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From: Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH -v2] kvm: Emulate MOVBE
Date: Mon, 22 Apr 2013 15:49:45 +0200
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Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Andre Przywara <andre@andrep.de>, kvm@vger.kernel.org,
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	"H. Peter Anvin" <hpa@zytor.com>, x86-ml <x86@kernel.org>
To: Gleb Natapov <gleb@redhat.com>
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On Mon, Apr 22, 2013 at 12:58:12PM +0300, Gleb Natapov wrote:
> For most instructions the decoder already sets op->bytes to correct
> value, given that all flags a correctly specified in opcode table.
> Explicit op->bytes setting should be done only if it cannot be
> expressed by opcode flags.

MOVBE encodes operands in ModRM and operand size is determined by the
effective operand size. By looking at that switch(mode) thing near
the beginning of x86_decode_insn, we make sure ctxt->op_bytes is set
accordingly. Then, we have the following definitions for MOVBE:

+       [0xf0] = I(DstReg | SrcMem | ModRM | Mov | ThreeByte | EmulateOnUD, em_movbe),
+       [0xf1] = I(DstMem | SrcReg | ModRM | Mov | ThreeByte | EmulateOnUD, em_movbe),

and from looking at decode_operand(), it makes sure that op->bytes gets
the correct value since we have the proper {Src,Dst}{Reg,Mem} flags in
the insn definition.

So everything is fine, I'll make sure it works that way too, though,
when testing.

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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