From mboxrd@z Thu Jan 1 00:00:00 1970 From: askb Date: Mon, 09 Nov 2009 13:57:31 +0000 Subject: Re: [PATCH] mm/ksm.c - Fix compile warnings (PS ignore my Message-Id: <1257774331.5381.70.camel@linux-k65f.site> List-Id: References: <1257317010.14838.55.camel@linux-k65f.site> <4AF15022.1020408@bfs.de> <1257334139.14838.264.camel@linux-k65f.site> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Hugh Dickins Cc: wharms@bfs.de, Izik Eidus , linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org On Mon, 2009-11-09 at 10:51 +0000, Hugh Dickins wrote: > On Wed, 4 Nov 2009, askb wrote: > > On Wed, 2009-11-04 at 10:57 +0100, walter harms wrote: > > > > > > askb schrieb: > > > > Found the compiler warning on linux-next: > > > > > > > > mm/ksm.c: In function ‘ksm_scan_thread’: > > > > mm/ksm.c:1083: warning: ‘page2[0u]’ may be used uninitialized in this > > > > function > > > > mm/ksm.c:1083: note: ‘page2[0u]’ was declared here > > > > > > > > fix for the above warning: > > > > > > > > Signed-off-by: Anil SB > > > > > > > > diff --git a/mm/ksm.c b/mm/ksm.c > > > > index bef1af4..2ea0fd3 100644 > > > > --- a/mm/ksm.c > > > > +++ b/mm/ksm.c > > > > @@ -1080,7 +1080,7 @@ static void stable_tree_append(struct rmap_item *rmap_item, > > > > */ > > > > static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) > > > > { > > > > - struct page *page2[1]; > > > > + struct page *page2[1] = {NULL}; > > > > struct rmap_item *tree_rmap_item; > > > > unsigned int checksum; > > > > int err; > > > > > > > > > > > > > > a 1 element array looks strange, did you look what kind of magic is here used ? > > > > > >From my understanding, it is used for place holder to check and return > > an identical page from stable_tree_search(). Can we do with a double > > indirection to struct page instead of the above? > > PS point me in the right direction. > > I don't particularly like things like page2[1] myself, but there's > nothing actually wrong with it, so no urgency to change it. > > mm/ksm.c is under active development (better Cc the people involved > with a sourcefile when considering changes to it), and I have a > collection of patches under testing, which do change some names > around here (along with more serious changes). So, thanks for looking > at this, but I'd prefer to avoid the interference of a trivial patch > at the moment - sorry. > > Which version of the compiler gave you that uninitialized warning? gcc version 4.3.2 [gcc-4_3-branch revision 141291] (SUSE Linux) > A version which lots of people are using, or just some snapshot? > I've never seen a warning there myself, but they do keep "refining" > that logic. > I got the warning while doing "make randconfig". However, now after a cleanup and redoing the same, the warning is not seen. > Hugh's hypothesis: for every variable x initialized by a subfunction, > there exists at least one version V of gcc, such that V reports that > x may be used uninitialized. > > Hugh Thanks.