On Tue, Aug 27, 2019 at 4:25 PM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > On Tue, Aug 27, 2019 at 8:49 AM Qian Cai <cai@xxxxxx> wrote: > > > > When compiling a kernel with W=1, there are several of those warnings > > due to arm64 override a field by purpose. Just disable those warnings > > for both GCC and Clang of this file, so it will help dig "gems" hidden > > in the W=1 warnings by reducing some noises. > > > > mm/init-mm.c:39:2: warning: initializer overrides prior initialization > > of this subobject [-Winitializer-overrides] > > INIT_MM_CONTEXT(init_mm) > > ^~~~~~~~~~~~~~~~~~~~~~~~ > > ./arch/arm64/include/asm/mmu.h:133:9: note: expanded from macro > > 'INIT_MM_CONTEXT' > > .pgd = init_pg_dir, > > ^~~~~~~~~~~ > > mm/init-mm.c:30:10: note: previous initialization is here > > .pgd = swapper_pg_dir, > > ^~~~~~~~~~~~~~ > > > > Note: there is a side project trying to support explicitly allowing > > specific initializer overrides in Clang, but there is no guarantee it > > will happen or not. > > > > https://github.com/ClangBuiltLinux/linux/issues/639 > > > > Signed-off-by: Qian Cai <cai@xxxxxx> > > --- > > mm/Makefile | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/mm/Makefile b/mm/Makefile > > index d0b295c3b764..5a30b8ecdc55 100644 > > --- a/mm/Makefile > > +++ b/mm/Makefile > > Hi Qian, thanks for the patch. > Rather than disable the warning outright, and bury the disabling in a > directory specific Makefile, why not move it to W=2 in > scripts/Makefile.extrawarn? > > > I think even better would be to use pragma's to disable the warning in > mm/init.c. Looks like __diag support was never ported for clang yet > from include/linux/compiler-gcc.h to include/linux/compiler-clang.h. > > Then you could do: > > 28 struct mm_struct init_mm = { > 29 .mm_rb = RB_ROOT, > 30 .pgd = swapper_pg_dir, > 31 .mm_users = ATOMIC_INIT(2), > 32 .mm_count = ATOMIC_INIT(1), > 33 .mmap_sem = __RWSEM_INITIALIZER(init_mm.mmap_sem), > 34 .page_table_lock = > __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock), > 35 .arg_lock = __SPIN_LOCK_UNLOCKED(init_mm.arg_lock), > 36 .mmlist = LIST_HEAD_INIT(init_mm.mmlist), > 37 .user_ns = &init_user_ns, > 38 .cpu_bitmap = { [BITS_TO_LONGS(NR_CPUS)] = 0}, > __diag_push(); > __diag_ignore(CLANG, 4, "-Winitializer-overrides") > 39 INIT_MM_CONTEXT(init_mm) > __diag_pop(); > 40 }; > > > I mean, the arm64 case is not a bug, but I worry about turning this > warning off. I'd expect it to only warn once during an arm64 build, > so does the warning really detract from "W=1 gem finding?" > > > @@ -21,6 +21,9 @@ KCOV_INSTRUMENT_memcontrol.o := n > > KCOV_INSTRUMENT_mmzone.o := n > > KCOV_INSTRUMENT_vmstat.o := n > > > > +CFLAGS_init-mm.o += $(call cc-disable-warning, override-init) > > -Woverride-init isn't mentioned in the commit message, so not sure if > it's meant to ride along? > > > +CFLAGS_init-mm.o += $(call cc-disable-warning, initializer-overrides) That said, it's not too bad to disable it for one object file that contains a single struct definition. -- Thanks, ~Nick Desaulniers
