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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 D5A22C282DD for ; Fri, 10 Jan 2020 17:35:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B507F2087F for ; Fri, 10 Jan 2020 17:35:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728400AbgAJRfW (ORCPT ); Fri, 10 Jan 2020 12:35:22 -0500 Received: from mout.kundenserver.de ([212.227.126.131]:36223 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728232AbgAJRfV (ORCPT ); Fri, 10 Jan 2020 12:35:21 -0500 Received: from mail-qv1-f49.google.com ([209.85.219.49]) by mrelayeu.kundenserver.de (mreue010 [212.227.15.129]) with ESMTPSA (Nemesis) id 1MpUEO-1jSHYK0bsK-00pwv1; Fri, 10 Jan 2020 18:35:20 +0100 Received: by mail-qv1-f49.google.com with SMTP id o18so1098049qvf.1; Fri, 10 Jan 2020 09:35:19 -0800 (PST) X-Gm-Message-State: APjAAAVMI5Ojdl+ku5tFrFPiY2uMT0tHB6T3uORVdrK9aLnO332pifmV CkjnUF8ZbjDuBgmpMRa35fsDLswLyNaLa4qBnBU= X-Google-Smtp-Source: APXvYqwWYC8X5W9oF1BgBx7VL/oeohJqrxVJjUso79ib5qHjpCfx0eXAy0BECqjDUxdnwEFL4yYFEX7TreByyDcsQXQ= X-Received: by 2002:a0c:d788:: with SMTP id z8mr3587885qvi.211.1578677718911; Fri, 10 Jan 2020 09:35:18 -0800 (PST) MIME-Version: 1.0 References: <20200110165636.28035-1-will@kernel.org> <20200110165636.28035-2-will@kernel.org> In-Reply-To: <20200110165636.28035-2-will@kernel.org> From: Arnd Bergmann Date: Fri, 10 Jan 2020 18:35:02 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 1/8] compiler/gcc: Emit build-time warning for GCC prior to version 4.8 To: Will Deacon Cc: "linux-kernel@vger.kernel.org" , linux-arch , Android Kernel Team , Michael Ellerman , Peter Zijlstra , Linus Torvalds , Segher Boessenkool , Christian Borntraeger , Luc Van Oostenryck Content-Type: text/plain; charset="UTF-8" X-Provags-ID: V03:K1:qNB50QxgYN6IoCxuOP5OUw+kvbtvU6FPj70Xpb3YkQHBzhScfGA LOMjhVZaQYk/fRyYSVS9s1D/Kmeo6MrkW8Aq1WdR4Wfdv9Scag4ZUTOzAOR1vgrr9AUlt83 NY4NgdMcX19Mmlx3uTymSbSJgoJIzd52ABKIauuObzBFHnc5hXJUD1D5eN7fpgO4dTRkwG6 XEdZii3mwfxOLHxIhyo1w== X-UI-Out-Filterresults: notjunk:1;V03:K0:CNzi4tqatmQ=:jzKjyLV2MH9toF091jMUH1 fYjwg7S1fuz8OVlWZbAZGM4es6TRvOgGYR7sHf4rWV5n+hIEuZi91Vaq6jGL9kagYQ9NLmEq9 FBjgN6spbsBkj4MZDF5+YKGqHJRPRwK6UTJqfdpEuozHAwLB0M8jcInrPgjaPAw3G3HPX/QEo k73XO1lVNh5Ng0SBLzEpG0B5dRVsaJnRUxs10AARwrlV/E+gpP+J2CrfQknVHfivI94p45ySY PNPlSJkLLjss/0dsWg8naPU1qM99iqw7Ag/75m4d+K0ABtHaszeDX3kky0xjPx/YDt/V9Eh2F ea2w2R7po3V6RglU295cXIZdMYmJ96wobdGePg5TyRsQE7lc6d0gab5QmW/Mjy2PGxsxvm96s Hp+71pBDybruMVKadfhIiqTxdKBB+Vfuh7XanlbBR7ZQT2aeoGGWtjuAW0M3Ppsnc6BfrkRr2 mnLQj1DIqq+DmKV5VDOs+fiZjoKGpAOzcWSJOwzMV0fhnPZiO8cayZEbFQ8XH1AELO1hTN1LV 8EJADa6DdyTKUZJycTto7i8nOK8Vdf6DuDUirOsN+1ZM1EMc+5JqL52QsaN2OkYqIXLcmLhKh GZRIa44knC7tG+KYwI8Huu2DYVRg+aEiPRURxcfeD+mpb3MKB74mRvJqZDIpOwFJ8IplSiHBk dPE3lQ+6FcquEI627fFEoIJsABZeujtF8isG8r1fobh3K5TtOwzzM3pGiwmy9h6Kpm0mF2OMj kGaQSWFh3pU8IVPF1lckMoRCfNSLlmXU+tsE0JzmE95FpU80oL9i4gnV/6W7Mh0xrq85wAWLX 58z6fxPmwgsziqqRxrXDEK8tdPzbXWMsaLPRLhPrcUaMcsmaaUzIo090Id5gpTMU9jTdEhV2+ tEMC4WG5Yqp66hDTda7w== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 10, 2020 at 5:56 PM Will Deacon wrote: > > Prior to version 4.8, GCC may miscompile READ_ONCE() by erroneously > discarding the 'volatile' qualifier: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 > > We've been working around this using some nasty hacks which make > READ_ONCE() both horribly complicated and also prevent us from enforcing > that it is only used on scalar types. Since GCC 4.8 is pretty old for > kernel builds now, emit a warning if we detect it during the build. No objection to recommending gcc-4.8, but I think this should either just warn once during the kernel build instead of for every file, or it should become a hard requirement. Arnd