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

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Message-ID: <CA+b37P337jcTCPTg4Ydxh6TKwqmyMngt-eEowzfsTNBDZ7-NEg@mail.gmail.com>
Date:	Wed, 19 Nov 2014 16:51:24 +0530
From:	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>
To:	Will Deacon <will.deacon@....com>
Cc:	David Long <dave.long@...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 18 November 2014 20:26, Will Deacon <will.deacon@....com> wrote:

> One thing I noticed looking through this patch is that we're effectively
> reinventing a bunch of the instruction decoding logic that we already have
> in the kernel (introduced since Sandeepa last sent his patch).
>
> Could you take a look at include/asm/insn.h and kernel/insn.c please, and
> see if you can at least consolidate some of this? Some of it should be easy
> (i.e. reusing masks, using existing #defines to construct BRK encodings),
> but I appreciate there may be places where kprobes needs to add extra bits,
> in which case I'd really like to keep this all together if at all possible.
>
> We're currently in a position where the module loader, BPF jit, ftrace and
> the proposed alternative patching scheme are all using the same instruction
> manipulation functions, so we should try to continue that trend if we can.
Will,

kernel/insn.c support generating instruction encodings(forming opcodes
with given specifications), so for kprobes, only BRK encoding can use
this mechanism.
For instruction simulation, the instruction behavior should be
simulated on saved pt_regs, which is not supported on insn.c routines,
so still need probes-simulate-insn.c. Please point me if I am missing
something here.

>
> Thanks,
>
> Will
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