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

From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	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>,
	virtualization@lists.linux-foundation.org, astrachan@google.com,
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	Greg Hackmann <ghackmann@google.com>,
	tstellar@redhat.com, Kees Cook <keescook@google.com>,
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	Michal Marek <michal.lkml@markovi.net>,
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	Josh Poimboeuf <jpoimboe@redhat.com>,
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	"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 13:28:26 +0200	[thread overview]
Message-ID: <20180608112826.GA7484@andrea> (raw)
In-Reply-To: <CA+icZUXDoeo5ktZZPFcFyLzk3xthM-98N88QJFzesg6t+Vr5cQ@mail.gmail.com>

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@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?

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@ -