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From: Nick Desaulniers <ndesaulniers@google.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>, Ard Biesheuvel <ardb@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Nathan Chancellor <nathan@kernel.org>,
	llvm@lists.linux.dev
Subject: Re: [PATCH 13/14] ARM: use .arch directives instead of assembler command line flags
Date: Wed, 29 Sep 2021 11:11:31 -0700	[thread overview]
Message-ID: <CAKwvOdnWFvs9aa3vrb+HiitPYV7camzQ8b4g64efh6AOGU6Wdg@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a2LezhdCczGsgWrrkShvowXMYSSdhfPJqSHwHEBRv4PvQ@mail.gmail.com>

On Tue, Sep 28, 2021 at 11:32 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Tue, Sep 28, 2021 at 7:10 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Tue, Sep 28, 2021 at 8:42 AM Arnd Bergmann <arnd@kernel.org> wrote:
> > >
> > > From: Nick Desaulniers <ndesaulniers@google.com>
> > >
> > > Similar to commit a6c30873ee4a ("ARM: 8989/1: use .fpu assembler
> > > directives instead of assembler arguments").
> > >
> > > GCC and GNU binutils support setting the "sub arch" via -march=,
> > > -Wa,-march, target function attribute, and .arch assembler directive.
> > >
> > > Clang's integrated assembler does not support -Wa,-march (and the logic
> > > to overrule one when multiple of the above are used), and this can
> > > cause annoying warnings such as:
> > >
> > > clang: warning: argument unused during compilation: '-march=armv6k' [-Wunused-command-line-argument]
> > > clang: warning: argument unused during compilation: '-march=armv6k' [-Wunused-command-line-argument]
> > > clang: warning: argument unused during compilation: '-march=armv6k' [-Wunused-command-line-argument]
> >
> > Note, the above lack of support was fixed in clang-13. That said, both
> > Clang and GCC defer to -Wa,-march when -march is also present, so
> > clang is still correct that -march is ignored.  Thanks for resending;
> > this is still helpful for earlier releases of clang that we still
> > support.
>
> The -Wunused-command-line-argument warning also caused a build
> failure for me when building with 'make W=1', and I think there are
> cases where the flags from the command line are contradictory.

There's also -Werror now, which is hurting allmodconfig builds.

> Isn't the patch also needed for LTO? All I know is that with this
> applied it all builds, but without it I run into link failures.

We don't support LTO on 32b ARM, yet.  I would be interested in
getting that support working.

>  I can dig
> more into the specific failures, but overall I think this is the right
> thing to do anyway.

I agree.  I was just adding additional context to the commit message
via my initial reply.
-- 
Thanks,
~Nick Desaulniers

WARNING: multiple messages have this Message-ID (diff)
From: Nick Desaulniers <ndesaulniers@google.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,  Ard Biesheuvel <ardb@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	 Nathan Chancellor <nathan@kernel.org>,
	llvm@lists.linux.dev
Subject: Re: [PATCH 13/14] ARM: use .arch directives instead of assembler command line flags
Date: Wed, 29 Sep 2021 11:11:31 -0700	[thread overview]
Message-ID: <CAKwvOdnWFvs9aa3vrb+HiitPYV7camzQ8b4g64efh6AOGU6Wdg@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a2LezhdCczGsgWrrkShvowXMYSSdhfPJqSHwHEBRv4PvQ@mail.gmail.com>

On Tue, Sep 28, 2021 at 11:32 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Tue, Sep 28, 2021 at 7:10 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Tue, Sep 28, 2021 at 8:42 AM Arnd Bergmann <arnd@kernel.org> wrote:
> > >
> > > From: Nick Desaulniers <ndesaulniers@google.com>
> > >
> > > Similar to commit a6c30873ee4a ("ARM: 8989/1: use .fpu assembler
> > > directives instead of assembler arguments").
> > >
> > > GCC and GNU binutils support setting the "sub arch" via -march=,
> > > -Wa,-march, target function attribute, and .arch assembler directive.
> > >
> > > Clang's integrated assembler does not support -Wa,-march (and the logic
> > > to overrule one when multiple of the above are used), and this can
> > > cause annoying warnings such as:
> > >
> > > clang: warning: argument unused during compilation: '-march=armv6k' [-Wunused-command-line-argument]
> > > clang: warning: argument unused during compilation: '-march=armv6k' [-Wunused-command-line-argument]
> > > clang: warning: argument unused during compilation: '-march=armv6k' [-Wunused-command-line-argument]
> >
> > Note, the above lack of support was fixed in clang-13. That said, both
> > Clang and GCC defer to -Wa,-march when -march is also present, so
> > clang is still correct that -march is ignored.  Thanks for resending;
> > this is still helpful for earlier releases of clang that we still
> > support.
>
> The -Wunused-command-line-argument warning also caused a build
> failure for me when building with 'make W=1', and I think there are
> cases where the flags from the command line are contradictory.

There's also -Werror now, which is hurting allmodconfig builds.

> Isn't the patch also needed for LTO? All I know is that with this
> applied it all builds, but without it I run into link failures.

We don't support LTO on 32b ARM, yet.  I would be interested in
getting that support working.

>  I can dig
> more into the specific failures, but overall I think this is the right
> thing to do anyway.

I agree.  I was just adding additional context to the commit message
via my initial reply.
-- 
Thanks,
~Nick Desaulniers

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-09-29 18:11 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-28 15:41 [PATCH 00/14] ARM: randconfig build fixes Arnd Bergmann
2021-09-28 15:41 ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 01/14] ARM: RiscPC needs older gcc version Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 16:03   ` Arnd Bergmann
2021-09-28 16:03     ` Arnd Bergmann
2021-09-28 16:03     ` Arnd Bergmann
2021-09-29  8:45     ` Arnd Bergmann
2021-09-29  8:45       ` Arnd Bergmann
2021-09-29  8:45       ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 02/14] ARM: patch: fix BE32 compilation Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 21:33   ` Linus Walleij
2021-09-28 21:33     ` Linus Walleij
2021-09-28 21:33     ` Linus Walleij
2021-09-28 15:41 ` [PATCH 03/14] ARM: remove duplicate memcpy() definition Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 21:39   ` Linus Walleij
2021-09-28 21:39     ` Linus Walleij
2021-09-28 21:39     ` Linus Walleij
2021-09-28 15:41 ` [PATCH 04/14] ARM: kprobes: address gcc -Wempty-body warning Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 05/14] ARM: ARMv7-M uses BE-8, not BE-32 Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 06/14] ARM: disallow CONFIG_THUMB with ARMv4 Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-29 18:52   ` Nick Desaulniers
2021-09-29 18:52     ` Nick Desaulniers
2021-09-29 18:52     ` Nick Desaulniers
2021-10-06 16:01   ` Ard Biesheuvel
2021-10-06 16:01     ` Ard Biesheuvel
2021-09-28 15:41 ` [PATCH 07/14] ARM: fix link warning with XIP + frame-pointer Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 08/14] ARM: kprobes: fix arch_init_kprobes() prototype Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 09/14] ARM: allow compile-testing without machine record Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 10/14] ARM: only warn about XIP address when not compile testing Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 11/14] ARM: kasan: work around LPAE build warning Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 15:41 ` [PATCH 12/14] ARM: add CONFIG_PHYS_OFFSET default values Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 16:02   ` Nicolas Pitre
2021-09-28 16:02     ` Nicolas Pitre
2021-09-28 16:02     ` Nicolas Pitre
2021-09-28 21:44   ` Linus Walleij
2021-09-28 21:44     ` Linus Walleij
2021-09-28 21:44     ` Linus Walleij
2021-09-28 15:41 ` [PATCH 13/14] ARM: use .arch directives instead of assembler command line flags Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 17:10   ` Nick Desaulniers
2021-09-28 17:10     ` Nick Desaulniers
2021-09-28 17:10     ` Nick Desaulniers
2021-09-28 18:32     ` Arnd Bergmann
2021-09-28 18:32       ` Arnd Bergmann
2021-09-28 18:32       ` Arnd Bergmann
2021-09-29 18:11       ` Nick Desaulniers [this message]
2021-09-29 18:11         ` Nick Desaulniers
2021-09-29 18:11         ` Nick Desaulniers
2022-01-21 22:17   ` Nathan Chancellor
2022-01-21 22:17     ` Nathan Chancellor
2021-09-28 15:41 ` [PATCH 14/14] [RFC] ARM: forbid ftrace with clang and thumb2_kernel Arnd Bergmann
2021-09-28 15:41   ` Arnd Bergmann
2021-09-28 17:20   ` Nick Desaulniers
2021-09-28 17:20     ` Nick Desaulniers
2021-09-28 17:20     ` Nick Desaulniers

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