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

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Date:   Mon, 26 Feb 2018 23:22:58 +0000
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, sam@...nborg.org,
        Matthias Kaehlcke <mka@...omium.org>,
        Cao jin <caoj.fnst@...fujitsu.com>,
        Mark Charlebois <charlebm@...il.com>, forney@...gle.com,
        LKML <linux-kernel@...r.kernel.org>,
        Doug Anderson <dianders@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 2/2] kbuild: simplify ld-option implementation

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

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

On Thu, Feb 22, 2018 at 8:57 PM Masahiro Yamada <
yamada.masahiro@...ionext.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@...ionext.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