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Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers directly from do_int3/do_debug
- From: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- To: Jiri Kosina <jkosina at suse dot cz>
- 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 19:31:46 +0900
- 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> <alpine dot LNX dot 2 dot 00 dot 1312121058220 dot 1413 at pobox dot suse dot cz>
(2013/12/12 18:59), Jiri Kosina wrote:
> 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).
Ah, I don't intended to remove notify_die from do_int3, since
notify_die notifies many other exceptions too. :)
Thank you,
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com