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=-6.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT 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 68E45C10F12 for ; Wed, 17 Apr 2019 09:53:55 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3C4D32173C for ; Wed, 17 Apr 2019 09:53:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="jfsy4ekl" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3C4D32173C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=whHDCDhCLYwRIvlM8hLriJ3ltwIms4Fj/tm48jxYO7o=; b=jfsy4eklxzkFdX RrGh9q00VF6C9ch9CNQx7A2w98X14y0k+5oIUdYy+mxqAt2KF/hKuVjxZ3/R23fzy/WkCFKHxtzt9 yh5symcEnjF0lBJDMBIIUMady5rNdvmJKwFdQsyPNVqvrnqm9EfZcnnZOtCclToZsbqqhp62+yPtR xzopLpnhWYjdLIsj0VfZ5+BlVXbgGUYc6NAVDP77zSwunRup5PHRwuOEZ3u+egWCIa1DntQEEohp3 AQYkStHVRxFBNidwHoCQGYSO4AVpvmjKY43z6nVi5Z4ctchh8X0Km9mhJPBa3eolJvsSeMbd4D2JW NJO8mECGA6NronQzp/Iw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hGhGE-00033o-On; Wed, 17 Apr 2019 09:53:46 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hGhGB-00032w-40 for linux-arm-kernel@lists.infradead.org; Wed, 17 Apr 2019 09:53:44 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4975A374; Wed, 17 Apr 2019 02:53:41 -0700 (PDT) Received: from mbp (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0FACD3F68F; Wed, 17 Apr 2019 02:53:39 -0700 (PDT) Date: Wed, 17 Apr 2019 10:53:37 +0100 From: Catalin Marinas To: Nathan Chancellor Subject: Re: [PATCH] arm64: futex: Restore oldval initialization to work around buggy compilers Message-ID: <20190417095337.xnbdaki7kolqmchx@mbp> References: <20190417072121.4450-1-natechancellor@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190417072121.4450-1-natechancellor@gmail.com> User-Agent: NeoMutt/20170113 (1.7.2) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190417_025343_168466_56ABB5AF X-CRM114-Status: GOOD ( 11.30 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Will Deacon , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Apr 17, 2019 at 12:21:21AM -0700, Nathan Chancellor wrote: > Commit 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with > non-zero result value") removed oldval's zero initialization in > arch_futex_atomic_op_inuser because it is not necessary. Unfortunately, > Android's arm64 GCC 4.9.4 [1] does not agree: > > ../kernel/futex.c: In function 'do_futex': > ../kernel/futex.c:1658:17: warning: 'oldval' may be used uninitialized > in this function [-Wmaybe-uninitialized] > return oldval == cmparg; > ^ > In file included from ../kernel/futex.c:73:0: > ../arch/arm64/include/asm/futex.h:53:6: note: 'oldval' was declared here > int oldval, ret, tmp; > ^ > > GCC fails to follow that when ret is non-zero, futex_atomic_op_inuser > returns right away, avoiding the uninitialized use that it claims. > Restoring the zero initialization works around this issue. > > [1]: https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/ > > Cc: stable@vger.kernel.org > Fixes: 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value") > Signed-off-by: Nathan Chancellor Thanks. That compiler version doesn't seem very smart. I'll queue this for -rc6. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel