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    SubjectRe: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)
    On 01/19/2010 07:47 PM, Jim Keniston wrote:
    >> This is still with a kernel entry, yes?
    > Yes, this involves setting a breakpoint and trapping into the kernel
    > when it's hit. The 6-7x figure is with the current 2-trap approach
    > (breakpoint, single-step). Boosting could presumably make that more
    > like 12-14x.

    A trap is IIRC ~1000 cycles, we can reduce this to ~50 (totally
    negligible from the executed code's point of view).

    >> 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?

    1. Write a trace entry into shared memory, trap into the kernel on overflow.
    2. Trap if a condition is satisfied (fast watchpoint implementation).

    > Is the instrumentation code
    > that corresponds to the uprobe handlers encoded in an ad hoc .so?

    Looks like a good idea, but it doesn't matter much to me.

    error compiling committee.c: too many arguments to function

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