Hi all,
On Fri, 17 Nov 2017 09:44:39 +1100 Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:
>
> On Mon, 13 Nov 2017 12:43:08 +0100 Arnd Bergmann <arnd@xxxxxxxx> wrote:
> >
> > On Mon, Nov 13, 2017 at 9:09 AM, Michal Hocko <mhocko@xxxxxxxxxx> 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
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