linux-kernel - Re: [PATCH] ARM: do not assemble iwmmxt.S with LLVM toolchain

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Date:   Fri, 10 Apr 2020 08:38:05 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Jian Cai <caij2003@...il.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>, manojgupta@...gle.com,
        Peter.Smith@....com, stefan@...er.ch, samitolvanen@...gle.com,
        ilie.halip@...il.com, jiancai@...gle.com,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Doug Anderson <armlinux@...isordat.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        David Howells <dhowells@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] ARM: do not assemble iwmmxt.S with LLVM toolchain

On Fri, Apr 10, 2020 at 1:28 AM Jian Cai <caij2003@...il.com> wrote:
>
> iwmmxt.S contains XScale instructions LLVM ARM backend does not support.
> Skip this file if LLVM integrated assemmbler or LLD is used to build ARM
> kernel.
>
> Signed-off-by: Jian Cai <caij2003@...il.com>
> ---
>  arch/arm/Kconfig | 2 +-
>  init/Kconfig     | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 66a04f6f4775..39de8fc64a73 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -804,7 +804,7 @@ source "arch/arm/mm/Kconfig"
>
>  config IWMMXT
>         bool "Enable iWMMXt support"
> -       depends on CPU_XSCALE || CPU_XSC3 || CPU_MOHAWK || CPU_PJ4 || CPU_PJ4B
> +       depends on !AS_IS_CLANG && !LD_IS_LLD && (CPU_XSCALE || CPU_XSC3 || CPU_MOHAWK || CPU_PJ4 || CPU_PJ4B)
>         default y if PXA27x || PXA3xx || ARCH_MMP || CPU_PJ4 || CPU_PJ4B
>         help
>           Enable support for iWMMXt context switching at run time if
> diff --git a/init/Kconfig b/init/Kconfig
> index 1c12059e0f7e..b0ab3271e900 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -19,6 +19,12 @@ config GCC_VERSION
>  config CC_IS_CLANG
>         def_bool $(success,$(CC) --version | head -n 1 | grep -q clang)
>
> +config AS_IS_CLANG
> +       def_bool $(success,$(AS) --version | head -n 1 | grep -q clang)
> +
> +config LD_IS_LLD
> +       def_bool $(success,$(LD) --version | head -n 1 | grep -q LLD)
> +
>  config CLANG_VERSION
>         int
>         default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
> --
> 2.26.0.110.g2183baf09c-goog

Yesterday, when looking trough commits in Linus tree, I saw:

"init/kconfig: Add LD_VERSION Kconfig"

Nick had a patchset to distinguish LINKER via Kconfig (I cannot find
it right now).

So we should do all this the way CC_IS_XXX CC_VERSION handling is done.

I just want to point to [2] where we can rework (simplify) this
handling for CC and LD handling in a further step.
In one of Peter Z. tree someone started to do so (I was inspired by that).

Unfortunately, the hunk from [1] is IMHO a bit mis-placed and CC and
LD handling should stay together:

CC_IS_XXX where XXX is GCC or CLANG
CC_VERSION where CC is GCC or CLANG

LD_IS_XXX where XXX is BFD or GOLD or LLD
LD_VERSION

Just my €0,02.

Regards,
- Sedat -

[1] https://git.kernel.org/linus/9553d16fa671b9621c5e2847d08bd90d3be3349c
[2] https://github.com/ClangBuiltLinux/linux/issues/941