linux-kernel - Re: [PATCH 1/2] arm64: Blacklist non-kprobe-able symbols

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Message-ID: <559A688D.1040501@hitachi.com>
Date:	Mon, 06 Jul 2015 20:37:49 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Will Deacon <will.deacon@....com>,
	Pratyush Anand <panand@...hat.com>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"wcohen@...hat.com" <wcohen@...hat.com>,
	"dave.long@...aro.org" <dave.long@...aro.org>,
	"steve.capper@...aro.org" <steve.capper@...aro.org>
Subject: Re: [PATCH 1/2] arm64: Blacklist non-kprobe-able symbols

On 2015/07/06 18:03, Will Deacon wrote:
> On Mon, Jul 06, 2015 at 06:03:21AM +0100, Pratyush Anand wrote:
>> Add all function symbols which are called from do_debug_exception under
>> NOKPROBE_SYMBOL, as they can not kprobed.
> 
> It's a shame this has to be so manual, but I suppose it's done on a
> best-effort basis to catch broken probe placement.

Ah, yes. You can use kprobe-tracer in ftrace by feeding all symbols to
them and enabling it (and pray).


> If we miss a function and somebody probes it, do we just get stuck in a
> recursive exception, or could we print something suggesting that a symbol
> be annotated as NOKPROBE?

For some cases we can detect recursion, but usually, it may reset
itself or infinite recursion loop before detecting it. :(

Thank you,

-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@...achi.com
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