forked from OSchip/llvm-project
534 lines
27 KiB
HTML
Executable File
534 lines
27 KiB
HTML
Executable File
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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<link href="style.css" rel="stylesheet" type="text/css" />
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<title>LLDB Python Reference</title>
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</head>
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<body>
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<div class="www_title">
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LLDB Python Reference
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</div>
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<div id="container">
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<div id="content">
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<!--#include virtual="sidebar.incl"-->
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<div id="middle">
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<div class="post">
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<h1 class ="postheader">Introduction</h1>
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<div class="postcontent">
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<p>The entire LLDB API is available as Python functions through a script bridging interface.
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This means the LLDB API's can be used directly from python either interactively or to build python apps that
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provide debugger features. </p>
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<p>Additionally, Python can be used as a programmatic interface within the
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lldb command interpreter (we refer to this for brevity as the embedded interpreter). Of course,
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in this context it has full access to the LLDB API - with some additional conveniences we will
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call out in the FAQ.</p>
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</div>
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<div class="postfooter"></div>
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<div class="post">
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<h1 class ="postheader">Documentation</h1>
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<div class="postcontent">
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<p>The LLDB API is contained in a python module named <b>lldb</b>. Help is available through the standard python help and documentation. To get an overview of the <b>lldb</b> python module you can execute the following command:</p>
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<code><pre><tt>(lldb) <b>script help(lldb)</b>
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Help on package lldb:
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NAME
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lldb - The lldb module contains the public APIs for Python binding.
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FILE
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/System/Library/PrivateFrameworks/LLDB.framework/Versions/A/Resources/Python/lldb/__init__.py
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DESCRIPTION
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...
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</tt></pre></code>
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<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>
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<code><pre><tt>(lldb) <b>script help(lldb.SBFrame)</b>
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Help on class SBFrame in module lldb:
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class SBFrame(__builtin__.object)
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| Represents one of the stack frames associated with a thread.
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| SBThread contains SBFrame(s). For example (from test/lldbutil.py),
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| def print_stacktrace(thread, string_buffer = False):
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| '''Prints a simple stack trace of this thread.'''
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...
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</tt></pre></code>
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<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>
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<code><pre><tt>(lldb) <b>script help(lldb.process)</b>
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Help on SBProcess in module lldb object:
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class SBProcess(__builtin__.object)
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| Represents the process associated with the target program.
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| SBProcess supports thread iteration. For example (from test/lldbutil.py),
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| # ==================================================
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| # Utility functions related to Threads and Processes
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| # ==================================================
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...
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</tt></pre></code>
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</div>
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<div class="postfooter"></div>
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<div class="post">
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<h1 class ="postheader">Embedded Python Interpreter</h1>
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<div class="postcontent">
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<p>The embedded python interpreter can be accessed in a variety of ways from within LLDB. The
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easiest way is to use the lldb command <b>script</b> with no arguments at the lldb command prompt:</p>
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<code><pre><tt>(lldb) <strong>script</strong>
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Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
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>>> 2+3
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5
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>>> hex(12345)
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'0x3039'
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>>>
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</tt></pre></code>
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<p>This drops you into the embedded python interpreter. When running under the <b>script</b> command,
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lldb sets some convenience variables that give you quick access to the currently selected entities that characterize
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the program and debugger state. In each case, if there is no currently selected entity of the appropriate
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type, the variable's <b>IsValid</b> method will return false.
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<p>Note also, these variables hold the values
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of the selected objects on entry to the embedded interpreter. They do not update as you use the LLDB
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API's to change, for example, the currently selected stack frame or thread.</p>
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These are all global variables contained in the <b>lldb</b> python namespace :</p>
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<table class="stats" width="620" cellspacing="0">
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<tr>
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<td class="hed" width="20%">Variable</td>
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<td class="hed" width="10%">Type</td>
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<td class="hed" width="70%">Description</td>
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</tr>
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<tr>
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<td class="content">
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<b>lldb.debugger</b>
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</td>
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<td class="content">
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<b>lldb.SBDebugger</b>
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</td>
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<td class="content">
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Contains the debugger object whose <b>script</b> command was invoked.
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The <b>lldb.SBDebugger</b> object owns the command interpreter
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and all the targets in your debug session. There will always be a
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Debugger in the embedded interpreter.
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</td>
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</tr>
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<tr>
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<td class="content">
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<b>lldb.target</b>
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</td>
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<td class="content">
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<b>lldb.SBTarget</b>
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</td>
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<td class="content">
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Contains the currently selected target - for instance the one made with the
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<b>file</b> or selected by the <b>target select <target-index></b> command.
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The <b>lldb.SBTarget</b> manages one running process, and all the executable
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and debug files for the process.
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</td>
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</tr>
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<tr>
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<td class="content">
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<b>lldb.process</b>
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</td>
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<td class="content">
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<b>lldb.SBProcess</b>
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</td>
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<td class="content">
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Contains the process of the currently selected target.
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The <b>lldb.SBProcess</b> object manages the threads and allows access to
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memory for the process.
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</td>
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</tr>
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<tr>
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<td class="content">
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<b>lldb.thread</b>
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</td>
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<td class="content">
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<b>lldb.SBThread</b>
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</td>
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<td class="content">
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Contains the currently selected thread.
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The <b>lldb.SBThread</b> object manages the stack frames in that thread.
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A thread is always selected in the command interpreter when a target stops.
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The <b>thread select <thread-index></b> commmand can be used to change the
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currently selected thread. So as long as you have a stopped process, there will be
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some selected thread.
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</td>
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</tr>
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<tr>
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<td class="content">
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<b>lldb.frame</b>
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</td>
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<td class="content">
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<b>lldb.SBFrame</b>
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</td>
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<td class="content">
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Contains the currently selected stack frame.
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The <b>lldb.SBFrame</b> object manage the stack locals and the register set for
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that stack.
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A stack frame is always selected in the command interpreter when a target stops.
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The <b>frame select <frame-index></b> commmand can be used to change the
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currently selected frame. So as long as you have a stopped process, there will
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be some selected frame.
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</td>
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</tr>
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</table>
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<p>Once in the embedded interpreter, these objects can be used. To get started, note that almost
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all of the <b>lldb</b> Python objects are able to briefly describe themselves when you pass them
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to the Python <b>print</b> function:
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<code><pre><tt>(lldb) <b>script</b>
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Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
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>>> <strong>print lldb.debugger</strong>
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Debugger (instance: "debugger_1", id: 1)
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>>> <strong>print lldb.target</strong>
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a.out
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>>> <strong>print lldb.process</strong>
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SBProcess: pid = 59289, state = stopped, threads = 1, executable = a.out
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>>> <strong>print lldb.thread</strong>
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SBThread: tid = 0x1f03
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>>> <strong>print lldb.frame</strong>
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frame #0: 0x0000000100000bb6 a.out main + 54 at main.c:16
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</tt></pre></code>
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</div>
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<div class="postfooter"></div>
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</div>
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<div class="post">
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<h1 class ="postheader">Running a Python script when a breakpoint gets hit</h1>
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<div class="postcontent">
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<p>One very powerful use of the lldb Python API is to have a python script run when a breakpoint gets hit. Adding python
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scripts to breakpoints provides a way to create complex breakpoint
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conditions and also allows for smart logging and data gathering.</p>
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<p>When your process hits a breakpoint to which you have attached some python code, the code is executed as the
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body of a function which takes two arguments:</p>
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<p>
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<code><pre><tt>def breakpoint_function_wrapper(<b>frame</b>, <b>bp_loc</b>):
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<font color=green># Your code goes here</font>
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</tt></pre></code>
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<p><table class="stats" width="620" cellspacing="0">
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<tr>
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<td class="hed" width="10%">Argument</td>
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<td class="hed" width="10%">Type</td>
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<td class="hed" width="80%">Description</td>
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</tr>
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<tr>
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<td class="content">
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<b>frame</b>
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</td>
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<td class="content">
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<b>lldb.SBFrame</b>
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</td>
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<td class="content">
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The current stack frame where the breakpoint got hit.
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The object will always be valid.
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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>.
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</td>
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</tr>
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<tr>
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<td class="content">
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<b>bp_loc</b>
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</td>
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<td class="content">
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<b>lldb.SBBreakpointLocation</b>
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</td>
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<td class="content">
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The breakpoint location that just got hit. Breakpoints are represented by <b>lldb.SBBreakpoint</b>
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objects. These breakpoint objects can have one or more locations. These locations
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are represented by <b>lldb.SBBreakpointLocation</b> objects.
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</td>
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</tr>
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</table>
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<p>An example will show how simple it is to write some python code and attach it to a breakpoint.
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The following example will allow you to track the order in which the functions in a given shared library
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are first executed during one run of your program. This is a simple method to gather an order file which
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can be used to optimize function placement within a binary for execution locality.</p>
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<p>We do this by setting a regular expression breakpoint
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that will match every function in the shared library. The regular expression '.' will match
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any string that has at least one character in it, so we will use that.
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This will result in one <b>lldb.SBBreakpoint</b> object
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that contains an <b>lldb.SBBreakpointLocation</b> object for each function. As the breakpoint gets
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hit, we use a counter to track the order in which the function at this particular breakpoint location got hit.
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Since our code is passed the location that was hit, we can get the name of the function from the location,
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disable the location so we won't count this function again; then log some info and continue the process.</p>
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<p>Note we also have to initialize our counter, which we do with the simple one-line version of the <b>script</b>
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command.
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<p>Here is the code:
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<code><pre><tt>(lldb) <strong>breakpoint set --func-regex=. --shlib=libfoo.dylib</strong>
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Breakpoint created: 1: regex = '.', module = libfoo.dylib, locations = 223
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(lldb) <strong>script counter = 0</strong>
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(lldb) <strong>breakpoint command add --script-type python 1</strong>
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Enter your Python command(s). Type 'DONE' to end.
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> <font color=green># Increment our counter. Since we are in a function, this must be a global python variable</font>
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> <strong>global counter</strong>
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> <strong>counter += 1</strong>
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> <font color=green># Get the name of the function</font>
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> <strong>name = frame.GetFunctionName()</strong>
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> <font color=green># Print the order and the function name</font>
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> <strong>print '[%i] %s' % (counter, name)</strong>
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> <font color=green># Disable the current breakpoint location so it doesn't get hit again</font>
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> <strong>bp_loc.SetEnabled(False)</strong>
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> <font color=green># How continue the process</font>
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> <strong>frame.GetThread().GetProcess().Continue()</strong>
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> <strong>DONE</strong>
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</tt></pre></code>
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<p>The <b>breakpoint command add</b> command above attaches a python script to breakpoint 1.
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To remove the breakpoint command:
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<p><code>(lldb) <strong>breakpoint command delete 1</strong></code>
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</div>
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</div>
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<div class="post">
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<h1 class ="postheader">Create a new LLDB command using a python function</h1>
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<div class="postcontent">
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<p>Python functions can be used to create new LLDB command interpreter commands, which will work
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like all the natively defined lldb commands. This provides a very flexible and easy way to extend LLDB to meet your
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debugging requirements. </p>
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<p>To write a python function that implements a new LDB command define the function to take four arguments as follows:</p>
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<code><pre><tt>def command_function(<b>debugger</b>, <b>command</b>, <b>result</b>, <b>dict</b>):
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<font color=green># Your code goes here</font>
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</tt></pre></code>
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Optionally, you can also provide a Python docstring, and LLDB will use it when providing help for your command, as in:
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<code><pre><tt>def command_function(<b>debugger</b>, <b>command</b>, <b>result</b>, <b>dict</b>):
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<font color=green>"""This command takes a lot of options and does many fancy things"""</font>
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<font color=green># Your code goes here</font>
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</tt></pre></code>
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<p><table class="stats" width="620" cellspacing="0">
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<tr>
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<td class="hed" width="10%">Argument</td>
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<td class="hed" width="10%">Type</td>
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<td class="hed" width="80%">Description</td>
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</tr>
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<tr>
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<td class="content">
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<b>debugger</b>
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</td>
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<td class="content">
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<b>lldb.SBDebugger</b>
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</td>
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<td class="content">
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The current debugger object.
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</td>
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</tr>
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<tr>
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<td class="content">
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<b>command</b>
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</td>
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<td class="content">
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<b>python string</b>
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</td>
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<td class="content">
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A python string containing all arguments for your command. If you need to chop up the arguments
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try using the <b>shlex</b> module's <code>shlex.split(command)</code> to properly extract the
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arguments.
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</td>
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</tr>
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<tr>
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<td class="content">
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<b>result</b>
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</td>
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<td class="content">
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<b>lldb.SBCommandReturnObject</b>
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</td>
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<td class="content">
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A return object where you can indicate the success or failure of your command. You can also
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provide information for the command result by printing data into it. You can also just print
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data as you normally would in a python script and the output will show up; this is useful for
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logging, but the real output for your command should go in the result object.
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</td>
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</tr>
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<tr>
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<td class="content">
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<b>dict</b>
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</td>
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<td class="content">
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<b>python dict object</b>
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</td>
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<td class="content">
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The dictionary for the current embedded script session which contains all variables
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and functions.
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</td>
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</tr>
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</table>
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<p>One other handy convenience when defining lldb command-line commands is the command
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<b>command script import</b> which will import a module specified by file path - so you
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don't have to change your PYTHONPATH for temporary scripts. It also has another convenience
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that if your new script module has a function of the form:</p>
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<code><pre><tt>def __lldb_init_module(<b>debugger</b>, <b>dict</b>):
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<font color=green># Command Initialization code goes here</font>
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</tt></pre></code>
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<p>where <b>debugger</b> and <b>dict</b> are as above, that function will get run when the module is loaded
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allowing you to add whatever commands you want into the current debugger. Note that
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this function will only be run when using the LLDB comand <b>command script import</b>,
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it will not get run if anyone imports your module from another module.
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If you want to always run code when your module is loaded from LLDB
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<u>or</u> when loaded via an <b>import</b> statement in python code
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you can test the <b>lldb.debugger</b> object, since you imported the
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<lldb> module at the top of the python <b>ls.py</b> module. This test
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must be in code that isn't contained inside of any function or class,
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just like the standard test for <b>__main__</b> like all python modules
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usally do. Sample code would look like:
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<code><pre><tt>if __name__ == '__main__':
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<font color=green># Create a new debugger instance in your module if your module
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# can be run from the command line. When we run a script from
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# the command line, we won't have any debugger object in
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# lldb.debugger, so we can just create it if it will be needed</font>
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lldb.debugger = lldb.SBDebugger.Create()
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elif lldb.debugger:
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<font color=green># Module is being run inside the LLDB interpreter</font>
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lldb.debugger.HandleCommand('command script add -f ls.ls ls')
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print 'The "ls" python command has been installed and is ready for use.'
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</tt></pre></code>
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<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
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can be used by LLDB's python command code:</p>
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<code><pre><tt><font color=green>#!/usr/bin/python</font>
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import lldb
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import commands
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import optparse
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import shlex
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def ls(debugger, command, result, dict):
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result.PutCString(commands.getoutput('/bin/ls %s' % command))
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<font color=green># And the initialization code to add your commands </font>
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def __lldb_init_module(debugger, dict):
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debugger.HandleCommand('command script add -f ls.ls ls')
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print 'The "ls" python command has been installed and is ready for use.'
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</tt></pre></code>
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<p>Now we can load the module into LLDB and use it</p>
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<code><pre><tt>% lldb
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(lldb) <strong>command script import ~/ls.py</strong>
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The "ls" python command has been installed and is ready for use.
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(lldb) <strong>ls -l /tmp/</strong>
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total 365848
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-rw-r--r--@ 1 someuser wheel 6148 Jan 19 17:27 .DS_Store
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-rw------- 1 someuser wheel 7331 Jan 19 15:37 crash.log
|
|
</tt></pre></code>
|
|
<p>A 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>
|
|
</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
|
|
|
|
<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>
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