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From: Paolo Bonzini <pbonzini@redhat.com>
Date: Wed, 16 Dec 2009 00:37:37 +0100
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References: <200912151948.53307.ck@iseclab.org>
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Subject: [Qemu-devel] Re: i386 emulation bug: mov reg, [addr]
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To: qemu-devel@nongnu.org

On 12/15/2009 10:26 PM, Jamie Lokier wrote:
> But that said, I'm not sure if this line from earlier breaks the test:
>
>              index = ((code>>  3)&  7) | REX_X(s);
>
> When is REX_X(s) not zero, and does it break the index != 4 test?

When %r12 (4+8=12) is used as an index.  That's a valid statement, so 
it's okay to test index != 4 (when REX_X(s) is not zero it is always 
eight, and you'd get index == 12):

    0:	8b 04 65 11 22 33 44    	mov    0x44332211(,%riz,2),%eax
    7:	42 8b 04 65 11 22 33 44 	mov    0x44332211(,%r12,2),%eax

(BTW %eiz/%riz are not accepted by my GAS, only produced by the 
disassembler).

Paolo