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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - LLVM should emit DW_OP_form_tls_address instead of DW_OP_GNU_push_tls_address"
href="http://llvm.org/bugs/show_bug.cgi?id=18423">18423</a>
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<th>Summary</th>
<td>LLVM should emit DW_OP_form_tls_address instead of DW_OP_GNU_push_tls_address
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>All
</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>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>DebugInfo
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>aprantl@apple.com
</td>
</tr>
<tr>
<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>For thread-local storage, LLVM currently uses the custom DWARF expression
DW_OP_GNU_push_tls_address. There is a DW_OP_form_tls_address that has been
part of the DWARF spec since version 3.
<a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140106/200694.html">http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140106/200694.html</a>
According to
<a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140106/200714.html">http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140106/200714.html</a>
the reason for this is that GDB up to 7.5 does not support
DW_OP_form_tls_address.
Here is a patch we can apply once GDB supports the official DWARF expression:
diff --git a/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
b/lib/CodeGen/AsmPrinter/Dwarf
index 04a2573..bfe1524 100644
--- a/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -1595,7 +1595,9 @@ void
DwarfCompileUnit::createGlobalVariableDIE(DIGlobalVar
addUInt(Block, dwarf::DW_FORM_udata, DU->getAddrPoolIndex(Expr));
}
// 3) followed by a custom OP to make the debugger do a TLS lookup.
- addUInt(Block, dwarf::DW_FORM_data1, dwarf::DW_OP_GNU_push_tls_address);
+ addUInt(Block, dwarf::DW_FORM_data1,
+ DD->getDwarfVersion() <= 2 ? dwarf::DW_OP_GNU_push_tls_address
+ : dwarf::DW_OP_form_tls_address);
} else {
DD->addArangeLabel(SymbolCU(this, Sym));
addOpAddress(Block, Sym);</pre>
</div>
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