[alsa-devel] Segmentation fault in libasound.so.2.0.0 (alsa-lib-1.1.6)

[Paul Bordukoff]

Hello everyone,

I am using ALSA (alsa-lib-1.1.6) on Gentoo laptop with x32 ABI (linux-4.16.7). My mpv (0.27.2) gets segfault each time I try to play video with sound:
pashgan at light ~/temp $ mpv ./SampleVideo_1280x720_10mb.mp4 
Playing: ./SampleVideo_1280x720_10mb.mp4
 (+) Video --vid=1 (*) (h264 1280x720 25.000fps)
 (+) Audio --aid=1 --alang=und (*) (aac 6ch 48000Hz)
AO: [alsa] 48000Hz stereo 2ch float
VO: [opengl] 1280x720 yuv420p
Segmentation fault

dmesg shows:
[12526.319909] traps: mpv/ao[13621] general protection ip:f28ce4fa sp:e46f2d60 error:0 in libasound.so.2.0.0[f2843000+fe000]

gdb session:
(gdb) bt
#0  0xf29b14fa in mix_areas_32_smp (size=3935624896, dst=0x56a6e7f0, src=0x56a6e7f0, sum=0x1, dst_step=4, src_step=4, sum_step=4)
    at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm_dmix_x86_64.h:143
#1  0xf29b2361 in mix_areas (size=3935493824, dst_ofs=4056, src_ofs=0, dst_areas=0x56a6cd90, src_areas=0x56a6dc30, dmix=0x56a6c900)
    at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm_dmix.c:197
#2  snd_pcm_dmix_sync_area (pcm=pcm at entry=0x56a6d270)
    at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm_dmix.c:379
#3  0xf29b267f in snd_pcm_dmix_start (pcm=<optimized out>)
    at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm_dmix.c:611
#4  0xf2972349 in __snd_pcm_start (pcm=0x56a6d270, pcm=0x56a6d270)
    at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm_local.h:434
#5  snd_pcm_start (pcm=<optimized out>) at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm.c:1226
#6  0xf2972349 in __snd_pcm_start (pcm=0x56a6d8b0, pcm=0x56a6d8b0)
    at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm_local.h:434
#7  snd_pcm_start (pcm=<optimized out>) at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm.c:1226
#8  0xf2979a78 in __snd_pcm_start (pcm=0x56a52e60, pcm=0x56a52e60)
    at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm_local.h:434
#9  snd1_pcm_write_areas (pcm=pcm at entry=0x56a52e60, areas=areas at entry=0xe47f2f00, offset=offset at entry=0, size=<optimized out>, 
    size at entry=12288, func=func at entry=0xf2988770 <snd_pcm_plugin_write_areas>)
    at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm.c:7421
#10 0xf29890e7 in snd_pcm_plugin_writei (pcm=<optimized out>, buffer=<optimized out>, size=12288)
    at /tmp/portage/media-libs/alsa-lib-1.1.6-r1/work/alsa-lib-1.1.6/src/pcm/pcm_plugin.c:358
#11 0x56590280 in ?? ()
#12 0x56594846 in ?? ()
#13 0xf1b9808b in start_thread () from /libx32/libpthread.so.0
#14 0xf18d4e2f in clone () from /libx32/libc.so.6
(gdb) 


Same bug in Gentoo bug tracker: https://bugs.gentoo.org/654754 

I need help to investigate pcm_dmix behaviour, I see asm code there (pcm_dmix_x86_64.h:143) but have no idea how can I debug it (my asm experience is far from ok). Can somebody guide me?

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