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

[Michael Niedermayer]

On Thu, Jun 10, 2010 at 12:57:42PM +0200, Reinhard Tartler wrote:
> On Thu, Jun 10, 2010 at 11:38:52 (CEST), Michael Niedermayer wrote:
> 
> > On Thu, Jun 10, 2010 at 09:52:13AM +0100, M?ns Rullg?rd wrote:
> >> Reinhard Tartler <siretart at tauware.de> writes:
> >> 
> >> > On Wed, Jun 09, 2010 at 19:41:33 (CEST), Michael Niedermayer wrote:
> >> >
> >> >> On Wed, Jun 09, 2010 at 03:42:13PM +0200, Reinhard Tartler wrote:
> >> >>> Two questions:
> >> >>>  a) doesn't this attribute need to be at symbol declaration and not
> >> >>>     definition?
> >> >>
> >> >> The way i understand it, it needs to be at the definition
> >> >> at the declaration it possibly means a weak refernce which is something
> >> >> that is 0 (instead of failing to link) if no definition is found
> >> >
> >> > I see.
> >> >
> >> > I've now tried your suggestion to (re)introduce the functions like you
> >> > propose:
> >> >
> >> > #if LIBAVFORMAT_VERSION_MAJOR < 53
> >> > [...]
> >> > void __attribute__((weak)) av_init_packet(AVPacket *pkt)
> >> > {
> >> >      abort();
> >> > }
> >> > #endif
> >> >
> >> > building a shared libavformat.so works without warnings/errors regarding
> >> > symbol collisions and results this
> >> >
> >> > $ readelf -s /tmp/ffmpeg-trunk/lib/libavformat.so | grep av_init_packet@
> >> >    466: 000abc00     8 FUNC    WEAK   DEFAULT   13 av_init_packet@@LIBAVFORMAT_52
> >> >
> >> > I guess this is exactly what you've expected here.
> >> >
> >> > With this setup, I've now tried both the ffplay binary from this
> >> > compilation and the system /usr/bin/ffplay (based on version 0.5.2). In
> >> > *both* cases, it seems that the binary at runtime picks up the version
> >> > in libavformat:
> >> >
> >> >>> readelf -s /tmp/ffmpeg-trunk/bin/ffplay | grep av_init_packet
> >> >     49: 00000000     0 FUNC    GLOBAL DEFAULT  UND av_init_packet at LIBAVFORMAT_52 (10)
> >> >
> >> >>> /tmp/ffmpeg-trunk/bin/ffplay /tmp/foo.avi
> >> > FFplay version SVN-r23556, Copyright (c) 2003-2010 the FFmpeg developers
> >> >   built on Jun 10 2010 08:09:17 with gcc 4.4.3
> >> >   configuration: --enable-avfilter --enable-libvpx --enable-shared --disable-static --enable-gpl --prefix=/tmp/ffmpeg-trunk --enable-postproc --enable-libvorbis
> >> >   libavutil     50.18. 0 / 50.18. 0
> >> >   libavcodec    52.75. 1 / 52.75. 1
> >> >   libavformat   52.68. 0 / 52.68. 0
> >> >   libavdevice   52. 2. 0 / 52. 2. 0
> >> >   libavfilter    1.20. 0 /  1.20. 0
> >> >   libswscale     0.11. 0 /  0.11. 0
> >> >   libpostproc   51. 2. 0 / 51. 2. 0
> >> > zsh: abort      /tmp/ffmpeg-trunk/bin/ffplay /srv/media/UDS-Sevilla.avi
> >> 
> >> This is what I would expect.  The weak attribute is only used when
> >> combining relocatable object files in to an executable or shared
> >> object, not during runtime dynamic linking.
> >
> > until reinhard posts a readelf of libavcodec that shows a global
> > av_init_packet at LIBAVFORMAT_52 this conclusion is unfounded
> 
> Right, I did not change the version tag in libavcodec. But also adding
> it doesn't matter:
> 
> $ readelf -s /tmp/ffmpeg-trunk/lib/libavcodec.so | grep av_init_packet@
>   1280: 000c3d90    88 FUNC    GLOBAL DEFAULT   13 av_init_packet@@LIBAVFORMAT_52
> 
> $ readelf -s /tmp/ffmpeg-trunk/lib/libavformat.so | grep av_init_packet@
>    466: 000abc00     8 FUNC    WEAK   DEFAULT   13 av_init_packet@@LIBAVFORMAT_52
> 
> $ readelf -s /tmp/ffmpeg-trunk/bin/ffplay | grep av_init_packet@
>     49: 00000000     0 FUNC    GLOBAL DEFAULT  UND av_init_packet at LIBAVFORMAT_52 (10)
> 
> $ /tmp/ffmpeg-trunk/bin/ffplay /srv/media/UDS-Sevilla.avi
> FFplay version SVN-r23556, Copyright (c) 2003-2010 the FFmpeg developers
>   built on Jun 10 2010 08:09:17 with gcc 4.4.3
>   configuration: --enable-avfilter --enable-libvpx --enable-shared --disable-static --enable-gpl --prefix=/tmp/ffmpeg-trunk --enable-postproc --enable-libvorbis
>   libavutil     50.18. 0 / 50.18. 0
>   libavcodec    52.75. 1 / 52.75. 1
>   libavformat   52.68. 0 / 52.68. 0
>   libavdevice   52. 2. 0 / 52. 2. 0
>   libavfilter    1.20. 0 /  1.20. 0
>   libswscale     0.11. 0 /  0.11. 0
>   libpostproc   51. 2. 0 / 51. 2. 0
> zsh: abort      /tmp/ffmpeg-trunk/bin/ffplay /srv/media/UDS-Sevilla.avi
> 
> $ /usr/bin/ffplay /srv/media/UDS-Sevilla.avi
> FFplay version SVN-r0.5.1-4:0.5.1-1ubuntu1, Copyright (c) 2003-2009 Fabrice Bellard, et al.
>   configuration: --extra-version=4:0.5.1-1ubuntu1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --disable-vhook --enable-runtime-cpudetect --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --enable-shared --disable-static
>   libavutil     49.15. 0 / 49.15. 0
>   libavcodec    52.20. 1 / 52.75. 1
>   libavformat   52.31. 0 / 52.68. 0
>   libavdevice   52. 1. 0 / 52. 2. 0
>   libavfilter    0. 4. 0 /  0. 4. 0
>   libswscale     0. 7. 1 /  0.11. 0
>   libpostproc   51. 2. 0 / 51. 2. 0
>   built on Mar  4 2010 12:35:30, gcc: 4.4.3
> zsh: abort      /usr/bin/ffplay /srv/media/UDS-Sevilla.avi
> 
> 
> anything else I can/should try?

for the record it works with export LD_DYNAMIC_WEAK=1
and the default of this variable has changed over time ;)


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

Observe your enemies, for they first find out your faults. -- Antisthenes
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