linux-kernel - Re: [PATCH RFC 2/6] arm64: Kprobes with single stepping support

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Message-ID: <20131113135807.GJ26898@twins.programming.kicks-ass.net>
Date:	Wed, 13 Nov 2013 14:58:07 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"steve.capper@...aro.org" <steve.capper@...aro.org>,
	"nico@...aro.org" <nico@...aro.org>,
	"srikar@...ux.vnet.ibm.com" <srikar@...ux.vnet.ibm.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"Vijaya.Kumar@...iumnetworks.com" <Vijaya.Kumar@...iumnetworks.com>,
	Jiang Liu <liuj97@...il.com>,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH RFC 2/6] arm64: Kprobes with single stepping support

On Mon, Nov 11, 2013 at 10:58:12AM +0000, Will Deacon wrote:
> Single-stepping on x86 is different to the step behaviour on arm64 afaik. On
> ARM, we have to manually remove the breakpoint, perform a single-step, then
> add the breakpoint again. If we re-enable debug exceptions in the kprobe
> handler, the step will complete early and we'll never step off the
> breakpoint.

This is about hardware breakpoints right? Which are per-cpu? Otherwise
removing the breakpoint would open up a hole for another thread to slip
through while you're single stepping.
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