diff --git a/libc/stdlib/atexit.c b/libc/stdlib/atexit.c
new file mode 100644
index 0000000..97eac4a
--- /dev/null
+++ b/libc/stdlib/atexit.c
@@ -0,0 +1,133 @@
+/*	$OpenBSD: atexit.c,v 1.12 2006/02/22 07:16:32 otto Exp $ */
+/*
+ * Copyright (c) 2002 Daniel Hartmeier
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *    - Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *    - Redistributions in binary form must reproduce the above
+ *      copyright notice, this list of conditions and the following
+ *      disclaimer in the documentation and/or other materials provided
+ *      with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include "atexit.h"
+#include "thread_private.h"
+
+int __atexit_invalid = 1;
+struct atexit *__atexit;
+
+/*
+ * Function pointers are stored in a linked list of pages. The list
+ * is initially empty, and pages are allocated on demand. The first
+ * function pointer in the first allocated page (the last one in
+ * the linked list) is reserved for the cleanup function.
+ *
+ * Outside the following two functions, all pages are mprotect()'ed
+ * to prevent unintentional/malicious corruption.
+ */
+
+/*
+ * Register a function to be performed at exit.
+ */
+int
+atexit(void (*fn)(void))
+{
+	struct atexit *p;
+	int pgsize = getpagesize();
+	int ret = -1;
+
+	if (pgsize < (int)sizeof(*p))
+		return (-1);
+	_ATEXIT_LOCK();
+	p = __atexit;
+	if (p != NULL) {
+		if (p->ind + 1 >= p->max)
+			p = NULL;
+		else if (mprotect(p, pgsize, PROT_READ | PROT_WRITE))
+			goto unlock;
+	}
+	if (p == NULL) {
+		p = mmap(NULL, pgsize, PROT_READ | PROT_WRITE,
+		    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+		if (p == MAP_FAILED)
+			goto unlock;
+		if (__atexit == NULL) {
+			p->fns[0] = NULL;
+			p->ind = 1;
+		} else
+			p->ind = 0;
+		p->max = (pgsize - ((char *)&p->fns[0] - (char *)p)) /
+		    sizeof(p->fns[0]);
+		p->next = __atexit;
+		__atexit = p;
+		if (__atexit_invalid)
+			__atexit_invalid = 0;
+	}
+	p->fns[p->ind++] = fn;
+	if (mprotect(p, pgsize, PROT_READ))
+		goto unlock;
+	ret = 0;
+unlock:
+	_ATEXIT_UNLOCK();
+	return (ret);
+}
+
+/*
+ * Register the cleanup function
+ */
+void
+__atexit_register_cleanup(void (*fn)(void))
+{
+	struct atexit *p;
+	int pgsize = getpagesize();
+
+	if (pgsize < (int)sizeof(*p))
+		return;
+	_ATEXIT_LOCK();
+	p = __atexit;
+	while (p != NULL && p->next != NULL)
+		p = p->next;
+	if (p == NULL) {
+		p = mmap(NULL, pgsize, PROT_READ | PROT_WRITE,
+		    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+		if (p == MAP_FAILED)
+			goto unlock;
+		p->ind = 1;
+		p->max = (pgsize - ((char *)&p->fns[0] - (char *)p)) /
+		    sizeof(p->fns[0]);
+		p->next = NULL;
+		__atexit = p;
+		if (__atexit_invalid)
+			__atexit_invalid = 0;
+	} else {
+		if (mprotect(p, pgsize, PROT_READ | PROT_WRITE))
+			goto unlock;
+	}
+	p->fns[0] = fn;
+	mprotect(p, pgsize, PROT_READ);
+unlock:
+	_ATEXIT_UNLOCK();
+}