linux-kernel - Re: [PATCH] Makefile: Add '-fno-builtin-bcmp' to CLANG

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Message-ID: <CAK8P3a206PXqaqv-B=S-4+sP04y5ZFkuP4XoN0bQNxrx56asKg@mail.gmail.com>
Date:   Wed, 13 Mar 2019 20:38:52 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        James Y Knight <jyknight@...gle.com>,
        clang-built-linux@...glegroups.com,
        "# 3.4.x" <stable@...r.kernel.org>
Subject: Re: [PATCH] Makefile: Add '-fno-builtin-bcmp' to CLANG_FLAGS

On Wed, Mar 13, 2019 at 6:27 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:

> > diff --git a/lib/string.c b/lib/string.c
> > index 38e4ca08e757..e6c1954f2716 100644
> > --- a/lib/string.c
> > +++ b/lib/string.c
> > @@ -845,7 +845,13 @@ void *memmove(void *dest, const void *src, size_t count)
> >  EXPORT_SYMBOL(memmove);
> >  #endif
> >
> > -#ifndef __HAVE_ARCH_MEMCMP
> > +#ifdef __HAVE_ARCH_MEMCMP
> > +int bcmp(const void *cs, const void *ct, size_t n)
> > +{
> > +       return memcmp(cs, ct, n);
> > +}
> > +EXPORT_SYMBOL(bcmp);
> > +#else
> >  /**
> >   * memcmp - Compare two areas of memory
> >   * @cs: One area of memory
> > @@ -864,6 +870,8 @@ __visible int memcmp(const void *cs, const void
> > *ct, size_t count)
> >         return res;
> >  }
> >  EXPORT_SYMBOL(memcmp);
> > +__weak __alias(memcmp) typeof(memcmp) bcmp;
> > +EXPORT_SYMBOL(bcmp);
> >  #endif
> >
> >  #ifndef __HAVE_ARCH_MEMSCAN
>
> Alternatively, just not worrying about __alias makes this simpler and
> seems to work (need to add comments, thoughts?):

Either way seems fine to me. If we don't plan to provide an
optimized version, I'd go with the simpler definition rather than
the alias.

       Arnd