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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 --- - thread_local accessor function for 'primitive' variable in anonymous namespace has wrong linkage"
href="http://llvm.org/bugs/show_bug.cgi?id=19655">19655</a>
</td>
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<th>Summary</th>
<td>thread_local accessor function for 'primitive' variable in anonymous namespace has wrong linkage
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.4
</td>
</tr>
<tr>
<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>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++11
</td>
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<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>michael@ensslin.cc
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>For thread-local variables, clang++ auto-generates a wrapper that will
initialize the memory on first access. In contrast to g++, this also happens
for primitive types, e.g. ints or simple structs without constructors. For
those primitive types, the wrapper is globally linked in clang++, with
-std=c++11
Minimal example:
mic@mic-nb /tmp/repr4 $ cat a.cpp
namespace {
thread_local int i {1};
}
void f() {
i = 2;
}
mic@mic-nb /tmp/repr4 $ cat b.cpp
namespace {
thread_local int i {0};
}
void f();
int main() {
f();
return i;
}
mic@mic-nb /tmp/repr4 $ g++ --version
g++ (GCC) 4.9.0
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
mic@mic-nb /tmp/repr4 $ clang++ --version
clang version 3.4 (tags/RELEASE_34/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
mic@mic-nb /tmp/repr4 $ g++ -std=c++11 a.cpp b.cpp; ./a.out; echo $?
0
mic@mic-nb /tmp/repr4 $ clang++ -std=c++11 a.cpp b.cpp; ./a.out; echo $?
2
As you can see, f() in a.o influences the variable i from b.o.
mic@mic-nb /tmp/repr4 $ nm -C a.o
U _GLOBAL_OFFSET_TABLE_
0000000000000000 T f()
0000000000000000 d (anonymous namespace)::i
0000000000000000 W TLS wrapper function for (anonymous namespace)::i
mic@mic-nb /tmp/repr4 $ nm -C b.o
U _GLOBAL_OFFSET_TABLE_
0000000000000000 T main
U f()
0000000000000000 b (anonymous namespace)::i
0000000000000000 W TLS wrapper function for (anonymous namespace)::i
mic@mic-nb /tmp/repr4 $ nm -C a.out
(...)
00000000004005b0 T f()
0000000000000000 d (anonymous namespace)::i
0000000000000004 b (anonymous namespace)::i
00000000004005d0 t TLS wrapper function for (anonymous namespace)::i
As you can see, both variables are linked into the finaly binary, but one of
the TLS wrappers is scrapped.
If a more complex type is used instead of int, the error does not occur.</pre>
</div>
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