[libcxx] Add support for linking libc++ against a static ABI library.

[EricWF]

Summary

This patch add the CMake option LIBCXX_ENABLE_STATIC_ABI_LIBRARY which, when enabled, will link libc++ against the static version of the ABI library.

[danalbert]

LGTM.

[compnerd]

cmake/Modules/HandleLibCXXABI.cmake

85

Why do you change the name of the library, the name should stay the same, its the extension that changes (and I believe should be implicit based on add_library).

lib/CMakeLists.txt

41

Can you add this in side of a check for the linker type? The options are very GNU centric.

test/CMakeLists.txt

47

Can you explain why this is correct? The tests are meant to test libc++abi. They should link to it either statically or dynamically as built. The libc++ tests however, should not.

[EricWF]

Address inline comments.

cmake/Modules/HandleLibCXXABI.cmake

85

The actual library name ('libc++abi.so' or 'libc++abi.a') doesn't change. These are CMake target names for when libc++abi and libc++ are being built intree together.

lib/CMakeLists.txt

41

Sounds like a good change. I'll look into it.

test/CMakeLists.txt

47

Because when libc++ statically links to libc++abi then all of the symbols from libc++abi should be available via libc++. If we don't do this and always link the tests to libc++abi then it could hide errors where libc++ doesn't properly expose the required symbols.

[EricWF]

lib/CMakeLists.txt

41

To comment on this further. The correct thing to do would be to use find_library with the static library name. However there are some consumers of libc++ that depend on libc++'s CMake not requiring that the library be found at configuration time since it will not yet exist.

This is also the reason why use use LIBCXX_CXX_ABI_LIBRARY_PATH to supply the library's directory and not the full path of the library file.
I'm hoping to change this in future.

[compnerd]

CMakeLists.txt

64

Maybe this should be something like LIBCXX_STATIC_LIBCXXABI. Otherwise, we need checks for the case that we are trying to use libsupc++/libcxxrt and don't have a static version available.

74

Any reason to not support this on Darwin really? I think that we can build a DSO for libc++ and just grab the $<TARGET_OBJECTS:c++abi> (or a static archive/library).

cmake/Modules/HandleLibCXXABI.cmake

85

Yeah, thats what happens when you look at a patch set out of order :-p.

test/CMakeLists.txt

47

Agreed, but the libc++abi tests shouldn't try to pull the symbols indirectly from libc++. They should have direct access to libc++abi symbols.

[EricWF]

CMakeLists.txt

64

Perhaps. Since the option is OFF by default I don't think we *need* checks. I have no problem with these cases failing to link because the library is missing. If a user enables this option they should know that they have a static version of the library available.

74

Because linking libc++ on Darwin is already a mess and it would need to be cleaned up first. I also don't see the motivation to support this on Darwin because libc++ reexports libc++abi.dynlib.

test/CMakeLists.txt

47

This shouldn't affect the libc++abi tests because they don't use the lit.site.cfg generated by libc++.

[EricWF]

More cleanup and comments.

CMakeLists.txt

    This option may only be used when LIBCXX_ENABLE_THREADS=OFF." ON)
 option(LIBCXX_INSTALL_HEADERS "Install the libc++ headers." ON)
 option(LIBCXX_INSTALL_SUPPORT_HEADERS "Install libc++ support headers." ON)
+option(LIBCXX_ENABLE_STATIC_ABI_LIBRARY "Statically link the ABI library" OFF)
 set(LIBCXX_SYSROOT "" CACHE STRING "Use alternate sysroot.")
 set(LIBCXX_GCC_TOOLCHAIN "" CACHE STRING "Use alternate GCC toolchain.")
 if (LIBCXX_BUILT_STANDALONE)

       "Define the sanitizer used to build the library and tests")
 endif()
 
+if (LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
+  if (APPLE)
+    message(FATAL_ERROR "LIBCXX_ENABLE_STATIC_ABI_LIBRARY is not supported on OS X")
+  else()
+    message(WARNING "LIBCXX_ENABLE_STATIC_ABI_LIBRARY is an experimental option")
+  endif()
+endif()
+
 set(CXXABIS none libcxxabi libcxxrt libstdc++ libsupc++)
 if (NOT LIBCXX_CXX_ABI)
   if (NOT DEFINED LIBCXX_BUILT_STANDALONE AND

cmake/Modules/HandleLibCXXABI.cmake

 elseif ("${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "libcxxabi")
   if (LIBCXX_CXX_ABI_INTREE)
     # Link against just-built "cxxabi" target.
-    set(CXXABI_LIBNAME cxxabi)
+    if (LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
+        set(CXXABI_LIBNAME cxxabi_static)
+    else()
+        set(CXXABI_LIBNAME cxxabi_shared)
+    endif()
     set(LIBCXX_LIBCPPABI_VERSION "2" PARENT_SCOPE)
   else()
     # Assume c++abi is installed in the system, rely on -lc++abi link flag.

lib/CMakeLists.txt

     )
 endif()
 
+#if LIBCXX_CXX_ABI_LIBRARY_PATH is defined we want to add it to the search path.
+if (DEFINED LIBCXX_CXX_ABI_LIBRARY_PATH)
+  target_link_libraries(cxx "-L${LIBCXX_CXX_ABI_LIBRARY_PATH}")
+endif()
+
 if (DEFINED LIBCXX_CXX_ABI_DEPS)
   add_dependencies(cxx LIBCXX_CXX_ABI_DEPS)
 endif()
 
+set(libraries "")
+if (LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
+    # TODO(ericwf): Remove these GNU specific linker flags and let CMake do the
+    # configuration. This will be more portable.
+    list(APPEND libraries "-Wl,--whole-archive" "-Wl,-Bstatic")
+    list(APPEND libraries "${LIBCXX_CXX_ABI_LIBRARY}")
+    list(APPEND libraries "-Wl,-Bdynamic" "-Wl,--no-whole-archive")
+else()
+    list(APPEND libraries "${LIBCXX_CXX_ABI_LIBRARY}")
+endif()
+
 # Generate library list.
-set(libraries ${LIBCXX_CXX_ABI_LIBRARY})
 append_if(libraries LIBCXX_HAS_PTHREAD_LIB pthread)
 append_if(libraries LIBCXX_HAS_C_LIB c)
 append_if(libraries LIBCXX_HAS_M_LIB m)
 append_if(libraries LIBCXX_HAS_RT_LIB rt)
 append_if(libraries LIBCXX_HAS_GCC_S_LIB gcc_s)
 
-#if LIBCXX_CXX_ABI_LIBRARY_PATH is defined we want to add it to the search path.
-if (DEFINED LIBCXX_CXX_ABI_LIBRARY_PATH)
-  target_link_libraries(cxx "-L${LIBCXX_CXX_ABI_LIBRARY_PATH}")
-endif()
 target_link_libraries(cxx ${libraries})
 
 # Setup flags.

test/CMakeLists.txt

   pythonize_bool(LIBCXX_BUILD_32_BITS)
   pythonize_bool(LIBCXX_ENABLE_THREADS)
   pythonize_bool(LIBCXX_ENABLE_MONOTONIC_CLOCK)
+  # The tests shouldn't link to any ABI library when it has been linked into
+  # libc++ statically.
+  if (LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
+    set(LIBCXX_CXX_ABI_LIBNAME "none")
+  endif()
   set(LIBCXX_TARGET_INFO "libcxx.test.target_info.LocalTI" CACHE STRING
       "TargetInfo to use when setting up test environment.")
   set(LIBCXX_EXECUTOR "None" CACHE STRING