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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - c/c++ invalid -fsanitize=undefined crash with "offsetof" like code"
href="https://bugs.llvm.org/show_bug.cgi?id=49174">49174</a>
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<th>Summary</th>
<td>c/c++ invalid -fsanitize=undefined crash with "offsetof" like code
</td>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</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>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>ryan_greenblatt@brown.edu
</td>
</tr>
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>```
typedef struct type {
int member;
} type_t;
int main()
{
(char *)&((type_t *)(0))->member;
}
```
This crashes with:
```
temp.c:7:31: runtime error: member access within null pointer of type 'type_t'
(aka 'struct type')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior temp.c:7:31 in
```
<a href="https://gcc.godbolt.org/z/dbWc6h">https://gcc.godbolt.org/z/dbWc6h</a>
Note that the crash still occurs when using `((size_t)((char *)&((type_t
*)0)->member - (char *)0))`. See <a href="https://en.wikipedia.org/wiki/Offsetof">https://en.wikipedia.org/wiki/Offsetof</a> for an
explanation of what is going on here.
The crash doesn't occur with `__builtin_offsetof`, so that is a viable work
around.</pre>
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