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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - UB during unwinding from function target clone failure" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D23611&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=xFKSHwg35XMPwjAFJXsTR_pMLW7CFPIMjqjqxU18qzY&s=shde3APShQ8Uf5-8j8kMqmJaiuNqRQJ92E4e2Zkszpg&e=">23611</a>
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<th>Summary</th>
<td>UB during unwinding from function target clone failure
</td>
</tr>
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<th>Product</th>
<td>libc++
</td>
</tr>
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<th>Version</th>
<td>3.6
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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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
</td>
</tr>
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<th>Reporter</th>
<td>david_work@me.com
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu, mclow.lists@gmail.com
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Cloning a std::function target object goes like this:
1. Construct and call an allocator object.
2. Pass the newly allocated memory to a unique_ptr.
3. Placement-construct the new erasure object into the raw memory.
4. Release the handle from the now-valid unique_ptr.
After #2, the unique_ptr is attempting to manage raw memory, which is
dangerous. If #3 throws, unwinding will destroy the new erasure object before
reaching __clone. At this point the unique_ptr is destroyed, and destroys the
erasure a second time.
No misbehavior occurs, I suppose, because the erasure is polymorphic and its
root base class, aside from being polymorphic, would be trivially-destructible.
Each virtual destructor begins by resetting the vtable to its own class. The
post-destruction state points to a vtable with an empty destructor.
However, the destructor really isn't trivial, and accessing the destroyed
object at all is UB.
NB: I'm already working on some major upgrades to std::function.</pre>
</div>
</p>
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