[Bug 1882817] Re: Segfault in audio_pcm_sw_write with audio over VNC

[Thomas Huth]

** Changed in: qemu
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1882817

Title:
  Segfault in audio_pcm_sw_write with audio over VNC

Status in QEMU:
  Fix Released

Bug description:
  QEMU 5.0.0, built with ./configure --target-list=x86_64-softmmu
  --enable-debug --disable-strip --disable-docs --disable-sdl

  Running on a headless host (Ryzen 3600), Arch Linux, 64bit latest.
  Guest is also Arch Linux, 64bit.

  Started with qemu-system-x86_64 -vnc 0.0.0.0:0 -enable-kvm -m 4096 -cpu host 
-smp cores=2,threads=1,sockets=1 -machine q35 -vga std -device
   ich9-ahci,id=ahci -drive file=vm0.qcow2,format=qcow2,if=none,id=dsk0 -device 
ide-hd,drive=dsk0,bus=ahci.0 -soundhw hda

  So, a headless VM is running on a server and is being connected to
  over VNC. The virtual sound card is detected and speaker test is
  running inside the VM. So far so good.

  Then, i tell the VNC client to enable audio (QEMU Audio Client
  Message, 255,1,0). QEMU responds with a "stream is about to start"
  message (QEMU Audio Server Message, 255,1,1) and then promptly crashes
  without sending anything else.

  Running it in GDB produces a crash at audio/audio.c:739

  Thread 1 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
  audio_pcm_sw_write (sw=0x5555575bbf30, buf=0x0, size=1628) at 
audio/audio.c:739
  739             if (!sw->hw->pcm_ops->volume_out) {

  The exact sequence of events does not matter - i can enable sound
  before playing anything, and then it would say nothing and keep
  working, but crash with the same message once anything sound-playing
  is launched in the VM.

  Using different soundhw or adding various audiodev options does not
  seem to affect anything.

  I can't quite figure out if the QEMU Audio VNC extension is supposed
  to work at all or not, but it would be handy to me if it is.

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