[libcxx-commits] [libcxx] ebde6fc - [libcxxabi] Fix cmake order dependency wrt dllexporting

[Louis Dionne via libcxx-commits]

Author: Martin Storsjö
Date: 2022-03-07T15:36:04-05:00
New Revision: ebde6fc23bc0ee9d022fcd26b52bc82dfb7c8468

URL: https://github.com/llvm/llvm-project/commit/ebde6fc23bc0ee9d022fcd26b52bc82dfb7c8468
DIFF: https://github.com/llvm/llvm-project/commit/ebde6fc23bc0ee9d022fcd26b52bc82dfb7c8468.diff

LOG: [libcxxabi] Fix cmake order dependency wrt dllexporting

If LIBCXX_ENABLE_SHARED isn't explicitly set on the cmake command
line, isn't set in the cache, and the libcxxabi project is configured
before libcxx, then LIBCXX_ENABLE_SHARED isn't defined yet. Once
the libcxx cmake project has been parsed, LIBCXX_ENABLE_SHARED would
have been set to its default value of ON.

This makes sure that the symbols are properly dllexported in such
a configuration scenario.

Differential Revision: https://reviews.llvm.org/D120982

Added: 
    

Modified: 
    libcxx/docs/ReleaseNotes.rst
    libcxxabi/CMakeLists.txt

Removed: 
    


################################################################################
diff  --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
index c458705e9233c..01bc2a1d57cf5 100644
--- a/libcxx/docs/ReleaseNotes.rst
+++ b/libcxx/docs/ReleaseNotes.rst
@@ -93,3 +93,8 @@ Build System Changes
   ``{LIBCXX,LIBCXXABI,LIBUNWIND}_GCC_TOOLCHAIN`` CMake variables have been removed. Instead, please
   use the ``CMAKE_CXX_COMPILER_TARGET``, ``CMAKE_SYSROOT`` and ``CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN``
   variables provided by CMake.
+
+- When building for Windows, vendors who want to avoid dll-exporting symbols from the static libc++abi
+  library should set ``LIBCXXABI_HERMETIC_STATIC_LIBRARY=ON`` when configuring CMake. The current
+  behavior, which tries to guess the correct dll-export semantics based on whether we're building
+  the libc++ shared library, will be removed in LLVM 16.

diff  --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
index a7e8444e5a190..bf9f112d16237 100644
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -302,13 +302,20 @@ add_definitions(-D_LIBCPP_BUILDING_LIBRARY)
 
 # Disable DLL annotations on Windows for static builds.
 if (WIN32 AND LIBCXXABI_ENABLE_STATIC AND NOT LIBCXXABI_ENABLE_SHARED)
-  if (LIBCXX_ENABLE_SHARED AND LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
+  # If LIBCXX_ENABLE_SHARED isn't set (by the user on the cmake command
+  # line or via a cache file), use its expected default value (enabled).
+  if ((LIBCXX_ENABLE_SHARED OR NOT DEFINED LIBCXX_ENABLE_SHARED) AND LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
     # Building libcxxabi statically, but intending for it to be statically
     # linked into a shared libcxx; keep dllexport enabled within libcxxabi,
     # as the symbols will need to be exported from libcxx.
   else()
     # Regular static build; disable dllexports.
     add_definitions(-D_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS)
+    if (NOT LIBCXXABI_HERMETIC_STATIC_LIBRARY)
+      # TODO: Enable this warning message as soon as we're sure this is the solution.
+      # message(WARNING "Implicitly disabling dllexport on Win32 is not supported anymore. Please build with "
+      #                 "LIBCXXABI_HERMETIC_STATIC_LIBRARY=ON instead. This will become an error in LLVM 16.")
+    endif()
   endif()
 endif()