From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH] KVM: x86 emulator: add bsf/bsr instruction emulation
Date: Mon, 09 Aug 2010 23:14:21 -0400
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Cc: kvm@vger.kernel.org
To: Wei Yongjun <yjwei@cn.fujitsu.com>
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 On 08/09/2010 06:00 AM, Wei Yongjun wrote:
> Add bsf/bsr instruction emulation (opcode 0x0f 0xbc~0xbd)
>
> @@ -3464,6 +3464,30 @@ twobyte_insn:
>  	      btc:		/* btc */
>  		emulate_2op_SrcV_nobyte("btc", c->src, c->dst, ctxt->eflags);
>  		break;
> +	case 0xbc: {		/* bsf */
> +		int zf;
> +		__asm__ ("bsf %2, %0; setz %b1"
> +			 : "=r"(c->dst.val), "=q"(zf)
> +			 : "r"(c->src.val), "1" (0));

Won't the high bytes of zf remain clear? Please examine the assembly.

Declaring it u8 is probably better.


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.