diff options
Diffstat (limited to 'gcc/fortran/invoke.texi')
| -rw-r--r-- | gcc/fortran/invoke.texi | 81 |
1 files changed, 63 insertions, 18 deletions
diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi index 22f20dc..5385bba 100644 --- a/gcc/fortran/invoke.texi +++ b/gcc/fortran/invoke.texi @@ -143,7 +143,7 @@ by type. Explanations are in the following sections. @item Code Generation Options @xref{Code Gen Options,,Options for Code Generation Conventions}. @gccoptlist{ --fno-underscoring -fno-second-underscore @gol +-ff2c -fno-underscoring -fsecond-underscore @gol -fbounds-check -fmax-stack-var-size=@var{n} @gol -fpackderived -frepack-arrays} @end table @@ -518,8 +518,43 @@ it. @table @gcctabopt -@cindex -fno-underscoring option -@cindex options, -fno-underscoring +@cindex @option{-ff2c} option +@cindex options, @option{-ff2c} +@item -ff2c +@cindex calling convention +@cindex @command{f2c} calling convention +@cindex @command{g77} calling convention +@cindex libf2c calling convention +Generate code designed to be compatible with code generated +by @command{g77} and @command{f2c}. + +The calling conventions used by @command{g77} (originally implemented +in @command{f2c}) require functions that return type +default @code{REAL} to actually return the C type @code{double}, and +functions that return type @code{COMPLEX} to return the values via an +extra argument in the calling sequence that points to where to +store the return value. Under the default GNU calling conventions, such +functions simply return their results as they would in GNU +C -- default @code{REAL} functions return the C type @code{float}, and +@code{COMPLEX} functions return the GNU C type @code{complex}. +Additionally, this option implies the @options{-fsecond-underscore} +option, unless @options{-fno-second-underscore} is explicitly requested. + +This does not affect the generation of code that interfaces with +the @command{libgfortran} library. + +@emph{Caution:} It is not a good idea to mix Fortran code compiled +with @code{-ff2c} with code compiled with the default @code{-fno-f2c} +calling conventions as, calling @code{COMPLEX} or default @code{REAL} +functions between program parts which were compiled with different +calling conventions will break at execution time. + +@emph{Caution:} This will break code which passes intrinsic functions +of type default @code{REAL} or @code{COMPLEX} as actual arguments, as +the library implementations use the @command{-fno-f2c} calling conventions. + +@cindex @option{-fno-underscoring option} +@cindex options, @option{-fno-underscoring} @item -fno-underscoring @cindex underscore @cindex symbol names, underscores @@ -528,16 +563,17 @@ it. Do not transform names of entities specified in the Fortran source file by appending underscores to them. -With @option{-funderscoring} in effect, @command{gfortran} appends two -underscores to names with underscores and one underscore to external names -with no underscores. (@command{gfortran} also appends two underscores to -internal names with underscores to avoid naming collisions with external -names. The @option{-fno-second-underscore} option disables appending of the -second underscore in all cases.) +With @option{-funderscoring} in effect, @command{gfortran} appends one +underscore to external names with no underscores. This is done to ensure compatibility with code produced by many -UNIX Fortran compilers, including @command{f2c} which perform the -same transformations. +UNIX Fortran compilers. + +@emph{Caution}: The default behavior of @command{gfortran} is +incompatible with @command{f2c} and @command{g77}, please use the +@option{-ff2c} and @option{-fsecond-underscore} options if you want +object files compiled with @option{gfortran} to be compatible with +object code created with these tools. Use of @option{-fno-underscoring} is not recommended unless you are experimenting with issues such as integration of (GNU) Fortran into @@ -593,22 +629,31 @@ in the source, even if the names as seen by the linker are mangled to prevent accidental linking between procedures with incompatible interfaces. -@cindex -fno-second-underscore option -@cindex options, -fno-second-underscore -@item -fno-second-underscore +@cindex @option{-fsecond-underscore option} +@cindex options, @option{-fsecond-underscore} +@item -fsecond-underscore @cindex underscore @cindex symbol names, underscores @cindex transforming symbol names @cindex symbol names, transforming -Do not append a second underscore to names of entities specified -in the Fortran source file. +@cindex @command{f2c} calling convention +@cindex @command{g77} calling convention +@cindex libf2c calling convention +By default, @command{gfortran} appends an underscore to external +names. If this option is used @command{gfortran} appends two +underscores to names with underscores and one underscore to external names +with no underscores. (@command{gfortran} also appends two underscores to +internal names with underscores to avoid naming collisions with external +names. This option has no effect if @option{-fno-underscoring} is -in effect. +in effect. It is implied by the @option{-ff2c} option. Otherwise, with this option, an external name such as @samp{MAX_COUNT} is implemented as a reference to the link-time external symbol -@samp{max_count_}, instead of @samp{max_count__}. +@samp{max_count__}, instead of @samp{max_count_}. This is required +for compatibility with @command{g77} and @command{f2c}, and is implied +by use of the @option{-ff2c} option. @cindex -fbounds-check option |