RE: dmesg

["Michael L. Hitch" <mhitch%msu.oscs.montana.edu@localhost>]

"Georges Heinesch" <ghmlist%ibm.net@localhost> writes: 
> When I start NetBSD via the bootblock (Amiga Bootmenu), dmesg works
> properly and spits out what it should. The options are -ASn2
> (default).
> 
> However when I start NetBSD with the same options -aASn2 (I have to
> add -a since loadbsd starts in single-user mode), I get the following
> message:
> 
> dmesg: kvm_read: kvm_read: Bad address (0x50200000)
> 
> Q1: What's this message about?

  It probably means that /netbsd on your root filesystem is not the same
netbsd that you loaded with loadbsd.  Dmesg is using the kernel symbols
in /netbsd to locate where the message buffer is in the running kernel,
but if the running kernel does not match /netbsd, dmesg is likely to get
a bad address for the message buffer.

> The same message I get when I start NetBSD with the options -aS.
> 
> When I start NetBSD with loadbsd without the option -S (just -a), I
> get:
> 
> dmesg: kvm_read: kvm_read: Bad address (0x0)
> 
> Q2: What's that now?

  The same thing - except that since no kernel symbols were loaded into
memory when the kernel booted, the memory contents changed.  Dmesg is
probably just picking up different data.  [Kernel symbols are loaded
immediately after the kernal data segment, so it's possible that the
pointer to the message buffer in the running kernel is beyond the data
segment of the /netbsd kernel.  That would place the pointer into memory
that would be initialized differently depending upon whether the debugging
symbols where loaded or not.]

Michael
---
Michael L. Hitch                        mhitch%montana.edu@localhost
Computer Consultant,  Information Technology Center
Montana State University, Bozeman, MT     USA