Re: MinGW compilation warnings in libiberty's include/environ.h

[Pedro Alves <palves@redhat.com>]

On 05/08/2017 04:25 PM, Eli Zaretskii wrote:
> When compiling libiberty (as part of GDB) with MinGW on MS-Windows, I
> see the following warning:
> 
>      gcc -c -DHAVE_CONFIG_H -O2 -gdwarf-4 -g3 -D__USE_MINGW_ACCESS  -I. -I./../include   -W -Wall -Wwrite-strings -Wc++-compat -Wstrict-prototypes -pedantic  -D_GNU_SOURCE ./setenv.c -o setenv.o
>      In file included from ./setenv.c:64:0:
>      ./../include/environ.h:30:1: warning: function declaration isn't a prototype [-Wstrict-prototypes]
>       extern char **environ;
>       ^
> 
> This was already reported 4 years ago, here:
> 
>   https://gcc.gnu.org/ml/gcc-patches/2013-03/msg00471.html
> 
> and was solved back then.  But it looks like the offending code was
> copied to include/environ.h without the fix, and the warning is thus
> back.
> 
> The problem is with this code in environ.h:
> 
>   #ifndef HAVE_ENVIRON_DECL
>   #  ifdef __APPLE__
>   #     include <crt_externs.h>
>   #     define environ (*_NSGetEnviron ())
>   #  else
>   extern char **environ;
>   #  endif
>   #  define HAVE_ENVIRON_DECL
>   #endif
> 
> which causes the MinGW compiler to see the declaration of environ,
> whereas MinGW's stdlib.h has this:
> 
>   #ifdef __MSVCRT__
>   # define _environ  (*__p__environ())
>   extern _CRTIMP __cdecl __MINGW_NOTHROW  char ***__p__environ(void);
>   # define _wenviron  (*__p__wenviron())
>   extern _CRTIMP __cdecl __MINGW_NOTHROW  wchar_t ***__p__wenviron(void);
> 
>   #else  /* ! __MSVCRT__ */
>   # ifndef __DECLSPEC_SUPPORTED
>   # define _environ (*_imp___environ_dll)
>   extern char ***_imp___environ_dll;
> 
>   # else  /* __DECLSPEC_SUPPORTED */
>   # define _environ  _environ_dll
>   __MINGW_IMPORT char ** _environ_dll;
>   # endif  /* __DECLSPEC_SUPPORTED */
>   #endif  /* ! __MSVCRT__ */
> 
>   #define environ _environ

So again there's a system header that defines the symbol
but for some reason libiberty still wants to declare/define
it is if it weren't?

That sounds to me like the root issue that should be fixed,
so that these fallback definitions don't come into into play at all.
I.e., why isn't HAVE_ENVIRON_DECL defined on mingw when
setenv.o is built?  Sounds like a decl check is missing
in configure.ac.

Thanks,
Pedro Alves