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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - UndrefReturn false positive"
href="https://bugs.llvm.org/show_bug.cgi?id=46215">46215</a>
</td>
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<th>Summary</th>
<td>UndrefReturn false positive
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Static Analyzer
</td>
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<th>Assignee</th>
<td>dcoughlin@apple.com
</td>
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<th>Reporter</th>
<td>kim.grasman@gmail.com
</td>
</tr>
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<th>CC</th>
<td>dcoughlin@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>The following minimal program triggers a false positive in Clang SA's
UndefReturn checker:
// t.c
char T(char **d) {
char *entries[2];
entries[0] = d[0];
char *buf1 = (char *)entries;
return buf1[1];
}
$ clang-11 -cc1 -analyze -analyzer-checker=core.uninitialized.UndefReturn t.c
t.c:9:2: warning: Undefined or garbage value returned to caller
[core.uninitialized.UndefReturn]
return buf1[1];
^~~~~~~~~~~~~~
1 warning generated.
I've tried to debug this, and it looks like the region store gets confused
about the type and size of the region. I believe I narrowed it down to this old
FIXME:
<a href="https://github.com/llvm/llvm-project/blob/e93f7e6d1ab973be717e00966f66739930361a80/clang/lib/StaticAnalyzer/Core/RegionStore.cpp#L1455">https://github.com/llvm/llvm-project/blob/e93f7e6d1ab973be717e00966f66739930361a80/clang/lib/StaticAnalyzer/Core/RegionStore.cpp#L1455</a>.
We hit a similar issue for production code when hashing an array of pointer
values, but
a) it triggers in UndefResultChecker, not ReturnUndefChecker
b) I haven't been able to reduce it as effectively
They both seem to be based on the region store's isUndef logic, so I suspect
they're related.</pre>
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</p>
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