diff --git a/apps/app.c b/apps/app.c
index 4f1419f1..30759530 100644
--- a/apps/app.c
+++ b/apps/app.c
@@ -1,9 +1,16 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+void bye()
+{
+    console_print("byeee!\n");
+}
+
 int main()
 {
-    for (int i = 0; i < strtol("010", NULL, 0); i++) { console_print("."); }
+    atexit(bye);
+
+    for (int i = 0; i < atoi("8"); i++) { console_print("."); }
 
     console_print("\n");
 }
diff --git a/libc/CMakeLists.txt b/libc/CMakeLists.txt
index cb407399..331380c0 100644
--- a/libc/CMakeLists.txt
+++ b/libc/CMakeLists.txt
@@ -7,6 +7,7 @@ set(SOURCES
     src/unistd.cpp
     src/errno.cpp
     src/string.cpp
+    src/atexit.cpp
 )
 
 if(${ARCH} STREQUAL "x86_64")
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index 7e6a0f56..736c2f93 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -1,21 +1,26 @@
+/* stdlib.h: General utilities header. */
+
 #ifndef _STDLIB_H
 #define _STDLIB_H
 
 #include <bits/attrs.h>
 #include <stddef.h>
 
+/* The result of a division operation on two integers. */
 typedef struct
 {
     int quot;
     int rem;
 } div_t;
 
+/* The result of a division operation on two long integers. */
 typedef struct
 {
     long quot;
     long rem;
 } ldiv_t;
 
+/* The result of a division operation on two long long integers. */
 typedef struct
 {
     long long quot;
@@ -27,12 +32,22 @@ extern "C"
 {
 #endif
 
-    int abs(int);
-    long labs(long);
-    long long llabs(long long);
+    /* Returns the absolute value of v. */
+    int abs(int v);
 
-    div_t div(int, int);
+    /* Returns the absolute value of v. */
+    long labs(long v);
+
+    /* Returns the absolute value of v. */
+    long long llabs(long long v);
+
+    /* Returns the result of dividing num by den, including the remainder. */
+    div_t div(int num, int den);
+
+    /* Returns the result of dividing num by den, including the remainder. */
     ldiv_t ldiv(long, long);
+
+    /* Returns the result of dividing num by den, including the remainder. */
     lldiv_t lldiv(long long, long long);
 
     void* malloc(size_t);
@@ -40,25 +55,42 @@ extern "C"
     void* realloc(void*, size_t);
     void free(void*);
 
+    /* Aborts the program without performing any normal cleanup. */
     __noreturn void abort();
-    int atexit(void (*)(void));
 
-    int atoi(const char*);
-    long atol(const char*);
-    long long atoll(const char*);
+    /* Registers a handler to be run at normal program termination. */
+    int atexit(void (*func)(void));
+
+    /* Parses a decimal integer from the provided string. */
+    int atoi(const char* s);
+
+    /* Parses a decimal integer from the provided string. */
+    long atol(const char* s);
+
+    /* Parses a decimal integer from the provided string. */
+    long long atoll(const char* s);
 
     double atof(const char*);
 
     double strtod(const char*, char**);
 
-    long strtol(const char*, char**, int);
-    unsigned long strtoul(const char*, char**, int);
+    /* Parses an integer of the specified base from the string str, storing the first non-number character in endptr if
+     * nonnull. */
+    long strtol(const char* str, char** endptr, int base);
+
+    /* Parses an unsigned integer of the specified base from the string str, storing the first non-number character in
+     * endptr if nonnull. */
+    unsigned long strtoul(const char* str, char** endptr, int base);
 
     int rand();
     void srand(int);
 
+    /* Exits the program normally, performing any registered cleanup actions. */
     __noreturn void exit(int);
 
+    /* Exits the program abnormally, without performing any registered cleanup actions. */
+    __noreturn void _Exit(int);
+
     int system(const char*);
 
     char* getenv(const char*);
diff --git a/libc/src/atexit.cpp b/libc/src/atexit.cpp
new file mode 100644
index 00000000..94f86e08
--- /dev/null
+++ b/libc/src/atexit.cpp
@@ -0,0 +1,28 @@
+#include <stdlib.h>
+
+typedef void (*atexit_func_t)(void);
+
+const int ATEXIT_MAX_FUNCS = 48;
+
+int atexit_registered_funcs = 0;
+
+atexit_func_t atexit_funcs[ATEXIT_MAX_FUNCS];
+
+extern "C"
+{
+    int atexit(atexit_func_t func)
+    {
+        if (atexit_registered_funcs == ATEXIT_MAX_FUNCS) return -1;
+
+        atexit_funcs[atexit_registered_funcs++] = func;
+
+        return 0;
+    }
+
+    __noreturn void exit(int status)
+    {
+        while (atexit_registered_funcs--) { atexit_funcs[atexit_registered_funcs](); }
+
+        _Exit(status);
+    }
+}
diff --git a/libc/src/stdlib.cpp b/libc/src/stdlib.cpp
index 87fb244d..12f338a4 100644
--- a/libc/src/stdlib.cpp
+++ b/libc/src/stdlib.cpp
@@ -1,19 +1,91 @@
+#include <limits.h>
 #include <luna/NumberParsing.h>
 #include <stdlib.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
+template <typename ArgT, typename ResultT> static inline ResultT __generic_div(ArgT a, ArgT b)
+{
+    ResultT result;
+    result.quot = a / b;
+    result.rem = a % b;
+
+    if (a >= 0 && result.rem < 0)
+    {
+        result.quot++;
+        result.rem -= b;
+    }
+
+    return result;
+}
+
 extern "C"
 {
-    // FIXME: Check for overflow in both strtol() and strtoul().
+    int abs(int v)
+    {
+        return __builtin_abs(v);
+    }
+
+    long labs(long v)
+    {
+        return __builtin_labs(v);
+    }
+
+    long long llabs(long long v)
+    {
+        return __builtin_llabs(v);
+    }
+
+    div_t div(int num, int den)
+    {
+        return __generic_div<int, div_t>(num, den);
+    }
+
+    ldiv_t ldiv(long num, long den)
+    {
+        return __generic_div<long, ldiv_t>(num, den);
+    }
+
+    lldiv_t lldiv(long long num, long long den)
+    {
+        return __generic_div<long long, lldiv_t>(num, den);
+    }
+
+    int atoi(const char* s)
+    {
+        return (int)strtol(s, NULL, 10);
+    }
+
+    long atol(const char* s)
+    {
+        return strtol(s, NULL, 10);
+    }
+
+    // Assuming LP64, long long == long.
+    long long atoll(const char* s)
+    {
+        return (long long)strtol(s, NULL, 10);
+    }
+
+    // These checks are only necessary on LLP64 platforms, where long won't match size_t/ssize_t. Probably redundant
+    // then (since Luna follows the regular LP64 model), but oh well...
     long strtol(const char* str, char** endptr, int base)
     {
-        return (long)parse_signed_integer(str, const_cast<const char**>(endptr), base);
+        isize rc = parse_signed_integer(str, const_cast<const char**>(endptr), base);
+
+        if (rc > (isize)LONG_MAX) return LONG_MAX;
+        if (rc < (isize)LONG_MIN) return LONG_MIN;
+
+        return rc;
     }
 
     unsigned long strtoul(const char* str, char** endptr, int base)
     {
-        return (unsigned long)parse_unsigned_integer(str, const_cast<const char**>(endptr), base);
+        usize rc = parse_unsigned_integer(str, const_cast<const char**>(endptr), base);
+
+        if (rc > (usize)ULONG_MAX) return ULONG_MAX;
+
+        return rc;
     }
 
     __noreturn void abort()
@@ -22,7 +94,7 @@ extern "C"
         __builtin_unreachable();
     }
 
-    __noreturn void exit(int)
+    __noreturn void _Exit(int)
     {
         syscall(SYS_exit);
         __builtin_unreachable();