linux-kernel - Re: ARM + jprobes/kretprobes SEGV/hangs/OOPS in 2.6.29 kernel

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Message-Id: <1251816239.10349.66.camel@pc1117.cambridge.arm.com>
Date:	Tue, 01 Sep 2009 15:43:59 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King <rmk+lkml@....linux.org.uk>
Cc:	venki kaps <venkiece2005@...il.com>, Nicolas Pitre <nico@....org>,
	"sagar.abhishek@...il.com" <sagar.abhishek@...il.com>,
	"jkenisto@...ibm.com" <jkenisto@...ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"prasanna@...ibm.com" <prasanna@...ibm.com>
Subject: Re: ARM + jprobes/kretprobes SEGV/hangs/OOPS in 2.6.29 kernel

On Tue, 2009-09-01 at 15:25 +0100, Russell King wrote:
> On Tue, Sep 01, 2009 at 02:54:54PM +0100, Catalin Marinas wrote:
> > venki kaps <venkiece2005@...il.com> wrote:
> > > I have found the exact problem with respect to ARM jprobes.
> > >
> > > The problem with configure i.e, CONFIG_ARM_UNWIND = y; is enabled.
> > 
> > I haven't followed the kprobes implementation for ARM but does it make
> > any assumptions about the existence of a frame pointer on the stack?
> > Enabling stack unwinding automatically disables the framepointer.
> 
> If it uses CALLER_ADDRESSx() then it won't work with unwinding enabled.
> See 5613/1 (which is pending in the devel branch.)

In addition to that, when CONFIG_FRAME_POINTER is disabled, the lr
register isn't always saved on the stack by the called function. I'm not
sure whether kretprobe_trampoline is aware of this.

-- 
Catalin

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