Bug#872503: ffmpeg: armhf SIGBUS in ff_diff_pixels_armv6 running winff autopkgtest

[James Cowgill]

Hi,

On 19/08/17 21:20, Carl Eugen Hoyos wrote:
>> Am 19.08.2017 um 20:26 schrieb James Cowgill <jcowgill at debian.org>:
>>> On 19/08/17 10:36, Carl Eugen Hoyos wrote:
>>> Could you confirm that this is a regression since 31326143 (ie since
>>> forever) and is not reproducible with f73a626a?
>>
>> Yes the code fails in the same place with 31326143 and worlds with
>> f73a626a, although I don't think the ARM code is at fault here since the
>> misaligned argument is coming from further up the call chain.
> 
> (Not so sure: The new functions with stricter requirements are meant as replacement for functions with lower requirements.)

pixblockdsp.h says "align 8" next to s2 which I assume means that the
caller will guarantee the argument is aligned to 8 bytes. It wasn't
aligned in this case which is why the ARM code blew up.

> Thanks again for the very complete tests!
> 
>>> Since I cannot produce the required gdb output, you will have to open
>>> a ticket, sorry!
>>
>> OK. I'll see if the arguments are misaligned on x86 as well first.
> 
> Probably, but that doesn't hurt or does it?

I can reproduce the misalignment on x86 as well. x86 handles misaligned
addresses (with a performance penalty) which is probably why it doesn't
crash there.

Thanks,
James

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