On Tue, 15 Jun 2021, Matthew Wilcox wrote:
On Tue, Jun 15, 2021 at 11:50:40AM -0700, Nick Desaulniers wrote:
> On Tue, Jun 15, 2021 at 11:32 AM Nathan Chancellor <nathan(a)kernel.org> wrote:
> > On Tue, Jun 15, 2021 at 05:03:40PM +0100, Matthew Wilcox wrote:
> > > On Tue, Jun 15, 2021 at 11:58:36PM +0800, kernel test robot wrote:
> > > > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross
ARCH=arm64
> > > >
> > > > If you fix the issue, kindly add following tag as appropriate
> > > > Reported-by: kernel test robot <lkp(a)intel.com>
> > > >
> > > > All warnings (new ones prefixed by >>):
> > > >
> > > > >> mm/hugetlb.c:1591:9: warning: no previous prototype for
function 'hugetlb_basepage_index' [-Wmissing-prototypes]
> > > > pgoff_t hugetlb_basepage_index(struct page *page)
> > >
> > > So clang requires the prototype to still be in scope, while gcc
doesn't.
> > > Does one of our clangers want to file a bug about that?
> >
> > I see the exact same warning with GCC 11.1.0:
> >
> > $ curl -LSs
https://lore.kernel.org/linux-mm/202106152328.Mh5S48hE-lkp@intel.com/2-a.bin | gzip -d
> .config
> >
> > $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux- W=1
olddefconfig mm/hugetlb.c
> > mm/hugetlb.c:1591:9: warning: no previous prototype for
'hugetlb_basepage_index' [-Wmissing-prototypes]
> > 1591 | pgoff_t hugetlb_basepage_index(struct page *page)
> > | ^~~~~~~~~~~~~~~~~~~~~~
>
> Since this is a commonly recurring warning for W=1 builds, then this
> function either should be declared as having static linkage if its
> uses are local to the same file, or a prototype should be declared in
> a header so that callers and callee agree on function signature.
Oh, you haven't understood the problem.
static inline int bar(void)
{
int foo(void);
return foo();
}
int foo(void) { return 1; }
The prototype isn't _missing_. It's just no longer in scope.
Since gcc and clang behave the same way here, we should adjust the source
to make foo visible outside bar. But this is a case where both compilers
are wrong.
I guess I'd better start W=1-ing - not my habit before, sorry.
I can't tell what's right or wrong for the compiler, but it sure is
odd that if I add a bogus ", int flags" to hugetlb_basepage_index()
in mm/hugetlb.c, then building with gcc (10) and W=1 says
CC mm/hugetlb.o
mm/hugetlb.c:1591:9: warning: no previous prototype for ‘hugetlb_basepage_index’
[-Wmissing-prototypes]
1591 | pgoff_t hugetlb_basepage_index(struct page *page, int flags)
| ^~~~~~~~~~~~~~~~~~~~~~
mm/hugetlb.c:1591:9: error: conflicting types for ‘hugetlb_basepage_index’
In file included from mm/hugetlb.c:14:
./include/linux/pagemap.h:543:18: note: previous declaration of ‘hugetlb_basepage_index’
was here
543 | extern pgoff_t hugetlb_basepage_index(struct page *page);
| ^~~~~~~~~~~~~~~~~~~~~~
So, it manages to conflict with no previous prototype!
(I didn't try clang with W=1, presumably similar.)
Both gcc and clang with W=0 do issue the conflicting types error,
as I hoped and assumed that they would when I put in the prototype.
Oh well, thanks for moving it Matthew: whatever the rights and wrongs,
neither of us want to be generating unnecessary noise.
Hugh