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

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Message-ID: <20130509092554.GB32023@redhat.com>
Date:	Thu, 9 May 2013 12:25:54 +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 11:16:07AM +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

> +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.
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