#7751 closed defect (invalid)

Runtime CPU detection on 32-bit PowerPC isn't helpful

Reported by: awilfox Owned by:
Priority: normal Component: build system
Version: git-master Keywords: ppc
Cc: Blocked By:
Blocking: Reproduced by developer: no
Analyzed by developer: no


Summary of the bug:
FFmpeg's runtime CPU detection correctly detects that a G3 CPU does not have AltiVec?, but since FFmpeg adds -mabi=altivec to CFLAGS when AltiVec? support is enabled, GCC generates AltiVec? instructions in function prologues, which cause it to SIGILL anyway.

How to reproduce:

% ffprobe test.png
ffprobe version 4.1 Copyright (c) 2007-2018 the FFmpeg developers
  built with gcc 6.4.0 (Adelie 6.4.0)
  configuration: --prefix=/usr --enable-avresample --enable-avfilter --enable-gnutls --enable-gpl --enable-libmp3lame --enable-libmodplug --enable-librtmp --enable-libvorbis --disable-libvpx --enable-libxvid --enable-libx264 --enable-libx265 --enable-libtheora --enable-libv4l2 --enable-postproc --enable-pic --enable-pthreads --enable-shared --enable-libxcb --disable-stripping --disable-static --enable-vaapi --enable-vdpau --enable-libopus --enable-libcdio --enable-ladspa --enable-lzma --enable-libspeex --enable-libfreetype --enable-libwavpack --enable-libwebp --enable-libpulse --optflags='-O2 -ggdb -mcpu=G3 -fno-omit-frame-pointer -mfpu=dp_full -g -g' --disable-debug
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Illegal instruction

The crash happens in the prologue of sbg_read_probe:

Program received signal SIGILL, Illegal instruction.
0xb7a3b808 in sbg_read_probe (p=0xbffff44c) at libavformat/sbgdec.c:1373
(gdb) x/i $pc
=> 0xb7a3b808 <sbg_read_probe+12>:      vxor    v0,v0,v0

Change History (2)

comment:1 Changed 18 months ago by cehoyos

  • Keywords ppc added
  • Version changed from 4.1 to git-master

comment:2 Changed 17 months ago by cehoyos

  • Resolution set to invalid
  • Status changed from new to closed

Please understand that using optflags makes such bug reports invalid.

If the issue is reproducible with current FFmpeg git head and an empty configuration (I suspect it is), please use --cpu=g3.

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