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Merge pull request #1700 from xexyl/mills2018-dmr-c

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Landon Curt Noll authored and GitHub committed 2023-12-14 06:40:52 -08:00
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@@ -5,6 +5,17 @@ make
```
### Bugs and (Mis)features:
The current status of this entry is:
```
STATUS: INABIAF - please **DO NOT** fix
```
For more detailed information see [2018 mills in bugs.md](/bugs.md#2018-mills).
## To use:
```sh
@@ -18,13 +29,38 @@ make
./prog
```
At the `>boot` prompt, type return
At the `>boot` prompt, type return.
At the `:` prompt, type `rk(0,0)rkunix`
At the `:` prompt, type `rk(0,0)rkunix` and wait for it to initialise itself.
Now try typing:
```sh
cat > prog.c
main(){ printf("Hello, world!\n"); }
^D
cc prog.c
a.out
```
where `^D` is EOF.
Next try:
```sh
cc mullender.c
a.out
```
... and enjoy the classic [1984/mullender](/1984/mullender/README.md) entry as
it would have been in 1984 with a VAX-11/PDP-11! Once it reaches the end of the
line, hit enter and see what happens again. When you're tired of it hit ctrl-c.
But there is much more to this entry! See below.
NOTE: To quit, press Control-E.
### Selected Judges' Remarks:
### Judges' remarks:
Do small machines only need small programs? This program weighs in at just
3636 bytes, which is considerably lighter than the original machine it can replace.
@@ -57,14 +93,15 @@ program that replaces an even larger machine that can run BSD 2.9. To start this
./prog
```
At the ">boot" prompt, type return
At the `>boot` prompt, type return.
At the ":" prompt, type "rk(0,0)rkunix"
At the ":" prompt, type `rk(0,0)rkunix`.
NOTE: To quit prog, press Control-E.
This should now be very familiar and it is possible to compile and run one of
the very first IOCCC entires "mullender.c".
the very first IOCCC entries [mullender.c](/1984/mullender/mullender.c), as
shown earlier.
But wait, there is even more! Try:
@@ -72,7 +109,7 @@ But wait, there is even more! Try:
./v6
```
At the "@" prompt, type `rkunix`. You might want to type `stty -lcase` as
At the `@` prompt, type `rkunix`. You might want to type `stty -lcase` as
otherwise the output will be in all caps.
NOTE: To quit v6, press Control-E.
@@ -80,7 +117,9 @@ NOTE: To quit v6, press Control-E.
## Author's remarks:
> *This IOCCC entry is dedicated to the late Dennis M. Ritchie*
### *This IOCCC entry is dedicated to the late Dennis M. Ritchie*
### The Program:
@@ -92,7 +131,7 @@ system whose history is so entwined with.
The program delivered here is both a full machine emulation of the original
PDP-7 that Ken Thompson used to write the first version of UNIX and a full
machine emulation of the PDP-11/40 used by subsequent UNIXes. The `Makefile`
machine emulation of the PDP-11/40 used by subsequent UNICES. The `Makefile`
can build versions that can run each of the following:
1. UNIX v0 for the PDP-7 (circa 1969)
@@ -101,28 +140,33 @@ can build versions that can run each of the following:
For reasons to be described in a bit, the last (BSD 2.9) is the default.
### Building and Running BSD 2.9:
To run BSD 2.9, do `make` to build `prog` and then `./prog` to run it.
You should see a prompt from the first-stage bootloader that looks like
>boot
```
>boot
```
Hit enter/return at this point and you will get to the second-stage boot loader
that looks like
40Boot
:
```
40Boot
:
```
The 40 in the prompt indicates that the bootloader has correctly determined
that we are running on a PDP-11/40.
At this point, type the rather cryptic command `rk(0,0)rkunix` -- this tells
the system to look at the first partition on the first RK05 fixed disk, find
the system to look at the first partition on the first `RK05` fixed disk, find
the `rkunix` file and load it. You should eventually see the following:
``
```
>boot
40Boot
@@ -154,16 +198,17 @@ Erase=^?, kill=^U, intr=^C
Congratulations, you are running BSD UNIX 2.9 in single-user mode as root.
On the other hand, if you did a typo somewhere, the boot loader has probably
crashed and halted -- if so, type Control-E to quit the simulation and try
crashed and halted -- if so, type Control-E to quit the emulator and try
again. If you did really badly, you might have corrupted the virtual disk.
If so, consider a `make clean` to start from scratch.
Assuming you managed to type 15 characters correctly, You should be at the
Assuming you managed to type 15 characters correctly, you should be at the
root prompt. Most of the commands you are familiar with work here (this was
only a quarter of a century ago -- how much could things have changed?).
Let's try some:
```
```sh
# ls
.cshrc .profile boot hkunix mnt tmp
.login 2.9stamp dev lib mullender.c unix
@@ -177,7 +222,7 @@ Filesystem Mounted on kbytes used free % used
The program you've just run was the [winner of the first IOCCC contest from
1984] [1] (or was it 1894?), a personal favorite of mine. It is rather
tightly bound to running on either a PDP-11 or a VAX. Now you have one.
tightly bound to running on either a PDP-11 or a VAX-11. Now you have one.
Hitting Control-C will return you to the BSD UNIX prompt. Hitting Control-D
will log you out of the single-user session and get you back to the `:login:`
@@ -196,6 +241,7 @@ possible, but I didn't get around to it... As the Judges can no doubt attest,
Once you've had enough fun in BSD 2.9, type Control-E to exit the emulation.
### Building and Running Research UNIX v6:
Research UNIX v6 and BSD 2.9 use the same executable, but require a different
@@ -225,7 +271,7 @@ You are now running a single-user session of v6 UNIX. You might want to start
with `stty -lcase` because otherwise everything will be IN ALL CAPS.
Again, if you failed typing seven characters without making a mistake, you
may need to use Control-E to quit the simulation.
may need to use Control-E to quit the emulation.
Assuming you're more careful than that, we can try a few commands:
@@ -283,13 +329,14 @@ This version of UNIX doesn't go into multi-user mode if you do a Control-D.
Single-user mode was entered because the front-panel console switches were
set to the magic number 0173030 (this can be changed with a recompile).
Once you are done with Version 6, Type Control-E to exit the simulation.
Once you are done with Version 6, Type Control-E to exit the emulation.
Note that since both BSD 2.9 and UNIX v6 use the same PDP-11/40 emulation
code, and they use the same name for the disk (`rk05.fs`), if you want to go
back to the BSD simulation, you should either delete `rk05.fs` or do a
back to the BSD emulation, you should either delete `rk05.fs` or do a
`make clean` before you do a `make`.
### Building and Running UNIX v0:
We now set the Wayback Machine to the very start of it all, 1969.
@@ -404,7 +451,7 @@ Hello, World!
The last command is invoking the compiler for an extremely early version of
the [B programming language] [3], the predecessor to C. Thompson missed the
convenience of writing code in a high-level language -- Multics was written
a version of PL/1 -- and wanted the same convenience on UNIX. He preferred
in a version of PL/1 -- and wanted the same convenience in UNIX. He preferred
BCPL (a typeless language) to PL/1. As Dennis Ritchie [wrote] [6]:
> B can be thought of as C without types; more accurately,
@@ -424,18 +471,18 @@ on the command line, concatenated together and assembled, producing a single
remained the default name of the binary generated by the linker (and hence
also by `cc`).
This system is still has the familiarity of UNIX, with all the two and
three letter commands, device files, shell redirection and the same core system
calls (`read`, `write`, `open`, `close`, `creat`, `fork`, etc.). There are a
number of differences still:
This system still has the familiarity of UNIX, with all the two and three letter
commands, device files, shell redirection and the same core system calls
(`read(2)`, `write(2)`, `open(2)`, `close(2)`, `creat(2)`, `fork(2)`, etc.).
There are a number of differences still:
* As noted, there are no file paths.
* `read` and `write` do I/O on (18-bit) words. Character I/O on files need
* `read(2)` and `write(2)` do I/O on (18-bit) words. Character I/O on files need
to unpack those bytes, and of course deal with `NUL` characters.
* `exec` was performed by the shell directly. Arguments are passed as
* `exec(2)` was performed by the shell directly. Arguments are passed as
four words (eight bytes), and space padded. This matches the format for
file names for `open` and `creat`.
* `wait` does not yet exist. A more complicated mechanism for sending and
file names for `open(2)` and `creat(2)`.
* `wait(2)` does not yet exist. A more complicated mechanism for sending and
receiving messages (`smes` and `rmes`) are used instead.
* File permission bits are all different, since groups don't exist yet.
* User programs are not allowed to run during disk I/O. This is because the
@@ -452,7 +499,8 @@ addresses of useful kernel routines so that user code can call them
directly).
As usual, when you are done exploring UNIX v0, type Control-E to exit the
simulator.
emulator.
### About the Program:
@@ -461,15 +509,17 @@ The program came about when I was looking for something to honor the pending
contest scheduling, I chose not to wait for the actual 50th anniversary).
I had thought of writing self-hosting compilers for a stripped-down version of
C, or maybe even a version of the B language... At the same time, I was
obsessed with the idea of allowing `mullender.c` from 1984 to run. Although
obsessed with the idea of allowing [mullender.c from
1984](/1984/mullender/README.md) to run. Although
that was still a possibility on an interpreted version of B or a stripped-down
version of C, it felt cheap, as it would be `mullender.c` only in spirit.
version of C, it felt cheap, as it would be
[mullender.c](/1984/mullender/mullender.c) only in spirit.
It was during this time that I discovered that in 2016, members of the Unix
Heritage Society got access to [printouts of assembly-language source for the
original version of UNIX] [7]. With what was a [huge amount of work] [8],
they scanned in the printouts, fixed up the OCR translations, built assembler
and file system tools from scratch and made an accurate simulation of
and file system tools from scratch and made an accurate emulation of
Thompson's PDP-7 that allowed them to get the system up and running. Although
source for the entire kernel and about half of the user-space commands were
present (including the runtime and libraries for the B compiler), the
@@ -490,14 +540,14 @@ I decided that implementing this PDP-7 would be possible as an IOCCC entry.
The emulator emulates the full machine:
* PDP-7 Central Processor
* Core Memory Module Type 147 -- extends the core to 8,192 18-bit words
* PDP-7 Central Processor.
* Core Memory Module Type 147 -- extends the core to 8,192 18-bit words.
* Extended Arithmetic Element Type 177 -- adds one's-complement multiplication,
division and shifting
* Real Time Clock
* Teletype Model 33 KSR
* Perforated Tape Reader Type 444
* RB09 Fixed Disk Controller
division and shifting.
* Real Time Clock.
* Teletype Model 33 KSR.
* Perforated Tape Reader Type 444.
* RB09 Fixed Disk Controller.
The [PDP-7] [10] is an odd duck by modern computer standards:
@@ -512,7 +562,7 @@ address and the PC jumps to the location after it).
instruction.
* An instruction `LAW` that loads the instruction opcode into the
accumulator.
* Heavy use of "inline" operands. For instance the `MUL` instruction expects
* Heavy use of `inline` operands. For instance the `MUL` instruction expects
the second operand to be stored in memory after the instruction. This
pretty much requires the use of self-modifying code.
* No immediates. Almost all constants have to live in memory locations and
@@ -528,7 +578,7 @@ particularly annoying encoding of track and sector offsets in
is needed to convert into and out of BCD, along with an equivalent amount
of code in the UNIX kernel itself.
The simulation handles everything I was able to discover about the PDP-7, even
The emulation handles everything I was able to discover about the PDP-7, even
things that the UNIX code itself doesn't use. For instance, it correctly
implements the "trap mode" feature (a primitive form of supervisor mode) even
though the kernel does not enable it. It also implements the microcoding of
@@ -536,7 +586,7 @@ the EAE instructions even though the UNIX environment uses only the standard
encodings. If you wanted to do a 11-bit multiply instead of an 18-bit one,
it will probably work.
The simulation starts by loading a boot program off of the virtualized paper
The emulation starts by loading a boot program off of the virtualized paper
tape, which is in a modified version of the RIM boot loader format. The
RIM format encodes each 18-bit word as three six-bit characters, using one bit
to denote the final word (which is executed directly and is usually a `JMP` or
@@ -545,12 +595,13 @@ Both of these are controlled by compile-time flags.
The emulator continues emulating instructions until it sees a `HLT` instruction
which will cause it to exit. Console I/O is emulated by setting the terminal
into raw mode and polling via `read`. Line-clock ticks (at 60 Hz) are done
by polling `gettimeofday`. Dynamic frequency code arranges to reduce the
polling interval to a few polls per tick, so that simulation remains
into raw mode and polling via `read(2)`. Line-clock ticks (at 60 Hz) are done
by polling `gettimeofday(2)`. Dynamic frequency code arranges to reduce the
polling interval to a few polls per tick, so that emulation remains
responsive. Since we use the real wall-clock time, this means that the
emulated system will see time advance at the correct rate.
### Licencing Fun
So now I have a system that can run UNIX v0. One problem remains... I don't
@@ -561,16 +612,16 @@ this problem in two ways:
First, I didn't submit the source code or binary image for v0 UNIX as part of
my IOCCC entry. I merely submitted a `Makefile` that can issue a `curl`
command to fetch a prebuilt v0 disk image from the github repository. I am
command to fetch a pre-built v0 disk image from the GitHub repository. I am
hoping this is considered part of "Legal abuse of the rules" which is supposed
to be "somewhat encouraged". As per RULE 12, I am justifying said abuse here,
in the remarks file.
Secondly, the choice to run the UNIX v0 code is optional. If you are worried
about Nokia's lawyers running you to ground for running a 50-year old copy
about Nokia's lawyers running you to the ground for running a 50-year old copy
of a binary image for a machine that is almost completely non-existent, you
can just not do so. Delete the lines from the `Makefile` and sleep well.
You still have two other UNIXes to play with.
You still have two other UNICES to play with.
What about the other two UNIX variants? These are both covered by licences
that allow me to use them. Back in 2002, Caldera International released
@@ -579,22 +630,23 @@ BSD UNIX is based off of v7 UNIX, and of course has its own permissive
BSD licence. And in 2017, Nokia also released versions 8-10 under the
condition that it will not assert copyright rights for non-commercial use.
So the newer UNIXes are in the clear. I doubt anyone actually cares about
So the newer UNICES are in the clear. I doubt anyone actually cares about
version 0 either, but technically it's still under copyright.
### PDP-11/40
So if I have a PDP-7 emulator, how do I run operating systems that expect a
PDP-11? Simple... *I emulate a PDP-11/40 on the PDP-7*. I have written
PDP-7 assembler code to emulate a PDP-11/40 with the following equipment:
* PDP-11/40 (KD11-A)
* EIS instruction set (KE11-E)
* Memory management unit (KJ11-A)
* Line time clock (KT11-D)
* 124 Kwords of memory (244 Kbytes)
* RK05 fixed disk drive (RK11)
* Console TTY (DL11)
* PDP-11/40 (KD11-A).
* EIS instruction set (KE11-E).
* Memory management unit (KJ11-A).
* Line time clock (KT11-D).
* 124 Kwords of memory (244 Kbytes).
* RK05 fixed disk drive (RK11).
* Console TTY (DL11).
This required a few tweaks to the emulator. The first problem is that the
RK05 disk is about 2.5 MB, but the RB09 is only about 2 MB. That's easily
@@ -602,7 +654,7 @@ solvable -- just add more tracks to the RB09. UNIX v0 is unlikely to notice
(although the number of tracks is a compile time parameter, and the `v0`
build commands set it to the correct value).
The second problem is that we are simulating a system that can have up to
The second problem is that we are emulating a system that can have up to
124K words of memory on a system with only 8K words total. That meant I needed
to virtualize the PDP-11/40's physical memory (and add a few more tracks to
the disk to hold the virtualization).
@@ -625,8 +677,8 @@ The one remaining problem is building the disk images themselves. Since the
PDP-11's disk is 16-bit, but the PDP-7's is 18-bit (which the emulator stores
in 32-bit `int`s), a conversion program is needed to unpack the binary disk
images from 16 bits per word to 32. This in turn needs to be done in the
`Makefile` using standard POSIX tools, which aren't exactly good with binary.
I had a weirdly clever way to do this with `od`, `awk` and `uudecode` that
Makefile using standard POSIX tools, which aren't exactly good with binary.
I had a weirdly clever way to do this with `od(1)`, `awk(1)` and `uudecode(1)` that
I will leave as an exercise for the curious, but I decided it would be easier
to do it with the PDP-7 emulator itself, feeding a simple program in on its
boot tape. This required an additional tweak to the emulator, since by default
@@ -655,6 +707,7 @@ window on the dawn of the UNIX era. I feel that someone should complete the
circle here by emulating a VAX 780 on the PDP-11 and run 4.2BSD on it, so that
we can get the [original runtime environment used for the first IOCCC] [13].
### Compile-time Options:
The following command flags control the compilation:
@@ -666,31 +719,33 @@ bootloader where to load the boot image.
* `-DS=0`: Setting of the console data switches. The PDP-7 emulation can
read these with the microcoded `OAS` (OR switches into AC) instruction.
By proxy, the PDP-11 emulation can read them via the `CSW` device.
* `-DW=MAP_PRIVATE`: This sets the memory mapping for `mmap`. Setting to
* `-DW=MAP_PRIVATE`: This sets the memory mapping for `mmap(2)`. Setting to
`MAP_PRIVATE` makes the disk image be copy-on-write. Setting it to
`MAP_SHARED` makes the disk image be shareable. Do the latter if you want
to preserve the disk contents between sessions.
* `-DT=`: List of initializers for the `termios` structure. The v0 UNIX
expects the terminal to be in half-duplex mode, echoing its input, with
swapped CR and NL. The PDP-11 UNIXes don't.
* `-DX=5`: The ASCII code of the control character that causes the simulation
swapped CR and NL. The PDP-11 UNICES don't.
* `-DX=5`: The ASCII code of the control character that causes the emulation
to abort. If set to 0, there is no abort code.
* `-DY=128`: Controls console I/O parity. If set to zero, the console is
eight-bit clean. If set to 128, the high bit is set on keyboard reads and
masked off on printer output ("mark" parity). UNIX v0 expects the latter.
* `-DV=270`: The size of the disk, in tracks. The UNIX v0 disk has 200
tracks (each has 80 sectors of 64 18-bit words). The PDP-11 UNIXes
tracks (each has 80 sectors of 64 18-bit words). The PDP-11 UNICES
increase this to 270, to allow for the larger RK05 disk emulation
(406 tracks of twelve 256-word sectors), plus the space for the 124K words
of virtualized memory and the 8K words of emulator code.
* `-DP="xxx"`: RIM bootstrap program paper tape image. Be careful with the
quoting here -- there is at least three levels going on. In particular,
quoting here -- there are at least three levels going on. In particular,
you will need to escape `$` as `$$` to protect it from `make`.
### What is the ASCII art supposed to be?
The ASCII art represents a torn piece of [paper tape] [14].
### Acknowledgements
None of this could have been possible without the hard work of
@@ -710,8 +765,8 @@ of UNIX, the C programming language, and the innumerable other innovations
that we now take for granted as part of the modern software landscape.
In particular, the [home page of the late Dennis Ritchie] [18] contained
a trove of useful information on the evolution of UNIX and C and is
recommended for perusal by others who share my peculiar retrocomputing
affectations.
recommended for perusal by others who share my peculiar retro computing
passion.
Finally, thanks to my spouse for putting up with the many hours I spent on this
nonsense, and treating "I'm working on my IOCCC entry" as an acceptable answer
@@ -722,14 +777,14 @@ time...
-------------------------------------------------------------------------------
[1]: http://ioccc.org/1984/mullender/mullender.c "mullender.c"
[1]: https://www.ioccc.org/1984/mullender/mullender.c "mullender.c"
[2]: http://minnie.tuhs.org/cgi-bin/utree.pl?file=2.9BSD "2.9 BSD"
[3]: https://www.bell-labs.com/usr/dmr/www/kbman.html "B Language"
[4]: https://www.bell-labs.com/usr/dmr/www/hist.html "UNIX history"
[5]: https://www.bell-labs.com/usr/dmr/www/spacetravel.html "Space Travel"
[6]: https://www.bell-labs.com/usr/dmr/www/chist.html "C History"
[7]: http://www.tuhs.org/Archive/Distributions/Research/McIlroy_v0/ "V0 Scans"
[8]: http://minnie.tuhs.org/Y5/wkt_hapop_paper.pdf "UNIX v0"
[8]: https://web.archive.org/web/20180826162445/https://minnie.tuhs.org//Y5/wkt_hapop_paper.pdf "UNIX v0"
[9]: https://github.com/DoctorWkt/pdp7-unix "PDP-7 UNIX"
[10]: http://bitsavers.trailing-edge.com/pdf/dec/pdp7/F-75P_PDP7prelimUM_Dec64.pdf "PDP-7 Manual"
[11]: https://en.wikipedia.org/wiki/Binary-coded_decimal "BCD"