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

Nick Desaulniers
2021-02-09T01:42:23Z

On Mon, Feb 8, 2021 at 4:58 PM Nathan Chancellor <nathan@kernel.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@arndb.de>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

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