linux-kernel - [PATCH v2 2/4] Makefile: clang: choose GCC_TOOLCHAIN

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Date:   Mon, 11 Feb 2019 11:30:04 -0800
From:   ndesaulniers@...gle.com
To:     yamada.masahiro@...ionext.com
Cc:     natechancellor@...il.com, sedat.dilek@...il.com,
        keescook@...omium.org, samitolvanen@...gle.com,
        michal.lkml@...kovi.net, akpm@...ux-foundation.org,
        hannes@...xchg.org, peterz@...radead.org,
        linux@...inikbrodowski.net, npiggin@...il.com,
        mathieu.desnoyers@...icios.com, gor@...ux.ibm.com, adrian@...as.de,
        rgb@...hat.com, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v2 2/4] Makefile: clang: choose GCC_TOOLCHAIN_DIR not on LD

This causes an issue when trying to build with `make LD=ld.lld` if
ld.lld and the rest of your cross tools aren't in the same directory
(ex. /usr/local/bin) (as is the case for Android's build system), as the
GCC_TOOLCHAIN_DIR then gets set based on `which $(LD)` which will point
where LLVM tools are, not GCC/binutils tools are located.

Instead, select the GCC_TOOLCHAIN_DIR based on another tool provided by
binutils for which LLVM does not provide a substitute for, such as
elfedit.

Fixes commit 785f11aa595b ("kbuild: Add better clang cross build support")

Link: https://github.com/ClangBuiltLinux/linux/issues/341
Suggested-by: Nathan Chancellor <natechancellor@...il.com>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Changes V1->V2:
* add reviewed and tested tags.

 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 86cf35d1d79d..d3b65e96d183 100644
--- a/Makefile
+++ b/Makefile
@@ -492,7 +492,7 @@ endif
 ifneq ($(shell $(CC) --version 2>&1 | head -n 1 | grep clang),)
 ifneq ($(CROSS_COMPILE),)
 CLANG_FLAGS	:= --target=$(notdir $(CROSS_COMPILE:%-=%))
-GCC_TOOLCHAIN_DIR := $(dir $(shell which $(LD)))
+GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
 CLANG_FLAGS	+= --prefix=$(GCC_TOOLCHAIN_DIR)
 GCC_TOOLCHAIN	:= $(realpath $(GCC_TOOLCHAIN_DIR)/..)
 endif
-- 
2.20.1.791.gb4d0f1c61a-goog