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List:       linux-kernel
Subject:    Re: How to debug boot sequence?
From:       Richard Guenther <zxmpm11 () student ! uni-tuebingen ! de>
Date:       1998-05-06 10:05:09
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Hi!

After doing some research on my BIOS and the Kernel loader (remember:
i486, no disks, netboot via BOOTP/TFTP code in BIOS - results:
Kernel ends up not being able to uncompress itself), I have some
facts for:
 - The TCP/IP BIOS emulates a floppy-disk (nice :))
 - The Kernel Image gets corrupted by itself! In the bootblock code
   the bootblock and the 'setup' get copied to 0x9000/0x9020 (i don't
   really understand ix86 segments/crap, so I hope you know what I
   mean...), where unfortunately the BIOS put the ramdisk... Uh! :)
   I verified this by transferring the zipped part of the kernel
   as 0xff's and hacking arch/i386/boot/compressed/misc.c to scan
   for not matching 0xffs in the image. This shows, that the first
   ~10k get corrupted, but the rest is intact (i.e. this would match
   the setup-code size).

Now, I tried to just change include/asm/boot.h INITSEG et al, but
this does not work... I'm using bzImages (zImages give the same
result), so in principle the loader code could be copied to 0x1000
instead of 0x9000, but I don't know how to change this...

If you know a soultion or know who actually wrote the loader, could
you tell me, please?

Still trying, Richard.

On Mon, 13 Apr 1998, H. Peter Anvin wrote:
> > > Invalid compressed format sounds like the protected-mode kernel
> > > doesn't end up where it should, or isn't intact.  It is hard without
> > > knowing more about your software setup (boot loaders, etc; just how
> > > exactly is the BIOS loading the kernel anyway) what's going on.
> > 
> > Yes, it seems to be more like a BIOS problem. What exactly does
> > the kernel loader depend on? How could I get a non-compressed version of
> > the bootimage?
> 
> The kernel loader only depends on being installed in the right
> location.

--
Richard Guenther <richard.guenther@student.uni-tuebingen.de>
PGP: 2E829319 - 2F 83 FC 93 E9 E4 19 E2 93 7A 32 42 45 37 23 57
WWW: http://www.anatom.uni-tuebingen.de/~richi/


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