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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - UBSan reports downcast/upcast of misaligned address in std::set<long long>"
href="https://llvm.org/bugs/show_bug.cgi?id=23413">23413</a>
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<th>Summary</th>
<td>UBSan reports downcast/upcast of misaligned address in std::set<long long>
</td>
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<th>Product</th>
<td>clang
</td>
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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>Linux
</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>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>public@hansmi.ch
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=14283" name="attach_14283" title="Test program and output after building with Clang 3.6 (using GCC toolchain 4.9)">attachment 14283</a> <a href="attachment.cgi?id=14283&action=edit" title="Test program and output after building with Clang 3.6 (using GCC toolchain 4.9)">[details]</a></span>
Test program and output after building with Clang 3.6 (using GCC toolchain 4.9)
Using `long long' as std::set's value type causes UBSan as included in Clang
3.5 and 3.6 to report an downcast/upcast of a misaligned address at runtime.
Platform: Debian 8 (Jessie) on Intel x86 (32 bit)
C++ library: libstdc++
Reproduced using:
- Clang 3.5 w/ GCC toolchain 4.9
- Clang 3.6 w/ GCC toolchain 4.9
- Clang 3.6 w/ GCC toolchain 5.1.0
The issue does not occur with libc++. Shorter value types for std::set, e.g.
`long' or `char', work. Packaging the `long long' in another type, e.g. a
struct, works too.
The fact that this is not reproducible when building with GCC 5.1.0 (with
-fsanitize=alignment) and neither when compiling for x86-64 leads me to believe
that this is an issue in Clang's implementation of UBSan.</pre>
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