<html>
<head>
<base href="https://llvm.org/bugs/" />
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - UBSan: missing check for accessing an inactive member of an union"
href="https://llvm.org/bugs/show_bug.cgi?id=25887">25887</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>UBSan: missing check for accessing an inactive member of an union
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</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>Frontend
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>gonzalobg88@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Just discussed in this range-v3 issue:
<a href="https://github.com/ericniebler/range-v3/issues/239">https://github.com/ericniebler/range-v3/issues/239</a>
both Eric and Casey give good examples. Here Eric's example:
template<typename F, typename S>
struct pair_data
{
union
{
F non_const_first_;
F const first;
};
union
{
S non_const_second_;
S const second;
};
};
template<typename F, typename S>
struct pair : private pair_data<F, S>
{
using pair_data<F, S>::first;
using pair_data<F, S>::second;
pair() : pair_data<F, S>{} {}
pair(F f, S s) : pair_data<F, S>{f, s} {}
~pair()
{
first.~F();
second.~S();
}
};
int main()
{
pair<int, float> f{1, 3.14f};
return f.first; // UB
// more UB: destructors of the non-active members (first, second) are
called
// instead of the destructors of the active members (first_, second_)
}
Aggregate initialization of the union initialize the first member "first_".
Accessing first thus access a non-active member of the union and results in
undefined behavior.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>