TUHS

tuhs@tuhs.org

21 participants
6412 discussions

by Caipenghui

UNIX history memoir has been published in China (publish by posts and Telecommunications Press in China) and translated into Chinese. It is also called name "UNIX legend" in China. I'm going to buy now. If you're in the computer industry, it's exciting just to understand how these buzzwords came into being. Even if you don't have a deep technical background, You can also benefit a lot from these ides that shine with genius. I have been looking forward to a Chinese book about the history of Unix development for so many years, and now I can finally see it. Thanks bwk and other guys.

3 years, 6 months

Re: [TUHS] Binary log files

by norman＠oclsc.org

Some of us have, literally for decades, been dealing with wtmp by rolling it weekly or monthly or quarterly or whatever, letting cron run something like cd /usr/adm # that's how long I've been doing this! umask 022 >wtmp.new ln wtmp wtmp.prev mv wtmp.new wtmp # also so long ago there was no seq(1) nums=`awk 'BEGIN {for (i = 12; i >= 0; i--) print i; exit}'` for i in $nums; do inext=`expr $i + 1` if [ -f wtmp.$i ]; then mv wtmp.$i wtmp.$inext fi done mv wtmp.prev wtmp.0 This really isn't rocket science. It isn't even particularly interesting UNIX history. Can we move on to something that IS interesting? Here are some things I find more interesting: 1. utmp came before wtmp: utmp(V) appears in the First Edition manual, wtmp(V) only in the Second. Apparently interest in who else is logged in right now predated interest in who has logged in recently. 2. Both files started out in /tmp. wtmp is first said to be in /usr/adm instead in the Fifth Edition manual, utmp in /etc in the Sixth. 3. The names /tmp/utmp and /tmp/wtmp appear to have been issued by the Department of Redundancy Department. I think it quite likely that Ken and Dennis would have been familiar with that joke once the recording containing it was issued in mid-1970, but I don't know whether utmp existed in some form before that. I see no sign of it in the fragments of PDP-7 source code we have (in particular init doesn't seem to use it), but what about later PDP-7 or very early PDP-11 code predating the late-1971 First Edition manual? Norman Wilson Toronto ON Not Insane

3 years, 6 months

Binary log files

by John Cowan

As long ago as the 7th Edition, several binary log files were maintained: the file generated by acct(2) (one record per process) and the utmp and wtmp files (one record per login). Both of these are defined by structs in .h files, so they are definitely not portable (int sizes, endianism, etc.)

3 years, 6 months

[tuhs] Dennis Ritchie's couch

by Nelson H. F. Beebe

The last article of the latest issue of the Communications of the ACM that appeared electronically earlier today is a brief interview with this year's ACM Turing Award winners, Al Aho and Jeff Ullman. The article is Last byte: Shaping the foundations of programming languages https://doi.org/10.1145/3460442 Comm. ACM 64(6), 120, 119, June 2021. and it includes a picture of the two winners sitting on Dennis Ritchie's couch. I liked this snippet from Jeff Ullman, praising fellow list member Steve Johnson's landmark program, yacc: >> ... >> At the time of the first Fortran compiler, it took several >> person-years to write a parser. By the time yacc came around, >> you could do it in an afternoon. >> ... ------------------------------------------------------------------------------- - 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/ - -------------------------------------------------------------------------------

3 years, 6 months

Re: [TUHS] The Unix shell: a 50-year view

by Jon Steinhart

Wow. This is a terrible paper. It's full of of incorrect, unsubstiantiated, and meaningless statements. It's so bad in my opinion that I'm not sorry that I dropped my ACM membership a while ago. These folks really needed an editor. The paper annoys me so much that I've decided to write a lengthy note to the authors which I'll post here once I'm done. Jon

3 years, 6 months

Disassemblers

by 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? I'll confess to being fairly ignorant of adb use since I always had dbx or the equivalent available. The first tool I'm aware of to purposefully/primarily produce a full listing is MIPS dis (ca. 1986?) but there must have been something before that for other systems, no? -Henry

3 years, 6 months

pointer disambiguation (was Re: Disassemers)

by Paul Winalski

On 7/1/21, scj(a)yaccman.com <scj(a)yaccman.com> wrote: > When PCC came along and started running on 32-bit machines, I started > thinking about algorithms for optimization. A problem that I had no > good solution for could be illustrated by a simple piece of code: > > x = *p; > > y = *q; > > q gets changed > > *q = z; > > The question is, do I need to reload x now because q might have been > changed to point to the same place as p? Yes, this is a very well-known problem in scalar optimization in compiler engineering. It's called pointer disambiguation and is part of the more general problem of data flow analysis. As you observed, getting it wrong can lead to very subtle and hard-to-debug correctness problems. In the worst case, one has to throw out all current data flow analysis of global and currently active local variables and start over. In your example, the statement "*q = z" may end up forcing the compiler to toss out all data flow information on x and z (and maybe p and q as well). If q could possibly point to x and x is in a register, the assignment forces x to be reloaded before its next use. Ambiguous pointers prohibit a lot of important optimizations. This problem is the source of a lot of bugs in compilers that do aggressive optimizations. Fortunately a bit of knowledge of just how "q gets changed" can rescue the situation. In strongly-typed languages, for example, if x and z are different data types, we know the assignment of z through q can't affect x. We also know that the assignment can't affect x if x and z have disjoint scopes. The 'restrict' keyword in C pointer declarations was added to help mitigate this problem. Some compilers also have a command line option that allows the user to say, "I solemnly swear that I won't do this sort of thing". -Paul W.

3 years, 6 months

Re: [TUHS] Using printf from Assembly Language in V6, and db.

by jnc＠mercury.lcs.mit.edu

> From: Paul Riley <paul(a)rileyriot.com> >> (I wrote a note, BITD, explaining how all this worked; I'll upload it >> to the CHWiki when I get a chance.) Now here: https://gunkies.org/wiki/PDP-11_C_stack_operation along with simple examples of args and auto variables, which are both referenced via the FP. > As a non-C consumer of printf, should I point R5 at some space for a > stack and call printf in the same manner as the C example I cited? Not necessary to do anything with R5 (you can leave it blank); the only things a PDP-11 C routine needs are: - a good stack - the arguments, and return point, on the top of the stack csv will set up the frame pointer, making no assumptions about the old contents of R5 - see the source: http://ana-3.lcs.mit.edu/~jnc/tech/unix/lib/csv.s although it does save the old R5 contents, and restore them on exit. Noel

3 years, 6 months

Re: [TUHS] Using printf from Assembly Language in V6, and db.

by jnc＠mercury.lcs.mit.edu

> From: Paul Riley > I want to use printf from an assembly language program, in V6. ... the > substitutional arguments for printf are pushed onto the stack in reverse > order, then the address of the string, and then printf is called. After > this, 6 is added to the stack pointer. This is all down to the standard C environment / calling sequence on the PDP-11 (at least, in V6 C; other compilers may do it differently). Calls to printf() are in no way special. Very briefly, there's a 'frame pointer' (R5) which points to the current stack frame; all arguments and automatics are relative to that. A pair of special routines, csv and cret (I couldn't find the source on TUHS, but it happens to be here: http://ana-3.lcs.mit.edu/~jnc/tech/unix/lib/csv.s if you want to see it), set up and tear down the frame on entry/exit to that routine. The SP (R6) points to a blank location on the top (i.e. lower address; PDP-11 stacks grow down) of the stack. To call a subroutine, the arguments are pushed, the routine is called (which pushes the return PC), and on return (which pops the return PC), the arguments are discarded by the caller. (I wrote a note, BITD, explaining how all this worked; I'll upload it to the CHWiki when I get a chance.) > I assume that the printf routine pops the address of the string off the > stack, but leaves the other values on the stack No, all C routines (including printf()) leave the stack more or less alone, except for CSV/CRET hackery, allocating space for automatic variables on routine entry (that would be at L1; try looking at the .s for a routine with automatic variables), and popping the return PC on exit. The exception to this is the stuff around calling _enother_ routine (sketched above). Another exception is alloca() (source here: http://ana-3.lcs.mit.edu/~jnc/tech/unix/lib/alloca.s again, couldn't find it in TUHS), which allocated a block of memory on the stack (automatically discarded when the routine which called alloca() returns). Note that since all automatic variables and incoming arguments are relative to the FP, alloca is _really_ simple; justs adjusts the SP, and it's done. > What troubles me is that the stack pointer is not decremented before the > first mov, in the example below. Is this some C convention? I would > assume that the first push in my example would overwrite the top of the > stack. That's right; that's because in the C runtime environment, the top location on the stack is a trash word (set up by csv). > I understand db only works on files like a.out or core dumps. If I > wanted to break the assembly language program to examine values, how can > I force a termination and core dump elegantly, so I can examine some > register values? Use 'cdb': https://minnie.tuhs.org//cgi-bin/utree.pl?file=V6/usr/man/man1/cdb.1 which can do interactive debugging. Noel

3 years, 6 months

Using printf from Assembly Language in V6, and db.

by Paul Riley

Hi, I want to use printf from an assembly language program, in V6. It seems that the Unix Programmer's Manual doesn't show how to use it from assembly, so I wrote a short C program and captured the assembler output, for some clues. Listings below. In my example, the substitutional arguments for printf are pushed onto the stack in reverse order, then the address of the string, and then printf is called. After this, 6 is added to the stack pointer. I assume that the printf routine pops the address of the string off the stack, but leaves the other values on the stack, hence the need to add 2x3=6 to the stack after calling printf in my example. What troubles me is that the stack pointer is not decremented before the first mov, in the example below. Is this some C convention? I would assume that the first push in my example would overwrite the top of the stack. Perhaps I'm not used to PDP-11 stack conventions. I understand db only works on files like a.out or core dumps. If I wanted to break the assembly language program to examine values, how can I force a termination and core dump elegantly, so I can examine some register values? Paul *Paul Riley* Email: paul(a)rileyriot.com int a, b, c; int main(){ printf("printf: start\n"); a = 1; b = 2; c = 3; printf("A = %d, B = %d, C = %d", a, b, c); printf("printf: end\n"); } .comm _a,2 .comm _b,2 .comm _c,2 .globl _main .text _main: ~~main: jsr r5,csv jbr L1 L2:mov $L4,(sp) jsr pc,*$_printf mov $1,_a mov $2,_b mov $3,_c mov _c,(sp) mov _b,-(sp) mov _a,-(sp) mov $L5,-(sp) jsr pc,*$_printf add $6,sp mov $L6,(sp) jsr pc,*$_printf L3:jmp cret L1:jbr L2 .globl .data L4:.byte 160,162,151,156,164,146,72,40,163,164,141,162,164,12,0 L5:.byte 101,40,75,40,45,144,54,40,102,40,75,40,45,144,54,40,103,40,75,40,45,144,0 L6:.byte 160,162,151,156,164,146,72,40,145,156,144,12,0 #

3 years, 6 months

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TUHS