libc.obj: add atexit and normal exit. add exit code save/read

programs/develop/ktcc/trunk/libc.obj/source/stdlib/atexit.c

@@ -0,0 +1,35 @@
+#include <stdlib.h>
+
+struct atexit_n {
+    struct atexit_n* last;
+    void (*func)(void);
+};
+
+static struct atexit_n* __last_n = NULL;
+
+int atexit(void (*func)(void))
+{
+    struct atexit_n* n = malloc(sizeof(struct atexit_n));
+
+    if (n == NULL) {
+        return 1;
+    }
+
+    n->last = __last_n;
+    n->func = func;
+
+    __last_n = n;
+
+    return 0;
+}
+
+void __run_atexit()
+{
+    struct atexit_n* n = __last_n;
+    while (n != NULL) {
+        n->func();
+        struct atexit_n* to_free = n;
+        n = n->last;
+        free(to_free);
+    }
+}