整体注释在notepad中完成，复制下来用notepad打开，格式应该会很完美。
#本文档仅做参考，注释随意写的
# SPDX-License-Identifier: GPL-2.0+
#
#如果 Tab 字符之后使用 # 字符，则会被 make 解释为命令行）。注释行的结尾如果存在反斜线（\），那么下一行也被作为注释行。如果#号以tab开头，makefile虽然不会执行，但是会回显到终端上。
VERSION = 2017
PATCHLEVEL = 03
SUBLEVEL =
EXTRAVERSION =
NAME =
#makefile中变量的定义等号两边可以有空格，而在shell中变量的定义赋值号两边不能有空格
# *DOCUMENTATION*
# To see a list of typical targets execute "make help"
# More info can be located in ./README
# Comments in this file are targeted only to the developer, do not
# expect to learn how to build the kernel reading this file.
# o Do not use make's built-in rules and variables内置的规则和变量。
# (this increases performance性能 and avoids hard-to-debug behaviour难以调试的行为);
# o Look for make include files relative to root of kernel src
MAKEFLAGS += -rR --include-dir=$(CURDIR)
#当前工作目录，（makefile所在目录），这是内置变量。在 make 的递归调用中，需要了解一下变量“ CURDIR”，此变量代表 make 的工作目录。当使用“ -C”选项进入一个子目录后，此变量将被重新赋值。总之，如果在Makefile 中没有对此变量进行显式的赋值操作，那么它代表 make 的工作目录。
#这是GNU make的的环境变量，为了避免覆盖已有值，所以使用+=来追加变量。变量MAKEFLAGS值中的字可以包含‘=’，make将它们按变量定义处理
#“-rR”表示禁止使用内置的隐含规则和变量定义，“--include-dir”指明搜索路径，”$(CURDIR)”表示当前目录。
# 在下一级子目录中执行的make时，这些选项会被附加作为make的命令行参数来执行，
#环境变量可以在Makefile里面定义，也可以在make命令的命令行参数中定义，还可以在操作系统的环境变量中定义。
#。有时候我们需要向子 make 传递变量，这个时候使用“export”来导出要传递给子 make 的变量即可。
#有两个特殊的变量：“SHELL”和“MAKEFLAGS”！！！！这两个变量除非使用“unexport”声明，否则的话在整个make的执行过程中，它们的值始终自动的传递给子make。
##使用“make -s”编译的时候，“-s”会作为 MAKEFLAGS 变量的一部分传递给 Makefile。
# Avoid funny character set dependencies
unexport LC_ALL
##非传递环境变量，不会传递到下一级Makefile
#export用于将上层makefile中定义的变量传递到子makefile中使用。当没有使用指示符“ export”对任何变量进行声明的情况下，上层 make 只将那些已经初始化的环境变量（在执行 make 之前已经存在的环境变量）和使用命令行指定的变量（如命令“ makeCFLAGS +=-g”或者“ make –e CFLAGS +=-g”）传递给子 make 程序。
LC_COLLATE=C
LC_NUMERIC=C
export LC_COLLATE LC_NUMERIC
# Avoid interference with shell env settings
unexport GREP_OPTIONS
# We are using a recursive递归 build, so we need to do a little thinking
# to get the ordering right.
#
# Most importantly: sub-Makefiles should only ever modify files in
# their own directory. If in some directory we have a dependency on
# a file in another dir (which doesn't happen often, but it's often
# unavoidable when linking the built-in.o targets which finally
# turn into vmlinux), we will call a sub make in that other dir, and
# after that we are sure that everything which is in that other dir
# is now up to date.？？？？？？？？？？
#
# The only cases where we need to modify files which have global
# effects are thus separated out分离 and done before the recursive
# descending is started. They are now explicitly明确 listed as the
# prepare rule.
# Beautify output上面这段没用，重点是下：
#uboot默认编译时输出短命令，要输出完整命令就 make V=1
# ---------------------------------------------------------------------------
#
# Normally, we echo the whole command before executing it. By making
# that echo $($(quiet)$(cmd)), we now have the possibility to set
# $(quiet) to choose other forms of output instead, e.g.
#
# quiet_cmd_cc_o_c = Compiling $(RELDIR)/$@
# cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
#
# If $(quiet) is empty, the whole command will be printed.
# If it is set to "quiet_", only the short version will be printed.
# If it is set to "silent_", nothing will be printed at all, since
# the variable $(silent_cmd_cc_o_c) doesn't exist!!!!!!
#
# A simple variant is to prefix前缀 commands with $(Q) - that's useful
# for commands that shall be hidden in non-verbose不冗长的 mode.
#
# $(Q)ln $@ :<
#
# If KBUILD_VERBOSE equals 0 then the above command will be hidden.
# If KBUILD_VERBOSE equals 1 then the above command is displayed.
#
# To put more focus on warnings, be less verbose as default
# Use 'make V=1' to see the full commands
ifeq ("$(origin V)", "command line")
#变量 V 的来源。如果变量 V 是在命令行定义的那么它的来源就是"command line"
#origin函数的返回值有：
# "undefined"从来没有定义过、“default”是一个默认的定义、“
# "environment"是一个环境变量、
# "file"这个变量被定义在Makefile中
# "command line"这个变量是被命令行定义的
# "override"是被override指示符重新定义的
# "automatic"是一个命令运行中的自动化变量
KBUILD_VERBOSE = $(V)
endif
ifndef KBUILD_VERBOSE
KBUILD_VERBOSE = 0
endif
ifeq ($(KBUILD_VERBOSE),1)
quiet =
Q =
else
quiet=quiet_
Q = @
endif
#uboot 默认编译是不会在终端中显示完整的命令，都是短命令。是不利于分析 uboot 的编译过程。可以通过设置变量“V=1“来实现完整的命令输出，这个在调试 uboot 的时候很有用。
#编译的时候使用“make -s”即可实现静默输出。
#设置 V=0 或者在命令行中不定义 V 的话，编译 uboot 的时候终端中显示的短命令，但是还是会有命令输出，有时候我们在编译 uboot 的时候不需要输出命令，这个时候就可以使用 uboot 的静默输出功能
# If the user is running make -s (silent mode), suppress抑制 echoing回声，回显 of
# commands 尚上面V是决定短命令和长命令，但一定会输出，这里决定输出与否。
#使用“make -s”编译的时候，“-s”会作为 MAKEFLAGS 变量的一部分传递给 Makefile。
ifneq ($(filter 4.%,$(MAKE_VERSION)),) # make-4 Makefile 中内置的标准变量
#是在字符串“MAKE_VERSION”中找出符合“4.%”的字符(%为通配符)， MAKE_VERSION 是make工具的版本号，ubuntu16.04里面默认自带的make工具版本号为4.1，大家可以输入“make -v”查看
ifneq ($(filter %s ,$(firstword x$(MAKEFLAGS))),) #取首单词
#$(filter PATTERN…,TEXT) 过滤掉字串“TEXT”中所有不符合模式“PATTERN”的单词，保留所有符合此模式的单词。
quiet=silent_
endif
else # make-3.8x
ifneq ($(filter s% -s%,$(MAKEFLAGS)),)
quiet=silent_
endif
endif
export quiet Q KBUILD_VERBOSE
# kbuild supports saving output files in a separate directory.
# To locate定位 output files in a separate directory two syntaxes语法 are supported.
# In both cases the working directory must be the root of the kernel src.？？？？？
# 1) O=
# Use "make O=dir/to/store/output/files/"
#
# 2) Set KBUILD_OUTPUT
# Set the environment variable KBUILD_OUTPUT to point to the directory
# where the output files shall be placed.
# export KBUILD_OUTPUT=dir/to/store/output/files/
# make
#
# The O= assignment分配，指定takes precedence优先 over the KBUILD_OUTPUT environment
# variable.
#将编译出来的目标文件输出到单独的目录中
# KBUILD_SRC is set设置 on 在invocation调用 of make in OBJ directory（OBJ目录调用make时设置KBUILD_SRC）
#应该是make KBUILD_SRC=***这样。
# KBUILD_SRC is not intended to be used by the regular user (for now)
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") #O来自命令行
KBUILD_OUTPUT := $(O) #"make O=dir/to/store/output/files/"
endif
# That's our default target when none is given on the command line
PHONY := _all #本文档最后一行有.PHONY: $(PHONY)
#在Makefile中，.PHONY后面的target表示的也是一个伪造的target, 而不是真实存在的文件target，注意Makefile的target默认是文件。
_all: #在这里好像就是没有什么意义的。
#这是默认目标，第一个目标！！！！make编译的时候就执行这个目标。后面还会出现这个目标，是会合并的。
#这里出现个空的目的应该就是抢第一个目标的位置。
# Cancel implicit隐含的 rules on top Makefile？
$(CURDIR)/Makefile Makefile: ; #操作查看当前目录Makefile是否为最新
#makefile的规则中命令可以和目标：依赖写在一行，用分号隔开！！！！不写在同一行的时候必须TAB开头。
#这是一条"空指令"，Makefile中使用空命令行来阻止make使用隐含规则构建指定目标！！但目标：依赖后面没有命令的时候，就会使用makefile的隐含规则进行处理。加上一个空命令，就不会套用隐含规则了。
插入：分号是什么时候用，什么时候不用，可以参考经典示例代码如下：
var=3 # a
target:
echo $(var) # b
var=4 # c
echo $(var) # d
echo $$var # e
a：定义Makefile中的变量var，值为3
b：打印Makefile中的变量，值为3
c：定义shell命令中的变量var，值为4，Makefile的变量var不受影响
d：打印Makefile中的变量，值为3！！！！！！！！！！！！！！！
e：打印shell命令中的变量。此时var为未定义的变量。
读者可能会奇怪，shell命令中的var明明已经定义了，为什么是未定义呢？
原因：在Makefile的规则命令，如果相互之间没有使用';\'连接起来的话，相互之间是不能共享变量的！！！！！
修改示例代码，使用';\'连接shell规则命令行。
var=3 # a
target:
echo $(var);\ # b
var=4;\ # c
echo $(var);\ # d
echo $$var # e
此时，b、d、e行的输出结果分别为3、3、4，符合用户的预期。
ifneq ($(KBUILD_OUTPUT),)
# Invoke引起，调用 a second make in the output directory, passing relevant variables传递相关变量
# check that the output directory actually exists
saved-output := $(KBUILD_OUTPUT) #貌似没什么用，后面没出现了。
KBUILD_OUTPUT := $(shell mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) \
&& /bin/pwd)
#调用 mkdir 命令，创建 KBUILD_OUTPUT 目录，并且将创建成功以后的绝对路径赋值给 KBUILD_OUTPUT。至此，通过 O 指定的输出目录就存在了。
#makefile中每一行命令会用一个进程来处理，所以，需要一起执行的命令用\连起来，不要另起一行。否则，pwd就不是上面cd的目录了，相当于重新开了一个终端。
$(if $(KBUILD_OUTPUT),, \
$(error failed to create output directory "$(saved-output)"))
#if函数：$(if <condition>,<then-part>,<else-part>)
PHONY += $(MAKECMDGOALS) sub-make
#有一个 make 的环境变量叫“MAKECMDGOALS”，这个变量中会存放你所指定的终极目标的列表，如果在命令行上，你没有指定目标，那么，这个变量是空值。make ***_defconfig,这个***_defconfig就会给MAKECMDGOALS
$(filter-out _all sub-make $(CURDIR)/Makefile, $(MAKECMDGOALS)) _all: sub-make
@:
#命令中仅有一个：是什么意思？：冒号在shell中为空命令。
#命令前加@表示禁止回显。filter函数是扔掉不符合的，filter-out是挑出不符合的用。
sub-make: FORCE
$(Q)$(MAKE) -C $(KBUILD_OUTPUT) KBUILD_SRC=$(CURDIR) \
-f $(CURDIR)/Makefile $(filter-out _all sub-make,$(MAKECMDGOALS))
#最后有FORCE:只有一个目标没依赖没命令。这样的目标在作为一个规则的依赖时，因为依赖总被认为被更新过，因此作为依赖所在的规则中定义的命令总会被执行。
#-C表示进入那个文件夹读取那里的makefile.-f指定要执行的make的文件名。
#Makefile的文件名 默认的情况下，make命令会在当前目录下按顺序找寻文件名为“GNUmakefile”、“makefile”、“Makefile”的文件。如果要指定特定的Makefile，你可以使用make的“- f”和“--file”参数。
#？？？？？？？？？？？？？？
# Leave processing to above invocation of make
skip-makefile := 1
endif # ifneq ($(KBUILD_OUTPUT),)
endif # ifeq ($(KBUILD_SRC),)
# We process the rest of the Makefile if this is the final invocation of make
ifeq ($(skip-makefile),)
# Do not print "Entering directory ...",
# but we want to display it when entering to the output directory
# so that IDEs/editors are able to understand relative filenames.
MAKEFLAGS += --no-print-directory
# Call a source code checker (by default, "sparse") as part of the
# C compilation.
#
# Use 'make C=1' to enable checking of only re-compiled files.
#使用命令“make C=1”使能代码检查，检查那些需要重新编译的文件。
# Use 'make C=2' to enable checking of *all* source files, regardless
# of whether they are re-compiled or not.
#
# See the file "Documentation/sparse.txt" for more details, including
# where to get the "sparse稀疏的零散的" utility效用，实用程序.
ifeq ("$(origin C)", "command line")
KBUILD_CHECKSRC = $(C)
endif
ifndef KBUILD_CHECKSRC
KBUILD_CHECKSRC = 0
endif
# Use make M=dir to specify指定，明确 directory of external module to build
#uboot可以编译模块，一般不用。
# Old syntax make ... SUBDIRS=$PWD is still supported
# Setting the environment variable KBUILD_EXTMOD take precedence
#SUBDIRS 这个变量是通过执行 make 的时候传进来的,我们没有定义。
ifdef SUBDIRS
KBUILD_EXTMOD ?= $(SUBDIRS)
endif
ifeq ("$(origin M)", "command line") #判断是否在命令行定义了 M
KBUILD_EXTMOD := $(M)
endif
# If building an external module we do not care about the all: rule
# but instead _all depend on modules
PHONY += all
ifeq ($(KBUILD_EXTMOD),)
_all: all
#！！！！！！！！！！！！这里就是第一个目标。依赖于all。看另一个makefile吧，这个文件中被我删了，因为我们make **_defconfig 的时候有很多没用的。下面都是为了make ***defconfig注释的。
else
_all: modules
endif
#判断 KBUILD_EXTMOD 时为空，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，也就是编译模块。一般情况下我们不会在 uboot 中编译模块，所以此处会编译 all 这个目标。
ifeq ($(KBUILD_SRC),)
# building in the source tree
srctree := .
else
ifeq ($(KBUILD_SRC)/,$(dir $(CURDIR)))
# building in a subdirectory of the source tree
srctree := ..
else
srctree := $(KBUILD_SRC)
endif
#判断 KBUILD_SRC 是否为空，如果为空的话就设置变量 srctree 为当前目录，即srctree 为“.”，一般不设置 KBUILD_SRC。
endif
objtree := .
src := $(srctree)
obj := $(objtree)
#两个都是当前目录
#以上，使用变量立即展开方式分别设置源码树目录，顶层目录，目标数目录，源文件目录、目标目录。
VPATH := $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))
# “VPATH”是Makefile文件中的特殊变量。通过变量“ VPATH”可以指定makefile中所有文件（包括依赖文件和目标文件）的搜索路径。
# 如果没有指明这个变量，make只会在当前的目录中去找寻依赖文件和目标文件。
# 如果定义了这个变量，那么，make就会在当当前目录找不到的情况下，到所指定的目录中去找寻文件了。
#变量大写的一般都是特殊的变量，比如环境变量。
export srctree objtree VPATH
#关键词export用来声明变量，被声明的变量要被传递到下级Makefile中。
# Make sure CDPATH settings don't interfere干涉
unexport CDPATH
#########################################################################
#sed 是一种在线编辑器，它一次处理一行内容。
# Sed主要用来自动编辑一个或多个文件；简化对文件的反复操作；编写转换程序等。
#顶层 Makefile 会获取主机架构和系统，也就是我们电脑的架构和系统
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/)
#HOSTARCH是主机架构
#uname -m是shell命令，显示电脑类型。-s或--sysname 显示操作系统名称。|是管道。
#一次更改多替换文本中多个值，点是正则表达式中的单字符通配符。
#对于386架构而言，SUBARCH将会被展开成i386
#sed -e 是替换命令，“sed -e s/i.86/x86/”表示将管道输入的字符串中的“i.86”替换为“x86”
HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \
sed -e 's/\(cygwin\).*/cygwin/')
# uname -s得到Linux. 最终得到就是全部变成小写，成了linux.
#tr命令可以对来自标准输入的字符进行替换、压缩和删除。它可以将一组字符变成另一组字符
export HOSTARCH HOSTOS
#导出 HOSTARCH=x86_64，HOSTOS=linux。
#########################################################################
# set default to nothing for native builds
#编 译 uboot 的 时 候 需 要 设 置 目 标 板 架 构 和 交 叉 编 译 器
#这么看ARCH是需要在命令行当做选项输入的。又或者是已经在环境变量中。
#make 在运行时，系统中的所有环境变量对它都是可见的。
#正因为如此，我们就可以设置一个命名为“CFLAGS”的环境变量，用它来指定一个默认的编译选项。就可以在所有的Makefile 中直接使用这个变量来对 c 源代码就行编译。
ifeq ($(HOSTARCH),$(ARCH))
CROSS_COMPILE ?=
endif
#判断 HOSTARCH 和 ARCH 这两个变量是否相等，主机架构(变量 HOSTARCH)是 x86_64，而我们编译的是 ARM 版本 uboot，肯定不相等，所以 CROS_COMPILE= arm-linuxgnueabihf-。从示例代码 31.3.9.1 可以看出，每次编译 uboot 的时候都要在 make 命令后面设置ARCH 和 CROS_COMPILE，使用起来很麻烦，可以直接修改顶层 Makefile，在里面加入 ARCH和 CROSS_COMPILE 的定义（摘自原子）
#但是韦东山老师这里也没有加入呀，为什么编译的时候不指定选项ARCH、CROSS_COMPILE 也可以呢？？？？？
#在ubuntu中echo $ARCH或者直接env查看所有环境变量，可以看到环境变量已经设置成了：ARCH=arm；CROSS_COMPILE=arm-linux-gnueabihf-
#不过并没有人明确的说make中这两个变量会采用系统环境变量的，只是我的猜测，不知道为什么。
KCONFIG_CONFIG ?= .config
export KCONFIG_CONFIG
#如果没有指定配置文件则使用默认配置文件，.config为默认的配置文件，赋值给KCONFIG_CONFIG变量供后面的规则使用。
#uboot 是可以配置的，这里设置配置文件为.config，.config 默认是没有的，需要使用命令“make xxx_defconfig” 对 uboot 进行配置，配置完成以后就会在 uboot 根目录下生成.config。默认情况下.config 和xxx_defconfig 内容是一样的，因为.config 就是从 xxx_defconfig 复制过来的。如果后续自行调整了 uboot 的一些配置参数，那么这些新的配置参数就添加到了.config 中，而不是 xxx_defconfig。相当于 xxx_defconfig 只是一些初始配置，而.config 里面的才是实时有效的配置。
# SHELL used by kbuild 设定kbuild使用的Shell
CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
else if [ -x /bin/bash ]; then echo /bin/bash; \
else echo sh; fi ; fi)
#使用make的shell函数来执行shell程序！！！！shell函数也不像其它的函数，它的参数应该就是操作系统Shell的命令。它和反引号“`”是相同的功能。这就是说，shell函数把执行操作系统命令后的输出作为函数返回。于是，我们可以用操作系统命令以及字符串处理命令awk，sed等等命令来生成一个变量，如：contents := $(shell cat foo)。
# if [-x]判断文件/程序存在且是可执行。貌似是shell变量用两个$。make的变量用一个。注意这里有两个fi。
#BASH为shell的内部变量，在make中使用双$$来引用shell中的变量
#在Makefile中的规则命令行中：$var：将Makefile中的变量var的值，传给shell命令。
#$$var：访问shell命令中定义的变量var。
#if语句直接就echo了，返回值是什么呢？给这个变量什么呢？？应该就是echo什么就给他什么。
HOSTCC = cc
HOSTCXX = c++
HOSTCFLAGS = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer \
$(if $(CONFIG_TOOLS_DEBUG),-g)
HOSTCXXFLAGS = -O2
ifeq ($(HOSTOS),cygwin)
HOSTCFLAGS += -ansi
endif
# Mac OS X / Darwin's C preprocessor is Apple specific. It
# generates numerous errors and warnings. We want to bypass it
# and use GNU C's cpp. To do this we pass the -traditional-cpp
# option to the compiler. Note that the -traditional-cpp flag
# DOES NOT have the same semantics as GNU C's flag, all it does
# is invoke the GNU preprocessor in stock ANSI/ISO C fashion.
#
# Apple's linker is similar, thanks to the new 2 stage linking
# multiple symbol definitions are treated as errors, hence the
# -multiply_defined suppress option to turn off this error.
#
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")
# since Lion (10.7) ASLR is on by default, but we use linker generated lists
# in some host tools which is a problem then ... so disable ASLR for these
# tools
HOSTLDFLAGS += $(call os_x_before, 10, 7, "", "-Xlinker -no_pie")
endif
# Decide whether to build built-in, modular, or both.
#决定是否编译为内置对象、模块、或者两者同时编译，通常编译为内置对象
# Normally, just do built-in.
KBUILD_MODULES :=
KBUILD_BUILTIN := 1 # 编译built-in
# If we have only "make modules", don't compile built-in objects.
# When we're building modules with modversions, we need to consider
# the built-in objects during the descend as well, in order to
# make sure the checksums are up to date before we record them.
ifeq ($(MAKECMDGOALS),modules)
KBUILD_BUILTIN := $(if $(CONFIG_MODVERSIONS),1)
endif
# If we have "make <whatever> modules", compile modules
# in addition to whatever we do anyway.
# Just "make" or "make all" shall build modules as well
# U-Boot does not need modules！！！！！！！！
#ifneq ($(filter all _all modules,$(MAKECMDGOALS)),)
# KBUILD_MODULES := 1
#endif
#如果make的终极目标列表中有all、_all、modules中任何一个，变量KBUILD_MODULES赋值为1
#ifeq ($(MAKECMDGOALS),) 如果make终极目标列表变量MAKECMDGOALS为空
# KBUILD_MODULES := 1
#endif
export KBUILD_MODULES KBUILD_BUILTIN
export KBUILD_CHECKSRC KBUILD_SRC KBUILD_EXTMOD
# We need some generic definitions (do not try to remake the file).
scripts/Kbuild.include: ; #为什么要这句呢？？？？上面说了
include scripts/Kbuild.include
#include”指示符告诉 make 暂停读取当前的 Makefile，而转去读取“ include”指定的一个或者多个文件，完成以后再继续当前 Makefile 的读取。
#文件 scripts/Kbuild.include，此文件里面定义了很多变量。459行附近$(build)就是这里面的变量
#在 uboot 的编译过程中会用到 scripts/Kbuild.include 中的这些变量
# 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)
#定义 KBuild 编译参数
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)))$(EXTRAVERSION)
#$(if CONDITION,THEN-PART[,ELSE-PART])如果“CONDITION”的展开结果非空，则条件为真，就将第二个参数“THEN_PATR”作为函数的计算表达式
export VERSION PATCHLEVEL SUBLEVEL UBOOTRELEASE UBOOTVERSION
export ARCH CPU BOARD VENDOR SOC CPUDIR BOARDDIR
#这 7 个变量在顶层 Makefile 是找不到的，来自uboot 根目录下有个文件叫做 config.mk
#其中原材料来自顶层的.config文件。
# 最终ARCH = arm
# CPU = armv7
# BOARD = mx6ullevk
# VENDOR = freescale
# SOC = mx6
# CPUDIR = arch/arm/cpu/armv7
# BOARDDIR = freescale/mx6ullevk
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 CHECK CHECKFLAGS DTC DTC_FLAGS
export KBUILD_CPPFLAGS NOSTDINC_FLAGS UBOOTINCLUDE OBJCOPYFLAGS LDFLAGS
export KBUILD_CFLAGS KBUILD_AFLAGS
# When compiling out-of-tree modules, put MODVERDIR in the module
# tree rather than in the kernel tree. The kernel tree might
# even be read-only.
export MODVERDIR := $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/).tmp_versions
#由于内核树或许是只读的，因此在编译内核树外的模块的时候，需要为这些编译的模块指定存储的目录，变量MODVERDIR 就是模块存储目录，如果KBUILD_EXTMOD为空则默认目录为.tmp_versions。
# Files to ignore in find ... statements
export RCS_FIND_IGNORE := \( -name SCCS -o -name BitKeeper -o -name .svn -o \
-name CVS -o -name .pc -o -name .hg -o -name .git \) \
-prune -o
export RCS_TAR_IGNORE := --exclude SCCS --exclude BitKeeper --exclude .svn \
--exclude CVS --exclude .pc --exclude .hg --exclude .git
# ===========================================================================
# Rules shared between *config targets and build targets
# Basic helpers built in scripts/
#下面make ***_defcongfig的依赖就有这个，伪目标，一定执行命令。
PHONY += scripts_basic
#进入scripts/basic目录可以看到有Docproc.c和Fixdep.c两个文件，这里生成基本的scripts配置工具fixdep docproc
scripts_basic:
$(Q)$(MAKE) $(build)=scripts/basic
$(Q)rm -f .tmp_quiet_recordmcount
# Q = @，MAKE = make环境变量，build 变量的定义在 scripts/Kbuild.include 文件中，上面已经包含了。
#build := -f $(srctree)/scripts/Makefile.build obj = -f ./scripts/Makefile.build obj
#展开即为：make -f ./scripts/Makefile.build obj=scripts/basic（-f执行非makefile命名的makefile.）
#根据传入的 obj 参数显示的执行 ./scripts/Makefile.build 文件
#make 解析执行scripts/Makefile.build文件，且参数obj= scripts/basic。而在解析执行scripts/Makefile.build文件的时候，scripts/Makefile.build又会通过解析传入参数来包含对应文件夹下的Makefile文件（scripts/basic/Makefile），从中获得需要编译的目标。
# To avoid any implicit rule to kick in, define an empty command.
scripts/basic/%: scripts_basic ;
#下面make ***_defcongfig的依赖就有这个，伪目标，一定执行命令。
PHONY += outputmakefile
# outputmakefile generates a Makefile in the output directory, if using a
# separate output directory. This allows convenient use of make in the
# output directory.
outputmakefile:
ifneq ($(KBUILD_SRC),)
# KBUILD_SRC 为空，所以ifneq 中的语句不会执行。 outputmakefile 为空
#指定O=dir，编译输出目录和源代码目录分开时才会有效。
$(Q)ln -fsn $(srctree) source
$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile \
$(srctree) $(objtree) $(VERSION) $(PATCHLEVEL)
endif
#如果使用了一个独立的输出目录，outputmakefile目标在输出目录中产生一个Makefile文件，这可以允许在输出目录中很方便的使用make。这个规则的命令运行一个shell脚本scripts/mkmakefile，并传递四个参数。这个脚本主要是在$(objtree)参数指定的目录中生成一个Makefile文件。
# To make sure we do not include .config for any of the *config targets
# catch them early, and hand them over to scripts/kconfig/Makefile
# It is allowed to specify more targets when calling make, including
# mixing *config targets and build targets.
# For example 'make oldconfig all'.
# Detect when mixed targets is specified, and make a second invocation
# of make so .config is not included in this case either (for *config).？？？？？？？
插入：上面的英文大概意思是说make后面的目标可以为配置目标(*config targets)、编译目标(build targets)、或者二者的混合目标，在使用的时候通过设置不同的变量来别处理。
make后面的目标包括三类:
(1)和.config无关的目标即(no_dot_config-targets)比如:clean,mrproper,distclean,
headers_install,kernelrelease,kernelversion等等；
(2)和.config相关的目标dot_config
a:配置目标(config targets)主要是产生.config文件
b:构建目标(build targets)主要是使用.config像all,vmlinux,modules,zImage,等等
(3)single targets
上面没有列出的,如:dir/,dir/file，dir/file.ko*/
#version_h := include/generated/version_autogenerated.h
#版本号文件，此文件是自动生成的
#timestamp_h := include/generated/timestamp_autogenerated.h
#时间戳文件，此文件是自动生成的
#这两句本来没有被注释掉的，本文件没有再出现过，也没export,不知道有什么用，我注释了试一下
no-dot-config-targets := clean clobber mrproper distclean \
help %docs check% coccicheck \
ubootversion backup tests
#makefile对于大小写敏感，这个并不是开始的版本号
#no-dot-config-targets指代的是那些和 .config 没有关系的目标
config-targets := 0 #配置目标
mixed-targets := 0 #混合目标
dot-config := 1
ifneq ($(filter $(no-dot-config-targets), $(MAKECMDGOALS)),)
ifeq ($(filter-out $(no-dot-config-targets), $(MAKECMDGOALS)),)
dot-config := 0
endif
endif
#如果终极目标列表变量MAKECMDGOALS只包含no-dot-config-targets变量中的目标，则make不依赖.config隐含文件。
#！！！！如果make命令行带有menuconfig/xconfig等目标，则表示这是一条配置命令，如make menuconfig，那么变量config-targets置为1，标识应该生成.config文件；如果不仅有config目标，还有其他目标，表示为混合目标模式
ifeq ($(KBUILD_EXTMOD),) #一般是空
ifneq ($(filter config %config,$(MAKECMDGOALS)),)
#make 在执行时会设置一个特殊变量 -- "MAKECMDGOALS"!!!是我们make ***_defconfig中的***_defconfig.
config-targets := 1 #这里确实是1
ifneq ($(words $(MAKECMDGOALS)),1)
#统计 MAKECMDGOALS 中的单词个数，如果不为 1的话条件成立
mixed-targets := 1 #这一般是0,编译时我们make后面只带一个目标。
endif
endif
endif
ifeq ($(mixed-targets),1) #一般不成立
# ===========================================================================
# We're called with mixed targets (*config and build targets).
# Handle them one by one.
#对于一个没有依赖而只有命令行的双冒号规则，当引用此目标时，规则的命令将会被无条件执行。
#？？？？？？？？？？？？？？？？？？？？？？？？？
%:: FORCE
$(Q)$(MAKE) -C $(srctree) KBUILD_SRC= $@
#*%代表make 后带任何目标都执行该命令，从代码中可以看出，这里使用了一个双冒号的模式匹配规则。百分号代表任何目标都使用这个规则，其中$(srctree) 为内核代码树所在目 录 ， KBUILD_SRC 定义为目标。所以如果 make 命令为 ： make s3c2410_defconfig all 那么构建系统就会分别执行下面两条命令：make -C $(srctree) KBUILD_SRC= s3c2410_defconfig；make -C $(srctree) KBUILD_SRC= all；这其实和简单的用手动的输入两条连续命令(make s3c2410_defconfig 和 make all) 是一样效果的。
else
ifeq ($(config-targets),1) #如果是make **config时，我们在这里成立！！！
# ===========================================================================
# *config targets only - make sure prerequisites 先决条件，这段代码执行前面有一个if的判断的。are updated, and descend下降
# in scripts/kconfig to make the *config target貌似是去这个文件里面编译？？？？？
#如果是配置目标要确定先决条件是最新的，并且进入到scripts/kconfig目录执行配置目标，读取体系结构对应的Makefile文件，同时设置KBUILD_DEFCONFIG变量。
KBUILD_DEFCONFIG := sandbox_defconfig
#不知何用，export了的是给后面调用的make使用的
export KBUILD_DEFCONFIG KBUILD_KCONFIG
#config: scripts_basic outputmakefile FORCE
# $(Q)$(MAKE) $(build)=scripts/kconfig $@这两行本来没注释掉，我觉得没用，试试。
#重点来了！！！！！！！！！！！！！！！！！！！！！！！！！！！！！
#make xxx_defconfig 的执行主要分成三个部分：
#执行 make -f ./scripts/Makefile.build obj=scripts/basic，编译生成 scripts/basic/fixdep 工具
#执行 make -f ./scripts/Makefile.build obj=scripts/kconfig rpi_3_32b_defconfig 编译生成 scripts/kconfig/conf 工具
#执行 scripts/kconfig/conf --defconfig=arch/../configs/xxx_defconfig Kconfig生成最终的 .config 配置文件
#参考https://www.cnblogs.com/kele-dad/p/8979447.html
#类似于内核的：“当make %config 时，内核根目录的顶层Makefile会临时编译出scripts/kconfig 中的工具程序conf/mconf/qconf 等负责对arch/$(SRCARCH)/Kconfig 文件进行解析。这个Kconfig 又通过source标记调用各个目录下的Kconfig文件构建出一个Kconfig树，使得工具程序构建出整个内核的配置界面！！！！！！！！！！！！！！！！！！！！！！！！在配置结束后，工具程序就会生成我们常见的.config文件。”
#make ***——defconfig的时候就是匹配的这里：
%config: scripts_basic outputmakefile FORCE #因为有Force所以规则总会执行。outputmakefile 无效。
$(Q)$(MAKE) $(build)=scripts/kconfig $@
#变量 build 是在 scripts/Kbuild.include 文件中有定义，build := -f $(srctree)/scripts/Makefile.build obj
#这命令彻底展开为：@make -f ./scripts/Makefile.build obj=scripts/kconfig xxx_defconfig
#！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！
#此命令最终结果：编译生成 scripts/kconfig/conf 工具
#也跟文件./scripts/Makefile.build 有关
#下文有1610 PHONY += FORCE FORCE: FORCE 是没有规则和依赖的，所以每次都会重新生成 FORCE。当 FORCE 作为其他目标的依赖时，由于 FORCE 总是被更新过的，因此依赖所在的规则总是会执行的。
#上面第一个依赖是这样的：scripts_basic:
# make -f ./scripts/Makefile.build obj=scripts/basic # 根据传入的 obj 参数显示的执行./scripts/Makefile.build 文件。
#命令由于没有指定目标，所以会在 script/Makefile.build 中处理默认目标__build：
#综上，这里会执行两次./scripts/Makefile.build（生成scripts_basic和%config时各调用一次）。但是两次make的目标不同，上面这个是默认，%congfig的那次指定了目标就是xxx_defconfig。看到这里可以进入这个文件分析了。
#
#比如在顶层目录执行make menuconfig，在这里展开就是make -f scripts/Makefile.build obj=scripts/kconfig menuconfig；而scripts/Makefile.build 会包含scripts/kconfig/Makefile，在scripts/kconfig/Makefile中有menuconfig目标如下：
#menuconfig: $(obj)/mconf
#$< $(Kconfig)
#$<表示依赖文件，$(obj)/mconf是一个解析Kconfig的程序，$(Kconfig)是被解析的文件。
#这里删除一千行没用的else的情况了！！！！！！爽！！！！！
#我又把这一千行拿过来了，上面的分析是make ***_defconfig的，用不到下面。而编译make的分析就会用到后面这里else的内容了。
#分析make才需要看下面。否则忽略下面，直接到endif #ifeq ($(config-targets),1)那一行。
else
# ===========================================================================
# Build targets only - this includes vmlinux, arch specific targets, clean
# targets and others. In general all targets except *config targets.
# Additional helpers built in scripts/
# Carefully list dependencies so we do not try to build scripts twice
# in parallel
PHONY += scripts
scripts: scripts_basic include/config/auto.conf
$(Q)$(MAKE) $(build)=$(@)
ifeq ($(dot-config),1)
# Read in config
-include include/config/auto.conf
#通常我们在 Makefile 中可使用“ -include”来代替“ include”，来忽略由于包含文件不存在或者无法创建时的错误提示（“ -”的意思是告诉 make，忽略此操作的错误。make 继续执行）
# Read in dependencies to all Kconfig* files, make sure to run
# oldconfig if changes are detected.
-include include/config/auto.conf.cmd
#读所有Kconfig*文件的依赖关系，如果有任何改变，必须运行make oldconfig
# To avoid any implicit rule to kick in, define an empty command
$(KCONFIG_CONFIG) include/config/auto.conf.cmd: ;
# If .config is newer than include/config/auto.conf, someone tinkered
# with it and forgot to run make oldconfig.
# if auto.conf.cmd is missing then we are probably in a cleaned tree so
# we execute the config step to be sure to catch updated Kconfig files
#如果.config文件比include/config/auto.conf文件更新，那么可能是有人修改了.config文件而忘记运行make oldconfig命令！！！！！！！！如果auto.conf.cmd文件丢失，我们可能处于执行了clean命令的源码树中，因此我们必须执行配置步骤来确保获得更新了的Kconfig文件
include/config/%.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd
$(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig #规则命令产生新的auto.conf文件
@# If the following part fails, include/config/auto.conf should be
@# deleted so "make silentoldconfig" will be re-run on the next build.
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.autoconf || \
{ rm -f include/config/auto.conf; false; }
@# include/config.h has been updated after "make silentoldconfig".
@# We need to touch include/config/auto.conf so it gets newer
@# than include/config.h.
@# Otherwise, 'make silentoldconfig' would be invoked twice.
$(Q)touch include/config/auto.conf
-include include/autoconf.mk
-include include/autoconf.mk.dep
# We want to include arch/$(ARCH)/config.mk only when include/config/auto.conf
# is up-to-date. When we switch to a different board configuration, old CONFIG
# macros are still remaining in include/config/auto.conf. Without the following
# gimmick, wrong config.mk would be included leading nasty warnings/errors.
ifneq ($(wildcard $(KCONFIG_CONFIG)),)
ifneq ($(wildcard include/config/auto.conf),)
autoconf_is_old := $(shell find . -path ./$(KCONFIG_CONFIG) -newer \
include/config/auto.conf)
ifeq ($(autoconf_is_old),)
include config.mk
include arch/$(ARCH)/Makefile
#下文会用到head-y := arch/arm/cpu/armv7/start.o就是在这个makefile中定义的。
endif
endif
endif
# These are set by the arch-specific config.mk. Make sure they are exported
# so they can be used when building an EFI application.
export EFI_LDS # Filename of EFI link script in arch/$(ARCH)/lib
export EFI_CRT0 # Filename of EFI CRT0 in arch/$(ARCH)/lib
export EFI_RELOC # Filename of EFU relocation code in arch/$(ARCH)/lib
export CFLAGS_EFI # Compiler flags to add when building EFI app
export CFLAGS_NON_EFI # Compiler flags to remove when building EFI app
export EFI_TARGET # binutils target if EFI is natively supported
# If board code explicitly specified LDSCRIPT or CONFIG_SYS_LDSCRIPT, use
# that (or fail if absent). Otherwise, search for a linker script in a
# standard location.
ifndef LDSCRIPT
#LDSCRIPT := $(srctree)/board/$(BOARDDIR)/u-boot.lds.debug
ifdef CONFIG_SYS_LDSCRIPT
# need to strip off double quotes
LDSCRIPT := $(srctree)/$(CONFIG_SYS_LDSCRIPT:"%"=%)
endif
endif
# If there is no specified link script, we look in a number of places for it
ifndef LDSCRIPT
ifeq ($(wildcard $(LDSCRIPT)),)
LDSCRIPT := $(srctree)/board/$(BOARDDIR)/u-boot.lds
endif
ifeq ($(wildcard $(LDSCRIPT)),)
LDSCRIPT := $(srctree)/$(CPUDIR)/u-boot.lds
endif
ifeq ($(wildcard $(LDSCRIPT)),)
LDSCRIPT := $(srctree)/arch/$(ARCH)/cpu/u-boot.lds
endif
endif
else
# Dummy target needed, because used as prerequisite
include/config/auto.conf: ;
endif # $(dot-config)
#
# Xtensa linker script cannot be preprocessed with -ansi because of
# preprocessor operations on strings that don't make C identifiers.
#
ifeq ($(CONFIG_XTENSA),)
LDPPFLAGS += -ansi
endif
ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
KBUILD_CFLAGS += -Os
else
KBUILD_CFLAGS += -O2
endif
KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks)
KBUILD_CFLAGS += -g
# $(KBUILD_AFLAGS) sets -g, which causes gcc to pass a suitable -g<format>
# option to the assembler.
KBUILD_AFLAGS += -g
# Report stack usage if supported
ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-stack-usage.sh $(CC)),y)
KBUILD_CFLAGS += -fstack-usage
endif
KBUILD_CFLAGS += $(call cc-option,-Wno-format-nonliteral)
# turn jbsr into jsr for m68k
ifeq ($(ARCH),m68k)
ifeq ($(findstring 3.4,$(shell $(CC) --version)),3.4)
KBUILD_AFLAGS += -Wa,-gstabs,-S
endif
endif
# Prohibit date/time macros, which would make the build non-deterministic
KBUILD_CFLAGS += $(call cc-option,-Werror=date-time)
include scripts/Makefile.extrawarn
# Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments
KBUILD_CPPFLAGS += $(KCPPFLAGS)
KBUILD_AFLAGS += $(KAFLAGS)
KBUILD_CFLAGS += $(KCFLAGS)
# Use UBOOTINCLUDE when you must reference the include/ directory.
# Needed to be compatible with the O= option
UBOOTINCLUDE := \
-Iinclude \
$(if $(KBUILD_SRC), -I$(srctree)/include) \
$(if $(CONFIG_SYS_THUMB_BUILD), $(if $(CONFIG_HAS_THUMB2),, \
-I$(srctree)/arch/$(ARCH)/thumb1/include),) \
-I$(srctree)/arch/$(ARCH)/include \
-include $(srctree)/include/linux/kconfig.h \
-I$(srctree)
NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
CHECKFLAGS += $(NOSTDINC_FLAGS)
# FIX ME
cpp_flags := $(KBUILD_CPPFLAGS) $(PLATFORM_CPPFLAGS) $(UBOOTINCLUDE) \
$(NOSTDINC_FLAGS)
c_flags := $(KBUILD_CFLAGS) $(cpp_flags)
#########################################################################
# U-Boot objects....order is important (i.e. start must be first)
HAVE_VENDOR_COMMON_LIB = $(if $(wildcard $(srctree)/board/$(VENDOR)/common/Makefile),y,n)
#以下一串就是各个子目录，构成libs-y这个变量，后文会有，每个子目录最终编译成一个built-in.o，按照连接脚本共同编译成u-boot这个目标（文件），然后再根据这个生成u-boot-nodtb.bin，再生成u-boot.bin。
libs-y += lib/
libs-$(HAVE_VENDOR_COMMON_LIB) += board/$(VENDOR)/common/
libs-$(CONFIG_OF_EMBED) += dts/
libs-y += fs/
libs-y += net/
libs-y += disk/
libs-y += drivers/
libs-y += drivers/dma/
libs-y += drivers/gpio/
libs-y += drivers/i2c/
libs-y += drivers/mmc/
libs-y += drivers/mtd/
libs-$(CONFIG_CMD_NAND) += drivers/mtd/nand/
libs-y += drivers/mtd/onenand/
libs-$(CONFIG_CMD_UBI) += drivers/mtd/ubi/
libs-y += drivers/mtd/spi/
libs-y += drivers/net/
libs-y += drivers/net/phy/
libs-y += drivers/pci/
libs-y += drivers/power/ \
drivers/power/domain/ \
drivers/power/fuel_gauge/ \
drivers/power/mfd/ \
drivers/power/pmic/ \
drivers/power/battery/ \
drivers/power/regulator/
libs-y += drivers/spi/
libs-$(CONFIG_FMAN_ENET) += drivers/net/fm/
libs-$(CONFIG_SYS_FSL_DDR) += drivers/ddr/fsl/
libs-$(CONFIG_SYS_FSL_MMDC) += drivers/ddr/fsl/
libs-$(CONFIG_ALTERA_SDRAM) += drivers/ddr/altera/
libs-y += drivers/serial/
libs-y += drivers/usb/cdns3/
libs-y += drivers/usb/dwc3/
libs-y += drivers/usb/common/
libs-y += drivers/usb/emul/
libs-y += drivers/usb/eth/
libs-y += drivers/usb/gadget/
libs-y += drivers/usb/gadget/udc/
libs-y += drivers/usb/host/
libs-y += drivers/usb/musb/
libs-y += drivers/usb/musb-new/
libs-y += drivers/usb/phy/
libs-y += drivers/usb/ulpi/
libs-y += cmd/
libs-y += common/
libs-$(CONFIG_API) += api/
libs-$(CONFIG_HAS_POST) += post/
libs-y += test/
libs-y += test/dm/
libs-$(CONFIG_UT_ENV) += test/env/
libs-$(CONFIG_UT_OVERLAY) += test/overlay/
libs-y += $(if $(BOARDDIR),board/$(BOARDDIR)/)
libs-y := $(sort $(libs-y))
u-boot-dirs := $(patsubst %/,%,$(filter %/, $(libs-y))) tools examples
u-boot-alldirs := $(sort $(u-boot-dirs) $(patsubst %/,%,$(filter %/, $(libs-))))
libs-y := $(patsubst %/, %/built-in.o, $(libs-y))
u-boot-init := $(head-y)
#head-y 在 arch/arm/Makefile 中被指定为：head-y := arch/arm/cpu/$(CPU)/start.o
#CPU=armv7，留问，哪里被包含，哪里定义。
#u-boot-init= arch/arm/cpu/armv7/start.o
u-boot-main := $(libs-y)
#$(libs-y)在顶层 Makefile 中被定义为 uboot 所有子目录下 build-in.o 的集合
#有个重点就是各子目录下的 built-in.o 是怎么生成的，以 drivers/gpio/built-in.o 为例，
#在drivers/gpio/目录下会有个名为.built-in.o.cmd 的文件
#此文件内容如下：cmd_drivers/gpio/built-in.o := arm-linux-gnueabihf-ld.bfd -r -o drivers/gpio/built-in.o drivers/gpio/mxc_gpio.o
#
# Add GCC lib
ifeq ($(CONFIG_USE_PRIVATE_LIBGCC),y)
PLATFORM_LIBGCC = arch/$(ARCH)/lib/lib.a
else
PLATFORM_LIBGCC := -L $(shell dirname `$(CC) $(c_flags) -print-libgcc-file-name`) -lgcc
endif
PLATFORM_LIBS += $(PLATFORM_LIBGCC)
export PLATFORM_LIBS
export PLATFORM_LIBGCC
# Special flags for CPP when processing the linker script.
# Pass the version down so we can handle backwards compatibility
# on the fly.
LDPPFLAGS += \
-include $(srctree)/include/u-boot/u-boot.lds.h \
-DCPUDIR=$(CPUDIR) \
$(shell $(LD) --version | \
sed -ne 's/GNU ld version \([0-9][0-9]*\)\.\([0-9][0-9]*\).*/-DLD_MAJOR=\1 -DLD_MINOR=\2/p')
#########################################################################
#########################################################################
ifneq ($(CONFIG_BOARD_SIZE_LIMIT),)
BOARD_SIZE_CHECK = \
@actual=`wc -c $@ | awk '{print $$1}'`; \
limit=`printf "%d" $(CONFIG_BOARD_SIZE_LIMIT)`; \
if test $$actual -gt $$limit; then \
echo "$@ exceeds file size limit:" >&2 ; \
echo " limit: $$limit bytes" >&2 ; \
echo " actual: $$actual bytes" >&2 ; \
echo " excess: $$((actual - limit)) bytes" >&2; \
exit 1; \
fi
else
BOARD_SIZE_CHECK =
endif
# Statically apply RELA-style relocations (currently arm64 only)
ifneq ($(CONFIG_STATIC_RELA),)
# $(1) is u-boot ELF, $(2) is u-boot bin, $(3) is text base
DO_STATIC_RELA = \
start=$$($(NM) $(1) | grep __rel_dyn_start | cut -f 1 -d ' '); \
end=$$($(NM) $(1) | grep __rel_dyn_end | cut -f 1 -d ' '); \
tools/relocate-rela $(2) $(3) $$start $$end
else
DO_STATIC_RELA =
endif
# Always append ALL so that arch config.mk's can add custom ones
ALL-y += u-boot.srec u-boot.bin u-boot.sym System.map binary_size_check
ALL-$(CONFIG_ONENAND_U_BOOT) += u-boot-onenand.bin
#如果我们使能了ONENAND，那么在.config 配置文件中就会有“CONFIG_ONENAND_U_BOOT=y”这一句。相当于 CONFIG_ONENAND_U_BOOT 是个变量，这个变量的值为“y”，所以展开以后就是：ALL-y += u-boot-onenand.bin。这个就是.config 里面的配置参数的含义，这些参数其实都是变量，后面跟着变量值，会在顶层 Makefile 或者其他 Makefile 中调用这些变量。
ifeq ($(CONFIG_SPL_FSL_PBL),y)
ALL-$(CONFIG_RAMBOOT_PBL) += u-boot-with-spl-pbl.bin
else
ifneq ($(CONFIG_SECURE_BOOT), y)
# For Secure Boot The Image needs to be signed and Header must also
# be included. So The image has to be built explicitly
ALL-$(CONFIG_RAMBOOT_PBL) += u-boot.pbl
endif
endif
ALL-$(CONFIG_SPL) += spl/u-boot-spl.bin
ifeq ($(CONFIG_MX6)$(CONFIG_SECURE_BOOT), yy)
ALL-$(CONFIG_SPL_FRAMEWORK) += u-boot-ivt.img
else
ALL-$(CONFIG_SPL_FRAMEWORK) += u-boot.img
endif
ALL-$(CONFIG_TPL) += tpl/u-boot-tpl.bin
ALL-$(CONFIG_OF_SEPARATE) += u-boot.dtb
ifeq ($(CONFIG_SPL_FRAMEWORK),y)
ALL-$(CONFIG_OF_SEPARATE) += u-boot-dtb.img
endif
ALL-$(CONFIG_OF_HOSTFILE) += u-boot.dtb
ifneq ($(CONFIG_SPL_TARGET),)
ALL-$(CONFIG_SPL) += $(CONFIG_SPL_TARGET:"%"=%)
endif
ALL-$(CONFIG_REMAKE_ELF) += u-boot.elf
ALL-$(CONFIG_EFI_APP) += u-boot-app.efi
ALL-$(CONFIG_EFI_STUB) += u-boot-payload.efi
ifneq ($(BUILD_ROM),)
ALL-$(CONFIG_X86_RESET_VECTOR) += u-boot.rom
endif
# enable combined SPL/u-boot/dtb rules for tegra
ifeq ($(CONFIG_TEGRA)$(CONFIG_SPL),yy)
ALL-y += u-boot-tegra.bin u-boot-nodtb-tegra.bin
ALL-$(CONFIG_OF_SEPARATE) += u-boot-dtb-tegra.bin
endif
# Add optional build target if defined in board/cpu/soc headers
ifneq ($(CONFIG_BUILD_TARGET),)
ALL-y += $(CONFIG_BUILD_TARGET:"%"=%)
endif
LDFLAGS_u-boot += $(LDFLAGS_FINAL)
ifneq ($(CONFIG_SYS_TEXT_BASE),)
LDFLAGS_u-boot += -Ttext $(CONFIG_SYS_TEXT_BASE)
endif
# Normally we fill empty space with 0xff
quiet_cmd_objcopy = OBJCOPY $@
cmd_objcopy = $(OBJCOPY) --gap-fill=0xff $(OBJCOPYFLAGS) \
$(OBJCOPYFLAGS_$(@F)) $< $@
#类似，sym 命令分为“quiet_cmd_sym”和“cmd_sym”两个版本，这两个命令的功能都是一样的，
#区别在于 make 执行的时候输出的命令不同。quiet_cmd_xxx 命令输出信息少，也就是短命令，
#而 cmd_xxx 命令输出信息多，也就是完整的命令。
# Provide a version which does not do this, for use by EFI
quiet_cmd_zobjcopy = OBJCOPY $@
cmd_zobjcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
quiet_cmd_efipayload = OBJCOPY $@
cmd_efipayload = $(OBJCOPY) -I binary -O $(EFIPAYLOAD_BFDTARGET) -B $(EFIPAYLOAD_BFDARCH) $< $@
MKIMAGEOUTPUT ?= /dev/null
quiet_cmd_mkimage = MKIMAGE $@
cmd_mkimage = $(objtree)/tools/mkimage $(MKIMAGEFLAGS_$(@F)) -d $< $@ \
$(if $(KBUILD_VERBOSE:1=), >$(MKIMAGEOUTPUT))
##$(KBUILD_VERBOSE:1=)是变量的替换引用，表示将KBUILD_VERBOSE中的1替换为空后的值作为if函数的条件判断
quiet_cmd_mkfitimage = MKIMAGE $@
cmd_mkfitimage = $(objtree)/tools/mkimage $(MKIMAGEFLAGS_$(@F)) -f $(U_BOOT_ITS) -E $@ \
$(if $(KBUILD_VERBOSE:1=), >$(MKIMAGEOUTPUT))
quiet_cmd_cat = CAT $@
cmd_cat = cat $(filter-out $(PHONY), $^) > $@
append = cat $(filter-out $< $(PHONY), $^) >> $@
quiet_cmd_pad_cat = CAT $@
cmd_pad_cat = $(cmd_objcopy) && $(append) || rm -f $@
cfg: u-boot.cfg
quiet_cmd_cfgcheck = CFGCHK $2
cmd_cfgcheck = $(srctree)/scripts/check-config.sh $2 \
$(srctree)/scripts/config_whitelist.txt $(srctree)
##！！！！！！！！！！！这是就是make编译时的重点了！！！！！
#上面主要是make config时的重点。
all: $(ALL-y)
#ALL-y 包含 u-boot.srec、u-boot.bin、u-boot.sym、System.map、u-boot.cfg 和 binary_size_check 这几个文件。。根据 uboot 的配置情况也可能包含其他的文件，比如：ALL-$(CONFIG_ONENAND_U_BOOT) += u-boot-onenand.bin
#我们主要分析u-boot.bin！！！！！！！这个就是我们最终需要的 uboot 二进制可执行文件，所作的所有工作就是为了它
ifeq ($(CONFIG_DM_I2C_COMPAT)$(CONFIG_SANDBOX),y)
@echo "===================== WARNING ======================"
@echo "This board uses CONFIG_DM_I2C_COMPAT. Please remove"
@echo "(possibly in a subsequent patch in your series)"
@echo "before sending patches to the mailing list."
@echo "===================================================="
endif
@# Check that this build does not use CONFIG options that we do not
@# know about unless they are in Kconfig. All the existing CONFIG
@# options are whitelisted, so new ones should not be added.
$(call cmd,cfgcheck,u-boot.cfg)
PHONY += dtbs
dtbs: dts/dt.dtb
@:
dts/dt.dtb: checkdtc u-boot
$(Q)$(MAKE) $(build)=dts dtbs
quiet_cmd_copy = COPY $@
cmd_copy = cp $< $@
ifeq ($(CONFIG_OF_SEPARATE),y)
#在.config 中搜索“CONFIG_OF_SEPARAT”，没有找到，说明条件不成立。
#留问:.config什么时候包含的？
u-boot-dtb.bin: u-boot-nodtb.bin dts/dt.dtb FORCE
$(call if_changed,cat)
u-boot.bin: u-boot-dtb.bin FORCE
$(call if_changed,copy)
else
#这里就是重点，我们make时直接最终想要得到的就是u-boot.bin。
u-boot.bin: u-boot-nodtb.bin FORCE
$(call if_changed,copy)
#call函数，调用自定义的函数if_changed并把后面的当成参数传入。
#if_changed 在 Kbuild.include 中的定义
#，if_changed 函数引用的变量比较多，也比较绕，我们只需要知道它可以从 u-boot-nodtb.bin 生成 u-boot.bin 就行了。然后就关注一下u-boot-nodtb.bin吧。
endif
%.imx: %.bin
$(Q)$(MAKE) $(build)=arch/arm/imx-common $@
%.vyb: %.imx
$(Q)$(MAKE) $(build)=arch/arm/cpu/armv7/vf610 $@
quiet_cmd_copy = COPY $@
cmd_copy = cp $< $@
u-boot.dtb: dts/dt.dtb
$(call cmd,copy)
OBJCOPYFLAGS_u-boot.hex := -O ihex
OBJCOPYFLAGS_u-boot.srec := -O srec
u-boot.hex u-boot.srec: u-boot FORCE
$(call if_changed,objcopy)
OBJCOPYFLAGS_u-boot-nodtb.bin := -O binary \
$(if $(CONFIG_X86_16BIT_INIT),-R .start16 -R .resetvec)
binary_size_check: u-boot-nodtb.bin FORCE
@file_size=$(shell wc -c u-boot-nodtb.bin | awk '{print $$1}') ; \
map_size=$(shell cat u-boot.map | \
awk '/_image_copy_start/ {start = $$1} /_image_binary_end/ {end = $$1} END {if (start != "" && end != "") print "ibase=16; " toupper(end) " - " toupper(start)}' \
| sed 's/0X//g' \
| bc); \
if [ "" != "$$map_size" ]; then \
if test $$map_size -ne $$file_size; then \
echo "u-boot.map shows a binary size of $$map_size" >&2 ; \
echo " but u-boot-nodtb.bin shows $$file_size" >&2 ; \
exit 1; \
fi \
fi
#还是会执行到这里
u-boot-nodtb.bin: u-boot FORCE
$(call if_changed,objcopy)
$(call DO_STATIC_RELA,$<,$@,$(CONFIG_SYS_TEXT_BASE))
$(BOARD_SIZE_CHECK)
u-boot.ldr: u-boot
$(CREATE_LDR_ENV)
$(LDR) -T $(CONFIG_CPU) -c $@ $< $(LDR_FLAGS)
$(BOARD_SIZE_CHECK)
# binman
# ---------------------------------------------------------------------------
quiet_cmd_binman = BINMAN $@
cmd_binman = $(srctree)/tools/binman/binman -d u-boot.dtb -O . \
-I . -I $(srctree)/board/$(BOARDDIR) $<
OBJCOPYFLAGS_u-boot.ldr.hex := -I binary -O ihex
OBJCOPYFLAGS_u-boot.ldr.srec := -I binary -O srec
u-boot.ldr.hex u-boot.ldr.srec: u-boot.ldr FORCE
$(call if_changed,objcopy)
#
# U-Boot entry point, needed for booting of full-blown U-Boot
# from the SPL U-Boot version.
#
ifndef CONFIG_SYS_UBOOT_START
CONFIG_SYS_UBOOT_START := 0
endif
# Create a file containing the configuration options the image was built with
quiet_cmd_cpp_cfg = CFG $@
cmd_cpp_cfg = $(CPP) -Wp,-MD,$(depfile) $(cpp_flags) $(LDPPFLAGS) -ansi \
-DDO_DEPS_ONLY -D__ASSEMBLY__ -x assembler-with-cpp -P -dM -E -o $@ $<
# Boards with more complex image requirments can provide an .its source file
# or a generator script
ifneq ($(CONFIG_SPL_FIT_SOURCE),"")
U_BOOT_ITS = $(subst ",,$(CONFIG_SPL_FIT_SOURCE))
else
ifneq ($(CONFIG_SPL_FIT_GENERATOR),"")
U_BOOT_ITS := u-boot.its
$(U_BOOT_ITS): FORCE
$(srctree)/$(CONFIG_SPL_FIT_GENERATOR) \
$(patsubst %,arch/$(ARCH)/dts/%.dtb,$(subst ",,$(CONFIG_OF_LIST))) > $@
endif
endif
ifdef CONFIG_SPL_LOAD_FIT
MKIMAGEFLAGS_u-boot.img = -f auto -A $(ARCH) -T firmware -C none -O u-boot \
-a $(CONFIG_SYS_TEXT_BASE) -e $(CONFIG_SYS_UBOOT_START) \
-n "U-Boot $(UBOOTRELEASE) for $(BOARD) board" -E \
$(patsubst %,-b arch/$(ARCH)/dts/%.dtb,$(subst ",,$(CONFIG_OF_LIST)))
else
ifdef CONFIG_ARCH_IMX8M
MKIMAGEFLAGS_u-boot.img = -A $(ARCH) -T firmware -C none -O u-boot \
-a 0x40001000 -e 0x40001000 \
-n "U-Boot $(UBOOTRELEASE) for $(BOARD) board"
else
MKIMAGEFLAGS_u-boot.img = -A $(ARCH) -T firmware -C none -O u-boot \
-a $(CONFIG_SYS_TEXT_BASE) -e $(CONFIG_SYS_UBOOT_START) \
-n "U-Boot $(UBOOTRELEASE) for $(BOARD) board"
MKIMAGEFLAGS_u-boot-ivt.img = -A $(ARCH) -T firmware_ivt -C none -O u-boot \
-a $(CONFIG_SYS_TEXT_BASE) -e $(CONFIG_SYS_UBOOT_START) \
-n "U-Boot $(UBOOTRELEASE) for $(BOARD) board"
u-boot-ivt.img: MKIMAGEOUTPUT = u-boot-ivt.img.log
CLEAN_FILES += u-boot-ivt.img.log u-boot-dtb.imx.log SPL.log u-boot.imx.log
endif
endif
MKIMAGEFLAGS_u-boot-dtb.img = $(MKIMAGEFLAGS_u-boot.img)
MKIMAGEFLAGS_u-boot.kwb = -n $(srctree)/$(CONFIG_SYS_KWD_CONFIG:"%"=%) \
-T kwbimage -a $(CONFIG_SYS_TEXT_BASE) -e $(CONFIG_SYS_TEXT_BASE)
MKIMAGEFLAGS_u-boot-spl.kwb = -n $(srctree)/$(CONFIG_SYS_KWD_CONFIG:"%"=%) \
-T kwbimage -a $(CONFIG_SYS_TEXT_BASE) -e $(CONFIG_SYS_TEXT_BASE) \
$(if $(KEYDIR),-k $(KEYDIR))
MKIMAGEFLAGS_u-boot.pbl = -n $(srctree)/$(CONFIG_SYS_FSL_PBL_RCW:"%"=%) \
-R $(srctree)/$(CONFIG_SYS_FSL_PBL_PBI:"%"=%) -T pblimage
u-boot-dtb.img u-boot.img u-boot.kwb u-boot.pbl u-boot-ivt.img: \
$(if $(CONFIG_SPL_LOAD_FIT),u-boot-nodtb.bin dts/dt.dtb,u-boot.bin) FORCE
$(call if_changed,mkimage)
u-boot.itb: u-boot-nodtb.bin dts/dt.dtb $(U_BOOT_ITS) FORCE
$(call if_changed,mkfitimage)
u-boot-spl.kwb: u-boot.img spl/u-boot-spl.bin FORCE
$(call if_changed,mkimage)
u-boot.sha1: u-boot.bin
tools/ubsha1 u-boot.bin
u-boot.dis: u-boot
$(OBJDUMP) -d $< > $@
ifdef CONFIG_TPL
SPL_PAYLOAD := tpl/u-boot-with-tpl.bin
else
SPL_PAYLOAD := u-boot.bin
endif
OBJCOPYFLAGS_u-boot-with-spl.bin = -I binary -O binary \
--pad-to=$(CONFIG_SPL_PAD_TO)
u-boot-with-spl.bin: spl/u-boot-spl.bin $(SPL_PAYLOAD) FORCE
$(call if_changed,pad_cat)
MKIMAGEFLAGS_lpc32xx-spl.img = -T lpc32xximage -a $(CONFIG_SPL_TEXT_BASE)
lpc32xx-spl.img: spl/u-boot-spl.bin FORCE
$(call if_changed,mkimage)
OBJCOPYFLAGS_lpc32xx-boot-0.bin = -I binary -O binary --pad-to=$(CONFIG_SPL_PAD_TO)
lpc32xx-boot-0.bin: lpc32xx-spl.img FORCE
$(call if_changed,objcopy)
OBJCOPYFLAGS_lpc32xx-boot-1.bin = -I binary -O binary --pad-to=$(CONFIG_SPL_PAD_TO)
lpc32xx-boot-1.bin: lpc32xx-spl.img FORCE
$(call if_changed,objcopy)
lpc32xx-full.bin: lpc32xx-boot-0.bin lpc32xx-boot-1.bin u-boot.img FORCE
$(call if_changed,cat)
CLEAN_FILES += lpc32xx-*
OBJCOPYFLAGS_u-boot-with-tpl.bin = -I binary -O binary \
--pad-to=$(CONFIG_TPL_PAD_TO)
tpl/u-boot-with-tpl.bin: tpl/u-boot-tpl.bin u-boot.bin FORCE
$(call if_changed,pad_cat)
SPL: spl/u-boot-spl.bin FORCE
$(Q)$(MAKE) $(build)=arch/arm/imx-common $@
u-boot-with-spl.imx u-boot-with-nand-spl.imx: SPL u-boot.bin FORCE
$(Q)$(MAKE) $(build)=arch/arm/imx-common $@
MKIMAGEFLAGS_u-boot.ubl = -n $(UBL_CONFIG) -T ublimage -e $(CONFIG_SYS_TEXT_BASE)
u-boot.ubl: u-boot-with-spl.bin FORCE
$(call if_changed,mkimage)
MKIMAGEFLAGS_u-boot-spl.ais = -s -n $(if $(CONFIG_AIS_CONFIG_FILE), \
$(srctree)/$(CONFIG_AIS_CONFIG_FILE:"%"=%),"/dev/null") \
-T aisimage -e $(CONFIG_SPL_TEXT_BASE)
spl/u-boot-spl.ais: spl/u-boot-spl.bin FORCE
$(call if_changed,mkimage)
OBJCOPYFLAGS_u-boot.ais = -I binary -O binary --pad-to=$(CONFIG_SPL_PAD_TO)
u-boot.ais: spl/u-boot-spl.ais u-boot.img FORCE
$(call if_changed,pad_cat)
u-boot-signed.sb: u-boot.bin spl/u-boot-spl.bin
$(Q)$(MAKE) $(build)=arch/arm/cpu/arm926ejs/mxs u-boot-signed.sb
u-boot.sb: u-boot.bin spl/u-boot-spl.bin
$(Q)$(MAKE) $(build)=arch/arm/cpu/arm926ejs/mxs u-boot.sb
# On x600 (SPEAr600) U-Boot is appended to U-Boot SPL.
# Both images are created using mkimage (crc etc), so that the ROM
# bootloader can check its integrity. Padding needs to be done to the
# SPL image (with mkimage header) and not the binary. Otherwise the resulting image
# which is loaded/copied by the ROM bootloader to SRAM doesn't fit.
# The resulting image containing both U-Boot images is called u-boot.spr
MKIMAGEFLAGS_u-boot-spl.img = -A $(ARCH) -T firmware -C none \
-a $(CONFIG_SPL_TEXT_BASE) -e $(CONFIG_SPL_TEXT_BASE) -n XLOADER
spl/u-boot-spl.img: spl/u-boot-spl.bin FORCE
$(call if_changed,mkimage)
OBJCOPYFLAGS_u-boot.spr = -I binary -O binary --pad-to=$(CONFIG_SPL_PAD_TO) \
--gap-fill=0xff
u-boot.spr: spl/u-boot-spl.img u-boot.img FORCE
$(call if_changed,pad_cat)
ifneq ($(CONFIG_ARCH_SOCFPGA),)
quiet_cmd_socboot = SOCBOOT $@
cmd_socboot = cat spl/u-boot-spl.sfp spl/u-boot-spl.sfp \
spl/u-boot-spl.sfp spl/u-boot-spl.sfp \
u-boot.img > $@ || rm -f $@
u-boot-with-spl.sfp: spl/u-boot-spl.sfp u-boot.img FORCE
$(call if_changed,socboot)
endif
# x86 uses a large ROM. We fill it with 0xff, put the 16-bit stuff (including
# reset vector) at the top, Intel ME descriptor at the bottom, and U-Boot in
# the middle. This is handled by binman based on an image description in the
# board's device tree.
ifneq ($(CONFIG_X86_RESET_VECTOR),)
rom: u-boot.rom FORCE
refcode.bin: $(srctree)/board/$(BOARDDIR)/refcode.bin FORCE
$(call if_changed,copy)
quiet_cmd_ldr = LD $@
cmd_ldr = $(LD) $(LDFLAGS_$(@F)) \
$(filter-out FORCE,$^) -o $@
u-boot.rom: u-boot-x86-16bit.bin u-boot.bin \
$(if $(CONFIG_SPL_X86_16BIT_INIT),spl/u-boot-spl.bin) \
$(if $(CONFIG_HAVE_REFCODE),refcode.bin) FORCE
$(call if_changed,binman)
OBJCOPYFLAGS_u-boot-x86-16bit.bin := -O binary -j .start16 -j .resetvec
u-boot-x86-16bit.bin: u-boot FORCE
$(call if_changed,objcopy)
endif
ifneq ($(CONFIG_ARCH_SUNXI),)
u-boot-sunxi-with-spl.bin: spl/sunxi-spl.bin u-boot.img u-boot.dtb FORCE
$(call if_changed,binman)
endif
ifneq ($(CONFIG_TEGRA),)
OBJCOPYFLAGS_u-boot-nodtb-tegra.bin = -O binary --pad-to=$(CONFIG_SYS_TEXT_BASE)
u-boot-nodtb-tegra.bin: spl/u-boot-spl u-boot-nodtb.bin FORCE
$(call if_changed,pad_cat)
OBJCOPYFLAGS_u-boot-tegra.bin = -O binary --pad-to=$(CONFIG_SYS_TEXT_BASE)
u-boot-tegra.bin: spl/u-boot-spl u-boot.bin FORCE
$(call if_changed,pad_cat)
u-boot-dtb-tegra.bin: u-boot-tegra.bin FORCE
$(call if_changed,copy)
endif
OBJCOPYFLAGS_u-boot-app.efi := $(OBJCOPYFLAGS_EFI)
u-boot-app.efi: u-boot FORCE
$(call if_changed,zobjcopy)
u-boot.bin.o: u-boot.bin FORCE
$(call if_changed,efipayload)
u-boot-payload.lds: $(LDSCRIPT_EFI) FORCE
$(call if_changed_dep,cpp_lds)
# Rule to link the EFI payload which contains a stub and a U-Boot binary
quiet_cmd_u-boot_payload ?= LD $@
cmd_u-boot_payload ?= $(LD) $(LDFLAGS_EFI_PAYLOAD) -o $@ \
-T u-boot-payload.lds arch/x86/cpu/call32.o \
lib/efi/efi.o lib/efi/efi_stub.o u-boot.bin.o \
$(addprefix arch/$(ARCH)/lib/,$(EFISTUB))
u-boot-payload: u-boot.bin.o u-boot-payload.lds FORCE
$(call if_changed,u-boot_payload)
OBJCOPYFLAGS_u-boot-payload.efi := $(OBJCOPYFLAGS_EFI)
u-boot-payload.efi: u-boot-payload FORCE
$(call if_changed,zobjcopy)
u-boot-img.bin: spl/u-boot-spl.bin u-boot.img FORCE
$(call if_changed,cat)
#Add a target to create boot binary having SPL binary in PBI format
#concatenated with u-boot binary. It is need by PowerPC SoC having
#internal SRAM <= 512KB.
MKIMAGEFLAGS_u-boot-spl.pbl = -n $(srctree)/$(CONFIG_SYS_FSL_PBL_RCW:"%"=%) \
-R $(srctree)/$(CONFIG_SYS_FSL_PBL_PBI:"%"=%) -T pblimage \
-A $(ARCH) -a $(CONFIG_SPL_TEXT_BASE)
spl/u-boot-spl.pbl: spl/u-boot-spl.bin FORCE
$(call if_changed,mkimage)
ifeq ($(ARCH),arm)
UBOOT_BINLOAD := u-boot.img
else
UBOOT_BINLOAD := u-boot.bin
endif
OBJCOPYFLAGS_u-boot-with-spl-pbl.bin = -I binary -O binary --pad-to=$(CONFIG_SPL_PAD_TO) \
--gap-fill=0xff
u-boot-with-spl-pbl.bin: spl/u-boot-spl.pbl $(UBOOT_BINLOAD) FORCE
$(call if_changed,pad_cat)
# PPC4xx needs the SPL at the end of the image, since the reset vector
# is located at 0xfffffffc. So we can't use the "u-boot-img.bin" target
# and need to introduce a new build target with the full blown U-Boot
# at the start padded up to the start of the SPL image. And then concat
# the SPL image to the end.
OBJCOPYFLAGS_u-boot-img-spl-at-end.bin := -I binary -O binary \
--pad-to=$(CONFIG_UBOOT_PAD_TO) --gap-fill=0xff
u-boot-img-spl-at-end.bin: u-boot.img spl/u-boot-spl.bin FORCE
$(call if_changed,pad_cat)
# Create a new ELF from a raw binary file. This is useful for arm64
# where static relocation needs to be performed on the raw binary,
# but certain simulators only accept an ELF file (but don't do the
# relocation).
# FIXME refactor dts/Makefile to share target/arch detection
u-boot.elf: u-boot.bin
@$(OBJCOPY) -B aarch64 -I binary -O elf64-littleaarch64 \
$< u-boot-elf.o
@$(LD) u-boot-elf.o -o $@ \
--defsym=_start=$(CONFIG_SYS_TEXT_BASE) \
-Ttext=$(CONFIG_SYS_TEXT_BASE)
# Rule to link u-boot
# May be overridden by arch/$(ARCH)/config.mk
quiet_cmd_u-boot__ ?= LD $@
cmd_u-boot__ ?= $(LD) $(LDFLAGS) $(LDFLAGS_u-boot) -o $@ \
-T u-boot.lds $(u-boot-init) \
--start-group $(u-boot-main) --end-group \
$(PLATFORM_LIBS) -Map u-boot.map
quiet_cmd_smap = GEN common/system_map.o
cmd_smap = \
smap=`$(call SYSTEM_MAP,u-boot) | \
awk '$$2 ~ /[tTwW]/ {printf $$1 $$3 "\\\\000"}'` ; \
$(CC) $(c_flags) -DSYSTEM_MAP="\"$${smap}\"" \
-c $(srctree)/common/system_map.c -o common/system_map.o
#要想生成uboot.bin ,定会执行到这里。
u-boot: $(u-boot-init) $(u-boot-main) u-boot.lds FORCE #这俩变量前文有定义
$(call if_changed,u-boot__)
#u-boot-init= arch/arm/cpu/armv7/start.o
#u-boot-main := $(libs-y)，$(libs-y)在顶层 Makefile 中被定义为 uboot 所有子目录下 build-in.o 的集合。
#这个规则就相当于将以 u-boot.lds 为链接脚本，将 arch/arm/cpu/armv7/start.o （u-boot-init）和各个子目录下的 built-in.o （u-boot-main）链接在一起生成 u-boot。
ifeq ($(CONFIG_KALLSYMS),y)
$(call cmd,smap)
$(call cmd,u-boot__) common/system_map.o
endif
quiet_cmd_sym ?= SYM $@
cmd_sym ?= $(OBJDUMP) -t $< > $@
u-boot.sym: u-boot FORCE
$(call if_changed,sym)
# The actual objects are generated when descending,
# make sure no implicit rule kicks in
$(sort $(u-boot-init) $(u-boot-main)): $(u-boot-dirs) ;
# Handle descending into subdirectories listed in $(vmlinux-dirs)
# Preset locale variables to speed up the build process. Limit locale
# tweaks to this spot to avoid wrong language settings when running
# make menuconfig etc.
# Error messages still appears in the original language
PHONY += $(u-boot-dirs)
$(u-boot-dirs): prepare scripts
$(Q)$(MAKE) $(build)=$@
#这一步完成了uboot编译的主要工作：
#这个命令，引入各个目录下的Kbuild或Makefile，依据Makefile.build中定义的规则构建目标
#如果定义了obj-y，依据Makefile.build中的规则构建各个.o文件，并最终链接成build-in.o文件
#下面以构建arch/arm/cpu/armv8为例，简单说明：
#arch/arm/cpu/armv8 : prepare scripts
# $(Q)$(MAKE) $(build)=$@
#执行make -f scripts/basic/Makefile.build obj=arch/arm/cpu/armv8
#在Makefile.build中，include arch/arm/cpu/armv8/Makefile:
#未完省略，参考于下面博客4.5部分
#https://blog.csdn.net/weixin_41469511/article/details/78856047
#最终结果就是将编译出来的.o文件使用cmd_link_o_target链接成arch/arm/cpu/armv8/build-in.o。
#主要工作还是在scripts/basic/Makefile.build中完成的。
tools: prepare
# The "tools" are needed early
$(filter-out tools, $(u-boot-dirs)): tools
# The "examples" conditionally depend on U-Boot (say, when USE_PRIVATE_LIBGCC
# is "yes"), so compile examples after U-Boot is compiled.
examples: $(filter-out examples, $(u-boot-dirs))
define filechk_uboot.release
echo "$(UBOOTVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))"
endef
# Store (new) UBOOTRELEASE string in include/config/uboot.release
include/config/uboot.release: include/config/auto.conf FORCE
$(call filechk,uboot.release)
# Things we need to do before we recursively start building the kernel
# or the modules are listed in "prepare".
# A multi level approach is used. prepareN is processed before prepareN-1.
# archprepare is used in arch Makefiles and when processed asm symlink,
# version.h and scripts_basic is processed / created.
# Listed in dependency order
PHONY += prepare archprepare prepare0 prepare1 prepare2 prepare3
# prepare3 is used to check if we are building in a separate output directory,
# and if so do:
# 1) Check that make has not been executed in the kernel src $(srctree)
prepare3: include/config/uboot.release
ifneq ($(KBUILD_SRC),)
@$(kecho) ' Using $(srctree) as source for U-Boot'
$(Q)if [ -f $(srctree)/.config -o -d $(srctree)/include/config ]; then \
echo >&2 " $(srctree) is not clean, please run 'make mrproper'"; \
echo >&2 " in the '$(srctree)' directory.";\
/bin/false; \
fi;
endif
# prepare2 creates a makefile if using a separate output directory
prepare2: prepare3 outputmakefile
prepare1: prepare2 $(version_h) $(timestamp_h) \
include/config/auto.conf
ifeq ($(wildcard $(LDSCRIPT)),)
@echo >&2 " Could not find linker script."
@/bin/false
endif
archprepare: prepare1 scripts_basic
prepare0: archprepare FORCE
$(Q)$(MAKE) $(build)=.
# All the preparing..
prepare: prepare0
# Generate some files
# ---------------------------------------------------------------------------
define filechk_version.h
(echo \#define PLAIN_VERSION \"$(UBOOTRELEASE)\"; \
echo \#define U_BOOT_VERSION \"U-Boot \" PLAIN_VERSION; \
echo \#define CC_VERSION_STRING \"$$(LC_ALL=C $(CC) --version | head -n 1)\"; \
echo \#define LD_VERSION_STRING \"$$(LC_ALL=C $(LD) --version | head -n 1)\"; )
endef
# The SOURCE_DATE_EPOCH mechanism requires a date that behaves like GNU date.
# The BSD date on the other hand behaves different and would produce errors
# with the misused '-d' switch. Respect that and search a working date with
# well known pre- and suffixes for the GNU variant of date.
define filechk_timestamp.h
(if test -n "$${SOURCE_DATE_EPOCH}"; then \
SOURCE_DATE="@$${SOURCE_DATE_EPOCH}"; \
DATE=""; \
for date in gdate date.gnu date; do \
$${date} -u -d "$${SOURCE_DATE}" >/dev/null 2>&1 && DATE="$${date}"; \
done; \
if test -n "$${DATE}"; then \
LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_DATE "%b %d %C%y"'; \
LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_TIME "%T"'; \
LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_TZ "%z"'; \
LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_DMI_DATE "%m/%d/%Y"'; \
else \
return 42; \
fi; \
else \
LC_ALL=C date +'#define U_BOOT_DATE "%b %d %C%y"'; \
LC_ALL=C date +'#define U_BOOT_TIME "%T"'; \
LC_ALL=C date +'#define U_BOOT_TZ "%z"'; \
LC_ALL=C date +'#define U_BOOT_DMI_DATE "%m/%d/%Y"'; \
fi)
endef
$(version_h): include/config/uboot.release FORCE
$(call filechk,version.h)
$(timestamp_h): $(srctree)/Makefile FORCE
$(call filechk,timestamp.h)
# ---------------------------------------------------------------------------
quiet_cmd_cpp_lds = LDS $@
cmd_cpp_lds = $(CPP) -Wp,-MD,$(depfile) $(cpp_flags) $(LDPPFLAGS) \
-D__ASSEMBLY__ -x assembler-with-cpp -P -o $@ $<
u-boot.lds: $(LDSCRIPT) prepare FORCE
$(call if_changed_dep,cpp_lds)
spl/u-boot-spl.bin: spl/u-boot-spl
@:
spl/u-boot-spl: tools prepare \
$(if $(CONFIG_OF_SEPARATE)$(CONFIG_SPL_OF_PLATDATA),dts/dt.dtb)
$(Q)$(MAKE) obj=spl -f $(srctree)/scripts/Makefile.spl all
spl/sunxi-spl.bin: spl/u-boot-spl
@:
spl/u-boot-spl.sfp: spl/u-boot-spl
@:
spl/boot.bin: spl/u-boot-spl
@:
tpl/u-boot-tpl.bin: tools prepare
$(Q)$(MAKE) obj=tpl -f $(srctree)/scripts/Makefile.spl all
TAG_SUBDIRS := $(patsubst %,$(srctree)/%,$(u-boot-dirs) include)
FIND := find
FINDFLAGS := -L
tags ctags:
ctags -w -o ctags `$(FIND) $(FINDFLAGS) $(TAG_SUBDIRS) \
-name '*.[chS]' -print`
ln -s ctags tags
etags:
etags -a -o etags `$(FIND) $(FINDFLAGS) $(TAG_SUBDIRS) \
-name '*.[chS]' -print`
cscope:
$(FIND) $(FINDFLAGS) $(TAG_SUBDIRS) -name '*.[chS]' -print > \
cscope.files
cscope -b -q -k
SYSTEM_MAP = \
$(NM) $1 | \
grep -v '\(compiled\)\|\(\.o$$\)\|\( [aUw] \)\|\(\.\.ng$$\)\|\(LASH[RL]DI\)' | \
LC_ALL=C sort
System.map: u-boot
@$(call SYSTEM_MAP,$<) > $@
checkdtc:
@if test $(call dtc-version) -lt 0104; then \
echo '*** Your dtc is too old, please upgrade to dtc 1.4 or newer'; \
false; \
fi
#########################################################################
# ARM relocations should all be R_ARM_RELATIVE (32-bit) or
# R_AARCH64_RELATIVE (64-bit).
checkarmreloc: u-boot
@RELOC="`$(CROSS_COMPILE)readelf -r -W $< | cut -d ' ' -f 4 | \
grep R_A | sort -u`"; \
if test "$$RELOC" != "R_ARM_RELATIVE" -a \
"$$RELOC" != "R_AARCH64_RELATIVE"; then \
echo "$< contains unexpected relocations: $$RELOC"; \
false; \
fi
env: scripts_basic
$(Q)$(MAKE) $(build)=tools/$@
tools-only: scripts_basic $(version_h) $(timestamp_h)
$(Q)$(MAKE) $(build)=tools
tools-all: export HOST_TOOLS_ALL=y
tools-all: env tools ;
cross_tools: export CROSS_BUILD_TOOLS=y
cross_tools: tools ;
.PHONY : CHANGELOG
CHANGELOG:
git log --no-merges U-Boot-1_1_5.. | \
unexpand -a | sed -e 's/\s\s*$$//' > $@
#########################################################################
###
# Cleaning is done on three levels.
# make clean Delete most generated files
# Leave enough to build external modules
# make mrproper Delete the current configuration, and all generated files
# make distclean Remove editor backup files, patch leftover files and the like
# Directories & files removed with 'make clean'
CLEAN_DIRS += $(MODVERDIR) \
$(foreach d, spl tpl, $(patsubst %,$d/%, \
$(filter-out include, $(shell ls -1 $d 2>/dev/null))))
CLEAN_FILES += include/bmp_logo.h include/bmp_logo_data.h \
boot* u-boot* MLO* SPL System.map
# Directories & files removed with 'make mrproper'
MRPROPER_DIRS += include/config include/generated spl tpl \
.tmp_objdiff
MRPROPER_FILES += .config .config.old include/autoconf.mk* include/config.h \
ctags etags tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS
# clean - Delete most, but leave enough to build external modules
#
clean: rm-dirs := $(CLEAN_DIRS)
clean: rm-files := $(CLEAN_FILES)
clean-dirs := $(foreach f,$(u-boot-alldirs),$(if $(wildcard $(srctree)/$f/Makefile),$f))
clean-dirs := $(addprefix _clean_, $(clean-dirs) doc/DocBook)
PHONY += $(clean-dirs) clean archclean
$(clean-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)
# TODO: Do not use *.cfgtmp
clean: $(clean-dirs)
$(call cmd,rmdirs)
$(call cmd,rmfiles)
@find $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \
\( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
-o -name '*.ko.*' -o -name '*.su' -o -name '*.cfgtmp' \
-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
-o -name '*.symtypes' -o -name 'modules.order' \
-o -name modules.builtin -o -name '.tmp_*.o.*' \
-o -name 'dsdt.aml' -o -name 'dsdt.asl.tmp' -o -name 'dsdt.c' \
-o -name '*.gcno' \) -type f -print | xargs rm -f
# mrproper - Delete all generated files, including .config
#
mrproper: rm-dirs := $(wildcard $(MRPROPER_DIRS))
mrproper: rm-files := $(wildcard $(MRPROPER_FILES))
mrproper-dirs := $(addprefix _mrproper_,scripts)
PHONY += $(mrproper-dirs) mrproper archmrproper
$(mrproper-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _mrproper_%,%,$@)
mrproper: clean $(mrproper-dirs)
$(call cmd,rmdirs)
$(call cmd,rmfiles)
@rm -f arch/*/include/asm/arch
# distclean
#
PHONY += distclean
distclean: mrproper
@find $(srctree) $(RCS_FIND_IGNORE) \
\( -name '*.orig' -o -name '*.rej' -o -name '*~' \
-o -name '*.bak' -o -name '#*#' -o -name '.*.orig' \
-o -name '.*.rej' -o -name '*%' -o -name 'core' \
-o -name '*.pyc' \) \
-type f -print | xargs rm -f
@rm -f boards.cfg
backup:
F=`basename $(srctree)` ; cd .. ; \
gtar --force-local -zcvf `LC_ALL=C date "+$$F-%Y-%m-%d-%T.tar.gz"` $$F
help:
@echo 'Cleaning targets:'
@echo ' clean - Remove most generated files but keep the config'
@echo ' mrproper - Remove all generated files + config + various backup files'
@echo ' distclean - mrproper + remove editor backup and patch files'
@echo ''
@echo 'Configuration targets:'
@$(MAKE) -f $(srctree)/scripts/kconfig/Makefile help
@echo ''
@echo 'Other generic targets:'
@echo ' all - Build all necessary images depending on configuration'
@echo ' tests - Build U-Boot for sandbox and run tests'
@echo '* u-boot - Build the bare u-boot'
@echo ' dir/ - Build all files in dir and below'
@echo ' dir/file.[oisS] - Build specified target only'
@echo ' dir/file.lst - Build specified mixed source/assembly target only'
@echo ' (requires a recent binutils and recent build (System.map))'
@echo ' tags/ctags - Generate ctags file for editors'
@echo ' etags - Generate etags file for editors'
@echo ' cscope - Generate cscope index'
@echo ' ubootrelease - Output the release version string (use with make -s)'
@echo ' ubootversion - Output the version stored in Makefile (use with make -s)'
@echo " cfg - Don't build, just create the .cfg files"
@echo ''
@echo 'Static analysers'
@echo ' checkstack - Generate a list of stack hogs'
@echo ''
@echo 'Documentation targets:'
@$(MAKE) -f $(srctree)/doc/DocBook/Makefile dochelp
@echo ''
@echo ' make V=0|1 [targets] 0 => quiet build (default), 1 => verbose build'
@echo ' make V=2 [targets] 2 => give reason for rebuild of target'
@echo ' make O=dir [targets] Locate all output files in "dir", including .config'
@echo ' make C=1 [targets] Check all c source with $$CHECK (sparse by default)'
@echo ' make C=2 [targets] Force check of all c source with $$CHECK'
@echo ' make RECORDMCOUNT_WARN=1 [targets] Warn about ignored mcount sections'
@echo ' make W=n [targets] Enable extra gcc checks, n=1,2,3 where'
@echo ' 1: warnings which may be relevant and do not occur too often'
@echo ' 2: warnings which occur quite often but may still be relevant'
@echo ' 3: more obscure warnings, can most likely be ignored'
@echo ' Multiple levels can be combined with W=12 or W=123'
@echo ''
@echo 'Execute "make" or "make all" to build all targets marked with [*] '
@echo 'For further info see the ./README file'
tests:
$(srctree)/test/run
# Documentation targets
# ---------------------------------------------------------------------------
%docs: scripts_basic FORCE
$(Q)$(MAKE) $(build)=scripts build_docproc
$(Q)$(MAKE) $(build)=doc/DocBook $@
endif #ifeq ($(config-targets),1)
endif #ifeq ($(mixed-targets),1)
PHONY += checkstack ubootrelease ubootversion
checkstack:
$(OBJDUMP) -d u-boot $$(find . -name u-boot-spl) | \
$(PERL) $(src)/scripts/checkstack.pl $(ARCH)
ubootrelease:
@echo "$(UBOOTVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))"
ubootversion:
@echo $(UBOOTVERSION)
# Single targets
# ---------------------------------------------------------------------------
# Single targets are compatible with:
# - build with mixed source and output
# - build with separate output dir 'make O=...'
# - external modules
#
# target-dir => where to store outputfile
# build-dir => directory in kernel source tree to use
ifeq ($(KBUILD_EXTMOD),)
build-dir = $(patsubst %/,%,$(dir $@))
target-dir = $(dir $@)
else
zap-slash=$(filter-out .,$(patsubst %/,%,$(dir $@)))
build-dir = $(KBUILD_EXTMOD)$(if $(zap-slash),/$(zap-slash))
target-dir = $(if $(KBUILD_EXTMOD),$(dir $<),$(dir $@))
endif
%.s: %.c prepare scripts FORCE
$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
%.i: %.c prepare scripts FORCE
$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
%.o: %.c prepare scripts FORCE
$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
%.lst: %.c prepare scripts FORCE
$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
%.s: %.S prepare scripts FORCE
$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
%.o: %.S prepare scripts FORCE
$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
%.symtypes: %.c prepare scripts FORCE
$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
# Modules
/: prepare scripts FORCE
$(cmd_crmodverdir)
$(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
$(build)=$(build-dir)
%/: prepare scripts FORCE
$(cmd_crmodverdir)
$(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
$(build)=$(build-dir)
%.ko: prepare scripts FORCE
$(cmd_crmodverdir)
$(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
$(build)=$(build-dir) $(@:.ko=.o)
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
# FIXME Should go into a make.lib or something
# ===========================================================================
quiet_cmd_rmdirs = $(if $(wildcard $(rm-dirs)),CLEAN $(wildcard $(rm-dirs)))
cmd_rmdirs = rm -rf $(rm-dirs)
quiet_cmd_rmfiles = $(if $(wildcard $(rm-files)),CLEAN $(wildcard $(rm-files)))
cmd_rmfiles = rm -f $(rm-files)
# read all saved command lines
targets := $(wildcard $(sort $(targets)))
cmd_files := $(wildcard .*.cmd $(foreach f,$(targets),$(dir $(f)).$(notdir $(f)).cmd))
ifneq ($(cmd_files),)
$(cmd_files): ; # Do not try to update included dependency files
include $(cmd_files)
endif
endif # skip-makefile
PHONY += FORCE
FORCE:
# Declare the contents of the .PHONY variable as phony. We keep that
# information in a variable so we can use it in if_changed and friends.
.PHONY: $(PHONY)
根目录下Makefile.build文件注释（建议看正点原子的教程）
# ==========================================================================
# Building
# ==========================================================================
#注：这个文件是多功能的，很多注释只是针对于分析主makefile时跳到这里的一种情况，很多注释并不是一直对的
#从主makefile的make menuconfig得到两个操作都是会进入到这个文件进行：
#@make -f ./scripts/Makefile.build obj=scripts/basic
#@make -f ./scripts/Makefile.build obj=scripts/kconfig xxx_defconfig
#几乎所有的我们分析的工作都是在这个文件完成的。重点分析的就是这两个命令。
# SPDX-License-Identifier: GPL-2.0
#重点参考正点原子资料P760页，很好。
# Modified for U-Boot
prefix := tpl
src := $(patsubst $(prefix)/%,%,$(obj))
#$(patsubst PATTERN,REPLACEMENT,TEXT)
#搜索“TEXT”中以空格分开的单词，将否符合模式“TATTERN”替换为“REPLACEMENT”
#在“scripts/basic”中查找符合“tpl/%”的部分，然后将“tpl/”取消掉，但是“scripts/basic”没有“tpl/”，所以 src= scripts/basic。此时 src=obj=scripts/basic。
ifeq ($(obj),$(src)) #成立
prefix := spl
src := $(patsubst $(prefix)/%,%,$(obj))
ifeq ($(obj),$(src))#大多数时候，src和obj是一样的。
prefix := . #这里是成立的。
endif
endif
PHONY := __build
__build:
#后面还有__build，这两个相同的target1会被合并。
#打开这个文件的时候传入了一个环境变量 obj=scripts/kconfig！！！！注意。
# Init all relevant variables used in kbuild files so
# 1) they have correct type初始化变量防止被“上级”干扰。
# 2) they do not inherit any value from the environment环境变量
obj-y :=
obj-m :=
lib-y :=
lib-m :=
always :=
targets :=
subdir-y :=
subdir-m :=
EXTRA_AFLAGS :=
EXTRA_CFLAGS :=
EXTRA_CPPFLAGS :=
EXTRA_LDFLAGS :=
asflags-y :=
ccflags-y :=
cppflags-y :=
ldflags-y :=
subdir-asflags-y :=
subdir-ccflags-y :=
# Read auto.conf if it exists, otherwise ignore
# Modified for U-Boot
-include include/config/auto.conf
#auto.conf不一定存在，但由于在include前面加了一个-，故即使该语句执行失败，makefile也不会出错退出。
-include $(prefix)/include/autoconf.mk
include scripts/Makefile.uncmd_spl
include scripts/Kbuild.include
# For backward compatibility向后兼容性 check that these variables do not change
save-cflags := $(CFLAGS) #是个环境变量
#变量“CFLAGS”是编译.c 文件时 gcc 的编译选项，可以在 Makefile 中给它指定明确的值、也可以使用隐含的定义值。
# The filename Kbuild has precedence over Makefile
kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))
#展开为$(if $(filter /%, scripts/basic), scripts/basic, ./scripts/basic)
#因为没有以“/”为开头的单词，所以$(filter /%, scripts/basic)的结果为空！！！！！
#kbuild-dir=./scripts/basic。对于主mf中scripts_basic这个目标而言。
kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile)
#展开为：$(if $(wildcard ./scripts/basic/Kbuild), ./scripts/basic/Kbuild, ./scripts/basic/Makefile)
#因为 scrpts/basic 目录中没有 Kbuild 这个文件，所以 kbuild-file= ./scripts/basic/Makefile。
#在规则中，通配符会被自动展开。但在变量的定义和函数引用时，通配符将失效。
#这种情况下如果需要通配符有效，就需要使用函数“wildcard”
#在 Makefile 中，它被展开为已经存在的、使用空格分开的、匹配此模式的所有文件列表。
#如果不存在任何符合此模式的文件，函数会忽略模式字符并返回空。这里就是空，没有这样的文件，所以包含后面的makefile
include $(kbuild-file) #！！%_defconfig这个目标就是在这个包含的makefile中，不过那种情况下这个变量的值就不是下面写的这样了，参考正点原子资料P761页。
#文件 scripts/Makefile.build 会包含obj变量所指代目录内的 Makefile的，在这里就是./script/kconfig/Makefile。
#其实就是include scripts/basic/Makefile(对于主mf中scripts_basic这个目标而言)
#kbuild-dir根据src变量（等于obj变量）是绝对路径还是相对路径来确定当前编译的目录，若为绝对路径则该目录即src变量的值，若为相对路径则该变量就是src变量相对于源码根目录的目录。kbuild-file即在该目录下查找Kbuild文件，若能找到，则使用kbuild作为该目录的编译文件，若找不到则使用该目录下的Makefile作为该目录的编译文件，然后将该文件包含进来。
#scripts/basic没有Kbuild文件，因此include scripts/basic/Makefile
#注：在生成built-in.o的时候，这个文件就是各个子文件夹下面的makefile。makefile里都是些类似于：obj-$(CONFIG_DWAPB_GPIO) += dwapb_gpio.o，所以obj-y可能就是被定义的了。
#这时候kbuild-dir就是各个子文件夹路径。
#scripts/basic/Makefile内容如下：
#hostprogs-y := fixdep
#always := $(hostprogs-y)
# Added for U-Boot
asflags-y += $(PLATFORM_CPPFLAGS)
ccflags-y += $(PLATFORM_CPPFLAGS)
cppflags-y += $(PLATFORM_CPPFLAGS)
# If the save-* variables changed error out
ifeq ($(KBUILD_NOPEDANTIC),)
ifneq ("$(save-cflags)","$(CFLAGS)")
$(error CFLAGS was changed in "$(kbuild-file)". Fix it to use ccflags-y)
endif
endif
include scripts/Makefile.lib
#ifdef host-progs这一段陈注释掉
#ifneq ($(hostprogs-y),$(host-progs))
#$(warning kbuild: $(obj)/Makefile - Usage of host-progs is deprecated. Please replace with hostprogs-y!)
#hostprogs-y += $(host-progs)
#endif
#endif
# Do not include host rules unless needed
ifneq ($(hostprogs-y)$(hostprogs-m),)
include scripts/Makefile.host #这里确实包含进来了。
endif
# Uncommented for U-Boot
# We need to create output dicrectory for SPL and TPL even for in-tree build
#ifneq ($(KBUILD_SRC),)
# Create output directory if not already present
_dummy := $(shell [ -d $(obj) ] || mkdir -p $(obj))
# Create directories for object files if directory does not exist
# Needed when obj-y := dir/file.o syntax is used
_dummy := $(foreach d,$(obj-dirs), $(shell [ -d $(d) ] || mkdir -p $(d)))
#endif
ifndef obj
$(warning kbuild: Makefile.build is included improperly)
endif
# ===========================================================================
ifneq ($(strip $(lib-y) $(lib-m) $(lib-)),) #注意这里不是libs-y。
lib-target := $(obj)/lib.a
#obj=scripts/kconfig，主makefile给我们这个文件传入的。
endif
ifneq ($(strip $(obj-y) $(obj-m) $(obj-) $(subdir-m) $(lib-target)),)
#去掉字串（若干单词，使用若干空字符分割）“STRINT”开头和结尾的空字符，
#并将其中多个连续空字符合并为一个空字符。
builtin-target := $(obj)/built-in.o
#在生成buily.o的时候，obj就是个个子文件夹，具体可查看主makefile。
endif
modorder-target := $(obj)/modules.order
# We keep a list of all modules in $(MODVERDIR)
#这里就是默认的目标，第一个目标！！！！！！！！！！！！！
#主MK中make -f ./scripts/Makefile.build obj=scripts/basic会执行这个。
__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \
$(if $(KBUILD_MODULES),$(obj-m) $(modorder-target)) \
$(subdir-ym) $(always)
@:
#KBUILD_BUILTIN在主makefile中，确实等于1。KBUILD_MODULES=0。
#在scripts/Makefile.build 中会包含进 scripts/basic目录下的#Kbuild/Makefile，always是这个文件中有赋值fixdep。
#！！展开:__build:$(builtin-target) $(lib-target) $(extra-y)) $(subdir-ym) $(always)
#经过分析，或者直接在uboot中这个位置加入@echo builtin-target=$(builtin-target)等语句重新编译查看信息
#可以看到前四个都是空，只有最后一个 always=scripts/basic/fixdep有效。
#所以这个目标简单就是：__build: scripts/basic/fixdep
#重要的就是下面这里生成了一个工具。
#__build 依赖于 scripts/basic/fixdep，所以要先 scripts/basic/fixdep.c 编译，生成 fixdep，
#前面已经读取了 scripts/basic/Makefile 文件。
#综上所述，scripts_basic 目标的作用就是编译出 scripts/basic/fixdep 这个软件。
#always:=fixdep，__build依赖fixdep，所以先构建fixdep，构建的规则在scripts/Makefile.host中定义！！！！
#这个文件中展开后就是scripts/basic/fixdep ： scripts/basic/fixdep.c FORCE
#在scripts/basic下生成了fixdep程序文件。
#subdir-ym记录了当前目录里边要参与编译连接的子文件夹
######################################################################
#省略一大段没看的内容
######################################################################
# Build the compiled-in targets
# ---------------------------------------------------------------------------
# To build objects in subdirs, we need to descend into the directories
$(sort $(subdir-obj-y)): $(subdir-ym) ;
#
# Rule to compile a set of .o files into one .o file
#
ifdef builtin-target
quiet_cmd_link_o_target = LD $@
# If the list of objects to link is empty, just create an empty built-in.o
cmd_link_o_target = $(if $(strip $(obj-y)),\
$(LD) $(ld_flags) -r -o $@ $(filter $(obj-y), $^) \
$(cmd_secanalysis),\
rm -f $@; $(AR) rcs$(KBUILD_ARFLAGS) $@)
#举例：这里展开就是cmd_link_o_target = arm-linux-ld -EL -r -o test/built-in.o test.o arm-linux-ar rcs test/built-in.o
$(builtin-target): $(obj-y) FORCE
$(call if_changed,link_o_target)
#这里就是生成built_in.o的，这个if_changed函数挺麻烦，没细看。
#各个文件夹下面的.cmd文件应该也是if_changed函数生成的。
#参考https://www.cnblogs.com/amanlikethis/p/3675486.html
#https://www.cnblogs.com/andyfly/p/9401647.html
targets += $(builtin-target)
endif # builtin-target
#。。。。。。。。
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