From mboxrd@z Thu Jan  1 00:00:00 1970
From: will.deacon@arm.com (Will Deacon)
Date: Fri, 6 Nov 2015 16:25:38 +0000
Subject: [PATCH] arm64: remove redundant FRAME_POINTER kconfig option
In-Reply-To: <20151106162109.GZ7637@e104818-lin.cambridge.arm.com>
References: <1446658671-16238-1-git-send-email-yang.shi@linaro.org>
 <20151106123008.GK6087@arm.com> <20151106125002.GA8116@leverpostej>
 <20151106162109.GZ7637@e104818-lin.cambridge.arm.com>
Message-ID: <20151106162538.GU6087@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Nov 06, 2015 at 04:21:09PM +0000, Catalin Marinas wrote:
> On Fri, Nov 06, 2015 at 12:50:02PM +0000, Mark Rutland wrote:
> > On Fri, Nov 06, 2015 at 12:30:09PM +0000, Will Deacon wrote:
> > > On Wed, Nov 04, 2015 at 09:37:51AM -0800, Yang Shi wrote:
> > > > FRAME_POINTER is defined in lib/Kconfig.debug, it is unnecessary to redefine
> > > > it in arch/arm64/Kconfig.debug.
> > > 
> > > It might be worth noting that this adds a dependency on DEBUG_KERNEL
> > > for building with frame pointers. I'm ok with that (it appears to be
> > > enabled in defconfig and follows the vast majority of other archs) but
> > > it is a change in behaviour.
> > > 
> > > With that:
> > > 
> > >   Acked-by: Will Deacon <will.deacon@arm.com>
> > 
> > The code in arch/arm64/kernel/stacktrace.c assumes we have frame
> > pointers regardless of FRAME_POINTER. Depending on what the compiler
> > decides to use x29 for, we could get some weird fake unwinding and/or
> > dodgy memory accesses.
> > 
> > I think we should first audit the uses of frame pointers to ensure that
> > they are guarded for !FRAME_POINTER.
> 
> Or we just select FRAME_POINTER in the ARM64 Kconfig entry.

Yang, did you see any benefit disabling frame pointers, or was this patch
purely based on you spotting a duplicate Kconfig entry?

Will