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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - clang and GCC disagree on attribute usage for explicitly instantiated templates"
href="https://llvm.org/bugs/show_bug.cgi?id=24815">24815</a>
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<th>Summary</th>
<td>clang and GCC disagree on attribute usage for explicitly instantiated templates
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</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>C++11
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>dcheng@google.com
</td>
</tr>
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<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
</td>
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<p>
<div>
<pre>Sorry, I don't really know the build magic so I don't have any good examples.
In Chrome, we have some templated classes with explicit instantiations that
look something like this:
#define EXPORT __attribute((visibility("default")))
template <class T>
class EXPORT Property {
// ...
};
extern template class Property<uint8>;
extern template class Property<bool>;
// etc
When building with clang, uses of the explicitly instantiated templates outside
the shared library fail to link: the linker complains that there are undefined
references to Property<uint8>'s constructor, destructor, etc.
To fix this for clang, I tried exporting the explicit template instantiations:
extern template class EXPORT Property<uint8>;
extern template class EXPORT Property<bool>;
But now this doesn't compile in GCC:
../../dbus/property.h:437:42: error: type attributes ignored after type is
already defined [-Werror=attributes]
extern template class CHROME_DBUS_EXPORT Property<uint8>;
^
../../dbus/property.h:447:42: error: type attributes ignored after type is
already defined [-Werror=attributes]
extern template class CHROME_DBUS_EXPORT Property<bool>;
It turns out GCC ignores attributes on explicit template instantiations
(<a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=17470</a>): their fix for this was to
change it so the original template definition controls visibility, and any
attributes on explicit instantiations are ignored (and trigger a
warning/error).</pre>
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