Brian Rose <lists@brianrose.net> writes:

> Are there any docs that explain how to select (or list) which -m
> options are available?

--help should list the available options.

As you know, the NetBSD assembler is the GNU assembler.  The GNU
assembler documentation is available here:
    http://sourceware.org/binutils/docs-2.15/as/index.html
Specifically, m68k options are listed here:
    http://sourceware.org/binutils/docs-2.15/as/M68K-Opts.html#M68K-Opts

> I tried -m5200, but it does not like %SECMBAR (secondary module base
> address register). Nor does it like %MBAR2 (used by diab).

I haven't tried it, but it looks like %SECMBAR should be available if
you use the -mcfv4e option.  Apparectly %SECMBAR is not available on
all variants of the m5200.  Or gas is wrong, which is quite possible.

I don't see %MBAR2 listed anywhere in gas, although %MBAR, %MBAR0, and
%MBAR1 should be available using -mcfv4e.

Ian