Refactor process_init_stack to add asserts and comments

src/userprog/process.c

@@ -191,6 +191,10 @@ start_process (void *proc_start_data)
 static bool
 process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
   {
+    ASSERT (cmd_saveptr != NULL);
+    ASSERT (esp != NULL);
+    ASSERT (file_name != NULL);
+
     /* Load command line argument *data* to user process stack.
        This can't cause overflow due to enforcing that the size of
        command line input must fit in a page. Also keep track
@@ -202,7 +206,10 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
     int arg_count = 0;
     while (arg != NULL)
       {
-        push_to_stack (esp, arg, (strlen (arg) + 1) * sizeof (char));
+        /* filename has already been validated to be a safe-to-access string,
+           so we can safely use strlen here. Filename has already been
+           split from the command line arguments. */
+        push_to_stack (esp, arg, strlen (arg) + 1);
         
         struct arg_elem *arg_elem = malloc (sizeof (struct arg_elem));
         if (arg_elem == NULL)