>Has anyone considered what's involved in emulating a NetBSD environment on
>NetBSD.  Or rather, a different NetBSD environment on NetBSD.  I want to
>switch to an SPARC elf64 format but still be able to run SPARC a.out
>executables.

Are you sure you mean elf64 and not elf32?  Does the sparc pmap
support 64-bit address spaces? If it doesn't, you probably want elf32,
or weird things will happen when you try and access memory via
pointers with the high 32 bits set.  (64-bit ints and 32-bit pointers
would work better, but it may be hard to set up a toolchain for.)

Either way, there's not that much to change in the kernel. Add
	options 	EXEC_ELF32
in the std.sparc file, rerun config and recompile.

You'll need to configure a current GNU binutils to make an sparc Elf
toolchain, and you'll probably need to reconfigure gcc to emit the
appropriate assembler pseudo-ops for ELF. And you'll need an elf
ld.so; perhaps it's easiest to start with statically-linked binaries.