TUHS June 2021

tuhs@tuhs.org

34 participants
27 discussions

Re: [TUHS] [EXT] "The programmer must have been carried away ...

by Angelo Papenhoff

On 23/06/21, silas poulson wrote: > I’m aware line 2238’s famous “You are not expected to understand > this.” Comment is due to odd PDP-11/45 behaviour. Actually there are two different takes on what it is exactly that you're not expected to understand. The "obvious" one in Lions' book, (i.e. saved stack being overwritten when swapping so you have to restore from the special swap-saved stack), but dmr had a different take on it, that it had to do with functions really not being happy if you switch the stack underneath them. You can find dummy variables in the interdata port that make sure the stack frames of some functions (newproc and swtch?) match. So not really a hardware thing but a consequence of the compiler. > Do you know if other sections of the C show remnants of B or the PDP? > Or is it just those spots? For the kernel I'm just aware of this one. printf was copied over a number of times (the c compiler also includes a version) but the kernel was never written in B, so i wouldn't expect any B-ness in there otherwise. aap

1 year, 9 months

"The programmer must have been carried away ...

by Angelo Papenhoff

... when he declared all the parameters for this procedure" I'm sure some of you remember this quote expressing John Lions' puzzlement over the declaration of printf in the UNIX kernel: printf(fmt,x1,x2,x3,x4,x5,x6,x7,x8,x9,xa,xb,xc) Note that parameters x2 and following are never referenced by name in the function body, only by pointer arithmetic from &x1. The historical reason for this long list of parameters is probably not well known, so I want to explain it and hope that you will find it as enjoyable as I did when I came across it some time ago while studying leftover files of B. To call a function in B, there's a little dance you have to do: first push the function address onto the stack, remember the stack pointer, push all the arguments, then restore the stack pointer and do the actual call. In diagrams, this is what happens to the B stack: push func addr: +------------+ | | <- sp +------------+ | func addr | +------------+ mark (n2): +------------+ | | <- sp +------------+ | | <- old sp (saved on native stack) +------------+ | func addr | +------------+ push arguments: +------------+ | | <- sp +------------+ | arg n | +------------+ | ... | +------------+ | arg 0 | +------------+ | | <- old sp (saved on native stack) +------------+ | func addr | +------------+ call (n3): pop old sp from stack jump to func addr on stack set ret addr and old fp +------------+ | arg n | +------------+ | ... | +------------+ | arg 0 | +------------+ | ret addr | +------------+ | old fp | <- sp, fp +------------+ The callee then sets sp, so has to know how many args and automatics! +------------+ | | <- sp +------------+ | auto n | +------------+ | ... | +------------+ | auto 0 | +------------+ | arg n | +------------+ | ... | +------------+ | arg 0 | +------------+ | ret addr | +------------+ | old fp | <- fp +------------+ So because the arguments to a functions were grouped together with the automatics and not below the ret addr and saved fp, there has to be space on the stack lest they clash. This of course means that this printf in B would probably break if called with more arguments than it expects. So there you have it. Just a line of B code that wasn't updated to C. Cheers, aap

1 year, 9 months

Arithmetic expansion in Unix shells

by Michael Siegel

Hello, I'm currently trying out the rc shell (using Byron Rakitzis' implementation for Unix). Compared to Bash, which I normally use, this shell has a rather small feature set (which isn't to say that that's necessarily a bad thing). Now, one of the features that Bash has and rc doesn't have is the ability to perform arithmetic expansion. That's not really a problem because you can just use `expr` instead. I wonder, though, when arithmetic expansion as a shell built-in became a thing, especially in POSIX sh. POSIX has included that feature since at least 2001, and probably quite some years earlier, given that Bash already had it in 1995 (going by the manual page of version 1.14.7, the oldest I could find). So, maybe someone here can help me find out when this was actually standardized. Thanks. -- Michael

1 year, 9 months

Re: [TUHS] Arithmetic expansion in Unix shells

by Brian Walden

even tho it was there, in-shell integer arithmetic had a few issues before ksh86. pre-ksh86 these had problems -- A. decimal point in a number $ integer I $ I=2.2 would error on the assignment, but with ksh86 $I is truncated to 2 (yes "integer" is an builtin alias to typeset -i and ksh courses at the time instructed to use that over typset) B. negative numbers $ integer I $ I=-2 here pre-86 $I would be assigned a large value like 2147483646 also ksh was not stardard until SVR4 (very late 80s) so it was found in paths like /usr/add-on/bin/ksh or /usr/exptools/bin/ksh, or not even there at all, you could not reliably #! ksh scripts also with ksh86 the double paren ((...)) notation was exactly the same as "let ..." and were completely optional if the variable was predefined as an integer, so $ I=0 $ ((I=I+1)) and $ integer I $ I=0 $ I=I+1 are the same. All internal integers in ksh were C longs (at least 32-bits) where Bourne shell all vars are strings so you would need to do this -- $ I=`expr $I + 1` But also at that time expr(1) could NOT deal with negative numbers on input, they became strings. So $ expr -9 + 1 is an error with "non-numeric argument", and $ expr -11 '<' -1 returns 0, a false statement, which are hidden bugs with variables. expr(1) was also 32-bits, as was test (i.e [ ) which could deal with negative numbers just fine. for arbitrarily large numbers you needed use dc(1) or bc(1). but dc(1) also has a issue with inputing negative numbers as it uses an _ not a - to denote a negatve number on input, but does use the - on output. $ I=`echo _9 1 - p | dc` is how you would do ((I=-9 - 1)) in bourne with dc which is cumbersome if you have a variable with a neagtive number in it, and required a "tr - _" first. however $ I=`echo -9 - 1 | bc` worked just fine in bourne. -Brian Chet Ramey wrote: > On 6/21/21 5:57 AM, arnold at skeeve.com wrote: > > Arithmetic expansion dates back at least as far as ksh88. > > ksh had the `let' builtin from at least 1983. The ((...)) compound command > was there by ksh-86. > > > Bash likely picked it up from there. > > Sort of, see below. > > > The original was only integer math and Bash remains that way (IIRC, > > Chet can correct me if I'm wrong). ksh93 added floating point math. > > Yes, bash only has integer arithmetic, since it's all POSIX requires. > > > POSIX would have picked it up from ksh88. > > The $((...)) form of arithmetic expansion is something POSIX picked up > from ksh-88, eventually. The early drafts of the standard (through 1003.2 > d9, at least), used $[...], but they eventually adopted $((...)) because > ksh-88 had already implemented it, though it's not documented in Bolsky > and Korn. > > I put $[...] into bash first (it's still there, though deprecated), then > `let', then $((...)) after POSIX added it, and finally `((' for > compatibility. > > Chet

1 year, 9 months

demand paged 32V / Contacting Kelleman and/or Buroff

by Paul Ruizendaal

I’m still researching John Reiser’s 32V with demand paging, copy-on-write and mmap. Unfortunately, JFR does not have the bits or a listing for this version of 32V. I’ve read the MSc theses of Leffler and Shannon with interest (https://www.tuhs.org/Archive/Documentation/Theses/). The thesis of Shannon has an interesting discussion of a demand paged version of his Harris/6 Unix (Chapter 5). It is based on the Tenex ideas, just as JFR mentioned for his version. The thesis of Leffler contains a gant chart that shows that the demand paged version was written in the first months of 1980 -- concurrently with or slightly after the 32V version. I’ve also (superficially) read the papers on Tenex memory management. The design is closely tied to PDP-10 MMU that BBN designed for Tenex. Some of its data structuring is recognisable in Shannon’s version. One defining aspect is that the design for both is for a virtual address space that is smaller than the physical address space; on a 1980 VAX it was the reverse. If 32V followed the same design ideas (a big if), it most likely limited processes to a capped address space (e.g. 2MB). It might also have contained an in-core flag/data vector with as many entries as there are pages frames in swap space. If true, these downsides may have been why it did not go on to become the root for SysVR1 or R2 paging. The demand paging code for SysVR2 was written by Keith A. Kelleman and Steven J. Buroff, and in contemporary conference talks they were saying that they wanted to combine the best parts of demand-paged 32V and BSD. They may have some additional memories that could help with getting a better understanding of the final version of 32V. Does anybody have contact details for these two gentlemen?

1 year, 9 months

70th anniversary of (official) programming errors

by Steffen Nurpmeso

Not Unix in particular. At least in Germany it is already the 16th, and my BSD calendar notifies that "first programming error is encountered at the U. S. Census Bureau". As not being hard-to-the-core i may have missed it, but also in 1951, in March, the wonderful Grace Hopper "conceives the first compiler, called A-O and later released as Math-Matic. Hopper is also credited with coining the term 'bug' following an incident involving a moth and a Mark II. All (hm!) according to COMPUTERWORLD January 18th, 1999 (i was young!), with assistance of the Computer Museum of Boston. Like McCartney said in the legendary 1999 concert at the Cavern club, the first after his wonderful wife Linda died, "See, with this band, if we don't get it right ... we start again!". Thank you. --steffen | |Der Kragenbaer, The moon bear, |der holt sich munter he cheerfully and one by one |einen nach dem anderen runter wa.ks himself off |(By Robert Gernhardt)

1 year, 9 months

Re: [TUHS] Disassemblers

by norman＠oclsc.org

Rob Pike: Although upon reflection, I think what I did was fix 'adb' and call it 'db'. Haven't had my coffee yet this morning. ==== I don't think so. I did quite a lot of work on adb during my time at the Labs. I remember clearly that it still used all the Bournegol macros when I started; I doubt Rob would have left that there. (It was Rob who translated the shell back to C, I believe.) I got into adb because it still used ptrace and everyone else seemed scared to touch the code to convert it to use /proc. So I fixed that, and fixed sdb too, and finally removed the ptrace call from the kernel. I remember celebrating by expunging ptrace from the UNIX Room copy of the V8 manual. ptrace happened to occupt two facing pages, which I glued together. I did a lot more hacking on adb after that, ranging from little stuff like making # a synonym for 0x in input (so that adb's output could be picked up from the screen and re-used as input, a principle established firmly and correctly by Rob!) to a major restructuring to isolate machine-dependent pieces like instruction decoding and word formats, so that it was simpler not only to make adb work on a new processor architecture but even to make a sort of cross-adb that could, say, correctly interpret a PDP-11 core image on a VAX. (This actually mattered; by the time I arrived Research had no PDP-11s running general-purpose UNIX, but did have LSI-11s acting as Datakit controllers and a standalone power-backed-up LSI-11 that decoded the time signal from WWVB.) I was never really happy about the restructuring; it did more or less what I wanted but it wasn't really graceful. And cross-adb needed a distinct binary for each target. I had thoughts of trying to make a meta-language to describe the target's data formats (simple except for floating point) and how to print its instructions (messier, but I remember being inspired by the clever table-driven code in an disassembler Ken wrote for, I think it was, the NS32000), so that one could load a table from a file at startup; never had the time or the courage to carry through on it. Norman Wilson Toronto ON

1 year, 9 months

Re: [TUHS] Disassemblers

by jnc＠mercury.lcs.mit.edu

> From: Henry Bent > From what I can gather the only way to reasonably examine the > disassembly of a program in the early days of Unix was adb. Is this > true? Was there a way to easily produce a full disassembly? 'adb' is quite late. We had it on the PWB1 (V6 enhanced, basically) system at MIT, so its roots lie before V7. (Every time I run across people who think V7 is early, I go into 'get off my lawn' mode.) The first thing I know of that could disassemble PDP-11 code on Unix was 'db', which dates back to V1: https://minnie.tuhs.org//cgi-bin/utree.pl?file=V1/man/man1/db.1 It wasn't optimal for doing disassembly, because it was non-trivial to dump an entire object file as assembler source - but it could be done. Later (V5 era) there was something called 'cdb', which was 'db' with extensions to make it useful for debugging code whose source was in C: https://minnie.tuhs.org//cgi-bin/utree.pl?file=V4/man/man1/cdb.1 There were other non-Unix disassembler (such as DDT), also. Noel

1 year, 9 months

[tuhs] New version of a paper on Unix evolution

by Nelson H. F. Beebe

A new journal issue published today carries this paper: Diomidis Spinellis and Paris Avgeriou Evolution of the Unix System Architecture: An Exploratory Case Study IEEE Transactions on Software Engineering 47(6) 1134--1163 June 2021 https://doi.org/10.1109/TSE.2019.2892149 A preprint is available here: https://www.researchgate.net/publication/332826685_Evolution_of_the_Unix_Sy… However, it is dated four years ago, and after removing its cover page, diffpdf shows numerous changes compared to today's publication. In the new version, a footnote on the first page says Manuscript received 19 May 2018; revised 18 Dec. 2018; accepted 28 Dec. 2018. Date of publication 2 May 2019; date of current version 14 June 2021. ------------------------------------------------------------------------------- - Nelson H. F. Beebe Tel: +1 801 581 5254 - - University of Utah FAX: +1 801 581 4148 - - Department of Mathematics, 110 LCB Internet e-mail: beebe(a)math.utah.edu - - 155 S 1400 E RM 233 beebe(a)acm.org beebe(a)computer.org - - Salt Lake City, UT 84112-0090, USA URL: http://www.math.utah.edu/~beebe/ - -------------------------------------------------------------------------------

1 year, 9 months

Re: [TUHS] 70th anniversary of (official) programming errors

by Jason Stevens

Sounds very "Deus ex machina" like. Although it's hard to staple a ghost to your notebook. -----Original Message----- From: Bakul Shah To: Rob Pike Cc: The Eunuchs Hysterical Society Sent: 6/16/21 12:13 PM Subject: Re: [TUHS] 70th anniversary of (official) programming errors https://spectrum.ieee.org/the-institute/ieee-history/did-you-know-edison -coined-the-term-bug <https://spectrum.ieee.org/the-institute/ieee-history/did-you-know-ediso n-coined-the-term-bug> Like Edison, she (Grace Hopper) was recalling the word’s older origins in the Welsh bwg, the Scottish bogill or bogle, the German bögge, and the Middle English bugge: the hobgoblins of pre-modern life, resurrected in the 19th century as, to paraphrase philosopher Gilbert Ryle, ghosts in the machine. Electrical circuits can have "bad connections" so I do wonder if Edison coined this word based on "ghost like" faults that magically appear and disappear! -- Bakul On Jun 15, 2021, at 8:48 PM, Rob Pike <robpike(a)gmail.com> wrote: There are citations from Edison in the 19th century using the word, and a quote somewhere by Maurice Wilkes about the stairwell moment when he realized much of the rest of his life would be spent finding programming errors. That moth was not the first bug, nor the first "bug", it was the first recorded "actual bug". -rob On Wed, Jun 16, 2021 at 9:46 AM Dan Cross < crossd(a)gmail.com <mailto:crossd@gmail.com> > wrote: On Tue, Jun 15, 2021 at 6:55 PM John Cowan < cowan(a)ccil.org <mailto:cowan@ccil.org> > wrote: On Tue, Jun 15, 2021 at 6:25 PM Steffen Nurpmeso < steffen(a)sdaoden.eu <mailto:steffen@sdaoden.eu> > wrote: As not being hard-to-the-core i may have missed it, but also in 1951, in March, the wonderful Grace Hopper "conceives the first compiler, called A-O and later released as Math-Matic. Hopper is also credited with coining the term 'bug' following an incident involving a moth and a Mark II. Yes, but wrongly. The label next to the moth is "First actual case of bug being found", and the word "actual" shows that the slang term already existed then. Brief unexplained faults on telephony (and before that telegraphy) lines were "bugs on the line" back in the 19C. Vibroplex telegraph keys, first sold in 1905, had a picture of a beetle on the top of the key, and were notorious for creating bugs when inexperienced operators used them. (Vibroplex is still in business, still selling its continuous-operation telegraph keys, which ditt as long as you hold the paddle to the right.) Indeed, the Vibroplex key is called a "bug". I suspect this has something to do with its appearance more than anything else, though (it kinda sorta looks like, er, a bug). - Dan C.

1 year, 9 months

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TUHS June 2021