linux-kernel - Re: [PATCH v2 1/2] compiler-gcc.h: add gnu

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Date:   Thu, 7 Jun 2018 10:29:10 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     joe@...ches.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>, akataria@...are.com,
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        Cao jin <caoj.fnst@...fujitsu.com>,
        Greg KH <gregkh@...uxfoundation.org>, hpa@...or.com,
        "J. Kiszka" <jan.kiszka@...mens.com>,
        jarkko.sakkinen@...ux.intel.com, jgross@...e.com,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        kirill.shutemov@...ux.intel.com, mingo@...hat.com,
        mjg59@...gle.com, Matthias Kaehlcke <mka@...omium.org>,
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        rostedt@...dmis.org, Thomas Gleixner <tglx@...utronix.de>,
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        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        geert@...ux-m68k.org, Will Deacon <will.deacon@....com>,
        mawilcox@...rosoft.com, Arnd Bergmann <arnd@...db.de>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v2 1/2] compiler-gcc.h: add gnu_inline to all inline declarations

On Thu, Jun 7, 2018 at 10:26 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Tue, Jun 5, 2018 at 10:23 AM Joe Perches <joe@...ches.com> wrote:
> >
> > On Tue, 2018-06-05 at 10:05 -0700, Nick Desaulniers wrote:
> > > Functions marked extern inline do not emit an externally visible
> > > function when the gnu89 C standard is used. Some KBUILD Makefiles
> > > overwrite KBUILD_CFLAGS. This is an issue for GCC 5.1+ users as without
> > > an explicit C standard specified, the default is gnu11. Since c99, the
> > > semantics of extern inline have changed such that an externally visible
> > > function is always emitted. This can lead to multiple definition errors
> > > of extern inline functions at link time of compilation units whose build
> > > files have removed an explicit C standard compiler flag for users of GCC
> > > 5.1+ or Clang.
> > []
> > > diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> > []
> > > @@ -72,17 +72,24 @@
> > >   * -Wunused-function.  This turns out to avoid the need for complex #ifdef
> > >   * directives.  Suppress the warning in clang as well by using "unused"
> > >   * function attribute, which is redundant but not harmful for gcc.
> > > + * Prefer gnu_inline, so that extern inline functions do not emit an
> > > + * externally visible function. This makes extern inline behave as per gnu89
> > > + * semantics rather than c99. This prevents multiple symbol definition errors
> > > + * of extern inline functions at link time.
> > >   */
> > >  #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||             \
> > >      !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
> > > -#define inline inline                __attribute__((always_inline,unused)) notrace
> > > -#define __inline__ __inline__        __attribute__((always_inline,unused)) notrace
> > > -#define __inline __inline    __attribute__((always_inline,unused)) notrace
> > > +#define inline \
> > > +     inline __attribute__((always_inline, unused, gnu_inline)) notrace
> > > +#define __inline__ \
> > > +     __inline__ __attribute__((always_inline, unused, gnu_inline)) notrace
> > > +#define __inline \
> > > +     __inline __attribute__((always_inline, unused, gnu_inline)) notrace
> >
> > Perhaps these are simpler as
> >
> > #define __inline__      inline
> > #define __inline        inline
>
> Probably want:
>
> #define __inline__ __inline__ inline
> #define __inline __inline inline

Oh, never mind, if my changes to `inline` add the `inline` keyword,
then we can remove the redefinition __inline__ and __inline.  All that
to say your original suggestion is better than my follow up.
-- 
Thanks,
~Nick Desaulniers