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295 lines
13 KiB
HTML
Executable File
295 lines
13 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 Architecture</title>
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</head>
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<body>
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<div class="www_title">
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The <strong>LLDB</strong> Debugger
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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">Architecture</h1>
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<div class="postcontent">
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<p>LLDB is a large and complex codebase. This section will help you become more familiar with
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the pieces that make up LLDB and give a general overview of the general architecture.</p>
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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">Code Layout</h1>
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<div class="postcontent">
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<p>LLDB has many code groupings that makeup the source base:</p>
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<ul>
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<li><a href="#api">API</a></li>
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<li><a href="#breakpoint">Breakpoint</a></li>
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<li><a href="#commands">Commands</a></li>
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<li><a href="#core">Core</a></li>
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<li><a href="#dataformatters">DataFormatters</a></li>
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<li><a href="#expression">Expression</a></li>
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<li><a href="#host">Host</a></li>
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<li><a href="#interpreter">Interpreter</a></li>
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<li><a href="#symbol">Symbol</a></li>
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<li><a href="#targ">Target</a></li>
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<li><a href="#utility">Utility</a></li>
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</ul>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="api"></a>
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<div class="post">
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<h1 class ="postheader">API</h1>
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<div class="postcontent">
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<p>The API folder contains the public interface to LLDB.</p>
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<p>We are currently vending a C++ API. In order to be able to add
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methods to this API and allow people to link to our classes,
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we have certain rules that we must follow:</p>
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<ul>
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<li>Classes can't inherit from any other classes.</li>
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<li>Classes can't contain virtual methods.</li>
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<li>Classes should be compatible with script bridging utilities like <a href="http://www.swig.org/">swig</a>.</li>
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<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>
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<li>The interface should be as minimal as possible in order to give a complete API.</li>
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</ul>
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<p>By adhering to these rules we should be able to continue to
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vend a C++ API, and make changes to the API as any additional
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methods added to these classes will just be a dynamic loader
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lookup and they won't affect the class layout (since they
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aren't virtual methods, and no members can be added to the
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class).</p>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="breakpoint"></a>
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<div class="post">
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<h1 class ="postheader">Breakpoint</h1>
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<div class="postcontent">
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<p>A collection of classes that implement our breakpoint classes.
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Breakpoints are resolved symbolically and always continue to
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resolve themselves as your program runs. Whether settings breakpoints
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by file and line, by symbol name, by symbol regular expression,
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or by address, breakpoints will keep trying to resolve new locations
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each time shared libraries are loaded. Breakpoints will of course
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unresolve themselves when shared libraries are unloaded. Breakpoints
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can also be scoped to be set only in a specific shared library. By
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default, breakpoints can be set in any shared library and will continue
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to attempt to be resolved with each shared library load.</p>
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<p>Breakpoint options can be set on the breakpoint,
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or on the individual locations. This allows flexibility when dealing
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with breakpoints and allows us to do what the user wants.</p>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="commands"></a>
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<div class="post">
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<h1 class ="postheader">Commands</h1>
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<div class="postcontent">
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<p>The command source files represent objects that implement
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the functionality for all textual commands available
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in our command line interface.</p>
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<p>Every command is backed by a <b>lldb_private::CommandObject</b>
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or <b>lldb_private::CommandObjectMultiword</b> object.</p>
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<p><b>lldb_private::CommandObjectMultiword</b> are commands that
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have subcommands and allow command line commands to be
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logically grouped into a hierarchy.</p>
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<p><b>lldb_private::CommandObject</b> command line commands
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are the objects that implement the functionality of the
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command. They can optionally define
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options for themselves, as well as group those options into
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logical groups that can go together. The help system is
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tied into these objects and can extract the syntax and
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option groupings to display appropriate help for each
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command.</p>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="core"></a>
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<div class="post">
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<h1 class ="postheader">Core</h1>
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<div class="postcontent">
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<p>The Core source files contain basic functionality that
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is required in the debugger. A wide variety of classes
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are implemented:</p>
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<ul>
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<li>Address (section offset addressing)</li>
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<li>AddressRange</li>
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<li>Architecture specification</li>
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<li>Broadcaster / Event / Listener </li>
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<li>Communication classes that use Connection objects</li>
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<li>Uniqued C strings</li>
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<li>Data extraction</li>
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<li>File specifications</li>
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<li>Mangled names</li>
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<li>Regular expressions</li>
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<li>Source manager</li>
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<li>Streams</li>
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<li>Value objects</li>
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</ul>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="dataformatters"></a>
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<div class="post">
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<h1 class ="postheader">DataFormatters</h1>
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<div class="postcontent">
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<p>A collection of classes that implement the data formatters subsystem.</p>
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<p>For a general user-level introduction to data formatters, you can look <a href="varformats.html">here</a>.
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<p>A 10,000 foot view of the data formatters is based upon the <code>DataVisualization</code> class.
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<code>DataVisualization</code> is the very high level entry point into the data formatters. It vends a stable interface in face of changing internals
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and is the recommended entry point for components of LLDB that need to ask questions of the data formatters.
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The main questions one can ask of <code>DataVisualization</code> are:
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<ul>
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<li>given a ValueObject, retrieve the formatters to be used for it</li>
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<li>given a type, retrieve the formatters to be used for it. This is not an "exact" question,
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i.e. one can retrieve a formatter from a type name which would not be used to then format ValueObjects of that type</li>
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<li>given a name, retrieve a category of that name, optionally creating it if needed - more generally, categories management</li>
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<li>given an identifier and a summary, store it as a named summary - more generally, named summary management</li>
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</ul>
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<p>For people actively maintaining the data formatters subsystem itself, however, the FormatManager class is the relevant point of entry.
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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
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that each export a group of formatters.
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</p>
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<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
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is provided by default and loaded upon debugger startup.
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="expression"></a>
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<div class="post">
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<h1 class ="postheader">Expression</h1>
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<div class="postcontent">
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<p>Expression parsing files cover everything from evaluating
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DWARF expressions, to evaluating expressions using
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Clang.</p>
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<p>The DWARF expression parser has been heavily modified to
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support type promotion, new opcodes needed for evaluating
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expressions with symbolic variable references (expression local variables,
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program variables), and other operators required by
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typical expressions such as assign, address of, float/double/long
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double floating point values, casting, and more. The
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DWARF expression parser uses a stack of lldb_private::Value
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objects. These objects know how to do the standard C type
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promotion, and allow for symbolic references to variables
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in the program and in the LLDB process (expression local
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and expression global variables).</p>
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<p>The expression parser uses a full instance of the Clang
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compiler in order to accurately evaluate expressions.
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Hooks have been put into Clang so that the compiler knows
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to ask about identifiers it doesn't know about. Once
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expressions have be compiled into an AST, we can then
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traverse this AST and either generate a DWARF expression
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that contains simple opcodes that can be quickly re-evaluated
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each time an expression needs to be evaluated, or JIT'ed
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up into code that can be run on the process being debugged.</p>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="host"></a>
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<div class="post">
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<h1 class ="postheader">Host</h1>
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<div class="postcontent">
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<p>LLDB tries to abstract itself from the host upon which
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it is currently running by providing a host abstraction
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layer. This layer involves everything from spawning, detaching,
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joining and killing native in-process threads, to getting
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current information about the current host.</p>
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<p>Host functionality includes abstraction layers for:</p>
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<ul>
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<li>Mutexes</li>
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<li>Conditions</li>
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<li>Timing functions</li>
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<li>Thread functions</li>
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<li>Host target triple</li>
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<li>Host child process notifications</li>
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<li>Host specific types</li>
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</ul>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="interpreter"></a>
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<div class="post">
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<h1 class ="postheader">Interpreter</h1>
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<div class="postcontent">
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<p>The interpreter classes are the classes responsible for
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being the base classes needed for each command object,
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and is responsible for tracking and running command line
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commands.</p>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="symbol"></a>
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<div class="post">
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<h1 class ="postheader">Symbol</h1>
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<div class="postcontent">
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<p>Symbol classes involve everything needed in order to parse
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object files and debug symbols. All the needed classes
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for compilation units (code and debug info for a source file),
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functions, lexical blocks within functions, inlined
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functions, types, declaration locations, and variables
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are in this section.</p>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="targ"></a>
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<div class="post">
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<h1 class ="postheader">Target</h1>
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<div class="postcontent">
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<p>Classes that are related to a debug target include:</p>
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<ul>
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<li>Target</li>
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<li>Process</li>
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<li>Thread</li>
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<li>Stack frames</li>
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<li>Stack frame registers</li>
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<li>ABI for function calling in process being debugged</li>
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<li>Execution context batons</li>
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</ul>
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</div>
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<div class="postfooter"></div>
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</div>
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<a name="utility"></a>
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<div class="post">
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<h1 class ="postheader">Utility</h1>
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<div class="postcontent">
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<p>Utility files should be as stand alone as possible and
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available for LLDB, plug-ins or related
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applications to use.</p>
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<p>Files found in the Utility section include:</p>
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<ul>
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<li>Pseudo-terminal support</li>
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<li>Register numbering for specific architectures.</li>
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<li>String data extractors</li>
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</ul>
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</div>
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<div class="postfooter"></div>
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</div>
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</div>
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</div>
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</div>
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</body>
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</html>
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