kbuild: use $(src) instead of $(srctree)/$(src) for source directory

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:

    src := $(obj)

When the kernel is built in a separate output directory, $(src) does
not accurately reflect the source directory location. While Kbuild
resolves this discrepancy by specifying VPATH=$(srctree) to search for
source files, it does not cover all cases. For example, when adding a
header search path for local headers, -I$(srctree)/$(src) is typically
passed to the compiler.

This introduces inconsistency between upstream and downstream Makefiles
because $(src) is used instead of $(srctree)/$(src) for the latter.

To address this inconsistency, this commit changes the semantics of
$(src) so that it always points to the directory in the source tree.

Going forward, the variables used in Makefiles will have the following
meanings:

  $(obj)     - directory in the object tree
  $(src)     - directory in the source tree  (changed by this commit)
  $(objtree) - the top of the kernel object tree
  $(srctree) - the top of the kernel source tree

Consequently, $(srctree)/$(src) in upstream Makefiles need to be replaced
with $(src).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Author: masahir0y

Documentation/Makefile

@@ -76,22 +76,22 @@ loop_cmd = $(echo-cmd) $(cmd_$(1)) || exit;
 #    * dest folder relative to $(BUILDDIR) and
 #    * cache folder relative to $(BUILDDIR)/.doctrees
 # $4 dest subfolder e.g. "man" for man pages at userspace-api/media/man
-# $5 reST source folder relative to $(srctree)/$(src),
+# $5 reST source folder relative to $(src),
 #    e.g. "userspace-api/media" for the linux-tv book-set at ./Documentation/userspace-api/media
 
 quiet_cmd_sphinx = SPHINX  $@ --> file://$(abspath $(BUILDDIR)/$3/$4)
       cmd_sphinx = $(MAKE) BUILDDIR=$(abspath $(BUILDDIR)) $(build)=Documentation/userspace-api/media $2 && \
 	PYTHONDONTWRITEBYTECODE=1 \
-	BUILDDIR=$(abspath $(BUILDDIR)) SPHINX_CONF=$(abspath $(srctree)/$(src)/$5/$(SPHINX_CONF)) \
+	BUILDDIR=$(abspath $(BUILDDIR)) SPHINX_CONF=$(abspath $(src)/$5/$(SPHINX_CONF)) \
 	$(PYTHON3) $(srctree)/scripts/jobserver-exec \
 	$(CONFIG_SHELL) $(srctree)/Documentation/sphinx/parallel-wrapper.sh \
 	$(SPHINXBUILD) \
 	-b $2 \
-	-c $(abspath $(srctree)/$(src)) \
+	-c $(abspath $(src)) \
 	-d $(abspath $(BUILDDIR)/.doctrees/$3) \
 	-D version=$(KERNELVERSION) -D release=$(KERNELRELEASE) \
 	$(ALLSPHINXOPTS) \
-	$(abspath $(srctree)/$(src)/$5) \
+	$(abspath $(src)/$5) \
 	$(abspath $(BUILDDIR)/$3/$4) && \
 	if [ "x$(DOCS_CSS)" != "x" ]; then \
 		cp $(if $(patsubst /%,,$(DOCS_CSS)),$(abspath $(srctree)/$(DOCS_CSS)),$(DOCS_CSS)) $(BUILDDIR)/$3/_static/; \

Documentation/devicetree/bindings/Makefile

@@ -25,7 +25,7 @@ quiet_cmd_extract_ex = DTEX    $@
 $(obj)/%.example.dts: $(src)/%.yaml check_dtschema_version FORCE
 	$(call if_changed,extract_ex)
 
-find_all_cmd = find $(srctree)/$(src) \( -name '*.yaml' ! \
+find_all_cmd = find $(src) \( -name '*.yaml' ! \
 		-name 'processed-schema*' \)
 
 find_cmd = $(find_all_cmd) | \
@@ -37,12 +37,12 @@ CHK_DT_EXAMPLES := $(patsubst $(srctree)/%.yaml,%.example.dtb, $(shell $(find_cm
 quiet_cmd_yamllint = LINT    $(src)
       cmd_yamllint = ($(find_cmd) | \
                      xargs -n200 -P$$(nproc) \
-		     $(DT_SCHEMA_LINT) -f parsable -c $(srctree)/$(src)/.yamllint >&2) \
+		     $(DT_SCHEMA_LINT) -f parsable -c $(src)/.yamllint >&2) \
 		     && touch $@ || true
 
 quiet_cmd_chk_bindings = CHKDT   $(src)
       cmd_chk_bindings = ($(find_cmd) | \
-			  xargs -n200 -P$$(nproc) $(DT_DOC_CHECKER) -u $(srctree)/$(src)) \
+			  xargs -n200 -P$$(nproc) $(DT_DOC_CHECKER) -u $(src)) \
 			  && touch $@ || true
 
 quiet_cmd_mk_schema = SCHEMA  $@

Documentation/kbuild/makefiles.rst

@@ -346,7 +346,7 @@ ccflags-y, asflags-y and ldflags-y
   Example::
 
     #arch/cris/boot/compressed/Makefile
-    ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds
+    ldflags-y += -T $(src)/decompress_$(arch-y).lds
 
 subdir-ccflags-y, subdir-asflags-y
   The two flags listed above are similar to ccflags-y and asflags-y.
@@ -426,14 +426,14 @@ path to prerequisite files and target files.
 Two variables are used when defining custom rules:
 
 $(src)
-  $(src) is a relative path which points to the directory
-  where the Makefile is located. Always use $(src) when
+  $(src) is the directory where the Makefile is located. Always use $(src) when
   referring to files located in the src tree.
 
 $(obj)
-  $(obj) is a relative path which points to the directory
-  where the target is saved. Always use $(obj) when
-  referring to generated files.
+  $(obj) is the directory where the target is saved. Always use $(obj) when
+  referring to generated files. Use $(obj) for pattern rules that need to work
+  for both generated files and real sources (VPATH will help to find the
+  prerequisites not only in the object tree but also in the source tree).
 
   Example::
 

Makefile

@@ -263,7 +263,14 @@ srctree := $(abs_srctree)
 endif
 
 objtree		:= .
+
+VPATH		:=
+
+ifeq ($(KBUILD_EXTMOD),)
+ifdef building_out_of_srctree
 VPATH		:= $(srctree)
+endif
+endif
 
 export building_out_of_srctree srctree objtree VPATH
 

arch/arc/boot/dts/Makefile

@@ -10,8 +10,7 @@ obj-y   += $(builtindtb-y).dtb.o
 dtb-y := $(builtindtb-y).dtb
 
 # for CONFIG_OF_ALL_DTBS test
-dtstree	:= $(srctree)/$(src)
-dtb-	:= $(patsubst $(dtstree)/%.dts,%.dtb, $(wildcard $(dtstree)/*.dts))
+dtb-	:= $(patsubst $(src)/%.dts,%.dtb, $(wildcard $(src)/*.dts))
 
 # board-specific dtc flags
 DTC_FLAGS_hsdk += --pad 20

arch/arm/Kbuild

@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_FPE_NWFPE)		+= nwfpe/
 # Put arch/arm/fastfpe/ to use this.
-obj-$(CONFIG_FPE_FASTFPE)	+= $(patsubst $(srctree)/$(src)/%,%,$(wildcard $(srctree)/$(src)/fastfpe/))
+obj-$(CONFIG_FPE_FASTFPE)	+= $(patsubst $(src)/%,%,$(wildcard $(src)/fastfpe/))
 obj-$(CONFIG_VFP)		+= vfp/
 obj-$(CONFIG_XEN)		+= xen/
 obj-$(CONFIG_VDSO)		+= vdso/

arch/arm/boot/Makefile

@@ -25,8 +25,7 @@ targets := Image zImage xipImage bootpImage uImage
 
 ifeq ($(CONFIG_XIP_KERNEL),y)
 
-cmd_deflate_xip_data = $(CONFIG_SHELL) -c \
-	'$(srctree)/$(src)/deflate_xip_data.sh $< $@'
+cmd_deflate_xip_data = $(CONFIG_SHELL) -c '$(src)/deflate_xip_data.sh $< $@'
 
 ifeq ($(CONFIG_XIP_DEFLATED_DATA),y)
 quiet_cmd_mkxip = XIPZ    $@

arch/arm/mach-s3c/Makefile

@@ -2,7 +2,7 @@
 #
 # Copyright 2009 Simtec Electronics
 
-include $(srctree)/$(src)/Makefile.s3c64xx
+include $(src)/Makefile.s3c64xx
 
 # Objects we always build independent of SoC choice
 

arch/arm/plat-orion/Makefile

@@ -2,7 +2,7 @@
 #
 # Makefile for the linux kernel.
 #
-ccflags-y := -I$(srctree)/$(src)/include
+ccflags-y := -I$(src)/include
 
 orion-gpio-$(CONFIG_GPIOLIB)      += gpio.o
 obj-$(CONFIG_PLAT_ORION_LEGACY)   += irq.o pcie.o time.o common.o mpp.o

arch/arm/tools/Makefile

@@ -9,7 +9,7 @@ gen := arch/$(ARCH)/include/generated
 kapi := $(gen)/asm
 uapi := $(gen)/uapi/asm
 syshdr := $(srctree)/scripts/syscallhdr.sh
-sysnr := $(srctree)/$(src)/syscallnr.sh
+sysnr := $(src)/syscallnr.sh
 systbl := $(srctree)/scripts/syscalltbl.sh
 syscall := $(src)/syscall.tbl