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

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Message-ID: <20250925104251.GZ4067720@noisy.programming.kicks-ass.net>
Date: Thu, 25 Sep 2025 12:42:51 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Alexandre Chartre <alexandre.chartre@...cle.com>
Cc: jpoimboe@...nel.org, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] objtool/x86: Fix NOP decode

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;