Hi Nick 2017-10-27 5:17 GMT+09:00 Nick Desaulniers <ndesaulni...@google.com>: > I was not seeing my linker flags getting added when using ld-option when > cross compiling with Clang. Upon investigation, this seems to be due to > a difference in how GCC vs Clang handle cross compilation. > > GCC is configured at build time to support one backend, that is implicit > when compiling. Clang is explicit via the use of `-target <triple>` and > ships with all supported backends by default. > > GNU Make feature test macros that compile then link will always fail > when cross compiling with Clang unless Clang's triple is passed along to > the compiler. For example: > > $ clang -x c /dev/null -c -o temp.o > $ aarch64-linux-android/bin/ld -E temp.o > aarch64-linux-android/bin/ld: > unknown architecture of input file `temp.o' is incompatible with > aarch64 output > aarch64-linux-android/bin/ld: > warning: cannot find entry symbol _start; defaulting to > 0000000000400078 > $ echo $? > 1 > > $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o > $ aarch64-linux-android/bin/ld -E temp.o > aarch64-linux-android/bin/ld: > warning: cannot find entry symbol _start; defaulting to 00000000004002e4 > $ echo $? > 0 > > This causes conditional checks that invoke $(CC) without the target > triple, then $(LD) on the result, to always fail. > > Signed-off-by: Nick Desaulniers <ndesaulni...@google.com> > Reviewed-by: Matthias Kaehlcke <m...@chromium.org> > --- > scripts/Kbuild.include | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include > index 9ffd3dda3889..23c4df90e8ff 100644 > --- a/scripts/Kbuild.include > +++ b/scripts/Kbuild.include > @@ -160,12 +160,12 @@ cc-if-fullversion = $(shell [ $(cc-fullversion) $(1) > $(2) ] && echo $(3) || echo > # cc-ldoption > # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both) > cc-ldoption = $(call try-run,\ > - $(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2)) > + $(CC) $(CLANG_TARGET) $(1) -nostdlib -x c /dev/null -o > "$$TMP",$(1),$(2)) > > # ld-option > # Usage: LDFLAGS += $(call ld-option, -X) > ld-option = $(call try-run,\ > - $(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o > "$$TMP",$(1),$(2)) > + $(CC) $(CLANG_TARGET) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) > "$$TMPO" -o "$$TMP",$(1),$(2)) > > # ar-option > # Usage: KBUILD_ARFLAGS := $(call ar-option,D) > --
I do not like to add $(CLANG_TARGET) to a place for common helpers. Instead of $(CLANG_TARGET), please add $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) to cc-ldoption and ld-option. I have two requests next time: - please include linux-kbu...@vger.kernel.org in your To list - please base your patch on linux-kbuild/kbuild branch The URL of the tree is described in MAINTAINERS. Thanks. -- Best Regards Masahiro Yamada
