Documentation/networking/Makefile - third_party/linux - Git at Google

 # kbuild trick to avoid linker error. Can be omitted if a module is built.
 obj- := dummy.o

 # Tell kbuild to always build the programs
 always := $(hostprogs-y)

 obj-m := timestamping/
	# kbuild trick to avoid linker error. Can be omitted if a module is built.
	obj- := dummy.o

	# Tell kbuild to always build the programs
	always := $(hostprogs-y)

	obj-m := timestamping/