linux-kernel - [PATCH 4.9 26/42] kbuild: initialize CLANG

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Message-Id: <20190805124928.061617180@linuxfoundation.org>
Date:   Mon,  5 Aug 2019 15:02:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH 4.9 26/42] kbuild: initialize CLANG_FLAGS correctly in the top Makefile

From: Masahiro Yamada <yamada.masahiro@...ionext.com>

commit 5241ab4cf42d3a93b933b55d3d53f43049081fa1 upstream.

CLANG_FLAGS is initialized by the following line:

  CLANG_FLAGS     := --target=$(notdir $(CROSS_COMPILE:%-=%))

..., which is run only when CROSS_COMPILE is set.

Some build targets (bindeb-pkg etc.) recurse to the top Makefile.

When you build the kernel with Clang but without CROSS_COMPILE,
the same compiler flags such as -no-integrated-as are accumulated
into CLANG_FLAGS.

If you run 'make CC=clang' and then 'make CC=clang bindeb-pkg',
Kbuild will recompile everything needlessly due to the build command
change.

Fix this by correctly initializing CLANG_FLAGS.

Fixes: 238bcbc4e07f ("kbuild: consolidate Clang compiler flags")
Cc: <stable@...r.kernel.org> # v5.0+
Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Acked-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 Makefile |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/Makefile
+++ b/Makefile
@@ -400,6 +400,7 @@ KBUILD_AFLAGS_MODULE  := -DMODULE
 KBUILD_CFLAGS_MODULE  := -DMODULE
 KBUILD_LDFLAGS_MODULE := -T $(srctree)/scripts/module-common.lds
 GCC_PLUGINS_CFLAGS :=
+CLANG_FLAGS :=
 
 # Read KERNELRELEASE from include/config/kernel.release (if it exists)
 KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
@@ -506,7 +507,7 @@ endif
 
 ifeq ($(cc-name),clang)
 ifneq ($(CROSS_COMPILE),)
-CLANG_FLAGS	:= --target=$(notdir $(CROSS_COMPILE:%-=%))
+CLANG_FLAGS	+= --target=$(notdir $(CROSS_COMPILE:%-=%))
 GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
 CLANG_FLAGS	+= --prefix=$(GCC_TOOLCHAIN_DIR)
 GCC_TOOLCHAIN	:= $(realpath $(GCC_TOOLCHAIN_DIR)/..)