Index: libcxx/CMakeLists.txt
===================================================================
--- libcxx/CMakeLists.txt
+++ libcxx/CMakeLists.txt
@@ -101,59 +101,71 @@
    to provide compile-time errors when using features unavailable on some version of
    the shared library they shipped should turn this on and see `include/__availability`
    for more details." OFF)
-
-if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-  set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-gcc.cfg.in")
-elseif(MINGW)
-  set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-mingw.cfg.in")
-elseif(WIN32) # clang-cl
-  if (LIBCXX_ENABLE_SHARED)
-    set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-clangcl.cfg.in")
-  else()
-    set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-static-clangcl.cfg.in")
-  endif()
+option(LIBCXX_FREESTANDING OFF
+  "Build libc++ with freestanding headers. This toggle allows the libc to work for
+  freestanding environments like operating systems kernels or embedded systems.")
+
+if (LIBCXX_FREESTANDING)
+  set(LIBCXX_ENABLE_FILESYSTEM OFF)
+  set(LIBCXX_ENABLE_SHARED OFF)
+  set(LIBCXX_ENABLE_STATIC OFF)
+  set(CMAKE_C_COMPILER_WORKS ON)
+  set(CMAKE_CXX_COMPILER_WORKS ON)
+  set(LIBCXX_ENABLE_LOCALIZATION OFF)
 else()
-  if (LIBCXX_ENABLE_SHARED)
-    set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared.cfg.in")
+  if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+    set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-gcc.cfg.in")
+  elseif(MINGW)
+    set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-mingw.cfg.in")
+  elseif(WIN32) # clang-cl
+    if (LIBCXX_ENABLE_SHARED)
+      set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-clangcl.cfg.in")
+    else()
+      set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-static-clangcl.cfg.in")
+    endif()
   else()
-    set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-static.cfg.in")
+    if (LIBCXX_ENABLE_SHARED)
+      set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared.cfg.in")
+    else()
+      set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-static.cfg.in")
+    endif()
   endif()
-endif()
-set(LIBCXX_TEST_CONFIG "${LIBCXX_DEFAULT_TEST_CONFIG}" CACHE STRING
-    "The path to the Lit testing configuration to use when running the tests.
-     If a relative path is provided, it is assumed to be relative to '<monorepo>/libcxx/test/configs'.")
-if (NOT IS_ABSOLUTE "${LIBCXX_TEST_CONFIG}")
-  set(LIBCXX_TEST_CONFIG "${CMAKE_CURRENT_SOURCE_DIR}/test/configs/${LIBCXX_TEST_CONFIG}")
-endif()
-message(STATUS "Using libc++ testing configuration: ${LIBCXX_TEST_CONFIG}")
-set(LIBCXX_TEST_PARAMS "" CACHE STRING
-    "A list of parameters to run the Lit test suite with.")
-
-# Benchmark options -----------------------------------------------------------
-option(LIBCXX_INCLUDE_BENCHMARKS "Build the libc++ benchmarks and their dependencies" ON)
-
-set(LIBCXX_BENCHMARK_TEST_ARGS_DEFAULT --benchmark_min_time=0.01)
-set(LIBCXX_BENCHMARK_TEST_ARGS "${LIBCXX_BENCHMARK_TEST_ARGS_DEFAULT}" CACHE STRING
-    "Arguments to pass when running the benchmarks using check-cxx-benchmarks")
-
-set(LIBCXX_BENCHMARK_NATIVE_STDLIB "" CACHE STRING
-        "Build the benchmarks against the specified native STL.
-         The value must be one of libc++/libstdc++")
-set(LIBCXX_BENCHMARK_NATIVE_GCC_TOOLCHAIN "" CACHE STRING
-    "Use alternate GCC toolchain when building the native benchmarks")
-
-if (LIBCXX_BENCHMARK_NATIVE_STDLIB)
-  if (NOT (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libc++"
-        OR LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libstdc++"))
-    message(FATAL_ERROR "Invalid value for LIBCXX_BENCHMARK_NATIVE_STDLIB: "
-            "'${LIBCXX_BENCHMARK_NATIVE_STDLIB}'")
+  set(LIBCXX_TEST_CONFIG "${LIBCXX_DEFAULT_TEST_CONFIG}" CACHE STRING
+      "The path to the Lit testing configuration to use when running the tests.
+      If a relative path is provided, it is assumed to be relative to '<monorepo>/libcxx/test/configs'.")
+  if (NOT IS_ABSOLUTE "${LIBCXX_TEST_CONFIG}")
+    set(LIBCXX_TEST_CONFIG "${CMAKE_CURRENT_SOURCE_DIR}/test/configs/${LIBCXX_TEST_CONFIG}")
+  endif()
+  message(STATUS "Using libc++ testing configuration: ${LIBCXX_TEST_CONFIG}")
+  set(LIBCXX_TEST_PARAMS "" CACHE STRING
+      "A list of parameters to run the Lit test suite with.")
+
+  # Benchmark options -----------------------------------------------------------
+  option(LIBCXX_INCLUDE_BENCHMARKS "Build the libc++ benchmarks and their dependencies" ON)
+
+  set(LIBCXX_BENCHMARK_TEST_ARGS_DEFAULT --benchmark_min_time=0.01)
+  set(LIBCXX_BENCHMARK_TEST_ARGS "${LIBCXX_BENCHMARK_TEST_ARGS_DEFAULT}" CACHE STRING
+      "Arguments to pass when running the benchmarks using check-cxx-benchmarks")
+
+  set(LIBCXX_BENCHMARK_NATIVE_STDLIB "" CACHE STRING
+          "Build the benchmarks against the specified native STL.
+          The value must be one of libc++/libstdc++")
+  set(LIBCXX_BENCHMARK_NATIVE_GCC_TOOLCHAIN "" CACHE STRING
+      "Use alternate GCC toolchain when building the native benchmarks")
+
+  if (LIBCXX_BENCHMARK_NATIVE_STDLIB)
+    if (NOT (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libc++"
+          OR LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libstdc++"))
+      message(FATAL_ERROR "Invalid value for LIBCXX_BENCHMARK_NATIVE_STDLIB: "
+              "'${LIBCXX_BENCHMARK_NATIVE_STDLIB}'")
+    endif()
   endif()
 endif()
-
 option(LIBCXX_INCLUDE_DOCS "Build the libc++ documentation." ${LLVM_INCLUDE_DOCS})
 set(LIBCXX_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXX_INSTALL_HEADERS "Install the libc++ headers." ON)
+if(NOT LIBCXX_FREESTANDING)
 option(LIBCXX_INSTALL_LIBRARY "Install the libc++ library." ON)
 cmake_dependent_option(LIBCXX_INSTALL_STATIC_LIBRARY
   "Install the static libc++ library." ON
@@ -161,6 +173,7 @@
 cmake_dependent_option(LIBCXX_INSTALL_SHARED_LIBRARY
   "Install the shared libc++ library." ON
   "LIBCXX_ENABLE_SHARED;LIBCXX_INSTALL_LIBRARY" OFF)
+endif()
 
 option(LIBCXX_ABI_UNSTABLE "Use the unstable ABI of libc++. This is equivalent to specifying LIBCXX_ABI_VERSION=n, where n is the not-yet-stable version." OFF)
 if (LIBCXX_ABI_UNSTABLE)
@@ -299,6 +312,11 @@
 set(LIBCXX_COVERAGE_LIBRARY "" CACHE STRING
     "The Profile-rt library used to build with code coverage")
 
+if (LIBCXX_FREESTANDING)
+set(LIBCXX_ENABLE_THREADS OFF)
+set(LIBCXX_ENABLE_MONOTONIC_CLOCK OFF)
+endif()
+
 set(LIBCXX_CONFIGURE_IDE_DEFAULT OFF)
 if (XCODE OR MSVC_IDE)
   set(LIBCXX_CONFIGURE_IDE_DEFAULT ON)
@@ -319,6 +337,7 @@
 
 # Ensure LIBCXX_ENABLE_MONOTONIC_CLOCK is set to ON only when
 # LIBCXX_ENABLE_THREADS is on.
+if (NOT LIBCXX_FREESTANDING)
 if(LIBCXX_ENABLE_THREADS AND NOT LIBCXX_ENABLE_MONOTONIC_CLOCK)
   message(FATAL_ERROR "LIBCXX_ENABLE_MONOTONIC_CLOCK can only be set to OFF"
                       " when LIBCXX_ENABLE_THREADS is also set to OFF.")
@@ -341,7 +360,6 @@
     message(FATAL_ERROR "LIBCXX_HAS_WIN32_THREAD_API can only be set to ON"
                         " when LIBCXX_ENABLE_THREADS is also set to ON.")
   endif()
-
 endif()
 
 if (LIBCXX_HAS_EXTERNAL_THREAD_API)
@@ -394,7 +412,7 @@
 if (LIBCXX_ABI_FORCE_ITANIUM AND LIBCXX_ABI_FORCE_MICROSOFT)
   message(FATAL_ERROR "Only one of LIBCXX_ABI_FORCE_ITANIUM and LIBCXX_ABI_FORCE_MICROSOFT can be specified.")
 endif ()
-
+endif ()
 #===============================================================================
 # Configure System
 #===============================================================================
@@ -745,7 +763,7 @@
     # default libunwind (which may be missing still).
     target_add_link_flags_if_supported(${target} PRIVATE "--unwindlib=none")
   endif()
-
+  if (NOT LIBCXX_FREESTANDING)
   if (LIBCXX_HAS_SYSTEM_LIB)
     target_link_libraries(${target} PRIVATE System)
   endif()
@@ -799,12 +817,12 @@
     # Required for standards-complaint wide character formatting functions
     # (e.g. `printfw`/`scanfw`)
     target_link_libraries(${target} PRIVATE iso_stdio_wide_specifiers)
-  endif()
-
+    endif()
   if (ANDROID AND ANDROID_PLATFORM_LEVEL LESS 21)
     target_link_libraries(${target} PUBLIC android_support)
   endif()
   target_link_libraries(${target} PUBLIC "${LIBCXX_ADDITIONAL_LIBRARIES}")
+  endif()
 endfunction()
 
 # Windows-related flags =======================================================
@@ -870,6 +888,10 @@
   config_define(0 _LIBCPP_ENABLE_ASSERTIONS_DEFAULT)
 endif()
 
+if (LIBCXX_FREESTANDING)
+  config_define(LIBCXX_FREESTANDING _LIBCPP_FREESTANDING)
+endif()
+
 if (LIBCXX_ABI_DEFINES)
   set(abi_defines)
   foreach (abi_define ${LIBCXX_ABI_DEFINES})
@@ -922,6 +944,7 @@
 # Setup Source Code And Tests
 #===============================================================================
 add_subdirectory(include)
+if (NOT LIBCXX_FREESTANDING)
 add_subdirectory(src)
 add_subdirectory(utils)
 
@@ -939,6 +962,7 @@
   add_subdirectory(test)
   add_subdirectory(lib/abi)
 endif()
+endif()
 
 if (LIBCXX_INCLUDE_DOCS)
   add_subdirectory(docs)
Index: libcxx/include/__compare/strong_order.h
===================================================================
--- libcxx/include/__compare/strong_order.h
+++ libcxx/include/__compare/strong_order.h
@@ -15,7 +15,9 @@
 #include <__config>
 #include <__utility/forward.h>
 #include <__utility/priority_tag.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <cmath>
+#endif
 #include <cstdint>
 #include <limits>
 #include <type_traits>
@@ -41,7 +43,7 @@
             noexcept(noexcept(strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
             -> decltype(      strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
             { return          strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
-
+#ifndef _LIBCPP_FREESTANDING
         template<class _Tp, class _Up, class _Dp = decay_t<_Tp>>
             requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp>
         _LIBCPP_HIDE_FROM_ABI static constexpr strong_ordering
@@ -106,7 +108,7 @@
                 }
             }
         }
-
+#endif
         template<class _Tp, class _Up>
             requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
         _LIBCPP_HIDE_FROM_ABI static constexpr auto
Index: libcxx/include/__compare/weak_order.h
===================================================================
--- libcxx/include/__compare/weak_order.h
+++ libcxx/include/__compare/weak_order.h
@@ -15,7 +15,9 @@
 #include <__config>
 #include <__utility/forward.h>
 #include <__utility/priority_tag.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <cmath>
+#endif
 #include <type_traits>
 
 #ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
@@ -37,6 +39,7 @@
             -> decltype(      weak_ordering(weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
             { return          weak_ordering(weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
 
+#ifndef _LIBCPP_FREESTANDING
         template<class _Tp, class _Up, class _Dp = decay_t<_Tp>>
             requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp>
         _LIBCPP_HIDE_FROM_ABI static constexpr weak_ordering
@@ -64,6 +67,7 @@
                 }
             }
         }
+#endif
 
         template<class _Tp, class _Up>
             requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
Index: libcxx/include/__config
===================================================================
--- libcxx/include/__config
+++ libcxx/include/__config
@@ -32,6 +32,11 @@
 #  define _LIBCPP_COMPILER_GCC
 #endif
 
+#  if __STDC_HOSTED__ == 0
+#    undef _LIBCPP_FREESTANDING
+#    define _LIBCPP_FREESTANDING
+#  endif
+
 #ifdef __cplusplus
 
 // _LIBCPP_VERSION represents the version of libc++, which matches the version of LLVM.
@@ -46,10 +51,6 @@
 // generate identifiers that must be unique for every released libc++ version.
 #  define _LIBCPP_VERSIONED_IDENTIFIER _LIBCPP_CONCAT(v, _LIBCPP_VERSION)
 
-#  if __STDC_HOSTED__ == 0
-#    define _LIBCPP_FREESTANDING
-#  endif
-
 #  ifndef _LIBCPP_STD_VER
 #    if __cplusplus <= 201103L
 #      define _LIBCPP_STD_VER 11
@@ -253,16 +254,20 @@
 
 // Need to detect which libc we're using if we're on Linux.
 #  if defined(__linux__)
-#    include <features.h>
-#    if defined(__GLIBC_PREREQ)
-#      define _LIBCPP_GLIBC_PREREQ(a, b) __GLIBC_PREREQ(a, b)
-#    else
-#      define _LIBCPP_GLIBC_PREREQ(a, b) 0
-#    endif // defined(__GLIBC_PREREQ)
+#    if __has_include(<features.h>)
+#      include <features.h>
+#      if defined(__GLIBC_PREREQ)
+#        define _LIBCPP_GLIBC_PREREQ(a, b) __GLIBC_PREREQ(a, b)
+#      else
+#        define _LIBCPP_GLIBC_PREREQ(a, b) 0
+#      endif // defined(__GLIBC_PREREQ)
+#    endif
 #  endif   // defined(__linux__)
 
 #  if defined(__MVS__)
-#    include <features.h> // for __NATIVE_ASCII_F
+#    if __has_include(<features.h>)
+#      include <features.h> // for __NATIVE_ASCII_F
+#    endif
 #  endif
 
 #  ifdef __LITTLE_ENDIAN__
@@ -286,22 +291,26 @@
 #  endif   // __BYTE_ORDER__
 
 #  ifdef __FreeBSD__
-#    include <sys/endian.h>
-#    include <osreldate.h>
-#    if _BYTE_ORDER == _LITTLE_ENDIAN
-#      define _LIBCPP_LITTLE_ENDIAN
-#    else // _BYTE_ORDER == _LITTLE_ENDIAN
-#      define _LIBCPP_BIG_ENDIAN
-#    endif // _BYTE_ORDER == _LITTLE_ENDIAN
+#    if __has_include(<sys/endian.h>) && __has_include(<osreldate.h>)
+#      include <sys/endian.h>
+#      include <osreldate.h>
+#      if _BYTE_ORDER == _LITTLE_ENDIAN
+#        define _LIBCPP_LITTLE_ENDIAN
+#      else // _BYTE_ORDER == _LITTLE_ENDIAN
+#        define _LIBCPP_BIG_ENDIAN
+#      endif // _BYTE_ORDER == _LITTLE_ENDIAN
+#    endif
 #  endif   // __FreeBSD__
 
 #  if defined(__NetBSD__) || defined(__OpenBSD__)
-#    include <sys/endian.h>
-#    if _BYTE_ORDER == _LITTLE_ENDIAN
-#      define _LIBCPP_LITTLE_ENDIAN
-#    else // _BYTE_ORDER == _LITTLE_ENDIAN
-#      define _LIBCPP_BIG_ENDIAN
-#    endif // _BYTE_ORDER == _LITTLE_ENDIAN
+#    if __has_include(<sys/endian.h>)
+#      include <sys/endian.h>
+#      if _BYTE_ORDER == _LITTLE_ENDIAN
+#        define _LIBCPP_LITTLE_ENDIAN
+#      else // _BYTE_ORDER == _LITTLE_ENDIAN
+#        define _LIBCPP_BIG_ENDIAN
+#      endif // _BYTE_ORDER == _LITTLE_ENDIAN
+#    endif
 #  endif   // defined(__NetBSD__) || defined(__OpenBSD__)
 
 #  if defined(_WIN32)
@@ -322,11 +331,13 @@
 #  endif // defined(_WIN32)
 
 #  ifdef __sun__
+#    if __has_include(<sys/isa_defs.h>)
 #    include <sys/isa_defs.h>
-#    ifdef _LITTLE_ENDIAN
-#      define _LIBCPP_LITTLE_ENDIAN
-#    else
-#      define _LIBCPP_BIG_ENDIAN
+#      ifdef _LITTLE_ENDIAN
+#        define _LIBCPP_LITTLE_ENDIAN
+#      else
+#        define _LIBCPP_BIG_ENDIAN
+#      endif
 #    endif
 #  endif // __sun__
 
Index: libcxx/include/__config_site.in
===================================================================
--- libcxx/include/__config_site.in
+++ libcxx/include/__config_site.in
@@ -31,6 +31,7 @@
 #cmakedefine _LIBCPP_HAS_NO_WIDE_CHARACTERS
 #cmakedefine01 _LIBCPP_ENABLE_ASSERTIONS_DEFAULT
 #cmakedefine _LIBCPP_ENABLE_DEBUG_MODE
+#cmakedefine _LIBCPP_FREESTANDING
 
 // __USE_MINGW_ANSI_STDIO gets redefined on MinGW
 #ifdef __clang__
Index: libcxx/include/__random/uniform_int_distribution.h
===================================================================
--- libcxx/include/__random/uniform_int_distribution.h
+++ libcxx/include/__random/uniform_int_distribution.h
@@ -16,7 +16,9 @@
 #include <bit>
 #include <cstddef>
 #include <cstdint>
+#ifndef _LIBCPP_FREESTANDING
 #include <iosfwd>
+#endif
 #include <limits>
 #include <type_traits>
 
@@ -254,6 +256,8 @@
     return static_cast<result_type>(__u + __p.a());
 }
 
+#ifndef _LIBCPP_FREESTANDING
+
 template <class _CharT, class _Traits, class _IT>
 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
 operator<<(basic_ostream<_CharT, _Traits>& __os,
@@ -285,6 +289,7 @@
         __x.param(param_type(__a, __b));
     return __is;
 }
+#endif
 
 _LIBCPP_END_NAMESPACE_STD
 
Index: libcxx/include/__string/char_traits.h
===================================================================
--- libcxx/include/__string/char_traits.h
+++ libcxx/include/__string/char_traits.h
@@ -21,10 +21,12 @@
 #include <__type_traits/is_constant_evaluated.h>
 #include <cstddef>
 #include <cstdint>
+#ifndef _LIBCPP_FREESTANDING
 #include <cstdio>
+#endif
 #include <iosfwd>
 
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+#if !defined(_LIBCPP_HAS_NO_WIDE_CHARACTERS) && !defined(_LIBCPP_FREESTANDING)
 #   include <cwchar> // for wmemcpy
 #endif
 
@@ -42,10 +44,11 @@
 {
     using char_type  = _CharT;
     using int_type   = int;
+#ifndef _LIBCPP_FREESTANDING
     using off_type   = streamoff;
     using pos_type   = streampos;
     using state_type = mbstate_t;
-
+#endif
     static inline void _LIBCPP_CONSTEXPR_SINCE_CXX17
         assign(char_type& __c1, const char_type& __c2) _NOEXCEPT {__c1 = __c2;}
     static inline _LIBCPP_CONSTEXPR bool eq(char_type __c1, char_type __c2) _NOEXCEPT
@@ -67,17 +70,20 @@
     _LIBCPP_INLINE_VISIBILITY
     static _LIBCPP_CONSTEXPR_SINCE_CXX20
     char_type*       assign(char_type* __s, size_t __n, char_type __a);
-
+#if defined(EOF)
     static inline _LIBCPP_CONSTEXPR int_type  not_eof(int_type __c) _NOEXCEPT
         {return eq_int_type(__c, eof()) ? ~eof() : __c;}
+#endif
     static inline _LIBCPP_CONSTEXPR char_type to_char_type(int_type __c) _NOEXCEPT
         {return char_type(__c);}
     static inline _LIBCPP_CONSTEXPR int_type  to_int_type(char_type __c) _NOEXCEPT
         {return int_type(__c);}
     static inline _LIBCPP_CONSTEXPR bool      eq_int_type(int_type __c1, int_type __c2) _NOEXCEPT
         {return __c1 == __c2;}
+#if defined(EOF)
     static inline _LIBCPP_CONSTEXPR int_type  eof() _NOEXCEPT
         {return int_type(EOF);}
+#endif
 };
 
 template <class _CharT>
@@ -191,9 +197,11 @@
 {
     using char_type           = char;
     using int_type            = int;
+#ifndef _LIBCPP_FREESTANDING
     using off_type            = streamoff;
     using pos_type            = streampos;
     using state_type          = mbstate_t;
+#endif
 #if _LIBCPP_STD_VER > 17
     using comparison_category = strong_ordering;
 #endif
@@ -243,17 +251,20 @@
         std::fill_n(__s, __n, __a);
         return __s;
     }
-
+#if defined(EOF)
     static inline _LIBCPP_CONSTEXPR int_type  not_eof(int_type __c) _NOEXCEPT
         {return eq_int_type(__c, eof()) ? ~eof() : __c;}
+#endif
     static inline _LIBCPP_CONSTEXPR char_type to_char_type(int_type __c) _NOEXCEPT
         {return char_type(__c);}
     static inline _LIBCPP_CONSTEXPR int_type to_int_type(char_type __c) _NOEXCEPT
         {return int_type((unsigned char)__c);}
     static inline _LIBCPP_CONSTEXPR bool eq_int_type(int_type __c1, int_type __c2) _NOEXCEPT
         {return __c1 == __c2;}
+#if defined(EOF)
     static inline _LIBCPP_CONSTEXPR int_type  eof() _NOEXCEPT
         {return int_type(EOF);}
+#endif
 };
 
 inline _LIBCPP_CONSTEXPR_SINCE_CXX17
@@ -307,10 +318,12 @@
 struct _LIBCPP_TEMPLATE_VIS char_traits<wchar_t>
 {
     using char_type           = wchar_t;
+#if defined(WEOF)
     using int_type            = wint_t;
     using off_type            = streamoff;
     using pos_type            = streampos;
     using state_type          = mbstate_t;
+#endif
 #if _LIBCPP_STD_VER > 17
     using comparison_category = strong_ordering;
 #endif
@@ -347,17 +360,19 @@
         std::fill_n(__s, __n, __a);
         return __s;
     }
-
+#if defined(WEOF)
     static inline _LIBCPP_CONSTEXPR int_type  not_eof(int_type __c) _NOEXCEPT
         {return eq_int_type(__c, eof()) ? ~eof() : __c;}
     static inline _LIBCPP_CONSTEXPR char_type to_char_type(int_type __c) _NOEXCEPT
         {return char_type(__c);}
     static inline _LIBCPP_CONSTEXPR int_type to_int_type(char_type __c) _NOEXCEPT
         {return int_type(__c);}
+
     static inline _LIBCPP_CONSTEXPR bool eq_int_type(int_type __c1, int_type __c2) _NOEXCEPT
         {return __c1 == __c2;}
     static inline _LIBCPP_CONSTEXPR int_type eof() _NOEXCEPT
         {return int_type(WEOF);}
+#endif
 };
 
 inline _LIBCPP_CONSTEXPR_SINCE_CXX17
@@ -368,7 +383,7 @@
         return 0;
 #if __has_feature(cxx_constexpr_string_builtins)
     return __builtin_wmemcmp(__s1, __s2, __n);
-#elif _LIBCPP_STD_VER <= 14
+#elif _LIBCPP_STD_VER <= 14 && !defined(_LIBCPP_FREESTANDING)
     return _VSTD::wmemcmp(__s1, __s2, __n);
 #else
     for (; __n; --__n, ++__s1, ++__s2)
@@ -406,7 +421,7 @@
         return nullptr;
 #if __has_feature(cxx_constexpr_string_builtins)
     return __builtin_wmemchr(__s, __a, __n);
-#elif _LIBCPP_STD_VER <= 14
+#elif _LIBCPP_STD_VER <= 14 && !defined(_LIBCPP_FREESTANDING)
     return _VSTD::wmemchr(__s, __a, __n);
 #else
     for (; __n; --__n)
@@ -427,9 +442,11 @@
 {
     using char_type           = char8_t;
     using int_type            = unsigned int;
+#ifndef _LIBCPP_FREESTANDING
     using off_type            = streamoff;
     using pos_type            = u8streampos;
     using state_type          = mbstate_t;
+#endif
 #if _LIBCPP_STD_VER > 17
     using comparison_category = strong_ordering;
 #endif
@@ -468,17 +485,20 @@
         std::fill_n(__s, __n, __a);
         return __s;
     }
-
+#if defined(EOF)
     static inline constexpr int_type  not_eof(int_type __c) noexcept
         {return eq_int_type(__c, eof()) ? ~eof() : __c;}
+#endif
     static inline constexpr char_type to_char_type(int_type __c) noexcept
         {return char_type(__c);}
     static inline constexpr int_type to_int_type(char_type __c) noexcept
         {return int_type(__c);}
     static inline constexpr bool eq_int_type(int_type __c1, int_type __c2) noexcept
         {return __c1 == __c2;}
+#if defined(EOF)
     static inline constexpr int_type eof() noexcept
         {return int_type(EOF);}
+#endif
 };
 
 // TODO use '__builtin_strlen' if it ever supports char8_t ??
@@ -531,9 +551,11 @@
 {
     using char_type           = char16_t;
     using int_type            = uint_least16_t;
+#ifndef _LIBCPP_FREESTANDING
     using off_type            = streamoff;
     using pos_type            = u16streampos;
     using state_type          = mbstate_t;
+#endif
 #if _LIBCPP_STD_VER > 17
     using comparison_category = strong_ordering;
 #endif
@@ -625,9 +647,11 @@
 {
     using char_type           = char32_t;
     using int_type            = uint_least32_t;
+#ifndef _LIBCPP_FREESTANDING
     using off_type            = streamoff;
     using pos_type            = u32streampos;
     using state_type          = mbstate_t;
+#endif
 #if _LIBCPP_STD_VER > 17
     using comparison_category = strong_ordering;
 #endif
Index: libcxx/include/__thread/poll_with_backoff.h
===================================================================
--- libcxx/include/__thread/poll_with_backoff.h
+++ libcxx/include/__thread/poll_with_backoff.h
@@ -9,13 +9,16 @@
 #ifndef _LIBCPP___THREAD_POLL_WITH_BACKOFF_H
 #define _LIBCPP___THREAD_POLL_WITH_BACKOFF_H
 
+#include <__config>
+
+#ifndef _LIBCPP_FREESTANDING
 #include <__availability>
 #include <__chrono/duration.h>
 #include <__chrono/high_resolution_clock.h>
 #include <__chrono/steady_clock.h>
 #include <__chrono/time_point.h>
-#include <__config>
 #include <__filesystem/file_time_type.h>
+#endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -23,6 +26,17 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+
+template<class _Fn>
+_LIBCPP_INLINE_VISIBILITY
+bool __libcpp_thread_poll_with_backoff_freestanding(_Fn&& __f) {
+    for (;;) {
+      if (__f())
+        return true; // _Fn completion means success
+    }
+}
+
+#ifndef _LIBCPP_FREESTANDING
 static _LIBCPP_CONSTEXPR const int __libcpp_polling_count = 64;
 
 // Polls a thread for a condition given by a predicate, and backs off based on a backoff policy
@@ -55,6 +69,7 @@
     }
 }
 
+
 // A trivial backoff policy that always immediately returns the control to
 // the polling loop.
 //
@@ -67,7 +82,7 @@
       return false;
   }
 };
-
+#endif
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___THREAD_POLL_WITH_BACKOFF_H
Index: libcxx/include/atomic
===================================================================
--- libcxx/include/atomic
+++ libcxx/include/atomic
@@ -523,14 +523,16 @@
 #include <__chrono/duration.h>
 #include <__config>
 #include <__thread/poll_with_backoff.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <__thread/timed_backoff_policy.h>
+#endif
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
 #include <type_traits>
 #include <version>
 
-#ifndef _LIBCPP_HAS_NO_THREADS
+#if !defined(_LIBCPP_HAS_NO_THREADS) && !defined(_LIBCPP_FREESTANDING)
 # include <__threading_support>
 #endif
 
@@ -1431,7 +1433,7 @@
 
 using __cxx_atomic_contention_t = __cxx_atomic_impl<__cxx_contention_t>;
 
-#ifndef _LIBCPP_HAS_NO_THREADS
+#if !defined(_LIBCPP_HAS_NO_THREADS) && !defined(_LIBCPP_FREESTANDING)
 
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(void const volatile*);
 _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(void const volatile*);
@@ -1482,7 +1484,11 @@
 template <class _Atp, class _Fn>
 _LIBCPP_INLINE_VISIBILITY bool __cxx_atomic_wait(_Atp*, _Fn && __test_fn)
 {
+#ifdef _LIBCPP_FREESTANDING
+    return __libcpp_thread_poll_with_backoff_freestanding(__test_fn);
+#else
     return __libcpp_thread_poll_with_backoff(__test_fn, __spinning_backoff_policy());
+#endif
 }
 
 #endif // _LIBCPP_HAS_NO_THREADS
Index: libcxx/include/bitset
===================================================================
--- libcxx/include/bitset
+++ libcxx/include/bitset
@@ -127,8 +127,10 @@
 // standard-mandated includes
 
 // [bitset.syn]
+#ifndef _LIBCPP_FREESTANDING
 #include <iosfwd>
 #include <string>
+#endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -691,11 +693,17 @@
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR bitset() _NOEXCEPT {}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
         bitset(unsigned long long __v) _NOEXCEPT : base(__v) {}
+
     template<class _CharT, class = __enable_if_t<_IsCharLikeType<_CharT>::value> >
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
         explicit bitset(const _CharT* __str,
+#ifndef _LIBCPP_FREESTANDING
                         typename basic_string<_CharT>::size_type __n = basic_string<_CharT>::npos,
+#else
+                        ::std::size_t __n = ::std::size_t(-1),
+#endif
                         _CharT __zero = _CharT('0'), _CharT __one = _CharT('1'));
+#ifndef _LIBCPP_FREESTANDING
     template<class _CharT, class _Traits, class _Allocator>
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
         explicit bitset(const basic_string<_CharT,_Traits,_Allocator>& __str,
@@ -703,7 +711,7 @@
                         typename basic_string<_CharT,_Traits,_Allocator>::size_type __n =
                                 (basic_string<_CharT,_Traits,_Allocator>::npos),
                         _CharT __zero = _CharT('0'), _CharT __one = _CharT('1'));
-
+#endif
     // 23.3.5.2 bitset operations:
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
     bitset& operator&=(const bitset& __rhs) _NOEXCEPT;
@@ -741,6 +749,7 @@
     unsigned long to_ulong() const;
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
     unsigned long long to_ullong() const;
+#ifndef _LIBCPP_FREESTANDING
     template <class _CharT, class _Traits, class _Allocator>
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
         basic_string<_CharT, _Traits, _Allocator> to_string(_CharT __zero = _CharT('0'),
@@ -756,6 +765,7 @@
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
     basic_string<char, char_traits<char>, allocator<char> > to_string(char __zero = '0',
                                                                       char __one = '1') const;
+#endif
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
     size_t count() const _NOEXCEPT;
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR size_t size() const _NOEXCEPT {return _Size;}
@@ -787,7 +797,11 @@
 template<class _CharT, class>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
 bitset<_Size>::bitset(const _CharT* __str,
+#ifdef _LIBCPP_FREESTANDING
+                      _VSTD::size_t __n,
+#else
                       typename basic_string<_CharT>::size_type __n,
+#endif
                       _CharT __zero, _CharT __one)
 {
     size_t __rlen = _VSTD::min(__n, char_traits<_CharT>::length(__str));
@@ -804,7 +818,7 @@
     }
     _VSTD::fill(base::__make_iter(__i), base::__make_iter(_Size), false);
 }
-
+#ifndef _LIBCPP_FREESTANDING
 template <size_t _Size>
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
@@ -830,6 +844,7 @@
     }
     _VSTD::fill(base::__make_iter(__i), base::__make_iter(_Size), false);
 }
+#endif
 
 template <size_t _Size>
 inline
@@ -979,6 +994,7 @@
     return base::to_ullong();
 }
 
+#ifndef _LIBCPP_FREESTANDING
 template <size_t _Size>
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
@@ -1022,6 +1038,7 @@
 {
     return to_string<char, char_traits<char>, allocator<char> >(__zero, __one);
 }
+#endif
 
 template <size_t _Size>
 inline
@@ -1140,6 +1157,7 @@
         {return __bs.__hash_code();}
 };
 
+#ifndef _LIBCPP_FREESTANDING
 template <class _CharT, class _Traits, size_t _Size>
 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
 operator>>(basic_istream<_CharT, _Traits>& __is, bitset<_Size>& __x);
@@ -1147,6 +1165,7 @@
 template <class _CharT, class _Traits, size_t _Size>
 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
 operator<<(basic_ostream<_CharT, _Traits>& __os, const bitset<_Size>& __x);
+#endif
 
 _LIBCPP_END_NAMESPACE_STD
 
Index: libcxx/include/compare
===================================================================
--- libcxx/include/compare
+++ libcxx/include/compare
@@ -141,6 +141,7 @@
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
+#include <__config>
 #include <__compare/common_comparison_category.h>
 #include <__compare/compare_partial_order_fallback.h>
 #include <__compare/compare_strong_order_fallback.h>
Index: libcxx/include/cstdlib
===================================================================
--- libcxx/include/cstdlib
+++ libcxx/include/cstdlib
@@ -84,6 +84,34 @@
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if defined(_LIBCPP_FREESTANDING)
+
+// Referenced from GNU libstdc++
+#ifndef EXIT_SUCCESS
+#define EXIT_SUCCESS 0
+#endif
+#ifndef EXIT_FAILURE
+#define EXIT_FAILURE 1
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+extern "C" _LIBCPP_NORETURN void abort(void) _NOEXCEPT;
+extern "C" int atexit(void (*)(void)) _NOEXCEPT;
+extern "C" _LIBCPP_NORETURN void exit(int) _NOEXCEPT;
+#if __cplusplus >= 201103L
+extern "C" int at_quick_exit(void (*)(void)) _NOEXCEPT;
+extern "C" _LIBCPP_NORETURN void quick_exit(int) _NOEXCEPT;
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+#else
+
 #include <stdlib.h>
 
 #ifndef _LIBCPP_STDLIB_H
@@ -94,10 +122,6 @@
           not be the case.
 #endif
 
-#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#  pragma GCC system_header
-#endif
-
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 using ::size_t _LIBCPP_USING_IF_EXISTS;
@@ -149,5 +173,6 @@
 #endif
 
 _LIBCPP_END_NAMESPACE_STD
+#endif
 
 #endif // _LIBCPP_CSTDLIB
Index: libcxx/include/functional
===================================================================
--- libcxx/include/functional
+++ libcxx/include/functional
@@ -512,10 +512,14 @@
 #include <__functional/bind_front.h>
 #include <__functional/binder1st.h>
 #include <__functional/binder2nd.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <__functional/boyer_moore_searcher.h>
+#endif
 #include <__functional/compose.h>
 #include <__functional/default_searcher.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <__functional/function.h>
+#endif
 #include <__functional/hash.h>
 #include <__functional/identity.h>
 #include <__functional/invoke.h>
Index: libcxx/include/iosfwd
===================================================================
--- libcxx/include/iosfwd
+++ libcxx/include/iosfwd
@@ -96,7 +96,9 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+#ifndef _LIBCPP_FREESTANDING
 #include <__mbstate_t.h>
+#endif
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -105,7 +107,9 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+#ifndef _LIBCPP_FREESTANDING
 class _LIBCPP_TYPE_VIS ios_base;
+#endif
 
 template<class _CharT>  struct _LIBCPP_TEMPLATE_VIS char_traits;
 template<> struct char_traits<char>;
@@ -118,6 +122,8 @@
 template<> struct char_traits<wchar_t>;
 #endif
 
+
+#ifndef _LIBCPP_FREESTANDING
 template<class _Tp>     class _LIBCPP_TEMPLATE_VIS allocator;
 
 template <class _CharT, class _Traits = char_traits<_CharT> >
@@ -285,6 +291,8 @@
     }
 };
 
+#endif
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_IOSFWD
Index: libcxx/include/iterator
===================================================================
--- libcxx/include/iterator
+++ libcxx/include/iterator
@@ -693,8 +693,10 @@
 #include <__iterator/incrementable_traits.h>
 #include <__iterator/indirectly_comparable.h>
 #include <__iterator/insert_iterator.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <__iterator/istream_iterator.h>
 #include <__iterator/istreambuf_iterator.h>
+#endif
 #include <__iterator/iter_move.h>
 #include <__iterator/iter_swap.h>
 #include <__iterator/iterator.h>
@@ -703,8 +705,10 @@
 #include <__iterator/move_iterator.h>
 #include <__iterator/move_sentinel.h>
 #include <__iterator/next.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <__iterator/ostream_iterator.h>
 #include <__iterator/ostreambuf_iterator.h>
+#endif
 #include <__iterator/permutable.h>
 #include <__iterator/prev.h>
 #include <__iterator/projected.h>
Index: libcxx/include/memory
===================================================================
--- libcxx/include/memory
+++ libcxx/include/memory
@@ -866,11 +866,15 @@
 #include <__memory/align.h>
 #include <__memory/allocate_at_least.h>
 #include <__memory/allocation_guard.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <__memory/allocator.h>
+#endif
 #include <__memory/allocator_arg_t.h>
 #include <__memory/allocator_traits.h>
 #include <__memory/assume_aligned.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <__memory/auto_ptr.h>
+#endif
 #include <__memory/compressed_pair.h>
 #include <__memory/concepts.h>
 #include <__memory/construct_at.h>
@@ -878,7 +882,9 @@
 #include <__memory/ranges_construct_at.h>
 #include <__memory/ranges_uninitialized_algorithms.h>
 #include <__memory/raw_storage_iterator.h>
+#ifndef _LIBCPP_FREESTANDING
 #include <__memory/shared_ptr.h>
+#endif
 #include <__memory/temporary_buffer.h>
 #include <__memory/uninitialized_algorithms.h>
 #include <__memory/unique_ptr.h>
Index: libcxx/include/new
===================================================================
--- libcxx/include/new
+++ libcxx/include/new
@@ -330,7 +330,7 @@
 #endif
 }
 
-#if !defined(_LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION)
+#if !defined(_LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION) && !defined(_LIBCPP_FREESTANDING)
 // Low-level helpers to call the aligned allocation and deallocation functions
 // on the target platform. This is used to implement libc++'s own memory
 // allocation routines -- if you need to allocate memory inside the library,
Index: libcxx/include/numeric
===================================================================
--- libcxx/include/numeric
+++ libcxx/include/numeric
@@ -146,7 +146,9 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+#ifndef _LIBCPP_FREESTANDING
 #include <cmath> // for isnormal
+#endif
 #include <version>
 
 #include <__numeric/accumulate.h>
Index: libcxx/include/stdexcept
===================================================================
--- libcxx/include/stdexcept
+++ libcxx/include/stdexcept
@@ -43,14 +43,18 @@
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
-#include <cstdlib>
-#include <exception>
-#include <iosfwd>  // for string forward decl
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
+
+#if !defined(_LIBCPP_FREESTANDING)
+
+#include <cstdlib>
+#include <exception>
+#include <iosfwd>  // for string forward decl
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #ifndef _LIBCPP_ABI_VCRUNTIME
@@ -211,16 +215,22 @@
 };
 
 } // namespace std
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+
+#ifdef _LIBCPP_FREESTANDING
+_LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY void __throw_runtime_error(const char*){}
+#else
 // in the dylib
 _LIBCPP_NORETURN _LIBCPP_FUNC_VIS void __throw_runtime_error(const char*);
+#endif
 
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 void __throw_logic_error(const char*__msg)
 {
-#ifndef _LIBCPP_NO_EXCEPTIONS
+#if !defined(_LIBCPP_NO_EXCEPTIONS) && !defined(_LIBCPP_FREESTANDING)
     throw logic_error(__msg);
 #else
     ((void)__msg);
@@ -231,7 +241,7 @@
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 void __throw_domain_error(const char*__msg)
 {
-#ifndef _LIBCPP_NO_EXCEPTIONS
+#if !defined(_LIBCPP_NO_EXCEPTIONS) && !defined(_LIBCPP_FREESTANDING)
     throw domain_error(__msg);
 #else
     ((void)__msg);
@@ -242,7 +252,7 @@
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 void __throw_invalid_argument(const char*__msg)
 {
-#ifndef _LIBCPP_NO_EXCEPTIONS
+#if !defined(_LIBCPP_NO_EXCEPTIONS) && !defined(_LIBCPP_FREESTANDING)
     throw invalid_argument(__msg);
 #else
     ((void)__msg);
@@ -253,7 +263,7 @@
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 void __throw_length_error(const char*__msg)
 {
-#ifndef _LIBCPP_NO_EXCEPTIONS
+#if !defined(_LIBCPP_NO_EXCEPTIONS) && !defined(_LIBCPP_FREESTANDING)
     throw length_error(__msg);
 #else
     ((void)__msg);
@@ -264,7 +274,7 @@
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 void __throw_out_of_range(const char*__msg)
 {
-#ifndef _LIBCPP_NO_EXCEPTIONS
+#if !defined(_LIBCPP_NO_EXCEPTIONS) && !defined(_LIBCPP_FREESTANDING)
     throw out_of_range(__msg);
 #else
     ((void)__msg);
@@ -275,7 +285,7 @@
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 void __throw_range_error(const char*__msg)
 {
-#ifndef _LIBCPP_NO_EXCEPTIONS
+#if !defined(_LIBCPP_NO_EXCEPTIONS) && !defined(_LIBCPP_FREESTANDING)
     throw range_error(__msg);
 #else
     ((void)__msg);
@@ -286,7 +296,7 @@
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 void __throw_overflow_error(const char*__msg)
 {
-#ifndef _LIBCPP_NO_EXCEPTIONS
+#if !defined(_LIBCPP_NO_EXCEPTIONS) && !defined(_LIBCPP_FREESTANDING)
     throw overflow_error(__msg);
 #else
     ((void)__msg);
@@ -297,7 +307,7 @@
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
 void __throw_underflow_error(const char*__msg)
 {
-#ifndef _LIBCPP_NO_EXCEPTIONS
+#if !defined(_LIBCPP_NO_EXCEPTIONS) && !defined(_LIBCPP_FREESTANDING)
     throw underflow_error(__msg);
 #else
     ((void)__msg);
Index: libcxx/include/stdlib.h
===================================================================
--- libcxx/include/stdlib.h
+++ libcxx/include/stdlib.h
@@ -90,6 +90,18 @@
 #  pragma GCC system_header
 #endif
 
+#if defined(_LIBCPP_FREESTANDING)
+#include <cstdlib>
+
+using std::abort;
+using std::atexit;
+using std::exit;
+#if __cplusplus >= 201103L
+  using std::at_quick_exit;
+  using std::quick_exit;
+#endif
+
+#else
 #include_next <stdlib.h>
 
 #ifdef __cplusplus
@@ -157,5 +169,6 @@
 #endif // _LIBCPP_MSVCRT / __sun__
 } // extern "C++"
 #endif // __cplusplus
+#endif
 
 #endif // _LIBCPP_STDLIB_H
Index: libcxx/include/string.h
===================================================================
--- libcxx/include/string.h
+++ libcxx/include/string.h
@@ -56,7 +56,26 @@
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
+#ifdef _LIBCPP_FREESTANDING
 
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void* memcpy(void*,void const*,size_t);
+void* memmove(void*,void const*,size_t);
+int memcmp(void const*, void const*, size_t);
+int memset(void const*, int, size_t);
+size_t strlen(void const*);
+
+#ifdef __cplusplus
+}
+#endif
+
+
+#else
 #include_next <string.h>
 
 // MSVCRT, GNU libc and its derivates may already have the correct prototype in
@@ -105,5 +124,5 @@
       char* strstr(      char* __s1, const char* __s2) {return __libcpp_strstr(__s1, __s2);}
 }
 #endif
-
+#endif
 #endif // _LIBCPP_STRING_H
Index: libcxx/include/string_view
===================================================================
--- libcxx/include/string_view
+++ libcxx/include/string_view
@@ -950,10 +950,12 @@
 
 #endif //  _LIBCPP_STD_VER > 17
 
+#ifndef _LIBCPP_FREESTANDING
 template<class _CharT, class _Traits>
 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
 operator<<(basic_ostream<_CharT, _Traits>& __os,
            basic_string_view<_CharT, _Traits> __str);
+#endif
 
 // [string.view.hash]
 template<class _CharT>