[TUHS] kernel boots kernel in 1977

[Warner Losh]

On Wed, Sep 18, 2024, 2:47 PM ron minnich <rminnich at gmail.com> wrote:

> I noticed there are kexec talks this year at Linux Plumbers. Kexec, kernel
> boots kernel, has had a 25 year gestation in Linux, but it looks like it's
> finally coming together, driven by need.
>

Yes. LinuxBoot is fun... trick can be to slim the kernel + inird down
enough to fit in the NOR flash so it can be the second stage payload rather
than UEFI... i hacked FreeBSD's boot loader to be a Linux binary and use
kexec.

Thereby hangs a tale.
>
> in 1977, I was working at udel with Ed Szurkowski, the first sysadmin of
> the Unix systems we got in 1976 (first machine was an 11/70). Ed was a
> gifted engineer and did all kinds of neat work on v6. He later went to the
> Labs once he got his PhD and I lost track of him.
>
> Ed got tired of watching the bootstrap slowness, and wrote a system call
> that did the following:
> 1. load kernel in memory from system call argument
> 2. put special signature in low memory telling bootstrap "look in memory"
> 3. reboot via reset.
>
> Now, this works, because back then, ROM boot code did not zero memory.
> Memory was unchanged across reset. So the bootstrap could find the magic
> bits and start the kernel.
>
> I've lost the code, I carried the listings for decades but finally dumped
> them. A shame.
>

I saw similar code that would jump to location 0 to do the reset...  it
formed the basis of an interview question i used for two decades..

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

I've seen references to older mainframe systems doing that, but my quick
searches can't find a references to this, apart from the Chain command in
BASIC.

Warner

>
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