[FFmpeg-devel] [PATCH] restoring binary compatibility with ffmpeg 0.5

[Michael Niedermayer]

On Mon, Jun 07, 2010 at 11:08:46AM +0200, Reinhard Tartler wrote:
> On Mo, Jun 07, 2010 at 10:40:04 (CEST), Michael Niedermayer wrote:
> 
> > On Mon, Jun 07, 2010 at 07:52:11AM +0200, Reinhard Tartler wrote:
> >> On Mo, Jun 07, 2010 at 01:44:30 (CEST), Michael Niedermayer wrote:
> >> 
> >> >> > we can duplicate the symbols and code in lavf under #if
> >> >> 
> >> >> I suspect that might cause a conflict during linking since the same
> >> >> symbol would be provided by two libraries.  If it doesn't fail, the
> >> >> version chosen is unpredictable.  We'd end up with apps linked against
> >> >> a mix of sym at LIBAVFORMAT_XX and sym at LIBAVCODEC_XX which is obviously
> >> >> not good.
> >> >
> >> > marking one as weak symbol might work.
> >> > weak symbols are part of the ELF spec ... doesnt mean gnu tools support
> >> > them of course ;)
> >> 
> >> I've (of course) tried that as well, but it doesn't work in this
> >> case. The problem here is that you must not create symbol collisions in
> >> the same compilation unit. Removing the symbols from libavcodec, even
> >> conditionally, is not an option that we have. Using weak symbols, like
> >> this version
> >> 
> >> #if HAVE_SYMBOL_VERSIONING && LIBAVFORMAT_VERSION_MAJOR < 53
> >> /* compatibility trampolines for packet functions */
> >> 
> >> #define av_weak_alias(x)  __attribute__ (( weak, alias ("x") ))
> >> 
> >> void av_init_packet(AVPacket *pkt) av_weak_alias(av_init_packet);
> >> void av_init_packet(AVPacket *pkt)
> >
> > what about
> >
> > void __attribute__ (( weak )) av_init_packet(AVPacket *pkt)
> >
> >> {
> >>     av_log(NULL, AV_LOG_WARNING, "diverting av_*_packet function calls to libavcodec. Recompile to improve performance\n");
> >>     av_init_packet(pkt);
> >> }
> >
> > ?
> 
> did you try that? In my tests, I get these compiler errors:
> 
> causes this compiler error:
> .../ffmpeg/libavformat/utils.c:326: error: redefinition of 'av_init_packet'
> .../ffmpeg/libavformat/utils.c:325: note: previous definition of 'av_init_packet' was here

i tried:
int __attribute__((weak)) func(int x)
{
        return 5;
}

and i can make a .so out of that


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you really think that XML is the answer, then you definitly missunderstood
the question -- Attila Kinali
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