Index: libc/config/linux/x86_64/entrypoints.txt
===================================================================
--- libc/config/linux/x86_64/entrypoints.txt
+++ libc/config/linux/x86_64/entrypoints.txt
@@ -216,6 +216,8 @@
     # stdlib.h entrypoints
     libc.src.stdlib._Exit
     # libc.src.stdlib.abort
+    libc.src.stdlib.atexit
+    libc.src.stdlib.exit
 
     # signal.h entrypoints
     # TODO: Enable signal.h entrypoints after fixing signal.h
Index: libc/src/stdlib/CMakeLists.txt
===================================================================
--- libc/src/stdlib/CMakeLists.txt
+++ libc/src/stdlib/CMakeLists.txt
@@ -248,6 +248,34 @@
     .${LIBC_TARGET_OS}._Exit
 )
 
+if(LLVM_LIBC_INCLUDE_SCUDO OR NOT LLVM_LIBC_FULL_BUILD)
+  set(vector_dep libc.src.__support.CPP.vector)
+  add_compile_definitions(LLVM_LIBC_HAS_MALLOC=1)
+else()
+  set(vector_dep "")
+endif()
+
+add_entrypoint_object(
+  atexit
+  SRCS
+    atexit.cpp
+  HDRS
+    atexit.h
+  DEPENDS
+    ${vector_dep}
+)
+
+add_entrypoint_object(
+  exit
+  SRCS
+    exit.cpp
+  HDRS
+    exit.h
+  DEPENDS
+    ._Exit
+    .atexit
+)
+
 # add_entrypoint_object(
 #   abort
 #   ALIAS
Index: libc/src/stdlib/atexit.h
===================================================================
--- /dev/null
+++ libc/src/stdlib/atexit.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for atexit ------------------------*- 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_STDLIB_ATEXIT_H
+#define LLVM_LIBC_SRC_STDLIB_ATEXIT_H
+
+namespace __llvm_libc {
+
+void atexit(void (*function)());
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDLIB_ATEXIT_H
Index: libc/src/stdlib/atexit.cpp
===================================================================
--- /dev/null
+++ libc/src/stdlib/atexit.cpp
@@ -0,0 +1,58 @@
+//===-- Implementation of atexit ------------------------------------------===//
+//
+// 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/stdlib/atexit.h"
+#include "src/__support/common.h"
+
+#ifdef LLVM_LIBC_HAS_MALLOC
+#include "src/__support/CPP/vector.h"
+#endif
+
+namespace __llvm_libc {
+
+namespace {
+
+// TOOD should we make cpp::vector like llvm::SmallVector<T, N> where it will
+// allocate at least N before needing dynamic allocation?
+#ifdef LLVM_LIBC_HAS_MALLOC
+static cpp::vector<void (*)(void)> handlers;
+#else
+struct {
+  // POSIX requries at least 32 handlers be possible.
+  void (*arr[32])(void);
+  unsigned arr_size = 0;
+
+  unsigned size() const { return arr_size; }
+
+  decltype(*arr) operator[](unsigned i) { return arr[i]; }
+
+  void push_back(void (*func)()) {
+    if (arr_size == 32)
+      return;
+    arr[arr_size++] = func;
+  }
+} handlers;
+#endif
+
+} // namespace
+
+namespace internal {
+
+void call_exit_handlers() {
+  // TODO: implement rbegin() + rend() for cpp::vector
+  for (int i = handlers.size() - 1; i >= 0; i--)
+    handlers[i]();
+}
+
+} // namespace internal
+
+LLVM_LIBC_FUNCTION(void, atexit, (void (*function)(void))) {
+  handlers.push_back(function);
+}
+
+} // namespace __llvm_libc
Index: libc/src/stdlib/exit.h
===================================================================
--- /dev/null
+++ libc/src/stdlib/exit.h
@@ -0,0 +1,20 @@
+//===-- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <stdlib.h>
+
+#ifndef LLVM_LIBC_SRC_STDLIB_EXIT_H
+#define LLVM_LIBC_SRC_STDLIB_EXIT_H
+
+namespace __llvm_libc {
+
+void exit(int status);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDLIB_EXIT_H
Index: libc/src/stdlib/exit.cpp
===================================================================
--- /dev/null
+++ libc/src/stdlib/exit.cpp
@@ -0,0 +1,24 @@
+//===-- 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 "src/stdlib/exit.h"
+#include "src/__support/common.h"
+#include "src/stdlib/_Exit.h"
+
+namespace __llvm_libc {
+
+namespace internal {
+void call_exit_handlers();
+}
+
+LLVM_LIBC_FUNCTION(void, exit, (int status)) {
+  internal::call_exit_handlers();
+  _Exit(status);
+}
+
+} // namespace __llvm_libc
Index: libc/test/src/stdlib/CMakeLists.txt
===================================================================
--- libc/test/src/stdlib/CMakeLists.txt
+++ libc/test/src/stdlib/CMakeLists.txt
@@ -110,35 +110,6 @@
     libc.src.stdlib.strtoull
 )
 
-if(NOT LLVM_LIBC_FULL_BUILD)
-  return()
-endif()
-
-add_libc_unittest(
-  _Exit_test
-  SUITE
-    libc_stdlib_unittests
-  SRCS
-    _Exit_test.cpp
-  DEPENDS
-    libc.include.stdlib
-    libc.src.stdlib._Exit
-)
-
-# add_libc_unittest(
-#   abort_test
-#   SUITE
-#     libc_stdlib_unittests
-#   SRCS
-#     abort_test.cpp
-#   DEPENDS
-#     libc.include.stdlib
-#     libc.include.signal
-#     libc.src.stdlib.abort
-#     libc.src.stdlib._Exit
-#     libc.src.signal.raise
-# )
-
 add_libc_unittest(
   abs_test
   SUITE
@@ -229,3 +200,51 @@
     libc.include.stdlib
     libc.src.stdlib.qsort
 )
+
+if(NOT LLVM_LIBC_FULL_BUILD)
+  return()
+endif()
+
+add_libc_unittest(
+  _Exit_test
+  SUITE
+    libc_stdlib_unittests
+  SRCS
+    _Exit_test.cpp
+  DEPENDS
+    libc.include.stdlib
+    libc.src.stdlib._Exit
+    libc.src.stdlib.exit
+)
+
+if(LLVM_LIBC_INCLUDE_SCUDO OR NOT LLVM_LIBC_FULL_BUILD)
+  add_compile_definitions(LLVM_LIBC_HAS_MALLOC=1)
+endif()
+
+add_libc_unittest(
+  atexit_test
+  SUITE
+    libc_stdlib_unittests
+  SRCS
+    atexit_test.cpp
+  DEPENDS
+    libc.include.stdlib
+    libc.src.stdlib._Exit
+    libc.src.stdlib.exit
+    libc.src.stdlib.atexit
+    libc.src.__support.CPP.standalone_cpp
+)
+
+# add_libc_unittest(
+#   abort_test
+#   SUITE
+#     libc_stdlib_unittests
+#   SRCS
+#     abort_test.cpp
+#   DEPENDS
+#     libc.include.stdlib
+#     libc.include.signal
+#     libc.src.stdlib.abort
+#     libc.src.stdlib._Exit
+#     libc.src.signal.raise
+# )
Index: libc/test/src/stdlib/_Exit_test.cpp
===================================================================
--- libc/test/src/stdlib/_Exit_test.cpp
+++ libc/test/src/stdlib/_Exit_test.cpp
@@ -8,9 +8,13 @@
 
 #include "include/stdlib.h"
 #include "src/stdlib/_Exit.h"
+#include "src/stdlib/exit.h"
 #include "utils/UnitTest/Test.h"
 
 TEST(LlvmLibcStdlib, _Exit) {
   EXPECT_EXITS([] { __llvm_libc::_Exit(1); }, 1);
   EXPECT_EXITS([] { __llvm_libc::_Exit(65); }, 65);
+
+  EXPECT_EXITS([] { __llvm_libc::exit(1); }, 1);
+  EXPECT_EXITS([] { __llvm_libc::exit(65); }, 65);
 }
Index: libc/test/src/stdlib/atexit_test.cpp
===================================================================
--- /dev/null
+++ libc/test/src/stdlib/atexit_test.cpp
@@ -0,0 +1,81 @@
+//===-- Unittests for atexit ----------------------------------------------===//
+//
+// 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/CPP/Array.h"
+#include "src/__support/CPP/Utility.h"
+#include "src/stdlib/atexit.h"
+#include "src/stdlib/exit.h"
+#include "utils/UnitTest/Test.h"
+
+static int a;
+TEST(LlvmLibcAtExit, Basic) {
+  // In case tests ever run multiple times.
+  a = 0;
+
+  auto test = [] {
+    __llvm_libc::atexit(+[] {
+      if (a != 1)
+        __builtin_trap();
+    });
+    __llvm_libc::atexit(+[] { a++; });
+
+    __llvm_libc::exit(0);
+  };
+  EXPECT_EXITS(test, 0);
+}
+
+TEST(LlvmLibcAtExit, AtExitCallsSysExit) {
+  auto test = [] {
+    __llvm_libc::atexit(+[] { _Exit(1); });
+    __llvm_libc::exit(0);
+  };
+  EXPECT_EXITS(test, 1);
+}
+
+static int size;
+static __llvm_libc::cpp::Array<int, 256> arr;
+
+template <int... Ts>
+void register_atexit_handlers(__llvm_libc::cpp::IntegerSequence<int, Ts...>) {
+  (__llvm_libc::atexit(+[] { arr[size++] = Ts; }), ...);
+}
+
+template <int count> constexpr auto getTest() {
+  return [] {
+    __llvm_libc::atexit(+[] {
+      if (size != count)
+        __builtin_trap();
+      for (int i = 0; i < count; i++)
+        if (arr[i] != count - 1 - i)
+          __builtin_trap();
+    });
+    register_atexit_handlers(
+        __llvm_libc::cpp::MakeIntegerSequence<int, count>{});
+    __llvm_libc::exit(0);
+  };
+}
+
+TEST(LlvmLibcAtExit, ReverseOrder) {
+  // In case tests ever run multiple times.
+  size = 0;
+
+  auto test = getTest<32>();
+  EXPECT_EXITS(test, 0);
+}
+
+#ifdef LLVM_LIBC_HAS_MALLOC
+
+TEST(LlvmLibcAtExit, Many) {
+  // In case tests ever run multiple times.
+  size = 0;
+
+  auto test = getTest<256>();
+  EXPECT_EXITS(test, 0);
+}
+
+#endif