[lldb-dev] Python API

snare at ho.ax snare at ho.ax
Wed Oct 9 19:01:06 PDT 2013 

Hi Jim,

I think you're right - a generalised hooking mechanism that could call arbitrary commands on various events would make more sense than a "template" mechanism. It would probably be easier to use than exposing the SBListener/SBBroadcaster stuff through the python API, and more useful than the current mechanism. 

The current mechanism is useful for individual cases, but not for general cases the way that GDB's "hook-stop" macro is. The inspiration for this tool came from fractalg's .gdbinit script[1], which (among other things) defines a stop hook that prints a bunch of nicely formatted context information whenever the debugger stops - registers, some disassembly, whether the branch will be taken if the current instruction is a branch, etc. It just defines a single stop-hook and does some magic based on what architecture the current target is. If I want to do this with LLDB it seems that I would have to manually add a stop-hook to every target.

> (lldb) hook add target.create --arch x86_64 --executable-name MyProg --platform-name remote-macosx
> Enter Target Create hook code, type DONE when done
>>>> hook add process.stop-hook -o "voltron update"
>>>> DONE

This looks good to me. If this had something like the -f option in `command script`  for calling a python function directly it would be even better :D

> Note, if we're going to do this, I'd also like to move the target stop-hooks into a general hook mechanism.  And you could add "process created/died" "shared library loaded" and "thread created/died" hooks for platforms that track this.  Some of these already get published by the event system, for those these "life cycle" hooks would just provide a convenient way to access the events from the command line.

Yeah this would be great.

Cheers,
Loukas

[1] https://github.com/gdbinit/Gdbinit


>> 
>> 
>> On 10/10/2013, at 3:58 AM, jingham at apple.com wrote:
>> 
>>> Right now, having multiple listeners getting process events doesn't really work.  So if you have both the driver listening to process events, and you try to peek at them from your code as well, that very likely will cause problems.
>>> 
>>> It wouldn't be impossible to make this work.  There is some asymmetry in process events, since some work goes on when the event is first fetched off the public queue (breakpoint commands get run, etc.)  So you'd have to be careful to make sure that work doesn't get re-done.  But it still could be made to work if needed.  It is on our queue of things to clean up, but not high on the list...
>>> 
>>> Jim
>>> 
>>> On Oct 9, 2013, at 9:45 AM, snare at ho.ax wrote:
>>> 
>>>> Hi Yin,
>>>> 
>>>> Voltron is not so much built "on top" of LLDB as it is "glued to the side". You still use the main LLDB CLI for interaction with the debugger, voltron just spins off a background thread to send out data updates to client views (e.g. stack view, register view, etc). Have a look at the screenshot on the github page and you'll see what I mean (though the screenshot is GDB): https://github.com/snarez/voltron
>>>> 
>>>> As such, it does not control everything that goes into and comes out of the CLI, so parsing the output isn't an option.
>>>> 
>>>> Loukas
>>>> 
>>>> On 10/10/2013, at 3:36 AM, "Yin Ma" <yin at affinic.com> wrote:
>>>> 
>>>>> Hi Loukas,
>>>>> 
>>>>> We are also developing a terminal-based GUI for lldb. Our
>>>>> Approach is to check the output from lldb to detect
>>>>> The status change. So far it seems working fine. 
>>>>> Could you let me know why you use listener approach?
>>>>> Do you get any case that parsing output doesn't work?
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> Yin
>>>>> 
>>>>> -----Original Message-----
>>>>> From: lldb-dev-bounces at cs.uiuc.edu [mailto:lldb-dev-bounces at cs.uiuc.edu] On Behalf Of Malea, Daniel
>>>>> Sent: Wednesday, October 09, 2013 8:20 AM
>>>>> To: snare at ho.ax; lldb-dev at cs.uiuc.edu
>>>>> Cc: Redmond, Paul
>>>>> Subject: Re: [lldb-dev] Python API
>>>>> 
>>>>> Hi Loukas,
>>>>> 
>>>>> I too have been working on a terminal UI for LLDB (but not GDB) with some
>>>>> colleagues (CC'd). I will commit what we have thus far shortly and you can
>>>>> see what we did, and maybe share some efforts/ideas.
>>>>> 
>>>>> BTW, in terms of listeners, we initialize them like so:
>>>>> 
>>>>> self.listener = debugger.GetListener()
>>>>> 
>>>>>    self.listener.StartListeningForEventClass(self.debugger,
>>>>> lldb.SBTarget.GetBroadcasterClassName(),
>>>>> | lldb.SBTarget.eBroadcastBitBreakpointChanged
>>>>> | lldb.SBTarget.eBroadcastBitWatchpointChanged
>>>>>                                       )
>>>>> 
>>>>>    self.listener.StartListeningForEventClass(self.debugger,
>>>>> 
>>>>> lldb.SBThread.GetBroadcasterClassName(),
>>>>> 
>>>>> lldb.SBThread.eBroadcastBitStackChanged
>>>>> |  lldb.SBThread.eBroadcastBitThreadSuspended
>>>>> | lldb.SBThread.eBroadcastBitThreadResumed
>>>>> | lldb.SBThread.eBroadcastBitSelectedFrameChanged
>>>>> | lldb.SBThread.eBroadcastBitThreadSelected
>>>>>                                       )
>>>>> 
>>>>>    self.listener.StartListeningForEventClass(self.debugger,
>>>>> lldb.SBProcess.GetBroadcasterClassName(),
>>>>> lldb.SBProcess.eBroadcastBitStateChanged
>>>>> | lldb.SBProcess.eBroadcastBitInterrupt
>>>>> | lldb.SBProcess.eBroadcastBitSTDOUT
>>>>> | lldb.SBProcess.eBroadcastBitSTDERR
>>>>> | lldb.SBProcess.eBroadcastBitProfileData
>>>>>                                       )
>>>>>    self.listener.StartListeningForEventClass(self.debugger,
>>>>> lldb.SBCommandInterpreter.GetBroadcasterClass(),
>>>>> lldb.SBCommandInterpreter.eBroadcastBitThreadShouldExit
>>>>> | lldb.SBCommandInterpreter.eBroadcastBitResetPrompt
>>>>> | lldb.SBCommandInterpreter.eBroadcastBitQuitCommandReceived
>>>>> | lldb.SBCommandInterpreter.eBroadcastBitAsynchronousOutputData
>>>>> | lldb.SBCommandInterpreter.eBroadcastBitAsynchronousErrorData
>>>>>                                       )
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> Cheers,
>>>>> Dan
>>>>> 
>>>>> 
>>>>> 
>>>>> On 2013-10-09 10:13 AM, "snare at ho.ax" <snare at ho.ax> wrote:
>>>>> 
>>>>>> Hi,
>>>>>> 
>>>>>> I've been working on a terminal-based UI for LLDB (and GDB)[1] recently
>>>>>> and I have a few questions about the Python API.
>>>>>> 
>>>>>> The way this tool works currently is by registering a new command that
>>>>>> sends updates to client views, and then registering a stop-hook that
>>>>>> calls that command whenever the debugger stops.
>>>>>> 
>>>>>> From looking at the sample python code and the LLDB source I think maybe
>>>>>> I could do the same thing using SBListener/SBBroadcaster/etc.
>>>>>> 
>>>>>> I've tried stuff like this:
>>>>>> 
>>>>>> listener = lldb.SBListener()
>>>>>> listener.StartListeningForEventClass(lldb.debugger, 'lldb.process',
>>>>>> 0xffffffff)
>>>>>> while 1:
>>>>>> if listener.WaitForEvent(1, event):
>>>>>>   print('got event: ' + event.GetDataFlavor())
>>>>>> 
>>>>>> But I don't get notifications for processes starting and stopping.
>>>>>> 
>>>>>> I've also tried stealing lldb.debugger's listener:
>>>>>> 
>>>>>> listener = lldb.debugger.GetListener()
>>>>>> 
>>>>>> Š but that hangs when I get the first event. I suspect maybe that's a
>>>>>> terrible idea, and not how it's meant to be done when the LLDB CLI has
>>>>>> created the SBDebugger instance and its listener.
>>>>>> 
>>>>>> Is it possible to do this from a script run within an existing LLDB
>>>>>> instance? It seems like all the sample code doing things like this is
>>>>>> actually instantiating the SBDebugger itself and fully automating the
>>>>>> debugging session, rather than being imported into LLDB and running from
>>>>>> there. 
>>>>>> 
>>>>>> I'd also like to receive notifications for the following events:
>>>>>> - a new file being loaded
>>>>>> - a target being run
>>>>>> - a target exiting
>>>>>> 
>>>>>> Thanks,
>>>>>> Loukas
>>>>>> 
>>>>>> [1] https://github.com/snarez/voltron
>>>>>> 
>>>>>> 
>>>>>> _______________________________________________
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>>>>>> lldb-dev at cs.uiuc.edu
>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
>>>>> 
>>>>> 
>>>>> _______________________________________________
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>>>> 
>>>> 
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> 

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