ffmpeg segfaults in ff_msmpeg4_encode_block with "-r 12 -codec msmpeg4 -mbd rd" options

[tom.vercauteren@gmail.com]

This is a followup of:
​http://ffmpeg.org/pipermail/libav-user/2012-February/001256.html

Running

ffmpeg -r 12 -i test-%04d.png -codec msmpeg4 -mbd rd test.avi

on the attached png file leads to a segfault.

A quick debugging session shows that an array index in ff_msmpeg4_encode_block becomes -1 at line 930 of msmpeg4.c (version 0.10)
​http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavcodec/msmpeg4.c;h=d37cac9862380a339e64d663ba21c76728751a1a;hb=1b7ff901078064ccd7df3640e0958a344b2c00cb

[Carl Eugen Hoyos]

$ (gdb) r -r 12 -i test-%04d.png -codec msmpeg4 -mbd rd test.avi
Starting program: ffmpeg_g -r 12 -i test-%04d.png -codec msmpeg4 -mbd rd test.avi
ffmpeg version N-37711-g1b7ff90 Copyright (c) 2000-2012 the FFmpeg developers
  built on Feb 10 2012 10:47:16 with gcc 4.5.3
  configuration: --cc=/usr/local/gcc-4.5.3/bin/gcc
  libavutil      51. 39.100 / 51. 39.100
  libavcodec     54.  1.100 / 54.  1.100
  libavformat    54.  0.100 / 54.  0.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 62.100 /  2. 62.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  6.100 /  0.  6.100
Input #0, image2, from 'test-%04d.png':
  Duration: 00:00:00.25, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: png, rgba, 912x912, 12 fps, 12 tbr, 12 tbn, 12 tbc
Incompatible pixel format 'rgba' for codec 'msmpeg4', auto-selecting format 'yuv420p'
[buffer @ 0x13d7200] w:912 h:912 pixfmt:rgba tb:1/1000000 sar:0/1 sws_param:
[buffersink @ 0x13d7600] auto-inserting filter 'auto-inserted scale 0' between the filter 'src' and the filter 'out'
[scale @ 0x13d7ee0] w:912 h:912 fmt:rgba -> w:912 h:912 fmt:yuv420p flags:0x4
Output #0, avi, to 'test.avi':
  Metadata:
    ISFT            : Lavf54.0.100
    Stream #0:0: Video: msmpeg4 (hq) (MP43 / 0x3334504D), yuv420p, 912x912, q=2-31, 200 kb/s, 12 tbn, 12 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (png -> msmpeg4)
Press [q] to stop, [?] for help

Program received signal SIGSEGV, Segmentation fault.
get_rl_index (level=1, run=0, last=0, rl=0xe44c58) at libavcodec/rl.h:78
78          index = rl->index_run[last][run];
(gdb) disass $pc-32,$pc+32
Dump of assembler code for function get_rl_index:
0x00000000007c6d6a <get_rl_index+0>:    lea    0x4(%r12),%rcx
0x00000000007c6d6f <get_rl_index+5>:    mov    (%r9),%ebp
0x00000000007c6d72 <get_rl_index+8>:    mov    (%r9,%rcx,8),%rcx
0x00000000007c6d76 <get_rl_index+12>:   mov    %ebp,%r13d
0x00000000007c6d79 <get_rl_index+15>:   movzbl (%rcx,%r14,1),%ecx
0x00000000007c6d7e <get_rl_index+20>:   cmp    %ebp,%ecx
0x00000000007c6d80 <get_rl_index+22>:   jge    0x7c6d9a <ff_msmpeg4_encode_block+666>
0x00000000007c6d82 <get_rl_index+24>:   lea    0x6(%r12),%rbx
0x00000000007c6d87 <get_rl_index+29>:   lea    -0x1(%rsi,%rcx,1),%ecx
0x00000000007c6d8b <get_rl_index+33>:   mov    (%r9,%rbx,8),%rbx
0x00000000007c6d8f <get_rl_index+37>:   movsbl (%rbx,%r14,1),%ebx
0x00000000007c6d94 <get_rl_index+42>:   cmp    %ebx,%esi
0x00000000007c6d96 <get_rl_index+44>:   cmovle %ecx,%r13d
End of assembler dump.
(gdb) info registers
rax            0x1      1
rbx            0x1459bb0        21339056
rcx            0x0      0
rdx            0xffffffff       4294967295
rsi            0x1      1
rdi            0x13d3671        20788849
rbp            0x3      0x3
rsp            0x7ffffffee268   0x7ffffffee268
r8             0x13d34e0        20788448
r9             0xe44c58 14961752
r10            0x0      0
r11            0x82     130
r12            0x0      0
r13            0x3      3
r14            0x0      0
r15            0x41     65
rip            0x7c6d79 0x7c6d79 <get_rl_index+15>
eflags         0x10202  [ IF RF ]
cs             0x33     51
ss             0x2b     43
ds             0x0      0
es             0x0      0
fs             0x0      0
gs             0x0      0
fctrl          0x37f    895
fstat          0x0      0
ftag           0xaaaa   43690
fiseg          0x0      0
fioff          0x0      0
foseg          0x0      0
fooff          0x0      0
fop            0x0      0
mxcsr          0x1fa0   [ PE IM DM ZM OM UM PM ]

[Michael Niedermayer]

locally fixed