Hello hikaru,
just saw your report and tried if I could reproduce your issue.
But probably you want to reproduce these steps on your hardware to verify
that this is really the issue on real hardware.
These steps I tried to reproduce:
- install a qemu virtual machine with current jessie with some desktop
environment and following packages: gdb vlc-dbg libav-dbg
- shut down the VM and restarted with forcing it to i586 with these
parameters: "qemu-system-i386 -cpu pentium ..."
- started vlc without starting a video
- started in a terminal gdb: "gdb --pid 984"
- issue the command "cont"
- play in vlc a video
- at some point I came to the following exception
- the command "bt" shows you the call stack which led to the exception
- (to end the crashed vlc issue commands "kill" and "quit")
Stack without having debug symbols installed:
Program received signal SIGILL, Illegal instruction.
[Switching to Thread 0xb17ffb40 (LWP 545)]
0xaf282c93 in ?? () from /usr/lib/i386-linux-gnu/libavcodec.so.56
(gdb) bt
#0 0xaf282c93 in ?? () from /usr/lib/i386-linux-gnu/libavcodec.so.56
#1 0xaf2b9680 in ?? () from /usr/lib/i386-linux-gnu/libavcodec.so.56
#2 0xaf2bd816 in ?? () from /usr/lib/i386-linux-gnu/libavcodec.so.56
#3 0xaf274c86 in ?? () from /usr/lib/i386-linux-gnu/libavcodec.so.56
#4 0xaf4e9c9c in avcodec_decode_video2 () from
/usr/lib/i386-linux-gnu/libavcodec.so.56
#5 0xb1582801 in ?? () from /usr/lib/vlc/plugins/codec/libavcodec_plugin.so
#6 0xb743928e in ?? () from /usr/lib/libvlccore.so.8
#7 0xb743ae57 in ?? () from /usr/lib/libvlccore.so.8
#8 0xb76a0d97 in start_thread (arg=0xb17ffb40) at pthread_create.c:309
#9 0xb75f7dfe in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:129
(gdb)
With debug symbols installed:
Program received signal SIGILL, Illegal instruction.
[Switching to Thread 0xb227fb40 (LWP 1002)]
0xafcd9c93 in mid_pred (c=0, b=0, a=0) at
/build/libav-H9AQHK/libav-11.3/libavcodec/x86/mathops.h:77
77 /build/libav-H9AQHK/libav-11.3/libavcodec/x86/mathops.h: Datei oder
Verzeichnis nicht gefunden.
(gdb) bt
#0 0xafcd9c93 in mid_pred (c=0, b=0, a=0) at
/build/libav-H9AQHK/libav-11.3/libavcodec/x86/mathops.h:77
#1 pred_motion (my=<synthetic pointer>, mx=<synthetic pointer>, ref=0,
list=0, part_width=4, n=0, h=0xb233e4c0) at
/build/libav-H9AQHK/libav-11.3/libavcodec/h264_mvpred.h:140
#2 ff_h264_decode_mb_cavlc (h=0xb233e4c0) at
/build/libav-H9AQHK/libav-11.3/libavcodec/h264_cavlc.c:959
#3 0xafd10680 in decode_slice (avctx=0xb2338ea0, arg=0xb227f050) at
/build/libav-H9AQHK/libav-11.3/libavcodec/h264_slice.c:2275
#4 0xafd14816 in ff_h264_execute_decode_slices (h=0xb233e4c0,
context_count=1) at /build/libav-H9AQHK/libav-11.3/libavcodec/h264_slice.c:2369
#5 0xafccbc86 in decode_nal_units (parse_extradata=0, buf_size=74,
buf=0xb2302500 "", h=0xb233e4c0) at
/build/libav-H9AQHK/libav-11.3/libavcodec/h264.c:1662
#6 h264_decode_frame (avctx=0xb2338ea0, data=0xb2303040,
got_frame=0xb227f1a8, avpkt=0xb227f1d4) at
/build/libav-H9AQHK/libav-11.3/libavcodec/h264.c:1782
#7 0xaff40c9c in avcodec_decode_video2 (avctx=0xb2338ea0,
picture=0xb2303040, got_picture_ptr=0xb227f1a8, avpkt=0xb227f1d4) at
/build/libav-H9AQHK/libav-11.3/libavcodec/utils.c:1600
#8 0xb2003801 in DecodeVideo (p_dec=0xb2335180, pp_block=0xb227f1a8) at
codec/avcodec/video.c:631
#9 0xb74d428e in DecoderDecodeVideo (p_dec=0xb2335180, p_block=0xb2302490)
at input/decoder.c:1385
#10 0xb74d5e57 in DecoderProcessVideo (b_flush=<optimized out>,
p_block=0xb2302490, p_dec=<optimized out>) at input/decoder.c:1631
#11 DecoderProcess (p_block=<optimized out>, p_dec=<optimized out>) at
input/decoder.c:1810
#12 DecoderThread (p_data=0xb2335180) at input/decoder.c:909
#13 0xb773bd97 in start_thread (arg=0xb227fb40) at pthread_create.c:309
#14 0xb7692dfe in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:129
(gdb)
Current instruction:
(gdb) display/i $pc
1: x/i $pc
=> 0xafc39c93 <ff_h264_decode_mb_cavlc+11395>: cmovg %edx,%edi
libavcodec/x86/mathops.h:77
There we find some inline assembly guarded by an #if HAVE_I686.
It looks like that the package libavcodec56 has exactly for
this use case 2 version of the shared object packaged:
/usr/lib/i386-linux-gnu/libavcodec.so.56.1.0
/usr/lib/i386-linux-gnu/i686/cmov/libavcodec.so.56.1.0
So I started up a local package build for libav which is still
running with following lines in:
libav-11.3/debian-shared/config.h
#define LIBAV_CONFIGURATION "--arch=i386 ... --cpu=586"
#define HAVE_I686 1
So probably this upstream commit could already be sufficient?
[1] configure: Disable i686 for i586 and lower CPUs
Kind regards,
Bernhard
[1]
https://git.libav.org/?p=libav.git;a=commit;h=9030c58a780a02fb8256cb75cd39275eaad786d1
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