Re: [PATCH v4 1/3] compiler-gcc.h: add gnu_inline to all inline declarations

From: Sedat Dilek <sedat.dilek@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-efi@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
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	tstellar@redhat.com, Kees Cook <keescook@google.com>,
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	Michal Marek <michal.lkml@markovi.net>,
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	Geert Uytterhoeven <geert@linux-m68k.org>,
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	Matthias Kaehlcke <mka@chromium.org>,
	"Lendacky, Thomas" <thomas.lendacky@amd.com>,
	Thiebaud Weksteen <tweek@google.com>,
	mjg59@google.com, Joe Perches <joe@perches.com>
Subject: Re: [PATCH v4 1/3] compiler-gcc.h: add gnu_inline to all inline declarations
Date: Fri, 8 Jun 2018 12:04:36 +0200	[thread overview]
Message-ID: <CA+icZUXDoeo5ktZZPFcFyLzk3xthM-98N88QJFzesg6t+Vr5cQ@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a0yi+MrOS=+pjCeUu==YBE_AppB8vfqdsQS-1NpSO2c4A@mail.gmail.com>

On Fri, Jun 8, 2018 at 9:59 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Thu, Jun 7, 2018 at 10:49 PM, Nick Desaulniers
> <ndesaulniers@google.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@google.com>
>> Suggested-by: H. Peter Anvin <hpa@zytor.com>
>> Suggested-by: Joe Perches <joe@perches.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.

- sed@ -