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From: Joel Stanley <joel@jms.id.au>
Date: Wed, 19 Sep 2018 17:15:46 +0930
Message-ID: <CACPK8XdF=orE8UtGu_K=p612L=iuDsnmrVrXJ6CNn6iDXi8znQ@mail.gmail.com>
Subject: Re: [PATCH v2 4/5] powerpc: Fix duplicate const clang warning in user
 access code
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: linuxppc-dev@lists.ozlabs.org, Anton Blanchard <anton@samba.org>,
 Anton Blanchard <anton@ozlabs.org>
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On Sat, 15 Sep 2018 at 03:27, Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> On Thu, Sep 13, 2018 at 9:07 PM Joel Stanley <joel@jms.id.au> wrote:
> >
> > From: Anton Blanchard <anton@samba.org>
> >
> > This re-applies b91c1e3e7a6f which was reverted in f2ca80905929
> > d466f6c5cac1 f84ed59a612d (powerpc/sparse: Constify the address pointer
> > ...").
> >
> > We see a large number of duplicate const errors in the user access
> > code when building with llvm/clang:
> >
> >   include/linux/pagemap.h:576:8: warning: duplicate 'const' declaration specifier
> >       [-Wduplicate-decl-specifier]
> >         ret = __get_user(c, uaddr);
> >
> > The problem is we are doing const __typeof__(*(ptr)), which will hit the
> > warning if ptr is marked const.
> >
> > Removing const does not seem to have any effect on GCC code generation.
>
> I wouldn't expect it to for a local variable with such localized
> usage.  I myself am quite liberal in applying `const` to everything,
> so I will try to fix this in Clang as well, but this should silence
> the warning for users of older versions of Clang and results in no
> functional change.
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

Nick has written a clang patch that suppresses the warning in the same
way as GCC. Assuming it gets merged, as we depend on clang-8 we could
chose to not merge the kernel patch.

https://reviews.llvm.org/D52248

Cheers,

Joel