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- Xref: sparky comp.os.os2.advocacy:12066 comp.os.ms-windows.advocacy:3782
- Newsgroups: comp.os.os2.advocacy,comp.os.ms-windows.advocacy
- Path: sparky!uunet!grebyn!daily!richk
- From: richk@grebyn.com (Richard Krehbiel)
- Subject: Re: If things had been different... (was: FCC etc)
- In-Reply-To: tracer@majestix.cs.uoregon.edu's message of 10 Jan 93 23:15:49 GMT
- Message-ID: <1993Jan11.123417.4982@grebyn.com>
- Lines: 25
- Sender: richk@grebyn.com (Richard Krehbiel)
- Organization: Grebyn Timesharing
- References: <1993Jan4.190822.1001@pphbau.atr.bso.nl> <1993Jan5.154612.27051@wam.umd.edu>
- <1icr5gINNgh2@shelley.u.washington.edu>
- <1993Jan10.231549.14308@cs.uoregon.edu>
- Date: Mon, 11 Jan 1993 12:34:17 GMT
-
- In article <1993Jan10.231549.14308@cs.uoregon.edu> tracer@majestix.cs.uoregon.edu (Roger M. Wilcox) writes:
-
- > In article <1icr5gINNgh2@shelley.u.washington.edu> tzs@carson.u.washington.edu (Tim Smith) writes:
- > >> in the transition from 68000 to 68010.
- > >
- > >If I recall correctly, the problem was that the condition codes were in
- > >half of the status register. Code that wanted to set condition codes
- > >directly did so via a move to SR. This became priveledge on the 68010,
- > >and a new move to CCR instruction was added for user-mode access to the
- > >condition code half of the status register. Thus user-mode code that
- > >tried to directly set the condition codes would trap.
-
- Close, but it was the move FROM the SR that was unprivileged on the
- 68000 and became privileged on the 68010. Move TO the SR was always
- privileged.
-
- > Not making the Move-into-SR instruction privileged was a really
- > really stupid move on Motorola's part. The Status Register
- > contains, among other things, the User/Supervisor Mode bit! Move
- > a 0 into this bit and Bingo, you're running in Supervisor Mode.
-
- Why, yes, this would have been an incredibly stupid thing to do,
- especially since the bit that controls super/user mode is in the
- status register and would therefore have been writable in user mode.
- Thankfully, the SR was never writable from user mode.
- --
- Richard Krehbiel richk@grebyn.com
- OS/2 2.0 will do for me until AmigaDOS for the 386 comes along...
-