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 9968EC282DD for ; Fri, 10 Jan 2020 17:54:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6D4122467A for ; Fri, 10 Jan 2020 17:54:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729043AbgAJRyd (ORCPT ); Fri, 10 Jan 2020 12:54:33 -0500 Received: from smtprelay0023.hostedemail.com ([216.40.44.23]:54847 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728232AbgAJRyc (ORCPT ); Fri, 10 Jan 2020 12:54:32 -0500 Received: from filter.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay05.hostedemail.com (Postfix) with ESMTP id 32B71180008AC; Fri, 10 Jan 2020 17:54:31 +0000 (UTC) X-Session-Marker: 6A6F6540706572636865732E636F6D X-HE-Tag: food82_7e88326182d0f X-Filterd-Recvd-Size: 2379 Received: from XPS-9350.home (unknown [47.151.135.224]) (Authenticated sender: joe@perches.com) by omf13.hostedemail.com (Postfix) with ESMTPA; Fri, 10 Jan 2020 17:54:29 +0000 (UTC) Message-ID: <8fe4f81699517758b44afbe0e1a53bc080f64a62.camel@perches.com> Subject: Re: [RFC PATCH 1/8] compiler/gcc: Emit build-time warning for GCC prior to version 4.8 From: Joe Perches To: Arnd Bergmann , 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 Date: Fri, 10 Jan 2020 09:53:36 -0800 In-Reply-To: References: <20200110165636.28035-1-will@kernel.org> <20200110165636.28035-2-will@kernel.org> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.34.1-2 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2020-01-10 at 18:35 +0100, Arnd Bergmann wrote: > 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. It might as well be a hard requirement as gcc 4.8.0 is already nearly 7 years old. gcc 4.6.0 released 2011-03-25 gcc 4.8.0 released 2013-03-22 Perhaps there are exceedingly few to zero new instances using gcc compiler versions < 4.8