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| author | Shoaib Meenai <smeenai@fb.com> | 2016-09-19 18:29:07 +0000 |
|---|---|---|
| committer | Shoaib Meenai <smeenai@fb.com> | 2016-09-19 18:29:07 +0000 |
| commit | e5cbce437b5df127d1e1896d4b9b112eb66b5458 (patch) | |
| tree | 63413718d9125f29d29fc6271250e5b2a1a0294c /docs | |
| parent | 7d7f3cc9b169e0464d0df67b714515652ce49042 (diff) | |
[libc++] Fix extern template visibility for Windows
On Windows, marking an `extern template class` declaration as exported
actually forces an instantiation, which is not the desired behavior.
Instead, the actual explicit instantiations need to be exported.
Differential Revision: https://reviews.llvm.org/D24679
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@281925 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/DesignDocs/VisibilityMacros.rst | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/docs/DesignDocs/VisibilityMacros.rst b/docs/DesignDocs/VisibilityMacros.rst index d6fdb287f..f7d140034 100644 --- a/docs/DesignDocs/VisibilityMacros.rst +++ b/docs/DesignDocs/VisibilityMacros.rst @@ -71,6 +71,26 @@ Visibility Macros However since `_LIBCPP_TYPE_VIS_ONLY` is the same as `_LIBCPP_TYPE_VIS` the visibility is already correct. The macro has an empty definition with GCC. + **Windows Behavior**: `extern template` and `dllexport` are fundamentally + incompatible *on a template class* on Windows; the former suppresses + instantiation, while the latter forces it. Specifying both on the same + declaration makes the template class be instantiated, which is not desirable + inside headers. This macro therefore expands to `dllimport` outside of libc++ + but nothing inside of it (rather than expanding to `dllexport`); instead, the + explicit instantiations themselves are marked as exported. Note that this + applies *only* to extern template *classes*. Extern template *functions* obey + regular import/export semantics, and applying `dllexport` directly to the + extern template declaration is the correct thing to do for them. + +**_LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS** + Mark the member functions, typeinfo, and vtable of an explicit instantiation + of a class template as being exported by the libc++ library. This attribute + must be specified on all template class explicit instantiations. + + It is only necessary to mark the explicit instantiation itself (as opposed to + the extern template declaration) as exported on Windows, as discussed above. + On all other platforms, this macro has an empty definition. + **_LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY** Mark a member function of a class template as hidden and inline except when building the libc++ library where it marks the symbol as being exported by |