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From: geof@imagen.UUCP (Geoffrey Cooper)
Newsgroups: comp.sys.m68k
Subject: move sr/move ccr: crock
Message-ID: <809@imagen.UUCP>
Date: Wed, 21-Jan-87 16:26:29 EST
Article-I.D.: imagen.809
Posted: Wed Jan 21 16:26:29 1987
Date-Received: Thu, 22-Jan-87 04:41:03 EST
Organization: IMAGEN Corporation, Santa Clara, CA 95052-8101
Lines: 20
Keywords: logic?


In the 68000, the move from sr instruction is not a privileged
instruction.  In the 68010 and 68020 a new instruction exists,
move from ccr, which just moves the condition codes out of the
SR, the other bits being zero.  In the 68010 and 68020 move from
SR is a privileged instruction.

This appears to be a crock.  It means that simple assembly
language routines must be different for 68010 and 68020.  It
significantly affects the portability of code between them
(especially when compilers like to generate code to save the
condition codes on the stack).

My question is why the lords of 68000-land did this?  Presumably
there is some lack or portability or security loophole in allowing
a user program to look at the SR.  I don't know what it is.
Does anyone else?

- Geof Cooper
  IMAGEN