[vlc-devel] [HELP] Tracking down an audio transcoding segfault with the mpgatofixed32 filter

[Rafaël Carré]

On Fri, 2008-06-13 at 10:49 -0400, Kevin DuBois wrote:
> So the when using the mpgatofixed32 filter in the new audio
> transcoding chain configuration, segfaulting occurs. This filter is
> used whenever mpga is input, so this effectively breaks the streaming
> of dvb, mpeg files, etc.  I beleive that this bug would also manifest
> itself in other audio filter2 modules like headphone, but it does not
> exist in format. This bug was not present before about june 4th.
> 
> I have seen it segfault in three different ways (i.e. different
> backtraces for different runs), all with the same binary/libraries.
> They are listed below, the third one being the rarest to see. 
> 
> I've spent some time looking into it, and only got pretty confused as
> to where to look, so even if no one can fix it, pointers as to how to
> procede would be most appreciated. The best i can come up with for an
> explanation is that something is getting improperly allocated or
> deallocated in the code for the audio buffers. I'm a bit new to coding
> in such a big project, so I appreciate any help I can get!
> 
> configuration:
> ./configure --prefix=/usr/local --enable-dvb --enable-ffmpeg
> --disable-qt4 --disable-skins2 --enable-debug 
> 
> (gdb) show args
> Argument list to give program being debugged when it is started is
> "dvb:// --dvb-frequency=12020000 --dvb-srate=2034000
> --dvb-lnb-lof1=10750000 --dvb-satno=0 --dvb-high-voltage
> --dvb-voltage=18 -vvv --sout
> '#transcode{acodec=mp4a}:rtp{dst=10.0.9.121,
> sdp=file:///home/kdubois/test.sdp}'".
> 
> 
> SEGFAULT 1
> 
> *** glibc detected *** double free or corruption (!prev): 0x082da820
> ***

That message makes me want to use valgrind

> Program received signal SIGABRT, Aborted.
> [Switching to Thread -1362109520 (LWP 16179)]
> 0xffffe410 in __kernel_vsyscall ()
> (gdb) bt
> #0  0xffffe410 in __kernel_vsyscall ()
> #1  0xb7d1d811 in raise () from /lib/tls/i686/cmov/libc.so.6
> #2  0xb7d1efb9 in abort () from /lib/tls/i686/cmov/libc.so.6
> #3  0xb7d52dfa in __fsetlocking () from /lib/tls/i686/cmov/libc.so.6
> #4  0xb7d5a68f in mallopt () from /lib/tls/i686/cmov/libc.so.6
> #5  0xb7d5a732 in free () from /lib/tls/i686/cmov/libc.so.6

Use valgrind

> SEGFAULT 2
> 
> Program received signal SIGSEGV, Segmentation fault.
> [Switching to Thread -1362109520 (LWP 16249)]
> 0xb7da036f in mallopt () from /lib/tls/i686/cmov/libc.so.6
> (gdb) bt
> #0  0xb7da036f in mallopt () from /lib/tls/i686/cmov/libc.so.6
> #1  0xb7da0732 in free () from /lib/tls/i686/cmov/libc.so.6

Use valgrind

-- 
Rafaël Carré <rcarre at m2x.nl>