From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44480C47255 for ; Fri, 8 May 2020 17:32:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 225402184D for ; Fri, 8 May 2020 17:32:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="qyX9hwha" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727802AbgEHRcW (ORCPT ); Fri, 8 May 2020 13:32:22 -0400 Received: from terminus.zytor.com ([198.137.202.136]:59021 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726746AbgEHRcW (ORCPT ); Fri, 8 May 2020 13:32:22 -0400 Received: from carbon-x1.hos.anvin.org ([IPv6:2601:646:8600:3281:e7ea:4585:74bd:2ff0]) (authenticated bits=0) by mail.zytor.com (8.15.2/8.15.2) with ESMTPSA id 048HVftM3921978 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Fri, 8 May 2020 10:31:41 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 048HVftM3921978 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2020042201; t=1588959104; bh=j4Wt5+zHny+jNVeWIommm01rPqJoQDpyDmv65ZQS5Sw=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=qyX9hwhasKyR0D6xlFQuduuCpCaongWidyAWUxb/fhwYDsxx7V0Mfg1EIX1k21YmX nBAyONHj/k8sjGGcKRrDex9b0FjXOWMx2KBZtVizuPQo9zSjzCoSCWNPi1CB2myIIK 6mlS7GT+BqZCcU0iQ+6qqC5m1o1K9ORGf+h4UFQkrIrlGChUGrklB9GYUKAiW6moF3 DQyMt39w1+13n709biF1A6K8nz94ih9AeZVZ0Y1otScfo1PwknvYrUyGA64Vi2JJuy wkXgU+ZJpjnZCca+JM4BjvvlTmKII+Y763LfO/WBIap8QVGV2k4ADuL988yQ4De3C5 HXAHTXjBpuM5Q== Subject: Re: [PATCH] x86: bitops: fix build regression To: Nick Desaulniers , Brian Gerst Cc: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Sedat Dilek , stable , Jesse Brandeburg , "kernelci . org bot" , Andy Shevchenko , Ilie Halip , the arch/x86 maintainers , Marco Elver , "Paul E. McKenney" , Daniel Axtens , Masahiro Yamada , Luc Van Oostenryck , Linux Kernel Mailing List , clang-built-linux References: <20200505174423.199985-1-ndesaulniers@google.com> <8A776DBC-03AF-485B-9AA6-5920E3C4ACB2@zytor.com> <20200507113422.GA3762@hirez.programming.kicks-ass.net> From: "H. Peter Anvin" Message-ID: <8f53b69e-86cc-7ff9-671e-5e0a67ff75a2@zytor.com> Date: Fri, 8 May 2020 10:31:36 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-05-08 10:21, Nick Desaulniers wrote: >> >> One last suggestion. Add the "b" modifier to the mask operand: "orb >> %b1, %0". That forces the compiler to use the 8-bit register name >> instead of trying to deduce the width from the input. > > Ah right: https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#x86Operandmodifiers > > Looks like that works for both compilers. In that case, we can likely > drop the `& 0xff`, too. Let me play with that, then I'll hopefully > send a v3 today. > Good idea. I requested a while ago that they document these modifiers; they chose not to document them all which in some ways is good; it shows what they are willing to commit to indefinitely. -hpa