Re: [PATCH 2/2] kbuild: simplify ld-option implementation

[Nick Desaulniers <ndesaulniers@google.com>]

Nice! Now we don't need to invoke $CC to find out info about linker support.

Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

On Thu, Feb 22, 2018 at 8:57 PM Masahiro Yamada <
yamada.masahiro@socionext.com> wrote:

> Currently, linker options are tested by the coordination of $(CC) and
> $(LD) because LD needs some object to link.

> As commit 86a9df597cdd ("kbuild: fix linker feature test macros when
> cross compiling with Clang") addressed, we need to make sure $(CC)
> and $(LD) agree the underlying architecture of the passed object.

> This could be a bit complex when we combine tools from different groups.
> For example, we can use clang for $(CC), but we still need to rely on
> GCC toolchain for $(LD).

> So, I was searching a way for standalone testing of linker options.
> A trick I found is to use '-v'.  This prints the version string, but
> also tests if the given option is recognized.

> If a given option is supported,

>    $ aarch64-linux-gnu-ld -v --fix-cortex-a53-843419
>    GNU ld (Linaro_Binutils-2017.11) 2.28.2.20170706
>    $ echo $?
>    0

> If unsupported,

>    $ aarch64-linux-gnu-ld -v --fix-cortex-a53-843419
>    GNU ld (crosstool-NG linaro-1.13.1-4.7-2013.04-20130415 - Linaro GCC
> 2013.04) 2.23.1
>    aarch64-linux-gnu-ld: unrecognized option '--fix-cortex-a53-843419'
>    aarch64-linux-gnu-ld: use the --help option for usage information
>    $ echo $?
>    1

> Gold works likewise.

>    $ aarch64-linux-gnu-ld.gold -v --fix-cortex-a53-843419
>    GNU gold (Linaro_Binutils-2017.11 2.28.2.20170706) 1.14
>    masahiro@pug:~/ref/linux$ echo $?
>    0
>    $ aarch64-linux-gnu-ld.gold -v --fix-cortex-a53-999999
>    GNU gold (Linaro_Binutils-2017.11 2.28.2.20170706) 1.14
>    aarch64-linux-gnu-ld.gold: --fix-cortex-a53-999999: unknown option
>    aarch64-linux-gnu-ld.gold: use the --help option for usage information
>    $ echo $?
>    1

> LLD too.

>    $ ld.lld -v --gc-sections
>    LLD 7.0.0 (http://llvm.org/git/lld.git
> 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers)
>    $ echo $?
>    0
>    $ ld.lld -v --fix-cortex-a53-843419
>    LLD 7.0.0 (http://llvm.org/git/lld.git
> 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers)
>    $ echo $?
>    0
>    $ ld.lld -v --fix-cortex-a53-999999
>    ld.lld: error: unknown argument: --fix-cortex-a53-999999
>    LLD 7.0.0 (http://llvm.org/git/lld.git
> 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers)
>    $ echo $?
>    1

> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---

>   scripts/Kbuild.include | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)

> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 34cbd81..f9c2f07 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -237,9 +237,7 @@ cc-ldoption = $(call try-run-cached,\

>   # ld-option
>   # Usage: LDFLAGS += $(call ld-option, -X)
> -ld-option = $(call try-run-cached,\
> -       $(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c -o
> "$$TMPO"; \
> -       $(LD) $(LDFLAGS) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
> +ld-option = $(call try-run-cached, $(LD) $(LDFLAGS) $(1) -v,$(1),$(2))

>   # ar-option
>   # Usage: KBUILD_ARFLAGS := $(call ar-option,D)
> --
> 2.7.4



-- 
Thanks,
~Nick Desaulniers