-extern int environment_add(environment_t *env, const char *format, ...);
-extern void environment_update(environment_t *env, int pos, const char *format, ...);
+extern int environment_add(environment_t *env, const char *format, ...) ATTR_FORMAT(printf, 2, 3);
+extern void environment_update(environment_t *env, int pos, const char *format, ...) ATTR_FORMAT(printf, 3, 4);