linux-kernel - [PATCH 1/4] kbuild: remove LLVM=1 test from HAS_LTO

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Date:   Thu,  4 Mar 2021 03:33:30 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] kbuild: remove LLVM=1 test from HAS_LTO_CLANG

This guarding is wrong. As Documentation/kbuild/llvm.rst notes, LLVM=1
switches the default of tools, but you can still override CC, LD, etc.
individually.

BTW, LLVM is not 1/0 flag. If LLVM is not passed in, it is empty.

Non-zero return code is all treated as failure anyway.

So, $(success,test $(LLVM) -eq 1) and $(success,test "$(LLVM)" = 1)
works equivalently in the sense that both are expanded to 'n' if LLVM
is not given. The difference is that the former internally fails due
to syntax error.

  $ test ${LLVM} -eq 1
  bash: test: -eq: unary operator expected
  $ echo $?
  2

  $ test "${LLVM}" -eq 1
  bash: test: : integer expression expected
  $ echo $?
  2

  $ test "${LLVM}" = 1
  echo $?
  1

  $ test -n "${LLVM}"
  $ echo $?
  1

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 arch/Kconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 2bb30673d8e6..2af10ebe5ed0 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -632,7 +632,6 @@ config HAS_LTO_CLANG
 	def_bool y
 	# Clang >= 11: https://github.com/ClangBuiltLinux/linux/issues/510
 	depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD
-	depends on $(success,test $(LLVM) -eq 1)
 	depends on $(success,test $(LLVM_IAS) -eq 1)
 	depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
 	depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
-- 
2.27.0