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

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Date:   Wed, 11 May 2022 12:48:34 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
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>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 0/8] s390: allow to build with llvm's integrated assembler

On Wed, May 11, 2022 at 5:05 AM Heiko Carstens <hca@...ux.ibm.com> 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.
>
> This patch series is based on linux-next, which contains two additional
> required s390 specific patches to make llvm's IAS work.

I did a quick test of just a defconfig via:
$ ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- make CC=clang -j72 defconfig all
and this assembled then booted in qemu for me. Thanks for the work
that went into this!

Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

Sounds like Nathan is doing additional testing as well.

>
> 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(-)
>
> --
> 2.32.0
>


-- 
Thanks,
~Nick Desaulniers