linux-kernel - Re: [PATCH] arm64: remove redundant FRAME

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Message-ID: <20151106125002.GA8116@leverpostej>
Date:	Fri, 6 Nov 2015 12:50:02 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Will Deacon <will.deacon@....com>
Cc:	Yang Shi <yang.shi@...aro.org>, catalin.marinas@....com,
	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: remove redundant FRAME_POINTER kconfig option

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@....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.

Thanks,
Mark.
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