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=-6.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 108A4C433E6 for ; Thu, 14 Jan 2021 08:19:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B8B02239EB for ; Thu, 14 Jan 2021 08:19:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728075AbhANITA (ORCPT ); Thu, 14 Jan 2021 03:19:00 -0500 Received: from mail.kernel.org ([198.145.29.99]:60892 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726677AbhANIS7 (ORCPT ); Thu, 14 Jan 2021 03:18:59 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 59A76239EF for ; Thu, 14 Jan 2021 08:18:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1610612299; bh=N5a/atXasUevjqMzJiK/W4ty6kZ/4vCWt3gzActcTYg=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=mjy6JA9jSp5PfOvVAi+GvjeqdW/DO59+DyAwcGONOdCYfddZ9U0BRXguQ63inG7B3 V9D2wta4Qtl8EtjRvAiRUnqgpVXdtR8crp0+QSC/YfnI1PHiJHjbMWwbAHTXQad3iM wD5DhEhTrYjPfGPQkK0JcYaK1Jv2yq5244F1j7LFlhOCnVwOSQiFydufTRzPr2qHxr mwSWA4ulBIZA3DqN8+IuNc7/z4qDQnNjquw7C2HLjm2onsjlLUBmQco/ZtdTcpGLY1 tVVcGCM9vnQelSg3rXF+zk61G9nGj6H84cAbke7hsgwT5DcvssQikdmtnvCjl18N4C xgr3r8uTCTWQQ== Received: by mail-oo1-f46.google.com with SMTP id x203so1185647ooa.9 for ; Thu, 14 Jan 2021 00:18:19 -0800 (PST) X-Gm-Message-State: AOAM5317KmmrOQdOMlfbN71AuJlvOOnHwijI8VV8I/GZEemKIKcK8rr4 /qvaxuEmQsUct50+MslyY4XjTZu/RODqHaxvns0= X-Google-Smtp-Source: ABdhPJzx8azhVF1beD/V0rXaIBuAZoNnC2aHwFxMLkKAVC5qCL4dJBDnifu5IYM1MfZXDwuJ0FTcRUp6xtCPtx/OeUg= X-Received: by 2002:a05:6820:41:: with SMTP id v1mr3970890oob.41.1610612298532; Thu, 14 Jan 2021 00:18:18 -0800 (PST) MIME-Version: 1.0 References: <20210112224832.10980-1-will@kernel.org> <161055398865.21762.12236232732054213928.b4-ty@arm.com> <20210113214436.GL1551@shell.armlinux.org.uk> In-Reply-To: From: Ard Biesheuvel Date: Thu, 14 Jan 2021 09:18:07 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] compiler.h: Raise minimum version of GCC to 5.1 for arm64 To: Linus Torvalds Cc: Russell King - ARM Linux admin , Florian Weimer , Arnd Bergmann , "Cc: Android Kernel" , "Theodore Ts'o" , Peter Zijlstra , Catalin Marinas , Masahiro Yamada , Nick Desaulniers , Linux Kernel Mailing List , Will Deacon , linux-arm-kernel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 13 Jan 2021 at 23:09, Linus Torvalds wrote: > > On Wed, Jan 13, 2021 at 1:44 PM Russell King - ARM Linux admin > wrote: > > > > So, maybe the Sparc issue was just a similar but different bug in gcc > > 4.9.x. > > Good catch. And I know this bug has happened independently on > different architectures several times (I remember this on x86-64 as > well), so I started looking around. > > And in fact, 4.9 was buggy on x86-64 too: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61904 > > And yeah, _that_ gcc bug wasn't actually x86-64 specific, but > apparently a generic instruction scheduling bug. > > So it's an independent bug, but I do have to admit that the arguments > against 4.9 are piling up (even if that particular fix apparently got > fixed in the gcc branches and apparently backported to distro > compilers too). > So if the arguments are piling up, what is holding us back, other than inertia? RHEL 7 used to be a factor, but it ships with 4.8 not 4.9, so its users already need to upgrade. Is anyone aware of a good reason to keep 4.9 supported? Are any other long term supported distros using 4.9.x? I know that distros probably backported fixes for all of these issues, but without a way to interrogate the compiler about this, that doesn't really make a difference IMHO. Note that banning 4.9 for arm64 and banning it in general should be two different changes in any case, as the former will need to be backported to -stable kernels as well. -- Ard.