Index: libc/cmake/modules/LLVMLibCObjectRules.cmake
===================================================================
--- libc/cmake/modules/LLVMLibCObjectRules.cmake
+++ libc/cmake/modules/LLVMLibCObjectRules.cmake
@@ -161,7 +161,7 @@
     ${objects_target_name}
     BEFORE
     PRIVATE
-      -fpie ${LLVM_CXX_STD_default} -ffreestanding
+      -fpie ${LLVM_CXX_STD_default} -ffreestanding -nostdinc++
   )
   target_include_directories(
     ${objects_target_name}
@@ -199,6 +199,16 @@
     set(alias_attributes "${alias_attributes},hidden")
   endif()
 
+  if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
+    add_custom_command(
+    OUTPUT ${object_file}
+    DEPENDS ${object_file_raw}
+    COMMAND ${CMAKE_COMMAND} -E copy
+            ${object_file_raw}
+            ${object_file}
+                )
+  else()
+
   add_custom_command(
     OUTPUT ${object_file}
     # We llvm-objcopy here as GNU-binutils objcopy does not support the 'hidden' flag.
@@ -208,6 +218,8 @@
             ${object_file_raw} ${object_file}
   )
 
+  endif()
+
   add_custom_target(
     ${fq_target_name}
     ALL
Index: libc/config/CMakeLists.txt
===================================================================
--- libc/config/CMakeLists.txt
+++ libc/config/CMakeLists.txt
@@ -1 +1,2 @@
 add_subdirectory(linux)
+add_subdirectory(darwin)
Index: libc/config/darwin/CMakeLists.txt
===================================================================
--- /dev/null
+++ libc/config/darwin/CMakeLists.txt
@@ -0,0 +1 @@
+
Index: libc/config/darwin/api.td
===================================================================
--- /dev/null
+++ libc/config/darwin/api.td
@@ -0,0 +1,157 @@
+include "config/public_api.td"
+
+include "spec/gnu_ext.td"
+include "spec/llvm_libc_ext.td"
+include "spec/stdc.td"
+
+def SizeT : TypeDecl<"size_t"> {
+  let Decl = [{
+    #define __need_size_t
+    #include <stddef.h>
+  }];
+}
+
+def NullMacro : MacroDef<"NULL"> {
+  let Defn = [{
+    #define __need_NULL
+    #include <stddef.h>
+  }];
+}
+
+def ErrnoMacro : MacroDef<"errno"> {
+  let Defn = [{
+    #ifdef __cplusplus
+    extern "C"
+    #endif
+    int *__errno_location();
+    #define errno (*__errno_location())
+  }];
+}
+
+def MathErrHandlingMacro : MacroDef<"math_errhandling"> {
+  let Defn = [{
+    #ifndef math_errhandling
+    #ifdef __FAST_MATH__
+    #define math_errhandling 0
+    #elif defined __NO_MATH_ERRNO__
+    #define math_errhandling (MATH_ERREXCEPT)
+    #else
+    #define math_errhandling (MATH_ERRNO | MATH_ERREXCEPT)
+    #endif
+    #endif // math_errhandling not defined
+  }];
+}
+
+def IsFiniteMacro : MacroDef<"isfinite"> {
+  let Defn = [{
+    #define isfinite(x) __builtin_isfinite(x)
+  }];
+}
+
+def IsInfMacro : MacroDef<"isinf"> {
+  let Defn = [{
+    #define isinf(x) __builtin_isinf(x)
+  }];
+}
+
+def IsNanMacro : MacroDef<"isnan"> {
+  let Defn = [{
+    #define isnan(x) __builtin_isnan(x)
+  }];
+}
+
+def FloatT : TypeDecl<"float_t"> {
+  let Decl = [{
+    #define __need_float_t
+    #include <__llvm-libc-stdc-types.h>
+  }];
+}
+
+def DoubleT : TypeDecl<"double_t"> {
+  let Decl = [{
+    #define __need_double_t
+    #include <__llvm-libc-stdc-types.h>
+  }];
+}
+
+def MathAPI : PublicAPI<"math.h"> {
+  let Macros = [
+    SimpleMacroDef<"MATH_ERRNO", "1">,
+    SimpleMacroDef<"MATH_ERREXCEPT", "2">,
+    MathErrHandlingMacro,
+
+    SimpleMacroDef<"INFINITY", "__builtin_inff()">,
+    SimpleMacroDef<"NAN", "__builtin_nanf(\"\")">,
+
+    IsFiniteMacro,
+    IsInfMacro,
+    IsNanMacro,
+  ];
+  let TypeDeclarations = [
+    DoubleT,
+    FloatT,
+  ];
+  let Functions = [
+   "copysign",
+   "copysignf",
+   "ceil",
+   "ceilf",
+   "cosf",
+   "fabs",
+   "fabsf",
+   "fabsl",
+   "floor",
+   "floorf",
+   "frexp",
+   "frexpf",
+   "logb",
+   "logbf",
+   "modf",
+   "modff",
+   "expf",
+   "exp2f",
+   "round",
+   "roundf",
+   "sincosf",
+   "sinf",
+   "trunc",
+   "truncf",
+   "truncl",
+  ];
+}
+
+def StringAPI : PublicAPI<"string.h"> {
+  let Functions = [
+    "bzero",
+    "memcpy",
+    "memmove",
+    "memcmp",
+    "memchr",
+    "memset",
+    "strcpy",
+    "strncpy",
+    "strcat",
+    "strncat",
+    "strcmp",
+    "strcoll",
+    "strncmp",
+    "strxfrm",
+    "strchr",
+    "strcspn",
+    "strpbrk",
+    "strrchr",
+    "strspn",
+    "strstr",
+    "strtok",
+    "strerror",
+    "strlen",
+  ];
+
+  let TypeDeclarations = [
+    SizeT,
+  ];
+
+  let Macros = [
+    NullMacro,
+  ];
+}
Index: libc/config/darwin/platfrom_defs.h.inc
===================================================================
--- /dev/null
+++ libc/config/darwin/platfrom_defs.h.inc
@@ -0,0 +1,19 @@
+//===----- Definition of platform specific macros for Mach-O platforms -------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+%%begin()
+
+#define LLVM_LIBC_ALIAS(_ret_type, _name, _arglist, ...) \
+  extern "C" {                                           \
+    _ret_type _name(__VA_ARGS__) {                       \
+      return __llvm_libc::_name _arglist ;               \
+    }                                                    \
+}
+
+#define LLVM_LIBC_ENTRYPOINT(name) name
+
Index: libc/config/darwin/x86_64/entrypoints.txt
===================================================================
--- /dev/null
+++ libc/config/darwin/x86_64/entrypoints.txt
@@ -0,0 +1,41 @@
+set(TARGET_LIBC_ENTRYPOINTS
+    # errno.h entrypoints
+    libc.src.errno.__errno_location
+
+    # string.h entrypoints
+    libc.src.string.bzero
+    libc.src.string.memcpy
+    libc.src.string.memset
+    libc.src.string.strcpy
+    libc.src.string.strcat
+    libc.src.string.strlen
+)
+
+set(TARGET_LIBM_ENTRYPOINTS
+    # math.h entrypoints
+    libc.src.math.copysign
+    libc.src.math.copysignf
+    libc.src.math.ceil
+    libc.src.math.ceilf
+    libc.src.math.cosf
+    libc.src.math.expf
+    libc.src.math.exp2f
+    libc.src.math.fabs
+    libc.src.math.fabsf
+    libc.src.math.fabsl
+    libc.src.math.floor
+    libc.src.math.floorf
+    libc.src.math.frexp
+    libc.src.math.frexpf
+    libc.src.math.logb
+    libc.src.math.logbf
+    libc.src.math.modf
+    libc.src.math.modff
+    libc.src.math.round
+    libc.src.math.roundf
+    libc.src.math.sincosf
+    libc.src.math.sinf
+    libc.src.math.trunc
+    libc.src.math.truncf
+    libc.src.math.truncl
+)
Index: libc/config/darwin/x86_64/headers.txt
===================================================================
--- /dev/null
+++ libc/config/darwin/x86_64/headers.txt
@@ -0,0 +1,6 @@
+set(PUBLIC_HEADERS
+    libc.include.errno
+    libc.include.math
+    libc.include.sys_syscall
+)
+
Index: libc/config/linux/platfrom_defs.h.inc
===================================================================
--- libc/config/linux/platfrom_defs.h.inc
+++ libc/config/linux/platfrom_defs.h.inc
@@ -1,4 +1,4 @@
-//===----- Definition of platform specific macros for ELF paltforms -------===//
+//===----- Definition of platform specific macros for ELF platforms -------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
Index: libc/src/string/bzero.h
===================================================================
--- libc/src/string/bzero.h
+++ libc/src/string/bzero.h
@@ -10,6 +10,7 @@
 #define LLVM_LIBC_SRC_STRING_BZERO_H
 
 #include "include/string.h"
+#include <stddef.h> // size_t
 
 namespace __llvm_libc {
 
Index: libc/src/string/bzero.cpp
===================================================================
--- libc/src/string/bzero.cpp
+++ libc/src/string/bzero.cpp
@@ -10,6 +10,8 @@
 #include "src/__support/common.h"
 #include "src/string/memory_utils/memset_utils.h"
 
+LLVM_LIBC_ALIAS(void, bzero, (ptr, count), void* ptr, size_t count); // NOLINT
+
 namespace __llvm_libc {
 
 void LLVM_LIBC_ENTRYPOINT(bzero)(void *ptr, size_t count) {
Index: libc/src/string/memset.h
===================================================================
--- libc/src/string/memset.h
+++ libc/src/string/memset.h
@@ -10,6 +10,7 @@
 #define LLVM_LIBC_SRC_STRING_MEMSET_H
 
 #include "include/string.h"
+#include <stddef.h> // size_t
 
 namespace __llvm_libc {
 
Index: libc/src/string/strlen.h
===================================================================
--- libc/src/string/strlen.h
+++ libc/src/string/strlen.h
@@ -10,6 +10,7 @@
 #define LLVM_LIBC_SRC_STRING_STRLEN_H
 
 #include "include/string.h"
+#include <stddef.h> // size_t
 
 namespace __llvm_libc {
 
Index: libc/src/string/strlen.cpp
===================================================================
--- libc/src/string/strlen.cpp
+++ libc/src/string/strlen.cpp
@@ -9,6 +9,9 @@
 #include "src/string/strlen.h"
 
 #include "src/__support/common.h"
+#include <stddef.h> // size_t
+
+LLVM_LIBC_ALIAS(size_t, strlen, (src), const char* src); // NOLINT
 
 namespace __llvm_libc {
 
Index: libc/test/config/darwin/CMakeLists.txt
===================================================================
--- /dev/null
+++ libc/test/config/darwin/CMakeLists.txt
@@ -0,0 +1,5 @@
+add_libc_testsuite(libc_darwin_tests)
+
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_MACHINE})
+  add_subdirectory(${LIBC_TARGET_MACHINE})
+endif()
Index: libc/test/config/darwin/x86_64/CMakeLists.txt
===================================================================
--- /dev/null
+++ libc/test/config/darwin/x86_64/CMakeLists.txt
@@ -0,0 +1,9 @@
+add_libc_unittest(
+  libc_darwin_x86_64_strlen_test
+  SUITE
+    libc_darwin_tests
+  SRCS
+    darwin.cpp
+  DEPENDS
+    libc.src.string.strlen
+)
Index: libc/test/config/darwin/x86_64/darwin.cpp
===================================================================
--- /dev/null
+++ libc/test/config/darwin/x86_64/darwin.cpp
@@ -0,0 +1,24 @@
+//===-- Unittests for strlen          -------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/string/strlen.h"
+#include "utils/UnitTest/Test.h"
+
+TEST(StrLenTest, EmptyString) {
+  const char *empty = "";
+
+  size_t result = __llvm_libc::strlen(empty);
+  ASSERT_EQ((size_t)0, result);
+}
+
+TEST(StrLenTest, AnyString) {
+  const char *any = "Hello World!";
+
+  size_t result = __llvm_libc::strlen(any);
+  ASSERT_EQ((size_t)12, result);
+}