diff --git a/docs/DesignDocs/VisibilityMacros.rst b/docs/DesignDocs/VisibilityMacros.rst
index 08debbcdd..d0d4f0adb 100644
--- a/docs/DesignDocs/VisibilityMacros.rst
+++ b/docs/DesignDocs/VisibilityMacros.rst
@@ -22,11 +22,11 @@ Visibility Macros
   Mark a symbol as being exported by the libc++ library. This attribute must
   be applied to the declaration of all functions exported by the libc++ dylib.
 
-**_LIBCPP_EXTERN_VIS**
+**_LIBCPP_EXPORTED_FROM_ABI**
   Mark a symbol as being exported by the libc++ library. This attribute may
-  only be applied to objects defined in the libc++ library. On Windows this
-  macro applies `dllimport`/`dllexport` to the symbol. On all other platforms
-  this macro has no effect.
+  only be applied to objects defined in the libc++ runtime library. On Windows,
+  this macro applies `dllimport`/`dllexport` to the symbol, and on other
+  platforms it gives the symbol default visibility.
 
 **_LIBCPP_OVERRIDABLE_FUNC_VIS**
   Mark a symbol as being exported by the libc++ library, but allow it to be
diff --git a/include/__config b/include/__config
index 51068b33b..f6020748e 100644
--- a/include/__config
+++ b/include/__config
@@ -675,21 +675,23 @@ _LIBCPP_BEGIN_NAMESPACE_STD _LIBCPP_END_NAMESPACE_STD
 #  define _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
 #  define _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS
 #  define _LIBCPP_OVERRIDABLE_FUNC_VIS
+#  define _LIBCPP_EXPORTED_FROM_ABI
 #elif defined(_LIBCPP_BUILDING_LIBRARY)
 #  define _LIBCPP_DLL_VIS __declspec(dllexport)
 #  define _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
 #  define _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS _LIBCPP_DLL_VIS
 #  define _LIBCPP_OVERRIDABLE_FUNC_VIS _LIBCPP_DLL_VIS
+#  define _LIBCPP_EXPORTED_FROM_ABI __declspec(dllexport)
 #else
 #  define _LIBCPP_DLL_VIS __declspec(dllimport)
 #  define _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS _LIBCPP_DLL_VIS
 #  define _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS
 #  define _LIBCPP_OVERRIDABLE_FUNC_VIS
+#  define _LIBCPP_EXPORTED_FROM_ABI __declspec(dllimport)
 #endif
 
 #define _LIBCPP_TYPE_VIS            _LIBCPP_DLL_VIS
 #define _LIBCPP_FUNC_VIS            _LIBCPP_DLL_VIS
-#define _LIBCPP_EXTERN_VIS          _LIBCPP_DLL_VIS
 #define _LIBCPP_EXCEPTION_ABI       _LIBCPP_DLL_VIS
 #define _LIBCPP_HIDDEN
 #define _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
@@ -743,8 +745,8 @@ _LIBCPP_BEGIN_NAMESPACE_STD _LIBCPP_END_NAMESPACE_STD
 #  endif
 #endif
 
-#ifndef _LIBCPP_EXTERN_VIS
-#define _LIBCPP_EXTERN_VIS
+#ifndef _LIBCPP_EXPORTED_FROM_ABI
+#  define _LIBCPP_EXPORTED_FROM_ABI __attribute__((__visibility__("default")))
 #endif
 
 #ifndef _LIBCPP_OVERRIDABLE_FUNC_VIS
diff --git a/include/__debug b/include/__debug
index d01bacdf7..a8788f68f 100644
--- a/include/__debug
+++ b/include/__debug
@@ -74,7 +74,7 @@ typedef void(*__libcpp_debug_function_type)(__libcpp_debug_info const&);
 
 /// __libcpp_debug_function - The handler function called when a _LIBCPP_ASSERT
 ///    fails.
-extern _LIBCPP_EXTERN_VIS __libcpp_debug_function_type __libcpp_debug_function;
+extern _LIBCPP_EXPORTED_FROM_ABI __libcpp_debug_function_type __libcpp_debug_function;
 
 /// __libcpp_abort_debug_function - A debug handler that aborts when called.
 _LIBCPP_NORETURN _LIBCPP_FUNC_VIS
diff --git a/include/__functional_base b/include/__functional_base
index 188797439..032be99bf 100644
--- a/include/__functional_base
+++ b/include/__functional_base
@@ -562,7 +562,7 @@ struct __is_transparent<_Tp, _Up,
 struct _LIBCPP_TEMPLATE_VIS allocator_arg_t { };
 
 #if defined(_LIBCPP_CXX03_LANG) || defined(_LIBCPP_BUILDING_LIBRARY)
-extern const allocator_arg_t allocator_arg;
+extern _LIBCPP_EXPORTED_FROM_ABI const allocator_arg_t allocator_arg;
 #else
 /* _LIBCPP_INLINE_VAR */ constexpr allocator_arg_t allocator_arg = allocator_arg_t();
 #endif
diff --git a/include/__locale b/include/__locale
index f43e7b430..cde9cc85f 100644
--- a/include/__locale
+++ b/include/__locale
@@ -1255,13 +1255,13 @@ struct __narrow_to_utf8<8>
 };
 
 template <>
-struct __narrow_to_utf8<16>
+struct _LIBCPP_TEMPLATE_VIS __narrow_to_utf8<16>
     : public codecvt<char16_t, char, mbstate_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     __narrow_to_utf8() : codecvt<char16_t, char, mbstate_t>(1) {}
 
-    ~__narrow_to_utf8();
+    _LIBCPP_EXPORTED_FROM_ABI ~__narrow_to_utf8();
 
     template <class _OutputIterator, class _CharT>
     _LIBCPP_INLINE_VISIBILITY
@@ -1289,13 +1289,13 @@ struct __narrow_to_utf8<16>
 };
 
 template <>
-struct __narrow_to_utf8<32>
+struct _LIBCPP_TEMPLATE_VIS __narrow_to_utf8<32>
     : public codecvt<char32_t, char, mbstate_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     __narrow_to_utf8() : codecvt<char32_t, char, mbstate_t>(1) {}
 
-    ~__narrow_to_utf8();
+    _LIBCPP_EXPORTED_FROM_ABI ~__narrow_to_utf8();
 
     template <class _OutputIterator, class _CharT>
     _LIBCPP_INLINE_VISIBILITY
@@ -1345,13 +1345,13 @@ struct __widen_from_utf8<8>
 };
 
 template <>
-struct __widen_from_utf8<16>
+struct _LIBCPP_TEMPLATE_VIS __widen_from_utf8<16>
     : public codecvt<char16_t, char, mbstate_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     __widen_from_utf8() : codecvt<char16_t, char, mbstate_t>(1) {}
 
-    ~__widen_from_utf8();
+    _LIBCPP_EXPORTED_FROM_ABI ~__widen_from_utf8();
 
     template <class _OutputIterator>
     _LIBCPP_INLINE_VISIBILITY
@@ -1379,13 +1379,13 @@ struct __widen_from_utf8<16>
 };
 
 template <>
-struct __widen_from_utf8<32>
+struct _LIBCPP_TEMPLATE_VIS __widen_from_utf8<32>
     : public codecvt<char32_t, char, mbstate_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     __widen_from_utf8() : codecvt<char32_t, char, mbstate_t>(1) {}
 
-    ~__widen_from_utf8();
+    _LIBCPP_EXPORTED_FROM_ABI ~__widen_from_utf8();
 
     template <class _OutputIterator>
     _LIBCPP_INLINE_VISIBILITY
diff --git a/include/__mutex_base b/include/__mutex_base
index 4659ca929..da21a5f8e 100644
--- a/include/__mutex_base
+++ b/include/__mutex_base
@@ -76,9 +76,9 @@ struct _LIBCPP_TYPE_VIS adopt_lock_t {};
 
 #if defined(_LIBCPP_CXX03_LANG) || defined(_LIBCPP_BUILDING_LIBRARY)
 
-extern const defer_lock_t  defer_lock;
-extern const try_to_lock_t try_to_lock;
-extern const adopt_lock_t  adopt_lock;
+extern _LIBCPP_EXPORTED_FROM_ABI const defer_lock_t  defer_lock;
+extern _LIBCPP_EXPORTED_FROM_ABI const try_to_lock_t try_to_lock;
+extern _LIBCPP_EXPORTED_FROM_ABI const adopt_lock_t  adopt_lock;
 
 #else
 
diff --git a/include/charconv b/include/charconv
index 7cb790e1b..c0cb9c52a 100644
--- a/include/charconv
+++ b/include/charconv
@@ -89,6 +89,11 @@ namespace std {
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+namespace __itoa {
+_LIBCPP_FUNC_VIS char* __u64toa(uint64_t __value, char* __buffer);
+_LIBCPP_FUNC_VIS char* __u32toa(uint32_t __value, char* __buffer);
+}
+
 #if _LIBCPP_STD_VER > 11
 
 enum class _LIBCPP_ENUM_VIS chars_format
@@ -147,9 +152,6 @@ static constexpr uint32_t __pow10_32[] = {
     UINT32_C(1000000000),
 };
 
-_LIBCPP_FUNC_VIS char* __u64toa(uint64_t __value, char* __buffer);
-_LIBCPP_FUNC_VIS char* __u32toa(uint32_t __value, char* __buffer);
-
 template <typename _Tp, typename = void>
 struct _LIBCPP_HIDDEN __traits_base
 {
diff --git a/include/locale b/include/locale
index e240799f3..7be358e4d 100644
--- a/include/locale
+++ b/include/locale
@@ -2408,6 +2408,23 @@ private:
     string_type __analyze(char __fmt, const ctype<_CharT>&);
 };
 
+#define _LIBCPP_TIME_GET_STORAGE_EXPLICIT_INSTANTIATION(_CharT) \
+template <> _LIBCPP_FUNC_VIS time_base::dateorder __time_get_storage<_CharT>::__do_date_order() const; \
+template <> _LIBCPP_FUNC_VIS __time_get_storage<_CharT>::__time_get_storage(const char*); \
+template <> _LIBCPP_FUNC_VIS __time_get_storage<_CharT>::__time_get_storage(const string&); \
+template <> _LIBCPP_FUNC_VIS void __time_get_storage<_CharT>::init(const ctype<_CharT>&); \
+template <> _LIBCPP_FUNC_VIS __time_get_storage<_CharT>::string_type __time_get_storage<_CharT>::__analyze(char, const ctype<_CharT>&); \
+extern template _LIBCPP_FUNC_VIS time_base::dateorder __time_get_storage<_CharT>::__do_date_order() const; \
+extern template _LIBCPP_FUNC_VIS __time_get_storage<_CharT>::__time_get_storage(const char*); \
+extern template _LIBCPP_FUNC_VIS __time_get_storage<_CharT>::__time_get_storage(const string&); \
+extern template _LIBCPP_FUNC_VIS void __time_get_storage<_CharT>::init(const ctype<_CharT>&); \
+extern template _LIBCPP_FUNC_VIS __time_get_storage<_CharT>::string_type __time_get_storage<_CharT>::__analyze(char, const ctype<_CharT>&); \
+/**/
+
+_LIBCPP_TIME_GET_STORAGE_EXPLICIT_INSTANTIATION(char)
+_LIBCPP_TIME_GET_STORAGE_EXPLICIT_INSTANTIATION(wchar_t)
+#undef _LIBCPP_TIME_GET_STORAGE_EXPLICIT_INSTANTIATION
+
 template <class _CharT, class _InputIterator = istreambuf_iterator<_CharT> >
 class _LIBCPP_TEMPLATE_VIS time_get_byname
     : public time_get<_CharT, _InputIterator>,
diff --git a/include/thread b/include/thread
index 0629d70ef..8c0115f87 100644
--- a/include/thread
+++ b/include/thread
@@ -151,7 +151,7 @@ class __thread_specific_ptr
     __thread_specific_ptr(const __thread_specific_ptr&);
     __thread_specific_ptr& operator=(const __thread_specific_ptr&);
 
-    static void _LIBCPP_TLS_DESTRUCTOR_CC __at_thread_exit(void*);
+    _LIBCPP_HIDDEN static void _LIBCPP_TLS_DESTRUCTOR_CC __at_thread_exit(void*);
 
 public:
     typedef _Tp* pointer;
diff --git a/include/utility b/include/utility
index 5388585ec..30e26f163 100644
--- a/include/utility
+++ b/include/utility
@@ -297,7 +297,7 @@ template <class _Tp>                        void as_const(const _Tp&&) = delete;
 
 struct _LIBCPP_TEMPLATE_VIS piecewise_construct_t { };
 #if defined(_LIBCPP_CXX03_LANG) || defined(_LIBCPP_BUILDING_LIBRARY)
-extern const piecewise_construct_t piecewise_construct;// = piecewise_construct_t();
+extern _LIBCPP_EXPORTED_FROM_ABI const piecewise_construct_t piecewise_construct;// = piecewise_construct_t();
 #else
 /* _LIBCPP_INLINE_VAR */ constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
 #endif
diff --git a/lib/abi/CHANGELOG.TXT b/lib/abi/CHANGELOG.TXT
index 4c9a59746..a5451bc4b 100644
--- a/lib/abi/CHANGELOG.TXT
+++ b/lib/abi/CHANGELOG.TXT
@@ -16,6 +16,34 @@ New entries should be added directly below the "Version" header.
 Version 7.0
 -----------
 
+* rXXXXX - Making libc++ build under -fvisibility=hidden
+
+  The change marks __thread_specific_ptr<__thread_struct>::__at_thread_exit(void*)
+  with hidden visibility. This removes a symbol from the shared libraries,
+  however this is not an ABI break because it's impossible for programs linking
+  against libc++.dylib to actually depend on that symbol. The reason is that
+  the symbol is exported from the shared library through an implicit
+  instantiation present in the dylib itself only. Furthermore, if a user's
+  dylib was implicitly instantiating __thread_specific_ptr<T>::__at_thread_exit
+  (because it's defined in the headers), marking that symbol as hidden would
+  not be an ABI break for them because none of their users could actually be
+  using the symbol in their dylib (because it's an implicit instantiation).
+
+  This change also marks __start_std_streams as hidden -- this variable is
+  only required to initialize the streams, and nobody should depend on it
+  from outside the dylib.
+
+  x86_64-linux-gnu
+  ----------------
+  Symbol removed: _ZNSt3__121__thread_specific_ptrINS_15__thread_structEE16__at_thread_exitEPv
+  Symbol removed: _ZNSt3__119__start_std_streamsE
+
+  x86_64-apple-darwin16.0
+  -----------------------
+  Symbol removed: __ZNSt3__221__thread_specific_ptrINS_15__thread_structEE16__at_thread_exitEPv
+  Symbol removed: __ZNSt3__119__start_std_streamsE
+
+
 * r338479 - Elementary string conversions for integral types
 
   The change emits __u64toa and __u32toa under std::__1::__itoa.
diff --git a/lib/abi/x86_64-apple-darwin.v1.abilist b/lib/abi/x86_64-apple-darwin.v1.abilist
index 6d011616d..88cfa90f1 100644
--- a/lib/abi/x86_64-apple-darwin.v1.abilist
+++ b/lib/abi/x86_64-apple-darwin.v1.abilist
@@ -1197,13 +1197,11 @@
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__119__shared_weak_countD0Ev'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__119__shared_weak_countD1Ev'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__119__shared_weak_countD2Ev'}
-{'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__119__start_std_streamsE', 'size': 0}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__119__thread_local_dataEv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__119declare_no_pointersEPcm'}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__119piecewise_constructE', 'size': 0}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__120__get_collation_nameEPKc'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__120__throw_system_errorEiPKc'}
-{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121__thread_specific_ptrINS_15__thread_structEE16__at_thread_exitEPv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121__throw_runtime_errorEPKc'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121__undeclare_reachableEPv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121recursive_timed_mutex4lockEv'}
diff --git a/lib/abi/x86_64-apple-darwin.v2.abilist b/lib/abi/x86_64-apple-darwin.v2.abilist
index e77b9f045..3896b38d9 100644
--- a/lib/abi/x86_64-apple-darwin.v2.abilist
+++ b/lib/abi/x86_64-apple-darwin.v2.abilist
@@ -1119,13 +1119,11 @@
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__219__shared_weak_countD0Ev'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__219__shared_weak_countD1Ev'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__219__shared_weak_countD2Ev'}
-{'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__219__start_std_streamsE', 'size': 0}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__219__thread_local_dataEv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__219declare_no_pointersEPcm'}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__219piecewise_constructE', 'size': 0}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__220__get_collation_nameEPKc'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__220__throw_system_errorEiPKc'}
-{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__221__thread_specific_ptrINS_15__thread_structEE16__at_thread_exitEPv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__221__throw_runtime_errorEPKc'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__221__undeclare_reachableEPv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__221recursive_timed_mutex4lockEv'}
diff --git a/lib/abi/x86_64-unknown-linux-gnu.v1.abilist b/lib/abi/x86_64-unknown-linux-gnu.v1.abilist
index 833342ca8..f8af75793 100644
--- a/lib/abi/x86_64-unknown-linux-gnu.v1.abilist
+++ b/lib/abi/x86_64-unknown-linux-gnu.v1.abilist
@@ -1098,13 +1098,11 @@
 {'name': '_ZNSt3__119__shared_weak_countD0Ev', 'is_defined': True, 'type': 'FUNC'}
 {'name': '_ZNSt3__119__shared_weak_countD1Ev', 'is_defined': True, 'type': 'FUNC'}
 {'name': '_ZNSt3__119__shared_weak_countD2Ev', 'is_defined': True, 'type': 'FUNC'}
-{'name': '_ZNSt3__119__start_std_streamsE', 'is_defined': True, 'type': 'OBJECT', 'size': 1}
 {'name': '_ZNSt3__119__thread_local_dataEv', 'is_defined': True, 'type': 'FUNC'}
 {'name': '_ZNSt3__119declare_no_pointersEPcm', 'is_defined': True, 'type': 'FUNC'}
 {'name': '_ZNSt3__119piecewise_constructE', 'is_defined': True, 'type': 'OBJECT', 'size': 1}
 {'name': '_ZNSt3__120__get_collation_nameEPKc', 'is_defined': True, 'type': 'FUNC'}
 {'name': '_ZNSt3__120__throw_system_errorEiPKc', 'is_defined': True, 'type': 'FUNC'}
-{'name': '_ZNSt3__121__thread_specific_ptrINS_15__thread_structEE16__at_thread_exitEPv', 'is_defined': True, 'type': 'FUNC'}
 {'name': '_ZNSt3__121__throw_runtime_errorEPKc', 'is_defined': True, 'type': 'FUNC'}
 {'name': '_ZNSt3__121__undeclare_reachableEPv', 'is_defined': True, 'type': 'FUNC'}
 {'name': '_ZNSt3__121recursive_timed_mutex4lockEv', 'is_defined': True, 'type': 'FUNC'}
diff --git a/src/iostream.cpp b/src/iostream.cpp
index 2b47cf25b..66abdaf99 100644
--- a/src/iostream.cpp
+++ b/src/iostream.cpp
@@ -77,7 +77,7 @@ __asm__("?wclog@" _LIBCPP_NAMESPACE_STR "@std@@3V?$basic_ostream@_WU?$char_trait
 #endif
 ;
 
-ios_base::Init __start_std_streams;
+_LIBCPP_HIDDEN ios_base::Init __start_std_streams;
 
 ios_base::Init::Init()
 {