[FFmpeg-devel] [PATCH v4] vaapi_encode_mjpeg: fix bad component id bug

[Andreas Rheinhardt]

Dominik 'Rathann' Mierzejewski:
> On Friday, 07 June 2019 at 23:45, U. Artie Eoff wrote:
>> The compound literals assigned to "components"
>> only exist within the scope of the if/else
>> block (thanks Mark Thompson for the better
>> explanation).
>>
>> Thus, after this if/else block, "components"
>> ends up pointing to an arbitrary/undefined
>> array.  With some compilers and depending on
>> optimization settings, these arbitrary values
>> may end up being the same value (i.e. 0 with
>> GNU GCC 9.x).  Unfortunately, the GNU GCC
>> compiler, at least, never prints any warnings
>> about this.
>>
>> This patch fixes this issue by assigning the
>> constant arrays to local variables at function
>> scope and then pointing "components" to those
>> as necessary.
>>
>> Fixes #7915
> 
> Brilliant detective work, Artie. Could you open a bug report with gcc
> upstream? A case like this should get an explicit warning from gcc like
> you pointed out.
> 
> Regards,
> Dominik
> 
A request for this has already been opened [1].
It seems that this is also responsible for filesystem corruption on
linux when using a SSD cache + HDD combination (see [2]).

- Andreas

[1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89990
[2]: https://bugzilla.kernel.org/show_bug.cgi?id=203573