linux-kernel - Re: [PATCH v3 1/5] arm64: Kprobes with single stepping support

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Date:	Wed, 26 Nov 2014 10:09:19 +0000
From:	Will Deacon <will.deacon@....com>
To:	David Long <dave.long@...aro.org>
Cc:	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>,
	William Cohen <wcohen@...hat.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/5] arm64: Kprobes with single stepping support

On Wed, Nov 26, 2014 at 06:46:12AM +0000, David Long wrote:
> On 11/19/14 09:55, David Long wrote:
> > On 11/19/14 06:25, Will Deacon wrote:
> >> I was thinking of the magic hex numbers in the kprobes decode tables,
> >> which
> >> seem to correspond directly to the instruction classes described in
> >> insn.c
> >>
> >> Keeping the actual emulation code separate makes sense.
> >>
> > Of course that follows the model of the much more complex arm32
> > kprobes/uprobes decoding.  I can have a go at replacing it with insn.c
> > calls.
> 
> While the existing aarch64_get_insn_class() function in insn.c is 
> somewhat useful here what is really needed is a function that identifies 
> if an instruction uses the pc (branch, load literal, load address). 
> Such instructions cannot be arbitrarily moved around in isolation, and 
> do not fall neatly into the existing "class"es.  I've written a simple 
> aarch64_insn_uses_pc() function to add to insn.c but I'd like to hear 
> agreement that this is a good approach before sending out the patch. 
> Thoughts?

I'm perfectly happy with extending insn.c with extra helpers if they're
useful to you.

Will
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