<html>
<head>
<base href="https://bugs.llvm.org/">
</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 - printf bug when arguments from a member of union"
href="https://bugs.llvm.org/show_bug.cgi?id=40196">40196</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>printf bug when arguments from a member of union
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>6.0
</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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>metora@x-legend.com.tw
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
</td>
</tr></table>
<p>
<div>
<pre>Hi
We found a bug in printf.
It may have included below
1. 64bit union
2. a bit number in union
3. out of register count (x64-ABI limit)
#include <stdio.h>
union U {
unsigned long long Value;
struct {
unsigned long long Data:2;
};
};
int main ()
{
int a = 0;
U b = { 0 };
printf ("%d, %llu\n", a, b.Data);
printf ("%d, %d, %llu\n", a, a, b.Data);
printf ("%d, %d, %d, %llu\n", a, a, a, b.Data);
printf ("%d, %d, %d, %d, %llu\n", a, a, a, a, b.Data);
printf ("%d, %d, %d, %d, %d, %llu\n", a, a, a, a, a, b.Data);
printf ("%d, %d, %d, %d, %d, %d, %llu\n", a, a, a, a, a, a, b.Data);
printf ("%d, %d, %d, %d, %d, %d, %d, %llu\n", a, a, a, a, a, a, a, b.Data);
printf ("%d, %d, %d, %d, %d, %d, %d, %d, %llu\n", a, a, a, a, a, a, a, a,
b.Data);
printf ("%d, %d, %d, %d, %d, %d, %d, %d, %d, %llu\n", a, a, a, a, a, a, a,
a, a, b.Data);
return 0;
}
metora@pro-debian:$ clang-6.0 1.cc
metora@pro-debian:$ ./a.out
0, 0
0, 0, 0
0, 0, 0, 0
0, 0, 0, 0, 0
0, 0, 0, 0, 0, 140724603453440
0, 0, 0, 0, 0, 0, 140724603453440
0, 0, 0, 0, 0, 0, 0, 0
0, 0, 0, 0, 0, 0, 0, 0, 0
0, 0, 0, 0, 0, 0, 0, 0, 0, 0
How to fix or prevent it?
Thank you</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>