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=-0.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 0AA87C47257 for ; Thu, 7 May 2020 19:31:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D906E21582 for ; Thu, 7 May 2020 19:31:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="diBzyttg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728166AbgEGTbz (ORCPT ); Thu, 7 May 2020 15:31:55 -0400 Received: from terminus.zytor.com ([198.137.202.136]:45865 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726367AbgEGTby (ORCPT ); Thu, 7 May 2020 15:31:54 -0400 Received: from [IPv6:2601:646:8600:3281:6547:66ee:1a90:d675] ([IPv6:2601:646:8600:3281:6547:66ee:1a90:d675]) (authenticated bits=0) by mail.zytor.com (8.15.2/8.15.2) with ESMTPSA id 047JVQfh3526709 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Thu, 7 May 2020 12:31:27 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 047JVQfh3526709 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2020042201; t=1588879887; bh=KE1Z5fw6ohOckf8wSoQnCowGQBds5ZKNZR3BEwYeyEg=; h=Date:In-Reply-To:References:Subject:To:CC:From:From; b=diBzyttgruastg6TqrrbhDE00dWFbIySD01pQ8S1/yuYc48lvPH0h95qvE8Na0EeT WIvVKOdl6tfwQxaOlytjPfXBCqE2cR/9MWiJo13OLHGJNn1eQHxUMF70yBFfAswzEL CQzbPbrzUgKPsimuMEHvACZonqqamq5JZay7lBTrRC/2K4SnruCL1Wr8CMBfzR5pEI x2fdERyhHJ3Gc2Ad/nImKmU5w8UsiPQXz4XqCBwAPUpfM7bkpYv5emzH9OojYdLlai wbi6skR+XQ2U/UAYiMZxNkzp29SXGcB6XWJK/46XiT/1ZIPZmfNhGrZEy2EslrSeHL 7UX1/YpAbBcNQ== Date: Thu, 07 May 2020 12:31:19 -0700 User-Agent: K-9 Mail for Android In-Reply-To: <9c701ca55bc442c1899a70896f3ea73e@AcuMS.aculab.com> References: <20200505174423.199985-1-ndesaulniers@google.com> <6A99766A-59FB-42DF-9350-80EA671A42B0@zytor.com> <9c701ca55bc442c1899a70896f3ea73e@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: RE: [PATCH] x86: bitops: fix build regression To: David Laight , "'Brian Gerst'" CC: Nick Desaulniers , 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" , "Peter Zijlstra (Intel)" , Daniel Axtens , Masahiro Yamada , Luc Van Oostenryck , Linux Kernel Mailing List , "clang-built-linux@googlegroups.com" From: hpa@zytor.com Message-ID: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On May 7, 2020 8:09:35 AM PDT, David Laight w= rote: >From: Brian Gerst >> Sent: 07 May 2020 14:32 >=2E=2E=2E >> I think the bug this worked around was that the compiler didn't >detect >> that CONST_MASK(nr) was also constant and doesn't need to be put into >> a register=2E The question is does that bug still exist on compiler >> versions we care about? > >Hmmm=2E=2E=2E >That ought to have been fixed instead of worrying about the fact >that an invalid register was used=2E > >Alternatively is there any reason not to use the bts/btc instructions? >Yes, I know they'll do wider accesses, but variable bit numbers do=2E >It is also possible that the assembler will support constant bit >numbers >=3D 32 by adding to the address offset=2E > > David > >- >Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, >MK1 1PT, UK >Registration No: 1397386 (Wales) They're slower, and for unaligned locked fields can be severely so=2E --=20 Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E