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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 - Clang produces an incomplete comdat"
href="https://bugs.llvm.org/show_bug.cgi?id=47747">47747</a>
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<th>Summary</th>
<td>Clang produces an incomplete comdat
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<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>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>rafael@espindo.la
</td>
</tr>
<tr>
<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>
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<pre>Given
common.hh:
-------------------------
struct zed {
zed() noexcept;
};
template <typename T>
thread_local zed var;
-------------------------
test1.cc:
-------------------------
#include "common.hh"
inline void* foobaz() {
return &var<int>;
}
-------------------------
test2.cc:
-------------------------
#include "common.hh"
void* foobar() {
return &var<int>;
}
-------------------------
Compile with just
$ clang++ -c test1.cc -o test1.o
$ clang++ -c test2.cc -o test2.o
$ readelf -gsW test2.o
....
COMDAT group section [ 7] `.group' [_Z3varIiE] contains 4 sections:
[Index] Name
[ 8] .text.startup
[ 9] .rela.text.startup
[ 10] .tbss._Z3varIiE
[ 11] .tbss._ZGV3varIiE
...
10: 0000000000000000 56 FUNC WEAK DEFAULT 8 _ZTH3varIiE
So the symbol _ZTH3varIiE is in a section that is in the _Z3varIiE
comdat.
But in the other file:
$ readelf -gsW test1.o
COMDAT group section [ 3] `.group' [_Z3varIiE] contains 4 sections:
[Index] Name
[ 4] .text.startup
[ 5] .rela.text.startup
[ 6] .tbss._Z3varIiE
[ 7] .tbss._ZGV3varIiE
We have the same comdat, but the symbol _ZTH3varIiE is missing. This
means that if the two files are linked, _ZTH3varIiE can be resolved to
0.
GCC correctly outputs _ZTH3varIiE in both files.</pre>
</div>
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