Subject: kern/68: call of null function ptr not handled well by i386 ddb.
To: None <gnats-admin>
From: None <>
List: netbsd-bugs
Date: 01/12/1994 19:05:06
>Number:         68
>Category:       kern
>Synopsis:       call through null function ptr in kernel confuses ddb
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    gnats-admin (Kernel Bug People)
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jan 12 19:05:03 1994
>Originator:     Bill Sommerfeld
>Release:        -current
System: NetBSD 0.9a ORCHARD#17 i386

	A call through a null function pointer in the kernel results
in a trap into ddb, which immediately attempts to disassemble the pc of
the fault, which is zero; this generates a recursive fault which makes 
it hard to get at the original fault..

	add a int (*fn)() = NULL; (*fn)(); to your kernel, either
	intentionally or accidentally.
	haven't looked at code yet; ddb should "step carefully" when 
	disassembling to avoid this kind of thing.