LibC: add __cxa_at_exit() for libc

libc/CMakeLists.txt

@@ -13,6 +13,7 @@ set(LIBC_SOURCES
 	termios.cpp
 	unistd.cpp
 	math.S
+	icxxabi.cpp
 )
 
 add_custom_target(libc-headers

libc/icxxabi.cpp

@@ -0,0 +1,35 @@
+#define ATEXIT_MAX_FUNCS 128
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef unsigned uarch_t;
+
+struct atexit_func_entry_t
+{
+	/*
+	* Each member is at least 4 bytes large. Such that each entry is 12bytes.
+	* 128 * 12 = 1.5KB exact.
+	**/
+	void (*destructor_func)(void *);
+	void *obj_ptr;
+	void *dso_handle;
+};
+
+atexit_func_entry_t __atexit_funcs[ATEXIT_MAX_FUNCS];
+uarch_t __atexit_func_count = 0;
+
+int __cxa_atexit(void (*f)(void *), void *objptr, void *dso)
+{
+	if (__atexit_func_count >= ATEXIT_MAX_FUNCS) {return -1;};
+	__atexit_funcs[__atexit_func_count].destructor_func = f;
+	__atexit_funcs[__atexit_func_count].obj_ptr = objptr;
+	__atexit_funcs[__atexit_func_count].dso_handle = dso;
+	__atexit_func_count++;
+	return 0; /*I would prefer if functions returned 1 on success, but the ABI says...*/
+};
+
+#ifdef __cplusplus
+};
+#endif