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

JIRA: https://issues.redhat.com/browse/RHEL-107194

commit b1992c3
Author: Masahiro Yamada <masahiroy@kernel.org>
Date:   Sat Apr 27 23:55:02 2024 +0900

    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>

Conflicts:

There is a extensive list of fixes/conflicts due the amount of files originally
changed by this commit, plus the difference of rhel-9 code against upstream. All
conflicts/differences are listed below:

- Context difference at Documentation/Makefile since RHEL 9 does not have the
  change "docs: allow to pass extra DOCS_CSS themes via make" and later changes.
- Conflict at Documentation/devicetree/bindings/Makefile, patch find_cmd instead
  of find_all_cmd since RHEL-9 doesn't have "dt-bindings: Consider
  DT_SCHEMA_FILES when finding all json-schema", "dt-bindings: kbuild: Split
  targets out to separate rules" and later changes.
- Conflict at Documentation/kbuild/makefiles.rst due different identation since
  RHEL-9 doesn't have the change "docs/kbuild/makefiles: clean up indentation
  and whitespace"
- Patched additional $(srctree)/$(src) references at:
   * arch/arm/mach-davinci/Makefile
   * arch/arm/mach-omap2/Makefile
   * arch/arm/mach-spear/Makefile
   * arch/arm/plat-pxa/Makefile
   * arch/arm/plat-versatile/Makefile
   * arch/ia64/kernel/Makefile
   * arch/nds32/boot/Makefile
   * arch/nds32/kernel/vdso/Makefile
   * drivers/net/ethernet/hisilicon/hns3/hns3pf/Makefile
   * drivers/net/ethernet/hisilicon/hns3/hns3vf/Makefile
   * drivers/staging/rtl8188eu/Makefile
   * drivers/staging/unisys/visorhba/Makefile
   * drivers/staging/unisys/visornic/Makefile
   * scripts/gcc-plugins/Makefile
  Since RHEL-9 does not have later upstream changes that dropped/made those
  references uneeded.
- Conflict at arch/arm/mach-s3c/Makefile since RHEL-9 doesn't have
  "ARM: s3c: remove s3c24xx specific hacks" and related changes. Also,
  extra locations needed patching because of not having the changes
  "ARM: s3c: remove all s3c24xx support" and "ARM: s3c: fix include path".
  Due lacking the last change also arch/arm/mach-s3c/Makefile.s3c64xx needs
  additional two places patched as well.
- Conflict at arch/arm/plat-orion/Makefile since RHEL-9 doesn't have
  the commit "ARM: orion: fix include path" and its previous related
  changes.
- Dropped changes for arch/loongarch since it doesn't exist on rhel-9
- Dropped changes to arch/parisc/kernel/{vdso32,vdso64}/Makefile since RHEL 9
  does not have the change "parisc: Add vDSO support" and later updates to it.
- Dropped change to arch/riscv/kernel/compat_vdso/Makefile since RHEL 9 does
  not have the change "riscv: compat: vdso: Add COMPAT_VDSO base code implementation"
- Dropped change to arch/riscv/kvm/Makefile since there is no KVM support/commits
  in RHEL 9 for riscv.
- Apply change for arch/riscv/kernel/vdso/Makefile in a different place since
  RHEL-9 does not have the change "riscv: explicitly use symbol offsets for VDSO"
  which changed the location of the $(srctree)/$(src) reference
- Dropped change to certs/Makefile related to check-blacklist-hashes.awk since
  that script was only added with commit "certs: Check that builtin blacklist
  hashes are valid" which is not backported/available in RHEL 9 code right now.
- Dropped change to drivers/md/dm-vdo/Makefile since dm-vdo was never backported
  to RHEL-9 main.
- Dropped change to drivers/net/ethernet/fungible/funeth/Makefile since fungible
  ethernet driver/devices code is not available/backported to RHEL-9.
- Fixed conflict at drivers/net/ethernet/hisilicon/hns3/Makefile since RHEL-9
  does not have the change "net: hns3: refactor hns3 makefile to support
  hns3_common module"
- Fixed conflict at drivers/net/wireless/intel/iwlwifi/mvm/Makefile due already
  backported commit "wifi: iwlwifi: mvm: implement link grading"
- Dropped change to init/Makefile since we are not backporting
  "kbuild: build init/built-in.a just once" that introduced the section patched.
- Dropped change to rust/Makefile since there is no rust support backported
  to RHEL-9.
- Fixed conflict at scripts/dtc/Makefile since RHEL-9 does not have the change
  "dt-bindings: kbuild: Use DTB files for validation"
- Dropped change to security/tomoyo/Makefile since it's not needed, it's just
  reverting the change "tomoyo: fix broken dependency on *.conf.default" which
  was never applied to RHEL-9. However, we also bring a different change/patch
  location since RHEL-9 does not have the change "tomoyo: Omit use of bin2c".
- Dropped change to usr/include/Makefile since "kbuild: move headers_check.pl to
  usr/include/" is not being backported to RHEL-9.
- Misc/minor context differences at other places.

Signed-off-by: Herton R. Krzesinski <herton@redhat.com>

Author: Herton R. Krzesinski

Documentation/Makefile

@@ -68,22 +68,22 @@ 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)
 
 YNL_INDEX:=$(srctree)/Documentation/networking/netlink_spec/index.rst

Documentation/devicetree/bindings/Makefile

@@ -22,17 +22,17 @@ $(obj)/%.example.dts: $(src)/%.yaml check_dtschema_version FORCE
 # Use full schemas when checking %.example.dts
 DT_TMP_SCHEMA := $(obj)/processed-schema-examples.json
 
-find_cmd = find $(srctree)/$(src) \( -name '*.yaml' ! \
+find_cmd = find $(src) \( -name '*.yaml' ! \
 		-name 'processed-schema*' ! \
 		-name '*.example.dt.yaml' \)
 
 quiet_cmd_yamllint = LINT    $(src)
       cmd_yamllint = ($(find_cmd) | \
-                     xargs $(DT_SCHEMA_LINT) -f parsable -c $(srctree)/$(src)/.yamllint) || true
+                     xargs $(DT_SCHEMA_LINT) -f parsable -c $(src)/.yamllint) || true
 
 quiet_cmd_chk_bindings = CHKDT   $@
       cmd_chk_bindings = ($(find_cmd) | \
-                         xargs -n200 -P$$(nproc) $(DT_DOC_CHECKER) -u $(srctree)/$(src)) || true
+                         xargs -n200 -P$$(nproc) $(DT_DOC_CHECKER) -u $(src)) || true
 
 quiet_cmd_mk_schema = SCHEMA  $@
       cmd_mk_schema = f=$$(mktemp) ; \

Documentation/kbuild/makefiles.rst

@@ -421,7 +421,7 @@ more details, with real examples.
 	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.
@@ -502,14 +502,14 @@ more details, with real examples.
 	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

@@ -264,7 +264,14 @@ 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

@@ -31,8 +31,7 @@ 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-davinci/Makefile

@@ -4,7 +4,7 @@
 #
 #
 
-ccflags-$(CONFIG_ARCH_MULTIPLATFORM) := -I$(srctree)/$(src)/include
+ccflags-$(CONFIG_ARCH_MULTIPLATFORM) := -I$(src)/include
 
 # Common objects
 obj-y 					:= serial.o usb.o common.o sram.o

arch/arm/mach-omap2/Makefile

@@ -3,7 +3,7 @@
 # Makefile for the linux kernel.
 #
 
-ccflags-y := -I$(srctree)/$(src)/include \
+ccflags-y := -I$(src)/include \
 	-I$(srctree)/arch/arm/plat-omap/include
 
 # Common support

arch/arm/mach-s3c/Makefile

@@ -2,14 +2,14 @@
 #
 # Copyright 2009 Simtec Electronics
 
-ccflags-$(CONFIG_ARCH_MULTIPLATFORM) += -I$(srctree)/$(src)/include
+ccflags-$(CONFIG_ARCH_MULTIPLATFORM) += -I$(src)/include
 
 ifdef CONFIG_ARCH_S3C24XX
-include $(srctree)/$(src)/Makefile.s3c24xx
+include $(src)/Makefile.s3c24xx
 endif
 
 ifdef CONFIG_ARCH_S3C64XX
-include $(srctree)/$(src)/Makefile.s3c64xx
+include $(src)/Makefile.s3c64xx
 endif
 
 # Objects we always build independent of SoC choice