linux-kernel - Re: clang asm-goto support (Was Re: [PATCH v2] x86/retpoline: Add clang support)

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Date:   Wed, 14 Feb 2018 19:39:55 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...gle.com>
Cc:     "Yatsina, Marina" <marina.yatsina@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Chandler Carruth <chandlerc@...gle.com>,
        "Kreitzer, David L" <david.l.kreitzer@...el.com>,
        "Grischenko, Andrei L" <andrei.l.grischenko@...el.com>,
        "rnk@...gle.com" <rnk@...gle.com>,
        LLVM Developers <llvm-dev@...ts.llvm.org>,
        "ehsan@...illa.com" <ehsan@...illa.com>,
        "Tayree, Coby" <coby.tayree@...el.com>,
        Matthias Braun <matze@...unis.de>,
        Dean Michael Berris <dean.berris@...il.com>,
        James Y Knight <jyknight@...gle.com>,
        Guenter Roeck <linux@...ck-us.net>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Rik van Riel <riel@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Paul Turner <pjt@...gle.com>,
        Stephen Hines <srhines@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: clang asm-goto support (Was Re: [PATCH v2] x86/retpoline: Add
 clang support)

On Wed, Feb 14, 2018 at 09:31:22AM -0800, Kees Cook wrote:
> On Wed, Feb 14, 2018 at 1:08 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > If you ever get to the point where it makes sense to build a kernel with
> > LLVM [...]
> 
> Just to speak to this point in particular: it makes sense to build
> kernels with LLVM right now. It's already happened; millions of Pixel
> 2 phones are already running with Clang-built kernels. And even if
> you're only interested in x86, that works too.

Only if you really don't care about performance. And as should be
evident from the rest of this thread, you soon won't be able to build
it anymore.