source: drbl_ui/backup/test_busybox/busybox-1.7.2/scripts/Kbuild.include @ 59

####
# kbuild: Generic definitions

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

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

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

###
# 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

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

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

as-option = $(shell if $(CC) $(CFLAGS) $(1) -Wa,-Z -c -o /dev/null \
       -xassembler /dev/null > /dev/null 2>&1; then echo "$(1)"; \
       else echo "$(2)"; fi ;)

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

cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
             > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)

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

hostcc-option = $(shell if $(HOSTCC) $(HOSTCFLAGS) $(1) -S -o /dev/null -xc /dev/null \
             > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)

# cc-option-yn
# Usage: flag := $(call cc-option-yn, -march=winchip-c6)
cc-option-yn = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
                > /dev/null 2>&1; then echo "y"; else echo "n"; fi;)

# 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-version
# Usage gcc-ver := $(call cc-version, $(CC))
cc-version = $(shell PATH="$(PATH)" $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh \
              $(if $(1), $(1), $(CC)))

# cc-ifversion
# Usage:  EXTRA_CFLAGS += $(call cc-ifversion, -lt, 0402, -O1)
cc-ifversion = $(shell if [ $(call cc-version, $(CC)) $(1) $(2) ]; then \
                       echo $(3); fi;)

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

# 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)))

# If quiet is set, only print short version of command
cmd = @$(echo-cmd) $(cmd_$(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 '  $(call escsq,$($(quiet)cmd_$(1)))';)

make-cmd = $(subst \#,\\\#,$(subst $$,$$$$,$(call escsq,$(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 $(filter-out $(PHONY),$?)          \
    $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
  @set -e; \
  $(echo-cmd) $(cmd_$(1)); \
  echo 'cmd_$@ := $(make-cmd)' > $(@D)/.$(@F).cmd)

# execute the command and also postprocess generated .d dependencies
# file
if_changed_dep = $(if $(strip $(filter-out $(PHONY),$?)  \
    $(filter-out FORCE $(wildcard $^),$^)    \
  $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),     \
  @set -e; \
  $(echo-cmd) $(cmd_$(1)); \
  scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(@D)/.$(@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 $(filter-out $(PHONY),$?)            \
      $(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),\
      @set -e; \
      $(rule_$(1)))