[libcxx] Use libtool when merging archives on Apple platforms

[phosek]

Summary

ar doesn't produce correct results when used for linking static
archives on Apple platforms, so instead use libtool -static which is
the official way to build static archives on those platforms.

[mcgrathr]

lgtm

[mclow.lists]

This looks fine to me, but I'd like @ldionne to weigh in on this.

[ldionne]

LGTM

libcxx/src/CMakeLists.txt

if (LIBCXX_CXX_ABI_LIBRARY_PATH)
       set(MERGE_ARCHIVES_SEARCH_PATHS "-L${LIBCXX_CXX_ABI_LIBRARY_PATH}")
     endif()
     if (TARGET "${LIBCXX_CXX_STATIC_ABI_LIBRARY}" OR HAVE_LIBCXXABI)
       set(MERGE_ARCHIVES_ABI_TARGET "$<TARGET_LINKER_FILE:${LIBCXX_CXX_STATIC_ABI_LIBRARY}>")
     else()
       set(MERGE_ARCHIVES_ABI_TARGET
         "${CMAKE_STATIC_LIBRARY_PREFIX}${LIBCXX_CXX_STATIC_ABI_LIBRARY}${CMAKE_STATIC_LIBRARY_SUFFIX}")
     endif()
+    if (APPLE)
+      set(MERGE_ARCHIVES_LIBTOOL "--use-libtool" "--libtool" "${CMAKE_LIBTOOL}")
+    endif()
     add_custom_command(TARGET cxx_static POST_BUILD
     COMMAND
       ${PYTHON_EXECUTABLE} ${LIBCXX_SOURCE_DIR}/utils/merge_archives.py
     ARGS
       -o $<TARGET_LINKER_FILE:cxx_static>
       --ar "${CMAKE_AR}"
       "$<TARGET_LINKER_FILE:cxx_static>"
       "${MERGE_ARCHIVES_ABI_TARGET}"
       "${MERGE_ARCHIVES_SEARCH_PATHS}"
+      ${MERGE_ARCHIVES_LIBTOOL}
     WORKING_DIRECTORY ${LIBCXX_BUILD_DIR}
     )
   endif()
 endif()
 
 # Add a meta-target for both libraries.
 add_custom_target(cxx DEPENDS cxx-headers ${LIBCXX_BUILD_TARGETS})
 

libcxx/utils/merge_archives.py

parser.add_argument(
         '-L', dest='search_paths',
         help='Paths to search for the libraries along', action='append',
         nargs=1)
     parser.add_argument(
         '--ar', dest='ar_exe', required=False,
         help='The ar executable to use, finds \'ar\' in the path if not given',
         type=str, action='store')
     parser.add_argument(
+        '-l', '--use-libtool', dest='use_libtool', action='store_true', default=False)
+    parser.add_argument(
+        '--libtool', dest='libtool_exe', required=False,
+        help='The libtool executable to use, finds \'libtool\' in the path if not given',
+        type=str, action='store')
+    parser.add_argument(
         'archives', metavar='archives',  nargs='+',
         help='The archives to merge')
 
     args = parser.parse_args()
 
     ar_exe = args.ar_exe
     if not ar_exe:
         ar_exe = distutils.spawn.find_executable('ar')
     if not ar_exe:
         print_and_exit("failed to find 'ar' executable")
 
+    if args.use_libtool:
+        libtool_exe = args.libtool_exe
+        if not libtool_exe:
+            libtool_exe = distutils.spawn.find_executable('libtool')
+        if not libtool_exe:
+            print_and_exit("failed to find 'libtool' executable")
+
     if len(args.archives) < 2:
         print_and_exit('fewer than 2 inputs provided')
     archives = [find_and_diagnose_missing(ar, args.search_paths)
                 for ar in args.archives]
     print ('Merging archives: %s' % archives)
     if not os.path.exists(os.path.dirname(args.output)):
         print_and_exit("output path doesn't exist: '%s'" % args.output)
 
     global temp_directory_root
     temp_directory_root = tempfile.mkdtemp('.libcxx.merge.archives')
 
     files = []
     for arc in archives:
         execute_command_verbose([ar_exe, 'x', arc],
                                 cwd=temp_directory_root, verbose=args.verbose)
         out = execute_command_verbose([ar_exe, 't', arc])
         files.extend(out.splitlines())
 
+    if args.use_libtool:
+        files = [f for f in files if not f.startswith('__.SYMDEF')]
+        execute_command_verbose([libtool_exe, '-static', '-o', args.output] + files,
+                                cwd=temp_directory_root, verbose=args.verbose)
+    else:
         execute_command_verbose([ar_exe, 'rcs', args.output] + files,
                                 cwd=temp_directory_root, verbose=args.verbose)
 
 
 if __name__ == '__main__':
     main()
     exit_with_cleanups(0)

libcxxabi/src/CMakeLists.txt

target_compile_definitions(cxxabi_static
         _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
   endif()
 
   list(APPEND LIBCXXABI_BUILD_TARGETS "cxxabi_static")
   if (LIBCXXABI_INSTALL_STATIC_LIBRARY)
     list(APPEND LIBCXXABI_INSTALL_TARGETS "cxxabi_static")
   endif()
 
+  if (APPLE)
+    set(MERGE_ARCHIVES_LIBTOOL "--use-libtool" "--libtool" "${CMAKE_LIBTOOL}")
+  endif()
+
   # Merge the the libc++abi.a and libunwind.a into one.
   if(LIBCXXABI_USE_LLVM_UNWINDER AND LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY)
     add_custom_command(TARGET cxxabi_static POST_BUILD
       COMMAND ${PYTHON_EXECUTABLE} ${LIBCXXABI_LIBCXX_PATH}/utils/merge_archives.py
       ARGS
         -o "$<TARGET_LINKER_FILE:cxxabi_static>"
         --ar "${CMAKE_AR}"
         "$<TARGET_LINKER_FILE:cxxabi_static>"
         "$<TARGET_LINKER_FILE:unwind_static>"
+        ${MERGE_ARCHIVES_LIBTOOL}
       WORKING_DIRECTORY ${LIBCXXABI_BUILD_DIR}
     )
   endif()
 endif()
 
 # Add a meta-target for both libraries.
 add_custom_target(cxxabi DEPENDS ${LIBCXXABI_BUILD_TARGETS})