diff --git a/Makefile b/Makefile
index 99336b60f1a4..91ad737ff538 100644
--- a/Makefile
+++ b/Makefile
@@ -228,9 +228,12 @@ ifeq ("$(origin M)", "command line")
   KBUILD_EXTMOD := $(M)
 endif
 
+export KBUILD_CHECKSRC KBUILD_EXTMOD
+
 ifeq ($(abs_srctree),$(abs_objtree))
         # building in the source tree
         srctree := .
+	building_out_of_srctree :=
 else
         ifeq ($(abs_srctree)/,$(dir $(abs_objtree)))
                 # building in a subdirectory of the source tree
@@ -238,19 +241,13 @@ else
         else
                 srctree := $(abs_srctree)
         endif
-
-	# TODO:
-	# KBUILD_SRC is only used to distinguish in-tree/out-of-tree build.
-	# Replace it with $(srctree) or something.
-	KBUILD_SRC := $(abs_srctree)
+	building_out_of_srctree := 1
 endif
 
-export KBUILD_CHECKSRC KBUILD_EXTMOD KBUILD_SRC
-
 objtree		:= .
 VPATH		:= $(srctree)
 
-export srctree objtree VPATH
+export building_out_of_srctree srctree objtree VPATH
 
 # To make sure we do not include .config for any of the *config targets
 # catch them early, and hand them over to scripts/kconfig/Makefile
@@ -453,7 +450,7 @@ USERINCLUDE    := \
 LINUXINCLUDE    := \
 		-I$(srctree)/arch/$(SRCARCH)/include \
 		-I$(objtree)/arch/$(SRCARCH)/include/generated \
-		$(if $(filter .,$(srctree)),,-I$(srctree)/include) \
+		$(if $(building_out_of_srctree),-I$(srctree)/include) \
 		-I$(objtree)/include \
 		$(USERINCLUDE)
 
@@ -514,7 +511,7 @@ PHONY += outputmakefile
 # At the same time when output Makefile generated, generate .gitignore to
 # ignore whole output directory
 outputmakefile:
-ifneq ($(srctree),.)
+ifdef building_out_of_srctree
 	$(Q)ln -fsn $(srctree) source
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile $(srctree)
 	$(Q)test -e .gitignore || \
@@ -1101,7 +1098,7 @@ PHONY += prepare archprepare prepare1 prepare3
 # and if so do:
 # 1) Check that make has not been executed in the kernel src $(srctree)
 prepare3: include/config/kernel.release
-ifneq ($(srctree),.)
+ifdef building_out_of_srctree
 	@$(kecho) '  Using $(srctree) as source for kernel'
 	$(Q)if [ -f $(srctree)/.config -o \
 		 -d $(srctree)/include/config -o \
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 776842b7e6a3..be38198d98b2 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -513,7 +513,7 @@ existing-targets := $(wildcard $(sort $(targets)))
 
 -include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
 
-ifneq ($(srctree),.)
+ifdef building_out_of_srctree
 # Create directories for object files if they do not exist
 obj-dirs := $(sort $(obj) $(patsubst %/,%, $(dir $(targets))))
 # If targets exist, their directories apparently exist. Skip mkdir.
diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index b6a54bdf0965..fcf0213e6ac8 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -69,7 +69,7 @@ _hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
 
 # $(objtree)/$(obj) for including generated headers from checkin source files
 ifeq ($(KBUILD_EXTMOD),)
-ifneq ($(srctree),.)
+ifdef building_out_of_srctree
 _hostc_flags   += -I $(objtree)/$(obj)
 _hostcxx_flags += -I $(objtree)/$(obj)
 endif
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 281864fcf0fe..8f2eb799a9b2 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -154,7 +154,7 @@ endif
 # $(srctree)/$(src) for including checkin headers from generated source files
 # $(objtree)/$(obj) for including generated headers from checkin source files
 ifeq ($(KBUILD_EXTMOD),)
-ifneq ($(srctree),.)
+ifdef building_out_of_srctree
 _c_flags   += -I $(srctree)/$(src) -I $(objtree)/$(obj)
 _a_flags   += -I $(srctree)/$(src) -I $(objtree)/$(obj)
 _cpp_flags += -I $(srctree)/$(src) -I $(objtree)/$(obj)
diff --git a/scripts/Makefile.modbuiltin b/scripts/Makefile.modbuiltin
index ea90a90b41a0..50a9990760f3 100644
--- a/scripts/Makefile.modbuiltin
+++ b/scripts/Makefile.modbuiltin
@@ -15,7 +15,7 @@ include include/config/tristate.conf
 
 include scripts/Kbuild.include
 
-ifneq ($(srctree),.)
+ifdef building_out_of_srctree
 # Create output directory if not already present
 _dummy := $(shell [ -d $(obj) ] || mkdir -p $(obj))
 endif
diff --git a/scripts/gdb/linux/Makefile b/scripts/gdb/linux/Makefile
index 9fd3d8ed731a..124755087510 100644
--- a/scripts/gdb/linux/Makefile
+++ b/scripts/gdb/linux/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 
-ifneq ($(srctree),.)
+ifdef building_out_of_srctree
 
 symlinks := $(patsubst $(srctree)/$(src)/%,%,$(wildcard $(srctree)/$(src)/*.py))
 
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 9781ca79794a..25b43a8c2b15 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -74,7 +74,7 @@ endif
 # Append kselftest to KBUILD_OUTPUT to avoid cluttering
 # KBUILD_OUTPUT with selftest objects and headers installed
 # by selftests Makefile or lib.mk.
-ifneq ($(KBUILD_SRC),)
+ifdef building_out_of_srctree
 override LDFLAGS =
 endif
 
diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
index 077337195783..1c8a1963d03f 100644
--- a/tools/testing/selftests/lib.mk
+++ b/tools/testing/selftests/lib.mk
@@ -70,7 +70,7 @@ define RUN_TESTS
 endef
 
 run_tests: all
-ifneq ($(KBUILD_SRC),)
+ifdef building_out_of_srctree
 	@if [ "X$(TEST_PROGS) $(TEST_PROGS_EXTENDED) $(TEST_FILES)" != "X" ]; then
 		@rsync -aq $(TEST_PROGS) $(TEST_PROGS_EXTENDED) $(TEST_FILES) $(OUTPUT)
 	fi
@@ -125,7 +125,7 @@ clean:
 # When make O= with kselftest target from main level
 # the following aren't defined.
 #
-ifneq ($(KBUILD_SRC),)
+ifdef building_out_of_srctree
 LINK.c = $(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) $(TARGET_ARCH)
 COMPILE.S = $(CC) $(ASFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c
 LINK.S = $(CC) $(ASFLAGS) $(CPPFLAGS) $(LDFLAGS) $(TARGET_ARCH)