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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 312ACC282DD for ; Fri, 10 Jan 2020 16:56:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 08ABA2072E for ; Fri, 10 Jan 2020 16:56:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578675407; bh=4nVI30gKryW63hLtZQ4pIBrmPzl/yd4sdMuuHmRHkD4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=U/pv3BLGmiPi7iu4vEeiQBRpttHBhaOslIcYcjXCPIlD/gTrfULcO8MJTLYmtwz0X J1trYkrG0AXoY3siwsDA8QOOPR0pv88PKMmrM8D/qgtCgc8gZvkMYEdGUfxSRNi+0Y GPYFT7diralBqzLI8C5WIA2K2R0x//3wBRSR5sNk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728593AbgAJQ4q (ORCPT ); Fri, 10 Jan 2020 11:56:46 -0500 Received: from mail.kernel.org ([198.145.29.99]:59888 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728258AbgAJQ4p (ORCPT ); Fri, 10 Jan 2020 11:56:45 -0500 Received: from localhost.localdomain (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A5B9920721; Fri, 10 Jan 2020 16:56:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578675404; bh=4nVI30gKryW63hLtZQ4pIBrmPzl/yd4sdMuuHmRHkD4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ubqczTcX2w73nHNzdZZqcmMn1Bl482OS8axtgQHMS9EalHO7PdFYszzyYDhn7MjSO 6cMFkzD6bOSEqBIEeFyqmxH/sKhjzlY10OTQF6c2NXk8dmVmQWNhKC4TGQgEkREkkh KQdzij/G1jPYzm2m6R7Twb+zXyE4MT/j2wavyDTE= From: Will Deacon To: linux-kernel@vger.kernel.org Cc: linux-arch@vger.kernel.org, kernel-team@android.com, Will Deacon , Michael Ellerman , Peter Zijlstra , Linus Torvalds , Segher Boessenkool , Christian Borntraeger , Luc Van Oostenryck , Arnd Bergmann Subject: [RFC PATCH 1/8] compiler/gcc: Emit build-time warning for GCC prior to version 4.8 Date: Fri, 10 Jan 2020 16:56:29 +0000 Message-Id: <20200110165636.28035-2-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200110165636.28035-1-will@kernel.org> References: <20200110165636.28035-1-will@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Suggested-by: Linus Torvalds Cc: Peter Zijlstra Cc: Michael Ellerman Cc: Arnd Bergmann Cc: Christian Borntraeger Signed-off-by: Will Deacon --- include/linux/compiler-gcc.h | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index d7ee4c6bad48..62afe874073e 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -14,6 +14,10 @@ # 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 */ -- 2.25.0.rc1.283.g88dfdc4193-goog