forked from OSchip/llvm-project
193 lines
7.2 KiB
ReStructuredText
193 lines
7.2 KiB
ReStructuredText
Architecture
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============
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LLDB is a large and complex codebase. This section will help you become more
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familiar with the pieces that make up LLDB and give a general overview of the
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general architecture.
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LLDB has many code groupings that makeup the source base:
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.. contents::
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:local:
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API
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---
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The API folder contains the public interface to LLDB.
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We are currently vending a C++ API. In order to be able to add methods to this
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API and allow people to link to our classes, we have certain rules that we must
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follow:
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- Classes can't inherit from any other classes.
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- Classes can't contain virtual methods.
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- Classes should be compatible with script bridging utilities like swig.
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- Classes should be lightweight and be backed by a single member. Pointers (or
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shared pointers) are the preferred choice since they allow changing the
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contents of the backend without affecting the public object layout.
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- The interface should be as minimal as possible in order to give a complete
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API.
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By adhering to these rules we should be able to continue to vend a C++ API, and
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make changes to the API as any additional methods added to these classes will
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just be a dynamic loader lookup and they won't affect the class layout (since
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they aren't virtual methods, and no members can be added to the class).
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Breakpoint
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----------
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A collection of classes that implement our breakpoint classes. Breakpoints are
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resolved symbolically and always continue to resolve themselves as your program
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runs. Whether settings breakpoints by file and line, by symbol name, by symbol
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regular expression, or by address, breakpoints will keep trying to resolve new
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locations each time shared libraries are loaded. Breakpoints will of course
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unresolve themselves when shared libraries are unloaded. Breakpoints can also
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be scoped to be set only in a specific shared library. By default, breakpoints
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can be set in any shared library and will continue to attempt to be resolved
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with each shared library load.
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Breakpoint options can be set on the breakpoint, or on the individual
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locations. This allows flexibility when dealing with breakpoints and allows us
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to do what the user wants.
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Commands
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--------
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The command source files represent objects that implement the functionality for
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all textual commands available in our command line interface.
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Every command is backed by a ``lldb_private::CommandObject`` or
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``lldb_private::CommandObjectMultiword`` object.
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``lldb_private::CommandObjectMultiword`` are commands that have subcommands and
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allow command line commands to be logically grouped into a hierarchy.
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``lldb_private::CommandObject`` command line commands are the objects that
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implement the functionality of the command. They can optionally define options
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for themselves, as well as group those options into logical groups that can go
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together. The help system is tied into these objects and can extract the syntax
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and option groupings to display appropriate help for each command.
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Core
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----
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The Core source files contain basic functionality that is required in the
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debugger as well as the class represeting the debugger it self (Debugger). A
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wide variety of classes are implemented:
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- Address (section offset addressing)
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- AddressRange
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- Broadcaster / Event / Listener
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- Communication classes that use Connection objects
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- Mangled names
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- Source manager
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- Value objects
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Dataformatters
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--------------
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A collection of classes that implement the data formatters subsystem.
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Data formatters provide a set of user-tweakable hooks in the ValueObjects world
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that allow to customize presentation aspects of variables. While users interact
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with formatters mostly through the type command, inside LLDB there are a few
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layers to the implementation: DataVisualization at the highest end of the
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spectrum, backed by classes implementing individual formatters, matching rules,
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etc.
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For a general user-level introduction to data formatters, you can look here.
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More details on the architecture are to be found here.
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Expression
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----------
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Expression parsing files cover everything from evaluating DWARF expressions, to
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evaluating expressions using Clang.
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The DWARF expression parser has been heavily modified to support type
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promotion, new opcodes needed for evaluating expressions with symbolic variable
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references (expression local variables, program variables), and other operators
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required by typical expressions such as assign, address of, float/double/long
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double floating point values, casting, and more. The DWARF expression parser
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uses a stack of lldb_private::Value objects. These objects know how to do the
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standard C type promotion, and allow for symbolic references to variables in
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the program and in the LLDB process (expression local and expression global
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variables).
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The expression parser uses a full instance of the Clang compiler in order to
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accurately evaluate expressions. Hooks have been put into Clang so that the
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compiler knows to ask about identifiers it doesn't know about. Once expressions
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have be compiled into an AST, we can then traverse this AST and either generate
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a DWARF expression that contains simple opcodes that can be quickly
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re-evaluated each time an expression needs to be evaluated, or JIT'ed up into
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code that can be run on the process being debugged.
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Host
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----
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LLDB tries to abstract itself from the host upon which it is currently running
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by providing a host abstraction layer. This layer includes functionality, whose
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implementation varies wildly from host to host.
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Host functionality includes abstraction layers for:
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- Information about the host system (triple, list of running processes, etc.)
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- Launching processes
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- Various OS primitives like pipes and sockets
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It also includes the base classes of the NativeProcess/Thread hierarchy, which
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is used by lldb-server.
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Interpreter
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-----------
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The interpreter classes are the classes responsible for being the base classes
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needed for each command object, and is responsible for tracking and running
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command line commands.
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Symbol
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------
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Symbol classes involve everything needed in order to parse object files and
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debug symbols. All the needed classes for compilation units (code and debug
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info for a source file), functions, lexical blocks within functions, inlined
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functions, types, declaration locations, and variables are in this section.
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Target
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------
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Classes that are related to a debug target include:
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- Target
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- Process
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- Thread
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- Stack frames
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- Stack frame registers
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- ABI for function calling in process being debugged
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- Execution context batons
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Utility
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-------
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This module contains the lowest layers of LLDB. A lot of these classes don't
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really have anything to do with debugging -- they are just there because the
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higher layers of the debugger use these clasess to implement their
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functionality. Others are data structures used in many other parts of the
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debugger (TraceOptions). Most of the functionality in this module could be
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useful in an application that is not a debugger; however, providing a general
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purpose C++ library is an explicit non-goal of this module.
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This module provides following functionality:
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- Abstract path manipulation (FileSpec)
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- Architecture specification
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- Data buffers (DataBuffer, DataEncoder, DataExtractor)
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- Logging
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- Structured data manipulation (JSON)
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- Streams
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- Timers
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For historic reasons, some of this functionality overlaps that which is
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provided by the LLVM support library.
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