Blame - www/architecture.html - fp2-dev/platform/external/lldb

Greg Clayton

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The <strong>LLDB</strong> Debugger

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Eric Christopher

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Greg Clayton

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Chris Lattner

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<h1 class ="postheader">Architecture</h1>

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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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<h1 class ="postheader">Code Layout</h1>

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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="#breakpoint">Breakpoint</a></li>

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<li><a href="#commands">Commands</a></li>

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<li><a href="#expression">Expression</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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<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 object pointer, shared pointer or global variable in the lldb_private.</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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<h1 class ="postheader">Breakpoint</h1>

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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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<h1 class ="postheader">Commands</h1>

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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

command.</p>

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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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<h1 class ="postheader">Expression</h1>

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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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<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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<li>Mutexes</li>

<li>Conditions</li>

<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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<h1 class ="postheader">Interpreter</h1>

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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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<h1 class ="postheader">Symbol</h1>

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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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<h1 class ="postheader">Target</h1>

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<p>Classes that are related to a debug target include:</p>

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<li>Target</li>

<li>Process</li>

<li>Thread</li>

<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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<h1 class ="postheader">Utility</h1>

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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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<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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Eric Christopher

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