From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: linux-next: build warning after merge of the akpm-current tree Date: Mon, 13 Nov 2017 13:24:14 +0100 Message-ID: References: <20171113164206.187a790d@canb.auug.org.au> <20171113080955.zcdzx2p5kzoa4d7s@dhcp22.suse.cz> <20171113115430.pms47vgz5uszqsjm@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: Received: from mail-qk0-f195.google.com ([209.85.220.195]:48787 "EHLO mail-qk0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751375AbdKMMYQ (ORCPT ); Mon, 13 Nov 2017 07:24:16 -0500 In-Reply-To: <20171113115430.pms47vgz5uszqsjm@dhcp22.suse.cz> Sender: linux-next-owner@vger.kernel.org List-ID: To: Michal Hocko Cc: Stephen Rothwell , Andrew Morton , Linux-Next Mailing List , Linux Kernel Mailing List On Mon, Nov 13, 2017 at 12:54 PM, Michal Hocko wrote: > On Mon 13-11-17 12:43:08, 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: >> >> 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? >> >> 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 > > OK, that is a reasonable workaround. I was talking to our gcc guy and > he suggested to report a bug for this. That might also be useful. Some warnings in gcc get disabled when they show up inside of a macro, and that could presumably be done here too. Arnd