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From: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Newsgroups: comp.sys.mac.programmer,comp.sys.mac
Subject: Re: System 7.0 Q & A
Message-ID: <13472@dartvax.Dartmouth.EDU>
Date: 13 May 89 02:42:03 GMT
References: <30353@apple.Apple.COM> <4666@okstate.UUCP> <1787@internal.Apple.COM> <7266@hoptoad.uucp>
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Reply-To: earleh@eleazar.dartmouth.edu (Earle R. Horton)
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Organization: Thayer School of Engineering
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In article <7266@hoptoad.uucp> tim@hoptoad.UUCP (Tim Maroney) writes:

[Discussion of System 7.0 non-elimination of writable lowmem globals.]

>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.

     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.

     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.

     Still want them to do it now?


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