Be warned: on at least some architectures (notably IA-64), this sort of read has been known to cause untrapped machine checks (a.k.a., lockups or spontaneous reboots). Arguably the kernel should trap this sort of nonsense, so you may be in the mood to file a bug against "kernel" after running this program.
wow, this is such a bad idea. the kernel *can't* trap that sort of thing in a lot of cases. simply the hardware goes catatonic. this is true of ultrasparc machines as well. you may also access some random "device" memory causing it do do something unexpected. "read" can be very destructive of device state... why don't you use /dev/urandom if it exists, as it does on pretty much all modern UNIX platforms? *shudder* .mrg.