> /usr/mdec/boot and /usr/mdec/boot.net differ only in their headers (one is
> a NetBSD/a.out header, and the other is SunOS ..? a.out).  I see that they
> are built from the same sources, but I can't figure out:
> 
> (a) the structure of a SunOS header and

The structure is the same as NetBSD's. The difference is in the first
word that holds the magic numbers.

> (b) where in the build process the proper header is put on boot.net.
> 
`sys/arch/sparc/stand/boot/Makefile'.

You'll also find that the second word (`a_text') is munged to contain
a sparc branch instruction that branches to the first word after the
a.out header. This is to make the boot program work on sun4 machines
which don't expect the a.out header to be present.

-pk