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

[Doug Gale]

** Description changed:

  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
+ attach-gdb: Run GDB and attach to QEMU 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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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 QEMU 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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