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

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Date:   Fri, 8 Feb 2019 09:27:19 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, sedat.dilek@...il.com
Subject: Re: [PATCH 3/4] Makefile: lld: tell clang to use lld

On Thu, Feb 7, 2019 at 9:51 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> On Thu, Feb 07, 2019 at 02:01:51PM -0800, ndesaulniers@...gle.com wrote:
> > This is needed because clang doesn't select which linker to use based on
> > $LD but rather -fuse-ld=$(LD). This is problematic especially for
> > cc-ldoption, which checks for linker flag support via invoking the
> > compiler, rather than the linker.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/342
> > Suggested-by: Nathan Chancellor <natechancellor@...il.com>
> > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > ---
> >  Makefile | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/Makefile b/Makefile
> > index 0eae4277206e..6307c17259ea 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -502,6 +502,9 @@ endif
> >  CLANG_FLAGS  += -no-integrated-as
> >  KBUILD_CFLAGS        += $(CLANG_FLAGS)
> >  KBUILD_AFLAGS        += $(CLANG_FLAGS)
> > +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),)
> > +CLANG_FLAGS  += -fuse-ld=lld

Sorry, Sedat reports [0] that this is not quite correct; if $(LD)
matches LLD, then we need to set -fuse-ld=$(LD), not -fuse-ld=lld,
since you may have lld installed as lld-7 or lld-8, for example:
https://github.com/ClangBuiltLinux/linux/issues/358

> > +endif
>
> This section needs to be moved up above KBUILD_CFLAGS otherwise it never
> actually gets passed along.
>
> With that change, please add:
>
> Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> Tested-by: Nathan Chancellor <natechancellor@...il.com>
>
> >  export CLANG_FLAGS
> >  endif
> >
> > --
> > 2.20.1.791.gb4d0f1c61a-goog
> >



-- 
Thanks,
~Nick Desaulniers