# Cancel implicit rules on top Makefile
$(CURDIR)/Makefile Makefile: ;
+ifneq ($(words $(subst :, ,$(CURDIR))), 1)
+ $(error main directory cannot contain spaces nor colons)
+endif
+
ifneq ($(KBUILD_OUTPUT),)
# Invoke a second make in the output directory, passing relevant variables
# check that the output directory actually exists