[FFmpeg-devel] [PATCH 1/2] avformat/mov: zero initialize codec_name in mov_parse_stsd_video()

[Andreas Cadhalpun]

On 20.10.2016 03:25, Michael Niedermayer wrote:
> On Wed, Oct 19, 2016 at 07:30:29PM +0200, Andreas Cadhalpun wrote:
>> On 19.10.2016 04:15, James Almer wrote:
>>> On 10/17/2016 9:57 PM, Michael Niedermayer wrote:
>>>> On Sun, Oct 16, 2016 at 09:34:50PM -0300, James Almer wrote:
>>>>> Fixes valgrind warning about "Conditional jump or move depends on uninitialised value(s)"
>>>>>
>>>>> Signed-off-by: James Almer <jamrial at gmail.com>
>>>>> ---
>>>>>  libavformat/mov.c | 2 +-
>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> This should be suppressable by adding it to
>>>> tests/fate-valgrind.supp
>>>
>>> I'll leave that to someone else. No idea how to add stuff to that file.
>>>
>>> Should i drop this patch? Zero initializing a buffer in stack wouldn't
>>> hurt IMO.
>>
>> I prefer fixing such things in the code if it's reasonable possible, which
>> is the case here. In other words, the patch looks good to me.
> 
> I think the bug is that valgrind misinterprets highly optimized libc/gcc
> code, i might be wrong though as i didnt disassemble and analyze this,
> that was just my feeling ...
> But if true a change to ffmpeg can only workaround but not fix this

Yes, this seems to be a false positive. But working around it is good, because
it increases the signal to noise ratio of valgrind.
This is similar to false positive compiler warnings: Not working around them
has high chances of wasting the time of the next one to look into it.

Best regards,
Andreas