linux-kernel - Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers directly from do_int3/do

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Date:	Thu, 12 Dec 2013 10:59:34 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>, x86@...nel.org,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>, systemtap@...rceware.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Seiji Aguchi <seiji.aguchi@....com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers
 directly from do_int3/do_debug

On Thu, 12 Dec 2013, Masami Hiramatsu wrote:

> > Yeah, it's broken. Obviously, if you happen to trigger int3 before the 
> > notifier has been registered, it'd cause int3 exception to be unhandled. 
> > See
> > 
> > 	commit 17f41571bb2c4a398785452ac2718a6c5d77180e
> > 	Author: Jiri Kosina <jkosina@...e.cz>
> > 	Date:   Tue Jul 23 10:09:28 2013 +0200
> > 
> > 	    kprobes/x86: Call out into INT3 handler directly instead of using notifier
> > 
> > for one such issue that happened with jump labels.
> > 
> >> Hmm, if there's no users of the int3 notifier, should we just remove it?
> > 
> > Hmm, there are still uprobes, right?
> 
> Right, uprobes still use it, however, since it only handles user-space
> breakpoint, there is no problem.

Agreed. But therefore the notifier can't just be removed, unless uprobes 
are converted to direct call as well (but I don't think that'd be 
beneficial, notifier is sufficient in this case).

-- 
Jiri Kosina
SUSE Labs
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