TUHS

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6418 discussions

Re: [TUHS] Harvard and Von Neumann Architectures and Unix

by jnc＠mercury.lcs.mit.edu

> From: Doug McIlroy > But if that had been in D space, it couldn't have been executed. Along those lines, I was wondering about modern OS's, which I gather for security reasons prevent execution of data, and prevent writing to code. Programs which emit these little 'custom code fragments' (I prefer that term, since they aren't really 'self-modifying code' - which I define as 'a program which _changes_ _existing_ instructions) must have some way of having a chunk of memory into which they can write, but which can also be executed. > Where is the boundary between changing one instruction and changing them > all? Or is this boundary a figment of imagination? Well, the exec() call only overwrites existing instruction memory because of the semantics of process address space in Unix - there's only one, so it has to be over-written. An OS operating in a large segmented single-level memory could implement an exec() as a jump.... BTW, note that although exec() in a single address-space OS is conventionally something the OS does, this functionality _could_ be moved into the user space, provided the right address space primitives were provided by the OS, e.g. 'expand instruction space'. So the exec() code in user space would i) find the executable, ii) see how much of each kind of memory it needs, iii) get the OS to give it a block of memory/address space where the exec() code can live while it's reading in the new code, iv) move itself there, v) use standard read() calls to read the new image in, and then vi) jump to it. Yes, it's probably simpler to implement it in the OS, but if one's goal is to minimize the functionality in the kernel... Noel

7 years, 1 month

A sober reminder of why distributed archiving is important

by Will Senn

In case you missed it: https://www.spectrum.ieee.org/view-from-the-valley/tech-history/silicon-rev… It is important to keep the conversations alive and not to file your memory boxes away in the attic. Thanks for sharing what you know and especially for making your documents and bits available. -will -- GPG Fingerprint: 68F4 B3BD 1730 555A 4462 7D45 3EAA 5B6D A982 BAAF

7 years, 1 month

TTY8

by Ron Natalie

OK, we were discussing terminals this morning with some other old guys. If I knew the answer to this I've forgotten. Every PDP-11 UNIX I ever used had the console KL-11 as /dev/tty8. The question is why. My guess is that for some reason an 8 terminal multiplexor (DZ-11?) was stuck at tty0, but why?

7 years, 1 month

Re: [TUHS] Harvard and Von Neumann Architectures and Unix

by jnc＠mercury.lcs.mit.edu

> From: Larry McVoy >> they aren't really 'self-modifying code' - which I define as 'a program >> which _changes_ _existing_ instructions > Isn't that how dtrace works? I'm not familiar with dtrace(), but if it modifies some other routine's code, then it would not be "self" modifying, right? Oh, another category, sort of like biological viruses (which are in a grey zone between 'alive' and not): the PDP-11 paper tape bootstrap: http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/bootloader.mac in which the program's own code _is_ modified - but not by program instructions, but by data on the paper tape it is reading in. It's entertainingly convoluted (the copy above should be well-enough commented to make it pretty easy to understand what's going on). Noel

7 years, 1 month

RIP J.F.Ossanna

by Dave Horsfall

We lost J.F. Ossanna on this day in 1977; he had a hand in developing Unix, and was responsible for "roff" and its descendants. Remember him, the next time you see "jfo" in Unix documentation. -- Dave Horsfall DTM (VK2KFU) "Those who don't understand security will suffer."

7 years, 1 month

Re: [TUHS] UNIX on S/370

by jnc＠mercury.lcs.mit.edu

> From: Kevin Bowling > The earliest stuff may be covered by Novell's grant of early code. > ... > Would be fun to run *ix on any of them. Alas, the Bell port of Unix to the /370 needs that underlying layer of code from IBM, and that's probably not going to escape. Too bad, it would be pretty cool. Noel

7 years, 1 month

Harvard and Von Neumann Architectures and Unix

by Will Senn

I am curious about how the Harvard Architecture relates to Unix, historically. If the Harvard Architecture is predicated on the separation of code from data in order to prevent self-modifying code (my interpretation), then it would seem to me to be somewhat at odds with a Unix philosophy of extreme abstraction (code, data, it's all 0's and 1's, after all). In my naive understanding, the PDP-11 itself, with the Unibus and apparently agnostic ISA seem to summarily reject the Harvard Architecure... My question is - was there tension around Harvard and Von Neumann architectures in Unix circles and if so, how was it resolved? Thanks, Will -- GPG Fingerprint: 68F4 B3BD 1730 555A 4462 7D45 3EAA 5B6D A982 BAAF

7 years, 1 month

Datakit in V7

by Paul Ruizendaal

There are some little bits in the public V7 source code that suggest that it had support for Datakit, but that it was scrubbed from the public release: There is a Datakit header file: http://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/include/dk.h and Datakit state bits are defined in 'sys/tty.h': http://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/include/sys/tty.h Does anyone know if this assumption (Datakit support in V7) is correct? Perhaps more specific, was there a remote login program for V7/Datakit, of for V6/Spider? For V8/Datakit there was 'dcon', but perhaps this was built on earlier programs. (I'm aware of 'cu' of course, but that does not support Datakit or Spider). Being able to login to another host on the network seems so useful that it is hard to believe that a precursor to 'dcon' did not exist for V6 and/or V7.

7 years, 1 month

Re: [TUHS] TCP/IP networking in 8th edition unix

by Paul Ruizendaal

Thanks for explaining that. I think it may be for 10th edition though. I searched for ipcopen() and 'gated' in the 8th edition source and could not find them. In that search I did find a few bits that strongly suggest that IP over Datakit was what was used in late '85 (when dmr posted about this). In /usr/src/cmd/inet/READ_ME there is an example configuration that seems to match with dmr's example. In that file an IP over a Datakit channel appears to be configured. (see http://chiselapp.com/user/pnr/repository/v8unix/artifact/6d09b05c7f06a2cc?l…) The program 'dkipconfig' sets up a circuit and pushes the IP discipline on the stream, both on the local end and on the remote end. It sets fixed local and remote addresses, much the same as with a 'slip' line. (see http://chiselapp.com/user/pnr/repository/v8unix/artifact/6c5f3267b58721a6?l…) On Sat, Nov 25, 2017 at 4:50 PM, William Cheswick <ches at cheswick.com> wrote: > > Nope, not IP over Datakit, as I recall. It was quite interesting to work at > a site (Bell Labs) where there were two distinct network technologies. > > [--snip--] > > This library was socks about seven years before socks, originally written by > Presotto and Howard Trickey. The relay program was originally called > “gated”, but that wouldn’t do after a while. I renamed it “proxyd”, and > that is the first use of “proxy" in this context that I am aware of. > > If you were on AT&T’s intranet and wanted to connect externally, you ripped > out the entire socket dance and replaced it with an ipcopen call. I also > distributed common modified clients, like ptelnet, pftp, pfinger, etc. > > I still have all this code, and I suppose it ought to go in an archival > repository. I can’t imagine that AT&T/Lucent/Alcatel/Nokia would care at > this point. Anyone want it? >

7 years, 1 month

TCP/IP networking in 8th edition unix

by Paul Ruizendaal

I'm trying to figure out how tcp/ip networking worked in 8th edition Unix. I'm starting from dmr's paper about streams (http://cm.bell-labs.co/who/dmr/st.html) the V8 man pages (http://man.cat-v.org/unix_8th/3/) and browsing the source code (tarball here http://www.tuhs.org/Archive/Distributions/Research/Dan_Cross_v8/) In the below I use 'socket' to mean a file descriptor bound to a network connection. My current understanding is like this: - The hardware interface is exposed as a character device; for tcp/ip only ethernet is supported. Directly accessing this device reads/writes ethernet frames. - One can push an 'ip' module (only) onto an ethernet device; this module also handles ARP. Once this is done IP messages are queued to the virtual ip devices, /dev/ipXX. The device minor number XX equals the protocol number, i.e. the ip packets are demultiplexed into separate virtual devices. IP packets from multiple ethernet cards all end up on the same virtual ip devices. I'm not sure if one can still read/write to the ethernet device after pushing the ip module, but I think you can, creating a raw IP interface so to say. - On /dev/ip6 one can push a TCP module. The TCP module handles the TCP protocol and demultiplexes incoming traffic to the virtual /dev/tcpXX devices. On /dev/ip17 one can push a UDP module. The UDP module handles the UDP protocol and demultiplexes incoming traffic to the virtual /dev/udpXX devices. Not sure wether the ip6 and ip17 devices can still be read/written after pushing these disciplines. - There are 100 udp devices, /dev/updXX. To open a UPD socket, one opens an unused udp device (through linear search). This socket accepts binary commands ('struct upduser') through the read()/write() system calls. There is a command to set the local port (effectively 'bind') and a comment to also set the foreign address and port (effectively 'bind+connect'). As long as the socket is not connected actual datagrams are preceded by a command header with the address/port information (effectively 'sendto'/'recvfrom'). Once the socket is connected, it is no longer possible to send further commands, but each write/read is a datagram. For udp sockets it is not possible to specify the local address: it is chosen by the system to match with the given foreign address. - There are 100 tcp devices /dev/tcpXX. Initial connection is always over an odd numbered device. To open a TCP socket, one opens an unused tcp device (through linear search). This socket accepts binary commands ('struct tcpuser') through the read()/write() system calls. There is a command to actively connect (effectively 'connect' with optional 'bind'), and a command to passively listen (effectively 'bind'+'listen'). If the connect command is sent, one can read one more response block and then the socket becomes a regular tcp socket. If the listen command is sent, one can read multiple response blocks, one for each new client (effectively 'accept'). Those response blocks contain a device number for the new client connection, i.e. one has to subsequently open device /dev/tcpXY to talk to the client. This number is always even, i.e. locally initiated tcp connections are over odd numbered tcp devices, and remotely initiated connections are over even numbered tcp devices - not sure what the significance of this is. - The above seems to be modeled on the Datakit setup, where the network is exposed as 520 virtual devices, one for each channel, as /dev/dk/dkXXX. These channels than also seem to accept binary command blocks through the read()/write() interface, with a 'connect' type command changing the connection into a data only channel. Anybody on the list with 8th edition experience who can confirm that the above understanding is about correct? Paul

7 years, 1 month

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