kernel init exception

[wilbur.chan]

We are   porting linux 2.6.21.7 to a powerpc e500mc board , p4080.

But something is wrong when loading init file:

log:

free init memory...

init has generated signal  4  but has no handler for it


I found it print in _exception --->

                                   if (is_init(current)) {
                                         if (handler == SIG_DFL) {
    			  printk(KERN_CRIT "init has generated signal %d "
			        "but has no handler for it\n", signr);
			do_exit(signr);
		          }
                                   }


why there generated a signal 4  in  init  process?

Thanks