linux-kernel - Re: [PATCH v2 2/5] kbuild: implement {gcc,clang}-min-version only with built-in functions

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Message-ID: <Y36Ef3ie05YO1moS@bergen.fjasle.eu>
Date:   Wed, 23 Nov 2022 21:37:19 +0100
From:   Nicolas Schier <nicolas@...sle.eu>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, llvm@...ts.linux.dev
Subject: Re: [PATCH v2 2/5] kbuild: implement {gcc,clang}-min-version only
 with built-in functions

On Thu 24 Nov 2022 00:18:25 GMT, Masahiro Yamada wrote:
> Converting clang-min-version is straightforward because the versions
> are always 6-digit.
> 
> gcc-min-version is somewhat tricky because the minimal GCC version
> is GCC 5.2; prepend '0' to the version that is less than 10 so that
> test-ge is always passed with 6-digit versions.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
> 
> Changes in v2:
>   - Covert gcc-min-version in a different way
> 
>  scripts/Makefile.compiler | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
> index 20d353dcabfb..cd75f81e88ef 100644
> --- a/scripts/Makefile.compiler
> +++ b/scripts/Makefile.compiler
> @@ -63,11 +63,15 @@ cc-disable-warning = $(call try-run,\
>  
>  # gcc-min-version
>  # Usage: cflags-$(call gcc-min-version, 70100) += -foo
> -gcc-min-version = $(shell [ $(CONFIG_GCC_VERSION)0 -ge $(1)0 ] && echo y)
> +
> +# Preprend 0 to the version that is less than 10 so test-ge works.
> +gcc-min-version = $(call test-ge, \
> +                  $(or $(filter 1%, $(CONFIG_GCC_VERSION)), 0$(CONFIG_GCC_VERSION)), \
> +                  $(or $(filter 1%, $1), 0$(strip $1)))

Hm, this silently expects a gcc version < 20, which we should expect in 
about seven-eight years [1].   I am thinking about the possibility of 
silent (but unlikely) breaks when someone in far future uses a gcc 20 
against a kernel with this line.  Probably we should not care about 
that today, yet, right?

Reviewed-by: Nicolas Schier <nicolas@...sle.eu>

[1]: https://gcc.gnu.org/develop.html#timeline

>  
>  # clang-min-version
>  # Usage: cflags-$(call clang-min-version, 110000) += -foo
> -clang-min-version = $(shell [ $(CONFIG_CLANG_VERSION)0 -ge $(1)0 ] && echo y)
> +clang-min-version = $(call test-ge, $(CONFIG_CLANG_VERSION), $1)
>  
>  # ld-option
>  # Usage: KBUILD_LDFLAGS += $(call ld-option, -X, -Y)
> -- 
> 2.34.1

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