[Ffmpeg-devel] valgrind error in decoding jpeg files

[Michael Niedermayer]

Hi

On Monday 04 July 2005 16:40, Luca Ognibene wrote:
> Hi! First thanks for all your work!
> I've a valgrind error while decoding a single jpeg files.
> I'm using gstreamer but i've reproduced the error with a simple
> test case (mainly copied from apiexample.c).
> btw, the image is decoded fine :)
>
> Test case: www.freedesktop.org/~skaboy/decodejpeg.c
> Simple image: http://www.freedesktop.org/~skaboy/simple.jpeg
> command used to test: valgrind --num-callers=15 ./apiexample
> /home/luogni/simple.jpeg
>
> output:
> Video decoding
> ==6303== Conditional jump or move depends on uninitialised value(s)
> ==6303==    at 0x1BA04B37: decode_block (bitstream.h:577)
> ==6303==    by 0x1BA0485A: mjpeg_decode_scan (mjpeg.c:1426)
> ==6303==    by 0x1BA033E2: mjpeg_decode_sos (mjpeg.c:1564)
> ==6303==    by 0x1BA0206A: mjpeg_decode_frame (mjpeg.c:1948)
> ==6303==    by 0x1B9D75B4: avcodec_decode_video (utils.c:621)
> ==6303==    by 0x80496CA: video_decode_example (in
> /home/luogni/Temp/ffmpeg_bug/apiexample)
> ==6303==    by 0x80498F4: main (in
> /home/luogni/Temp/ffmpeg_bug/apiexample)
>
>
> versions used:
> i can reproduce it on debian sarge. (gcc 3.3.5, valgrind 2.4.0,
> ffmpeg cvs from 5 minutes ago)
>
> I hope this can be usefull

i think valgrind is wrong here, the read reads 32bit, the jump depends upon 
the first bit, but that bit is initalized just the later bytes arent
note though thats just what i think happens i didnt confirm if thats really 
what happens, so if you notice a jpeg which shows some distortions, report 
it ...

[...]
-- 
Michael