libcxxabi/www/index.html

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  34   <!--*********************************************************************-->
  35   <h1>"libc++abi" C++ Standard Library Support</h1>
  36   <!--*********************************************************************-->
  37
  38   <p>libc++abi is a new implementation of low level support for a standard
  39      C++ library.</p>
  40
  41   <p>All of the code in libc++abi is <a
  42      href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">dual licensed</a>
  43      under the MIT license and the UIUC License (a BSD-like license).</p>
  44
  45   <!--=====================================================================-->
  46   <h2 id="goals">Features and Goals</h2>
  47   <!--=====================================================================-->
  48
  49     <ul>
  50         <li>Correctness as defined by the C++11 standard.</li>
  51         <li>Provide a portable sublayer to ease the porting of <a href="https://libcxx.llvm.org/">libc++</a></li>
  52         <li>On Mac OS X, be ABI compatible with the existing low-level support.</li>
  53     </ul>
  54
  55   <!--=====================================================================-->
  56   <h2 id="requirements">Platform Support</h2>
  57   <!--=====================================================================-->
  58
  59    <p>libc++abi is known to work on the following platforms, using clang.</p>
  60
  61     <ul>
  62     <li>Darwin</li>
  63     </ul>
  64
  65   <!--=====================================================================-->
  66   <h2 id="dir-structure">Current Status</h2>
  67   <!--=====================================================================-->
  68
  69    <p>libc++abi is complete.  <a href="spec.html">Here</a> is a
  70    list of functionality.</p>
  71
  72   <!--=====================================================================-->
  73   <h2>Get it and get involved!</h2>
  74   <!--=====================================================================-->
  75
  76   <p>To check out the code (including llvm and others), use:</p>
  77
  78   <ul>
  79   <li><code>git clone https://github.com/llvm/llvm-project.git</code></li>
  80   </ul>
  81
  82   <p>To build:</p>
  83   <ul>
  84   <li><code>cd llvm-project</code></li>
  85   <li><code>mkdir build &amp;&amp; cd build</code></li>
  86   <li><code>cmake -DLLVM_ENABLE_PROJECTS=libcxxabi ../llvm # on linux you may need to specify -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
  87   <li><code>make</code></li>
  88   </ul>
  89
  90   <p>To do a standalone build:</p>
  91   <ul>
  92   <li>
  93     Check out the source tree. This includes the other subprojects, but you'll only use the libcxxabi part.
  94   </li>
  95   <li><code>cd llvm-project</code></li>
  96   <li><code>mkdir build-libcxxabi &amp;&amp; cd build-libcxxabi</code></li>
  97   <li><code>cmake -DLIBCXXABI_LIBCXX_PATH=path/to/libcxx ../libcxxabi # on
  98     linux you may need -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
  99   <li><code>make</code></li>
 100   </ul>
 101   <p> By default CMake uses <code>llvm-config</code> to locate the required
 102       LLVM sources. If CMake cannot find <code>llvm-config</code> then you must
 103       configure CMake using either of the following options.
 104   </p>
 105   <ul>
 106   <li><code>-DLLVM_CONFIG_PATH=path/to/llvm-config</code></li>
 107   <li><code>-DLLVM_PATH=path/to/llvm-source-root</code></li>
 108   </ul>
 109
 110   </p>
 111
 112   <p>To run the tests:</p>
 113   <ul>
 114   <li><code>make check-cxxabi</code></li>
 115   </ul>
 116   <p>Note: in a standalone build, the system's libc++ will be used for tests. If
 117   the system's libc++ was statically linked against libc++abi (or linked against
 118   a different ABI library), this may interfere with test results.</p>
 119
 120   <p>Send discussions to the
 121   (<a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev mailing list</a>).</p>
 122
 123   <!--=====================================================================-->
 124   <h2>Frequently asked questions</h2>
 125   <!--=====================================================================-->
 126
 127   <p>Q: Why are the destructors for the standard exception classes defined in libc++abi?
 128      They're just empty, can't they be defined inline?</p>
 129   <p>A: The destructors for them live in libc++abi because they are "key" functions.
 130      The Itanium ABI describes a "key" function as the first virtual declared.
 131      And wherever the key function is defined, that is where the <code>type_info</code> gets defined.
 132      And in libc++ types are the same type if and only if they have the same <code>type_info</code>
 133      (as in there must be only one type info per type in the entire application).
 134      And on OS X, libstdc++ and libc++ share these exception types.
 135      So to be able to throw in one dylib and catch in another (a <code>std::exception</code> for example),
 136      there must be only one <code>std::exception type_info</code> in the entire app.
 137      That typeinfo gets laid down beside <code>~exception()</code> in libc++abi (for both libstdc++ and libc++).</p>
 138      <p>--Howard Hinnant</p>
 139
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