linux-kernel - Re: [PATCH 3/3] KVM: emulator: emulate SALC

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Date:	Thu, 9 May 2013 12:31:49 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, j-nomura@...jp.nec.com
Subject: Re: [PATCH 3/3] KVM: emulator: emulate SALC

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-nomura@...jp.nec.com>
> >> Cc: stable@...nel.org # 3.9
> >> Signed-off-by: Paolo Bonzini <pbonzini@...hat.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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