linux-kernel - Re: [PATCH] arm: Add unwinding annotations for 64bit division functions

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Message-ID: <20110922115713.GJ12025@e102109-lin.cambridge.arm.com>
Date:	Thu, 22 Sep 2011 12:57:13 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	"Jon Medhurst (Tixy)" <jon.medhurst@...aro.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Dave Martin <dave.martin@...aro.org>,
	Laura Abbott <lauraa@...eaurora.org>,
	Nicolas Pitre <nico@...xnic.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm: Add unwinding annotations for 64bit division
 functions

On Thu, Sep 22, 2011 at 12:06:46PM +0100, Jon Medhurst (Tixy) wrote:
> On Thu, 2011-09-22 at 10:48 +0100, Catalin Marinas wrote:
> > We could improve things a bit in the unwinder and assume
> > that if the fault address is the same as the .fnstart address, the
> > return value is always in LR and the SP not affected (that's unwinding
> > bytecode 0xb0). For a few instructions into the function prologue we
> > can't reliably get the unwinding information.
> 
> That would help make it possible to unwind out of kprobes handlers to
> the probed function. The kprobes code itself would need work as well,
> and possibly the undef handler. Do we think it is worthwhile to do
> this? 

Does kprobes need to trace beyond the probed function? If not, you get
the address of the probed function via pt_regs anyway, so no need for
unwinding beyond that.

-- 
Catalin

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