linux-kernel - Re: [PATCH v2] arm64: Make CPU_BIG_ENDIAN depend on ld.bfd or ld.lld 13.0.0+

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Message-ID: <CAKwvOdkwoF8OqSY0mJbPh658N3QBPHARgiHP6K3H+=gPT6+R8g@mail.gmail.com>
Date:   Mon, 8 Feb 2021 17:39:16 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>,
        Fangrui Song <maskray@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2] arm64: Make CPU_BIG_ENDIAN depend on ld.bfd or ld.lld 13.0.0+

On Mon, Feb 8, 2021 at 4:58 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Similar to commit 28187dc8ebd9 ("ARM: 9025/1: Kconfig: CPU_BIG_ENDIAN
> depends on !LD_IS_LLD"), ld.lld prior to 13.0.0 does not properly
> support aarch64 big endian, leading to the following build error when
> CONFIG_CPU_BIG_ENDIAN is selected:
>
> ld.lld: error: unknown emulation: aarch64linuxb
>
> This has been resolved in LLVM 13. To avoid errors like this, only allow
> CONFIG_CPU_BIG_ENDIAN to be selected if using ld.bfd or ld.lld 13.0.0
> and newer.
>
> 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
> Link: https://github.com/llvm/llvm-project/commit/7605a9a009b5fa3bdac07e3131c8d82f6d08feb7
> Link: https://github.com/llvm/llvm-project/commit/eea34aae2e74e9b6fbdd5b95f479bc7f397bf387
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

LGTM, thanks for implementing BE support for aarch64 in LLD, Fangrui!
(And Nathan for the kernel patch+testing)
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>
> v1 -> v2:
>
> * Conditionally disable CONFIG_CPU_BIG_ENDIAN for older versions of
>   ld.lld now that proper support has been added to ld.lld 13+ (thanks to
>   the quick work of Fangrui Song).
>
>  arch/arm64/Kconfig | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index f39568b28ec1..912da4e2ab59 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 || LLD_VERSION >= 130000
> +       help
>           Say Y if you plan on running a kernel with a big-endian userspace.
>
>  config CPU_LITTLE_ENDIAN
>
> base-commit: 92bf22614b21a2706f4993b278017e437f7785b3
> --
> 2.30.1
>


-- 
Thanks,
~Nick Desaulniers