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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - UBSan doesn't catch misaligned memcpy"
href="https://llvm.org/bugs/show_bug.cgi?id=28025">28025</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>UBSan doesn't catch misaligned memcpy
</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>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>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>ch3root@openwall.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>When optimizing memcpy, clang uses alignment of types arguments point to. It
would be nice for UBSan to catch misaligned pointer in this context in the same
way as in dereferences.
Example of misaligned memcpy:
----------------------------------------------------------------------
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
int main(int argc, char **argv)
{
(void)argv;
long double *p = malloc(16);
memset(p, 123, 16);
char *q = malloc(17);
long double *q1 = (void *)(q + 1);
// *q1 = *p; // this is caught by UBSan
memcpy(q1, p, 16); // this is not caught
printf("%d\n", q[argc]);
}
----------------------------------------------------------------------
Results on x86-64:
----------------------------------------------------------------------
$ clang -std=c11 -Weverything -O3 -fsanitize=undefined test.c && ./a.out
Segmentation fault
----------------------------------------------------------------------
clang version: clang version 3.9.0 (trunk 271312)</pre>
</div>
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