[FFmpeg-devel] mjpeg and llvm-gcc

[Alexander Strange]

On Jun 17, 2009, at 9:16 AM, Derk-Jan Hartman wrote:

> For VLC media player Mac OS X, we were working on using llvm-gcc for  
> the new binaries. VLC and FFmpeg was behaving very well with it, but  
> recently I noticed it crashed in ff_mjpeg_decode_sos() for almost  
> all MJPEGs.
>
> Example file: http://samples.mplayerhq.hu/V-codecs/MJPEGs/angels_480-mjpegcompress.avi
>
> This file (and other mjpeg files) was producing "error dc" errors,  
> and eventually crashed.
> I have been able to determine that when I switch from llvm-gcc-4.2  
> back to gcc-4.2, the crash disappeared. I have little experience  
> trying to track causes to things like this, so if anyone has any  
> tips on how to proceed, I would welcome them. If someone could try  
> with llvm on Linux, that might be useful as well. I guess this might  
> possibly be a compiler bug ? Should I try different optimization  
> settings ?

It disappears for me if I disable x86 code (using --arch=none). I  
believe llvm has trouble with some inline asm - some configuration  
makes llvm-gcc and clang crash on h264, I can't remember which - so  
you might try hunting those down and disabling them individually.

By the way, where did "--enable-memalign-hack" and "-mtune=prescott"  
come from? The first should be unnecessary on OS X and the second is  
worse than defaults.

> [..]
> FFmpeg version SVN-r19206, Copyright (c) 2000-2009 Fabrice Bellard,  
> et al.
>  configuration: --enable-libmp3lame --enable-libgsm --enable- 
> memalign-hack --cc=/Developer/usr/llvm-gcc-4.2/bin/llvm-gcc-4.2 -- 
> arch=i386 --disable-libfaac --enable-gpl --enable-postproc --disable- 
> ffserver --enable-ffmpeg --enable-ffplay --disable-devices --disable- 
> protocols --disable-network --prefix=/Users/hartman/Development/vlc- 
> old/extras/contrib --extra-cflags='-I/Users/hartman/Development/vlc- 
> old/extras/contrib/include -march=pentium-m -mtune=prescott -arch  
> i386 -DMACOSX_DEPLOYMENT_TARGET=10.5 -isysroot /Developer/SDKs/ 
> MacOSX10.5.sdk -mmacosx-version-min=10.5 -isystem /Users/hartman/ 
> Development/vlc-old/extras/contrib/include -DHAVE_LRINTF - 
> DRUNTIME_CPUDETECT' --extra-ldflags='-L/Users/hartman/Development/ 
> vlc-old/extras/contrib/lib -arch i386 -isysroot /Developer/SDKs/ 
> MacOSX10.5.sdk -Wl,-syslibroot,/Developer/SDKs/MacOSX10.5.sdk' -- 
> enable-libmp3lame --enable-libgsm --enable-memalign-hack --cc=/ 
> Developer/usr/llvm-gcc-4.2/bin/llvm-gcc-4.2 --arch=i386 --disable- 
> libfaac --enable-gpl --enable-postproc --disable-ffserver --enable- 
> ffmpeg --enable-ffplay --disable-devices --disable-protocols -- 
> disable-network --disable-shared --enable-static
>  libavutil     50. 3. 0 / 50. 3. 0
>  libavcodec    52.31. 2 / 52.31. 2
>  libavformat   52.34. 0 / 52.34. 0
>  libavdevice   52. 2. 0 / 52. 2. 0
>  libswscale     0. 7. 1 /  0. 7. 1
>  libpostproc   51. 2. 0 / 51. 2. 0
>  built on Jun 17 2009 14:23:53, gcc: 4.2.1 (Based on Apple Inc.  
> build 5555) (LLVM build 2056)
> /Users/hartman/angels_480-mjpegcompress.avi: no such file or directory