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From: Terry Lambert <terry@lambert.org>
Message-Id: <199512122110.OAA01741@phaeton.artisoft.com>
Subject: Re: What is this thing in locore.s?
To: bde@zeta.org.au (Bruce Evans)
Date: Tue, 12 Dec 1995 14:10:05 -0700 (MST)
Cc: current@freebsd.org, terry@lambert.org
In-Reply-To: <199512120940.UAA25385@godzilla.zeta.org.au> from "Bruce Evans" at Dec 12, 95 08:40:17 pm
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> >What is the purpose of:
> >=============================================================================
> >	movl	%esi,%ebx		/* calculate pte offset to ptd */
> >	shrl	$PGSHIFT-2,%ebx
> >	addl	%esi,%ebx		/* address of page directory */
> >	addl	$((1+UPAGES+1)*NBPG),%ebx /* offset to kernel page tables */
> >=============================================================================
> 
> This initializes %ebx :-).
> 
> >The kernel boots and runs fine without it -- it doesn't seem to do
> >anything really useful?!?
> 
> There are some ifdefs before it.  Apparently %ebx is left with the
> correct value for the case that you use.  I think it is left with the
> correct value for all cases, but this is only true now that the kernel
> is loaded above 1MB.  Previously, in the BDE_DEBUGGER case, %ebx was
> left pointing to the pte for physical address 0xa0000, while the page
> dir was either somewhat lower (at KERNend - KERNBASE) or perhaps at 1MB.
> This depends on the page dir going at (KERNend - KERNBASE).

I think that %ebx is definitely preserved.   Looking at the code from
Oct 1994, it was preserved there as well.  I don't think the 4.4BSD
code was ever loading kernels below 1M, was it?


BTW: since you *are* "BDE"... 8-).

I am apparently having a problem with either PTD initialization or
something else on a second processor.  I presume that the envirnment
for the second processor should be identical to the environment for
the first.  Any chance of you looking at my hacked up locore.s and
telling me what you think is different between the processor settings
after the code has executed?


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.