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Re: 32-bit ABI

To: "Maciej W. Rozycki" <>
Subject: Re: 32-bit ABI
From: Stanislaw Skowronek <sskowron@ET.PUT.Poznan.PL>
Date: Sat, 24 Apr 2004 10:14:13 +0200 (MET DST)
Cc: Ralf Baechle <>,
In-reply-to: <>
Original-recipient: rfc822;
>  Well, the exception arrangement requires RAM starting from the physical
> address 0.  It seems natural to place RAM just there, avoiding additional
> complexity to address decoders.  But then firmware has to be somewere
> around 0x1fc00000, so to support more than 508MB of RAM the designers
> would have to create a hole in RAM, which would have to be handled by the
> OS then.  Thus abandoning the idea of putting RAM low, placing it
> somewhere above 0x1fffffff and just mapping some of it at 0 for the
> exceptions seems a better solution.

OK, I forgot about the firmware placement. Why didn't they move it to
somewhere else when booting 64-bit? (A rhetorical question, I know.)

I would place some fixed code there. Or a different memory, maybe 16 kB of
static RAM so it will always be fast. With what is now, we have physical
and virtual aliasing and it's all a bit like a 

> Fortunately everything is not a PC. :-)

Yes, fortunately. The 386 memory management is a joke. The BIOS in the
middle is an even darker joke. Well, in my opinion the R8000 was right in
not having compatibility segments.


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