evtchn_port_t evtchn_from_irq(unsigned irq)
{
	const struct irq_info *info = NULL;

	if (likely(irq < nr_irqs))
		info = info_for_irq(irq);
	if (!info)
		return 0;

	return info->evtchn;
}
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.