linux-kernel - Re: [PATCH] arm64: Make CPU_BIG_ENDIAN depend on !LD_IS_LLD

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Message-ID: <20210207023041.GA655027@ubuntu-m3-large-x86>
Date:   Sat, 6 Feb 2021 19:30:41 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: Make CPU_BIG_ENDIAN depend on !LD_IS_LLD

On Mon, Feb 01, 2021 at 07:24:42PM -0700, Nathan Chancellor wrote:
> Similar to commit 28187dc8ebd9 ("ARM: 9025/1: Kconfig: CPU_BIG_ENDIAN
> depends on !LD_IS_LLD"), ld.lld does not support aarch64 big endian,
> leading to the following build error when CONFIG_CPU_BIG_ENDIAN is
> selected:
> 
> ld.lld: error: unknown emulation: aarch64linuxb
> 
> There are not currently plans to implement big endian support for
> aarch64 in ld.lld but if it should be supported in the future, this
> symbol can depend on the version that first supports it. In the
> meantime, prevent this symbol from being selected to avoid these type
> of build errors.
> 
> While we are here, the indentation of this symbol used spaces since its
> introduction in commit a872013d6d03 ("arm64: kconfig: allow
> CPU_BIG_ENDIAN to be selected"). Change it to tabs to be consistent with
> kernel coding style.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/380
> Link: https://github.com/ClangBuiltLinux/linux/issues/1288
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Fangrui has pushed proper aarch64linuxb and elf64-bigaarch64 for ld.lld:

https://reviews.llvm.org/D96211
https://reviews.llvm.org/D96188

This patch is needed for OUTPUT_FORMAT in the vDSO to work properly:

https://reviews.llvm.org/D96214

Once these are all merged into LLVM 13, I will update this to be:

depends on !LD_IS_LLD || LLD_VERSION >= 130000

Cheers,
Nathan

> ---
>  arch/arm64/Kconfig | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index f39568b28ec1..5ddf9fe7b4ee 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -952,8 +952,9 @@ choice
>  	  that is selected here.
>  
>  config CPU_BIG_ENDIAN
> -       bool "Build big-endian kernel"
> -       help
> +	bool "Build big-endian kernel"
> +	depends on !LD_IS_LLD
> +	help
>  	  Say Y if you plan on running a kernel with a big-endian userspace.
>  
>  config CPU_LITTLE_ENDIAN
> 
> base-commit: 88bb507a74ea7d75fa49edd421eaa710a7d80598
> -- 
> 2.30.0
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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