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> r~
