Path: utzoo!attcan!uunet!lll-winken!ncis.tis.llnl.gov!helios.ee.lbl.gov!pasteur!ucbvax!hoptoad!tim
From: tim@hoptoad.uucp (Tim Maroney)
Newsgroups: comp.sys.mac.programmer
Subject: Re: System 7.0 Q & A
Message-ID: <7321@hoptoad.uucp>
Date: 16 May 89 17:14:39 GMT
References: <30353@apple.Apple.COM> <4666@okstate.UUCP> <1787@internal.Apple.COM> <7266@hoptoad.uucp> <13472@dartvax.Dartmouth.EDU>
Reply-To: tim@hoptoad.UUCP (Tim Maroney)
Organization: Eclectic Software, San Francisco
Lines: 38

In article <7266@hoptoad.uucp> tim@hoptoad.UUCP (Tim Maroney) writes:
>or other applications.  Double plus ungood.  I'd prefer that Apple just
>go ahead and break the programs that ignore the guidelines on low
>memory and the system heap, rather than leave us all floundering about
>having to reboot the system constantly during early development.

In article <13472@dartvax.Dartmouth.EDU> earleh@eleazar.dartmouth.edu (Earle
R. Horton) writes:
>     Any Macintosh application written in a high-level language, using
>library glue derived from Apple's, and making calls to the Memory
>Manager will break when Apple makes low memory a protected area.  A
>side effect of using Apple glue to call a Memory Manager routine is to
>have the glue store a result code in the word at decimal 544.  Note
>that the programmer, along with the marketer of the development system
>used, is completely innocent of intent to write to low memory.  The
>Memory Manager glue is only an example, too.  There are many, many
>explicit stores to lowmem in Apple glue.

And all of these low memory locations can be trapped by the MMU and handled
transparently to the application.

>     If Apple ever does implement a protection scheme that covers
>lowmem and the System heap (which I also think is a good idea, don't
>get me wrong) then they will have to distribute library glue which is
>compatible with it, and allow time for some large percentage of
>existing Macintosh programs to be recompiled, relinked, and reshipped
>to customers.

I don't see why.  There are a number of different ways that an MMU can
be set up to provide compatibility with the most common low memory
globals, without the current memory copying on context switch overhead.

>     Still want them to do it now?

Absolutely.
-- 
Tim Maroney, Consultant, Eclectic Software, sun!hoptoad!tim
"This signature is not to be quoted." -- Erland Sommarskog