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| <div class="www_title"> | |
| The <strong>LLDB</strong> Debugger | |
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| <h1 class ="postheader">Architecture</h1> | |
| <div class="postcontent"> | |
| <p>LLDB is a large and complex codebase. This section will help you become more familiar with | |
| the pieces that make up LLDB and give a general overview of the general architecture.</p> | |
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| <div class="postfooter"></div> | |
| </div> | |
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| <h1 class ="postheader">Code Layout</h1> | |
| <div class="postcontent"> | |
| <p>LLDB has many code groupings that makeup the source base:</p> | |
| <ul> | |
| <li><a href="#api">API</a></li> | |
| <li><a href="#breakpoint">Breakpoint</a></li> | |
| <li><a href="#commands">Commands</a></li> | |
| <li><a href="#core">Core</a></li> | |
| <li><a href="#dataformatters">DataFormatters</a></li> | |
| <li><a href="#expression">Expression</a></li> | |
| <li><a href="#host">Host</a></li> | |
| <li><a href="#interpreter">Interpreter</a></li> | |
| <li><a href="#symbol">Symbol</a></li> | |
| <li><a href="#targ">Target</a></li> | |
| <li><a href="#utility">Utility</a></li> | |
| </ul> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="api"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">API</h1> | |
| <div class="postcontent"> | |
| <p>The API folder contains the public interface to LLDB.</p> | |
| <p>We are currently vending a C++ API. In order to be able to add | |
| methods to this API and allow people to link to our classes, | |
| we have certain rules that we must follow:</p> | |
| <ul> | |
| <li>Classes can't inherit from any other classes.</li> | |
| <li>Classes can't contain virtual methods.</li> | |
| <li>Classes should be compatible with script bridging utilities like <a href="http://www.swig.org/">swig</a>.</li> | |
| <li>Classes should be lightweight and be backed by a single member. Pointers (or shared pointers) are the preferred choice since they allow changing the contents of the backend without affecting the public object layout.</li> | |
| <li>The interface should be as minimal as possible in order to give a complete API.</li> | |
| </ul> | |
| <p>By adhering to these rules we should be able to continue to | |
| vend a C++ API, and make changes to the API as any additional | |
| methods added to these classes will just be a dynamic loader | |
| lookup and they won't affect the class layout (since they | |
| aren't virtual methods, and no members can be added to the | |
| class).</p> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="breakpoint"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">Breakpoint</h1> | |
| <div class="postcontent"> | |
| <p>A collection of classes that implement our breakpoint classes. | |
| Breakpoints are resolved symbolically and always continue to | |
| resolve themselves as your program runs. Whether settings breakpoints | |
| by file and line, by symbol name, by symbol regular expression, | |
| or by address, breakpoints will keep trying to resolve new locations | |
| each time shared libraries are loaded. Breakpoints will of course | |
| unresolve themselves when shared libraries are unloaded. Breakpoints | |
| can also be scoped to be set only in a specific shared library. By | |
| default, breakpoints can be set in any shared library and will continue | |
| to attempt to be resolved with each shared library load.</p> | |
| <p>Breakpoint options can be set on the breakpoint, | |
| or on the individual locations. This allows flexibility when dealing | |
| with breakpoints and allows us to do what the user wants.</p> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="commands"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">Commands</h1> | |
| <div class="postcontent"> | |
| <p>The command source files represent objects that implement | |
| the functionality for all textual commands available | |
| in our command line interface.</p> | |
| <p>Every command is backed by a <b>lldb_private::CommandObject</b> | |
| or <b>lldb_private::CommandObjectMultiword</b> object.</p> | |
| <p><b>lldb_private::CommandObjectMultiword</b> are commands that | |
| have subcommands and allow command line commands to be | |
| logically grouped into a hierarchy.</p> | |
| <p><b>lldb_private::CommandObject</b> command line commands | |
| are the objects that implement the functionality of the | |
| command. They can optionally define | |
| options for themselves, as well as group those options into | |
| logical groups that can go together. The help system is | |
| tied into these objects and can extract the syntax and | |
| option groupings to display appropriate help for each | |
| command.</p> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="core"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">Core</h1> | |
| <div class="postcontent"> | |
| <p>The Core source files contain basic functionality that | |
| is required in the debugger. A wide variety of classes | |
| are implemented:</p> | |
| <ul> | |
| <li>Address (section offset addressing)</li> | |
| <li>AddressRange</li> | |
| <li>Architecture specification</li> | |
| <li>Broadcaster / Event / Listener </li> | |
| <li>Communication classes that use Connection objects</li> | |
| <li>Uniqued C strings</li> | |
| <li>Data extraction</li> | |
| <li>File specifications</li> | |
| <li>Mangled names</li> | |
| <li>Regular expressions</li> | |
| <li>Source manager</li> | |
| <li>Streams</li> | |
| <li>Value objects</li> | |
| </ul> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="dataformatters"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">DataFormatters</h1> | |
| <div class="postcontent"> | |
| <p>A collection of classes that implement the data formatters subsystem.</p> | |
| <p>The main entry point for interacting with the LLDB data formatters is the DataVisualization class. It provides | |
| a relatively stable front-end interface to ask questions of the data formatters regardless of the internal implementation.</p> | |
| <p>For people actively maintaining the data formatters subsystem itself, however, the FormatManager class is the relevant point of entry. | |
| This class is subject to more frequent changes as the formatters evolve. Currently, it provides a thin caching layer on top of a list of categories | |
| that each export a group of formatters. | |
| </p> | |
| <p>From an end-user perspective, the "type" LLDB command is the point of access to the data formatters. A large group of generally-useful formatters | |
| is provided by default and loaded upon debugger startup. | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="expression"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">Expression</h1> | |
| <div class="postcontent"> | |
| <p>Expression parsing files cover everything from evaluating | |
| DWARF expressions, to evaluating expressions using | |
| Clang.</p> | |
| <p>The DWARF expression parser has been heavily modified to | |
| support type promotion, new opcodes needed for evaluating | |
| expressions with symbolic variable references (expression local variables, | |
| program variables), and other operators required by | |
| typical expressions such as assign, address of, float/double/long | |
| double floating point values, casting, and more. The | |
| DWARF expression parser uses a stack of lldb_private::Value | |
| objects. These objects know how to do the standard C type | |
| promotion, and allow for symbolic references to variables | |
| in the program and in the LLDB process (expression local | |
| and expression global variables).</p> | |
| <p>The expression parser uses a full instance of the Clang | |
| compiler in order to accurately evaluate expressions. | |
| Hooks have been put into Clang so that the compiler knows | |
| to ask about identifiers it doesn't know about. Once | |
| expressions have be compiled into an AST, we can then | |
| traverse this AST and either generate a DWARF expression | |
| that contains simple opcodes that can be quickly re-evaluated | |
| each time an expression needs to be evaluated, or JIT'ed | |
| up into code that can be run on the process being debugged.</p> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="host"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">Host</h1> | |
| <div class="postcontent"> | |
| <p>LLDB tries to abstract itself from the host upon which | |
| it is currently running by providing a host abstraction | |
| layer. This layer involves everything from spawning, detaching, | |
| joining and killing native in-process threads, to getting | |
| current information about the current host.</p> | |
| <p>Host functionality includes abstraction layers for:</p> | |
| <ul> | |
| <li>Mutexes</li> | |
| <li>Conditions</li> | |
| <li>Timing functions</li> | |
| <li>Thread functions</li> | |
| <li>Host target triple</li> | |
| <li>Host child process notifications</li> | |
| <li>Host specific types</li> | |
| </ul> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="interpreter"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">Interpreter</h1> | |
| <div class="postcontent"> | |
| <p>The interpreter classes are the classes responsible for | |
| being the base classes needed for each command object, | |
| and is responsible for tracking and running command line | |
| commands.</p> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="symbol"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">Symbol</h1> | |
| <div class="postcontent"> | |
| <p>Symbol classes involve everything needed in order to parse | |
| object files and debug symbols. All the needed classes | |
| for compilation units (code and debug info for a source file), | |
| functions, lexical blocks within functions, inlined | |
| functions, types, declaration locations, and variables | |
| are in this section.</p> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="targ"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">Target</h1> | |
| <div class="postcontent"> | |
| <p>Classes that are related to a debug target include:</p> | |
| <ul> | |
| <li>Target</li> | |
| <li>Process</li> | |
| <li>Thread</li> | |
| <li>Stack frames</li> | |
| <li>Stack frame registers</li> | |
| <li>ABI for function calling in process being debugged</li> | |
| <li>Execution context batons</li> | |
| </ul> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <a name="utility"></a> | |
| <div class="post"> | |
| <h1 class ="postheader">Utility</h1> | |
| <div class="postcontent"> | |
| <p>Utility files should be as stand alone as possible and | |
| available for LLDB, plug-ins or related | |
| applications to use.</p> | |
| <p>Files found in the Utility section include:</p> | |
| <ul> | |
| <li>Pseudo-terminal support</li> | |
| <li>Register numbering for specific architectures.</li> | |
| <li>String data extractors</li> | |
| </ul> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
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