Re: MinGW compilation warnings in libiberty's xstrndup.c

[Pedro Alves <palves@redhat.com>]

[Adding Thomas]

On 05/08/2017 04:30 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 ./xstrndup.c -o xstrndup.o
>      ./xstrndup.c: In function 'xstrndup':
>      ./xstrndup.c:51:16: warning: implicit declaration of function 'strnlen' [-Wimplicit-function-declaration]
> 	size_t len = strnlen (s, n);
> 		     ^
> 
> This happens because libiberty.h uses incorrect guards for the
> prototype of strnlen:
> 
>   #if defined (HAVE_DECL_STRNLEN) && !HAVE_DECL_STRNLEN
>   extern size_t strnlen (const char *, size_t);
>   #endif
> 
> It should use HAVE_STRNLEN instead, because that's the only
> strnlen-related macro defined in config.g when strnlen is probed by
> the configure script.

Looks like the declaration check got added to gcc's configure, but not
elsewhere, with:

commit d968efeac356364c01445013a1a3660e5087cb15
Author:     tschwinge <tschwinge@138bc75d-0d04-0410-961f-82ee72b054a4>
AuthorDate: Tue Jun 10 09:45:00 2014 +0000

    [PR lto/61334] Declare prototype for strnlen, if needed.
    
        include/
        * libiberty.h [defined (HAVE_DECL_STRNLEN) &&
        !HAVE_DECL_STRNLEN] (strnlen): New prototype.
        gcc/
        * configure.ac: Use gcc_AC_CHECK_DECLS to check for strnlen
        prototype.
        * config.in: Regenerate.
        * configure: Likewise.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@211401 138bc75d-0d04-0410-961f-82ee72b054a4


But then, xstrndup.c has at the top:

#ifdef HAVE_STRING_H
#include <string.h>
#else
# ifdef HAVE_STRINGS_H
#  include <strings.h>
# endif
#endif

So I would expect your build to pick the strnlen declaration from
one of the string.h or strings.h mingw headers.  Why didn't it?

Thanks,
Pedro Alves