IEEE 754-2008, 7.5 Underflow:
The underflow exception shall be signaled ...
... the underflow flag shall be raised and the inexact (see 7.6) exception shall be signaled.
Here we see that:
Simple question: is inexact flag required to be raised?
Reason of the question: as I understand: flag is raised != exception is signaled. Is that correct?
Yes.
7.6 Inexact (emphaisis added):
When all of these exceptions are handled by default, the inexact flag is always raised when either the overflow or underflow flag is raised.