[libc++abi] Add option to enable definitions for the new/delete overloads.

[EricWF]

Summary

Currently both libc++ and libc++abi provide definitions for operator new/delete. However I believe this is incorrect and that one or the other should offer them.

This patch adds the CMake option -DLIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS which defaults to OFF unless otherwise specified. This means that by default
only libc++ provides the new/delete definitions.

[mehdi_amini]

LGTM.

CMakeLists.txt

416

It is unrelated to this change, but I'm wondering about the LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY condition. I see undefined reference to libc symbols.
That said we're linking to libSystem which provided everything, so I'm not even sure why dynamic_lookup is needed at all?

[EricWF]

In D30517#690328, @mehdi_amini wrote:

LGTM.

CMakeLists.txt

416

The external thread library configuration is not something you have to worry about. The issue this configuration handles is that libc++abi.so in unable to link to libc++external_threads.a, and instead expects the user to manually link libc++external_threads.a or it expects libc++ to handle the linking and undefined symbols later.

Once again you're never going to run into this since you don't use an externalized threading library.

CMakeLists.txt

 option(LIBCXXABI_ENABLE_THREADS "Build with threads enabled" ON)
 option(LIBCXXABI_HAS_PTHREAD_API "Ignore auto-detection and force use of pthread API" OFF)
 option(LIBCXXABI_HAS_EXTERNAL_THREAD_API
   "Build libc++abi with an externalized threading API.
   This option may only be set to ON when LIBCXXABI_ENABLE_THREADS=ON." OFF)
 option(LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY
   "Build libc++abi with an externalized threading library.
    This option may only be set to ON when LIBCXXABI_ENABLE_THREADS=ON" OFF)
+option(LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS
+    "Build libc++abi with definitions for operator new/delete. Normally libc++
+    provides these definitions" OFF)
 option(LIBCXXABI_BUILD_32_BITS "Build 32 bit libc++abi." ${LLVM_BUILD_32_BITS})
 option(LIBCXXABI_INCLUDE_TESTS "Generate build targets for the libc++abi unit tests." ${LLVM_INCLUDE_TESTS})
 set(LIBCXXABI_TARGET_TRIPLE "" CACHE STRING "Target triple for cross compiling.")
 set(LIBCXXABI_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
 set(LIBCXXABI_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
 set(LIBCXXABI_LIBCXX_LIBRARY_PATH "" CACHE PATH "The path to libc++ library.")
 
 # Default to building a shared library so that the default options still test
if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)
   endif()
   if (LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY)
     message(FATAL_ERROR "The options LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY"
                         " and LIBCXXABI_HAS_EXTERNAL_THREAD_API cannot be both"
                         " set to ON at the same time.")
   endif()
 endif()
 
-if (LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY AND LIBCXXABI_ENABLE_SHARED)
+set(LIBCXXABI_HAS_UNDEFINED_SYMBOLS ((NOT LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS)
+    OR (LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY AND LIBCXXABI_ENABLE_SHARED)))
+
+if (LIBCXXABI_HAS_UNDEFINED_SYMBOLS)
   # Need to allow unresolved symbols if this is to work with shared library builds
   if (APPLE)
     add_link_flags("-undefined dynamic_lookup")
   else()
     # Relax this restriction from HandleLLVMOptions
     string(REPLACE "-Wl,-z,defs" "" CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS}")
   endif()
 endif()

src/CMakeLists.txt

set(LIBCXXABI_SOURCES
   stdlib_stdexcept.cpp
   stdlib_typeinfo.cpp
   # Internal files
   abort_message.cpp
   fallback_malloc.cpp
   private_typeinfo.cpp
 )
 
-# FIXME: This file should only be compiled in special configurations such
-#  as building the Apple system dylib where libc++abi is expected to provide
-#  the new/delete definitions instead of libc++.
+if (LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS)
   list(APPEND LIBCXXABI_SOURCES stdlib_new_delete.cpp)
+endif()
 
 if (LIBCXXABI_ENABLE_EXCEPTIONS)
   list(APPEND LIBCXXABI_SOURCES cxa_exception.cpp)
   list(APPEND LIBCXXABI_SOURCES cxa_personality.cpp)
 else()
   list(APPEND LIBCXXABI_SOURCES cxa_noexception.cpp)
 endif()