Bug#882598: libavutil55: segfault after upgrade

James Cowgill jcowgill at debian.org
Fri Nov 24 20:40:09 UTC 2017


On 24/11/17 15:40, James Cowgill wrote:
> Control: severity -1 grave
> Control: retitle -1 libavutil55: ABI broken by "add vector_dmac_scalar()"
> Control: forwarded -1 https://trac.ffmpeg.org/ticket/6861
> Control: tag -1 - moreinfo
> Control: found -1 7:3.4-1
> On 24/11/17 14:46, Carl Eugen Hoyos wrote:
>> Hi!
>> I created FFmpeg ticket #6861, thank you for the report!
>> https://trac.ffmpeg.org/ticket/6861
> That is not a nice bug.
> I'll have to think about the best way to handle this. I guess we will
> have to revert the ABI breaking commit, identify the packages which are
> broken (including ffmpeg itself like in this bug), add some Breaks for
> them, and finally binNMU them. Alternatively we could force an ABI
> transition and rebuild everything, but I'm not sure if I want to do
> that (especially since we'll have to do another in a few months anyway).

On closer inspection (and reading the upstream bug), the ABI break
occurs in the private float_dsp.h header and the only consumers are
libavcodec and libavfilter. This makes things much easier than I
originally thought since the breakage is internal to ffmpeg.

I think this can be fixed by keeping the new ABI and use package
dependencies to enforce that it's used only with 3.4.

We need to ensure 3.4 libavcodec/libavfilter uses 3.4 libavutil, but
this is already guaranteed through the existing symbols system. We then
need to prevent 3.4 libavutil from being used with pre-3.4
libavcodec/libavfilter by adding this to libavutil55:

 libavcodec57 (<< 7:3.4),
 libavcodec-extra57 (<< 7:3.4),
 libavfilter6 (<< 7:3.4),
 libavfilter-extra6 (<< 7:3.4)

I think that will fix the bug. Can anyone see anything I've missed?


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