In arm linux how multiple interrupt irq line mapped to the processor interrupt line ?

Hi, As we know for arm processor have only one interrupt line, so to process multiple interrupt line, need to use PIC and interrupt vector. we know during system bootup kernel does interrupt vector table setup at a specified higher address. Now My question is when any interrupt comes how processor gets updated which irq line has been interrupted, could you please explain how actually multiple irq line mapped with the processor interrupt line? Thanks, Deba