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.. |with| replace:: *with*
.. |withs| replace:: *with*\ s
.. |withed| replace:: *with*\ ed
.. |withing| replace:: *with*\ ing
.. -- Example: A |withing| unit has a |with| clause, it |withs| a |withed| unit
.. role:: switch(samp)
.. _Building_Executable_Programs_With_GNAT:
**************************************
Building Executable Programs with GNAT
**************************************
This chapter describes first the gnatmake tool
(:ref:`The_GNAT_Make_Program_gnatmake`),
which automatically determines the set of sources
needed by an Ada compilation unit and executes the necessary
(re)compilations, binding and linking.
It also explains how to use each tool individually: the
compiler (gcc, see :ref:`Compiling_with_gcc`),
binder (gnatbind, see :ref:`Binding_with_gnatbind`),
and linker (gnatlink, see :ref:`Linking_with_gnatlink`)
to build executable programs.
Finally, this chapter provides examples of
how to make use of the general GNU make mechanism
in a GNAT context (see :ref:`Using_the_GNU_make_Utility`).
.. only:: PRO or GPL
For building large systems with components possibly written
in different languages (such as Ada, C, C++ and Fortran)
and organized into subsystems and libraries, the GPRbuild
tool can be used. This tool, and the Project Manager
facility that it is based upon, is described in
*GPRbuild and GPR Companion Tools User's Guide*.
.. _The_GNAT_Make_Program_gnatmake:
Building with ``gnatmake``
==========================
.. index:: gnatmake
A typical development cycle when working on an Ada program consists of
the following steps:
#. Edit some sources to fix bugs;
#. Add enhancements;
#. Compile all sources affected;
#. Rebind and relink; and
#. Test.
.. index:: Dependency rules (compilation)
The third step in particular can be tricky, because not only do the modified
files have to be compiled, but any files depending on these files must also be
recompiled. The dependency rules in Ada can be quite complex, especially
in the presence of overloading, ``use`` clauses, generics and inlined
subprograms.
``gnatmake`` automatically takes care of the third and fourth steps
of this process. It determines which sources need to be compiled,
compiles them, and binds and links the resulting object files.
Unlike some other Ada make programs, the dependencies are always
accurately recomputed from the new sources. The source based approach of
the GNAT compilation model makes this possible. This means that if
changes to the source program cause corresponding changes in
dependencies, they will always be tracked exactly correctly by
``gnatmake``.
Note that for advanced forms of project structure, we recommend creating
a project file as explained in the *GNAT_Project_Manager* chapter in the
*GPRbuild User's Guide*, and using the
``gprbuild`` tool which supports building with project files and works similarly
to ``gnatmake``.
.. _Running_gnatmake:
Running ``gnatmake``
--------------------
The usual form of the ``gnatmake`` command is
.. code-block:: sh
$ gnatmake [<switches>] <file_name> [<file_names>] [<mode_switches>]
The only required argument is one ``file_name``, which specifies
a compilation unit that is a main program. Several ``file_names`` can be
specified: this will result in several executables being built.
If ``switches`` are present, they can be placed before the first
``file_name``, between ``file_names`` or after the last ``file_name``.
If ``mode_switches`` are present, they must always be placed after
the last ``file_name`` and all ``switches``.
If you are using standard file extensions (:file:`.adb` and
:file:`.ads`), then the
extension may be omitted from the ``file_name`` arguments. However, if
you are using non-standard extensions, then it is required that the
extension be given. A relative or absolute directory path can be
specified in a ``file_name``, in which case, the input source file will
be searched for in the specified directory only. Otherwise, the input
source file will first be searched in the directory where
``gnatmake`` was invoked and if it is not found, it will be search on
the source path of the compiler as described in
:ref:`Search_Paths_and_the_Run-Time_Library_RTL`.
All ``gnatmake`` output (except when you specify :switch:`-M`) is sent to
:file:`stderr`. The output produced by the
:switch:`-M` switch is sent to :file:`stdout`.
.. _Switches_for_gnatmake:
Switches for ``gnatmake``
-------------------------
You may specify any of the following switches to ``gnatmake``:
.. index:: --version (gnatmake)
:switch:`--version`
Display Copyright and version, then exit disregarding all other options.
.. index:: --help (gnatmake)
:switch:`--help`
If ``--version`` was not used, display usage, then exit disregarding
all other options.
.. index:: --GCC=compiler_name (gnatmake)
:switch:`--GCC={compiler_name}`
Program used for compiling. The default is ``gcc``. You need to use
quotes around ``compiler_name`` if ``compiler_name`` contains
spaces or other separator characters.
As an example ``--GCC="foo -x -y"``
will instruct ``gnatmake`` to use ``foo -x -y`` as your
compiler. A limitation of this syntax is that the name and path name of
the executable itself must not include any embedded spaces. Note that
switch :switch:`-c` is always inserted after your command name. Thus in the
above example the compiler command that will be used by ``gnatmake``
will be ``foo -c -x -y``. If several ``--GCC=compiler_name`` are
used, only the last ``compiler_name`` is taken into account. However,
all the additional switches are also taken into account. Thus,
``--GCC="foo -x -y" --GCC="bar -z -t"`` is equivalent to
``--GCC="bar -x -y -z -t"``.
.. index:: --GNATBIND=binder_name (gnatmake)
:switch:`--GNATBIND={binder_name}`
Program used for binding. The default is ``gnatbind``. You need to
use quotes around ``binder_name`` if ``binder_name`` contains spaces
or other separator characters.
As an example ``--GNATBIND="bar -x -y"``
will instruct ``gnatmake`` to use ``bar -x -y`` as your
binder. Binder switches that are normally appended by ``gnatmake``
to ``gnatbind`` are now appended to the end of ``bar -x -y``.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.
.. index:: --GNATLINK=linker_name (gnatmake)
:switch:`--GNATLINK={linker_name}`
Program used for linking. The default is ``gnatlink``. You need to
use quotes around ``linker_name`` if ``linker_name`` contains spaces
or other separator characters.
As an example ``--GNATLINK="lan -x -y"``
will instruct ``gnatmake`` to use ``lan -x -y`` as your
linker. Linker switches that are normally appended by ``gnatmake`` to
``gnatlink`` are now appended to the end of ``lan -x -y``.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.
:switch:`--create-map-file`
When linking an executable, create a map file. The name of the map file
has the same name as the executable with extension ".map".
:switch:`--create-map-file={mapfile}`
When linking an executable, create a map file with the specified name.
.. index:: --create-missing-dirs (gnatmake)
:switch:`--create-missing-dirs`
When using project files (:switch:`-P{project}`), automatically create
missing object directories, library directories and exec
directories.
:switch:`--single-compile-per-obj-dir`
Disallow simultaneous compilations in the same object directory when
project files are used.
:switch:`--subdirs={subdir}`
Actual object directory of each project file is the subdirectory subdir of the
object directory specified or defaulted in the project file.
:switch:`--unchecked-shared-lib-imports`
By default, shared library projects are not allowed to import static library
projects. When this switch is used on the command line, this restriction is
relaxed.
:switch:`--source-info={source info file}`
Specify a source info file. This switch is active only when project files
are used. If the source info file is specified as a relative path, then it is
relative to the object directory of the main project. If the source info file
does not exist, then after the Project Manager has successfully parsed and
processed the project files and found the sources, it creates the source info
file. If the source info file already exists and can be read successfully,
then the Project Manager will get all the needed information about the sources
from the source info file and will not look for them. This reduces the time
to process the project files, especially when looking for sources that take a
long time. If the source info file exists but cannot be parsed successfully,
the Project Manager will attempt to recreate it. If the Project Manager fails
to create the source info file, a message is issued, but gnatmake does not
fail. ``gnatmake`` "trusts" the source info file. This means that
if the source files have changed (addition, deletion, moving to a different
source directory), then the source info file need to be deleted and recreated.
.. index:: -a (gnatmake)
:switch:`-a`
Consider all files in the make process, even the GNAT internal system
files (for example, the predefined Ada library files), as well as any
locked files. Locked files are files whose ALI file is write-protected.
By default,
``gnatmake`` does not check these files,
because the assumption is that the GNAT internal files are properly up
to date, and also that any write protected ALI files have been properly
installed. Note that if there is an installation problem, such that one
of these files is not up to date, it will be properly caught by the
binder.
You may have to specify this switch if you are working on GNAT
itself. The switch ``-a`` is also useful
in conjunction with ``-f``
if you need to recompile an entire application,
including run-time files, using special configuration pragmas,
such as a ``Normalize_Scalars`` pragma.
By default
``gnatmake -a`` compiles all GNAT
internal files with
``gcc -c -gnatpg`` rather than ``gcc -c``.
.. index:: -b (gnatmake)
:switch:`-b`
Bind only. Can be combined with :switch:`-c` to do
compilation and binding, but no link.
Can be combined with :switch:`-l`
to do binding and linking. When not combined with
:switch:`-c`
all the units in the closure of the main program must have been previously
compiled and must be up to date. The root unit specified by ``file_name``
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.
.. index:: -c (gnatmake)
:switch:`-c`
Compile only. Do not perform binding, except when :switch:`-b`
is also specified. Do not perform linking, except if both
:switch:`-b` and
:switch:`-l` are also specified.
If the root unit specified by ``file_name`` is not a main unit, this is the
default. Otherwise ``gnatmake`` will attempt binding and linking
unless all objects are up to date and the executable is more recent than
the objects.
.. index:: -C (gnatmake)
:switch:`-C`
Use a temporary mapping file. A mapping file is a way to communicate
to the compiler two mappings: from unit names to file names (without
any directory information) and from file names to path names (with
full directory information). A mapping file can make the compiler's
file searches faster, especially if there are many source directories,
or the sources are read over a slow network connection. If
:switch:`-P` is used, a mapping file is always used, so
:switch:`-C` is unnecessary; in this case the mapping file
is initially populated based on the project file. If
:switch:`-C` is used without
:switch:`-P`,
the mapping file is initially empty. Each invocation of the compiler
will add any newly accessed sources to the mapping file.
.. index:: -C= (gnatmake)
:switch:`-C={file}`
Use a specific mapping file. The file, specified as a path name (absolute or
relative) by this switch, should already exist, otherwise the switch is
ineffective. The specified mapping file will be communicated to the compiler.
This switch is not compatible with a project file
(-P`file`) or with multiple compiling processes
(-jnnn, when nnn is greater than 1).
.. index:: -d (gnatmake)
:switch:`-d`
Display progress for each source, up to date or not, as a single line:
::
completed x out of y (zz%)
If the file needs to be compiled this is displayed after the invocation of
the compiler. These lines are displayed even in quiet output mode.
.. index:: -D (gnatmake)
:switch:`-D {dir}`
Put all object files and ALI file in directory ``dir``.
If the :switch:`-D` switch is not used, all object files
and ALI files go in the current working directory.
This switch cannot be used when using a project file.
.. index:: -eI (gnatmake)
:switch:`-eI{nnn}`
Indicates that the main source is a multi-unit source and the rank of the unit
in the source file is nnn. nnn needs to be a positive number and a valid
index in the source. This switch cannot be used when ``gnatmake`` is
invoked for several mains.
.. index:: -eL (gnatmake)
.. index:: symbolic links
:switch:`-eL`
Follow all symbolic links when processing project files.
This should be used if your project uses symbolic links for files or
directories, but is not needed in other cases.
.. index:: naming scheme
This also assumes that no directory matches the naming scheme for files (for
instance that you do not have a directory called "sources.ads" when using the
default GNAT naming scheme).
When you do not have to use this switch (i.e., by default), gnatmake is able to
save a lot of system calls (several per source file and object file), which
can result in a significant speed up to load and manipulate a project file,
especially when using source files from a remote system.
.. index:: -eS (gnatmake)
:switch:`-eS`
Output the commands for the compiler, the binder and the linker
on standard output,
instead of standard error.
.. index:: -f (gnatmake)
:switch:`-f`
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 :switch:`-a` switch is also specified.
.. index:: -F (gnatmake)
:switch:`-F`
When using project files, if some errors or warnings are detected during
parsing and verbose mode is not in effect (no use of switch
-v), then error lines start with the full path name of the project
file, rather than its simple file name.
.. index:: -g (gnatmake)
:switch:`-g`
Enable debugging. This switch is simply passed to the compiler and to the
linker.
.. index:: -i (gnatmake)
:switch:`-i`
In normal mode, ``gnatmake`` compiles all object files and ALI files
into the current directory. If the :switch:`-i` switch is used,
then instead object files and ALI files that already exist are overwritten
in place. This means that once a large project is organized into separate
directories in the desired manner, then ``gnatmake`` will automatically
maintain and update this organization. If no ALI files are found on the
Ada object path (see :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, ``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.
.. index:: -j (gnatmake)
.. index:: Parallel make
:switch:`-j{n}`
Use ``n`` processes to carry out the (re)compilations. On a multiprocessor
machine compilations will occur in parallel. If ``n`` is 0, then the
maximum number of parallel compilations is the number of core processors
on the platform. In the event of compilation errors, messages from various
compilations might get interspersed (but ``gnatmake`` will give you the
full ordered list of failing compiles at the end). If this is problematic,
rerun the make process with n set to 1 to get a clean list of messages.
.. index:: -k (gnatmake)
:switch:`-k`
Keep going. Continue as much as possible after a compilation error. To
ease the programmer's task in case of compilation errors, the list of
sources for which the compile fails is given when ``gnatmake``
terminates.
If ``gnatmake`` is invoked with several :file:`file_names` and with this
switch, if there are compilation errors when building an executable,
``gnatmake`` will not attempt to build the following executables.
.. index:: -l (gnatmake)
:switch:`-l`
Link only. Can be combined with :switch:`-b` to binding
and linking. Linking will not be performed if combined with
:switch:`-c`
but not with :switch:`-b`.
When not combined with :switch:`-b`
all the units in the closure of the main program must have been previously
compiled and must be up to date, and the main program needs to have been bound.
The root unit specified by ``file_name``
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.
.. index:: -m (gnatmake)
:switch:`-m`
Specify that the minimum necessary amount of recompilations
be performed. In this mode ``gnatmake`` ignores time
stamp differences when the only
modifications to a source file consist in adding/removing comments,
empty lines, spaces or tabs. This means that if you have changed the
comments in a source file or have simply reformatted it, using this
switch will tell ``gnatmake`` not to recompile files that depend on it
(provided other sources on which these files depend have undergone no
semantic modifications). Note that the debugging information may be
out of date with respect to the sources if the :switch:`-m` switch causes
a compilation to be switched, so the use of this switch represents a
trade-off between compilation time and accurate debugging information.
.. index:: Dependencies, producing list
.. index:: -M (gnatmake)
:switch:`-M`
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 :switch:`-aI`
and :switch:`-I` switches. If you use
``gnatmake -M`` :switch:`-q`
(see below), only the source file names,
without relative paths, are output. If you just specify the :switch:`-M`
switch, dependencies of the GNAT internal system files are omitted. This
is typically what you want. If you also specify
the :switch:`-a` switch,
dependencies of the GNAT internal files are also listed. Note that
dependencies of the objects in external Ada libraries (see
switch :switch:`-aL{dir}` in the following list)
are never reported.
.. index:: -n (gnatmake)
:switch:`-n`
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.
.. index:: -o (gnatmake)
:switch:`-o {exec_name}`
Output executable name. The name of the final executable program will be
``exec_name``. If the :switch:`-o` switch is omitted the default
name for the executable will be the name of the input file in appropriate form
for an executable file on the host system.
This switch cannot be used when invoking ``gnatmake`` with several
:file:`file_names`.
.. index:: -p (gnatmake)
:switch:`-p`
Same as :switch:`--create-missing-dirs`
.. index:: -P (gnatmake)
:switch:`-P{project}`
Use project file ``project``. Only one such switch can be used.
.. -- Comment:
:ref:`gnatmake_and_Project_Files`.
.. index:: -q (gnatmake)
:switch:`-q`
Quiet. When this flag is not set, the commands carried out by
``gnatmake`` are displayed.
.. index:: -s (gnatmake)
:switch:`-s`
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,
:switch:`-O -O2` is different than :switch:`-O2 -O`, but :switch:`-g -O`
is equivalent to :switch:`-O -g`.
This switch is recommended when Integrated Preprocessing is used.
.. index:: -u (gnatmake)
:switch:`-u`
Unique. Recompile at most the main files. It implies -c. Combined with
-f, it is equivalent to calling the compiler directly. Note that using
-u with a project file and no main has a special meaning.
.. --Comment
(See :ref:`Project_Files_and_Main_Subprograms`.)
.. index:: -U (gnatmake)
:switch:`-U`
When used without a project file or with one or several mains on the command
line, is equivalent to -u. When used with a project file and no main
on the command line, all sources of all project files are checked and compiled
if not up to date, and libraries are rebuilt, if necessary.
.. index:: -v (gnatmake)
:switch:`-v`
Verbose. Display the reason for all recompilations ``gnatmake``
decides are necessary, with the highest verbosity level.
.. index:: -vl (gnatmake)
:switch:`-vl`
Verbosity level Low. Display fewer lines than in verbosity Medium.
.. index:: -vm (gnatmake)
:switch:`-vm`
Verbosity level Medium. Potentially display fewer lines than in verbosity High.
.. index:: -vm (gnatmake)
:switch:`-vh`
Verbosity level High. Equivalent to -v.
:switch:`-vP{x}`
Indicate the verbosity of the parsing of GNAT project files.
See :ref:`Switches_Related_to_Project_Files`.
.. index:: -x (gnatmake)
:switch:`-x`
Indicate that sources that are not part of any Project File may be compiled.
Normally, when using Project Files, only sources that are part of a Project
File may be compile. When this switch is used, a source outside of all Project
Files may be compiled. The ALI file and the object file will be put in the
object directory of the main Project. The compilation switches used will only
be those specified on the command line. Even when
:switch:`-x` is used, mains specified on the
command line need to be sources of a project file.
:switch:`-X{name}={value}`
Indicate that external variable ``name`` has the value ``value``.
The Project Manager will use this value for occurrences of
``external(name)`` when parsing the project file.
:ref:`Switches_Related_to_Project_Files`.
.. index:: -z (gnatmake)
:switch:`-z`
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.
.. rubric:: GCC switches
Any uppercase or multi-character switch that is not a ``gnatmake`` switch
is passed to ``gcc`` (e.g., :switch:`-O`, :switch:`-gnato,` etc.)
.. rubric:: Source and library search path switches
.. index:: -aI (gnatmake)
:switch:`-aI{dir}`
When looking for source files also look in directory ``dir``.
The order in which source files search is undertaken is
described in :ref:`Search_Paths_and_the_Run-Time_Library_RTL`.
.. index:: -aL (gnatmake)
:switch:`-aL{dir}`
Consider ``dir`` as being an externally provided Ada library.
Instructs ``gnatmake`` to skip compilation units whose :file:`.ALI`
files have been located in directory ``dir``. This allows you to have
missing bodies for the units in ``dir`` and to ignore out of date bodies
for the same units. You still need to specify
the location of the specs for these units by using the switches
:switch:`-aI{dir}` or :switch:`-I{dir}`.
Note: this switch is provided for compatibility with previous versions
of ``gnatmake``. The easier method of causing standard libraries
to be excluded from consideration is to write-protect the corresponding
ALI files.
.. index:: -aO (gnatmake)
:switch:`-aO{dir}`
When searching for library and object files, look in directory
``dir``. The order in which library files are searched is described in
:ref:`Search_Paths_for_gnatbind`.
.. index:: Search paths, for gnatmake
.. index:: -A (gnatmake)
:switch:`-A{dir}`
Equivalent to :switch:`-aL{dir}` :switch:`-aI{dir}`.
.. index:: -I (gnatmake)
:switch:`-I{dir}`
Equivalent to :switch:`-aO{dir} -aI{dir}`.
.. index:: -I- (gnatmake)
.. index:: Source files, suppressing search
:switch:`-I-`
Do not look for source files in the directory containing the source
file named in the command line.
Do not look for ALI or object files in the directory
where ``gnatmake`` was invoked.
.. index:: -L (gnatmake)
.. index:: Linker libraries
:switch:`-L{dir}`
Add directory ``dir`` to the list of directories in which the linker
will search for libraries. This is equivalent to
:switch:`-largs` :switch:`-L{dir}`.
Furthermore, under Windows, the sources pointed to by the libraries path
set in the registry are not searched for.
.. index:: -nostdinc (gnatmake)
:switch:`-nostdinc`
Do not look for source files in the system default directory.
.. index:: -nostdlib (gnatmake)
:switch:`-nostdlib`
Do not look for library files in the system default directory.
.. index:: --RTS (gnatmake)
:switch:`--RTS={rts-path}`
Specifies the default location of the run-time library. GNAT looks for the
run-time
in the following directories, and stops as soon as a valid run-time is found
(:file:`adainclude` or :file:`ada_source_path`, and :file:`adalib` or
:file:`ada_object_path` present):
* *<current directory>/$rts_path*
* *<default-search-dir>/$rts_path*
* *<default-search-dir>/rts-$rts_path*
* The selected path is handled like a normal RTS path.
.. _Mode_Switches_for_gnatmake:
Mode Switches for ``gnatmake``
------------------------------
The mode switches (referred to as ``mode_switches``) allow the
inclusion of switches that are to be passed to the compiler itself, the
binder or the linker. The effect of a mode switch is to cause all
subsequent switches up to the end of the switch list, or up to the next
mode switch, to be interpreted as switches to be passed on to the
designated component of GNAT.
.. index:: -cargs (gnatmake)
:switch:`-cargs {switches}`
Compiler switches. Here ``switches`` is a list of switches
that are valid switches for ``gcc``. They will be passed on to
all compile steps performed by ``gnatmake``.
.. index:: -bargs (gnatmake)
:switch:`-bargs {switches}`
Binder switches. Here ``switches`` is a list of switches
that are valid switches for ``gnatbind``. They will be passed on to
all bind steps performed by ``gnatmake``.
.. index:: -largs (gnatmake)
:switch:`-largs {switches}`
Linker switches. Here ``switches`` is a list of switches
that are valid switches for ``gnatlink``. They will be passed on to
all link steps performed by ``gnatmake``.
.. index:: -margs (gnatmake)
:switch:`-margs {switches}`
Make switches. The switches are directly interpreted by ``gnatmake``,
regardless of any previous occurrence of :switch:`-cargs`, :switch:`-bargs`
or :switch:`-largs`.
.. _Notes_on_the_Command_Line:
Notes on the Command Line
-------------------------
This section contains some additional useful notes on the operation
of the ``gnatmake`` command.
.. index:: Recompilation (by gnatmake)
* If ``gnatmake`` finds no ALI files, it recompiles the main program
and all other units required by the main program.
This means that ``gnatmake``
can be used for the initial compile, as well as during subsequent steps of
the development cycle.
* If you enter ``gnatmake foo.adb``, where ``foo``
is a subunit or body of a generic unit, ``gnatmake`` recompiles
:file:`foo.adb` (because it finds no ALI) and stops, issuing a
warning.
* In ``gnatmake`` the switch :switch:`-I`
is used to specify both source and
library file paths. Use :switch:`-aI`
instead if you just want to specify
source paths only and :switch:`-aO`
if you want to specify library paths
only.
* ``gnatmake`` will ignore any files whose ALI file is write-protected.
This may conveniently be used to exclude standard libraries from
consideration and in particular it means that the use of the
:switch:`-f` switch will not recompile these files
unless :switch:`-a` is also specified.
* ``gnatmake`` has been designed to make the use of Ada libraries
particularly convenient. Assume you have an Ada library organized
as follows: *obj-dir* contains the objects and ALI files for
of your Ada compilation units,
whereas *include-dir* contains the
specs of these units, but no bodies. Then to compile a unit
stored in ``main.adb``, which uses this Ada library you would just type:
.. code-block:: sh
$ gnatmake -aI`include-dir` -aL`obj-dir` main
* Using ``gnatmake`` along with the :switch:`-m (minimal recompilation)`
switch provides a mechanism for avoiding unnecessary recompilations. Using
this switch,
you can update the comments/format of your
source files without having to recompile everything. Note, however, that
adding or deleting lines in a source files may render its debugging
info obsolete. If the file in question is a spec, the impact is rather
limited, as that debugging info will only be useful during the
elaboration phase of your program. For bodies the impact can be more
significant. In all events, your debugger will warn you if a source file
is more recent than the corresponding object, and alert you to the fact
that the debugging information may be out of date.
.. _How_gnatmake_Works:
How ``gnatmake`` Works
----------------------
Generally ``gnatmake`` automatically performs all necessary
recompilations and you don't need to worry about how it works. However,
it may be useful to have some basic understanding of the ``gnatmake``
approach and in particular to understand how it uses the results of
previous compilations without incorrectly depending on them.
First a definition: an object file is considered *up to date* if the
corresponding ALI file exists and if all the source files listed in the
dependency section of this ALI file have time stamps matching those in
the ALI file. This means that neither the source file itself nor any
files that it depends on have been modified, and hence there is no need
to recompile this file.
``gnatmake`` works by first checking if the specified main unit is up
to date. If so, no compilations are required for the main unit. If not,
``gnatmake`` compiles the main program to build a new ALI file that
reflects the latest sources. Then the ALI file of the main unit is
examined to find all the source files on which the main program depends,
and ``gnatmake`` recursively applies the above procedure on all these
files.
This process ensures that ``gnatmake`` only trusts the dependencies
in an existing ALI file if they are known to be correct. Otherwise it
always recompiles to determine a new, guaranteed accurate set of
dependencies. As a result the program is compiled 'upside down' from what may
be more familiar as the required order of compilation in some other Ada
systems. In particular, clients are compiled before the units on which
they depend. The ability of GNAT to compile in any order is critical in
allowing an order of compilation to be chosen that guarantees that
``gnatmake`` will recompute a correct set of new dependencies if
necessary.
When invoking ``gnatmake`` with several ``file_names``, if a unit is
imported by several of the executables, it will be recompiled at most once.
Note: when using non-standard naming conventions
(:ref:`Using_Other_File_Names`), changing through a configuration pragmas
file the version of a source and invoking ``gnatmake`` to recompile may
have no effect, if the previous version of the source is still accessible
by ``gnatmake``. It may be necessary to use the switch
-f.
.. _Examples_of_gnatmake_Usage:
Examples of ``gnatmake`` Usage
------------------------------
*gnatmake hello.adb*
Compile all files necessary to bind and link the main program
:file:`hello.adb` (containing unit ``Hello``) and bind and link the
resulting object files to generate an executable file :file:`hello`.
*gnatmake main1 main2 main3*
Compile all files necessary to bind and link the main programs
:file:`main1.adb` (containing unit ``Main1``), :file:`main2.adb`
(containing unit ``Main2``) and :file:`main3.adb`
(containing unit ``Main3``) and bind and link the resulting object files
to generate three executable files :file:`main1`,
:file:`main2` and :file:`main3`.
*gnatmake -q Main_Unit -cargs -O2 -bargs -l*
Compile all files necessary to bind and link the main program unit
``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. ``gnatmake`` will operate in quiet mode, not
displaying commands it is executing.
.. _Compiling_with_gcc:
Compiling with ``gcc``
======================
This section discusses how to compile Ada programs using the ``gcc``
command. It also describes the set of switches
that can be used to control the behavior of the compiler.
.. _Compiling_Programs:
Compiling Programs
------------------
The first step in creating an executable program is to compile the units
of the program using the ``gcc`` command. You must compile the
following files:
* the body file (:file:`.adb`) for a library level subprogram or generic
subprogram
* the spec file (:file:`.ads`) for a library level package or generic
package that has no body
* the body file (:file:`.adb`) for a library level package
or generic package that has a body
You need *not* compile the following files
* the spec of a library unit which has a body
* subunits
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.
.. index:: cannot generate code
If you attempt to compile any of these files, you will get one of the
following error messages (where ``fff`` is the name of the file you
compiled):
::
cannot generate code for file ``fff`` (package spec)
to check package spec, use -gnatc
cannot generate code for file ``fff`` (missing subunits)
to check parent unit, use -gnatc
cannot generate code for file ``fff`` (subprogram spec)
to check subprogram spec, use -gnatc
cannot generate code for file ``fff`` (subunit)
to check subunit, use -gnatc
As indicated by the above error messages, if you want to submit
one of these files to the compiler to check for correct semantics
without generating code, then use the :switch:`-gnatc` switch.
The basic command for compiling a file containing an Ada unit is:
.. code-block:: sh
$ gcc -c [switches] <file name>
where ``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
:switch:`-c` switch to tell ``gcc`` to compile, but not link, the file.
The result of a successful compilation is an object file, which has the
same name as the source file but an extension of :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.
TESTING: the :switch:`--foobar{NN}` switch
.. index:: gnat1
``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 ``gcc`` driver also calls the assembler and any other
utilities needed to complete the generation of the required object
files.
It is possible to supply several file names on the same ``gcc``
command. This causes ``gcc`` to call the appropriate compiler for
each file. For example, the following command lists two separate
files to be compiled:
.. code-block:: sh
$ gcc -c x.adb y.adb
calls ``gnat1`` (the Ada compiler) twice to compile :file:`x.adb` and
:file:`y.adb`.
The compiler generates two object files :file:`x.o` and :file:`y.o`
and the two ALI files :file:`x.ali` and :file:`y.ali`.
Any switches apply to all the files listed, see :ref:`Switches_for_gcc` for a
list of available ``gcc`` switches.
.. _Search_Paths_and_the_Run-Time_Library_RTL:
Search Paths and the Run-Time Library (RTL)
-------------------------------------------
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:
* The directory containing the source file of the main unit being compiled
(the file name on the command line).
* Each directory named by an :switch:`-I` switch given on the ``gcc``
command line, in the order given.
.. index:: ADA_PRJ_INCLUDE_FILE
* Each of the directories listed in the text file whose name is given
by the :envvar:`ADA_PRJ_INCLUDE_FILE` environment variable.
:envvar:`ADA_PRJ_INCLUDE_FILE` is normally set by gnatmake or by the gnat
driver when project files are used. It should not normally be set
by other means.
.. index:: ADA_INCLUDE_PATH
* Each of the directories listed in the value of the
:envvar:`ADA_INCLUDE_PATH` environment variable.
Construct this value
exactly as the :envvar:`PATH` environment variable: a list of directory
names separated by colons (semicolons when working with the NT version).
* The content of the :file:`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_a_library`
Specifying the switch :switch:`-I-`
inhibits the use of the directory
containing the source file named in the command line. You can still
have this directory on your search path, but in this case it must be
explicitly requested with a :switch:`-I` switch.
Specifying the switch :switch:`-nostdinc`
inhibits the search of the default location for the GNAT Run Time
Library (RTL) source files.
The compiler outputs its object files and ALI files in the current
working directory.
Caution: The object file can be redirected with the :switch:`-o` switch;
however, ``gcc`` and ``gnat1`` have not been coordinated on this
so the :file:`ALI` file will not go to the right place. Therefore, you should
avoid using the :switch:`-o` switch.
.. index:: System.IO
The packages ``Ada``, ``System``, and ``Interfaces`` and their
children make up the GNAT RTL, together with the simple ``System.IO``
package used in the ``"Hello World"`` example. The sources for these units
are needed by the compiler and are kept together in one directory. Not
all of the bodies are needed, but all of the sources are kept together
anyway. In a normal installation, you need not specify these directory
names when compiling or binding. Either the environment variables or
the built-in defaults cause these files to be found.
In addition to the language-defined hierarchies (``System``, ``Ada`` and
``Interfaces``), the GNAT distribution provides a fourth hierarchy,
consisting of child units of ``GNAT``. This is a collection of generally
useful types, subprograms, etc. See the :title:`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.
.. _Order_of_Compilation_Issues:
Order of Compilation Issues
---------------------------
If, in our earlier example, there was a spec for the ``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:
* 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.
* 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.
* There is no library as such, apart from the ALI files
(:ref:`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.
* When you compile a unit, the source files for the specs of all units
that it |withs|, 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.
.. _Examples:
Examples
--------
The following are some typical Ada compilation command line examples:
.. code-block:: sh
$ gcc -c xyz.adb
Compile body in file :file:`xyz.adb` with all default options.
.. code-block:: sh
$ gcc -c -O2 -gnata xyz-def.adb
Compile the child unit package in file :file:`xyz-def.adb` with extensive
optimizations, and pragma ``Assert``/`Debug` statements
enabled.
.. code-block:: sh
$ gcc -c -gnatc abc-def.adb
Compile the subunit in file :file:`abc-def.adb` in semantic-checking-only
mode.
.. _Switches_for_gcc:
Compiler Switches
=================
The ``gcc`` command accepts switches that control the
compilation process. These switches are fully described in this section:
first an alphabetical listing of all switches with a brief description,
and then functionally grouped sets of switches with more detailed
information.
More switches exist for GCC than those documented here, especially
for specific targets. However, their use is not recommended as
they may change code generation in ways that are incompatible with
the Ada run-time library, or can cause inconsistencies between
compilation units.
.. _Alphabetical_List_of_All_Switches:
Alphabetical List of All Switches
---------------------------------
.. index:: -b (gcc)
:switch:`-b {target}`
Compile your program to run on ``target``, which is the name of a
system configuration. You must have a GNAT cross-compiler built if
``target`` is not the same as your host system.
.. index:: -B (gcc)
:switch:`-B{dir}`
Load compiler executables (for example, ``gnat1``, the Ada compiler)
from ``dir`` instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See the "Options for Directory Search" section in the
:title:`Using the GNU Compiler Collection (GCC)` manual for further details.
You would normally use the :switch:`-b` or :switch:`-V` switch instead.
.. index:: -c (gcc)
:switch:`-c`
Compile. Always use this switch when compiling Ada programs.
Note: for some other languages when using ``gcc``, notably in
the case of C and C++, it is possible to use
use ``gcc`` without a :switch:`-c` switch to
compile and link in one step. In the case of GNAT, you
cannot use this approach, because the binder must be run
and ``gcc`` cannot be used to run the GNAT binder.
.. index:: -fcallgraph-info (gcc)
:switch:`-fcallgraph-info[=su,da]`
Makes the compiler output callgraph information for the program, on a
per-file basis. The information is generated in the VCG format. It can
be decorated with additional, per-node and/or per-edge information, if a
list of comma-separated markers is additionally specified. When the
``su`` marker is specified, the callgraph is decorated with stack usage
information; it is equivalent to :switch:`-fstack-usage`. When the ``da``
marker is specified, the callgraph is decorated with information about
dynamically allocated objects.
.. index:: -fdump-scos (gcc)
:switch:`-fdump-scos`
Generates SCO (Source Coverage Obligation) information in the ALI file.
This information is used by advanced coverage tools. See unit :file:`SCOs`
in the compiler sources for details in files :file:`scos.ads` and
:file:`scos.adb`.
.. index:: -fgnat-encodings (gcc)
:switch:`-fgnat-encodings=[all|gdb|minimal]`
This switch controls the balance between GNAT encodings and standard DWARF
emitted in the debug information.
.. index:: -flto (gcc)
:switch:`-flto[={n}]`
Enables Link Time Optimization. This switch must be used in conjunction
with the :switch:`-Ox` switches (but not with the :switch:`-gnatn` switch
since it is a full replacement for the latter) and instructs the compiler
to defer most optimizations until the link stage. The advantage of this
approach is that the compiler can do a whole-program analysis and choose
the best interprocedural optimization strategy based on a complete view
of the program, instead of a fragmentary view with the usual approach.
This can also speed up the compilation of big programs and reduce the
size of the executable, compared with a traditional per-unit compilation
with inlining across units enabled by the :switch:`-gnatn` switch.
The drawback of this approach is that it may require more memory and that
the debugging information generated by -g with it might be hardly usable.
The switch, as well as the accompanying :switch:`-Ox` switches, must be
specified both for the compilation and the link phases.
If the ``n`` parameter is specified, the optimization and final code
generation at link time are executed using ``n`` parallel jobs by
means of an installed ``make`` program.
.. index:: -fno-inline (gcc)
:switch:`-fno-inline`
Suppresses all inlining, unless requested with pragma ``Inline_Always``. The
effect is enforced regardless of other optimization or inlining switches.
Note that inlining can also be suppressed on a finer-grained basis with
pragma ``No_Inline``.
.. index:: -fno-inline-functions (gcc)
:switch:`-fno-inline-functions`
Suppresses automatic inlining of subprograms, which is enabled
if :switch:`-O3` is used.
.. index:: -fno-inline-small-functions (gcc)
:switch:`-fno-inline-small-functions`
Suppresses automatic inlining of small subprograms, which is enabled
if :switch:`-O2` is used.
.. index:: -fno-inline-functions-called-once (gcc)
:switch:`-fno-inline-functions-called-once`
Suppresses inlining of subprograms local to the unit and called once
from within it, which is enabled if :switch:`-O1` is used.
.. index:: -fno-ivopts (gcc)
:switch:`-fno-ivopts`
Suppresses high-level loop induction variable optimizations, which are
enabled if :switch:`-O1` is used. These optimizations are generally
profitable but, for some specific cases of loops with numerous uses
of the iteration variable that follow a common pattern, they may end
up destroying the regularity that could be exploited at a lower level
and thus producing inferior code.
.. index:: -fno-strict-aliasing (gcc)
:switch:`-fno-strict-aliasing`
Causes the compiler to avoid assumptions regarding non-aliasing
of objects of different types. See
:ref:`Optimization_and_Strict_Aliasing` for details.
.. index:: -fno-strict-overflow (gcc)
:switch:`-fno-strict-overflow`
Causes the compiler to avoid assumptions regarding the rules of signed
integer overflow. These rules specify that signed integer overflow will
result in a Constraint_Error exception at run time and are enforced in
default mode by the compiler, so this switch should not be necessary in
normal operating mode. It might be useful in conjunction with :switch:`-gnato0`
for very peculiar cases of low-level programming.
.. index:: -fstack-check (gcc)
:switch:`-fstack-check`
Activates stack checking.
See :ref:`Stack_Overflow_Checking` for details.
.. index:: -fstack-usage (gcc)
:switch:`-fstack-usage`
Makes the compiler output stack usage information for the program, on a
per-subprogram basis. See :ref:`Static_Stack_Usage_Analysis` for details.
.. index:: -g (gcc)
:switch:`-g`
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
:switch:`-g` switch if you plan on using the debugger.
.. index:: -gnat05 (gcc)
:switch:`-gnat05`
Allow full Ada 2005 features.
.. index:: -gnat12 (gcc)
:switch:`-gnat12`
Allow full Ada 2012 features.
.. index:: -gnat83 (gcc)
.. index:: -gnat2005 (gcc)
:switch:`-gnat2005`
Allow full Ada 2005 features (same as :switch:`-gnat05`)
.. index:: -gnat2012 (gcc)
:switch:`-gnat2012`
Allow full Ada 2012 features (same as :switch:`-gnat12`)
:switch:`-gnat83`
Enforce Ada 83 restrictions.
.. index:: -gnat95 (gcc)
:switch:`-gnat95`
Enforce Ada 95 restrictions.
Note: for compatibility with some Ada 95 compilers which support only
the ``overriding`` keyword of Ada 2005, the :switch:`-gnatd.D` switch can
be used along with :switch:`-gnat95` to achieve a similar effect with GNAT.
:switch:`-gnatd.D` instructs GNAT to consider ``overriding`` as a keyword
and handle its associated semantic checks, even in Ada 95 mode.
.. index:: -gnata (gcc)
:switch:`-gnata`
Assertions enabled. ``Pragma Assert`` and ``pragma Debug`` to be
activated. Note that these pragmas can also be controlled using the
configuration pragmas ``Assertion_Policy`` and ``Debug_Policy``.
It also activates pragmas ``Check``, ``Precondition``, and
``Postcondition``. Note that these pragmas can also be controlled
using the configuration pragma ``Check_Policy``. In Ada 2012, it
also activates all assertions defined in the RM as aspects: preconditions,
postconditions, type invariants and (sub)type predicates. In all Ada modes,
corresponding pragmas for type invariants and (sub)type predicates are
also activated. The default is that all these assertions are disabled,
and have no effect, other than being checked for syntactic validity, and
in the case of subtype predicates, constructions such as membership tests
still test predicates even if assertions are turned off.
.. index:: -gnatA (gcc)
:switch:`-gnatA`
Avoid processing :file:`gnat.adc`. If a :file:`gnat.adc` file is present,
it will be ignored.
.. index:: -gnatb (gcc)
:switch:`-gnatb`
Generate brief messages to :file:`stderr` even if verbose mode set.
.. index:: -gnatB (gcc)
:switch:`-gnatB`
Assume no invalid (bad) values except for 'Valid attribute use
(:ref:`Validity_Checking`).
.. index:: -gnatc (gcc)
:switch:`-gnatc`
Check syntax and semantics only (no code generation attempted). When the
compiler is invoked by ``gnatmake``, if the switch :switch:`-gnatc` is
only given to the compiler (after :switch:`-cargs` or in package Compiler of
the project file, ``gnatmake`` will fail because it will not find the
object file after compilation. If ``gnatmake`` is called with
:switch:`-gnatc` as a builder switch (before :switch:`-cargs` or in package
Builder of the project file) then ``gnatmake`` will not fail because
it will not look for the object files after compilation, and it will not try
to build and link.
.. index:: -gnatC (gcc)
:switch:`-gnatC`
Generate CodePeer intermediate format (no code generation attempted).
This switch will generate an intermediate representation suitable for
use by CodePeer (:file:`.scil` files). This switch is not compatible with
code generation (it will, among other things, disable some switches such
as -gnatn, and enable others such as -gnata).
.. index:: -gnatd (gcc)
:switch:`-gnatd`
Specify debug options for the compiler. The string of characters after
the :switch:`-gnatd` specify the specific debug options. The possible
characters are 0-9, a-z, A-Z, optionally preceded by a dot. See
compiler source file :file:`debug.adb` for details of the implemented
debug options. Certain debug options are relevant to applications
programmers, and these are documented at appropriate points in this
users guide.
.. index:: -gnatD[nn] (gcc)
:switch:`-gnatD`
Create expanded source files for source level debugging. This switch
also suppresses generation of cross-reference information
(see :switch:`-gnatx`). Note that this switch is not allowed if a previous
-gnatR switch has been given, since these two switches are not compatible.
.. index:: -gnateA (gcc)
:switch:`-gnateA`
Check that the actual parameters of a subprogram call are not aliases of one
another. To qualify as aliasing, the actuals must denote objects of a composite
type, their memory locations must be identical or overlapping, and at least one
of the corresponding formal parameters must be of mode OUT or IN OUT.
.. code-block:: ada
type Rec_Typ is record
Data : Integer := 0;
end record;
function Self (Val : Rec_Typ) return Rec_Typ is
begin
return Val;
end Self;
procedure Detect_Aliasing (Val_1 : in out Rec_Typ; Val_2 : Rec_Typ) is
begin
null;
end Detect_Aliasing;
Obj : Rec_Typ;
Detect_Aliasing (Obj, Obj);
Detect_Aliasing (Obj, Self (Obj));
In the example above, the first call to ``Detect_Aliasing`` fails with a
``Program_Error`` at run time because the actuals for ``Val_1`` and
``Val_2`` denote the same object. The second call executes without raising
an exception because ``Self(Obj)`` produces an anonymous object which does
not share the memory location of ``Obj``.
.. index:: -gnatec (gcc)
:switch:`-gnatec={path}`
Specify a configuration pragma file
(the equal sign is optional)
(:ref:`The_Configuration_Pragmas_Files`).
.. index:: -gnateC (gcc)
:switch:`-gnateC`
Generate CodePeer messages in a compiler-like format. This switch is only
effective if :switch:`-gnatcC` is also specified and requires an installation
of CodePeer.
.. index:: -gnated (gcc)
:switch:`-gnated`
Disable atomic synchronization
.. index:: -gnateD (gcc)
:switch:`-gnateDsymbol[={value}]`
Defines a symbol, associated with ``value``, for preprocessing.
(:ref:`Integrated_Preprocessing`).
.. index:: -gnateE (gcc)
:switch:`-gnateE`
Generate extra information in exception messages. In particular, display
extra column information and the value and range associated with index and
range check failures, and extra column information for access checks.
In cases where the compiler is able to determine at compile time that
a check will fail, it gives a warning, and the extra information is not
produced at run time.
.. index:: -gnatef (gcc)
:switch:`-gnatef`
Display full source path name in brief error messages.
.. index:: -gnateF (gcc)
:switch:`-gnateF`
Check for overflow on all floating-point operations, including those
for unconstrained predefined types. See description of pragma
``Check_Float_Overflow`` in GNAT RM.
.. index:: -gnateg (gcc)
:switch:`-gnateg`
:switch:`-gnatceg`
The :switch:`-gnatc` switch must always be specified before this switch, e.g.
:switch:`-gnatceg`. Generate a C header from the Ada input file. See
:ref:`Generating_C_Headers_for_Ada_Specifications` for more
information.
.. index:: -gnateG (gcc)
:switch:`-gnateG`
Save result of preprocessing in a text file.
.. index:: -gnatei (gcc)
:switch:`-gnatei{nnn}`
Set maximum number of instantiations during compilation of a single unit to
``nnn``. This may be useful in increasing the default maximum of 8000 for
the rare case when a single unit legitimately exceeds this limit.
.. index:: -gnateI (gcc)
:switch:`-gnateI{nnn}`
Indicates that the source is a multi-unit source and that the index of the
unit to compile is ``nnn``. ``nnn`` needs to be a positive number and need
to be a valid index in the multi-unit source.
.. index:: -gnatel (gcc)
:switch:`-gnatel`
This switch can be used with the static elaboration model to issue info
messages showing
where implicit ``pragma Elaborate`` and ``pragma Elaborate_All``
are generated. This is useful in diagnosing elaboration circularities
caused by these implicit pragmas when using the static elaboration
model. See See the section in this guide on elaboration checking for
further details. These messages are not generated by default, and are
intended only for temporary use when debugging circularity problems.
.. index:: -gnatel (gcc)
:switch:`-gnateL`
This switch turns off the info messages about implicit elaboration pragmas.
.. index:: -gnatem (gcc)
:switch:`-gnatem={path}`
Specify a mapping file
(the equal sign is optional)
(:ref:`Units_to_Sources_Mapping_Files`).
.. index:: -gnatep (gcc)
:switch:`-gnatep={file}`
Specify a preprocessing data file
(the equal sign is optional)
(:ref:`Integrated_Preprocessing`).
.. index:: -gnateP (gcc)
:switch:`-gnateP`
Turn categorization dependency errors into warnings.
Ada requires that units that WITH one another have compatible categories, for
example a Pure unit cannot WITH a Preelaborate unit. If this switch is used,
these errors become warnings (which can be ignored, or suppressed in the usual
manner). This can be useful in some specialized circumstances such as the
temporary use of special test software.
.. index:: -gnateS (gcc)
:switch:`-gnateS`
Synonym of :switch:`-fdump-scos`, kept for backwards compatibility.
.. index:: -gnatet=file (gcc)
:switch:`-gnatet={path}`
Generate target dependent information. The format of the output file is
described in the section about switch :switch:`-gnateT`.
.. index:: -gnateT (gcc)
:switch:`-gnateT={path}`
Read target dependent information, such as endianness or sizes and alignments
of base type. If this switch is passed, the default target dependent
information of the compiler is replaced by the one read from the input file.
This is used by tools other than the compiler, e.g. to do
semantic analysis of programs that will run on some other target than
the machine on which the tool is run.
The following target dependent values should be defined,
where ``Nat`` denotes a natural integer value, ``Pos`` denotes a
positive integer value, and fields marked with a question mark are
boolean fields, where a value of 0 is False, and a value of 1 is True:
::
Bits_BE : Nat; -- Bits stored big-endian?
Bits_Per_Unit : Pos; -- Bits in a storage unit
Bits_Per_Word : Pos; -- Bits in a word
Bytes_BE : Nat; -- Bytes stored big-endian?
Char_Size : Pos; -- Standard.Character'Size
Double_Float_Alignment : Nat; -- Alignment of double float
Double_Scalar_Alignment : Nat; -- Alignment of double length scalar
Double_Size : Pos; -- Standard.Long_Float'Size
Float_Size : Pos; -- Standard.Float'Size
Float_Words_BE : Nat; -- Float words stored big-endian?
Int_Size : Pos; -- Standard.Integer'Size
Long_Double_Size : Pos; -- Standard.Long_Long_Float'Size
Long_Long_Size : Pos; -- Standard.Long_Long_Integer'Size
Long_Size : Pos; -- Standard.Long_Integer'Size
Maximum_Alignment : Pos; -- Maximum permitted alignment
Max_Unaligned_Field : Pos; -- Maximum size for unaligned bit field
Pointer_Size : Pos; -- System.Address'Size
Short_Enums : Nat; -- Foreign enums use short size?
Short_Size : Pos; -- Standard.Short_Integer'Size
Strict_Alignment : Nat; -- Strict alignment?
System_Allocator_Alignment : Nat; -- Alignment for malloc calls
Wchar_T_Size : Pos; -- Interfaces.C.wchar_t'Size
Words_BE : Nat; -- Words stored big-endian?
``Bits_Per_Unit`` is the number of bits in a storage unit, the equivalent of
GCC macro ``BITS_PER_UNIT`` documented as follows: `Define this macro to be
the number of bits in an addressable storage unit (byte); normally 8.`
``Bits_Per_Word`` is the number of bits in a machine word, the equivalent of
GCC macro ``BITS_PER_WORD`` documented as follows: `Number of bits in a word;
normally 32.`
``Double_Scalar_Alignment`` is the alignment for a scalar whose size is two
machine words. It should be the same as the alignment for C ``long_long`` on
most targets.
``Maximum_Alignment`` is the maximum alignment that the compiler might choose
by default for a type or object, which is also the maximum alignment that can
be specified in GNAT. It is computed for GCC backends as ``BIGGEST_ALIGNMENT
/ BITS_PER_UNIT`` where GCC macro ``BIGGEST_ALIGNMENT`` is documented as
follows: `Biggest alignment that any data type can require on this machine,
in bits.`
``Max_Unaligned_Field`` is the maximum size for unaligned bit field, which is
64 for the majority of GCC targets (but can be different on some targets like
AAMP).
``Strict_Alignment`` is the equivalent of GCC macro ``STRICT_ALIGNMENT``
documented as follows: `Define this macro to be the value 1 if instructions
will fail to work if given data not on the nominal alignment. If instructions
will merely go slower in that case, define this macro as 0.`
``System_Allocator_Alignment`` is the guaranteed alignment of data returned
by calls to ``malloc``.
The format of the input file is as follows. First come the values of
the variables defined above, with one line per value:
::
name value
where ``name`` is the name of the parameter, spelled out in full,
and cased as in the above list, and ``value`` is an unsigned decimal
integer. Two or more blanks separates the name from the value.
All the variables must be present, in alphabetical order (i.e. the
same order as the list above).
Then there is a blank line to separate the two parts of the file. Then
come the lines showing the floating-point types to be registered, with
one line per registered mode:
::
name digs float_rep size alignment
where ``name`` is the string name of the type (which can have
single spaces embedded in the name (e.g. long double), ``digs`` is
the number of digits for the floating-point type, ``float_rep`` is
the float representation (I/V/A for IEEE-754-Binary, Vax_Native,
AAMP), ``size`` is the size in bits, ``alignment`` is the
alignment in bits. The name is followed by at least two blanks, fields
are separated by at least one blank, and a LF character immediately
follows the alignment field.
Here is an example of a target parameterization file:
::
Bits_BE 0
Bits_Per_Unit 8
Bits_Per_Word 64
Bytes_BE 0
Char_Size 8
Double_Float_Alignment 0
Double_Scalar_Alignment 0
Double_Size 64
Float_Size 32
Float_Words_BE 0
Int_Size 64
Long_Double_Size 128
Long_Long_Size 64
Long_Size 64
Maximum_Alignment 16
Max_Unaligned_Field 64
Pointer_Size 64
Short_Size 16
Strict_Alignment 0
System_Allocator_Alignment 16
Wchar_T_Size 32
Words_BE 0
float 15 I 64 64
double 15 I 64 64
long double 18 I 80 128
TF 33 I 128 128
.. index:: -gnateu (gcc)
:switch:`-gnateu`
Ignore unrecognized validity, warning, and style switches that
appear after this switch is given. This may be useful when
compiling sources developed on a later version of the compiler
with an earlier version. Of course the earlier version must
support this switch.
.. index:: -gnateV (gcc)
:switch:`-gnateV`
Check that all actual parameters of a subprogram call are valid according to
the rules of validity checking (:ref:`Validity_Checking`).
.. index:: -gnateY (gcc)
:switch:`-gnateY`
Ignore all STYLE_CHECKS pragmas. Full legality checks
are still carried out, but the pragmas have no effect
on what style checks are active. This allows all style
checking options to be controlled from the command line.
.. index:: -gnatE (gcc)
:switch:`-gnatE`
Full dynamic elaboration checks.
.. index:: -gnatf (gcc)
:switch:`-gnatf`
Full errors. Multiple errors per line, all undefined references, do not
attempt to suppress cascaded errors.
.. index:: -gnatF (gcc)
:switch:`-gnatF`
Externals names are folded to all uppercase.
.. index:: -gnatg (gcc)
:switch:`-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. Note that :switch:`-gnatg`
implies :switch:`-gnatw.ge` and :switch:`-gnatyg` so that all standard
warnings and all standard style options are turned on. All warnings and style
messages are treated as errors.
.. index:: -gnatG[nn] (gcc)
:switch:`-gnatG=nn`
List generated expanded code in source form.
.. index:: -gnath (gcc)
:switch:`-gnath`
Output usage information. The output is written to :file:`stdout`.
.. index:: -gnatH (gcc)
:switch:`-gnatH`
Legacy elaboration-checking mode enabled. When this switch is in effect, the
pre-18.x access-before-elaboration model becomes the de facto model.
.. index:: -gnati (gcc)
:switch:`-gnati{c}`
Identifier character set (``c`` = 1/2/3/4/8/9/p/f/n/w).
For details of the possible selections for ``c``,
see :ref:`Character_Set_Control`.
.. index:: -gnatI (gcc)
:switch:`-gnatI`
Ignore representation clauses. When this switch is used,
representation clauses are treated as comments. This is useful
when initially porting code where you want to ignore rep clause
problems, and also for compiling foreign code (particularly
for use with ASIS). The representation clauses that are ignored
are: enumeration_representation_clause, record_representation_clause,
and attribute_definition_clause for the following attributes:
Address, Alignment, Bit_Order, Component_Size, Machine_Radix,
Object_Size, Scalar_Storage_Order, Size, Small, Stream_Size,
and Value_Size. Pragma Default_Scalar_Storage_Order is also ignored.
Note that this option should be used only for compiling -- the
code is likely to malfunction at run time.
Note that when :switch:`-gnatct` is used to generate trees for input
into ASIS tools, these representation clauses are removed
from the tree and ignored. This means that the tool will not see them.
.. index:: -gnatjnn (gcc)
:switch:`-gnatj{nn}`
Reformat error messages to fit on ``nn`` character lines
.. index:: -gnatJ (gcc)
:switch:`-gnatJ`
Permissive elaboration-checking mode enabled. When this switch is in effect,
the post-18.x access-before-elaboration model ignores potential issues with:
- Accept statements
- Activations of tasks defined in instances
- Assertion pragmas
- Calls from within an instance to its enclosing context
- Calls through generic formal parameters
- Calls to subprograms defined in instances
- Entry calls
- Indirect calls using 'Access
- Requeue statements
- Select statements
- Synchronous task suspension
and does not emit compile-time diagnostics or run-time checks.
.. index:: -gnatk (gcc)
:switch:`-gnatk={n}`
Limit file names to ``n`` (1-999) characters (``k`` = krunch).
.. index:: -gnatl (gcc)
:switch:`-gnatl`
Output full source listing with embedded error messages.
.. index:: -gnatL (gcc)
:switch:`-gnatL`
Used in conjunction with -gnatG or -gnatD to intersperse original
source lines (as comment lines with line numbers) in the expanded
source output.
.. index:: -gnatm (gcc)
:switch:`-gnatm={n}`
Limit number of detected error or warning messages to ``n``
where ``n`` is in the range 1..999999. The default setting if
no switch is given is 9999. If the number of warnings reaches this
limit, then a message is output and further warnings are suppressed,
but the compilation is continued. If the number of error messages
reaches this limit, then a message is output and the compilation
is abandoned. The equal sign here is optional. A value of zero
means that no limit applies.
.. index:: -gnatn (gcc)
:switch:`-gnatn[12]`
Activate inlining across units for subprograms for which pragma ``Inline``
is specified. This inlining is performed by the GCC back-end. An optional
digit sets the inlining level: 1 for moderate inlining across units
or 2 for full inlining across units. If no inlining level is specified,
the compiler will pick it based on the optimization level.
.. index:: -gnatN (gcc)
:switch:`-gnatN`
Activate front end inlining for subprograms for which
pragma ``Inline`` is specified. This inlining is performed
by the front end and will be visible in the
:switch:`-gnatG` output.
When using a gcc-based back end (in practice this means using any version
of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of
:switch:`-gnatN` is deprecated, and the use of :switch:`-gnatn` is preferred.
Historically front end inlining was more extensive than the gcc back end
inlining, but that is no longer the case.
.. index:: -gnato0 (gcc)
:switch:`-gnato0`
Suppresses overflow checking. This causes the behavior of the compiler to
match the default for older versions where overflow checking was suppressed
by default. This is equivalent to having
``pragma Suppress (Overflow_Check)`` in a configuration pragma file.
.. index:: -gnato?? (gcc)
:switch:`-gnato??`
Set default mode for handling generation of code to avoid intermediate
arithmetic overflow. Here ``??`` is two digits, a
single digit, or nothing. Each digit is one of the digits ``1``
through ``3``:
===== ===============================================================
Digit Interpretation
----- ---------------------------------------------------------------
*1* All intermediate overflows checked against base type (``STRICT``)
*2* Minimize intermediate overflows (``MINIMIZED``)
*3* Eliminate intermediate overflows (``ELIMINATED``)
===== ===============================================================
If only one digit appears, then it applies to all
cases; if two digits are given, then the first applies outside
assertions, pre/postconditions, and type invariants, and the second
applies within assertions, pre/postconditions, and type invariants.
If no digits follow the :switch:`-gnato`, then it is equivalent to
:switch:`-gnato11`,
causing all intermediate overflows to be handled in strict
mode.
This switch also causes arithmetic overflow checking to be performed
(as though ``pragma Unsuppress (Overflow_Check)`` had been specified).
The default if no option :switch:`-gnato` is given is that overflow handling
is in ``STRICT`` mode (computations done using the base type), and that
overflow checking is enabled.
Note that division by zero is a separate check that is not
controlled by this switch (divide-by-zero checking is on by default).
See also :ref:`Specifying_the_Desired_Mode`.
.. index:: -gnatp (gcc)
:switch:`-gnatp`
Suppress all checks. See :ref:`Run-Time_Checks` for details. This switch
has no effect if cancelled by a subsequent :switch:`-gnat-p` switch.
.. index:: -gnat-p (gcc)
:switch:`-gnat-p`
Cancel effect of previous :switch:`-gnatp` switch.
.. index:: -gnatP (gcc)
:switch:`-gnatP`
Enable polling. This is required on some systems (notably Windows NT) to
obtain asynchronous abort and asynchronous transfer of control capability.
See ``Pragma_Polling`` in the :title:`GNAT_Reference_Manual` for full
details.
.. index:: -gnatq (gcc)
:switch:`-gnatq`
Don't quit. Try semantics, even if parse errors.
.. index:: -gnatQ (gcc)
:switch:`-gnatQ`
Don't quit. Generate :file:`ALI` and tree files even if illegalities.
Note that code generation is still suppressed in the presence of any
errors, so even with :switch:`-gnatQ` no object file is generated.
.. index:: -gnatr (gcc)
:switch:`-gnatr`
Treat pragma Restrictions as Restriction_Warnings.
.. index:: -gnatR (gcc)
:switch:`-gnatR[0|1|2|3|4][e][j][m][s]`
Output representation information for declared types, objects and
subprograms. Note that this switch is not allowed if a previous
:switch:`-gnatD` switch has been given, since these two switches
are not compatible.
.. index:: -gnats (gcc)
:switch:`-gnats`
Syntax check only.
.. index:: -gnatS (gcc)
:switch:`-gnatS`
Print package Standard.
.. index:: -gnatt (gcc)
:switch:`-gnatt`
Generate tree output file.
.. index:: -gnatT (gcc)
:switch:`-gnatT{nnn}`
All compiler tables start at ``nnn`` times usual starting size.
.. index:: -gnatu (gcc)
:switch:`-gnatu`
List units for this compilation.
.. index:: -gnatU (gcc)
:switch:`-gnatU`
Tag all error messages with the unique string 'error:'
.. index:: -gnatv (gcc)
:switch:`-gnatv`
Verbose mode. Full error output with source lines to :file:`stdout`.
.. index:: -gnatV (gcc)
:switch:`-gnatV`
Control level of validity checking (:ref:`Validity_Checking`).
.. index:: -gnatw (gcc)
:switch:`-gnatw{xxx}`
Warning mode where
``xxx`` is a string of option letters that denotes
the exact warnings that
are enabled or disabled (:ref:`Warning_Message_Control`).
.. index:: -gnatW (gcc)
:switch:`-gnatW{e}`
Wide character encoding method
(``e``\ =n/h/u/s/e/8).
.. index:: -gnatx (gcc)
:switch:`-gnatx`
Suppress generation of cross-reference information.
.. index:: -gnatX (gcc)
:switch:`-gnatX`
Enable GNAT implementation extensions and latest Ada version.
.. index:: -gnaty (gcc)
:switch:`-gnaty`
Enable built-in style checks (:ref:`Style_Checking`).
.. index:: -gnatz (gcc)
:switch:`-gnatz{m}`
Distribution stub generation and compilation
(``m``\ =r/c for receiver/caller stubs).
.. index:: -I (gcc)
:switch:`-I{dir}`
.. index:: RTL
Direct GNAT to search the ``dir`` directory for source files needed by
the current compilation
(see :ref:`Search_Paths_and_the_Run-Time_Library_RTL`).
.. index:: -I- (gcc)
:switch:`-I-`
.. index:: RTL
Except for the source file named in the command line, do not look for source
files in the directory containing the source file named in the command line
(see :ref:`Search_Paths_and_the_Run-Time_Library_RTL`).
.. index:: -o (gcc)
:switch:`-o {file}`
This switch is used in ``gcc`` to redirect the generated object file
and its associated ALI file. Beware of this switch with GNAT, because it may
cause the object file and ALI file to have different names which in turn
may confuse the binder and the linker.
.. index:: -nostdinc (gcc)
:switch:`-nostdinc`
Inhibit the search of the default location for the GNAT Run Time
Library (RTL) source files.
.. index:: -nostdlib (gcc)
:switch:`-nostdlib`
Inhibit the search of the default location for the GNAT Run Time
Library (RTL) ALI files.
.. index:: -O (gcc)
:switch:`-O[{n}]`
``n`` controls the optimization level:
======= ==================================================================
*n* Effect
------- ------------------------------------------------------------------
*0* No optimization, the default setting if no :switch:`-O` appears
*1* Normal optimization, the default if you specify :switch:`-O` without an
operand. A good compromise between code quality and compilation
time.
*2* Extensive optimization, may improve execution time, possibly at
the cost of substantially increased compilation time.
*3* Same as :switch:`-O2`, and also includes inline expansion for small
subprograms in the same unit.
*s* Optimize space usage
======= ==================================================================
See also :ref:`Optimization_Levels`.
.. index:: -pass-exit-codes (gcc)
:switch:`-pass-exit-codes`
Catch exit codes from the compiler and use the most meaningful as
exit status.
.. index:: --RTS (gcc)
:switch:`--RTS={rts-path}`
Specifies the default location of the run-time library. Same meaning as the
equivalent ``gnatmake`` flag (:ref:`Switches_for_gnatmake`).
.. index:: -S (gcc)
:switch:`-S`
Used in place of :switch:`-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.
.. index:: -fverbose-asm (gcc)
:switch:`-fverbose-asm`
Used in conjunction with :switch:`-S`
to cause the generated assembly code file to be annotated with variable
names, making it significantly easier to follow.
.. index:: -v (gcc)
:switch:`-v`
Show commands generated by the ``gcc`` driver. Normally used only for
debugging purposes or if you need to be sure what version of the
compiler you are executing.
.. index:: -V (gcc)
:switch:`-V {ver}`
Execute ``ver`` version of the compiler. This is the ``gcc``
version, not the GNAT version.
.. index:: -w (gcc)
:switch:`-w`
Turn off warnings generated by the back end of the compiler. Use of
this switch also causes the default for front end warnings to be set
to suppress (as though :switch:`-gnatws` had appeared at the start of
the options).
.. index:: Combining GNAT switches
You may combine a sequence of GNAT switches into a single switch. For
example, the combined switch
::
-gnatofi3
is equivalent to specifying the following sequence of switches:
::
-gnato -gnatf -gnati3
The following restrictions apply to the combination of switches
in this manner:
* The switch :switch:`-gnatc` if combined with other switches must come
first in the string.
* The switch :switch:`-gnats` if combined with other switches must come
first in the string.
* The switches
:switch:`-gnatzc` and :switch:`-gnatzr` may not be combined with any other
switches, and only one of them may appear in the command line.
* The switch :switch:`-gnat-p` may not be combined with any other switch.
* Once a 'y' appears in the string (that is a use of the :switch:`-gnaty`
switch), then all further characters in the switch are interpreted
as style modifiers (see description of :switch:`-gnaty`).
* Once a 'd' appears in the string (that is a use of the :switch:`-gnatd`
switch), then all further characters in the switch are interpreted
as debug flags (see description of :switch:`-gnatd`).
* Once a 'w' appears in the string (that is a use of the :switch:`-gnatw`
switch), then all further characters in the switch are interpreted
as warning mode modifiers (see description of :switch:`-gnatw`).
* Once a 'V' appears in the string (that is a use of the :switch:`-gnatV`
switch), then all further characters in the switch are interpreted
as validity checking options (:ref:`Validity_Checking`).
* Option 'em', 'ec', 'ep', 'l=' and 'R' must be the last options in
a combined list of options.
.. _Output_and_Error_Message_Control:
Output and Error Message Control
--------------------------------
.. index:: stderr
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:
::
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:4:20: ";" should be "is"
The first integer after the file name is the line number in the file,
and the second integer is the column number within the line.
``GPS`` can parse the error messages
and point to the referenced character.
The following switches provide control over the error message
format:
.. index:: -gnatv (gcc)
:switch:`-gnatv`
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
:switch:`-gnatv` switch would generate:
::
3. funcion X (Q : Integer)
|
>>> Incorrect spelling of keyword "function"
4. return Integer;
|
>>> ";" should be "is"
The vertical bar indicates the location of the error, and the ``>>>``
prefix can be used to search for error messages. When this switch is
used the only source lines output are those with errors.
.. index:: -gnatl (gcc)
:switch:`-gnatl`
The ``l`` stands for list.
This switch causes a full listing of
the file to be generated. In the case where a body is
compiled, the corresponding spec is also listed, along
with any subunits. Typical output from compiling a package
body :file:`p.adb` might look like::
Compiling: p.adb
1. package body p is
2. procedure a;
3. procedure a is separate;
4. begin
5. null
|
>>> missing ";"
6. end;
Compiling: p.ads
1. package p is
2. pragma Elaborate_Body
|
>>> missing ";"
3. end p;
Compiling: p-a.adb
1. separate p
|
>>> missing "("
2. procedure a is
3. begin
4. null
|
>>> missing ";"
5. end;
When you specify the :switch:`-gnatv` or :switch:`-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.
.. index:: -gnatl=fname (gcc)
:switch:`-gnatl={fname}`
This has the same effect as :switch:`-gnatl` except that the output is
written to a file instead of to standard output. If the given name
:file:`fname` does not start with a period, then it is the full name
of the file to be written. If :file:`fname` is an extension, it is
appended to the name of the file being compiled. For example, if
file :file:`xyz.adb` is compiled with :switch:`-gnatl=.lst`,
then the output is written to file xyz.adb.lst.
.. index:: -gnatU (gcc)
:switch:`-gnatU`
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.
.. index:: -gnatb (gcc)
:switch:`-gnatb`
The ``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).
.. index:: -gnatm (gcc)
:switch:`-gnatm={n}`
The ``m`` stands for maximum.
``n`` is a decimal integer in the
range of 1 to 999999 and limits the number of error or warning
messages to be generated. For example, using
:switch:`-gnatm2` might yield
::
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:5:35: missing ".."
fatal error: maximum number of errors detected
compilation abandoned
The default setting if
no switch is given is 9999. If the number of warnings reaches this
limit, then a message is output and further warnings are suppressed,
but the compilation is continued. If the number of error messages
reaches this limit, then a message is output and the compilation
is abandoned. A value of zero means that no limit applies.
Note that the equal sign is optional, so the switches
:switch:`-gnatm2` and :switch:`-gnatm=2` are equivalent.
.. index:: -gnatf (gcc)
:switch:`-gnatf`
.. index:: Error messages, suppressing
The ``f`` stands for full.
Normally, the compiler suppresses error messages that are likely to be
redundant. This switch causes all error
messages to be generated. In particular, in the case of
references to undefined variables. If a given variable is referenced
several times, the normal format of messages is
::
e.adb:7:07: "V" is undefined (more references follow)
where the parenthetical comment warns that there are additional
references to the variable ``V``. Compiling the same program with the
:switch:`-gnatf` switch yields
::
e.adb:7:07: "V" is undefined
e.adb:8:07: "V" is undefined
e.adb:8:12: "V" is undefined
e.adb:8:16: "V" is undefined
e.adb:9:07: "V" is undefined
e.adb:9:12: "V" is undefined
The :switch:`-gnatf` switch also generates additional information for
some error messages. Some examples are:
* Details on possibly non-portable unchecked conversion
* List possible interpretations for ambiguous calls
* Additional details on incorrect parameters
.. index:: -gnatjnn (gcc)
:switch:`-gnatjnn`
In normal operation mode (or if :switch:`-gnatj0` is used), then error messages
with continuation lines are treated as though the continuation lines were
separate messages (and so a warning with two continuation lines counts as
three warnings, and is listed as three separate messages).
If the :switch:`-gnatjnn` switch is used with a positive value for nn, then
messages are output in a different manner. A message and all its continuation
lines are treated as a unit, and count as only one warning or message in the
statistics totals. Furthermore, the message is reformatted so that no line
is longer than nn characters.
.. index:: -gnatq (gcc)
:switch:`-gnatq`
The ``q`` stands for quit (really 'don't quit').
In normal operation mode, the compiler first parses the program and
determines if there are any syntax errors. If there are, appropriate
error messages are generated and compilation is immediately terminated.
This switch tells
GNAT to continue with semantic analysis even if syntax errors have been
found. This may enable the detection of more errors in a single run. On
the other hand, the semantic analyzer is more likely to encounter some
internal fatal error when given a syntactically invalid tree.
.. index:: -gnatQ (gcc)
:switch:`-gnatQ`
In normal operation mode, the :file:`ALI` file is not generated if any
illegalities are detected in the program. The use of :switch:`-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 browsing tools or integrated development
environments) that are driven from the :file:`ALI` file. This switch
implies :switch:`-gnatq`, since the semantic phase must be run to get a
meaningful ALI file.
In addition, if :switch:`-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 :switch:`-gnatq` to ensure that full semantic processing
occurs. The resulting tree file can be processed by ASIS, for the purpose
of providing partial information about illegal units, but if the error
causes the tree to be badly malformed, then ASIS may crash during the
analysis.
When :switch:`-gnatQ` is used and the generated :file:`ALI` file is marked as
being in error, ``gnatmake`` will attempt to recompile the source when it
finds such an :file:`ALI` file, including with switch :switch:`-gnatc`.
Note that :switch:`-gnatQ` has no effect if :switch:`-gnats` is specified,
since ALI files are never generated if :switch:`-gnats` is set.
.. _Warning_Message_Control:
Warning Message Control
-----------------------
.. index:: Warning messages
In addition to error messages, which correspond to illegalities as defined
in the Ada Reference Manual, the compiler detects two kinds of warning
situations.
First, the compiler considers some constructs suspicious and generates a
warning message to alert you to a possible error. Second, if the
compiler detects a situation that is sure to raise an exception at
run time, it generates a warning message. The following shows an example
of warning messages:
::
e.adb:4:24: warning: creation of object may raise Storage_Error
e.adb:10:17: warning: static value out of range
e.adb:10:17: warning: "Constraint_Error" will be raised at run time
GNAT considers a large number of situations as appropriate
for the generation of warning messages. As always, warnings are not
definite indications of errors. For example, if you do an out-of-range
assignment with the deliberate intention of raising a
``Constraint_Error`` exception, then the warning that may be
issued does not indicate an error. Some of the situations for which GNAT
issues warnings (at least some of the time) are given in the following
list. This list is not complete, and new warnings are often added to
subsequent versions of GNAT. The list is intended to give a general idea
of the kinds of warnings that are generated.
* Possible infinitely recursive calls
* Out-of-range values being assigned
* Possible order of elaboration problems
* Size not a multiple of alignment for a record type
* Assertions (pragma Assert) that are sure to fail
* Unreachable code
* Address clauses with possibly unaligned values, or where an attempt is
made to overlay a smaller variable with a larger one.
* Fixed-point type declarations with a null range
* Direct_IO or Sequential_IO instantiated with a type that has access values
* Variables that are never assigned a value
* Variables that are referenced before being initialized
* Task entries with no corresponding ``accept`` statement
* Duplicate accepts for the same task entry in a ``select``
* Objects that take too much storage
* Unchecked conversion between types of differing sizes
* Missing ``return`` statement along some execution path in a function
* Incorrect (unrecognized) pragmas
* Incorrect external names
* Allocation from empty storage pool
* Potentially blocking operation in protected type
* Suspicious parenthesization of expressions
* Mismatching bounds in an aggregate
* Attempt to return local value by reference
* Premature instantiation of a generic body
* Attempt to pack aliased components
* Out of bounds array subscripts
* Wrong length on string assignment
* Violations of style rules if style checking is enabled
* Unused |with| clauses
* ``Bit_Order`` usage that does not have any effect
* ``Standard.Duration`` used to resolve universal fixed expression
* Dereference of possibly null value
* Declaration that is likely to cause storage error
* Internal GNAT unit |withed| by application unit
* Values known to be out of range at compile time
* Unreferenced or unmodified variables. Note that a special
exemption applies to variables which contain any of the substrings
``DISCARD, DUMMY, IGNORE, JUNK, UNUSED``, in any casing. Such variables
are considered likely to be intentionally used in a situation where
otherwise a warning would be given, so warnings of this kind are
always suppressed for such variables.
* Address overlays that could clobber memory
* Unexpected initialization when address clause present
* Bad alignment for address clause
* Useless type conversions
* Redundant assignment statements and other redundant constructs
* Useless exception handlers
* Accidental hiding of name by child unit
* Access before elaboration detected at compile time
* A range in a ``for`` loop that is known to be null or might be null
The following section lists compiler switches that are available
to control the handling of warning messages. It is also possible
to exercise much finer control over what warnings are issued and
suppressed using the GNAT pragma Warnings (see the description
of the pragma in the :title:`GNAT_Reference_manual`).
.. index:: -gnatwa (gcc)
:switch:`-gnatwa`
*Activate most optional warnings.*
This switch activates most optional warning messages. See the remaining list
in this section for details on optional warning messages that can be
individually controlled. The warnings that are not turned on by this
switch are:
* :switch:`-gnatwd` (implicit dereferencing)
* :switch:`-gnatw.d` (tag warnings with -gnatw switch)
* :switch:`-gnatwh` (hiding)
* :switch:`-gnatw.h` (holes in record layouts)
* :switch:`-gnatw.j` (late primitives of tagged types)
* :switch:`-gnatw.k` (redefinition of names in standard)
* :switch:`-gnatwl` (elaboration warnings)
* :switch:`-gnatw.l` (inherited aspects)
* :switch:`-gnatw.n` (atomic synchronization)
* :switch:`-gnatwo` (address clause overlay)
* :switch:`-gnatw.o` (values set by out parameters ignored)
* :switch:`-gnatw.q` (questionable layout of record types)
* :switch:`-gnatw.s` (overridden size clause)
* :switch:`-gnatwt` (tracking of deleted conditional code)
* :switch:`-gnatw.u` (unordered enumeration)
* :switch:`-gnatw.w` (use of Warnings Off)
* :switch:`-gnatw.y` (reasons for package needing body)
All other optional warnings are turned on.
.. index:: -gnatwA (gcc)
:switch:`-gnatwA`
*Suppress all optional errors.*
This switch suppresses all optional warning messages, see remaining list
in this section for details on optional warning messages that can be
individually controlled. Note that unlike switch :switch:`-gnatws`, the
use of switch :switch:`-gnatwA` does not suppress warnings that are
normally given unconditionally and cannot be individually controlled
(for example, the warning about a missing exit path in a function).
Also, again unlike switch :switch:`-gnatws`, warnings suppressed by
the use of switch :switch:`-gnatwA` can be individually turned back
on. For example the use of switch :switch:`-gnatwA` followed by
switch :switch:`-gnatwd` will suppress all optional warnings except
the warnings for implicit dereferencing.
.. index:: -gnatw.a (gcc)
:switch:`-gnatw.a`
*Activate warnings on failing assertions.*
.. index:: Assert failures
This switch activates warnings for assertions where the compiler can tell at
compile time that the assertion will fail. Note that this warning is given
even if assertions are disabled. The default is that such warnings are
generated.
.. index:: -gnatw.A (gcc)
:switch:`-gnatw.A`
*Suppress warnings on failing assertions.*
.. index:: Assert failures
This switch suppresses warnings for assertions where the compiler can tell at
compile time that the assertion will fail.
.. index:: -gnatwb (gcc)
:switch:`-gnatwb`
*Activate warnings on bad fixed values.*
.. index:: Bad fixed values
.. index:: Fixed-point Small value
.. index:: Small value
This switch activates warnings for static fixed-point expressions whose
value is not an exact multiple of Small. Such values are implementation
dependent, since an implementation is free to choose either of the multiples
that surround the value. GNAT always chooses the closer one, but this is not
required behavior, and it is better to specify a value that is an exact
multiple, ensuring predictable execution. The default is that such warnings
are not generated.
.. index:: -gnatwB (gcc)
:switch:`-gnatwB`
*Suppress warnings on bad fixed values.*
This switch suppresses warnings for static fixed-point expressions whose
value is not an exact multiple of Small.
.. index:: -gnatw.b (gcc)
:switch:`-gnatw.b`
*Activate warnings on biased representation.*
.. index:: Biased representation
This switch activates warnings when a size clause, value size clause, component
clause, or component size clause forces the use of biased representation for an
integer type (e.g. representing a range of 10..11 in a single bit by using 0/1
to represent 10/11). The default is that such warnings are generated.
.. index:: -gnatwB (gcc)
:switch:`-gnatw.B`
*Suppress warnings on biased representation.*
This switch suppresses warnings for representation clauses that force the use
of biased representation.
.. index:: -gnatwc (gcc)
:switch:`-gnatwc`
*Activate warnings on conditionals.*
.. index:: Conditionals, constant
This switch activates warnings for conditional expressions used in
tests that are known to be True or False at compile time. The default
is that such warnings are not generated.
Note that this warning does
not get issued for the use of boolean variables or constants whose
values are known at compile time, since this is a standard technique
for conditional compilation in Ada, and this would generate too many
false positive warnings.
This warning option also activates a special test for comparisons using
the operators '>=' and' <='.
If the compiler can tell that only the equality condition is possible,
then it will warn that the '>' or '<' part of the test
is useless and that the operator could be replaced by '='.
An example would be comparing a ``Natural`` variable <= 0.
This warning option also generates warnings if
one or both tests is optimized away in a membership test for integer
values if the result can be determined at compile time. Range tests on
enumeration types are not included, since it is common for such tests
to include an end point.
This warning can also be turned on using :switch:`-gnatwa`.
.. index:: -gnatwC (gcc)
:switch:`-gnatwC`
*Suppress warnings on conditionals.*
This switch suppresses warnings for conditional expressions used in
tests that are known to be True or False at compile time.
.. index:: -gnatw.c (gcc)
:switch:`-gnatw.c`
*Activate warnings on missing component clauses.*
.. index:: Component clause, missing
This switch activates warnings for record components where a record
representation clause is present and has component clauses for the
majority, but not all, of the components. A warning is given for each
component for which no component clause is present.
.. index:: -gnatwC (gcc)
:switch:`-gnatw.C`
*Suppress warnings on missing component clauses.*
This switch suppresses warnings for record components that are
missing a component clause in the situation described above.
.. index:: -gnatwd (gcc)
:switch:`-gnatwd`
*Activate warnings on implicit dereferencing.*
If this switch is set, then the use of a prefix of an access type
in an indexed component, slice, or selected component without an
explicit ``.all`` will generate a warning. With this warning
enabled, access checks occur only at points where an explicit
``.all`` appears in the source code (assuming no warnings are
generated as a result of this switch). The default is that such
warnings are not generated.
.. index:: -gnatwD (gcc)
:switch:`-gnatwD`
*Suppress warnings on implicit dereferencing.*
.. index:: Implicit dereferencing
.. index:: Dereferencing, implicit
This switch suppresses warnings for implicit dereferences in
indexed components, slices, and selected components.
.. index:: -gnatw.d (gcc)
:switch:`-gnatw.d`
*Activate tagging of warning and info messages.*
If this switch is set, then warning messages are tagged, with one of the
following strings:
- *[-gnatw?]*
Used to tag warnings controlled by the switch :switch:`-gnatwx` where x
is a letter a-z.
- *[-gnatw.?]*
Used to tag warnings controlled by the switch :switch:`-gnatw.x` where x
is a letter a-z.
- *[-gnatel]*
Used to tag elaboration information (info) messages generated when the
static model of elaboration is used and the :switch:`-gnatel` switch is set.
- *[restriction warning]*
Used to tag warning messages for restriction violations, activated by use
of the pragma ``Restriction_Warnings``.
- *[warning-as-error]*
Used to tag warning messages that have been converted to error messages by
use of the pragma Warning_As_Error. Note that such warnings are prefixed by
the string "error: " rather than "warning: ".
- *[enabled by default]*
Used to tag all other warnings that are always given by default, unless
warnings are completely suppressed using pragma *Warnings(Off)* or
the switch :switch:`-gnatws`.
.. index:: -gnatw.d (gcc)
:switch:`-gnatw.D`
*Deactivate tagging of warning and info messages messages.*
If this switch is set, then warning messages return to the default
mode in which warnings and info messages are not tagged as described above for
:switch:`-gnatw.d`.
.. index:: -gnatwe (gcc)
.. index:: Warnings, treat as error
:switch:`-gnatwe`
*Treat warnings and style checks as errors.*
This switch causes warning messages and style check messages to be
treated as errors.
The warning string still appears, but the warning messages are counted
as errors, and prevent the generation of an object file. Note that this
is the only -gnatw switch that affects the handling of style check messages.
Note also that this switch has no effect on info (information) messages, which
are not treated as errors if this switch is present.
.. index:: -gnatw.e (gcc)
:switch:`-gnatw.e`
*Activate every optional warning.*
.. index:: Warnings, activate every optional warning
This switch activates all optional warnings, including those which
are not activated by :switch:`-gnatwa`. The use of this switch is not
recommended for normal use. If you turn this switch on, it is almost
certain that you will get large numbers of useless warnings. The
warnings that are excluded from :switch:`-gnatwa` are typically highly
specialized warnings that are suitable for use only in code that has
been specifically designed according to specialized coding rules.
.. index:: -gnatwE (gcc)
.. index:: Warnings, treat as error
:switch:`-gnatwE`
*Treat all run-time exception warnings as errors.*
This switch causes warning messages regarding errors that will be raised
during run-time execution to be treated as errors.
.. index:: -gnatwf (gcc)
:switch:`-gnatwf`
*Activate warnings on unreferenced formals.*
.. index:: Formals, unreferenced
This switch causes a warning to be generated if a formal parameter
is not referenced in the body of the subprogram. This warning can
also be turned on using :switch:`-gnatwu`. The
default is that these warnings are not generated.
.. index:: -gnatwF (gcc)
:switch:`-gnatwF`
*Suppress warnings on unreferenced formals.*
This switch suppresses warnings for unreferenced formal
parameters. Note that the
combination :switch:`-gnatwu` followed by :switch:`-gnatwF` has the
effect of warning on unreferenced entities other than subprogram
formals.
.. index:: -gnatwg (gcc)
:switch:`-gnatwg`
*Activate warnings on unrecognized pragmas.*
.. index:: Pragmas, unrecognized
This switch causes a warning to be generated if an unrecognized
pragma is encountered. Apart from issuing this warning, the
pragma is ignored and has no effect. The default
is that such warnings are issued (satisfying the Ada Reference
Manual requirement that such warnings appear).
.. index:: -gnatwG (gcc)
:switch:`-gnatwG`
*Suppress warnings on unrecognized pragmas.*
This switch suppresses warnings for unrecognized pragmas.
.. index:: -gnatw.g (gcc)
:switch:`-gnatw.g`
*Warnings used for GNAT sources.*
This switch sets the warning categories that are used by the standard
GNAT style. Currently this is equivalent to
:switch:`-gnatwAao.q.s.CI.V.X.Z`
but more warnings may be added in the future without advanced notice.
.. index:: -gnatwh (gcc)
:switch:`-gnatwh`
*Activate warnings on hiding.*
.. index:: Hiding of Declarations
This switch activates warnings on hiding declarations that are considered
potentially confusing. Not all cases of hiding cause warnings; for example an
overriding declaration hides an implicit declaration, which is just normal
code. The default is that warnings on hiding are not generated.
.. index:: -gnatwH (gcc)
:switch:`-gnatwH`
*Suppress warnings on hiding.*
This switch suppresses warnings on hiding declarations.
.. index:: -gnatw.h (gcc)
:switch:`-gnatw.h`
*Activate warnings on holes/gaps in records.*
.. index:: Record Representation (gaps)
This switch activates warnings on component clauses in record
representation clauses that leave holes (gaps) in the record layout.
If this warning option is active, then record representation clauses
should specify a contiguous layout, adding unused fill fields if needed.
.. index:: -gnatw.H (gcc)
:switch:`-gnatw.H`
*Suppress warnings on holes/gaps in records.*
This switch suppresses warnings on component clauses in record
representation clauses that leave holes (haps) in the record layout.
.. index:: -gnatwi (gcc)
:switch:`-gnatwi`
*Activate warnings on implementation units.*
This switch activates warnings for a |with| of an internal GNAT
implementation unit, defined as any unit from the ``Ada``,
``Interfaces``, ``GNAT``,
or ``System``
hierarchies that is not
documented in either the Ada Reference Manual or the GNAT
Programmer's Reference Manual. Such units are intended only
for internal implementation purposes and should not be |withed|
by user programs. The default is that such warnings are generated
.. index:: -gnatwI (gcc)
:switch:`-gnatwI`
*Disable warnings on implementation units.*
This switch disables warnings for a |with| of an internal GNAT
implementation unit.
.. index:: -gnatw.i (gcc)
:switch:`-gnatw.i`
*Activate warnings on overlapping actuals.*
This switch enables a warning on statically detectable overlapping actuals in
a subprogram call, when one of the actuals is an in-out parameter, and the
types of the actuals are not by-copy types. This warning is off by default.
.. index:: -gnatw.I (gcc)
:switch:`-gnatw.I`
*Disable warnings on overlapping actuals.*
This switch disables warnings on overlapping actuals in a call..
.. index:: -gnatwj (gcc)
:switch:`-gnatwj`
*Activate warnings on obsolescent features (Annex J).*
.. index:: Features, obsolescent
.. index:: Obsolescent features
If this warning option is activated, then warnings are generated for
calls to subprograms marked with ``pragma Obsolescent`` and
for use of features in Annex J of the Ada Reference Manual. In the
case of Annex J, not all features are flagged. In particular use
of the renamed packages (like ``Text_IO``) and use of package
``ASCII`` are not flagged, since these are very common and
would generate many annoying positive warnings. The default is that
such warnings are not generated.
In addition to the above cases, warnings are also generated for
GNAT features that have been provided in past versions but which
have been superseded (typically by features in the new Ada standard).
For example, ``pragma Ravenscar`` will be flagged since its
function is replaced by ``pragma Profile(Ravenscar)``, and
``pragma Interface_Name`` will be flagged since its function
is replaced by ``pragma Import``.
Note that this warning option functions differently from the
restriction ``No_Obsolescent_Features`` in two respects.
First, the restriction applies only to annex J features.
Second, the restriction does flag uses of package ``ASCII``.
.. index:: -gnatwJ (gcc)
:switch:`-gnatwJ`
*Suppress warnings on obsolescent features (Annex J).*
This switch disables warnings on use of obsolescent features.
.. index:: -gnatw.j (gcc)
:switch:`-gnatw.j`
*Activate warnings on late declarations of tagged type primitives.*
This switch activates warnings on visible primitives added to a
tagged type after deriving a private extension from it.
.. index:: -gnatw.J (gcc)
:switch:`-gnatw.J`
*Suppress warnings on late declarations of tagged type primitives.*
This switch suppresses warnings on visible primitives added to a
tagged type after deriving a private extension from it.
.. index:: -gnatwk (gcc)
:switch:`-gnatwk`
*Activate warnings on variables that could be constants.*
This switch activates warnings for variables that are initialized but
never modified, and then could be declared constants. The default is that
such warnings are not given.
.. index:: -gnatwK (gcc)
:switch:`-gnatwK`
*Suppress warnings on variables that could be constants.*
This switch disables warnings on variables that could be declared constants.
.. index:: -gnatw.k (gcc)
:switch:`-gnatw.k`
*Activate warnings on redefinition of names in standard.*
This switch activates warnings for declarations that declare a name that
is defined in package Standard. Such declarations can be confusing,
especially since the names in package Standard continue to be directly
visible, meaning that use visibiliy on such redeclared names does not
work as expected. Names of discriminants and components in records are
not included in this check.
.. index:: -gnatwK (gcc)
:switch:`-gnatw.K`
*Suppress warnings on redefinition of names in standard.*
This switch activates warnings for declarations that declare a name that
is defined in package Standard.
.. index:: -gnatwl (gcc)
:switch:`-gnatwl`
*Activate warnings for elaboration pragmas.*
.. index:: Elaboration, warnings
This switch activates warnings for possible elaboration problems,
including suspicious use
of ``Elaborate`` pragmas, when using the static elaboration model, and
possible situations that may raise ``Program_Error`` when using the
dynamic elaboration model.
See the section in this guide on elaboration checking for further details.
The default is that such warnings
are not generated.
.. index:: -gnatwL (gcc)
:switch:`-gnatwL`
*Suppress warnings for elaboration pragmas.*
This switch suppresses warnings for possible elaboration problems.
.. index:: -gnatw.l (gcc)
:switch:`-gnatw.l`
*List inherited aspects.*
This switch causes the compiler to list inherited invariants,
preconditions, and postconditions from Type_Invariant'Class, Invariant'Class,
Pre'Class, and Post'Class aspects. Also list inherited subtype predicates.
.. index:: -gnatw.L (gcc)
:switch:`-gnatw.L`
*Suppress listing of inherited aspects.*
This switch suppresses listing of inherited aspects.
.. index:: -gnatwm (gcc)
:switch:`-gnatwm`
*Activate warnings on modified but unreferenced variables.*
This switch activates warnings for variables that are assigned (using
an initialization value or with one or more assignment statements) but
whose value is never read. The warning is suppressed for volatile
variables and also for variables that are renamings of other variables
or for which an address clause is given.
The default is that these warnings are not given.
.. index:: -gnatwM (gcc)
:switch:`-gnatwM`
*Disable warnings on modified but unreferenced variables.*
This switch disables warnings for variables that are assigned or
initialized, but never read.
.. index:: -gnatw.m (gcc)
:switch:`-gnatw.m`
*Activate warnings on suspicious modulus values.*
This switch activates warnings for modulus values that seem suspicious.
The cases caught are where the size is the same as the modulus (e.g.
a modulus of 7 with a size of 7 bits), and modulus values of 32 or 64
with no size clause. The guess in both cases is that 2**x was intended
rather than x. In addition expressions of the form 2*x for small x
generate a warning (the almost certainly accurate guess being that
2**x was intended). The default is that these warnings are given.
.. index:: -gnatw.M (gcc)
:switch:`-gnatw.M`
*Disable warnings on suspicious modulus values.*
This switch disables warnings for suspicious modulus values.
.. index:: -gnatwn (gcc)
:switch:`-gnatwn`
*Set normal warnings mode.*
This switch sets normal warning mode, in which enabled warnings are
issued and treated as warnings rather than errors. This is the default
mode. the switch :switch:`-gnatwn` can be used to cancel the effect of
an explicit :switch:`-gnatws` or
:switch:`-gnatwe`. It also cancels the effect of the
implicit :switch:`-gnatwe` that is activated by the
use of :switch:`-gnatg`.
.. index:: -gnatw.n (gcc)
.. index:: Atomic Synchronization, warnings
:switch:`-gnatw.n`
*Activate warnings on atomic synchronization.*
This switch actives warnings when an access to an atomic variable
requires the generation of atomic synchronization code. These
warnings are off by default.
.. index:: -gnatw.N (gcc)
:switch:`-gnatw.N`
*Suppress warnings on atomic synchronization.*
.. index:: Atomic Synchronization, warnings
This switch suppresses warnings when an access to an atomic variable
requires the generation of atomic synchronization code.
.. index:: -gnatwo (gcc)
.. index:: Address Clauses, warnings
:switch:`-gnatwo`
*Activate warnings on address clause overlays.*
This switch activates warnings for possibly unintended initialization
effects of defining address clauses that cause one variable to overlap
another. The default is that such warnings are generated.
.. index:: -gnatwO (gcc)
:switch:`-gnatwO`
*Suppress warnings on address clause overlays.*
This switch suppresses warnings on possibly unintended initialization
effects of defining address clauses that cause one variable to overlap
another.
.. index:: -gnatw.o (gcc)
:switch:`-gnatw.o`
*Activate warnings on modified but unreferenced out parameters.*
This switch activates warnings for variables that are modified by using
them as actuals for a call to a procedure with an out mode formal, where
the resulting assigned value is never read. It is applicable in the case
where there is more than one out mode formal. If there is only one out
mode formal, the warning is issued by default (controlled by -gnatwu).
The warning is suppressed for volatile
variables and also for variables that are renamings of other variables
or for which an address clause is given.
The default is that these warnings are not given.
.. index:: -gnatw.O (gcc)
:switch:`-gnatw.O`
*Disable warnings on modified but unreferenced out parameters.*
This switch suppresses warnings for variables that are modified by using
them as actuals for a call to a procedure with an out mode formal, where
the resulting assigned value is never read.
.. index:: -gnatwp (gcc)
.. index:: Inlining, warnings
:switch:`-gnatwp`
*Activate warnings on ineffective pragma Inlines.*
This switch activates warnings for failure of front end inlining
(activated by :switch:`-gnatN`) to inline a particular call. There are
many reasons for not being able to inline a call, including most
commonly that the call is too complex to inline. The default is
that such warnings are not given.
Warnings on ineffective inlining by the gcc back-end can be activated
separately, using the gcc switch -Winline.
.. index:: -gnatwP (gcc)
:switch:`-gnatwP`
*Suppress warnings on ineffective pragma Inlines.*
This switch suppresses warnings on ineffective pragma Inlines. If the
inlining mechanism cannot inline a call, it will simply ignore the
request silently.
.. index:: -gnatw.p (gcc)
.. index:: Parameter order, warnings
:switch:`-gnatw.p`
*Activate warnings on parameter ordering.*
This switch activates warnings for cases of suspicious parameter
ordering when the list of arguments are all simple identifiers that
match the names of the formals, but are in a different order. The
warning is suppressed if any use of named parameter notation is used,
so this is the appropriate way to suppress a false positive (and
serves to emphasize that the "misordering" is deliberate). The
default is that such warnings are not given.
.. index:: -gnatw.P (gcc)
:switch:`-gnatw.P`
*Suppress warnings on parameter ordering.*
This switch suppresses warnings on cases of suspicious parameter
ordering.
.. index:: -gnatwq (gcc)
.. index:: Parentheses, warnings
:switch:`-gnatwq`
*Activate warnings on questionable missing parentheses.*
This switch activates warnings for cases where parentheses are not used and
the result is potential ambiguity from a readers point of view. For example
(not a > b) when a and b are modular means ((not a) > b) and very likely the
programmer intended (not (a > b)). Similarly (-x mod 5) means (-(x mod 5)) and
quite likely ((-x) mod 5) was intended. In such situations it seems best to
follow the rule of always parenthesizing to make the association clear, and
this warning switch warns if such parentheses are not present. The default
is that these warnings are given.
.. index:: -gnatwQ (gcc)
:switch:`-gnatwQ`
*Suppress warnings on questionable missing parentheses.*
This switch suppresses warnings for cases where the association is not
clear and the use of parentheses is preferred.
.. index:: -gnatw.q (gcc)
.. index:: Layout, warnings
:switch:`-gnatw.q`
*Activate warnings on questionable layout of record types.*
This switch activates warnings for cases where the default layout of
a record type, that is to say the layout of its components in textual
order of the source code, would very likely cause inefficiencies in
the code generated by the compiler, both in terms of space and speed
during execution. One warning is issued for each problematic component
without representation clause in the nonvariant part and then in each
variant recursively, if any.
The purpose of these warnings is neither to prescribe an optimal layout
nor to force the use of representation clauses, but rather to get rid of
the most blatant inefficiencies in the layout. Therefore, the default
layout is matched against the following synthetic ordered layout and
the deviations are flagged on a component-by-component basis:
* first all components or groups of components whose length is fixed
and a multiple of the storage unit,
* then the remaining components whose length is fixed and not a multiple
of the storage unit,
* then the remaining components whose length doesn't depend on discriminants
(that is to say, with variable but uniform length for all objects),
* then all components whose length depends on discriminants,
* finally the variant part (if any),
for the nonvariant part and for each variant recursively, if any.
The exact wording of the warning depends on whether the compiler is allowed
to reorder the components in the record type or precluded from doing it by
means of pragma ``No_Component_Reordering``.
The default is that these warnings are not given.
.. index:: -gnatw.Q (gcc)
:switch:`-gnatw.Q`
*Suppress warnings on questionable layout of record types.*
This switch suppresses warnings for cases where the default layout of
a record type would very likely cause inefficiencies.
.. index:: -gnatwr (gcc)
:switch:`-gnatwr`
*Activate warnings on redundant constructs.*
This switch activates warnings for redundant constructs. The following
is the current list of constructs regarded as redundant:
* Assignment of an item to itself.
* Type conversion that converts an expression to its own type.
* Use of the attribute ``Base`` where ``typ'Base`` is the same
as ``typ``.
* Use of pragma ``Pack`` when all components are placed by a record
representation clause.
* Exception handler containing only a reraise statement (raise with no
operand) which has no effect.
* Use of the operator abs on an operand that is known at compile time
to be non-negative
* Comparison of an object or (unary or binary) operation of boolean type to
an explicit True value.
The default is that warnings for redundant constructs are not given.
.. index:: -gnatwR (gcc)
:switch:`-gnatwR`
*Suppress warnings on redundant constructs.*
This switch suppresses warnings for redundant constructs.
.. index:: -gnatw.r (gcc)
:switch:`-gnatw.r`
*Activate warnings for object renaming function.*
This switch activates warnings for an object renaming that renames a
function call, which is equivalent to a constant declaration (as
opposed to renaming the function itself). The default is that these
warnings are given.
.. index:: -gnatwT (gcc)
:switch:`-gnatw.R`
*Suppress warnings for object renaming function.*
This switch suppresses warnings for object renaming function.
.. index:: -gnatws (gcc)
:switch:`-gnatws`
*Suppress all warnings.*
This switch completely suppresses the
output of all warning messages from the GNAT front end, including
both warnings that can be controlled by switches described in this
section, and those that are normally given unconditionally. The
effect of this suppress action can only be cancelled by a subsequent
use of the switch :switch:`-gnatwn`.
Note that switch :switch:`-gnatws` does not suppress
warnings from the ``gcc`` back end.
To suppress these back end warnings as well, use the switch :switch:`-w`
in addition to :switch:`-gnatws`. Also this switch has no effect on the
handling of style check messages.
.. index:: -gnatw.s (gcc)
.. index:: Record Representation (component sizes)
:switch:`-gnatw.s`
*Activate warnings on overridden size clauses.*
This switch activates warnings on component clauses in record
representation clauses where the length given overrides that
specified by an explicit size clause for the component type. A
warning is similarly given in the array case if a specified
component size overrides an explicit size clause for the array
component type.
.. index:: -gnatw.S (gcc)
:switch:`-gnatw.S`
*Suppress warnings on overridden size clauses.*
This switch suppresses warnings on component clauses in record
representation clauses that override size clauses, and similar
warnings when an array component size overrides a size clause.
.. index:: -gnatwt (gcc)
.. index:: Deactivated code, warnings
.. index:: Deleted code, warnings
:switch:`-gnatwt`
*Activate warnings for tracking of deleted conditional code.*
This switch activates warnings for tracking of code in conditionals (IF and
CASE statements) that is detected to be dead code which cannot be executed, and
which is removed by the front end. This warning is off by default. This may be
useful for detecting deactivated code in certified applications.
.. index:: -gnatwT (gcc)
:switch:`-gnatwT`
*Suppress warnings for tracking of deleted conditional code.*
This switch suppresses warnings for tracking of deleted conditional code.
.. index:: -gnatw.t (gcc)
:switch:`-gnatw.t`
*Activate warnings on suspicious contracts.*
This switch activates warnings on suspicious contracts. This includes
warnings on suspicious postconditions (whether a pragma ``Postcondition`` or a
``Post`` aspect in Ada 2012) and suspicious contract cases (pragma or aspect
``Contract_Cases``). A function postcondition or contract case is suspicious
when no postcondition or contract case for this function mentions the result
of the function. A procedure postcondition or contract case is suspicious
when it only refers to the pre-state of the procedure, because in that case
it should rather be expressed as a precondition. This switch also controls
warnings on suspicious cases of expressions typically found in contracts like
quantified expressions and uses of Update attribute. The default is that such
warnings are generated.
.. index:: -gnatw.T (gcc)
:switch:`-gnatw.T`
*Suppress warnings on suspicious contracts.*
This switch suppresses warnings on suspicious contracts.
.. index:: -gnatwu (gcc)
:switch:`-gnatwu`
*Activate warnings on unused entities.*
This switch activates warnings to be generated for entities that
are declared but not referenced, and for units that are |withed|
and not
referenced. In the case of packages, a warning is also generated if
no entities in the package are referenced. This means that if a with'ed
package is referenced but the only references are in ``use``
clauses or ``renames``
declarations, a warning is still generated. A warning is also generated
for a generic package that is |withed| but never instantiated.
In the case where a package or subprogram body is compiled, and there
is a |with| on the corresponding spec
that is only referenced in the body,
a warning is also generated, noting that the
|with| can be moved to the body. The default is that
such warnings are not generated.
This switch also activates warnings on unreferenced formals
(it includes the effect of :switch:`-gnatwf`).
.. index:: -gnatwU (gcc)
:switch:`-gnatwU`
*Suppress warnings on unused entities.*
This switch suppresses warnings for unused entities and packages.
It also turns off warnings on unreferenced formals (and thus includes
the effect of :switch:`-gnatwF`).
.. index:: -gnatw.u (gcc)
:switch:`-gnatw.u`
*Activate warnings on unordered enumeration types.*
This switch causes enumeration types to be considered as conceptually
unordered, unless an explicit pragma ``Ordered`` is given for the type.
The effect is to generate warnings in clients that use explicit comparisons
or subranges, since these constructs both treat objects of the type as
ordered. (A *client* is defined as a unit that is other than the unit in
which the type is declared, or its body or subunits.) Please refer to
the description of pragma ``Ordered`` in the
:title:`GNAT Reference Manual` for further details.
The default is that such warnings are not generated.
.. index:: -gnatw.U (gcc)
:switch:`-gnatw.U`
*Deactivate warnings on unordered enumeration types.*
This switch causes all enumeration types to be considered as ordered, so
that no warnings are given for comparisons or subranges for any type.
.. index:: -gnatwv (gcc)
.. index:: Unassigned variable warnings
:switch:`-gnatwv`
*Activate warnings on unassigned variables.*
This switch activates warnings for access to variables which
may not be properly initialized. The default is that
such warnings are generated.
.. index:: -gnatwV (gcc)
:switch:`-gnatwV`
*Suppress warnings on unassigned variables.*
This switch suppresses warnings for access to variables which
may not be properly initialized.
For variables of a composite type, the warning can also be suppressed in
Ada 2005 by using a default initialization with a box. For example, if
Table is an array of records whose components are only partially uninitialized,
then the following code:
.. code-block:: ada
Tab : Table := (others => <>);
will suppress warnings on subsequent statements that access components
of variable Tab.
.. index:: -gnatw.v (gcc)
.. index:: bit order warnings
:switch:`-gnatw.v`
*Activate info messages for non-default bit order.*
This switch activates messages (labeled "info", they are not warnings,
just informational messages) about the effects of non-default bit-order
on records to which a component clause is applied. The effect of specifying
non-default bit ordering is a bit subtle (and changed with Ada 2005), so
these messages, which are given by default, are useful in understanding the
exact consequences of using this feature.
.. index:: -gnatw.V (gcc)
:switch:`-gnatw.V`
*Suppress info messages for non-default bit order.*
This switch suppresses information messages for the effects of specifying
non-default bit order on record components with component clauses.
.. index:: -gnatww (gcc)
.. index:: String indexing warnings
:switch:`-gnatww`
*Activate warnings on wrong low bound assumption.*
This switch activates warnings for indexing an unconstrained string parameter
with a literal or S'Length. This is a case where the code is assuming that the
low bound is one, which is in general not true (for example when a slice is
passed). The default is that such warnings are generated.
.. index:: -gnatwW (gcc)
:switch:`-gnatwW`
*Suppress warnings on wrong low bound assumption.*
This switch suppresses warnings for indexing an unconstrained string parameter
with a literal or S'Length. Note that this warning can also be suppressed
in a particular case by adding an assertion that the lower bound is 1,
as shown in the following example:
.. code-block:: ada
procedure K (S : String) is
pragma Assert (S'First = 1);
...
.. index:: -gnatw.w (gcc)
.. index:: Warnings Off control
:switch:`-gnatw.w`
*Activate warnings on Warnings Off pragmas.*
This switch activates warnings for use of ``pragma Warnings (Off, entity)``
where either the pragma is entirely useless (because it suppresses no
warnings), or it could be replaced by ``pragma Unreferenced`` or
``pragma Unmodified``.
Also activates warnings for the case of
Warnings (Off, String), where either there is no matching
Warnings (On, String), or the Warnings (Off) did not suppress any warning.
The default is that these warnings are not given.
.. index:: -gnatw.W (gcc)
:switch:`-gnatw.W`
*Suppress warnings on unnecessary Warnings Off pragmas.*
This switch suppresses warnings for use of ``pragma Warnings (Off, ...)``.
.. index:: -gnatwx (gcc)
.. index:: Export/Import pragma warnings
:switch:`-gnatwx`
*Activate warnings on Export/Import pragmas.*
This switch activates warnings on Export/Import pragmas when
the compiler detects a possible conflict between the Ada and
foreign language calling sequences. For example, the use of
default parameters in a convention C procedure is dubious
because the C compiler cannot supply the proper default, so
a warning is issued. The default is that such warnings are
generated.
.. index:: -gnatwX (gcc)
:switch:`-gnatwX`
*Suppress warnings on Export/Import pragmas.*
This switch suppresses warnings on Export/Import pragmas.
The sense of this is that you are telling the compiler that
you know what you are doing in writing the pragma, and it
should not complain at you.
.. index:: -gnatwm (gcc)
:switch:`-gnatw.x`
*Activate warnings for No_Exception_Propagation mode.*
This switch activates warnings for exception usage when pragma Restrictions
(No_Exception_Propagation) is in effect. Warnings are given for implicit or
explicit exception raises which are not covered by a local handler, and for
exception handlers which do not cover a local raise. The default is that
these warnings are given for units that contain exception handlers.
:switch:`-gnatw.X`
*Disable warnings for No_Exception_Propagation mode.*
This switch disables warnings for exception usage when pragma Restrictions
(No_Exception_Propagation) is in effect.
.. index:: -gnatwy (gcc)
.. index:: Ada compatibility issues warnings
:switch:`-gnatwy`
*Activate warnings for Ada compatibility issues.*
For the most part, newer versions of Ada are upwards compatible
with older versions. For example, Ada 2005 programs will almost
always work when compiled as Ada 2012.
However there are some exceptions (for example the fact that
``some`` is now a reserved word in Ada 2012). This
switch activates several warnings to help in identifying
and correcting such incompatibilities. The default is that
these warnings are generated. Note that at one point Ada 2005
was called Ada 0Y, hence the choice of character.
.. index:: -gnatwY (gcc)
.. index:: Ada compatibility issues warnings
:switch:`-gnatwY`
*Disable warnings for Ada compatibility issues.*
This switch suppresses the warnings intended to help in identifying
incompatibilities between Ada language versions.
.. index:: -gnatw.y (gcc)
.. index:: Package spec needing body
:switch:`-gnatw.y`
*Activate information messages for why package spec needs body.*
There are a number of cases in which a package spec needs a body.
For example, the use of pragma Elaborate_Body, or the declaration
of a procedure specification requiring a completion. This switch
causes information messages to be output showing why a package
specification requires a body. This can be useful in the case of
a large package specification which is unexpectedly requiring a
body. The default is that such information messages are not output.
.. index:: -gnatw.Y (gcc)
.. index:: No information messages for why package spec needs body
:switch:`-gnatw.Y`
*Disable information messages for why package spec needs body.*
This switch suppresses the output of information messages showing why
a package specification needs a body.
.. index:: -gnatwz (gcc)
.. index:: Unchecked_Conversion warnings
:switch:`-gnatwz`
*Activate warnings on unchecked conversions.*
This switch activates warnings for unchecked conversions
where the types are known at compile time to have different
sizes. The default is that such warnings are generated. Warnings are also
generated for subprogram pointers with different conventions.
.. index:: -gnatwZ (gcc)
:switch:`-gnatwZ`
*Suppress warnings on unchecked conversions.*
This switch suppresses warnings for unchecked conversions
where the types are known at compile time to have different
sizes or conventions.
.. index:: -gnatw.z (gcc)
.. index:: Size/Alignment warnings
:switch:`-gnatw.z`
*Activate warnings for size not a multiple of alignment.*
This switch activates warnings for cases of record types with
specified ``Size`` and ``Alignment`` attributes where the
size is not a multiple of the alignment, resulting in an object
size that is greater than the specified size. The default
is that such warnings are generated.
.. index:: -gnatw.Z (gcc)
.. index:: Size/Alignment warnings
:switch:`-gnatw.Z`
*Suppress warnings for size not a multiple of alignment.*
This switch suppresses warnings for cases of record types with
specified ``Size`` and ``Alignment`` attributes where the
size is not a multiple of the alignment, resulting in an object
size that is greater than the specified size.
The warning can also be
suppressed by giving an explicit ``Object_Size`` value.
.. index:: -Wunused (gcc)
:switch:`-Wunused`
The warnings controlled by the :switch:`-gnatw` switch are generated by
the front end of the compiler. The GCC back end can provide
additional warnings and they are controlled by the :switch:`-W` switch.
For example, :switch:`-Wunused` activates back end
warnings for entities that are declared but not referenced.
.. index:: -Wuninitialized (gcc)
:switch:`-Wuninitialized`
Similarly, :switch:`-Wuninitialized` activates
the back end warning for uninitialized variables. This switch must be
used in conjunction with an optimization level greater than zero.
.. index:: -Wstack-usage (gcc)
:switch:`-Wstack-usage={len}`
Warn if the stack usage of a subprogram might be larger than ``len`` bytes.
See :ref:`Static_Stack_Usage_Analysis` for details.
.. index:: -Wall (gcc)
:switch:`-Wall`
This switch enables most warnings from the GCC back end.
The code generator detects a number of warning situations that are missed
by the GNAT front end, and this switch can be used to activate them.
The use of this switch also sets the default front end warning mode to
:switch:`-gnatwa`, that is, most front end warnings activated as well.
.. index:: -w (gcc)
:switch:`-w`
Conversely, this switch suppresses warnings from the GCC back end.
The use of this switch also sets the default front end warning mode to
:switch:`-gnatws`, that is, front end warnings suppressed as well.
.. index:: -Werror (gcc)
:switch:`-Werror`
This switch causes warnings from the GCC back end 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.
A string of warning parameters can be used in the same parameter. For example::
-gnatwaGe
will turn on all optional warnings except for unrecognized pragma warnings,
and also specify that warnings should be treated as errors.
When no switch :switch:`-gnatw` is used, this is equivalent to:
* :switch:`-gnatw.a`
* :switch:`-gnatwB`
* :switch:`-gnatw.b`
* :switch:`-gnatwC`
* :switch:`-gnatw.C`
* :switch:`-gnatwD`
* :switch:`-gnatw.D`
* :switch:`-gnatwF`
* :switch:`-gnatw.F`
* :switch:`-gnatwg`
* :switch:`-gnatwH`
* :switch:`-gnatw.H`
* :switch:`-gnatwi`
* :switch:`-gnatwJ`
* :switch:`-gnatw.J`
* :switch:`-gnatwK`
* :switch:`-gnatw.K`
* :switch:`-gnatwL`
* :switch:`-gnatw.L`
* :switch:`-gnatwM`
* :switch:`-gnatw.m`
* :switch:`-gnatwn`
* :switch:`-gnatw.N`
* :switch:`-gnatwo`
* :switch:`-gnatw.O`
* :switch:`-gnatwP`
* :switch:`-gnatw.P`
* :switch:`-gnatwq`
* :switch:`-gnatw.Q`
* :switch:`-gnatwR`
* :switch:`-gnatw.R`
* :switch:`-gnatw.S`
* :switch:`-gnatwT`
* :switch:`-gnatw.t`
* :switch:`-gnatwU`
* :switch:`-gnatw.U`
* :switch:`-gnatwv`
* :switch:`-gnatw.v`
* :switch:`-gnatww`
* :switch:`-gnatw.W`
* :switch:`-gnatwx`
* :switch:`-gnatw.X`
* :switch:`-gnatwy`
* :switch:`-gnatw.Y`
* :switch:`-gnatwz`
* :switch:`-gnatw.z`
.. _Debugging_and_Assertion_Control:
Debugging and Assertion Control
-------------------------------
.. index:: -gnata (gcc)
:switch:`-gnata`
.. index:: Assert
.. index:: Debug
.. index:: Assertions
.. index:: Precondition
.. index:: Postcondition
.. index:: Type invariants
.. index:: Subtype predicates
The :switch:`-gnata` option is equivalent to the following ``Assertion_Policy`` pragma::
pragma Assertion_Policy (Check);
Which is a shorthand for::
pragma Assertion_Policy
(Assert => Check,
Static_Predicate => Check,
Dynamic_Predicate => Check,
Pre => Check,
Pre'Class => Check,
Post => Check,
Post'Class => Check,
Type_Invariant => Check,
Type_Invariant'Class => Check);
The pragmas ``Assert`` and ``Debug`` normally have no effect and
are ignored. This switch, where ``a`` stands for 'assert', causes
pragmas ``Assert`` and ``Debug`` to be activated. This switch also
causes preconditions, postconditions, subtype predicates, and
type invariants to be activated.
The pragmas have the form::
pragma Assert (<Boolean-expression> [, <static-string-expression>])
pragma Debug (<procedure call>)
pragma Type_Invariant (<type-local-name>, <Boolean-expression>)
pragma Predicate (<type-local-name>, <Boolean-expression>)
pragma Precondition (<Boolean-expression>, <string-expression>)
pragma Postcondition (<Boolean-expression>, <string-expression>)
The aspects have the form::
with [Pre|Post|Type_Invariant|Dynamic_Predicate|Static_Predicate]
=> <Boolean-expression>;
The ``Assert`` pragma causes ``Boolean-expression`` to be tested.
If the result is ``True``, the pragma has no effect (other than
possible side effects from evaluating the expression). If the result is
``False``, the exception ``Assert_Failure`` declared in the package
``System.Assertions`` is raised (passing ``static-string-expression``, if
present, as the message associated with the exception). If no string
expression is given, the default is a string containing the file name and
line number of the pragma.
The ``Debug`` pragma causes ``procedure`` to be called. Note that
``pragma Debug`` may appear within a declaration sequence, allowing
debugging procedures to be called between declarations.
For the aspect specification, the ``Boolean-expression`` is evaluated.
If the result is ``True``, the aspect has no effect. If the result
is ``False``, the exception ``Assert_Failure`` is raised.
.. _Validity_Checking:
Validity Checking
-----------------
.. index:: Validity Checking
The Ada Reference Manual defines the concept of invalid values (see
RM 13.9.1). The primary source of invalid values is uninitialized
variables. A scalar variable that is left uninitialized may contain
an invalid value; the concept of invalid does not apply to access or
composite types.
It is an error to read an invalid value, but the RM does not require
run-time checks to detect such errors, except for some minimal
checking to prevent erroneous execution (i.e. unpredictable
behavior). This corresponds to the :switch:`-gnatVd` switch below,
which is the default. For example, by default, if the expression of a
case statement is invalid, it will raise Constraint_Error rather than
causing a wild jump, and if an array index on the left-hand side of an
assignment is invalid, it will raise Constraint_Error rather than
overwriting an arbitrary memory location.
The :switch:`-gnatVa` may be used to enable additional validity checks,
which are not required by the RM. These checks are often very
expensive (which is why the RM does not require them). These checks
are useful in tracking down uninitialized variables, but they are
not usually recommended for production builds, and in particular
we do not recommend using these extra validity checking options in
combination with optimization, since this can confuse the optimizer.
If performance is a consideration, leading to the need to optimize,
then the validity checking options should not be used.
The other :switch:`-gnatV{x}` switches below allow finer-grained
control; you can enable whichever validity checks you desire. However,
for most debugging purposes, :switch:`-gnatVa` is sufficient, and the
default :switch:`-gnatVd` (i.e. standard Ada behavior) is usually
sufficient for non-debugging use.
The :switch:`-gnatB` switch tells the compiler to assume that all
values are valid (that is, within their declared subtype range)
except in the context of a use of the Valid attribute. This means
the compiler can generate more efficient code, since the range
of values is better known at compile time. However, an uninitialized
variable can cause wild jumps and memory corruption in this mode.
The :switch:`-gnatV{x}` switch allows control over the validity
checking mode as described below.
The ``x`` argument is a string of letters that
indicate validity checks that are performed or not performed in addition
to the default checks required by Ada as described above.
.. index:: -gnatVa (gcc)
:switch:`-gnatVa`
*All validity checks.*
All validity checks are turned on.
That is, :switch:`-gnatVa` is
equivalent to ``gnatVcdfimorst``.
.. index:: -gnatVc (gcc)
:switch:`-gnatVc`
*Validity checks for copies.*
The right hand side of assignments, and the initializing values of
object declarations are validity checked.
.. index:: -gnatVd (gcc)
:switch:`-gnatVd`
*Default (RM) validity checks.*
Some validity checks are done by default following normal Ada semantics
(RM 13.9.1 (9-11)).
A check is done in case statements that the expression is within the range
of the subtype. If it is not, Constraint_Error is raised.
For assignments to array components, a check is done that the expression used
as index is within the range. If it is not, Constraint_Error is raised.
Both these validity checks may be turned off using switch :switch:`-gnatVD`.
They are turned on by default. If :switch:`-gnatVD` is specified, a subsequent
switch :switch:`-gnatVd` will leave the checks turned on.
Switch :switch:`-gnatVD` should be used only if you are sure that all such
expressions have valid values. If you use this switch and invalid values
are present, then the program is erroneous, and wild jumps or memory
overwriting may occur.
.. index:: -gnatVe (gcc)
:switch:`-gnatVe`
*Validity checks for elementary components.*
In the absence of this switch, assignments to record or array components are
not validity checked, even if validity checks for assignments generally
(:switch:`-gnatVc`) are turned on. In Ada, assignment of composite values do not
require valid data, but assignment of individual components does. So for
example, there is a difference between copying the elements of an array with a
slice assignment, compared to assigning element by element in a loop. This
switch allows you to turn off validity checking for components, even when they
are assigned component by component.<