On Thu, May 09, 2013 at 11:30:27AM +0200, Paolo Bonzini wrote:
> Il 09/05/2013 11:25, Gleb Natapov ha scritto:
> > On Thu, May 09, 2013 at 11:16:07AM +0200, Paolo Bonzini wrote:
> >> This is an almost-undocumented instruction available in 32-bit mode.
> >> I say "almost" undocumented because AMD documents it in their opcode
> >> maps just to say that it is unavailable in 64-bit mode (sections
> >> "A.2.1 One-Byte Opcodes" and "B.3 Invalid and Reassigned Instructions
> >> in 64-Bit Mode").
> >>
> >> It is roughly equivalent to "sbb %al, %al" except it does not
> >> set the flags. Use fastop to emulate it, but do not use the opcode
> >> directly because it would fail if the host is 64-bit!
> >>
> >> Reported-by: Jun'ichi Nomura <j-nom...@ce.jp.nec.com>
> >> Cc: sta...@kernel.org # 3.9
> >> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> >> ---
> >> arch/x86/kvm/emulate.c | 6 +++++-
> >> 1 file changed, 5 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> >> index 210bb4e..f62d4c8 100644
> >> --- a/arch/x86/kvm/emulate.c
> >> +++ b/arch/x86/kvm/emulate.c
> >> @@ -534,6 +534,9 @@ FOP_SETCC(setle)
> >> FOP_SETCC(setnle)
> >> FOP_END;
> >>
> >> +FOP_START(salc) "pushf; sbb %al, %al; popf; ret \n\t"
> >
> > FOP_RET
>
> Ah, I missed that macro. I was mimicking FOP_SETCC which doesn't use
> it. Will resend.
>
I think it does not use it by mistake.
> Paolo
>
> >> +FOP_END;
> >> +
> >> #define __emulate_1op_rax_rdx(ctxt, _op, _suffix, _ex)
> >> \
> >> do { \
> >> unsigned long _tmp; \
> >> @@ -3951,7 +3954,8 @@ static const struct opcode opcode_table[256] = {
> >> G(Src2One | ByteOp, group2), G(Src2One, group2),
> >> G(Src2CL | ByteOp, group2), G(Src2CL, group2),
> >> I(DstAcc | SrcImmUByte | No64, em_aam),
> >> - I(DstAcc | SrcImmUByte | No64, em_aad), N,
> >> + I(DstAcc | SrcImmUByte | No64, em_aad),
> >> + F(DstAcc | ByteOp | No64, em_salc),
> >> I(DstAcc | SrcXLat | ByteOp, em_mov),
> >> /* 0xD8 - 0xDF */
> >> N, E(0, &escape_d9), N, E(0, &escape_db), N, E(0, &escape_dd), N, N,
> >> --
> >> 1.8.1.4
> >
> > --
> > Gleb.
> >
--
Gleb.
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