linux-kernel - Re: [PATCH V4] ARM : unwinder : Prevent data abort due to stack overflow

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Message-ID: <20131206152140.GB4897@e103592.cambridge.arm.com>
Date:	Fri, 6 Dec 2013 15:21:41 +0000
From:	Dave Martin <Dave.Martin@....com>
To:	Anurag Aggarwal <anurag19aggarwal@...il.com>
Cc:	Anurag Aggarwal <a.anurag@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"cpgs@...sung.com" <cpgs@...sung.com>,
	"narendra.m1@...sung.com" <narendra.m1@...sung.com>,
	"poorva.s@...sung.com" <poorva.s@...sung.com>,
	"naveen.sel@...sung.com" <naveen.sel@...sung.com>,
	"ashish.kalra@...sung.com" <ashish.kalra@...sung.com>,
	"mohammad.a2@...sung.com" <mohammad.a2@...sung.com>,
	"rajat.suri@...sung.com" <rajat.suri@...sung.com>,
	"naveenkrishna.ch@...il.com" <naveenkrishna.ch@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	"nico@...aro.org" <nico@...aro.org>,
	Catalin Marinas <Catalin.Marinas@....com>
Subject: Re: [PATCH V4] ARM : unwinder : Prevent data abort due to stack
 overflow

On Thu, Dec 05, 2013 at 03:15:22PM +0000, Anurag Aggarwal wrote:
> >>if (unlikely(check) &&
> >>    *vsp >= (unsigned long *)ctrl->sp_high))
> 
> Good idea, It can help in optimizing the code and will leave code more readable
> and it will be easy to maintain also.

That was my goal -- it's not always easy to achieve both, but we should
try where possible, especially for non-performance-critical code.

> >>Does the code check anywhere that SP is word-aligned?
> >>
> >>That should probably be checked if it's not done already.
> 
> I think this should be handled in separate patch
> I would also like to hear more your ideas for the file

There are some limitations on how backtracing works with ARM_UNWIND.
The backtracer interface assumes that the compiler's register use with
ARM_UNWIND is "almost the same" as with !ARM_UNWIND.  But this is not
always true, and we've seen some problems.  

I think the best solution will involve some refactoring of the interface
between the backtracer and the unwinder backends, but I don't have it
all figured out yet...

Cheers
---Dave
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