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From: Sergey Shkonda <serg@bcs1.bcs.zaporizhzhe.ua>
Message-Id: <199510141010.AA02527@bcs1.bcs.zaporizhzhe.ua>
Subject: Re: netboot patch
To: bde@zeta.org.au (Bruce Evans)
Date: Sat, 14 Oct 1995 12:10:30 +0200 (UKR)
Cc: hackers@freebsd.org
In-Reply-To: <199510140008.KAA25340@godzilla.zeta.org.au> from "Bruce Evans" at Oct 14, 95 10:08:09 am
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> 
> >> >           Troubles detected when DOS memory managers used
> >> > after netboot.com. (I type 'N' when question "Boot from Network")
> >> > IMHO there are incorrect switching from P-mode to R-mode at exit.
> >> 
> >> I have heard this from other people as well, but I don't really know
> >> what I'm doing incorrectly on the switch back.
> >   I found this bug. You need to load selector with limit 64k
> > to ss, ds, es, fs and fs registers _before_ cleaning PE flag.
> > Then shadow registers filled correctly.
> 
> fs and gs need not be switched back because they aren't switched to.
> 
> The standard boot loader probably doesn't need this because it doesn't
> support an 'N' question.  It seems unlikely that there are any BIOSes
> sensitive to the segment limits.  It's more likely that there are
> BIOSes sensitive to gateA20, and we don't bother switching gateA20
> back and forth.
> 
> Bruce
> 
   If this question not supported, then you can't boot from
floppy with boot ROM.

--
Serg              |  Relcom:
(Sergey Shkonda)  |            serg@bcs1.bcs.zaporizhzhe.ua