Makefile.build

###
# Main build makefile.
#
#  Lots of this code have been borrowed or heavily inspired from parts
#  of kbuild code, which is not credited, but mostly developed by:
#
#  Copyright (C) Sam Ravnborg <sam@mars.ravnborg.org>, 2015
#  Copyright (C) Linus Torvalds <torvalds@linux-foundation.org>, 2015
#

PHONY := __build
__build:

ifeq ($(V),1)
  quiet =
else
  quiet=quiet_
endif

build-dir := $(srctree)/tools/build

# Generic definitions
include $(build-dir)/Build.include

# do not force detected configuration
-include .config-detected

# Init all relevant variables used in build files so
# 1) they have correct type
# 2) they do not inherit any value from the environment
subdir-y     :=
obj-y        :=
subdir-y     :=
subdir-obj-y :=

# Build definitions
build-file := $(dir)/Build
include $(build-file)

# Create directory unless it exists
quiet_cmd_mkdir = MKDIR    $(dir $@)
      cmd_mkdir = mkdir -p $(dir $@)
     rule_mkdir = $(if $(wildcard $(dir $@)),,@$(call echo-cmd,mkdir) $(cmd_mkdir))

# Compile command
quiet_cmd_cc_o_c = CC       $@
      cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<

# Link agregate command
# If there's nothing to link, create empty $@ object.
quiet_cmd_ld_multi = LD       $@
      cmd_ld_multi = $(if $(strip $(obj-y)),\
		       $(LD) -r -o $@ $(obj-y),rm -f $@; $(AR) rcs $@)

# Build rules
$(OUTPUT)%.o: %.c FORCE
	$(call rule_mkdir)
	$(call if_changed_dep,cc_o_c)

$(OUTPUT)%.o: %.S FORCE
	$(call rule_mkdir)
	$(call if_changed_dep,cc_o_c)

# Gather build data:
#   obj-y        - list of build objects
#   subdir-y     - list of directories to nest
#   subdir-obj-y - list of directories objects 'dir/$(obj)-in.o'
obj-y        := $($(obj)-y)
subdir-y     := $(patsubst %/,%,$(filter %/, $(obj-y)))
obj-y        := $(patsubst %/, %/$(obj)-in.o, $(obj-y))
subdir-obj-y := $(filter %/$(obj)-in.o, $(obj-y))

# '$(OUTPUT)/dir' prefix to all objects
prefix       := $(subst ./,,$(OUTPUT)$(dir)/)
obj-y        := $(addprefix $(prefix),$(obj-y))
subdir-obj-y := $(addprefix $(prefix),$(subdir-obj-y))

# Final '$(obj)-in.o' object
in-target := $(prefix)$(obj)-in.o

PHONY += $(subdir-y)

$(subdir-y):
	@$(MAKE) -f $(build-dir)/Makefile.build dir=$(dir)/$@ obj=$(obj)

$(sort $(subdir-obj-y)): $(subdir-y) ;

$(in-target): $(obj-y) FORCE
	$(call rule_mkdir)
	$(call if_changed,ld_multi)

__build: $(in-target)
	@:

PHONY += FORCE
FORCE:

# Include all cmd files to get all the dependency rules
# for all objects included
targets   := $(wildcard $(sort $(obj-y) $(in-target)))
cmd_files := $(wildcard $(foreach f,$(targets),$(dir $(f)).$(notdir $(f)).cmd))

ifneq ($(cmd_files),)
  include $(cmd_files)
endif

.PHONY: $(PHONY)