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Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers directly from do_int3/do_debug
- From: Jiri Kosina <jkosina at suse dot cz>
- To: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- Cc: Steven Rostedt <rostedt at goodmis dot org>, Ingo Molnar <mingo at kernel dot org>, Andi Kleen <ak at linux dot intel dot com>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Sandeepa Prabhu <sandeepa dot prabhu at linaro dot org>, Frederic Weisbecker <fweisbec at gmail dot com>, x86 at kernel dot org, lkml <linux-kernel at vger dot kernel dot org>, Andrew Morton <akpm at linux-foundation dot org>, Ingo Molnar <mingo at redhat dot com>, systemtap at sourceware dot org, "H. Peter Anvin" <hpa at zytor dot com>, Sasha Levin <sasha dot levin at oracle dot com>, Thomas Gleixner <tglx at linutronix dot de>, Seiji Aguchi <seiji dot aguchi at hds dot com>, "David S. Miller" <davem at davemloft dot net>
- Date: Thu, 12 Dec 2013 10:59:34 +0100 (CET)
- Subject: Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers directly from do_int3/do_debug
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- References: <20131204012841 dot 22118 dot 82992 dot stgit at kbuild-fedora dot novalocal> <20131204012856 dot 22118 dot 91079 dot stgit at kbuild-fedora dot novalocal> <20131203213904 dot 5ff1794c at gandalf dot local dot home> <alpine dot LRH dot 2 dot 00 dot 1312111418550 dot 6318 at twin dot jikos dot cz> <52A93E3A dot 9080600 at hitachi dot com>
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@suse.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