TUHS January 2016

tuhs@tuhs.org

41 participants
51 discussions

by jnc＠mercury.lcs.mit.edu

> From: Will Senn > How did folks debug assembly routines in Unix v6, back in the day? There are three different questions here, although you may not realize it: - How did folks debug assembly routines in user programs in Unix v6 - How did folks debug assembly routines in the kernel in Unix v6 - How did folks debug assembly routines in PDP-11 standalone code created with Unix v6 I did all three, and I used different methods for each. For user code, there was no source-level debugger, so debugging C programs and debugging code written in assembler were the same thing. I used 'adb' (which is, stricly speaking, slightly post-V6 - our system at MIT was actually sort of an early PWB clone), but V6 itself provides 'db' (and also, IIRC, 'cdb'); all three are very similar. For standalone code (in my case, a packet switch that ran on PDP-11's), I used a version of DDT that was linked in with the rest of the code. The original version was one in MACRO-11 which I inherited from Jim Mathis at SRI, but I eventually re-wrote it in portable C, and it was used on the 68K, uVax and 29K. For kernel assembler code... I can't remember what I did! Although I wrote a fair amount of it (I modified m45.s very extensively, to work with the Able ENABLE card), so I must have done _something_, but I have no idea what. In theory I could have linked DDT in with the kernel, but I don't think I ever did so? Recently I was debugging some kernel code (the splice() system call we were discussing here), and I debugged it using... printf()'s! It was written in C, but I don't really differentiate between debugging C code, and assembler. > 2. No map file created by ld. LD normally includes a symbol table in the output file, which 'nm' can dump. > 3. No debugger that I can find. See above. > My workarounds include using OD to view the generated machine code Use db/cdb/adb if you want to look at compiled code. Also, for 'cc', use the -S flag. Noel

8 years, 3 months

v6 debugging

by Will Senn

All, I'm finally returning to my study of v6 after digging a bit further into assembly language and "other" pdp-11 operating systems. I even managed to get hello, world working in assembly in v6 and interestingly enough, I actually see how it works... for the most part :). Mini-note here: http://decuser.blogspot.com/2016/01/hello-world-in-assembly-on-research.html My question for y'all today is as follows (asked previously with a much larger gap in understanding): How did folks debug assembly routines in Unix v6, back in the day? I realize that most folks didn't do assembly, but some did and I'm curious what their approach might have been. After having worked with RT-11 for a bit, I can see how I might develop using RT-11 and then "port" a program across, but that seems less than ideal. Here is my short list of missing features as I see them: 1. No listing file/cross reference list created by as. 2. No map file created by ld. 3. No debugger that I can find. 4. This is not a missing feature, but it deserves inclusion in the list, the command as has possibly the most terse error messages I have ever seen - B 12? Really? Thankfully, the awesome man command comes to the rescue with the list of error codes. My workarounds include using OD to view the generated machine code and adding mesg calls. Thoughts? Will

8 years, 3 months

Another book

by Warren Toomey

All, Don Libes and Sandy Ressler just donated a PDF of their book "Life with Unix" to the archive. It's at: http://minnie.tuhs.org/Archive/Documentation/Books/ I've also found PDF copies of a bunch of other books, so look through http://wiki.tuhs.org/doku.php?id=publications:books for links. Cheers, Warren

8 years, 3 months

PDF of "A Quarter Century of Unix"

by Warren Toomey

All, I asked Peter Salus if there is an electronic version of his great book "A Quarter Century of Unix". There isn't one, so I scanned my book in. Peter has given TUHS the right to distribute the scanned version. I've just added a link to the PDF of the scan here: http://wiki.tuhs.org/doku.php?id=publications:quarter_century_of_unix But, if you can, buy the paper version as well! Many thanks to Peter for his generosity. Cheers, Warren

8 years, 3 months

Missing pages in Berkeley_Unix_History.pdf

by markus schnalke

Hoi. Yesterday, I came across the file Berkeley_Unix_History.pdf on my disk. It contains scanned articles of UNIX Review January 1985, October 1985 and January 1986. Searching the web brought up this online location for the file: http://simson.net/ref/free_software/Berkeley_Unix_History.pdf I read the articles for the first time and had a great time doing so. Especially the ``Berkeley Underground'' article was pure fun! Here, have some impression: We modified the kernel to support asynchronous I/O, distri- buted files, security traces, "real- time" interrupts for subprocess multitasking, limited screen editing, and various new system calls. We wrote compilers, ass- emblers, linkers, disassemblers, database utilities, cryptographic utilities, tutorial help systems, games, and screen-oriented ver- sions of standard utilities. User friendly utilities for new users that avoided accidental file deletion, libraries to support common operations on data structures such as lists, strings, trees, sym- bol tables, and libraries to perform arbitrary precision arithmetic and symbolic mathematics were other contributions. We suggested im- provements to many system calls and to most utilities. We offered to fix the option flags so that the dif- ferent utilities were consistent with one another. To Us, nothing was sacred, and We saw a great deal in UNIX that could stand improvement. Much of what We implemented, or asked to be allowed to implement, is now a part of System V and 4.2 BSD; others of our innovations are still missing from all versions of UNIX. Despite these accom- plishments, it seemed that whenever We asked The Powers That Be to install Our software and make it available to the rest of the system's users, We were greeted with stony silence. Unfortunately, the scan is not complete as some pages are missing. For example, page 43 (the title page of the mentioned article) is among them. Does anyone know where to get the full articles? meillo

8 years, 3 months

Re: [TUHS] etymology of cron

by jnc＠mercury.lcs.mit.edu

> From: Ronald Natalie > a new GADS (Gateway Architecture and Data Structures) under Dave > Mills's leadership would form which I attended until they morphed it > into the IETF To give a bit more detail, GADS was not producing needed stuff as fast as was needed, so it was split into InArc and InEng, with Dave running InArc and Corrigan (initially, Gross later) in charge. Noel

8 years, 3 months

Re: [TUHS] etymology of cron

by David

It has been updated again: The origin of the name cron is from the Greek word for time, χρόνος (chronos).[2][3] (Ken Thompson, author of cron, has confirmed this in a private communication with Brian Kernighan.) So it would appear that if enough people bang on enough keyboards on the Wikipedia site, things can change. David

8 years, 3 months

More wiki work: free Unix licenses

by Warren Toomey

All, although I can't contribute to the actual history of Unix, I can at least document what happened "afterwards". Here's a piece about the journey to make free Unix source code licenses available: http://wiki.tuhs.org/doku.php?id=events:free_licenses Comments welcome. Cheers, Warren

8 years, 3 months

Re: [TUHS] PDP-11 MARK (was: Early Unix function calls: expensive?)

by Johnny Billquist

On 2016-01-06 01:54, Dave Horsfall <dave(a)horsfall.org> wrote: > On Mon, 4 Jan 2016, Ronald Natalie wrote: >> >Just never figured out how to make good use of the MARK instruction on >> >the PDP-11. > RSX-11 probably used it, though, as could've RSTS... Nope. Nothing in RSX uses it. As others said, probably nothing anywhere used it. And, as I pointed out, if you use MARK, then you cannot really use split I/D-space, since the stack (data) needs to be in instruction space. 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, 3 months

Re: [TUHS] PDP-11 MARK (was: Early Unix function calls: expensive?)

by Johnny Billquist

On 2016-01-05 18:43, Ronald Natalie<ron(a)ronnatalie.com> wrote: > > Just never figured out how to make good use of the MARK instruction on the PDP-11. Not surprising. As others noted, few ever did. And apparently none responding actually do either. It *is* a stupid instruction in many ways. And it's not for multiple returns either. It's an odd way of handling stack cleanup without a frame pointer. It's extremely bad, since it actually requires the stack to be in instruction space. And yes, you are expected to execute on the stack. The idea is that the caller pushes arguments on the stack, but the cleanup of the stack is implicitly done in the subroutine itself, and at the same time you get an argument pointer. Example: Calling: MOV R5,-(SP) ; Save old R5 MOV <argn>,-(SP) MOV <argn-1>,-(SP) . MOV <arg1>,-(SP) MOV #MARKN,-(SP) ; Where the N in MARK N is the number of arguments you just pushed. MOV SP,R5 JSR PC,SUB . . In the subroutine you then have the arguments available relative to R5. So that arg1 is available at 2(R5) for example. SUB: . . . RTS R5 There is a lot going on at this point. The trick is to note that the code does an RTS R5 to return. If people remember what happens at that point, PC gets loaded with R5, while R5 gets loaded with the PC that we actually would like to return to (since that's what is at the top of the stack). And R5 is pointing into the stack, at the MARK instruction, so execution continues with actually performing the MARK. MARK, in turn, will case SP <- PC + 2*N, thus restoring the stack pointer to point to the place where the original R5 was stored. Next, it does a PC <- R5, so that we now have the PC point to where we actually want to return. Next it does a R5 <- (SP)+, meaning we actually restored the original R5. And so we have cleaned up the stack, preserved R5, and returned to the caller again. Also notice that the subroutine could have pushed any amount of data on the stack before the return, and I suspect the idea was that the process would not have needed to clean that up either. However, that fails, since the RTS needs the return address at the top. But you can essentially solve that by pushing -2(R5) before returning. Ugly, isn't it? :-) Johnny

8 years, 3 months

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TUHS January 2016