linux-kernel - Re: [PATCH v4 1/3] compiler-gcc.h: add gnu

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Date:   Fri, 8 Jun 2018 13:28:26 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-efi@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        virtualization@...ts.linux-foundation.org, astrachan@...gle.com,
        Manoj Gupta <manojgupta@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>, tstellar@...hat.com,
        Kees Cook <keescook@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Will Deacon <will.deacon@....com>, mawilcox@...rosoft.com,
        David Rientjes <rientjes@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        akataria@...are.com, Brijesh Singh <brijesh.singh@....com>,
        Cao jin <caoj.fnst@...fujitsu.com>,
        gregkh <gregkh@...uxfoundation.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        "Lendacky, Thomas" <thomas.lendacky@....com>,
        Thiebaud Weksteen <tweek@...gle.com>, mjg59@...gle.com,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v4 1/3] compiler-gcc.h: add gnu_inline to all inline
 declarations

On Fri, Jun 08, 2018 at 12:04:36PM +0200, Sedat Dilek wrote:
> On Fri, Jun 8, 2018 at 9:59 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Thu, Jun 7, 2018 at 10:49 PM, Nick Desaulniers
> > <ndesaulniers@...gle.com> 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.
> >>
> >> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> >> Suggested-by: H. Peter Anvin <hpa@...or.com>
> >> Suggested-by: Joe Perches <joe@...ches.com>
> >
> > I suspect this will break Geert's gcc-4.1.2, which I think doesn't have that
> > attribute yet (4.1.3 or higher have it according to the documentation.
> >
> > It wouldn't be hard to work around that if we want to keep that version
> > working, or we could decide that it's time to officially stop supporting
> > that version, but we should probably decide on one or the other.
> >
> 
> Good point.
> What is the minimum requirement of GCC version currently?

Good question ;-)  (I recently had the impression that
Documentation/process/changes.rst was making fun of me ;-)


> AFAICS x86/asm-goto support requires GCC >= 4.5?
> 
> Just FYI...
> ...saw the last days in upstream commits that kbuild/kconfig for
> 4.18-rc1 offers possibilities to check for cc-version dependencies.

Good to know!  Mind retrieving/sharing the commit id(s)
or links to the corresponding discussion on LKML?

Thanks,
  Andrea


> 
> - sed@ -