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

From: Frederic Weisbecker
Date: Tue Jan 19 2010 - 13:06:24 EST

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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