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From: Nick Desaulniers <ndesaulniers@google.com>
To: Arnd Bergmann <arnd@kernel.org>, Masahiro Yamada <masahiroy@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Fangrui Song <maskray@google.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH] arm64: drop CROSS_COMPILE for LLVM=1 LLVM_IAS=1
Date: Fri, 2 Jul 2021 11:29:31 -0700	[thread overview]
Message-ID: <CAKwvOdkgEeQktLgEN7CAh7bTjTN+TQNE27aETgvbXep9=xb1DQ@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a1EfBNxaMbsp+s2BiYHGKPK4NeRR+ugM82jfY43Pq7-Uw@mail.gmail.com>

On Fri, Jul 2, 2021 at 4:59 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Fri, Jul 2, 2021 at 1:55 AM 'Nick Desaulniers' via Clang Built
> Linux <clang-built-linux@googlegroups.com> wrote:
> >
> > +ifneq ($(LLVM),)
> > +ifneq ($(LLVM_IAS),)
> > +ifeq ($(CROSS_COMPILE),)
> > +CLANG_TARGET   :=--target=aarch64-linux
> > +CLANG_FLAGS    += $(CLANG_TARGET)
> > +KBUILD_CFLAGS  += $(CLANG_TARGET)
> > +KBUILD_AFLAGS  += $(CLANG_TARGET)
> > +endif
> > +endif
> > +endif
>
> I think only the "CLANG_TARGET   :=--target=aarch64-linux" line should
> go into the
> per-architecture Makefile. It doesn't hurt to just set that
> unconditionally here,
> and then change the CLANG_FLAGS logic in the top-level Makefile to use this
> in place of $(notdir $(CROSS_COMPILE:%-=%)).

I don't think we can do that. Based on the order the arch/ specific
Makefiles are included, if we don't eagerly add --target to the
KBUILD_{C|A}FLAGS, then cc-option, as-option, and as-instr macros
(defined in scripts/Makefile.compiler) checks in per arch/ Makefiles
may fail erroneously because --target was not set for
KBUILD_{C|A}FLAGS yet.

Another issue is the order of operations between the top level
Makefile and the per arch/ Makefiles.  The `notdir` block you
reference occurs earlier than the per-arch includes:

 609 TENTATIVE_CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
...
 648 include $(srctree)/arch/$(SRCARCH)/Makefile

We would need the opposite order to do what you describe. Reordering
these would effectively be a revert of
commit ae6b289a3789 ("kbuild: Set KBUILD_CFLAGS before incl. arch Makefile")
which I'm not sure we want to do.  But maybe there's another way I'm
not seeing yet?
-- 
Thanks,
~Nick Desaulniers

  reply	other threads:[~2021-07-02 18:29 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
2021-07-02 11:59 ` Arnd Bergmann
2021-07-02 18:29   ` Nick Desaulniers [this message]
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

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