From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754509AbeBGTBe (ORCPT ); Wed, 7 Feb 2018 14:01:34 -0500 Received: from mail-io0-f193.google.com ([209.85.223.193]:41750 "EHLO mail-io0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754149AbeBGTBc (ORCPT ); Wed, 7 Feb 2018 14:01:32 -0500 X-Google-Smtp-Source: AH8x226vqojca9Fxq3paFr2mC3B9QeA8f/6rUTWOvA3zhmg3Iff/hhO1UjwwXE0kdKqQAFp6MMwqPmnfSFVvl2xbhdU= MIME-Version: 1.0 In-Reply-To: References: <5a7ae6af.WSMpvDEeUt6oucKB%fengguang.wu@intel.com> From: Linus Torvalds Date: Wed, 7 Feb 2018 11:01:29 -0800 X-Google-Sender-Auth: faHirCX9MpS_SlrXIlkNjbP3DB8 Message-ID: Subject: Re: [linus:master] BUILD REGRESSION a2e5790d841658485d642196dbb0927303d6c22f To: Randy Dunlap Cc: kbuild test robot , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , LKML , "the arch/x86 maintainers" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 7, 2018 at 10:38 AM, Randy Dunlap wrote: > On 02/07/2018 10:13 AM, Linus Torvalds wrote: >> >> That said, intel only _documents_ UD2 (0f 0b). > > Intel Order Number: 325383-064US, October 2017, documents UD0, UD1, and UD2. > Section A.2.5, Table A-1, says: Ahh, I had an older version. Looking at the latest one I can find (325462-065US), it does specify that it has a modrm byte: 0F FF /r UD0 1 r32, r/m32 so I think that our opcode maps are wrong, and it's a bit dangerous to put random constants right after the UD0. Maybe we should make our use of UD0 have a third byte: add a harmless modrm byte before the warning constants? But yes, at least my objdump just thinks it's a bad 2-byte sequence, and doesn't look at any modrm bytes at all. Linus