Bug#639948: Bug#638250: Needs to be adapted for libav/0.7

[Reinhard Tartler]

On Sun, Sep 04, 2011 at 11:23:34 (CEST), Elimar Riesebieter wrote:

> * Reinhard Tartler [110904 08:47 +0200]:
>
>> tags 638250 help
>> stop
>> 
>> On Sun, Sep 04, 2011 at 06:45:36 (CEST), Elimar Riesebieter wrote:
>> 
>> > block 638250 by 639948
>> > thanks
>> 
>> I strongly disagree that this arch specific defect on ppc is in any way
>> a blocking bug for recompiling moc-ffmpeg-plugin against the new libav
>> libraries.
>
> moc-ffmpeg-plugin on ppc compiles well against libav 0.7.1 libraries
> but produces exactly the same backtraces as ffplay 0.7.1 on ppc. So
> this is surely a libav bug.

Nobody doubts that. My objection in that the 'block' relationship is
wrong. As soon as a change for the altivec assembler code is found,
surely moc-ffmpeg-plugin will work again.

>> It only affects (some?) altivec enabled machines and can be
>> easily avoided by disabling the altivec variant.
>
> What do you mean with only? PPC is an officialy supported
> architecture in Debian!

I mean that we know that the bug appears on your particular machine. I
question that it might not be broken on *every* altivec machine
available. The code in question has passed an intensive regression
suite, which includes testing on altivec machines. I'm curious how this
could slip through:

http://fate.libav.org/

> Most of the powerpc machines are altivev capable. Apple's G4 and G5,
> IBM's Power6 and Power7 are all have altivec which is very useful to
> accelerate multimedia applications. And please notice, that altivec
> was working well on ffmpeg 0.6.2-5 so it turns out that #639948 is a
> regression!

Again, nobody doubts that. I just don't consider #639948 release
critical.

>> [...]
>> 
>> > Thanks again for the patch but there is no solution for #639948 yet.
>> > Please advice me what to do? I filed the ppc bug to libav-upstream
>> > http://bugzilla.libav.org/show_bug.cgi?id=40 but there is no
>> > response either from Debian-multimedia. Removing ppc from supported
>> > archs isn't practicable as 639948 is a regression.
>> 
>> Ideally, we find a porter that can identify the bug and provide a patch
>> for fixing the segmentation fault. I've copied the powerpc porters and
>> ask them hereby for their assistance.
>
> I'll check the CC settings in libav package, but as far as I can see
> they are equal for ppc. Hmmm. Compiling ith gcc-4.5 would be a first
> attempt to eleminate a compiler bug.

Thanks.

>> Or, if porters approached me, I also could disable the altivec builds in
>> libav completely, penalizing potential altivec users that do not
>> experience this issue.
>
> This might not be a very intelligent solution.

Well, I just state the available options.

-- 
Gruesse/greetings,
Reinhard Tartler, KeyID 945348A4