TUHS

tuhs@tuhs.org

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6557 discussions

by David

Arnold gets it right on the Pascal indexing. In UCSD Pascal you could specify any array bounds you would like and the compiler would 0 base them for you by always doing a subtraction, or addition if your min was negative, of your min array index. So a little run time cost for non-zero based arrays. I’m not sure how other Pascal compilers did this. I find it interesting that there are now a slew of testing programs (Valgrind, Address Sanitizer, Purify, etc) that will add the ‘missing’ array bounds checking for C. David > On Jun 7, 2017, at 10:01 AM, tuhs-request(a)minnie.tuhs.org wrote: > > Date: Wed, 07 Jun 2017 07:20:43 -0600 > From: arnold(a)skeeve.com > To: tuhs(a)tuhs.org, ag4ve.us(a)gmail.com > Subject: Re: [TUHS] Array index history > Message-ID: <201706071320.v57DKhmJ026303(a)freefriends.org> > Content-Type: text/plain; charset=us-ascii > > Pascal (IIRC) allowed you to specify upper and lower bounds, something > like > > foo : array[5..10] of integer; > > with runtime bounds checking on array accesses. (I could be wrong --- > it's been a LLLLOOONNNGGG time.) > > HTH, > > Arnold

8 years, 2 months

Re: [TUHS] Array index history

by Johnny Billquist

On 2017-06-07 19:01, "Ron Natalie"<ron(a)ronnatalie.com> wrote: > The original FORTRAN and BASIC arrays started indexing at one because everybody other than computer scientists start counting at 1. FORTRAN, yes. BASIC (which dialect might we be talking about?) normally actually start with 0. However, BASIC is weird, in that the DIM statement is actually specifying the highest usable index, and not the size of the array. Thus: DIM X(10) means you get an array with 11 elements. So, people who wanted to use array starting at 1 would still be happy, and if you wanted to start at 0, that also worked. You might unintentionally have a bit of wasted memory, though. > These languages were for scientists and the beginner, so you wanted to make things compatible with their normal concepts. True. > PASCAL on the other hand required you to give the minimum and maximum index for the array. In a way, PASCAL makes the most sense. You still what range you want, and you get that. Anything works, and it's up to you. That said, PASCAL could get a bit ugly when passing arrays as arguments to functions because of this. > Of course, C’s half-assaed implementation of arrays kind of depends on zero-indexing to work. :-) 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, 2 months

Re: [TUHS] 211bsd: kernel panic after a 'here document' in tcsh

by Johnny Billquist

On 2017-06-07 22:14, "Walter F.J. Mueller"<w.f.j.mueller(a)retro11.de> wrote: > Hi, > > a few remarks on the feedback on the kernel panic after a 'here document' in tcsh. > > To Michael Kjörling question: > > I'm curious whether the same thing happens if you try that in some > > other shell? (Not sure how widely here documents were supported back > > then, but I'm asking anyway.) > And Johnny Billquist remark > > Not sure if any of the other shells have this. > > 'here documents' are available and work fine in sh and csh. > And are in fact used, examples Ah. Thanks. Too lazy to check. > To Michael Kjörling remark > > The PC value in the panic report ("pc 161324") strikes me as high > and Johnny Billquist remark > > This is in kernel mode, and that is in the I/O page. > > 211bsd uses split I/D space and uses all 64 kB I space for code. D'oh! Color me stupid. I should have thought of that. > The top 8 kB are in fact the overlay area, and the crash happened > in overlay 4 (as indicated by ov 4). With a simple > > nm /unix | sort | grep " 4" > > one gets > > 161254 t ~psignal 4 > 162302 t ~issignal 4 > > so the crash is just 050 bytes after the entry point of psignal. So the > PC address is fine and not the problem. For psignal look at > > http://www.retro11.de/ouxr/211bsd/usr/src/sys/sys/kern_sig.c.html#s:_psignal > > the crash must be one of the first lines. psignal is an internal kernel > function, called from > > http://www.retro11.de/ouxr/211bsd/usr/src/sys/sys/kern_sig.c.html#xref:s:_p… > > and has nothing to do with the libc function psignal > > http://www.retro11.de/ouxr/211bsd/usr/man/cat3/psignal.0.html > http://www.retro11.de/ouxr/211bsd/usr/src/lib/libc/gen/psignal.c.html The libc function would be in user mode, so that one was pretty clear. Ok. Digging through this a little for real then. psignal gets called with a signal from the trap handler. The actual signal is weird. It would appear to be 0160750, which would be -7704 if I'm counting right. That does not make sense as a signal. The psignal code pulls a value based on the signal number, which is the line: prop = sigprop[sig]; which uses the signal number as an index. With a random, weird signal number, this access wherever that might end up. Which is when you get the crash. On my system, sigprop is at address 0012172, which, with a signal of -7704 ends up at address 0173142, which by (un)luck happens to be in the middle of the diagnostics bootstrap rom space. So I don't get a Unibus timeout error, while you do. Probably because sigprop is at a slightly different address in your kernel. So, the real question is how trap can be calling psignal with such a broken signal number. I might dig further down that question another day. But unless you already got this far, I might have saved you a few minutes of digging. I did start looking into the trap code, which is in pdp/trap.c, but this is not entirely straight forward. It goes through a bunch of things trying to decide what signal to send, before actually calling psignal. > To Johnny Billquist remark > > Could you (Walter) try the latest version of 2.11BSD and see if you > > still get that crash? > > very interesting that you see a core dump of tcsh rather a kernel panic. Indeed. > Whatever tcsh does, it should not lead to a kernel panic, and if it does, > it is primarily a bug of the kernel. It looks like there are two issues, > one in tcsh, and one in the kernel. I've a hunch were this might come from, > but that will take a weekend or two to check on. Agree that the kernel should not crash on this. Also, tcsh should not really crash either, but it's a separate issue, even though one might have triggered the other here. But yes, there are two bugs in here. If you can recreate the kernel crash on the latest version, that would be good. But it smells like trap.c have some path where it does not even set what signal to deliver, and then calls psignal with whatever the variable i got at the function start. Which would be some random stuff on the stack. 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, 2 months

Re: [TUHS] Array index history

by Johnny Billquist

On 2017-06-08 22:17, Dave Horsfall<dave(a)horsfall.org> wrote: > > Just to diverge from this thread a little, it probably isn't all that > remarkable that programming languages tend to reflect the hardware for > which they were designed. > > Thus, for example, we have the C construct: > > do { ... } while (--i); > > which translated right into the PDP-11's "SOB" instruction (and > reminiscent of FORTRAN's insistence that DO loops are run at least once > (there was a CACM article about that once; anyone have a pointer to it?)). > > And of course the afore-mentioned FORTRAN, which really reflects the > underlying IBM 70x architecture (shudder). FORTRAN stopped running the loops at least once already with FORTRAN 77. The last who insisted on running loops at least once was FORTRAN IV. 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, 2 months

Array index history

by shawn wilson

I learned the other day that array indexes in some languages start at 1 instead of 0. This seems to be an old trend that changed around the 70s? Who started this? Why was the change made? It seems to have come about around the same time as C, but interestingly enough Lua is kinda in between (you can start an array at 0 or 1). Smalltalk can probably have a 0 base index just by it's nature, but I wonder whether that would work in a 40 year old interpreter.

8 years, 2 months

Re: [TUHS] Array index history

by Richard Tobin

> Basically, until C came along, the standard practice was for indices > to start at 1. Certainly Fortran and Pascal did it that way. Mercury Autocode used 0. http://www.homepages.ed.ac.uk/jwp/history/mercury/manual/autocode/4.jpg -- Richard -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.

8 years, 2 months

Re: [TUHS] 211bsd: kernel panic after a 'here document' in tcsh

by Walter F.J. Mueller

Hi, a few remarks on the feedback on the kernel panic after a 'here document' in tcsh. To Michael Kjörling question: > I'm curious whether the same thing happens if you try that in some > other shell? (Not sure how widely here documents were supported back > then, but I'm asking anyway.) And Johnny Billquist remark > Not sure if any of the other shells have this. 'here documents' are available and work fine in sh and csh. And are in fact used, examples /usr/adm/daily (a /bin/sh script) su uucp << EOF /etc/uucp/clean.daily EOF /usr/crash/why (a /bin/csh script) adb -k {unix,core}.$1 << 'EOF' version/sn"Backtrace:"n $c 'EOF' To Michael Kjörling remark > The PC value in the panic report ("pc 161324") strikes me as high and Johnny Billquist remark > This is in kernel mode, and that is in the I/O page. 211bsd uses split I/D space and uses all 64 kB I space for code. The top 8 kB are in fact the overlay area, and the crash happened in overlay 4 (as indicated by ov 4). With a simple nm /unix | sort | grep " 4" one gets 161254 t ~psignal 4 162302 t ~issignal 4 so the crash is just 050 bytes after the entry point of psignal. So the PC address is fine and not the problem. For psignal look at http://www.retro11.de/ouxr/211bsd/usr/src/sys/sys/kern_sig.c.html#s:_psignal the crash must be one of the first lines. psignal is an internal kernel function, called from http://www.retro11.de/ouxr/211bsd/usr/src/sys/sys/kern_sig.c.html#xref:s:_p… and has nothing to do with the libc function psignal http://www.retro11.de/ouxr/211bsd/usr/man/cat3/psignal.0.html http://www.retro11.de/ouxr/211bsd/usr/src/lib/libc/gen/psignal.c.html To Johnny Billquist remark > Could you (Walter) try the latest version of 2.11BSD and see if you > still get that crash? very interesting that you see a core dump of tcsh rather a kernel panic. Whatever tcsh does, it should not lead to a kernel panic, and if it does, it is primarily a bug of the kernel. It looks like there are two issues, one in tcsh, and one in the kernel. I've a hunch were this might come from, but that will take a weekend or two to check on. With best regards, Walter

8 years, 2 months

Re: [TUHS] 211bsd: kernel panic after a 'here document' in tcsh

by Johnny Billquist

On 2017-06-06 04:00, Michael Kjörling <michael(a)kjorling.se> wrote: > > On 5 Jun 2017 16:12 +0200, from w.f.j.mueller(a)retro11.de (Walter F.J. Mueller): >> I'm using 211bsd (Version 447) and found that a 'here document' in tcsh >> leads to a kernel panic. It's absolutely reproducible on my system, both >> when run it on my FPGA PDP-11 or in simh. Just doing >> >> tcsh >> cat << EOF > I'm curious whether the same thing happens if you try that in some > other shell? (Not sure how widely here documents were supported back > then, but I'm asking anyway.) Not sure if any of the other shells have this. We're basically talking csh, sh and ksh unless I remember wrong. But it's a good question. If noone else have tried it by tomorrow, I could check. >> is enough, and I get >> >> ka6 31333 aps 147472 >> pc 161324 ps 30004 >> ov 4 >> cpuerr 20 >> trap type 0 >> panic: trap >> syncing disks... done >> >> looking at the crash dump gives >> >> cd /etc/crash >> ./why 4 >> Backtrace: >> 0147372: _boot(05000,0100) from ~panic+072 >> 0147414: _etext(011350) from ~trap+0350 >> 0147450: ~trap() from call+040 >> 0147516: _psignal(0101520,0160750) from ~trap+0364 >> 0147554: ~trap() from call+040 >> >> so the crash is in psignal, which is afaik the kernel internal >> mechanism to dispatch signals. > The PC value in the panic report ("pc 161324") strikes me as high, but > 161324 octal is 58068 decimal, so it's not excessively so, and perhaps > in line with what one might expect to see with a kernel pinned near > top of memory. Are the offsets in the backtrace constant, i.e. does it > always crash on the same code? 161324 is way high. This is in kernel mode, and that is in the I/O page. Basically no code lives in the I/O page (some boot roms and hardware diagnostics excepted). This smells like corrupted memory (pointer or stack), or something else very funny. > Not knowing what cpuerr 20 is specifically doesn't help, and at least > http://www.retro11.de/ouxr/29bsd/usr/src/sys/sys/trap.c.html#n:112 > (which doesn't seem to be too far from what you are running) isn't > terribly enlightening; CPUERR is simply a pointer into a memory-mapped > register of some kind, as seen at > http://www.retro11.de/ouxr/29bsd/usr/include/sys/iopage.h.html#m:CPUERR, > and at least pdp11_cpumod.c from the simh source code at > http://simh.trailing-edge.com/interim/pdp11_cpumod.c wasn't terribly > enlightening, though of course I could be looking in entirely the > wrong place. Like others said - the cpu error register is documented in the processor handbook. 020 means Unibus Timeout, which is consistent with trying to access something in the I/O page, where there is no device configured to respond to that address. I just tried the same thing on a simh system here, and I do not get a crash. This on 2.11BSD at patch level 449, running on an emulated 11/94. I do however get tcsh to crash. simh:/home/bqt> su - Password: erase, kill ^U, intr ^C # tcsh simh:/# cat << EOF Illegal instruction - core dumped # Suspended (tty input) simh:/home/bqt> simh:/home/bqt> cat /VERSION Current Patch Level: 448 Date: January 5, 2010 Yes, it says patch level 448, but it really is 449. This was the system where I worked together with Steven when doing the 449 patch set, but I never got around to actually updating the VERSION file itself. Also, this was while running on the console. Could you (Walter) try the latest version of 2.11BSD and see if you still get that crash? 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, 2 months

211bsd: kernel panic after a 'here document' in tcsh

by Walter F.J. Mueller

Hi, I'm using 211bsd (Version 447) and found that a 'here document' in tcsh leads to a kernel panic. It's absolutely reproducible on my system, both when run it on my FPGA PDP-11 or in simh. Just doing tcsh cat << EOF is enough, and I get ka6 31333 aps 147472 pc 161324 ps 30004 ov 4 cpuerr 20 trap type 0 panic: trap syncing disks... done looking at the crash dump gives cd /etc/crash ./why 4 Backtrace: 0147372: _boot(05000,0100) from ~panic+072 0147414: _etext(011350) from ~trap+0350 0147450: ~trap() from call+040 0147516: _psignal(0101520,0160750) from ~trap+0364 0147554: ~trap() from call+040 so the crash is in psignal, which is afaik the kernel internal mechanism to dispatch signals. Questions: 1. has anybody seen this before ? 2. any idea what the reason could be ? With best regards, Walter

8 years, 2 months

Re: [TUHS] 211bsd: kernel panic after a 'here document' in tcsh

by jnc＠mercury.lcs.mit.edu

> From: Jacob Ritorto > Where might one find the list of trap_types Look in: http://minnie.tuhs.org/cgi-bin/utree.pl?file=2.11BSD/sys/pdp/scb.s which maps from trap vector locations (built into the hardware; consult a PDP-11 CPU manual for details) to trap type numbers, which are defined here: http://minnie.tuhs.org/cgi-bin/utree.pl?file=2.11BSD/sys/pdp/trap.h and handled here: http://minnie.tuhs.org/cgi-bin/utree.pl?file=2.11BSD/sys/pdp/trap.c > and cpuerrs? That just prints the contents of the CPU Error Register; see an appropriate PDP-11 CPU manual - 11/70, /44, /73, /83 or /84 for what all the bits mean. Also the "KDJ11-A CPU Module User's Guide", which also documents it. In theory, there's also a KDJ11-B UG, but it's not online. If anyone has one, can we please get it scanned? Thanks! Noel

8 years, 2 months

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TUHS