scripts/Makefile.lib - kernel/msm-4.9 - Gitiles

 # ===========================================================================
 # kbuild: Generic definitions
 # ===========================================================================

 # Standard vars

 comma   := ,
 empty   :=
 space   := $(empty) $(empty)

 # Backward compatibility - to be removed...
 extra-y	+= $(EXTRA_TARGETS)
 # Figure out what we need to build from the various variables
 # ===========================================================================

 # When an object is listed to be built compiled-in and modular,
 # only build the compiled-in version

 obj-m := $(filter-out $(obj-y),$(obj-m))

 # Libraries are always collected in one lib file.
 # Filter out objects already built-in

 lib-y := $(filter-out $(obj-y), $(sort $(lib-y) $(lib-m)))


 # Handle objects in subdirs
 # ---------------------------------------------------------------------------
 # o if we encounter foo/ in $(obj-y), replace it by foo/built-in.o
 #   and add the directory to the list of dirs to descend into: $(subdir-y)
 # o if we encounter foo/ in $(obj-m), remove it from $(obj-m)
 #   and add the directory to the list of dirs to descend into: $(subdir-m)

 __subdir-y	:= $(patsubst %/,%,$(filter %/, $(obj-y)))
 subdir-y	+= $(__subdir-y)
 __subdir-m	:= $(patsubst %/,%,$(filter %/, $(obj-m)))
 subdir-m	+= $(__subdir-m)
 obj-y		:= $(patsubst %/, %/built-in.o, $(obj-y))
 obj-m		:= $(filter-out %/, $(obj-m))

 # Subdirectories we need to descend into

 subdir-ym	:= $(sort $(subdir-y) $(subdir-m))

 # if $(foo-objs) exists, foo.o is a composite object
 multi-used-y := $(sort $(foreach m,$(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))), $(m))))
 multi-used-m := $(sort $(foreach m,$(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))), $(m))))
 multi-used   := $(multi-used-y) $(multi-used-m)
 single-used-m := $(sort $(filter-out $(multi-used-m),$(obj-m)))

 # Build list of the parts of our composite objects, our composite
 # objects depend on those (obviously)
 multi-objs-y := $(foreach m, $(multi-used-y), $($(m:.o=-objs)) $($(m:.o=-y)))
 multi-objs-m := $(foreach m, $(multi-used-m), $($(m:.o=-objs)) $($(m:.o=-y)))
 multi-objs   := $(multi-objs-y) $(multi-objs-m)

 # $(subdir-obj-y) is the list of objects in $(obj-y) which do not live
 # in the local directory
 subdir-obj-y := $(foreach o,$(obj-y),$(if $(filter-out $(o),$(notdir $(o))),$(o)))

 # $(obj-dirs) is a list of directories that contain object files
 obj-dirs := $(dir $(multi-objs) $(subdir-obj-y))

 # Replace multi-part objects by their individual parts, look at local dir only
 real-objs-y := $(foreach m, $(filter-out $(subdir-obj-y), $(obj-y)), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))),$($(m:.o=-objs)) $($(m:.o=-y)),$(m))) $(extra-y)
 real-objs-m := $(foreach m, $(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))),$($(m:.o=-objs)) $($(m:.o=-y)),$(m)))

 # Add subdir path

 extra-y		:= $(addprefix $(obj)/,$(extra-y))
 always		:= $(addprefix $(obj)/,$(always))
 targets		:= $(addprefix $(obj)/,$(targets))
 obj-y		:= $(addprefix $(obj)/,$(obj-y))
 obj-m		:= $(addprefix $(obj)/,$(obj-m))
 lib-y		:= $(addprefix $(obj)/,$(lib-y))
 subdir-obj-y	:= $(addprefix $(obj)/,$(subdir-obj-y))
 real-objs-y	:= $(addprefix $(obj)/,$(real-objs-y))
 real-objs-m	:= $(addprefix $(obj)/,$(real-objs-m))
 single-used-m	:= $(addprefix $(obj)/,$(single-used-m))
 multi-used-y	:= $(addprefix $(obj)/,$(multi-used-y))
 multi-used-m	:= $(addprefix $(obj)/,$(multi-used-m))
 multi-objs-y	:= $(addprefix $(obj)/,$(multi-objs-y))
 multi-objs-m	:= $(addprefix $(obj)/,$(multi-objs-m))
 subdir-ym	:= $(addprefix $(obj)/,$(subdir-ym))
 obj-dirs	:= $(addprefix $(obj)/,$(obj-dirs))

 # The temporary file to save gcc -MD generated dependencies must not
 # contain a comma
 depfile = $(subst $(comma),_,$(@D)/.$(@F).d)

 # These flags are needed for modversions and compiling, so we define them here
 # already
 # $(modname_flags) #defines KBUILD_MODNAME as the name of the module it will
 # end up in (or would, if it gets compiled in)
 # Note: It's possible that one object gets potentially linked into more
 #       than one module. In that case KBUILD_MODNAME will be set to foo_bar,
 #       where foo and bar are the name of the modules.
 basename_flags = -DKBUILD_BASENAME=$(subst $(comma),_,$(subst -,_,$(*F)))
 modname_flags  = $(if $(filter 1,$(words $(modname))),-DKBUILD_MODNAME=$(subst $(comma),_,$(subst -,_,$(modname))))

 _c_flags       = $(CFLAGS) $(EXTRA_CFLAGS) $(CFLAGS_$(*F).o)
 _a_flags       = $(AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$(*F).o)
 _cpp_flags     = $(CPPFLAGS) $(EXTRA_CPPFLAGS) $(CPPFLAGS_$(@F))

 # If building the kernel in a separate objtree expand all occurrences
 # of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').

 ifeq ($(KBUILD_SRC),)
 __c_flags	= $(_c_flags)
 __a_flags	= $(_a_flags)
 __cpp_flags     = $(_cpp_flags)
 else

 # Prefix -I with $(srctree) if it is not an absolute path
 addtree = $(if $(filter-out -I/%,$(1)),$(patsubst -I%,-I$(srctree)/%,$(1))) $(1)
 # Find all -I options and call addtree
 flags = $(foreach o,$($(1)),$(if $(filter -I%,$(o)),$(call addtree,$(o)),$(o)))

 # -I$(obj) locates generated .h files
 # $(call addtree,-I$(obj)) locates .h files in srctree, from generated .c files
 #   and locates generated .h files
 # FIXME: Replace both with specific CFLAGS* statements in the makefiles
 __c_flags	= $(call addtree,-I$(obj)) $(call flags,_c_flags)
 __a_flags	=                          $(call flags,_a_flags)
 __cpp_flags     =                          $(call flags,_cpp_flags)
 endif

 c_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
 		 $(__c_flags) $(modkern_cflags) \
 		 $(basename_flags) $(modname_flags)

 a_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
 		 $(__a_flags) $(modkern_aflags)

 cpp_flags      = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(__cpp_flags)

 ld_flags       = $(LDFLAGS) $(EXTRA_LDFLAGS)

 # Finds the multi-part object the current object will be linked into
 modname-multi = $(sort $(foreach m,$(multi-used),\
 		$(if $(filter $(subst $(obj)/,,$*.o), $($(m:.o=-objs)) $($(m:.o=-y))),$(m:.o=))))

 # Shipped files
 # ===========================================================================

 quiet_cmd_shipped = SHIPPED $@
 cmd_shipped = cat $< > $@

 $(obj)/%:: $(src)/%_shipped
 	$(call cmd,shipped)

 # Commands useful for building a boot image
 # ===========================================================================
 #
 #	Use as following:
 #
 #	target: source(s) FORCE
 #		$(if_changed,ld/objcopy/gzip)
 #
 #	and add target to EXTRA_TARGETS so that we know we have to
 #	read in the saved command line

 # Linking
 # ---------------------------------------------------------------------------

 quiet_cmd_ld = LD      $@
 cmd_ld = $(LD) $(LDFLAGS) $(EXTRA_LDFLAGS) $(LDFLAGS_$(@F)) \
 	       $(filter-out FORCE,$^) -o $@

 # Objcopy
 # ---------------------------------------------------------------------------

 quiet_cmd_objcopy = OBJCOPY $@
 cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@

 # Gzip
 # ---------------------------------------------------------------------------

 quiet_cmd_gzip = GZIP    $@
 cmd_gzip = gzip -f -9 < $< > $@

 # ===========================================================================
 # Generic stuff
 # ===========================================================================

 ifneq ($(KBUILD_NOCMDDEP),1)
 # Check if both arguments has same arguments. Result in empty string if equal
 # User may override this check using make KBUILD_NOCMDDEP=1
 arg-check = $(strip $(filter-out $(1), $(2)) $(filter-out $(2), $(1)) )

 endif

 # echo command. Short version is $(quiet) equals quiet, otherwise full command
 echo-cmd = $(if $($(quiet)cmd_$(1)), \
 	echo '  $(subst ','\'',$($(quiet)cmd_$(1)))';)

 # function to only execute the passed command if necessary
 # >'< substitution is for echo to work, >$< substitution to preserve $ when reloading .cmd file
 # note: when using inline perl scripts [perl -e '...$$t=1;...'] in $(cmd_xxx) double $$ your perl vars
 #
 if_changed = $(if $(strip $? $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
 	@set -e; \
 	$(echo-cmd) \
 	$(cmd_$(1)); \
 	echo 'cmd_$@ := $(subst $$,$$$$,$(subst ','\'',$(cmd_$(1))))' > $(@D)/.$(@F).cmd)


 # execute the command and also postprocess generated .d dependencies
 # file

 if_changed_dep = $(if $(strip $? $(filter-out FORCE $(wildcard $^),$^)\
 	$(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),                  \
 	@set -e; \
 	$(echo-cmd) \
 	$(cmd_$(1)); \
 	scripts/basic/fixdep $(depfile) $@ '$(subst $$,$$$$,$(subst ','\'',$(cmd_$(1))))' > $(@D)/.$(@F).tmp; \
 	rm -f $(depfile); \
 	mv -f $(@D)/.$(@F).tmp $(@D)/.$(@F).cmd)

 # Usage: $(call if_changed_rule,foo)
 # will check if $(cmd_foo) changed, or any of the prequisites changed,
 # and if so will execute $(rule_foo)

 if_changed_rule = $(if $(strip $? $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),\
 			@set -e; \
 			$(rule_$(1)))

 # If quiet is set, only print short version of command

 cmd = @$(if $($(quiet)cmd_$(1)),echo '  $(subst ','\'',$($(quiet)cmd_$(1)))' &&) $(cmd_$(1))

 #	$(call descend,<dir>,<target>)
 #	Recursively call a sub-make in <dir> with target <target>
 # Usage is deprecated, because make do not see this as an invocation of make.
 descend =$(Q)$(MAKE) -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.build obj=$(1) $(2)

 # Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
 # Usage:
 # $(Q)$(MAKE) $(build)=dir
 build := -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.build obj

 # filechk is used to check if the content of a generated file is updated.
 # Sample usage:
 # define filechk_sample
 #	echo $KERNELRELEASE
 # endef
 # version.h : Makefile
 #	$(call filechk,sample)
 # The rule defined shall write to stdout the content of the new file.
 # The existing file will be compared with the new one.
 # - If no file exist it is created
 # - If the content differ the new file is used
 # - If they are equal no change, and no timestamp update

 define filechk
 	$(Q)set -e;				\
 	echo '  CHK     $@';			\
 	mkdir -p $(dir $@);			\
 	$(filechk_$(1)) $(2) > $@.tmp;		\
 	if [ -r $@ ] && cmp -s $@ $@.tmp; then	\
 		rm -f $@.tmp;			\
 	else					\
 		echo '  UPD     $@';		\
 		mv -f $@.tmp $@;		\
 	fi
 endef
	# ===========================================================================
	# kbuild: Generic definitions
	# ===========================================================================

	# Standard vars

	comma := ,
	empty :=
	space := $(empty) $(empty)

	# Backward compatibility - to be removed...
	extra-y += $(EXTRA_TARGETS)
	# Figure out what we need to build from the various variables
	# ===========================================================================

	# When an object is listed to be built compiled-in and modular,
	# only build the compiled-in version

	obj-m := $(filter-out $(obj-y),$(obj-m))

	# Libraries are always collected in one lib file.
	# Filter out objects already built-in

	lib-y := $(filter-out $(obj-y), $(sort $(lib-y) $(lib-m)))


	# Handle objects in subdirs
	# ---------------------------------------------------------------------------
	# o if we encounter foo/ in $(obj-y), replace it by foo/built-in.o
	# and add the directory to the list of dirs to descend into: $(subdir-y)
	# o if we encounter foo/ in $(obj-m), remove it from $(obj-m)
	# and add the directory to the list of dirs to descend into: $(subdir-m)

	__subdir-y := $(patsubst %/,%,$(filter %/, $(obj-y)))
	subdir-y += $(__subdir-y)
	__subdir-m := $(patsubst %/,%,$(filter %/, $(obj-m)))
	subdir-m += $(__subdir-m)
	obj-y := $(patsubst %/, %/built-in.o, $(obj-y))
	obj-m := $(filter-out %/, $(obj-m))

	# Subdirectories we need to descend into

	subdir-ym := $(sort $(subdir-y) $(subdir-m))

	# if $(foo-objs) exists, foo.o is a composite object
	multi-used-y := $(sort $(foreach m,$(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))), $(m))))
	multi-used-m := $(sort $(foreach m,$(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))), $(m))))
	multi-used := $(multi-used-y) $(multi-used-m)
	single-used-m := $(sort $(filter-out $(multi-used-m),$(obj-m)))

	# Build list of the parts of our composite objects, our composite
	# objects depend on those (obviously)
	multi-objs-y := $(foreach m, $(multi-used-y), $($(m:.o=-objs)) $($(m:.o=-y)))
	multi-objs-m := $(foreach m, $(multi-used-m), $($(m:.o=-objs)) $($(m:.o=-y)))
	multi-objs := $(multi-objs-y) $(multi-objs-m)

	# $(subdir-obj-y) is the list of objects in $(obj-y) which do not live
	# in the local directory
	subdir-obj-y := $(foreach o,$(obj-y),$(if $(filter-out $(o),$(notdir $(o))),$(o)))

	# $(obj-dirs) is a list of directories that contain object files
	obj-dirs := $(dir $(multi-objs) $(subdir-obj-y))

	# Replace multi-part objects by their individual parts, look at local dir only
	real-objs-y := $(foreach m, $(filter-out $(subdir-obj-y), $(obj-y)), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))),$($(m:.o=-objs)) $($(m:.o=-y)),$(m))) $(extra-y)
	real-objs-m := $(foreach m, $(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))),$($(m:.o=-objs)) $($(m:.o=-y)),$(m)))

	# Add subdir path

	extra-y := $(addprefix $(obj)/,$(extra-y))
	always := $(addprefix $(obj)/,$(always))
	targets := $(addprefix $(obj)/,$(targets))
	obj-y := $(addprefix $(obj)/,$(obj-y))
	obj-m := $(addprefix $(obj)/,$(obj-m))
	lib-y := $(addprefix $(obj)/,$(lib-y))
	subdir-obj-y := $(addprefix $(obj)/,$(subdir-obj-y))
	real-objs-y := $(addprefix $(obj)/,$(real-objs-y))
	real-objs-m := $(addprefix $(obj)/,$(real-objs-m))
	single-used-m := $(addprefix $(obj)/,$(single-used-m))
	multi-used-y := $(addprefix $(obj)/,$(multi-used-y))
	multi-used-m := $(addprefix $(obj)/,$(multi-used-m))
	multi-objs-y := $(addprefix $(obj)/,$(multi-objs-y))
	multi-objs-m := $(addprefix $(obj)/,$(multi-objs-m))
	subdir-ym := $(addprefix $(obj)/,$(subdir-ym))
	obj-dirs := $(addprefix $(obj)/,$(obj-dirs))

	# The temporary file to save gcc -MD generated dependencies must not
	# contain a comma
	depfile = $(subst $(comma),_,$(@D)/.$(@F).d)

	# These flags are needed for modversions and compiling, so we define them here
	# already
	# $(modname_flags) #defines KBUILD_MODNAME as the name of the module it will
	# end up in (or would, if it gets compiled in)
	# Note: It's possible that one object gets potentially linked into more
	# than one module. In that case KBUILD_MODNAME will be set to foo_bar,
	# where foo and bar are the name of the modules.
	basename_flags = -DKBUILD_BASENAME=$(subst $(comma),_,$(subst -,_,$(*F)))
	modname_flags = $(if $(filter 1,$(words $(modname))),-DKBUILD_MODNAME=$(subst $(comma),_,$(subst -,_,$(modname))))

	_c_flags = $(CFLAGS) $(EXTRA_CFLAGS) $(CFLAGS_$(*F).o)
	_a_flags = $(AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$(*F).o)
	_cpp_flags = $(CPPFLAGS) $(EXTRA_CPPFLAGS) $(CPPFLAGS_$(@F))

	# If building the kernel in a separate objtree expand all occurrences
	# of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').

	ifeq ($(KBUILD_SRC),)
	__c_flags = $(_c_flags)
	__a_flags = $(_a_flags)
	__cpp_flags = $(_cpp_flags)
	else

	# Prefix -I with $(srctree) if it is not an absolute path
	addtree = $(if $(filter-out -I/%,$(1)),$(patsubst -I%,-I$(srctree)/%,$(1))) $(1)
	# Find all -I options and call addtree
	flags = $(foreach o,$($(1)),$(if $(filter -I%,$(o)),$(call addtree,$(o)),$(o)))

	# -I$(obj) locates generated .h files
	# $(call addtree,-I$(obj)) locates .h files in srctree, from generated .c files
	# and locates generated .h files
	# FIXME: Replace both with specific CFLAGS* statements in the makefiles
	__c_flags = $(call addtree,-I$(obj)) $(call flags,_c_flags)
	__a_flags = $(call flags,_a_flags)
	__cpp_flags = $(call flags,_cpp_flags)
	endif

	c_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
	$(__c_flags) $(modkern_cflags) \
	$(basename_flags) $(modname_flags)

	a_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
	$(__a_flags) $(modkern_aflags)

	cpp_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(__cpp_flags)

	ld_flags = $(LDFLAGS) $(EXTRA_LDFLAGS)

	# Finds the multi-part object the current object will be linked into
	modname-multi = $(sort $(foreach m,$(multi-used),\
	$(if $(filter $(subst $(obj)/,,$*.o), $($(m:.o=-objs)) $($(m:.o=-y))),$(m:.o=))))

	# Shipped files
	# ===========================================================================

	quiet_cmd_shipped = SHIPPED $@
	cmd_shipped = cat $< > $@

	$(obj)/%:: $(src)/%_shipped
	$(call cmd,shipped)

	# Commands useful for building a boot image
	# ===========================================================================
	#
	# Use as following:
	#
	# target: source(s) FORCE
	# $(if_changed,ld/objcopy/gzip)
	#
	# and add target to EXTRA_TARGETS so that we know we have to
	# read in the saved command line

	# Linking
	# ---------------------------------------------------------------------------

	quiet_cmd_ld = LD $@
	cmd_ld = $(LD) $(LDFLAGS) $(EXTRA_LDFLAGS) $(LDFLAGS_$(@F)) \
	$(filter-out FORCE,$^) -o $@

	# Objcopy
	# ---------------------------------------------------------------------------

	quiet_cmd_objcopy = OBJCOPY $@
	cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@

	# Gzip
	# ---------------------------------------------------------------------------

	quiet_cmd_gzip = GZIP $@
	cmd_gzip = gzip -f -9 < $< > $@

	# ===========================================================================
	# Generic stuff
	# ===========================================================================

	ifneq ($(KBUILD_NOCMDDEP),1)
	# Check if both arguments has same arguments. Result in empty string if equal
	# User may override this check using make KBUILD_NOCMDDEP=1
	arg-check = $(strip $(filter-out $(1), $(2)) $(filter-out $(2), $(1)) )

	endif

	# echo command. Short version is $(quiet) equals quiet, otherwise full command
	echo-cmd = $(if $($(quiet)cmd_$(1)), \
	echo ' $(subst ','\'',$($(quiet)cmd_$(1)))';)

	# function to only execute the passed command if necessary
	# >'< substitution is for echo to work, >$< substitution to preserve $ when reloading .cmd file
	# note: when using inline perl scripts [perl -e '...$$t=1;...'] in $(cmd_xxx) double $$ your perl vars
	#
	if_changed = $(if $(strip $? $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
	@set -e; \
	$(echo-cmd) \
	$(cmd_$(1)); \
	echo 'cmd_$@ := $(subst $$,$$$$,$(subst ','\'',$(cmd_$(1))))' > $(@D)/.$(@F).cmd)


	# execute the command and also postprocess generated .d dependencies
	# file

	if_changed_dep = $(if $(strip $? $(filter-out FORCE $(wildcard $^),$^)\
	$(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
	@set -e; \
	$(echo-cmd) \
	$(cmd_$(1)); \
	scripts/basic/fixdep $(depfile) $@ '$(subst $$,$$$$,$(subst ','\'',$(cmd_$(1))))' > $(@D)/.$(@F).tmp; \
	rm -f $(depfile); \
	mv -f $(@D)/.$(@F).tmp $(@D)/.$(@F).cmd)

	# Usage: $(call if_changed_rule,foo)
	# will check if $(cmd_foo) changed, or any of the prequisites changed,
	# and if so will execute $(rule_foo)

	if_changed_rule = $(if $(strip $? $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),\
	@set -e; \
	$(rule_$(1)))

	# If quiet is set, only print short version of command

	cmd = @$(if $($(quiet)cmd_$(1)),echo ' $(subst ','\'',$($(quiet)cmd_$(1)))' &&) $(cmd_$(1))

	# $(call descend,<dir>,<target>)
	# Recursively call a sub-make in <dir> with target <target>
	# Usage is deprecated, because make do not see this as an invocation of make.
	descend =$(Q)$(MAKE) -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.build obj=$(1) $(2)

	# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
	# Usage:
	# $(Q)$(MAKE) $(build)=dir
	build := -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.build obj

	# filechk is used to check if the content of a generated file is updated.
	# Sample usage:
	# define filechk_sample
	# echo $KERNELRELEASE
	# endef
	# version.h : Makefile
	# $(call filechk,sample)
	# The rule defined shall write to stdout the content of the new file.
	# The existing file will be compared with the new one.
	# - If no file exist it is created
	# - If the content differ the new file is used
	# - If they are equal no change, and no timestamp update

	define filechk
	$(Q)set -e; \
	echo ' CHK $@'; \
	mkdir -p $(dir $@); \
	$(filechk_$(1)) $(2) > $@.tmp; \
	if [ -r $@ ] && cmp -s $@ $@.tmp; then \
	rm -f $@.tmp; \
	else \
	echo ' UPD $@'; \
	mv -f $@.tmp $@; \
	fi
	endef