[PATCH] D25145: [libc++] Correct explanation of _LIBCPP_NEW_DELETE_VIS
Shoaib Meenai via cfe-commits
cfe-commits at lists.llvm.org
Fri Sep 30 17:38:13 PDT 2016
smeenai created this revision.
smeenai added reviewers: compnerd, EricWF, mclow.lists.
smeenai added a subscriber: cfe-commits.
The behavior of this macro actually needs to apply universally on
Windows and not just when using the Microsoft CRT. Update the macro
definition and documentation accordingly.
@@ -125,7 +125,7 @@
} // std
-#if defined(_LIBCPP_MSVCRT) && !defined(_LIBCPP_BUILDING_LIBRARY)
+#if defined(_WIN32) && !defined(_LIBCPP_BUILDING_LIBRARY)
# define _LIBCPP_NEW_DELETE_VIS
# define _LIBCPP_NEW_DELETE_VIS _LIBCPP_FUNC_VIS
@@ -112,14 +112,15 @@
Mark a symbol as being exported by the libc++ library. This macro must be
applied to all `operator new` and `operator delete` overloads.
- **Windows Behavior**: When using the Microsoft CRT, all the `operator new` and
- `operator delete` overloads are defined statically in `msvcrt.lib`. Marking
- them as `dllimport` in the libc++ `<new>` header is therefore undesirable: if
- we were to mark them as `dllimport` and then link against libc++, source files
- which included `<new>` would end up linking against libc++'s `operator new`
- and `operator delete`, while source files which did not include `<new>` would
- end up linking against msvcrt's `operator new` and `operator delete`, which
- would be a confusing and potentially error-prone inconsistency.
+ **Windows Behavior**: The `operator new` and `operator delete` overloads
+ should not be marked as `dllimport`; if they were, source files including the
+ `<new>` header (either directly or transitively) would lose the ability to use
+ local overloads of `operator new` and `operator delete`. On Windows, this
+ macro therefore expands to `__declspec(dllexport)` when building the library
+ and has an empty definition otherwise. A related caveat is that libc++ must be
+ included on the link line before `msvcrt.lib`, otherwise Microsoft's
+ definitions of `operator new` and `operator delete` inside `msvcrt.lib` will
+ end up being used instead of libc++'s.
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