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| <!--*********************************************************************--> |
| <h1>The LLDB Debugger</h1> |
| <!--*********************************************************************--> |
| |
| <p>LLDB is a next generation, high-performance debugger. It is built as a set |
| of reusable components which highly leverage existing libraries in the |
| larger LLVM Project, such as the Clang expression parser and LLVM |
| disassembler.</p> |
| <p>LLDB is in early development, but is mature enough to support basic |
| debugging scenarios on Mac OS X in C, Objective-C and C++.</p> |
| |
| <p>All of the code in the LLDB project is available under the standard |
| <a href="http://llvm.org/docs/DeveloperPolicy.html#license">LLVM |
| License</a>, an open source "BSD-style" license.</p> |
| |
| <!--=====================================================================--> |
| <h2 id="goals">Goals</h2> |
| <!--=====================================================================--> |
| |
| <p>The current state of the art in open source debuggers are that |
| they work in the common cases for C applications, but don't |
| handle many "hard cases" properly. For example, C++ expression |
| parsing, handling overloading, templates, multi-threading, and |
| other non-trivial scenarios all work in some base cases, but |
| don't work reliably.</p> |
| |
| <p>The goal of LLDB is to provide an amazing debugging experience that "just |
| works". We aim to solve these long-standing problems where debuggers get |
| confused, so that you can think about debugging your problem, not |
| about deficiencies in the debugger.</p> |
| |
| <p>With a long view, there is no good reason for a debugger to |
| reinvent its own C/C++ parser, type system, know all the |
| target calling convention details, implement its own disassembler, |
| etc. By using the existing libraries vended by the LLVM |
| project, we believe that many of these problems will be defined |
| away, and the debugger can focus on important issues like |
| process control, efficient symbol reading and indexing, thread |
| management, and other debugger-specific problems.</p> |
| |
| <p>Some more specific goals include:</p> |
| |
| <ul> |
| <li>Build libraries for inclusion in IDEs, command line tools, and |
| other analysis tools</li> |
| <li>High performance and efficient memory use</li> |
| <li>Extensible: Python scriptable and use a plug-in architecture</li> |
| <li>Reuse existing compiler technology where it makes sense</li> |
| <li>Excellent multi-threaded debugging support</li> |
| <li>Great support for C, Objective-C and C++</li> |
| <li>Retargetable to support multiple platforms</li> |
| <li>Provide a base for debugger research and other innovation</li> |
| </ul> |
| |
| <!--=====================================================================--> |
| <h2 id="why">Why a new debugger?</h2> |
| <!--=====================================================================--> |
| |
| <p>In order to achieve our goals we decided to start with a fresh architecture |
| that would support modern multi-threaded programs, handle debugging symbols |
| in an efficient manner, use compiler based code knowledge and have plug-in |
| support for functionality and extensions. Additionally we want the debugger |
| capabilities to be available to other analysis tools, be they scripts or |
| compiled programs, without requiring them to be GPL.</p> |
| |
| <!--=====================================================================--> |
| <h2 id="features">Features</h2> |
| <!--=====================================================================--> |
| |
| <p>LLDB supports a broad variety of basic debugging features such as |
| reading DWARF, supporting step, next, finish, backtraces, etc. Some |
| more interested bits are:</p> |
| |
| <ul> |
| <li>Plug-in architecture for portability and extensibility: |
| <ul> |
| <li>Object file parsers for executable file formats. Support currently |
| includes Mach-O (32 and 64-bit) & ELF (32-bit).</li> |
| <li>Object container parsers to extract object files contained within a file. |
| Support currently includes universal Mach-O files & BSD Archives. |
| </li> |
| <li>Debug symbol file parsers to incrementally extract debug information from |
| object files. Support currently includes DWARF & Mach-O symbol |
| tables.</li> |
| <li>Symbol vendor plug-ins collect data from a variety of different sources |
| for an executable object.</li> |
| <li>Disassembly plug-ins for each architecture. Support currently includes |
| an LLVM disassembler for <a |
| href="http://blog.llvm.org/2010/01/x86-disassembler.html">i386, |
| x86_64</a>, & ARM/Thumb.</li> |
| <li>Debugger plug-ins implement the host and target specific functions |
| required to debug.</li> |
| </ul> |
| <li>SWIG-generated script bridging allows Python to access and control the |
| public API of the debugger library.</li> |
| <li>A remote protocol server, debugserver, implements Mac OS X debugging on |
| i386 and x86_64.</li> |
| <li>A command line debugger - the lldb executable itself.</li> |
| <li>A framework API to the library.</li> |
| </ul> |
| |
| <!--=====================================================================--> |
| <h2 id="requirements">Platform Support</h2> |
| <!--=====================================================================--> |
| |
| <p>LLDB is known to work on the following platforms, but ports to new |
| platforms are welcome:</p> |
| |
| <li>Machine Architectures: |
| <ul> |
| <li>Mac OS X i386 and X86-64</li> |
| </ul></li> |
| |
| <!--=====================================================================--> |
| <h2 id="status">Current Status</h2> |
| <!--=====================================================================--> |
| |
| <p>LLDB is in early development and supports basic debugging scenarios on |
| Mac OS X. The public API has not been finalized, and different parts are |
| at different levels of maturity. We welcome any help fleshing out missing |
| pieces and improving the code.</p> |
| |
| <p>What works well:</p> |
| <ul> |
| <li>Process control, including external process control via debugserver |
| (which is included as part of the lldb project)</li> |
| <li>Breakpoints: Source-line, symbolic, C++ mangled names, module |
| scoping</li> |
| <li>Symbol reading and object file introspection</li> |
| <li>Script bridging</li> |
| <li>Thread inspection and stepping</li> |
| <li>Disassembly of i386, x86_64, & ARM/Thumb machine code, and |
| backtracing on i386 & x86_64</li> |
| <li>The basic command line prompt system, shared library tracking, |
| source listings.</li> |
| </ul> |
| |
| <p>What is still pretty new:</p> |
| <ul> |
| <li>The public API to the library</li> |
| <li>Expression evaluation</li> |
| <li>Objective-C support: stepping into/over, printing the description of |
| an object ("po")</li> |
| <li>Breakpoint actions & scripts</li> |
| <li>Attaching to existing processes</li> |
| </ul> |
| |
| <p>What isn't there yet:</p> |
| <ul> |
| <li>Regression test suite</li> |
| <li>Operating system support hasn't been fully modularized yet</li> |
| <li><a href="http://clang.llvm.org/docs/LanguageExtensions.html#blocks">Blocks</a> support</li> |
| <li>Calling functions in expressions</li> |
| <li>Objective-C 2.0 Support: Printing properties, synthetic properties, |
| Objective-C expressions, KVO, dynamic types, dot syntax, runtime data</li> |
| <li>C++ support: Method access, handling demangled names, dynamic types</li> |
| <li>Exception support: Breaking by name, thrown object, thrower</li> |
| </li> |
| </ul> |
| |
| <!--=====================================================================--> |
| <h2>Get it and get involved!</h2> |
| <!--=====================================================================--> |
| |
| <p>To check out the code, use:</p> |
| |
| <ul> |
| <li>svn co http://llvm.org/svn/llvm-project/lldb/trunk lldb</li> |
| </ul> |
| |
| <p>Note that LLDB currently only builds out of the box on Darwin with |
| Xcode, but patches to improve portability are definitely welcome.</p> |
| |
| <p>Discussions about LLDB should go to the <a |
| href="http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev">lldb-dev</a> mailing |
| list. Commit messages for the lldb SVN module are automatically sent to the |
| <a |
| href="http://lists.cs.uiuc.edu/mailman/listinfo/lldb-commits">lldb-commits</a> |
| mailing list, and this is also the preferred mailing list for patch |
| submissions.</p> |
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