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[Bug 1748296] Re: TCG throws Invalid Opcode when executing x86 BMI shlx
From: |
Thomas Huth |
Subject: |
[Bug 1748296] Re: TCG throws Invalid Opcode when executing x86 BMI shlx instruction |
Date: |
Thu, 22 Apr 2021 05:33:47 -0000 |
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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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