Questions regarding use of 'gdb -k'

[Greg 'groggy' Lehey]

On Sunday, 23 November 2003 at 18:26:38 -1000, Kent Kuriyama wrote:
>> On Sunday, 23 November 2003 at 17:02:09 -1000, Kent Kuriyama wrote:
>>> I am having difficulty in using 'gdb -k' to track down a kernel panic.  I
>>> have built a version of the kernel with the debugging symbols.  After
>>> the crash I use the 'gdb -k' command but get the following output:
>>> ....
>>> IdlePTD at phsyical address 0x00000000
>>> initial pcb at physical address 0x0048cee0
>>>
>>> cannot read proc at 0
>>> (kgdb) where
>>> #0  0x0 in ?? ()
>>> (kgdb) exit
>>> Undefined command: "exit".  Try "help".
>>> (kgdb) chinmon1#
>>> ------------------
>>>
>>> Can you tell me what I am doing wrong?  Thanks.
>>
>> Unfortunately, this looks like you have a corrupted dump.  What you've
>> done (with the exception of "exit") is correct.  You might find it
>> better to use serial debugging if this is repeatable.
>
> Thanks.  Regarding the suspected corrupt dump file.  In the syslog I can
> see the dump file being created (actually 'vmcore') and there are no
> error messages.  Are you saying that the corruption occurs during
> the writing of the file or is the data resident in memory corrupt?

I suspect that the problem is that the contents of memory are so
scrambled that you can't do much with them.  I get this kind of
problem from time to time.  The whole purpose of having a dump is to
find out what went wrong on the system.  If it goes too far wrong,
there's nothing much left to see.

You could try debugging over a serial link.

> I suspect that something is wrong with the hardware on this box.  We
> moved the hard drive from one motherboard to another but the problem
> remains.  This leaves the hard drive as suspect but there are no
> syslog messages to indicate a drive problem.

You won't get syslog messages when the system crashes.  You could look
in msgbuf and see if there's any clue there:

# msgbuf: print msgbuf.  Can take forever.
define msgbuf
printf "%s", msgbufp->msg_ptr
end
document msgbuf
Print the system message buffer (dmesg).  This can take a long time due to the time it takes to transmit the data across a serial line.
end

Greg
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