On Fri, Jan 06, 2023 at 05:55:14PM -0800, Richard Henderson wrote: > On 1/6/23 16:59, Al Viro wrote: > > Type 3 instruction fault (FPU insn with FPU disabled) is handled > > by quietly enabling FPU and returning. Which is fine, except that > > we need to do that both for fault in userland and in the kernel; > > the latter *can* legitimately happen - all it takes is this: > > > > .global _start > > _start: > > call_pal 0xae > > lda $0, 0 > > ldq $0, 0($0) > > > > - call_pal CLRFEN to clear "FPU enabled" flag and arrange for > > a signal delivery (SIGSEGV in this case). > > > > Fixed by moving the handling of type 3 into the common part of > > do_entIF(), before we check for kernel vs. user mode. > > > > Incidentally, check for kernel mode is unidiomatic; the normal > > way to do that is !user_mode(regs). The difference is that > > the open-coded variant treats any of bits 63..3 of regs->ps being > > set as "it's user mode" while the normal approach is to check just > > the bit 3. PS is a 4-bit register and regs->ps always will have > > bits 63..4 clear, so the open-code variant here is actually equivalent > > to !user_mode(regs). Harder to follow, though... > > > > Reproducer above will crash any box where CLRFEN is not ignored by > > PAL (== any actual hardware, AFAICS; PAL used in qemu doesn't > > bother implementing that crap). > > I didn't realize I'd forgotten this in qemu. Anyway, > > Reviewed-by: Richard Henderson <rth@xxxxxxxxxxx> Not sure it's worth bothering with in palcode-clipper - for Linux it's useless (run out of timeslice and FEN will end up set, no matter what), nothing in NetBSD or OpenBSD trees generates that call_pal, current FreeBSD doesn't support alpha and their last version to do so hadn't generated that call_pal either... What else is out there? OSF?
