[PATCH 5.4 121/138] Makefile: Fix GCC_TOOLCHAIN_DIR prefix for Clang cross compilation

From: Greg Kroah-Hartman
Date: Mon Jul 27 2020 - 10:33:15 EST

From: Fangrui Song <maskray@xxxxxxxxxx>

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
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

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/1099
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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 $(CROSS_COMPILE)elfedit))
ifneq ($(GCC_TOOLCHAIN),)