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From: Gary Kendall <gdk@ccomp.inode.COM>
Message-Id: <199708251905.PAA00599@ccomp.inode.com>
Subject: Re: Sizing mem > 64MB at boot-time
To: Mike Smith <mike@smith.net.AU>
Date: Mon, 25 Aug 1997 15:05:53 -0400 (EDT)
Cc: freebsd-hackers@freebsd.ORG
In-Reply-To: <199708250232.MAA01084@word.smith.net.au> from Mike Smith at "Aug 25, 97 12:02:01 pm"
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> > Any help anyone can give me in sorting out segments and/or operand sizes
> > in real-mode would be greatly appreciated.
> 
> Jonathan Lemon (jlemon@freebsd.org) recently announced some code for 
> calling real-mode BIOS functions from the FreeBSD kernel, which should 
> cover everything you want to do here. 
> 
> I haven't had time to follow it through yet, regrettably, but you should
> definitely coordinate with him.
> 
> mike
> 
Mike,

    I saw Jonathan's post re real-mode access from the kernel, and I got a
copy of the code (which should prove to be quite usefull for DOS emulation),
but it won't solve the problem I'm trying to solve.  I want the boot program
to size the memory so that the kernel, during initialization, can use the
memory size to allocate buffers, etc.  Jonathan's code doesn't come into
play until the machine has already booted the kernel, and is executing it.
His real-mode code is through a system call interface, and as such, happens
"too late" for my purposes.

    However, it would be nice if someone familiar with the biosboot code
and/or Intel processors could look at what I have written and point me in
the right direction with respect to accessing a buffer while in real-mode.
As near as I can tell, prot_to_real() (in /sys/i386/apm/apm_init/real_prot.S)
sets all of the segment registers (cs, ds, es, and ss) to APM_INIT_CS16_SEL.
This means that the code, data, extra, and ??stack?? segments are all the
same.  What I can't seem to figure out is how to get gas to assign a buffer
pointer in this configuration.  Does this mean that I can't use .lcomm to
allocate the buffer, and that I have to use .space, with the buffer in
the code segment?  Huh? ;-)

Regards,
Gary Kendall <gdk@inode.com>

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