[Unix-jun72] UNIX V1 bootstrap

James A. Markevitch jam at magic.com
Sat May 17 21:04:48 EDT 2008

> > I've ported the bootstrap stuff over the whole UNIX V1 build process.
> > (Note: it would be nice to have a V1 as, so that all of these hacks
> > we've been doing can go away).
> Did you write bos.s and msys.s from scratch?   I noticed your
> wunix contains no header, just the binary bits.  Was this standard
> procedure in other versions of unix or is it possible that
> the msys program took in an 0405 or 0407 and stripped the header
> off before writing it?  Is there an easy way to strip the header
> from within the unix system with standard commands?

I wrote bos.s and msys.s from scratch.  I am not aware of any binaries
or source for these.

bos is written in an entirely position-independent manner so that it can be
compiled with a v1 assembler, v2 assembler, etc. and still run when loaded
at location 54000 in core.  Other than the option to load a paper tape, I
believe this to be as true to V1 as possible.

msys was implemented to be as true to V1 as I believed possible.  It copies
images directly from disk without modifying them, as I believe the original
V1 msys did.  There is no header kludging, since a V1 a.out UNIX kernel
should be bootable without modification.

For wunix (warm unix), I took the build/loadfile, stripped off the
first 6 bytes, then copied the next 16K bytes, just as the boot/installboot
script does.

For building under UNIX itself, there are a variety of strategies.  Here
is my list, in order of preference:

1. Use the V1 assembler.  This will produce a 12-byte header that is
exactly compatible with the kernel source as it appears in the listing.  As
many people on this are aware, the first 12 bytes get manually patched
by the UNIX code when it starts up.  But, I don't think the V1 assembler
exists anywhere, or at least not that has been found.  That kind of makes
this option moot.

2. Modify the V2 assembler to produce V1 binaries.  If the V2 assembler
can be built from sources, then it should be straighforward to edit it
to produce V1 binaries (i.e. 405 instead of 407).  This would allow a
kernel in the true spirit of V1 to be created, then copied into the
boot area by msys.  It would also allow other programs to all be created
as V1 binaries, which has a lot of attraction to me.

3. Modify msys.s to be msys2.s to strip the 407 header and also truncate
the copy to not overrun the size of the area being copied into (1K, 6K,
6K, 3K).  I just tested a modified version of this and attached it below,
since that should help to get things going; but I really think that
option #2 would be nice to have eventually.

Note to use msys2, you need to copy build/a.out to fs/usr/boot/unix.out,
and to put msys2.s into fs/usr/boot/msys2.s.  Then after you boot, do:
	chdir /usr/boot
	as msys2.s
	mv a.out msys2
	msys2 u unix.out
I'll clean up the source and send a complete fs/usr/boot out later

James Markevitch

--------------------------- fs/usr/boot/msys2.s -------------------------
/ msys2 -- copy file to RF read only slot
/ re-creation, based on description in UNIX_ProgammersManual_Nov71.pdf,
/ page 7-06, BOOT PROCEDURES (VII)
/ 5/9/08 jam at magic.com
/ 5/17/08 jam at magic.com -- hacked to copy 407-format a.out files

/ b bos		1700
/ u warm unix	1704
/ 1 cold unix	1734
/ 2 unassigned	1764

	mov	sp,r5
	mov	(r5)+,r3	/ argc
	cmp	$3,r3		/ must be 3
	bne	badcmd		/ else error
	tst	(r5)+
	mov	(r5)+,r4	/ get first arg

	cmpb	(r4),$'b
	bne	1f
	mov	$1700,r3
	mov	$4,r4
	br	2f
	cmpb	(r4),$'u
	bne	1f
	mov	$1704,r3
	mov	$30,r4
	br	2f
	cmpb	(r4),$'1
	bne	1f
	mov	$1734,r3
	mov	$30,r4
	br	2f
	cmpb	(r4),$'2
	bne	badcmd
	mov	$1764,r3
	mov	$14,r4

	/ open file
	mov	(r5),r5
	mov	r5,0f
	sys	open; 0:..; 0
	bes	error
	mov	r0,r1
	sys	seek; 20; 0
	bes	error

	/ open rf0 and seek to correct block
	sys	open; disk; 1
	bes	error
	mov	r0,r2
	mov	r3,0f
	sys	seek; 0:..; 0
	bes	error

	/ copy file from file to disk one block at a time
	mov	r1,r0
	sys	read; buf; 512.
	mov	r0,r5
	mov	r2,r0
	sys	write; buf; 512.
	bes	error
	dec	r4
	beq	3f
	tst	r5
	bne	1b

	sys	exit

	mov	$1,r0
	sys	write; 1f; 2
	sys	exit

	mov	$1,r0
	sys	write; 1f; 2
	sys	exit


buf:	.=.+512.

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