[linux-next:master 9529/10007] mm/hugetlb.c:1591:9: warning: no previous prototype for function 'hugetlb_basepage_index'

[linux-next:master 9529/10007] mm/hugetlb.c:1591:9: warning: no previous prototype for function 'hugetlb_basepage_index'

[kernel test robot]

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   19ae1f2bd9c091059f80646604ccef8a1e614f57
commit: 1878ae46bd82ef0403393aee4935f29c07d5848b [9529/10007] mm, futex: fix shared futex pgoff on shmem huge page
config: arm64-randconfig-r014-20210615 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 64720f57bea6a6bf033feef4a5751ab9c0c3b401)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install arm64 cross compiling tool for clang build
        # apt-get install binutils-aarch64-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=1878ae46bd82ef0403393aee4935f29c07d5848b
        git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
        git fetch --no-tags linux-next master
        git checkout 1878ae46bd82ef0403393aee4935f29c07d5848b
        # save the attached .config to linux build tree
        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@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)
           ^
   mm/hugetlb.c:1591:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   pgoff_t hugetlb_basepage_index(struct page *page)
   ^
   static 
   include/linux/types.h:131:17: note: expanded from macro 'pgoff_t'
   #define pgoff_t unsigned long
                   ^
   1 warning generated.


vim +/hugetlb_basepage_index +1591 mm/hugetlb.c

  1590	
> 1591	pgoff_t hugetlb_basepage_index(struct page *page)
  1592	{
  1593		struct page *page_head = compound_head(page);
  1594		pgoff_t index = page_index(page_head);
  1595		unsigned long compound_idx;
  1596	
  1597		if (compound_order(page_head) >= MAX_ORDER)
  1598			compound_idx = page_to_pfn(page) - page_to_pfn(page_head);
  1599		else
  1600			compound_idx = page - page_head;
  1601	
  1602		return (index << compound_order(page_head)) + compound_idx;
  1603	}
  1604	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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Re: [linux-next:master 9529/10007] mm/hugetlb.c:1591:9: warning: no previous prototype for function 'hugetlb_basepage_index'

[Matthew Wilcox]

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@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?

Re: [linux-next:master 9529/10007] mm/hugetlb.c:1591:9: warning: no previous prototype for function 'hugetlb_basepage_index'

[Nathan Chancellor]

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@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)
      |         ^~~~~~~~~~~~~~~~~~~~~~

Cheers,
Nathan

Re: [linux-next:master 9529/10007] mm/hugetlb.c:1591:9: warning: no previous prototype for function 'hugetlb_basepage_index'

[Nick Desaulniers]

On Tue, Jun 15, 2021 at 11:32 AM Nathan Chancellor <nathan@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@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.
-- 
Thanks,
~Nick Desaulniers

Re: [linux-next:master 9529/10007] mm/hugetlb.c:1591:9: warning: no previous prototype for function 'hugetlb_basepage_index'

[Matthew Wilcox]

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@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@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.

Re: [linux-next:master 9529/10007] mm/hugetlb.c:1591:9: warning: no previous prototype for function 'hugetlb_basepage_index'

[Hugh Dickins]

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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@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@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