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    SubjectRe: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)
    On Mon, Jan 18, 2010 at 06:52:32PM +0200, Avi Kivity wrote:
    > On 01/18/2010 05:43 PM, Ananth N Mavinakayanahalli wrote:
    >>>> Well, the alternatives are very unappealing. Emulation and single-stepping
    >>>> are going to be very slow compared to a couple of jumps.
    >>> So how big chunks of the address space are we talking here for uprobes?
    >> As Srikar mentioned, the least we start with is 1 page. Though you can
    >> have as many probes as you want, there are certain optimizations we can
    >> do, depending on the most common usecases.
    >> For eg., if you'd consider the start of a routine to be the most
    >> commonly traced location, most routines in a binary would generally
    >> start with the same instruction (say push %ebp), and we can refcount a
    >> slot with that instruction to be used for all probes of the same
    >> instruction.
    > But then you can't follow the instruction with a jump back to the code...

    Right. This will work only for the non boosted case where single-stepping
    is mandatory. I guess the tradeoff is vma space and speed.


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