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

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Message-ID: <A3D6595E4CE1DA4A80538CC077C51A2B84771848@hasmsx107.ger.corp.intel.com>
Date:   Wed, 14 Feb 2018 08:33:39 +0000
From:   "Yatsina, Marina" <marina.yatsina@...el.com>
To:     Kees Cook <keescook@...gle.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>,
        "Yatsina, Marina" <marina.yatsina@...el.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>
CC:     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>,
        Peter Zijlstra <peterz@...radead.org>,
        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)

Hi Kees,

When I raised the question of whether we want to add support for "asm goto" in llvm I got some feedback from the community that "asm goto" might not be the best solution for the problem it was invented for (optimizing support for tracepoints), so I stopped perusing this issue.
I'm CC-ing the developers that participated in the original thread and a few developers that might be interested in adding support of "asm goto".
I'm also adding the llvm-dev mailing list, in case there are additional parties interested in voicing their opinion.

I hope this will give this issue a push forward and we will find a solution that will not prevent llvm from compiling linux kernel.

Thanks,
Marina

-----Original Message-----
From: Kees Cook [mailto:keescook@...gle.com] 
Sent: Wednesday, February 14, 2018 02:29
To: David Woodhouse <dwmw2@...radead.org>; Chandler Carruth <chandlerc@...gle.com>; Yatsina, Marina <marina.yatsina@...el.com>
Cc: 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>; Peter Zijlstra <peterz@...radead.org>; 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: clang asm-goto support (Was Re: [PATCH v2] x86/retpoline: Add clang support)

On Tue, Feb 13, 2018 at 4:10 PM, David Woodhouse <dwmw2@...radead.org> wrote:
> We also need to resolve the asm-goto thing.

Yes, this is becoming much more urgent, assuming we'll be raising the minimum GCC version soon and drop support for lacking asm-goto...

Do you happen to know who the right people are to include to move the discussion forward? I know various kernel folks that are passionate about it, but I'm still getting to know who to talk with from llvm.

I see an earlier thread here:
http://lists.llvm.org/pipermail/llvm-dev/2017-April/111748.html

It seems to end there? I'm still coming up to speed on it, so I'm likely missing other context.

-Kees

--
Kees Cook
Pixel Security
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