Originally Posted by
matsp
It is, technically, NOT unblockable. However, the "block" is a "oneshot", so it will automatically unblock the signal when you receive the first one, and the way almost all processors work on these type of faults is to set the return address such that it retries the failing instruction, so whilst it it possible to block the signal on the first attempt, very soon after (like nanoseconds or microseconds later) it will retry the same instruction, so unless something has changed [unlikely if it's just a bad pointer], then it will signal and stop the application.
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Mats