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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 - rte_table: lookup functions have UB for ctz"
href="https://bugs.dpdk.org/show_bug.cgi?id=1289">1289</a>
</td>
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<tr>
<th>Summary</th>
<td>rte_table: lookup functions have UB for ctz
</td>
</tr>
<tr>
<th>Product</th>
<td>DPDK
</td>
</tr>
<tr>
<th>Version</th>
<td>23.11
</td>
</tr>
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<th>Hardware</th>
<td>x86
</td>
</tr>
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<th>OS</th>
<td>Linux
</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>other
</td>
</tr>
<tr>
<th>Assignee</th>
<td>dev@dpdk.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>qrealka@gmail.com
</td>
</tr>
<tr>
<th>Target Milestone</th>
<td>---
</td>
</tr></table>
<p>
<div class="bz_comment_block">
<pre class="bz_comment_text">Macros 'lookup2_stage0_with_odd_support' can call rte_ctz with zero value
(pkt_mask), which is undefined behaviour based on the GCC manual:
<a href="https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html">https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html</a>
Quote: "
Built-in Function: int __builtin_ctz (unsigned int x)
Returns the number of trailing 0-bits in x, starting at the least significant
bit position. If x is 0, the result is undefined.
"
It is confirmed by checking this code in GCC-13 with ASAN.
</pre>
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</p>
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