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| <label>libc++abi Info</label> |
| <a href="/index.html">About</a> |
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| <!--*********************************************************************--> |
| <h1>"libc++abi" C++ Standard Library Support</h1> |
| <!--*********************************************************************--> |
| |
| <p>libc++abi is a new implementation of low level support for a standard |
| C++ library.</p> |
| |
| <p>All of the code in libc++abi is <a |
| href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">dual licensed</a> |
| under the MIT license and the UIUC License (a BSD-like license).</p> |
| |
| <!--=====================================================================--> |
| <h2 id="goals">Features and Goals</h2> |
| <!--=====================================================================--> |
| |
| <ul> |
| <li>Correctness as defined by the C++11 standard.</li> |
| <li>Provide a portable sublayer to ease the porting of <a href="https://libcxx.llvm.org/">libc++</a></li> |
| <li>On Mac OS X, be ABI compatible with the existing low-level support.</li> |
| </ul> |
| |
| <!--=====================================================================--> |
| <h2 id="requirements">Platform Support</h2> |
| <!--=====================================================================--> |
| |
| <p>libc++abi is known to work on the following platforms, using clang.</p> |
| |
| <ul> |
| <li>Darwin</li> |
| </ul> |
| |
| <!--=====================================================================--> |
| <h2 id="dir-structure">Current Status</h2> |
| <!--=====================================================================--> |
| |
| <p>libc++abi is complete. <a href="spec.html">Here</a> is a |
| list of functionality.</p> |
| |
| <!--=====================================================================--> |
| <h2>Get it and get involved!</h2> |
| <!--=====================================================================--> |
| |
| <p>To check out the code (including llvm and others), use:</p> |
| |
| <ul> |
| <li><code>git clone https://github.com/llvm/llvm-project.git</code></li> |
| </ul> |
| |
| <p>To build:</p> |
| <ul> |
| <li><code>cd llvm-project</code></li> |
| <li><code>mkdir build && cd build</code></li> |
| <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> |
| <li><code>make</code></li> |
| </ul> |
| |
| <p>To do a standalone build:</p> |
| <ul> |
| <li> |
| Check out the source tree. This includes the other subprojects, but you'll only use the libcxxabi part. |
| </li> |
| <li><code>cd llvm-project</code></li> |
| <li><code>mkdir build-libcxxabi && cd build-libcxxabi</code></li> |
| <li><code>cmake ../libcxxabi # on linux you may need -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li> |
| <li><code>make</code></li> |
| </ul> |
| <p> By default CMake uses <code>llvm-config</code> to locate the required |
| LLVM sources. If CMake cannot find <code>llvm-config</code> then you must |
| configure CMake using either of the following options. |
| </p> |
| <ul> |
| <li><code>-DLLVM_CONFIG_PATH=path/to/llvm-config</code></li> |
| <li><code>-DLLVM_PATH=path/to/llvm-source-root</code></li> |
| </ul> |
| |
| </p> |
| |
| <p>To run the tests:</p> |
| <ul> |
| <li><code>make check-cxxabi</code></li> |
| </ul> |
| <p>Note: in a standalone build, the system's libc++ will be used for tests. If |
| the system's libc++ was statically linked against libc++abi (or linked against |
| a different ABI library), this may interfere with test results.</p> |
| |
| <p>Send discussions to the |
| (<a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev mailing list</a>).</p> |
| |
| <!--=====================================================================--> |
| <h2>Frequently asked questions</h2> |
| <!--=====================================================================--> |
| |
| <p>Q: Why are the destructors for the standard exception classes defined in libc++abi? |
| They're just empty, can't they be defined inline?</p> |
| <p>A: The destructors for them live in libc++abi because they are "key" functions. |
| The Itanium ABI describes a "key" function as the first virtual declared. |
| And wherever the key function is defined, that is where the <code>type_info</code> gets defined. |
| And in libc++ types are the same type if and only if they have the same <code>type_info</code> |
| (as in there must be only one type info per type in the entire application). |
| And on OS X, libstdc++ and libc++ share these exception types. |
| So to be able to throw in one dylib and catch in another (a <code>std::exception</code> for example), |
| there must be only one <code>std::exception type_info</code> in the entire app. |
| That typeinfo gets laid down beside <code>~exception()</code> in libc++abi (for both libstdc++ and libc++).</p> |
| <p>--Howard Hinnant</p> |
| |
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