Bug#647824: please backport upstream's workaround

[Reinhard Tartler]

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;
+
     __asm__ volatile(
 #if defined(PIC)
         "mov               %%"REG_b", %5        \n\t"


With this patch applied, the backtrace looks like this:
(gdb) bt
#0  0x000000000132ad00 in ?? ()
#1  0x00000000009d79fd in hyscale_fast_MMX2 (c=0x1329040, dst=0x0, dstWidth=20100256, src=0x135a6c0 "", srcW=160, xInc=16404)
    at libswscale/x86/swscale_template.c:1665
#2  0x00000000009c8fa9 in hyscale (isAlpha=0, pal=0x133d5a0, formatConvBuffer=0x132eb40 "\310\064\"\367\377\177", hLumFilterSize=0, 
    hLumFilterPos=0x132ece0, hLumFilter=0x132b4a0, xInc=16404, srcW=160, src=<optimized out>, dstWidth=640, dst=0x1329040, c=0x133d520)
    at libswscale/swscale.c:1990
#3  swScale (c=0x133d520, src=<optimized out>, srcStride=<optimized out>, srcSliceY=0, srcSliceH=120, dst=0x7fffffffc9a0, dstStride=0x7fffffffc9d0)
    at libswscale/swscale.c:2429
#4  0x00000000009b11bf in sws_scale (c=0x133d520, srcSlice=<optimized out>, srcStride=<optimized out>, srcSliceY=0, srcSliceH=<optimized out>, 
    dst=<optimized out>, dstStride=0x1329608) at libswscale/swscale_unscaled.c:913
#5  0x000000000045094c in draw_slice (link=0x132a640, y=<optimized out>, h=<optimized out>, slice_dir=1) at libavfilter/vf_scale.c:279
#6  0x0000000000445b74 in avfilter_draw_slice (link=0x132a640, y=0, h=120, slice_dir=1) at libavfilter/avfilter.c:484
#7  0x0000000000454069 in request_frame (link=0x132a640) at libavfilter/vsrc_buffer.c:141
#8  0x0000000000444c7b in avfilter_request_frame (link=<optimized out>) at libavfilter/avfilter.c:373


Ronald, do you have any clue what's going on/wrong here?

Cheers,
Reinhard.

-- 
Gruesse/greetings,
Reinhard Tartler, KeyID 945348A4