1Python Reference 2================ 3 4The entire LLDB API is available as Python functions through a script bridging 5interface. This means the LLDB API's can be used directly from python either 6interactively or to build python apps that provide debugger features. 7 8Additionally, Python can be used as a programmatic interface within the lldb 9command interpreter (we refer to this for brevity as the embedded interpreter). 10Of course, in this context it has full access to the LLDB API - with some 11additional conveniences we will call out in the FAQ. 12 13.. contents:: 14 :local: 15 16Documentation 17-------------- 18 19The LLDB API is contained in a python module named lldb. A useful resource when 20writing Python extensions is the lldb Python classes reference guide. 21 22The documentation is also accessible in an interactive debugger session with 23the following command: 24 25:: 26 27 (lldb) script help(lldb) 28 Help on package lldb: 29 30 NAME 31 lldb - The lldb module contains the public APIs for Python binding. 32 33 FILE 34 /System/Library/PrivateFrameworks/LLDB.framework/Versions/A/Resources/Python/lldb/__init__.py 35 36 DESCRIPTION 37 ... 38 39You can also get help using a module class name. The full API that is exposed 40for that class will be displayed in a man page style window. Below we want to 41get help on the lldb.SBFrame class: 42 43:: 44 45 (lldb) script help(lldb.SBFrame) 46 Help on class SBFrame in module lldb: 47 48 class SBFrame(__builtin__.object) 49 | Represents one of the stack frames associated with a thread. 50 | SBThread contains SBFrame(s). For example (from test/lldbutil.py), 51 | 52 | def print_stacktrace(thread, string_buffer = False): 53 | '''Prints a simple stack trace of this thread.''' 54 | 55 ... 56 57Or you can get help using any python object, here we use the lldb.process 58object which is a global variable in the lldb module which represents the 59currently selected process: 60 61:: 62 63 (lldb) script help(lldb.process) 64 Help on SBProcess in module lldb object: 65 66 class SBProcess(__builtin__.object) 67 | Represents the process associated with the target program. 68 | 69 | SBProcess supports thread iteration. For example (from test/lldbutil.py), 70 | 71 | # ================================================== 72 | # Utility functions related to Threads and Processes 73 | # ================================================== 74 | 75 ... 76 77Embedded Python Interpreter 78--------------------------- 79 80The embedded python interpreter can be accessed in a variety of ways from 81within LLDB. The easiest way is to use the lldb command script with no 82arguments at the lldb command prompt: 83 84:: 85 86 (lldb) script 87 Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D. 88 >>> 2+3 89 5 90 >>> hex(12345) 91 '0x3039' 92 >>> 93 94This drops you into the embedded python interpreter. When running under the 95script command, lldb sets some convenience variables that give you quick access 96to the currently selected entities that characterize the program and debugger 97state. In each case, if there is no currently selected entity of the 98appropriate type, the variable's IsValid method will return false. These 99variables are: 100 101+-------------------+---------------------+-------------------------------------------------------------------------------------+ 102| Variable | Type | Description | 103+-------------------+---------------------+-------------------------------------------------------------------------------------+ 104| **lldb.debugger** | **lldb.SBDebugger** | Contains the debugger object whose **script** command was invoked. | 105| | | The **lldb.SBDebugger** object owns the command interpreter | 106| | | and all the targets in your debug session. There will always be a | 107| | | Debugger in the embedded interpreter. | 108+-------------------+---------------------+-------------------------------------------------------------------------------------+ 109| **lldb.target** | **lldb.SBTarget** | Contains the currently selected target - for instance the one made with the | 110| | | **file** or selected by the **target select <target-index>** command. | 111| | | The **lldb.SBTarget** manages one running process, and all the executable | 112| | | and debug files for the process. | 113+-------------------+---------------------+-------------------------------------------------------------------------------------+ 114| **lldb.process** | **lldb.SBProcess** | Contains the process of the currently selected target. | 115| | | The **lldb.SBProcess** object manages the threads and allows access to | 116| | | memory for the process. | 117+-------------------+---------------------+-------------------------------------------------------------------------------------+ 118| **lldb.thread** | **lldb.SBThread** | Contains the currently selected thread. | 119| | | The **lldb.SBThread** object manages the stack frames in that thread. | 120| | | A thread is always selected in the command interpreter when a target stops. | 121| | | The **thread select <thread-index>** command can be used to change the | 122| | | currently selected thread. So as long as you have a stopped process, there will be | 123| | | some selected thread. | 124+-------------------+---------------------+-------------------------------------------------------------------------------------+ 125| **lldb.frame** | **lldb.SBFrame** | Contains the currently selected stack frame. | 126| | | The **lldb.SBFrame** object manage the stack locals and the register set for | 127| | | that stack. | 128| | | A stack frame is always selected in the command interpreter when a target stops. | 129| | | The **frame select <frame-index>** command can be used to change the | 130| | | currently selected frame. So as long as you have a stopped process, there will | 131| | | be some selected frame. | 132+-------------------+---------------------+-------------------------------------------------------------------------------------+ 133 134 135While extremely convenient, these variables have a couple caveats that you 136should be aware of. First of all, they hold the values of the selected objects 137on entry to the embedded interpreter. They do not update as you use the LLDB 138API's to change, for example, the currently selected stack frame or thread. 139 140Moreover, they are only defined and meaningful while in the interactive Python 141interpreter. There is no guarantee on their value in any other situation, hence 142you should not use them when defining Python formatters, breakpoint scripts and 143commands (or any other Python extension point that LLDB provides). As a 144rationale for such behavior, consider that lldb can run in a multithreaded 145environment, and another thread might call the "script" command, changing the 146value out from under you. 147 148To get started with these objects and LLDB scripting, please note that almost 149all of the lldb Python objects are able to briefly describe themselves when you 150pass them to the Python print function: 151 152:: 153 154 (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:16 166 167 168Running a python script when a breakpoint gets hit 169-------------------------------------------------- 170 171One very powerful use of the lldb Python API is to have a python script run 172when a breakpoint gets hit. Adding python scripts to breakpoints provides a way 173to create complex breakpoint conditions and also allows for smart logging and 174data gathering. 175 176When your process hits a breakpoint to which you have attached some python 177code, the code is executed as the body of a function which takes three 178arguments: 179 180:: 181 182 def breakpoint_function_wrapper(frame, bp_loc, internal_dict): 183 # Your code goes here 184 185or: 186 187:: 188 189 def breakpoint_function_wrapper(frame, bp_loc, extra_args, internal_dict): 190 # Your code goes here 191 192 193+-------------------+-------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+ 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+-------------------+-------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+ 211 212Optionally, a Python breakpoint command can return a value. Returning False 213tells LLDB that you do not want to stop at the breakpoint. Any other return 214value (including None or leaving out the return statement altogether) is akin 215to telling LLDB to actually stop at the breakpoint. This can be useful in 216situations where a breakpoint only needs to stop the process when certain 217conditions are met, and you do not want to inspect the program state manually 218at every stop and then continue. 219 220An example will show how simple it is to write some python code and attach it 221to a breakpoint. The following example will allow you to track the order in 222which the functions in a given shared library are first executed during one run 223of your program. This is a simple method to gather an order file which can be 224used to optimize function placement within a binary for execution locality. 225 226We do this by setting a regular expression breakpoint that will match every 227function in the shared library. The regular expression '.' will match any 228string that has at least one character in it, so we will use that. This will 229result in one lldb.SBBreakpoint object that contains an 230lldb.SBBreakpointLocation object for each function. As the breakpoint gets hit, 231we use a counter to track the order in which the function at this particular 232breakpoint location got hit. Since our code is passed the location that was 233hit, we can get the name of the function from the location, disable the 234location so we won't count this function again; then log some info and continue 235the process. 236 237Note we also have to initialize our counter, which we do with the simple 238one-line version of the script command. 239 240Here is the code: 241 242:: 243 244 (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 261 262The breakpoint command add command above attaches a python script to breakpoint 1. To remove the breakpoint command: 263 264:: 265 266 (lldb) breakpoint command delete 1 267 268 269Using the python api's to create custom breakpoints 270--------------------------------------------------- 271 272 273Another use of the Python API's in lldb is to create a custom breakpoint 274resolver. This facility was added in r342259. 275 276It allows you to provide the algorithm which will be used in the breakpoint's 277search of the space of the code in a given Target to determine where to set the 278breakpoint locations - the actual places where the breakpoint will trigger. To 279understand how this works you need to know a little about how lldb handles 280breakpoints. 281 282In lldb, a breakpoint is composed of three parts: the Searcher, the Resolver, 283and the Stop Options. The Searcher and Resolver cooperate to determine how 284breakpoint locations are set and differ between each breakpoint type. Stop 285options determine what happens when a location triggers and includes the 286commands, conditions, ignore counts, etc. Stop options are common between all 287breakpoint types, so for our purposes only the Searcher and Resolver are 288relevant. 289 290The Searcher's job is to traverse in a structured way the code in the current 291target. It proceeds from the Target, to search all the Modules in the Target, 292in each Module it can recurse into the Compile Units in that module, and within 293each Compile Unit it can recurse over the Functions it contains. 294 295The Searcher can be provided with a SearchFilter that it will use to restrict 296this search. For instance, if the SearchFilter specifies a list of Modules, the 297Searcher will not recurse into Modules that aren't on the list. When you pass 298the -s modulename flag to break set you are creating a Module-based search 299filter. When you pass -f filename.c to break set -n you are creating a file 300based search filter. If neither of these is specified, the breakpoint will have 301a no-op search filter, so all parts of the program are searched and all 302locations accepted. 303 304The Resolver has two functions. The most important one is the callback it 305provides. This will get called at the appropriate time in the course of the 306search. The callback is where the job of adding locations to the breakpoint 307gets done. 308 309The other function is specifying to the Searcher at what depth in the above 310described recursion it wants to be called. Setting a search depth also provides 311a stop for the recursion. For instance, if you request a Module depth search, 312then the callback will be called for each Module as it gets added to the 313Target, but the searcher will not recurse into the Compile Units in the module. 314 315One other slight sublety is that the depth at which you get called back is not 316necessarily the depth at which the the SearchFilter is specified. For instance, 317if you are doing symbol searches, it is convenient to use the Module depth for 318the search, since symbols are stored in the module. But the SearchFilter might 319specify some subset of CompileUnits, so not all the symbols you might find in 320each module will pass the search. You don't need to handle this situation 321yourself, since SBBreakpoint::AddLocation will only add locations that pass the 322Search Filter. This API returns an SBError to inform you whether your location 323was added. 324 325When the breakpoint is originally created, its Searcher will process all the 326currently loaded modules. The Searcher will also visit any new modules as they 327are added to the target. This happens, for instance, when a new shared library 328gets added to the target in the course of running, or on rerunning if any of 329the currently loaded modules have been changed. Note, in the latter case, all 330the locations set in the old module will get deleted and you will be asked to 331recreate them in the new version of the module when your callback gets called 332with that module. For this reason, you shouldn't try to manage the locations 333you add to the breakpoint yourself. Note that the Breakpoint takes care of 334deduplicating equal addresses in AddLocation, so you shouldn't need to worry 335about that anyway. 336 337At present, when adding a scripted Breakpoint type, you can only provide a 338custom Resolver, not a custom SearchFilter. 339 340The custom Resolver is provided as a Python class with the following methods: 341 342+--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+ 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+--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+ 381 382To define a new breakpoint command defined by this class from the lldb command 383line, use the command: 384 385:: 386 387 (lldb) breakpoint set -P MyModule.MyResolverClass 388 389You can also populate the extra_args SBStructuredData with a dictionary of 390key/value pairs with: 391 392:: 393 394 (lldb) breakpoint set -P MyModule.MyResolverClass -k key_1 -v value_1 -k key_2 -v value_2 395 396Although you can't write a scripted SearchFilter, both the command line and the 397SB API's for adding a scripted resolver allow you to specify a SearchFilter 398restricted to certain modules or certain compile units. When using the command 399line to create the resolver, you can specify a Module specific SearchFilter by 400passing the -s ModuleName option - which can be specified multiple times. You 401can also specify a SearchFilter restricted to certain compile units by passing 402in the -f CompUnitName option. This can also be specified more than once. And 403you can mix the two to specify "this comp unit in this module". So, for 404instance, 405 406:: 407 408 (lldb) breakpoint set -P MyModule.MyResolverClass -s a.out 409 410will use your resolver, but will only recurse into or accept new locations in 411the module a.out. 412 413Another option for creating scripted breakpoints is to use the 414SBTarget.CreateBreakpointFromScript API. This one has the advantage that you 415can pass in an arbitrary SBStructuredData object, so you can create more 416complex parametrizations. SBStructuredData has a handy SetFromJSON method which 417you can use for this purpose. Your __init__ function gets passed this 418SBStructuredData object. This API also allows you to directly provide the list 419of Modules and the list of CompileUnits that will make up the SearchFilter. If 420you pass in empty lists, the breakpoint will use the default "search 421everywhere,accept everything" filter. 422 423Using the python API' to create custom stepping logic 424----------------------------------------------------- 425 426A slightly esoteric use of the Python API's is to construct custom stepping 427types. LLDB's stepping is driven by a stack of "thread plans" and a fairly 428simple state machine that runs the plans. You can create a Python class that 429works as a thread plan, and responds to the requests the state machine makes to 430run its operations. 431 432There is a longer discussion of scripted thread plans and the state machine, 433and several interesting examples of their use in: 434 435https://github.com/llvm/llvm-project/blob/main/lldb/examples/python/scripted_step.py 436 437And for a MUCH fuller discussion of the whole state machine, see: 438 439https://github.com/llvm/llvm-project/blob/main/lldb/include/lldb/Target/ThreadPlan.h 440 441If you are reading those comments it is useful to know that scripted thread 442plans are set to be "MasterPlans", and not "OkayToDiscard". 443 444To implement a scripted step, you define a python class that has the following 445methods: 446 447+-------------------+------------------------------------+---------------------------------------------------------------------------------------+ 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+-------------------+------------------------------------+---------------------------------------------------------------------------------------+ 469 470To use this class to implement a step, use the command: 471 472:: 473 474 (lldb) thread step-scripted -C MyModule.MyStepPlanClass 475 476Or use the SBThread.StepUsingScriptedThreadPlan API. The SBThreadPlan passed 477into your __init__ function can also push several common plans (step 478in/out/over and run-to-address) in front of itself on the stack, which can be 479used to compose more complex stepping operations. When you use subsidiary plans 480your explains_stop and should_stop methods won't get called until the 481subsidiary plan is done, or the process stops for an event the subsidiary plan 482doesn't explain. For instance, step over plans don't explain a breakpoint hit 483while performing the step-over. 484 485 486Create a new lldb command using a Python function 487------------------------------------------------- 488 489Python functions can be used to create new LLDB command interpreter commands, 490which will work like all the natively defined lldb commands. This provides a 491very flexible and easy way to extend LLDB to meet your debugging requirements. 492 493To write a python function that implements a new LLDB command define the 494function to take four arguments as follows: 495 496:: 497 498 def command_function(debugger, command, result, internal_dict): 499 # Your code goes here 500 501Optionally, you can also provide a Python docstring, and LLDB will use it when providing help for your command, as in: 502 503:: 504 505 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 508 509Since lldb 3.5.2, LLDB Python commands can also take an SBExecutionContext as an 510argument. This is useful in cases where the command's notion of where to act is 511independent of the currently-selected entities in the debugger. 512 513This feature is enabled if the command-implementing function can be recognized 514as taking 5 arguments, or a variable number of arguments, and it alters the 515signature as such: 516 517:: 518 519 def command_function(debugger, command, exe_ctx, result, internal_dict): 520 # Your code goes here 521 522+-------------------+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------+ 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+-------------------+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------+ 542 543Since lldb 3.7, Python commands can also be implemented by means of a class 544which should implement the following interface: 545 546:: 547 548 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] 557 558[1] This method is optional. 559 560As a convenience, you can treat the result object as a Python file object, and 561say 562 563:: 564 565 print >>result, "my command does lots of cool stuff" 566 567SBCommandReturnObject and SBStream both support this file-like behavior by 568providing write() and flush() calls at the Python layer. 569 570One other handy convenience when defining lldb command-line commands is the 571command command script import which will import a module specified by file 572path, so you don't have to change your PYTHONPATH for temporary scripts. It 573also has another convenience that if your new script module has a function of 574the form: 575 576:: 577 578 def __lldb_init_module(debugger, internal_dict): 579 # Command Initialization code goes here 580 581where debugger and internal_dict are as above, that function will get run when 582the module is loaded allowing you to add whatever commands you want into the 583current debugger. Note that this function will only be run when using the LLDB 584command command script import, it will not get run if anyone imports your 585module from another module. If you want to always run code when your module is 586loaded from LLDB or when loaded via an import statement in python code you can 587test the lldb.debugger object, since you imported the module at the top of the 588python ls.py module. This test must be in code that isn't contained inside of 589any function or class, just like the standard test for __main__ like all python 590modules usually do. Sample code would look like: 591 592:: 593 594 if __name__ == '__main__': 595 # Create a new debugger instance in your module if your module 596 # can be run from the command line. When we run a script from 597 # the command line, we won't have any debugger object in 598 # lldb.debugger, so we can just create it if it will be needed 599 lldb.debugger = lldb.SBDebugger.Create() 600 elif lldb.debugger: 601 # Module is being run inside the LLDB interpreter 602 lldb.debugger.HandleCommand('command script add -f ls.ls ls') 603 print 'The "ls" python command has been installed and is ready for use.' 604 605Now we can create a module called ls.py in the file ~/ls.py that will implement 606a function that can be used by LLDB's python command code: 607 608:: 609 610 #!/usr/bin/python 611 612 import lldb 613 import commands 614 import optparse 615 import shlex 616 617 def ls(debugger, command, result, internal_dict): 618 print >>result, (commands.getoutput('/bin/ls %s' % command)) 619 620 # And the initialization code to add your commands 621 def __lldb_init_module(debugger, internal_dict): 622 debugger.HandleCommand('command script add -f ls.ls ls') 623 print 'The "ls" python command has been installed and is ready for use.' 624 625Now we can load the module into LLDB and use it 626 627:: 628 629 % lldb 630 (lldb) command script import ~/ls.py 631 The "ls" python command has been installed and is ready for use. 632 (lldb) ls -l /tmp/ 633 total 365848 634 -rw-r--r--@ 1 someuser wheel 6148 Jan 19 17:27 .DS_Store 635 -rw------- 1 someuser wheel 7331 Jan 19 15:37 crash.log 636 637A more interesting template has been created in the source repository that can 638help you to create lldb command quickly: 639 640https://github.com/llvm/llvm-project/blob/main/lldb/examples/python/cmdtemplate.py 641 642A commonly required facility is being able to create a command that does some 643token substitution, and then runs a different debugger command (usually, it 644po'es the result of an expression evaluated on its argument). For instance, 645given the following program: 646 647:: 648 649 #import <Foundation/Foundation.h> 650 NSString* 651 ModifyString(NSString* src) 652 { 653 return [src stringByAppendingString:@"foobar"]; 654 } 655 656 int main() 657 { 658 NSString* aString = @"Hello world"; 659 NSString* anotherString = @"Let's be friends"; 660 return 1; 661 } 662 663you may want a pofoo X command, that equates po [ModifyString(X) 664capitalizedString]. The following debugger interaction shows how to achieve 665that goal: 666 667:: 668 669 (lldb) script 670 Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D. 671 >>> def pofoo_funct(debugger, command, result, internal_dict): 672 ... cmd = "po [ModifyString(" + command + ") capitalizedString]" 673 ... lldb.debugger.HandleCommand(cmd) 674 ... 675 >>> ^D 676 (lldb) command script add pofoo -f pofoo_funct 677 (lldb) pofoo aString 678 $1 = 0x000000010010aa00 Hello Worldfoobar 679 (lldb) pofoo anotherString 680 $2 = 0x000000010010aba0 Let's Be Friendsfoobar 681 682Using the lldb.py module in Python 683---------------------------------- 684 685LLDB has all of its core code build into a shared library which gets used by 686the `lldb` command line application. On macOS this shared library is a 687framework: LLDB.framework and on other unix variants the program is a shared 688library: lldb.so. LLDB also provides an lldb.py module that contains the 689bindings from LLDB into Python. To use the LLDB.framework to create your own 690stand-alone python programs, you will need to tell python where to look in 691order to find this module. This is done by setting the PYTHONPATH environment 692variable, adding a path to the directory that contains the lldb.py python 693module. The lldb driver program has an option to report the path to the lldb 694module. You can use that to point to correct lldb.py: 695 696For csh and tcsh: 697 698:: 699 700 % setenv PYTHONPATH `lldb -P` 701 702For sh and bash: 703 704:: 705 706 % export PYTHONPATH=`lldb -P` 707 708Alternately, you can append the LLDB Python directory to the sys.path list 709directly in your Python code before importing the lldb module. 710 711Now your python scripts are ready to import the lldb module. Below is a python 712script that will launch a program from the current working directory called 713"a.out", set a breakpoint at "main", and then run and hit the breakpoint, and 714print the process, thread and frame objects if the process stopped: 715 716:: 717 718 #!/usr/bin/python 719 720 import lldb 721 import os 722 723 def disassemble_instructions(insts): 724 for i in insts: 725 print i 726 727 # Set the path to the executable to debug 728 exe = "./a.out" 729 730 # Create a new debugger instance 731 debugger = lldb.SBDebugger.Create() 732 733 # When we step or continue, don't return from the function until the process 734 # stops. Otherwise we would have to handle the process events ourselves which, while doable is 735 #a little tricky. We do this by setting the async mode to false. 736 debugger.SetAsync (False) 737 738 # Create a target from a file and arch 739 print "Creating a target for '%s'" % exe 740 741 target = debugger.CreateTargetWithFileAndArch (exe, lldb.LLDB_ARCH_DEFAULT) 742 743 if target: 744 # If the target is valid set a breakpoint at main 745 main_bp = target.BreakpointCreateByName ("main", target.GetExecutable().GetFilename()); 746 747 print main_bp 748 749 # Launch the process. Since we specified synchronous mode, we won't return 750 # from this function until we hit the breakpoint at main 751 process = target.LaunchSimple (None, None, os.getcwd()) 752 753 # Make sure the launch went ok 754 if process: 755 # Print some simple process info 756 state = process.GetState () 757 print process 758 if state == lldb.eStateStopped: 759 # Get the first thread 760 thread = process.GetThreadAtIndex (0) 761 if thread: 762 # Print some simple thread info 763 print thread 764 # Get the first frame 765 frame = thread.GetFrameAtIndex (0) 766 if frame: 767 # Print some simple frame info 768 print frame 769 function = frame.GetFunction() 770 # See if we have debug info (a function) 771 if function: 772 # We do have a function, print some info for the function 773 print function 774 # Now get all instructions for this function and print them 775 insts = function.GetInstructions(target) 776 disassemble_instructions (insts) 777 else: 778 # See if we have a symbol in the symbol table for where we stopped 779 symbol = frame.GetSymbol(); 780 if symbol: 781 # We do have a symbol, print some info for the symbol 782 print symbol 783 784Writing lldb frame recognizers in Python 785---------------------------------------- 786 787Frame recognizers allow for retrieving information about special frames based 788on ABI, arguments or other special properties of that frame, even without 789source code or debug info. Currently, one use case is to extract function 790arguments that would otherwise be unaccesible, or augment existing arguments. 791 792Adding a custom frame recognizer is done by implementing a Python class and 793using the 'frame recognizer add' command. The Python class should have a 794'get_recognized_arguments' method and it will receive an argument of type 795lldb.SBFrame representing the current frame that we are trying to recognize. 796The method should return a (possibly empty) list of lldb.SBValue objects that 797represent the recognized arguments. 798 799An example of a recognizer that retrieves the file descriptor values from libc 800functions 'read', 'write' and 'close' follows: 801 802:: 803 804 class LibcFdRecognizer(object): 805 def get_recognized_arguments(self, frame): 806 if frame.name in ["read", "write", "close"]: 807 fd = frame.EvaluateExpression("$arg1").unsigned 808 value = lldb.target.CreateValueFromExpression("fd", "(int)%d" % fd) 809 return [value] 810 return [] 811 812The file containing this implementation can be imported via 'command script 813import' and then we can register this recognizer with 'frame recognizer add'. 814It's important to restrict the recognizer to the libc library (which is 815libsystem_kernel.dylib on macOS) to avoid matching functions with the same name 816in other modules: 817 818:: 819 820 (lldb) command script import .../fd_recognizer.py 821 (lldb) frame recognizer add -l fd_recognizer.LibcFdRecognizer -n read -s libsystem_kernel.dylib 822 823When the program is stopped at the beginning of the 'read' function in libc, we can view the recognizer arguments in 'frame variable': 824 825:: 826 827 (lldb) b read 828 (lldb) r 829 Process 1234 stopped 830 * thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.3 831 frame #0: 0x00007fff06013ca0 libsystem_kernel.dylib`read 832 (lldb) frame variable 833 (int) fd = 3 834 835Writing Target Stop-Hooks in Python: 836------------------------------------ 837 838Stop hooks fire whenever the process stops just before control is returned to the 839user. Stop hooks can either be a set of lldb command-line commands, or can 840be implemented by a suitably defined Python class. The Python based stop-hooks 841can also be passed as set of -key -value pairs when they are added, and those 842will get packaged up into a SBStructuredData Dictionary and passed to the 843constructor of the Python object managing the stop hook. This allows for 844parametrization of the stop hooks. 845 846To add a Python-based stop hook, first define a class with the following methods: 847 848+--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+ 849| Name | Arguments | Description | 850+--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+ 851| **__init__** | **target: lldb.SBTarget** | This is the constructor for the new stop-hook. | 852| | **extra_args: lldb.SBStructuredData** | | 853| | | | 854| | | **target** is the SBTarget to which the stop hook is added. | 855| | | | 856| | | **extra_args** is an SBStructuredData object that the user can pass in when creating instances of this | 857| | | breakpoint. It is not required, but allows for reuse of stop-hook classes. | 858+--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+ 859| **handle_stop** | **exe_ctx: lldb.SBExecutionContext** | This is the called when the target stops. | 860| | **stream: lldb.SBStream** | | 861| | | **exe_ctx** argument will be filled with the current stop point for which the stop hook is | 862| | | being evaluated. | 863| | | | 864| | | **stream** an lldb.SBStream, anything written to this stream will be written to the debugger console. | 865| | | | 866| | | The return value is a "Should Stop" vote from this thread. If the method returns either True or no return | 867| | | this thread votes to stop. If it returns False, then the thread votes to continue after all the stop-hooks | 868| | | are evaluated. | 869| | | Note, the --auto-continue flag to 'target stop-hook add' overrides a True return value from the method. | 870+--------------------+---------------------------------------+------------------------------------------------------------------------------------------------------------------+ 871 872To use this class in lldb, run the command: 873 874:: 875 876 (lldb) command script import MyModule.py 877 (lldb) target stop-hook add -P MyModule.MyStopHook -k first -v 1 -k second -v 2 878 879where MyModule.py is the file containing the class definition MyStopHook. 880