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

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Date:   Fri, 8 Jun 2018 12:04:36 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     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 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?
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.

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