linux-kernel - Re: [PATCH 2/3] kbuild: LD

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Date:   Mon, 14 Dec 2020 23:05:22 +0000
From:   Will Deacon <will@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/3] kbuild: LD_VERSION redenomination

On Sun, Dec 13, 2020 at 01:54:30AM +0900, Masahiro Yamada wrote:
> Commit ccbef1674a15 ("Kbuild, lto: add ld-version and ld-ifversion
> macros") introduced scripts/ld-version.sh for GCC LTO.
> 
> At that time, this script handled 5 version fields because GCC LTO
> needed the downstream binutils. (https://lkml.org/lkml/2014/4/8/272)
> 
> The code snippet from the submitted patch was as follows:
> 
>     # We need HJ Lu's Linux binutils because mainline binutils does not
>     # support mixing assembler and LTO code in the same ld -r object.
>     # XXX check if the gcc plugin ld is the expected one too
>     # XXX some Fedora binutils should also support it. How to check for that?
>     ifeq ($(call ld-ifversion,-ge,22710001,y),y)
>         ...
> 
> However, GCC LTO was not merged into the mainline after all.
> (https://lkml.org/lkml/2014/4/8/272)
> 
> So, the 4th and 5th fields were never used, and finally removed by
> commit 0d61ed17dd30 ("ld-version: Drop the 4th and 5th version
> components").
> 
> Since then, the last 4-digits returned by this script is always zeros.
> 
> Remove the meaningless last 4-digits. This makes the version format
> consistent with GCC_VERSION, CLANG_VERSION, LLD_VERSION.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
> 
>  arch/arm64/Kconfig            | 2 +-
>  arch/mips/loongson64/Platform | 2 +-
>  arch/mips/vdso/Kconfig        | 2 +-
>  arch/powerpc/Makefile         | 2 +-
>  arch/powerpc/lib/Makefile     | 2 +-
>  scripts/ld-version.sh         | 2 +-
>  6 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index a6b5b7ef40ae..69d56b21a6ec 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1499,7 +1499,7 @@ config ARM64_PTR_AUTH
>  	depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_PAC
>  	# Modern compilers insert a .note.gnu.property section note for PAC
>  	# which is only understood by binutils starting with version 2.33.1.
> -	depends on LD_IS_LLD || LD_VERSION >= 233010000 || (CC_IS_GCC && GCC_VERSION < 90100)
> +	depends on LD_IS_LLD || LD_VERSION >= 23301 || (CC_IS_GCC && GCC_VERSION < 90100)
>  	depends on !CC_IS_CLANG || AS_HAS_CFI_NEGATE_RA_STATE
>  	depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS)
>  	help

Acked-by: Will Deacon <will@...nel.org>

Will