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@xxxxxxxxxx> 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@xxxxxxxxx> > > > > > > > > > > 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@xxxxxxxxx/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 ʽhugetlb_basepage_indexʼ [-Wmissing-prototypes] 1591 | pgoff_t hugetlb_basepage_index(struct page *page, int flags) | ^~~~~~~~~~~~~~~~~~~~~~ mm/hugetlb.c:1591:9: error: conflicting types for ʽhugetlb_basepage_indexʼ In file included from mm/hugetlb.c:14: ./include/linux/pagemap.h:543:18: note: previous declaration of ʽhugetlb_basepage_indexʼ 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
