From: Kenn Humborg (kenn at domain linux.ie)
Date: Fri 04 Feb 2000 - 00:13:28 GMT
On Thu, Feb 03, 2000 at 09:17:01PM +0000, Vincent Murphy wrote:
> correct me if i'm wrong, but aren't you are always going to have to have a
> `here's one i made earlier' system to build a from-scratch system, or a
> bootdisk system (much the same thing), unless you want to bootstrap the
> system to such a state that you can build stuff manually yourself, which i
> presume is non-trivial.
>
> how would one go about doing this? i guess it is possible, because people
> porting kernels to new architectures must have to do it.
First you cross-copmile a kernel on another machine. Doesn't have to
be Linux, it just needs to run gcc.
Then you get the machine to boot this kernel. Nice architectures
will let you netboot, speeding things up nicely. Crappy ones will
require you to copy this kernel to some type of boot medium (tape,
hard disk, floppy, paper tape, or toggle it in at the front panel...)
The usual next step is to write a network driver for the target
and NFS mount a root filesystem from your dev box. If this isn't
possible, you put your root fs on a floppy disk or hard disk
(removable hard disk makes this easier). Again note that the 'host'
system doesn't have to be Linux. It just needs to be able to
create a filesystem that the new kernel can read and write to
a disk that the target can read.
This method of using another (possibly older, slower) machine to
bootstrap development of a newer one goes all the way back to when
the first assembler was written. Before that everything was hand
assembled and probably toggled in.
So it isn't really cheating cause they don't make front panels with
address and data bus toggle switches anymore :-( (Although you can
get pretty close in principle on some machines. VAXen have smart
enough console firmware to examine and modify memory and registers.
So you _could_ hand assemble a VAX kernel and load it in manually.
You'd be one sick puppy to do that!)
Later,
Kenn
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