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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - False positive (divide by zero), involving ALIGNOF()" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D23893&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=rszuyExV_blTn5EjLoiob0DuBerTQLAVT27Y6B7o3xg&s=jpcyAJh8w43aO3IjF24LuOfdTv1bRyr1pANBnIUbQeM&e=">23893</a>
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<th>Summary</th>
<td>False positive (divide by zero), involving ALIGNOF()
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.4
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Static Analyzer
</td>
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<th>Assignee</th>
<td>kremenek@apple.com
</td>
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<th>Reporter</th>
<td>arnsholt@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>In the MoarVM project, we have some code that looks like this (computing
offsets for struct members):
size_t cur_size;
size_t align = ALIGNOF(void *);
/* Stuff we don't care about here, setting cur_size */
if (cur_size % align)
cur_size += align - cur_size % align;
The static analyzer thinks that `align` is initialized to 0 and thus that
there's a potential divide-by-zero in the modulo operation. This is clearly not
possible, since the smallest possible ALIGNOF value is 1.
Our ALIGNOF is implemented like this:
#define ALIGNOF(t) ((char *)(&((struct { char c; t _h; } *)0)->_h) - (char
*)0)</pre>
</div>
</p>
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