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From: fnf@mcdsun.UUCP
Newsgroups: comp.unix.wizards,comp.emacs
Subject: Re: building a.outs in COFF format
Message-ID: <239@mcdsun.UUCP>
Date: Sun, 1-Feb-87 14:37:52 EST
Article-I.D.: mcdsun.239
Posted: Sun Feb  1 14:37:52 1987
Date-Received: Tue, 3-Feb-87 02:09:08 EST
References: <358@ttidca.UUCP> <368@ttidca.UUCP>
Reply-To: fnf@mcdsun.UUCP (Fred Fish)
Organization: Motorola Microcomputer Division
Lines: 32
Xref: watmath comp.unix.wizards:786 comp.emacs:379

In article <368@ttidca.UUCP> mb@ttidca.UUCP (Michael Bloom) writes:
>While paging granularity itself is much smaller, 64kb is the
>granularity used for protection (read/write/shared, etc).  I don't
>know yet whether this is peculiar to the ICM-3216 architecture, or is
>generic for SysVr2.  Would someone care to comment on this?
>
>I'd like to hear from anyone who knows if this 64k region size is
>typical of other system Vr2 ports.

As the guilty party who did the first known port of GNU emacs to System V,
and the original unexec stuff for COFF, guess I'll comment on this.  One
of the most frustrating artifacts of Motorola not having a fast flexible
MMU available for the 68000 family, until just recently with the MC68851, is
that practically everyone and their brother producing 68K based Unix systems
did their own MMU hardware.  Just ask the folks at Unisoft (my previous
employer) who have done literally hundreds of ports of Unix to 68K based
hardware, about some of the bizarre MMU schemes they have had to deal with.

Where text starts, where data starts, and how big (if any) a hole there is
between the two, are dictated by MMU considerations.  Many configurations
require text to start at some non-zero address (0x80000 for example).
Some require as much as a 4Mb hole between the end of text and the
start of data.  In short, there are no guarantees about where text and
data are located and whether or not they are even relatively close to
each other in the address space.

-Fred
-- 
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Fred Fish  Motorola Computer Division, 3013 S 52nd St, Tempe, Az 85282  USA
{seismo!noao!mcdsun,hplabs!well}!fnf    (602) 438-5976
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