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From: Michal Hocko <mhocko@kernel.org>
To: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Linux-Next Mailing List <linux-next@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: linux-next: build warning after merge of the akpm-current tree
Date: Mon, 13 Nov 2017 09:23:58 +0100
Message-ID: <20171113082358.w34pdipoeels47xc@dhcp22.suse.cz> (raw)
In-Reply-To: <20171113080955.zcdzx2p5kzoa4d7s@dhcp22.suse.cz>

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 <stdio.h>

#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

  reply index

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-13  5:42 Stephen Rothwell
2017-11-13  8:09 ` Michal Hocko
2017-11-13  8:23   ` Michal Hocko [this message]
2017-11-13 11:43   ` Arnd Bergmann
2017-11-13 11:54     ` Michal Hocko
2017-11-13 12:24       ` Arnd Bergmann
2017-11-13 12:29       ` Michal Hocko
2017-11-16 22:44     ` Stephen Rothwell
2017-11-17  3:53       ` Stephen Rothwell
2017-11-17  9:36         ` Zhangshaokun
2017-11-17  9:56         ` Arnd Bergmann
2017-11-17 10:15           ` [PATCH] mm: fix nodemask printing Arnd Bergmann
2017-11-20  8:22             ` Michal Hocko
2017-11-20 11:33               ` Arnd Bergmann
  -- strict thread matches above, loose matches on Subject: below --
2019-11-06  7:05 linux-next: build warning after merge of the akpm-current tree Stephen Rothwell
2019-11-06  7:52 ` Shaokun Zhang
2019-11-06  6:54 Stephen Rothwell
2019-08-07  8:00 Stephen Rothwell
2019-08-07 11:29 ` Rikard Falkeborn
2019-08-07 23:31   ` Stephen Rothwell
2019-07-31  6:16 Stephen Rothwell
2019-07-31 12:01 ` Jia-Ju Bai
2019-07-31  6:11 Stephen Rothwell
2019-07-31  6:28 ` Miles Chen
2019-08-01  5:51   ` Stephen Rothwell
2019-08-01  6:15     ` Michal Hocko
2019-08-01  6:30       ` Miles Chen
2019-08-01  6:38         ` Michal Hocko
2019-08-01  6:39         ` Stephen Rothwell
2019-08-01  6:42           ` Miles Chen
2019-07-29  3:48 Stephen Rothwell
2019-07-29  3:44 Stephen Rothwell
2019-05-30  4:55 Stephen Rothwell
2019-05-30  9:02 ` Matteo Croce
2019-03-29  2:39 Stephen Rothwell
2019-04-16  6:52 ` Stephen Rothwell
2019-04-16 22:45   ` Andrew Morton
2019-01-31  5:01 Stephen Rothwell
2018-06-08  4:45 Stephen Rothwell
2018-05-04  4:17 Stephen Rothwell
2018-05-04 15:39 ` Randy Dunlap
2018-05-07 14:10   ` Minchan Kim
2018-05-07 16:47     ` Randy Dunlap
2018-05-08 10:48       ` Minchan Kim
2018-04-06  4:53 Stephen Rothwell
2018-01-02  7:04 Stephen Rothwell
2017-12-15  2:48 Stephen Rothwell
2017-11-23  2:01 Stephen Rothwell
2017-11-13  5:54 Stephen Rothwell
2017-08-01  5:22 Stephen Rothwell
2017-05-26  2:43 Stephen Rothwell
2017-05-26 10:16 ` Jeff Layton
2017-05-26 11:28   ` Dave Kleikamp
2017-05-19  4:44 Stephen Rothwell
2017-05-15  1:56 Stephen Rothwell
2017-05-15  4:02 ` Xunlei Pang
2017-05-15  5:07   ` Stephen Rothwell
2017-02-02  6:49 Stephen Rothwell
2016-11-09  4:10 Stephen Rothwell
2016-11-09  7:18 ` Huang Shijie
2016-11-09 21:21   ` Andrew Morton
2016-11-10  2:56     ` Stephen Rothwell
2016-06-23  6:53 Stephen Rothwell
2016-06-23 14:00 ` Mel Gorman
2016-05-27  3:07 Stephen Rothwell
2016-05-27 19:53 ` Andrew Morton
2016-04-29  6:45 Stephen Rothwell
2016-04-29  6:55 ` Stephen Rothwell
2016-04-29 13:32 ` Josh Poimboeuf
2016-04-29 14:03   ` Josh Poimboeuf
2016-04-30  5:52     ` Stephen Rothwell
2015-07-16  5:26 Stephen Rothwell
2015-07-16 23:00 ` Andrew Morton
2015-06-04 12:29 Stephen Rothwell
2015-06-04 13:56 ` Andrea Arcangeli
2015-02-04  7:48 Stephen Rothwell
2015-02-04  7:53 ` Jan Kiszka
2015-01-19  7:45 Stephen Rothwell
2015-01-19 15:50 ` Chris Mason
2014-10-30  5:19 Stephen Rothwell
2014-10-30  9:00 ` Aneesh Kumar K.V
2014-09-26 10:42 Stephen Rothwell
2014-09-29 21:30 ` Andrew Morton
2014-09-08  8:57 Stephen Rothwell
2014-06-20  5:27 Stephen Rothwell
2014-06-20  5:29 ` Yinghai Lu
2014-06-16  1:57 Stephen Rothwell

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