"Ronald S. Bultje" <[email protected]> writes: > Hi, > > 2011/11/7 Måns Rullgård <[email protected]>: >> Reinhard Tartler <[email protected]> writes: >> >>> tags 647824 upstream >>> stop >>> >>> On So, Nov 06, 2011 at 17:53:30 (CET), Harald Dunkel wrote: >>> >>>> Package: libav >>>> Version: 4:0.7.2-1 >>>> >>>> If I build the current xbmc snapshot, then it dies at runtime when >>>> creating thumbnails for wmv files. See http://trac.xbmc.org/ticket/11789 >>>> for more details >>>> >>>> http://article.gmane.org/gmane.comp.video.ffmpeg.devel/134444 >>>> >>>> provides a workaround. Do you think this could be included in the >>>> libav and libav-extra packages? >>>> >>> >>> That patch does not apply to Debian's libav package. In fact, it seems >>> that this bug is still present in the master branch. >>> >>> I was able to reproduce the segmentation fault using the following >>> command in libav *master* (inspired by >>> https://ffmpeg.org/trac/ffmpeg/ticket/397): >>> >>> ./ffmpeg -v 9 -loglevel 99 -i >>> /srv/scratch/fate-suite/amv/MTV_high_res_320x240_sample_Penguin_Joke_MTV_from_WMV.amv >>> -sws_flags fast_bilinear -vf "scale=640:480" -vframes 1 -vcodec png >>> output.png >>> >>> Unforutnately, this (adapted) patch does not seem to fix the >>> segmentation fault: >>> >>> diff --git a/libswscale/x86/swscale_template.c >>> b/libswscale/x86/swscale_template.c >>> index 5e7df5c..51ea303 100644 >>> --- a/libswscale/x86/swscale_template.c >>> +++ b/libswscale/x86/swscale_template.c >>> @@ -1657,6 +1657,11 @@ static void RENAME(hyscale_fast)(SwsContext *c, >>> int16_t *dst, >>> DECLARE_ALIGNED(8, uint64_t, ebxsave); >>> #endif >>> >>> + // HACK: gcc 4.6 no longer decrements esp, >>> + // use this to make it reserve space for the call >>> + // return address >>> + void *dummy; >> >> The real problem here comes from hiding a call inside inline asm. On >> x86_64 leaf functions have a "red zone" of 128 bytes below the stack >> pointer which can be used for whatever the compiler feels like. If the >> compiler has made use of this (gcc frequently does) and a call is >> injected with inline asm, any values kept in the red zone are destroyed. >> >> There are 3 solutions to this problem: >> >> 1. Do the calls in C. >> 2. Convert the function to yasm. >> 3. Manually protect the red zone in the inline asm. >> >> Option 3 is difficult to do if any asm parameters might reference the >> stack as is the case here. >> >> Why is this using asm at all? It's only a few function calls. > > You should check what it's calling. :-).
It's calling some generated code. So what? Use a function pointer. -- Måns Rullgård [email protected] _______________________________________________ libav-devel mailing list [email protected] https://lists.libav.org/mailman/listinfo/libav-devel
