(g77.info.gz) Adding Options
To add a new command-line option to `g77', first decide what kind of
option you wish to add. Search the `g77' and `gcc' documentation for
one or more options that is most closely like the one you want to add
(in terms of what kind of effect it has, and so on) to help clarify its
* *Fortran options* are options that apply only when compiling
Fortran programs. They are accepted by `g77' and `gcc', but they
apply only when compiling Fortran programs.
* *Compiler options* are options that apply when compiling most any
kind of program.
*Fortran options* are listed in the file `egcs/gcc/f/lang-options.h',
which is used during the build of `gcc' to build a list of all options
that are accepted by at least one language's compiler. This list goes
into the `lang_options' array in `gcc/toplev.c', which uses this array
to determine whether a particular option should be offered to the
linked-in front end for processing by calling `lang_option_decode',
which, for `g77', is in `egcs/gcc/f/com.c' and just calls
If the linked-in front end "rejects" a particular option passed to
it, `toplev.c' just ignores the option, because *some* language's
compiler is willing to accept it.
This allows commands like `gcc -fno-asm foo.c bar.f' to work, even
though Fortran compilation does not currently support the `-fno-asm'
option; even though the `f771' version of `lang_decode_option' rejects
`-fno-asm', `toplev.c' doesn't produce a diagnostic because some other
language (C) does accept it.
This also means that commands like `g77 -fno-asm foo.f' yield no
diagnostics, despite the fact that no phase of the command was able to
recognize and process `-fno-asm'--perhaps a warning about this would be
helpful if it were possible.
Code that processes Fortran options is found in `egcs/gcc/f/top.c',
function `ffe_decode_option'. This code needs to check positive and
negative forms of each option.
The defaults for Fortran options are set in their global
definitions, also found in `egcs/gcc/f/top.c'. Many of these defaults
are actually macros defined in `egcs/gcc/f/target.h', since they might
be machine-specific. However, since, in practice, GNU compilers should
behave the same way on all configurations (especially when it comes to
language constructs), the practice of setting defaults in `target.h' is
likely to be deprecated and, ultimately, stopped in future versions of
Accessor macros for Fortran options, used by code in the `g77' FFE,
are defined in `egcs/gcc/f/top.h'.
*Compiler options* are listed in `gcc/toplev.c' in the array
`f_options'. An option not listed in `lang_options' is looked up in
`f_options' and handled from there.
The defaults for compiler options are set in the global definitions
for the corresponding variables, some of which are in `gcc/toplev.c'.
You can set different defaults for *Fortran-oriented* or
*Fortran-reticent* compiler options by changing the source code of
`g77' and rebuilding. How to do this depends on the version of `g77':
`G77 0.5.24 (EGCS 1.1)'
`G77 0.5.25 (EGCS 1.2)'
Change the `lang_init_options' routine in `egcs/gcc/f/com.c'.
(Note that these versions of `g77' perform internal consistency
checking automatically when the `-fversion' option is specified.)
`G77 0.5.24 (EGCS 1.0)'
Change the way `f771' handles the `-fset-g77-defaults' option,
which is always provided as the first option when called by `g77'
This code is in `ffe_decode_options' in `egcs/gcc/f/top.c'. Have
it change just the variables that you want to default to a
different setting for Fortran compiles compared to compiles of
The `-fset-g77-defaults' option is passed to `f771' automatically
because of the specification information kept in
`egcs/gcc/f/lang-specs.h'. This file tells the `gcc' command how
to recognize, in this case, Fortran source files (those to be
preprocessed, and those that are not), and further, how to invoke
the appropriate programs (including `f771') to process those
It is in `egcs/gcc/f/lang-specs.h' that `-fset-g77-defaults',
`-fversion', and other options are passed, as appropriate, even
when the user has not explicitly specified them. Other "internal"
options such as `-quiet' also are passed via this mechanism.
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