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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - libc++ passes invalid values to pthread_equal"
href="https://bugs.llvm.org/show_bug.cgi?id=42918">42918</a>
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<th>Summary</th>
<td>libc++ passes invalid values to pthread_equal
</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>All
</td>
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<th>OS</th>
<td>FreeBSD
</td>
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<th>Status</th>
<td>NEW
</td>
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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
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>mclow.lists@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
</td>
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<p>
<div>
<pre>[ received from Ed Maste at FreeBSD ]
We just had a FreeBSD bug submitted for a failure arising from
libc++'s use of pthread_equal.
FreeBSD's pthread_equal stub implementation (used in non-threaded
programs) returns true unconditionally, since a non-threaded program
cannot have two different threads. However, std::thread::id defines a
special value that should not equal any real thread, and this is may
be passed to pthread_equal. See FreeBSD PR 239550 for more details,
and PR 239038 for the user-facing issue that prompted this.
<a href="https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=239550">https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=239550</a>
<a href="https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=239038">https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=239038</a>
Now the most expedient fix is probably for us to make pthread_equal
somewhat less of a stub, but for correctness it seems
__libcpp_thread_id_equal would need to check for libc++'s special
value before calling pthread_equal.</pre>
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