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    Subject[PATCH 4.9 26/42] kbuild: initialize CLANG_FLAGS correctly in the top Makefile
    Date
    From: Masahiro Yamada <yamada.masahiro@socionext.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@vger.kernel.org> # v5.0+
    Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
    Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
    Acked-by: Nick Desaulniers <ndesaulniers@google.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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)/..)

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