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

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Date:   Mon,  8 Feb 2021 17:57:20 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <nathan@...nel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH v2] arm64: Make CPU_BIG_ENDIAN depend on ld.bfd or ld.lld 13.0.0+

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>
---

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