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=-3.8 required=3.0 tests=BAYES_00, 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 54167C433DF for ; Sat, 22 Aug 2020 10:35:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3223B2075E for ; Sat, 22 Aug 2020 10:35:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727932AbgHVKfh (ORCPT ); Sat, 22 Aug 2020 06:35:37 -0400 Received: from mout.kundenserver.de ([212.227.126.187]:55743 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726728AbgHVKfe (ORCPT ); Sat, 22 Aug 2020 06:35:34 -0400 Received: from mail-qk1-f179.google.com ([209.85.222.179]) by mrelayeu.kundenserver.de (mreue012 [212.227.15.129]) with ESMTPSA (Nemesis) id 1M9ZRc-1kEuVk0PNU-005csu for ; Sat, 22 Aug 2020 12:35:32 +0200 Received: by mail-qk1-f179.google.com with SMTP id g26so3562227qka.3 for ; Sat, 22 Aug 2020 03:35:31 -0700 (PDT) X-Gm-Message-State: AOAM53183iKXKigtP9KCOFjBu9H28szEg8Yf4vjGVIhKAj5WlTfC/0Uz QMWElAAIJXiMFrO4oTw1nIHKZWm6flurd/5r2UU= X-Google-Smtp-Source: ABdhPJxfOSbyHes4JbOJ50pcCa6e32q/bcIpNVdrdDO3DrVesAm8MO8Z++Sd7VBuHvoFpyIigRLJwM63DrH1Fxk3puQ= X-Received: by 2002:ae9:f449:: with SMTP id z9mr6592119qkl.352.1598092530943; Sat, 22 Aug 2020 03:35:30 -0700 (PDT) MIME-Version: 1.0 References: <875z9dioll.fsf@nanos.tec.linutronix.de> <20200820130641.GA536306@rani.riverdale.lan> <87zh6ohm03.fsf@nanos.tec.linutronix.de> <20200821230435.GA56974@rani.riverdale.lan> <87eenzqzmr.fsf@nanos.tec.linutronix.de> <20200822035552.GA104886@rani.riverdale.lan> <20200822084133.GL28786@gate.crashing.org> <20200822102637.GM28786@gate.crashing.org> In-Reply-To: <20200822102637.GM28786@gate.crashing.org> From: Arnd Bergmann Date: Sat, 22 Aug 2020 12:35:14 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] x86: work around clang IAS bug referencing __force_order To: Segher Boessenkool Cc: Sedat Dilek , Arvind Sankar , Thomas Gleixner , Nick Desaulniers , "Paul E. McKenney" , Ingo Molnar , Borislav Petkov , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "H. Peter Anvin" , "Kirill A. Shutemov" , Zhenzhong Duan , Kees Cook , Peter Zijlstra , Juergen Gross , Andy Lutomirski , Andrew Cooper , LKML , clang-built-linux , Will Deacon , Linus Torvalds , Miguel Ojeda Content-Type: text/plain; charset="UTF-8" X-Provags-ID: V03:K1:LDzWpBX2wbh2eX4DaBnZT6R1VRWJw20Qo93SRU2M+0ATQk/zTWM N1SKBMTaNLqYW5mIULTLzEfFsStnap4wQxHnWdK1QSRPTdCJWBb+yIV5WmeG606jy5ErXL8 4uPG4CLbLGyMTF4g9rHGmv/pxyvWGy5LnVY4csHVwgPV3QeMgYSWAxkp7O19NbD6+MIZThs Z9CN7yRSVgYGO2RZWJdhQ== X-UI-Out-Filterresults: notjunk:1;V03:K0:ujKyGxYqi5s=:l+5mYrv9/JL5V68hpxcsLI +ySgK1avJshH8cEbrC58UUuG9CnVDOHp4c+EOnR16vGveeAvOWuGe8xnTpjQSN4+6F8uCO4WZ uQPLm2piJj6JDpC5SCeHJvWdK5iacFbpQQeUP4qYAf48wVUVKKKkHxRyH/ZPK5mSPkOIGuwxk rhSkoaLUp/fuXXZb6k6uOPPtiLKc1nr7NHqM/56D5qt2XK5GhWk9iVUzarER5ByeZlVYFS6w9 buGT0kpmk7k5TmME6bFMO8WmkTQnS5oL0cZlVK1f6Y4zeiyxVct24//saVYx2p2RlHerSlnZW vJIXHZe1B5JULGgRMhR/VoD1uPtRvVlbFBpmMwKCTiCxPYVq+p19RQR4CQMs+9HGVmKtrMe0M B3zHB9CtvE6V2QbVT6JYAXkZz8otXE55GrPOXM+r+2K9IMlkZDmno2dXKuZiKS4SZjGJSQf2X gaoM1FLOAreNqoMbUCeFfbc/yw0vHZ+2qoNslBWhfJYee4HQZffzT/aG7mUhLpWvz+ZjkdYL0 uL1LelRpD5oK37f3xN81od59xyazZx9F+CCuzB0m3Sn+xo9Ur+2cLuO3WOXvXknsb46EQ0UZI LRcdINmskWc4hGtnjk3j9bXehPaYcgr7Iu9g7yl15VtQ/22jDyp/p3WwyYYej6NSYwp5FpksJ bJ7UljfJ5SFcxZnCQxQrpORNhndvhLS9hXPOe72owNfgkxN/YSHngRG4giY5+FYnV7vzIckyg VjjLKZQRh1eV7TH4mXnNgWN53GbfIP/00FzL8HyFd8rnLbACgmBoRLQotVyU7raGbEfEyMNjz 8M3eAKNDkAOQmizHeA/Adz0k5TE10+RxrT2sgH24Q0bu4KXitDfRGVcnO1gCJGL5Zcd9RkJDd nskFNUtn8sWtQdMxbyX+53PF8acVrG8pOvcQkTgivH7r0IQeSufgjMFwXEn1xMlxNTk1fsOqP 32w7bs87Wh+VMtyWzLXuLTNxFQRL3epitejUdfsc0oXoqyDhbgF47 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 22, 2020 at 12:26 PM Segher Boessenkool wrote: > [ There is GCC 4.9.4, no one should use an older 4.9. ] > > I mentioned 5 for a reason: the whole function this patch is to did not > exist before then! That does not mean the bug existed or did not exist > before GCC 5, but it does for example mean that a backport to 4.9 or > older isn't trivial at all. > > > I am asking myself who is using such ancient compilers? > > Some distros have a GCC 4.8 as system compiler. We allow building GCC > itself with a compiler that far back, for various reasons as well (and > this is very sharp already, the last mainline GCC 4.8 release is from > June 2015, not all that long ago at all). > > But, one reason this works is because people actually test it. Does > anyone actually test the kernel with old compilers? It isn't hard to > build a new compiler (because we make sure building a newer compiler > works with older compilers, etc. :-) ), and as you say, most distros > have newer compilers available nowadays. We only recently changed the minimum from 4.6 to 4.8, and subsequently to 4.9. Most people have fairly recent compilers, but there are a number of notable kernel developers that intentionally stick to old versions because of compile speed. Each major compiler release adds about 4% overhead in total time to compile a kernel, so between gcc-4.6 and gcc-11 you add over 50% in build time. Arnd