linux-kernel - Re: [PATCH] LoongArch: Error out if clang version is less than 17.0.0

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Date:   Wed, 2 Aug 2023 10:45:53 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        loongarch@...ts.linux.dev, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: Error out if clang version is less than 17.0.0

Hi,

On Tue, Aug 1, 2023 at 9:40 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Hi Tiezhu,
>
> On Tue, Aug 01, 2023 at 02:30:46PM +0800, Tiezhu Yang wrote:
> > On my test machine, the clang version is 16.0.4, when build kernel
> > with clang:
> >
> >   make CC=clang loongson3_defconfig
> >   make CC=clang
> >
> > there exist many errors such as:
> >
> >   clang-16: error: argument unused during compilation: '-mabi=lp64s'
> >   error: unknown register name 'a0' in asm
> >   error: unknown register name 't0' in asm
> >
> > the above issues have been fixed in the upstream llvm project recently,
> > it works well when update clang version to 17.0.0:
> >
> >   make CC=clang loongson3_defconfig
> >   make CC=clang menuconfig (set CONFIG_MODULES=n and CONFIG_RELOCATABLE=n)
> >   make CC=clang
> >
> > thus 17.0.0 is the minimal clang version to build kernel on LoongArch,
> > it is better to error out if clang version is less than 17.0.0, then
> > we can do the right thing to update clang version and avoid wasting
> > time to analysis kernel errors.
> >
> > By the way, the clang 17.0.0 still have some issues to build kernel on
> > LoongArch, you need to unset CONFIG_MODULES and CONFIG_RELOCATABLE to
> > avoid build errors. Additionally, if you want a workable kernel, some
> > modules should be set as y instead of m if CONFIG_MODULES=n.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1787
> > Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> > ---
> >  arch/loongarch/Makefile | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> > index b1e5db5..f07f62a 100644
> > --- a/arch/loongarch/Makefile
> > +++ b/arch/loongarch/Makefile
> > @@ -10,6 +10,12 @@ KBUILD_DEFCONFIG := loongson3_defconfig
> >  image-name-y                 := vmlinux
> >  image-name-$(CONFIG_EFI_ZBOOT)       := vmlinuz
> >
> > +ifdef CONFIG_CC_IS_CLANG
> > +  ifneq ($(call clang-min-version, 170000),y)
> > +    $(error Sorry, you need a newer clang version >= 17.0.0)
> > +  endif
> > +endif
> > +
>
> Thanks for the patch! I agree that we should restrict LoongArch to LLVM
> 17 and newer. However, there is already existing infrastructure for this
> type of check in Kconfig, so we don't need to add anything to
> arch/loongarch. Just modify scripts/min-tool-version.sh like so then
> there will be a message during configuration time that the compiler is
> too old.
>
> diff --git a/scripts/min-tool-version.sh b/scripts/min-tool-version.sh
> index 2ade63149466..572c0526ad61 100755
> --- a/scripts/min-tool-version.sh
> +++ b/scripts/min-tool-version.sh
> @@ -26,6 +26,8 @@ gcc)
>  llvm)
>         if [ "$SRCARCH" = s390 ]; then
>                 echo 15.0.0
> +       elif [ "$SRCARCH" = loongarch ]; then
> +               echo 17.0.0
>         else
>                 echo 11.0.0
>         fi
>
> ***
> *** C compiler is too old.
> ***   Your Clang version:    16.0.6
> ***   Minimum Clang version: 17.0.0
> ***
> scripts/Kconfig.include:44: Sorry, this C compiler is not supported.
This method is better, but since Clang17 cannot build a
full-functional kernel (CONFIG_MODULES, may be solved in Clang18), I
suggest "fix" it in future until all features can be enabled.

Huacai
>
> >  ifndef CONFIG_EFI_STUB
> >  KBUILD_IMAGE := $(boot)/vmlinux.elf
> >  else
> > --
> > 2.1.0
> >
> >
>
> Cheers,
> Nathan