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    SubjectRe: [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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