kbuild: introduce hostprogs-always-y and userprogs-always-y

To build host programs, you need to add the program names to 'hostprogs'
to use the necessary build rule, but it is not enough to build them
because there is no dependency.

There are two types of host programs: built as the prerequisite of
another (e.g. gen_crc32table in lib/Makefile), or always built when
Kbuild visits the Makefile (e.g. genksyms in scripts/genksyms/Makefile).

The latter is typical in Makefiles under scripts/, which contains host
programs globally used during the kernel build. To build them, you need
to add them to both 'hostprogs' and 'always-y'.

This commit adds hostprogs-always-y as a shorthand.

The same applies to user programs. net/bpfilter/Makefile builds
bpfilter_umh on demand, hence always-y is unneeded. In contrast,
programs under samples/ are added to both 'userprogs' and 'always-y'
so they are always built when Kbuild visits the Makefiles.

userprogs-always-y works as a shorthand.

Signed-off-by: Masahiro Yamada <[e-mail]>
Acked-by: Miguel Ojeda <[e-mail]>

Documentation/kbuild/makefiles.rst

···
 		hostprogs     := lxdialog
 		always-y      := $(hostprogs)
 
+	Kbuild provides the following shorthand for this:
+
+		hostprogs-always-y := lxdialog
+
 	This will tell kbuild to build lxdialog even if not referenced in
 	any rule.
 
···
 5.4 When userspace programs are actually built
 ----------------------------------------------
 
-	Same as "When host programs are actually built".
+	Kbuild builds userspace programs only when told to do so.
+	There are two ways to do this.
+
+	(1) Add it as the prerequisite of another file
+
+	Example::
+
+		#net/bpfilter/Makefile
+		userprogs := bpfilter_umh
+		$(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh
+
+	$(obj)/bpfilter_umh is built before $(obj)/bpfilter_umh_blob.o
+
+	(2) Use always-y
+
+	Example::
+
+		userprogs := binderfs_example
+		always-y := $(userprogs)
+
+	Kbuild provides the following shorthand for this:
+
+		userprogs-always-y := binderfs_example
+
+	This will tell Kbuild to build binderfs_example when it visits this
+	Makefile.
 
 6 Kbuild clean infrastructure
 =============================

samples/auxdisplay/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-userprogs := cfag12864b-example
-always-y := $(userprogs)
+userprogs-always-y += cfag12864b-example

samples/binderfs/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
-userprogs := binderfs_example
-always-y := $(userprogs)
+userprogs-always-y += binderfs_example
 
 userccflags += -I usr/include

samples/connector/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_SAMPLE_CONNECTOR) += cn_test.o
 
-userprogs := ucon
-always-$(CONFIG_CC_CAN_LINK) := $(userprogs)
+userprogs-always-$(CONFIG_CC_CAN_LINK) += ucon
 
 userccflags += -I usr/include

samples/hidraw/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-userprogs := hid-example
-always-y := $(userprogs)
+userprogs-always-y += hid-example
 
 userccflags += -I usr/include

samples/mei/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 # Copyright (c) 2012-2019, Intel Corporation. All rights reserved.
-
-userprogs := mei-amt-version
-always-y := $(userprogs)
+userprogs-always-y += mei-amt-version
 
 userccflags += -I usr/include

samples/pidfd/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-
-usertprogs := pidfd-metadata
-always-y := $(userprogs)
+usertprogs-always-y += pidfd-metadata
 
 userccflags += -I usr/include

samples/seccomp/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-userprogs := bpf-fancy dropper bpf-direct user-trap
+userprogs-always-y += bpf-fancy dropper bpf-direct user-trap
 
 bpf-fancy-objs := bpf-fancy.o bpf-helper.o
 
 userccflags += -I usr/include
-
-always-y := $(userprogs)

samples/timers/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-userprogs := hpet_example
-always-y := $(userprogs)
+userprogs-always-y += hpet_example
 
 userccflags += -I usr/include

samples/uhid/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
-userprogs := uhid-example
-always-y := $(userprogs)
+userprogs-always-y += uhid-example
 
 userccflags += -I usr/include

samples/vfs/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
-userprogs := test-fsmount test-statx
-always-y := $(userprogs)
+userprogs-always-y += test-fsmount test-statx
 
 userccflags += -I usr/include

samples/watch_queue/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
-userprogs := watch_test
-always-y := $(userprogs)
+userprogs-always-y += watch_test
 
 userccflags += -I usr/include

samples/watchdog/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-userprogs := watchdog-simple
-always-y := $(userprogs)
+userprogs-always-y += watchdog-simple

scripts/Makefile

···
 # scripts contains sources for various helper programs used throughout
 # the kernel for the build process.
 
-always-$(CONFIG_BUILD_BIN2C)			+= bin2c
-always-$(CONFIG_KALLSYMS)			+= kallsyms
-always-$(BUILD_C_RECORDMCOUNT)			+= recordmcount
-always-$(CONFIG_BUILDTIME_TABLE_SORT)		+= sorttable
-always-$(CONFIG_ASN1)				+= asn1_compiler
-always-$(CONFIG_MODULE_SIG_FORMAT)		+= sign-file
-always-$(CONFIG_SYSTEM_TRUSTED_KEYRING)		+= extract-cert
-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)	+= insert-sys-cert
+hostprogs-always-$(CONFIG_BUILD_BIN2C)			+= bin2c
+hostprogs-always-$(CONFIG_KALLSYMS)			+= kallsyms
+hostprogs-always-$(BUILD_C_RECORDMCOUNT)		+= recordmcount
+hostprogs-always-$(CONFIG_BUILDTIME_TABLE_SORT)		+= sorttable
+hostprogs-always-$(CONFIG_ASN1)				+= asn1_compiler
+hostprogs-always-$(CONFIG_MODULE_SIG_FORMAT)		+= sign-file
+hostprogs-always-$(CONFIG_SYSTEM_TRUSTED_KEYRING)	+= extract-cert
+hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)	+= insert-sys-cert
 
 HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include
 HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include
···
 HOSTCFLAGS_sorttable.o += -DUNWINDER_ORC_ENABLED
 HOSTLDLIBS_sorttable = -lpthread
 endif
-
-hostprogs := $(always-y) $(always-m)
 
 # The following programs are only built on demand
 hostprogs += unifdef

scripts/Makefile.clean

···
 # build a list of files to remove, usually relative to the current
 # directory
 
-__clean-files	:= $(extra-y) $(extra-m) $(extra-)       \
-		   $(always) $(always-y) $(always-m) $(always-) $(targets) $(clean-files)   \
-		   $(hostprogs) $(hostprogs-y) $(hostprogs-m) $(hostprogs-) $(userprogs)
+__clean-files	:= \
+	$(clean-files) $(targets) $(hostprogs) $(userprogs) \
+	$(extra-y) $(extra-m) $(extra-) \
+	$(always-y) $(always-m) $(always-) \
+	$(hostprogs-always-y) $(hostprogs-always-m) $(hostprogs-always-) \
+	$(userprogs-always-y) $(userprogs-always-m) $(userprogs-always-)
+
+# deprecated
+__clean-files	+= $(always) $(hostprogs-y) $(hostprogs-m) $(hostprogs-)
 
 __clean-files   := $(filter-out $(no-clean-files), $(__clean-files))
 

scripts/Makefile.lib

···
 
 always-y += $(always-m)
 
+# hostprogs-always-y += foo
+# ... is a shorthand for
+# hostprogs += foo
+# always-y  += foo
+hostprogs += $(hostprogs-always-y) $(hostprogs-always-m)
+always-y += $(hostprogs-always-y) $(hostprogs-always-m)
+
+# userprogs-always-y is likewise.
+userprogs += $(userprogs-always-y) $(userprogs-always-m)
+always-y += $(userprogs-always-y) $(userprogs-always-m)
+
 # DTB
 # If CONFIG_OF_ALL_DTBS is enabled, all DT blobs are built
 extra-y				+= $(dtb-y)

scripts/basic/Makefile

···
 #
 # fixdep: used to generate dependency information during build process
 
-hostprogs	:= fixdep
-always-y	:= $(hostprogs)
+hostprogs-always-y	+= fixdep

scripts/dtc/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 # scripts/dtc makefile
 
-hostprogs			:= dtc
-always-$(CONFIG_DTC)		+= $(hostprogs)
-always-$(CHECK_DT_BINDING)	+= $(hostprogs)
+hostprogs-always-$(CONFIG_DTC)		+= dtc
+hostprogs-always-$(CHECK_DT_BINDING)	+= dtc
 
 dtc-objs	:= dtc.o flattree.o fstree.o data.o livetree.o treesource.o \
 		   srcpos.o checks.o util.o

scripts/genksyms/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 
-hostprogs	:= genksyms
-always-y	:= $(hostprogs)
+hostprogs-always-y	+= genksyms
 
 genksyms-objs	:= genksyms.o parse.tab.o lex.lex.o
 

scripts/mod/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 OBJECT_FILES_NON_STANDARD := y
 
-hostprogs	:= modpost mk_elfconfig
-always-y	:= $(hostprogs) empty.o
+hostprogs-always-y	+= modpost mk_elfconfig
+always-y		+= empty.o
 
 modpost-objs	:= modpost.o file2alias.o sumversion.o
 

scripts/selinux/genheaders/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-hostprogs	:= genheaders
+hostprogs-always-y += genheaders
 HOST_EXTRACFLAGS += \
 	-I$(srctree)/include/uapi -I$(srctree)/include \
 	-I$(srctree)/security/selinux/include
-
-always-y	:= $(hostprogs)

scripts/selinux/mdp/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-hostprogs	:= mdp
+hostprogs-always-y += mdp
 HOST_EXTRACFLAGS += \
 	-I$(srctree)/include/uapi -I$(srctree)/include \
 	-I$(srctree)/security/selinux/include -I$(objtree)/include
 
-always-y	:= $(hostprogs)
 clean-files	:= policy.* file_contexts