gm2 - The GNU Modula-2 Compiler
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:
- Modula-2 implementation or program source files. See the -fmod= option if you wish to compile a project which uses a different source file extension.
- Modula-2 definition module source files. Definition modules are not compiled separately, in GNU Modula-2 definition modules are parsed as required when program or implementation modules are compiled. See the -fdef= option if you wish to compile a project which uses a different source file extension.
You can specify more than one input file on the gm2 command line,
- create debugging information so that debuggers such as gdb can inspect and control executables.
- used to specify the search path for definition and implementation modules. An example is: "gm2 -g -c -I.:../../libs foo.mod". 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.
- used to specify the path for objects during the linking stage. An example is: "gm2 -g -fobject-path=.:../../libs/O2 -I.:../../libs foo.mod". The combination of "-I" and "-fobject-path=" 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 "-fobject-path=" option is not specified then it is set internally by using the path as specified by the "-I" option. If the "-I" 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.
- 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.
- display all inbuilt system items. This is an internal command line option.
- generate a swig interface file.
- generate a shared library from the module.
- generate the start up C++ code for the module, a file _m2_modulename.cpp is created. This is an internal command line option.
- 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 "Storage,SYSTEM,M2RTS,RTExceptions,IOLink". 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.
- generate code to detect accessing data through a "NIL" value pointer.
- do not generate code to detect accessing data through a "NIL" value pointer.
- generate code to detect whole number division by zero or modulus by zero.
- do not generate code to detect whole number division by zero or modulus by zero.
- generate code to check whether array index values are out of bounds.
- do not generate code to check whether array index values are out of bounds.
- generate code to check the assignment range, return value range set range and constructor range.
- do not generate code to check the assignment range, return value range set range and constructor range.
- generate code to check that functions always exit with a "RETURN" and do not fall out at the end.
- turns on compile time checking to check whether a "CASE" statement requires an "ELSE" clause when on was not specified.
- turns on all runtime checks. This is the same as invoking GNU Modula-2 using the command options "-fnil" "-frange" "-findex" "-fwholediv" "-fcase" "-freturn".
- turns on auto initialization of pointers to NIL. Whenever a block is created all pointers declarated within this scope will have their addresses assigned to NIL.
- turns off all generation of exception handling code and no references are made to the runtime exception libraries.
- display all calls to subsidiary programs, such as the C preprocessor, the GNU Modula-2 linker and compiler.
- generates quadruple information: number of quadruples generated, number of quadruples remaining after optimisation and number of source lines compiled.
- 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 "-O3", can deliver huge performance improvements.
- improve the debugging experience for new programmers at the expense of generating "nop" 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 "IF" statements where multiple "END" keywords are mapped onto a sequence of "nop" instructions.
- render keywords in error messages using lower case.
- this option is only applicable when linking a program module. The compiler will generate a modulename.lst file which contains a list indicating the initialisation order of all modules which are to be linked. The actual link does not occur. The GNU Modula-2 linker scans all "IMPORT"s, 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 .lst file is plain text and can be modified if required. Once the .lst file is created it can be used by the compiler to link your project via the -fuselist option. It has no effect if the -c option is present.
- 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 GNU Modula-2 uses the GCC pthread libraries to implement coroutines (see the SYSTEM implementation module).
- providing gm2 has been told to link the program module this option uses the file modulename.lst for the initialisation order of modules.
- preprocess the source with cpp -lang-asm -traditional-cpp For further details about these options see If -fcpp is supplied then all definition modules and implementation modules which are parsed will be preprocessed by cpp.
- turn on ISO standard features. Currently this enables the ISO "SYSTEM" module and alters the default library search path so that the ISO libraries are searched before the PIM libraries. It also effects the behaviour of "DIV" and "MOD" operators. See
- turn on PIM standard features. Currently this enables the PIM "SYSTEM" module and determines which identifiers are pervasive (declared in the base module). If no other -fpim switch is used then division and modulus operators behave as defined in PIM4. See
- turn on PIM-2 standard features. Currently this removes "SIZE" from being a pervasive identifier (declared in the base module). It places "SIZE" in the "SYSTEM" module. It also effects the behaviour of "DIV" and "MOD" operators. See
- turn on PIM-3 standard features. Currently this only effects the behaviour of "DIV" and "MOD" operators. See
- turn on PIM-4 standard features. Currently this only effects the behaviour of "DIV" and "MOD" operators. See
- forces the "DIV" and "MOD" operators to behave as defined by PIM4. All modulus results are positive and the results from the division are rounded to the floor. See
- 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, ISO 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.
- allows opaque types to be implemented as any type. This is a GNU 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.
- 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.
- displays the path to each modules object file. This option can only be invoked with the "-c" option. It is used to see the location of objects when linking occurs.
- recognise the specified suffix as a definition module filename. The default implmentation and module filename suffix is .def. If this option is used GNU Modula-2 will still fall back to this default if a requested definition module is not found.
- recognise the specified suffix as implementation and module filenames. The default implmentation and module filename suffix is .mod. If this option is used GNU 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.
- issues all errors and warnings in the Xcode format.
- only link the modula-2 application, do not compile the program module beforehand.
- enable optimization of unbounded parameters by attempting to pass non
"VAR" unbounded parameters by reference.
This optimization avoids the implicit copy inside the callee procedure.
GNU 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
"VAR" 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
Due to the dangerous nature of this option it is not enabled when the -O option is specified.
- inform the user which non "VAR" unbounded parameters will be passed by reference. This only produces output if the option -funbounded-by-reference is also supplied on the command line.
- 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.
- forces the compiler to reject nested "WITH" 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 "FOR" loop indices are not used outside the end of this loop without being reset.
- procedure parameter names are checked in the definition module against their implementation module counterpart. This is not necessary in ISO or PIM versions of Modula-2, but it can be extremely useful, as long as code is intentionally written in this way.
- warns if the ISO system function is used and if the size of the variable is different from that of the type. This is legal in ISO Modula-2, however it can be dangerous. Some users may prefer to use "VAL" instead in these situations and use "CAST" exclusively for changes in type on objects which have the same size.
- warns if a variable has been declared and it not used.
- warns if a parameter has been declared and it not used.
- turn on all Modula-2 warnings.
gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entries for gm2 and gcc.
Copyright (c) 1999-2021 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU 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 gfdl(7).