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Date: Thu, 1 Jul 2010 20:43:06 +0400 (MSD)
From: malc <av1474@comtv.ru>
Subject: Re: [Qemu-devel] [Bug 600589] [NEW] xchg r8,rax treated as nop
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To: Richard Henderson <rth@twiddle.net>
Cc: Vic3Dexe <vic3dexe@gmail.com>, qemu-devel@nongnu.org, Bug 600589 <600589@bugs.launchpad.net>

On Thu, 1 Jul 2010, Richard Henderson wrote:

> On 07/01/2010 05:04 AM, Vic3Dexe wrote:
> > Public bug reported:
> > 
> > xchg r8,rax (49h 90h) executed as nop (90h) in long mode, in other words
> > REX not used.
> > 
> > qemu 0.12.4, host Win 7 x64,  running qemu-system-x86_64.exe.
> > 
> > ** Affects: qemu
> >      Importance: Undecided
> >          Status: New
> > 
> 
> Verified.  Test case for x86_64-linux-user:
> 
> 	.globl	main
> 	.type	main, @function
> main:
> 	movl	$0, %r8d
> 	movl	$1, %eax
> 	xchgq	%r8, %rax
> 	ret
> 
> Expected result is exit status 0.
> 

No surprise really:

target-i386/translate.c lines 6665-...

    case 0x90: /* nop */
        /* XXX: xchg + rex handling */
        /* XXX: correct lock test for all insn */

The code to handle that just isn't there.

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