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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - UBSan: No warning for misaligned load of extern"
href="http://bugs.llvm.org/show_bug.cgi?id=32630">32630</a>
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<th>Summary</th>
<td>UBSan: No warning for misaligned load of extern
</td>
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<th>Product</th>
<td>clang
</td>
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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>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>LLVM Codegen
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>vsk@apple.com
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Presently, UBSan does not diagnose misaligned loads/stores from extern
variables. Example:
// a.c
struct S { int I; }
extern S global_S;
int getI() { return global_S.I; }
// b.c
char ...;
char global_S[4];
char ...;
UBSan can emit an alignment check for loads from DeclRefExprs. However, this
isn't enough to catch the issue, because the IRBuilder constant folds the
alignment test away to 'true': (and (ptrtoint (gep &global_S ...)) 3) => 0.
This makes the test ineffective.
We might try and fix this by disabling constant folding when emitting UBSan
checks.</pre>
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</p>
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