linux-kernel - Re: [RFC] [PATCH 4/7] Uprobes Implementation

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Date:	Fri, 15 Jan 2010 15:40:36 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Jim Keniston <jkenisto@...ibm.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Mark Wielaard <mjw@...hat.com>,
	utrace-devel <utrace-devel@...hat.com>
Subject: Re: [RFC] [PATCH 4/7] Uprobes Implementation

On Fri, 2010-01-15 at 09:22 -0500, Frank Ch. Eigler wrote:
> Hi -
> 
> > > Well, I'm not in a position to argue line by line about the necessity
> > > or the cost of utrace low level guts, but this may represent the most
> > > practical engineering balance between functionality / modularity /
> > > undesirably intrusive modifications. 
> > 
> > How intrusive and non-modular is installing a DIE_INT3 notifier?
> 
> I'm not sure about all the reasons pro/con, but it looks like
> installing such a systemwide hook would force every userspace
> breakpoint or kprobe event machine wide to pass through the
> hypothetical uprobes layer, whether or not applicable to a current
> task.

Well, we'll have to pass through the global die notifier anyway, but a
quick per task filter sounds like a good idea, we can do that by keeping
a per-task count of the number of uprobes in use.

Then the uprobe code can avoid the lookup if there are no task users and
no global users.

The advantage of this construct is that is easily allows for global
users, whereas a utrace based one doesn't.



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