation level
required. 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 @code{--} starting on a column that is a multiple of
the alignment level.

@item a (check attribute casing)
If the letter a appears in the string after @code{-gnaty} then
attribute names, including the case of keywords such as @code{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.

@item b (blanks not allowed at statement end)
If the letter b appears in the string after @code{-gnaty} then
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.

@item c (check comments)
If the letter c appears in the string after @code{-gnaty} then
comments must meet the following set of rules:

@itemize @bullet

@item
The "--" that starts the column must either start in column one, or else
at least one blank must precede this sequence.

@item
Comments that follow other tokens on a line must have at least one blank
following the "--" at the start of the comment.

@item
Full line comments must have two blanks following the "--" that starts
the comment, with the following exceptions.

@item
A line consisting only of the "--" characters, possibly preceded by blanks
is permitted.

@item
A comment starting with "--x" where x is a special character is permitted.
This alows proper processing of the output generated by specialized tools
including @code{gnatprep} (where --! is used) and the SPARK annnotation
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#.

@item
A line consisting entirely of minus signs, possibly preceded by blanks, is
permitted. This allows the construction of box comments where lines of minus
signs are used to form the top and bottom of the box.

@item
If a comment starts and ends with "--" 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:
@smallexample
---------------------------
-- This is a box comment --
-- with two text lines.  --
---------------------------
@end smallexample
@end itemize

@item e (check end/exit labels)
If the letter e appears in the string after @code{-gnaty} then
optional labels on @code{end} statements ending subprograms and on
@code{exit} statements exiting named loops, are required to be present.

@item f (no form feeds or vertical tabs)
If the letter f appears in the string after @code{-gnaty} then
neither form feeds nor vertical tab characters are not permitted
in the source text.

@item h (no horizontal tabs)
If the letter h appears in the string after @code{-gnaty} then
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.

@item i (check if-then layout)
If the letter i appears in the string after @code{-gnaty},
then the keyword @code{then} must appear either on the same
line as corresponding @code{if}, or on a line on its own, lined
up under the @code{if} with at least one non-blank line in between
containing all or part of the condition to be tested.

@item k (check keyword casing)
If the letter k appears in the string after @code{-gnaty} then
all keywords must be in lower case (with the exception of keywords
such as @code{digits} used as attribute names to which this check
does not apply).

@item l (check layout)
If the letter l appears in the string after @code{-gnaty} then
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 @code{else} keyword must
be lined up with the corresponding @code{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
@code{record} keyword on the same line as the @code{type} keyword, and
then the @code{end} in @code{end record} must line up under @code{type}.
For example, either of the following two layouts is acceptable:

@smallexample
@group
@cartouche
@b{type} q @b{is record}
   a : integer;
   b : integer;
@b{end record};

@b{type} q @b{is}
   @b{record}
      a : integer;
      b : integer;
   @b{end record};
@end cartouche
@end group
@end smallexample

@noindent
Second, in the case of a block statement, a permitted alternative
is to put the block label on the same line as the @code{declare} or
@code{begin} keyword, and then line the @code{end} keyword up under
the block label. For example both the following are permitted:

@smallexample
@group
@cartouche
Block : @b{declare}
   A : Integer := 3;
@b{begin}
   Proc (A, A);
@b{end} Block;

Block :
   @b{declare}
      A : Integer := 3;
   @b{begin}
      Proc (A, A);
   @b{end} Block;
@end cartouche
@end group
@end smallexample

@noindent
The same alternative format is allowed for loops. For example, both of
the following are permitted:

@smallexample
@group
@cartouche
Clear : @b{while} J < 10 @b{loop}
   A (J) := 0;
@b{end loop} Clear;

Clear :
   @b{while} J < 10 @b{loop}
      A (J) := 0;
   @b{end loop} Clear;
@end cartouche
@end group
@end smallexample

@item m (check maximum line length)
If the letter m appears in the string after @code{-gnaty}
then 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.

@item Mnnn (set maximum line length)
If the sequence Mnnn, where nnn is a decimal number, appears in
the string after @code{-gnaty} then the length of lines must not exceed the
given value.

@item n (check casing of entities in Standard)
If the letter n appears in the string
after @code{-gnaty} then any identifier from Standard must be cased
to match the presentation in the Ada Reference Manual (for example,
@code{Integer} and @code{ASCII.NUL}).

@item o (check order of subprogram bodies)
If the letter o appears in the string
after @code{-gnaty} then 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).

@item p (check pragma casing)
If the letter p appears in the string after @code{-gnaty} then
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.

@item r (check references)
If the letter r appears in the string after @code{-gnaty}
then 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.

@item s (check separate specs)
If the letter s appears in the string after @code{-gnaty} then
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.

@item t (check token spacing)
If the letter t appears in the string after @code{-gnaty} then
the following token spacing rules are enforced:

@itemize @bullet

@item
The keywords @code{abs} and @code{not} must be followed by a space.

@item
The token @code{=>} must be surrounded by spaces.

@item
The token @code{<>} must be preceded by a space or a left parenthesis.

@item
Binary operators other than @code{**} must be surrounded by spaces.
There is no restriction on the layout of the @code{**} binary operator.

@item
Colon must be surrounded by spaces.

@item
Colon-equal (assignment) must be surrounded by spaces.

@item
Comma must be the first non-blank character on the line, or be
immediately preceded by a non-blank character, and must be followed
by a space.

@item
Left parenthesis must be preceded by a space, and must not be followed
by a space (it can be at the end of a line).

@item
A right parenthesis must either be the first non-blank character on
a line, or it must be preceded by a non-blank character.

@item
A semicolon must not be preceded by a space, and must not be followed by
a non-blank character.

@item
A unary plus or minus may not be followed by a space.

@item
A vertical bar must be surrounded by spaces.
@end itemize

@noindent
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.

@end table

@noindent
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 @code{-gnatwe} switch can be used to treat warning messages,
including style messages, as fatal errors.

@noindent
The switch
@code{-gnaty} on its own (that is not followed by any letters or digits),
is equivalent to @code{gnaty3abcefhiklmprst}, that is all checking
options are enabled with
the exception of -gnatyo,
with an indentation level of 3. This is the standard
checking option that is used for the GNAT sources.

@node Run-Time Checks
@subsection Run-Time Checks
@cindex Division by zero
@cindex Access before elaboration
@cindex Checks, division by zero
@cindex Checks, access before elaboration

@noindent
If you compile with the default options, GNAT will insert many run-time
checks into the compiled code, including code that performs range
checking against constraints, but not arithmetic overflow checking for
integer operations (including division by zero) or checks for access
before elaboration on subprogram calls. All other run-time checks, as
required by the Ada 95 Reference Manual, are generated by default.
The following @code{gcc} switches refine this default behavior:

@table @code
@item -gnatp
@cindex @code{-gnatp} (@code{gcc})
@cindex Suppressing checks
@cindex Checks, suppressing
@findex Suppress
Suppress all run-time checks as though @code{pragma Suppress (all_checks})
had been present in the source. Use this switch to improve the performance
of the code at the expense of safety in the presence of invalid data or
program bugs.

@item -gnato
@cindex @code{-gnato} (@code{gcc})
@cindex Overflow checks
@cindex Check, overflow
Enables overflow checking for integer operations.
This causes GNAT to generate slower and larger executable
programs by adding code to check for both overflow and division by zero
(resulting in raising @code{Constraint_Error} as required by standard Ada
semantics). These overflow checks correspond to situations in which
the true value of the result of an operation may be outside the base
range of the result type. The following example shows the distinction:

@smallexample
X1 : Integer := Integer'Last;
X2 : Integer range 1 .. 5 := 5;
...
X1 := X1 + 1;   -- @code{-gnato} required to catch the Constraint_Error
X2 := X2 + 1;   -- range check, @code{-gnato} has no effect here
@end smallexample

@noindent
Here the first addition results in a value that is outside the base range
of Integer, and hence requires an overflow check for detection of the
constraint error. The second increment operation results in a violation
of the explicit range constraint, and such range checks are always
performed. Basically the compiler can assume that in the absence of
the @code{-gnato} switch that any value of type @code{xxx} is
in range of the base type of @code{xxx}.

@findex Machine_Overflows
Note that the @code{-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 @code{Machine_Overflows}
attribute set to @code{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 can
generate an incorrect value, but cannot cause erroneous behavior. This
is unlike the situation with a constraint check on an array subscript,
where failure to perform the check can result in random memory description,
or the range check on a case statement, where failure to perform the check
can cause a wild jump.

Note again that @code{-gnato} is off by default, 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 @code{gnatmake} or
@code{gcc} command.

@item -gnatE
@cindex @code{-gnatE} (@code{gcc})
@cindex Elaboration checks
@cindex Check, elaboration
Enables dynamic checks for access-before-elaboration
on subprogram calls and generic instantiations.
For full details of the effect and use of this switch,
@xref{Compiling Using gcc}.
@end table

@findex Unsuppress
@noindent
The setting of these switches only controls the default setting of the
checks. You may modify them using either @code{Suppress} (to remove
checks) or @code{Unsuppress} (to add back suppressed checks) pragmas in
the program source.

@node Stack Overflow Checking
@subsection Stack Overflow Checking
@cindex Stack Overflow Checking
@cindex -fstack-check

@noindent
For most operating systems, @code{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.

To activate stack checking, compile all units with the gcc option
@code{-fstack-check}. For example:

@smallexample
gcc -c -fstack-check package1.adb
@end smallexample

@noindent
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) do not exceed the available stack space.
If the space is exceeded, then a @code{Storage_Error} exception is raised.

For declared tasks, the stack size is always controlled by the size
given in an applicable @code{Storage_Size} pragma (or is set to
the default size if no pragma is used.

For the environment task, the stack size depends on
system defaults and is unknown to the compiler. The stack
may even dynamically grow on some systems, precluding the
normal Ada semantics for stack overflow. In the worst case,
unbounded stack usage, causes unbounded stack expansion
resulting in the system running out of virtual memory.

The 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
@code{GNAT_STACK_LIMIT} to indicate the maximum
stack area that can be used, as in:
@cindex GNAT_STACK_LIMIT

@smallexample
SET GNAT_STACK_LIMIT 1600
@end smallexample

@noindent
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.

@node Run-Time Control
@subsection Run-Time Control

@table @code
@item -gnatT nnn
@cindex @code{-gnatT} (@code{gcc})
@cindex Time Slicing

@noindent
The @code{gnatT} switch can be used to specify the time-slicing value
to be used for task switching between equal priority tasks. The value
@code{nnn} is given in microseconds as a decimal integer.

Setting the time-slicing value is only effective if the underlying thread
control system can accomodate time slicing. Check the documentation of
your operating system for details. Note that the time-slicing value can
also be set by use of pragma @code{Time_Slice} or by use of the
@code{t} switch in the gnatbind step. The pragma overrides a command
line argument if both are present, and the @code{t} switch for gnatbind
overrides both the pragma and the @code{gcc} command line switch.
@end table

@node Using gcc for Syntax Checking
@subsection Using @code{gcc} for Syntax Checking
@table @code
@item -gnats
@cindex @code{-gnats} (@code{gcc})

@noindent
The @code{s} stands for syntax.

Run GNAT in syntax checking only mode. For
example, the command

@smallexample
$ gcc -c -gnats x.adb
@end smallexample

@noindent
compiles file @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 @code{-c} (compile
only) flag in addition to the @code{-gnats} flag.
.

You may use other switches in conjunction with @code{-gnats}. In
particular, @code{-gnatl} and @code{-gnatv} are useful to control the
format of any generated error messages.

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 @code{X}
@code{with}'s a unit @code{Y}, compiling unit @code{X} in syntax
check only mode does not access the source file containing unit
@code{Y}.

@cindex Multiple units, syntax checking
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 @code{gnatchop} utility
(@pxref{Renaming Files Using gnatchop}).
@end table

@node Using gcc for Semantic Checking
@subsection Using @code{gcc} for Semantic Checking
@table @code
@item -gnatc
@cindex @code{-gnatc} (@code{gcc})

@noindent
The @code{c} stands for check.
Causes the compiler to operate in semantic check mode,
with full checking for all illegalities specified in the
Ada 95 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:

@itemize @bullet
@item
The needed source files must be accessible
(@pxref{Search Paths and the Run-Time Library (RTL)}).

@item
Each file must contain only one compilation unit.

@item
The file name and unit name must match (@pxref{File Naming Rules}).
@end itemize

The output consists of error messages as appropriate. No object file is
generated. An @file{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 95 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).
@end table

@node Compiling Ada 83 Programs
@subsection Compiling Ada 83 Programs
@table @code
@cindex Ada 83 compatibility
@item -gnat83
@cindex @code{-gnat83} (@code{gcc})
@cindex ACVC, Ada 83 tests

@noindent
Although GNAT is primarily an Ada 95 compiler, it accepts this switch to
specify that an Ada 83 program is to be compiled in Ada83 mode. If you specify
this switch, GNAT rejects most Ada 95 extensions and applies Ada 83 semantics
where this can be done easily.
It is not possible to guarantee this switch does a perfect
job; for example, some subtle tests, such as are
found in earlier ACVC tests (that have been removed from the ACVC suite for Ada
95), may not compile correctly. However, for most purposes, using
this switch should help to ensure that programs that compile correctly
under the @code{-gnat83} switch can be ported easily to an Ada 83
compiler. This is the main use of the switch.

With few exceptions (most notably the need to use @code{<>} on
@cindex Generic formal parameters
unconstrained generic formal parameters, the use of the new Ada 95
keywords, and the use of packages
with optional bodies), it is not necessary to use the
@code{-gnat83} switch when compiling Ada 83 programs, because, with rare
exceptions, Ada 95 is upwardly compatible with Ada 83. This
means that a correct Ada 83 program is usually also a correct Ada 95
program.

@end table

@node Character Set Control
@subsection Character Set Control
@table @code
@item -gnati@var{c}
@cindex @code{-gnati} (@code{gcc})

@noindent
Normally GNAT recognizes the Latin-1 character set in source program
identifiers, as described in the Ada 95 Reference Manual.
This switch causes
GNAT to recognize alternate character sets in identifiers. @var{c} is a
single character  indicating the character set, as follows:

@table @code
@item 1
Latin-1 identifiers

@item 2
Latin-2 letters allowed in identifiers

@item 3
Latin-3 letters allowed in identifiers

@item 4
Latin-4 letters allowed in identifiers

@item p
IBM PC letters (code page 437) allowed in identifiers

@item 8
IBM PC letters (code page 850) allowed in identifiers

@item f
Full upper-half codes allowed in identifiers

@item n
No upper-half codes allowed in identifiers

@item w
Wide-character codes allowed in identifiers
@end table

@xref{Foreign Language Representation}, for full details on the
implementation of these character sets.

@item -gnatW@var{e}
@cindex @code{-gnatW} (@code{gcc})
Specify the method of encoding for wide characters.
@var{e} is one of the following:

@table @code

@item h
Hex encoding (brackets coding also recognized)

@item u
Upper half encoding (brackets encoding also recognized)

@item s
Shift/JIS encoding (brackets encoding also recognized)

@item e
EUC encoding (brackets encoding also recognized)

@item 8
UTF-8 encoding (brackets encoding also recognized)

@item b
Brackets encoding only (default value)
@end table
For full details on the these encoding
methods see @xref{Wide Character Encodings}.
Note that brackets coding is always accepted, even if one of the other
options is specified, so for example @code{-gnatW8} specifies that both
brackets and @code{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.
scheme. If no @code{-gnatW?} parameter is present, then the default
representation is Brackets encoding only.

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.

@end table
@node File Naming Control
@subsection File Naming Control

@table @code
@item -gnatk@var{n}
@cindex @code{-gnatk} (@code{gcc})
Activates file name "krunching". @var{n}, a decimal integer in the range
1-999, indicates the maximum allowable length of a file name (not
including the @file{.ads} or @file{.adb} extension). The default is not
to enable file name krunching.

For the source file naming rules, @xref{File Naming Rules}.
@end table

@node Subprogram Inlining Control
@subsection Subprogram Inlining Control

@table @code
@item -gnatn
@cindex @code{-gnatn} (@code{gcc})
The @code{n} here is intended to suggest the first syllable of the
word "inline".
GNAT recognizes and processes @code{Inline} pragmas. However, for the
inlining to actually occur, optimization must be enabled. To enable
inlining across unit boundaries, this is, inlining a call in one unit of
a subprogram declared in a @code{with}'ed unit, you must also specify
this switch.
In the absence of this switch, GNAT does not attempt
inlining across units and does not need to access the bodies of
subprograms for which @code{pragma Inline} is specified if they are not
in the current unit.

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 @xref{Inlining of Subprograms}.

@item -gnatN
@cindex @code{-gnatN} (@code{gcc})
The front end inlining activated by this switch is generally more extensive,
and quite often more effective than the standard @code{-gnatn} inlining mode.
It will also generate additional dependencies.

@end table

@node Auxiliary Output Control
@subsection Auxiliary Output Control

@table @code
@item -gnatt
@cindex @code{-gnatt} (@code{gcc})
@cindex Writing internal trees
@cindex Internal trees, writing to file
Cause GNAT to write the internal tree for a unit to a file (with the
extension @file{.adt}.
This not normally required, but is used by separate analysis tools.
Typically
these tools do the necessary compilations automatically, so you should
never have to specify this switch in normal operation.

@item -gnatu
@cindex @code{-gnatu} (@code{gcc})
Print a list of units required by this compilation on @file{stdout}.
The listing includes all units on which the unit being compiled depends
either directly or indirectly.

@item -pass-exit-codes
@cindex @code{-pass-exit-codes} (@code{gcc})
If this switch is not used, the exit code returned by @code{gcc} when
compiling multiple files indicates whether all source files have
been successfully used to generate object files or not.

When @code{-pass-exit-codes} is used, @code{gcc} exits with an extended
exit status and allows an integrated development environment to better
react to a compilation failure. Those exit status are:

@table @asis
@item 5
There was an error in at least one source file.
@item 3
At least one source file did not generate an object file.
@item 2
The compiler died unexpectedly (internal error for example).
@item 0
An object file has been generated for every source file.
@end table
@end table

@node Debugging Control
@subsection Debugging Control

@table @code
@cindex Debugging options
@item -gnatd@var{x}
Activate internal debugging switches. @var{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 @code{Debug} unit in the compiler source
file @file{debug.adb}.

@item -gnatG
@cindex @code{-gnatG} (@code{gcc})
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 @code{-gnatG} you can identify
these cases, and consider whether it may be desirable to modify the coding
approach to improve efficiency.

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 specification
of package @code{Sprint} in file @file{sprint.ads} for a full list.

@table @code
@item new @var{xxx} [storage_pool = @var{yyy}]
Shows the storage pool being used for an allocator.

@item at end @var{procedure-name};
Shows the finalization (cleanup) procedure for a scope.

@item (if @var{expr} then @var{expr} else @var{expr})
Conditional expression equivalent to the @code{x?y:z} construction in C.

@item @var{target}^(@var{source})
A conversion with floating-point truncation instead of rounding.

@item @var{target}?(@var{source})
A conversion that bypasses normal Ada semantic checking. In particular
enumeration types and fixed-point types are treated simply as integers.

@item @var{target}?^(@var{source})
Combines the above two cases.

@item @var{x} #/ @var{y}
@itemx @var{x} #mod @var{y}
@itemx @var{x} #* @var{y}
@itemx @var{x} #rem @var{y}
A division or multiplication of fixed-point values which are treated as
integers without any kind of scaling.

@item free @var{expr} [storage_pool = @var{xxx}]
Shows the storage pool associated with a @code{free} statement.

@item freeze @var{typename} [@var{actions}]
Shows the point at which @var{typename} is frozen, with possible
associated actions to be performed at the freeze point.

@item reference @var{itype}
Reference (and hence definition) to internal type @var{itype}.

@item @var{function-name}! (@var{arg}, @var{arg}, @var{arg})
Intrinsic function call.

@item @var{labelname} : label
Declaration of label @var{labelname}.

@item @var{expr} && @var{expr} && @var{expr} ... && @var{expr}
A multiple concatenation (same effect as @var{expr} & @var{expr} &
@var{expr}, but handled more efficiently).

@item [constraint_error]
Raise the @code{Constraint_Error} exception.

@item @var{expression}'reference
A pointer to the result of evaluating @var{expression}.

@item @var{target-type}!(@var{source-expression})
An unchecked conversion of @var{source-expression} to @var{target-type}.

@item [@var{numerator}/@var{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).

@item -gnatD
@cindex @code{-gnatD} (@code{gcc})
This switch is used in conjunction with @code{-gnatG} to cause the expanded
source, as described above to be written to files with names
@file{xxx.dg}, where @file{xxx} is the normal file name,
for example, if the source file name is @file{hello.adb},
then a file @file{hello.adb.dg} will be written.
The debugging information generated
by the @code{gcc} @code{-g} switch will refer to the generated
@file{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).

@item -gnatC
@cindex @code{-gnatE} (@code{gcc})
In the generated debugging information, and also in the case of long external
names, the compiler uses a compression mechanism if the name is very long.
This compression method uses a checksum, and avoids trouble on some operating
systems which have difficulty with very long names. The @code{-gnatC} switch
forces this compression approach to be used on all external names and names
in the debugging information tables. This reduces the size of the generated
executable, at the expense of making the naming scheme more complex. The
compression only affects the qualification of the name. Thus a name in
the source:

@smallexample
Very_Long_Package.Very_Long_Inner_Package.Var
@end smallexample

@noindent
would normally appear in these tables as:

@smallexample
very_long_package__very_long_inner_package__var
@end smallexample

@noindent
but if the @code{-gnatC} switch is used, then the name appears as

@smallexample
XCb7e0c705__var
@end smallexample

@noindent
Here b7e0c705 is a compressed encoding of the qualification prefix.
The GNAT Ada aware version of GDB understands these encoded prefixes, so if this
debugger is used, the encoding is largely hidden from the user of the compiler.

@end table

@item -gnatRx
@cindex @code{-gnatR} (@code{gcc})
This switch controls output from the compiler of a listing showing
representation information for declared types and objects. For
@code{-gnatR0}, no information is output (equivalent to omitting
the @code{-gnatR} switch). For @code{-gnatR1} (which is the default,
so @code{-gnatR} with no parameter has the same effect), size and alignment
information is listed for declared array and record types. For
@code{-gnatR2}, size and alignment information is listed for all
declared types and objects.

@item -gnatx
@cindex @code{-gnatx} (@code{gcc})
Normally the compiler generates full cross-referencing information in
the @file{ALI} file. This information is used by a number of tools,
including @code{gnatfind} and @code{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.

@end table
@node Search Paths and the Run-Time Library (RTL)
@section Search Paths and the Run-Time Library (RTL)

@noindent
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:

@enumerate
@item
The directory containing the source file of the main unit being compiled
(the file name on the command line).

@item
Each directory named by an @code{-I} switch given on the @code{gcc}
command line, in the order given.

@item
@findex ADA_INCLUDE_PATH
Each of the directories listed in the value of the
@code{ADA_INCLUDE_PATH} environment variable.
Construct this value
exactly as the @code{PATH} environment variable: a list of directory
names separated by colons.
@item
The content of the "ada_source_path" file which is part of the GNAT
installation tree and is used to store standard libraries such as the
GNAT Run Time Library (RTL) source files.
@ref{Installing an Ada Library}
@end enumerate

@noindent
Specifying the switch @code{-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 @code{-I} switch.

Specifying the switch @code{-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 @code{-o} switch;
however, @code{gcc} and @code{gnat1} have not been coordinated on this
so the ALI file will not go to the right place. Therefore, you should
avoid using the @code{-o} switch.

@findex System.IO
The packages @code{Ada}, @code{System}, and @code{Interfaces} and their
children make up the GNAT RTL, together with the simple @code{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 routines. See the 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.

@node Order of Compilation Issues
@section Order of Compilation Issues

@noindent
If, in our earlier example, there was a spec for the @code{hello}
procedure, it would be contained in the file @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:

@itemize @bullet
@item
There is no point in compiling specs (except for package
specs with no bodies) because these are compiled as needed by clients. If
you attempt a useless compilation, you will receive an error message.
It is also useless to compile subunits because they are compiled as needed
by the parent.

@item
There are no order of compilation requirements: performing a
compilation never obsoletes anything. The only way you can obsolete
something and require recompilations is to modify one of the
source files on which it depends.

@item
There is no library as such, apart from the ALI files
(@pxref{The Ada Library Information Files}, for information on the format of these
files). For now we find it convenient to create separate ALI files, but
eventually the information therein may be incorporated into the object
file directly.

@item
When you compile a unit, the source files for the specs of all units
that it @code{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.
@end itemize

@node Examples
@section Examples

@noindent
The following are some typical Ada compilation command line examples:

@table @code
@item $ gcc -c xyz.adb
Compile body in file @file{xyz.adb} with all default options.

@item $ gcc -c -O2 -gnata xyz-def.adb

Compile the child unit package in file @file{xyz-def.adb} with extensive
optimizations, and pragma @code{Assert}/@code{Debug} statements
enabled.

@item $ gcc -c -gnatc abc-def.adb
Compile the subunit in file @file{abc-def.adb} in semantic-checking-only
mode.
@end table

@node Binding Using gnatbind
@chapter Binding Using @code{gnatbind}
@findex gnatbind

@menu
* Running gnatbind::
* Generating the Binder Program in C::
* Consistency-Checking Modes::
* Binder Error Message Control::
* Elaboration Control::
* Output Control::
* Binding with Non-Ada Main Programs::
* Binding Programs with No Main Subprogram::
* Summary of Binder Switches::
* Command-Line Access::
* Search Paths for gnatbind::
* Examples of gnatbind Usage::
@end menu

@noindent
This chapter describes the GNAT binder, @code{gnatbind}, which is used
to bind compiled GNAT objects. The @code{gnatbind} program performs
four separate functions:

@enumerate
@item
Checks that a program is consistent, in accordance with the rules in
Chapter 10 of the Ada 95 Reference Manual. In particular, error
messages are generated if a program uses inconsistent versions of a
given unit.

@item
Checks that an acceptable order of elaboration exists for the program
and issues an error message if it cannot find an order of elaboration
that satisfies the rules in Chapter 10 of the Ada 95 Language Manual.

@item
Generates a main program incorporating the given elaboration order.
This program is a small Ada package (body and spec) that
must be subsequently compiled
using the GNAT compiler. The necessary compilation step is usually
performed automatically by @code{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.

@item
Determines the set of object files required by the given main program.
This information is output in the forms of comments in the generated C program,
to be read by the @code{gnatlink} utility used to link the Ada application.
@end enumerate

@node Running gnatbind
@section Running @code{gnatbind}

@noindent
The form of the @code{gnatbind} command is

@smallexample
$ gnatbind [@var{switches}] @var{mainprog}[.ali] [@var{switches}]
@end smallexample

@noindent
where @var{mainprog}.adb is the Ada file containing the main program
unit body. If no switches are specified, @code{gnatbind} constructs an Ada
package in two files whose names are
@file{b~@var{ada_main}.ads}, and
@file{b~@var{ada_main}.adb}.
For example, if given the
parameter @samp{hello.ali}, for a main program contained in file
@file{hello.adb}, the binder output files would be @file{b~hello.ads}
and @file{b~hello.adb}.

When doing consistency checking, the binder takes any source files it
can locate into consideration. For example, if the binder determines
that the given main program requires the package @code{Pack}, whose
@file{.ali}
file is @file{pack.ali} and whose corresponding source spec file is
@file{pack.ads}, it attempts to locate the source file @file{pack.ads}
(using the same search path conventions as previously described for the
@code{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 @file{ali} files
match. In other words, any @file{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).

@cindex Source files, use by binder
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 @file{hello.adb} and a
package @code{P}, from file @file{p.ads} and you perform the following
steps:

@enumerate
@item
Enter @code{gcc -c hello.adb} to compile the main program.

@item
Enter @code{gcc -c p.ads} to compile package @code{P}.

@item
Edit file @file{p.ads}.

@item
Enter @code{gnatbind hello}.
@end enumerate

At this point, the file @file{p.ali} contains an out-of-date time stamp
because the file @file{p.ads} has been edited. The attempt at binding
fails, and the binder generates the following error messages:

@smallexample
error: "hello.adb" must be recompiled ("p.ads" has been modified)
error: "p.ads" has been modified and must be recompiled
@end smallexample

@noindent
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 it is similar to the following which
is the binder file generated for a simple "hello world" program.

@smallexample
@iftex
@leftskip=0cm
@end iftex
--  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

   --  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);

   --  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);

   --  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);

   --  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 swich 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.

   u00001 : constant Integer := 16#425FD0AF#;
   u00002 : constant Integer := 16#077A2651#;
   u00003 : constant Integer := 16#08ADDC9E#;
   u00004 : constant Integer := 16#1D370323#;
   u00005 : constant Integer := 16#3043D77B#;
   u00006 : constant Integer := 16#2359F9ED#;
   u00007 : constant Integer := 16#0CA940CF#;
   u00008 : constant Integer := 16#69BA6A59#;
   u00009 : constant Integer := 16#156A40CF#;
   u00010 : constant Integer := 16#033DABE0#;
   u00011 : constant Integer := 16#6AB38FEA#;
   u00012 : constant Integer := 16#7AAA368C#;
   u00013 : constant Integer := 16#7D13B305#;
   u00014 : constant Integer := 16#62D2B79D#;
   u00015 : constant Integer := 16#2E865F1E#;
   u00016 : constant Integer := 16#6379D875#;
   u00017 : constant Integer := 16#72D6A51D#;
   u00018 : constant Integer := 16#6E88E3D7#;
   u00019 : constant Integer := 16#45C8383C#;
   u00020 : constant Integer := 16#385E7AC2#;
   u00021 : constant Integer := 16#08FE4C1F#;
   u00022 : constant Integer := 16#23B87757#;
   u00023 : constant Integer := 16#3A4BFD9A#;
   u00024 : constant Integer := 16#4C9F3930#;
   u00025 : constant Integer := 16#2F1EB794#;
   u00026 : constant Integer := 16#0E2A461A#;
   u00027 : constant Integer := 16#5570D114#;
   u00028 : constant Integer := 16#501FA6BF#;
   u00029 : constant Integer := 16#57692181#;
   u00030 : constant Integer := 16#7C25DE96#;
   u00031 : constant Integer := 16#521B9399#;
   u00032 : constant Integer := 16#689CC1B9#;
   u00033 : constant Integer := 16#0357E00A#;
   u00034 : constant Integer := 16#1345CFE9#;
   u00035 : constant Integer := 16#343244DE#;
   u00036 : constant Integer := 16#6725DC79#;
   u00037 : constant Integer := 16#2DAF477E#;
   u00038 : constant Integer := 16#4F0184F2#;
   u00039 : constant Integer := 16#0A0669D8#;
   u00040 : constant Integer := 16#26610831#;
   u00041 : constant Integer := 16#0B5A4DF9#;
   u00042 : constant Integer := 16#1D4F93E8#;
   u00043 : constant Integer := 16#30B2EC3D#;
   u00044 : constant Integer := 16#34054F96#;
   u00045 : constant Integer := 16#6598BA3E#;
   u00046 : constant Integer := 16#2C9C021D#;
   u00047 : constant Integer := 16#177A51F6#;
   u00048 : constant Integer := 16#1CBC39CD#;
   u00049 : constant Integer := 16#5461BB3E#;
   u00050 : constant Integer := 16#03F36D98#;
   u00051 : constant Integer := 16#208D3EF6#;
   u00052 : constant Integer := 16#33AF4230#;
   u00053 : constant Integer := 16#0B97C6BF#;
   u00054 : constant Integer := 16#34B32999#;

   --  The following Export pragms 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, "systemS");
   pragma Export (C, u00005, "system__exceptionsS");
   pragma Export (C, u00006, "adaS");
   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, "system__exception_tableB");
   pragma Export (C, u00013, "system__exception_tableS");
   pragma Export (C, u00014, "gnat__htableB");
   pragma Export (C, u00015, "gnat__htableS");
   pragma Export (C, u00016, "system__machine_codeS");
   pragma Export (C, u00017, "system__secondary_stackB");
   pragma Export (C, u00018, "system__secondary_stackS");
   pragma Export (C, u00019, "system__parametersB");
   pragma Export (C, u00020, "system__parametersS");
   pragma Export (C, u00021, "system__soft_linksB");
   pragma Export (C, u00022, "system__soft_linksS");
   pragma Export (C, u00023, "system__stack_checkingB");
   pragma Export (C, u00024, "system__stack_checkingS");
   pragma Export (C, u00025, "system__storage_elementsB");
   pragma Export (C, u00026, "system__storage_elementsS");
   pragma Export (C, u00027, "text_ioS");
   pragma Export (C, u00028, "ada__text_ioB");
   pragma Export (C, u00029, "ada__text_ioS");
   pragma Export (C, u00030, "ada__streamsS");
   pragma Export (C, u00031, "ada__tagsB");
   pragma Export (C, u00032, "ada__tagsS");
   pragma Export (C, u00033, "interfacesS");
   pragma Export (C, u00034, "interfaces__c_streamsB");
   pragma Export (C, u00035, "interfaces__c_streamsS");
   pragma Export (C, u00036, "system__file_ioB");
   pragma Export (C, u00037, "system__file_ioS");
   pragma Export (C, u00038, "ada__finalizationB");
   pragma Export (C, u00039, "ada__finalizationS");
   pragma Export (C, u00040, "system__finalization_rootB");
   pragma Export (C, u00041, "system__finalization_rootS");
   pragma Export (C, u00042, "system__stream_attributesB");
   pragma Export (C, u00043, "system__stream_attributesS");
   pragma Export (C, u00044, "ada__io_exceptionsS");
   pragma Export (C, u00045, "system__unsigned_typesS");
   pragma Export (C, u00046, "system__finalization_implementationB");
   pragma Export (C, u00047, "system__finalization_implementationS");
   pragma Export (C, u00048, "system__string_ops_concat_3B");
   pragma Export (C, u00049, "system__string_ops_concat_3S");
   pragma Export (C, u00050, "system__string_opsB");
   pragma Export (C, u00051, "system__string_opsS");
   pragma Export (C, u00052, "system__file_control_blockS");
   pragma Export (C, u00053, "ada__finalization__list_controllerB");
   pragma Export (C, u00054, "ada__finalization__list_controllerS");

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");

package body Ada_Main is

--  Generated package body for Ada_Main starts here

   -------------
   -- adainit --
   -------------

@findex adainit
   procedure adainit is

      --  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 : Boolean;
         Exception_Tracebacks     : Boolean);
@findex __gnat_set_globals
      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/setjump exception mode.

@findex SDP_Table_Build
@findex Zero Cost Exceptions
      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 .. 21) of System.Address := (
        Hello'UET_Address,
        Ada.Exceptions'UET_Address,
        Gnat.Heap_Sort_A'UET_Address,
        System.Exception_Table'UET_Address,
        System.Secondary_Stack'UET_Address,
        System.Parameters'UET_Address,
        System.Soft_Links'UET_Address,
        System.Stack_Checking'UET_Address,
        Ada.Text_Io'UET_Address,
        Ada.Streams'UET_Address,
        Ada.Tags'UET_Address,
        Interfaces.C_Streams'UET_Address,
        System.File_Io'UET_Address,
        Ada.Finalization'UET_Address,
        System.Finalization_Root'UET_Address,
        System.Stream_Attributes'UET_Address,
        System.Finalization_Implementation'UET_Address,
        System.String_Ops_Concat_3'UET_Address,
        System.String_Ops'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 .. 22) of System.Address := (
        adainit'Code_Address,
        adafinal'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,
        Ada.Tags'Elab_Spec'Address,
        Ada.Tags'Elab_Body'Address,
        Ada.Streams'Elab_Spec'Address,
        System.Stack_Checking'Elab_Spec'Address,
        System.Soft_Links'Elab_Body'Address,
        System.Secondary_Stack'Elab_Body'Address,
        Ada.Exceptions'Elab_Body'Address,
        System.Finalization_Root'Elab_Spec'Address,
        System.Finalization_Implementation'Elab_Spec'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/setjump mode).

      SDP_Table_Build (ST'Address, 21, EA'Address, 22);

      --  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.

@findex __gnat_set_globals
      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                 => adafinal'Address,
         --  Address of generated ada final routine

         Unreserve_All_Interrupts => False,
         --  Set true if pragma Unreserve_All_Interrupts was used

         Exception_Tracebacks     => False);
         --  Indicates if exception tracebacks are enabled

      --  Now we have the elaboration calls for all units in the
      --  partition. The all is commented out if the given unit
      --  has no elaboration code. We retain the commented out call
      --  to indicate the full order chosen. The Elab_Spec and
      --  Elab_Body attributes generate references to the implicit
      --  elaboration procedures generated by the compiler for each
      --  unit that requires elaboration.

      -- System'Elab_Spec;
      -- Ada'Elab_Spec;
      -- Gnat'Elab_Spec;
      -- Gnat.Heap_Sort_A'Elab_Spec;
      -- Gnat.Htable'Elab_Spec;
      -- Gnat.Htable'Elab_Body;
      -- Interfaces'Elab_Spec;
      -- System.Machine_Code'Elab_Spec;
      -- System.Parameters'Elab_Spec;
      -- System.Standard_Library'Elab_Spec;
         Ada.Exceptions'Elab_Spec;
         System.Exceptions'Elab_Spec;
      -- System.Parameters'Elab_Body;
      -- Gnat.Heap_Sort_A'Elab_Body;
         Interfaces.C_Streams'Elab_Spec;
      -- Interfaces.C_Streams'Elab_Body;
      -- System.Exception_Table'Elab_Spec;
         System.Exception_Table'Elab_Body;
         Ada.Io_Exceptions'Elab_Spec;
      -- System.Storage_Elements'Elab_Spec;
      -- System.Storage_Elements'Elab_Body;
      -- System.Secondary_Stack'Elab_Spec;
         Ada.Tags'Elab_Spec;
         Ada.Tags'Elab_Body;
         Ada.Streams'Elab_Spec;
         System.Stack_Checking'Elab_Spec;
      -- System.Soft_Links'Elab_Spec;
         System.Soft_Links'Elab_Body;
      -- System.Stack_Checking'Elab_Body;
         System.Secondary_Stack'Elab_Body;
         Ada.Exceptions'Elab_Body;
      -- System.Standard_Library'Elab_Body;
      -- System.String_Ops'Elab_Spec;
      -- System.String_Ops'Elab_Body;
      -- System.String_Ops_Concat_3'Elab_Spec;
      -- System.String_Ops_Concat_3'Elab_Body;
      -- System.Unsigned_Types'Elab_Spec;
      -- System.Stream_Attributes'Elab_Spec;
      -- System.Stream_Attributes'Elab_Body;
         System.Finalization_Root'Elab_Spec;
      -- System.Finalization_Root'Elab_Body;
         System.Finalization_Implementation'Elab_Spec;
      -- System.Finalization_Implementation'Elab_Body;
         Ada.Finalization'Elab_Spec;
      -- Ada.Finalization'Elab_Body;
         Ada.Finalization.List_Controller'Elab_Spec;
      -- Ada.Finalization.List_Controller'Elab_Body;
         System.File_Control_Block'Elab_Spec;
      -- System.File_Io'Elab_Spec;
         System.File_Io'Elab_Body;
         Ada.Text_Io'Elab_Spec;
         Ada.Text_Io'Elab_Body;
      -- Text_Io'Elab_Spec;
      -- hello'elab_body;
      null;
   end adainit;

   --------------
   -- adafinal --
   --------------

@findex adafinal
   procedure adafinal is

      --  The actual finalization is performed by calling the
      --  library routine in System.Finalization_Implementation.

      procedure do_finalize;
      pragma Import
        (C, do_finalize,
         "system__finalization_implementation__finalize_global_list");

   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.

@findex Main Program
   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.

@findex __gnat_initialize
      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.

@findex __gnat_finalize
      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.

@findex Object file list
-- BEGIN Object file/option list
   --   ./system.o
   --   ./ada.o
   --   ./gnat.o
   --   ./g-htable.o
   --   ./interfac.o
   --   ./s-maccod.o
   --   ./s-except.o
   --   ./s-parame.o
   --   ./g-hesora.o
   --   ./i-cstrea.o
   --   ./s-exctab.o
   --   ./a-ioexce.o
   --   ./s-stoele.o
   --   ./a-tags.o
   --   ./a-stream.o
   --   ./s-soflin.o
   --   ./s-stache.o
   --   ./s-secsta.o
   --   ./a-except.o
   --   ./s-stalib.o
   --   ./s-strops.o
   --   ./s-sopco3.o
   --   ./s-unstyp.o
   --   ./s-stratt.o
   --   ./s-finroo.o
   --   ./s-finimp.o
   --   ./a-finali.o
   --   ./a-filico.o
   --   ./s-ficobl.o
   --   ./s-fileio.o
   --   ./a-textio.o
   --   ./text_io.o
   --   ./hello.o
   --   -L./
...  Target/System specific library search directives
   --   -lgnat
-- END Object file/option list

end Ada_Main;

@end smallexample

@noindent
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 @code{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 blowing up
during elaboration of the body of @code{Ada.Text_IO}. To chase this bug
down, you can place a breakpoint on the call:

@smallexample
Ada.Text_Io'Elab_Body;
@end smallexample

@noindent
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).

@node Generating the Binder Program in C
@section Generating the Binder Program in C
@noindent
In most normal usage, the default mode of @code{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 @code{-g} switch is used for @code{gnatbind}
and @code{gnatlink}.

However for some purposes it may be convenient to generate the main
program in C rather than Ada. This may for example be helpful when you
are generating a mixed language program with the main program in C. The
GNAT compiler itself is an example. The use of the @code{-C} switch
for both @code{gnatbind} and @code{gnatlink} will cause the program to
be generated in C (and compiled using the gnu C compiler). The
following shows the C code generated for the same "Hello World"
program:

@smallexample
extern int gnat_argc;
extern char **gnat_argv;
extern char **gnat_envp;
extern int gnat_exit_status;
void adafinal ();

void adainit ()
@{
   extern void *__gnat_hello__SDP;
   extern void *__gnat_ada__exceptions__SDP;
   extern void *__gnat_gnat__heap_sort_a__SDP;
   extern void *__gnat_system__exception_table__SDP;
   extern void *__gnat_system__secondary_stack__SDP;
   extern void *__gnat_system__parameters__SDP;
   extern void *__gnat_system__soft_links__SDP;
   extern void *__gnat_system__stack_checking__SDP;
   extern void *__gnat_ada__text_io__SDP;
   extern void *__gnat_ada__streams__SDP;
   extern void *__gnat_ada__tags__SDP;
   extern void *__gnat_interfaces__c_streams__SDP;
   extern void *__gnat_system__file_io__SDP;
   extern void *__gnat_ada__finalization__SDP;
   extern void *__gnat_system__finalization_root__SDP;
   extern void *__gnat_system__stream_attributes__SDP;
   extern void *__gnat_system__finalization_implementation__SDP;
   extern void *__gnat_system__string_ops_concat_3__SDP;
   extern void *__gnat_system__string_ops__SDP;
   extern void *__gnat_system__file_control_block__SDP;
   extern void *__gnat_ada__finalization__list_controller__SDP;

   void **st[21] = @{
     &__gnat_hello__SDP,
     &__gnat_ada__exceptions__SDP,
     &__gnat_gnat__heap_sort_a__SDP,
     &__gnat_system__exception_table__SDP,
     &__gnat_system__secondary_stack__SDP,
     &__gnat_system__parameters__SDP,
     &__gnat_system__soft_links__SDP,
     &__gnat_system__stack_checking__SDP,
     &__gnat_ada__text_io__SDP,
     &__gnat_ada__streams__SDP,
     &__gnat_ada__tags__SDP,
     &__gnat_interfaces__c_streams__SDP,
     &__gnat_system__file_io__SDP,
     &__gnat_ada__finalization__SDP,
     &__gnat_system__finalization_root__SDP,
     &__gnat_system__stream_attributes__SDP,
     &__gnat_system__finalization_implementation__SDP,
     &__gnat_system__string_ops_concat_3__SDP,
     &__gnat_system__string_ops__SDP,
     &__gnat_system__file_control_block__SDP,
     &__gnat_ada__finalization__list_controller__SDP@};

   extern void ada__exceptions___elabs ();
   extern void system__exceptions___elabs ();
   extern void interfaces__c_streams___elabs ();
   extern void system__exception_table___elabb ();
   extern void ada__io_exceptions___elabs ();
   extern void ada__tags___elabs ();
   extern void ada__tags___elabb ();
   extern void ada__streams___elabs ();
   extern void system__stack_checking___elabs ();
   extern void system__soft_links___elabb ();
   extern void system__secondary_stack___elabb ();
   extern void ada__exceptions___elabb ();
   extern void system__finalization_root___elabs ();
   extern void system__finalization_implementation___elabs ();
   extern void ada__finalization___elabs ();
   extern void ada__finalization__list_controller___elabs ();
   extern void system__file_control_block___elabs ();
   extern void system__file_io___elabb ();
   extern void ada__text_io___elabs ();
   extern void ada__text_io___elabb ();

   void (*ea[22]) () = @{
     adainit,
     adafinal,
     ada__exceptions___elabs,
     system__exceptions___elabs,
     interfaces__c_streams___elabs,
     system__exception_table___elabb,
     ada__io_exceptions___elabs,
     ada__tags___elabs,
     ada__tags___elabb,
     ada__streams___elabs,
     system__stack_checking___elabs,
     system__soft_links___elabb,
     system__secondary_stack___elabb,
     ada__exceptions___elabb,
     system__finalization_root___elabs,
     system__finalization_implementation___elabs,
     ada__finalization___elabs,
     ada__finalization__list_controller___elabs,
     system__file_control_block___elabs,
     system__file_io___elabb,
     ada__text_io___elabs,
     ada__text_io___elabb@};

   __gnat_SDP_Table_Build (&st, 21, ea, 22);
   __gnat_set_globals (
      -1,      /* Main_Priority              */
      -1,      /* Time_Slice_Value           */
      'b',     /* WC_Encoding                */
      ' ',     /* Locking_Policy             */
      ' ',     /* Queuing_Policy             */
      ' ',     /* Tasking_Dispatching_Policy */
      adafinal,/* Finalization routine address */
      0,       /* Unreserve_All_Interrupts */
      0);      /* Exception_Tracebacks */

/* system___elabs (); */
/* ada___elabs (); */
/* gnat___elabs (); */
/* gnat__heap_sort_a___elabs (); */
/* gnat__htable___elabs (); */
/* gnat__htable___elabb (); */
/* interfaces___elabs (); */
/* system__machine_code___elabs (); */
/* system__parameters___elabs (); */
/* system__standard_library___elabs (); */
   ada__exceptions___elabs ();
   system__exceptions___elabs ();
/* system__parameters___elabb (); */
/* gnat__heap_sort_a___elabb (); */
   interfaces__c_streams___elabs ();
/* interfaces__c_streams___elabb (); */
/* system__exception_table___elabs (); */
   system__exception_table___elabb ();
   ada__io_exceptions___elabs ();
/* system__storage_elements___elabs (); */
/* system__storage_elements___elabb (); */
/* system__secondary_stack___elabs (); */
   ada__tags___elabs ();
   ada__tags___elabb ();
   ada__streams___elabs ();
   system__stack_checking___elabs ();
/* system__soft_links___elabs (); */
   system__soft_links___elabb ();
/* system__stack_checking___elabb (); */
   system__secondary_stack___elabb ();
   ada__exceptions___elabb ();
/* system__standard_library___elabb (); */
/* system__string_ops___elabs (); */
/* system__string_ops___elabb (); */
/* system__string_ops_concat_3___elabs (); */
/* system__string_ops_concat_3___elabb (); */
/* system__unsigned_types___elabs (); */
/* system__stream_attributes___elabs (); */
/* system__stream_attributes___elabb (); */
   system__finalization_root___elabs ();
/* system__finalization_root___elabb (); */
   system__finalization_implementation___elabs ();
/* system__finalization_implementation___elabb (); */
   ada__finalization___elabs ();
/* ada__finalization___elabb (); */
   ada__finalization__list_controller___elabs ();
/* ada__finalization__list_controller___elabb (); */
   system__file_control_block___elabs ();
/* system__file_io___elabs (); */
   system__file_io___elabb ();
   ada__text_io___elabs ();
   ada__text_io___elabb ();
/* text_io___elabs (); */
/* hello___elabb (); */
@}
void adafinal () @{
   system__finalization_implementation__finalize_global_list ();
@}
int main (argc, argv, envp)
    int argc;
    char **argv;
    char **envp;
@{
   gnat_argc = argc;
   gnat_argv = argv;
   gnat_envp = envp;

   __gnat_initialize();
   adainit();
   __gnat_break_start();

   _ada_hello ();

   adafinal();
   __gnat_finalize();
   exit (gnat_exit_status);
@}
unsigned helloB = 0x425FD0AF;
unsigned system__standard_libraryB = 0x077A2651;
unsigned system__standard_libraryS = 0x08ADDC9E;
unsigned systemS = 0x1D370323;
unsigned system__exceptionsS = 0x3043D77B;
unsigned adaS = 0x2359F9ED;
unsigned ada__exceptionsB = 0x0CA940CF;
unsigned ada__exceptionsS = 0x69BA6A59;
unsigned gnatS = 0x156A40CF;
unsigned gnat__heap_sort_aB = 0x033DABE0;
unsigned gnat__heap_sort_aS = 0x6AB38FEA;
unsigned system__exception_tableB = 0x7AAA368C;
unsigned system__exception_tableS = 0x7D13B305;
unsigned gnat__htableB = 0x62D2B79D;
unsigned gnat__htableS = 0x2E865F1E;
unsigned system__machine_codeS = 0x6379D875;
unsigned system__secondary_stackB = 0x72D6A51D;
unsigned system__secondary_stackS = 0x6E88E3D7;
unsigned system__parametersB = 0x45C8383C;
unsigned system__parametersS = 0x385E7AC2;
unsigned system__soft_linksB = 0x08FE4C1F;
unsigned system__soft_linksS = 0x23B87757;
unsigned system__stack_checkingB = 0x3A4BFD9A;
unsigned system__stack_checkingS = 0x4C9F3930;
unsigned system__storage_elementsB = 0x2F1EB794;
unsigned system__storage_elementsS = 0x0E2A461A;
unsigned text_ioS = 0x5570D114;
unsigned ada__text_ioB = 0x501FA6BF;
unsigned ada__text_ioS = 0x57692181;
unsigned ada__streamsS = 0x7C25DE96;
unsigned ada__tagsB = 0x521B9399;
unsigned ada__tagsS = 0x689CC1B9;
unsigned interfacesS = 0x0357E00A;
unsigned interfaces__c_streamsB = 0x1345CFE9;
unsigned interfaces__c_streamsS = 0x343244DE;
unsigned system__file_ioB = 0x6725DC79;
unsigned system__file_ioS = 0x2DAF477E;
unsigned ada__finalizationB = 0x4F0184F2;
unsigned ada__finalizationS = 0x0A0669D8;
unsigned system__finalization_rootB = 0x26610831;
unsigned system__finalization_rootS = 0x0B5A4DF9;
unsigned system__stream_attributesB = 0x1D4F93E8;
unsigned system__stream_attributesS = 0x30B2EC3D;
unsigned ada__io_exceptionsS = 0x34054F96;
unsigned system__unsigned_typesS = 0x6598BA3E;
unsigned system__finalization_implementationB = 0x2C9C021D;
unsigned system__finalization_implementationS = 0x177A51F6;
unsigned system__string_ops_concat_3B = 0x1CBC39CD;
unsigned system__string_ops_concat_3S = 0x5461BB3E;
unsigned system__string_opsB = 0x03F36D98;
unsigned system__string_opsS = 0x208D3EF6;
unsigned system__file_control_blockS = 0x33AF4230;
unsigned ada__finalization__list_controllerB = 0x0B97C6BF;
unsigned ada__finalization__list_controllerS = 0x34B32999;

/* BEGIN Object file/option list
./system.o
./ada.o
./gnat.o
./g-htable.o
./interfac.o
./s-maccod.o
./s-except.o
./s-parame.o
./g-hesora.o
./i-cstrea.o
./s-exctab.o
./a-ioexce.o
./s-stoele.o
./a-tags.o
./a-stream.o
./s-soflin.o
./s-stache.o
./s-secsta.o
./a-except.o
./s-stalib.o
./s-strops.o
./s-sopco3.o
./s-unstyp.o
./s-stratt.o
./s-finroo.o
./s-finimp.o
./a-finali.o
./a-filico.o
./s-ficobl.o
./s-fileio.o
./a-textio.o
./text_io.o
./hello.o
-L./
...  Target/System specific library search directives
-lgnat
   END Object file/option list */

@end smallexample

@noindent
Here again, the C code is exactly what is generated by the binder. The
functions of the various parts of this code correspond in an obvious
manner with the commented Ada code shown in the example in the previous
section.

@node Consistency-Checking Modes
@section Consistency-Checking Modes

@noindent
As described in the previous section, by default @code{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.

@table @code
@item -s
@cindex @code{-s} (@code{gnatbind})
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.

@item -x
@cindex @code{-x} (@code{gnatbind})
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 @code{gnatmake} because in this
case the checking against sources has already been performed by
@code{gnatmake} in the course of compilation (i.e. before binding).

@end table

@node Binder Error Message Control
@section Binder Error Message Control

@noindent
The following switches provide control over the generation of error
messages from the binder:

@table @code
@item -v
@cindex @code{-v} (@code{gnatbind})
Verbose mode. In the normal mode, brief error messages are generated to
@file{stderr}. If this switch is present, a header is written
to @file{stdout} and any error messages are directed to @file{stdout}.
All that is written to @file{stderr} is a brief summary message.

@item -b
@cindex @code{-b} (@code{gnatbind})
Generate brief error messages to @file{stderr} even if verbose mode is
specified. This is relevant only when used with the
@code{-v} switch.

@item -m@var{n}
@cindex @code{-m} (@code{gnatbind})
Limits the number of error messages to @var{n}, a decimal integer in the
range 1-999. The binder terminates immediately if this limit is reached.

@item -M@var{xxx}
@cindex @code{-M} (@code{gnatbind})
Renames the generated main program from @code{main} to @code{xxx}.
This is useful in the case of some cross-building environments, where
the actual main program is separate from the one generated
by @code{gnatbind}.

@item -ws
@cindex @code{-ws} (@code{gnatbind})
@cindex Warnings
Suppress all warning messages.

@item -we
@cindex @code{-we} (@code{gnatbind})
Treat any warning messages as fatal errors.


@item -t
@cindex @code{-t} (@code{gnatbind})
@cindex Time stamp checks, in binder
@cindex Binder consistency checks
@cindex Consistency checks, in binder
The binder performs a number of consistency checks including:

@itemize @bullet
@item
Check that time stamps of a given source unit are consistent
@item
Check that checksums of a given source unit are consistent
@item
Check that consistent versions of @code{GNAT} were used for compilation
@item
Check consistency of configuration pragmas as required
@end itemize

@noindent
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 @code{-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.
@emph{This means that
@code{-t} should be used only in unusual situations,
with extreme care.}
@end table

@node Elaboration Control
@section Elaboration Control

@noindent
The following switches provide additional control over the elaboration
order. For full details see @xref{Elaboration Order Handling in GNAT}.

@table @code
@item -f
@cindex @code{-f} (@code{gnatbind})
Instructs the binder to ignore directives from the compiler about
implied @code{Elaborate_All} pragmas, and to use full Ada 95 Reference
Manual semantics in an attempt to find a legal elaboration order,
even if it seems likely that this order will cause an elaboration
exception.

@item -p
@cindex @code{-h} (@code{gnatbind})
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 @code{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 @code{-p} switch if dynamic
elaboration checking is used (@code{-gnatE} switch used for compilation).
This is because in the default static elaboration mode, all necessary
@code{Elaborate_All} pragmas are implicitly inserted. These implicit
pragmas are still respected by the binder in @code{-p} mode, so a
safe elaboration order is assured.
@end table

@node Output Control
@section Output Control

@noindent
The following switches allow additional control over the output
generated by the binder.

@table @code

@item -A
@cindex @code{-A} (@code{gnatbind})
Generate binder program in Ada (default). The binder program is named
@file{b~@var{mainprog}.adb} by default. This can be changed with
@code{-o} @code{gnatbind} option.

@item -C
@cindex @code{-C} (@code{gnatbind})
Generate binder program in C. The binder program is named
@file{b_@var{mainprog}.c}. This can be changed with @code{-o} @code{gnatbind}
option.

@item -e
@cindex @code{-e} (@code{gnatbind})
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 @file{stdout}.

@item -h
@cindex @code{-h} (@code{gnatbind})
Output usage information. The output is written to @file{stdout}.

@item -l
@cindex @code{-l} (@code{gnatbind})
Output chosen elaboration order. The output is written to @file{stdout}.

@item -O
@cindex @code{-O} (@code{gnatbind})
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 @file{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.

@item -o @var{file}
@cindex @code{-o} (@code{gnatbind})
Set name of output file to @var{file} instead of the normal
@file{b~@var{mainprog}.adb} default. Note that @var{file} denote the Ada
binder generated body filename. In C mode you would normally give
@var{file} an extension of @file{.c} because it will be a C source program.
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.

@item -c
@cindex @code{-c} (@code{gnatbind})
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.
@end table

@node Binding with Non-Ada Main Programs
@section Binding with Non-Ada Main Programs

@noindent
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 @code{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 (@pxref{Mixed Language Programming}).
The following switch is used in this situation:

@table @code
@item -n
@cindex @code{-n} (@code{gnatbind})
No main program. The main program is not in Ada.
@end table

@noindent
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:

@table @code
@item adainit
@findex adainit
You must call this routine to initialize the Ada part of the program by
calling the necessary elaboration routines. A call to @code{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.

@item adafinal
@findex adafinal
You must call this routine to perform any library-level finalization
required by the Ada subprograms. A call to @code{adafinal} is required
after the last call to an Ada subprogram, and before the program
terminates.
@end table

@noindent
If the @code{-n} switch
@cindex Binder, multiple input files
is given, more than one ALI file may appear on
the command line for @code{gnatbind}. The normal @dfn{closure}
calculation is performed for each of the specified units. Calculating
the closure means finding out the set of units involved by tracing
@code{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 @code{\-o
file\/OUTPUT=file\}. The output is an Ada unit in source form that can
be compiled with GNAT unless the -C switch is used in which case the
output is a C source file, which must be compiled using the C compiler.
This compilation occurs automatically as part of the @code{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.

@node Binding Programs with No Main Subprogram
@section Binding Programs with No Main Subprogram

@noindent
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:

@table @code
@item -z
@cindex @code{-z} (@code{gnatbind})
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.
@end table

@node Summary of Binder Switches
@section Summary of Binder Switches

@noindent
The following are the switches available with @code{gnatbind}:

@table @code
@item -aO
Specify directory to be searched for ALI files.

@item -aI
Specify directory to be searched for source file.

@item -A
Generate binder program in Ada (default)

@item -b
Generate brief messages to @file{stderr} even if verbose mode set.

@item -c
Check only, no generation of binder output file.

@item -C
Generate binder program in C

@item -e
Output complete list of elaboration-order dependencies.

@item -E
Store tracebacks in exception occurrences when the target supports it.
This is the default with the zero cost exception mechanism.
This option is currently only supported on Solaris, Linux and Windows
ix86. Under Solaris and Linux you need to use explicitly the @code{gcc}
flag @code{-funwind-tables} when compiling every file in your
application. See also the packages @code{GNAT.Traceback} and
@code{GNAT.Traceback.Symbolic}. Under Windows there is no specific
option to use to enable this feature but you must not use
@code{-fomit-frame-pointer} @code{gcc} option.

@item -f
@cindex @code{-f} (@code{gnatlink})
On some targets, the command line length is limited, and @code{gnatlink}
will generate a separate file for the linker if the list of object files
is too long. The @code{-f} flag 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.

@item -h
Output usage (help) information

@item -I
Specify directory to be searched for source and ALI files.

@item -I-
Do not look for sources in the current directory where @code{gnatbind} was
invoked, and do not look for ALI files in the directory containing the
ALI file named in the @code{gnatbind} command line.

@item -l
Output chosen elaboration order.

@item -Mxyz
Rename generated main program from main to xyz

@item -m@var{n}
Limit number of detected errors to @var{n} (1-999).

@item -n
No main program.

@item -nostdinc
Do not look for sources in the system default directory.

@item -nostdlib
Do not look for library files in the system default directory.

@item -o @var{file}
Name the output file @var{file} (default is @file{b~@var{xxx}.adb}).
Note that if this option is used, then linking must be done manually,
gnatlink cannot be used.

@item -O
Output object list.

@item -p
Pessimistic (worst-case) elaboration order

@item -s
Require all source files to be present.

@item -static
Link against a static GNAT run time.

@item -shared
Link against a shared GNAT run time when available.

@item -t
Tolerate time stamp and other consistency errors

@item -T@var{n}
Set the time slice value to n microseconds. A value of zero means no time
slicing and also indicates to the tasking run time to match as close as
possible to the annex D requirements of the RM.

@item -v
Verbose mode. Write error messages, header, summary output to
@file{stdout}.

@item -w@var{x}
Warning mode (@var{x}=s/e for suppress/treat as error)


@item -x
Exclude source files (check object consistency only).


@item -z
No main subprogram.

@end table

You may obtain this listing by running the program @code{gnatbind} with
no arguments.

@node Command-Line Access
@section Command-Line Access

@noindent
The package @code{Ada.Command_Line} provides access to the command-line
arguments and program name. In order for this interface to operate
correctly, the two variables

@smallexample
@group
@cartouche
int gnat_argc;
char **gnat_argv;
@end cartouche
@end group
@end smallexample

@noindent
@findex gnat_argv
@findex gnat_argc
are declared in one of the GNAT library routines. These variables must
be set from the actual @code{argc} and @code{argv} values passed to the
main program. With no @code{n} present, @code{gnatbind}
generates the C main program to automatically set these variables.
If the @code{n} switch is used, there is no automatic way to
set these variables. If they are not set, the procedures in
@code{Ada.Command_Line} will not be available, and any attempt to use
them will raise @code{Constraint_Error}. If command line access is
required, your main program must set @code{gnat_argc} and
@code{gnat_argv} from the @code{argc} and @code{argv} values passed to
it.

@node Search Paths for gnatbind
@section Search Paths for @code{gnatbind}

@noindent
The 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 @code{gcc}
(@pxref{Search Paths and the Run-Time Library (RTL)}). For ALI files the
directories searched are:

@enumerate
@item
The directory containing the ALI file named in the command line, unless
the switch @code{-I-} is specified.

@item
All directories specified by @code{-I}
switches on the @code{gnatbind}
command line, in the order given.

@item
@findex ADA_OBJECTS_PATH
Each of the directories listed in the value of the
@code{ADA_OBJECTS_PATH} environment variable.
Construct this value
exactly as the @code{PATH} environment variable: a list of directory
names separated by colons.

@item
The content of the "ada_object_path" file which is part of the GNAT
installation tree and is used to store standard libraries such as the
GNAT Run Time Library (RTL) unless the switch @code{-nostdlib} is
specified.
@ref{Installing an Ada Library}
@end enumerate

@noindent
In the binder the switch @code{-I}
is used to specify both source and
library file paths. Use @code{-aI}
instead if you want to specify
source paths only, and @code{-aO}
if you want to specify library paths
only. This means that for the binder
@code{-I}@var{dir} is equivalent to
@code{-aI}@var{dir}
@code{-aO}@var{dir}.
The binder generates the bind file (a C language source file) in the
current working directory.

@findex Ada
@findex System
@findex Interfaces
@findex GNAT
The packages @code{Ada}, @code{System}, and @code{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.

@node Examples of gnatbind Usage
@section Examples of @code{gnatbind} Usage

@noindent
This section contains a number of examples of using the GNAT binding
utility @code{gnatbind}.

@table @code
@item gnatbind hello
The main program @code{Hello} (source program in @file{hello.adb}) is
bound using the standard switch settings. The generated main program is
@file{b~hello.adb}. This is the normal, default use of the binder.

@item gnatbind hello -o mainprog.adb
The main program @code{Hello} (source program in @file{hello.adb}) is
bound using the standard switch settings. The generated main program is
@file{mainprog.adb} with the associated spec in
@file{mainprog.ads}. Note that you must specify the body here not the
spec, in the case where the output is in Ada. Note that if this option
is used, then linking must be done manually, since gnatlink will not
be able to find the generated file.

@item gnatbind main -C -o mainprog.c -x
The main program @code{Main} (source program in
@file{main.adb}) is bound, excluding source files from the
consistency checking, generating
the file @file{mainprog.c}.

@item gnatbind -x main_program -C -o mainprog.c
This command is exactly the same as the previous example. Switches may
appear anywhere in the command line, and single letter switches may be
combined into a single switch.

@item gnatbind -n math dbase -C -o ada-control.c
The main program is in a language other than Ada, but calls to
subprograms in packages @code{Math} and @code{Dbase} appear. This call
to @code{gnatbind} generates the file @file{ada-control.c} containing
the @code{adainit} and @code{adafinal} routines to be called before and
after accessing the Ada units.
@end table

@node Linking Using gnatlink
@chapter Linking Using @code{gnatlink}
@findex gnatlink

@noindent
This chapter discusses @code{gnatlink}, a utility program used to link
Ada programs and build an executable file. This is a simple program
that invokes the UNIX linker (via the @code{gcc}
command) with a correct list of object files and library references.
@code{gnatlink} automatically determines the list of files and
references for the Ada part of a program. It uses the binder file
generated by the binder to determine this list.

@menu
* Running gnatlink::
* Switches for gnatlink::
* Setting Stack Size from gnatlink::
* Setting Heap Size from gnatlink::
@end menu

@node Running gnatlink
@section Running @code{gnatlink}

@noindent
The form of the @code{gnatlink} command is

@smallexample
$ gnatlink [@var{switches}] @var{mainprog}[.ali] [@var{non-Ada objects}]
      [@var{linker options}]
@end smallexample

@noindent
@file{@var{mainprog}.ali} references the ALI file of the main program.
The @file{.ali} extension of this file can be omitted. From this
reference, @code{gnatlink} locates the corresponding binder file
@file{b~@var{mainprog}.adb} and, using the information in this file along
with the list of non-Ada objects and linker options, constructs a UNIX
linker command file to create the executable.

The arguments following @file{@var{mainprog}.ali} 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 @code{pragma Import} statements in any Ada units.

@var{linker options} is an optional list of linker specific
switches. The default linker called by gnatlink is @var{gcc} which in
turn calls the appropriate system linker usually called
@var{ld}. Standard options for the linker such as @code{-lmy_lib} or
@code{-Ldir} can be added as is. For options that are not recognized by
@var{gcc} as linker options, the @var{gcc} switches @code{-Xlinker} or
@code{-Wl,} shall be used. Refer to the GCC documentation for
details. Here is an example showing how to generate a linker map
assuming that the underlying linker is GNU ld:

@smallexample
$ gnatlink my_prog -Wl,-Map,MAPFILE
@end smallexample

Using @var{linker options} it is possible to set the program stack and
heap size. See @pxref{Setting Stack Size from gnatlink} and
@pxref{Setting Heap Size from gnatlink}.

@code{gnatlink} determines the list of objects required by the Ada
program and prepends them to the list of objects passed to the linker.
@code{gnatlink} also gathers any arguments set by the use of
@code{pragma Linker_Options} and adds them to the list of arguments
presented to the linker.


@node Switches for gnatlink
@section Switches for @code{gnatlink}

@noindent
The following switches are available with the @code{gnatlink} utility:

@table @code

@item -A
@cindex @code{-A} (@code{gnatlink})
The binder has generated code in Ada. This is the default.

@item -C
@cindex @code{-C} (@code{gnatlink})
If instead of generating a file in Ada, the binder has generated one in
C, then the linker needs to know about it. Use this switch to signal
to @code{gnatlink} that the binder has generated C code rather than
Ada code.

@item -g
@cindex Debugging information, including
@cindex @code{-g} (@code{gnatlink})
The option to include debugging information causes the Ada bind file (in
other words, @file{b~@var{mainprog}.adb}) to be compiled with
@code{-g}.
In addition, the binder does not delete the @file{b~@var{mainprog}.adb},
@file{b~@var{mainprog}.o} and @file{b~@var{mainprog}.ali} files.
Without @code{-g}, the binder removes these files by
default. The same procedure apply if a C bind file was generated using
@code{-C} @code{gnatbind} option, in this case the filenames are
@file{b_@var{mainprog}.c} and @file{b_@var{mainprog}.o}.

@item -n
@cindex @code{-n} (@code{gnatlink})
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.

@item -v
@cindex @code{-v} (@code{gnatlink})
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.

@item -v -v
@cindex @code{-v -v} (@code{gnatlink})
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.

@item -o @var{exec-name}
@cindex @code{-o} (@code{gnatlink})
@var{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, @code{gnatlink try.ali} creates
an executable called @file{try}.

@item -b @var{target}
@cindex @code{-b} (@code{gnatlink})
Compile your program to run on @var{target}, which is the name of a
system configuration. You must have a GNAT cross-compiler built if
@var{target} is not the same as your host system.

@item -B@var{dir}
@cindex @code{-B} (@code{gnatlink})
Load compiler executables (for example, @code{gnat1}, the Ada compiler)
from @var{dir} instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available. See the
@code{gcc} manual page for further details. You would normally use the
@code{-b} or @code{-V} switch instead.

@item --GCC=@var{compiler_name}
@cindex @code{--GCC=compiler_name} (@code{gnatlink})
Program used for compiling the binder file. The default is
@code{gcc}'. You need to use quotes around @var{compiler_name} if
@code{compiler_name} contains spaces or other separator characters. As
an example @code{--GCC="foo -x -y"} will instruct @code{gnatlink} to use
@code{foo -x -y} as your compiler. Note that switch @code{-c} is always
inserted after your command name. Thus in the above example the compiler
command that will be used by @code{gnatlink} will be @code{foo -c -x -y}.
If several @code{--GCC=compiler_name} are used, only the last
@var{compiler_name} is taken into account. However, all the additional
switches are also taken into account. Thus,
@code{--GCC="foo -x -y" --GCC="bar -z -t"} is equivalent to
@code{--GCC="bar -x -y -z -t"}.

@item --LINK=@var{name}
@cindex @code{--LINK=} (@code{gnatlink})
@var{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 (@file{gcc}). When this switch is used, the
specified linker is called instead of (@file{gcc}) with exactly the same
parameters that would have been passed to (@file{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.



@end table

@node Setting Stack Size from gnatlink
@section Setting Stack Size from @code{gnatlink}

@noindent
It is possible to specify the program stack size from @code{gnatlink}.
Assuming that the underlying linker is GNU ld there is two ways to do so:

@itemize @bullet

@item using @code{-Xlinker} linker option

@smallexample
$ gnatlink hello -Xlinker --stack=0x10000,0x1000
@end smallexample

This set the stack reserve size to 0x10000 bytes and the stack commit
size to 0x1000 bytes.

@item using @code{-Wl} linker option

@smallexample
$ gnatlink hello -Wl,--stack=0x1000000
@end smallexample

This set the stack reserve size to 0x1000000 bytes. Note that with
@code{-Wl} option it is not possible to set the stack commit size
because the coma is a separator for this option.

@end itemize

@node Setting Heap Size from gnatlink
@section Setting Heap Size from @code{gnatlink}

@noindent
It is possible to specify the program heap size from @code{gnatlink}.
Assuming that the underlying linker is GNU ld there is two ways to do so:

@itemize @bullet

@item using @code{-Xlinker} linker option

@smallexample
$ gnatlink hello -Xlinker --heap=0x10000,0x1000
@end smallexample

This set the heap reserve size to 0x10000 bytes and the heap commit
size to 0x1000 bytes.

@item using @code{-Wl} linker option

@smallexample
$ gnatlink hello -Wl,--heap=0x1000000
@end smallexample

This set the heap reserve size to 0x1000000 bytes. Note that with
@code{-Wl} option it is not possible to set the heap commit size
because the coma is a separator for this option.

@end itemize

@node The GNAT Make Program gnatmake
@chapter The GNAT Make Program @code{gnatmake}
@findex gnatmake

@menu
* Running gnatmake::
* Switches for gnatmake::
* Mode Switches for gnatmake::
* Notes on the Command Line::
* How gnatmake Works::
* Examples of gnatmake Usage::
@end menu
@noindent
A typical development cycle when working on an Ada program consists of
the following steps:

@enumerate
@item
Edit some sources to fix bugs.

@item
Add enhancements.

@item
Compile all sources affected.

@item
Rebind and relink.

@item
Test.
@end enumerate

@noindent
The third step can be tricky, because not only do the modified files
@cindex Dependency rules
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, @code{use} clauses, generics and inlined
subprograms.

@code{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
@code{gnatmake}.

@node Running gnatmake
@section Running @code{gnatmake}

@noindent
The form of the @code{gnatmake} command is

@smallexample
$ gnatmake [@var{switches}] @var{file_name} [@var{mode_switches}]
@end smallexample

@noindent
The only required argument is @var{file_name}, which specifies
the compilation unit that is the main program. If @code{switches} are
present, they can be placed before of after @var{file_name}.
If @var{mode_switches} are present, they must always be placed after
@var{file_name} and all @code{switches}.

If you are using standard file extensions (.adb and .ads), then the
extension may be omitted from the @var{file_name} argument. 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 @var{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
@code{gnatmake} was invoked and if it is not found, it will be search on
the source path of the compiler as described in
@ref{Search Paths and the Run-Time Library (RTL)}.

All @code{gnatmake} output (except when you specify
@code{-M}) is to
@file{stderr}. The output produced by the
@code{-M} switch is send to
@file{stdout}.

@node Switches for gnatmake
@section Switches for @code{gnatmake}

@noindent
You may specify any of the following switches to @code{gnatmake}:

@table @code
@item --GCC=@var{compiler_name}
@cindex @code{--GCC=compiler_name} (@code{gnatmake})
Program used for compiling. The default is @code{gcc}'. You need to use
quotes around @var{compiler_name} if @code{compiler_name} contains
spaces or other separator characters. As an example @code{--GCC="foo -x
-y"} will instruct @code{gnatmake} to use @code{foo -x -y} as your
compiler. Note that switch @code{-c} is always inserted after your
command name. Thus in the above example the compiler command that will
be used by @code{gnatmake} will be @code{foo -c -x -y}.
If several @code{--GCC=compiler_name} are used, only the last
@var{compiler_name} is taken into account. However, all the additional
switches are also taken into account. Thus,
@code{--GCC="foo -x -y" --GCC="bar -z -t"} is equivalent to
@code{--GCC="bar -x -y -z -t"}.

@item --GNATBIND=@var{binder_name}
@cindex @code{--GNATBIND=binder_name} (@code{gnatmake})
Program used for binding. The default is @code{gnatbind}'. You need to
use quotes around @var{binder_name} if @var{binder_name} contains spaces
or other separator characters. As an example @code{--GNATBIND="bar -x
-y"} will instruct @code{gnatmake} to use @code{bar -x -y} as your
binder. Binder switches that are normally appended by @code{gnatmake} to
@code{gnatbind}' are now appended to the end of @code{bar -x -y}.

@item --GNATLINK=@var{linker_name}
@cindex @code{--GNATLINK=linker_name} (@code{gnatmake})
Program used for linking. The default is @code{gnatlink}'. You need to
use quotes around @var{linker_name} if @var{linker_name} contains spaces
or other separator characters. As an example @code{--GNATLINK="lan -x
-y"} will instruct @code{gnatmake} to use @code{lan -x -y} as your
linker. Linker switches that are normally appended by @code{gnatmake} to
@code{gnatlink}' are now appended to the end of @code{lan -x -y}.

@item -a
@cindex @code{-a} (@code{gnatmake})
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,
@code{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. @code{-a} is also useful in conjunction with
@code{-f}
if you need to recompile an entire application,
including run-time files, using special configuration pragma settings,
such as a non-standard @code{Float_Representation} pragma.
By default
@code{gnatmake -a} compiles all GNAT
internal files with
@code{gcc -c -gnatg} rather than @code{gcc -c}.

@item -c
@cindex @code{-c} (@code{gnatmake})
Compile only. Do not perform binding and linking. If the root unit
specified by @var{file_name} is not a main unit, this is the
default. Otherwise @code{gnatmake} will attempt binding and linking
unless all objects are up to date and the executable is more recent than
the objects.

@item -f
@cindex @code{-f} (@code{gnatmake})
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 @code{-a} switch is also specified.

@item -i
@cindex @code{-i} (@code{gnatmake})
In normal mode, @code{gnatmake} compiles all object files and ALI files
into the current directory. If the @code{-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 @code{gnatmake} will automatically
maintain and update this organization. If no ALI files are found on the
Ada object path (@ref{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, @code{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.

@item -j@var{n}
@cindex @code{-j} (@code{gnatmake})
@cindex Parallel make
Use @var{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 @code{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.

@item -k
@cindex @code{-k} (@code{gnatmake})
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 @code{gnatmake}
terminates.

@item -m
@cindex @code{-m} (@code{gnatmake})
Specifies that the minimum necessary amount of recompilations
be performed. In this mode @code{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).

@item -M
@cindex Dependencies, producing list
@cindex @code{-M} (@code{gnatmake})
Check if all objects are up to date. If they are, output the object
dependences to @file{stdout} in a form that can be directly exploited in
a @file{Makefile}. By default, each source file is prefixed with its
(relative or absolute) directory name. This name is whatever you
specified in the various @code{-aI}
and @code{-I} switches. If you use
@code{gnatmake -M}
@code{-q}
(see below), only the source file names,
without relative paths, are output. If you just specify the
@code{-M}
switch, dependencies of the GNAT internal system files are omitted. This
is typically what you want. If you also specify
the @code{-a} switch,
dependencies of the GNAT internal files are also listed. Note that
dependencies of the objects in external Ada libraries (see switch
@code{-aL}@var{dir} in the following list) are never reported.

@item -n
@cindex @code{-n} (@code{gnatmake})
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.

@item -o @var{exec_name}
@cindex @code{-o} (@code{gnatmake})
Output executable name. The name of the final executable program will be
@var{exec_name}. If the @code{-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.

@item -q
@cindex @code{-q} (@code{gnatmake})
Quiet. When this flag is not set, the commands carried out by
@code{gnatmake} are displayed.

@item -s
@cindex @code{-s} (@code{gnatmake})
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,
@code{-O -O2} is different than @code{-O2 -O}, but @code{-g -O} is equivalent
to @code{-O -g}.

@item -u
@cindex @code{-u} (@code{gnatmake})
Unique. Recompile at most the main file. It implies -c. Combined with
-f, it is equivalent to calling the compiler directly.

@item -v
@cindex @code{-v} (@code{gnatmake})
Verbose. Displays the reason for all recompilations @code{gnatmake}
decides are necessary.

@item -z
@cindex @code{-z} (@code{gnatmake})
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.

@item @code{gcc} @asis{switches}
The switch @code{-g} or any uppercase switch (other than @code{-A}, or
@code{-L}) or any switch that is more than one character is passed to
@code{gcc} (e.g. @code{-O}, @code{-gnato,} etc.)
@end table

@noindent
Source and library search path switches:

@table @code
@item -aI@var{dir}
@cindex @code{-aI} (@code{gnatmake})
When looking for source files also look in directory @var{dir}.
The order in which source files search is undertaken is
described in @ref{Search Paths and the Run-Time Library (RTL)}.

@item -aL@var{dir}
@cindex @code{-aL} (@code{gnatmake})
Consider @var{dir} as being an externally provided Ada library.
Instructs @code{gnatmake} to skip compilation units whose @file{.ali}
files have been located in directory @var{dir}. This allows you to have
missing bodies for the units in @var{dir}. You still need to specify
the location of the specs for these units by using the switches
@code{-aI@var{dir}}
or @code{-I@var{dir}}.
Note: this switch is provided for compatibility with previous versions
of @code{gnatmake}. The easier method of causing standard libraries
to be excluded from consideration is to write-protect the corresponding
ALI files.

@item -aO@var{dir}
@cindex @code{-aO} (@code{gnatmake})
When searching for library and object files, look in directory
@var{dir}. The order in which library files are searched is described in
@ref{Search Paths for gnatbind}.

@item -A@var{dir}
@cindex Search paths, for @code{gnatmake}
@cindex @code{-A} (@code{gnatmake})
Equivalent to @code{-aL@var{dir}
-aI@var{dir}}.

@item -I@var{dir}
@cindex @code{-I} (@code{gnatmake})
Equivalent to @code{-aO@var{dir}
-aI@var{dir}}.

@item -I-
@cindex @code{-I-} (@code{gnatmake})
@cindex Source files, suppressing search
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 @code{gnatmake} was invoked.

@item -L@var{dir}
@cindex @code{-L} (@code{gnatmake})
@cindex Linker libraries
Add directory @var{dir} to the list of directories in which the linker
will search for libraries. This is equivalent to
@code{-largs -L}@var{dir}.

@item -nostdinc
@cindex @code{-nostdinc} (@code{gnatmake})
Do not look for source files in the system default directory.

@item -nostdlib
@cindex @code{-nostdlib} (@code{gnatmake})
Do not look for library files in the system default directory.
@end table

@node Mode Switches for gnatmake
@section Mode Switches for @code{gnatmake}

@noindent
The mode switches (referred to as @code{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.

@table @code
@item -cargs @var{switches}
@cindex @code{-cargs} (@code{gnatmake})
Compiler switches. Here @var{switches} is a list of switches
that are valid switches for @code{gcc}. They will be passed on to
all compile steps performed by @code{gnatmake}.

@item -bargs @var{switches}
@cindex @code{-bargs} (@code{gnatmake})
Binder switches. Here @var{switches} is a list of switches
that are valid switches for @code{gcc}. They will be passed on to
all bind steps performed by @code{gnatmake}.

@item -largs @var{switches}
@cindex @code{-largs} (@code{gnatmake})
Linker switches. Here @var{switches} is a list of switches
that are valid switches for @code{gcc}. They will be passed on to
all link steps performed by @code{gnatmake}.
@end table

@node Notes on the Command Line
@section Notes on the Command Line

@noindent
This section contains some additional useful notes on the operation
of the @code{gnatmake} command.

@itemize @bullet
@item
@cindex Recompilation, by @code{gnatmake}
If @code{gnatmake} finds no ALI files, it recompiles the main program
and all other units required by the main program.
This means that @code{gnatmake}
can be used for the initial compile, as well as during subsequent steps of
the development cycle.

@item
If you enter @code{gnatmake @var{file}.adb}, where @file{@var{file}.adb}
is a subunit or body of a generic unit, @code{gnatmake} recompiles
@file{@var{file}.adb} (because it finds no ALI) and stops, issuing a
warning.

@item
In @code{gnatmake} the switch @code{-I}
is used to specify both source and
library file paths. Use @code{-aI}
instead if you just want to specify
source paths only and @code{-aO}
if you want to specify library paths
only.

@item
@code{gnatmake} examines both an ALI file and its corresponding object file
for consistency. If an ALI is more recent than its corresponding object,
or if the object file is missing, the corresponding source will be recompiled.
Note that @code{gnatmake} expects an ALI and the corresponding object file
to be in the same directory.

@item
@code{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
@code{-f} switch will not recompile these files
unless @code{-a} is also specified.

@item
@code{gnatmake} has been designed to make the use of Ada libraries
particularly convenient. Assume you have an Ada library organized
as follows: @var{obj-dir} contains the objects and ALI files for
of your Ada compilation units,
whereas @var{include-dir} contains the
specs of these units, but no bodies. Then to compile a unit
stored in @code{main.adb}, which uses this Ada library you would just type

@smallexample
$ gnatmake -aI@var{include-dir}  -aL@var{obj-dir}  main
@end smallexample

@item
Using @code{gnatmake} along with the
@code{-m (minimal recompilation)}
switch provides an
extremely powerful tool: you can freely 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 therefore obsolescence of
debugging information will go unnoticed.
@end itemize

@node How gnatmake Works
@section How @code{gnatmake} Works

@noindent
Generally @code{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 @code{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 @dfn{up to date} if the
corresponding ALI file exists and its time stamp predates that of the
object file 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.

@code{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,
@code{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 @code{gnatmake} recursively applies the above procedure on all these files.

This process ensures that @code{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
@code{gnatmake} will recompute a correct set of new dependencies if
necessary.

@node Examples of gnatmake Usage
@section Examples of @code{gnatmake} Usage

@table @code
@item gnatmake hello.adb
Compile all files necessary to bind and link the main program
@file{hello.adb} (containing unit @code{Hello}) and bind and link the
resulting object files to generate an executable file @file{hello}.

@item gnatmake -q Main_Unit -cargs -O2 -bargs -l

Compile all files necessary to bind and link the main program unit
@code{Main_Unit} (from file @file{main_unit.adb}). All compilations will
be done with optimization level 2 and the order of elaboration will be
listed by the binder. @code{gnatmake} will operate in quiet mode, not
displaying commands it is executing.
@end table

@node Renaming Files Using gnatchop
@chapter Renaming Files Using @code{gnatchop}
@findex gnatchop

@noindent
This chapter discusses how to handle files with multiple units by using
the @code{gnatchop} utility. This utility is also useful in renaming
files to meet the standard GNAT default file naming conventions.

@menu
* Handling Files with Multiple Units::
* Operating gnatchop in Compilation Mode::
* Command Line for gnatchop::
* Switches for gnatchop::
* Examples of gnatchop Usage::
@end menu

@node Handling Files with Multiple Units
@section Handling Files with Multiple Units

@noindent
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 @code{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. @code{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 @code{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 @code{gnatchop} each
time you compile, regarding the source files that it writes as temporary
files that you throw away.

@node Operating gnatchop in Compilation Mode
@section Operating gnatchop in Compilation Mode

@noindent
The basic function of @code{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 @code{gnatchop}.

However, using a special option to activate "compilation mode",
@code{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 @code{gnatchop} is given a file that consists of
only configuration pragmas, then this file is appended to the
@file{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
@file{gnat.adc} file is the representation
of a compilation environment. For more information on the
@file{gnat.adc} file, see the section on handling of configuration
pragmas @pxref{Handling of Configuration Pragmas}.

Second, in compilation mode, if @code{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, @code{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 @code{gnatchop} with the compilation mode
switch provides the required behavior, and is for example the mode
in which GNAT processes the ACVC tests.

@node Command Line for gnatchop
@section Command Line for @code{gnatchop}

@noindent
The @code{gnatchop} command has the form:

@smallexample
$ gnatchop switches @var{file name} [@var{file name} @var{file name} ...]
      [@var{directory}]
@end smallexample

@noindent
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, @code{gnatchop} generates one output file in
the current directory for each unit in each of the files.

@var{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 @file{hellofiles} containing

@smallexample
@group
@cartouche
@b{procedure} hello;

@b{with} Text_IO; @b{use} Text_IO;
@b{procedure} hello @b{is}
@b{begin}
   Put_Line ("Hello");
@b{end} hello;
@end cartouche
@end group
@end smallexample

@noindent
the command

@smallexample
$ gnatchop hellofiles
@end smallexample

@noindent
generates two files in the current directory, one called
@file{hello.ads} containing the single line that is the procedure spec,
and the other called @file{hello.adb} containing the remaining text. The
original file is not affected. The generated files can be compiled in
the normal manner.

@node Switches for gnatchop
@section Switches for @code{gnatchop}

@noindent
@code{gnatchop} recognizes the following switches:

@table @code

@item -c
@cindex @code{-c} (@code{gnatchop})
Causes @code{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.

@item -gnatxxx
This passes the given @code{-gnatxxx} switch to @code{gnat} which is
used to parse the given file. Not all @code{xxx} options make sense,
but for example, the use of @code{-gnati2} allows @code{gnatchop} to
process a source file that uses Latin-2 coding for identifiers.

@item -h
Causes @code{gnatchop} to generate a brief help summary to the standard
output file showing usage information.

@item -k@var{mm}
@cindex @code{-k} (@code{gnatchop})
Limit generated file names to the specified number @code{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 @code{-k} and the numeric value. The numeric
value may be omitted in which case a default of @code{-k8},
suitable for use
with DOS-like file systems, is used. If no @code{-k} switch
is present then
there is no limit on the length of file names.

@item -q
@cindex @code{-q} (@code{gnatchop})
Causes output of informational messages indicating the set of generated
files to be suppressed. Warnings and error messages are unaffected.

@item -r
@cindex @code{-r} (@code{gnatchop})
@findex Source_Reference
Generate @code{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
@code{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 @code{-g} switch of @code{gcc} or @code{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 @code{Source_Reference}
pragma referencing a third file, then gnatchop respects
this pragma, and the generated @code{Source_Reference} pragmas
in the chopped file refer to the original file, with appropriate
line numbers. This is particularly useful when @code{gnatchop}
is used in conjunction with @code{gnatprep} to compile files that
contain preprocessing statements and multiple units.

@item -v
@cindex @code{-v} (@code{gnatchop})
Causes @code{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.

@item -w
@cindex @code{-w} (@code{gnatchop})
Overwrite existing file names. Normally @code{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.
@end table

@node Examples of gnatchop Usage
@section Examples of @code{gnatchop} Usage

@table @code
@item gnatchop -w hello_s.ada ichbiah/files

Chops the source file @file{hello_s.ada}. The output files will be
placed in the directory @file{ichbiah/files},
overwriting any
files with matching names in that directory (no files in the current
directory are modified).

@item gnatchop archive
Chops the source file @file{archive}
into the current directory. One
useful application of @code{gnatchop} is in sending sets of sources
around, for example in email messages. The required sources are simply
concatenated (for example, using a UNIX @code{cat}
command), and then
@code{gnatchop} is used at the other end to reconstitute the original
file names.

@item gnatchop file1 file2 file3 direc
Chops all units in files @file{file1}, @file{file2}, @file{file3}, placing
the resulting files in the directory @file{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
@code{-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.
@end table

@node Configuration Pragmas
@chapter Configuration Pragmas
@cindex Configuration pragmas
@cindex Pragmas, configuration

@noindent
In Ada 95, configuration pragmas include those pragmas described as
such in the Ada 95 Reference Manual, as well as
implementation-dependent pragmas that are configuration pragmas. See the
individual descriptions of pragmas in the GNAT Reference Manual for
details on these additional GNAT-specific configuration pragmas. Most
notably, the pragma @code{Source_File_Name}, which allows
specifying non-default names for source files, is a configuration
pragma.

@menu
* Handling of Configuration Pragmas::
* The Configuration Pragmas File::
@end menu

@node Handling of Configuration Pragmas
@section Handling of Configuration Pragmas

Configuration pragmas may either appear at the start of a compilation
unit, in which case they apply only to that unit, or they may apply to
all compilations performed in a given compilation environment.

GNAT also provides the @code{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 section @pxref{Operating gnatchop in Compilation Mode} for details.
However, for most purposes, it will be more convenient to edit the
@file{gnat.adc} file that contains configuration pragmas directly,
as described in the following section.

@node The Configuration Pragmas File
@section The Configuration Pragmas File
@cindex @file{gnat.adc}

@noindent
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 @file{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.

Configuration pragmas may be entered into the @file{gnat.adc} file
either by running @code{gnatchop} on a source file that consists only of
configuration pragmas, or more conveniently  by
direct editing of the @file{gnat.adc} file, which is a standard format
source file.


@node Elaboration Order Handling in GNAT
@chapter Elaboration Order Handling in GNAT
@cindex Order of elaboration
@cindex Elaboration control

@menu
* Elaboration Code in Ada 95::
* Checking the Elaboration Order in Ada 95::
* Controlling the Elaboration Order in Ada 95::
* Controlling Elaboration in GNAT - Internal Calls::
* Controlling Elaboration in GNAT - External Calls::
* Default Behavior in GNAT - Ensuring Safety::
* Elaboration Issues for Library Tasks::
* Mixing Elaboration Models::
* What to Do If the Default Elaboration Behavior Fails::
* Elaboration for Access-to-Subprogram Values::
* Summary of Procedures for Elaboration Control::
* Other Elaboration Order Considerations::
@end menu

@noindent
This chapter describes the handling of elaboration code in Ada 95 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.

@node Elaboration Code in Ada 95
@section Elaboration Code in Ada 95

@noindent
Ada 95 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:

@table @asis
@item Initializers for variables.
Variables declared at the library level, in package specs or bodies, can
require initialization that is performed at elaboration time, as in:
@smallexample
@cartouche
Sqrt_Half : Float := Sqrt (0.5);
@end cartouche
@end smallexample

@item Package initialization code
Code in a @code{BEGIN-END} section at the outer level of a package body is
executed as part of the package body elaboration code.

@item Library level task allocators
Tasks that are declared using task allocators at the library level
start executing immediately and hence can execute at elaboration time.
@end table

@noindent
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 @code{Sqrt_Half},
if some other piece of
elaboration code references @code{Sqrt_Half},
then it must run after the
section of elaboration code that contains the declaration of
@code{Sqrt_Half}.

There would never be any order of elaboration problem if we made a rule
that whenever you @code{with} a unit, you must elaborate both the spec and body
of that unit before elaborating the unit doing the @code{with}'ing:

@smallexample
@group
@cartouche
@b{with} Unit_1;
@b{package} Unit_2 @b{is} ...
@end cartouche
@end group
@end smallexample

@noindent
would require that both the body and spec of @code{Unit_1} be elaborated
before the spec of @code{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 @code{Unit_1}, we have a procedure @code{Func_1}
that references
the variable @code{Sqrt_1}, which is declared in the elaboration code
of the body of @code{Unit_1}:

@smallexample
@cartouche
Sqrt_1 : Float := Sqrt (0.1);
@end cartouche
@end smallexample

@noindent
The elaboration code of the body of @code{Unit_1} also contains:

@smallexample
@group
@cartouche
@b{if} expression_1 = 1 @b{then}
   Q := Unit_2.Func_2;
@b{end if};
@end cartouche
@end group
@end smallexample

@noindent
@code{Unit_2} is exactly parallel,
it has a procedure @code{Func_2} that references
the variable @code{Sqrt_2}, which is declared in the elaboration code of
the body @code{Unit_2}:

@smallexample
@cartouche
Sqrt_2 : Float := Sqrt (0.1);
@end cartouche
@end smallexample

@noindent
The elaboration code of the body of @code{Unit_2} also contains:

@smallexample
@group
@cartouche
@b{if} expression_2 = 2 @b{then}
   Q := Unit_1.Func_1;
@b{end if};
@end cartouche
@end group
@end smallexample

@noindent
Now the question is, which of the following orders of elaboration is
acceptable:

@smallexample
@group
Spec of Unit_1
Spec of Unit_2
Body of Unit_1
Body of Unit_2
@end group
@end smallexample

@noindent
or

@smallexample
@group
Spec of Unit_2
Spec of Unit_1
Body of Unit_2
Body of Unit_1
@end group
@end smallexample

@noindent
If you carefully analyze the flow here, you will see that you cannot tell
at compile time the answer to this question.
If @code{expression_1} is not equal to 1,
and @code{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 @code{expression_1} = 1 and @code{expression_2} /= 2,
then the call to @code{Func_2}
will occur, but not the call to @code{Func_1.}
This means that it is essential
to elaborate the body of @code{Unit_1} before
the body of @code{Unit_2}, so the first
order of elaboration is correct and the second is wrong.

By making @code{expression_1} and @code{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.

@node Checking the Elaboration Order in Ada 95
@section Checking the Elaboration Order in Ada 95

@noindent
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 95 is designed to be a safe language, and a programmer-beware approach is
clearly not sufficient. Consequently, the language provides three lines
of defense:

@table @asis
@item Standard rules
Some standard rules restrict the possible choice of elaboration
order. In particular, if you @code{with} a unit, then its spec is always
elaborated before the unit doing the @code{with}. Similarly, a parent
spec is always elaborated before the child spec, and finally
a spec is always elaborated before its corresponding body.

@item Dynamic elaboration checks
@cindex Elaboration checks
@cindex Checks, elaboration
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 (@code{Program_Error}) is raised.

@item Elaboration control
Facilities are provided for the programmer to specify the desired order
of elaboration.
@end table

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 95 has two
rules which are a little more restrictive, but easier to check, and
easier to state:

@table @asis
@item Restrictions on calls
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 @code{Program_Error} is raised.

@item Restrictions on instantiations
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 @code{Program_Error} is raised.
@end table

@noindent
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 @code{Program_Error} if the variable is False.

@node Controlling the Elaboration Order in Ada 95
@section Controlling the Elaboration Order in Ada 95

@noindent
In the previous section we discussed the rules in Ada 95 which ensure
that @code{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 95 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:

@table @asis
@item packages that do not require a body
In Ada 95, a library package that does not require a body does not permit
a body. This means that if we have a such a package, as in:

@smallexample
@group
@cartouche
@b{package} Definitions @b{is}
   @b{generic}
      @b{type} m @b{is new} integer;
   @b{package} Subp @b{is}
      @b{type} a @b{is array} (1 .. 10) @b{of} m;
      @b{type} b @b{is array} (1 .. 20) @b{of} m;
   @b{end} Subp;
@b{end} Definitions;
@end cartouche
@end group
@end smallexample

@noindent
A package that @code{with}'s @code{Definitions} may safely instantiate
@code{Definitions.Subp} because the compiler can determine that there
definitely is no package body to worry about in this case

@item pragma Pure
@cindex pragma Pure
@findex Pure
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.

@item pragma Preelaborate
@findex Preelaborate
@cindex pragma Preelaborate
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.

@item pragma Elaborate_Body
@findex Elaborate_Body
@cindex pragma Elaborate_Body
This pragma requires that the body of a unit be elaborated immediately
after its spec. Suppose a unit @code{A} has such a pragma,
and unit @code{B} does
a @code{with} of unit @code{A}. Recall that the standard rules require
the spec of unit @code{A}
to be elaborated before the @code{with}'ing unit; given the pragma in
@code{A}, we also know that the body of @code{A}
will be elaborated before @code{B}, so
that calls to @code{A} are safe and do not need a check.
@end table

@noindent
Note that,
unlike pragma @code{Pure} and pragma @code{Preelaborate},
the use of
@code{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 @code{Unit_1} and @code{Unit_2}.
If a programmer
marks @code{Unit_1} as @code{Elaborate_Body},
and not @code{Unit_2,} then the order of
elaboration will be:

@smallexample
@group
Spec of Unit_2
Spec of Unit_1
Body of Unit_1
Body of Unit_2
@end group
@end smallexample

@noindent
Now that means that the call to @code{Func_1} in @code{Unit_2}
need not be checked,
it must be safe. But the call to @code{Func_2} in
@code{Unit_1} may still fail if
@code{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 @code{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 @code{Unit_1}/@code{Unit_2} example, if
we marked both of them as having pragma @code{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 in
Ada 95 is to mark units as @code{Pure} or @code{Preelaborate} if possible,
and if this is not possible,
mark them as @code{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:

@table @asis
@item pragma Elaborate (unit)
@findex Elaborate
@cindex pragma Elaborate
This pragma is placed in the context clause, after a @code{with} statement,
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.

@item pragma Elaborate_All (unit)
@findex Elaborate_All
@cindex pragma Elaborate_All
This is a stronger version of the Elaborate pragma. Consider the
following example:

@smallexample
Unit A @code{with}'s unit B and calls B.Func in elab code
Unit B @code{with}'s unit C, and B.Func calls C.Func
@end smallexample

@noindent
Now if we put a pragma @code{Elaborate (B)}
in unit @code{A}, this ensures that the
body of @code{B} is elaborated before the call, but not the
body of @code{C}, so
the call to @code{C.Func} could still cause @code{Program_Error} to
be raised.

The effect of a pragma @code{Elaborate_All} is stronger, it requires
not only that the body of the named unit be elaborated before the
unit doing the @code{with}, but also the bodies of all units that the
named unit uses, following @code{with} links transitively. For example,
if we put a pragma @code{Elaborate_All (B)} in unit @code{A},
then it requires
not only that the body of @code{B} be elaborated before @code{A},
but also the
body of @code{C}, because @code{B} @code{with}'s @code{C}.
@end table

@noindent
We are now in a position to give a usage rule in Ada 95 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 @code{with}'ed unit, or instantiate
a generic unit in a @code{with}'ed unit,
then if the @code{with}'ed unit does not have
pragma Pure, Preelaborate, or Elaborate_Body, then the client should have
an Elaborate_All for the @code{with}'ed unit. By following this rule a client is
assured that calls can be made without risk of an exception.
If this rule is not followed, then a program may be in one of four
states:

@table @asis
@item No order exists
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 95 compiler must diagnose the situation at bind
time, and refuse to build an executable program.

@item One or more orders exist, all incorrect
One or more acceptable elaboration orders exists, and all of them
generate an elaboration order problem. In this case, the binder
can build an executable program, but @code{Program_Error} will be raised
when the program is run.

@item Several orders exist, some right, some incorrect
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.

@item One or more orders exists, all correct
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.
@end table

@noindent
Note that one additional advantage of following our Elaborate_All rule
is that the program continues to stay in the ideal (all orders OK) state
even if maintenance
changes some bodies of some subprograms. 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.

@node Controlling Elaboration in GNAT - Internal Calls
@section Controlling Elaboration in GNAT - Internal Calls

@noindent
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:

@smallexample
@group
@cartouche
@b{function} One @b{return} Float;

Q : Float := One;

@b{function} One @b{return} Float @b{is}
@b{begin}
     return 1.0;
@b{end} One;
@end cartouche
@end group
@end smallexample

@noindent
will obviously raise @code{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 @code{Program_Error}:

@smallexample
@group
@cartouche
 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;
@end cartouche
@end group
@end smallexample

@noindent
Note that in this particular case, it is likely that the call is safe, because
the function @code{One} does not access any global variables.
Nevertheless in Ada 95, 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,
declarations can appear in any order, so there is no restriction that
would prevent this reordering, and if we write:

@smallexample
@group
@cartouche
@b{function} One @b{return} Float;

@b{function} One @b{return} Float @b{is}
@b{begin}
     return 1.0;
@b{end} One;

Q : Float := One;
@end cartouche
@end group
@end smallexample

@noindent
then all is well, no warning is generated, and no
@code{Program_Error} exception
will be raised.
Things are more complicated when a chain of subprograms is executed:

@smallexample
@group
@cartouche
@b{function} A @b{return} Integer;
@b{function} B @b{return} Integer;
@b{function} C @b{return} Integer;

@b{function} B @b{return} Integer @b{is begin return} A; @b{end};
@b{function} C @b{return} Integer @b{is begin return} B; @b{end};

X : Integer := C;

@b{function} A @b{return} Integer @b{is begin return} 1; @b{end};
@end cartouche
@end group
@end smallexample

@noindent
Now the call to @code{C}
at elaboration time in the declaration of @code{X} is correct, because
the body of @code{C} is already elaborated,
and the call to @code{B} within the body of
@code{C} is correct, but the call
to @code{A} within the body of @code{B} is incorrect, because the body
of @code{A} has not been elaborated, so @code{Program_Error}
will be raised on the call to @code{A}.
In this case GNAT will generate a
warning that @code{Program_Error} may be
raised at the point of the call. Let's look at the warning:

@smallexample
@group
@cartouche
 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;
@end cartouche
@end group
@end smallexample

@noindent
Note that the message here says "may raise", instead of the direct case,
where the message says "will be raised". That's because whether
@code{A} is
actually called depends in general on run-time flow of control.
For example, if the body of @code{B} said

@smallexample
@group
@cartouche
@b{function} B @b{return} Integer @b{is}
@b{begin}
   @b{if} some-condition-depending-on-input-data @b{then}
      @b{return} A;
   @b{else}
      @b{return} 1;
   @b{end if};
@b{end} B;
@end cartouche
@end group
@end smallexample

@noindent
then we could not know until run time whether the incorrect call to A would
actually occur, so @code{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 @code{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:

@itemize @bullet
@item
Compile with the @code{-gnatws} switch set

@item
Suppress @code{Elaboration_Checks} for the called subprogram

@item
Use pragma @code{Warnings_Off} to turn warnings off for the call
@end itemize

@noindent
For the internal elaboration check case,
GNAT by default generates the
necessary run-time checks to ensure
that @code{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
@code{Suppress (Elaboration_Checks)} 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 @code{Program_Error} exception.

@node Controlling Elaboration in GNAT - External Calls
@section Controlling Elaboration in GNAT - External Calls

@noindent
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:

@smallexample
@cartouche
@group
@b{package} Math @b{is}
   @b{function} Sqrt (Arg : Float) @b{return} Float;
@b{end} Math;

@b{package body} Math @b{is}
   @b{function} Sqrt (Arg : Float) @b{return} Float @b{is}
   @b{begin}
         ...
   @b{end} Sqrt;
@b{end} Math;
@end group
@group
@b{with} Math;
@b{package} Stuff @b{is}
   X : Float := Math.Sqrt (0.5);
@b{end} Stuff;

@b{with} Stuff;
@b{procedure} Main @b{is}
@b{begin}
   ...
@b{end} Main;
@end group
@end cartouche
@end smallexample

@noindent
where @code{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 @code{Math},
the spec of @code{Stuff} and the body of @code{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 @code{with}
for a package @code{X}, then you
are assured that the spec of @code{X}
is elaborated before U , but you are
not assured that the body of @code{X}
is elaborated before U.
This means that in the above case, the binder is allowed to choose the
order:

@smallexample
spec of Math
spec of Stuff
body of Math
body of Main
@end smallexample

@noindent
but that's not good, because now the call to @code{Math.Sqrt}
that happens during
the elaboration of the @code{Stuff}
spec happens before the body of @code{Math.Sqrt} is
elaborated, and hence causes @code{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 @code{with}
first, but
that is not a general rule that can be followed in all cases. Consider

@smallexample
@group
@cartouche
@b{package} X @b{is} ...

@b{package} Y @b{is} ...

@b{with} X;
@b{package body} Y @b{is} ...

@b{with} Y;
@b{package body} X @b{is} ...
@end cartouche
@end group
@end smallexample

@noindent
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
@code{with} cannot work in this case
(the body of @code{X} @code{with}'s @code{Y},
which means you would have to
elaborate the body of @code{Y} first, but that @code{with}'s @code{X},
which means
you have to elaborate the body of @code{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 @code{Program_Error}
exception to be raised, and it tries to do so (in the
above example of @code{Math/Stuff/Spec}, the GNAT binder will
in fact always
elaborate the body of @code{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.

@node Default Behavior in GNAT - Ensuring Safety
@section Default Behavior in GNAT - Ensuring Safety

@noindent
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:

@noindent
If a unit has elaboration code that can directly or indirectly make a
call to a subprogram in a @code{with}'ed unit, or instantiate a generic unit
in a @code{with}'ed unit, then if the @code{with}'ed unit
does not have pragma @code{Pure},
@code{Preelaborate}, or @code{Elaborate_Body},
then the client should have an
@code{Elaborate_All} for the @code{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 @code{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 @code{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
@code{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
@code{-gnatwl}
(warn on elaboration problems) switch. This will cause warning messages
to be generated indicating the missing @code{Elaborate_All} pragmas.
Consider the following source program:

@smallexample
@group
@cartouche
@b{with} k;
@b{package} j @b{is}
  m : integer := k.r;
@b{end};
@end cartouche
@end group
@end smallexample

@noindent
where it is clear that there
should be a pragma @code{Elaborate_All}
for unit @code{k}. An implicit pragma will be generated, and it is
likely that the binder will be able to honor it. However,
it is safer to include the pragma explicitly in the source. If this
unit is compiled with the
@code{-gnatwl}
switch, then the compiler outputs a warning:

@smallexample
@group
@cartouche
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;
@end cartouche
@end group
@end smallexample

@noindent
and these warnings can be used as a guide for supplying manually
the missing pragmas.

This default mode is not strictly compatible with 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 @code{-gnatE} switch on the compiler (@code{gcc} or @code{gnatmake})
command, or by the use of the configuration pragma:

@smallexample
pragma Elaboration_Checks (RM);
@end smallexample

@noindent
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
is issue is further discussed in the section
"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, you are assured that your program will
work using the dynamic model.

@node Elaboration Issues for Library Tasks
@section Elaboration Issues for Library Tasks
@cindex Library tasks, elaboration issues
@cindex Elaboration of library tasks

@noindent
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

@smallexample
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;
@end smallexample

@noindent
If the above example is compiled in the default static elaboration
mode, then a circularity occurs. The circularity comes from the call
@code{Utils.Put_Val} in the task body of @code{Decls.Lib_Task}. Since
this call occurs in elaboration code, we need an implicit pragma
@code{Elaborate_All} for @code{Utils}. This means that not only must
the spec and body of @code{Utils} be elaborated before the body
of @code{Decls}, but also the spec and body of any unit that is
@code{with'ed} by the body of @code{Utils} must also be elaborated before
the body of @code{Decls}. This is the transitive implication of
pragma @code{Elaborate_All} and it makes sense, because in general
the body of @code{Put_Val} might have a call to something in a
@code{with'ed} unit.

In this case, the body of Utils (actually its spec) @code{with's}
@code{Decls}. Unfortunately this means that the body of @code{Decls}
must be elaborated before itself, in case there is a call from the
body of @code{Utils}.

Here is the exact chain of events we are worrying about:

@enumerate
@item
In the body of @code{Decls} a call is made from within the body of a library
task to a subprogram in the package @code{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.

@item
This means that the body and spec of @code{Util} must be elaborated before
the body of @code{Decls} so that this call does not cause an access before
elaboration.

@item
Within the body of @code{Util}, specifically within the body of
@code{Util.Put_Val} there may be calls to any unit @code{with}'ed
by this package.

@item
One such @code{with}'ed package is package @code{Decls}, so there
might be a call to a subprogram in @code{Decls} in @code{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 @code{Decls} knowing what
is in the body of @code{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.

@item
This means that the spec and body of @code{Decls} must also be
elaborated before we elaborate the unit containing the call, but
that unit is @code{Decls}! This means that the body of @code{Decls}
must be elaborated before itself, and that's a circularity.
@end enumerate

@noindent
Indeed, if you add an explicit pragma Elaborate_All for @code{Utils} in
the body of @code{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 @code{-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:

@itemize @bullet

@item
Use the dynamic model of elaboration.

If we use the @code{-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
@code{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.

@item
Split library tasks into separate packages.

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.

@smallexample
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;
@end smallexample

@noindent
All we have done is to split @code{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.

@item
Declare separate task types.

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 95 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:

@smallexample
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;
@end smallexample

@noindent
What we have done here is to replace the @code{task} declaration in
package @code{Decls} with a @code{task type} declaration. Then we
introduce a separate package @code{Declst} to contain the actual
task object. This separates the elaboration issues for
the @code{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  @code{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.

@item
Use No_Entry_Calls_In_Elaboration_Code restriction.
@cindex No_Entry_Calls_In_Elaboration_Code

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 @code{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 @code{accept} or
@code{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:

@smallexample
pragma Restrictions (No_Entry_Calls_In_Elaboration_Code);
@end smallexample

@noindent
This pragma can be placed in the @file{gnat.adc} file in the usual
manner. If we take our original unmodified program and compile it
in the presence of a @file{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 @code{accept}
or @code{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.

@end itemize

@node Mixing Elaboration Models
@section Mixing Elaboration Models
@noindent
So far, we have assumed that the entire program is either compiled
using the dynamic model or static model, ensuring consistencty. 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 @code{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
@code{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 @code{with} a unit that meets at least one of the
following criteria:

@itemize @bullet

@item
The @code{with'ed} unit is itself compiled with dynamic elaboration
checks (that is with the @code{-gnatE} switch.

@item
The @code{with'ed} unit is an internal GNAT implementation unit from
the System, Interfaces, Ada, or GNAT hierarchies.

@item
The @code{with'ed} unit has pragma Preelaborate or pragma Pure.

@item
The @code{with'ing} unit (that is the client) has an explicit pragma
@code{Elaborate_All} for the @code{with'ed} unit.

@end itemize

@noindent
If this rule is violated, that is if a unit with dynamic elaboration
checks @code{with's} a unit that does not meet one of the above four
criteria, then the binder (@code{gnatbind}) will issue a warning
similar to that in the following example:

@smallexample
warning: "x.ads" has dynamic elaboration checks and with's
warning:   "y.ads" which has static elaboration checks
@end smallexample

@noindent
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 @code{-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 @code{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, without
allowing the main application that uses this subsystem to be compiled
using the more reliable default static model.

@node What to Do If the Default Elaboration Behavior Fails
@section What to Do If the Default Elaboration Behavior Fails

@noindent
If the binder cannot find an acceptable order, it outputs detailed
diagnostics. For example:
@smallexample
@group
@iftex
@leftskip=0cm
@end iftex
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)"
@end group

@end smallexample

@noindent
In this case we have a cycle that the binder cannot break. On the one
hand, there is an explicit pragma Elaborate in @code{proc} for
@code{pack}. This means that the body of @code{pack} must be elaborated
before the body of @code{proc}. On the other hand, there is elaboration
code in @code{pack} that calls a subprogram in @code{proc}. This means
that for maximum safety, there should really be a pragma
Elaborate_All in @code{pack} for @code{proc} which would require that
the body of @code{proc} be elaborated before the body of
@code{pack}. Clearly both requirements cannot be satisfied.
Faced with a circularity of this kind, you have three different options.

@table @asis
@item Fix the program
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.

@item Perform dynamic checks
If the compilations are done using the
@code{-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 @code{Elaborate_All} pragmas.
The behavior then is exactly as specified in the Ada 95 Reference Manual.
The binder will generate an executable program that may or may not
raise @code{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.

@item Suppress checks
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, then you can use the
@code{-f}
switch for the
@code{gnatbind}
step, or
@code{-bargs -f}
if you are using
@code{gnatmake}.
This switch tells the binder to ignore any implicit @code{Elaborate_All}
pragmas that were generated by the compiler, and suppresses any
circularity messages that they cause. The resulting executable will work
properly if there are no elaboration problems, but if there are some order of
elaboration problems they will not be detected, and unexpected
results may occur.
@end table

@noindent
It is hard to generalize on which of these three 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
@code{-gnatE}
or
@code{-f}
but the danger in either 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
@code{-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
@code{-h (horrible elaboration order)}
switch for
@code{gnatbind}.
Normally the binder tries to find an order that has the best chance of
of avoiding elaboration problems. With this switch, 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
@code{-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.)

@node Elaboration for Access-to-Subprogram Values
@section Elaboration for Access-to-Subprogram Values
@cindex Access-to-subprogram

@noindent
The introduction of access-to-subprogram types in Ada 95 complicates
the handling of elaboration. The trouble is that it becomes
impossible to tell at compile time which procedure
is being called. This means that it is not possible for the binder
to analyze the elaboration requirements in this case.

If at the point at which  the access value is created, the body of the subprogram is
known to have been elaborated, then the access value is safe, and its use
does not require a check. This may be achieved by appropriate arrangement
of the order of declarations if the subprogram is in the current unit,
or, if the subprogram is in another unit, by using pragma
@code{Pure}, @code{Preelaborate}, or @code{Elaborate_Body}
on the referenced unit.

If the referenced body is not known to have been elaborated at the point
the access value is created, then any use of the access value must do a
dynamic check, and this dynamic check will fail and raise a
@code{Program_Error} exception if the body has not been elaborated yet.
GNAT will generate the necessary checks, and in addition, if the
@code{-gnatwl}
switch is set, will generate warnings that such checks are required.

The use of dynamic dispatching for tagged types similarly generates
a requirement for dynamic checks, and premature calls to any primitive
operation of a tagged type before the body of the operation has been elaborated,
will result in the raising of @code{Program_Error}.

@node Summary of Procedures for Elaboration Control
@section Summary of Procedures for Elaboration Control
@cindex Elaboration control

@noindent
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
@code{-gnatwl}
switch to generate warnings about missing @code{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
@code{-gnatE} switch to generate dynamic elaboration checks,
or, if you are sure there really are no elaboration problems,
use the
@code{-f}
switch for the binder to cause it to ignore implicit @code{Elaborate_All}
pragmas generated by the compiler.

@node Other Elaboration Order Considerations
@section Other Elaboration Order Considerations
@noindent
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:

@smallexample
with Init_Constants;
package Constants is
   X : Integer := 0;
   Y : Integer := 0;
end Constants;

package Init_Constants is
   procedure Calc;
end Init_Constants;

with Constants;
package body Init_Constants is
   procedure Calc 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;
@end smallexample

@noindent
In this example, there is more than one valid order of elaboration. For
example both the following are correct orders:

@smallexample
Init_Constants spec
Constants spec
Calc spec
Main body
Init_Constants body

  and

Init_Constants spec
Init_Constants body
Constants spec
Calc spec
Main body
@end smallexample

@noindent
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 @code{Calc} initializes @code{Z} to zero, and then the main program
runs with this value of zero. But in the second order, the elaboration
routine of @code{Calc} runs after the body of Init_Constants has set
@code{X} and @code{Y} and thus @code{Z} is set to 7 before @code{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:

@smallexample
pragma Elaborate_All (Constants);
@end smallexample

@noindent
which requires that the body (if any) and spec of @code{Constants},
as well as the body and spec of any unit @code{with}'ed by
@code{Constants} be elaborated before @code{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 @code{Elaborate} or
@code{Elaborate_All} pragmas, then indeed it is possible that two different
compilers can choose different orders.

The @code{gnatbind}
@code{-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 @code{Elaborate} pragmas. For the example above, we have the
following output:

@smallexample
gnatmake -f -q main
main
 7
gnatmake -f -q main -bargs -p
main
 0
@end smallexample

@noindent
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
@code{Elaborate_All} pragmas to ensure the desired order.

@node The Cross-Referencing Tools gnatxref and gnatfind
@chapter  The Cross-Referencing Tools @code{gnatxref} and @code{gnatfind}
@findex gnatxref
@findex gnatfind

@noindent
The compiler generates cross-referencing information (unless
you set the @samp{-gnatx} switch), which are saved in the @file{.ali} files.
This information indicates where in the source each entity is declared and
referenced.

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 @code{gnatxref} and @code{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 @code{gnatfind} is intended for locating
definitions and/or references to a specified entity or entities, whereas
@code{gnatxref} is oriented to generating a full report of all
cross-references.

To use these tools, you must not compile your application using the
@samp{-gnatx} switch on the @file{gnatmake} command line (@inforef{The
GNAT Make Program gnatmake,,gnat_ug}). Otherwise, cross-referencing
information will not be generated.

@menu
* gnatxref Switches::
* gnatfind Switches::
* Project Files::
* Regular Expressions in gnatfind and gnatxref::
* Examples of gnatxref Usage::
* Examples of gnatfind Usage::
@end menu

@node gnatxref Switches
@section @code{gnatxref} Switches

@noindent
The command lines for @code{gnatxref} is:
@smallexample
$ gnatxref [switches] sourcefile1 [sourcefile2 ...]
@end smallexample

@noindent
where

@table @code
@item sourcefile1, sourcefile2
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'.

@end table

@noindent
The switches can be :
@table @code
@item -a
If this switch is present, @code{gnatfind} and @code{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 @code{gnatfind} and @code{gnatxref}
much faster, and their output much smaller.

@item -aIDIR
When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for @file{gnatmake}.

@item -aODIR
When searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
@file{gnatmake}.

@item -d
If this switch is set @code{gnatxref} will output the parent type
reference for each matching derived types.

@item -f
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.

@item -g
If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
@code{gnatfind} and @code{gnatxref}.

@item -IDIR
Equivalent to @samp{-aODIR -aIDIR}.

@item -pFILE
Specify a project file to use @xref{Project Files}.
By default, @code{gnatxref} and @code{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 @samp{-aI}
and @samp{-aO}.
@item -u
Output only unused symbols. This may be really useful if you give your
main compilation unit on the command line, as @code{gnatxref} will then
display every unused entity and 'with'ed package.

@item -v
Instead of producing the default output, @code{gnatxref} will generate a
@file{tags} file that can be used by vi. For examples how to use this
feature, see @xref{Examples of gnatxref Usage}. The tags file is output
to the standard output, thus you will have to redirect it to a file.

@end table

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 @samp{gnatxref -ag} instead of
@samp{gnatxref -a -g}.

@node gnatfind Switches
@section @code{gnatfind} Switches

@noindent
The command line for @code{gnatfind} is:

@smallexample
$ gnatfind [switches] pattern[:sourcefile[:line[:column]]]
      [file1 file2 ...]
@end smallexample

@noindent
where

@table @code
@item pattern
An entity will be output only if it matches the regular expression found
in @samp{pattern}, see @xref{Regular Expressions in gnatfind and gnatxref}.

Omitting the pattern is equivalent to specifying @samp{*}, 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.

@item sourcefile
@code{gnatfind} will look for references, bodies or declarations
of symbols referenced in @file{sourcefile}, at line @samp{line}
and column @samp{column}. See @pxref{Examples of gnatfind Usage}
for syntax examples.

@item line
is a decimal integer identifying the line number containing
the reference to the entity (or entities) to be located.

@item column
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.

@item file1 file2 ...
The search will be restricted to these 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'.

Not that if you specify at least one file in this part, @code{gnatfind} may
sometimes not be able to find the body of the subprograms...

@end table

At least one of 'sourcefile' or 'pattern' has to be present on
the command line.

The following switches are available:
@table @code

@item -a
If this switch is present, @code{gnatfind} and @code{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 @code{gnatfind} and @code{gnatxref}
much faster, and their output much smaller.

@item -aIDIR
When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for @file{gnatmake}.

@item -aODIR
When searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
@file{gnatmake}.

@item -d
If this switch is set, then @code{gnatfind} will output the parent type
reference for each matching derived types.

@item -e
By default, @code{gnatfind} accept the simple regular expression set for
@samp{pattern}. If this switch is set, then the pattern will be
considered as full Unix-style regular expression.

@item -f
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.

@item -g
If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
@code{gnatfind} and @code{gnatxref}.

@item -IDIR
Equivalent to @samp{-aODIR -aIDIR}.

@item -pFILE
Specify a project file (@pxref{Project Files}) to use.
By default, @code{gnatxref} and @code{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 @samp{-aI} and
@samp{-aO}.

@item -r
By default, @code{gnatfind} will output only the information about the
declaration, body or type completion of the entities. If this switch is
set, the @code{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).

@item -s
If this switch is set, then @code{gnatfind} will output the content
of the Ada source file lines were the entity was found.

@item -t
If this switch is set, then @code{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.

@end table

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 @samp{gnatxref -ag} instead of
@samp{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 @code{*} at the end of the command line.

@node Project Files
@section Project Files

@noindent
The project files allows a programmer to specify how to compile its
application, where to find sources,... These files are used primarily by
the Glide Ada mode, but they can also be used by the two tools
@code{gnatxref} and @code{gnatfind}.

A project file name must end with @file{.adp}. If a single one is
present in the current directory, then @code{gnatxref} and @code{gnatfind} will
extract the information from it. If multiple project files are found, none of
them is read, and you have to use the @samp{-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 @samp{src_dir} and @samp{obj_dir}, you can only have one instance of
each line. If you have multiple instances, only the last one is taken into
account.

@table @code
@item 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.

@item 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

@item comp_opt=SWITCHES   [default: ""]
creates a variable which can be referred to subsequently by using
the @samp{$@{comp_opt@}} notation. This is intended to store the default
switches given to @file{gnatmake} and @file{gcc}.

@item bind_opt=SWITCHES   [default: ""]
creates a variable which can be referred to subsequently by using
the @samp{$@{bind_opt@}} notation. This is intended to store the default
switches given to @file{gnatbind}.

@item link_opt=SWITCHES   [default: ""]
creates a variable which can be referred to subsequently by using
the @samp{$@{link_opt@}} notation. This is intended to store the default
switches given to @file{gnatlink}.

@item 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 @samp{$@{main@}} notation.

@item comp_cmd=COMMAND    [default: "gcc -c -I$@{src_dir@} -g -gnatq"]
specifies the command used to compile a single file in the application.

@item 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.

@item run_cmd=COMMAND     [default: "$@{main@}"]
specifies the command used to run the application.

@item debug_cmd=COMMAND   [default: "gdb $@{main@}"]
specifies the command used to debug the application

@end table

@code{gnatxref} and @code{gnatfind} only take into account the @samp{src_dir}
and @samp{obj_dir} lines, and ignore the others.

@node Regular Expressions in gnatfind and gnatxref
@section  Regular Expressions in @code{gnatfind} and @code{gnatxref}

@noindent
As specified in the section about @code{gnatfind}, the pattern can be a
regular expression. Actually, there are to set of regular expressions
which are recognized by the program :

@table @code
@item globbing patterns
These 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 :
@smallexample
@group
@iftex
@leftskip=.5cm
@end iftex
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
@end group
@end smallexample

@item full regular expression
The second set of regular expressions is much more powerful. This is the
type of regular expressions recognized by utilities such a @file{grep}.

The following is the form of a regular expression, expressed in Ada
reference manual style BNF is as follows

@smallexample
@iftex
@leftskip=.5cm
@end iftex
@group
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
@end group
@group
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 ()[].*+?^
@end group
@end smallexample

Following are a few examples :

@table @code
@item abcde|fghi
will match any of the two strings 'abcde' and 'fghi'.

@item abc*d
will match any string like 'abd', 'abcd', 'abccd', 'abcccd', and so on

@item [a-z]+
will match any string which has only lowercase characters in it (and at
least one character

@end table
@end table

@node Examples of gnatxref Usage
@section Examples of @code{gnatxref} Usage

@subsection General Usage

@noindent
For the following examples, we will consider the following units :

@smallexample
@group
@cartouche
main.ads:
1: @b{with} Bar;
2: @b{package} Main @b{is}
3:     @b{procedure} Foo (B : @b{in} Integer);
4:     C : Integer;
5: @b{private}
6:     D : Integer;
7: @b{end} Main;

main.adb:
1: @b{package body} Main @b{is}
2:     @b{procedure} Foo (B : @b{in} Integer) @b{is}
3:     @b{begin}
4:        C := B;
5:        D := B;
6:        Bar.Print (B);
7:        Bar.Print (C);
8:     @b{end} Foo;
9: @b{end} Main;

bar.ads:
1: @b{package} Bar @b{is}
2:     @b{procedure} Print (B : Integer);
3: @b{end} bar;
@end cartouche
@end group
@end smallexample

@table @code

@noindent
The first thing to do is to recompile your application (for instance, in
that case just by doing a @samp{gnatmake main}, so that GNAT generates
the cross-referencing information.
You can then issue any of the following commands:

@item gnatxref main.adb
@code{gnatxref} generates cross-reference information for main.adb
and every unit 'with'ed by main.adb.

The output would be:
@smallexample
@iftex
@leftskip=0cm
@end iftex
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
@end smallexample

@noindent
that is the entity @code{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 @code{Print} is declared in bar.ads, line 2, column 15 and it
it referenced in main.adb, line 6 column 12 and line 7 column 12.

@item gnatxref package1.adb package2.ads
@code{gnatxref} will generates cross-reference information for
package1.adb, package2.ads and any other package 'with'ed by any
of these.

@end table

@subsection Using gnatxref with vi

@code{gnatxref} can generate a tags file output, which can be used
directly from @file{vi}. Note that the standard version of @file{vi}
will not work properly with overloaded symbols. Consider using another
free implementation of @file{vi}, such as @file{vim}.

@smallexample
$ gnatxref -v gnatfind.adb > tags
@end smallexample

@noindent
will generate the tags file for @code{gnatfind} itself (if the sources
are in the search path!).

From @file{vi}, you can then use the command @samp{:tag @i{entity}}
(replacing @i{entity} by whatever you are looking for), and vi will
display a new file with the corresponding declaration of entity.

@node Examples of gnatfind Usage
@section Examples of @code{gnatfind} Usage

@table @code

@item gnatfind -f xyz:main.adb
Find 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 @samp{-f}
switch is set)

The output will look like:
@smallexample
directory/main.ads:106:14: xyz <= declaration
directory/main.adb:24:10: xyz <= body
directory/foo.ads:45:23: xyz <= declaration
@end smallexample

@noindent
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

@item gnatfind -fs xyz:main.adb
This is the same command as the previous one, instead @code{gnatfind} will
display the content of the Ada source file lines.

The output will look like:

@smallexample
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;
@end smallexample

@noindent
This can make it easier to find exactly the location your are looking
for.

@item gnatfind -r "*x*":main.ads:123 foo.adb
Find references to all entities containing an x that are
referenced on line 123 of main.ads.
The references will be searched only in main.adb and foo.adb.

@item gnatfind main.ads:123
Find declarations and bodies for all entities that are referenced on
line 123 of main.ads.

This is the same as @code{gnatfind "*":main.adb:123}.

@item gnatfind mydir/main.adb:123:45
Find 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.

@end table

@node File Name Krunching Using gnatkr
@chapter File Name Krunching Using @code{gnatkr}
@findex gnatkr

@noindent
This 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
@code{gnatkr} utility that can be used to determine the result of
applying this shortening.
@menu
* About gnatkr::
* Using gnatkr::
* Krunching Method::
* Examples of gnatkr Usage::
@end menu

@node About gnatkr
@section About @code{gnatkr}

@noindent
The 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:
@itemize @bullet
@item
Take the unit name and replace all dots by hyphens.
@item
If such a replacement occurs in the
second character position of a name, and the first character is
a, g, s, or i then replace the dot by the character
~ (tilde)
instead of a minus.
@end itemize
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 @code{-gnatk@var{nn}}
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 @code{gnatkr} utility can be used to determine the krunched name for
a given file, when krunched to a specified maximum length.

@node Using gnatkr
@section Using @code{gnatkr}

@noindent
The @code{gnatkr} command has the form

@smallexample
$ gnatkr @var{name} [@var{length}]
@end smallexample


@noindent
@var{name} can be an Ada name with dots or the GNAT name of the unit,
where the dots representing child units or subunit are replaced by
hyphens. The only confusion arises if a name ends in @code{.ads} or
@code{.adb}. @code{gnatkr} takes this to be an extension if there are
no other dots in the name and the whole name is in lowercase.

@var{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 which are
always 8.

@noindent
The output is the krunched name. The output has an extension only if the
original argument was a file name with an extension.

@node Krunching Method
@section Krunching Method

@noindent
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 @code{.ads} for a
specification and @code{.adb} for a body.
Krunching does not affect the extension, but the file name is shortened to
the specified length by following these rules:

@itemize @bullet
@item
The name is divided into segments separated by hyphens, tildes or
underscores and all hyphens, tildes, and underscores are
eliminated. If this leaves the name short enough, we are done.

@item
If the name is too long, the longest segment is located (left-most if there are two
of equal length), and shortened by dropping its last character. This is
repeated until the name is short enough.

As an example, consider the krunching of @*@file{our-strings-wide_fixed.adb}
to fit the name into 8 characters as required by some operating systems.

@smallexample
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
@end smallexample

@item
The file names for all predefined units are always krunched to eight
characters. The krunching of these predefined units uses the following
special prefix replacements:

@table @file
@item ada-
replaced by @file{a-}

@item gnat-
replaced by @file{g-}

@item interfaces-
replaced by @file{i-}

@item system-
replaced by @file{s-}
@end table

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
@*@file{ada-strings-wide_fixed.adb}, which gets krunched as follows:

@smallexample
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
@end smallexample
@end itemize

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 @code{gnatkr} is supplied for conveniently determining the
krunched name of a file.

@node Examples of gnatkr Usage
@section Examples of @code{gnatkr} Usage

@smallexample
@iftex
@leftskip=0cm
@end iftex
$ gnatkr very_long_unit_name.ads      --> velounna.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
@end smallexample

@node Preprocessing Using gnatprep
@chapter Preprocessing Using @code{gnatprep}
@findex gnatprep

@noindent
The @code{gnatprep} utility provides
a simple preprocessing capability for Ada programs.
It is designed for use with GNAT, but is not dependent on any special
features of GNAT.

@menu
* Using gnatprep::
* Switches for gnatprep::
* Form of Definitions File::
* Form of Input Text for gnatprep::
@end menu

@node Using gnatprep
@section Using @code{gnatprep}

@noindent
To call @code{gnatprep} use

@smallexample
$ gnatprep [-bcrsu] [-Dsymbol=value] infile outfile [deffile]
@end smallexample

@noindent
where
@table @code
@item infile
is the full name of the input file, which is an Ada source
file containing preprocessor directives.

@item outfile
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.

@item deffile
is the full name of a text file containing definitions of
symbols to be referenced by the preprocessor. This argument is
optional, and can be replaced by the use of the @code{-D} switch.

@item switches
is an optional sequence of switches as described in the next section.
@end table

@node Switches for gnatprep
@section Switches for @code{gnatprep}

@table @code

@item -b
Causes 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.

@item -c
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.

@item -Dsymbol=value
Defines a new symbol, associated with value. If no value is given on the
command line, then symbol is considered to be @code{True}. This switch
can be used in place of a definition file.


@item -r
Causes a @code{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 @code{-b} mode if
@code{-c}
has not been specified explicitly.

Note that if the file to be preprocessed contains multiple units, then
it will be necessary to @code{gnatchop} the output file from
@code{gnatprep}. If a @code{Source_Reference} pragma is present
in the preprocessed file, it will be respected by
@code{gnatchop -r}
so that the final chopped files will correctly refer to the original
input source file for @code{gnatprep}.

@item -s
Causes a sorted list of symbol names and values to be
listed on the standard output file.

@item -u
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 @code{#if} or @code{#elsif} test will be treated as an error.

@end table

@noindent
Note: if neither @code{-b} nor @code{-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.

@node Form of Definitions File
@section Form of Definitions File

@noindent
The definitions file contains lines of the form

@smallexample
symbol := value
@end smallexample

@noindent
where symbol is an identifier, following normal Ada (case-insensitive)
rules for its syntax, and value is one of the following:

@itemize @bullet
@item
Empty, corresponding to a null substitution
@item
A string literal using normal Ada syntax
@item
Any sequence of characters from the set
(letters, digits, period, underline).
@end itemize

@noindent
Comment lines may also appear in the definitions file, starting with
the usual @code{--},
and comments may be added to the definitions lines.

@node Form of Input Text for gnatprep
@section Form of Input Text for @code{gnatprep}

@noindent
The input text may contain preprocessor conditional inclusion lines,
as well as general symbol substitution sequences.
The preprocessor conditional inclusion commands have the form

@smallexample
@group
@cartouche
#if @i{expression} [then]
   lines
#elsif @i{expression} [then]
   lines
#elsif @i{expression} [then]
   lines
...
#else
   lines
#end if;
@end cartouche
@end group
@end smallexample

@noindent
In this example, @i{expression} is defined by the following grammar:
@smallexample
@i{expression} ::=  <symbol>
@i{expression} ::=  <symbol> = "<value>"
@i{expression} ::=  <symbol> = <symbol>
@i{expression} ::=  <symbol> 'Defined
@i{expression} ::=  not @i{expression}
@i{expression} ::=  @i{expression} and @i{expression}
@i{expression} ::=  @i{expression} or @i{expression}
@i{expression} ::=  @i{expression} and then @i{expression}
@i{expression} ::=  @i{expression} or else @i{expression}
@i{expression} ::=  ( @i{expression} )
@end smallexample

@noindent
For the first test (@i{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
@code{True} or @code{False}. If the value is true, then the
corresponding lines are included, and if the value is false, they are
excluded.

The test (@i{expression} ::= <symbol> @code{'Defined}) is true only if
the symbol has been defined in the definition file or by a @code{-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 @code{-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 @code{True}
or @code{False}.

The use of the @code{not} operator inverts the sense of this logical test, so
that the lines are included only if the symbol is not defined.
The @code{then} keyword is optional as shown

The @code{#} must be the first non-blank character on a line, but
otherwise the format is free form. Spaces or tabs may appear between
the @code{#} 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 @code{elsif} clauses can be present,
including none at all. The @code{else} is optional, as in Ada.

The @code{#} 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

@smallexample
$symbol
@end smallexample

@noindent
anywhere within a source line, except in a comment. The identifier
following the @code{$} must match one of the symbols defined in the symbol
definition file, and the result is to substitute the value of the
symbol in place of @code{$symbol} in the output file.


@node The GNAT Library Browser gnatls
@chapter The GNAT Library Browser @code{gnatls}
@findex gnatls
@cindex Library browser

@noindent
@code{gnatls} 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.

@menu
* Running gnatls::
* Switches for gnatls::
* Examples of gnatls Usage::
@end menu

@node Running gnatls
@section Running @code{gnatls}

@noindent
The @code{gnatls} command has the form

@smallexample
$ gnatls switches @var{object_or_ali_file}
@end smallexample

@noindent
The main argument is the list of object or @file{ali} files
(@pxref{The Ada Library Information Files})
for which information is requested.

In normal mode, without additional option, @code{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:

@smallexample
$ 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
@end smallexample

@noindent
The first line can be interpreted as follows: the main unit which is
contained in
object file @file{demo1.o} is demo1, whose main source is in
@file{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:

@table @code
@item OK (unchanged)
The version of the source file used for the compilation of the
specified unit corresponds exactly to the actual source file.

@item 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
@code{-m (minimal recompilation)}, a file marked
MOK will not be recompiled.

@item DIF (modified)
No version of the source found on the path corresponds to the source
used to build this object.

@item ??? (file not found)
No source file was found for this unit.

@item 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.

@end table

@node Switches for gnatls
@section Switches for @code{gnatls}

@noindent
@code{gnatls} recognizes the following switches:

@table @code
@item -a
@cindex @code{-a} (@code{gnatls})
Consider all units, including those of the predefined Ada library.
Especially useful with @code{-d}.

@item -d
@cindex @code{-d} (@code{gnatls})
List sources from which specified units depend on.

@item -h
@cindex @code{-h} (@code{gnatls})
Output the list of options.

@item -o
@cindex @code{-o} (@code{gnatls})
Only output information about object files.

@item -s
@cindex @code{-s} (@code{gnatls})
Only output information about source files.

@item -u
@cindex @code{-u} (@code{gnatls})
Only output information about compilation units.

@item -aO@var{dir}
@itemx -aI@var{dir}
@itemx -I@var{dir}
@itemx  -I-
@itemx -nostdinc
Source and Object path manipulation. Same meaning as the equivalent
@code{gnatmake} flags (see @ref{Switches for gnatmake}).

@item -v
@cindex @code{-s} (@code{gnatls})
Verbose mode. Output the complete source and object 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:

@table @code
@item  Preelaborable
The unit is preelaborable in the Ada 95 sense.

@item No_Elab_Code
No elaboration code has been produced by the compiler for this unit.

@item Pure
The unit is pure in the Ada 95 sense.

@item Elaborate_Body
The unit contains a pragma Elaborate_Body.

@item Remote_Types
The unit contains a pragma Remote_Types.

@item Shared_Passive
The unit contains a pragma Shared_Passive.

@item Predefined
This unit is part of the predefined environment and cannot be modified
by the user.

@item Remote_Call_Interface
The unit contains a pragma Remote_Call_Interface.

@end table

@end table

@node Examples of gnatls Usage
@section Example of @code{gnatls} Usage

@noindent
Example of using the verbose switch. Note how the source and
object paths are affected by the -I switch.

@smallexample
$ gnatls -v -I.. demo1.o

GNATLS 3.10w (970212) Copyright 1999 Free Software Foundation, Inc.

Source Search Path:
   <Current_Directory>
   ../
   /home/comar/local/adainclude/

Object Search Path:
   <Current_Directory>
   ../
   /home/comar/local/lib/gcc-lib/mips-sni-sysv4/2.7.2/adalib/

./demo1.o
   Unit =>
     Name   => demo1
     Kind   => subprogram body
     Flags  => No_Elab_Code
     Source => demo1.adb    modified
@end smallexample

@noindent
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.

@smallexample
$ 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
/home/comar/local/adainclude/s-exctab.ads
/home/comar/local/adainclude/s-finimp.ads
/home/comar/local/adainclude/s-finroo.ads
/home/comar/local/adainclude/s-secsta.ads
/home/comar/local/adainclude/s-stalib.ads
/home/comar/local/adainclude/s-stoele.ads
/home/comar/local/adainclude/s-stratt.ads
/home/comar/local/adainclude/s-tasoli.ads
/home/comar/local/adainclude/s-unstyp.ads
/home/comar/local/adainclude/unchconv.ads
@end smallexample


@node GNAT and Libraries
@chapter GNAT and Libraries
@cindex Library, building, installing

@noindent
This chapter addresses some of the issues related to building and using
a library with GNAT. It also shows how the GNAT runtime library can be
recompiled.

@menu
* Creating an Ada Library::
* Installing an Ada Library::
* Using an Ada Library::
* Rebuilding the GNAT Run-Time Library::
@end menu

@node Creating an Ada Library
@section Creating an Ada Library

@noindent
In the GNAT environment, a library has two components:
@itemize @bullet
@item
Source files.
@item
Compiled code and Ali files. See @ref{The Ada Library Information Files}.
@end itemize

@noindent
In order to use other packages @ref{The GNAT Compilation Model}
requires a certain number of sources to be available to the compiler.
The minimal set of
sources required includes the specs of all the packages that make up the
visible part of the library as well as all the sources upon which they
depend. The bodies of all visible generic units must also be provided.
@noindent
Although it is not strictly mandatory, it is recommended that all sources
needed to recompile the library be provided, so that the user can make
full use of interunit inlining and source-level debugging. This can also
make the situation easier for users that need to upgrade their compilation
toolchain and thus need to recompile the library from sources.

@noindent
The compiled code can be provided in different ways. The simplest way is
to provide directly the set of objects produced by the compiler during
the compilation of the library. It is also possible to group the objects
into an archive using whatever commands are provided by the operating
system. Finally, it is also possible to create a shared library (see
option -shared in the GCC manual).

@noindent
There are various possibilities for compiling the units that make up the
library: for example with a Makefile @ref{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, in order to build all the necessary objects. Here is an example
of such a dummy program and the generic commands used to build an
archive or a shared library.

@smallexample
@iftex
@leftskip=.7cm
@end iftex
@b{with} My_Lib.Service1;
@b{with} My_Lib.Service2;
@b{with} My_Lib.Service3;
@b{procedure} My_Lib_Dummy @b{is}
@b{begin}
   @b{null};
@b{end};

# 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
@end smallexample

@noindent
When the objects are grouped in an archive or a shared library, the user
needs to specify the desired library at link time, unless a pragma
linker_options has been used in one of the sources:
@smallexample
@b{pragma} Linker_Options ("-lmy_lib");
@end smallexample

@node Installing an Ada Library
@section Installing an Ada Library

@noindent
In the GNAT model, installing a library consists in copying into a specific
location the files that make up this library. It is possible to install
the sources in a different directory from the other files (ALI, objects,
archives) since the source path and the object path can easily be
specified separately.

@noindent
For general purpose libraries, it is possible for the system
administrator to put those libraries in the default compiler paths. To
achieve this, he must specify their location in the configuration files
"ada_source_path" and "ada_object_path" that 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:
@smallexample
$ gcc -v
@end smallexample

@noindent
The configuration files mentioned above have simple format: each line in them
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.

@noindent
"ada_source_path" and "ada_object_path" might actually 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" at all, 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").

@noindent
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.

@node Using an Ada Library
@section Using an Ada Library

@noindent
In order to use a Ada library, you need to make sure that this
library is on both your source and object path
@ref{Search Paths and the Run-Time Library (RTL)}
and @ref{Search Paths for gnatbind}. For
instance, you can use the library "mylib" installed in "/dir/my_lib_src"
and "/dir/my_lib_obj" with the following commands:

@smallexample
$ gnatmake -aI/dir/my_lib_src -aO/dir/my_lib_obj my_appl \
  -largs -lmy_lib
@end smallexample

@noindent
This can be simplified down to the following:
@smallexample
$ gnatmake my_appl
@end smallexample
when the following conditions are met:
@itemize @bullet
@item
"/dir/my_lib_src" has been added by the user to the environment
variable "ADA_INCLUDE_PATH", or by the administrator to the file
"ada_source_path"
@item
"/dir/my_lib_obj" has been added by the user to the environment
variable "ADA_OBJECTS_PATH", or by the administrator to the file
"ada_object_path"
@item
a pragma linker_options, as mentioned in @ref{Creating an Ada Library}
as been added to the sources.
@end itemize
@noindent

@node  Rebuilding the GNAT Run-Time Library
@section Rebuilding the GNAT Run-Time Library

@noindent
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_Scalar. A special Makefile called
@code{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:

@smallexample
$ gnatls -v
@end smallexample

@noindent
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.

@node Using the GNU make Utility
@chapter Using the GNU @code{make} Utility
@findex make

@noindent
This chapter offers some examples of makefiles that solve specific
problems. It does not explain how to write a makefile (see the GNU make
documentation), nor does it try to replace the @code{gnatmake} utility
(@pxref{The GNAT Make Program gnatmake}).

All the examples in this section are specific to the GNU version of
make. Although @code{make} is a standard utility, and the basic language
is the same, these examples use some advanced features found only in
@code{GNU make}.

@menu
* Using gnatmake in a Makefile::
* Automatically Creating a List of Directories::
* Generating the Command Line Switches::
* Overcoming Command Line Length Limits::
@end menu

@node Using gnatmake in a Makefile
@section Using gnatmake in a Makefile
@findex makefile
@cindex GNU make

@noindent
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
@code{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 (@pxref{Automatically Creating a List of Directories})
which might help you in case your project has a lot of
subdirectories.

@smallexample
@iftex
@leftskip=0cm
@font@heightrm=cmr8
@heightrm
@end iftex
## 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@}
@end smallexample

@node Automatically Creating a List of Directories
@section Automatically Creating a List of Directories

@noindent
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, altough less
general, gives you more control over the list. It involves wildcard
characters, that are automatically expanded by @code{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 @code{find}, which is standard on all Unix systems. All
the directories found under a given root directory will be added to the
list.

@smallexample
@iftex
@leftskip=0cm
@font@heightrm=cmr8
@heightrm
@end iftex
# 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's @code{dir} and @code{sort} functions.
# 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@}

@end smallexample

@node Generating the Command Line Switches
@section Generating the Command Line Switches

@noindent
Once you have created the list of directories as explained in the
previous section (@pxref{Automatically Creating a List of Directories}),
you can easily generate the command line arguments to pass to gnatmake.

For the sake of completness, this example assumes that the source path
is not the same as the object path, and that you have two separate lists
of directories.

@smallexample
# 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
@end smallexample

@node Overcoming Command Line Length Limits
@section Overcoming Command Line Length Limits

@noindent
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 @code{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
@ref{Automatically Creating a List of Directories}.
For the sake of completness, 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 immediatly by @code{make}. This way we overcome the standard
make behavior which is to expand the variables only when they are
actually used.

@smallexample
@iftex
@leftskip=0cm
@font@heightrm=cmr8
@heightrm
@end iftex
# In this example, we create both ADA_INCLUDE_PATH and ADA_OBJECT_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_OBJECT_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_OBJECT_PATH += $@{OBJECT_LIST@}
export ADA_INCLUDE_PATH
export ADA_OBJECT_PATH

all:
        gnatmake main_unit
@end smallexample

@node Finding Memory Problems with gnatmem
@chapter Finding Memory Problems with @code{gnatmem}
@findex gnatmem

@noindent
@code{gnatmem}, is a tool that monitors dynamic allocation and
deallocation activity in a program, and displays information about
incorrect deallocations and possible sources of memory leaks. Gnatmem
provides three type of information:
@itemize @bullet
@item
General information concerning memory management, such as the total
number of allocations and deallocations, the amount of allocated
memory and the high water mark, i.e. the largest amount of allocated
memory in the course of program execution.

@item
Backtraces for all incorrect deallocations, that is to say deallocations
which do not correspond to a valid allocation.

@item
Information on each allocation that is potentially the origin of a memory
leak.
@end itemize

The @code{gnatmem} command has two modes. It can be used with @code{gdb}
or with instrumented allocation and deallocation routines. The later
mode is called the @code{GMEM} mode. Both modes produce the very same
output.

@menu
* Running gnatmem (GDB Mode)::
* Running gnatmem (GMEM Mode)::
* Switches for gnatmem::
* Examples of gnatmem Usage::
* GDB and GMEM Modes::
* Implementation Note::
@end menu

@node Running gnatmem (GDB Mode)
@section Running @code{gnatmem} (GDB Mode)

@noindent
The @code{gnatmem} command has the form

@smallexample
   $ gnatmem [-q] [n] [-o file] user_program [program_arg]*
or
   $ gnatmem [-q] [n] -i file
@end smallexample

@noindent
Gnatmem must be supplied with the executable to examine, followed by its
run-time inputs. For example, if a program is executed with the command:
@smallexample
$ my_program arg1 arg2
@end smallexample
then it can be run under @code{gnatmem} control using the command:
@smallexample
$ gnatmem my_program arg1 arg2
@end smallexample

The program is transparently executed under the control of the debugger
@ref{The GNAT Debugger GDB}. This does not affect the behavior
of the program, except for sensitive real-time programs. When the program
has completed execution, @code{gnatmem} outputs a report containing general
allocation/deallocation information and potential memory leak.
For better results, the user program should be compiled with
debugging options @ref{Switches for gcc}.

Here is a simple example of use:

*************** debut cc
@smallexample
$ gnatmem test_gm

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                          :
   test_gm.adb:23 test_gm.alloc
.
.
.
@end smallexample

The first block of output give general information. In this case, the
Ada construct "@b{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 "@b{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.

@node Running gnatmem (GMEM Mode)
@section Running @code{gnatmem} (GMEM Mode)
@cindex @code{GMEM} (@code{gnatmem})

@noindent
The @code{gnatmem} command has the form

@smallexample
   $ gnatmem [-q] [n] -i gmem.out user_program [program_arg]*
@end smallexample

The program must have been linked with the instrumented version of the
allocation and deallocation routines. This is done with linking with the
@file{libgmem.a} library. For better results, the user program should be
compiled with debugging options @ref{Switches for gcc}. For example to
build @file{my_program}:

@smallexample
$ gnatmake -g my_program -largs -lgmem
@end smallexample

@noindent
Under Solaris it is required to build the application with
@code{-funwind-tables} options @ref{Switches for gcc}.

@noindent
When running @file{my_program} the file @file{gmem.out} is produced. This file
contains information about all allocations and deallocations done by the
program. It is produced by the instrumented allocations and
deallocations routines and will be used by @code{gnatmem}.

@noindent
Gnatmem must be supplied with the @file{gmem.out} file and the executable to
examine followed by its run-time inputs. For example, if a program is
executed with the command:
@smallexample
$ my_program arg1 arg2
@end smallexample
then @file{gmem.out} can be analysed by @code{gnatmem} using the command:
@smallexample
$ gnatmem -i gmem.out my_program arg1 arg2
@end smallexample

@node Switches for gnatmem
@section Switches for @code{gnatmem}

@noindent
@code{gnatmem} recognizes the following switches:

@table @code

@item @code{-q}
@cindex @code{-q} (@code{gnatmem})
Quiet. Gives the minimum output needed to identify the origin of the
memory leaks. Omit statistical information.

@item @code{n}
@cindex @code{n} (@code{gnatmem})
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.

@item @code{-o file}
@cindex @code{-o} (@code{gnatmem})
Direct the gdb output to the specified file. The @code{gdb} script used
to generate this output is also saved in the file @file{gnatmem.tmp}.

@item @code{-i file}
@cindex @code{-i} (@code{gnatmem})
Do the @code{gnatmem} processing starting from @file{file} which has
been generated by a previous call to @code{gnatmem} with the -o
switch or @file{gmem.out} produced by @code{GMEM} mode. This is useful
for post mortem processing.

@end table

@node Examples of gnatmem Usage
@section Example of @code{gnatmem} Usage

@noindent
This section is based on the @code{GDB} mode of @code{gnatmem}. The same
results can be achieved using @code{GMEM} mode. See section
@ref{Running gnatmem (GMEM Mode)}.

@noindent
The first example shows the use of @code{gnatmem}
on a simple leaking program.
Suppose that we have the following Ada program:

@smallexample
@group
@cartouche
@b{with} Unchecked_Deallocation;
@b{procedure} Test_Gm @b{is}

   @b{type} T @b{is array} (1..1000) @b{of} Integer;
   @b{type} Ptr @b{is access} T;
   @b{procedure} Free @b{is new} Unchecked_Deallocation (T, Ptr);
   A : Ptr;

   @b{procedure} My_Alloc @b{is}
   @b{begin}
      A := @b{new} T;
   @b{end} My_Alloc;

   @b{procedure} My_DeAlloc @b{is}
      B : Ptr := A;
   @b{begin}
      Free (B);
   @b{end} My_DeAlloc;

@b{begin}
   My_Alloc;
   @b{for} I @b{in} 1 .. 5 @b{loop}
      @b{for} J @b{in} I .. 5 @b{loop}
         My_Alloc;
      @b{end loop};
      My_Dealloc;
   @b{end loop};
@b{end};
@end cartouche
@end group
@end smallexample

@noindent
The program needs to be compiled with debugging option:

@smallexample
$ gnatmake -g test_gm
@end smallexample

@code{gnatmem} is invoked simply with
@smallexample
$ gnatmem test_gm
@end smallexample

@noindent
which produces the following output:

@smallexample
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
@end smallexample

@noindent
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
#1. This is a normal behavior when the number of non freed allocations
is one, it locates 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:

@smallexample
$ gnatmem 3 test_gm
@end smallexample

@noindent
which will give the following output:

@smallexample
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
@end smallexample

@noindent
The allocation root #1 of the first example has been split in 2 roots #1
and #3 thanks to the more precise associated backtrace.

@node GDB and GMEM Modes
@section GDB and GMEM Modes

@noindent
The main advantage of the @code{GMEM} mode is that it is a lot faster than the
@code{GDB} mode where the application must be monitored by a @code{GDB} script.
But the @code{GMEM} mode is available only for DEC Unix, SGI Irix, Linux x86,
Solaris (sparc and x86) and Windows 95/98/NT/2000 (x86).

@noindent
The main advantage of the @code{GDB} mode is that it is available on all
supported platforms. But it can be very slow if the application does a
lot of allocations and deallocations.

@node Implementation Note
@section Implementation Note

@menu
* gnatmem Using GDB Mode::
* gnatmem Using GMEM Mode::
@end menu

@node gnatmem Using GDB Mode
@subsection @code{gnatmem} Using @code{GDB} Mode

@noindent
@code{gnatmem} executes the user program under the control of @code{GDB} using
a script that sets breakpoints and gathers information on each dynamic
allocation and deallocation. The output of the script is then analyzed
by @code{gnatmem}
in order to locate memory leaks and their origin in the
program. Gnatmem works by recording each address returned by the
allocation procedure (@code{__gnat_malloc})
along with the backtrace at the
allocation point. On each deallocation, the deallocated address is
matched with the corresponding allocation. At the end of the processing,
the unmatched allocations are considered potential leaks. All the
allocations associated with the same backtrace are grouped together and
form an allocation root. The allocation roots are then sorted so that
those with the biggest number of unmatched allocation are printed
first. A delicate aspect of this technique is to distinguish between the
data produced by the user program and the data produced by the gdb
script. Currently, on systems that allow probing the terminal, the gdb
command "tty" is used to force the program output to be redirected to the
current terminal while the @code{gdb} output is directed to a file or to a
pipe in order to be processed subsequently by @code{gnatmem}.

@node gnatmem Using GMEM Mode
@subsection @code{gnatmem} Using @code{GMEM} Mode

@noindent
This mode use the same algorithm to detect memory leak as the @code{GDB}
mode of @code{gnatmem}, the only difference is in the way data are
gathered. In @code{GMEM} mode the program is linked with instrumented
version of @code{__gnat_malloc} and @code{__gnat_free}
routines. Information needed to find memory leak are recorded by these
routines in file @file{gmem.out}. This mode also require that the stack
traceback be available, this is only implemented on some platforms
@ref{GDB and GMEM Modes}.


@node Finding Memory Problems with GNAT Debug Pool
@chapter Finding Memory Problems with GNAT Debug Pool
@findex Debug Pool
@cindex storage, pool, memory corruption

@noindent
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 @code{GNAT.Debug_Pools}.

@noindent
In order to use the GNAT specifc 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.
@smallexample
@b{type} Ptr @b{is} @b{access} Some_Type;
Pool : GNAT.Debug_Pools.Debug_Pool;
@b{for} Ptr'Storage_Pool @b{use} Pool;
@end smallexample

@code{GNAT.Debug_Pools} is derived from of 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 @code{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:
@itemize @bullet
@item
@code{GNAT.Debug_Pools.Accessing_Not_Allocated_Storage}
@item
@code{GNAT.Debug_Pools.Accessing_Deallocated_Storage}
@item
@code{GNAT.Debug_Pools.Freeing_Not_Allocated_Storage}
@item
@code{GNAT.Debug_Pools.Freeing_Deallocated_Storage }
@end itemize

@noindent
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. The deallocation strategy consists
in not releasing the memory to the underlying system but rather to fill
it with a memory pattern easily recognizable during debugging sessions:
The memory pattern is the old IBM hexadecimal convention: 16#DEADBEEF#.
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
@code{Debug_Pools}, that includes typical instances of  memory corruption:
@smallexample
@iftex
@leftskip=0cm
@end iftex
@b{with} Gnat.Io; @b{use} Gnat.Io;
@b{with} Unchecked_Deallocation;
@b{with} Unchecked_Conversion;
@b{with} GNAT.Debug_Pools;
@b{with} System.Storage_Elements;
@b{with} Ada.Exceptions; @b{use} Ada.Exceptions;
@b{procedure} Debug_Pool_Test @b{is}

   @b{type} T @b{is} @b{access} Integer;
   @b{type} U @b{is} @b{access} @b{all} T;

   P : GNAT.Debug_Pools.Debug_Pool;
   @b{for} T'Storage_Pool @b{use} P;

   @b{procedure} Free @b{is} @b{new} Unchecked_Deallocation (Integer, T);
   @b{function} UC @b{is} @b{new} Unchecked_Conversion (U, T);
   A, B : @b{aliased} T;

   @b{procedure} Info @b{is} @b{new} GNAT.Debug_Pools.Print_Info(Put_Line);

@b{begin}
   Info (P);
   A := @b{new} Integer;
   B := @b{new} Integer;
   B := A;
   Info (P);
   Free (A);
   @b{begin}
      Put_Line (Integer'Image(B.@b{all}));
   @b{exception}
      @b{when} E : @b{others} => Put_Line ("raised: " & Exception_Name (E));
   @b{end};
   @b{begin}
      Free (B);
   @b{exception}
      @b{when} E : @b{others} => Put_Line ("raised: " & Exception_Name (E));
   @b{end};
   B := UC(A'Access);
   @b{begin}
      Put_Line (Integer'Image(B.@b{all}));
   @b{exception}
      @b{when} E : @b{others} => Put_Line ("raised: " & Exception_Name (E));
   @b{end};
   @b{begin}
      Free (B);
   @b{exception}
      @b{when} E : @b{others} => Put_Line ("raised: " & Exception_Name (E));
   @b{end};
   Info (P);
@b{end} Debug_Pool_Test;
@end smallexample
@noindent
The debug pool mechanism provides the following precise diagnostics on the
execution of this erroneous program:
@smallexample
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

@end smallexample

@node Creating Sample Bodies Using gnatstub
@chapter Creating Sample Bodies Using @code{gnatstub}
@findex gnatstub

@noindent
@code{gnatstub} creates body stubs, that is, empty but compilable bodies
for library unit declarations.

To create a body stub, @code{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 @code{gnatstub}, see the description
of @code{gnatstub} switches below.

@menu
* Running gnatstub::
* Switches for gnatstub::
@end menu

@node Running gnatstub
@section Running @code{gnatstub}

@noindent
@code{gnatstub} has the command-line interface of the form

@smallexample
$ gnatstub [switches] filename [directory]
@end smallexample

@noindent
where
@table @code
@item filename
is the name of the source file that contains a library unit declaration
for which a body must be created. This name should follow the GNAT file name
conventions. No crunching is allowed for this file name. The file
name may contain the path information.

@item directory
indicates the directory to place a body stub (default is the
current directory)

@item switches
is an optional sequence of switches as described in the next section
@end table

@node Switches for gnatstub
@section Switches for @code{gnatstub}

@table @code

@item -f
If the destination directory already contains a file with a name of the body file
for the argument spec file, replace it with the generated body stub.

@item -hs
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.

@item -hg
Put a sample comment header into the body stub.

@item -IDIR
@itemx -I-
These switches have the same meaning as in calls to gcc.
They define the source search path in the call to gcc issued
by @code{gnatstub} to compile an argument source file.

@item -i@var{n}
(@var{n} is a decimal natural number). Set the indentation level in the
generated body sample to n, '-i0' means "no indentation",
the default indentation is 3.

@item -k
Do not remove the tree file (i.e. the snapshot of the compiler internal
structures used by @code{gnatstub}) after creating the body stub.

@item -l@var{n}
(@var{n} is a decimal positive number) Set the maximum line length in the
body stub to n, the default is 78.

@item -q
Quiet mode: do not generate a confirmation when a body is
successfully created or a message when a body is not required for an
argument unit.

@item -r
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. @code{-r}
also implies @code{-k}, whether or not
@code{-k} is set explicitly.

@item -t
Overwrite the existing tree file: if the current directory already
contains the file which, according to the GNAT file name 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 body sampler,
unless @code{-t} option is set

@item -v
Verbose mode: generate version information.

@end table

@node Reducing the Size of Ada Executables with gnatelim
@chapter Reducing the Size of Ada Executables with @code{gnatelim}
@findex gnatelim

@menu
* About gnatelim::
* Eliminate Pragma::
* Tree Files::
* Preparing Tree and Bind Files for gnatelim::
* Running gnatelim::
* Correcting the List of Eliminate Pragmas::
* Making Your Executables Smaller::
* Summary of the gnatelim Usage Cycle::
@end menu

@node About gnatelim
@section About @code{gnatelim}

@noindent
When 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.

@code{gnatelim} tracks unused subprograms in an Ada program and
outputs a list of GNAT-specific @code{Eliminate} pragmas (see next
section) marking all the subprograms that are declared but never called.
By placing the list of @code{Eliminate} pragmas in the GNAT configuration
file @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.

@code{gnatelim} needs as its input data a set of tree files
(see @ref{Tree Files}) representing all the components of a program to
process and a bind file for a main subprogram (see
@ref{Preparing Tree and Bind Files for gnatelim}).

@node Eliminate Pragma
@section @code{Eliminate} Pragma
@findex Eliminate

@noindent
The simplified syntax of the Eliminate pragma used by @code{gnatelim} is:

@smallexample
@cartouche
@b{pragma} Eliminate (Library_Unit_Name, Subprogram_Name);
@end cartouche
@end smallexample

@noindent
where
@table @code
@item Library_Unit_Name
full expanded Ada name of a library unit

@item Subprogram_Name
a simple or expanded name of a subprogram declared within this
compilation unit

@end table

@noindent
The effect of an @code{Eliminate} pragma placed in the GNAT configuration
file @file{gnat.adc} is:

@itemize @bullet

@item
If the subprogram @code{Subprogram_Name} is declared within
the library unit @code{Library_Unit_Name}, the compiler will not generate
code for this subprogram. This applies to all overloaded subprograms denoted
by @code{Subprogram_Name}.

@item
If a subprogram marked by the pragma @code{Eliminate} is used (called)
in a program, the compiler will produce an error message in the place where
it is called.
@end itemize

@node Tree Files
@section Tree Files
@cindex Tree file

@noindent
A tree file stores a snapshot of the compiler internal data
structures at the very end of a successful compilation. It contains all the
syntactic and semantic information for the copmiled unit and all the
units upon which it depends semantically.
To use tools that make use of tree files, you
need to first produce the right set of tree files.

GNAT produces correct tree files when -gnatt -gnatc options are set
in a gcc call. The tree files have an .adt extension.
Therefore, to produce a tree file for the compilation unit contained in a file
named @file{foo.adb}, you must use the command

@smallexample
$ gcc -c -gnatc -gnatt foo.adb
@end smallexample

@noindent
and you will get the tree file @file{foo.adt}.
compilation.

@node Preparing Tree and Bind Files for gnatelim
@section Preparing Tree and Bind Files for @code{gnatelim}

@noindent
A set of tree files covering the program to be analyzed with
@code{gnatelim} and
the bind file for the main subprogram does not have to
be in the current directory.
'-T' gnatelim option may be used to provide
the search path for tree files, and '-b'
option may be used to point to the bind
file to process (see @ref{Running gnatelim})

If you do not have the appropriate set of tree
files and the right bind file, you
may create them in the current directory using the following procedure.

Let @code{Main_Prog} be the name of a main subprogram, and suppose
this subprogram is in a file named @file{main_prog.adb}.

To create a bind file for @code{gnatelim}, run @code{gnatbind} for
the main subprogram. @code{gnatelim} can work with both Ada and C
bind files; when both are present, it uses the Ada bind file.
The following commands will build the program and create the bind file:

@smallexample
$ gnatmake -c Main_Prog
$ gnatbind main_prog
@end smallexample

@noindent
To create a minimal set of tree files covering the whole program, call
@code{gnatmake} for this program as follows:

@smallexample
$ gnatmake -f -c -gnatc -gnatt Main_Prog
@end smallexample

@noindent
The @code{-c} gnatmake option turns off the bind and link steps,
that are useless anyway because the sources are compiled with
@code{-gnatc} option which turns off code generation.

The @code{-f} gnatmake option forces
recompilation of all the needed sources.

This sequence of actions will create all the data needed by @code{gnatelim}
from scratch and therefore guarantee its consistency. If you would like to
use some existing set of files as @code{gnatelim} output, you must make
sure that the set of files is complete and consistent. You can use the
@code{-m} switch to check if there are missed tree files

Note, that @code{gnatelim} needs neither object nor ALI files.

@node Running gnatelim
@section Running @code{gnatelim}

@noindent
@code{gnatelim} has the following command-line interface:

@smallexample
$ gnatelim [options] name
@end smallexample

@noindent
@code{name} should be a full expanded Ada name of a main subprogram
of a program (partition).

@code{gnatelim} options:

@table @code
@item -q
Quiet mode: by default @code{gnatelim} generates to the standard error
stream a trace of the source file names of the compilation units being
processed. This option turns this trace off.

@item -v
Verbose mode: @code{gnatelim} version information is printed as Ada
comments to the standard output stream.

@item -a
Also look for subprograms from the GNAT run time that can be eliminated.

@item -m
Check if any tree files are missing for an accurate result.

@item \-T\@var{dir}
When looking for tree files also look in directory @var{dir}

@item \-b\@var{bind_file}
Specifices @var{bind_file} as the bind file to process. If not set, the name
of the bind file is computed from the full expanded Ada name of a main subprogram.

@item -d@var{x}
Activate internal debugging switches. @var{x} is a letter or digit, or
string of letters or digits, which specifies the type of debugging
mode 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 @code{Gnatelim.Options} unit in the compiler
source file @file{gnatelim-options.adb}.
@end table

@noindent
@code{gnatelim} sends its output to the standard output stream, and all the
tracing and debug information is sent to the standard error stream.
In order to produce a proper GNAT configuration file
@file{gnat.adc}, redirection must be used:

@smallexample
$ gnatelim Main_Prog > gnat.adc
@end smallexample

@noindent
or

@smallexample
$ gnatelim Main_Prog >> gnat.adc
@end smallexample

@noindent
In order to append the @code{gnatelim} output to the existing contents of
@file{gnat.adc}.

@node Correcting the List of Eliminate Pragmas
@section Correcting the List of Eliminate Pragmas

@noindent
In some rare cases it may happen that @code{gnatelim} will try to eliminate
subprograms which are actually called in the program. In this case, the
compiler will generate an error message of the form:

@smallexample
file.adb:106:07: cannot call eliminated subprogram "My_Prog"
@end smallexample

@noindent
You will need to manually remove the wrong @code{Eliminate} pragmas from
the @file{gnat.adc} file. It is advised that you recompile your program
from scratch after that because you need a consistent @file{gnat.adc} file
during the entire compilation.

@node Making Your Executables Smaller
@section Making Your Executables Smaller

@noindent
In order to get a smaller executable for your program you now have to
recompile the program completely with the new @file{gnat.adc} file
created by @code{gnatelim} in your current directory:

@smallexample
$ gnatmake -f Main_Prog
@end smallexample

@noindent
(you will need @code{-f} option for gnatmake to
recompile everything
with the set of pragmas @code{Eliminate} you have obtained with
@code{gnatelim}).

Be aware that the set of @code{Eliminate} pragmas is specific to each
program. It is not recommended to merge sets of @code{Eliminate}
pragmas created for different programs in one @file{gnat.adc} file.

@node Summary of the gnatelim Usage Cycle
@section Summary of the gnatelim Usage Cycle

@noindent
Here is a quick summary of the steps to be taken in order to reduce
the size of your executables with @code{gnatelim}. You may use
other GNAT options to control the optimization level,
to produce the debugging information, to set search path, etc.

@enumerate
@item
Produce a bind file and a set of tree files

@smallexample
$ gnatmake -c Main_Prog
$ gnatbind main_prog
$ gnatmake -f -c -gnatc -gnatt Main_Prog
@end smallexample

@item
Generate a list of @code{Eliminate} pragmas
@smallexample
$ gnatelim Main_Prog >[>] gnat.adc
@end smallexample

@item
Recompile the application

@smallexample
$ gnatmake -f Main_Prog
@end smallexample

@end enumerate

@node Other Utility Programs
@chapter Other Utility Programs

@noindent
This chapter discusses some other utility programs available in the Ada
environment.

@menu
* Using Other Utility Programs with GNAT::
* The gnatpsys Utility Program::
* The gnatpsta Utility Program::
* The External Symbol Naming Scheme of GNAT::
* Ada Mode for Glide::
* Converting Ada Files to html with gnathtml::
* Installing gnathtml::
@end menu

@node Using Other Utility Programs with GNAT
@section Using Other Utility Programs with GNAT

@noindent
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), @code{gdb} (the FSF debugger), and utilities such
as Purify.

@node The gnatpsys Utility Program
@section The @code{gnatpsys} Utility Program

@noindent
Many of the definitions in package System are implementation-dependent.
Furthermore, although the source of the package System is available
for inspection, it uses special attributes for parameterizing many of
the critical values, so the source is not informative for the casual user.

The @code{gnatpsys} utility is designed to deal with this situation.
It is an Ada program that dynamically determines the
values of all the relevant parameters in System, and prints them
out in the form of an Ada source listing for System, displaying all
the values of interest. This output is generated to
@file{stdout}.

To determine the value of any parameter in package System, simply
run @code{gnatpsys} with no qualifiers or arguments, and examine
the output. This is preferable to consulting documentation, because
you know that the values you are getting are the actual ones provided
by the executing system.

@node The gnatpsta Utility Program
@section The @code{gnatpsta} Utility Program

@noindent
Many of the definitions in package Standard are implementation-dependent.
However, the source of this package does not exist as an Ada source
file, so these values cannot be determined by inspecting the source.
They can be determined by examining in detail the coding of
@file{cstand.adb} which creates the image of Standard in the compiler,
but this is awkward and requires a great deal of internal knowledge
about the system.

The @code{gnatpsta} utility is designed to deal with this situation.
It is an Ada program that dynamically determines the
values of all the relevant parameters in Standard, and prints them
out in the form of an Ada source listing for Standard, displaying all
the values of interest. This output is generated to
@file{stdout}.

To determine the value of any parameter in package Standard, simply
run @code{gnatpsta} with no qualifiers or arguments, and examine
the output. This is preferable to consulting documentation, because
you know that the values you are getting are the actual ones provided
by the executing system.

@node The External Symbol Naming Scheme of GNAT
@section The External Symbol Naming Scheme of GNAT

@noindent
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:

@smallexample
@group
@cartouche
@b{package} QRS @b{is}
   MN : Integer;
@b{end} QRS;
@end cartouche
@end group
@end smallexample

@noindent
The variable @code{MN} has a full expanded Ada name of @code{QRS.MN}, so
the corresponding link name is @code{qrs__mn}.
@findex Export
Of course if a @code{pragma Export} is used this may be overridden:

@smallexample
@group
@cartouche
@b{package} Exports @b{is}
   Var1 : Integer;
   @b{pragma} Export (Var1, C, External_Name => "var1_name");
   Var2 : Integer;
   @b{pragma} Export (Var2, C, Link_Name => "var2_link_name");
@b{end} Exports;
@end cartouche
@end group
@end smallexample

@noindent
In this case, the link name for @var{Var1} is whatever link name the
C compiler would assign for the C function @var{var1_name}. This typically
would be either @var{var1_name} or @var{_var1_name}, depending on operating
system conventions, but other possibilities exist. The link name for
@var{Var2} is @var{var2_link_name}, and this is not operating system
dependent.

@findex _main
One exception occurs for library level procedures. A potential ambiguity
arises between the required name @code{_main} for the C main program,
and the name we would otherwise assign to an Ada library level procedure
called @code{Main} (which might well not be the main program).

To avoid this ambiguity, we attach the prefix @code{_ada_} to such
names. So if we have a library level procedure such as

@smallexample
@group
@cartouche
@b{procedure} Hello (S : String);
@end cartouche
@end group
@end smallexample

@noindent
the external name of this procedure will be @var{_ada_hello}.

@node Ada Mode for Glide
@section Ada Mode for @code{Glide}

@noindent
The Glide mode for programming in Ada (both, Ada83 and Ada95) helps the
user in understanding existing code and facilitates writing new code. It
furthermore provides some utility functions for easier integration of
standard Emacs features when programming in Ada.

@subsection General Features:

@itemize @bullet
@item
Full Integrated Development Environment :

@itemize @bullet
@item
support of 'project files' for the configuration (directories,
compilation options,...)

@item
compiling and stepping through error messages.

@item
running and debugging your applications within Glide.
@end itemize

@item
easy to use for beginners by pull-down menus,

@item
user configurable by many user-option variables.
@end itemize

@subsection Ada Mode Features That Help Understanding Code:

@itemize @bullet
@item
functions for easy and quick stepping through Ada code,

@item
getting cross reference information for identifiers (e.g. find the
defining place by a keystroke),

@item
displaying an index menu of types and subprograms and move point to
the chosen one,

@item
automatic color highlighting of the various entities in Ada code.
@end itemize

@subsection Glide Support for Writing Ada Code:

@itemize @bullet
@item
switching between spec and body files with possible
autogeneration of body files,

@item
automatic formating of subprograms parameter lists.

@item
automatic smart indentation according to Ada syntax,

@item
automatic completion of identifiers,

@item
automatic casing of identifiers, keywords, and attributes,

@item
insertion of statement templates,

@item
filling comment paragraphs like filling normal text,
@end itemize

For more information, please see @xref{Ada Mode for Glide}.

@node Converting Ada Files to html with gnathtml
@section Converting Ada Files to html with @code{gnathtml}

@noindent
This @code{Perl} script allows Ada source files to be browsed using
standard Web browsers. For installation procedure, see the section
@xref{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 @code{-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:
@smallexample
$ perl gnathtml.pl [switches] ada-files
@end smallexample

You can pass it as many Ada files as you want. @code{gnathtml} will generate
an html file for every ada file, and a global file called @file{index.htm}.
This file is an index of every identifier defined in the files.

The available switches are the following ones :

@table @code
@item -83
@cindex @code{-83} (@code{gnathtml})
Only the subset on the Ada 83 keywords will be highlighted, not the full
Ada 95 keywords set.

@item -cc @var{color}
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.

@item -d
@cindex @code{-d} (@code{gnathtml})
If the ada files depend on some other files (using for instance the
@code{with} command, the latter 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.

@item -D
This command is the same as -d above, but @code{gnathtml} will also look
for files in the run-time library, and generate html files for them.

@item -f
@cindex @code{-f} (@code{gnathtml})
By default, gnathtml will generate html links only for global entities
('with'ed units, global variables and types,...). If you specify the
@code{-f} on the command line, then links will be generated for local
entities too.

@item -l @var{number}
@cindex @code{-l} (@code{gnathtml})
If this switch is provided and @var{number} is not 0, then @code{gnathtml}
will number the html files every @var{number} line.

@item -I @var{dir}
@cindex @code{-I} (@code{gnathtml})
Specify a directory to search for library files (@file{.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.

@item -o @var{dir}
@cindex @code{-o} (@code{gnathtml})
Specify the output directory for html files. By default, gnathtml will
saved the generated html files in a subdirectory named @file{html/}.

@item -p @var{file}
@cindex @code{-p} (@code{gnathtml})
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 be using @file{.adp} 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.

@item -sc @var{color}
@cindex @code{-sc} (@code{gnathtml})
This option 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.

@item -t @var{file}
@cindex @code{-t} (@code{gnathtml})
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.

@end table

@node Installing gnathtml
@section Installing @code{gnathtml}

@noindent
@code{Perl} needs to be installed on your machine to run this script.
@code{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
@code{gnathtml},  to explicitly  tell  the Operating  system  where Perl
is. The syntax of this line is :
@smallexample
#!full_path_name_to_perl
@end smallexample

@noindent
Alternatively, you may run the script using the following command line:

@smallexample
$ perl gnathtml.pl [switches] files
@end smallexample


@node Running and Debugging Ada Programs
@chapter Running and Debugging Ada Programs
@cindex Debugging

@noindent
This chapter discusses how to debug Ada programs. An incorrect Ada program
may be handled in three ways by the GNAT compiler:

@enumerate
@item
The illegality may be a violation of the static semantics of Ada. In
that case GNAT diagnoses the constructs in the program that are illegal.
It is then a straightforward matter for the user to modify those parts of
the program.

@item
The illegality may be a violation of the dynamic semantics of Ada. In
that case the program compiles and executes, but may generate incorrect
results, or may terminate abnormally with some exception.

@item
When presented with a program that contains convoluted errors, GNAT
itself may terminate abnormally without providing full diagnostics on
the incorrect user program.
@end enumerate

@menu
* The GNAT Debugger GDB::
* Running GDB::
* Introduction to GDB Commands::
* Using Ada Expressions::
* Calling User-Defined Subprograms::
* Ada Exceptions::
* Ada Tasks::
* Debugging Generic Units::
* GNAT Abnormal Termination or Failure to Terminate::
* Naming Conventions for GNAT Source Files::
* Getting Internal Debugging Information::
@end menu

@cindex Debugger
@findex gdb

@node The GNAT Debugger GDB
@section The GNAT Debugger GDB

@noindent
@code{GDB} is a general purpose, platform-independent debugger that can
be used to
debug mixed-language programs compiled with @code{GCC}, and in particular
is capable of debugging Ada programs compiled with GNAT. The latest
versions of @code{GDB} are Ada-aware and can handle complex Ada data
structures.
The manual @cite{Debugging with GDB}
contains full details on the usage of @code{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 @code{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 @code{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 @code{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 @code{GDB}
were not present. This is a crucial part of the @code{GDB} design philosophy.
@code{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,
@code{GDB} accesses the debugging information and can respond to user
commands to inspect variables, and more generally to report on the state of
execution.

@node Running GDB
@section Running GDB

@noindent
The debugger can be launched directly and simply from emacs which allows
to browse and modify directly the source code during the debugging
session, @xref{Ada Mode for Glide}. Here is described the basic use of
@code{GDB} is text mode.

@noindent
The command to run @code{GDB} is

@smallexample
$ gdb program
@end smallexample

@noindent
where @code{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 @code{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 @code{GDB}.

@node Introduction to GDB Commands
@section Introduction to GDB Commands

@noindent
@code{GDB} contains a large repertoire of commands. The manual
@cite{Debugging with GDB}
includes extensive documentation on the use
of these commands, together with examples of their use. Furthermore,
the command @var{help} invoked from within @code{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 @code{GDB} is about. You should create
a simple program with debugging information and experiment with the use of
these @code{GDB} commands on the program as you read through the
following section.

@table @code
@item set args @var{arguments}
The @var{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 @code{set args}
command is not needed if the program does not require arguments.

@item run
The @code{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.

@item breakpoint @var{location}
The breakpoint command sets a breakpoint, that is to say a point at which
execution will halt and @code{GDB} will await further
commands. @var{location} is
either a line number within a file, given in the format @code{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 @code{GDB} signals that the breakpoint was encountered by
printing the line of code before which the program is halted.

@item breakpoint exception @var{name}
A special form of the breakpoint command which breakpoints whenever
exception @var{name} is raised.
If @var{name} is omitted,
then a breakpoint will occur when any exception is raised.

@item print @var{expression}
This will print the value of the given expression. Most simple
Ada expression formats are properly handled by @code{GDB}, so the expression
can contain function calls, variables, operators, and attribute references.

@item continue
Continues execution following a breakpoint, until the next breakpoint or the
termination of the program.

@item step
Executes a single line after a breakpoint. If the next statement is a subprogram
call, execution continues into (the first statement of) the
called subprogram.

@item next
Executes a single line. If this line is a subprogram call, executes and
returns from the call.

@item list
Lists 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.

@item backtrace
Displays 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.

@item up
At a breakpoint, @code{GDB} can display the values of variables local
to the current frame. The command @code{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.

@item down
Moves the focus of @code{GDB} down from the frame currently being
examined to the frame of its callee (the reverse of the previous command),

@item frame @var{n}
Inspect 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.

@end table

The above list is a very short introduction to the commands that
@code{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 @cite{Debugging with GDB}.
Note that most commands can be abbreviated
(for example, c for continue, bt for backtrace).

@node Using Ada Expressions
@section Using Ada Expressions
@cindex Ada expressions

@noindent
@code{GDB} supports a fairly large subset of Ada expression syntax, with some
extensions. The philosophy behind the design of this subset is

@itemize @bullet
@item
That @code{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 @code{GDB}).

@item
That type safety and strict adherence to Ada language restrictions
are not particularly important to the @code{GDB} user.

@item
That brevity is important to the @code{GDB} user.
@end itemize

Thus, for brevity, the debugger acts as if there were
implicit @code{with} and @code{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,
@code{GDB} asks the user's intent.

For details on the supported Ada syntax, see @cite{Debugging with GDB}.

@node Calling User-Defined Subprograms
@section Calling User-Defined Subprograms

@noindent
An important capability of @code{GDB} is the ability to call user-defined
subprograms while debugging. This is achieved simply by entering
a subprogram call statement in the form:

@smallexample
call subprogram-name (parameters)
@end smallexample

@noindent
The keyword @code{call} can be omitted in the normal case where the
@code{subprogram-name} does not coincide with any of the predefined
@code{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 @code{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
@code{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 @code{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.

@node Ada Exceptions
@section Breaking on Ada Exceptions
@cindex Exceptions

@noindent
You can set breakpoints that trip when your program raises
selected exceptions.

@table @code
@item break exception
Set a breakpoint that trips whenever (any task in the) program raises
any exception.

@item break exception @var{name}
Set a breakpoint that trips whenever (any task in the) program raises
the exception @var{name}.

@item break exception unhandled
Set a breakpoint that trips whenever (any task in the) program raises an
exception for which there is no handler.

@item info exceptions
@itemx info exceptions @var{regexp}
The @code{info exceptions} command permits the user to examine all defined
exceptions within Ada programs. With a regular expression, @var{regexp}, as
argument, prints out only those exceptions whose name matches @var{regexp}.
@end table

@node Ada Tasks
@section Ada Tasks
@cindex Tasks

@noindent
@code{GDB} allows the following task-related commands:

@table @code
@item info tasks
This command shows a list of current Ada tasks, as in the following example:

@smallexample
@iftex
@leftskip=0cm
@end iftex
(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
@end smallexample

@noindent
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.

@item break @var{linespec} task @var{taskid}
@itemx break @var{linespec} task @var{taskid} if @dots{}
@cindex Breakpoints and tasks
These commands are like the @code{break @dots{} thread @dots{}}.
@var{linespec} specifies source lines.

Use the qualifier @samp{task @var{taskid}} with a breakpoint command
to specify that you only want @code{GDB} to stop the program when a
particular Ada task reaches this breakpoint. @var{taskid} is one of the
numeric task identifiers assigned by @code{GDB}, shown in the first
column of the @samp{info tasks} display.

If you do not specify @samp{task @var{taskid}} when you set a
breakpoint, the breakpoint applies to @emph{all} tasks of your
program.

You can use the @code{task} qualifier on conditional breakpoints as
well; in this case, place @samp{task @var{taskid}} before the
breakpoint condition (before the @code{if}).

@item task @var{taskno}
@cindex Task switching

This command allows to switch to the task referred by @var{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
perturbated.
@end table

@noindent
For more detailed information on the tasking support, see @cite{Debugging with GDB}.

@node Debugging Generic Units
@section Debugging Generic Units
@cindex Debugging Generic Units
@cindex Generics

@noindent
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
@code{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

@smallexample
@group
@cartouche
@b{procedure} g @b{is}

   @b{generic package} k @b{is}
      @b{procedure} kp (v1 : @b{in out} integer);
   @b{end} k;

   @b{package body} k @b{is}
      @b{procedure} kp (v1 : @b{in out} integer) @b{is}
      @b{begin}
         v1 := v1 + 1;
      @b{end} kp;
   @b{end} k;

   @b{package} k1 @b{is new} k;
   @b{package} k2 @b{is new} k;

   var : integer := 1;

@b{begin}
   k1.kp (var);
   k2.kp (var);
   k1.kp (var);
   k2.kp (var);
@b{end};
@end cartouche
@end group
@end smallexample

@noindent
Then to break on a call to procedure kp in the k2 instance, simply
use the command:

@smallexample
(gdb) break g.k2.kp
@end smallexample

@noindent
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.


@node GNAT Abnormal Termination or Failure to Terminate
@section GNAT Abnormal Termination or Failure to Terminate
@cindex GNAT Abnormal Termination or Failure to Terminate

@noindent
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.

@enumerate
@item
Run @code{gcc} with the @code{-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 @code{-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.

@item
Run @code{gcc} with the @code{-v (verbose)} switch. In this mode,
@code{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.

@item
@cindex @code{-gnatdc} switch
Run @code{gcc} with the @code{-gnatdc} switch. This is a GNAT specific
switch that does for the front-end what @code{-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.
@item
Finally, you can start
@code{gdb} directly on the @code{gnat1} executable. @code{gnat1} is the
front-end of GNAT, and can be run independently (normally it is just
called from @code{gcc}). You can use @code{gdb} on @code{gnat1} as you
would on a C program (but @pxref{The GNAT Debugger GDB} for caveats). The
@code{where} command is the first line of attack; the variable
@code{lineno} (seen by @code{print lineno}), used by the second phase of
@code{gnat1} and by the @code{gcc} backend, indicates the source line at
which the execution stopped, and @code{input_file name} indicates the name of
the source file.
@end enumerate

@node Naming Conventions for GNAT Source Files
@section Naming Conventions for GNAT Source Files

@noindent
In order to examine the workings of the GNAT system, the following
brief description of its organization may be helpful:

@itemize @bullet
@item
Files with prefix @file{sc} contain the lexical scanner.

@item
All files prefixed with @file{par} are components of the parser. The
numbers correspond to chapters of the Ada 95 Reference Manual. For example,
parsing of select statements can be found in @file{par-ch9.adb}.

@item
All files prefixed with @file{sem} perform semantic analysis. The
numbers correspond to chapters of the Ada standard. For example, all
issues involving context clauses can be found in @file{sem_ch10.adb}. In
addition, some features of the language require sufficient special processing
to justify their own semantic files: sem_aggr for aggregates, sem_disp for
dynamic dispatching, etc.

@item
All files prefixed with @file{exp} perform normalization and
expansion of the intermediate representation (abstract syntax tree, or AST).
these files use the same numbering scheme as the parser and semantics files.
For example, the construction of record initialization procedures is done in
@file{exp_ch3.adb}.

@item
The files prefixed with @file{bind} implement the binder, which
verifies the consistency of the compilation, determines an order of
elaboration, and generates the bind file.

@item
The files @file{atree.ads} and @file{atree.adb} detail the low-level
data structures used by the front-end.

@item
The files @file{sinfo.ads} and @file{sinfo.adb} detail the structure of
the abstract syntax tree as produced by the parser.

@item
The files @file{einfo.ads} and @file{einfo.adb} detail the attributes of
all entities, computed during semantic analysis.

@item
Library management issues are dealt with in files with prefix
@file{lib}.

@item
@findex Ada
@cindex Annex A
Ada files with the prefix @file{a-} are children of @code{Ada}, as
defined in Annex A.

@item
@findex Interfaces
@cindex Annex B
Files with prefix @file{i-} are children of @code{Interfaces}, as
defined in Annex B.

@item
@findex System
Files with prefix @file{s-} are children of @code{System}. This includes
both language-defined children and GNAT run-time routines.

@item
@findex GNAT
Files with prefix @file{g-} are children of @code{GNAT}. These are useful
general-purpose packages, fully documented in their specifications. All
the other @file{.c} files are modifications of common @code{gcc} files.
@end itemize

@node Getting Internal Debugging Information
@section Getting Internal Debugging Information

@noindent
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 @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.





@node Performance Considerations
@chapter Performance Considerations
@cindex Performance

@noindent
The GNAT system provides a number of options that allow a trade-off
between

@itemize @bullet
@item
performance of the generated code

@item
speed of compilation

@item
minimization of dependences and recompilation

@item
the degree of run-time checking.
@end itemize

@noindent
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:

@itemize @bullet
@item
no optimization

@item
no inlining of subprogram calls

@item
all run-time checks enabled except overflow and elaboration checks
@end itemize

@noindent
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.

@menu
* Controlling Run-Time Checks::
* Optimization Levels::
* Debugging Optimized Code::
* Inlining of Subprograms::
@end menu

@node Controlling Run-Time Checks
@section Controlling Run-Time Checks

@noindent
By default, GNAT produces all run-time checks, except arithmetic overflow
checking for integer operations (that includes division by zero) and checks
for access before elaboration on subprogram calls.
@cindex @code{-gnatp} (@code{gcc})
@cindex @code{-gnato} (@code{gcc})
Two gnat switches, @code{-gnatp} and @code{-gnato} allow this default to
be modified. @xref{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.

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.

@cindex Overflow checks
@cindex Checks, overflow
@findex Suppress
@findex Unsuppress
@cindex pragma Suppress
@cindex pragma Unsuppress
Note that the setting of the switches controls the default setting of
the checks. They may be modified using either @code{pragma Suppress} (to
remove checks) or @code{pragma Unsuppress} (to add back suppressed
checks) in the program source.

@node Optimization Levels
@section Optimization Levels
@cindex @code{-O} (@code{gcc})

@noindent
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
@code{-O@var{n}} switch, where @var{n} is an integer from 0 to 3,
on the @code{gcc} command line to control the optimization level:

@table @code
@item -O0
no optimization (the default)

@item -O1
medium level optimization

@item -O2
full optimization

@item -O3
full optimization, and also attempt automatic inlining of small
subprograms within a unit (@pxref{Inlining of Subprograms}).
@end table

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.

Note: Unlike some other compilation systems, @code{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 @emph{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.

@node Debugging Optimized Code
@section Debugging Optimized Code

@noindent
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.  This
section describes the most common cases.

@enumerate
@item
@i{The "hopping Program Counter":}  Repeated 'step' or 'next' commands show the PC
bouncing back and forth in the code.  This may result from any of the following
optimizations:

@itemize @bullet
@item
@i{Common subexpression elimination:} using a single instance of code for a
quantity that the source computes several times.  As a result you
may not be able to stop on what looks like a statement.

@item
@i{Invariant code motion:} moving an expression that does not change within a
loop, to the beginning of the loop.

@item
@i{Instruction scheduling:} moving instructions so as to
overlap loads and stores (typically) with other code, or in
general to move computations of values closer to their uses. Often
this causes you to pass an assignment statement without the assignment
happening and then later bounce back to the statement when the
value is actually needed.  Placing a breakpoint on a line of code
and then stepping over it may, therefore, not always cause all the
expected side-effects.
@end itemize

@item
@i{The "big leap":} More commonly known as @i{cross-jumping}, in which two
identical pieces of code are merged and the program counter suddenly
jumps to a statement that is not supposed to be executed, simply because
it (and the code following) translates to the same thing as the code
that @emph{was} supposed to be executed.  This effect is typically seen in
sequences that end in a jump, such as a @code{goto}, a @code{return}, or
a @code{break} in a C @code{switch} statement.

@item
@i{The "roving variable":} The symptom is an unexpected value in a variable.
There are various reasons for this effect:

@itemize @bullet
@item
In a subprogram prologue, a parameter may not yet have been moved to its
"home".

@item
A variable may be dead, and its register re-used.  This is
probably the most common cause.

@item
As mentioned above, the assignment of a value to a variable may
have been moved.

@item
A variable may be eliminated entirely by value propagation or
other means.  In this case, GCC may incorrectly generate debugging
information for the variable
@end itemize

@noindent
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 @emph{from} the point of the
strange value to see if code motion had simply moved the variable's
assignments later.
@end enumerate

@node Inlining of Subprograms
@section Inlining of Subprograms

@noindent
A call to a subprogram in the current unit is inlined if all the
following conditions are met:

@itemize @bullet
@item
The optimization level is at least @code{-O1}.

@item
The called subprogram is suitable for inlining: It must be small enough
and not contain nested subprograms or anything else that @code{gcc}
cannot support in inlined subprograms.

@item
The call occurs after the definition of the body of the subprogram.

@item
@cindex pragma Inline
@findex Inline
Either @code{pragma Inline} applies to the subprogram or it is
small and automatic inlining (optimization level @code{-O3}) is
specified.
@end itemize

@noindent
Calls to subprograms in @code{with}'ed units are normally not inlined.
To achieve this level of inlining, the following conditions must all be
true:

@itemize @bullet
@item
The optimization level is at least @code{-O1}.

@item
The called subprogram is suitable for inlining: It must be small enough
and not contain nested subprograms or anything else @code{gcc} cannot
support in inlined subprograms.

@item
The call appears in a body (not in a package spec).

@item
There is a @code{pragma Inline} for the subprogram.

@item
@cindex @code{-gnatn} (@code{gcc})
The @code{-gnatn} switch
is used in the @code{gcc} command line
@end itemize

Note that specifying the @code{-gnatn} switch causes additional
compilation dependencies. Consider the following:

@smallexample
@group
@cartouche
@b{package} R @b{is}
   @b{procedure} Q;
   @b{pragma} Inline (Q);
@b{end} R;
@b{package body} R @b{is}
   ...
@b{end} R;

@b{with} R;
@b{procedure} Main @b{is}
@b{begin}
   ...
   R.Q;
@b{end} Main;
@end cartouche
@end group
@end smallexample

@noindent
With the default behavior (no @code{-gnatn} switch specified), the
compilation of the @code{Main} procedure depends only on its own source,
@file{main.adb}, and the spec of the package in file @file{r.ads}. This
means that editing the body of @code{R} does not require recompiling
@code{Main}.

On the other hand, the call @code{R.Q} is not inlined under these
circumstances. If the @code{-gnatn} switch is present when @code{Main}
is compiled, the call will be inlined if the body of @code{Q} is small
enough, but now @code{Main} depends on the body of @code{R} in
@file{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 @code{gcc}.

The use of front end inlining with @code{-gnatN} generates similar
additional dependencies.

@cindex @code{-fno-inline} (@code{gcc})
Note: The @code{-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
@code{-gnatn} will still be active, even if
this switch is used to suppress the resulting inlining actions.


@node Index,, Performance Considerations, Top
@unnumbered Index

@printindex cp

@contents

@bye
