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    SubjectRe: [RFC] [PATCH 2.6.37-rc5-tip 10/20] 10: uprobes: task specific information.
    On Tue, 2011-01-25 at 10:38 -0800, Josh Stone wrote:
    > On 01/25/2011 05:56 AM, Peter Zijlstra wrote:
    > > Ah, I think I found it while reading patch 13, you need the pre/post_xol
    > > callbacks, can't you simply synthesize their effect into the replacement
    > > sequence?
    > >
    > > push %rax
    > > mov $vaddr, %rax
    > > $INSN
    > > pop %rax
    > > jmp $next_insn
    > >
    > > like replacements would obviate the need for the pre/post callbacks and
    > > allow you to run straight through.
    > For this particular example, you'd better be sure that $INSN doesn't
    > need %rsp intact.

    Well, either that of fix up the %rsp offset, but yes I had not
    considered this.

    > Control flow in general also makes this challenging. If $INSN is a
    > call, then any inline fixups won't get a chance until after return. If
    > $INSN is a jump, then its target must be modified so that both taken and
    > not-taken paths land in respective fixup locations. I'm sure there are
    > more cases that I'm not thinking of.


    > > It would also remove the whole single-step need since they're proper
    > > boosted probes.
    > Kprobes has boosting, but it doesn't apply to all opcodes. I would
    > guess that the same could be done for uprobes, where certain opcodes get
    > a fixup sequence like you suggest, but the pre/post_xol mechanism is
    > still needed in general.


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