xa65 and GeckOS

I'm trying to build André Fachat's GeckOS:

http://www.6502.org/users/andre/osa/oa-2.0.9.tar.gz

using the xa cross-assembler from xa65 2.3.8 (Debian package), and I'm
getting an error I don't understand:

rsh.a65:line 688: 2ed0:65816 mode used/required error
rsh.a65:line 701: 2eed:65816 mode used/required error

The lines in question (in sysapps/slipd) are calling "jsr flib2osa_w"
and "jsr flib2osa_r"; these labels are defined in a jump table as:

#define    flib2osa_r      LIB6502-6
#define    flib2osa_w      LIB6502-3

There's no -W (no 65816 code) in the xa options in the Makefile, but
that's supposed to be the default. Is it the subtraction?

Also, is there a better (more specific) place to ask about this?

-- 
Glenn Holmer (Linux registered user #16682)
"After the vintage season came the aftermath -- and Cenbe."