From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932491AbdKQDxg (ORCPT ); Thu, 16 Nov 2017 22:53:36 -0500 Received: from ozlabs.org ([103.22.144.67]:52065 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932283AbdKQDxX (ORCPT ); Thu, 16 Nov 2017 22:53:23 -0500 Date: Fri, 17 Nov 2017 14:53:20 +1100 From: Stephen Rothwell To: Michal Hocko , Andrew Morton Cc: Arnd Bergmann , Linux-Next Mailing List , Linux Kernel Mailing List Subject: Re: linux-next: build warning after merge of the akpm-current tree Message-ID: <20171117145320.714972ca@canb.auug.org.au> In-Reply-To: <20171117094439.5287c715@canb.auug.org.au> References: <20171113164206.187a790d@canb.auug.org.au> <20171113080955.zcdzx2p5kzoa4d7s@dhcp22.suse.cz> <20171117094439.5287c715@canb.auug.org.au> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, On Fri, 17 Nov 2017 09:44:39 +1100 Stephen Rothwell wrote: > > On Mon, 13 Nov 2017 12:43:08 +0100 Arnd Bergmann wrote: > > > > On Mon, Nov 13, 2017 at 9:09 AM, Michal Hocko wrote: > > > On Mon 13-11-17 16:42:06, Stephen Rothwell wrote: > > >> > > >> 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? > > > > As I understand it, the warning tries to address a common typo of accidentally > > testing the pointer to a stack object for being non-NULL, rather than the object > > pointed to for being non-zero. > > > > Adding an extra '!= NULL' comparison gets rid of the warning for me: > > > > #define nodemask_pr_args(maskp) \ > > ((maskp) != NULL) ? MAX_NUMNODES : 0, \ > > ((maskp) != NULL) ?(maskp)->bits : NULL > > > > Arnd > > This warning now exists in Linus' tree :-( Looking closer, it seems that the above workaround doesn't work for my compiler (gcc v5.2.0): 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:108:11: warning: the comparison will always evaluate as 'true' for the address of 'nodes' will never be NULL [-Waddress] ((maskp) != NULL) ? MAX_NUMNODES : 0, \ ^ mm/mempolicy.c:2817:11: note: in expansion of macro 'nodemask_pr_args' nodemask_pr_args(&nodes)); ^ include/linux/nodemask.h:109:11: warning: the comparison will always evaluate as 'true' for the address of 'nodes' will never be NULL [-Waddress] ((maskp) != NULL) ? (maskp)->bits : NULL ^ mm/mempolicy.c:2817:11: note: in expansion of macro 'nodemask_pr_args' nodemask_pr_args(&nodes)); ^ -- Cheers, Stephen Rothwell