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Message-ID: <20100115101056.GD26396@in.ibm.com>
Date: Fri, 15 Jan 2010 15:40:56 +0530
From: Ananth N Mavinakayanahalli <ananth@...ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Jim Keniston <jkenisto@...ibm.com>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>,
Arnaldo Carvalho de Melo <acme@...radead.org>,
utrace-devel <utrace-devel@...hat.com>,
Frederic Weisbecker <fweisbec@...il.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 Fri, Jan 15, 2010 at 10:50:14AM +0100, Peter Zijlstra wrote:
> On Fri, 2010-01-15 at 15:08 +0530, Ananth N Mavinakayanahalli wrote:
> > On Fri, Jan 15, 2010 at 10:03:48AM +0100, Peter Zijlstra wrote:
> > > On Thu, 2010-01-14 at 11:46 -0800, Jim Keniston wrote:
> > > >
> > > > discussed elsewhere.
> > >
> > > Thanks for the pointer...
> >
> > :-)
> >
> > Peter,
> > I think Jim was referring to
> > http://sources.redhat.com/ml/systemtap/2007-q1/msg00571.html
>
> That's a 2007 email from some obscure list... that's hardly something
> that can be referenced to without link.
>
> As previously stated, I think poking at a process's address space is an
> utter no-go.
In which case we'll need to find a different solution to it. The gdb
style of 'breakpoint hit' -> 'put original instruction back in place' ->
single-step -> 'put back the breakpoint' would be a big limiter,
especially for multithreaded cases.
The design here is to have a small vma sufficiently high enough in
memory a-la vDSO that most apps won't reach, though there is still no
ironclad guarantee.
Ideally, we will need to single-step on a copy of the instruction, in the
user address space of the traced process.
Ideas?
Ananth
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