[Qemu-devel] [Bug 1748296] [NEW] TCG throws Invalid Opcode when executing x86 BMI shlx instruction

[Doug Gale]

Public bug reported:

I am unable to use BMI in my project when running under TCG. I narrowed
the problem down to incorrect instruction decoding for BMI instructions
(which have a 2 byte VEX prefix). The gen_sse function in translate.c
reaches the goto label do_0f_38_fx, but b does not equal 0x1f7, 0x2f7,
or 0x3f7, so the switch takes the default path and raises an invalid
opcode exception.

The code executes correctly and passes the test under KVM.

I have created a complete repro here: https://github.com/doug65536/qemu-
bmibug

The makefile has the following utility targets:

debug-kvm: Build and run the VM using KVM and wait for gdbstub attach

run: Run the test case with TCG, make fails if the test fails. (It will
fail)

run-kvm: Run the test case with KVM, make fails if the test fails. (It
will succeed)

debug: Build and run the VM with TCG and wait for GDB attach

attach-gdb: Run GDB and attach to KVM gdbstub

The VM runs with -cpu max. CPUID reports support for BMI, BMI2, and ABM.

You can quickly verify the issue by executing `make run-kvm` to confirm
that KVM passes, then `make run` to confirm that TCG fails.

I believe the bug affects other BMI, BMI2, and ABM instructions, but I
have only completely verified incorrect execution of SHLX.

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1748296

Title:
  TCG throws Invalid Opcode when executing x86 BMI shlx instruction

Status in QEMU:
  New

Bug description:
  I am unable to use BMI in my project when running under TCG. I
  narrowed the problem down to incorrect instruction decoding for BMI
  instructions (which have a 2 byte VEX prefix). The gen_sse function in
  translate.c reaches the goto label do_0f_38_fx, but b does not equal
  0x1f7, 0x2f7, or 0x3f7, so the switch takes the default path and
  raises an invalid opcode exception.

  The code executes correctly and passes the test under KVM.

  I have created a complete repro here: https://github.com/doug65536
  /qemu-bmibug

  The makefile has the following utility targets:

  debug-kvm: Build and run the VM using KVM and wait for gdbstub attach

  run: Run the test case with TCG, make fails if the test fails. (It
  will fail)

  run-kvm: Run the test case with KVM, make fails if the test fails. (It
  will succeed)

  debug: Build and run the VM with TCG and wait for GDB attach

  attach-gdb: Run GDB and attach to KVM gdbstub

  The VM runs with -cpu max. CPUID reports support for BMI, BMI2, and
  ABM.

  You can quickly verify the issue by executing `make run-kvm` to
  confirm that KVM passes, then `make run` to confirm that TCG fails.

  I believe the bug affects other BMI, BMI2, and ABM instructions, but I
  have only completely verified incorrect execution of SHLX.

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