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Subject: Re: [PATCH 2/2] Kbuild: lto: add make version checking
To:     Lecopzer Chen <lecopzer.chen@mediatek.com>, keescook@chromium.org,
        samitolvanen@google.com, linux-kbuild@vger.kernel.org
Cc:     clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org,
        yj.chiang@mediatek.com, masahiroy@kernel.org,
        michal.lkml@markovi.net
References: <20210630121436.19581-1-lecopzer.chen@mediatek.com>
 <20210630121436.19581-3-lecopzer.chen@mediatek.com>
From:   Nathan Chancellor <nathan@kernel.org>
Message-ID: <6d687b9a-c295-ce8b-9472-d2859977be2d@kernel.org>
Date:   Wed, 30 Jun 2021 10:08:48 -0700
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On 6/30/2021 5:14 AM, Lecopzer Chen wrote:
> LTO with MODVERSION will fail in generating correct CRC because
> the makefile rule doesn't work for make with version 3.8X.[1]
> 
> Thus we need to check make version during selecting on LTO Kconfig.
> and the suitable version should be 4.2(40200) which release in 2016[2].
> 
> [1] https://lore.kernel.org/lkml/20210616080252.32046-1-lecopzer.chen@mediatek.com/
> [2] https://ftp.gnu.org/gnu/make/
> Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
> ---
>   arch/Kconfig | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index c45b770d3579..1571957bade5 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -632,6 +632,7 @@ config HAS_LTO_CLANG
>   	def_bool y
>   	# Clang >= 11: https://github.com/ClangBuiltLinux/linux/issues/510
>   	depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD && AS_IS_LLVM
> +	depends on MAKE_VERSION_INT >= 40200

If the bug depends on CONFIG_MODVERSIONS, should this be

depends on !MODVERSIONS || MAKE_VERSION >= 40200

? Especially since the problematic block in your original report is 
gated on CONFIG_LTO_CLANG + CONFIG_MODVERSIONS.

>   	depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
>   	depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
>   	depends on ARCH_SUPPORTS_LTO_CLANG
>