linux-kernel - Re: Clang patch stacks for LTS kernels (v4.4 and v4.9) and status update

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Date:   Sun, 6 May 2018 08:35:45 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     lkml <linux-kernel@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <nick.desaulniers@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: Clang patch stacks for LTS kernels (v4.4 and v4.9) and status update

On Mon, Apr 23, 2018 at 7:42 PM, Matthias Kaehlcke <mka@...omium.org> wrote:
[...]
>> [ ASM-GOTO ]
>>
>> Foremore, I have seen you have a "refs/sandbox/mka/llvm/v4.14" Git branch.
>> Linux v4.14 is also an LTS release.
>
> Yes, there is also a follow up post:
> https://lkml.org/lkml/2017/11/22/943
>
>> After Linux v4.9 "asm-goto" support was added which is GCC specific.
>
> asm-goto was optional until a few weeks ago, when x86 maintainers
> decided to make it mandatory, and thus break clang builds for x86:
>
> https://lkml.org/lkml/2018/4/2/486
>
>> Is there a workaround to compile Linux-kernel with any CLANG
>> version?
>
> You could revert the patch that makes asm-goto mandatory.
>
>> You happen to know the status in LLVM upstream?
>
> I know people are actively working on this, but don't know an ETA.
>

[ CC Dimitry ]

Sorry for the late response.
This weekend I had some time to play with clang-7 and Linux-4.17-rcN.

I tried with Linux v4.17-rc3-261-gc1c07416cdd4 and reverted the
mandatory patch [1].

commit e501ce957a786ecd076ea0cfb10b114e6e4d0f40
"x86: Force asm-goto"

This needed a follow up [2]...

commit d0266046ad54e0c964941364cd82a0d0478ce286
"x86: Remove FAST_FEATURE_TESTS"

...but breaks my build.

That seems to be a known issue [3] and Dimitry bisected this to [4].
Is there a fix for this?

I have attached my kernel-config and the broken build-log.

Hope this helps.

Regards,
- Sedat -

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e501ce957a786ecd076ea0cfb10b114e6e4d0f40
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/x86/include/asm/cpufeature.h?id=d0266046ad54e0c964941364cd82a0d0478ce286
[3] https://www.spinics.net/lists/linux-mm/msg147669.html
[4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8bf705d130396e69c04cd8e6e010244ad2ce71f4

Download attachment "config-4.17.0-rc3-261.1-iniza-llvmlinux" of type "application/octet-stream" (202847 bytes)

Download attachment "build-log_4.17.0-rc3-261.1-iniza-llvmlinux.txt.gz" of type "application/gzip" (34923 bytes)