Re: [PATCH v2] Makefile.extrawarn: enable -Wmissing-variable-declarations for W=1

[Masahiro Yamada <masahiroy@kernel.org>]

On Wed, Aug 9, 2023 at 1:17 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> On Tue, Aug 08, 2023 at 09:01:38AM -0700, Nick Desaulniers wrote:
> > On Tue, Aug 8, 2023 at 1:03 AM kernel test robot <lkp@intel.com> wrote:
> > >
> > > Hi Nick,
> > >
> > > kernel test robot noticed the following build errors:
> > >
> > > [auto build test ERROR on 52a93d39b17dc7eb98b6aa3edb93943248e03b2f]
> > >
> > > url:    https://github.com/intel-lab-lkp/linux/commits/Nick-Desaulniers/Makefile-extrawarn-enable-Wmissing-variable-declarations-for-W-1/20230808-005859
> > > base:   52a93d39b17dc7eb98b6aa3edb93943248e03b2f
> > > patch link:    https://lore.kernel.org/r/20230807-missing_proto-v2-1-3ae2e188bb0c%40google.com
> > > patch subject: [PATCH v2] Makefile.extrawarn: enable -Wmissing-variable-declarations for W=1
> > > config: arm64-randconfig-r013-20230807 (https://download.01.org/0day-ci/archive/20230808/202308081508.EI3CRzQo-lkp@intel.com/config)
> > > compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
> > > reproduce: (https://download.01.org/0day-ci/archive/20230808/202308081508.EI3CRzQo-lkp@intel.com/reproduce)
> > >
> > > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > > the same patch/commit), kindly add following tags
> > > | Reported-by: kernel test robot <lkp@intel.com>
> > > | Closes: https://lore.kernel.org/oe-kbuild-all/202308081508.EI3CRzQo-lkp@intel.com/
> > >
> > > All errors (new ones prefixed by >>):
> > >
> > >    In file included from lib/test_bitops.c:9:
> > >    In file included from include/linux/module.h:13:
> > >    In file included from include/linux/stat.h:19:
> > >    In file included from include/linux/time.h:60:
> > >    In file included from include/linux/time32.h:13:
> > >    In file included from include/linux/timex.h:67:
> > >    In file included from arch/arm64/include/asm/timex.h:8:
> > >    In file included from arch/arm64/include/asm/arch_timer.h:18:
> > >    In file included from include/linux/smp.h:110:
> > >    In file included from include/linux/preempt.h:79:
> > >    In file included from arch/arm64/include/asm/preempt.h:6:
> > >    In file included from include/linux/thread_info.h:60:
> > >    In file included from arch/arm64/include/asm/thread_info.h:18:
> > > >> arch/arm64/include/asm/stack_pointer.h:8:24: error: no previous extern declaration for non-static variable 'current_stack_pointer' [-Werror,-Wmissing-variable-declarations]
> > >        8 | register unsigned long current_stack_pointer asm ("sp");
> > >          |                        ^
> > >    arch/arm64/include/asm/stack_pointer.h:8:10: note: declare 'static' if the variable is not intended to be used outside of this translation unit
> > >        8 | register unsigned long current_stack_pointer asm ("sp");
> > >          |          ^
> >
> > I actually don't think that either compiler should warn for variables
> > with register storage.  I spoke briefly with some GCC folks on IRC and
> > the initial assesment was agreed.  I've filed
> > - https://github.com/llvm/llvm-project/issues/64509
> > - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110947
> >
> > Also, I've received 3 emails from zero day; this is expected as the
> > tree is not W=1 clean (actually, I think Arnd has been a lot of
> > cleanup around these groups of warnings, so I take that back).  What's
> > more curious to me is that none are GCC builds. I wonder if 0day bot
> > team is only testing W=1 with clang and not GCC?  That would seem like
> > perhaps the bar is higher for LLVM?
>
> As far as I am aware, the 0day bot tests both compilers with W=1. I
> think the more likely explanation is that the robot is not testing with
> prerelease versions of GCC, which is currently 14.x, which is the only
> version of GCC that has this warning implemented.
>
> > Masahiro, Nathan,
> > What are your thoughts on how to proceed here? Do we need the tree to
> > be free of warnings before it can be added to W=1? Hopefully not; I
>
> No, otherwise we wouldn't be adding it to W=1 ;)
>
> > would think that's the criteria for promoting a warning from being
> > hidden behind W=1 to being on by default in the top level Makefile.
> > What are your thoughts?
>
> I think the register storage issue should be resolved in at least clang
> before this patch is accepted, as that seems to be where the majority of
> warnings are coming from so far. Like we talked about, I'll take a shot
> at fixing that. Once that is fixed, I'll build mainline with
> -Wmissing-variable-declarations to see how many instances there are and
> if there are any other interesting edge cases that should be fixed in
> the compiler. After that, I think this should be good to go in. Does
> that sound reasonable?


Sounds reasonable!
Thank you.





-- 
Best Regards
Masahiro Yamada