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 EC46CC433E0 for ; Tue, 9 Jun 2020 00:33:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C90DB2072F for ; Tue, 9 Jun 2020 00:33:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591662824; bh=tp/HQEMAxy6eE4ZBdZZxf6X4ju8GZ6SIyB/TvQ0Vugc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=v6+JCOLumFmc4MeJXaWc2zOTpDMUxL+iOry/SCUKdBGTaxgBFFcB4is6M0/gKIRRx K9+nUmcMEoCsNLDNvMbiXLHa42otE8UaYb5Ngr+I12PebJHXpLJX0jK1WK44MAGooC im1NIiPt7Baw5LeJMbNbpWP2ys1GiKLgG1cQ02HU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731984AbgFIAdn (ORCPT ); Mon, 8 Jun 2020 20:33:43 -0400 Received: from mail.kernel.org ([198.145.29.99]:35354 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729912AbgFHXOt (ORCPT ); Mon, 8 Jun 2020 19:14:49 -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 98C0321556; Mon, 8 Jun 2020 23:14:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591658089; bh=tp/HQEMAxy6eE4ZBdZZxf6X4ju8GZ6SIyB/TvQ0Vugc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=P99xro6GVJ6VAA5+vO4W2kfCs/a+xHLwkdPjRmHMRmhq341RoIuRYYhclvV5SwMXm DKiz25EQDhe94NpjL9o/0LSoxhwrUofKaaAvgTf/qvB/mLRxICngFlUpaz8K+wWg0P ELV9NIHeUcTFSpDj53fyEkisIy6rEvz7gopzl/TM= 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 5.6 132/606] ARM: futex: Address build warning Date: Mon, 8 Jun 2020 19:04:17 -0400 Message-Id: <20200608231211.3363633-132-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200608231211.3363633-1-sashal@kernel.org> References: <20200608231211.3363633-1-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 83c391b597d4..fdc4ae3e7378 100644 --- a/arch/arm/include/asm/futex.h +++ b/arch/arm/include/asm/futex.h @@ -164,8 +164,13 @@ 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; } -- 2.25.1