Path: ...!news.misty.com!weretis.net!feeder9.news.weretis.net!panix!.POSTED.2602:f977:0:1::5!not-for-mail
From: Rich Alderson <news@alderson.users.panix.com>
Newsgroups: comp.os.linux.advocacy,comp.os.linux.misc,alt.folklore.computers
Subject: Re: Can't Avoid That Shit Rust - Even On Gentoo
Followup-To: alt.folklore.computers
Date: 06 Oct 2024 19:59:48 -0400
Organization: PANIX Public Access Internet and UNIX, NYC
Lines: 38
Sender: alderson+news@panix5.panix.com
Message-ID: <mdd34l84waz.fsf@panix5.panix.com>
References: <pan$96411$d204da43$cc34bb91$1fe98651@linux.rocks> <5mqdnZuGq4lgwm_7nZ2dnZfqnPSdnZ2d@earthlink.com> <pan$3ac1d$92afd8da$2552f614$ebf3c267@gnu.rocks> <PL-dncdcxJXTlJ_6nZ2dnZfqnPadnZ2d@earthlink.com> <SMpMO.249150$v8v2.8876@fx18.iad> <lmeosnFmgllU1@mid.individual.net> <vdv6h5$1dc01$6@dont-email.me>
Injection-Info: reader1.panix.com; posting-host="2602:f977:0:1::5";
	logging-data="2899"; mail-complaints-to="abuse@panix.com"
X-Newsreader: Gnus v5.7/Emacs 22.3
Bytes: 2343

Lawrence D'Oliveiro <ldo@nz.invalid> writes:

> On 6 Oct 2024 06:26:32 GMT, rbowman wrote:

>> ... as I recall you could twiddle octal locations in the opcodes.

> Sounds PDP-11-ish. The instruction layout was such that, if an instruction 
> was expressed as an integer, register numbers and addressing modes fitted 
> neatly into particular octal digits.

> Not sure if that was true of the PDP-10. The later VAX went all hex, of 
> course.

The PDP-10 instruction layout is

		    1 1 1  1 1 2         3    3
	0......8 9..2 3 4..7 890123456789012345
	op code   AC  I  IX   address offset

All represented in octal.  The HALT instruction (a variant on the JRST) is a
good example:

	HALT RESUME(17)		;RESUME is a symbolic address, let's say 654321

The assembly representation is

	254 04 0 17 654321

The in-memory representation is 254217654321.  Patching from the front panel of
a 166, KA-10, or KI-10 processor is simple enough, if you know where your program
lives in memory (not a given, since the entire line is intended for multiuser
usage).

-- 
Rich Alderson					  news@alderson.users.panix.com
      Audendum est, et veritas investiganda; quam etiamsi non assequamur,
	  omnino tamen proprius, quam nunc sumus, ad eam perveniemus.
									--Galen