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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 639AEC433E0 for ; Tue, 26 May 2020 18:54:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 44FC02084C for ; Tue, 26 May 2020 18:54:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590519296; bh=qmmqje5lx1UrCsdVoet4XTvHST2272MfsIJhAwFmf58=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=lyQjhd2Oj5/7MKwUzwjr6Lsq1I+KR31FKAd/8WqeC5zUDL6UWIh8hyqYIHHoxCmC6 6vxZO7mIfRHhLset9OAQWBTYonJLiIrp7yHTdYAiAi4WRaa4oHv5tN49P5viBFsf6g 3K00/aFmF+UI7KOs/Lx2H+RQYl/hA4KNSV1B+TMc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389224AbgEZSyz (ORCPT ); Tue, 26 May 2020 14:54:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:47092 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389192AbgEZSyx (ORCPT ); Tue, 26 May 2020 14:54:53 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 D0B6B207FB; Tue, 26 May 2020 18:54:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590519293; bh=qmmqje5lx1UrCsdVoet4XTvHST2272MfsIJhAwFmf58=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JvVyPuWbIMh+GtRtXPQHoSB5vr1mp3XsuwUI43NL4N+0ycR6rIoAtyLspYuKX+hSk WXch+Q45OHGF12+WIuIBl4IMjgr+7UJeovX21mW1v2wNRBJ51uUchl9hm7HeJx9QGy ovuSmY9wzIr39aSm8C69E1S7W6G3jmI0wqxeUfOA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Stephen Rothwell , Thomas Gleixner , Sasha Levin Subject: [PATCH 4.4 12/65] ARM: futex: Address build warning Date: Tue, 26 May 2020 20:52:31 +0200 Message-Id: <20200526183911.012112892@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200526183905.988782958@linuxfoundation.org> References: <20200526183905.988782958@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 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 cc414382dab4..561b2ba6bc28 100644 --- a/arch/arm/include/asm/futex.h +++ b/arch/arm/include/asm/futex.h @@ -162,8 +162,13 @@ 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