linux-kernel - Re: [PATCH v2 3/4] Makefile: lld: tell clang to use lld

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Message-ID: <CAK7LNATZY-K4g81LLvXpjp=+oMSY8L0wQoVXgHt-Bjrb2WXnNg@mail.gmail.com>
Date:   Wed, 13 Feb 2019 23:58:18 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Nicholas Piggin <npiggin@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Adrian Reber <adrian@...as.de>,
        Richard Guy Briggs <rgb@...hat.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] Makefile: lld: tell clang to use lld

On Tue, Feb 12, 2019 at 5:42 AM <ndesaulniers@...gle.com> wrote:
>
> This is needed because clang doesn't select which linker to use based on
> $LD but rather -fuse-ld=lld. This is problematic especially for
> cc-ldoption, which checks for linker flag support via invoking the
> compiler, rather than the linker.


Sorry, please explain what kind of problem
this patch solves.



[1] $(LD) is used to link vmlinux, modules, etc.

[2] $(CC) is used to link vdso, etc.
    and -fuse-ld= selects which linker is invoked from $(CC)


Is it a problem to use a different
type of linker for [1] and [2] ?


Thanks.





> Link: https://github.com/ClangBuiltLinux/linux/issues/342
> Suggested-by: Nathan Chancellor <natechancellor@...il.com>
> Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> Tested-by: Nathan Chancellor <natechancellor@...il.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> Changes V1->V2:
> * add reviewed and tested by tags.
> * move this addition up 2 statments so that it's properly added to
>   KBUILD_*FLAGS as per Nathan.
>
>  Makefile | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/Makefile b/Makefile
> index d3b65e96d183..00e8e01d23fc 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -500,6 +500,9 @@ ifneq ($(GCC_TOOLCHAIN),)
>  CLANG_FLAGS    += --gcc-toolchain=$(GCC_TOOLCHAIN)
>  endif
>  CLANG_FLAGS    += -no-integrated-as
> +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),)
> +CLANG_FLAGS    += -fuse-ld=lld
> +endif
>  KBUILD_CFLAGS  += $(CLANG_FLAGS)
>  KBUILD_AFLAGS  += $(CLANG_FLAGS)
>  export CLANG_FLAGS
> --
> 2.20.1.791.gb4d0f1c61a-goog
>


--
Best Regards
Masahiro Yamada