A signal handler is allowed to call signal(), and if that fails, signal() returns SIG_ERR and sets errno to a positive value. However, if the event that caused a signal was external (not as the result of the program calling abort() or raise()), the only functions the signal handler must only may call are _Exit() or abort(), or call signal() on the signal currently being handled, and if signal() fails, the value of errno is indeterminate.
...