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

[Michael Niedermayer]

On Sun, Jun 06, 2010 at 10:32:19PM +0100, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> 
> > On Sun, Jun 06, 2010 at 10:59:09PM +0200, Reimar D?ffinger wrote:
> >> On Sun, Jun 06, 2010 at 10:45:18PM +0200, Michael Niedermayer wrote:
> >> > On Sun, Jun 06, 2010 at 10:29:25PM +0200, Reimar D?ffinger wrote:
> >> > > On Sun, Jun 06, 2010 at 09:38:07PM +0200, Reinhard Tartler wrote:
> >> > > > In any case, find below the 'best' fix, that admittedly only works on
> >> > > > gnu platforms. Michael, please comment if you prefer the half fix that
> >> > > > fixes the issue on gcc/gas platforms (and doesn't regress on others) or
> >> > > > bumping major of libavformat.
> >> > > 
> >> > > How sure are we this is actually correct?
> >> > > The cases I could find documented (which only involve one library)
> >> > > also require changes to the version script.
> >> > > In case it was only one library, something like this:
> >> > > Index: libavcodec.v
> >> > > ===================================================================
> >> > > --- libavcodec.v        (revision 23508)
> >> > > +++ libavcodec.v        (working copy)
> >> > > @@ -1,3 +1,7 @@
> >> > > +LIBAVFORMAT_52 {
> >> > > +        global: av_init_packet;
> >> > > +};
> >> > >  LIBAVCODEC_$MAJOR {
> >> > > +        global: av_init_packet;
> >> > >          global: *;
> >> > > -};
> >> > > +} LIBAVFORMAT_52;
> >> > > 
> >> > > However here we have the problem that this would break e.g. on Solaris,
> >> > > since a symbol is not allowed to have multiple versions there.
> >> > 
> >> > +LIBAVFORMAT_52 {
> >> > +        global: av_init_packet;
> >> > +};
> >> >  LIBAVCODEC_$MAJOR {
> >> >          global: *;
> >> > -};
> >> > +} LIBAVFORMAT_52;
> >> > 
> >> > above does not work?
> >> 
> >> It does, but it does not do what I guess you want.
> >> It will only generate av_init_packet@@LIBAVFORMAT_52,
> >
> > yes
> >
> >> so it will still break compatibility to some previous versions.
> >
> > do you assume this or have you tested this?
> 
> It changes the name of the symbol.  Anything linked against current
> libavcodec will fail after this change.

IMO the linker is suposed to find symbols in the linked versions
gnu ldso does not, so this doesnt work for us. I still think though
that this behavior of gnu ldso is not terribly sane

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

Avoid a single point of failure, be that a person or equipment.
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