Messages in this thread | | | Date | Tue, 25 Jan 2011 10:38:15 -0800 | From | Josh Stone <> | Subject | Re: [RFC] [PATCH 2.6.37-rc5-tip 10/20] 10: uprobes: task specific information. |
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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.
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.
Josh
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