Re: visibility.m4

[Simon Josefsson]

Bruno, ping?  Ok to push?

/Simon

Simon Josefsson <address@hidden> writes:

> Mike Gran <address@hidden> writes:
>
>> Hello-
>>
>> If I use visibility.m4 on a platform with a recent GCC (4.x) on 
>> Cygwin, the visibility.m4 correctly discovers that gcc can compile with 
>> -fvisibility="hidden".  But, on Cygwin (and probably most non-ELF) gcc does 
>> not actualy implement the visibility and emits the warning "visibility 
>> attribute not supported in this configuration" instead.  Even so, the tests 
>> in visibility.m4 pass, and HAVE_VISIBILITY is set in the affirmative.
>>
>> In my humble opinion, it would be a good idea to add a "-werror" to the test 
>> in visibility.m4 so that it won't set CFLAGS_VISIBILITY and HAVE_VISIBILITY 
>> on those platforms that don't actually support it.
>>
>> What do you think?
>
> I agree, and I recall that this was also suggested earlier.  The current
> approach leads to one warning per compiled source file, which is rather
> annoying.
>
> Bruno, how about this patch?
>
> /Simon
>
> diff --git a/m4/visibility.m4 b/m4/visibility.m4
> index 35a6dc0..06537d6 100644
> --- a/m4/visibility.m4
> +++ b/m4/visibility.m4
> @@ -29,7 +29,11 @@ AC_DEFUN([gl_VISIBILITY],
>      AC_MSG_CHECKING([for simple visibility declarations])
>      AC_CACHE_VAL([gl_cv_cc_visibility], [
>        gl_save_CFLAGS="$CFLAGS"
> -      CFLAGS="$CFLAGS -fvisibility=hidden"
> +      # We use -Werror here because Cygwin/MinGW gives a warning
> +      # 'visibility attribute not supported in this configuration'
> +      # instead of doing what we want.  Using -Werror makes gcc fail
> +      # instead, so we detect the problem.
> +      CFLAGS="$CFLAGS -fvisibility=hidden -Werror"
>        AC_TRY_COMPILE(
>          [extern __attribute__((__visibility__("hidden"))) int hiddenvar;
>           extern __attribute__((__visibility__("default"))) int exportedvar;