>I have this nagging notion in the back of my head about GNU ld trying to
>convert zero'd data to bss, and perhaps it's getting confused by that very
>large data segment....

Space for miniroots is initialized to "this is the miniroot" or
some such.

probably stupid question: coudl this be an .sbss ve .bss screwup?

If you link a kernel with -m, does the link map look sane?
What about objdump output?

If you build a miniroot kernel but dont stuffing a .fs into the
miniroot space, and try and boot it, does that at least get loaded (up
to trying to mount root)?