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| LLDB Python Reference |
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| <div class="post"> |
| <h1 class ="postheader">Introduction</h1> |
| <div class="postcontent"> |
| |
| <p>The entire LLDB API is available as Python functions through a script bridging interface. |
| This means the LLDB API's can be used directly from python either interactively or to build python apps that |
| provide debugger features. </p> |
| <p>Additionally, Python can be used as a programmatic interface within the |
| lldb command interpreter (we refer to this for brevity as the embedded interpreter). Of course, |
| in this context it has full access to the LLDB API - with some additional conveniences we will |
| call out in the FAQ.</p> |
| |
| </div> |
| <div class="postfooter"></div> |
| <div class="post"> |
| <h1 class ="postheader">Documentation</h1> |
| <div class="postcontent"> |
| |
| <p>The LLDB API is contained in a python module named <b>lldb</b>. A useful resource when writing Python extensions is the <a href="python_reference/index.html">lldb Python classes reference guide</a>.</p> |
| <p>The documentation is also accessible in an interactive debugger session with the following command:</p> |
| <code><pre><tt>(lldb) <b>script help(lldb)</b> |
| Help on package lldb: |
| |
| NAME |
| lldb - The lldb module contains the public APIs for Python binding. |
| |
| FILE |
| /System/Library/PrivateFrameworks/LLDB.framework/Versions/A/Resources/Python/lldb/__init__.py |
| |
| DESCRIPTION |
| ... |
| </tt></pre></code> |
| <p>You can also get help using a module class name. The full API that is exposed for that class will be displayed in a man page style window. Below we want to get help on the lldb.SBFrame class:</p> |
| <code><pre><tt>(lldb) <b>script help(lldb.SBFrame)</b> |
| Help on class SBFrame in module lldb: |
| |
| class SBFrame(__builtin__.object) |
| | Represents one of the stack frames associated with a thread. |
| | SBThread contains SBFrame(s). For example (from test/lldbutil.py), |
| | |
| | def print_stacktrace(thread, string_buffer = False): |
| | '''Prints a simple stack trace of this thread.''' |
| | |
| ... |
| </tt></pre></code> |
| <p>Or you can get help using any python object, here we use the <b>lldb.process</b> object which is a global variable in the <b>lldb</b> module which represents the currently selected process:</p> |
| <code><pre><tt>(lldb) <b>script help(lldb.process)</b> |
| Help on SBProcess in module lldb object: |
| |
| class SBProcess(__builtin__.object) |
| | Represents the process associated with the target program. |
| | |
| | SBProcess supports thread iteration. For example (from test/lldbutil.py), |
| | |
| | # ================================================== |
| | # Utility functions related to Threads and Processes |
| | # ================================================== |
| | |
| ... |
| </tt></pre></code> |
| |
| </div> |
| <div class="postfooter"></div> |
| |
| <div class="post"> |
| <h1 class ="postheader">Embedded Python Interpreter</h1> |
| <div class="postcontent"> |
| |
| <p>The embedded python interpreter can be accessed in a variety of ways from within LLDB. The |
| easiest way is to use the lldb command <b>script</b> with no arguments at the lldb command prompt:</p> |
| <code><pre><tt>(lldb) <strong>script</strong> |
| Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D. |
| >>> 2+3 |
| 5 |
| >>> hex(12345) |
| '0x3039' |
| >>> |
| </tt></pre></code> |
| |
| <p>This drops you into the embedded python interpreter. When running under the <b>script</b> command, |
| lldb sets some convenience variables that give you quick access to the currently selected entities that characterize |
| the program and debugger state. In each case, if there is no currently selected entity of the appropriate |
| type, the variable's <b>IsValid</b> method will return false. These variables are:</p> |
| |
| <table class="stats" width="620" cellspacing="0"> |
| <tr> |
| <td class="hed" width="20%">Variable</td> |
| <td class="hed" width="10%">Type</td> |
| <td class="hed" width="70%">Description</td> |
| </tr> |
| |
| <tr> |
| <td class="content"> |
| <b>lldb.debugger</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBDebugger</b> |
| </td> |
| <td class="content"> |
| Contains the debugger object whose <b>script</b> command was invoked. |
| The <b>lldb.SBDebugger</b> object owns the command interpreter |
| and all the targets in your debug session. There will always be a |
| Debugger in the embedded interpreter. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>lldb.target</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBTarget</b> |
| </td> |
| <td class="content"> |
| Contains the currently selected target - for instance the one made with the |
| <b>file</b> or selected by the <b>target select <target-index></b> command. |
| The <b>lldb.SBTarget</b> manages one running process, and all the executable |
| and debug files for the process. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>lldb.process</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBProcess</b> |
| </td> |
| <td class="content"> |
| Contains the process of the currently selected target. |
| The <b>lldb.SBProcess</b> object manages the threads and allows access to |
| memory for the process. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>lldb.thread</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBThread</b> |
| </td> |
| <td class="content"> |
| Contains the currently selected thread. |
| The <b>lldb.SBThread</b> object manages the stack frames in that thread. |
| A thread is always selected in the command interpreter when a target stops. |
| The <b>thread select <thread-index></b> command can be used to change the |
| currently selected thread. So as long as you have a stopped process, there will be |
| some selected thread. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>lldb.frame</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBFrame</b> |
| </td> |
| <td class="content"> |
| Contains the currently selected stack frame. |
| The <b>lldb.SBFrame</b> object manage the stack locals and the register set for |
| that stack. |
| A stack frame is always selected in the command interpreter when a target stops. |
| The <b>frame select <frame-index></b> command can be used to change the |
| currently selected frame. So as long as you have a stopped process, there will |
| be some selected frame. |
| </td> |
| </tr> |
| </table> |
| |
| <p>While extremely convenient, these variables have a couple caveats that you should be aware of. |
| First of all, they hold the values |
| of the selected objects on entry to the embedded interpreter. They do not update as you use the LLDB |
| API's to change, for example, the currently selected stack frame or thread. |
| <p>Moreover, they are only defined and meaningful while in the interactive Python interpreter. |
| There is no guarantee on their value in any other situation, hence you should not use them when defining |
| Python formatters, breakpoint scripts and commands (or any other Python extension point that LLDB provides). |
| As a rationale for such behavior, consider that lldb can |
| run in a multithreaded environment, and another thread might call the "script" command, changing the value out |
| from under you.</p> |
| |
| <p>To get started with these objects and LLDB scripting, please note that almost |
| all of the <b>lldb</b> Python objects are able to briefly describe themselves when you pass them |
| to the Python <b>print</b> function: |
| <code><pre><tt>(lldb) <b>script</b> |
| Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D. |
| >>> <strong>print lldb.debugger</strong> |
| Debugger (instance: "debugger_1", id: 1) |
| >>> <strong>print lldb.target</strong> |
| a.out |
| >>> <strong>print lldb.process</strong> |
| SBProcess: pid = 59289, state = stopped, threads = 1, executable = a.out |
| >>> <strong>print lldb.thread</strong> |
| SBThread: tid = 0x1f03 |
| >>> <strong>print lldb.frame</strong> |
| frame #0: 0x0000000100000bb6 a.out main + 54 at main.c:16 |
| </tt></pre></code> |
| |
| </div> |
| <div class="postfooter"></div> |
| |
| </div> |
| <div class="post"> |
| <h1 class ="postheader">Running a Python script when a breakpoint gets hit</h1> |
| <div class="postcontent"> |
| |
| <p>One very powerful use of the lldb Python API is to have a python script run when a breakpoint gets hit. Adding python |
| scripts to breakpoints provides a way to create complex breakpoint |
| conditions and also allows for smart logging and data gathering.</p> |
| <p>When your process hits a breakpoint to which you have attached some python code, the code is executed as the |
| body of a function which takes three arguments:</p> |
| <p> |
| <code><pre><tt>def breakpoint_function_wrapper(<b>frame</b>, <b>bp_loc</b>, <b>dict</b>): |
| <font color=green># Your code goes here</font> |
| </tt></pre></code> |
| <p><table class="stats" width="620" cellspacing="0"> |
| <tr> |
| <td class="hed" width="10%">Argument</td> |
| <td class="hed" width="10%">Type</td> |
| <td class="hed" width="80%">Description</td> |
| </tr> |
| |
| <tr> |
| <td class="content"> |
| <b>frame</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBFrame</b> |
| </td> |
| <td class="content"> |
| The current stack frame where the breakpoint got hit. |
| The object will always be valid. |
| This <b>frame</b> argument might <i>not</i> match the currently selected stack frame found in the <b>lldb</b> module global variable <b>lldb.frame</b>. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>bp_loc</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBBreakpointLocation</b> |
| </td> |
| <td class="content"> |
| The breakpoint location that just got hit. Breakpoints are represented by <b>lldb.SBBreakpoint</b> |
| objects. These breakpoint objects can have one or more locations. These locations |
| are represented by <b>lldb.SBBreakpointLocation</b> objects. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>dict</b> |
| </td> |
| <td class="content"> |
| <b>dict</b> |
| </td> |
| <td class="content"> |
| The python session dictionary as a standard python dictionary object. |
| </td> |
| </tr> |
| </table> |
| <p>Optionally, a Python breakpoint command can return a value. Returning False tells LLDB that you do not want to stop at the breakpoint. |
| Any other return value (including None or leaving out the return statement altogether) is akin to telling LLDB to actually stop at the breakpoint. |
| This can be useful in situations where a breakpoint only needs to stop the process when certain conditions are met, and you do not want to inspect the |
| program state manually at every stop and then continue. |
| <p>An example will show how simple it is to write some python code and attach it to a breakpoint. |
| The following example will allow you to track the order in which the functions in a given shared library |
| are first executed during one run of your program. This is a simple method to gather an order file which |
| can be used to optimize function placement within a binary for execution locality.</p> |
| <p>We do this by setting a regular expression breakpoint |
| that will match every function in the shared library. The regular expression '.' will match |
| any string that has at least one character in it, so we will use that. |
| This will result in one <b>lldb.SBBreakpoint</b> object |
| that contains an <b>lldb.SBBreakpointLocation</b> object for each function. As the breakpoint gets |
| hit, we use a counter to track the order in which the function at this particular breakpoint location got hit. |
| Since our code is passed the location that was hit, we can get the name of the function from the location, |
| disable the location so we won't count this function again; then log some info and continue the process.</p> |
| <p>Note we also have to initialize our counter, which we do with the simple one-line version of the <b>script</b> |
| command. |
| <p>Here is the code: |
| |
| <code><pre><tt>(lldb) <strong>breakpoint set --func-regex=. --shlib=libfoo.dylib</strong> |
| Breakpoint created: 1: regex = '.', module = libfoo.dylib, locations = 223 |
| (lldb) <strong>script counter = 0</strong> |
| (lldb) <strong>breakpoint command add --script-type python 1</strong> |
| Enter your Python command(s). Type 'DONE' to end. |
| > <font color=green># Increment our counter. Since we are in a function, this must be a global python variable</font> |
| > <strong>global counter</strong> |
| > <strong>counter += 1</strong> |
| > <font color=green># Get the name of the function</font> |
| > <strong>name = frame.GetFunctionName()</strong> |
| > <font color=green># Print the order and the function name</font> |
| > <strong>print '[%i] %s' % (counter, name)</strong> |
| > <font color=green># Disable the current breakpoint location so it doesn't get hit again</font> |
| > <strong>bp_loc.SetEnabled(False)</strong> |
| > <font color=green># No need to stop here</font> |
| > <strong>return False</strong> |
| > <strong>DONE</strong> |
| </tt></pre></code> |
| <p>The <b>breakpoint command add</b> command above attaches a python script to breakpoint 1. |
| To remove the breakpoint command: |
| <p><code>(lldb) <strong>breakpoint command delete 1</strong></code> |
| </div> |
| |
| </div> |
| <div class="post"> |
| <h1 class ="postheader">Using the Python API's to create custom stepping logic</h1> |
| <div class="postcontent"> |
| |
| <p>A slightly esoteric use of the Python API's is to construct custom stepping types. LLDB's stepping is |
| driven by a stack of "thread plans" and a fairly simple state machine that runs the plans. You can create |
| a Python class that works as a thread plan, and responds to the requests the state machine makes to run |
| its operations. </p> |
| <p>There is a longer discussion of scripted thread plans and the state machine, and several interesting examples |
| of their use in:</p> |
| <a href="http://llvm.org/svn/llvm-project/lldb/trunk/examples/python/scripted_step.py">scripted_step.py</a> |
| |
| <p> And for a MUCH fuller discussion of the whole state machine, see:</p> |
| |
| <a href="http://llvm.org/svn/llvm-project/lldb/trunk/include/lldb/Target/ThreadPlan.h">ThreadPlan.h</a> |
| |
| <p>If you are reading those comments it is useful to know that scripted thread plans are set to be |
| "MasterPlans", and not "OkayToDiscard". |
| |
| <p>To implement a scripted step, you define a python class that has the following methods:</p> |
| </tt></pre></code> |
| <p><table class="stats" width="620" cellspacing="0"> |
| <tr> |
| <td class="hed" width="10%">Name</td> |
| <td class="hed" width="10%">Arguments</td> |
| <td class="hed" width="80%">Description</td> |
| </tr> |
| |
| |
| <tr> |
| <td class="content"> |
| <b>__init__</b> |
| </td> |
| <td class="content"> |
| <b>thread_plan: lldb.SBThreadPlan</b> |
| </td> |
| <td class="content"> |
| This is the underlying SBThreadPlan that is pushed onto the plan stack. |
| You will want to store this away in an ivar. Also, if you are going to |
| use one of the canned thread plans, you can queue it at this point. |
| </td> |
| </tr> |
| |
| <tr> |
| <td class="content"> |
| <b>explains_stop</b> |
| </td> |
| <td class="content"> |
| <b>event: lldb.SBEvent</b> |
| </td> |
| <td class="content"> |
| Return True if this stop is part of your thread plans logic, false otherwise. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>is_stale</b> |
| </td> |
| <td class="content"> |
| <b>None</b> |
| </td> |
| <td class="content"> |
| If your plan is no longer relevant (for instance, you were |
| stepping in a particular stack frame, but some other operation |
| pushed that frame off the stack) return True and your plan will |
| get popped. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>should_step</b> |
| </td> |
| <td class="content"> |
| <b>None</b> |
| </td> |
| <td class="content"> |
| Return True if you want lldb to instruction step one instruction, |
| or False to continue till the next breakpoint is hit. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>should_stop</b> |
| </td> |
| <td class="content"> |
| <b>event: lldb.SBEvent</b> |
| </td> |
| <td class="content"> |
| If your plan wants to stop and return control to the user at this point, return True. |
| If your plan is done at this point, call SetPlanComplete on your |
| thread plan instance. |
| Also, do any work you need here to set up the next stage of stepping. |
| </td> |
| </tr> |
| </table> |
| |
| <p>To use this class to implement a step, use the command:</p> |
| |
| <code><pre><tt>(lldb) <strong>thread step-scripted -C MyModule.MyStepPlanClass</strong> |
| </tt></pre></code> |
| <p>Or use the SBThread.StepUsingScriptedThreadPlan API. The SBThreadPlan passed into |
| your __init__ function can also push several common plans (step in/out/over and run-to-address) |
| in front of itself on the stack, which can be used to compose more complex stepping operations. |
| When you use subsidiary plans your explains_stop and should_stop methods won't get called until |
| the subsidiary plan is done, or the process stops for an event the subsidiary plan doesn't |
| explain. For instance, step over plans don't explain a breakpoint hit while performing the |
| step-over.</p> |
| |
| </div> |
| |
| </div> |
| <div class="post"> |
| <h1 class ="postheader">Create a new LLDB command using a python function</h1> |
| <div class="postcontent"> |
| |
| <p>Python functions can be used to create new LLDB command interpreter commands, which will work |
| like all the natively defined lldb commands. This provides a very flexible and easy way to extend LLDB to meet your |
| debugging requirements. </p> |
| <p>To write a python function that implements a new LLDB command define the function to take four arguments as follows:</p> |
| |
| <code><pre><tt>def command_function(<b>debugger</b>, <b>command</b>, <b>result</b>, <b>internal_dict</b>): |
| <font color=green># Your code goes here</font> |
| </tt></pre></code> |
| |
| Optionally, you can also provide a Python docstring, and LLDB will use it when providing help for your command, as in: |
| <code><pre><tt>def command_function(<b>debugger</b>, <b>command</b>, <b>result</b>, <b>internal_dict</b>): |
| <font color=green>"""This command takes a lot of options and does many fancy things"""</font> |
| <font color=green># Your code goes here</font> |
| </tt></pre></code> |
| |
| Starting with SVN revision 218834, LLDB Python commands can also take an SBExecutionContext as an argument. |
| This is useful in cases where the command's notion of <i>where to act</i> is independent of the currently-selected entities in the debugger.<br/> |
| This feature is enabled if the command-implementing function can be recognized as taking 5 arguments, or a variable number of arguments, and it alters the signature as such: |
| <code><pre><tt>def command_function(<b>debugger</b>, <b>command</b>, <b>exe_ctx</b>, <b>result</b>, <b>internal_dict</b>): |
| <font color=green># Your code goes here</font> |
| </tt></pre></code> |
| |
| |
| <p><table class="stats" width="620" cellspacing="0"> |
| <tr> |
| <td class="hed" width="10%">Argument</td> |
| <td class="hed" width="10%">Type</td> |
| <td class="hed" width="80%">Description</td> |
| </tr> |
| |
| <tr> |
| <td class="content"> |
| <b>debugger</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBDebugger</b> |
| </td> |
| <td class="content"> |
| The current debugger object. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>command</b> |
| </td> |
| <td class="content"> |
| <b>python string</b> |
| </td> |
| <td class="content"> |
| A python string containing all arguments for your command. If you need to chop up the arguments |
| try using the <b>shlex</b> module's <code>shlex.split(command)</code> to properly extract the |
| arguments. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>exe_ctx</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBExecutionContext</b> |
| </td> |
| <td class="content"> |
| An execution context object carrying around information on the inferior process' context in which the command is expected to act |
| <br/><i>Optional since SVN r218834, unavailable before</i> |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>result</b> |
| </td> |
| <td class="content"> |
| <b>lldb.SBCommandReturnObject</b> |
| </td> |
| <td class="content"> |
| A return object which encapsulates success/failure information for the command and output text |
| that needs to be printed as a result of the command. The plain Python "print" command also works but |
| text won't go in the result by default (it is useful as a temporary logging facility). |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>internal_dict</b> |
| </td> |
| <td class="content"> |
| <b>python dict object</b> |
| </td> |
| <td class="content"> |
| The dictionary for the current embedded script session which contains all variables |
| and functions. |
| </td> |
| </tr> |
| </table> |
| |
| <p>Starting with SVN revision 232224, Python commands can also be implemented by means of a class |
| which should implement the following interface:</p> |
| |
| <code> |
| <font color=blue>class</font> CommandObjectType:<br/> |
| <font color=blue>def</font> __init__(self, debugger, session_dict):<br/> |
| <i>this call should initialize the command with respect to the command interpreter for the passed-in debugger</i> <br/> |
| <font color=blue>def</font> __call__(self, debugger, command, exe_ctx, result): <br/> |
| <i>this is the actual bulk of the command, akin to Python command functions</i> <br/> |
| <font color=blue>def</font> get_short_help(self): <br/> |
| <i>this call should return the short help text for this command</i><sup>[1]</sup><br/> |
| <font color=blue>def</font> get_long_help(self): <br/> |
| <i>this call should return the long help text for this command</i><sup>[1]</sup><br/> |
| </code> |
| |
| <sup>[1]</sup> This method is optional. |
| |
| <p>As a convenience, you can treat the result object as a Python file object, and say |
| <code><pre><tt>print >>result, "my command does lots of cool stuff"</tt></pre></code> |
| SBCommandReturnObject and SBStream |
| both support this file-like behavior by providing write() and flush() calls at the Python layer.</p> |
| <p>One other handy convenience when defining lldb command-line commands is the command |
| <b>command script import</b> which will import a module specified by file path - so you |
| don't have to change your PYTHONPATH for temporary scripts. It also has another convenience |
| that if your new script module has a function of the form:</p> |
| |
| <code><pre><tt>def __lldb_init_module(<b>debugger</b>, <b>internal_dict</b>): |
| <font color=green># Command Initialization code goes here</font> |
| </tt></pre></code> |
| |
| <p>where <b>debugger</b> and <b>internal_dict</b> are as above, that function will get run when the module is loaded |
| allowing you to add whatever commands you want into the current debugger. Note that |
| this function will only be run when using the LLDB command <b>command script import</b>, |
| it will not get run if anyone imports your module from another module. |
| If you want to always run code when your module is loaded from LLDB |
| <u>or</u> when loaded via an <b>import</b> statement in python code |
| you can test the <b>lldb.debugger</b> object, since you imported the |
| <lldb> module at the top of the python <b>ls.py</b> module. This test |
| must be in code that isn't contained inside of any function or class, |
| just like the standard test for <b>__main__</b> like all python modules |
| usually do. Sample code would look like: |
| |
| <code><pre><tt>if __name__ == '__main__': |
| <font color=green># Create a new debugger instance in your module if your module |
| # can be run from the command line. When we run a script from |
| # the command line, we won't have any debugger object in |
| # lldb.debugger, so we can just create it if it will be needed</font> |
| lldb.debugger = lldb.SBDebugger.Create() |
| elif lldb.debugger: |
| <font color=green># Module is being run inside the LLDB interpreter</font> |
| lldb.debugger.HandleCommand('command script add -f ls.ls ls') |
| print 'The "ls" python command has been installed and is ready for use.' |
| </tt></pre></code> |
| <p>Now we can create a module called <b>ls.py</b> in the file <b>~/ls.py</b> that will implement a function that |
| can be used by LLDB's python command code:</p> |
| |
| <code><pre><tt><font color=green>#!/usr/bin/python</font> |
| |
| import lldb |
| import commands |
| import optparse |
| import shlex |
| |
| def ls(debugger, command, result, internal_dict): |
| print >>result, (commands.getoutput('/bin/ls %s' % command)) |
| |
| <font color=green># And the initialization code to add your commands </font> |
| def __lldb_init_module(debugger, internal_dict): |
| debugger.HandleCommand('command script add -f ls.ls ls') |
| print 'The "ls" python command has been installed and is ready for use.' |
| </tt></pre></code> |
| <p>Now we can load the module into LLDB and use it</p> |
| <code><pre><tt>% lldb |
| (lldb) <strong>command script import ~/ls.py</strong> |
| The "ls" python command has been installed and is ready for use. |
| (lldb) <strong>ls -l /tmp/</strong> |
| total 365848 |
| -rw-r--r--@ 1 someuser wheel 6148 Jan 19 17:27 .DS_Store |
| -rw------- 1 someuser wheel 7331 Jan 19 15:37 crash.log |
| </tt></pre></code> |
| <p>A more interesting template has been created in the source repository that can help you to create |
| lldb command quickly:</p> |
| <a href="http://llvm.org/svn/llvm-project/lldb/trunk/examples/python/cmdtemplate.py">cmdtemplate.py</a> |
| <p> |
| A commonly required facility is being able to create a command that does some token substitution, and then runs a different debugger command |
| (usually, it po'es the result of an expression evaluated on its argument). For instance, given the following program: |
| <code><pre><tt> |
| #import <Foundation/Foundation.h> |
| NSString* |
| ModifyString(NSString* src) |
| { |
| return [src stringByAppendingString:@"foobar"]; |
| } |
| |
| int main() |
| { |
| NSString* aString = @"Hello world"; |
| NSString* anotherString = @"Let's be friends"; |
| return 1; |
| } |
| </tt></pre></code> |
| you may want a pofoo X command, that equates po [ModifyString(X) capitalizedString]. |
| The following debugger interaction shows how to achieve that goal: |
| <code><pre><tt> |
| (lldb) <b>script</b> |
| Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D. |
| >>> <b>def pofoo_funct(debugger, command, result, internal_dict):</b> |
| ... <b>cmd = "po [ModifyString(" + command + ") capitalizedString]"</b> |
| ... <b>lldb.debugger.HandleCommand(cmd)</b> |
| ... |
| >>> ^D |
| (lldb) <b>command script add pofoo -f pofoo_funct</b> |
| (lldb) <b>pofoo aString</b> |
| $1 = 0x000000010010aa00 Hello Worldfoobar |
| (lldb) <b>pofoo anotherString</b> |
| $2 = 0x000000010010aba0 Let's Be Friendsfoobar</tt></pre></code> |
| </div> |
| <div class="post"> |
| <h1 class ="postheader">Using the lldb.py module in python</h1> |
| <div class="postcontent"> |
| |
| <p>LLDB has all of its core code build into a shared library which gets |
| used by the <b>lldb</b> command line application. On Mac OS X this |
| shared library is a framework: <b>LLDB.framework</b> and on other |
| unix variants the program is a shared library: <b>lldb.so</b>. LLDB also |
| provides an lldb.py module that contains the bindings from LLDB into Python. |
| To use the |
| <b>LLDB.framework</b> to create your own stand-alone python programs, you will |
| need to tell python where to look in order to find this module. This |
| is done by setting the <b>PYTHONPATH</b> environment variable, adding |
| a path to the directory that contains the <b>lldb.py</b> python module. On |
| Mac OS X, this is contained inside the LLDB.framework, so you would do: |
| |
| <p>For csh and tcsh:</p> |
| <p><code>% <b>setenv PYTHONPATH /Developer/Library/PrivateFrameworks/LLDB.framework/Resources/Python</b></code></p> |
| <p>For sh and bash: |
| <p><code>% <b>export PYTHONPATH=/Developer/Library/PrivateFrameworks/LLDB.framework/Resources/Python</b></code></p> |
| |
| <p> Alternately, you can append the LLDB Python directory to the <b>sys.path</b> list directly in |
| your Python code before importing the lldb module.</p> |
| |
| <p> |
| Now your python scripts are ready to import the lldb module. Below is a |
| python script that will launch a program from the current working directory |
| called "a.out", set a breakpoint at "main", and then run and hit the breakpoint, |
| and print the process, thread and frame objects if the process stopped: |
| |
| </p> |
| <code><pre><tt><font color=green>#!/usr/bin/python</font> |
| |
| import lldb |
| import os |
| |
| def disassemble_instructions(insts): |
| for i in insts: |
| print i |
| |
| <font color=green># Set the path to the executable to debug</font> |
| exe = "./a.out" |
| |
| <font color=green># Create a new debugger instance</font> |
| debugger = lldb.SBDebugger.Create() |
| |
| <font color=green># When we step or continue, don't return from the function until the process |
| # stops. Otherwise we would have to handle the process events ourselves which, while doable is |
| #a little tricky. We do this by setting the async mode to false.</font> |
| debugger.SetAsync (False) |
| |
| <font color=green># Create a target from a file and arch</font> |
| print "Creating a target for '%s'" % exe |
| |
| target = debugger.CreateTargetWithFileAndArch (exe, lldb.LLDB_ARCH_DEFAULT) |
| |
| if target: |
| <font color=green># If the target is valid set a breakpoint at main</font> |
| main_bp = target.BreakpointCreateByName ("main", target.GetExecutable().GetFilename()); |
| |
| print main_bp |
| |
| <font color=green># Launch the process. Since we specified synchronous mode, we won't return |
| # from this function until we hit the breakpoint at main</font> |
| process = target.LaunchSimple (None, None, os.getcwd()) |
| |
| <font color=green># Make sure the launch went ok</font> |
| if process: |
| <font color=green># Print some simple process info</font> |
| state = process.GetState () |
| print process |
| if state == lldb.eStateStopped: |
| <font color=green># Get the first thread</font> |
| thread = process.GetThreadAtIndex (0) |
| if thread: |
| <font color=green># Print some simple thread info</font> |
| print thread |
| <font color=green># Get the first frame</font> |
| frame = thread.GetFrameAtIndex (0) |
| if frame: |
| <font color=green># Print some simple frame info</font> |
| print frame |
| function = frame.GetFunction() |
| <font color=green># See if we have debug info (a function)</font> |
| if function: |
| <font color=green># We do have a function, print some info for the function</font> |
| print function |
| <font color=green># Now get all instructions for this function and print them</font> |
| insts = function.GetInstructions(target) |
| disassemble_instructions (insts) |
| else: |
| <font color=green># See if we have a symbol in the symbol table for where we stopped</font> |
| symbol = frame.GetSymbol(); |
| if symbol: |
| <font color=green># We do have a symbol, print some info for the symbol</font> |
| print symbol |
| </tt></pre></code> |
| </div> |
| <div class="postfooter"></div> |
| |
| </div> |
| </div> |
| </div> |
| </body> |
| </html> |
