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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 C2E45C33CAD for ; Mon, 13 Jan 2020 14:27:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 944172081E for ; Mon, 13 Jan 2020 14:27:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578925648; bh=lDi3yhRp4PbF/E8j+iB9FGNiI7wABd2r9c3DUhzLcZ0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=gNrN8P4MhnQVw3M4GhtS78dD9KM0JSdFcIV23wUqdoPekeCul7jFG2zk4rNUF6YuE WpS8G9iuQ3vjPrp1ZJ48ZBIpqiUXdAyV9MlHk+b5PRDy28l4vf2ucxpKVTFDRT9uw/ COw1LViCys54s2s+ks8OXJaUtySepV+7LN7LbHQE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728819AbgAMO11 (ORCPT ); Mon, 13 Jan 2020 09:27:27 -0500 Received: from mail.kernel.org ([198.145.29.99]:53916 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726074AbgAMO11 (ORCPT ); Mon, 13 Jan 2020 09:27:27 -0500 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3CFC72073D; Mon, 13 Jan 2020 14:27:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578925646; bh=lDi3yhRp4PbF/E8j+iB9FGNiI7wABd2r9c3DUhzLcZ0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Wkc4M0JI8URUydIBo+uimk/TWQjQKQTf3136LlrNh1UnY0vMI6s8zMP/j7qyJZvwV CiX/MHjFZUUbeBIKbAgwCQnjiZWJpqEADJkoam5OX2jj/y8hm8cPhTLlfxc8loY6eN a784eL6XoIt/Z4piiOxqlwe9TJPqDCZYsgSknflA= Date: Mon, 13 Jan 2020 14:27:20 +0000 From: Will Deacon To: Arnd Bergmann Cc: "linux-kernel@vger.kernel.org" , linux-arch , Android Kernel Team , Michael Ellerman , Peter Zijlstra , Linus Torvalds , Segher Boessenkool , Christian Borntraeger , Luc Van Oostenryck , masahiroy@kernel.org Subject: Re: [RFC PATCH 1/8] compiler/gcc: Emit build-time warning for GCC prior to version 4.8 Message-ID: <20200113142720.GA4458@willie-the-truck> References: <20200110165636.28035-1-will@kernel.org> <20200110165636.28035-2-will@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [+Masahiro] On Fri, Jan 10, 2020 at 06:35:02PM +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. Oops, yes, good point. I blindly followed the '< 4.6' check, but that's actually a '#error' so it doesn't have the issue you mention. I've had a crack at moving the check into kbuild -- see below. Will --->8 diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 62afe874073e..d7ee4c6bad48 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -14,10 +14,6 @@ # error Sorry, your compiler is too old - please upgrade it. #endif -#if GCC_VERSION < 40800 -# warning Your compiler is old and may miscompile the kernel due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 - please upgrade it. -#endif - /* Optimization barrier */ /* The "volatile" is due to gcc bugs */ diff --git a/init/Kconfig b/init/Kconfig index a34064a031a5..bdc2f1b1667b 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -10,11 +10,11 @@ config DEFCONFIG_LIST default "arch/$(ARCH)/defconfig" config CC_IS_GCC - def_bool $(success,$(CC) --version | head -n 1 | grep -q gcc) + def_bool $(cc-is-gcc) config GCC_VERSION int - default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC + default $(gcc-version) if CC_IS_GCC default 0 config CC_IS_CLANG diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include index d4adfbe42690..4e645a798b56 100644 --- a/scripts/Kconfig.include +++ b/scripts/Kconfig.include @@ -40,3 +40,9 @@ $(error-if,$(success, $(LD) -v | grep -q gold), gold linker '$(LD)' not supporte # gcc version including patch level gcc-version := $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) + +# Return y if the compiler is GCC, n otherwise +cc-is-gcc := $(success,$(CC) --version | head -n 1 | grep -q gcc) + +# Warn if the compiler is GCC prior to 4.8 +$(warning-if,$(if-success,[ $(gcc-version) -lt 40800 ],$(cc-is-gcc),n),"Your compiler is old and may miscompile the kernel due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 - please upgrade it.")