Index: libc/include/CMakeLists.txt
===================================================================
--- libc/include/CMakeLists.txt
+++ libc/include/CMakeLists.txt
@@ -55,6 +55,14 @@
     ../config/${LIBC_TARGET_OS}/signal.h.in
 )
 
+add_gen_header(
+  stdlib_h
+  DEF_FILE stdlib.h.def
+  GEN_HDR stdlib.h
+  DEPENDS
+    llvm_libc_common_h
+)
+
 # TODO: Not all platforms will have a include/sys directory. Add the sys
 # directory and the targets for sys/*.h files conditional to the OS requiring
 # them.
Index: libc/include/stdlib.h.def
===================================================================
--- /dev/null
+++ libc/include/stdlib.h.def
@@ -0,0 +1,16 @@
+//===---------------- C standard library header stdlib.h ------------------===//
+//
+// 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 LLVM_LIBC_STDLIB_H
+#define LLVM_LIBC_STDLIB_H
+
+#include <__llvm-libc-common.h>
+
+%%public_api()
+
+#endif // LLVM_LIBC_STDLIB_H
Index: libc/spec/stdc.td
===================================================================
--- libc/spec/stdc.td
+++ libc/spec/stdc.td
@@ -167,6 +167,16 @@
       ]
   >;
 
+  HeaderSpec StdLib = HeaderSpec<
+      "stdlib.h",
+      [], // Macros
+      [], // Types
+      [
+          FunctionSpec<"abort", RetValSpec<VoidType>, [ArgSpec<VoidType>]>,
+          FunctionSpec<"_Exit", RetValSpec<VoidType>, [ArgSpec<IntType>]>,
+      ]
+  >;
+
   HeaderSpec Errno = HeaderSpec<
       "errno.h",
       [
Index: libc/src/CMakeLists.txt
===================================================================
--- libc/src/CMakeLists.txt
+++ libc/src/CMakeLists.txt
@@ -1,6 +1,7 @@
 add_subdirectory(errno)
 add_subdirectory(math)
 add_subdirectory(signal)
+add_subdirectory(stdlib)
 add_subdirectory(string)
 # TODO: Add this target conditional to the target OS.
 add_subdirectory(sys)
Index: libc/src/stdlib/CMakeLists.txt
===================================================================
--- /dev/null
+++ libc/src/stdlib/CMakeLists.txt
@@ -0,0 +1,15 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${LIBC_TARGET_OS})
+endif()
+
+add_entrypoint_object(
+  abort
+  SRCS
+    abort.cpp
+  HDRS
+    abort.h
+  DEPENDS
+    raise
+    _Exit
+    stdlib_h
+)
Index: libc/src/stdlib/_Exit.h
===================================================================
--- /dev/null
+++ libc/src/stdlib/_Exit.h
@@ -0,0 +1,18 @@
+//===----------------- Implementation header for _Exit ---------*- 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 LLVM_LIBC_SRC__EXIT_H
+#define LLVM_LIBC_SRC__EXIT_H
+
+namespace __llvm_libc {
+
+[[noreturn]] void _Exit(int status);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC__EXIT_H
Index: libc/src/stdlib/abort.h
===================================================================
--- /dev/null
+++ libc/src/stdlib/abort.h
@@ -0,0 +1,18 @@
+//===----------------- Implementation header for abort ---------*- 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 LLVM_LIBC_SRC_ABORT_H
+#define LLVM_LIBC_SRC_ABORT_H
+
+namespace __llvm_libc {
+
+[[noreturn]] void abort();
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_ABORT_H
Index: libc/src/stdlib/abort.cpp
===================================================================
--- /dev/null
+++ libc/src/stdlib/abort.cpp
@@ -0,0 +1,24 @@
+//===---------------------- Implementation of abort -----------------------===//
+//
+// 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/__support/common.h"
+#include "src/signal/raise.h"
+#include "src/stdlib/_Exit.h"
+
+#include "src/stdlib/abort.h"
+
+namespace __llvm_libc {
+
+void LLVM_LIBC_ENTRYPOINT(abort)() {
+  // TODO: when sigaction(3) is implemented make sure SIGABRT is SIG_DFL.
+  __llvm_libc::raise(SIGABRT);
+  __llvm_libc::raise(SIGKILL);
+  __llvm_libc::_Exit(127);
+}
+
+} // namespace __llvm_libc
Index: libc/src/stdlib/linux/CMakeLists.txt
===================================================================
--- /dev/null
+++ libc/src/stdlib/linux/CMakeLists.txt
@@ -0,0 +1,11 @@
+add_entrypoint_object(
+  _Exit
+  SRCS
+    _Exit.cpp
+  HDRS
+    ../_Exit.h
+  DEPENDS
+    sys_syscall_h
+    linux_syscall_h
+    stdlib_h
+)
Index: libc/src/stdlib/linux/_Exit.cpp
===================================================================
--- /dev/null
+++ libc/src/stdlib/linux/_Exit.cpp
@@ -0,0 +1,24 @@
+//===------------------- Linux Implementation of _Exit --------------------===//
+//
+// 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 "config/linux/syscall.h" // For internal syscall function.
+#include "include/sys/syscall.h"  // For syscall numbers.
+#include "src/__support/common.h"
+
+#include "src/stdlib/_Exit.h"
+
+namespace __llvm_libc {
+
+void LLVM_LIBC_ENTRYPOINT(_Exit)(int status) {
+  for (;;) {
+    __llvm_libc::syscall(SYS_exit_group, status);
+    __llvm_libc::syscall(SYS_exit, status);
+  }
+}
+
+} // namespace __llvm_libc