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1 Python Reference
2 ================
4 The entire LLDB API is available as Python functions through a script bridging
5 interface. This means the LLDB API's can be used directly from python either
6 interactively or to build python apps that provide debugger features.
8 Additionally, Python can be used as a programmatic interface within the lldb
9 command interpreter (we refer to this for brevity as the embedded interpreter).
10 Of course, in this context it has full access to the LLDB API - with some
11 additional conveniences we will call out in the FAQ.
13 Documentation
14 --------------
16 The LLDB API is contained in a python module named lldb. A useful resource when
17 writing Python extensions is the lldb Python classes reference guide.
19 The documentation is also accessible in an interactive debugger session with
20 the following command:
22 ::
24 (lldb) script help(lldb)
25 Help on package lldb:
27 NAME
28 lldb - The lldb module contains the public APIs for Python binding.
30 FILE
31 /System/Library/PrivateFrameworks/LLDB.framework/Versions/A/Resources/Python/lldb/__init__.py
33 DESCRIPTION
34 ...
36 You can also get help using a module class name. The full API that is exposed
37 for that class will be displayed in a man page style window. Below we want to
38 get help on the lldb.SBFrame class:
40 ::
42 (lldb) script help(lldb.SBFrame)
43 Help on class SBFrame in module lldb:
45 class SBFrame(__builtin__.object)
46 | Represents one of the stack frames associated with a thread.
47 | SBThread contains SBFrame(s). For example (from test/lldbutil.py),
48 |
49 | def print_stacktrace(thread, string_buffer = False):
50 | '''Prints a simple stack trace of this thread.'''
51 |
52 ...
54 Or you can get help using any python object, here we use the lldb.process
55 object which is a global variable in the lldb module which represents the
56 currently selected process:
58 ::
60 (lldb) script help(lldb.process)
61 Help on SBProcess in module lldb object:
63 class SBProcess(__builtin__.object)
64 | Represents the process associated with the target program.
65 |
66 | SBProcess supports thread iteration. For example (from test/lldbutil.py),
67 |
68 | # ==================================================
69 | # Utility functions related to Threads and Processes
70 | # ==================================================
71 |
72 ...
74 Embedded Python Interpreter
75 ---------------------------
77 The embedded python interpreter can be accessed in a variety of ways from
78 within LLDB. The easiest way is to use the lldb command script with no
79 arguments at the lldb command prompt:
81 ::
83 (lldb) script
84 Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
85 >>> 2+3
86 5
87 >>> hex(12345)
88 '0x3039'
89 >>>
91 This drops you into the embedded python interpreter. When running under the
92 script command, lldb sets some convenience variables that give you quick access
93 to the currently selected entities that characterize the program and debugger
94 state. In each case, if there is no currently selected entity of the
95 appropriate type, the variable's IsValid method will return false. These
96 variables are:
98 +-------------------+---------------------+-------------------------------------+-------------------------------------------------------------------------------------+
99 | Variable | Type | Equivalent | Description |
100 +-------------------+---------------------+-------------------------------------+-------------------------------------------------------------------------------------+
101 | ``lldb.debugger`` | `lldb.SBDebugger` | `SBTarget.GetDebugger` | Contains the debugger object whose ``script`` command was invoked. |
102 | | | | The `lldb.SBDebugger` object owns the command interpreter |
103 | | | | and all the targets in your debug session. There will always be a |
104 | | | | Debugger in the embedded interpreter. |
105 +-------------------+---------------------+-------------------------------------+-------------------------------------------------------------------------------------+
106 | ``lldb.target`` | `lldb.SBTarget` | `SBDebugger.GetSelectedTarget` | Contains the currently selected target - for instance the one made with the |
107 | | | | ``file`` or selected by the ``target select <target-index>`` command. |
108 | | | `SBProcess.GetTarget` | The `lldb.SBTarget` manages one running process, and all the executable |
109 | | | | and debug files for the process. |
110 +-------------------+---------------------+-------------------------------------+-------------------------------------------------------------------------------------+
111 | ``lldb.process`` | `lldb.SBProcess` | `SBTarget.GetProcess` | Contains the process of the currently selected target. |
112 | | | | The `lldb.SBProcess` object manages the threads and allows access to |
113 | | | `SBThread.GetProcess` | memory for the process. |
114 +-------------------+---------------------+-------------------------------------+-------------------------------------------------------------------------------------+
115 | ``lldb.thread`` | `lldb.SBThread` | `SBProcess.GetSelectedThread` | Contains the currently selected thread. |
116 | | | | The `lldb.SBThread` object manages the stack frames in that thread. |
117 | | | `SBFrame.GetThread` | A thread is always selected in the command interpreter when a target stops. |
118 | | | | The ``thread select <thread-index>`` command can be used to change the |
119 | | | | currently selected thread. So as long as you have a stopped process, there will be |
120 | | | | some selected thread. |
121 +-------------------+---------------------+-------------------------------------+-------------------------------------------------------------------------------------+
122 | ``lldb.frame`` | `lldb.SBFrame` | `SBThread.GetSelectedFrame` | Contains the currently selected stack frame. |
123 | | | | The `lldb.SBFrame` object manage the stack locals and the register set for |
124 | | | | that stack. |
125 | | | | A stack frame is always selected in the command interpreter when a target stops. |
126 | | | | The ``frame select <frame-index>`` command can be used to change the |
127 | | | | currently selected frame. So as long as you have a stopped process, there will |
128 | | | | be some selected frame. |
129 +-------------------+---------------------+-------------------------------------+-------------------------------------------------------------------------------------+
131 While extremely convenient, these variables have a couple caveats that you
132 should be aware of. First of all, they hold the values of the selected objects
133 on entry to the embedded interpreter. They do not update as you use the LLDB
134 API's to change, for example, the currently selected stack frame or thread.
136 Moreover, they are only defined and meaningful while in the interactive Python
137 interpreter. There is no guarantee on their value in any other situation, hence
138 you should not use them when defining Python formatters, breakpoint scripts and
139 commands (or any other Python extension point that LLDB provides). For the
140 latter you'll be passed an `SBDebugger`, `SBTarget`, `SBProcess`, `SBThread` or
141 `SBFrame` instance and you can use the functions from the "Equivalent" column
142 to navigate between them.
144 As a rationale for such behavior, consider that lldb can run in a multithreaded
145 environment, and another thread might call the "script" command, changing the
146 value out from under you.
148 To get started with these objects and LLDB scripting, please note that almost
149 all of the lldb Python objects are able to briefly describe themselves when you
150 pass them to the Python print function:
152 ::
154 (lldb) script
155 Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
156 >>> print lldb.debugger
157 Debugger (instance: "debugger_1", id: 1)
158 >>> print lldb.target
159 a.out
160 >>> print lldb.process
161 SBProcess: pid = 59289, state = stopped, threads = 1, executable = a.out
162 >>> print lldb.thread
163 SBThread: tid = 0x1f03
164 >>> print lldb.frame
165 frame #0: 0x0000000100000bb6 a.out main + 54 at main.c:16
168 Running a python script when a breakpoint gets hit
169 --------------------------------------------------
171 One very powerful use of the lldb Python API is to have a python script run
172 when a breakpoint gets hit. Adding python scripts to breakpoints provides a way
173 to create complex breakpoint conditions and also allows for smart logging and
174 data gathering.
176 When your process hits a breakpoint to which you have attached some python
177 code, the code is executed as the body of a function which takes three
178 arguments:
180 ::
182 def breakpoint_function_wrapper(frame, bp_loc, internal_dict):
183 # Your code goes here
185 or:
187 ::
189 def breakpoint_function_wrapper(frame, bp_loc, extra_args, internal_dict):
190 # Your code goes here
193 +-------------------+-------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+
194 | Argument | Type | Description |
195 +-------------------+-------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+
196 | ``frame`` | `lldb.SBFrame` | The current stack frame where the breakpoint got hit. |
197 | | | The object will always be valid. |
198 | | | This ``frame`` argument might *not* match the currently selected stack frame found in the `lldb` module global variable ``lldb.frame``. |
199 +-------------------+-------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+
200 | ``bp_loc`` | `lldb.SBBreakpointLocation` | The breakpoint location that just got hit. Breakpoints are represented by `lldb.SBBreakpoint` |
201 | | | objects. These breakpoint objects can have one or more locations. These locations |
202 | | | are represented by `lldb.SBBreakpointLocation` objects. |
203 +-------------------+-------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+
204 | ``extra_args`` | `lldb.SBStructuredData` | ``Optional`` If your breakpoint callback function takes this extra parameter, then when the callback gets added to a breakpoint, its |
205 | | | contents can parametrize this use of the callback. For instance, instead of writing a callback that stops when the caller is "Foo", |
206 | | | you could take the function name from a field in the ``extra_args``, making the callback more general. The ``-k`` and ``-v`` options |
207 | | | to ``breakpoint command add`` will be passed as a Dictionary in the ``extra_args`` parameter, or you can provide it with the SB API's. |
208 +-------------------+-------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+
209 | ``internal_dict`` | ``dict`` | The python session dictionary as a standard python dictionary object. |
210 +-------------------+-------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+
212 Optionally, a Python breakpoint command can return a value. Returning False
213 tells LLDB that you do not want to stop at the breakpoint. Any other return
214 value (including None or leaving out the return statement altogether) is akin
215 to telling LLDB to actually stop at the breakpoint. This can be useful in
216 situations where a breakpoint only needs to stop the process when certain
217 conditions are met, and you do not want to inspect the program state manually
218 at every stop and then continue.
220 An example will show how simple it is to write some python code and attach it
221 to a breakpoint. The following example will allow you to track the order in
222 which the functions in a given shared library are first executed during one run
223 of your program. This is a simple method to gather an order file which can be
224 used to optimize function placement within a binary for execution locality.
226 We do this by setting a regular expression breakpoint that will match every
227 function in the shared library. The regular expression '.' will match any
228 string that has at least one character in it, so we will use that. This will
229 result in one lldb.SBBreakpoint object that contains an
230 lldb.SBBreakpointLocation object for each function. As the breakpoint gets hit,
231 we use a counter to track the order in which the function at this particular
232 breakpoint location got hit. Since our code is passed the location that was
233 hit, we can get the name of the function from the location, disable the
234 location so we won't count this function again; then log some info and continue
235 the process.
237 Note we also have to initialize our counter, which we do with the simple
238 one-line version of the script command.
240 Here is the code:
242 ::
244 (lldb) breakpoint set --func-regex=. --shlib=libfoo.dylib
245 Breakpoint created: 1: regex = '.', module = libfoo.dylib, locations = 223
246 (lldb) script counter = 0
247 (lldb) breakpoint command add --script-type python 1
248 Enter your Python command(s). Type 'DONE' to end.
249 > # Increment our counter. Since we are in a function, this must be a global python variable
250 > global counter
251 > counter += 1
252 > # Get the name of the function
253 > name = frame.GetFunctionName()
254 > # Print the order and the function name
255 > print '[%i] %s' % (counter, name)
256 > # Disable the current breakpoint location so it doesn't get hit again
257 > bp_loc.SetEnabled(False)
258 > # No need to stop here
259 > return False
260 > DONE
262 The breakpoint command add command above attaches a python script to breakpoint 1. To remove the breakpoint command:
264 ::
266 (lldb) breakpoint command delete 1
269 Using the python api's to create custom breakpoints
270 ---------------------------------------------------
273 Another use of the Python API's in lldb is to create a custom breakpoint
274 resolver. This facility was added in r342259.
276 It allows you to provide the algorithm which will be used in the breakpoint's
277 search of the space of the code in a given Target to determine where to set the
278 breakpoint locations - the actual places where the breakpoint will trigger. To
279 understand how this works you need to know a little about how lldb handles
280 breakpoints.
282 In lldb, a breakpoint is composed of three parts: the Searcher, the Resolver,
283 and the Stop Options. The Searcher and Resolver cooperate to determine how
284 breakpoint locations are set and differ between each breakpoint type. Stop
285 options determine what happens when a location triggers and includes the
286 commands, conditions, ignore counts, etc. Stop options are common between all
287 breakpoint types, so for our purposes only the Searcher and Resolver are
288 relevant.
290 The Searcher's job is to traverse in a structured way the code in the current
291 target. It proceeds from the Target, to search all the Modules in the Target,
292 in each Module it can recurse into the Compile Units in that module, and within
293 each Compile Unit it can recurse over the Functions it contains.
295 The Searcher can be provided with a SearchFilter that it will use to restrict
296 this search. For instance, if the SearchFilter specifies a list of Modules, the
297 Searcher will not recurse into Modules that aren't on the list. When you pass
298 the -s modulename flag to break set you are creating a Module-based search
299 filter. When you pass -f filename.c to break set -n you are creating a file
300 based search filter. If neither of these is specified, the breakpoint will have
301 a no-op search filter, so all parts of the program are searched and all
302 locations accepted.
304 The Resolver has two functions. The most important one is the callback it
305 provides. This will get called at the appropriate time in the course of the
306 search. The callback is where the job of adding locations to the breakpoint
307 gets done.
309 The other function is specifying to the Searcher at what depth in the above
310 described recursion it wants to be called. Setting a search depth also provides
311 a stop for the recursion. For instance, if you request a Module depth search,
312 then the callback will be called for each Module as it gets added to the
313 Target, but the searcher will not recurse into the Compile Units in the module.
315 One other slight subtlety is that the depth at which you get called back is not
316 necessarily the depth at which the SearchFilter is specified. For instance,
317 if you are doing symbol searches, it is convenient to use the Module depth for
318 the search, since symbols are stored in the module. But the SearchFilter might
319 specify some subset of CompileUnits, so not all the symbols you might find in
320 each module will pass the search. You don't need to handle this situation
321 yourself, since SBBreakpoint::AddLocation will only add locations that pass the
322 Search Filter. This API returns an SBError to inform you whether your location
323 was added.
325 When the breakpoint is originally created, its Searcher will process all the
326 currently loaded modules. The Searcher will also visit any new modules as they
327 are added to the target. This happens, for instance, when a new shared library
328 gets added to the target in the course of running, or on rerunning if any of
329 the currently loaded modules have been changed. Note, in the latter case, all
330 the locations set in the old module will get deleted and you will be asked to
331 recreate them in the new version of the module when your callback gets called
332 with that module. For this reason, you shouldn't try to manage the locations
333 you add to the breakpoint yourself. Note that the Breakpoint takes care of
334 deduplicating equal addresses in AddLocation, so you shouldn't need to worry
335 about that anyway.
337 At present, when adding a scripted Breakpoint type, you can only provide a
338 custom Resolver, not a custom SearchFilter.
340 The custom Resolver is provided as a Python class with the following methods:
342 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
343 | Name | Arguments | Description |
344 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
345 | ``__init__`` | ``bkpt``:`lldb.SBBreakpoint` | This is the constructor for the new Resolver. |
346 | | ``extra_args``:`lldb.SBStructuredData`| |
347 | | | |
348 | | | ``bkpt`` is the breakpoint owning this Resolver. |
349 | | | |
350 | | | |
351 | | | ``extra_args`` is an `SBStructuredData` object that the user can pass in when creating instances of this |
352 | | | breakpoint. It is not required, but is quite handy. For instance if you were implementing a breakpoint on some |
353 | | | symbol name, you could write a generic symbol name based Resolver, and then allow the user to pass |
354 | | | in the particular symbol in the extra_args |
355 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
356 | ``__callback__`` | ``sym_ctx``:`lldb.SBSymbolContext` | This is the Resolver callback. |
357 | | | The ``sym_ctx`` argument will be filled with the current stage |
358 | | | of the search. |
359 | | | |
360 | | | |
361 | | | For instance, if you asked for a search depth of lldb.eSearchDepthCompUnit, then the |
362 | | | target, module and compile_unit fields of the sym_ctx will be filled. The callback should look just in the |
363 | | | context passed in ``sym_ctx`` for new locations. If the callback finds an address of interest, it |
364 | | | can add it to the breakpoint with the `SBBreakpoint.AddLocation` method, using the breakpoint passed |
365 | | | in to the ``__init__`` method. |
366 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
367 | ``__get_depth__`` | ``None`` | Specify the depth at which you wish your callback to get called. The currently supported options are: |
368 | | | |
369 | | | `lldb.eSearchDepthModule` |
370 | | | `lldb.eSearchDepthCompUnit` |
371 | | | `lldb.eSearchDepthFunction` |
372 | | | |
373 | | | For instance, if you are looking |
374 | | | up symbols, which are stored at the Module level, you will want to get called back module by module. |
375 | | | So you would want to return `lldb.eSearchDepthModule`. This method is optional. If not provided the search |
376 | | | will be done at Module depth. |
377 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
378 | ``get_short_help`` | ``None`` | This is an optional method. If provided, the returned string will be printed at the beginning of |
379 | | | the description for this breakpoint. |
380 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
382 To define a new breakpoint command defined by this class from the lldb command
383 line, use the command:
385 ::
387 (lldb) breakpoint set -P MyModule.MyResolverClass
389 You can also populate the extra_args SBStructuredData with a dictionary of
390 key/value pairs with:
392 ::
394 (lldb) breakpoint set -P MyModule.MyResolverClass -k key_1 -v value_1 -k key_2 -v value_2
396 Although you can't write a scripted SearchFilter, both the command line and the
397 SB API's for adding a scripted resolver allow you to specify a SearchFilter
398 restricted to certain modules or certain compile units. When using the command
399 line to create the resolver, you can specify a Module specific SearchFilter by
400 passing the -s ModuleName option - which can be specified multiple times. You
401 can also specify a SearchFilter restricted to certain compile units by passing
402 in the -f CompUnitName option. This can also be specified more than once. And
403 you can mix the two to specify "this comp unit in this module". So, for
404 instance,
406 ::
408 (lldb) breakpoint set -P MyModule.MyResolverClass -s a.out
410 will use your resolver, but will only recurse into or accept new locations in
411 the module a.out.
413 Another option for creating scripted breakpoints is to use the
414 SBTarget.CreateBreakpointFromScript API. This one has the advantage that you
415 can pass in an arbitrary SBStructuredData object, so you can create more
416 complex parametrizations. SBStructuredData has a handy SetFromJSON method which
417 you can use for this purpose. Your __init__ function gets passed this
418 SBStructuredData object. This API also allows you to directly provide the list
419 of Modules and the list of CompileUnits that will make up the SearchFilter. If
420 you pass in empty lists, the breakpoint will use the default "search
421 everywhere,accept everything" filter.
423 Using the python API' to create custom stepping logic
424 -----------------------------------------------------
426 A slightly esoteric use of the Python API's is to construct custom stepping
427 types. LLDB's stepping is driven by a stack of "thread plans" and a fairly
428 simple state machine that runs the plans. You can create a Python class that
429 works as a thread plan, and responds to the requests the state machine makes to
430 run its operations.
432 There is a longer discussion of scripted thread plans and the state machine,
433 and several interesting examples of their use in:
435 https://github.com/llvm/llvm-project/blob/main/lldb/examples/python/scripted_step.py
437 And for a MUCH fuller discussion of the whole state machine, see:
439 https://github.com/llvm/llvm-project/blob/main/lldb/include/lldb/Target/ThreadPlan.h
441 If you are reading those comments it is useful to know that scripted thread
442 plans are set to be "ControllingPlans", and not "OkayToDiscard".
444 To implement a scripted step, you define a python class that has the following
445 methods:
447 +-------------------+------------------------------------+---------------------------------------------------------------------------------------+
448 | Name | Arguments | Description |
449 +-------------------+------------------------------------+---------------------------------------------------------------------------------------+
450 | ``__init__`` | ``thread_plan``:`lldb.SBThreadPlan`| This is the underlying `SBThreadPlan` that is pushed onto the plan stack. |
451 | | | You will want to store this away in an ivar. Also, if you are going to |
452 | | | use one of the canned thread plans, you can queue it at this point. |
453 +-------------------+------------------------------------+---------------------------------------------------------------------------------------+
454 | ``explains_stop`` | ``event``: `lldb.SBEvent` | Return True if this stop is part of your thread plans logic, false otherwise. |
455 +-------------------+------------------------------------+---------------------------------------------------------------------------------------+
456 | ``is_stale`` | ``None`` | If your plan is no longer relevant (for instance, you were |
457 | | | stepping in a particular stack frame, but some other operation |
458 | | | pushed that frame off the stack) return True and your plan will |
459 | | | get popped. |
460 +-------------------+------------------------------------+---------------------------------------------------------------------------------------+
461 | ``should_step`` | ``None`` | Return ``True`` if you want lldb to instruction step one instruction, |
462 | | | or False to continue till the next breakpoint is hit. |
463 +-------------------+------------------------------------+---------------------------------------------------------------------------------------+
464 | ``should_stop`` | ``event``: `lldb.SBEvent` | If your plan wants to stop and return control to the user at this point, return True. |
465 | | | If your plan is done at this point, call SetPlanComplete on your |
466 | | | thread plan instance. |
467 | | | Also, do any work you need here to set up the next stage of stepping. |
468 +-------------------+------------------------------------+---------------------------------------------------------------------------------------+
470 To use this class to implement a step, use the command:
472 ::
474 (lldb) thread step-scripted -C MyModule.MyStepPlanClass
476 Or use the SBThread.StepUsingScriptedThreadPlan API. The SBThreadPlan passed
477 into your __init__ function can also push several common plans (step
478 in/out/over and run-to-address) in front of itself on the stack, which can be
479 used to compose more complex stepping operations. When you use subsidiary plans
480 your explains_stop and should_stop methods won't get called until the
481 subsidiary plan is done, or the process stops for an event the subsidiary plan
482 doesn't explain. For instance, step over plans don't explain a breakpoint hit
483 while performing the step-over.
486 Create a new lldb command using a Python function
487 -------------------------------------------------
489 Python functions can be used to create new LLDB command interpreter commands,
490 which will work like all the natively defined lldb commands. This provides a
491 very flexible and easy way to extend LLDB to meet your debugging requirements.
493 To write a python function that implements a new LLDB command define the
494 function to take four arguments as follows:
496 ::
498 def command_function(debugger, command, result, internal_dict):
499 # Your code goes here
501 Optionally, you can also provide a Python docstring, and LLDB will use it when providing help for your command, as in:
503 ::
505 def command_function(debugger, command, result, internal_dict):
506 """This command takes a lot of options and does many fancy things"""
507 # Your code goes here
509 Since lldb 3.5.2, LLDB Python commands can also take an SBExecutionContext as an
510 argument. This is useful in cases where the command's notion of where to act is
511 independent of the currently-selected entities in the debugger.
513 This feature is enabled if the command-implementing function can be recognized
514 as taking 5 arguments, or a variable number of arguments, and it alters the
515 signature as such:
517 ::
519 def command_function(debugger, command, exe_ctx, result, internal_dict):
520 # Your code goes here
522 +-------------------+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------+
523 | Argument | Type | Description |
524 +-------------------+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------+
525 | ``debugger`` | `lldb.SBDebugger` | The current debugger object. |
526 +-------------------+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------+
527 | ``command`` | ``python string`` | A python string containing all arguments for your command. If you need to chop up the arguments |
528 | | | try using the ``shlex`` module's ``shlex.split(command)`` to properly extract the |
529 | | | arguments. |
530 +-------------------+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------+
531 | ``exe_ctx`` | `lldb.SBExecutionContext` | An execution context object carrying around information on the inferior process' context in which the command is expected to act |
532 | | | |
533 | | | *Optional since lldb 3.5.2, unavailable before* |
534 +-------------------+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------+
535 | ``result`` | `lldb.SBCommandReturnObject` | A return object which encapsulates success/failure information for the command and output text |
536 | | | that needs to be printed as a result of the command. The plain Python "print" command also works but |
537 | | | text won't go in the result by default (it is useful as a temporary logging facility). |
538 +-------------------+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------+
539 | ``internal_dict`` | ``python dict object`` | The dictionary for the current embedded script session which contains all variables |
540 | | | and functions. |
541 +-------------------+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------+
543 Since lldb 3.7, Python commands can also be implemented by means of a class
544 which should implement the following interface:
546 ::
548 class CommandObjectType:
549 def __init__(self, debugger, internal_dict):
550 this call should initialize the command with respect to the command interpreter for the passed-in debugger
551 def __call__(self, debugger, command, exe_ctx, result):
552 this is the actual bulk of the command, akin to Python command functions
553 def get_short_help(self):
554 this call should return the short help text for this command[1]
555 def get_long_help(self):
556 this call should return the long help text for this command[1]
558 [1] This method is optional.
560 As a convenience, you can treat the result object as a Python file object, and
561 say
563 ::
565 print >>result, "my command does lots of cool stuff"
567 SBCommandReturnObject and SBStream both support this file-like behavior by
568 providing write() and flush() calls at the Python layer.
570 One other handy convenience when defining lldb command-line commands is the
571 command command script import which will import a module specified by file
572 path, so you don't have to change your PYTHONPATH for temporary scripts. It
573 also has another convenience that if your new script module has a function of
574 the form:
576 ::
578 def __lldb_init_module(debugger, internal_dict):
579 # Command Initialization code goes here
581 where debugger and internal_dict are as above, that function will get run when
582 the module is loaded allowing you to add whatever commands you want into the
583 current debugger. Note that this function will only be run when using the LLDB
584 command ``command script import``, it will not get run if anyone imports your
585 module from another module.
587 The standard test for ``__main__``, like many python modules do, is useful for
588 creating scripts that can be run from the command line. However, for command
589 line scripts, the debugger instance must be created manually. Sample code would
590 look like:
592 ::
594 if __name__ == '__main__':
595 # Initialize the debugger before making any API calls.
596 lldb.SBDebugger.Initialize()
597 # Create a new debugger instance in your module if your module
598 # can be run from the command line. When we run a script from
599 # the command line, we won't have any debugger object in
600 # lldb.debugger, so we can just create it if it will be needed
601 debugger = lldb.SBDebugger.Create()
603 # Next, do whatever work this module should do when run as a command.
604 # ...
606 # Finally, dispose of the debugger you just made.
607 lldb.SBDebugger.Destroy(debugger)
608 # Terminate the debug session
609 lldb.SBDebugger.Terminate()
612 Now we can create a module called ls.py in the file ~/ls.py that will implement
613 a function that can be used by LLDB's python command code:
615 ::
617 #!/usr/bin/env python
619 import lldb
620 import commands
621 import optparse
622 import shlex
624 def ls(debugger, command, result, internal_dict):
625 print >>result, (commands.getoutput('/bin/ls %s' % command))
627 # And the initialization code to add your commands
628 def __lldb_init_module(debugger, internal_dict):
629 debugger.HandleCommand('command script add -f ls.ls ls')
630 print 'The "ls" python command has been installed and is ready for use.'
632 Now we can load the module into LLDB and use it
634 ::
636 $ lldb
637 (lldb) command script import ~/ls.py
638 The "ls" python command has been installed and is ready for use.
639 (lldb) ls -l /tmp/
640 total 365848
641 -rw-r--r--@ 1 someuser wheel 6148 Jan 19 17:27 .DS_Store
642 -rw------- 1 someuser wheel 7331 Jan 19 15:37 crash.log
644 You can also make "container" commands to organize the commands you are adding to
645 lldb. Most of the lldb built-in commands structure themselves this way, and using
646 a tree structure has the benefit of leaving the one-word command space free for user
647 aliases. It can also make it easier to find commands if you are adding more than
648 a few of them. Here's a trivial example of adding two "utility" commands into a
649 "my-utilities" container:
651 ::
653 #!/usr/bin/env python
655 import lldb
657 def first_utility(debugger, command, result, internal_dict):
658 print("I am the first utility")
660 def second_utility(debugger, command, result, internal_dict):
661 print("I am the second utility")
663 # And the initialization code to add your commands
664 def __lldb_init_module(debugger, internal_dict):
665 debugger.HandleCommand('command container add -h "A container for my utilities" my-utilities')
666 debugger.HandleCommand('command script add -f my_utilities.first_utility -h "My first utility" my-utilities first')
667 debugger.HandleCommand('command script add -f my_utilities.second_utility -h "My second utility" my-utilities second')
668 print('The "my-utilities" python command has been installed and its subcommands are ready for use.')
670 Then your new commands are available under the my-utilities node:
672 ::
674 (lldb) help my-utilities
675 A container for my utilities
677 Syntax: my-utilities
679 The following subcommands are supported:
681 first -- My first utility Expects 'raw' input (see 'help raw-input'.)
682 second -- My second utility Expects 'raw' input (see 'help raw-input'.)
684 For more help on any particular subcommand, type 'help <command> <subcommand>'.
685 (lldb) my-utilities first
686 I am the first utility
689 A more interesting template has been created in the source repository that can
690 help you to create lldb command quickly:
692 https://github.com/llvm/llvm-project/blob/main/lldb/examples/python/cmdtemplate.py
694 A commonly required facility is being able to create a command that does some
695 token substitution, and then runs a different debugger command (usually, it
696 po'es the result of an expression evaluated on its argument). For instance,
697 given the following program:
699 ::
701 #import <Foundation/Foundation.h>
702 NSString*
703 ModifyString(NSString* src)
704 {
705 return [src stringByAppendingString:@"foobar"];
706 }
708 int main()
709 {
710 NSString* aString = @"Hello world";
711 NSString* anotherString = @"Let's be friends";
712 return 1;
713 }
715 you may want a pofoo X command, that equates po [ModifyString(X)
716 capitalizedString]. The following debugger interaction shows how to achieve
717 that goal:
719 ::
721 (lldb) script
722 Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
723 >>> def pofoo_funct(debugger, command, result, internal_dict):
724 ... cmd = "po [ModifyString(" + command + ") capitalizedString]"
725 ... debugger.HandleCommand(cmd)
726 ...
727 >>> ^D
728 (lldb) command script add pofoo -f pofoo_funct
729 (lldb) pofoo aString
730 $1 = 0x000000010010aa00 Hello Worldfoobar
731 (lldb) pofoo anotherString
732 $2 = 0x000000010010aba0 Let's Be Friendsfoobar
734 Using the lldb.py module in Python
735 ----------------------------------
737 LLDB has all of its core code build into a shared library which gets used by
738 the `lldb` command line application. On macOS this shared library is a
739 framework: LLDB.framework and on other unix variants the program is a shared
740 library: lldb.so. LLDB also provides an lldb.py module that contains the
741 bindings from LLDB into Python. To use the LLDB.framework to create your own
742 stand-alone python programs, you will need to tell python where to look in
743 order to find this module. This is done by setting the PYTHONPATH environment
744 variable, adding a path to the directory that contains the lldb.py python
745 module. The lldb driver program has an option to report the path to the lldb
746 module. You can use that to point to correct lldb.py:
748 For csh and tcsh:
750 ::
752 % setenv PYTHONPATH `lldb -P`
754 For sh and bash:
756 ::
758 $ export PYTHONPATH=`lldb -P`
760 Alternately, you can append the LLDB Python directory to the sys.path list
761 directly in your Python code before importing the lldb module.
763 Now your python scripts are ready to import the lldb module. Below is a python
764 script that will launch a program from the current working directory called
765 "a.out", set a breakpoint at "main", and then run and hit the breakpoint, and
766 print the process, thread and frame objects if the process stopped:
768 ::
770 #!/usr/bin/env python
772 import lldb
773 import os
775 def disassemble_instructions(insts):
776 for i in insts:
777 print i
779 # Set the path to the executable to debug
780 exe = "./a.out"
782 # Create a new debugger instance
783 debugger = lldb.SBDebugger.Create()
785 # When we step or continue, don't return from the function until the process
786 # stops. Otherwise we would have to handle the process events ourselves which, while doable is
787 #a little tricky. We do this by setting the async mode to false.
788 debugger.SetAsync (False)
790 # Create a target from a file and arch
791 print "Creating a target for '%s'" % exe
793 target = debugger.CreateTargetWithFileAndArch (exe, lldb.LLDB_ARCH_DEFAULT)
795 if target:
796 # If the target is valid set a breakpoint at main
797 main_bp = target.BreakpointCreateByName ("main", target.GetExecutable().GetFilename());
799 print main_bp
801 # Launch the process. Since we specified synchronous mode, we won't return
802 # from this function until we hit the breakpoint at main
803 process = target.LaunchSimple (None, None, os.getcwd())
805 # Make sure the launch went ok
806 if process:
807 # Print some simple process info
808 state = process.GetState ()
809 print process
810 if state == lldb.eStateStopped:
811 # Get the first thread
812 thread = process.GetThreadAtIndex (0)
813 if thread:
814 # Print some simple thread info
815 print thread
816 # Get the first frame
817 frame = thread.GetFrameAtIndex (0)
818 if frame:
819 # Print some simple frame info
820 print frame
821 function = frame.GetFunction()
822 # See if we have debug info (a function)
823 if function:
824 # We do have a function, print some info for the function
825 print function
826 # Now get all instructions for this function and print them
827 insts = function.GetInstructions(target)
828 disassemble_instructions (insts)
829 else:
830 # See if we have a symbol in the symbol table for where we stopped
831 symbol = frame.GetSymbol();
832 if symbol:
833 # We do have a symbol, print some info for the symbol
834 print symbol
836 Writing lldb frame recognizers in Python
837 ----------------------------------------
839 Frame recognizers allow for retrieving information about special frames based
840 on ABI, arguments or other special properties of that frame, even without
841 source code or debug info. Currently, one use case is to extract function
842 arguments that would otherwise be inaccessible, or augment existing arguments.
844 Adding a custom frame recognizer is done by implementing a Python class and
845 using the 'frame recognizer add' command. The Python class should have a
846 'get_recognized_arguments' method and it will receive an argument of type
847 lldb.SBFrame representing the current frame that we are trying to recognize.
848 The method should return a (possibly empty) list of lldb.SBValue objects that
849 represent the recognized arguments.
851 An example of a recognizer that retrieves the file descriptor values from libc
852 functions 'read', 'write' and 'close' follows:
854 ::
856 class LibcFdRecognizer(object):
857 def get_recognized_arguments(self, frame):
858 if frame.name in ["read", "write", "close"]:
859 fd = frame.EvaluateExpression("$arg1").unsigned
860 target = frame.thread.process.target
861 value = target.CreateValueFromExpression("fd", "(int)%d" % fd)
862 return [value]
863 return []
865 The file containing this implementation can be imported via ``command script import``
866 and then we can register this recognizer with ``frame recognizer add``.
867 It's important to restrict the recognizer to the libc library (which is
868 libsystem_kernel.dylib on macOS) to avoid matching functions with the same name
869 in other modules:
871 ::
873 (lldb) command script import .../fd_recognizer.py
874 (lldb) frame recognizer add -l fd_recognizer.LibcFdRecognizer -n read -s libsystem_kernel.dylib
876 When the program is stopped at the beginning of the 'read' function in libc, we can view the recognizer arguments in 'frame variable':
878 ::
880 (lldb) b read
881 (lldb) r
882 Process 1234 stopped
883 * thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.3
884 frame #0: 0x00007fff06013ca0 libsystem_kernel.dylib`read
885 (lldb) frame variable
886 (int) fd = 3
888 Writing Target Stop-Hooks in Python:
889 ------------------------------------
891 Stop hooks fire whenever the process stops just before control is returned to the
892 user. Stop hooks can either be a set of lldb command-line commands, or can
893 be implemented by a suitably defined Python class. The Python based stop-hooks
894 can also be passed as set of -key -value pairs when they are added, and those
895 will get packaged up into a SBStructuredData Dictionary and passed to the
896 constructor of the Python object managing the stop hook. This allows for
897 parametrization of the stop hooks.
899 To add a Python-based stop hook, first define a class with the following methods:
901 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
902 | Name | Arguments | Description |
903 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
904 | ``__init__`` | ``target: lldb.SBTarget`` | This is the constructor for the new stop-hook. |
905 | | ``extra_args: lldb.SBStructuredData`` | |
906 | | | |
907 | | | ``target`` is the SBTarget to which the stop hook is added. |
908 | | | |
909 | | | ``extra_args`` is an SBStructuredData object that the user can pass in when creating instances of this |
910 | | | breakpoint. It is not required, but allows for reuse of stop-hook classes. |
911 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
912 | ``handle_stop`` | ``exe_ctx: lldb.SBExecutionContext`` | This is the called when the target stops. |
913 | | ``stream: lldb.SBStream`` | |
914 | | | ``exe_ctx`` argument will be filled with the current stop point for which the stop hook is |
915 | | | being evaluated. |
916 | | | |
917 | | | ``stream`` an lldb.SBStream, anything written to this stream will be written to the debugger console. |
918 | | | |
919 | | | The return value is a "Should Stop" vote from this thread. If the method returns either True or no return |
920 | | | this thread votes to stop. If it returns False, then the thread votes to continue after all the stop-hooks |
921 | | | are evaluated. |
922 | | | Note, the --auto-continue flag to 'target stop-hook add' overrides a True return value from the method. |
923 +--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+
925 To use this class in lldb, run the command:
927 ::
929 (lldb) command script import MyModule.py
930 (lldb) target stop-hook add -P MyModule.MyStopHook -k first -v 1 -k second -v 2
932 where MyModule.py is the file containing the class definition MyStopHook.