[Bug 1818075] Re: qemu x86 TCG doesn't support AVX insns

[Ronald Antony]

If I may be so free:

It seems that QEMU has stopped emphasizing the EMU part of the name, and
is too much focused on virtualization.

My interest is at running legacy operating systems, and as such, they must run 
on foreign CPU platforms. m68 on intel, intel on ARM, etc.
Time doesn't stand still, and reliance on KVM and similar x86-on-x86 tricks, 
which allow the delegation of certain CPU features to the host CPU is going to 
not work going forward.

If the rumored transition of Apple to ARM is going to take place, people
will want to e.g. emulate for testing or legacy purposes a variety of
operating systems, incl. earlier versions of MacOS.

Testing that scenario, i.e. macOS on an ARM board with the lowest
possible CPU capable of running modern macOS, results in these problems
(and of course utter failure achieving the goal):

qemu-system-x86_64: warning: TCG doesn't support requested feature: 
CPUID.01H:ECX.fma [bit 12]
qemu-system-x86_64: warning: TCG doesn't support requested feature: 
CPUID.01H:ECX.avx [bit 28]
qemu-system-x86_64: warning: TCG doesn't support requested feature: 
CPUID.07H:EBX.avx2 [bit 5]
qemu-system-x86_64: warning: TCG doesn't support requested feature: 
CPUID.80000007H:EDX.invtsc [bit 8]
qemu-system-x86_64: warning: TCG doesn't support requested feature: 
CPUID.0DH:EAX.xsavec [bit 1]

And this is emulating a lowly Penryn CPU with the required CPU flags for macOS:
-cpu 
Penryn,vendor=GenuineIntel,+sse3,+sse4.2,+aes,+xsave,+avx,+xsaveopt,+xsavec,+xgetbv1,+avx2,+bmi2,+smep,+bmi1,+fma,+movbe,+invtsc

Attempting to emulate a more feature laden intel CPU results in even
more issues.

I would propose that no CPU should be considered supported unless it can
be fully handled by TCG on a non-native host. KVM, native-on-native etc.
are nice to have, but peripheral to qEMUlation when it boils down to it.

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1818075

Title:
  qemu x86 TCG doesn't support AVX insns

Status in QEMU:
  New

Bug description:
  I'm trying to execute code that has been built with -march=skylake
  -mtune=generic -mavx2 under qemu-user x86-64 with -cpu Skylake-Client.
  However this code just hangs at 100% CPU.

  Adding input tracing shows that it is likely hanging when dealing with
  an AVX instruction:

  warning: TCG doesn't support requested feature: CPUID.01H:ECX.fma [bit 12]
  warning: TCG doesn't support requested feature: CPUID.01H:ECX.pcid [bit 17]
  warning: TCG doesn't support requested feature: CPUID.01H:ECX.x2apic [bit 21]
  warning: TCG doesn't support requested feature: CPUID.01H:ECX.tsc-deadline 
[bit 24]
  warning: TCG doesn't support requested feature: CPUID.01H:ECX.avx [bit 28]
  warning: TCG doesn't support requested feature: CPUID.01H:ECX.f16c [bit 29]
  warning: TCG doesn't support requested feature: CPUID.01H:ECX.rdrand [bit 30]
  warning: TCG doesn't support requested feature: CPUID.07H:EBX.hle [bit 4]
  warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx2 [bit 5]
  warning: TCG doesn't support requested feature: CPUID.07H:EBX.invpcid [bit 10]
  warning: TCG doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11]
  warning: TCG doesn't support requested feature: CPUID.07H:EBX.rdseed [bit 18]
  warning: TCG doesn't support requested feature: 
CPUID.80000001H:ECX.3dnowprefetch [bit 8]
  warning: TCG doesn't support requested feature: CPUID.0DH:EAX.xsavec [bit 1]

  IN:
  0x4000b4ef3b:  c5 fb 5c ca              vsubsd   %xmm2, %xmm0, %xmm1
  0x4000b4ef3f:  c4 e1 fb 2c d1           vcvttsd2si %xmm1, %rdx
  0x4000b4ef44:  4c 31 e2                 xorq     %r12, %rdx
  0x4000b4ef47:  48 85 d2                 testq    %rdx, %rdx
  0x4000b4ef4a:  79 9e                    jns      0x4000b4eeea

  [ hangs ]

  Attaching a gdb produces this stacktrace:

  (gdb) bt
  #0  canonicalize (status=0x55a20ff67a88, parm=0x55a20bb807e0 
<float64_params>, part=...)
      at 
/data/poky-tmp/master/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/fpu/softfloat.c:350
  #1  float64_unpack_canonical (s=0x55a20ff67a88, f=0)
      at 
/data/poky-tmp/master/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/fpu/softfloat.c:547
  #2  float64_sub (a=0, b=4890909195324358656, status=0x55a20ff67a88)
      at 
/data/poky-tmp/master/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/fpu/softfloat.c:776
  #3  0x000055a20baa1949 in helper_subsd (env=<optimized out>, 
d=0x55a20ff67ad8, s=<optimized out>)
      at 
/data/poky-tmp/master/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/target/i386/ops_sse.h:623
  #4  0x000055a20cfcfea8 in static_code_gen_buffer ()
  #5  0x000055a20ba3f764 in cpu_tb_exec (itb=<optimized out>, 
cpu=0x55a20cea2180 <static_code_gen_buffer+15684720>)
      at 
/data/poky-tmp/master/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/accel/tcg/cpu-exec.c:171
  #6  cpu_loop_exec_tb (tb_exit=<synthetic pointer>, last_tb=<synthetic 
pointer>, tb=<optimized out>,
      cpu=0x55a20cea2180 <static_code_gen_buffer+15684720>)
      at 
/data/poky-tmp/master/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/accel/tcg/cpu-exec.c:615
  #7  cpu_exec (cpu=cpu@entry=0x55a20ff5f4d0)
      at 
/data/poky-tmp/master/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/accel/tcg/cpu-exec.c:725
  #8  0x000055a20ba6d728 in cpu_loop (env=0x55a20ff67780)
      at 
/data/poky-tmp/master/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/linux-user/x86_64/../i386/cpu_loop.c:93
  #9  0x000055a20ba049ff in main (argc=<optimized out>, argv=0x7ffc58572868, 
envp=<optimized out>)
      at 
/data/poky-tmp/master/work/x86_64-linux/qemu-native/3.1.0-r0/qemu-3.1.0/linux-user/main.c:819

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1818075/+subscriptions