Comment 0 for bug 1748296

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.