linux-kernel - Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

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Message-ID: <20100119180610.GA11005@nowhere>
Date:	Tue, 19 Jan 2010 19:06:12 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jim Keniston <jkenisto@...ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, Pekka Enberg <penberg@...helsinki.fi>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>, ananth@...ibm.com,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	utrace-devel <utrace-devel@...hat.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Maneesh Soni <maneesh@...ibm.com>,
	Mark Wielaard <mjw@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

On Tue, Jan 19, 2010 at 09:47:45AM -0800, Jim Keniston wrote:
> > Do you have plans for a variant 
> > that's completely in userspace?
> 
> I don't know of any such plans, but I'd be interested to read more of
> your thoughts here.  As I understand it, you've suggested replacing the
> probed instruction with a jump into an instrumentation vma (the XOL
> area, or something similar).  Masami has demonstrated -- through his
> djprobes enhancement to kprobes -- that this can be done for many x86
> instructions.
> 
> What does the code in the jumped-to vma do?  Is the instrumentation code
> that corresponds to the uprobe handlers encoded in an ad hoc .so?


Once the instrumentation is requested by a process that is not the
instrumented one, this looks impossible to set a uprobe without a
minimal voluntary collaboration from the instrumented process
(events sent through IPC or whatever). So that looks too limited,
this is not anymore a true dynamic uprobe.

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