Linux uboot顶层makefile详解 一

VERSION = 2016       #主版本号
PATCHLEVEL = 03        #补丁版本号
SUBLEVEL =             #次版本号
EXTRAVERSION =          #附加版本信息
NAME =              #

MAKEFLAGS += -rR --include-dir=$(CURDIR)
#“-rR”表示禁止使用内置的隐含规则和变量定义，“--include-dir”指明搜索路径(引用其他makefile)，”$(CURDIR)”表示当前目录。
#主目录可以通过[$(MAKE) -C sudir]  来编译子目录.
#$(MAKE)就是调用“make”命令，-C 指定子目录。

unexport LC_ALL        #不导出变量给子make
LC_COLLATE=C
LC_NUMERIC=C
export LC_COLLATE LC_NUMERIC  #导出变量给子make(默认导出)

unexport GREP_OPTIONS

ifeq ("$(origin V)", "command line")   #origin函数用于告诉变量V的来源,若V来源于命令行,则V就等于命令行赋值.
  KBUILD_VERBOSE = $(V)
endif
ifndef KBUILD_VERBOSE
  KBUILD_VERBOSE = 0
endif

ifeq ($(KBUILD_VERBOSE),1)
  quiet =                       #用变量queit和Q来控制在编译的时候是否在终端输出完整的命令.
  Q =
else
  quiet=quiet_                 #quiet为silent_的话,整个命令都不会输出.为quiet_则输出短版本.
  Q = @
endif

#静默输出
ifneq ($(filter 4.%,$(MAKE_VERSION)),)	# filter函数表示过滤出MAKE_VERSION中符合4.%的字符(%为通配符).
ifneq ($(filter %s ,$(firstword x$(MAKEFLAGS))),)  #firstWord函数用于取出第一个单词,当使用“make -s”编译的时候，“-s”会作为 MAKEFLAGS 变量的一部分传递给 Makefile
  quiet=silent_
endif
else					# make-3.8x
ifneq ($(filter s% -s%,$(MAKEFLAGS)),)
  quiet=silent_
endif
endif

export quiet Q KBUILD_VERBOSE


ifeq ($(KBUILD_SRC),)

# OK, Make called in directory where kernel src resides
# Do we want to locate output files in a separate directory?
ifeq ("$(origin O)", "command line")
  KBUILD_OUTPUT := $(O)
endif

# That's our default target when none is given on the command line
PHONY := _all
_all:

# Cancel implicit rules on top Makefile
$(CURDIR)/Makefile Makefile: ;

ifneq ($(KBUILD_OUTPUT),)
# Invoke a second make in the output directory, passing relevant variables
# check that the output directory actually exists
saved-output := $(KBUILD_OUTPUT)
KBUILD_OUTPUT := $(shell mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) \
								&& /bin/pwd)
$(if $(KBUILD_OUTPUT),, \
     $(error failed to create output directory "$(saved-output)"))

PHONY += $(MAKECMDGOALS) sub-make

$(filter-out _all sub-make $(CURDIR)/Makefile, $(MAKECMDGOALS)) _all: sub-make
	@:

sub-make: FORCE
	$(Q)$(MAKE) -C $(KBUILD_OUTPUT) KBUILD_SRC=$(CURDIR) \
	-f $(CURDIR)/Makefile $(filter-out _all sub-make,$(MAKECMDGOALS))

# Leave processing to above invocation of make
skip-makefile := 1
endif # ifneq ($(KBUILD_OUTPUT),)
endif # ifeq ($(KBUILD_SRC),)

ifeq ($(skip-makefile),)

MAKEFLAGS += --no-print-directory


ifeq ("$(origin C)", "command line")
  KBUILD_CHECKSRC = $(C)
endif
ifndef KBUILD_CHECKSRC
  KBUILD_CHECKSRC = 0
endif

ifdef SUBDIRS
  KBUILD_EXTMOD ?= $(SUBDIRS)
endif

ifeq ("$(origin M)", "command line")
  KBUILD_EXTMOD := $(M)
endif

PHONY += all
ifeq ($(KBUILD_EXTMOD),)  #如果为空的话目标_all 依赖 all，因此要先编译出 all。否则的话默认目标_all 依赖 modules，要先编译出 modules
_all: all
else
_all: modules
endif

ifeq ($(KBUILD_SRC),)
        # building in the source tree   设置变量 srctree 为当前目录
        srctree := .
else
        ifeq ($(KBUILD_SRC)/,$(dir $(CURDIR)))
                # building in a subdirectory of the source tree
                srctree := ..
        else
                srctree := $(KBUILD_SRC)
        endif
endif
objtree		:= .
src		:= $(srctree)
obj		:= $(objtree)

VPATH		:= $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))

export srctree objtree VPATH


unexport CDPATH

#########################################################################
##   |表示管道,将左边的输出作为右边的输入,sed -e是替换命令,
#表示把i.86替换成x86,下面代码\后面不能有空格.
HOSTARCH := $(shell uname -m | \
	sed -e s/i.86/x86/ \
	    -e s/sun4u/sparc64/ \
	    -e s/arm.*/arm/ \
	    -e s/sa110/arm/ \
	    -e s/ppc64/powerpc/ \
	    -e s/ppc/powerpc/ \
	    -e s/macppc/powerpc/\
	    -e s/sh.*/sh/)
#“tr '[:upper:]' '[:lower:]'”表示将所有的大写字母替换为小写字母
HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \
	    sed -e 's/\(cygwin\).*/cygwin/')

export	HOSTARCH HOSTOS

#########################################################################
#
#
#
# set default to nothing for native builds
ifeq ($(HOSTARCH),$(ARCH))
CROSS_COMPILE ?=
endif

ARCH ?= arm
CROSS_COMPILE ?= arm-linux-gnueabihf-

KCONFIG_CONFIG	?= .config
export KCONFIG_CONFIG

# SHELL used by kbuild
CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
	  else if [ -x /bin/bash ]; then echo /bin/bash; \
	  else echo sh; fi ; fi)

HOSTCC       = cc
HOSTCXX      = c++
HOSTCFLAGS   = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
HOSTCXXFLAGS = -O2

ifeq ($(HOSTOS),cygwin)
HOSTCFLAGS	+= -ansi
endif

ifeq ($(HOSTOS),darwin)
# get major and minor product version (e.g. '10' and '6' for Snow Leopard)
DARWIN_MAJOR_VERSION	= $(shell sw_vers -productVersion | cut -f 1 -d '.')
DARWIN_MINOR_VERSION	= $(shell sw_vers -productVersion | cut -f 2 -d '.')

os_x_before	= $(shell if [ $(DARWIN_MAJOR_VERSION) -le $(1) -a \
	$(DARWIN_MINOR_VERSION) -le $(2) ] ; then echo "$(3)"; else echo "$(4)"; fi ;)

# Snow Leopards build environment has no longer restrictions as described above
HOSTCC       = $(call os_x_before, 10, 5, "cc", "gcc")
HOSTCFLAGS  += $(call os_x_before, 10, 4, "-traditional-cpp")
HOSTLDFLAGS += $(call os_x_before, 10, 5, "-multiply_defined suppress")


HOSTLDFLAGS += $(call os_x_before, 10, 7, "", "-Xlinker -no_pie")
endif

KBUILD_MODULES :=
KBUILD_BUILTIN := 1


ifeq ($(MAKECMDGOALS),modules)
  KBUILD_BUILTIN := $(if $(CONFIG_MODVERSIONS),1)
endif



export KBUILD_MODULES KBUILD_BUILTIN
export KBUILD_CHECKSRC KBUILD_SRC KBUILD_EXTMOD

#调用文件scripts/Kbuild.include
scripts/Kbuild.include: ;
include scripts/Kbuild.include

# Make variables (CC, etc...)

AS		= $(CROSS_COMPILE)as
# Always use GNU ld
ifneq ($(shell $(CROSS_COMPILE)ld.bfd -v 2> /dev/null),)
LD		= $(CROSS_COMPILE)ld.bfd
else
LD		= $(CROSS_COMPILE)ld
endif
CC		= $(CROSS_COMPILE)gcc
CPP		= $(CC) -E
AR		= $(CROSS_COMPILE)ar
NM		= $(CROSS_COMPILE)nm
LDR		= $(CROSS_COMPILE)ldr
STRIP		= $(CROSS_COMPILE)strip
OBJCOPY		= $(CROSS_COMPILE)objcopy
OBJDUMP		= $(CROSS_COMPILE)objdump
AWK		= awk
PERL		= perl
PYTHON		= python
DTC		= dtc
CHECK		= sparse

CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
		  -Wbitwise -Wno-return-void -D__CHECK_ENDIAN__ $(CF)

KBUILD_CPPFLAGS := -D__KERNEL__ -D__UBOOT__

KBUILD_CFLAGS   := -Wall -Wstrict-prototypes \
		   -Wno-format-security \
		   -fno-builtin -ffreestanding
KBUILD_AFLAGS   := -D__ASSEMBLY__

# Read UBOOTRELEASE from include/config/uboot.release (if it exists)
UBOOTRELEASE = $(shell cat include/config/uboot.release 2> /dev/null)
UBOOTVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)

export VERSION PATCHLEVEL SUBLEVEL UBOOTRELEASE UBOOTVERSION
export ARCH CPU BOARD VENDOR SOC CPUDIR BOARDDIR
export CONFIG_SHELL HOSTCC HOSTCFLAGS HOSTLDFLAGS CROSS_COMPILE AS LD CC
export CPP AR NM LDR STRIP OBJCOPY OBJDUMP
export MAKE AWK PERL PYTHON
export HOSTCXX HOSTCXXFLAGS DTC CHECK CHECKFLAGS

export KBUILD_CPPFLAGS NOSTDINC_FLAGS UBOOTINCLUDE OBJCOPYFLAGS LDFLAGS
export KBUILD_CFLAGS KBUILD_AFLAGS
my:
	@echo 'ARCH=' $(ARCH)
	@echo 'CPU=' $(CPU)
	@echo 'BOARD=' $(BOARD)
	@echo 'VENDOR=' $(VENDOR)
	@echo 'SOC=' $(SOC)
	@echo 'CPUDIR=' $(CPUDIR)
	@echo 'BOARDDIR=' $(BOARDDIR)