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<body><table border="1" cellspacing="0" cellpadding="8" class="bz_new_table">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_UNCONFIRMED "
title="UNCONFIRMED - Fix undefined behavior in RTE_IPV4 macro"
href="https://bugs.dpdk.org/show_bug.cgi?id=1506">1506</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Fix undefined behavior in RTE_IPV4 macro
</td>
</tr>
<tr>
<th>Product</th>
<td>DPDK
</td>
</tr>
<tr>
<th>Version</th>
<td>24.07
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>UNCONFIRMED
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>Normal
</td>
</tr>
<tr>
<th>Component</th>
<td>core
</td>
</tr>
<tr>
<th>Assignee</th>
<td>dev@dpdk.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>user202729@protonmail.com
</td>
</tr>
<tr>
<th>Target Milestone</th>
<td>---
</td>
</tr></table>
<p>
<div class="bz_comment_block">
<pre class="bz_comment_text">Currently we have the following definition
```
/** Create IPv4 address */
#define RTE_IPV4(a, b, c, d) ((uint32_t)(((a) & 0xff) << 24) | \
(((b) & 0xff) << 16) | \
(((c) & 0xff) << 8) | \
((d) & 0xff))
```
The problem is that the cast to `uint32_t` is done after the shift, and
overflowing left shift is undefined behavior in C and C++:
<a href="https://stackoverflow.com/questions/3784996/why-does-left-shift-operation-invoke-undefined-behaviour-when-the-left-side-oper">https://stackoverflow.com/questions/3784996/why-does-left-shift-operation-invoke-undefined-behaviour-when-the-left-side-oper</a>
.
The fix is easy, just cast the `(a) & 0xff` to `uint32_t` before shifting it by
24.
</pre>
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