kbuild: allow to use GCC toolchain not in Clang search path

commit ef8c4ed9db80261f397f0c0bf723684601ae3b52 upstream.

When using a GCC cross toolchain which is not in a compiled in
Clang search path, Clang reverts to the system assembler and
linker. This leads to assembler or linker errors, depending on
which tool is first used for a given architecture.

It seems that Clang is not searching $PATH for a matching
assembler or linker.

Make sure that Clang picks up the correct assembler or linker by
passing the cross compilers bin directory as search path.

This allows to use Clang provided by distributions with GCC
toolchains not in /usr/bin.

Link: ClangBuiltLinux/linux#78
Signed-off-by: Stefan Agner <[email protected]>
Reviewed-and-tested-by: Nick Desaulniers <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>
[nc: Adjust context]
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: agners

Makefile

@@ -540,18 +540,16 @@ endif
 
 ifeq ($(cc-name),clang)
 ifneq ($(CROSS_COMPILE),)
-CLANG_TRIPLE	?= $(CROSS_COMPILE)
-CLANG_TARGET	:= --target=$(notdir $(CLANG_TRIPLE:%-=%))
-ifeq ($(shell $(srctree)/scripts/clang-android.sh $(CC) $(CLANG_TARGET)), y)
-$(error "Clang with Android --target detected. Did you specify CLANG_TRIPLE?")
-endif
-GCC_TOOLCHAIN	:= $(realpath $(dir $(shell which $(LD)))/..)
+CLANG_TARGET	:= --target=$(notdir $(CROSS_COMPILE:%-=%))
+GCC_TOOLCHAIN_DIR := $(dir $(shell which $(LD)))
+CLANG_PREFIX	:= --prefix=$(GCC_TOOLCHAIN_DIR)
+GCC_TOOLCHAIN	:= $(realpath $(GCC_TOOLCHAIN_DIR)/..)
 endif
 ifneq ($(GCC_TOOLCHAIN),)
 CLANG_GCC_TC	:= --gcc-toolchain=$(GCC_TOOLCHAIN)
 endif
-KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC)
-KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC)
+KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX)
+KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX)
 KBUILD_CFLAGS += $(call cc-option, -no-integrated-as)
 KBUILD_AFLAGS += $(call cc-option, -no-integrated-as)
 endif