TUHS

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6532 discussions

Re: [TUHS] Moto and MMU issues -- was Unix & Memory Management Units (MMU)

by Clem Cole

On Thu, Dec 8, 2016 at 5:39 AM, Joerg Schilling <schily(a)schily.net> wrote: > Back to the Bourne Shell: > > The original Bourne Shell did not use malloc, but rather had a SIGSEGV > handler > that used to extend the "string stack" called "stak" via sbrk() whenever > the > code tried to access data beyond the end ot the heap. > Right although the 68K was not the first or the only system to have that problem - again IIRC Series/1 and maybe one of the PE systems. You are correct then SunOS and >>some<< of the 68000 based system did have the problem you suggested. And in fact, Masscomp (and Apollo) which used 68000's (but used two of them so could run full VM) could survive that style of fault (because it never occurred). BTW: the "conceptual problem" , you mentioned while true, is being a little harsh. As the one of the 68K designers (Les Crudele) said to me once, when they wrote the microcode, there were not thinking about instruction restart - so the issue was that Nick did not save enough state to do it. The model for the 68000 that they were using was the base/limit PDP-11 and the original PDP-10. Also at the time, the competition was the 6800, the 8080, Z80, 6502. They were trying to put a PDP-11/70 on chip (without getting into trouble like CalData did - which Les, Nick and team were very aware having been DEC and CalData customers before they were at Moto]. While we think of the 68000 family has being 32 bit, the fact is inside it is a 16 bit system (the barrel shifter and execution functions are 16). And it was a skunk works project -- the 6809 was Moto's real processor. It was an experiment done by a couple of rogue engineers that said - hey we can do better, The fact was they made a chip that was good enough to actually compete with the Vax in the end, because it was fast enough AND they had the wisdom to define 32 bits of address space and 32 bit operations (again having been PDP-11 users), but as Les used to say - part of the thinking was that while DEC was moving to the Vax, they had hoped to break into the area that they 16 bits minis claimed - which they in-fact did. And if you think in terms of a Clay Christensen's disruption theory, the fact that VM did not work easily (i.e. was a "worse" technology than the Vax) was ok - a new breed of customer did not care. 68000 was huge success, despite Moto marketing ;-) To me the larger issue with the 68010 was that when Nick did add the restart microcode, the new '10 microcode actually dumped version dependant state on the external stack (in Intel terminology -different "step" '10 put different state on the external stack or worse, could not restart an instruction that had been saved from a different step processor). This screw up was a huge issue when we did replaced the "executor" with a 68010, because it meant that all cpu boards had to be the same processor microcode revision. Masscomp was of course the first to make an MP, so was the the first firm to run into the issue (I remember debugging it - we could not reproduce the issue because of course tjt and my own machine's by chance had "MPU" boards as we called them with the same step -- it was one of the field service guys that realized that the customer system had a mixed step board -- i.e. when they replaced a single MPU in the field, the system stopped working). IIRC: Moto never fixed the '10, as that processor was reasonably short lived in the open market. They did fix the microcode in the '20 so the state on the external stack was independent of stepping. Clem

8 years, 6 months

That's not a computer...

by Dave Horsfall

*This* is a computer! http://archive.computerhistory.org/resources/text/EAI/EAI.HYDAC2400.1963.10… A hybrid analogue/digital box, what could possibly go wrong? And check out the dudes and dudess supporting it (except she'd better be careful when moving her chair, in case she takes out a paper tape unit...). -- Dave Horsfall DTM (VK2KFU) "Those who don't understand security will suffer."

8 years, 6 months

Re: [TUHS] Unix & Memory Management Units (MMU)

by jnc＠mercury.lcs.mit.edu

> Dennis Ritchie's home pages have some info on this Yeah, I'd read that - I was hoping for some actual technical info on the KS11, though. (I'm assuming he has given the name there correctly, or if his memory has dropped a bit - a thing which human memories do! :-) - since I've never been able to find a single mention of it, including in the Spare Module Handbook, which covers other Special Systems products). > I looked for (but did not find) information on what ""the classical > PDP-10 style "hi-seg" "low-seg" memory mapping unit"" was. The best description is in the DECSystem-10 Hardware Reference Manual (mine is EK-10/20-HR-001, but alas that version appears not to be online - I'll scan my copy and put it online when I get a chance.) This version: http://pdp10.nocrew.org/docs/ad-h391a-t1.pdf does appear to cover it: pp. 5-38 through 5-40 (pp. 352-354 of the PDF) for the KA10, and pp. 5-15 to 5-30 (pp. 329-344) for the KI10. The KA10 provided one (optionally) two base/bounds register pairs, where the base register contains the location in real memory. With two pairs (the second one applied to high user address space), the high part could be write-protected, for sharing pure code. The KI10 provided something similar to this, but more complicated; it included paging, but also something called User 'Concealed', which allowed proprietary subroutine packages to be used, while hidden from the rest of the user's code. > Does anyone have an idea what PDP-10 MMU Dennis may have been referring > to? Almost certainly the KA10. > Here my hypothesis would be that in kernel mode mapping was off, and > that in user mode there were two segments, each with a base and limit > into physical memory Hard to say. Kernel mode might or might not have mapping, and User mode might have provided one, or two, segments; the KA10 did have an option for single-segment. > this setup has an echo in how the later KL-11 MMU was used. Sorry, what's a KL-11? The only 'KL11' I know of is the serial line board (M780) which was the predecessor to the DL11. Noel

8 years, 6 months

Re: [TUHS] Unix & Memory Management Units (MMU)

by Paul Ruizendaal

Finally took a look at the V1 source. Referring to http://minnie.tuhs.org/cgi-bin/utree.pl?file=V1/u2.s Toward the end of the sysexec function there is: cmp core,$405 / br .+14 is first instruction if file is / standard a.out format bne 1f / branch, if not standard format mov core+2,r5 / put 2nd word of users program in r5; number of / bytes in program text sub $14,r5 / subtract 12 cmp r5,u.count / bgt 1f / branch if r5 greater than u.count mov r5,u.count jsr r0,readi / read in rest of user's program text add core+10,u.nread / add size of user data area to u.nread br 2f 1: jsr r0,readi / read in rest of file 2: mov u.nread,u.break / set users program break to end of / user code add $core+14,u.break / plus data area jsr r0,iclose / does nothing br sysret3 / return to core image at $core $core is equated to 040000 in another file (u0.s). In V1 apparently the a.out header was 6 words (http://minnie.tuhs.org/cgi-bin/utree.pl?file=V1/man/man5/a.out.5) not 8, and hence the magic for a standard executable was 0405. It was already used as magic to distinguish a.out format files from other executables. It also shows that indeed 'exec' jumped to the first word of the header (at location $core). From this I don't think we will find code for the KS-11 in the V1 source. The file http://minnie.tuhs.org/cgi-bin/utree.pl?file=V1/u3.s also seems to support a LSX /MX like approach where each process switch equates a swap. I'd say that the lost V2 is where memory protection first appeared in Unix, i.e. 1972. Paul PS Sorry for writing 'V0' earlier -- I meant V1 all along.

8 years, 6 months

Re: [TUHS] Unix & Memory Management Units (MMU)

by Johnny Billquist

On 2016-12-08 18:18, Paul Ruizendaal <pnr(a)planet.nl> wrote: > >>> DEC's Custom Special Systems (CSS) group .. build a simple base/limi >>> register device, soon after the 11/20 was released.> ... So an early >>> version of after the original 11/20 port from the PDP-7 had this >>> however..... >> Oh, right, I'd forgotten about that: the KS-11 - I've previously enquired to >> see if anyone had _any_ documentation for this, but so far, nada. > I was looking for that a few years back. Dennis Ritchie's home pages have > some info on this (https://www.bell-labs.com/usr/dmr/www/odd.html) > At the bottom of that page he writes: > > ""Back around 1970-71, Unix on the PDP-11/20 ran on hardware that not only did not support virtual memory, but didn't support any kind of hardware memory mapping or protection, for example against writing over the kernel. This was a pain, because we were using the machine for multiple users. When anyone was working on a program, it was considered a courtesy to yell "A.OUT?" before trying it, to warn others to save whatever they were editing. > [..snip..] > We knew the PDP-11/45, which did support memory mapping and protection for the kernel and other processes, was coming, but not instantly; in anticipation, we arranged with Digital Special Systems to buy a PDP-11/20 with KS-11 add-on. This was an extra system unit bolted to the processor that made it distinguish kernel from user mode, and provided a classical PDP-10 style "hi-seg" "low-seg" memory mapping unit. I seem to recall that maybe 6 of these had been made when we ordered it."" > > My hypothesis is that the very first versions of Unix were using a memory scheme similar to that used in the later LSX and MX derivatives: the kernel resides in lower memory and the user program in upper memory; each process switch implied a swap. Disclaimer: I have not studied the V0 source to verify this hypothesis. > > When this topic had my interest I looked for (but did not find) information on what ""the classical PDP-10 style "hi-seg" "low-seg" memory mapping unit"" was. Here my hypothesis would be that in kernel mode mapping was off, and that in user mode there were two segments, each with a base and limit into physical memory -- and that this setup has an echo in how the later KL-11 MMU was used. > > Does anyone have an idea what PDP-10 MMU Dennis may have been referring to? If you read the Wikipedia page about the PDP-10, you'd find the answer. Basically, kernel mode uses physical memory. User mode have a low segment and a high segment. This is decided by the high bit of the address. For each segment, there is a base register and a length register. Commonly, the low segment stored read/write data, while the high segment could be shared between processes, and have readonly data/code. But you could play in other ways with it, if you wanted to. Essex MUD, as far as I remember, had the game data in a shared hiseg, which could be written by the program. So your guessing is pretty good. Not sure I'd say this is similar to how the later PDP-11 MMU works, though. But I can see someone making the comparison, since the PDP-11 pages can vary in size, within limits. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt(a)softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol

8 years, 6 months

Re: [TUHS] Unix & Memory Management Units (MMU)

by jnc＠mercury.lcs.mit.edu

> From: Clem Cole > DEC's Custom Special Systems (CSS) group .. build a simple base/limi > register device, soon after the 11/20 was released.> ... So an early > version of after the original 11/20 port from the PDP-7 had this > however..... Oh, right, I'd forgotten about that: the KS-11 - I've previously enquired to see if anyone had _any_ documentation for this, but so far, nada. > I would look at Warren's First Edition work to see if there were dregs > of this in that code base Alas, I'd already had that idea (to try and at least re-create a programming spec, at least, for the KS11). There do not seem to be any traces there, perhaps because that code came from a document entitled "Preliminary Release of Unix Implementation", which argues that it's a very early 'version' of V0 (the early 'versions' weren't very formal, there was a continuous process of change/improvement going on, apparently). > It is also noted that the 45 class system (45/55/70/44) had "17th" > address bit - i.e. split I/D space. I believe that this is when "magic > numbers" were really introduced so that could be supported. No, they came in first for 'pure text' (0410): http://minnie.tuhs.org/cgi-bin/utree.pl?file=V4/nsys/ken/sys1.c which I would expect arrived to minimize swapping on machines with small amounts of real memmory. Support for user split-I/D (411) didn't arrive until Version 6: http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/sys/ken/sys1.c although IIRC split I/D in the kernel was supported supported slightly before it was in user - although V5 didn't: http://minnie.tuhs.org/cgi-bin/utree.pl?file=V5/usr/sys/conf/mch.s so it couldn't have been much earlier than V6. Noel

8 years, 6 months

Unix & Memory Management Units (MMU)

by Erik E. Fair

Which version of Unix first ran on a computer with virtual addressing (address translation) so that a process with non-position independent code (PIC) can be loaded anywhere in RAM that the kernel decided to put it, and memory protection such that no process could accidentally or deliberately access RAM not allocated to it by the kernel (or a SIGSEGV would be delivered to it)? Put another way, when did Unix processes stop playing Core War with each other? (OK, so long as no more than one is resident at a time, they can't play Core War with each other, but there still needs to be a mechanism to protect the kernel from inadvertent (or advertent) pointer use). Which is to say, when did Unix run on (and properly use) computers with memory management units (MMU)? My guess from a quick look at the history of the DEC PDP-11 is that the target computer was likely a PDP-11/35 or PDP-11/40 with a KT11-D "memory management" module. One imagines that many pointer mistakes (bugs) in assembly or C were discovered and squashed in that version, modulo the historical unhappiness resulting from address zero containing a zero if dereferenced ("NULL pointers") in process address space. What year did that come about? By the time I got to Unix (2.8BSD on the Cory Hall DEC PDP-11/70), those features (virtual addresses, memory protection from the kernel) had apparently been part of Unix for a long time - certainly earlier than Version 6. This is distinct from demand-paged virtual memory which so far as I know was developed on the DEC VAX-11. curious, Erik <fair(a)netbsd.org>

8 years, 6 months

Re: [TUHS] Unix & Memory Management Units (MMU)

by jnc＠mercury.lcs.mit.edu

> From: "Erik E. Fair" <f > One imagines that many pointer mistakes (bugs) in assembly or C were > discovered and squashed in that version, modulo the historical > unhappiness resulting from address zero containing a zero if > dereferenced ("NULL pointers") in process address space. PS: PDP-11 Unix didn't, I think, do much (anything?) to solve the null pointer problem. (This is for early C versions; I don't know about the later BSD ones.) Location 0 was a usable address for both read and write for everything except 'pure-text' (0410 magic word) processes; in those it was only legal for read. Address 0 mostly did not contain a 0, either; for C programs using the stock run-time, it contained a 'setd' instruction, except in split I+D processes, in which case data space location 0 probably (I'm too busy to spin up my V6 emulator to check) contained some of the program's initialized data (unless special arrangements had been made). Noel

8 years, 6 months

Re: [TUHS] Unix & Memory Management Units (MMU)

by jnc＠mercury.lcs.mit.edu

> From: "Erik E. Fair" > Which version of Unix first ran on a computer with virtual addressing That would be the first version to run on the PDP-11/45; I'm not sure which one that was, there's not enough left of Version 2 or Version 3 to see; Version 4 definitely ran on the 11/45: http://minnie.tuhs.org/cgi-bin/utree.pl?file=V4/nsys/ken/45.s > My guess from a quick look at the history of the DEC PDP-11 is that the > target computer was likely a PDP-11/35 or PDP-11/40 with a KT11-D > "memory management" module. No, they came after the -11/45 (with the KT11-C MMU). > What year did that come about? They got one of the first -11/45's, per a Unix history document I'm too busy to dig up, so 1972. Noel

8 years, 6 months

Re: [TUHS] looking for 4.1a BSD full kernel source

by Jason Stevens

I'm not sure if my other reply got though, so I'll try again... I found the source to the BBN stack in the CSRG CD's it's on CD 4 /sys/deprecated/bbnnet LINT.bbn 08-Aug-2016 06:37 3.5K NOTES 08-Aug-2016 06:37 4.6K RELAY.bbn 08-Aug-2016 06:37 1.2K SCCS/ 08-Aug-2016 06:37 - fsm.h 08-Aug-2016 06:37 1.2K fsmdef.h 08-Aug-2016 06:37 9.6K hmp.c 08-Aug-2016 06:37 12K hmp.h 08-Aug-2016 06:37 3.2K hmp_subr.c 08-Aug-2016 06:37 6.5K hmp_traps.c 08-Aug-2016 06:37 3.5K hmp_traps.h 08-Aug-2016 06:37 2.7K hmp_var.h 08-Aug-2016 06:37 1.4K ic_output.c 08-Aug-2016 06:37 5.7K icmp.c 08-Aug-2016 06:37 17K icmp.h 08-Aug-2016 06:37 3.3K in.c 08-Aug-2016 06:37 12K in.h 08-Aug-2016 06:37 2.0K in_pcb.c 08-Aug-2016 06:37 11K in_pcb.h 08-Aug-2016 06:37 1.9K in_proto.c 08-Aug-2016 06:37 4.9K in_var.h 08-Aug-2016 06:37 2.2K ip.h 08-Aug-2016 06:37 3.3K ip_input.c 08-Aug-2016 06:37 29K ip_output.c 08-Aug-2016 06:37 14K ip_usrreq.c 08-Aug-2016 06:37 3.8K macros.h 08-Aug-2016 06:37 4.4K net.h 08-Aug-2016 06:37 2.4K nopcb.h 08-Aug-2016 06:37 318 raw_input.c 08-Aug-2016 06:37 9.4K rdp.h 08-Aug-2016 06:37 15K rdp_cksum.s 08-Aug-2016 06:3 7 4.4K rdp_fsm.c 08-Aug-2016 06:37 4.5K rdp_input.c 08-Aug-2016 06:37 9.6K rdp_macros.h 08-Aug-2016 06:37 7.9K rdp_prim.c 08-Aug-2016 06:37 13K rdp_states.c 08-Aug-2016 06:37 34K rdp_subr.c 08-Aug-2016 06:37 8.4K rdp_usrreq.c 08-Aug-2016 06:37 21K seq.h 08-Aug-2016 06:37 415 sws.h 08-Aug-2016 06:37 326 tcp.h 08-Aug-2016 06:37 8.6K tcp_input.c 08-Aug-2016 06:37 12K tcp_prim.c 08-Aug-2016 06:37 9.8K tcp_procs.c 08-Aug-2016 06:37 28K tcp_states.c 08-Aug-2016 06:37 20K tcp_usrreq.c 08-Aug-2016 06:37 22K udp.c 08-Aug-2016 06:37 5.2K udp.h 08-Aug-2016 06:37 1.1K udp_usrreq.c 08-Aug-2016 06:37 7.0K I've been meaning to try to try to manually mash stuff together but just haven't gotten around to it. > ---------- > From: Paul Ruizendaal > Sent: Thursday, December 1, 2016 4:30 PM > To: tuhs(a)minnie.tuhs.org > Subject: [TUHS] looking for 4.1a BSD full kernel source > > > Hi, > > I'm trying to find out exactly what was in the 4.1a BSD distribution, as > far as the kernel is concerned. The image in the CSRG archive comes from a > tape that had a hard read error and does not include any kernel sources. > Some of the kernel files were already covered by SCCS around that time, > but not everything. My main focus is to understand tcp/ip networking in > 4.1a and whether the kernel could be built with either the Berkeley or the > BBN network stack. > > Does anybody know where I could find a full set of kernel sources for the > 4.1a BSD kernel? > > Many thanks in advance! > > Paul >

8 years, 7 months

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TUHS