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142 lines
5.7 KiB
142 lines
5.7 KiB
4 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->
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<html>
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<head>
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<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>"libc++abi" C++ Standard Library Support</title>
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<link type="text/css" rel="stylesheet" href="menu.css">
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<link type="text/css" rel="stylesheet" href="content.css">
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</head>
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<body>
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<div id="menu">
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<div>
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<a href="https://llvm.org/">LLVM Home</a>
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</div>
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<div class="submenu">
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<label>libc++abi Info</label>
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<a href="/index.html">About</a>
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</div>
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<div class="submenu">
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<label>Quick Links</label>
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<a href="https://libcxx.llvm.org/">libc++</a>
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<a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev</a>
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<a href="https://lists.llvm.org/mailman/listinfo/libcxx-commits">libcxx-commits</a>
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<a href="https://bugs.llvm.org/">Bug Reports</a>
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<a href="https://github.com/llvm/llvm-project/tree/master/libcxxabi/">Browse Sources</a>
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</div>
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</div>
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<div id="content">
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<!--*********************************************************************-->
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<h1>"libc++abi" C++ Standard Library Support</h1>
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<!--*********************************************************************-->
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<p>libc++abi is a new implementation of low level support for a standard
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C++ library.</p>
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<p>All of the code in libc++abi is <a
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href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">dual licensed</a>
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under the MIT license and the UIUC License (a BSD-like license).</p>
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<!--=====================================================================-->
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<h2 id="goals">Features and Goals</h2>
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<!--=====================================================================-->
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<ul>
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<li>Correctness as defined by the C++11 standard.</li>
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<li>Provide a portable sublayer to ease the porting of <a href="https://libcxx.llvm.org/">libc++</a></li>
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<li>On Mac OS X, be ABI compatible with the existing low-level support.</li>
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</ul>
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<!--=====================================================================-->
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<h2 id="requirements">Platform Support</h2>
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<!--=====================================================================-->
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<p>libc++abi is known to work on the following platforms, using clang.</p>
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<ul>
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<li>Darwin</li>
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</ul>
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<!--=====================================================================-->
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<h2 id="dir-structure">Current Status</h2>
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<!--=====================================================================-->
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<p>libc++abi is complete. <a href="spec.html">Here</a> is a
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list of functionality.</p>
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<!--=====================================================================-->
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<h2>Get it and get involved!</h2>
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<!--=====================================================================-->
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<p>To check out the code (including llvm and others), use:</p>
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<ul>
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<li><code>git clone https://github.com/llvm/llvm-project.git</code></li>
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</ul>
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<p>To build:</p>
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<ul>
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<li><code>cd llvm-project</code></li>
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<li><code>mkdir build && cd build</code></li>
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<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>
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<li><code>make</code></li>
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</ul>
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<p>To do a standalone build:</p>
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<ul>
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<li>
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Check out the source tree. This includes the other subprojects, but you'll only use the libcxxabi part.
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</li>
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<li><code>cd llvm-project</code></li>
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<li><code>mkdir build-libcxxabi && cd build-libcxxabi</code></li>
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<li><code>cmake ../libcxxabi # on linux you may need -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
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<li><code>make</code></li>
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</ul>
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<p> By default CMake uses <code>llvm-config</code> to locate the required
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LLVM sources. If CMake cannot find <code>llvm-config</code> then you must
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configure CMake using either of the following options.
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</p>
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<ul>
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<li><code>-DLLVM_CONFIG_PATH=path/to/llvm-config</code></li>
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<li><code>-DLLVM_PATH=path/to/llvm-source-root</code></li>
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</ul>
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</p>
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<p>To run the tests:</p>
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<ul>
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<li><code>make check-cxxabi</code></li>
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</ul>
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<p>Note: in a standalone build, the system's libc++ will be used for tests. If
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the system's libc++ was statically linked against libc++abi (or linked against
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a different ABI library), this may interfere with test results.</p>
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<p>Send discussions to the
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(<a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev mailing list</a>).</p>
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<!--=====================================================================-->
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<h2>Frequently asked questions</h2>
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<!--=====================================================================-->
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<p>Q: Why are the destructors for the standard exception classes defined in libc++abi?
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They're just empty, can't they be defined inline?</p>
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<p>A: The destructors for them live in libc++abi because they are "key" functions.
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The Itanium ABI describes a "key" function as the first virtual declared.
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And wherever the key function is defined, that is where the <code>type_info</code> gets defined.
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And in libc++ types are the same type if and only if they have the same <code>type_info</code>
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(as in there must be only one type info per type in the entire application).
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And on OS X, libstdc++ and libc++ share these exception types.
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So to be able to throw in one dylib and catch in another (a <code>std::exception</code> for example),
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there must be only one <code>std::exception type_info</code> in the entire app.
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That typeinfo gets laid down beside <code>~exception()</code> in libc++abi (for both libstdc++ and libc++).</p>
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<p>--Howard Hinnant</p>
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</div>
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</body>
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</html>
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