From owner-freebsd-current  Thu May 16  1:18:47 2002
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Date: Thu, 16 May 2002 18:20:57 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: John Baldwin <jhb@FreeBSD.ORG>
Cc: Dag-Erling Smorgrav <des@ofug.org>, <alpha@FreeBSD.ORG>,
	<current@FreeBSD.ORG>
Subject: Re: loader failure
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On Wed, 15 May 2002, John Baldwin wrote:

> On 15-May-2002 Dag-Erling Smorgrav wrote:
> > John Baldwin <jhb@FreeBSD.org> writes:
> >> The kernel overflowed it's stack.  In SRM, you can try to debug this
> >> by using 'e sp' to get the stack pointer then get a stack dump and save
> >> a copy of it in a log or something, reboot the machine, then use gdb's
> >> list command on the kernel.debug to figure out the source:line for all
> >> the kernel-text addresses in the stack dump to figure out the backtrace.
> >
> > How do I get a stack trace? I can't get the 'examine' command to
> > actually print anything...
>
> It depends on which machine actually. :-/  First do 'e sp' to get the
> stack pointer.  Then you want to do something like this:
>
> e -n 100 <value of sp without any leading 0x>

At least for i386's, it can be useful to set $esp and $eip to
non-preposterous values if they are hosed (record the old values first).
Bugs in the pagefault handler make the behaviour for invalid pointers
very bad.  The main one trap_pfault() doesn't give up immediately if
the pagefault is from within ddb.  In old versions of FreeBSD, this is
probably only fatal if trap_pfault() blocks, but in -current is is fatal
in the usual case where trap_fault() acquires a sleep lock.

Bruce


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