rules.mak - third_party/qemu - Git at Google


 COMMA := ,

 # Don't use implicit rules or variables
 # we have explicit rules for everything
 MAKEFLAGS += -rR

 # Files with this suffixes are final, don't try to generate them
 # using implicit rules
 %.d:
 %.h:
 %.c:
 %.cc:
 %.cpp:
 %.m:
 %.mak:

 # Flags for C++ compilation
 QEMU_CXXFLAGS = -D__STDC_LIMIT_MACROS $(filter-out -Wstrict-prototypes -Wmissing-prototypes -Wnested-externs -Wold-style-declaration -Wold-style-definition -Wredundant-decls, $(QEMU_CFLAGS))

 # Flags for dependency generation
 QEMU_DGFLAGS += -MMD -MP -MT $@ -MF $(@D)/$(*F).d

 # Same as -I$(SRC_PATH) -I., but for the nested source/object directories
 QEMU_INCLUDES += -I$(<D) -I$(@D)

 WL_U := -Wl,-u,
 find-symbols = $(if $1, $(sort $(shell $(NM) -P -g $1 | $2)))
 defined-symbols = $(call find-symbols,$1,awk '$$2!="U"{print $$1}')
 undefined-symbols = $(call find-symbols,$1,awk '$$2=="U"{print $$1}')

 # All the .mo objects in -m variables are also added into corresponding -y
 # variable in unnest-vars, but filtered out here, when LINK is called.
 #
 # The .mo objects are supposed to be linked as a DSO, for module build. So here
 # they are only used as a placeholders to generate those "archive undefined"
 # symbol options (-Wl,-u,$symbol_name), which are the archive functions
 # referenced by the code in the DSO.
 #
 # Also the presence in -y variables will also guarantee they are built before
 # linking executables that will load them. So we can look up symbol reference
 # in LINK.
 #
 # This is necessary because the exectuable itself may not use the function, in
 # which case the function would not be linked in. Then the DSO loading will
 # fail because of the missing symbol.
 process-archive-undefs = $(filter-out %.a %.mo,$1) \
                 $(addprefix $(WL_U), \
                      $(filter $(call defined-symbols,$(filter %.a, $1)), \
                               $(call undefined-symbols,$(filter %.mo,$1)))) \
                 $(filter %.a,$1)

 extract-libs = $(strip $(foreach o,$1,$($o-libs)))
 expand-objs = $(strip $(sort $(filter %.o,$1)) \
                   $(foreach o,$(filter %.mo,$1),$($o-objs)) \
                   $(filter-out %.o %.mo,$1))

 %.o: %.c
 	$(call quiet-command,$(CC) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<,"  CC    $(TARGET_DIR)$@")
 %.o: %.rc
 	$(call quiet-command,$(WINDRES) -I. -o $@ $<,"  RC    $(TARGET_DIR)$@")

 # If we have a CXX we might have some C++ objects, in which case we
 # must link with the C++ compiler, not the plain C compiler.
 LINKPROG = $(or $(CXX),$(CC))

 LINK = $(call quiet-command, $(LINKPROG) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o $@ \
        $(call process-archive-undefs, $1) \
        $(version-obj-y) $(call extract-libs,$1) $(LIBS),"  LINK  $(TARGET_DIR)$@")

 %.o: %.S
 	$(call quiet-command,$(CCAS) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -c -o $@ $<,"  CCAS  $(TARGET_DIR)$@")

 %.o: %.cc
 	$(call quiet-command,$(CXX) $(QEMU_INCLUDES) $(QEMU_CXXFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<,"  CXX   $(TARGET_DIR)$@")

 %.o: %.cpp
 	$(call quiet-command,$(CXX) $(QEMU_INCLUDES) $(QEMU_CXXFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<,"  CXX   $(TARGET_DIR)$@")

 %.o: %.m
 	$(call quiet-command,$(OBJCC) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<,"  OBJC  $(TARGET_DIR)$@")

 %.o: %.dtrace
 	$(call quiet-command,dtrace -o $@ -G -s $<, "  GEN   $(TARGET_DIR)$@")

 DSO_OBJ_CFLAGS := -fPIC -DBUILD_DSO
 module-common.o: CFLAGS += $(DSO_OBJ_CFLAGS)
 %$(DSOSUF): LDFLAGS += $(LDFLAGS_SHARED)
 %$(DSOSUF): %.mo
 	$(call LINK,$^)
 	@# Copy to build root so modules can be loaded when program started without install
 	$(if $(findstring /,$@),$(call quiet-command,cp $@ $(subst /,-,$@), "  CP    $(subst /,-,$@)"))


 LD_REL := $(CC) -nostdlib -Wl,-r $(LD_REL_FLAGS)

 %.mo:
 	$(call quiet-command,$(LD_REL) -o $@ $^,"  LD -r $(TARGET_DIR)$@")

 .PHONY: modules
 modules:

 %$(EXESUF): %.o
 	$(call LINK,$(filter %.o %.a %.mo, $^))

 %.a:
 	$(call quiet-command,rm -f $@ && $(AR) rcs $@ $^,"  AR    $(TARGET_DIR)$@")

 quiet-command = $(if $(V),$1,$(if $(2),@echo $2 && $1, @$1))

 # cc-option
 # Usage: CFLAGS+=$(call cc-option, -falign-functions=0, -malign-functions=0)

 cc-option = $(if $(shell $(CC) $1 $2 -S -o /dev/null -xc /dev/null \
               >/dev/null 2>&1 && echo OK), $2, $3)

 VPATH_SUFFIXES = %.c %.h %.S %.cc %.cpp %.m %.mak %.texi %.sh %.rc
 set-vpath = $(if $1,$(foreach PATTERN,$(VPATH_SUFFIXES),$(eval vpath $(PATTERN) $1)))

 # install-prog list, dir
 define install-prog
 	$(INSTALL_DIR) "$2"
 	$(INSTALL_PROG) $1 "$2"
 	$(if $(STRIP),$(STRIP) $(foreach T,$1,"$2/$(notdir $T)"),)
 endef

 # find-in-path
 # Usage: $(call find-in-path, prog)
 # Looks in the PATH if the argument contains no slash, else only considers one
 # specific directory.  Returns an # empty string if the program doesn't exist
 # there.
 find-in-path = $(if $(find-string /, $1), \
         $(wildcard $1), \
         $(wildcard $(patsubst %, %/$1, $(subst :, ,$(PATH)))))

 # Logical functions (for operating on y/n values like CONFIG_FOO vars)
 # Inputs to these must be either "y" (true) or "n" or "" (both false)
 # Output is always either "y" or "n".
 # Usage: $(call land,$(CONFIG_FOO),$(CONFIG_BAR))
 # Logical NOT
 lnot = $(if $(subst n,,$1),n,y)
 # Logical AND
 land = $(if $(findstring yy,$1$2),y,n)
 # Logical OR
 lor = $(if $(findstring y,$1$2),y,n)
 # Logical XOR (note that this is the inverse of leqv)
 lxor = $(if $(filter $(call lnot,$1),$(call lnot,$2)),n,y)
 # Logical equivalence (note that leqv "","n" is true)
 leqv = $(if $(filter $(call lnot,$1),$(call lnot,$2)),y,n)
 # Logical if: like make's $(if) but with an leqv-like test
 lif = $(if $(subst n,,$1),$2,$3)

 # String testing functions: inputs to these can be any string;
 # the output is always either "y" or "n". Leading and trailing whitespace
 # is ignored when comparing strings.
 # String equality
 eq = $(if $(subst $2,,$1)$(subst $1,,$2),n,y)
 # String inequality
 ne = $(if $(subst $2,,$1)$(subst $1,,$2),y,n)
 # Emptiness/non-emptiness tests:
 isempty = $(if $1,n,y)
 notempty = $(if $1,y,n)

 # Generate files with tracetool
 TRACETOOL=$(PYTHON) $(SRC_PATH)/scripts/tracetool.py

 # Generate timestamp files for .h include files

 config-%.h: config-%.h-timestamp
 	@cmp $< $@ >/dev/null 2>&1 || cp $< $@

 config-%.h-timestamp: config-%.mak $(SRC_PATH)/scripts/create_config
 	$(call quiet-command, sh $(SRC_PATH)/scripts/create_config < $< > $@, "  GEN   $(TARGET_DIR)config-$*.h")

 .PHONY: clean-timestamp
 clean-timestamp:
 	rm -f *.timestamp
 clean: clean-timestamp

 # will delete the target of a rule if commands exit with a nonzero exit status
 .DELETE_ON_ERROR:

 # save-vars
 # Usage: $(call save-vars, vars)
 # Save each variable $v in $vars as save-vars-$v, save their object's
 # variables, then clear $v.
 define save-vars
     $(foreach v,$1,
         $(eval save-vars-$v := $(value $v))
         $(foreach o,$($v),
             $(foreach k,cflags libs objs,
                 $(if $($o-$k),
                     $(eval save-vars-$o-$k := $($o-$k))
                     $(eval $o-$k := ))))
         $(eval $v := ))
 endef

 # load-vars
 # Usage: $(call load-vars, vars, add_var)
 # Load the saved value for each variable in @vars, and the per object
 # variables.
 # Append @add_var's current value to the loaded value.
 define load-vars
     $(eval $2-new-value := $(value $2))
     $(foreach v,$1,
         $(eval $v := $(value save-vars-$v))
         $(foreach o,$($v),
             $(foreach k,cflags libs objs,
                 $(if $(save-vars-$o-$k),
                     $(eval $o-$k := $(save-vars-$o-$k))
                     $(eval save-vars-$o-$k := ))))
         $(eval save-vars-$v := ))
     $(eval $2 := $(value $2) $($2-new-value))
 endef

 # fix-paths
 # Usage: $(call fix-paths, obj_path, src_path, vars)
 # Add prefix @obj_path to all objects in @vars, and add prefix @src_path to all
 # directories in @vars.
 define fix-paths
     $(foreach v,$3,
         $(foreach o,$($v),
             $(if $($o-libs),
                 $(eval $1$o-libs := $($o-libs)))
             $(if $($o-cflags),
                 $(eval $1$o-cflags := $($o-cflags)))
             $(if $($o-objs),
                 $(eval $1$o-objs := $(addprefix $1,$($o-objs)))))
         $(eval $v := $(addprefix $1,$(filter-out %/,$($v))) \
                      $(addprefix $2,$(filter %/,$($v)))))
 endef

 # unnest-var-recursive
 # Usage: $(call unnest-var-recursive, obj_prefix, vars, var)
 #
 # Unnest @var by including subdir Makefile.objs, while protect others in @vars
 # unchanged.
 #
 # @obj_prefix is the starting point of object path prefix.
 #
 define unnest-var-recursive
     $(eval dirs := $(sort $(filter %/,$($3))))
     $(eval $3 := $(filter-out %/,$($3)))
     $(foreach d,$(dirs:%/=%),
             $(call save-vars,$2)
             $(eval obj := $(if $1,$1/)$d)
             $(eval -include $(SRC_PATH)/$d/Makefile.objs)
             $(call fix-paths,$(if $1,$1/)$d/,$d/,$2)
             $(call load-vars,$2,$3)
             $(call unnest-var-recursive,$1,$2,$3))
 endef

 # unnest-vars
 # Usage: $(call unnest-vars, obj_prefix, vars)
 #
 # @obj_prefix: object path prefix, can be empty, or '..', etc. Don't include
 # ending '/'.
 #
 # @vars: the list of variable names to unnest.
 #
 # This macro will scan subdirectories's Makefile.objs, include them, to build
 # up each variable listed in @vars.
 #
 # Per object and per module cflags and libs are saved with relative path fixed
 # as well, those variables include -libs, -cflags and -objs. Items in -objs are
 # also fixed to relative path against SRC_PATH plus the prefix @obj_prefix.
 #
 # All nested variables postfixed by -m in names are treated as DSO variables,
 # and will be built as modules, if enabled.
 #
 # A simple example of the unnest:
 #
 #     obj_prefix = ..
 #     vars = hot cold
 #     hot  = fire.o sun.o season/
 #     cold = snow.o water/ season/
 #
 # Unnest through a faked source directory structure:
 #
 #     SRC_PATH
 #        ├── water
 #        │   └── Makefile.objs──────────────────┐
 #        │       │ hot += steam.o               │
 #        │       │ cold += ice.mo               │
 #        │       │ ice.mo-libs := -licemaker    │
 #        │       │ ice.mo-objs := ice1.o ice2.o │
 #        │       └──────────────────────────────┘
 #        │
 #        └── season
 #            └── Makefile.objs──────┐
 #                │ hot += summer.o  │
 #                │ cold += winter.o │
 #                └──────────────────┘
 #
 # In the end, the result will be:
 #
 #     hot  = ../fire.o ../sun.o ../season/summer.o
 #     cold = ../snow.o ../water/ice.mo ../season/winter.o
 #     ../water/ice.mo-libs = -licemaker
 #     ../water/ice.mo-objs = ../water/ice1.o ../water/ice2.o
 #
 # Note that 'hot' didn't include 'season/' in the input, so 'summer.o' is not
 # included.
 #
 define unnest-vars
     # In the case of target build (i.e. $1 == ..), fix path for top level
     # Makefile.objs objects
     $(if $1,$(call fix-paths,$1/,,$2))

     # Descend and include every subdir Makefile.objs
     $(foreach v, $2,
         $(call unnest-var-recursive,$1,$2,$v)
         # Pass the .mo-cflags and .mo-libs along to its member objects
         $(foreach o, $(filter %.mo,$($v)),
             $(foreach p,$($o-objs),
                 $(if $($o-cflags), $(eval $p-cflags += $($o-cflags)))
                 $(if $($o-libs), $(eval $p-libs += $($o-libs))))))

     # For all %.mo objects that are directly added into -y, just expand them
     $(foreach v,$(filter %-y,$2),
         $(eval $v := $(foreach o,$($v),$(if $($o-objs),$($o-objs),$o))))

     $(foreach v,$(filter %-m,$2),
         # All .o found in *-m variables are single object modules, create .mo
         # for them
         $(foreach o,$(filter %.o,$($v)),
             $(eval $(o:%.o=%.mo)-objs := $o))
         # Now unify .o in -m variable to .mo
         $(eval $v := $($v:%.o=%.mo))
         $(eval modules-m += $($v))

         # For module build, build shared libraries during "make modules"
         # For non-module build, add -m to -y
         $(if $(CONFIG_MODULES),
              $(foreach o,$($v),
                    $(eval $($o-objs): CFLAGS += $(DSO_OBJ_CFLAGS))
                    $(eval $o: $($o-objs)))
              $(eval $(patsubst %-m,%-y,$v) += $($v))
              $(eval modules: $($v:%.mo=%$(DSOSUF))),
              $(eval $(patsubst %-m,%-y,$v) += $(call expand-objs, $($v)))))

     # Post-process all the unnested vars
     $(foreach v,$2,
         $(foreach o, $(filter %.mo,$($v)),
             # Find all the .mo objects in variables and add dependency rules
             # according to .mo-objs. Report error if not set
             $(if $($o-objs),
                 $(eval $(o:%.mo=%$(DSOSUF)): module-common.o $($o-objs)),
                 $(error $o added in $v but $o-objs is not set)))
         $(shell mkdir -p ./ $(sort $(dir $($v))))
         # Include all the .d files
         $(eval -include $(patsubst %.o,%.d,$(patsubst %.mo,%.d,$($v))))
         $(eval $v := $(filter-out %/,$($v))))
 endef

	COMMA := ,

	# Don't use implicit rules or variables
	# we have explicit rules for everything
	MAKEFLAGS += -rR

	# Files with this suffixes are final, don't try to generate them
	# using implicit rules
	%.d:
	%.h:
	%.c:
	%.cc:
	%.cpp:
	%.m:
	%.mak:

	# Flags for C++ compilation
	QEMU_CXXFLAGS = -D__STDC_LIMIT_MACROS $(filter-out -Wstrict-prototypes -Wmissing-prototypes -Wnested-externs -Wold-style-declaration -Wold-style-definition -Wredundant-decls, $(QEMU_CFLAGS))

	# Flags for dependency generation
	QEMU_DGFLAGS += -MMD -MP -MT $@ -MF $(@D)/$(*F).d

	# Same as -I$(SRC_PATH) -I., but for the nested source/object directories
	QEMU_INCLUDES += -I$(<D) -I$(@D)

	WL_U := -Wl,-u,
	find-symbols = $(if $1, $(sort $(shell $(NM) -P -g $1 \| $2)))
	defined-symbols = $(call find-symbols,$1,awk '$$2!="U"{print $$1}')
	undefined-symbols = $(call find-symbols,$1,awk '$$2=="U"{print $$1}')

	# All the .mo objects in -m variables are also added into corresponding -y
	# variable in unnest-vars, but filtered out here, when LINK is called.
	#
	# The .mo objects are supposed to be linked as a DSO, for module build. So here
	# they are only used as a placeholders to generate those "archive undefined"
	# symbol options (-Wl,-u,$symbol_name), which are the archive functions
	# referenced by the code in the DSO.
	#
	# Also the presence in -y variables will also guarantee they are built before
	# linking executables that will load them. So we can look up symbol reference
	# in LINK.
	#
	# This is necessary because the exectuable itself may not use the function, in
	# which case the function would not be linked in. Then the DSO loading will
	# fail because of the missing symbol.
	process-archive-undefs = $(filter-out %.a %.mo,$1) \
	$(addprefix $(WL_U), \
	$(filter $(call defined-symbols,$(filter %.a, $1)), \
	$(call undefined-symbols,$(filter %.mo,$1)))) \
	$(filter %.a,$1)

	extract-libs = $(strip $(foreach o,$1,$($o-libs)))
	expand-objs = $(strip $(sort $(filter %.o,$1)) \
	$(foreach o,$(filter %.mo,$1),$($o-objs)) \
	$(filter-out %.o %.mo,$1))

	%.o: %.c
	$(call quiet-command,$(CC) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<," CC $(TARGET_DIR)$@")
	%.o: %.rc
	$(call quiet-command,$(WINDRES) -I. -o $@ $<," RC $(TARGET_DIR)$@")

	# If we have a CXX we might have some C++ objects, in which case we
	# must link with the C++ compiler, not the plain C compiler.
	LINKPROG = $(or $(CXX),$(CC))

	LINK = $(call quiet-command, $(LINKPROG) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o $@ \
	$(call process-archive-undefs, $1) \
	$(version-obj-y) $(call extract-libs,$1) $(LIBS)," LINK $(TARGET_DIR)$@")

	%.o: %.S
	$(call quiet-command,$(CCAS) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -c -o $@ $<," CCAS $(TARGET_DIR)$@")

	%.o: %.cc
	$(call quiet-command,$(CXX) $(QEMU_INCLUDES) $(QEMU_CXXFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<," CXX $(TARGET_DIR)$@")

	%.o: %.cpp
	$(call quiet-command,$(CXX) $(QEMU_INCLUDES) $(QEMU_CXXFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<," CXX $(TARGET_DIR)$@")

	%.o: %.m
	$(call quiet-command,$(OBJCC) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<," OBJC $(TARGET_DIR)$@")

	%.o: %.dtrace
	$(call quiet-command,dtrace -o $@ -G -s $<, " GEN $(TARGET_DIR)$@")

	DSO_OBJ_CFLAGS := -fPIC -DBUILD_DSO
	module-common.o: CFLAGS += $(DSO_OBJ_CFLAGS)
	%$(DSOSUF): LDFLAGS += $(LDFLAGS_SHARED)
	%$(DSOSUF): %.mo
	$(call LINK,$^)
	@# Copy to build root so modules can be loaded when program started without install
	$(if $(findstring /,$@),$(call quiet-command,cp $@ $(subst /,-,$@), " CP $(subst /,-,$@)"))


	LD_REL := $(CC) -nostdlib -Wl,-r $(LD_REL_FLAGS)

	%.mo:
	$(call quiet-command,$(LD_REL) -o $@ $^," LD -r $(TARGET_DIR)$@")

	.PHONY: modules
	modules:

	%$(EXESUF): %.o
	$(call LINK,$(filter %.o %.a %.mo, $^))

	%.a:
	$(call quiet-command,rm -f $@ && $(AR) rcs $@ $^," AR $(TARGET_DIR)$@")

	quiet-command = $(if $(V),$1,$(if $(2),@echo $2 && $1, @$1))

	# cc-option
	# Usage: CFLAGS+=$(call cc-option, -falign-functions=0, -malign-functions=0)

	cc-option = $(if $(shell $(CC) $1 $2 -S -o /dev/null -xc /dev/null \
	>/dev/null 2>&1 && echo OK), $2, $3)

	VPATH_SUFFIXES = %.c %.h %.S %.cc %.cpp %.m %.mak %.texi %.sh %.rc
	set-vpath = $(if $1,$(foreach PATTERN,$(VPATH_SUFFIXES),$(eval vpath $(PATTERN) $1)))

	# install-prog list, dir
	define install-prog
	$(INSTALL_DIR) "$2"
	$(INSTALL_PROG) $1 "$2"
	$(if $(STRIP),$(STRIP) $(foreach T,$1,"$2/$(notdir $T)"),)
	endef

	# find-in-path
	# Usage: $(call find-in-path, prog)
	# Looks in the PATH if the argument contains no slash, else only considers one
	# specific directory. Returns an # empty string if the program doesn't exist
	# there.
	find-in-path = $(if $(find-string /, $1), \
	$(wildcard $1), \
	$(wildcard $(patsubst %, %/$1, $(subst :, ,$(PATH)))))

	# Logical functions (for operating on y/n values like CONFIG_FOO vars)
	# Inputs to these must be either "y" (true) or "n" or "" (both false)
	# Output is always either "y" or "n".
	# Usage: $(call land,$(CONFIG_FOO),$(CONFIG_BAR))
	# Logical NOT
	lnot = $(if $(subst n,,$1),n,y)
	# Logical AND
	land = $(if $(findstring yy,$1$2),y,n)
	# Logical OR
	lor = $(if $(findstring y,$1$2),y,n)
	# Logical XOR (note that this is the inverse of leqv)
	lxor = $(if $(filter $(call lnot,$1),$(call lnot,$2)),n,y)
	# Logical equivalence (note that leqv "","n" is true)
	leqv = $(if $(filter $(call lnot,$1),$(call lnot,$2)),y,n)
	# Logical if: like make's $(if) but with an leqv-like test
	lif = $(if $(subst n,,$1),$2,$3)

	# String testing functions: inputs to these can be any string;
	# the output is always either "y" or "n". Leading and trailing whitespace
	# is ignored when comparing strings.
	# String equality
	eq = $(if $(subst $2,,$1)$(subst $1,,$2),n,y)
	# String inequality
	ne = $(if $(subst $2,,$1)$(subst $1,,$2),y,n)
	# Emptiness/non-emptiness tests:
	isempty = $(if $1,n,y)
	notempty = $(if $1,y,n)

	# Generate files with tracetool
	TRACETOOL=$(PYTHON) $(SRC_PATH)/scripts/tracetool.py

	# Generate timestamp files for .h include files

	config-%.h: config-%.h-timestamp
	@cmp $< $@ >/dev/null 2>&1 \|\| cp $< $@

	config-%.h-timestamp: config-%.mak $(SRC_PATH)/scripts/create_config
	$(call quiet-command, sh $(SRC_PATH)/scripts/create_config < $< > $@, " GEN $(TARGET_DIR)config-$*.h")

	.PHONY: clean-timestamp
	clean-timestamp:
	rm -f *.timestamp
	clean: clean-timestamp

	# will delete the target of a rule if commands exit with a nonzero exit status
	.DELETE_ON_ERROR:

	# save-vars
	# Usage: $(call save-vars, vars)
	# Save each variable $v in $vars as save-vars-$v, save their object's
	# variables, then clear $v.
	define save-vars
	$(foreach v,$1,
	$(eval save-vars-$v := $(value $v))
	$(foreach o,$($v),
	$(foreach k,cflags libs objs,
	$(if $($o-$k),
	$(eval save-vars-$o-$k := $($o-$k))
	$(eval $o-$k := ))))
	$(eval $v := ))
	endef

	# load-vars
	# Usage: $(call load-vars, vars, add_var)
	# Load the saved value for each variable in @vars, and the per object
	# variables.
	# Append @add_var's current value to the loaded value.
	define load-vars
	$(eval $2-new-value := $(value $2))
	$(foreach v,$1,
	$(eval $v := $(value save-vars-$v))
	$(foreach o,$($v),
	$(foreach k,cflags libs objs,
	$(if $(save-vars-$o-$k),
	$(eval $o-$k := $(save-vars-$o-$k))
	$(eval save-vars-$o-$k := ))))
	$(eval save-vars-$v := ))
	$(eval $2 := $(value $2) $($2-new-value))
	endef

	# fix-paths
	# Usage: $(call fix-paths, obj_path, src_path, vars)
	# Add prefix @obj_path to all objects in @vars, and add prefix @src_path to all
	# directories in @vars.
	define fix-paths
	$(foreach v,$3,
	$(foreach o,$($v),
	$(if $($o-libs),
	$(eval $1$o-libs := $($o-libs)))
	$(if $($o-cflags),
	$(eval $1$o-cflags := $($o-cflags)))
	$(if $($o-objs),
	$(eval $1$o-objs := $(addprefix $1,$($o-objs)))))
	$(eval $v := $(addprefix $1,$(filter-out %/,$($v))) \
	$(addprefix $2,$(filter %/,$($v)))))
	endef

	# unnest-var-recursive
	# Usage: $(call unnest-var-recursive, obj_prefix, vars, var)
	#
	# Unnest @var by including subdir Makefile.objs, while protect others in @vars
	# unchanged.
	#
	# @obj_prefix is the starting point of object path prefix.
	#
	define unnest-var-recursive
	$(eval dirs := $(sort $(filter %/,$($3))))
	$(eval $3 := $(filter-out %/,$($3)))
	$(foreach d,$(dirs:%/=%),
	$(call save-vars,$2)
	$(eval obj := $(if $1,$1/)$d)
	$(eval -include $(SRC_PATH)/$d/Makefile.objs)
	$(call fix-paths,$(if $1,$1/)$d/,$d/,$2)
	$(call load-vars,$2,$3)
	$(call unnest-var-recursive,$1,$2,$3))
	endef

	# unnest-vars
	# Usage: $(call unnest-vars, obj_prefix, vars)
	#
	# @obj_prefix: object path prefix, can be empty, or '..', etc. Don't include
	# ending '/'.
	#
	# @vars: the list of variable names to unnest.
	#
	# This macro will scan subdirectories's Makefile.objs, include them, to build
	# up each variable listed in @vars.
	#
	# Per object and per module cflags and libs are saved with relative path fixed
	# as well, those variables include -libs, -cflags and -objs. Items in -objs are
	# also fixed to relative path against SRC_PATH plus the prefix @obj_prefix.
	#
	# All nested variables postfixed by -m in names are treated as DSO variables,
	# and will be built as modules, if enabled.
	#
	# A simple example of the unnest:
	#
	# obj_prefix = ..
	# vars = hot cold
	# hot = fire.o sun.o season/
	# cold = snow.o water/ season/
	#
	# Unnest through a faked source directory structure:
	#
	# SRC_PATH
	# ├── water
	# │ └── Makefile.objs──────────────────┐
	# │ │ hot += steam.o │
	# │ │ cold += ice.mo │
	# │ │ ice.mo-libs := -licemaker │
	# │ │ ice.mo-objs := ice1.o ice2.o │
	# │ └──────────────────────────────┘
	# │
	# └── season
	# └── Makefile.objs──────┐
	# │ hot += summer.o │
	# │ cold += winter.o │
	# └──────────────────┘
	#
	# In the end, the result will be:
	#
	# hot = ../fire.o ../sun.o ../season/summer.o
	# cold = ../snow.o ../water/ice.mo ../season/winter.o
	# ../water/ice.mo-libs = -licemaker
	# ../water/ice.mo-objs = ../water/ice1.o ../water/ice2.o
	#
	# Note that 'hot' didn't include 'season/' in the input, so 'summer.o' is not
	# included.
	#
	define unnest-vars
	# In the case of target build (i.e. $1 == ..), fix path for top level
	# Makefile.objs objects
	$(if $1,$(call fix-paths,$1/,,$2))

	# Descend and include every subdir Makefile.objs
	$(foreach v, $2,
	$(call unnest-var-recursive,$1,$2,$v)
	# Pass the .mo-cflags and .mo-libs along to its member objects
	$(foreach o, $(filter %.mo,$($v)),
	$(foreach p,$($o-objs),
	$(if $($o-cflags), $(eval $p-cflags += $($o-cflags)))
	$(if $($o-libs), $(eval $p-libs += $($o-libs))))))

	# For all %.mo objects that are directly added into -y, just expand them
	$(foreach v,$(filter %-y,$2),
	$(eval $v := $(foreach o,$($v),$(if $($o-objs),$($o-objs),$o))))

	$(foreach v,$(filter %-m,$2),
	# All .o found in *-m variables are single object modules, create .mo
	# for them
	$(foreach o,$(filter %.o,$($v)),
	$(eval $(o:%.o=%.mo)-objs := $o))
	# Now unify .o in -m variable to .mo
	$(eval $v := $($v:%.o=%.mo))
	$(eval modules-m += $($v))

	# For module build, build shared libraries during "make modules"
	# For non-module build, add -m to -y
	$(if $(CONFIG_MODULES),
	$(foreach o,$($v),
	$(eval $($o-objs): CFLAGS += $(DSO_OBJ_CFLAGS))
	$(eval $o: $($o-objs)))
	$(eval $(patsubst %-m,%-y,$v) += $($v))
	$(eval modules: $($v:%.mo=%$(DSOSUF))),
	$(eval $(patsubst %-m,%-y,$v) += $(call expand-objs, $($v)))))

	# Post-process all the unnested vars
	$(foreach v,$2,
	$(foreach o, $(filter %.mo,$($v)),
	# Find all the .mo objects in variables and add dependency rules
	# according to .mo-objs. Report error if not set
	$(if $($o-objs),
	$(eval $(o:%.mo=%$(DSOSUF)): module-common.o $($o-objs)),
	$(error $o added in $v but $o-objs is not set)))
	$(shell mkdir -p ./ $(sort $(dir $($v))))
	# Include all the .d files
	$(eval -include $(patsubst %.o,%.d,$(patsubst %.mo,%.d,$($v))))
	$(eval $v := $(filter-out %/,$($v))))
	endef