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  <h1>The LLDB Debugger</h1>
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  <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>

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  <h2 id="goals">Goals</h2>
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  <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>

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  <h2 id="why">Why a new debugger?</h2>
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  <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>

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  <h2 id="features">Features</h2>
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   <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) &amp; ELF (32-bit).</li>
   <li>Object container parsers to extract object files contained within a file.
       Support currently includes universal Mach-O files &amp; BSD Archives.
       </li>
   <li>Debug symbol file parsers to incrementally extract debug information from
       object files. Support currently includes DWARF &amp; 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>, &amp; 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>

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  <h2 id="requirements">Platform Support</h2>
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   <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>

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  <h2 id="status">Current Status</h2>
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   <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, &amp; ARM/Thumb machine code, and
       backtracing on i386 &amp; 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 &amp; 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>

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  <h2>Get it and get involved!</h2>
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  <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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