[libc++] Allow testing Apple's system library as it is installed

libcxx/cmake/caches/Apple.cmake

@@ -15,3 +15,6 @@ set(LIBCXXABI_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
 set(LIBCXXABI_ENABLE_ASSERTIONS OFF CACHE BOOL "")
 set(LIBCXXABI_ENABLE_FORGIVING_DYNAMIC_CAST ON CACHE BOOL "")
 set(LIBCXXABI_USE_LLVM_UNWINDER OFF CACHE BOOL "") # libunwind is built separately
+
+set(LIBCXX_TEST_CONFIG "apple-libc++-shared.cfg.in" CACHE STRING "")
+set(LIBCXXABI_TEST_CONFIG "apple-libc++abi-shared.cfg.in" CACHE STRING "")

libcxx/test/configs/apple-libc++-shared.cfg.in

@@ -0,0 +1,51 @@
+# Testing configuration for Apple's system libc++.
+#
+# This configuration differs from a normal LLVM shared library configuration in
+# that we must use DYLD_LIBRARY_PATH to run the tests against the just-built library,
+# since Apple's libc++ has an absolute install_name.
+#
+# We also don't use a per-target include directory layout, so we have only one
+# include directory for the libc++ headers.
+#
+# Finally, we also link against an artificial shims library that provides
+# the functionality necessary for the upstream libc++ to be usable in place
+# of a system-provided libc++. Without that, attempting to replace the system
+# libc++ with DYLD_LIBRARY_PATH would result in missing symbols and other similar
+# issues since the upstream libc++ does not contain all the symbols provided by
+# the system library.
+
+lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
+
+import os, site
+site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
+import libcxx.test.params, libcxx.test.config, libcxx.test.dsl
+ADDITIONAL_PARAMETERS = [
+    libcxx.test.dsl.Parameter(name='apple_system_shims', type=str,
+        actions=lambda path: [libcxx.test.dsl.AddSubstitution('%{apple-system-shims}', path)],
+        help="""
+        Path to a pre-built object file or static archive that contains shims necessary to
+        allow replacing the system libc++ by the just-built one.
+        """),
+]
+
+config.substitutions.append(('%{flags}',
+    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
+))
+config.substitutions.append(('%{compile_flags}',
+    '-nostdinc++ -I %{include-dir} -I %{libcxx-dir}/test/support'
+))
+config.substitutions.append(('%{link_flags}',
+    '-nostdlib++ -L %{lib-dir} -lc++ %{apple-system-shims}'
+))
+config.substitutions.append(('%{exec}',
+    '%{executor} --execdir %T --env DYLD_LIBRARY_PATH=%{lib-dir} -- '
+))
+
+config.stdlib = 'apple-libc++'
+
+libcxx.test.config.configure(
+    libcxx.test.params.DEFAULT_PARAMETERS + ADDITIONAL_PARAMETERS,
+    libcxx.test.features.DEFAULT_FEATURES,
+    config,
+    lit_config
+)

libcxx/utils/ci/apple-install-libcxx.sh

@@ -114,8 +114,13 @@ for arch in ${architectures}; do
     #       Then LLVM would guess the LLVM_DEFAULT_TARGET_TRIPLE properly and we wouldn't have to specify it.
     target=$(xcrun clang -arch ${arch} -xc - -### 2>&1 | grep --only-matching -E '"-triple" ".+?"' | grep --only-matching -E '"[^ ]+-apple-[^ ]+?"' | tr -d '"')
 
-    step "Building libc++.dylib and libc++abi.dylib for architecture ${arch}"
     mkdir -p "${build_dir}/${arch}"
+
+    step "Building shims to make libc++ compatible with the system libc++ on Apple platforms when running the tests"
+    shims_library="${build_dir}/${arch}/apple-system-shims.a"
+    xcrun clang++ -c -std=c++2b -target ${target} "${llvm_root}/libcxxabi/src/vendor/apple/shims.cpp" -static -o "${shims_library}"
+
+    step "Building libc++.dylib and libc++abi.dylib for architecture ${arch}"
     xcrun cmake -S "${llvm_root}/runtimes" \
                 -B "${build_dir}/${arch}" \
                 -GNinja \
@@ -127,9 +132,9 @@ for arch in ${architectures}; do
                 -DCMAKE_OSX_ARCHITECTURES="${arch}" \
                 -DLIBCXXABI_LIBRARY_VERSION="${version}" \
                 -DLIBCXX_LIBRARY_VERSION="${version}" \
-                -DLIBCXX_TEST_PARAMS="target_triple=${target};stdlib=apple-libc++" \
-                -DLIBCXXABI_TEST_PARAMS="target_triple=${target};stdlib=apple-libc++" \
-                -DLIBUNWIND_TEST_PARAMS="target_triple=${target};stdlib=apple-libc++"
+                -DLIBCXX_TEST_PARAMS="target_triple=${target};apple_system_shims=${shims_library}" \
+                -DLIBCXXABI_TEST_PARAMS="target_triple=${target};apple_system_shims=${shims_library}" \
+                -DLIBUNWIND_TEST_PARAMS="target_triple=${target};apple_system_shims=${shims_library}"
 
     if [ "$headers_only" = true ]; then
         xcrun cmake --build "${build_dir}/${arch}" --target install-cxx-headers install-cxxabi-headers -- -v

libcxxabi/src/vendor/apple/shims.cpp

@@ -0,0 +1,65 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+//
+// These shims implement symbols that are present in the system libc++ on Apple platforms
+// but are not implemented in upstream libc++. This allows testing libc++ under a system
+// library configuration, which requires the just-built libc++ to be ABI compatible with
+// the system library it is replacing.
+//
+
+#include <cstddef>
+#include <new>
+
+namespace std { // purposefully not versioned, like align_val_t
+enum class __type_descriptor_t : unsigned long long;
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void* operator new(std::size_t __sz, std::__type_descriptor_t) {
+  return ::operator new(__sz);
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void* operator new(std::size_t __sz, const std::nothrow_t& __nt,
+                                                std::__type_descriptor_t) noexcept {
+  return ::operator new(__sz, __nt);
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void* operator new[](std::size_t __sz, std::__type_descriptor_t) {
+  return ::operator new[](__sz);
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void* operator new[](std::size_t __sz, const std::nothrow_t& __nt,
+                                                  std::__type_descriptor_t) noexcept {
+  return ::operator new(__sz, __nt);
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p, std::__type_descriptor_t) noexcept {
+  return ::operator delete(__p);
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p, const std::nothrow_t& __nt,
+                                                  std::__type_descriptor_t) noexcept {
+  return ::operator delete(__p, __nt);
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p, std::__type_descriptor_t) noexcept {
+  return ::operator delete[](__p);
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p, const std::nothrow_t& __nt,
+                                                    std::__type_descriptor_t) noexcept {
+  return ::operator delete[](__p, __nt);
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p, std::size_t __sz, std::__type_descriptor_t) noexcept {
+  return ::operator delete(__p, __sz);
+}
+
+_LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p, std::size_t __sz, std::__type_descriptor_t) noexcept {
+  return ::operator delete[](__p, __sz);
+}

libcxxabi/test/configs/apple-libc++abi-shared.cfg.in

@@ -0,0 +1,49 @@
+# Testing configuration for Apple's system libc++abi.
+#
+# This configuration differs from a normal LLVM shared library configuration in
+# that we must use DYLD_LIBRARY_PATH to run the tests against the just-built library,
+# since Apple's libc++abi has an absolute install_name.
+#
+# Finally, we also link against an artificial shims library that provides
+# the functionality necessary for the upstream libc++abi to be usable in place
+# of a system-provided libc++abi. Without that, attempting to replace the system
+# libc++abi with DYLD_LIBRARY_PATH would result in missing symbols and other similar
+# issues since the upstream libc++abi does not contain all the symbols provided by
+# the system library.
+
+lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
+
+import os, site
+site.addsitedir(os.path.join('@LIBCXXABI_LIBCXX_PATH@', 'utils'))
+import libcxx.test.params, libcxx.test.config, libcxx.test.dsl
+ADDITIONAL_PARAMETERS = [
+    libcxx.test.dsl.Parameter(name='apple_system_shims', type=str,
+        actions=lambda path: [libcxx.test.dsl.AddSubstitution('%{apple-system-shims}', path)],
+        help="""
+        Path to a pre-built object file or static archive that contains shims necessary to
+        allow replacing the system libc++abi by the just-built one.
+        """),
+]
+
+config.substitutions.append(('%{flags}',
+    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
+))
+config.substitutions.append(('%{compile_flags}',
+    '-nostdinc++ -I %{include} -I %{cxx-include} -I %{cxx-target-include} %{maybe-include-libunwind} -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS ' +
+    '-I %{libcxx}/test/support -I %{libcxx}/src'
+))
+config.substitutions.append(('%{link_flags}',
+    '-nostdlib++ -L %{lib} -lc++ %{apple-system-shims}'
+))
+config.substitutions.append(('%{exec}',
+    '%{executor} --execdir %T --env DYLD_LIBRARY_PATH=%{lib} -- '
+))
+
+config.stdlib = 'apple-libc++'
+
+libcxx.test.config.configure(
+    libcxx.test.params.DEFAULT_PARAMETERS + ADDITIONAL_PARAMETERS,
+    libcxx.test.features.DEFAULT_FEATURES,
+    config,
+    lit_config
+)