[yetihehe]

If you are interrupted by another higher priority handler, that handler ALSO saves and restores registers, so whatever was interrupted doesn't even know. the registers after interruption should have the same vaalues as before interruption, so whatever was saving, is saving properly. Typically the same interrupt is not called again while already servicing a signal. Interrupts are handled by flags, so when there are several flags raised at once, interrupt handlers of the same priiority run one after another and each one of them should clear it's own flag (sometimes it's done automatically by processor), often just at the start of routine. If then another interrupt sets the flag before routine finishes, routine will restart after finishing.