Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!valentin
From: valentin@cbmvax.commodore.com (Valentin Pepelea)
Newsgroups: comp.sys.amiga.tech
Subject: Re: MMU + A3000 + AmigaOS2.0 == Non-crashing system?
Message-ID: <13712@cbmvax.commodore.com>
Date: 8 Aug 90 21:52:26 GMT
References: <2489@clinet.FI> <20889@grebyn.com> <6405@wolfen.cc.uow.oz> <20927@grebyn.com> <13625@cbmvax.commodore.com> <20999@grebyn.com> <25174.26bd4fa9@kuhub.cc.ukans.edu>
Reply-To: valentin@cbmvax (Valentin Pepelea)
Organization: Commodore, West Chester, PA
Lines: 40

In article <25174.26bd4fa9@kuhub.cc.ukans.edu> markv@kuhub.cc.ukans.edu writes:
>
> MEMF_PUBLIC:
>
> This has to be the most misused and abused flag on the Amiga system.

Ignored, yes. Misused, maybe. Abused, no. It is impossible to abose this flag,
even if a fool might was to allocate CHIP or FAST by using it.

> System calls:
>
> Remember that many calls that deal with shared messages like
> Do/Send/BeginIO(), Get/PutMsg(), etc, execute in the callers context,
> so they can be patched to set up privleges/access correctly in a
> protected environment.  The message structure itself can be patched
> for R/W access by the system.  Based on the system calls, it can be
> known whether buffers are read only or read/write, etc.

Unfortunately not. The is a field in the message structure which specifies the
length of the message. Unfortunately, nobody ever sets that field to its proper
value. Therefore when a Task A sends a message to Task B, the operating system
has no way to know what length of memory should have its protection changed.

> Implementation:
>
> Set the standards NOW.  Provide the hooks to support it NOW.  Provide
> the tools to control it to users NOW.  Enforce the behavior LATER.

Well, we could come up with a tool that checks for the proper useage of the
MEMF_PUBLIC flag when necessary. As to the proper useage of the mn_Length
field of message structures, it too can be checked for, but so many
applications never set it, that it would be disastrous to enforce it in the
future.

Valentin
-- 
The Goddess of democracy? "The tyrants     Name:    Valentin Pepelea
may distroy a statue,  but they cannot     Phone:   (215) 431-9327
kill a god."                               UseNet:  cbmvax!valentin@uunet.uu.net
             - Ancient Chinese Proverb     Claimer: I not Commodore spokesman be