>could somebody point me to the ABI for the arm32?

I imagine you can find it on www.arm.com somewhere.

>Specifically, I am interested in reading about the calling conventions
>for C function on one of the Digital Shark machine running NetBSD 1.3.
>(i.e., what registers are caller/callee saved, etc.)

Briefly:

R13 is always the stack pointer.
On function call R0-R3 contain the first four scalar arguments, the remainder 
are on the stack (arg 4 is at [R13], arg 5 at [R13, #4], ...)
On return R0 contains the scalar result, R1-R3 may be clobbered, R4-R11 
contain the same values they did on entry, R12 may be clobbered.

p.