[deliverable/linux.git] / scripts / Kbuild.include

####
# kbuild: Generic definitions

# Convenient variables
comma   := ,
quote   := "
squote  := '
empty   :=
space   := $(empty) $(empty)

###
# Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
dot-target = $(dir $@).$(notdir $@)

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

###
# filename of target with directory and extension stripped
basetarget = $(basename $(notdir $@))

###
# filename of first prerequisite with directory and extension stripped
baseprereq = $(basename $(notdir $<))

###
# Escape single quote for use in echo statements
escsq = $(subst $(squote),'\$(squote)',$1)

###
# Easy method for doing a status message
       kecho := :
 quiet_kecho := echo
silent_kecho := :
kecho := $($(quiet)kecho)

###
# 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
#	$(call filechk,sample)
# The rule defined shall write to stdout the content of the new file.
# The existing file will be compared with the new one.
# - If no file exist it is created
# - If the content differ the new file is used
# - If they are equal no change, and no timestamp update
# - stdin is piped in from the first prerequisite ($<) so one has
#   to specify a valid file as first prerequisite (often the kbuild file)
define filechk
	$(Q)set -e;				\
	$(kecho) '  CHK     $@';		\
	mkdir -p $(dir $@);			\
	$(filechk_$(1)) < $< > $@.tmp;		\
	if [ -r $@ ] && cmp -s $@ $@.tmp; then	\
		rm -f $@.tmp;			\
	else					\
		$(kecho) '  UPD     $@';	\
		mv -f $@.tmp $@;		\
	fi
endef

######
# gcc support functions
# See documentation in Documentation/kbuild/makefiles.txt

# cc-cross-prefix
# Usage: CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu- m68k-linux-)
# Return first prefix where a prefix$(CC) is found in PATH.
# If no $(CC) found in PATH with listed prefixes return nothing
cc-cross-prefix =  \
	$(word 1, $(foreach c,$(1),                                   \
		$(shell set -e;                                       \
		if (which $(strip $(c))$(CC)) > /dev/null 2>&1 ; then \
			echo $(c);                                    \
		fi)))

# output directory for tests below
TMPOUT := $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/)

# try-run
# Usage: option = $(call try-run, $(CC)...-o "$$TMP",option-ok,otherwise)
# Exit code chooses option. "$$TMP" is can be used as temporary file and
# is automatically cleaned up.
try-run = $(shell set -e;		\
	TMP="$(TMPOUT).$$$$.tmp";	\
	TMPO="$(TMPOUT).$$$$.o";	\
	if ($(1)) >/dev/null 2>&1;	\
	then echo "$(2)";		\
	else echo "$(3)";		\
	fi;				\
	rm -f "$$TMP" "$$TMPO")

# as-option
# Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,)

as-option = $(call try-run,\
	$(CC) $(KBUILD_CFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2))

# as-instr
# Usage: cflags-y += $(call as-instr,instr,option1,option2)

as-instr = $(call try-run,\
	printf "%b\n" "$(1)" | $(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3))

# cc-option
# Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)

cc-option = $(call try-run,\
	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) $(1) -c -x c /dev/null -o "$$TMP",$(1),$(2))

# cc-option-yn
# Usage: flag := $(call cc-option-yn,-march=winchip-c6)
cc-option-yn = $(call try-run,\
	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) $(1) -c -x c /dev/null -o "$$TMP",y,n)

# cc-option-align
# Prefix align with either -falign or -malign
cc-option-align = $(subst -functions=0,,\
	$(call cc-option,-falign-functions=0,-malign-functions=0))

# cc-disable-warning
# Usage: cflags-y += $(call cc-disable-warning,unused-but-set-variable)
cc-disable-warning = $(call try-run,\
	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP",-Wno-$(strip $(1)))

# cc-version
cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))

# cc-fullversion
cc-fullversion = $(shell $(CONFIG_SHELL) \
	$(srctree)/scripts/gcc-version.sh -p $(CC))

# cc-ifversion
# Usage:  EXTRA_CFLAGS += $(call cc-ifversion, -lt, 0402, -O1)
cc-ifversion = $(shell [ $(cc-version) $(1) $(2) ] && echo $(3) || echo $(4))

# cc-ldoption
# Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
cc-ldoption = $(call try-run,\
	$(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))

# ld-option
# Usage: LDFLAGS += $(call ld-option, -X)
ld-option = $(call try-run,\
	$(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))

# ar-option
# Usage: KBUILD_ARFLAGS := $(call ar-option,D)
# Important: no spaces around options
ar-option = $(call try-run, $(AR) rc$(1) "$$TMP",$(1),$(2))

# ld-version
# Note this is mainly for HJ Lu's 3 number binutil versions
ld-version = $(shell $(LD) --version | $(srctree)/scripts/ld-version.sh)

# ld-ifversion
# Usage:  $(call ld-ifversion, -ge, 22252, y)
ld-ifversion = $(shell [ $(ld-version) $(1) $(2) ] && echo $(3) || echo $(4))

######

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

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

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

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

###
# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.headersinst obj=
# Usage:
# $(Q)$(MAKE) $(hdr-inst)=dir
hdr-inst := -f $(srctree)/scripts/Makefile.headersinst obj

# Prefix -I with $(srctree) if it is not an absolute path.
# skip if -I has no parameter
addtree = $(if $(patsubst -I%,%,$(1)), \
$(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)))

# echo command.
# Short version is used, if $(quiet) equals `quiet_', otherwise full one.
echo-cmd = $(if $($(quiet)cmd_$(1)),\
	echo '  $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)

# printing commands
cmd = @$(echo-cmd) $(cmd_$(1))

# Add $(obj)/ for paths that are not absolute
objectify = $(foreach o,$(1),$(if $(filter /%,$(o)),$(o),$(obj)/$(o)))

###
# if_changed      - execute command if any prerequisite is newer than
#                   target, or command line has changed
# if_changed_dep  - as if_changed, but uses fixdep to reveal dependencies
#                   including used config symbols
# if_changed_rule - as if_changed but execute rule instead
# See Documentation/kbuild/makefiles.txt for more info

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

# Replace >$< with >$$< to preserve $ when reloading the .cmd file
# (needed for make)
# Replace >#< with >\#< to avoid starting a comment in the .cmd file
# (needed for make)
# Replace >'< with >'\''< to be able to enclose the whole string in '...'
# (needed for the shell)
make-cmd = $(call escsq,$(subst \#,\\\#,$(subst $$,$$$$,$(cmd_$(1)))))

# Find any prerequisites that is newer than target or that does not exist.
# PHONY targets skipped in both cases.
any-prereq = $(filter-out $(PHONY),$?) $(filter-out $(PHONY) $(wildcard $^),$^)

# Execute command if command has changed or prerequisite(s) are updated.
#
if_changed = $(if $(strip $(any-prereq) $(arg-check)),                       \
	@set -e;                                                             \
	$(echo-cmd) $(cmd_$(1));                                             \
	printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd)

# Execute the command and also postprocess generated .d dependencies file.
if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ),                  \
	@set -e;                                                             \
	$(echo-cmd) $(cmd_$(1));                                             \
	scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\
	rm -f $(depfile);                                                    \
	mv -f $(dot-target).tmp $(dot-target).cmd)

# Usage: $(call if_changed_rule,foo)
# Will check if $(cmd_foo) or any of the prerequisites changed,
# and if so will execute $(rule_foo).
if_changed_rule = $(if $(strip $(any-prereq) $(arg-check) ),                 \
	@set -e;                                                             \
	$(rule_$(1)))

###
# why - tell why a a target got build
#       enabled by make V=2
#       Output (listed in the order they are checked):
#          (1) - due to target is PHONY
#          (2) - due to target missing
#          (3) - due to: file1.h file2.h
#          (4) - due to command line change
#          (5) - due to missing .cmd file
#          (6) - due to target not in $(targets)
# (1) PHONY targets are always build
# (2) No target, so we better build it
# (3) Prerequisite is newer than target
# (4) The command line stored in the file named dir/.target.cmd
#     differed from actual command line. This happens when compiler
#     options changes
# (5) No dir/.target.cmd file (used to store command line)
# (6) No dir/.target.cmd file and target not listed in $(targets)
#     This is a good hint that there is a bug in the kbuild file
ifeq ($(KBUILD_VERBOSE),2)
why =                                                                        \
    $(if $(filter $@, $(PHONY)),- due to target is PHONY,                    \
        $(if $(wildcard $@),                                                 \
            $(if $(strip $(any-prereq)),- due to: $(any-prereq),             \
                $(if $(arg-check),                                           \
                    $(if $(cmd_$@),- due to command line change,             \
                        $(if $(filter $@, $(targets)),                       \
                            - due to missing .cmd file,                      \
                            - due to $(notdir $@) not in $$(targets)         \
                         )                                                   \
                     )                                                       \
                 )                                                           \
             ),                                                              \
             - due to target missing                                         \
         )                                                                   \
     )

echo-why = $(call escsq, $(strip $(why)))
endif
Commit	Line	Data
	1	####
	2	# kbuild: Generic definitions
	3
	4	# Convenient variables
	5	comma := ,
	6	quote := "
	7	squote := '
	8	empty :=
	9	space := $(empty) $(empty)
	10
	11	###
	12	# Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
	13	dot-target = $(dir $@).$(notdir $@)
	14
	15	###
	16	# The temporary file to save gcc -MD generated dependencies must not
	17	# contain a comma
	18	depfile = $(subst $(comma),_,$(dot-target).d)
	19
	20	###
	21	# filename of target with directory and extension stripped
	22	basetarget = $(basename $(notdir $@))
	23
	24	###
	25	# filename of first prerequisite with directory and extension stripped
	26	baseprereq = $(basename $(notdir $<))
	27
	28	###
	29	# Escape single quote for use in echo statements
	30	escsq = $(subst $(squote),'\$(squote)',$1)
	31
	32	###
	33	# Easy method for doing a status message
	34	kecho := :
	35	quiet_kecho := echo
	36	silent_kecho := :
	37	kecho := $($(quiet)kecho)
	38
	39	###
	40	# filechk is used to check if the content of a generated file is updated.
	41	# Sample usage:
	42	# define filechk_sample
	43	# echo $KERNELRELEASE
	44	# endef
	45	# version.h : Makefile
	46	# $(call filechk,sample)
	47	# The rule defined shall write to stdout the content of the new file.
	48	# The existing file will be compared with the new one.
	49	# - If no file exist it is created
	50	# - If the content differ the new file is used
	51	# - If they are equal no change, and no timestamp update
	52	# - stdin is piped in from the first prerequisite ($<) so one has
	53	# to specify a valid file as first prerequisite (often the kbuild file)
	54	define filechk
	55	$(Q)set -e; \
	56	$(kecho) ' CHK $@'; \
	57	mkdir -p $(dir $@); \
	58	$(filechk_$(1)) < $< > $@.tmp; \
	59	if [ -r $@ ] && cmp -s $@ $@.tmp; then \
	60	rm -f $@.tmp; \
	61	else \
	62	$(kecho) ' UPD $@'; \
	63	mv -f $@.tmp $@; \
	64	fi
	65	endef
	66
	67	######
	68	# gcc support functions
	69	# See documentation in Documentation/kbuild/makefiles.txt
	70
	71	# cc-cross-prefix
	72	# Usage: CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu- m68k-linux-)
	73	# Return first prefix where a prefix$(CC) is found in PATH.
	74	# If no $(CC) found in PATH with listed prefixes return nothing
	75	cc-cross-prefix = \
	76	$(word 1, $(foreach c,$(1), \
	77	$(shell set -e; \
	78	if (which $(strip $(c))$(CC)) > /dev/null 2>&1 ; then \
	79	echo $(c); \
	80	fi)))
	81
	82	# output directory for tests below
	83	TMPOUT := $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/)
	84
	85	# try-run
	86	# Usage: option = $(call try-run, $(CC)...-o "$$TMP",option-ok,otherwise)
	87	# Exit code chooses option. "$$TMP" is can be used as temporary file and
	88	# is automatically cleaned up.
	89	try-run = $(shell set -e; \
	90	TMP="$(TMPOUT).$$$$.tmp"; \
	91	TMPO="$(TMPOUT).$$$$.o"; \
	92	if ($(1)) >/dev/null 2>&1; \
	93	then echo "$(2)"; \
	94	else echo "$(3)"; \
	95	fi; \
	96	rm -f "$$TMP" "$$TMPO")
	97
	98	# as-option
	99	# Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,)
	100
	101	as-option = $(call try-run,\
	102	$(CC) $(KBUILD_CFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2))
	103
	104	# as-instr
	105	# Usage: cflags-y += $(call as-instr,instr,option1,option2)
	106
	107	as-instr = $(call try-run,\
	108	printf "%b\n" "$(1)" \| $(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" -,$(2),$(3))
	109
	110	# cc-option
	111	# Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)
	112
	113	cc-option = $(call try-run,\
	114	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) $(1) -c -x c /dev/null -o "$$TMP",$(1),$(2))
	115
	116	# cc-option-yn
	117	# Usage: flag := $(call cc-option-yn,-march=winchip-c6)
	118	cc-option-yn = $(call try-run,\
	119	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) $(1) -c -x c /dev/null -o "$$TMP",y,n)
	120
	121	# cc-option-align
	122	# Prefix align with either -falign or -malign
	123	cc-option-align = $(subst -functions=0,,\
	124	$(call cc-option,-falign-functions=0,-malign-functions=0))
	125
	126	# cc-disable-warning
	127	# Usage: cflags-y += $(call cc-disable-warning,unused-but-set-variable)
	128	cc-disable-warning = $(call try-run,\
	129	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP",-Wno-$(strip $(1)))
	130
	131	# cc-version
	132	cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))
	133
	134	# cc-fullversion
	135	cc-fullversion = $(shell $(CONFIG_SHELL) \
	136	$(srctree)/scripts/gcc-version.sh -p $(CC))
	137
	138	# cc-ifversion
	139	# Usage: EXTRA_CFLAGS += $(call cc-ifversion, -lt, 0402, -O1)
	140	cc-ifversion = $(shell [ $(cc-version) $(1) $(2) ] && echo $(3) \|\| echo $(4))
	141
	142	# cc-ldoption
	143	# Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
	144	cc-ldoption = $(call try-run,\
	145	$(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
	146
	147	# ld-option
	148	# Usage: LDFLAGS += $(call ld-option, -X)
	149	ld-option = $(call try-run,\
	150	$(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
	151
	152	# ar-option
	153	# Usage: KBUILD_ARFLAGS := $(call ar-option,D)
	154	# Important: no spaces around options
	155	ar-option = $(call try-run, $(AR) rc$(1) "$$TMP",$(1),$(2))
	156
	157	# ld-version
	158	# Note this is mainly for HJ Lu's 3 number binutil versions
	159	ld-version = $(shell $(LD) --version \| $(srctree)/scripts/ld-version.sh)
	160
	161	# ld-ifversion
	162	# Usage: $(call ld-ifversion, -ge, 22252, y)
	163	ld-ifversion = $(shell [ $(ld-version) $(1) $(2) ] && echo $(3) \|\| echo $(4))
	164
	165	######
	166
	167	###
	168	# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj=
	169	# Usage:
	170	# $(Q)$(MAKE) $(build)=dir
	171	build := -f $(srctree)/scripts/Makefile.build obj
	172
	173	###
	174	# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.modbuiltin obj=
	175	# Usage:
	176	# $(Q)$(MAKE) $(modbuiltin)=dir
	177	modbuiltin := -f $(srctree)/scripts/Makefile.modbuiltin obj
	178
	179	###
	180	# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.dtbinst obj=
	181	# Usage:
	182	# $(Q)$(MAKE) $(dtbinst)=dir
	183	dtbinst := -f $(if $(KBUILD_SRC),$(srctree)/)scripts/Makefile.dtbinst obj
	184
	185	###
	186	# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.clean obj=
	187	# Usage:
	188	# $(Q)$(MAKE) $(clean)=dir
	189	clean := -f $(srctree)/scripts/Makefile.clean obj
	190
	191	###
	192	# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.headersinst obj=
	193	# Usage:
	194	# $(Q)$(MAKE) $(hdr-inst)=dir
	195	hdr-inst := -f $(srctree)/scripts/Makefile.headersinst obj
	196
	197	# Prefix -I with $(srctree) if it is not an absolute path.
	198	# skip if -I has no parameter
	199	addtree = $(if $(patsubst -I%,%,$(1)), \
	200	$(if $(filter-out -I/%,$(1)),$(patsubst -I%,-I$(srctree)/%,$(1))) $(1))
	201
	202	# Find all -I options and call addtree
	203	flags = $(foreach o,$($(1)),$(if $(filter -I%,$(o)),$(call addtree,$(o)),$(o)))
	204
	205	# echo command.
	206	# Short version is used, if $(quiet) equals `quiet_', otherwise full one.
	207	echo-cmd = $(if $($(quiet)cmd_$(1)),\
	208	echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
	209
	210	# printing commands
	211	cmd = @$(echo-cmd) $(cmd_$(1))
	212
	213	# Add $(obj)/ for paths that are not absolute
	214	objectify = $(foreach o,$(1),$(if $(filter /%,$(o)),$(o),$(obj)/$(o)))
	215
	216	###
	217	# if_changed - execute command if any prerequisite is newer than
	218	# target, or command line has changed
	219	# if_changed_dep - as if_changed, but uses fixdep to reveal dependencies
	220	# including used config symbols
	221	# if_changed_rule - as if_changed but execute rule instead
	222	# See Documentation/kbuild/makefiles.txt for more info
	223
	224	ifneq ($(KBUILD_NOCMDDEP),1)
	225	# Check if both arguments has same arguments. Result is empty string if equal.
	226	# User may override this check using make KBUILD_NOCMDDEP=1
	227	arg-check = $(strip $(filter-out $(cmd_$(1)), $(cmd_$@)) \
	228	$(filter-out $(cmd_$@), $(cmd_$(1))) )
	229	else
	230	arg-check = $(if $(strip $(cmd_$@)),,1)
	231	endif
	232
	233	# Replace >$< with >$$< to preserve $ when reloading the .cmd file
	234	# (needed for make)
	235	# Replace >#< with >\#< to avoid starting a comment in the .cmd file
	236	# (needed for make)
	237	# Replace >'< with >'\''< to be able to enclose the whole string in '...'
	238	# (needed for the shell)
	239	make-cmd = $(call escsq,$(subst \#,\\\#,$(subst $$,$$$$,$(cmd_$(1)))))
	240
	241	# Find any prerequisites that is newer than target or that does not exist.
	242	# PHONY targets skipped in both cases.
	243	any-prereq = $(filter-out $(PHONY),$?) $(filter-out $(PHONY) $(wildcard $^),$^)
	244
	245	# Execute command if command has changed or prerequisite(s) are updated.
	246	#
	247	if_changed = $(if $(strip $(any-prereq) $(arg-check)), \
	248	@set -e; \
	249	$(echo-cmd) $(cmd_$(1)); \
	250	printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd)
	251
	252	# Execute the command and also postprocess generated .d dependencies file.
	253	if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ), \
	254	@set -e; \
	255	$(echo-cmd) $(cmd_$(1)); \
	256	scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\
	257	rm -f $(depfile); \
	258	mv -f $(dot-target).tmp $(dot-target).cmd)
	259
	260	# Usage: $(call if_changed_rule,foo)
	261	# Will check if $(cmd_foo) or any of the prerequisites changed,
	262	# and if so will execute $(rule_foo).
	263	if_changed_rule = $(if $(strip $(any-prereq) $(arg-check) ), \
	264	@set -e; \
	265	$(rule_$(1)))
	266
	267	###
	268	# why - tell why a a target got build
	269	# enabled by make V=2
	270	# Output (listed in the order they are checked):
	271	# (1) - due to target is PHONY
	272	# (2) - due to target missing
	273	# (3) - due to: file1.h file2.h
	274	# (4) - due to command line change
	275	# (5) - due to missing .cmd file
	276	# (6) - due to target not in $(targets)
	277	# (1) PHONY targets are always build
	278	# (2) No target, so we better build it
	279	# (3) Prerequisite is newer than target
	280	# (4) The command line stored in the file named dir/.target.cmd
	281	# differed from actual command line. This happens when compiler
	282	# options changes
	283	# (5) No dir/.target.cmd file (used to store command line)
	284	# (6) No dir/.target.cmd file and target not listed in $(targets)
	285	# This is a good hint that there is a bug in the kbuild file
	286	ifeq ($(KBUILD_VERBOSE),2)
	287	why = \
	288	$(if $(filter $@, $(PHONY)),- due to target is PHONY, \
	289	$(if $(wildcard $@), \
	290	$(if $(strip $(any-prereq)),- due to: $(any-prereq), \
	291	$(if $(arg-check), \
	292	$(if $(cmd_$@),- due to command line change, \
	293	$(if $(filter $@, $(targets)), \
	294	- due to missing .cmd file, \
	295	- due to $(notdir $@) not in $$(targets) \
	296	) \
	297	) \
	298	) \
	299	), \
	300	- due to target missing \
	301	) \
	302	)
	303
	304	echo-why = $(call escsq, $(strip $(why)))
	305	endif