From patchwork Tue May 26 18:53:10 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 225221 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, 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 BE8E3C433E0 for ; Tue, 26 May 2020 19:29:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9E8FD20776 for ; Tue, 26 May 2020 19:29:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590521393; bh=o6xEWP3l3NxJIyh56Zls/j+EDwwS16Hn5+vt1XvPQsE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=E1WCLHQr/PAMfdWzvek9SXV1BdekfwH+extWhbuK4wRjFJ+gHthW7xs+Vc8tTmaNT 4BMd/PVEr3vJey6BPTCTRpGm+31nn0hFNqpYjUQse4EWSZ0FPQVc/dTzsD9b5F8OTY UYb4u63mlXXZbma2wBRPBvvKAlNuvpPZ15lA/MwU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390885AbgEZTBA (ORCPT ); Tue, 26 May 2020 15:01:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:55230 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389748AbgEZTA7 (ORCPT ); Tue, 26 May 2020 15:00:59 -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 B1386208C3; Tue, 26 May 2020 19:00:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590519659; bh=o6xEWP3l3NxJIyh56Zls/j+EDwwS16Hn5+vt1XvPQsE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tJ5zDCDsaXZVKWh10z1VyXJ/8SkONRX9E6zfFwJcTKA4jdXqOgusrSPoqZY2Tct36 8WMgWk5Rb4sPKW11zUUiRD+ISF2WTqaP3a92Sq1qC9CyvPksVe1xcAXX00jQC78HO+ 4D0DF7wTLtyX5xUD2Lbl2wt5LceX5obcGJuA+cEc= 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 4.14 25/59] ARM: futex: Address build warning Date: Tue, 26 May 2020 20:53:10 +0200 Message-Id: <20200526183916.587025373@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200526183907.123822792@linuxfoundation.org> References: <20200526183907.123822792@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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 ffebe7b7a5b7..91ca80035fc4 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; }