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<base href="https://llvm.org/bugs/" />
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<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Improper alignment in pointer cast in unordered_map of std::aligned_storage"
href="https://llvm.org/bugs/show_bug.cgi?id=31849">31849</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Improper alignment in pointer cast in unordered_map of std::aligned_storage
</td>
</tr>
<tr>
<th>Product</th>
<td>libc++
</td>
</tr>
<tr>
<th>Version</th>
<td>3.9
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>All Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david@doublewise.net
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>This might be related to <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED WONTFIX - operator new and STL containers silently ignore element alignment"
href="show_bug.cgi?id=22634">https://llvm.org/bugs/show_bug.cgi?id=22634</a>
#include <unordered_map>
struct S {
void emplace() {
m_map.emplace(
std::piecewise_construct,
std::forward_as_tuple(0),
std::forward_as_tuple()
);
}
private:
std::int64_t x;
// std::int64_t y;
using mapped_type = typename std::aligned_storage<3*sizeof(void*)>::type;
std::unordered_map<int, mapped_type> m_map;
};
int main() {
S s;
s.emplace();
}
clang++ -stdlib=libc++ -fsanitize=address -fsanitize=undefined -std=c++1z
main.cpp && ./a.out
include/c++/v1/__hash_table:2152:29: runtime error: downcast of misaligned
address 0x7ff2d6c62f8 for type
'std::__1::__hash_node<std::__1::__hash_value_type<int,
std::__1::aligned_storage<24, 16>::type, void *>', which requires 16 byte
alignment
However, unlike with <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED WONTFIX - operator new and STL containers silently ignore element alignment"
href="show_bug.cgi?id=22634">bug 22634</a> this can result from no particular use of
alignment specifiers in user code. This exact sanitizer error can also be
triggered by using std::function<anything(anything...)> as the mapped_type, as
it contains std::aligned_storage in it.</pre>
</div>
</p>
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