lkml.org 
[lkml]   [2017]   [Oct]   [30]   [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
    2017-10-29 0:00 GMT+09:00 Masahiro Yamada <yamada.masahiro@socionext.com>:
    > 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!



    I do not know the cause of the problem reported by the 0-day bot, but
    if the problem happens in the following line,

    ifeq ($(CONFIG_X86_32),y)
    LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
    else



    Does the following solve the issue? (adding $(LDFLAGS))

    ld-option = $(call try-run,\
    $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c
    -o "$$TMPO"; \
    $(LD) $(LDFLAGS) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))




    --
    Best Regards
    Masahiro Yamada

    \
     
     \ /
      Last update: 2017-10-30 07:52    [W:3.435 / U:0.612 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site