linux-kernel - Re: [tip:x86/mm 1/23] arch/x86/mm/init.c:75:6: warning: no previous prototype for function 'x86_has_pat

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Date:   Tue, 19 May 2020 15:12:24 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Philip Li <philip.li@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>, kbuild test robot <lkp@...el.com>,
        Christoph Hellwig <hch@....de>, kbuild-all@...ts.01.org,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Benjamin Thiel <b.thiel@...teo.de>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: [tip:x86/mm 1/23] arch/x86/mm/init.c:75:6: warning: no previous
 prototype for function 'x86_has_pat_wp'

Masahiro and Philip,
We're seeing a bunch of -Wmissing-prototypes warnings from 0day bot
suddenly today.  Did something change on the Kbuild or 0day bot side?

On Tue, May 19, 2020 at 2:25 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> On Tue, May 19, 2020 at 10:55:05PM +0200, Borislav Petkov wrote:
> > On Wed, May 20, 2020 at 01:51:25AM +0800, kbuild test robot wrote:
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/mm
> > > head:   bd1de2a7aace4d1d312fb1be264b8fafdb706208
> > > commit: 1f6f655e01adebf5bd5e6c3da2e843c104ded051 [1/23] x86/mm: Add a x86_has_pat_wp() helper
> > > config: x86_64-randconfig-r012-20200519 (attached as .config)
> > > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project 135b877874fae96b4372c8a3fbfaa8ff44ff86e3)
> > > reproduce:
> > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > >         chmod +x ~/bin/make.cross
> > >         # install x86_64 cross compiling tool for clang build
> > >         # apt-get install binutils-x86-64-linux-gnu
> > >         git checkout 1f6f655e01adebf5bd5e6c3da2e843c104ded051
> > >         # save the attached .config to linux build tree
> > >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64
> > >
> > > If you fix the issue, kindly add following tag as appropriate
> > > Reported-by: kbuild test robot <lkp@...el.com>
> > >
> > > All warnings (new ones prefixed by >>, old ones prefixed by <<):
> > >
> > > >> arch/x86/mm/init.c:75:6: warning: no previous prototype for function 'x86_has_pat_wp' [-Wmissing-prototypes]
> > > bool x86_has_pat_wp(void)
> > > ^
> >
> > Triggers with gcc too:
> >
> > make W=1 arch/x86/mm/init.o
> >
> > ...
> >
> > arch/x86/mm/init.c:81:6: warning: no previous prototype for ‘x86_has_pat_wp’ [-Wmissing-prototypes]
> >    81 | bool x86_has_pat_wp(void)
> >       |      ^~~~~~~~~~~~~~
> >
> >
> > -Wmissing-prototypes is default off, though, dunno why clang 11 has it
> > on.
>
> It doesn't: https://godbolt.org/z/rU5_5H
>
> I assume this is caused by some sort of internal change to the 0day
> infrastructure (testing W=1?)
>
> I cannot see this without adding W=1 to make at the listed commit with
> the provided config.
>
> Cheers,
> Nathan
>
> > Anyway, something for Benni to fix. CCed and leaving the rest for him as
> > reference.
> >
> > > arch/x86/mm/init.c:75:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
> > > bool x86_has_pat_wp(void)
> > > ^
> > > static
> > > arch/x86/mm/init.c:866:13: warning: no previous prototype for function 'mem_encrypt_free_decrypted_mem' [-Wmissing-prototypes]
> > > void __weak mem_encrypt_free_decrypted_mem(void) { }
> > > ^
> > > arch/x86/mm/init.c:866:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
> > > void __weak mem_encrypt_free_decrypted_mem(void) { }
> > > ^
> > > static
> > > 2 warnings generated.
> > >
> > > vim +/x86_has_pat_wp +75 arch/x86/mm/init.c
> > >
> > >     73
> > >     74      /* Check that the write-protect PAT entry is set for write-protect */
> > >   > 75      bool x86_has_pat_wp(void)
> > >     76      {
> > >     77              return __pte2cachemode_tbl[_PAGE_CACHE_MODE_WP] == _PAGE_CACHE_MODE_WP;
> > >     78      }
> > >     79
> > >
> > > ---
> > > 0-DAY CI Kernel Test Service, Intel Corporation
> > > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
> >
> >
> >
> > --
> > Regards/Gruss,
> >     Boris.
> >
> > https://people.kernel.org/tglx/notes-about-netiquette
> >
>
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-- 
Thanks,
~Nick Desaulniers