[FFmpeg-devel] [PATCH v2 1/4] libavutil/error: fix build with musl toolchain

[Reimar Döffinger]

On Thu, Sep 04, 2014 at 11:27:49PM +0200, Jörg Krause wrote:
> 
> On 09/04/2014 05:27 PM, Hendrik Leppkes wrote:
> >On Wed, Sep 3, 2014 at 11:53 AM, Jörg Krause <jkrause at posteo.de> wrote:
> >>Add the feature test macro which is required for building with the
> >>musl toolchain.
> >>
> >>The feature test macro _XOPEN_SOURCE = 600 provides the XSI-compliant
> >>version of strerror_r().
> >>
> >>[..]
> >  _XOPEN_SOURCE 600 is set as a compiler parameter for all other
> >toolchains that need it, including glibc and whatnot.
> >We should really do the same for musl here, using special treatment is weird.
> >
> >Detect musl in configure, add a new libc block, set
> >-D_XOPEN_SOURCE=600 in the cflags, and it would be consistent with
> >everything else.
> 
> We had a discussion about this issue here at the mailing list.
> 
> Detecting musl in configure is not possible. There is no __MUSL__ like
> __GLIBC__ in <features.h>. The maintainers of musl prefer that the library
> is tested for the exposed feature set.
> 
> Another approach is to set the desired feature test macro at source level,
> which is the recommation of the GNU C Library Reference Manual, instead of
> setting it with -D.
> 
> If we follow this approach, we have constintency for glibc, uclibc, and
> musl. And we do not need a libc block for them in configure (at least not
> for setting any feature test macro with -D).

This argument doesn't make any sense to me.
You would get the same effect by setting it with -D in configure
unconditionally, and without having to manually add the define in every single
file (if you add it only to some, you end up with a random set of
enable features in each file, making quite a maintenance mess).
The only problem with that approach is that there are some libraries
where e.g. setting ISO_C_SOURCE means all BSD feature are disabled
and impossible to enable, so we need special cases for these.
But again, it's still only a question of making special cases in the
files (and thus duplicating it all over), or doing it in configure.