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

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Message-ID: <A3D6595E4CE1DA4A80538CC077C51A2B84771946@hasmsx107.ger.corp.intel.com>
Date:   Wed, 14 Feb 2018 10:07:43 +0000
From:   "Yatsina, Marina" <marina.yatsina@...el.com>
To:     Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Chandler Carruth <chandlerc@...gle.com>
CC:     Kees Cook <keescook@...gle.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "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>,
        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>,
        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)

I believe we do have the infrastructure in llvm to implement a working patch.
The "asm goto" was introduced as a solution to a problem (optimizing tracepoints/ nop patching).
When we started the discussion in llvm about adding this feature, questions arose if we can design a better solution for this problem than "asm goto".

You can find a more about the discussion in the llvm community here:
http://lists.llvm.org/pipermail/llvm-dev/2017-April/111748.html

* This is the middle of the thread, and there are more messages later on.

Thanks,
Marina

-----Original Message-----
From: Greg Kroah-Hartman [mailto:gregkh@...ux-foundation.org] 
Sent: Wednesday, February 14, 2018 11:53
To: Chandler Carruth <chandlerc@...gle.com>
Cc: Yatsina, Marina <marina.yatsina@...el.com>; Kees Cook <keescook@...gle.com>; David Woodhouse <dwmw2@...radead.org>; Kreitzer, David L <david.l.kreitzer@...el.com>; Grischenko, Andrei L <andrei.l.grischenko@...el.com>; rnk@...gle.com; LLVM Developers <llvm-dev@...ts.llvm.org>; 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>; 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>; 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 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.

Why is there any need to discuss "options" here?  What is preventing the implementation of "asm goto" in llvm?  Is it the lack of a working patch, or something else?

thanks,

greg k-h
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