linux/scripts/Kbuild.include

####
# kbuild: Generic definitions

# Convinient variables
comma   := ,
empty   :=
space   := $(empty) $(empty)

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

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

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

# If quiet is set, only print short version of command
cmd = @$(if $($(quiet)cmd_$(1)),\
      echo '  $(subst ','\'',$($(quiet)cmd_$(1)))' &&) $(cmd_$(1))

# Add $(obj)/ for paths that is 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 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)))