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 14:25:41 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     kbuild test robot <lkp@...el.com>, Christoph Hellwig <hch@....de>,
        kbuild-all@...ts.01.org, clang-built-linux@...glegroups.com,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Benjamin Thiel <b.thiel@...teo.de>
Subject: Re: [tip:x86/mm 1/23] arch/x86/mm/init.c:75:6: warning: no previous
 prototype for function 'x86_has_pat_wp'

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
>