Wow, a full 3 years later! Well, better late than never...
-- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1201446 Title: Instructions not supported by targeted CPU do not throw SIGILL Status in QEMU: Fix Released Bug description: We encountered a bug in another package that caused it to include CMOV instructions when targetting i486, resulting in an inability to run the package on real i486 and i586 hardware. We then attempted to use QEMU to reproduce the bug for easier debugging, since most developers have long since got rid of such old hardware. QEMU appears to continue to support *all* instructions when -cpu=486 is selected, regardless of what is advertised in CPUID to the guest. CPUID describes the host environment as a reasonably close approximation to a late-model i486, with very few instruction extensions - specifically excluding CMOV, which on real hardware is an optional extension to the i686 architecture. The result was that we could not reproduce the bug using QEMU, and must therefore attempt to debug it using a very limited stock of real hardware, which also has very limited performance for rebuilding the package. This completely defeats one of the main uses of QEMU, in our opinion. If this bug extends to other CPU architectures, it would affect all developers wishing to check whether their code conforms to restrictions imposed by any older or more restrictive ISA specification than the latest that QEMU supports, including the distinctions between ARMv7-A-NEON, ARMv7-A-VFPv3, ARMv7-A-VFPv3-d16, ARMv7-R, ARMv7-M, ARMv6-VFPv2, ARMv5-TE, ARMv4-T... all of which are currently shipping in new devices. Attached is a small C program which can easily be compiled to include CMOV instructions. It can be used to reproduce the bug: $ gcc -march=i486 -O2 -c minmax.c -o minmax $ ./minmax No arguments! $ ./minmax 5 6 7 max: 7 min: 5 $ gcc -march=pentium2 -O2 -c minmax.c -o minmax-p2 $ ./minmax-p2 No arguments! $ ./minmax-p2 5 6 7 [Expected, occurs on real i4/586 hardware:] Illegal instruction [Actual, within QEMU v1.2.0 with -cpu=486:] max: 7 min: 5 $ The bug is likely not limited to CMOV, but would also apply to more recent ISA extensions - so 3DNow! instructions would appear to run on Intel guest CPUs, AVX on a Pentium-2, and other such weirdness. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1201446/+subscriptions
