Messages in this thread | | | Subject | Re: [RFC] [PATCH 2.6.37-rc5-tip 10/20] 10: uprobes: task specific information. | From | Peter Zijlstra <> | Date | Tue, 25 Jan 2011 20:56:35 +0100 |
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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.
Right.
> > 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.
Bummer..
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