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Kernel顶层Makefile文件分析

2013-12-04 22:09 381 查看
注： 基于Linux 2.6.25

新函数

origin函数
简介：函数origin并不操作变量的值，只是告诉你这个变量是来自哪里
语法：$(origin <variable>)
返回值：

"undefined":在这前还没有定已过
"default":默认的定义。。不太明白
"environment":来自环境变量
"file":变量被定义在makefile文件内
"commandline":是在环境变量中定义
"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，这个也不太懂

error函数

简介：输出错误信息，并且退出执行

语法： $(error <String>)

shell函数

简介：执行shell命令

语法： $(shell <Shell Command String>)

if 函数

简介: 一个简单if else

语法：
if <condition>,<then-part>

if <condition>,<then-part>,<else-part>

?= 条件复制

简介： 如果变量在之前未赋值，则对他赋值

语法: VAR1 ?= $

= 赋值

:= 赋值

+= 赋值

语法：$(findstring <targetStr>, <srcStr>)

描述：在srcStr中查找targetStr，如果找到回返回些什么，如果没找到，返回空

语法：$(dir <filepath>)

描述：获取filepath中的目录部分，如/foo/bar.c，返回/foo

语法：$(notdir <filepath>)

描述：获取filepath中除去目录的部分，如/foo/bar.c，返回bar.c

语法：$(basename <filepath>)

描述：去掉filepath中的.extension扩展名
VERSION = 2               #主版本号
PATCHLEVEL = 6            #次版本号
SUBLEVEL = 25             #子版本号
EXTRAVERSION =            #额外版本号
NAME = Funky Weasel is Jiggy wit it    #此版本的名字

# *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.

# Do not:
# o  use make's built-in rules and variables
#    (this increases performance and avoids hard-to-debug behaviour);
# o  print "Entering directory ...";
MAKEFLAGS += -rR --no-print-directory  # 设置Make不使用内置的规则和变量，并且在递归进行编译的时候，不打印"Entering directory"

# We are using a recursive 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 and done before the recursive
# descending is started. They are now explicitly listed as the
# prepare rule.

# To put more focus on warnings, be less verbose as default
# Use 'make V=1' to see the full commands

# 设置打印消息级别，通过调用make 时添加的参数V=NUM来修改
ifdef V
  ifeq ("$(origin V)", "command line")
    KBUILD_VERBOSE = $(V)
  endif
endif
# 默认的KBUILD_VERBOSE的值被设置为0，也就意味着在编译过程中，只输出
ifndef KBUILD_VERBOSE
  KBUILD_VERBOSE = 0
endif

# 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.
# 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" utility.

# 设置语法检查级别,默认级别为0
ifdef C
  ifeq ("$(origin C)", "command line")
    KBUILD_CHECKSRC = $(C)
  endif
endif
ifndef KBUILD_CHECKSRC
  KBUILD_CHECKSRC = 0
endif

# Use make M=dir to specify directory of external module to build
# Old syntax make ... SUBDIRS=$PWD is still supported
# Setting the environment variable KBUILD_EXTMOD take precedence
# 下面是为了支持旧语法格式的Makefile的设置，不用理。
ifdef SUBDIRS
  KBUILD_EXTMOD ?= $(SUBDIRS)
endif
ifdef M
  ifeq ("$(origin M)", "command line")
    KBUILD_EXTMOD := $(M)
  endif
endif

# kbuild supports saving output files in a separate directory.
# To locate output files in a separate directory two syntaxes 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 takes precedence over the KBUILD_OUTPUT environment
# variable.
#上面这里是介绍可以设置kbuild过程中的输出文件目的地址，有两种方式，一种是在make 参数中设置(make -O dir),第二种方式是设置环境变量(export KBUILD_OUTPU=dir)

# KBUILD_SRC is set on invocation of make in OBJ directory
# KBUILD_SRC
4000
is not intended to be used by the regular user (for now)
ifeq ($(KBUILD_SRC),) #如果KBUILD_SRC值为空，就执行下面的操作，正常情况下要执行
#上面说的这个功能当前对一般用户没有用，那就先不理了

# OK, Make called in directory where kernel src resides
# Do we want to locate output files in a separate directory?
#这个不是应该是和上面那大堆注释对应的吗？怎么放到了这里。。功能就是如果命令行中定义了O变量来修改输出目录，就用用户定义的这个目录。
ifdef O
  ifeq ("$(origin O)", "command line")
    KBUILD_OUTPUT := $(O)
  endif
endif

# That's our default target when none is given on the command line
#这里不太懂，大概意思是如果make没有给出任意参数，就执行这个默认的
PHONY := _all
_all:

# Cancel implicit rules on top Makefile
#取消隐式推倒原则，不懂有什么用
$(CURDIR)/Makefile Makefile: ;

# 如果输出目录值不为空，正常情况下进入
ifneq ($(KBUILD_OUTPUT),)
# Invoke a second make in the output directory, passing relevant variables
# check that the output directory actually exists
# 上面说在输出目录中执行第二个make命令，传入相关变量，并且检查输出目录是否存在
# 下面的
saved-output := $(KBUILD_OUTPUT)
KBUILD_OUTPUT := $(shell cd $(KBUILD_OUTPUT) && /bin/pwd)
$(if $(KBUILD_OUTPUT),, \
     $(error output directory "$(saved-output)" does not exist))

# MAKECMDGOALS 是make的一个环境变量，保存所有目标列表
# 下面这个命令将所有指明的目标列表和sub-make加入到PHONY中
PHONY += $(MAKECMDGOALS) sub-make

# 下面这个命令很是不明白，大概是用来过滤，太复杂了
# 简单分析下，过滤掉MAKECMDGOALS中的_all sub-make和$(CURDIR)/Makefile，并将它们都赋值为sub-make
$(filter-out _all sub-make $(CURDIR)/Makefile, $(MAKECMDGOALS)) _all: sub-make
$(Q)@:

# 这个就是sub-make的值，大致就是将顶层Makefile定义的规则传给下层文件夹中的Makefile中
sub-make: FORCE
$(if $(KBUILD_VERBOSE:1=),@)$(MAKE) -C $(KBUILD_OUTPUT) \
KBUILD_SRC=$(CURDIR) \
KBUILD_EXTMOD="$(KBUILD_EXTMOD)" -f $(CURDIR)/Makefile \
$(filter-out _all sub-make,$(MAKECMDGOALS))

# Leave processing to above invocation of make
# 表示执行完了子makefile,返回顶层make
skip-makefile := 1
endif # ifneq ($(KBUILD_OUTPUT),) #结束ifneq
endif # ifeq ($(KBUILD_SRC),)     #结束ifeq

# We process the rest of the Makefile if this is the final invocation of make
# 表示如果skip-makefile为空，这按照分类执行，也就是不是整体进行make
ifeq ($(skip-makefile),)

# If building an external module we do not care about the all: rule
# but instead _all depend on modules
# 如果make 外部模块，就不用执行all,之编译模块就可以了
PHONY += all
ifeq ($(KBUILD_EXTMOD),)
_all: all
else
_all: modules
endif

# 将srctree设置为源码根目录
srctree := $(if $(KBUILD_SRC),$(KBUILD_SRC),$(CURDIR))
TOPDIR := $(srctree)
# FIXME - TOPDIR is obsolete, use srctree/objtree
# 将objtree设定位当前目录
objtree := $(CURDIR)
# 将src设置为源码根目录
src := $(srctree)
将obj设定位当前目录
obj := $(objtree)

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

# 将上面这些变量输出为环境变量,可以给子makefile贡献
export srctree objtree VPATH TOPDIR

# SUBARCH tells the usermode build what the underlying arch is.  That is set
# first, and if a usermode build is happening, the "ARCH=um" on the command
# line overrides the setting of ARCH below.  If a native build is happening,
# then ARCH is assigned, getting whatever value it gets normally, and 
# SUBARCH is subsequently ignored.
# 获取CPU的具体型号，存在SUBARCH中，SUBARCH代表Host的架构
# sed -e -s/i.86/i386,表示匹配i.86的用i386替换
SUBARCH := $(shell uname -m | sed -e s/i.86/i386/ -e s/sun4u/sparc64/ \
  -e s/arm.*/arm/ -e s/sa110/arm/ \
  -e s/s390x/s390/ -e s/parisc64/parisc/ \
  -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
  -e s/sh.*/sh/ )

# Cross compiling and selecting different set of gcc/bin-utils
# ---------------------------------------------------------------------------
#
# When performing cross compilation for other architectures ARCH shall be set
# to the target architecture. (See arch/* for the possibilities).
# ARCH can be set during invocation of make:
# make ARCH=ia64
# Another way is to have ARCH set in the environment.
# The default ARCH is the host where make is executed.
# 当执行交叉编译的时候，要将ARCH的值设置为目标的架构，支持的交媾可以在arch目录下看到
# ARCH可以在执行make命令时设置，如make ARCH=arm
# 默认的ARCH是和Host相同

# CROSS_COMPILE specify the prefix used for all executables used
# during compilation. Only gcc and related bin-utils executables
# are prefixed with $(CROSS_COMPILE).
# CROSS_COMPILE can be set on the command line
# make CROSS_COMPILE=ia64-linux-
# Alternatively CROSS_COMPILE can be set in the environment.
# Default value for CROSS_COMPILE is not to prefix executables
# Note: Some architectures assign CROSS_COMPILE in their arch/*/Makefile
# 下面是处理交叉编译这块的，交叉编译需要知道Host的架构和Target的架构吧
# CROSS_COMPILE是编译时所有命令的前缀，可以在执行make的时候指定如make CROSS_COMPILE=ia64-linux-
# CROSS_COMPILE也可以通过环境变量来设定
# 默认情况下是不需要CROSS_COMPILE来执行的，也就是不交叉编译
export KBUILD_BUILDHOST := $(SUBARCH) # 将Host架构与子Make共享
ARCH ?= $(SUBARCH)  # 默认Host的架构与Target架构相同
CROSS_COMPILE ?=             # 默认CROSS_COMPILE为空

#下面不知哪里调用
# Architecture as present in compile.h
UTS_MACHINE  := $(ARCH)
SRCARCH  := $(ARCH)

#对x86结构的特殊照顾，不明白原因
# Additional ARCH settings for x86
ifeq ($(ARCH),i386)
        SRCARCH := x86
endif
ifeq ($(ARCH),x86_64)
        SRCARCH := x86
endif

# 声称的配置文件名
KCONFIG_CONFIG ?= .config

# 设定kbuild使用的Shell
# 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)

# 设定编译器，和全局编译FLAGS
HOSTCC       = gcc
HOSTCXX      = g++
HOSTCFLAGS   = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
HOSTCXXFLAGS = -O2

# Decide whether to build built-in, modular, or both.
# Normally, just do built-in.
# 下面决定是只编译build-in或modular,也可两个都编译
# 通常情况下，只编译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.
# 如果只是make modules的话，就不要编译built-in objects
# 

# 如果执行的是 make modules ，则在这里重新设置KBUILD_BUILTIN := 1
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
# 
# 如果执行的是make all/_all/modules有额外goal，则KBUILD_MODULES := 1
ifneq ($(filter all _all modules,$(MAKECMDGOALS)),)
  KBUILD_MODULES := 1
endif

# 只执行make，KBUILD_MODULES := 1
ifeq ($(MAKECMDGOALS),)
  KBUILD_MODULES := 1
endif

# 导出给子make
export KBUILD_MODULES KBUILD_BUILTIN
export KBUILD_CHECKSRC KBUILD_SRC KBUILD_EXTMOD

# Beautify output
# ---------------------------------------------------------------------------
#
# 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 $(RELDIR)/$@      这个是简化版的输出
#         cmd_cc_o_c       = $(CC) $(c_flags) -c -o $@ $<  这个是原版的输出
#
# 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 $(silent_cmd_cc_o_c) doesn't exist.
#
# 下面这里不太清楚，$(Q)用作前缀，如果$(Q)=@表示不回显，为空表示回显
# A simple variant is to prefix commands with $(Q) - that's useful
# for commands that shall be hidden in non-verbose 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.

# 美化编译过程中输出
# 如果$(quiet)为空，则输出原版编译命令
# 如果$(quiet)为quiet_，则输出简化版本的
# 如果$(quiet)为silent_，则任何都不输出，因为slient_cmd_cc_o_cc根本不存在
# 不过有个全局的控制，如果KBUILD_VERBOSE为0，则输出简化版本，如果为1，则输出简化版本
ifeq ($(KBUILD_VERBOSE),1)
  quiet =
  Q =
else
  quiet=quiet_
  Q = @
endif

# If the user is running make -s (silent mode), suppress echoing of
# commands
# 如果用户用户调用make -s，也就是slient模式，设置quit=silent_，也就是什么都不输出

ifneq ($(findstring s,$(MAKEFLAGS)),)
  quiet=silent_
endif

# 输出quiet给子make
export quiet Q KBUILD_VERBOSE

# Look for make include files relative to root of kernel src
# 在kernel原文件目录下查找make要include的文件，这个应该会自动化查找吧。
# 注意 --include-dir被定义为一个递归类型变量，所以只有到使用的时候才会赋值
MAKEFLAGS += --include-dir=$(srctree)

# We need some generic definitions (do not try to remake the file).
# 这里是定义了一些通用的srctree变量定义，这里执行remak
1b5d8
e操作
$(srctree)/scripts/Kbuild.include: ;
# 这里的文件包含了大量通用的函数和变量,已经为这个文件创建了笔记，抽个时间进行分析，
# 还是先对那个进行分析吧，因为下面会用到它定义的很多变量
include $(srctree)/scripts/Kbuild.include

# Make variables (CC, etc...)
# 定义一系列Make变量，大部分都是编译阶段使用的一些工具，如as,cc,ar,nm,objcopy等
AS = $(CROSS_COMPILE)as
LD = $(CROSS_COMPILE)ld
CC = $(CROSS_COMPILE)gcc
CPP = $(CC) -E
AR = $(CROSS_COMPILE)ar
NM = $(CROSS_COMPILE)nm
STRIP = $(CROSS_COMPILE)strip
OBJCOPY = $(CROSS_COMPILE)objcopy
OBJDUMP = $(CROSS_COMPILE)objdump
AWK = awk
GENKSYMS = scripts/genksyms/genksyms
DEPMOD = /sbin/depmod
KALLSYMS = scripts/kallsyms
PERL = perl
CHECK = sparse # 默认的字符串检查

CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ -Wbitwise $(CF)
MODFLAGS = -DMODULE
CFLAGS_MODULE   = $(MODFLAGS)
AFLAGS_MODULE   = $(MODFLAGS)
LDFLAGS_MODULE  =
CFLAGS_KERNEL =
AFLAGS_KERNEL =

# Use LINUXINCLUDE when you must reference the include/ directory.
# Needed to be compatible with the O= option
# 访问include/目录时使用这个变量
LINUXINCLUDE    := -Iinclude \
                   $(if $(KBUILD_SRC),-Iinclude2 -I$(srctree)/include) \
   -include include/linux/autoconf.h

KBUILD_CPPFLAGS := -D__KERNEL__ $(LINUXINCLUDE)

KBUILD_CFLAGS   := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
   -fno-strict-aliasing -fno-common \
   -Werror-implicit-function-declaration
KBUILD_AFLAGS   := -D__ASSEMBLY__

# Read KERNELRELEASE from include/config/kernel.release (if it exists)

KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
# 设置版本号
KERNELVERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)

# 输出环境变量给子make
export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
export ARCH SRCARCH CONFIG_SHELL HOSTCC HOSTCFLAGS CROSS_COMPILE AS LD CC
export CPP AR NM STRIP OBJCOPY OBJDUMP MAKE AWK GENKSYMS PERL UTS_MACHINE
export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS

export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE

# 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

# Files to ignore in find ... statements
# 定义在find ...命令中忽略的文件，主要是一些版本管理器遗留下来的文件
# 并将这个变量输出给子make
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/
# 生成基本的scripts配置工具 fixdep docproc
PHONY += scripts_basic # 定义一个伪目标
scripts_basic:
$(Q)$(MAKE) $(build)=scripts/basic

# To avoid any implicit rule to kick in, define an empty command.
scripts/basic/%: scripts_basic ;

# 添加伪目标outputmakefile
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.
# 当使用一个独立的ouput文件夹时，ouputmakefile目标执行的命令会在output文件夹下生成一个makefile文件。
# 这个可以方便的在输出文件夹内使用make
# 这里的意识在shell执行 /scripts/mkmakefile这个shell脚本，并且传入四个参数，结果是在$(objtree)文件夹下生成一个makefile
outputmakefile:
ifneq ($(KBUILD_SRC),)
$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile \ # 这里的意识在shell执行 /scripts/mkmakefile这个shell脚本
    $(srctree) $(objtree) $(VERSION) $(PATCHLEVEL)
endif

# 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).
# 下面这里是保证调用make的时候输入了*config目标，这是就不能包含.config文件
no-dot-config-targets := clean mrproper distclean \
 cscope TAGS tags help %docs check% \
 include/linux/version.h headers_% \
 kernelrelease kernelversion

config-targets := 0
mixed-targets  := 0
dot-config     := 1

ifneq ($(filter $(no-dot-config-targets), $(MAKECMDGOALS)),)
ifeq ($(filter-out $(no-dot-config-targets), $(MAKECMDGOALS)),)
dot-config := 0
endif
endif

ifeq ($(KBUILD_EXTMOD),)
        ifneq ($(filter config %config,$(MAKECMDGOALS)),)
                config-targets := 1
                ifneq ($(filter-out config %config,$(MAKECMDGOALS)),)
                        mixed-targets := 1
                endif
        endif
endif

ifeq ($(mixed-targets),1)
# ===========================================================================
# We're called with mixed targets (*config and build targets).
# Handle them one by one.

%:: FORCE
$(Q)$(MAKE) -C $(srctree) KBUILD_SRC= $@

else
ifeq ($(config-targets),1)
# ===========================================================================
# *config targets only - make sure prerequisites are updated, and descend
# in scripts/kconfig to make the *config target

# Read arch specific Makefile to set KBUILD_DEFCONFIG as needed.
# KBUILD_DEFCONFIG may point out an alternative default configuration
# used for 'make defconfig'
include $(srctree)/arch/$(SRCARCH)/Makefile
export KBUILD_DEFCONFIG

config %config: scripts_basic outputmakefile FORCE
$(Q)mkdir -p include/linux include/config
$(Q)$(MAKE) $(build)=scripts/kconfig $@

else
# ===========================================================================
# Build targets only - this includes vmlinux, arch specific targets, clean
# targets and others. In general all targets except *config targets.

ifeq ($(KBUILD_EXTMOD),)
# 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) $(build)=$(@)

# Objects we will link into vmlinux / subdirs we need to visit
# 需要链接到vmlinux中的对像，这些对象所在的文件夹，我们编译时要遍历的
init-y := init/
drivers-y := drivers/ sound/
net-y := net/
libs-y := lib/
core-y := usr/
endif # KBUILD_EXTMOD

ifeq ($(dot-config),1)
# Read in config
-include include/config/auto.conf

ifeq ($(KBUILD_EXTMOD),)
# Read in dependencies to all Kconfig* files, make sure to run
# oldconfig if changes are detected.
-include include/config/auto.conf.cmd

# To avoid any implicit rule to kick in, define an empty command
# 这个操作好几个地方都看到了，不过还没有理解，从翻译上来看是为了避免隐式的规则影响
$(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
include/config/auto.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd
$(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig
else
# external modules needs include/linux/autoconf.h and include/config/auto.conf
# but do not care if they are up-to-date. Use auto.conf to trigger the test
PHONY += include/config/auto.conf

include/config/auto.conf:
$(Q)test -e include/linux/autoconf.h -a -e $@ || (\
echo;
\
echo "  ERROR: Kernel configuration is invalid.";\
echo "         include/linux/autoconf.h or $@ are missing.";\
echo "         Run 'make oldconfig && make prepare' on kernel src to fix it.";\
echo;
\
/bin/false)

endif # KBUILD_EXTMOD

else
# Dummy target needed, because used as prerequisite
include/config/auto.conf: ;
endif # $(dot-config)

# The all: target is the default when no target is given on the
# command line.
# This allow a user to issue only 'make' to build a kernel including modules
# Defaults vmlinux but it is usually overridden in the arch makefile
# 默认的目标，执行make all活着make时执行
all: vmlinux

# 定义gcc都优化参数
ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
KBUILD_CFLAGS += -Os
else
KBUILD_CFLAGS += -O2
endif

# Force gcc to behave correct even for buggy distributions
# Arch Makefiles may override this setting
# 修改KBUILD_CFLAGS变量，使gcc工作正常
KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)

# 包含ARCH相关的Makefile,文件内会重新规定了一些变量的默认值
include $(srctree)/arch/$(SRCARCH)/Makefile

ifdef CONFIG_FRAME_POINTER
KBUILD_CFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
else
KBUILD_CFLAGS += -fomit-frame-pointer
endif

ifdef CONFIG_DEBUG_INFO
KBUILD_CFLAGS += -g
KBUILD_AFLAGS += -gdwarf-2
endif

# We trigger additional mismatches with less inlining
ifdef CONFIG_DEBUG_SECTION_MISMATCH
KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
endif

# arch Makefile may override CC so keep this after arch Makefile is included
NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
CHECKFLAGS     += $(NOSTDINC_FLAGS)

# warn about C99 declaration after statement
KBUILD_CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)

# disable pointer signed / unsigned warnings in gcc 4.0
KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,)

# Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments
# But warn user when we do so
warn-assign = \
$(warning "WARNING: Appending $$K$(1) ($(K$(1))) from $(origin K$(1)) to kernel $$$(1)")

ifneq ($(KCPPFLAGS),)
        $(call warn-assign,CPPFLAGS)
        KBUILD_CPPFLAGS += $(KCPPFLAGS)
endif
ifneq ($(KAFLAGS),)
        $(call warn-assign,AFLAGS)
        KBUILD_AFLAGS += $(KAFLAGS)
endif
ifneq ($(KCFLAGS),)
        $(call warn-assign,CFLAGS)
        KBUILD_CFLAGS += $(KCFLAGS)
endif

# Use --build-id when available.
LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\
      $(call ld-option, -Wl$(comma)--build-id,))
LDFLAGS_MODULE += $(LDFLAGS_BUILD_ID)
LDFLAGS_vmlinux += $(LDFLAGS_BUILD_ID)

# Default kernel image to build when no specific target is given.
# KBUILD_IMAGE may be overruled on the command line or
# set in the environment
# Also any assignments in arch/$(ARCH)/Makefile take precedence over
# this default value
# 如果没有指定target的话，默认的target(vmlinux)
# 但这个可以被命令行、环境变量、或arch/$(ARCH)/Makefile中的重置
export KBUILD_IMAGE ?= vmlinux

#
# INSTALL_PATH specifies where to place the updated kernel and system map
# images. Default is /boot, but you can set it to other values
# 默认的INSTALL_PATH，也就是放置更新的kernel和system map images文件的文件夹，默认为/boot，可以重置
export INSTALL_PATH ?= /boot

#
# INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
# relocations required by build roots.  This is not defined in the
# makefile but the argument can be passed to make if needed.
#

MODLIB = $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
export MODLIB

#
#  INSTALL_MOD_STRIP, if defined, will cause modules to be
#  stripped after they are installed.  If INSTALL_MOD_STRIP is '1', then
#  the default option --strip-debug will be used.  Otherwise,
#  INSTALL_MOD_STRIP will used as the options to the strip command.

ifdef INSTALL_MOD_STRIP
ifeq ($(INSTALL_MOD_STRIP),1)
mod_strip_cmd = $(STRIP) --strip-debug
else
mod_strip_cmd = $(STRIP) $(INSTALL_MOD_STRIP)
endif # INSTALL_MOD_STRIP=1
else
mod_strip_cmd = true
endif # INSTALL_MOD_STRIP
export mod_strip_cmd

# 下面是编译的主体
ifeq ($(KBUILD_EXTMOD),)
# 设置core-y需要的目录
core-y += kernel/ mm/ fs/ ipc/ security/ crypto/ block/

vmlinux-dirs := $(patsubst %/,%,$(filter %/, $(init-y) $(init-m) \
     $(core-y) $(core-m) $(drivers-y) $(drivers-m) \
     $(net-y) $(net-m) $(libs-y) $(libs-m)))

vmlinux-alldirs := $(sort $(vmlinux-dirs) $(patsubst %/,%,$(filter %/, \
     $(init-n) $(init-) \
     $(core-n) $(core-) $(drivers-n) $(drivers-) \
     $(net-n)  $(net-)  $(libs-n)    $(libs-))))

# 下面表示所有init/都被init/built-in.o所代替
init-y := $(patsubst %/, %/built-in.o, $(init-y))
core-y := $(patsubst %/, %/built-in.o, $(core-y))
drivers-y := $(patsubst %/, %/built-in.o, $(drivers-y))
net-y := $(patsubst %/, %/built-in.o, $(net-y))
libs-y1 := $(patsubst %/, %/lib.a, $(libs-y))
libs-y2 := $(patsubst %/, %/built-in.o, $(libs-y))
libs-y := $(libs-y1) $(libs-y2)

# Build vmlinux
# ---------------------------------------------------------------------------
# vmlinux is built from the objects selected by $(vmlinux-init) and
# $(vmlinux-main). Most are built-in.o files from top-level directories
# in the kernel tree, others are specified in arch/$(ARCH)/Makefile.
# Ordering when linking is important, and $(vmlinux-init) must be first.
#
# vmlinux是由$(vmlinux-init)和$(vmlinux-man)组成，大部分都是在内核跟目下的顶层子目录
# 编译出的build-in.o，其它的事定义在archi/$(ARCH)/Makefile中定义的了。在链接时顺序很重要，
# 无论怎样$(vmlinux-init)要在开头
# vmlinux
#   ^
#   |
#   +-< $(vmlinux-init)
#   |   +--< init/version.o + more
#   |
#   +--< $(vmlinux-main)
#   |    +--< driver/built-in.o mm/built-in.o + more
#   |
#   +-< kallsyms.o (see description in CONFIG_KALLSYMS section)
#
# vmlinux version (uname -v) cannot be updated during normal
# descending-into-subdirs phase since we do not yet know if we need to
# update vmlinux.
# Therefore this step is delayed until just before final link of vmlinux -
# except in the kallsyms case where it is done just before adding the
# symbols to the kernel.
#
# System.map is generated to document addresses of all kernel symbols

vmlinux-init := $(head-y) $(init-y) # head-y定义在/arch/$(ARCH)/Makefile中
vmlinux-main := $(core-y) $(libs-y) $(drivers-y) $(net-y)
vmlinux-all  := $(vmlinux-init) $(vmlinux-main)
vmlinux-lds  := arch/$(SRCARCH)/kernel/vmlinux.lds # target架构的链接文件
export KBUILD_VMLINUX_OBJS := $(vmlinux-all) # 输出给子make

# Rule to link vmlinux - also used during CONFIG_KALLSYMS
# May be overridden by arch/$(ARCH)/Makefile
# 链接vmlinux的规则
quiet_cmd_vmlinux__ ?= LD      $@
      cmd_vmlinux__ ?= $(LD) $(LDFLAGS) $(LDFLAGS_vmlinux) -o $@ \
      -T $(vmlinux-lds) $(vmlinux-init)                          \
      --start-group $(vmlinux-main) --end-group                  \
      $(filter-out $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o FORCE ,$^)

# Generate new vmlinux version
# 声称新的vmlinux .version文件
# set -e 是设置shell的状态，如果任何命令的退出码为0，都立即中止执行
quiet_cmd_vmlinux_version = GEN     .version
      cmd_vmlinux_version = set -e;                     \
if [ ! -r .version ]; then\
  rm -f .version;\
  echo 1 >.version;\
else
\
  mv .version .old_version;\
  expr 0$$(cat .old_version) + 1 >.version;\
fi;
\
$(MAKE) $(build)=init

# Generate System.map
# 声称System.map文件,执行scripts/mksysmap这个脚本文件
quiet_cmd_sysmap = SYSMAP
      cmd_sysmap = $(CONFIG_SHELL) $(srctree)/scripts/mksysmap

# Link of vmlinux
# If CONFIG_KALLSYMS is set .version is already updated
# Generate System.map and verify that the content is consistent
# Use + in front of the vmlinux_version rule to silent warning with make -j2
# First command is ':' to allow us to use + in front of the rule
# 链接vmlinux，前提是CONFIG_KALLSYSS已经被设置，并且.version已经被更新
# 生成System.map文件，并且验证内容是否已经稳定
# 下面是一些命令包，即一组命令可以在多个规则中使用
# 相同的一组命令，通过define来定义这组命令作为一个命令，以后再需要的规则中
# 通过变量名直接引用。
define rule_vmlinux__
:
$(if $(CONFIG_KALLSYMS),,+$(call cmd,vmlinux_version))

$(call cmd,vmlinux__)
$(Q)echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd

$(Q)$(if $($(quiet)cmd_sysmap),                                      \
  echo '  $($(quiet)cmd_sysmap)  System.map' &&)                     \
$(cmd_sysmap) $@ System.map;                                         \
if [ $$? -ne 0 ]; then                                               \
rm -f $@;                                                    \
/bin/false;                                                  \
fi;
$(verify_kallsyms)
endef

# 执行完上述命令，vmlinux就已经链接完成，后面还有bzimage

ifdef CONFIG_KALLSYMS
# Generate section listing all symbols and add it into vmlinux $(kallsyms.o)
# It's a three stage process:
# o .tmp_vmlinux1 has all symbols and sections, but __kallsyms is
#   empty
#   Running kallsyms on that gives us .tmp_kallsyms1.o with
#   the right size - vmlinux version (uname -v) is updated during this step
# o .tmp_vmlinux2 now has a __kallsyms section of the right size,
#   but due to the added section, some addresses have shifted.
#   From here, we generate a correct .tmp_kallsyms2.o
# o The correct .tmp_kallsyms2.o is linked into the final vmlinux.
# o Verify that the System.map from vmlinux matches the map from
#   .tmp_vmlinux2, just in case we did not generate kallsyms correctly.
# o If CONFIG_KALLSYMS_EXTRA_PASS is set, do an extra pass using
#   .tmp_vmlinux3 and .tmp_kallsyms3.o.  This is only meant as a
#   temporary bypass to allow the kernel to be built while the
#   maintainers work out what went wrong with kallsyms.

ifdef CONFIG_KALLSYMS_EXTRA_PASS
last_kallsyms := 3
else
last_kallsyms := 2
endif

kallsyms.o := .tmp_kallsyms$(last_kallsyms).o

define verify_kallsyms
$(Q)$(if $($(quiet)cmd_sysmap),                                      \
  echo '  $($(quiet)cmd_sysmap)  .tmp_System.map' &&)                \
  $(cmd_sysmap) .tmp_vmlinux$(last_kallsyms) .tmp_System.map
$(Q)cmp -s System.map .tmp_System.map ||                             \
(echo Inconsistent kallsyms data;                            \
 echo Try setting CONFIG_KALLSYMS_EXTRA_PASS;                \
 rm .tmp_kallsyms* ; /bin/false )
endef

# Update vmlinux version before link
# Use + in front of this rule to silent warning about make -j1
# First command is ':' to allow us to use + in front of this rule
cmd_ksym_ld = $(cmd_vmlinux__)
define rule_ksym_ld
: 
+$(call cmd,vmlinux_version)
$(call cmd,vmlinux__)
$(Q)echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd
endef

# Generate .S file with all kernel symbols
quiet_cmd_kallsyms = KSYM    $@
      cmd_kallsyms = $(NM) -n $< | $(KALLSYMS) \
                     $(if $(CONFIG_KALLSYMS_ALL),--all-symbols) > $@

.tmp_kallsyms1.o .tmp_kallsyms2.o .tmp_kallsyms3.o: %.o: %.S scripts FORCE
$(call if_changed_dep,as_o_S)

.tmp_kallsyms%.S: .tmp_vmlinux% $(KALLSYMS)
$(call cmd,kallsyms)

# .tmp_vmlinux1 must be complete except kallsyms, so update vmlinux version
.tmp_vmlinux1: $(vmlinux-lds) $(vmlinux-all) FORCE
$(call if_changed_rule,ksym_ld)

.tmp_vmlinux2: $(vmlinux-lds) $(vmlinux-all) .tmp_kallsyms1.o FORCE
$(call if_changed,vmlinux__)

.tmp_vmlinux3: $(vmlinux-lds) $(vmlinux-all) .tmp_kallsyms2.o FORCE
$(call if_changed,vmlinux__)

# Needs to visit scripts/ before $(KALLSYMS) can be used.
$(KALLSYMS): scripts ;

# Generate some data for debugging strange kallsyms problems
debug_kallsyms: .tmp_map$(last_kallsyms)

.tmp_map%: .tmp_vmlinux% FORCE
($(OBJDUMP) -h $< | $(AWK) '/^ +[0-9]/{print $$4 " 0 " $$2}'; $(NM) $<) | sort > $@

.tmp_map3: .tmp_map2

.tmp_map2: .tmp_map1

endif # ifdef CONFIG_KALLSYMS

# Do modpost on a prelinked vmlinux. The finally linked vmlinux has
# relevant sections renamed as per the linker script.
quiet_cmd_vmlinux-modpost = LD      $@
      cmd_vmlinux-modpost = $(LD) $(LDFLAGS) -r -o $@                          \
 $(vmlinux-init) --start-group $(vmlinux-main) --end-group             \
 $(filter-out $(vmlinux-init) $(vmlinux-main) $(vmlinux-lds) FORCE ,$^)
define rule_vmlinux-modpost
:
+$(call cmd,vmlinux-modpost)
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@
$(Q)echo 'cmd_$@ := $(cmd_vmlinux-modpost)' > $(dot-target).cmd
endef

# vmlinux image - including updated kernel symbols
vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o $(kallsyms.o) FORCE
ifdef CONFIG_HEADERS_CHECK
$(Q)$(MAKE) -f $(srctree)/Makefile headers_check
endif
ifdef CONFIG_SAMPLES
$(Q)$(MAKE) $(build)=samples
endif
$(call vmlinux-modpost)
$(call if_changed_rule,vmlinux__)
$(Q)rm -f .old_version

# build vmlinux.o first to catch section mismatch errors early
ifdef CONFIG_KALLSYMS
.tmp_vmlinux1: vmlinux.o
endif
vmlinux.o: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) FORCE
$(call if_changed_rule,vmlinux-modpost)

# 实际生成objects从这里开始
# The actual objects are generated when descending, 
# make sure no implicit rule kicks in
$(sort $(vmlinux-init) $(vmlinux-main)) $(vmlinux-lds): $(vmlinux-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 += $(vmlinux-dirs)
$(vmlinux-dirs): prepare scripts
$(Q)$(MAKE) $(build)=$@

# Build the kernel release string
#
# The KERNELRELEASE value built here is stored in the file
# include/config/kernel.release, and is used when executing several
# make targets, such as "make install" or "make modules_install."
#
# The eventual kernel release string consists of the following fields,
# shown in a hierarchical format to show how smaller parts are concatenated
# to form the larger and final value, with values coming from places like
# the Makefile, kernel config options, make command line options and/or
# SCM tag information.
#
# $(KERNELVERSION)
#   $(VERSION)eg, 2
#   $(PATCHLEVEL)eg, 6
#   $(SUBLEVEL)eg, 18
#   $(EXTRAVERSION)eg, -rc6
# $(localver-full)
#   $(localver)
#     localversion*(files without backups, containing '~')
#     $(CONFIG_LOCALVERSION)(from kernel config setting)
#   $(localver-auto)(only if CONFIG_LOCALVERSION_AUTO is set)
#     ./scripts/setlocalversion(SCM tag, if one exists)
#     $(LOCALVERSION)(from make command line if provided)
#
#  Note how the final $(localver-auto) string is included *only* if the
# kernel config option CONFIG_LOCALVERSION_AUTO is selected.  Also, at the
# moment, only git is supported but other SCMs can edit the script
# scripts/setlocalversion and add the appropriate checks as needed.
# 生成内核发布版本字符串

pattern = ".*/localversion[^~]*"
string  = $(shell cat /dev/null \
   `find $(objtree) $(srctree) -maxdepth 1 -regex $(pattern) | sort -u`)

localver = $(subst $(space),, $(string) \
      $(patsubst "%",%,$(CONFIG_LOCALVERSION)))

# If CONFIG_LOCALVERSION_AUTO is set scripts/setlocalversion is called
# and if the SCM is know a tag from the SCM is appended.
# The appended tag is determined by the SCM used.
#
# Currently, only git is supported.
# Other SCMs can edit scripts/setlocalversion and add the appropriate
# checks as needed.
ifdef CONFIG_LOCALVERSION_AUTO
_localver-auto = $(shell $(CONFIG_SHELL) \
                  $(srctree)/scripts/setlocalversion $(srctree))
localver-auto  = $(LOCALVERSION)$(_localver-auto)
endif

localver-full = $(localver)$(localver-auto)

# Store (new) KERNELRELASE string in include/config/kernel.release
# 将新生成的KERNELRELEASE字符串存储到include/config/kernel.release文件中
kernelrelease = $(KERNELVERSION)$(localver-full)
include/config/kernel.release: include/config/auto.conf FORCE
$(Q)rm -f $@
$(Q)echo $(kernelrelease) > $@

# 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
# 定义伪目标，并且按照以来顺序列出
# prepareN在PrepareN-1之前完成
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:
# prepare3 用来检查我们是否定义了独立输出目录，如果定义了，则
# 1） 检查make没有在kernel src目录下执行
# 2） 建立include2 目录，用来做第二级asm symlink
# 1) Check that make has not been executed in the kernel src $(srctree)
# 2) Create the include2 directory, used for the second asm symlink
prepare3: include/config/kernel.release
ifneq ($(KBUILD_SRC),)
@echo '  Using $(srctree) as source for kernel'
$(Q)if [ -f $(srctree)/.config -o -d $(srctree)/include/config ]; then \
echo "  $(srctree) is not clean, please run 'make mrproper'";\
echo "  in the '$(srctree)' directory.";\
/bin/false; \
fi;
$(Q)if [ ! -d include2 ]; then mkdir -p include2; fi;
$(Q)ln -fsn $(srctree)/include/asm-$(SRCARCH) include2/asm
endif

# prepare2 creates a makefile if using a separate output directory
# prepare2用来在输出目录下创建一个makefile
prepare2: prepare3 outputmakefile

prepare1: prepare2 include/linux/version.h include/linux/utsrelease.h \
                   include/asm include/config/auto.conf
$(cmd_crmodverdir)

archprepare: prepare1 scripts_basic

prepare0: archprepare FORCE
$(Q)$(MAKE) $(build)=.
$(Q)$(MAKE) $(build)=. missing-syscalls

# All the preparing..
# 所有prepare执行完成
prepare: prepare0

# Leave this as default for preprocessing vmlinux.lds.S, which is now
# done in arch/$(ARCH)/kernel/Makefile
# 默认预处理vmlinux.lds.S的CPPFLAGS,输出给子make
export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)

# The asm symlink changes when $(ARCH) changes.
# Detect this and ask user to run make mrproper
# 在$(ARCH)改变时symlink也需要改变
# 下面是对改变进行检测，如果有问题，则询问用户run make mrproper
include/asm: FORCE
$(Q)set -e; asmlink=`readlink include/asm | cut -d '-' -f 2`;   \
if [ -L include/asm ]; then                                     \
if [ "$$asmlink" != "$(SRCARCH)" ]; then                \
echo "ERROR: the symlink $@ points to asm-$$asmlink but asm-$(SRCARCH) was expected"; \
echo "       set ARCH or save .config and run 'make mrproper' to fix it";             \
exit 1;                                         \
fi;                                                     \
else                                                            \
echo '  SYMLINK $@ -> include/asm-$(SRCARCH)';          \
if [ ! -d include ]; then                               \
mkdir -p include;                               \
fi;                                                     \
ln -fsn asm-$(SRCARCH) $@;                              \
fi

# Generate some files
# ---------------------------------------------------------------------------

# KERNELRELEASE can change from a few different places, meaning version.h
# needs to be updated, so this check is forced on all builds
# 下面是检测是否有些文件需要更新，如version.h
uts_len := 64
define filechk_utsrelease.h
if [ `echo -n "$(KERNELRELEASE)" | wc -c ` -gt $(uts_len) ]; then \
  echo '"$(KERNELRELEASE)" exceeds $(uts_len) characters' >&2;    \
  exit 1;                                                         \
fi;                                                               \
(echo \#define UTS_RELEASE \"$(KERNELRELEASE)\";)
endef

define filechk_version.h
(echo \#define LINUX_VERSION_CODE $(shell                             \
expr $(VERSION) \* 65536 + $(PATCHLEVEL) \* 256 + $(SUBLEVEL));     \
echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))';)
endef

include/linux/version.h: $(srctree)/Makefile FORCE
$(call filechk,version.h)

include/linux/utsrelease.h: include/config/kernel.release FORCE
$(call filechk,utsrelease.h)

# ---------------------------------------------------------------------------

PHONY += depend dep
depend dep:
@echo '*** Warning: make $@ is unnecessary now.'

# ---------------------------------------------------------------------------
# Kernel headers
# 内核头文件路径
INSTALL_HDR_PATH=$(objtree)/usr
export INSTALL_HDR_PATH

HDRFILTER=generic i386 x86_64
HDRARCHES=$(filter-out $(HDRFILTER),$(patsubst $(srctree)/include/asm-%/Kbuild,%,$(wildcard $(srctree)/include/asm-*/Kbuild)))

PHONY += headers_install_all
headers_install_all: include/linux/version.h scripts_basic FORCE
$(Q)$(MAKE) $(build)=scripts scripts/unifdef
$(Q)for arch in $(HDRARCHES); do \
 $(MAKE) ARCH=$$arch -f $(srctree)/scripts/Makefile.headersinst obj=include BIASMDIR=-bi-$$arch ;\
 done

PHONY += headers_install
headers_install: include/linux/version.h scripts_basic FORCE
@if [ ! -r $(srctree)/include/asm-$(SRCARCH)/Kbuild ]; then \
  echo '*** Error: Headers not exportable for this architecture ($(SRCARCH))'; \
  exit 1 ; fi
$(Q)$(MAKE) $(build)=scripts scripts/unifdef
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.headersinst ARCH=$(SRCARCH) obj=include

PHONY += headers_check_all
headers_check_all: headers_install_all
$(Q)for arch in $(HDRARCHES); do \
 $(MAKE) ARCH=$$arch -f $(srctree)/scripts/Makefile.headersinst obj=include BIASMDIR=-bi-$$arch HDRCHECK=1 ;\
 done

PHONY += headers_check
headers_check: headers_install
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.headersinst ARCH=$(SRCARCH) obj=include HDRCHECK=1

# ---------------------------------------------------------------------------
# Modules

ifdef CONFIG_MODULES

# By default, build modules as well

all: modules

# Build modules
#
# A module can be listed more than once in obj-m resulting in
# duplicate lines in modules.order files.  Those are removed
# using awk while concatenating to the final file.

PHONY += modules
modules: $(vmlinux-dirs) $(if $(KBUILD_BUILTIN),vmlinux)
$(Q)$(AWK) '!x[$$0]++' $(vmlinux-dirs:%=$(objtree)/%/modules.order) > $(objtree)/modules.order
@echo '  Building modules, stage 2.';
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost

# Target to prepare building external modules
PHONY += modules_prepare
modules_prepare: prepare scripts

# Target to install modules
PHONY += modules_install
modules_install: _modinst_ _modinst_post

PHONY += _modinst_
_modinst_:
@if [ -z "`$(DEPMOD) -V 2>/dev/null | grep module-init-tools`" ]; then \
echo "Warning: you may need to install module-init-tools"; \
echo "See http://www.codemonkey.org.uk/docs/post-halloween-2.6.txt";\ sleep 1; \
fi
@rm -rf $(MODLIB)/kernel
@rm -f $(MODLIB)/source
@mkdir -p $(MODLIB)/kernel
@ln -s $(srctree) $(MODLIB)/source
@if [ ! $(objtree) -ef  $(MODLIB)/build ]; then \
rm -f $(MODLIB)/build ; \
ln -s $(objtree) $(MODLIB)/build ; \
fi
@cp -f $(objtree)/modules.order $(MODLIB)/
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modinst

# This depmod is only for convenience to give the initial
# boot a modules.dep even before / is mounted read-write.  However the
# boot script depmod is the master version.
PHONY += _modinst_post
_modinst_post: _modinst_
$(call cmd,depmod)

else # CONFIG_MODULES

# Modules not configured
# ---------------------------------------------------------------------------

modules modules_install: FORCE
@echo
@echo "The present kernel configuration has modules disabled."
@echo "Type 'make config' and enable loadable module support."
@echo "Then build a kernel with module support enabled."
@echo
@exit 1

endif # CONFIG_MODULES

###
# 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操作分三个等级来完成
# make clean 删除大部分生成的文件，不过保留那些勇于build外部模块的文件
# make mrproper 删除当前配置和所有生成的文件
# make distclean 删除可编辑的备份文件，patch文件和make clean需要删除的那些文件和目录
CLEAN_DIRS  += $(MODVERDIR)
CLEAN_FILES += vmlinux System.map \
                .tmp_kallsyms* .tmp_version .tmp_vmlinux* .tmp_System.map

# Directories & files removed with 'make mrproper'
# make mrproper需要删除的目录和文件
MRPROPER_DIRS  += include/config include2 usr/include
MRPROPER_FILES += .config .config.old include/asm .version .old_version \
                  include/linux/autoconf.h include/linux/version.h      \
                  include/linux/utsrelease.h                            \
  Module.symvers tags TAGS cscope*

# clean - Delete most, but leave enough to build external modules
#
clean: rm-dirs  := $(CLEAN_DIRS)
clean: rm-files := $(CLEAN_FILES)
clean-dirs      := $(addprefix _clean_,$(srctree) $(vmlinux-alldirs))

PHONY += $(clean-dirs) clean archclean
$(clean-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)

# clean目标
clean: archclean $(clean-dirs)
$(call cmd,rmdirs)
$(call cmd,rmfiles)
@find . $(RCS_FIND_IGNORE) \
\( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
-o -name '*.symtypes' -o -name 'modules.order' \) \
-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_,Documentation/DocBook scripts)

PHONY += $(mrproper-dirs) mrproper archmrproper
$(mrproper-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _mrproper_%,%,$@)

# mrproper目标
mrproper: clean archmrproper $(mrproper-dirs)
$(call cmd,rmdirs)
$(call cmd,rmfiles)

# distclean
#
PHONY += distclean

# distclean 目标
distclean: mrproper
@find $(srctree) $(RCS_FIND_IGNORE) \
\( -name '*.orig' -o -name '*.rej' -o -name '*~' \
-o -name '*.bak' -o -name '#*#' -o -name '.*.orig' \
-o -name '.*.rej' -o -size 0 \
-o -name '*%' -o -name '.*.cmd' -o -name 'core' \) \
-type f -print | xargs rm -f

# Packaging of the kernel to various formats
# ---------------------------------------------------------------------------
# rpm target kept for backward compatibility
# 各种内核打包格式，rpm目标保持向后兼容
package-dir := $(srctree)/scripts/package

%pkg: include/config/kernel.release FORCE
$(Q)$(MAKE) $(build)=$(package-dir) $@
rpm: include/config/kernel.release FORCE
$(Q)$(MAKE) $(build)=$(package-dir) $@

# Brief documentation of the typical targets used
# ---------------------------------------------------------------------------
# 典型的目标简短介绍文档
boards := $(wildcard $(srctree)/arch/$(ARCH)/configs/*_defconfig)
boards := $(notdir $(boards))

# help目标，执行make help会执行如下命令，输出帮助信息
help:
@echo  'Cleaning targets:'
@echo  '  clean  - Remove most generated files but keep the config and'
@echo  '                    enough build support to build external modules'
@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 targets marked with [*]'
@echo  '* vmlinux  - Build the bare kernel'
@echo  '* modules  - Build all modules'
@echo  '  modules_install - Install all modules to INSTALL_MOD_PATH (default: /)'
@echo  '  dir/            - Build all files in dir and below'
@echo  '  dir/file.[ois]  - Build specified target only'
@echo  '  dir/file.ko     - Build module including final link'
@echo  '  prepare         - Set up for building external modules'
@echo  '  tags/TAGS  - Generate tags file for editors'
@echo  '  cscope  - Generate cscope index'
@echo  '  kernelrelease  - Output the release version string'
@echo  '  kernelversion  - Output the version stored in Makefile'
@if [ -r $(srctree)/include/asm-$(SRCARCH)/Kbuild ]; then \
 echo  '  headers_install - Install sanitised kernel headers to INSTALL_HDR_PATH'; \
 echo  '                    (default: $(INSTALL_HDR_PATH))'; \
 fi
@echo  ''
@echo  'Static analysers'
@echo  '  checkstack      - Generate a list of stack hogs'
@echo  '  namespacecheck  - Name space analysis on compiled kernel'
@echo  '  versioncheck    - Sanity check on version.h usage'
@echo  '  includecheck    - Check for duplicate included header files'
@echo  '  export_report   - List the usages of all exported symbols'
@if [ -r $(srctree)/include/asm-$(SRCARCH)/Kbuild ]; then \
 echo  '  headers_check   - Sanity check on exported headers'; \
 fi
@echo  ''
@echo  'Kernel packaging:'
@$(MAKE) $(build)=$(package-dir) help
@echo  ''
@echo  'Documentation targets:'
@$(MAKE) -f $(srctree)/Documentation/DocBook/Makefile dochelp
@echo  ''
@echo  'Architecture specific targets ($(ARCH)):'
@$(if $(archhelp),$(archhelp),\
echo '  No architecture specific help defined for $(ARCH)')
@echo  ''
@$(if $(boards), \
$(foreach b, $(boards), \
printf "  %-24s - Build for %s\\n" $(b) $(subst _defconfig,,$(b));) \
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  ''
@echo  'Execute "make" or "make all" to build all targets marked with [*] '
@echo  'For further info see the ./README file'

# Documentation targets
# ---------------------------------------------------------------------------
# 文档目标，通过对Documentation/DocBook目录下的文件进行处理，声称文档文件
%docs: scripts_basic FORCE
$(Q)$(MAKE) $(build)=Documentation/DocBook $@

else # KBUILD_EXTMOD

# 编译外部模块
###
# External module support.
# When building external modules the kernel used as basis is considered
# read-only, and no consistency checks are made and the make
# system is not used on the basis kernel. If updates are required
# in the basis kernel ordinary make commands (without M=...) must
# be used.
#
# The following are the only valid targets when building external
# modules.
# make M=dir clean     Delete all automatically generated files
# make M=dir modules   Make all modules in specified dir
# make M=dir        Same as 'make M=dir modules'
# make M=dir modules_install
#                      Install the modules built in the module directory
#                      Assumes install directory is already created

# We are always building modules
KBUILD_MODULES := 1
PHONY += crmodverdir
crmodverdir:
$(cmd_crmodverdir)

PHONY += $(objtree)/Module.symvers
$(objtree)/Module.symvers:
@test -e $(objtree)/Module.symvers || ( \
echo; \
echo "  WARNING: Symbol version dump $(objtree)/Module.symvers"; \
echo "           is missing; modules will have no dependencies and modversions."; \
echo )

module-dirs := $(addprefix _module_,$(KBUILD_EXTMOD))
PHONY += $(module-dirs) modules
$(module-dirs): crmodverdir $(objtree)/Module.symvers
$(Q)$(MAKE) $(build)=$(patsubst _module_%,%,$@)

modules: $(module-dirs)
@echo '  Building modules, stage 2.';
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost

PHONY += modules_install
modules_install: _emodinst_ _emodinst_post

install-dir := $(if $(INSTALL_MOD_DIR),$(INSTALL_MOD_DIR),extra)
PHONY += _emodinst_
_emodinst_:
$(Q)mkdir -p $(MODLIB)/$(install-dir)
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modinst

PHONY += _emodinst_post
_emodinst_post: _emodinst_
$(call cmd,depmod)

clean-dirs := $(addprefix _clean_,$(KBUILD_EXTMOD))

PHONY += $(clean-dirs) clean
$(clean-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)

clean: rm-dirs := $(MODVERDIR)
clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers
clean: $(clean-dirs)
$(call cmd,rmdirs)
$(call cmd,rmfiles)
@find $(KBUILD_EXTMOD) $(RCS_FIND_IGNORE) \
\( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \) \
-type f -print | xargs rm -f

help:
@echo  '  Building external modules.'
@echo  '  Syntax: make -C path/to/kernel/src M=$$PWD target'
@echo  ''
@echo  '  modules         - default target, build the module(s)'
@echo  '  modules_install - install the module'
@echo  '  clean           - remove generated files in module directory only'
@echo  ''

# Dummies...
PHONY += prepare scripts
prepare: ;
scripts: ;
endif # KBUILD_EXTMOD

# Generate tags for editors
# ---------------------------------------------------------------------------

#We want __srctree to totally vanish out when KBUILD_OUTPUT is not set
#(which is the most common case IMHO) to avoid unneeded clutter in the big tags file.
#Adding $(srctree) adds about 20M on i386 to the size of the output file!

ifeq ($(src),$(obj))
__srctree =
else
__srctree = $(srctree)/
endif

ifeq ($(ALLSOURCE_ARCHS),)
ifeq ($(ARCH),um)
ALLINCLUDE_ARCHS := $(ARCH) $(SUBARCH)
else
ALLINCLUDE_ARCHS := $(SRCARCH)
endif
else
#Allow user to specify only ALLSOURCE_PATHS on the command line, keeping existing behaviour.
ALLINCLUDE_ARCHS := $(ALLSOURCE_ARCHS)
endif

ALLSOURCE_ARCHS := $(SRCARCH)

define find-sources
        ( for arch in $(ALLSOURCE_ARCHS) ; do \
       find $(__srctree)arch/$${arch} $(RCS_FIND_IGNORE) \
            -name $1 -print; \
  done ; \
  find $(__srctree)security/selinux/include $(RCS_FIND_IGNORE) \
       -name $1 -print; \
  find $(__srctree)include $(RCS_FIND_IGNORE) \
       \( -name config -o -name 'asm-*' \) -prune \
       -o -name $1 -print; \
  for arch in $(ALLINCLUDE_ARCHS) ; do \
       find $(__srctree)include/asm-$${arch} $(RCS_FIND_IGNORE) \
            -name $1 -print; \
  done ; \
  find $(__srctree)include/asm-generic $(RCS_FIND_IGNORE) \
       -name $1 -print; \
  find $(__srctree) $(RCS_FIND_IGNORE) \
       \( -name include -o -name arch -o -name '.tmp_*' \) -prune -o \
       -name $1 -print; \
  )
endef

define all-sources
$(call find-sources,'*.[chS]')
endef
define all-kconfigs
$(call find-sources,'Kconfig*')
endef
define all-defconfigs
$(call find-sources,'defconfig')
endef

define xtags
if $1 --version 2>&1 | grep -iq exuberant; then \
    $(all-sources) | xargs $1 -a \
-I __initdata,__exitdata,__acquires,__releases \
-I __read_mostly,____cacheline_aligned,____cacheline_aligned_in_smp,____cacheline_internodealigned_in_smp \
-I EXPORT_SYMBOL,EXPORT_SYMBOL_GPL \
--extra=+f --c-kinds=+px \
--regex-asm='/^ENTRY\(([^)]*)\).*/\1/'; \
    $(all-kconfigs) | xargs $1 -a \
--langdef=kconfig \
--language-force=kconfig \
--regex-kconfig='/^[[:blank:]]*config[[:blank:]]+([[:alnum:]_]+)/\1/'; \
    $(all-defconfigs) | xargs -r $1 -a \
--langdef=dotconfig \
--language-force=dotconfig \
--regex-dotconfig='/^#?[[:blank:]]*(CONFIG_[[:alnum:]_]+)/\1/'; \
elif $1 --version 2>&1 | grep -iq emacs; then \
    $(all-sources) | xargs $1 -a; \
    $(all-kconfigs) | xargs $1 -a \
--regex='/^[ \t]*config[ \t]+\([a-zA-Z0-9_]+\)/\1/'; \
    $(all-defconfigs) | xargs -r $1 -a \
--regex='/^#?[ \t]?\(CONFIG_[a-zA-Z0-9_]+\)/\1/'; \
else \
    $(all-sources) | xargs $1 -a; \
fi
endef

quiet_cmd_cscope-file = FILELST cscope.files
      cmd_cscope-file = (echo \-k; echo \-q; $(all-sources)) > cscope.files

quiet_cmd_cscope = MAKE    cscope.out
      cmd_cscope = cscope -b

cscope: FORCE
$(call cmd,cscope-file)
$(call cmd,cscope)

quiet_cmd_TAGS = MAKE   $@
define cmd_TAGS
rm -f $@; \
$(call xtags,etags)
endef

TAGS: FORCE
$(call cmd,TAGS)

quiet_cmd_tags = MAKE   $@
define cmd_tags
rm -f $@; \
$(call xtags,ctags)
endef

tags: FORCE
$(call cmd,tags)

# Scripts to check various things for consistency
# ---------------------------------------------------------------------------

includecheck:
find * $(RCS_FIND_IGNORE) \
-name '*.[hcS]' -type f -print | sort \
| xargs $(PERL) -w $(srctree)/scripts/checkincludes.pl

versioncheck:
find * $(RCS_FIND_IGNORE) \
-name '*.[hcS]' -type f -print | sort \
| xargs $(PERL) -w $(srctree)/scripts/checkversion.pl

namespacecheck:
$(PERL) $(srctree)/scripts/namespace.pl

export_report:
$(PERL) $(srctree)/scripts/export_report.pl

endif #ifeq ($(config-targets),1)
endif #ifeq ($(mixed-targets),1)

PHONY += checkstack kernelrelease kernelversion

# UML needs a little special treatment here.  It wants to use the host
# toolchain, so needs $(SUBARCH) passed to checkstack.pl.  Everyone
# else wants $(ARCH), including people doing cross-builds, which means
# that $(SUBARCH) doesn't work here.
ifeq ($(ARCH), um)
CHECKSTACK_ARCH := $(SUBARCH)
else
CHECKSTACK_ARCH := $(ARCH)
endif
checkstack:
$(OBJDUMP) -d vmlinux $$(find . -name '*.ko') | \
$(PERL) $(src)/scripts/checkstack.pl $(CHECKSTACK_ARCH)

kernelrelease:
$(if $(wildcard include/config/kernel.release), $(Q)echo $(KERNELRELEASE), \
$(error kernelrelease not valid - run 'make prepare' to update it))
kernelversion:
@echo $(KERNELVERSION)

# 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)
%.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)

# Run depmod only is we have System.map and depmod is executable
# and we build for the host arch
quiet_cmd_depmod = DEPMOD  $(KERNELRELEASE)
      cmd_depmod = \
if [ -r System.map -a -x $(DEPMOD) ]; then                              \
$(DEPMOD) -ae -F System.map                                     \
$(if $(strip $(INSTALL_MOD_PATH)), -b $(INSTALL_MOD_PATH) -r)   \
$(KERNELRELEASE);                                               \
fi

# Create temporary dir for module support files
# clean it up only when building all modules
cmd_crmodverdir = $(Q)mkdir -p $(MODVERDIR) \
                  $(if $(KBUILD_MODULES),; rm -f $(MODVERDIR)/*)

a_flags = -Wp,-MD,$(depfile) $(KBUILD_AFLAGS) $(AFLAGS_KERNEL) \
  $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
  $(modkern_aflags) $(EXTRA_AFLAGS) $(AFLAGS_$(basetarget).o)

quiet_cmd_as_o_S = AS      $@
cmd_as_o_S       = $(CC) $(a_flags) -c -o $@ $<

# 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

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

endif # skip-makefile

PHONY += FORCE
FORCE:

# Declare the contents of the .PHONY variable as phony.  We keep that
# information in a variable se we can use it in if_changed and friends.
.PHONY: $(PHONY)

有道笔记连接: http://note.youdao.com/share/?id=64eacaccf561bf04af84d2b6cd16c7bc&type=note
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