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    Subject[PATCH 5.4 121/138] Makefile: Fix GCC_TOOLCHAIN_DIR prefix for Clang cross compilation
    Date
    From: Fangrui Song <maskray@google.com>

    commit ca9b31f6bb9c6aa9b4e5f0792f39a97bbffb8c51 upstream.

    When CROSS_COMPILE is set (e.g. aarch64-linux-gnu-), if
    $(CROSS_COMPILE)elfedit is found at /usr/bin/aarch64-linux-gnu-elfedit,
    GCC_TOOLCHAIN_DIR will be set to /usr/bin/. --prefix= will be set to
    /usr/bin/ and Clang as of 11 will search for both
    $(prefix)aarch64-linux-gnu-$needle and $(prefix)$needle.

    GCC searchs for $(prefix)aarch64-linux-gnu/$version/$needle,
    $(prefix)aarch64-linux-gnu/$needle and $(prefix)$needle. In practice,
    $(prefix)aarch64-linux-gnu/$needle rarely contains executables.

    To better model how GCC's -B/--prefix takes in effect in practice, newer
    Clang (since
    https://github.com/llvm/llvm-project/commit/3452a0d8c17f7166f479706b293caf6ac76ffd90)
    only searches for $(prefix)$needle. Currently it will find /usr/bin/as
    instead of /usr/bin/aarch64-linux-gnu-as.

    Set --prefix= to $(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
    (/usr/bin/aarch64-linux-gnu-) so that newer Clang can find the
    appropriate cross compiling GNU as (when -no-integrated-as is in
    effect).

    Cc: stable@vger.kernel.org
    Reported-by: Nathan Chancellor <natechancellor@gmail.com>
    Signed-off-by: Fangrui Song <maskray@google.com>
    Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
    Tested-by: Nathan Chancellor <natechancellor@gmail.com>
    Tested-by: Nick Desaulniers <ndesaulniers@google.com>
    Link: https://github.com/ClangBuiltLinux/linux/issues/1099
    Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
    Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

    --- a/Makefile
    +++ b/Makefile
    @@ -528,7 +528,7 @@ ifneq ($(shell $(CC) --version 2>&1 | he
    ifneq ($(CROSS_COMPILE),)
    CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
    GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
    -CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)
    +CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
    GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..)
    endif
    ifneq ($(GCC_TOOLCHAIN),)

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