lkml.org 
[lkml]   [2017]   [Oct]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v2] kbuild: fix linker feature test macros when cross compiling with Clang
2017-10-28 5:13 GMT+09:00 Nick Desaulniers <ndesaulniers@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.
>
> Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> Changes since v1:
> * base patch off of
> git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
> kbuild branch, per Masahiro.
> * Use $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) rather than $(CLANG_TRIPLE), per
> Masahiro.
>
> scripts/Kbuild.include | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 064f477dfdca..0f09e4508554 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -228,12 +228,13 @@ 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-cached,\
> - $(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
> + $(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
>
> # ld-option
> # Usage: LDFLAGS += $(call ld-option, -X)
> ld-option = $(call try-run-cached,\
> - $(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
> + $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c -o "$$TMPO"; \
> + $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
>
> # ar-option
> # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
> --
> 2.15.0.rc2.357.g7e34df9404-goog
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html


Applied to linux-kbuild/kbuild. Thanks!


--
Best Regards
Masahiro Yamada

\
 
 \ /
  Last update: 2017-10-28 20:22    [W:0.181 / U:0.176 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site