Index: libcxxabi/CMakeLists.txt
===================================================================
--- libcxxabi/CMakeLists.txt
+++ libcxxabi/CMakeLists.txt
@@ -451,9 +451,7 @@
 
 include_directories(include)
 if (LIBCXXABI_USE_LLVM_UNWINDER OR LLVM_NATIVE_ARCH MATCHES ARM)
-  find_path(
-    LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL
-    libunwind.h
+  find_path(LIBCXXABI_LIBUNWIND_INCLUDES_INTERNAL libunwind.h
     PATHS ${LIBCXXABI_LIBUNWIND_INCLUDES}
           ${LIBCXXABI_LIBUNWIND_PATH}/include
           ${CMAKE_BINARY_DIR}/${LIBCXXABI_LIBUNWIND_INCLUDES}
Index: libcxxabi/src/CMakeLists.txt
===================================================================
--- libcxxabi/src/CMakeLists.txt
+++ libcxxabi/src/CMakeLists.txt
@@ -25,17 +25,23 @@
 endif()
 
 if (LIBCXXABI_ENABLE_EXCEPTIONS)
-  list(APPEND LIBCXXABI_SOURCES cxa_exception.cpp)
-  list(APPEND LIBCXXABI_SOURCES cxa_personality.cpp)
+  list(APPEND LIBCXXABI_SOURCES
+    cxa_exception.cpp
+    cxa_personality.cpp
+  )
 else()
-  list(APPEND LIBCXXABI_SOURCES cxa_noexception.cpp)
+  list(APPEND LIBCXXABI_SOURCES
+    cxa_noexception.cpp
+  )
 endif()
 
 if (LIBCXXABI_ENABLE_THREADS AND (UNIX OR FUCHSIA) AND NOT (APPLE OR CYGWIN))
   list(APPEND LIBCXXABI_SOURCES cxa_thread_atexit.cpp)
 endif()
 
-set(LIBCXXABI_HEADERS ../include/cxxabi.h)
+set(LIBCXXABI_HEADERS
+  ../include/cxxabi.h
+)
 
 # Add all the headers to the project for IDEs.
 if (MSVC_IDE OR XCODE)
Index: llvm/utils/gn/secondary/BUILD.gn
===================================================================
--- llvm/utils/gn/secondary/BUILD.gn
+++ llvm/utils/gn/secondary/BUILD.gn
@@ -12,6 +12,7 @@
   if (current_os == "linux") {
     deps += [
       "//compiler-rt",
+      "//libcxxabi",
       "//libunwind",
     ]
   }
Index: llvm/utils/gn/secondary/libcxxabi/BUILD.gn
===================================================================
--- /dev/null
+++ llvm/utils/gn/secondary/libcxxabi/BUILD.gn
@@ -0,0 +1,5 @@
+group("libcxxabi") {
+  deps = [
+    "//libcxxabi/src(//llvm/utils/gn/build/toolchain:stage2_unix)",
+  ]
+}
Index: llvm/utils/gn/secondary/libcxxabi/src/BUILD.gn
===================================================================
--- /dev/null
+++ llvm/utils/gn/secondary/libcxxabi/src/BUILD.gn
@@ -0,0 +1,147 @@
+import("//clang/runtimes.gni")
+
+declare_args() {
+  # Use exceptions.
+  libcxxabi_enable_exceptions = true
+
+  # Build libc++abi with definitions for operator new/delete.
+  libcxxabi_enable_new_delete_definitions = true
+
+  # Build libcxxabi as a shared library.
+  libcxxabi_enable_shared = true
+
+  # Build libcxxabi as a static library.
+  libcxxabi_enable_static = true
+
+  # Do not export any symbols from the static library.
+  libcxxabi_hermetic_static_library = false
+}
+
+# TODO: sync_source_lists_from_cmake.py doesn't handle these.
+#cxxabi_headers = [
+#  "../include/__cxxabi_config.h",
+#  "../include/cxxabi.h",
+#]
+
+cxxabi_sources = [
+  # C++ABI files
+  "cxa_aux_runtime.cpp",
+  "cxa_default_handlers.cpp",
+  "cxa_demangle.cpp",
+  "cxa_exception_storage.cpp",
+  "cxa_guard.cpp",
+  "cxa_handlers.cpp",
+  "cxa_unexpected.cpp",
+  "cxa_vector.cpp",
+  "cxa_virtual.cpp",
+
+  # C++ STL files"
+  "stdlib_exception.cpp",
+  "stdlib_stdexcept.cpp",
+  "stdlib_typeinfo.cpp",
+
+  # Internal files
+  "abort_message.cpp",
+  "fallback_malloc.cpp",
+  "private_typeinfo.cpp",
+]
+if (libcxxabi_enable_new_delete_definitions) {
+  cxxabi_sources += [ "stdlib_new_delete.cpp" ]
+}
+if (libcxxabi_enable_exceptions) {
+  cxxabi_sources += [
+    "cxa_exception.cpp",
+    "cxa_personality.cpp",
+  ]
+} else {
+  cxxabi_sources += [
+    # This comment prevents `gn format` from putting the file on the same line
+    # as `sources +=`, for sync_source_lists_from_cmake.py.
+    "cxa_noexception.cpp",
+  ]
+}
+if (target_os == "linux" || target_os == "fuchsia") {
+  cxxabi_sources += [
+    # This comment prevents `gn format` from putting the file on the same line
+    # as `sources +=`, for sync_source_lists_from_cmake.py.
+    "cxa_thread_atexit.cpp"
+  ]
+}
+
+config("cxxabi_config") {
+  include_dirs = [
+    "//libcxxabi/include",
+    "//libcxx/include",
+  ]
+  cflags_cc = [ "-nostdinc++" ]
+  defines = [ "_LIBCXXABI_BUILDING_LIBRARY" ]
+  if (target_os == "win") {
+    defines += [ "_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS" ]
+  }
+}
+
+if (libcxxabi_enable_shared) {
+  shared_library("cxxabi_shared") {
+    output_dir = runtimes_dir
+    output_name = "c++abi"
+    if (target_os == "linux" || target_os == "mac") {
+      cflags = [ "-fPIC" ]
+      ldflags = [ "-nostdlib++" ]
+      libs = [
+        "dl",
+        "pthread",
+      ]
+    }
+    sources = cxxabi_sources
+    # TODO: sync_source_lists_from_cmake.py doesn't handle these.
+    #public = cxxabi_headers
+    deps = [
+      "//compiler-rt/lib/builtins",
+      "//libunwind/src:unwind_shared",
+    ]
+    configs += [ ":cxxabi_config" ]
+    configs -= [
+      "//llvm/utils/gn/build:no_exceptions",
+      "//llvm/utils/gn/build:no_rtti",
+    ]
+  }
+}
+
+if (libcxxabi_enable_static) {
+  static_library("cxxabi_static") {
+    output_dir = runtimes_dir
+    output_name = "c++abi"
+    complete_static_lib = true
+    sources = cxxabi_sources
+    # TODO: sync_source_lists_from_cmake.py doesn't handle these.
+    #public = cxxabi_headers
+    if (libcxxabi_hermetic_static_library) {
+      cflags = [ "-fvisibility=hidden" ]
+      cflags_cc = [ "-fvisibility-global-new-delete-hidden" ]
+      defines = [
+        "_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS",
+        "_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS",
+      ]
+    }
+    deps = [
+      "//compiler-rt/lib/builtins",
+      "//libunwind/src:unwind_static",
+    ]
+    configs += [ ":cxxabi_config" ]
+    configs -= [
+      "//llvm/utils/gn/build:no_exceptions",
+      "//llvm/utils/gn/build:no_rtti",
+      "//llvm/utils/gn/build:thin_archive",
+    ]
+  }
+}
+
+group("src") {
+  deps = []
+  if (libcxxabi_enable_shared) {
+    deps += [ ":cxxabi_shared" ]
+  }
+  if (libcxxabi_enable_static) {
+    deps += [ ":cxxabi_static" ]
+  }
+}