[FFmpeg-devel] [PATCH] Fix a valgrind error in h264.c

[Michael Niedermayer]

On Tue, Mar 03, 2009 at 08:57:15PM +0100, Vitor Sessak wrote:
> Hi,
>
> I was wondering why MinGW fails decoding CVMAPAQP3_Sony_E.jsv in FATE 
> (http://fate.multimedia.cx/index.php?build_record=61129), so I tested it 
> with valgrind in my box:
>
>> ==10039== Conditional jump or move depends on uninitialised value(s)
>> ==10039==    at 0x8146DD5: ff_print_debug_info (mpegvideo.c:1092)
>> ==10039== ==10039== Conditional jump or move depends on uninitialised 
>> value(s)
>> ==10039==    at 0x82A3971: h264_parse (h264_parser.c:55)
>> ==10039== ==10039== Invalid read of size 1
>> ==10039==    at 0x828BFBE: filter_mb (h264.c:6471)
>> ==10039==  Address 0x49374a3 is not stack'd, malloc'd or (recently) free'd
>
> The attached patch fixes the last one, but I have no familiarity with h264 
> code (nor $bignum hours of free time to acquire it) so I don't know if it 
> is the right way to fix it...
>
> -Vitor
>
> PS: I don't know either if this actually fixes MinGW or not...

> Index: libavcodec/h264.c
> ===================================================================
> --- libavcodec/h264.c	(revision 16968)
> +++ libavcodec/h264.c	(working copy)
> @@ -6470,7 +6470,7 @@
>          int qp = s->current_picture.qscale_table[mb_xy];
>          if(qp <= qp_thresh
>             && (mb_x == 0 || ((qp + s->current_picture.qscale_table[mb_xy-1] + 1)>>1) <= qp_thresh)
> -           && (mb_y == 0 || ((qp + s->current_picture.qscale_table[h->top_mb_xy] + 1)>>1) <= qp_thresh)){
> +           && (mb_y == 0 || h->top_mb_xy < 0 || ((qp + s->current_picture.qscale_table[h->top_mb_xy] + 1)>>1) <= qp_thresh)){

my gut feeling says the check should be
is h->top_mb_xy < 0 alone not enough?

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I wish the Xiph folks would stop pretending they've got something they
do not.  Somehow I fear this will remain a wish. -- M?ns Rullg?rd
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