201     srcroot := $(realpath $(KBUILD_EXTMOD))  macro
202     $(if $(srcroot),,$(error specified external module directory "$(KBUILD_EXTMOD)" does not exist))
208 export objtree srcroot
259 srcroot := $(abs_srctree)  macro
262 ifeq ($(srcroot),$(CURDIR))
270 else ifeq ($(srcroot),$(CURDIR))
272     srcroot := .  macro
273 else ifeq ($(srcroot)/,$(dir $(CURDIR)))
275     srcroot := ..  macro
278 export srctree := $(if $(KBUILD_EXTMOD),$(abs_srctree),$(srcroot))
281 export VPATH := $(srcroot)
686 	@if [ -f $(srcroot)/modules.order ]; then \
694 	$(Q)ln -fsn $(srcroot) source
1072 KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srcroot)/=)