FPU Exception Emulation

Various control register settings have a uniform effect on whether FPU instructions raise an exception or execute normally.

Each of the following cr0 bits are tested:

• TS - Task Switched
• MP - Monitor Coprocessor
• EM - Emulate

against instructions from the following sets:

• x87
• x87 wait
• MMX
• SSE
• AVX

checking that appropriate exceptions are raised (#NM or #UD), or that no exception is raised.

Each test is run against real hardware, and forced through the x86 instruction emulator (if FEP is available).

This test covers XSA-190, where #NM was not being raised appropriately, therefore interfering with lazy FPU task switching in the guest.

Todo:

Extend to include unmasked pending exceptions. There is definitely work required in the instruction emulator to support this properly.

See also

tests/fpu-exception-emulation/main.c