From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zhangshaokun Subject: Re: linux-next: build warning after merge of the akpm-current tree Date: Fri, 17 Nov 2017 17:36:44 +0800 Message-ID: <24a5b70c-aac4-29b5-6a4d-38ac3d10d475@hisilicon.com> References: <20171113164206.187a790d@canb.auug.org.au> <20171113080955.zcdzx2p5kzoa4d7s@dhcp22.suse.cz> <20171117094439.5287c715@canb.auug.org.au> <20171117145320.714972ca@canb.auug.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 8bit Return-path: Received: from szxga05-in.huawei.com ([45.249.212.191]:11007 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751161AbdKQJhn (ORCPT ); Fri, 17 Nov 2017 04:37:43 -0500 In-Reply-To: <20171117145320.714972ca@canb.auug.org.au> Sender: linux-next-owner@vger.kernel.org List-ID: To: Stephen Rothwell , Michal Hocko , Andrew Morton Cc: Arnd Bergmann , Linux-Next Mailing List , Linux Kernel Mailing List Hi, On 2017/11/17 11:53, Stephen Rothwell wrote: > 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): > I also came across this issue using Linus' tree and my gcc is gcc version 5.4.0 20160609 (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.5). CC drivers/clk/renesas/rcar-gen3-cpg.o 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)); ^ CC drivers/clk/renesas/renesas-cpg-mssr.o Thanks, Shaokun > 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)); > ^ >