[mirror_ubuntu-zesty-kernel.git] / scripts / Makefile.lib

# ===========================================================================
# 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
Commit	Line	Data
1da177e4 LT	1	# ===========================================================================
	2	# kbuild: Generic definitions
	3	# ===========================================================================
	4
	5	# Standard vars
	6
	7	comma := ,
	8	empty :=
	9	space := $(empty) $(empty)
	10
	11	# Backward compatibility - to be removed...
	12	extra-y += $(EXTRA_TARGETS)
	13	# Figure out what we need to build from the various variables
	14	# ===========================================================================
	15
	16	# When an object is listed to be built compiled-in and modular,
	17	# only build the compiled-in version
	18
	19	obj-m := $(filter-out $(obj-y),$(obj-m))
	20
	21	# Libraries are always collected in one lib file.
	22	# Filter out objects already built-in
	23
	24	lib-y := $(filter-out $(obj-y), $(sort $(lib-y) $(lib-m)))
	25
	26
	27	# Handle objects in subdirs
	28	# ---------------------------------------------------------------------------
	29	# o if we encounter foo/ in $(obj-y), replace it by foo/built-in.o
	30	# and add the directory to the list of dirs to descend into: $(subdir-y)
	31	# o if we encounter foo/ in $(obj-m), remove it from $(obj-m)
	32	# and add the directory to the list of dirs to descend into: $(subdir-m)
	33
	34	__subdir-y := $(patsubst %/,%,$(filter %/, $(obj-y)))
	35	subdir-y += $(__subdir-y)
	36	__subdir-m := $(patsubst %/,%,$(filter %/, $(obj-m)))
	37	subdir-m += $(__subdir-m)
	38	obj-y := $(patsubst %/, %/built-in.o, $(obj-y))
	39	obj-m := $(filter-out %/, $(obj-m))
	40
	41	# Subdirectories we need to descend into
	42
	43	subdir-ym := $(sort $(subdir-y) $(subdir-m))
	44
	45	# if $(foo-objs) exists, foo.o is a composite object
	46	multi-used-y := $(sort $(foreach m,$(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))), $(m))))
	47	multi-used-m := $(sort $(foreach m,$(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))), $(m))))
	48	multi-used := $(multi-used-y) $(multi-used-m)
	49	single-used-m := $(sort $(filter-out $(multi-used-m),$(obj-m)))
	50
	51	# Build list of the parts of our composite objects, our composite
	52	# objects depend on those (obviously)
	53	multi-objs-y := $(foreach m, $(multi-used-y), $($(m:.o=-objs)) $($(m:.o=-y)))
	54	multi-objs-m := $(foreach m, $(multi-used-m), $($(m:.o=-objs)) $($(m:.o=-y)))
	55	multi-objs := $(multi-objs-y) $(multi-objs-m)
	56
	57	# $(subdir-obj-y) is the list of objects in $(obj-y) which do not live
	58	# in the local directory
	59	subdir-obj-y := $(foreach o,$(obj-y),$(if $(filter-out $(o),$(notdir $(o))),$(o)))
	60
	61	# $(obj-dirs) is a list of directories that contain object files
	62	obj-dirs := $(dir $(multi-objs) $(subdir-obj-y))
	63
	64	# Replace multi-part objects by their individual parts, look at local dir only
65	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)
66	real-objs-m := $(foreach m, $(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))),$($(m:.o=-objs)) $($(m:.o=-y)),$(m)))
67
68	# Add subdir path
69
70	extra-y := $(addprefix $(obj)/,$(extra-y))
71	always := $(addprefix $(obj)/,$(always))
72	targets := $(addprefix $(obj)/,$(targets))
73	obj-y := $(addprefix $(obj)/,$(obj-y))
74	obj-m := $(addprefix $(obj)/,$(obj-m))
75	lib-y := $(addprefix $(obj)/,$(lib-y))
76	subdir-obj-y := $(addprefix $(obj)/,$(subdir-obj-y))
77	real-objs-y := $(addprefix $(obj)/,$(real-objs-y))
78	real-objs-m := $(addprefix $(obj)/,$(real-objs-m))
79	single-used-m := $(addprefix $(obj)/,$(single-used-m))
80	multi-used-y := $(addprefix $(obj)/,$(multi-used-y))
81	multi-used-m := $(addprefix $(obj)/,$(multi-used-m))
82	multi-objs-y := $(addprefix $(obj)/,$(multi-objs-y))
83	multi-objs-m := $(addprefix $(obj)/,$(multi-objs-m))
84	subdir-ym := $(addprefix $(obj)/,$(subdir-ym))
85	obj-dirs := $(addprefix $(obj)/,$(obj-dirs))
86
87	# The temporary file to save gcc -MD generated dependencies must not
88	# contain a comma
89	depfile = $(subst $(comma),_,$(@D)/.$(@F).d)
90
91	# These flags are needed for modversions and compiling, so we define them here
92	# already
93	# $(modname_flags) #defines KBUILD_MODNAME as the name of the module it will
94	# end up in (or would, if it gets compiled in)
95	# Note: It's possible that one object gets potentially linked into more
96	# than one module. In that case KBUILD_MODNAME will be set to foo_bar,
97	# where foo and bar are the name of the modules.
98	basename_flags = -DKBUILD_BASENAME=$(subst $(comma),_,$(subst -,_,$(*F)))
99	modname_flags = $(if $(filter 1,$(words $(modname))),-DKBUILD_MODNAME=$(subst $(comma),_,$(subst -,_,$(modname))))
100
101	_c_flags = $(CFLAGS) $(EXTRA_CFLAGS) $(CFLAGS_$(*F).o)
102	_a_flags = $(AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$(*F).o)
103	_cpp_flags = $(CPPFLAGS) $(EXTRA_CPPFLAGS) $(CPPFLAGS_$(@F))
104
105	# If building the kernel in a separate objtree expand all occurrences
106	# of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').
107
108	ifeq ($(KBUILD_SRC),)
109	__c_flags = $(_c_flags)
110	__a_flags = $(_a_flags)
111	__cpp_flags = $(_cpp_flags)
112	else
113
114	# Prefix -I with $(srctree) if it is not an absolute path
115	addtree = $(if $(filter-out -I/%,$(1)),$(patsubst -I%,-I$(srctree)/%,$(1))) $(1)
116	# Find all -I options and call addtree
117	flags = $(foreach o,$($(1)),$(if $(filter -I%,$(o)),$(call addtree,$(o)),$(o)))
118
119	# -I$(obj) locates generated .h files
120	# $(call addtree,-I$(obj)) locates .h files in srctree, from generated .c files
121	# and locates generated .h files
122	# FIXME: Replace both with specific CFLAGS* statements in the makefiles
123	__c_flags = $(call addtree,-I$(obj)) $(call flags,_c_flags)
124	__a_flags = $(call flags,_a_flags)
125	__cpp_flags = $(call flags,_cpp_flags)
126	endif
127
128	c_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
129	$(__c_flags) $(modkern_cflags) \
130	$(basename_flags) $(modname_flags)
131
132	a_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
133	$(__a_flags) $(modkern_aflags)
134
135	cpp_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(__cpp_flags)
136
137	ld_flags = $(LDFLAGS) $(EXTRA_LDFLAGS)
138
139	# Finds the multi-part object the current object will be linked into
140	modname-multi = $(sort $(foreach m,$(multi-used),\
141	$(if $(filter $(subst $(obj)/,,$*.o), $($(m:.o=-objs)) $($(m:.o=-y))),$(m:.o=))))
142
143	# Shipped files
144	# ===========================================================================
145
146	quiet_cmd_shipped = SHIPPED $@
147	cmd_shipped = cat $< > $@
148
149	$(obj)/%:: $(src)/%_shipped
150	$(call cmd,shipped)
151
152	# Commands useful for building a boot image
153	# ===========================================================================
154	#
155	# Use as following:
156	#
157	# target: source(s) FORCE
158	# $(if_changed,ld/objcopy/gzip)
159	#
160	# and add target to EXTRA_TARGETS so that we know we have to
161	# read in the saved command line
162
163	# Linking
164	# ---------------------------------------------------------------------------
165
166	quiet_cmd_ld = LD $@
167	cmd_ld = $(LD) $(LDFLAGS) $(EXTRA_LDFLAGS) $(LDFLAGS_$(@F)) \
168	$(filter-out FORCE,$^) -o $@
169
170	# Objcopy
171	# ---------------------------------------------------------------------------
172
173	quiet_cmd_objcopy = OBJCOPY $@
174	cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
175
176	# Gzip
177	# ---------------------------------------------------------------------------
178
179	quiet_cmd_gzip = GZIP $@
180	cmd_gzip = gzip -f -9 < $< > $@
181
182	# ===========================================================================
183	# Generic stuff
184	# ===========================================================================
185
186	ifneq ($(KBUILD_NOCMDDEP),1)
187	# Check if both arguments has same arguments. Result in empty string if equal
188	# User may override this check using make KBUILD_NOCMDDEP=1
189	arg-check = $(strip $(filter-out $(1), $(2)) $(filter-out $(2), $(1)) )
190
191	endif
192
193	# echo command. Short version is $(quiet) equals quiet, otherwise full command
194	echo-cmd = $(if $($(quiet)cmd_$(1)), \
195	echo ' $(subst ','\'',$($(quiet)cmd_$(1)))';)
196
197	# function to only execute the passed command if necessary
198	# >'< substitution is for echo to work, >$< substitution to preserve $ when reloading .cmd file
199	# note: when using inline perl scripts [perl -e '...$$t=1;...'] in $(cmd_xxx) double $$ your perl vars
200	#
201	if_changed = $(if $(strip $? $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
202	@set -e; \
203	$(echo-cmd) \
204	$(cmd_$(1)); \
205	echo 'cmd_$@ := $(subst $$,$$$$,$(subst ','\'',$(cmd_$(1))))' > $(@D)/.$(@F).cmd)
206
207
208	# execute the command and also postprocess generated .d dependencies
209	# file
210
211	if_changed_dep = $(if $(strip $? $(filter-out FORCE $(wildcard $^),$^)\
212	$(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
213	@set -e; \
214	$(echo-cmd) \
215	$(cmd_$(1)); \
216	scripts/basic/fixdep $(depfile) $@ '$(subst $$,$$$$,$(subst ','\'',$(cmd_$(1))))' > $(@D)/.$(@F).tmp; \
217	rm -f $(depfile); \
218	mv -f $(@D)/.$(@F).tmp $(@D)/.$(@F).cmd)
219
220	# Usage: $(call if_changed_rule,foo)
221	# will check if $(cmd_foo) changed, or any of the prequisites changed,
222	# and if so will execute $(rule_foo)
223
224	if_changed_rule = $(if $(strip $? $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),\
225	@set -e; \
226	$(rule_$(1)))
227
228	# If quiet is set, only print short version of command
229
230	cmd = @$(if $($(quiet)cmd_$(1)),echo ' $(subst ','\'',$($(quiet)cmd_$(1)))' &&) $(cmd_$(1))
231
232	# $(call descend,<dir>,<target>)
233	# Recursively call a sub-make in <dir> with target <target>
234	# Usage is deprecated, because make do not see this as an invocation of make.
235	descend =$(Q)$(MAKE) -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.build obj=$(1) $(2)
236
237	# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
238	# Usage:
239	# $(Q)$(MAKE) $(build)=dir
240	build := -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.build obj
241
242	# filechk is used to check if the content of a generated file is updated.
243	# Sample usage:
244	# define filechk_sample
245	# echo $KERNELRELEASE
246	# endef
247	# version.h : Makefile
248	# $(call filechk,sample)
249	# The rule defined shall write to stdout the content of the new file.
250	# The existing file will be compared with the new one.
251	# - If no file exist it is created
252	# - If the content differ the new file is used
253	# - If they are equal no change, and no timestamp update
254
255	define filechk
256	$(Q)set -e; \
257	echo ' CHK $@'; \
258	mkdir -p $(dir $@); \
259	$(filechk_$(1)) $(2) > $@.tmp; \
260	if [ -r $@ ] && cmp -s $@ $@.tmp; then \
261	rm -f $@.tmp; \
262	else \
263	echo ' UPD $@'; \
264	mv -f $@.tmp $@; \
265	fi
266	endef
267