On 2011-06-15 13:26, Avi Kivity wrote: > On 06/15/2011 01:20 PM, Jan Kiszka wrote: >> > >> > So fopcode will usually be clear. >> > >> >> OK. So if bit 2 of IA32_MISC_ENABLE MSR, we must save that fields. But >> if it's off, how to test for that other condition "last non-transparent >> FP instruction ... had an unmasked exception" from the host? >> > > We save fopcode unconditionally. But if IA32_MISC_ENABLE_MSR[2]=0, then > fopcode will be zero, and we can skip the subsection (if the data and > instruction pointers are also zero, which they will be). > > If it isn't zero, there's still a good chance fopcode will be zero > (64-bit userspace, thread that hasn't used the fpu since the last > context switch, last opcode happened to be zero).
I do not yet find "if fopcode is invalid, it is zero, just as IP and DP" in the spec. What clears them reliably? Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
