Re: CURRENT kernel crashes on boot with BTX error

Hi John,

Thanks for your reply.

On Wed, 22 Oct 2008, John Baldwin wrote:
> On Wednesday 22 October 2008 12:50:15 am David Adam wrote:
> > I've been trying to build an 8-CURRENT kernel on my 7.0-RELEASE system in 
> > order to test out some patches that Pyun YongHyeon has prepared. 
> > Unfortunately, I cannot get a GENERIC+DDB kernel to boot on my 
> > machine.
> > 
> > This is an Intel SR1200 Pentium 3-class system - there is a dmesg from 
> > 7.0-RELEASE in the first part of 
> > http://www.freebsd.org/cgi/query-pr.cgi?prp=125769-1-txt&n=/patch.txt
> > 
<snip>
> > The kernel loads, the various modules I have specified in loader.conf are 
> > loaded, and the loader screen appears. However, when I select "boot", the 
> > expected line with the kernel version does not appear: instead, the 
> > spinner briefly spins, switches to the bold colour, and then crashes with 
> > a BTX error:
> > 
> > int=0000000d  err=00000000  efl=00010a13  eip=00000430
> > eax=ffffffb4  ebx=00006c47  ecx=0000000a  edx=00000080
> > esi=00000001  edi=ffff9414  ebp=00000000  esp=0008f8b4
> > cs=002b  ds=0033  es=002b    fs=0033  gs=0033  ss=0033
> > cs:eip=6c 7f 94 48 00 00 00 00-0f af c1 47 00 00 00 00
> >        00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00
> > ss:esp=2b 00 00 00 33 00 47 91-00 fc 03 00 5f ad 08 04
> >        00 00 00 00 3f 00 00 00-00 00 00 00 c4 0f 06 00
> > BTX halted
> 
> It went off into the weeds.  The cs is still a 32-bit loader segment, but the 
> eip value is a bit too low.  The instruction stream:
> 
> 00000000  6C                insb
> 00000001  7F94              jg 0xff97
> 00000003  48                dec ax
> 00000004  0000              add [bx+si],al
> 00000006  0000              add [bx+si],al
> 00000008  0FAFC1            imul ax,cx
> 0000000B  47                inc di
 
I'm afraid this means nothing to me - any likely proximate causes?

<snip>
> > 1. Is this an acceptable method of testing a CURRENT kernel? I also tried 
> > building a new world and kernel with DESTDIR set to another partition but 
> > had similar problems. Unforunately this machine does not have a reliable 
> > CD drive so I can't use a snapshot CD to install.
> 
> I wonder if building and install a new loader would fix it.  If it does, that 
> still indicates a bug (7.0 loader should be able to load and boot an 8.0 
> kernel).  Hmm, you see this after doing a boot?  It's possible that you are 
> actually in the kernel when you fault then, in which case it could be a 
> kernel issue with your hardware somehow.  If you do a boot -v, do you get any 
> output from the kernel before the machine crashes?

Yes, this occurs after the 'boot' command at the loader prompt. 'boot -v' 
(or at least the "verbose boot" option in the loader menu) produces no 
extra output.

I did try a loader from the CURRENT sources, which produced the same 
output.

However, the plot thickens. When I don't specify the kernel name with 
nextboot(8), but instead interrupt the loader and use 'unload; load 
/boot/kernel/gd-8; load /boot/kernel/gd-8/geom_mirror.ko' and so on for my 
other modules, the kernel boots quite happily - both using the 7.0 loader 
and the new one from the CURRENT sources.

Are there likely to be big differences in the boot process between using 
nextboot(8) and the unload/load method? I've used nextboot(8) to 
successfully load other kernels on this machine before.

In any case, now that I have a successful workaround I can try the patches 
I was after in the first place. If there's any more information I can 
provide, or you'd like access to this system (it has serial console and 
remote power control), let me know.

David Adam
zanchey_at_ucc.gu.uwa.edu.au