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

[Yatsina, Marina]

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@xxxxxxxxxx] 
Sent: Wednesday, February 14, 2018 02:29
To: David Woodhouse <dwmw2@xxxxxxxxxxxxx>; Chandler Carruth <chandlerc@xxxxxxxxxx>; Yatsina, Marina <marina.yatsina@xxxxxxxxx>
Cc: 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>; Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxxx>; Paul Turner <pjt@xxxxxxxxxx>; Stephen Hines <srhines@xxxxxxxxxx>; Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
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@xxxxxxxxxxxxx> 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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