Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 14 Feb 2018 11:44:08 +0100 (CET)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>
cc:     Chandler Carruth <chandlerc@google.com>,
        "Yatsina, Marina" <marina.yatsina@intel.com>,
        Kees Cook <keescook@google.com>,
        David Woodhouse <dwmw2@infradead.org>,
        "Kreitzer, David L" <david.l.kreitzer@intel.com>,
        "Grischenko, Andrei L" <andrei.l.grischenko@intel.com>,
        "rnk@google.com" <rnk@google.com>,
        LLVM Developers <llvm-dev@lists.llvm.org>,
        "ehsan@mozilla.com" <ehsan@mozilla.com>,
        "Tayree, Coby" <coby.tayree@intel.com>,
        Matthias Braun <matze@braunis.de>,
        Dean Michael Berris <dean.berris@gmail.com>,
        James Y Knight <jyknight@google.com>,
        Guenter Roeck <linux@roeck-us.net>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
        Rik van Riel <riel@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jiri Kosina <jikos@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linux-foundation.org>,
        Paul Turner <pjt@google.com>,
        Stephen Hines <srhines@google.com>,
        Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: clang asm-goto support (Was Re: [PATCH v2] x86/retpoline: Add
 clang support)
In-Reply-To: <20180214091042.GV25181@hirez.programming.kicks-ass.net>
Message-ID: <alpine.DEB.2.21.1802141030300.1292@nanos.tec.linutronix.de>
References: <CAGXu5j+7=61aY_Q4Zd4kRgovb07MYg9uej8B2KmdvZE3zPsbRw@mail.gmail.com> <A3D6595E4CE1DA4A80538CC077C51A2B84771848@hasmsx107.ger.corp.intel.com> <CAGCO0Kj01tAXdzRrL_p+LrTLK6-k-1-BFPm97jQMuJSPH7PTJQ@mail.gmail.com>
 <20180214091042.GV25181@hirez.programming.kicks-ass.net>
User-Agent: Alpine 2.21 (DEB 202 2017-01-01)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, 14 Feb 2018, Peter Zijlstra wrote:
> On Wed, Feb 14, 2018 at 08:41:43AM +0000, Chandler Carruth wrote:
> > Marina, Kees:
> > 
> > I think the combination of LKML and the LLVM developer's list is probably
> > too large a set of folks to have a (somewhat) lengthy exploration of
> > options and how to go about this and find a good path forward.
> 
> As one of the original authors of the jump-label implementation I'm
> saying there are no options. We're not going to do a second parallel
> implementation. If you want to build the kernel, you get to implement
> asm-goto, teh end.

Amen to that.

As x86 maintainer I'm really interested and willing to support llvm/clang
for x86 and the kernel in general, but asm-goto is not longer negotiable.

asm-goto is in the kernel since Oct 2010 and the relevant llvm/clang bug
#9295 is open since Feb 2011. All clang/llvm folks came up with in those 7
years is occasional handwaving about better solutions.

We really try to support old tools and tools which lack features for quite
a long time, but that's not a free pass for eternity.

That said, I'm not willing to wait another 7 years and I'm going to pull
the plug on compilers w/o asm-goto support soon whether llvm/clang gets
their act together or not.

Hint: GCC is not the only major compiler which supports asm-goto.

Thanks,

	tglx