[Qemu-devel] [Bug 1824768] Re: Qemu ARMv7 TCG MultiThreading for i386 guest doesn't work

[Peter Maydell]

This is expected. The warning from QEMU is telling you that MTTCG is not
supported for the combination of an Arm host and an x86 guest. It warns
that you might see "strange errors", and indeed you saw an error. Don't
try to use MTTCG here.

I think this warning should probably just be an error -- QEMU shouldn't
allow the user to select a feature which we know is not going to work
reliably.

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https://bugs.launchpad.net/bugs/1824768

Title:
  Qemu ARMv7 TCG MultiThreading for i386 guest doesn't work

Status in QEMU:
  New

Bug description:
  Using any Linux image (in this case Alpine Linux iso) I want to
  utilise all cores of my Raspberry with --accel,thread=multi. I know
  there is a probably still problem with memory ordering of the host,
  but I have also seen some very old commits which could potentially
  help with it.

  But anyway, with version qemu-i386 version 3.1.0 (Debian 1:3.1+dfsg-7)
  I can see OpenRC starting up services and then the kernel crash.

  With version QEMU emulator version 3.1.93 (v4.0.0-rc3-dirty)
  The whole machine crash with this error:
  Illegal instruction

  Using command:
  ./qemu-system-i386 -cdrom alpine.iso --accel tcg,thread=multi

  Full Console Output:
  qemu-system-i386: warning: Guest expects a stronger memory ordering than the 
host provides
  This may cause strange/hard to debug errors
  Illegal instruction

  Kernel:
  Linux raspberrypi 4.14.98-v7+ #1200 SMP Tue Feb 12 20:27:48 GMT 2019 armv7l 
GNU/Linux

  CPU:
  ARMv7 Processor rev 5 (v7l)
  Features: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt 
vfpd32 lpae evtstrm
  4 cores

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