linux-kernel - Re: [PATCH 0/8] s390: allow to build with llvm's integrated assembler

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Date:   Wed, 11 May 2022 13:52:13 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Jonas Paulsson <paulsson@...ux.vnet.ibm.com>,
        Ulrich Weigand <ulrich.weigand@...ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexander Egorenkov <egorenar@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Andreas Krebbel <krebbel@...ux.ibm.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 0/8] s390: allow to build with llvm's integrated assembler

Hi Heiko,

On Wed, May 11, 2022 at 02:05:24PM +0200, Heiko Carstens wrote:
> A couple of patches which in result make it finally possible to build the
> kernel for s390 with llvm's integrated assembler. Several configs build
> without errors or warnings, and the kernel also works as expected.
> 
> Note that patch 6 ("s390/boot: workaround llvm IAS bug") reveals a
> miscompile. This looks like a bug in the instruction definitions of the mvc
> and clc instructions(?). I'd like to ask people to look into this, since
> this silently generated broken code.

I think it should be pretty simple to file a bug report for this since
it occurs in a standalone assembly file? I agree with Nick that there
should be a bug report filed and linked to in patch 6 so that we don't
lose track of it.

> This patch series is based on linux-next, which contains two additional
> required s390 specific patches to make llvm's IAS work.
> 
> Thanks,
> Heiko
> 
> Heiko Carstens (8):
>   s390/alternatives: provide identical sized orginal/alternative sequences
>   s390/alternatives: remove padding generation code
>   s390/entry: shorten OUTSIDE macro
>   s390/entry: workaround llvm's IAS limitations
>   s390/purgatory: workaround llvm's IAS limitations
>   s390/boot: workaround llvm IAS bug
>   s390/boot: do not emit debug info for assembly with llvm's IAS
>   scripts/min-tool-version.sh: raise minimum clang version to 14.0.0 for s390
> 
>  arch/s390/Makefile                      |  2 +
>  arch/s390/boot/head.S                   | 34 +++++----
>  arch/s390/include/asm/alternative-asm.h | 76 +++-----------------
>  arch/s390/include/asm/alternative.h     | 93 ++++++-------------------
>  arch/s390/include/asm/spinlock.h        |  2 +-
>  arch/s390/kernel/alternative.c          | 61 +---------------
>  arch/s390/kernel/entry.S                | 39 +++++++----
>  arch/s390/lib/spinlock.c                |  4 +-
>  arch/s390/purgatory/head.S              | 29 ++++++--
>  scripts/min-tool-version.sh             |  3 +-
>  10 files changed, 104 insertions(+), 239 deletions(-)

I applied this series to the latest s390 for-next branch (c4fb15578802)
and built a few in-tree and distribution configurations with clang-14
and clang-15 then boot tested them in QEMU with a simple buildroot
userspace. I did not see any new warnings or errors. This is awesome, I
am excited to get this wired up in our CI!

In case it is worthwhile:

Tested-by: Nathan Chancellor <nathan@...nel.org>

Cheers,
Nathan