[libc++] Introduce ABI sensitive areas to avoid requiring _LIBCPP_HIDE_FROM_ABI everywhere (#131156)

This patch introduces `_LIBCPP_{BEGIN,END}_EXPLICIT_ABI_ANNOTATIONS`,
which allow us to have implicit annotations for most functions, and just
where it's not "hide_from_abi everything" we add explicit annotations.
This allows us to drop the `_LIBCPP_HIDE_FROM_ABI` macro from most
functions in libc++.

Author: philnik777

libcxx/include/__algorithm/shuffle.h

@@ -65,6 +65,7 @@ class _LIBCPP_EXPORTED_FROM_ABI __libcpp_debug_randomizer {
 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_RANDOM_SHUFFLE) || defined(_LIBCPP_BUILDING_LIBRARY)
 class _LIBCPP_EXPORTED_FROM_ABI __rs_default;
 
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
 _LIBCPP_EXPORTED_FROM_ABI __rs_default __rs_get();
 
 class _LIBCPP_EXPORTED_FROM_ABI __rs_default {
@@ -90,6 +91,7 @@ class _LIBCPP_EXPORTED_FROM_ABI __rs_default {
 };
 
 _LIBCPP_EXPORTED_FROM_ABI __rs_default __rs_get();
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 
 template <class _RandomAccessIterator>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX14 void

libcxx/include/__algorithm/sort.h

@@ -64,7 +64,7 @@ enum { __block_size = sizeof(uint64_t) * 8 };
 
 // Ensures that __c(*__x, *__y) is true by swapping *__x and *__y if necessary.
 template <class _Compare, class _RandomAccessIterator>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
+inline _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
 __cond_swap(_RandomAccessIterator __x, _RandomAccessIterator __y, _Compare __c) {
   // Note: this function behaves correctly even with proxy iterators (because it relies on `value_type`).
   using value_type = typename iterator_traits<_RandomAccessIterator>::value_type;
@@ -78,7 +78,7 @@ __cond_swap(_RandomAccessIterator __x, _RandomAccessIterator __y, _Compare __c)
 // Ensures that *__x, *__y and *__z are ordered according to the comparator __c,
 // under the assumption that *__y and *__z are already ordered.
 template <class _Compare, class _RandomAccessIterator>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
+inline _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
 __partially_sorted_swap(_RandomAccessIterator __x, _RandomAccessIterator __y, _RandomAccessIterator __z, _Compare __c) {
   // Note: this function behaves correctly even with proxy iterators (because it relies on `value_type`).
   using value_type = typename iterator_traits<_RandomAccessIterator>::value_type;
@@ -97,7 +97,7 @@ template <class,
           class _Compare,
           class _RandomAccessIterator,
           __enable_if_t<__use_branchless_sort<_Compare, _RandomAccessIterator>, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
+inline _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
 __sort3(_RandomAccessIterator __x1, _RandomAccessIterator __x2, _RandomAccessIterator __x3, _Compare __c) {
   bool __swapped1 = std::__cond_swap<_Compare>(__x2, __x3, __c);
   bool __swapped2 = std::__partially_sorted_swap<_Compare>(__x1, __x2, __x3, __c);
@@ -108,7 +108,7 @@ template <class _AlgPolicy,
           class _Compare,
           class _RandomAccessIterator,
           __enable_if_t<!__use_branchless_sort<_Compare, _RandomAccessIterator>, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
+inline _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
 __sort3(_RandomAccessIterator __x, _RandomAccessIterator __y, _RandomAccessIterator __z, _Compare __c) {
   using _Ops = _IterOps<_AlgPolicy>;
 
@@ -140,7 +140,7 @@ template <class,
           class _Compare,
           class _RandomAccessIterator,
           __enable_if_t<__use_branchless_sort<_Compare, _RandomAccessIterator>, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI void
+inline void
 __sort4(_RandomAccessIterator __x1,
         _RandomAccessIterator __x2,
         _RandomAccessIterator __x3,
@@ -157,7 +157,7 @@ template <class _AlgPolicy,
           class _Compare,
           class _RandomAccessIterator,
           __enable_if_t<!__use_branchless_sort<_Compare, _RandomAccessIterator>, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI void
+inline void
 __sort4(_RandomAccessIterator __x1,
         _RandomAccessIterator __x2,
         _RandomAccessIterator __x3,
@@ -182,7 +182,7 @@ template <class _AlgPolicy,
           class _Compare,
           class _RandomAccessIterator,
           __enable_if_t<__use_branchless_sort<_Compare, _RandomAccessIterator>, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI void
+inline void
 __sort5(_RandomAccessIterator __x1,
         _RandomAccessIterator __x2,
         _RandomAccessIterator __x3,
@@ -201,7 +201,7 @@ template <class _AlgPolicy,
           class _Compare,
           class _RandomAccessIterator,
           __enable_if_t<!__use_branchless_sort<_Compare, _RandomAccessIterator>, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI void
+inline void
 __sort5(_RandomAccessIterator __x1,
         _RandomAccessIterator __x2,
         _RandomAccessIterator __x3,
@@ -227,7 +227,7 @@ __sort5(_RandomAccessIterator __x1,
 
 // Assumes size > 0
 template <class _AlgPolicy, class _Compare, class _BidirectionalIterator>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
+_LIBCPP_CONSTEXPR_SINCE_CXX14 void
 __selection_sort(_BidirectionalIterator __first, _BidirectionalIterator __last, _Compare __comp) {
   _BidirectionalIterator __lm1 = __last;
   for (--__lm1; __first != __lm1; ++__first) {
@@ -240,7 +240,7 @@ __selection_sort(_BidirectionalIterator __first, _BidirectionalIterator __last,
 // Sort the iterator range [__first, __last) using the comparator __comp using
 // the insertion sort algorithm.
 template <class _AlgPolicy, class _Compare, class _BidirectionalIterator>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
+_LIBCPP_CONSTEXPR_SINCE_CXX26 void
 __insertion_sort(_BidirectionalIterator __first, _BidirectionalIterator __last, _Compare __comp) {
   using _Ops = _IterOps<_AlgPolicy>;
 
@@ -270,8 +270,7 @@ __insertion_sort(_BidirectionalIterator __first, _BidirectionalIterator __last,
 // Assumes that there is an element in the position (__first - 1) and that each
 // element in the input range is greater or equal to the element at __first - 1.
 template <class _AlgPolicy, class _Compare, class _RandomAccessIterator>
-_LIBCPP_HIDE_FROM_ABI void
-__insertion_sort_unguarded(_RandomAccessIterator const __first, _RandomAccessIterator __last, _Compare __comp) {
+void __insertion_sort_unguarded(_RandomAccessIterator const __first, _RandomAccessIterator __last, _Compare __comp) {
   using _Ops = _IterOps<_AlgPolicy>;
   typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
   typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type;
@@ -298,8 +297,7 @@ __insertion_sort_unguarded(_RandomAccessIterator const __first, _RandomAccessIte
 }
 
 template <class _AlgPolicy, class _Comp, class _RandomAccessIterator>
-_LIBCPP_HIDE_FROM_ABI bool
-__insertion_sort_incomplete(_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp) {
+bool __insertion_sort_incomplete(_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp) {
   using _Ops = _IterOps<_AlgPolicy>;
 
   typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
@@ -352,7 +350,7 @@ __insertion_sort_incomplete(_RandomAccessIterator __first, _RandomAccessIterator
 }
 
 template <class _AlgPolicy, class _RandomAccessIterator>
-inline _LIBCPP_HIDE_FROM_ABI void __swap_bitmap_pos(
+inline void __swap_bitmap_pos(
     _RandomAccessIterator __first, _RandomAccessIterator __last, uint64_t& __left_bitset, uint64_t& __right_bitset) {
   using _Ops = _IterOps<_AlgPolicy>;
   typedef typename std::iterator_traits<_RandomAccessIterator>::difference_type difference_type;
@@ -370,7 +368,7 @@ inline _LIBCPP_HIDE_FROM_ABI void __swap_bitmap_pos(
 template <class _Compare,
           class _RandomAccessIterator,
           class _ValueType = typename iterator_traits<_RandomAccessIterator>::value_type>
-inline _LIBCPP_HIDE_FROM_ABI void
+inline void
 __populate_left_bitset(_RandomAccessIterator __first, _Compare __comp, _ValueType& __pivot, uint64_t& __left_bitset) {
   // Possible vectorization. With a proper "-march" flag, the following loop
   // will be compiled into a set of SIMD instructions.
@@ -386,7 +384,7 @@ __populate_left_bitset(_RandomAccessIterator __first, _Compare __comp, _ValueTyp
 template <class _Compare,
           class _RandomAccessIterator,
           class _ValueType = typename iterator_traits<_RandomAccessIterator>::value_type>
-inline _LIBCPP_HIDE_FROM_ABI void
+inline void
 __populate_right_bitset(_RandomAccessIterator __lm1, _Compare __comp, _ValueType& __pivot, uint64_t& __right_bitset) {
   // Possible vectorization. With a proper "-march" flag, the following loop
   // will be compiled into a set of SIMD instructions.
@@ -403,7 +401,7 @@ template <class _AlgPolicy,
           class _Compare,
           class _RandomAccessIterator,
           class _ValueType = typename iterator_traits<_RandomAccessIterator>::value_type>
-inline _LIBCPP_HIDE_FROM_ABI void __bitset_partition_partial_blocks(
+inline void __bitset_partition_partial_blocks(
     _RandomAccessIterator& __first,
     _RandomAccessIterator& __lm1,
     _Compare __comp,
@@ -450,7 +448,7 @@ inline _LIBCPP_HIDE_FROM_ABI void __bitset_partition_partial_blocks(
 }
 
 template <class _AlgPolicy, class _RandomAccessIterator>
-inline _LIBCPP_HIDE_FROM_ABI void __swap_bitmap_pos_within(
+inline void __swap_bitmap_pos_within(
     _RandomAccessIterator& __first, _RandomAccessIterator& __lm1, uint64_t& __left_bitset, uint64_t& __right_bitset) {
   using _Ops = _IterOps<_AlgPolicy>;
   typedef typename std::iterator_traits<_RandomAccessIterator>::difference_type difference_type;
@@ -491,7 +489,7 @@ inline _LIBCPP_HIDE_FROM_ABI void __swap_bitmap_pos_within(
 // __bitset_partition uses bitsets for storing outcomes of the comparisons
 // between the pivot and other elements.
 template <class _AlgPolicy, class _RandomAccessIterator, class _Compare>
-_LIBCPP_HIDE_FROM_ABI std::pair<_RandomAccessIterator, bool>
+std::pair<_RandomAccessIterator, bool>
 __bitset_partition(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp) {
   using _Ops = _IterOps<_AlgPolicy>;
   typedef typename std::iterator_traits<_RandomAccessIterator>::value_type value_type;
@@ -583,7 +581,7 @@ __bitset_partition(_RandomAccessIterator __first, _RandomAccessIterator __last,
 // the provided range is already sorted, false otherwise.  We assume that the
 // length of the range is at least three elements.
 template <class _AlgPolicy, class _RandomAccessIterator, class _Compare>
-_LIBCPP_HIDE_FROM_ABI std::pair<_RandomAccessIterator, bool>
+std::pair<_RandomAccessIterator, bool>
 __partition_with_equals_on_right(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp) {
   using _Ops = _IterOps<_AlgPolicy>;
   typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
@@ -651,7 +649,7 @@ __partition_with_equals_on_right(_RandomAccessIterator __first, _RandomAccessIte
 // Similar to the above function.  Elements equivalent to the pivot are put to
 // the left of the pivot.  Returns the iterator to the pivot element.
 template <class _AlgPolicy, class _RandomAccessIterator, class _Compare>
-_LIBCPP_HIDE_FROM_ABI _RandomAccessIterator
+_RandomAccessIterator
 __partition_with_equals_on_left(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp) {
   using _Ops = _IterOps<_AlgPolicy>;
   typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
@@ -828,6 +826,7 @@ void __introsort(_RandomAccessIterator __first,
   }
 }
 
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
 template <class _Comp, class _RandomAccessIterator>
 void __sort(_RandomAccessIterator, _RandomAccessIterator, _Comp);
 
@@ -856,9 +855,10 @@ extern template _LIBCPP_EXPORTED_FROM_ABI void __sort<__less<float>&, float*>(fl
 extern template _LIBCPP_EXPORTED_FROM_ABI void __sort<__less<double>&, double*>(double*, double*, __less<double>&);
 extern template _LIBCPP_EXPORTED_FROM_ABI void
 __sort<__less<long double>&, long double*>(long double*, long double*, __less<long double>&);
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 
 template <class _AlgPolicy, class _RandomAccessIterator, class _Comp>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+_LIBCPP_CONSTEXPR_SINCE_CXX20 void
 __sort_dispatch(_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp& __comp) {
   typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
   difference_type __depth_limit = 2 * std::__bit_log2(std::__to_unsigned_like(__last - __first));
@@ -895,35 +895,35 @@ using __sort_is_specialized_in_library _LIBCPP_NODEBUG = __is_any_of<
     long double>;
 
 template <class _AlgPolicy, class _Type, __enable_if_t<__sort_is_specialized_in_library<_Type>::value, int> = 0>
-_LIBCPP_HIDE_FROM_ABI void __sort_dispatch(_Type* __first, _Type* __last, __less<>&) {
+void __sort_dispatch(_Type* __first, _Type* __last, __less<>&) {
   __less<_Type> __comp;
   std::__sort<__less<_Type>&, _Type*>(__first, __last, __comp);
 }
 
 template <class _AlgPolicy, class _Type, __enable_if_t<__sort_is_specialized_in_library<_Type>::value, int> = 0>
-_LIBCPP_HIDE_FROM_ABI void __sort_dispatch(_Type* __first, _Type* __last, less<_Type>&) {
+void __sort_dispatch(_Type* __first, _Type* __last, less<_Type>&) {
   __less<_Type> __comp;
   std::__sort<__less<_Type>&, _Type*>(__first, __last, __comp);
 }
 
 #if _LIBCPP_STD_VER >= 14
 template <class _AlgPolicy, class _Type, __enable_if_t<__sort_is_specialized_in_library<_Type>::value, int> = 0>
-_LIBCPP_HIDE_FROM_ABI void __sort_dispatch(_Type* __first, _Type* __last, less<>&) {
+void __sort_dispatch(_Type* __first, _Type* __last, less<>&) {
   __less<_Type> __comp;
   std::__sort<__less<_Type>&, _Type*>(__first, __last, __comp);
 }
 #endif
 
 #if _LIBCPP_STD_VER >= 20
 template <class _AlgPolicy, class _Type, __enable_if_t<__sort_is_specialized_in_library<_Type>::value, int> = 0>
-_LIBCPP_HIDE_FROM_ABI void __sort_dispatch(_Type* __first, _Type* __last, ranges::less&) {
+void __sort_dispatch(_Type* __first, _Type* __last, ranges::less&) {
   __less<_Type> __comp;
   std::__sort<__less<_Type>&, _Type*>(__first, __last, __comp);
 }
 #endif
 
 template <class _AlgPolicy, class _RandomAccessIterator, class _Comp>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+inline _LIBCPP_CONSTEXPR_SINCE_CXX20 void
 __sort_impl(_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp& __comp) {
   std::__debug_randomize_range<_AlgPolicy>(__first, __last);
 
@@ -937,14 +937,13 @@ __sort_impl(_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp&
 }
 
 template <class _RandomAccessIterator, class _Comp>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+inline _LIBCPP_CONSTEXPR_SINCE_CXX20 void
 sort(_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp) {
   std::__sort_impl<_ClassicAlgPolicy>(std::move(__first), std::move(__last), __comp);
 }
 
 template <class _RandomAccessIterator>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
-sort(_RandomAccessIterator __first, _RandomAccessIterator __last) {
+inline _LIBCPP_CONSTEXPR_SINCE_CXX20 void sort(_RandomAccessIterator __first, _RandomAccessIterator __last) {
   std::sort(__first, __last, __less<>());
 }
 

libcxx/include/__atomic/atomic_sync.h

@@ -58,6 +58,7 @@ struct __atomic_waitable< _Tp,
 #if _LIBCPP_STD_VER >= 20
 #  if _LIBCPP_HAS_THREADS
 
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(void const volatile*) _NOEXCEPT;
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(void const volatile*) _NOEXCEPT;
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t
@@ -73,6 +74,7 @@ _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t
 __libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
 __libcpp_atomic_wait(__cxx_atomic_contention_t const volatile*, __cxx_contention_t) _NOEXCEPT;
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 
 template <class _AtomicWaitable, class _Poll>
 struct __atomic_wait_backoff_impl {

libcxx/include/__charconv/from_chars_floating_point.h

@@ -35,6 +35,7 @@ struct __from_chars_result {
   errc __ec;
 };
 
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
 template <class _Fp>
 _LIBCPP_EXPORTED_FROM_ABI __from_chars_result<_Fp> __from_chars_floating_point(
     _LIBCPP_NOESCAPE const char* __first, _LIBCPP_NOESCAPE const char* __last, chars_format __fmt);
@@ -44,6 +45,7 @@ extern template __from_chars_result<float> __from_chars_floating_point(
 
 extern template __from_chars_result<double> __from_chars_floating_point(
     _LIBCPP_NOESCAPE const char* __first, _LIBCPP_NOESCAPE const char* __last, chars_format __fmt);
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 
 template <class _Fp>
 _LIBCPP_HIDE_FROM_ABI from_chars_result

libcxx/include/__charconv/to_chars_floating_point.h

@@ -18,10 +18,11 @@
 #  pragma GCC system_header
 #endif
 
-_LIBCPP_BEGIN_NAMESPACE_STD
-
 #if _LIBCPP_STD_VER >= 17
 
+_LIBCPP_BEGIN_NAMESPACE_STD
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
+
 _LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_EXPORTED_FROM_ABI to_chars_result
 to_chars(char* __first, char* __last, float __value);
 
@@ -48,8 +49,10 @@ to_chars(char* __first, char* __last, double __value, chars_format __fmt, int __
 
 _LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_EXPORTED_FROM_ABI to_chars_result
 to_chars(char* __first, char* __last, long double __value, chars_format __fmt, int __precision);
-#endif // _LIBCPP_STD_VER >= 17
 
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 _LIBCPP_END_NAMESPACE_STD
 
+#endif // _LIBCPP_STD_VER >= 17
+
 #endif // _LIBCPP___CHARCONV_TO_CHARS_FLOATING_POINT_H

libcxx/include/__chrono/exception.h

@@ -31,6 +31,7 @@
 #  endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
 
 #  if _LIBCPP_STD_VER >= 20
 
@@ -128,6 +129,7 @@ template <class _Duration>
 
 #  endif // _LIBCPP_STD_VER >= 20
 
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_HAS_EXPERIMENTAL_TZDB

libcxx/include/__chrono/file_clock.h

@@ -46,6 +46,7 @@ _LIBCPP_END_NAMESPACE_STD
 
 #ifndef _LIBCPP_CXX03_LANG
 _LIBCPP_BEGIN_NAMESPACE_FILESYSTEM
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
 struct _FilesystemClock {
 #  if _LIBCPP_HAS_INT128
   typedef __int128_t rep;
@@ -74,6 +75,7 @@ struct _FilesystemClock {
   }
 #  endif // _LIBCPP_STD_VER >= 20
 };
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 _LIBCPP_END_NAMESPACE_FILESYSTEM
 #endif // !_LIBCPP_CXX03_LANG
 

libcxx/include/__chrono/steady_clock.h

@@ -19,6 +19,7 @@
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
 
 namespace chrono {
 
@@ -37,6 +38,7 @@ class _LIBCPP_EXPORTED_FROM_ABI steady_clock {
 
 } // namespace chrono
 
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___CHRONO_STEADY_CLOCK_H

libcxx/include/__chrono/system_clock.h

@@ -20,6 +20,7 @@
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
 
 namespace chrono {
 
@@ -47,6 +48,7 @@ using sys_days    = sys_time<days>;
 
 } // namespace chrono
 
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___CHRONO_SYSTEM_CLOCK_H