linux-kernel - Re: [PATCH 5/5] ARM: add support for building ARM kernel with clang

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180320231832.GK2743@n2100.armlinux.org.uk>
Date:   Tue, 20 Mar 2018 23:18:33 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Stefan Agner <stefan@...er.ch>
Cc:     ard.biesheuvel@...aro.org, arnd@...db.de, nicolas.pitre@...aro.org,
        marc.zyngier@....com, behanw@...verseincode.com,
        keescook@...omium.org, Bernhard.Rosenkranzer@...aro.org,
        mka@...omium.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] ARM: add support for building ARM kernel with clang

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@...verseincode.com>
> Signed-off-by: Stefan Agner <stefan@...er.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