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

[Yatsina, Marina]

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@xxxxxxxxxxxxxxxxxxxx] 
Sent: Wednesday, February 14, 2018 11:53
To: Chandler Carruth <chandlerc@xxxxxxxxxx>
Cc: Yatsina, Marina <marina.yatsina@xxxxxxxxx>; Kees Cook <keescook@xxxxxxxxxx>; David Woodhouse <dwmw2@xxxxxxxxxxxxx>; Kreitzer, David L <david.l.kreitzer@xxxxxxxxx>; Grischenko, Andrei L <andrei.l.grischenko@xxxxxxxxx>; rnk@xxxxxxxxxx; LLVM Developers <llvm-dev@xxxxxxxxxxxxxx>; ehsan@xxxxxxxxxxx; Tayree, Coby <coby.tayree@xxxxxxxxx>; Matthias Braun <matze@xxxxxxxxxx>; Dean Michael Berris <dean.berris@xxxxxxxxx>; James Y Knight <jyknight@xxxxxxxxxx>; Guenter Roeck <linux@xxxxxxxxxxxx>; X86 ML <x86@xxxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>; Alan Cox <gnomes@xxxxxxxxxxxxxxxxxxx>; Rik van Riel <riel@xxxxxxxxxx>; Andi Kleen <ak@xxxxxxxxxxxxxxx>; Josh Poimboeuf <jpoimboe@xxxxxxxxxx>; Tom Lendacky <thomas.lendacky@xxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>; Jiri Kosina <jikos@xxxxxxxxxx>; Andy Lutomirski <luto@xxxxxxxxxxxxxx>; Hansen, Dave <dave.hansen@xxxxxxxxx>; Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>; Paul Turner <pjt@xxxxxxxxxx>; Stephen Hines <srhines@xxxxxxxxxx>; Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
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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