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.\" ========================================================================
.\"
.IX Title "GM2 1"
.TH GM2 1 "2023-07-07" "gcc-10" "GNU"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
gm2 \- The GNU Modula\-2 Compiler
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
.SH "OPTIONS"
.IX Header "OPTIONS"
For any given input file, the file name suffix determines what kind of
compilation is done.  The following kinds of input file names are supported:
.IP "\fIfile\fR\fB.mod\fR" 4
.IX Item "file.mod"
Modula\-2 implementation or program source files.  See the
\&\fB\-fmod=\fR option if you wish to compile a project which uses a
different source file extension.
.IP "\fIfile\fR\fB.def\fR" 4
.IX Item "file.def"
Modula\-2 definition module source files.  Definition modules are not
compiled separately, in \s-1GNU\s0 Modula\-2 definition modules are parsed as
required when program or implementation modules are compiled.  See the
\&\fB\-fdef=\fR option if you wish to compile a project which uses a
different source file extension.
.PP
You can specify more than one input file on the \fBgm2\fR command line,
.ie n .IP """\-g""" 4
.el .IP "\f(CW\-g\fR" 4
.IX Item "-g"
create debugging information so that debuggers such as \fIgdb\fR
can inspect and control executables.
.ie n .IP """\-I""" 4
.el .IP "\f(CW\-I\fR" 4
.IX Item "-I"
used to specify the search path for definition and implementation
modules.  An example is:  \f(CW\*(C`gm2 \-g \-c \-I.:../../libs foo.mod\*(C'\fR.
If this option is not specified then the default path is added
which consists of the current directory followed by the appropriate
language dialect library directories.
.ie n .IP """\-fobject\-path=""" 4
.el .IP "\f(CW\-fobject\-path=\fR" 4
.IX Item "-fobject-path="
used to specify the path for objects during the linking stage.  An
example is: \f(CW\*(C`gm2 \-g \-fobject\-path=.:../../libs/O2 \-I.:../../libs
foo.mod\*(C'\fR.  The combination of \f(CW\*(C`\-I\*(C'\fR and \f(CW\*(C`\-fobject\-path=\*(C'\fR
allows projects to keep various styles of objects separate from their
source counterparts.  For example it would be possible to compile
implementation modules with different levels of optimization and
with/without debugging and keep them in separate directories.  If the
\&\f(CW\*(C`\-fobject\-path=\*(C'\fR option is not specified then it is set
internally by using the path as specified by the \f(CW\*(C`\-I\*(C'\fR option.  If
the \f(CW\*(C`\-I\*(C'\fR was also not specified then it uses the current
directory.  In all cases the appropriate language dialect library
directories are appended to the end of the path.
.ie n .IP """\-fdebug\-builtins""" 4
.el .IP "\f(CW\-fdebug\-builtins\fR" 4
.IX Item "-fdebug-builtins"
call a real function, rather than the builtin equivalent.  This can
be useful for debugging parameter values to a builtin function as
it allows users to single step code into a real function.
.ie n .IP """\-fdump\-system\-exports""" 4
.el .IP "\f(CW\-fdump\-system\-exports\fR" 4
.IX Item "-fdump-system-exports"
display all inbuilt system items.
This is an internal command line option.
.ie n .IP """\-fswig""" 4
.el .IP "\f(CW\-fswig\fR" 4
.IX Item "-fswig"
generate a swig interface file.
.ie n .IP """\-fshared""" 4
.el .IP "\f(CW\-fshared\fR" 4
.IX Item "-fshared"
generate a shared library from the module.
.ie n .IP """\-fmakeinit""" 4
.el .IP "\f(CW\-fmakeinit\fR" 4
.IX Item "-fmakeinit"
generate the start up \*(C+ code for the module, a file
\&\fI_m2_modulename.cpp\fR is created.  This is an internal command
line option.
.ie n .IP """\-fruntime\-modules=""" 4
.el .IP "\f(CW\-fruntime\-modules=\fR" 4
.IX Item "-fruntime-modules="
specify, using a comma separated list, the runtime modules and their
order.  These modules will initialized first before any other modules
in the application dependancy.  By default the runtime modules list is
set to \f(CW\*(C`Storage,SYSTEM,M2RTS,RTExceptions,IOLink\*(C'\fR.  Note that
these modules will only be linked into your executable if they are
required.  So adding a long list of dependant modules will not effect
the size of the executable it merely states the initialisation order
should they be required.
.ie n .IP """\-fnil""" 4
.el .IP "\f(CW\-fnil\fR" 4
.IX Item "-fnil"
generate code to detect accessing data through a
\&\f(CW\*(C`NIL\*(C'\fR value pointer.
.ie n .IP """\-fno\-nil""" 4
.el .IP "\f(CW\-fno\-nil\fR" 4
.IX Item "-fno-nil"
do not generate code to detect accessing data through a
\&\f(CW\*(C`NIL\*(C'\fR value pointer.
.ie n .IP """\-fwholediv""" 4
.el .IP "\f(CW\-fwholediv\fR" 4
.IX Item "-fwholediv"
generate code to detect whole number division by zero or modulus by zero.
.ie n .IP """\-fno\-wholediv""" 4
.el .IP "\f(CW\-fno\-wholediv\fR" 4
.IX Item "-fno-wholediv"
do not generate code to detect whole number division by zero or
modulus by zero.
.ie n .IP """\-findex""" 4
.el .IP "\f(CW\-findex\fR" 4
.IX Item "-findex"
generate code to check whether array index values are out of bounds.
.ie n .IP """\-fno\-index""" 4
.el .IP "\f(CW\-fno\-index\fR" 4
.IX Item "-fno-index"
do not generate code to check whether array index values are out of
bounds.
.ie n .IP """\-frange""" 4
.el .IP "\f(CW\-frange\fR" 4
.IX Item "-frange"
generate code to check the assignment range, return value range
set range and constructor range.
.ie n .IP """\-fno\-range""" 4
.el .IP "\f(CW\-fno\-range\fR" 4
.IX Item "-fno-range"
do not generate code to check the assignment range, return value range
set range and constructor range.
.ie n .IP """\-freturn""" 4
.el .IP "\f(CW\-freturn\fR" 4
.IX Item "-freturn"
generate code to check that functions always exit with a \f(CW\*(C`RETURN\*(C'\fR
and do not fall out at the end.
.ie n .IP """\-fcase""" 4
.el .IP "\f(CW\-fcase\fR" 4
.IX Item "-fcase"
turns on compile time checking to check whether a \f(CW\*(C`CASE\*(C'\fR
statement requires an \f(CW\*(C`ELSE\*(C'\fR clause when on was not specified.
.ie n .IP """\-fsoft\-check\-all""" 4
.el .IP "\f(CW\-fsoft\-check\-all\fR" 4
.IX Item "-fsoft-check-all"
turns on all runtime checks.  This is the same as invoking
\&\s-1GNU\s0 Modula\-2 using the command options
\&\f(CW\*(C`\-fnil\*(C'\fR \f(CW\*(C`\-frange\*(C'\fR \f(CW\*(C`\-findex\*(C'\fR
\&\f(CW\*(C`\-fwholediv\*(C'\fR \f(CW\*(C`\-fcase\*(C'\fR \f(CW\*(C`\-freturn\*(C'\fR.
.ie n .IP """\-fauto\-init""" 4
.el .IP "\f(CW\-fauto\-init\fR" 4
.IX Item "-fauto-init"
turns on auto initialization of pointers to \s-1NIL.\s0  Whenever a block is
created all pointers declarated within this scope will have their
addresses assigned to \s-1NIL.\s0
.ie n .IP """\-fno\-exceptions""" 4
.el .IP "\f(CW\-fno\-exceptions\fR" 4
.IX Item "-fno-exceptions"
turns off all generation of exception handling code and no references
are made to the runtime exception libraries.
.ie n .IP """\-v""" 4
.el .IP "\f(CW\-v\fR" 4
.IX Item "-v"
display all calls to subsidiary programs, such as the C preprocessor,
the \s-1GNU\s0 Modula\-2 linker and compiler.
.ie n .IP """\-fm2\-statistics""" 4
.el .IP "\f(CW\-fm2\-statistics\fR" 4
.IX Item "-fm2-statistics"
generates quadruple information: number of quadruples generated,
number of quadruples remaining after optimisation and number of source
lines compiled.
.ie n .IP """\-fm2\-whole\-program""" 4
.el .IP "\f(CW\-fm2\-whole\-program\fR" 4
.IX Item "-fm2-whole-program"
compile all implementation modules and program module at once.  Notice
that you need to take care if you are compiling different dialect
modules (particularly with the negative operands to modulus).  But
this option, when coupled together with \f(CW\*(C`\-O3\*(C'\fR, can deliver huge
performance improvements.
.ie n .IP """\-fm2\-g""" 4
.el .IP "\f(CW\-fm2\-g\fR" 4
.IX Item "-fm2-g"
improve the debugging experience for new programmers at the expense
of generating \f(CW\*(C`nop\*(C'\fR instructions if necessary to ensure single
stepping precision over all code related keywords.  An example
of this is in termination of a list of nested \f(CW\*(C`IF\*(C'\fR statements
where multiple \f(CW\*(C`END\*(C'\fR keywords are mapped onto a sequence of
\&\f(CW\*(C`nop\*(C'\fR instructions.
.ie n .IP """\-fm2\-lower\-case""" 4
.el .IP "\f(CW\-fm2\-lower\-case\fR" 4
.IX Item "-fm2-lower-case"
render keywords in error messages using lower case.
.ie n .IP """\-fmakelist""" 4
.el .IP "\f(CW\-fmakelist\fR" 4
.IX Item "-fmakelist"
this option is only applicable when linking a program module.  The
compiler will generate a \fImodulename.lst\fR file which contains a
list indicating the initialisation order of all modules which are to
be linked. The actual link does not occur.  The \s-1GNU\s0 Modula\-2 linker
scans all \f(CW\*(C`IMPORT\*(C'\fRs, generates a list of dependencies and
produces an ordered list for initialisation. It will probably get the
order wrong if your project has cyclic dependencies, but the
\&\fI.lst\fR file is plain text and can be modified if required.  Once
the \fI.lst\fR file is created it can be used by the compiler to link
your project via the \fB\-fuselist\fR option.  It has no effect if the
\&\fB\-c\fR option is present.
.ie n .IP """fno\-pthread""" 4
.el .IP "\f(CWfno\-pthread\fR" 4
.IX Item "fno-pthread"
do not automatically link against the pthread library.  This option is
likely useful if gm2 is configured as a cross compiler targetting
embedded systems.  By default \s-1GNU\s0 Modula\-2 uses the \s-1GCC\s0 pthread
libraries to implement coroutines (see the \s-1SYSTEM\s0 implementation
module).
.ie n .IP """\-fuselist""" 4
.el .IP "\f(CW\-fuselist\fR" 4
.IX Item "-fuselist"
providing \fBgm2\fR has been told to link the program module this
option uses the file \fImodulename.lst\fR for the initialisation
order of modules.
.ie n .IP """\-fcpp""" 4
.el .IP "\f(CW\-fcpp\fR" 4
.IX Item "-fcpp"
preprocess the source with \fBcpp \-lang\-asm \-traditional\-cpp\fR
For further details about these options see 
If \fB\-fcpp\fR is supplied then all definition modules and
implementation modules which are parsed will be preprocessed by
\&\fBcpp\fR.
.ie n .IP """\-fiso""" 4
.el .IP "\f(CW\-fiso\fR" 4
.IX Item "-fiso"
turn on \s-1ISO\s0 standard features. Currently this enables the \s-1ISO\s0
\&\f(CW\*(C`SYSTEM\*(C'\fR module and alters the default library search path so
that the \s-1ISO\s0 libraries are searched before the \s-1PIM\s0 libraries.  It also
effects the behaviour of \f(CW\*(C`DIV\*(C'\fR and \f(CW\*(C`MOD\*(C'\fR operators.
See
.ie n .IP """\-fpim""" 4
.el .IP "\f(CW\-fpim\fR" 4
.IX Item "-fpim"
turn on \s-1PIM\s0 standard features. Currently this enables the \s-1PIM\s0
\&\f(CW\*(C`SYSTEM\*(C'\fR module and determines which identifiers are pervasive
(declared in the base module). If no other \fB\-fpim[234]\fR switch is
used then division and modulus operators behave as defined in \s-1PIM4.\s0
See
.ie n .IP """\-fpim2""" 4
.el .IP "\f(CW\-fpim2\fR" 4
.IX Item "-fpim2"
turn on \s-1PIM\-2\s0 standard features. Currently this removes \f(CW\*(C`SIZE\*(C'\fR
from being a pervasive identifier (declared in the base module).  It
places \f(CW\*(C`SIZE\*(C'\fR in the \f(CW\*(C`SYSTEM\*(C'\fR module.  It also effects the
behaviour of \f(CW\*(C`DIV\*(C'\fR and \f(CW\*(C`MOD\*(C'\fR operators.
See
.ie n .IP """\-fpim3""" 4
.el .IP "\f(CW\-fpim3\fR" 4
.IX Item "-fpim3"
turn on \s-1PIM\-3\s0 standard features. Currently this only effects the
behaviour of \f(CW\*(C`DIV\*(C'\fR and \f(CW\*(C`MOD\*(C'\fR operators.
See
.ie n .IP """\-fpim4""" 4
.el .IP "\f(CW\-fpim4\fR" 4
.IX Item "-fpim4"
turn on \s-1PIM\-4\s0 standard features. Currently this only effects the
behaviour of \f(CW\*(C`DIV\*(C'\fR and \f(CW\*(C`MOD\*(C'\fR operators.
See
.ie n .IP """\-fpositive\-mod\-floor\-div""" 4
.el .IP "\f(CW\-fpositive\-mod\-floor\-div\fR" 4
.IX Item "-fpositive-mod-floor-div"
forces the \f(CW\*(C`DIV\*(C'\fR and \f(CW\*(C`MOD\*(C'\fR operators to behave as defined by \s-1PIM4.\s0
All modulus results are positive and the results from the division are
rounded to the floor.
See
.ie n .IP """\-flibs=""" 4
.el .IP "\f(CW\-flibs=\fR" 4
.IX Item "-flibs="
modifies the default library search path.  The libraries supplied are:
m2pim, m2iso, m2min, m2log and m2cor.  These map onto the
Programming in Modula\-2 base libraries, \s-1ISO\s0 standard libraries, minimal
library support, Logitech compatible library and Programming in
Modula\-2 with coroutines.
Multiple libraries can be specified and are comma separated with precidence
going to the first in the list.  It is not necessary to use \-flibs=m2pim or
\&\-flibs=m2iso if you also specify \-fpim, \-fpim2, \-fpim3, \-fpim4 or
\&\-fiso.  Unless you are using \-flibs=m2min you should include m2pim as
the they provide the base modules which all other dialects utilize.
.ie n .IP """\-fextended\-opaque""" 4
.el .IP "\f(CW\-fextended\-opaque\fR" 4
.IX Item "-fextended-opaque"
allows opaque types to be implemented as any type. This is a \s-1GNU\s0
Modula\-2 extension and it requires that the implementation module
defining the opaque type is available so that it can be resolved when
compiling the module which imports the opaque type.
.ie n .IP """\-fsources""" 4
.el .IP "\f(CW\-fsources\fR" 4
.IX Item "-fsources"
displays the path to the source of each module.  This option
can be used at compile time to check the correct definition module
is being used.
.ie n .IP """\-fmodules""" 4
.el .IP "\f(CW\-fmodules\fR" 4
.IX Item "-fmodules"
displays the path to each modules object file.  This option
can only be invoked with the \f(CW\*(C`\-c\*(C'\fR option.
It is used to see the location of objects when linking occurs.
.ie n .IP """\-fdef=""" 4
.el .IP "\f(CW\-fdef=\fR" 4
.IX Item "-fdef="
recognise the specified suffix as a definition module filename.
The default implmentation and module filename suffix is \fI.def\fR.
If this option is used \s-1GNU\s0 Modula\-2 will still fall back to this
default if a requested definition module is not found.
.ie n .IP """\-fmod=""" 4
.el .IP "\f(CW\-fmod=\fR" 4
.IX Item "-fmod="
recognise the specified suffix as implementation and module filenames.
The default implmentation and module filename suffix is \fI.mod\fR.
If this option is used \s-1GNU\s0 Modula\-2 will still fall back to this
default if it needs to read an implmentation module and the specified
suffixed filename does not exist.
.ie n .IP """\-fxcode""" 4
.el .IP "\f(CW\-fxcode\fR" 4
.IX Item "-fxcode"
issues all errors and warnings in the \fIXcode\fR format.
.ie n .IP """\-fonlylink""" 4
.el .IP "\f(CW\-fonlylink\fR" 4
.IX Item "-fonlylink"
only link the modula\-2 application, do not compile the program module
beforehand.
.ie n .IP """\-funbounded\-by\-reference""" 4
.el .IP "\f(CW\-funbounded\-by\-reference\fR" 4
.IX Item "-funbounded-by-reference"
enable optimization of unbounded parameters by attempting to pass non
\&\f(CW\*(C`VAR\*(C'\fR unbounded parameters by reference.  This optimization
avoids the implicit copy inside the callee procedure. \s-1GNU\s0 Modula\-2
will only allow unbounded parameters to be passed by reference if,
inside the callee procedure, they are not written to, no address is
calculated on the array and it is not passed as a \f(CW\*(C`VAR\*(C'\fR
parameter.  Note that it is possible to write code to break this
optimization, therefore this option should be used carefully.
For example it would be possible to take the address of an array, pass
the address and the array to a procedure, read from the array in
the procedure and write to the location using the address parameter.
.Sp
Due to the dangerous nature of this option it is not enabled
when the \-O option is specified.
.ie n .IP """\-Wverbose\-unbounded""" 4
.el .IP "\f(CW\-Wverbose\-unbounded\fR" 4
.IX Item "-Wverbose-unbounded"
inform the user which non \f(CW\*(C`VAR\*(C'\fR unbounded parameters will be
passed by reference.  This only produces output if the option
\&\fB\-funbounded\-by\-reference\fR is also supplied on the command line.
.ie n .IP """\-Wstudents""" 4
.el .IP "\f(CW\-Wstudents\fR" 4
.IX Item "-Wstudents"
checks for bad programming style. This option is aimed at new users of
Modula\-2 in that it checks for situations which might cause confusion
and thus mistakes.  It checks whether variables of the same name are
declared in different scopes and whether variables look like keywords.
Experienced users might find this option too aggressive.
.ie n .IP """\-Wpedantic""" 4
.el .IP "\f(CW\-Wpedantic\fR" 4
.IX Item "-Wpedantic"
forces the compiler to reject nested \f(CW\*(C`WITH\*(C'\fR statements
referencing the same record type.  Does not allow multiple imports of
the same item from a module.  It also checks that: procedure variables
are written to before being read; variables are not only written to
but read from; variables are declared and used.  If the compiler
encounters a variable being read before written it will terminate with
a message.  It will check that \f(CW\*(C`FOR\*(C'\fR loop indices are not used
outside the end of this loop without being reset.
.ie n .IP """\-Wpedantic\-param\-names""" 4
.el .IP "\f(CW\-Wpedantic\-param\-names\fR" 4
.IX Item "-Wpedantic-param-names"
procedure parameter names are checked in the definition module
against their implementation module counterpart.  This is not
necessary in \s-1ISO\s0 or \s-1PIM\s0 versions of Modula\-2, but it can be
extremely useful, as long as code is intentionally
written in this way.
.ie n .IP """\-Wpedantic\-cast""" 4
.el .IP "\f(CW\-Wpedantic\-cast\fR" 4
.IX Item "-Wpedantic-cast"
warns if the \s-1ISO\s0 system function is used and if the size of
the variable is different from that of the type. This is legal
in \s-1ISO\s0 Modula\-2, however it can be dangerous. Some users may prefer
to use \f(CW\*(C`VAL\*(C'\fR instead in these situations and use \f(CW\*(C`CAST\*(C'\fR
exclusively for changes in type on objects which have the same size.
.ie n .IP """\-Wunused\-variable""" 4
.el .IP "\f(CW\-Wunused\-variable\fR" 4
.IX Item "-Wunused-variable"
warns if a variable has been declared and it not used.
.ie n .IP """\-Wunused\-parameter""" 4
.el .IP "\f(CW\-Wunused\-parameter\fR" 4
.IX Item "-Wunused-parameter"
warns if a parameter has been declared and it not used.
.ie n .IP """\-Wall""" 4
.el .IP "\f(CW\-Wall\fR" 4
.IX Item "-Wall"
turn on all Modula\-2 warnings.
.SH "ENVIRONMENT"
.IX Header "ENVIRONMENT"
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBgpl\fR\|(7), \fBgfdl\fR\|(7), \fBfsf\-funding\fR\|(7), \fBgcc\fR\|(1)
and the Info entries for \fIgm2\fR and \fIgcc\fR.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 1999\-2020 Free Software Foundation, Inc.
.PP
Permission is granted to copy, distribute and/or modify this document
under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the
man page \fBgfdl\fR\|(7).