Path: utzoo!attcan!uunet!mcsun!ukc!edcastle!aipna!almond!awb
From: awb@almond.ed.ac.uk (Alan W Black)
Newsgroups: comp.os.minix
Subject: Re: Receiving General Protection panic from 386 Minix
Keywords: general protection 386
Message-ID: <3070@aipna.ed.ac.uk>
Date: 23 Sep 90 14:21:06 GMT
References: <1990Sep22.055445.15470@dsuvax.uucp>
Sender: news@aipna.ed.ac.uk
Reply-To: awb@almond.UUCP (Alan W Black)
Organization: Dept of AI, Edinburgh, UK
Lines: 52

In article <1990Sep22.055445.15470@dsuvax.uucp> ghelmer@dsuvax.uucp (Guy Helmer) writes:
>I just built the 386 version of MINIX, and I've been searching for
>the source of this error for several hours now.  I receive a
>general protection from process number 1, pc = 0x0007:0x00000385
>and the friendly "Kernel panic: exception in kernel, mm, or fs"
>message immediately after pressing the '=' key at the boot menu.
>I'm trying to run this without shoelace or db.
>
>  [details deleted] 
>
>Guy Helmer
>work: DSU Computing Services, Business & Education Institute    (605) 256-5315
>play: MidIX System Support Services                             (605) 256-2788
>helmer@sdnet.bitnet, ghelmer@dsuvax.uucp, uunet!loft386!dsuvax!ghelmer

I recently did this on a 386 machine.  After a lot of searching and
debugging we discovered that the system corrupts itself when booting. 
We basically we had two problem one ours and one caused by a problem in
bootblok.s (as distributed -- I got mine from plains.nodak.edu)
If the size of the kernel is one sector bigger that the
number of tracks being loaded, it misses the last sector. 

The fix is something like (sorry I don't have the actual bootblok.s
here) at the end of the loop where it is loading sectors

        mov     ax,disksec      | see if we are done loading
        cmp     ax,final        | ditto
        jb      load            | jump if there is more to load

You should (I believe) decrement disksec before doing the test.  I
can't remember if this is right but it definately in this area
and after we changed this it worked.

Now it happens that if you build a kernel with the small number of
disk buffers (in minix/config.h) i.e. not the INTEL_32BITS default
but the old default.  It will work without the above change.

The other problem (which I actually think is what you are
getting first).  There were no instructions on how to build
the default db (x386_1.1/tools/db.s) I originally simply bcc'd it
but it seems it should be that you build the .o file then
ld it on its own without the library.

(thanks to Richard Tobin for doing most of this debugging)

Hope this doesn't just confuse the issue

Alan

Alan W Black                          80 South Bridge, Edinburgh, UK
Dept of Artificial Intelligence       tel: (+44) -31 225 7774 x228 or x223
University of Edinburgh               email: awb@ed.ac.uk