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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: peterz@infradead.org
Cc: alexandre.chartre@oracle.com, jpoimboe@kernel.org,
	linux-kernel@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH 3/3] objtool/x86: Fix NOP decode
Date: Thu, 25 Sep 2025 12:29:18 +0100	[thread overview]
Message-ID: <a2f6775f-0be5-401b-bc01-effd3f428482@citrix.com> (raw)
In-Reply-To: <20250925104251.GZ4067720@noisy.programming.kicks-ass.net>

> 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;

Legacy prefixes can come in any order.  What is F3 66 90 ?

Also, VEX/EVEX/REX2 want excluding too, all of which can encode rex_b
differently.

Is it really only rex_b which prevents NOP becoming a pause, or is it
any REX prefix?  I would have thought it was any REX prefix.

~Andrew


  reply	other threads:[~2025-09-25 11:29 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-09-24 13:45 [PATCH 0/3] objtool: Few x86 decoder updates Peter Zijlstra
2025-09-24 13:45 ` [PATCH 1/3] objtool/x86: Remove 0xea hack Peter Zijlstra
2025-09-25  9:55   ` Alexandre Chartre
2025-10-14 11:47   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2025-09-24 13:45 ` [PATCH 2/3] objtool/x86: Add UDB support Peter Zijlstra
2025-09-25  9:56   ` Alexandre Chartre
2025-10-14 11:47   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2025-09-24 13:45 ` [PATCH 3/3] objtool/x86: Fix NOP decode Peter Zijlstra
2025-09-24 17:34   ` Alexandre Chartre
2025-09-24 18:41     ` Peter Zijlstra
2025-09-25  9:55       ` Alexandre Chartre
2025-09-25 10:03         ` Peter Zijlstra
2025-09-25 10:42           ` Peter Zijlstra
2025-09-25 11:29             ` Andrew Cooper [this message]
2025-09-25 12:43               ` Peter Zijlstra
2025-09-25 13:04                 ` Alexandre Chartre
2025-09-25 14:11                 ` Peter Zijlstra
2025-09-25 13:05             ` Alexandre Chartre
2025-10-14 11:47   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra

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