[Ffmpeg-devel] Bug in snow pred_block

Michael Niedermayer michaelni
Sun Apr 17 15:39:31 CEST 2005


On Sunday 17 April 2005 04:12, Yartrebo wrote:
> There is a memory bug (segfault causing under some circumstances). Here
> is what I know about it:

if there is a segfault, then post gdb output

>  - Valgrind gives the following error quite frequently (maybe 50 a
> frame):
> ==8130== Use of uninitialised value of size 4
> ==8130==    at 0x83B6C4C: put_h264_qpel8_mc12_mmx2
> (in /home/yartrebo/compile/crap/main2/mplayer)
> ==8130==    by 0x7E7E7E7D: ???

line numbers missing

>  - It is only caused by calling s->dsp.put_h264_qpel_pixels_tab.
> mc_block works fine without giving valgrind any headaches.
>  - It appears to be caused by improper handling of edge motion blocks.
>  - It only appears on non-keyframes.
> This bug appears to be the source of a lot of various segfaults and
> freezing, so could you [Michael] have a look at it?

uninitialized does not mean not allocated, so i cant see how this could be 
related to a segfault, optimized code often reads over the end of arrays, you 
can just put a memset() where the tmp array is declared and the valgrind 
warnings should dissapear


"nothing is evil in the beginning. Even Sauron was not so." -- Elrond

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