[libc++] Annotate classes with _LIBCPP_PFP to enable pointer field protection

libcxx/include/CMakeLists.txt

@@ -375,6 +375,7 @@ set(files
   __flat_set/flat_set.h
   __flat_set/ra_iterator.h
   __flat_set/utils.h
+  __force_nonstandard_layout
   __format/buffer.h
   __format/concepts.h
   __format/container_adaptor.h

libcxx/include/__force_nonstandard_layout

@@ -0,0 +1,43 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___FORCE_NONSTANDARD_LAYOUT
+#define _LIBCPP___FORCE_NONSTANDARD_LAYOUT
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// Force a class to be non-standard layout by giving it two bases with the same
+// type. This is useful when structure protection is enabled because structure
+// protection cannot be applied to standard layout classes. We may use this in
+// cases where the standard does not specify whether a standard library class is
+// standard layout. See C++2a [class]p7:
+//   A class S is a standard-layout class if it:
+//     -- has at most one base class subobject of any given type
+_LIBCPP_DIAGNOSTIC_PUSH
+_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Winaccessible-base")
+class __force_nonstandard_layout_base1 {};
+class __force_nonstandard_layout_base2 : __force_nonstandard_layout_base1 {};
+class __force_nonstandard_layout : __force_nonstandard_layout_base1, __force_nonstandard_layout_base2 {};
+_LIBCPP_DIAGNOSTIC_POP
+
+#if __has_feature(pointer_field_protection)
+#  define _LIBCPP_MAYBE_FORCE_NONSTANDARD_LAYOUT : __force_nonstandard_layout
+#else
+#  define _LIBCPP_MAYBE_FORCE_NONSTANDARD_LAYOUT
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FORCE_NONSTANDARD_LAYOUT

libcxx/include/__functional/function.h

@@ -14,6 +14,7 @@
 #include <__config>
 #include <__cstddef/nullptr_t.h>
 #include <__exception/exception.h>
+#include <__force_nonstandard_layout>
 #include <__functional/binary_function.h>
 #include <__functional/invoke.h>
 #include <__functional/unary_function.h>
@@ -427,7 +428,7 @@ template <class _Fp>
 class __policy_func;
 
 template <class _Rp, class... _ArgTypes>
-class __policy_func<_Rp(_ArgTypes...)> {
+class __policy_func<_Rp(_ArgTypes...)> _LIBCPP_MAYBE_FORCE_NONSTANDARD_LAYOUT {
   // Inline storage for small objects.
   __policy_storage __buf_;
 

libcxx/include/__memory/shared_ptr.h

@@ -16,6 +16,7 @@
 #include <__cstddef/nullptr_t.h>
 #include <__cstddef/ptrdiff_t.h>
 #include <__exception/exception.h>
+#include <__force_nonstandard_layout>
 #include <__functional/binary_function.h>
 #include <__functional/operations.h>
 #include <__functional/reference_wrapper.h>
@@ -304,7 +305,7 @@ using __shared_ptr_nullptr_deleter_ctor_reqs _LIBCPP_NODEBUG =
 #endif
 
 template <class _Tp>
-class _LIBCPP_SHARED_PTR_TRIVIAL_ABI shared_ptr {
+class _LIBCPP_SHARED_PTR_TRIVIAL_ABI shared_ptr _LIBCPP_MAYBE_FORCE_NONSTANDARD_LAYOUT {
   struct __nullptr_sfinae_tag {};
 
 public:
@@ -1204,7 +1205,7 @@ inline _LIBCPP_HIDE_FROM_ABI _Dp* get_deleter(const shared_ptr<_Tp>& __p) _NOEXC
 #endif // _LIBCPP_HAS_RTTI
 
 template <class _Tp>
-class _LIBCPP_SHARED_PTR_TRIVIAL_ABI weak_ptr {
+class _LIBCPP_SHARED_PTR_TRIVIAL_ABI weak_ptr _LIBCPP_MAYBE_FORCE_NONSTANDARD_LAYOUT {
 public:
 #if _LIBCPP_STD_VER >= 17
   typedef remove_extent_t<_Tp> element_type;

libcxx/include/__memory/unique_ptr.h

@@ -17,6 +17,7 @@
 #include <__config>
 #include <__cstddef/nullptr_t.h>
 #include <__cstddef/size_t.h>
+#include <__force_nonstandard_layout>
 #include <__functional/hash.h>
 #include <__functional/operations.h>
 #include <__memory/allocator_traits.h> // __pointer
@@ -127,7 +128,7 @@ struct __unique_ptr_deleter_sfinae<_Deleter&> {
 #endif
 
 template <class _Tp, class _Dp = default_delete<_Tp> >
-class _LIBCPP_UNIQUE_PTR_TRIVIAL_ABI unique_ptr {
+class _LIBCPP_UNIQUE_PTR_TRIVIAL_ABI unique_ptr _LIBCPP_MAYBE_FORCE_NONSTANDARD_LAYOUT {
 public:
   typedef _Tp element_type;
   typedef _Dp deleter_type;
@@ -396,7 +397,7 @@ struct __unique_ptr_array_bounds_stored {
 };
 
 template <class _Tp, class _Dp>
-class _LIBCPP_UNIQUE_PTR_TRIVIAL_ABI unique_ptr<_Tp[], _Dp> {
+class _LIBCPP_UNIQUE_PTR_TRIVIAL_ABI unique_ptr<_Tp[], _Dp> _LIBCPP_MAYBE_FORCE_NONSTANDARD_LAYOUT {
 public:
   typedef _Tp element_type;
   typedef _Dp deleter_type;

libcxx/include/__tree

@@ -13,6 +13,7 @@
 #include <__algorithm/min.h>
 #include <__assert>
 #include <__config>
+#include <__force_nonstandard_layout>
 #include <__fwd/map.h>
 #include <__fwd/pair.h>
 #include <__fwd/set.h>
@@ -782,7 +783,7 @@ _LIBCPP_DIAGNOSE_WARNING(!__is_invocable_v<_Compare const&, _Tp const&, _Tp cons
 int __diagnose_non_const_comparator();
 
 template <class _Tp, class _Compare, class _Allocator>
-class __tree {
+class __tree _LIBCPP_MAYBE_FORCE_NONSTANDARD_LAYOUT {
 public:
   using value_type = __get_node_value_type_t<_Tp>;
   typedef _Compare value_compare;

libcxx/include/__vector/vector.h

@@ -21,6 +21,7 @@
 #include <__assert>
 #include <__config>
 #include <__debug_utils/sanitizers.h>
+#include <__force_nonstandard_layout>
 #include <__format/enable_insertable.h>
 #include <__fwd/vector.h>
 #include <__iterator/advance.h>
@@ -85,7 +86,7 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp, class _Allocator /* = allocator<_Tp> */>
-class vector {
+class vector _LIBCPP_MAYBE_FORCE_NONSTANDARD_LAYOUT {
 public:
   //
   // Types

libcxx/include/module.modulemap.in

@@ -2377,6 +2377,9 @@ module std [system] {
   module undef_macros {
     textual header "__undef_macros"
   }
+  module force_nonstandard_layout {
+    header "__force_nonstandard_layout"
+  }
 
   // This module needs to appear after __tree to work around issues with modules in Objective-C++ mode.
   module coroutine {

llvm/utils/gn/secondary/libcxx/include/BUILD.gn

@@ -1032,6 +1032,7 @@ if (current_toolchain == default_toolchain) {
       "__flat_set/flat_set.h",
       "__flat_set/ra_iterator.h",
       "__flat_set/utils.h",
+      "__force_nonstandard_layout",
       "__format/buffer.h",
       "__format/concepts.h",
       "__format/container_adaptor.h",