ron minnich wrote:
> But I'm wondering: is Ed's work in 1977 the first "kernel boots kernel" or
> was there something before?

There was!  The PDP-7 UNIX listings contain a program trysys.s
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/sys/trysys.s
that reboots the system by reading a.out into user memory (in the high
4K of core), then copies it to low memory and jumping to the entry
point.  The name suggests its original intended use was to test a new
system (kernel).

P.S.
Normal bootable system images seem to have been stored in reserved
tracks of the (fixed head) disk (that are inacessible via system calls):

https://github.com/DoctorWkt/pdp7-unix/blob/master/src/sys/maksys.s
reads a.out and uses I/O instructions to write it out.

P.P.S.
Accordingly, I put together a "paper tape" for booting the system:
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/pbboot.s

P.P.P.S.
The system (kernel) is 3K words, the last 1K of low memory
used for the character table for the vector graphics controller.

The definitions for the table are compiled by
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/cmd/cas.s
from definition file
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/sys/cas.in
(after, ISTR, figuring out the ordering of the listing pages!)

I don't think we ever figured out how the initial character table
is loaded into core.  One thing that was missing from the table
was the dispatch array, which I recreated:
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/chrtbl.s

The system (kernel) could be built for a "cold start", reloading the
disk (prone to head crashes?) from paper tape? But I don't think
anyone ever reconstructed the procedure for rebuilding a disk that way.

The disk was two sided, and the running system only used one side:
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/cmd/dsksav.s
https://github.com/DoctorWkt/pdp7-unix/blob/master/src/cmd/dskres.s
appear to be programs to save and restore the filesystem from the
"other" side of the disk.