Why page fault is considered as trap instead of interrupt? And what exactly is the stages take place when you try access null pointer until you get segmentation fault? and the signal which is sent in this situations I SIGILL, right? Thanks!
A trap is an exception in user-space caused by the user-space program. In this specific case the user-space program accessed a page that was not mapped using the memory management unit (MMU) and therefore caused the trap. Interrupts on the other hand are generated by external hardware events, such as a timer.