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

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Message-ID: <CAKwvOdmyNFsV=67eLQtETSDJJyDZ8aEJY1+LHuoP4OtpdQOdWQ@mail.gmail.com>
Date:   Wed, 13 Feb 2019 09:41:52 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.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 Wed, Feb 13, 2019 at 6:59 AM Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
>
> 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)

It solves case 2.

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

Ideally, no, but I can think of at least one case where it might be
problematic to mix linkers like that:
You might be mixing linker flags added via ld-option from one linker
that aren't actually supported by the other linker.

-- 
Thanks,
~Nick Desaulniers