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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - SmallVector: use-after-poison MSAN error in destructor"
href="https://bugs.llvm.org/show_bug.cgi?id=35889">35889</a>
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<th>Summary</th>
<td>SmallVector: use-after-poison MSAN error in destructor
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
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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
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<th>Component</th>
<td>Core LLVM classes
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>steve@obrien.cc
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>The topmost class, `SmallVector`, has internal storage for some elements; `N -
1` elements' bytes worth of space. Meanwhile a base class
`SmallVectorTemplateCommon` has room for one element as well, totaling `N`
elements' worth of space.
The space for the N elements is contiguous and straddles
`SmallVectorTemplateCommon` and `SmallVector`.
A class "between" those two owning the storage, `SmallVectorImpl`, in its
destructor, calls the destructor for elements contained in the vector, if any.
It uses `destroy_range(begin, end)` to destroy all items in sequence, starting
from the end.
By the time the destructor for `SmallVectorImpl` is running, though, the memory
for elements `[1, N)` is already poisoned, due to `SmallVector`'s destructor
having done its thing already.
So if the element type `T` has a nontrivial destructor that accesses any
members of the `T` instance being destroyed, we'll run into a use-after-poison
bug.
This patch moves the destruction loop into `SmallVector`'s destructor, so any
memory being accessed while dtors are running is not yet poisoned.
[Phabricator diff and repro steps coming]</pre>
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