archive mirror
 help / color / mirror / Atom feed
From: Nick Desaulniers <>
To: Will Deacon <>
Cc: Catalin Marinas <>,
	Masahiro Yamada <>,
	Arnd Bergmann <>,
	Fangrui Song <>,
	Nathan Chancellor <>,,,
Subject: Re: [PATCH] arm64: drop CROSS_COMPILE for LLVM=1 LLVM_IAS=1
Date: Fri, 2 Jul 2021 10:50:27 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20210702112210.GA11084@willie-the-truck>

On Fri, Jul 2, 2021 at 4:22 AM Will Deacon <> wrote:
> On Thu, Jul 01, 2021 at 04:55:05PM -0700, Nick Desaulniers wrote:
> > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> > index 7bc37d0a1b68..016873fddcc3 100644
> > --- a/arch/arm64/Makefile
> > +++ b/arch/arm64/Makefile
> > @@ -34,6 +34,17 @@ $(warning LSE atomics not supported by binutils)
> >    endif
> >  endif
> >
> > +ifneq ($(LLVM),)
> > +ifneq ($(LLVM_IAS),)
> > +ifeq ($(CROSS_COMPILE),)
> > +CLANG_TARGET :=--target=aarch64-linux
> Do we need to do anything extra for the linker here? I can't see how we
> avoid picking up the host copy.

That's handled by the top level Makefile when LLVM=1 is set.

There is $KBUILD_LDFLAGS, but we don't do anything with it at the
moment in terms of which linker we select; $LD controls which linker
we use.

LLD can figure out the target based on the object files it's given as
input, so it doesn't need any `--target=` flag. When clang is invoked
as the compiler or assembler, it does need --target.

> Have you tested the compat vDSO with this change? I think we'll just end
> up passing two --target options, which is hopefully ok, but thought I'd
> better check.

Good catch.  We don't reuse KBUILD_CFLAGS or KBUILD_AFLAGS for the
compat vdso for this very reason. In arch/arm64/kernel/vdso32/Makefile
you'll see no references to KBUILD_CFLAGS or KBUILD_AFLAGS; instead we
use VDSO_CFLAGS and VDSO_AFLAGS in their stead.

But, we could (and should) make this same change for the compat vdso,
and drop the need for CROSS_COMPILE_COMPAT for LLVM.

Let me play around with the changes Arnd suggested and see if I can
get that working.  I'm a bit nervous about making this depend on
something from the top level Makefile on initial glance; these changes
start to become tree wide rather than isolated per arch/, but let's
see.  Maybe at that point we carry a series in the kbuild tree with
acks for the arch/ specific changes from the respective maintainers?

Either way, I'll send a v2 that nixes CROSS_COMPILE_COMPAT for LLVM.
~Nick Desaulniers

  reply	other threads:[~2021-07-02 17:50 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-01 23:55 [PATCH] arm64: drop CROSS_COMPILE for LLVM=1 LLVM_IAS=1 Nick Desaulniers
2021-07-02  1:05 ` Tom Stellard
2021-07-02 17:37   ` Nick Desaulniers
2021-07-02 11:22 ` Will Deacon
2021-07-02 17:50   ` Nick Desaulniers [this message]
2021-07-02 11:59 ` Arnd Bergmann
2021-07-02 18:29   ` Nick Desaulniers
2021-07-04  0:47     ` Nathan Chancellor
2021-07-07 19:04       ` Nick Desaulniers
2021-07-07 19:08         ` Nathan Chancellor
2021-07-07 22:44           ` Nick Desaulniers

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).