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Re: [remote protocol] step range?



On Sep 4, 2008, at 7:38 PM, Michael Snyder wrote:


I don't think that's necessarily true -- the remote agent
could just do what gdb does, single-step repeatedly and
check the stop pc against the range.

Yeah, that'll work as long as you have some form of single-instruction- step support in your target environment. If not, then you'll need a disassembler to (a) determine the length of the current instruction so you can overwrite the next instruction with a trap opcode, and (b) determine if the current instruction branches/calls/jumps anywhere. It quickly becomes Complicated. I'm assuming you have some form of single-instruction-step in the target you're interested in, otherwise I council against pursuing this. :)


For what it's worth we use the remote protocol for debugging applications on the iPhone / iPod Touch devices. When we first got it up and running, we saw command-line level "step" commands taking multiple (4-5!) seconds to complete. We optimized it to no end and got this down to something like .2 seconds without doing anything too weird to the protocol. We didn't have any single-instruction-step feature so we didn't even consider trying to push range-stepping down to the device.

But I don't see any problems with adding this stepping capability for environments that could make use of it.

Well, if the remote can deal with threads at all (eg. gdbserver),
then it could probably treat this just as gdb would.  A preemptive
stop in another thread would be outside the step range, therefore
we would tell gdb that we stopped.

Since we've established that you must have single-instruction-step capability in the target to do this, I think it's safe to assume that only the current continue thread will execute. But as you say, if the remote agent determines that it stopped in a different thread than it began the step, it can give up and return control to gdb.


J


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