a question about btfixupprep

[Chan Kim]

Hi,
in arch/sparc/boot/Makefile, there is a rule below.

$(obj)/btfix.S: $(obj)/btfixupprep vmlinux FORCE
        $(call if_changed,btfix)

This makes btfix.S file using btfixupprep executable.
and from the definition below,

quiet_cmd_btfix         = BTFIX   $@
      cmd_btfix         = $(OBJDUMP) -x vmlinux | $(obj)/btfixupprep > $@

I can see to make the btfix.S, the make runs 
objdump -x vmlinux | btfixupprep > btfix.S

What does btfixupprep do? maybe relocations? or function name substitution(for sub architecture)?

Regards,
Chan