Some change in NASM 2.13.02 (I'm assuming 'Always generate symbol-relative relocations for the macho64 output format') has completely broken my Xcode/Mach-O build: all the fixups seem to be wrong. Reverting to 2.13.01 has fixed the problem, but there is obviously something seriously wrong with the modification. Incidentally I tried adding DEFAULT REL, but it made no difference.