From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751982AbdKMIYB (ORCPT ); Mon, 13 Nov 2017 03:24:01 -0500 Received: from mx2.suse.de ([195.135.220.15]:58013 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751261AbdKMIYA (ORCPT ); Mon, 13 Nov 2017 03:24:00 -0500 Date: Mon, 13 Nov 2017 09:23:58 +0100 From: Michal Hocko To: Stephen Rothwell Cc: Andrew Morton , Linux-Next Mailing List , Linux Kernel Mailing List Subject: Re: linux-next: build warning after merge of the akpm-current tree Message-ID: <20171113082358.w34pdipoeels47xc@dhcp22.suse.cz> References: <20171113164206.187a790d@canb.auug.org.au> <20171113080955.zcdzx2p5kzoa4d7s@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171113080955.zcdzx2p5kzoa4d7s@dhcp22.suse.cz> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 13-11-17 09:09:55, Michal Hocko wrote: > On Mon 13-11-17 16:42:06, Stephen Rothwell wrote: > > Hi Andrew, > > > > After merging the akpm-current tree, today's linux-next build (powerpc > > ppc64_defconfig) produced this warning: > > > > In file included from include/linux/mmzone.h:17:0, > > from include/linux/mempolicy.h:10, > > from mm/mempolicy.c:70: > > mm/mempolicy.c: In function 'mpol_to_str': > > include/linux/nodemask.h:107:41: warning: the address of 'nodes' will always evaluate as 'true' [-Waddress] > > #define nodemask_pr_args(maskp) (maskp) ? MAX_NUMNODES : 0, (maskp) ? (maskp)->bits : NULL > > ^ > > mm/mempolicy.c:2817:11: note: in expansion of macro 'nodemask_pr_args' > > nodemask_pr_args(&nodes)); > > ^ > > Hmm, this warning is quite surprising to me. Sure in this particular > case maskp will always be non-NULL so we always expand to > MAX_NUMNODES, maskp->bits > which is what we want. But we have other users which may be NULL. Does > anybody understan why this warns at all? Strange I played with the following minimal test case and it warns only for the explicit &m use while n is clearly never null as well. This all smells like -Waddress is just confused (at least with my gcc 7.2.0-12 #include #define MAX_NUMNODES 10 struct mask { void *bits; }; #define nodemask_pr_args(maskp) (maskp) ? MAX_NUMNODES : 0, (maskp) ? (maskp)->bits : NULL int foo(void) { struct mask m; struct mask *n = &m; printf("%*p\n", nodemask_pr_args(&m)); printf("%*p\n", nodemask_pr_args(n)); return 0; } -- Michal Hocko SUSE Labs