linux-kernel - Re: [PATCH 3/3] objtool/x86: Fix NOP decode

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Message-ID: <a04049a0-d626-4f42-92ca-0e6d3b847d6a@oracle.com>
Date: Thu, 25 Sep 2025 15:05:29 +0200
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: alexandre.chartre@...cle.com, jpoimboe@...nel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] objtool/x86: Fix NOP decode



On 9/25/25 12:42, Peter Zijlstra wrote:
> On Thu, Sep 25, 2025 at 12:03:23PM +0200, Peter Zijlstra wrote:
> 
>>>>>>     	case 0x90:
>>>>>> +		if (prefix != 0xf3) /* REP NOP := PAUSE */
>>>>>> +			insn->type = INSN_NOP;
>>>>>>     		break;
> 
>>> What about 0x49 0x90, which is xchg (XCHG r8,rAX) ?
> 
> I've made that:
> 
> 	case 0x90:
> 		if (rex_b) /* XCHG %r8, %rax */
> 			break;
> 
> 		if (prefix == 0xf3) /* REP NOP := PAUSE */
> 			break;
> 
> 		insn->type = INSN_NOP;
> 		break;
> 
> 

Sounds good.

Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.com>

alex.