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From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Stefan Agner <stefan@agner.ch>
Cc: ard.biesheuvel@linaro.org, arnd@arndb.de,
	nicolas.pitre@linaro.org, marc.zyngier@arm.com,
	behanw@converseincode.com, keescook@chromium.org,
	Bernhard.Rosenkranzer@linaro.org, mka@chromium.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] ARM: add support for building ARM kernel with clang
Date: Tue, 20 Mar 2018 23:18:33 +0000	[thread overview]
Message-ID: <20180320231832.GK2743@n2100.armlinux.org.uk> (raw)
In-Reply-To: <20180320230206.25289-6-stefan@agner.ch>

On Wed, Mar 21, 2018 at 12:02:06AM +0100, Stefan Agner wrote:
> Use cc-options call for compiler options which are not available
> in clang. With this patch an ARMv7 multi platform kernel can be
> successfully build using clang (tested with version 5.0.1).
> 
> Based-on-patches-by: Behan Webster <behanw@converseincode.com>
> Signed-off-by: Stefan Agner <stefan@agner.ch>
> ---
>  arch/arm/Makefile                 | 2 +-
>  arch/arm/boot/compressed/Makefile | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> index e9e3fde3c657..20e9fee1ccc5 100644
> --- a/arch/arm/Makefile
> +++ b/arch/arm/Makefile
> @@ -39,7 +39,7 @@ KBUILD_CFLAGS	+= $(call cc-option,-mno-unaligned-access)
>  endif
>  
>  ifeq ($(CONFIG_FRAME_POINTER),y)
> -KBUILD_CFLAGS	+=-fno-omit-frame-pointer -mapcs -mno-sched-prolog
> +KBUILD_CFLAGS	+=-fno-omit-frame-pointer $(call cc-option,-mapcs,) $(call cc-option,-mno-sched-prolog,)

Some of these options here are to ensure that we generate the following
code, so we can backtrace:

	mov	ip, sp
	stmfd	sp!, {fp, ip, lr, pc}
	sub	fp, ip, #4

If clang isn't producing that code at the start of functions with
CONFIG_FRAME_POINTER=y, then backtracing will not work, and arguably
CONFIG_FRAME_POINTER=y is useless there.  In that circumstance, it's
probably better to fail so the user can configure something more
debuggable, rather than having the kernel potentially producing
undebuggable oopses.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up
According to speedtest.net: 8.21Mbps down 510kbps up

  reply	other threads:[~2018-03-20 23:18 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-20 23:02 [PATCH 0/5] ARM: clang support Stefan Agner
2018-03-20 23:02 ` [PATCH 1/5] bus: arm-cci: use asm unreachable Stefan Agner
2018-03-20 23:30   ` Russell King - ARM Linux
2018-03-21  8:22     ` Stefan Agner
2018-03-20 23:02 ` [PATCH 2/5] efi/libstub/arm: add support for building with clang Stefan Agner
2018-03-20 23:02 ` [PATCH 3/5] ARM: trusted_foundations: do not use naked function Stefan Agner
2018-03-20 23:13   ` Russell King - ARM Linux
2018-03-21  8:41     ` Stefan Agner
2018-03-21 12:13   ` Robin Murphy
2018-03-21 14:09     ` Stefan Agner
2018-03-21 15:26       ` Dmitry Osipenko
2018-03-21 16:40         ` Stephen Warren
2018-03-21 17:16           ` Robin Murphy
2018-03-21 21:41             ` Stefan Agner
2018-03-22 11:48               ` Robin Murphy
2018-03-22 12:43                 ` Stefan Agner
2018-03-22 14:03                   ` Dmitry Osipenko
2018-03-20 23:02 ` [PATCH 4/5] ARM: drop no-thumb-interwork in EABI mode Stefan Agner
2018-03-20 23:02 ` [PATCH 5/5] ARM: add support for building ARM kernel with clang Stefan Agner
2018-03-20 23:18   ` Russell King - ARM Linux [this message]
2018-03-21  0:20     ` Matthias Kaehlcke
2018-03-21  9:03       ` Stefan Agner
2018-03-25 13:24     ` Stefan Agner

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