From mboxrd@z Thu Jan 1 00:00:00 1970 From: sms@moe.2bsd.com (Steven M. Schultz) Date: Wed, 8 Sep 1999 10:00:05 -0700 (PDT) Subject: Diff between 11/20 and 11/45? Message-ID: <199909081700.KAA26837@moe.2bsd.com> Hi - > From: Dave Horsfall > Do you recall the PC-board hack on the sep-ID machines that changed No, I do not recall seeing a PCB hack (hacking on an 11/70 was frowned upon ;)) > the MFPI instruction to do something that was expressly prohibited? But I do know what that 'something' was. In "user" or "supervisor" mode MPFI functioned as "MFPD" - a user program could not read its own I(nstruction) space. Only for "kernel" mode did MFPI access the I space. > Something about allowing a user program to access something else, for > some obscure hack or other... It was aimed at providing "execute only" code - a program could "run" but not "read" its code space. This caused problems though if trap handlers (floating point exception handling comes to mind) needed to retrieve the faulted instruction for inspection/analysis. Thus in 2BSD there is a system call that programs can issue to request the KERNEL to do the 'mfpi' for them and return the value. Steven Schultz sms at moe.2bsd.com Received: (from major at localhost) by minnie.cs.adfa.edu.au (8.9.3/8.9.3) id TAA10091 for pups-liszt; Thu, 9 Sep 1999 19:48:18 +1000 (EST) Received: from Zeke.Update.UU.SE (IDENT:2026 at Zeke.Update.UU.SE [130.238.11.14]) by minnie.cs.adfa.edu.au (8.9.3/8.9.3) with ESMTP id TAA10087 for ; Thu, 9 Sep 1999 19:48:09 +1000 (EST) Received: from localhost (bqt at localhost) by Zeke.Update.UU.SE (8.8.8/8.8.8) with SMTP id LAA22975; Thu, 9 Sep 1999 11:58:20 +0200 Date: Thu, 9 Sep 1999 11:58:19 +0200 (MET DST) From: Johnny Billquist To: Warren Toomey cc: Unix Heritage Society Subject: Re: Diff between 11/20 and 11/45? In-Reply-To: <199909062356.JAA12397 at henry.cs.adfa.edu.au> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-pups at minnie.cs.adfa.edu.au Precedence: bulk On Tue, 7 Sep 1999, Warren Toomey wrote: > These executables were written for a PDP-11/20. Are there any significant > USER-MODE differences between the 11/20 and later PDP-11 models? I'm > thinking missing instructions, different addressing mode behaviour etc. As far as I can remember, there aren't any huge differences. However, some stuff behave differently in the 11/20. On the other hand, some stuff behave differently in just about every implementation... Condition flags on some instructions specifically. And the 11/20 might have had some limitations on using the PC which differed as well. I have a processor handbook for the "modern" -11s, which has a chart with all differences between different models. I started writing it down, to place in the PDP-11 FAQ, but haven't come that far yet... Johnny Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at update.uu.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol