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,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 569FCC433E0 for ; Thu, 14 May 2020 19:00:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3268320675 for ; Thu, 14 May 2020 19:00:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589482834; bh=M7pvGnvnXA7VoSIGQiVFsoWdv3eCoTkXxemX1i2yzuI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=lMAag1oJPJ/F8UajCUrdCDZqmBthAQHTwXtvbWygsp+5C/9zJKele/QvZLQABqUsE WmecGsa8jwU4ONghlnmQUZtTs9qqIyRJuft/JSdxANNdAfGHBc4x9c4nelbPxR6DzY QStu2EnLxPZA7Gv6nGEuMw1KWWJYCNKOh+o6YA9c= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729938AbgENTAd (ORCPT ); Thu, 14 May 2020 15:00:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:56416 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729474AbgENSzq (ORCPT ); Thu, 14 May 2020 14:55:46 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (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 E8582207F9; Thu, 14 May 2020 18:55:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589482545; bh=M7pvGnvnXA7VoSIGQiVFsoWdv3eCoTkXxemX1i2yzuI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TVP9EWKLPfXZv36uJmL5aeEAK/xlywXjd8/6Dhopk/PPwWTHLmec94e44nRaFeZ1l I4UVE5pZGMQdBcAoyjOJloLkvJEkxZyyBAVt5AEX4HnY8ZbD3Ar3vO6i3IrWF+vX61 WVRpBctLnCCE7jDxKTu7BnBy1HX81UK8xXLjmQrc= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Thomas Gleixner , Stephen Rothwell , Sasha Levin , linux-arm-kernel@lists.infradead.org Subject: [PATCH AUTOSEL 4.14 37/39] ARM: futex: Address build warning Date: Thu, 14 May 2020 14:54:54 -0400 Message-Id: <20200514185456.21060-37-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200514185456.21060-1-sashal@kernel.org> References: <20200514185456.21060-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Thomas Gleixner [ Upstream commit 8101b5a1531f3390b3a69fa7934c70a8fd6566ad ] Stephen reported the following build warning on a ARM multi_v7_defconfig build with GCC 9.2.1: kernel/futex.c: In function 'do_futex': kernel/futex.c:1676:17: warning: 'oldval' may be used uninitialized in this function [-Wmaybe-uninitialized] 1676 | return oldval == cmparg; | ~~~~~~~^~~~~~~~~ kernel/futex.c:1652:6: note: 'oldval' was declared here 1652 | int oldval, ret; | ^~~~~~ introduced by commit a08971e9488d ("futex: arch_futex_atomic_op_inuser() calling conventions change"). While that change should not make any difference it confuses GCC which fails to work out that oldval is not referenced when the return value is not zero. GCC fails to properly analyze arch_futex_atomic_op_inuser(). It's not the early return, the issue is with the assembly macros. GCC fails to detect that those either set 'ret' to 0 and set oldval or set 'ret' to -EFAULT which makes oldval uninteresting. The store to the callsite supplied oldval pointer is conditional on ret == 0. The straight forward way to solve this is to make the store unconditional. Aside of addressing the build warning this makes sense anyway because it removes the conditional from the fastpath. In the error case the stored value is uninteresting and the extra store does not matter at all. Reported-by: Stephen Rothwell Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/87pncao2ph.fsf@nanos.tec.linutronix.de Signed-off-by: Sasha Levin --- arch/arm/include/asm/futex.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h index ffebe7b7a5b74..91ca80035fc42 100644 --- a/arch/arm/include/asm/futex.h +++ b/arch/arm/include/asm/futex.h @@ -163,8 +163,13 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr) preempt_enable(); #endif - if (!ret) - *oval = oldval; + /* + * Store unconditionally. If ret != 0 the extra store is the least + * of the worries but GCC cannot figure out that __futex_atomic_op() + * is either setting ret to -EFAULT or storing the old value in + * oldval which results in a uninitialized warning at the call site. + */ + *oval = oldval; return ret; } -- 2.20.1