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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Libc++ must guard against C++17 inline variable ABI breaks."
href="https://llvm.org/bugs/show_bug.cgi?id=28395">28395</a>
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<th>Summary</th>
<td>Libc++ must guard against C++17 inline variable ABI breaks.
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>All Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>eric@efcs.ca
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>C++17 inline variables change the semantics surrounding how static data members
are defined. Previously static data members were required to be explicitly
defined once. In C++17 the compiler emits a potentially-discardable
definition in every TU where the data member is ODR-used. Even explicit
definitions of inline variables can be discarded.
This is problematic for Libc++ since it causes definitions previously provided
by libc++.dylib to disappear. This can cause ABI breakage if a C++17 dylib is
linked with a C++14 program.
The following symbols in libc++.dylib are affected (as of July 1st, 2016):
* std::chrono::steady_clock::is_steady
* std::chrono::system_clock::is_steady
I will introduce a workaround in libc++ itself until PR28394 is resolved.
(<a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Explicit definitions of C++17 inline variables should be non-discardable."
href="show_bug.cgi?id=28394">https://llvm.org/bugs/show_bug.cgi?id=28394</a>)</pre>
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</p>
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