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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 6E4EBC47254 for ; Tue, 5 May 2020 13:48:14 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 40F91206A5 for ; Tue, 5 May 2020 13:48:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 40F91206A5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jVxvH-0007Ka-Vi; Tue, 05 May 2020 13:47:47 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jVxvH-0007KV-94 for xen-devel@lists.xenproject.org; Tue, 05 May 2020 13:47:47 +0000 X-Inumbo-ID: 0026d37c-8ed7-11ea-9dbf-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 0026d37c-8ed7-11ea-9dbf-12813bfff9fa; Tue, 05 May 2020 13:47:46 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id E47E7ABB2; Tue, 5 May 2020 13:47:47 +0000 (UTC) Subject: Re: [PATCH 1/3] x86/mm: do not attempt to convert _PAGE_GNTTAB to a boolean To: Roger Pau Monne References: <20200505092454.9161-1-roger.pau@citrix.com> <20200505092454.9161-2-roger.pau@citrix.com> From: Jan Beulich Message-ID: <20332b18-960c-a180-8150-55fae60bdc6e@suse.com> Date: Tue, 5 May 2020 15:47:43 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200505092454.9161-2-roger.pau@citrix.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: xen-devel@lists.xenproject.org, Wei Liu , Andrew Cooper Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 05.05.2020 11:24, Roger Pau Monne wrote: > Clang 10 complains with: > > mm.c:1239:10: error: converting the result of '<<' to a boolean always evaluates to true > [-Werror,-Wtautological-constant-compare] > if ( _PAGE_GNTTAB && (l1e_get_flags(l1e) & _PAGE_GNTTAB) && > ^ > xen/include/asm/x86_64/page.h:161:25: note: expanded from macro '_PAGE_GNTTAB' > #define _PAGE_GNTTAB (1U<<22) > ^ This is a rather odd warning. Do they also warn for "if ( 0 )" or "do { } while ( 0 )", as we use in various places? There's no difference to me between a plain number and a constant composed via an expression. > Remove the conversion of _PAGE_GNTTAB to a boolean, since the and > operation performed afterwards will already return false if the value > of the macro is 0. I'm sorry, but no. The expression was put there on purpose by 0932210ac095 ("x86: Address "Bitwise-and with zero CONSTANT_EXPRESSION_RESULT" Coverity issues"), and the description there is clearly telling us that this wants to stay unless Coverity changed in the meantime. Otherwise I'm afraid a more elaborate solution will be needed to please both. Or a more simplistic one, like using "#if _PAGE_GNTTAB" around the construct. Jan