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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 7B281C282C2 for ; Thu, 7 Feb 2019 07:51:42 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 EF4F72081B for ; Thu, 7 Feb 2019 07:51:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EF4F72081B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 43w9W0034JzDqS6 for ; Thu, 7 Feb 2019 18:51:40 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=permerror (mailfrom) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 43w9TH63KqzDqMs for ; Thu, 7 Feb 2019 18:50:11 +1100 (AEDT) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x177nnDV012367; Thu, 7 Feb 2019 01:49:49 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x177nl68012366; Thu, 7 Feb 2019 01:49:47 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Thu, 7 Feb 2019 01:49:47 -0600 From: Segher Boessenkool To: Andrew Donnellan Subject: Re: [PATCH 1/2] powerpc/64s: Work around spurious warning on old gccs with -fsanitize-coverage Message-ID: <20190207074947.GT14180@gate.crashing.org> References: <20190207053324.17541-1-andrew.donnellan@au1.ibm.com> <20190207063736.GS14180@gate.crashing.org> <630e392b-e9a7-6b1e-e3d8-c5382f94e5d7@au1.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <630e392b-e9a7-6b1e-e3d8-c5382f94e5d7@au1.ibm.com> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: syzkaller@googlegroups.com, linuxppc-dev@lists.ozlabs.org, dvyukov@google.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Feb 07, 2019 at 05:59:48PM +1100, Andrew Donnellan wrote: > On 7/2/19 5:37 pm, Segher Boessenkool wrote: > >On Thu, Feb 07, 2019 at 04:33:23PM +1100, Andrew Donnellan wrote: > >>Some older gccs ( >>cause a spurious uninitialised variable warning in dt_cpu_ftrs.c: > >> > >> arch/powerpc/kernel/dt_cpu_ftrs.c: In function > >> ‘cpufeatures_process_feature’: > >> arch/powerpc/kernel/dt_cpu_ftrs.c:686:7: warning: ‘m’ may be used > >> uninitialized in this function [-Wmaybe-uninitialized] > >> if (m->cpu_ftr_bit_mask) > > > >It seems to me the warning is correct? If enable_unknown is false and no > >cpu_feature is found, it will in > > > > if (m->cpu_ftr_bit_mask) > > cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask; > > > >enable random features (whatever was last in the table), or indeed access > >via NULL if the table is length 0? So maybe this should be > > > > if (known && m->cpu_ftr_bit_mask) > > cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask; > > > >instead? (The code would be much clearer if all the known vs. !known > >codepath was fully separated here). > > The table is never length 0, it's a statically defined array. Sure, and presumably that is why newer GCC doesn't warn. But what about the other point? Is this code ever correct? Enabling random features (in cur_cpu_spec->cpu_features) when the name isn't found seems wrong. Segher