emmoblin.github.com
分类： LINUX
2011-01-20 23:28:35
VERSION = 2
# 给变量VERSION赋值
PATCHLEVEL = 6
# 给变量PATCHLEVEL赋值
SUBLEVEL = 22
# 给变量SUBLEVEL赋值
EXTRAVERSION = .6
# 给变量EXTRAVERSION赋值
NAME = Holy Dancing Manatees, Batman!
# 给变量NAME赋值
# *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 avoid hard-to-debug behavour);
# o print "Entering directory ...";
MAKEFLAGS += -rR --no-print-directory
# 操作符“+=”的作用是给变量（“+=”前面的MAKEFLAGS）追加值。
# 如果变量（“+=”前面的MAKEFLAGS）之前没有定义过，那么，“+=”会自动变成“=”；
# 如果前面有变量（“+=”前面的MAKEFLAGS）定义，那么“+=”会继承于前次操作的赋值符；
# 如果前一次的是“:=”，那么“+=”会以“:=”作为其赋值符
# 在执行make时的命令行选项参数被通过变量 “MAKEFLAGS”传递给子目录下的make程序。
# 对于这个变量除非使用指示符“unexport”对它们进行声明，它们在整个make的执行过程中始终被自动的传递给所有的子make。
# 还有个特殊变量SHELL与MAKEFLAGS一样，默认情况（没有用“unexport”声明）下在整个make的执行过程中被自动的传递给所有的子make。
#
# -rR --no-print-directory
# -r disable the built-in impilict rules.
# -R disable the built-in variable setttings.
# --no-print-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
ifdef V
ifeq ("$(origin V)", "command line")
KBUILD_VERBOSE = $(V)
endif
endif
ifndef KBUILD_VERBOSE
KBUILD_VERBOSE = 0
endif
# “ifdef”是条件关键字。语法是ifdef
# ifdef只检验一个变量是否被赋值，它并不会去推导这个变量，并不会把变量扩展到当前位置。
# “ifeq”与“ifdef”类似。
# “ifeq”语法是ifeq (
#
# 函数origin并不操作变量的值，只是告诉你你的这个变量是哪里来的。
# 语法是： $(origin
# origin函数的返回值有：
# “undefined”从来没有定义过、“default”是一个默认的定义、“environment”是一个环境变量、
# “file”这个变量被定义在Makefile中、“command line”这个变量是被命令行定义的、
# “override”是被override指示符重新定义的、“automatic”是一个命令运行中的自动化变量
#
# 应用变量的语法是：$(变量名)。如KBUILD_VERBOSE = $(V)中的$(V)。
#
# KBUILD_VERBOSE的值根据在命令行中是否定义了变量V，
# 当没有定义时，默认为V＝O，输出为short version；可以用make V=1 来输出全部的命令。
#
# ifndef与ifdef语法类似，但功能恰好相反。ifndef是判断变量是不是没有被赋值。
# 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.
ifdef C
ifeq ("$(origin C)", "command line")
KBUILD_CHECKSRC = $(C)
endif
endif
ifndef KBUILD_CHECKSRC
KBUILD_CHECKSRC = 0
endif
# ifdef是Makefile的条件关键字，其语法是：ifdef
# 如果变量
# ifndef也是Makefile的条将关键字，功能与ifdef相反，语法相似。
# Use make M=dir to specify directory of external module to build
# Old syntax make ... SUBDIRS=$PWD is still supported
# Setting the environment variable KBUILD_EXTMOD take precedence
ifdef SUBDIRS
KBUILD_EXTMOD ?= $(SUBDIRS)
endif
ifdef M
ifeq ("$(origin M)", "command line")
KBUILD_EXTMOD := $(M)
endif
endif
# ifdef是Makefile的条件关键字，其语法是：ifdef
# 如果变量
#
# ifeq是Makefile的条件关键字，其语法是：ifeq (
#
# 操作符“：=”与操作符“+=”的功能相同，只是操作符“：=”后面的用来定义变量（KBUILD_EXTMOD）的变量M只能是前面定义好的，
# 如果操作符“？=”前面的变量KBUILD_EXTMOD没有定义过，那么就将SUBDIRS赋给KBUILD_EXTMOD；
# 如果定义过，则语句KBUILD_EXTMOD ?= $(SUBDIRS)什么也不做。
# kbuild supports saving output files in a separate directory.
# To locate output files in a separate directory two syntaxes are supported.
# In both cases the working directory must be the root of the kernel src.
# 1) O=
# Use "make O=dir/to/store/output/files/"
#
# 2) Set KBUILD_OUTPUT
# Set the environment variable KBUILD_OUTPUT to point to the directory
# where the output files shall be placed.
# export KBUILD_OUTPUT=dir/to/store/output/files/
# make
#
# The O= assignment takes precedence over the KBUILD_OUTPUT environment
# variable.
# KBUILD_SRC is set on invocation of make in OBJ directory
# KBUILD_SRC is not intended to be used by the regular user (for now)
ifeq ($(KBUILD_SRC),)
# ifeq是Makefile的条件关键字，其语法是：ifeq (
# OK, Make called in directory where kernel src resides
# Do we want to locate output files in a separate directory?
ifdef O
ifeq ("$(origin O)", "command line")
KBUILD_OUTPUT := $(O)
endif
endif
# ifdef是Makefile的条件关键字，其语法是：ifdef
# 如果变量
# ifeq是Makefile的条件关键字，其语法是：ifeq (
# origin是Makefile的一个判别变量是哪里来的函数，其语法是：$(origin
# That's our default target when none is given on the command line
PHONY := _all
_all:
# 为变量PHONY追加_all
# Makefile的规则：
# 目标：依赖文件
# 命令1
# 命令2
# ...
#
# 没有依赖文件的目标称为“伪目标”。伪目标并不是一个文件，只是一个标签。
# 由于伪目标不是一个文件，所以make无法生成它的依赖关系和决定它是否要执行，
# 只有在命令行中输入（即显示地指明）这个“目标”才能让其生效,此处为"make _all"。
ifneq ($(KBUILD_OUTPUT),)
# ifneq是Makefile的条件关键字，其语法是：ifneq (
# 功能是：比较参数“arg1”和“arg2”的值是否不相同，功能与ifeq相反。
# Invoke a second make in the output directory, passing relevant variables
# check that the output directory actually exists
saved-output := $(KBUILD_OUTPUT)
KBUILD_OUTPUT := $(shell cd $(KBUILD_OUTPUT) && /bin/pwd)
# 函数shell是make与外部环境的通讯工具，它用于命令的扩展。
# shell函数起着调用shell命令（cd $(KBUILD_OUTPUT) && /bin/pwd）和返回命令输出结果的参数的作用。
# Make仅仅处理返回结果，再返回结果替换调用点之前，make将每一个换行符或者一对回车/换行符处理为单个空格；
# 如果返回结果最后是换行符（和回车符），make将把它们去掉。
$(if $(KBUILD_OUTPUT),, \
$(error output directory "$(saved-output)" does not exist))
# 函数if对在函数上下文中扩展条件提供了支持（相对于GNU make makefile文件中的条件语句，例如ifeq指令。）
# if函数的语法是：$(if
# 如果条件$(KBUILD_OUTPUT)为真（非空字符串），那么两个逗号之间的空字符（注意连续两个逗号的作用）将会是整个函数的返回值，
# 如果$(KBUILD_OUTPUT)为假（空字符串），那么$(error output directory "$(saved-output)" does not exist）会是整个函数的返回值，
# 此时如果
#
# 函数error的语法是：$(error
# 函数error的功能是：产生一个致命的错误，output directory "$(saved-output)" does not exist是错误信息。
# 注意，error函数不会在一被使用就会产生错误信息，所以如果你把其定义在某个变量中，并在后续的脚本中使用这个变量，那么也是可以的。
PHONY += $(MAKECMDGOALS)
# 将变量KBUILD_OUTPUT的值追加给变量saved-output，
$(filter-out _all,$(MAKECMDGOALS)) _all:
$(if $(KBUILD_VERBOSE:1=),@)$(MAKE) -C $(KBUILD_OUTPUT) \
KBUILD_SRC=$(CURDIR) \
KBUILD_EXTMOD="$(KBUILD_EXTMOD)" -f $(CURDIR)/Makefile $@
# 反过滤函数——filter-out，语法是：$(filter-out
# 函数filter-out的功能是：去掉$(MAKECMDGOALS）中符合规则_all的所有字符串后，剩下的作为返回值。
# $(if $(KBUILD_VERBOSE:1=),@) 含义是如果$(KBUILD_VERBOSE:1=) 不为空，则等于$@
# 自动化变量"$@"表示规则中的目标文件集，在模式规则中，如果有多个目标，那么，"$@"就是匹配于目标中模式定义的集合。
# 自动化变量还有"$<"、"$%"、"$<"等。
#
# 宏变量$（MAKE）的值为make命令和参数（参数可省）。
#
# 执行命令KBUILD_SRC=$(CURDIR)的结果是把变量CURDIR的值赋给变量KBUILD_SRC。
# CURDIR这个变量是Makefile提供的,代表了make当前的工作路径。
# Leave processing to above invocation of make
skip-makefile := 1
endif # ifneq ($(KBUILD_OUTPUT),)
endif # ifeq ($(KBUILD_SRC),)
# 给变量skip-makefile追加值1.
# We process the rest of the Makefile if this is the final invocation of make
ifeq ($(skip-makefile),)
# 判断变量skip-makefile与空字符是否相同，即判断变量skip-makefile的值是否为空。
# If building an external module we do not care about the all: rule
# but instead _all depend on modules
PHONY += all
ifeq ($(KBUILD_EXTMOD),)
_all: all
else
_all: modules
endif
# 为变量PHONY追加值all。
# 判断变量KBUILD_EXTMOD的值是否为空。
# 定义两种不同情况下使用的规则_all: all和_all: modules
srctree := $(if $(KBUILD_SRC),$(KBUILD_SRC),$(CURDIR))
TOPDIR := $(srctree)
# FIXME - TOPDIR is obsolete, use srctree/objtree
# 调用if函数，根据变量KBUILD_SRC的值是否为空，决定将变量KBUILD_SRC或者变量CURDIR的值赋给变量srctree
# 为变量TOPDIR追加变量srctree的值
objtree := $(CURDIR)
src := $(srctree)
obj := $(objtree)
VPATH := $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))
# “VPATH”是Makefile文件中的特殊变量。
# ，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。
export srctree objtree VPATH TOPDIR
# 为变量objtree、src、obj分别追加变量CURDIR、srctree、objtree的值
# make使用“VPATH”变量来指定“依赖文件”的搜索路径。
# 为变量VPATH追加变量VPATH的值
# 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。
# export srctree objtree VPATH TOPDIR声明了四个变量，这四个变量在make嵌套时都将被传递到下级Makefile。
# 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.
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/ )
# 为变量SUBARCH追加调用shell执行sed后的返回值。
# 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。
# 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
# 上面已经说了，下面的这些是用于交叉编译（嵌入式linux的编译环境就是交叉编译）。
ARCH ?= $(SUBARCH)
CROSS_COMPILE ?=
# 变量ARCH用来指明目标cpu的构架
# 设置变量ARCH的方法有两种，
# 一是：在命令行中 如：make ARCH=ia64；
# 二是：设置环境变量，在环境变量中默认的ARCH的值是执行make的cpu构架
# 不论怎么弄，目的就是使编译出来的目标文件（可执行文件）面向的是你的目标平台（在嵌入式开发中）。
#
# 操作符“?= ”的作用是：如果ARCH未被定义过，那么将变量SUBARCH的值赋给变量ARCH，
# 如果变量ARCH已经被定义过，那么这条语句什么也不做。
#
# ARCH指定在嵌入式开发中你的目标板上的cpu类型（构架），如：arm，ppc，powerpc等
# 变量CROSS_COMPILE指定交叉编译用的交叉编译器，这里的CROSS_COMPILE就是让你指定交叉编译器的路径。
# 如果你设置好了PATH那么直接把这句加上就可以,如果没有那么请指定路径，
# Architecture as present in compile.h
UTS_MACHINE := $(ARCH)
# 将变量ARCH直接展开给变量UTS_MACHINE。
KCONFIG_CONFIG ?= .config
# 在变量KCONFIG_CONFIG没赋值的情况下，将.config赋给变量KCONFIG_CONFIG；如果已经赋值，那么什么也不做。
# 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)
# 将生成shell程序来执行if函数后返回的结果展开给变量CONFIG_SHELL；
# if函数中，在else中又嵌套了if函数。
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.
KBUILD_MODULES :=
KBUILD_BUILTIN := 1
# 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 $(CONFIG_MODVERSIONS),1)
endif
# ifeq判断变量MAKECMDGOALS的值与modules是否相同；
# 第二行将调用if后返回的值展开给变量KBUILD_BUILTIN；
# if函数判断变量CONFIG_MODVERSIONS的值是否为非空字符串，如果是非空字符串，则执行逗号后面的1
# If we have "make
# in addition to whatever we do anyway.
# Just "make" or "make all" shall build modules as well
ifneq ($(filter all _all modules,$(MAKECMDGOALS)),)
KBUILD_MODULES := 1
endif
# ifneq判断调用函数filter的返回值与空字符串是否相同。
# 如果相同，那么执行第二行，即把1赋给变量 KBUILD_MODULES
ifeq ($(MAKECMDGOALS),)
KBUILD_MODULES := 1
endif
#如果MAKE命令行为空，则编译module
export KBUILD_MODULES KBUILD_BUILTIN
export KBUILD_CHECKSRC KBUILD_SRC KBUILD_EXTMOD
# 用关键词export声明变量KBUILD_MODULES KBUILD_BUILTIN、KBUILD_CHECKSRC KBUILD_SRC KBUILD_EXTMOD。
# 如果用关键词export声明了变量，那么被声明的变量将会被传递到下级Makefile中。
# 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 $(RELDIR)/$@
# 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 commands with $(Q) - that's useful
# for commands that shall be hidden in non-verbose mode.
#
# $(Q)ln $@ :<
#
# If KBUILD_VERBOSE equals 0 then the above command will be hidden.
# If KBUILD_VERBOSE equals 1 then the above command is displayed.
ifeq ($(KBUILD_VERBOSE),1)
quiet =
Q =
else
quiet=quiet_
Q = @
endif
#这里非常有意思，编译的时候是否显示具体执行命令就是这里设置的。
#编译的时候内核会echo $($(quiet)$(cmd))，
# quiet_cmd_cc_o_c = Compiling $(RELDIR)/$@
# cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
#所以这里的设置就能决定echo哪个命令。
# If the user is running make -s (silent mode), suppress echoing of
# commands
ifneq ($(findstring s,$(MAKEFLAGS)),)
quiet=silent_
endif
# 函数ifneq判断函数findstring返回值与空字符是否相同，如果相同则执行第二行（将silent_赋给变量quiet）。
#如果flags中有-s则什么都不显示。
# 函数findstring的语法是：$(findstring
# 函数findstring的功能是：如果在$(MAKEFLAGS)中能找到字符s，那么返回字符s；否则返回空字符。
export quiet Q KBUILD_VERBOSE
# 用关键词export声明变量quiet Q KBUILD_VERBOSE，使得它们能被传到下级Makefile。
# Look for make include files relative to root of kernel src
MAKEFLAGS += --include-dir=$(srctree)
# 给变量MAKEFLAGS追加--include-dir=$(srctree)。
# --include-dir是make的参数，用来指定一个被包含makefile的搜索目标。
# 也可以使用多个“-I”参数来指定多个目录。
# We need some generic definitions.
include $(srctree)/scripts/Kbuild.include
# 在Makefile使用include关键字可以把别的Makefile包含进来。
# 这很像C语言的#include，被包含的文件会原模原样的放在当前文件的包含位置。
# include的语法是： include
#Kbuild.include中包含很多函数。
# Make variables (CC, etc...)
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
CHECKFLAGS := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ -Wbitwise $(CF)
MODFLAGS = -DMODULE
CFLAGS_MODULE = $(MODFLAGS)
AFLAGS_MODULE = $(MODFLAGS)
LDFLAGS_MODULE = -r
CFLAGS_KERNEL =
AFLAGS_KERNEL =
# 给一系列变量赋值。
# Use LINUXINCLUDE when you must reference the include/ directory.
# Needed to be compatible with the O= option
LINUXINCLUDE := -Iinclude \
$(if $(KBUILD_SRC),-Iinclude2 -I$(srctree)/include) \
-include include/linux/autoconf.h
# 所有的内核配置都在autoconf.h中
CPPFLAGS := -D__KERNEL__ $(LINUXINCLUDE)
CFLAGS := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
-fno-strict-aliasing -fno-common
AFLAGS := -D__ASSEMBLY__
# Read KERNELRELEASE from include/config/kernel.release (if it exists)
KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
KERNELRELEASE = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
# KERNELRELEASE获得内核版本号
# >是重定向符号。
# 第一行中cat和>连用的作用是：将文件include/config/kernel.release的内容写入到文件/dev/null中。
export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
export ARCH 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 CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
export CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
export AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
# 用关键词export声明变量，使得这些变量能传到下级Makefile中
# 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 $(KBUILD_EXTMOD))/).tmp_versions
# 将if函数的返回值展开后与.tmp_versions共同赋给变量MODVERDIR。
# if函数判断变量KBUILD_EXTMOD的值是否为空字符串，如果不为空字符串，执行函数firstword。
# 函数firstword的语法是：$(firstword
# 函数firstword在此处的功能是：取出变量KBUILD_EXTMOD的第一个字符。
# Files to ignore in find ... statements
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
# 分别为变量RCS_FIND_IGNORE、RCS_FIND_IGNORE赋值。
# 指定忽略的文件.svn CVS git BitKeeper SCCS
# -name是命令find的一个参数，参数-name用来指明要搜索的文件的部分或者全名。
# -o 是 OR 运算符，语法是：表达式-o 表达式、如果第一个表达式是真，就不会对第二个表达式求值。
# ===========================================================================
# Rules shared between *config targets and build targets
# Basic helpers built in scripts/
PHONY += scripts_basic
scripts_basic:
$(Q)$(MAKE) $(build)=scripts/basic
# 为变量PHONY追加scripts_basic。
# 定义了一个伪目标scripts_basic，第三行是针对伪目标scripts_basic要执行的命令。
# 第三行是将变量展开，展开后是一个命令。
# To avoid any implicit rule to kick in, define an empty command.
scripts/basic/%: scripts_basic ;
# 定义了一个规则，依赖关系为scripts/basic/%: scripts_basic
# 冒号：的作用是定义一个空命令（正如上面解释所说）。
PHONY += outputmakefile
# 为变量PHONY追加outputmakefile。
# outputmakefile generates a Makefile in the output directory, if using a
# separate output directory. This allows convenient use of make in the
# output directory.
outputmakefile:
ifneq ($(KBUILD_SRC),)
$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile \
$(srctree) $(objtree) $(VERSION) $(PATCHLEVEL)
endif
# 定义一个伪目标outputmakefile。
# 将三四行中所有的变量展开并且合并成一行命令。
# To make sure we do not include .config for any of the *config targets
# catch them early, and hand them over to scripts/kconfig/Makefile
# It is allowed to specify more targets when calling make, including
# mixing *config targets and build targets.
# For example 'make oldconfig all'.
# Detect when mixed targets is specified, and make a second invocation
# of make so .config is not included in this case either (for *config).
no-dot-config-targets := clean mrproper distclean \
cscope TAGS tags help %docs check% \
include/linux/version.h headers_% \
kernelrelease kernelversion
# 定义了一个依赖关系，但是没有命令。
config-targets := 0
mixed-targets := 0
dot-config := 1
# 给变量config-targets、mixed-targets、dot-config 赋值。
ifneq ($(filter $(no-dot-config-targets), $(MAKECMDGOALS)),)
ifeq ($(filter-out $(no-dot-config-targets), $(MAKECMDGOALS)),)
dot-config := 0
endif
endif
#如果指定了dot-config-targets，并且没有其他目标，则dot-config := 0
ifeq ($(KBUILD_EXTMOD),)
ifneq ($(filter config %config,$(MAKECMDGOALS)),)
config-targets := 1
ifneq ($(filter-out config %config,$(MAKECMDGOALS)),)
mixed-targets := 1
endif
endif
endif
# 条件关键词ifeq判断KBUILD_EXTMOD的值与空格是否相同，如果是则执行第二行。
# 条件关键词ifneq判断函数filter的返回值与空格是否不相同，如果不相同，则执行第三行。
# 函数filter返回字符串$(MAKECMDGOALS))中符合模式config %config的字符串。
# 第三行为变量config-targets赋值1
# 条件关键词ifneq判断函数filter-out返回值与空格是否不相同，如果不过不相同则执行第五行。
# 函数filter-out返回字符串$(MAKECMDGOALS)中不符合模式config %config的字符串。
# 第五行为变量mixed-targets赋值1.
ifeq ($(mixed-targets),1)
# 条件关键词ifeq判断变量mixed-targets的值与1是否相同，即是否为1
# ===========================================================================
# We're called with mixed targets (*config and build targets).
# Handle them one by one.
%:: FORCE
$(Q)$(MAKE) -C $(srctree) KBUILD_SRC= $@
# 定义了目标“%:”，依赖文件FORCE
# 第二行，将所有变量展开后组成一行命令。
# Read arch specific Makefile to set KBUILD_DEFCONFIG as needed.
# KBUILD_DEFCONFIG may point out an alternative default configuration
# used for 'make defconfig'
include $(srctree)/arch/$(ARCH)/Makefile
export KBUILD_DEFCONFIG
# 如果变量config-targets的值与1相同，则执行从第一行开始直到遇到下面的else结束。
# 关键词include将文件$(srctree)/arch/$(ARCH)/Makefile包含进来，
# 文件$(srctree)/arch/$(ARCH)/Makefile被原模原样的放在当前文件的包含位置。
# 关键词export声明变量KBUILD_DEFCONFIG使得变量KBUILD_DEFCONFIG能传到下级Makefile中。
config %config: scripts_basic outputmakefile FORCE
$(Q)mkdir -p include/linux include/config
$(Q)$(MAKE) $(build)=scripts/kconfig $@
# 定义了一个规则，目标位config %config其中有个通配符%。
# 通配符%只能代表一个字符，config %config可以表示xconfig和gconfig、menuconfig和oldconfig等。
# 二三行将变量展开后就规则得到要执行的命令。
else
# 如果变量config-targets的值与1不相同，则执行下面的
# ===========================================================================
# Build targets only - this includes vmlinux, arch specific targets, clean
# targets and others. In general all targets except *config targets.
ifeq ($(KBUILD_EXTMOD),)
# 条件关键词ifeq判断变量KBUILD_EXTMOD的值与空是否相同。
# 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) $(build)=$(@)
# 第一行给变量PHONY追加scripts。
# 定义了一个规则。目标是scripts，依赖文件是scripts_basic include/config/auto.conf
# 将第三行的所有命令展开就得到规则的命令。
# Objects we will link into vmlinux / subdirs we need to visit
init-y := init/
drivers-y := drivers/ sound/
net-y := net/
libs-y := lib/
core-y := usr/
endif # KBUILD_EXTMOD
# 为变量赋值。
# 上面的endif与ifeq ($(KBUILD_EXTMOD),)相对应。
ifeq ($(dot-config),1)
# Read in config
-include include/config/auto.conf
# 条件关键词ifeq判断变量dot-config的值与1是否相同，如果相同这执行上面这一条。
# 关键词include将文件include/config/auto.conf包含进来，该文件会原模原样的放在当前文件的包含位置。
# 关键词include前面的减号的作用是让make不理那些无法读取的文件，而继续执行。
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
$(KCONFIG_CONFIG) include/config/auto.conf.cmd: ;
# 定义了一个规则，目标是$(KCONFIG_CONFIG) include/config/auto.conf.cmd，没有依赖文件，命令。
# 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 $(srctree)/Makefile silentoldconfig
else
# 第一二行定义了一个规则。
# 目标是include/config/auto.conf，依赖文件是$(KCONFIG_CONFIG) include/config/auto.conf.cmd
# 将第二行的变量展开就得到命令,如果.config更新了，则执行make silentoldconfig。
# 上面的else与ifeq ($(KBUILD_EXTMOD),)对应
# 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
# 为变量PHONY追加值include/config/auto.conf
include/config/auto.conf:
# 定义了一个伪目标
$(Q)test -e include/linux/autoconf.h -a -e $@ || ( \
echo; \
echo " ERROR: Kernel configuration is invalid."; \
echo " include/linux/autoconf.h or $@ are missing."; \
echo " Run 'make oldconfig && make prepare' on kernel src to fix it."; \
echo; \
/bin/false)
#这几句话经常出现，需要执行make oldconfig 生成autoconf.h
# 自动变量$@表示当前规则的目标变量名。
# echo是shell中的显示命令，显示echo后面的字符串。
endif # KBUILD_EXTMOD
# 上面的endif与ifeq ($(KBUILD_EXTMOD),)对应。
else
# Dummy target needed, because used as prerequisite
include/config/auto.conf: ;
endif # $(dot-config)
# 定义了一个伪目标include/config/auto.conf，该规则没有依赖文件和命令。
# 上面的endif与ifeq ($(dot-config),1)对应。
# 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
all: vmlinux
# 定义了一个依赖关系，目标是all，依赖文件是vmlinux。
ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
CFLAGS += -Os
else
CFLAGS += -O2
endif
# 条件关键字ifdef只检验变量CONFIG_CC_OPTIMIZE_FOR_SIZE是否被赋值（非空）。
# 分别在两种情况下为变量CFLAGS追加不同的值。
include $(srctree)/arch/$(ARCH)/Makefile
# 用关键字声明文件$(srctree)/arch/$(ARCH)/Makefile，使得该文件能传递到下级Makefile
ifdef CONFIG_FRAME_POINTER
CFLAGS += -fno-omit-frame-pointer $(call cc-option,-fno-optimize-sibling-calls,)
else
CFLAGS += -fomit-frame-pointer
endif
# 条件关键字ifdef只检验变量CONFIG_FRAME_POINTER是否被赋值（非空）。
# 分别在两种情况下为变量CFLAGS追加不同的值。
ifdef CONFIG_DEBUG_INFO
CFLAGS += -g
endif
# 条件关键字ifdef只检验变量CONFIG_DEBUG_INFO是否被赋值（非空）。
# 为变量CFLAGS追加-g
# Force gcc to behave correct even for buggy distributions
CFLAGS += $(call cc-option, -fno-stack-protector)
# 为变量CFLAGS追加$(call cc-option, -fno-stack-protector)。
# 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)
# 分别为变量追加值
# 函数shell新生成一个Shell程序来执行由变量CC展开后形成的命令。
# warn about C99 declaration after statement
CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
# 为变量CFLAGS追加call函数返回的函数call的返回值。
# 函数call的语法：$(call
# 函数call的功能是：参数cc-option中的变量被字符串-Wdeclaration-after-statement和逗号后面的空格依次取代。
# 函数call的返回值是：被取代后的参数。
# disable pointer signed / unsigned warnings in gcc 4.0
CFLAGS += $(call cc-option,-Wno-pointer-sign,)
# Default kernel image to build when no specific target is given.
# KBUILD_IMAGE may be overruled on the command line or
# set in the environment
# Also any assignments in arch/$(ARCH)/Makefile take precedence over
# this default value
export KBUILD_IMAGE ?= vmlinux
# 用关键字声明了变量KBUILD_IMAGE，使得该变量能传递到下级Makefile中。
# 符号“?=”在变量KBUILD_IMAGE没有赋值的情况下给变量KBUILD_IMAGE赋值，如果已经赋值了则什么也不做。
#
# INSTALL_PATH specifies where to place the updated kernel and system map
# images. Default is /boot, but you can set it to other values
export INSTALL_PATH ?= /boot
# 用关键字声明了变量INSTALL_PATH，使得该变量能传递到下级Makefile中。
# 符号“?=”在变量INSTALL_PATH没有赋值的情况下给变量INSTALL_PATH赋值，如果已经赋值了则什么也不做。
#
# 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
# MODLIB指定模块的安装目录
#
# 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 = $(STRIP) --strip-debug
else # 这个else与ifeq ($(INSTALL_MOD_STRIP),1)对应。
mod_strip_cmd = $(STRIP) $(INSTALL_MOD_STRIP)
endif # INSTALL_MOD_STRIP=1
else # 这个else与ifdef INSTALL_MOD_STRIP对应。
mod_strip_cmd = true
endif # INSTALL_MOD_STRIP
export mod_strip_cmd
# 条件关键字ifdef判断变量INSTALL_MOD_STRIP是否被赋值，
# 条件关键字ifeq判断变量INSTALL_MOD_STRIP与1是否相同。
# 如果相同或被赋值则执行紧接着的命令，否则执行同一级的else后的命令。
# 上面命令就是在不同情况下给变量mod_strip_cmd赋值。
vmlinux-dirs := $(patsubst %/,%,$(filter %/, $(init-y) $(init-m) \
$(core-y) $(core-m) $(drivers-y) $(drivers-m) \
$(net-y) $(net-m) $(libs-y) $(libs-m)))
# 将函数patsubst的返回值赋给变量vmlinux-dirs。
# 函数patsubst的语法是：$(patsubst
# 函数patsubst的作用是：用“%”替换函数filter返回的字符串中的“%”。
# 函数filter的作用是：
# 函数filter的作用是：返回字符串中符合模式“%/”的字符串。
vmlinux-alldirs := $(sort $(vmlinux-dirs) $(patsubst %/,%,$(filter %/, \
$(init-n) $(init-) \
$(core-n) $(core-) $(drivers-n) $(drivers-) \
$(net-n) $(net-) $(libs-n) $(libs-))))
# 将函数sort返回的值赋给变量vmlinux-alldirs 。
# 函数sort的语法：$(sort ;)。
# 函数sort的返回值是：去掉相同的单词，给字符串;中的单词排序（升序），返回排序后的字符串。
# 在
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)
# 上面的几个命令中，前几个是把函数patsubst返回值赋给左边的变量，最后一个直接把变量展开赋给左边的变量。
# 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
# ^
# |
# +-< $(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)
vmlinux-main := $(core-y) $(libs-y) $(drivers-y) $(net-y)
vmlinux-all := $(vmlinux-init) $(vmlinux-main)
vmlinux-lds := arch/$(ARCH)/kernel/vmlinux.lds
export KBUILD_VMLINUX_OBJS := $(vmlinux-all)
# 指定需要编译的目标文件集。
# Rule to link vmlinux - also used during CONFIG_KALLSYMS
# May be overridden by arch/$(ARCH)/Makefile
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) $(vmlinux-main) FORCE ,$^)
# 赋值操作符"?="的作用是在他左边的变量还未赋值的情况下，把他右边的赋给左边的变量。
# 反过滤函数filter-out的语法是：$(filter-out
# 功能是:返回字符串$^中不符合模式(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) FORCE的字符串。
# Generate new vmlinux version
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$$(cat .old_version) + 1 >.version; \
fi; \
$(MAKE) $(build)=init
# 上面是给两个变量quiet_cmd_vmlinux_version、cmd_vmlinux_version 赋值。
# 其中set、if...then...else... 、rm、echo、expr等是linux shell中的命令。
# Generate System.map
quiet_cmd_sysmap = SYSMAP
cmd_sysmap = $(CONFIG_SHELL) $(srctree)/scripts/mksysmap
# 上面的是给变量quiet_cmd_sysmap和cmd_sysmap赋值。
# Link of vmlinux
# If CONFIG_KALLSYMS is set .version is already updated
# Generate System.map and verify that the content is consistent
# Use + in front of the vmlinux_version rule to silent warning with make -j2
# First command is ':' to allow us to use + in front of the rule
define rule_vmlinux__
:
$(if $(CONFIG_KALLSYMS),,+$(call cmd,vmlinux_version))
$(call cmd,vmlinux__)
$(Q)echo 'cmd_$@ := $(cmd_vmlinux__)' >
$(Q)$(if $($(quiet)cmd_sysmap), \
echo ' $($(quiet)cmd_sysmap) System.map' &&) \
$(cmd_sysmap) $@ System.map; \
if [ $$? -ne 0 ]; then \
rm -f $@; \
/bin/false; \
fi;
$(verify_kallsyms)
endef
# 关键词define...endef的作用是：为相同的命令序列定义一个变量，又称定义命令包。
# 上面定义了一个命令包，这个命令包的名字是（define后的）rule_vmlinux__；
# 命令序列是：从define下面的那一行开始，直到endef的（包括）上面一行。
# 在if函数中，如果CONFIG_KALLSYMS的值为非空字符串，
# 那么执行
# 如果CONFIG_KALLSYMS的值为空字符串（即为假），则执行+$(call cmd,vmlinux_version)。
# echo是linux shell中的一个显示文字的命令，语法是：：echo [-ne][字符串]或 echo [--help][--version]
# rm是linux shell中的一个删除文件、文件夹的命令。
ifdef CONFIG_KALLSYMS
# 条件关键词ifdef判断变量CONFIG_KALLSYMS是否非空。
# Generate section listing all symbols and add it into vmlinux $(kallsyms.o)
# It's a three stage process:
# o .tmp_vmlinux1 has all symbols and sections, but __kallsyms is
# empty
# Running kallsyms on that gives us .tmp_kallsyms1.o with
# the right size - vmlinux version (uname -v) is updated during this step
# o .tmp_vmlinux2 now has a __kallsyms section of the right size,
# but due to the added section, some addresses have shifted.
# From here, we generate a correct .tmp_kallsyms2.o
# o The correct .tmp_kallsyms2.o is linked into the final vmlinux.
# o Verify that the System.map from vmlinux matches the map from
# .tmp_vmlinux2, just in case we did not generate kallsyms correctly.
# o If CONFIG_KALLSYMS_EXTRA_PASS is set, do an extra pass using
# .tmp_vmlinux3 and .tmp_kallsyms3.o. This is only meant as a
# temporary bypass to allow the kernel to be built while the
# maintainers work out what went wrong with kallsyms.
#产生符号边分为三个阶段
ifdef CONFIG_KALLSYMS_EXTRA_PASS
last_kallsyms := 3
else # 这个else与ifdef CONFIG_KALLSYMS_EXTRA_PASS对应
last_kallsyms := 2
endif # 这个endif与ifdef CONFIG_KALLSYMS_EXTRA_PASS对应
# 嵌套了一个ifdef。
# 如果变量CONFIG_KALLSYMS_EXTRA_PASS是非空，则执行else前面的部分，否则执行else到endif之间的部分。
kallsyms.o := .tmp_kallsyms$(last_kallsyms).o
# 为变量kallsyms.o 赋值。
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
# 关键词define定义了一个叫verify_kallsyms的命令包。
# 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__)' >
endef
# 为变量cmd_ksym_ld赋值。
# 关键词define定义了名叫rule_ksym_ld的命令包。
# 命令包rule_ksym_ld里面的命令序列是define下面一行开始到endef上一行结束。
# echo是linux中的命令，它的语法是：echo [-ne][字符串]或 echo [--help][--version]
# echo的功能是：echo会将输入的字符串送往标准输出。输出的字符串间以空白字符隔开, 并在最后加上换行号。
# 符号>用来改变送出的数据信道(stdout,
# Generate .S file with all kernel symbols
quiet_cmd_kallsyms = KSYM $@
cmd_kallsyms = $(NM) -n $< | $(KALLSYMS) \
$(if $(CONFIG_KALLSYMS_ALL),--all-symbols) > $@
# 分别为变量quiet_cmd_kallsyms和cmd_kallsyms赋值。
# 自动变量“$@”表示表示规则中的目标文件集，自动变量“$<”表示依赖目标中的第一个目标名字。
.tmp_kallsyms1.o .tmp_kallsyms2.o .tmp_kallsyms3.o: %.o: %.S scripts FORCE
$(call if_changed_dep,as_o_S)
#if_changed_dep 函数是当目标有任何变化的时候，做相应的动作。
.tmp_kallsyms%.S: .tmp_vmlinux% $(KALLSYMS)
$(call cmd,kallsyms)
# 定义了一个规则，目标为.tmp_kallsyms%.S，依赖文件为.tmp_vmlinux% $(KALLSYMS)。
# .tmp_vmlinux1 must be complete except kallsyms, so update vmlinux version
.tmp_vmlinux1: $(vmlinux-lds) $(vmlinux-all) FORCE
$(call if_changed_rule,ksym_ld)
# 定义了一个规则，目标为.tmp_vmlinux1，依赖文件为$(vmlinux-lds) $(vmlinux-all)。
.tmp_vmlinux2: $(vmlinux-lds) $(vmlinux-all) .tmp_kallsyms1.o FORCE
$(call if_changed,vmlinux__)
# 定义了一个规则，目标是.tmp_vmlinux2。
.tmp_vmlinux3: $(vmlinux-lds) $(vmlinux-all) .tmp_kallsyms2.o FORCE
$(call if_changed,vmlinux__)
# 定义了一个规则，目标是.tmp_vmlinux3
# Needs to visit scripts/ before $(KALLSYMS) can be used.
$(KALLSYMS): scripts ;
# 定义了一个（分号前面没有命令）没有命令的规则，
# Generate some data for debugging strange kallsyms problems
debug_kallsyms: .tmp_map$(last_kallsyms)
# 定义了一个依赖关系，目标为debug_kallsyms，依赖文件为 .tmp_map$(last_kallsyms)
.tmp_map%: .tmp_vmlinux% FORCE
($(OBJDUMP) -h $< | $(AWK) '/^ +[0-9]/{print $$4 " 0 " $$2}'; $(NM) $<) | sort > $@
# 定义了一个规则，目标为.tmp_map%，依赖文件为.tmp_vmlinux%
# 自动化变量$<表示依赖目标中的目标文件集。自动化变量$@表示依赖目标中的第一个目标名字。
# 符号“|”表示管道，作用是：使上一个命令的stdout接到下一个命令的stdin。
# 符号“>”用来改变送出的数据信道，使之输出到指定的档案（文件等）。
.tmp_map3: .tmp_map2
# 定义了一个依赖关系，目标是.tmp_map3，依赖文件是.tmp_map2。
.tmp_map2: .tmp_map2
# 定义了一个依赖关系，目标是.tmp_map2，依赖文件是.tmp_map2。
endif # ifdef CONFIG_KALLSYMS
# 这个endif与ifdef CONFIG_KALLSYMS对应
.tmp_map2: .tmp_map2
# 定义了一个依赖关系，目标是.tmp_map2，依赖文件是.tmp_map2。
endif # ifdef CONFIG_KALLSYMS
# 这个endif与ifdef CONFIG_KALLSYMS对应
# vmlinux image - including updated kernel symbols
vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) $(kallsyms.o) FORCE
ifdef CONFIG_HEADERS_CHECK
$(Q)$(MAKE) -f $(srctree)/Makefile headers_check
endif
$(call if_changed_rule,vmlinux__)
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@
$(Q)rm -f .old_version
# 定义了一个规则，目标是vmlinux
# 条件关键词ifdef的语法是：ifdef
# 如果变量
# The actual objects are generated when descending,
# make sure no implicit rule kicks in
$(sort $(vmlinux-init) $(vmlinux-main)) $(vmlinux-lds): $(vmlinux-dirs) ;
# 排序函数sort的语法是：$(sort ;)，
# 功能是：去掉;中相同的单词，然后给字符串
;中剩下的单词排序（升序）。返回排好的字符串。
# 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) $(build)=$@
# 为变量PHONY追加变量vmlinux-dirs的值。
# 第二行定义了一个规则，目标是vmlinux-dirs，依赖文件是prepare和scripts。
# 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.
pattern = ".*/localversion[^~]*"
string = $(shell cat /dev/null \
`find $(objtree) $(srctree) -maxdepth 1 -regex $(pattern) | sort -u`)
# 为变量pattern和string赋值
# 函数shell新生成一个shell程序来执行shell函数后面的命令（如cat、find等）
# cat是linux中的一个命令，语法是cat filename ，功能是一次显示整个文件。
localver = $(subst $(space),, $(string) \
$(patsubst "%",%,$(CONFIG_LOCALVERSION)))
# 给变量localver赋值。
# subst是Makefile的一个字符串替换函数，语法是：$(subst
# 功能是：把字串
# 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
# ifdef是Makefile的一种条件关键字，语法是：ifdef
# 功能是：如果变量
# 如果变量
localver-full = $(localver)$(localver-auto)
# 为变量localver-full赋值。
# Store (new) KERNELRELASE string in include/config/kernel.release
kernelrelease = $(KERNELVERSION)$(localver-full)
include/config/kernel.release: include/config/auto.conf FORCE
$(Q)rm -f $@
$(Q)echo $(kernelrelease) > $@
# 为变量kernelrelease赋值。
# 定义了一个规则，目标为include/config/kernel.release，依赖文件为include/config/auto.conf FORCE。
# rm是linux中的一个命令，语法是：rm [选项]... 目录... ，功能是：目录... 删除指定的文件或目录
# echo是linux下的一个命令，语法是：echo 字符串，功能是：将字符串送往标准输出。
# 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
# 给变量PHONY追加值
# 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 $(srctree)
# 2) Create the include2 directory, used for the second asm symlink
prepare3: include/config/kernel.release
ifneq ($(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 $(srctree)/include/asm-$(ARCH) include2/asm
endif
# 定义了一个规则。目标是prepare3，依赖文件是include/config/kernel.release
# prepare2 creates a makefile if using a separate output directory
prepare2: prepare3 outputmakefile
# 定义了一个依赖关系。目标为prepare2，依赖文件是：prepare3和outputmakefile
prepare1: prepare2 include/linux/version.h include/linux/utsrelease.h \
include/asm include/config/auto.conf
ifneq ($(KBUILD_MODULES),)
$(Q)mkdir -p $(MODVERDIR)
$(Q)rm -f $(MODVERDIR)/*
endif
# 定义了一个规则，目标为prepare1。
archprepare: prepare1 scripts_basic
# 定义了一个依赖关系，目标是archprepare，依赖文件是prepare1 scripts_basic。
prepare0: archprepare FORCE
$(Q)$(MAKE) $(build)=.
$(Q)$(MAKE) $(build)=. missing-syscalls
# 定义了一个规则，目标是prepare0，依赖文件是archprepare FORCE
# All the preparing..
prepare: prepare0
# 定义了一个依赖关系，目标是prepare，依赖文件是prepare0
# Leave this as default for preprocessing vmlinux.lds.S, which is now
# done in arch/$(ARCH)/kernel/Makefile
export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)
# 为变量CPPFLAGS_vmlinux.lds追加值。
# FIXME: The asm symlink changes when $(ARCH) changes. That's
# hard to detect, but I suppose "make mrproper" is a good idea
# before switching between archs anyway.
include/asm:
@echo ' SYMLINK $@ -> include/asm-$(ARCH)'
$(Q)if [ ! -d include ]; then mkdir -p include; fi;
@ln -fsn asm-$(ARCH) $@
# 定义了一个伪目标include/asm
# 如果字符“@”在命令行前，那么这个命令将不被make显示出来。
# 通常make会把其要执行的命令行在命令执行前输出到屏幕上。
# Generate some files
# ---------------------------------------------------------------------------
# KERNELRELEASE can change from a few different places, meaning version.h
# needs to be updated, so this check is forced on all builds
uts_len := 64
define filechk_utsrelease.h
if [ `echo -n "$(KERNELRELEASE)" | wc -c ` -gt $(uts_len) ]; then \
echo '"$(KERNELRELEASE)" exceeds $(uts_len) characters' >&2; \
exit 1; \
fi; \
(echo \#define UTS_RELEASE \"$(KERNELRELEASE)\";)
endef
# 第一行为变量uts_len赋值。
# define是Makefile的一个关键字，用于定义命令包。此处定义了filechk_utsrelease.h命令包。
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
# expr是linux shell中的一个字符串处理命令。
include/linux/version.h: $(srctree)/Makefile FORCE
$(call filechk,version.h)
# 定义了一个规则，目标是include/linux/version.h，依赖文件是$(srctree)/Makefile和FORCE
include/linux/utsrelease.h: include/config/kernel.release FORCE
$(call filechk,utsrelease.h)
# 定义了一个规则，目标是include/linux/utsrelease.h，依赖文件是include/config/kernel.release和FORCE
# ---------------------------------------------------------------------------
PHONY += depend dep
depend dep:
@echo '*** Warning: make $@ is unnecessary now.'
# 第一行为变量PHONY追加值depend和dep，第二行定义了伪目标depend dep。
# ---------------------------------------------------------------------------
# Kernel headers
INSTALL_HDR_PATH=$(objtree)/usr
export INSTALL_HDR_PATH
# 第一行为变量INSTALL_HDR_PATH赋值。
HDRARCHES=$(filter-out generic,$(patsubst $(srctree)/include/asm-%/Kbuild,%,$(wildcard $(srctree)/include/asm-*/Kbuild)))
# 为变量HDRARCHES赋值。
# patsubst是Makefile中的模式字符串替换函数，其语法是：$(patsubst
# 功能是：查找
# wildcard是Makefile的一个关键字，在给变量赋值时，使通配符在变量中展开。
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
# 第一行为变量PHONY追加值
# 第二行定义了一个规则，目标是headers_install_all。
PHONY += headers_install
headers_install: include/linux/version.h scripts_basic FORCE
@if [ ! -r $(srctree)/include/asm-$(ARCH)/Kbuild ]; then \
echo '*** Error: Headers not exportable for this architecture ($(ARCH))'; \
exit 1 ; fi
$(Q)$(MAKE) $(build)=scripts scripts/unifdef
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.headersinst obj=include
# 第一行为变量PHONY追加值
# 第二行定义了一个规则，目标是headers_install。
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
# 第一行为变量PHONY追加值
# 第二行定义了一个规则，目标是headers_check_all。
PHONY += headers_check
headers_check: headers_install
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.headersinst obj=include HDRCHECK=1
# 第一行为变量PHONY追加值
# 第二行定义了一个规则，目标是headers_check。
ifdef CONFIG_MODULES
# ifdef是Makefile中的一个条件关键词，其语法是：ifdef
# 如果变量
# By default, build modules as well
all: modules
# 定义了一个依赖关系，目标是all，依赖文件是modules
# Build modules
PHONY += modules
modules: $(vmlinux-dirs) $(if $(KBUILD_BUILTIN),vmlinux)
@echo ' Building modules, stage 2.';
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
# 当“@”字符在命令行前，那么这个命令将不被make显示出来。
# Target to prepare building external modules
PHONY += modules_prepare
modules_prepare: prepare scripts
# 为变量PHONY追加值
# 第二行定义了依赖关系，目标是modules_prepare，依赖文件是prepare scripts
# Target to install modules
PHONY += modules_install
modules_install: _modinst_ _modinst_post
# 第一行为变量追加值。
# 第二行定义了依赖关系，目标是modules_install，依赖文件是_modinst_ _modinst_post
PHONY += _modinst_
_modinst_:
@if [ -z "`$(DEPMOD) -V 2>/dev/null | grep module-init-tools`" ]; then \
echo "Warning: you may need to install module-init-tools"; \
echo "See
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
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modinst
# 第一行为变量PHONY追加值。
# 第二行定义了伪目标_modinst_。
# If System.map exists, run depmod. This deliberately does not have a
# dependency on System.map since that would run the dependency tree on
# vmlinux. This depmod is only for convenience to give the initial
# boot a modules.dep even before / is mounted read-write. However the
# boot script depmod is the master version.
ifeq "$(strip $(INSTALL_MOD_PATH))" ""
depmod_opts :=
else
depmod_opts := -b $(INSTALL_MOD_PATH) -r
endif
PHONY += _modinst_post
_modinst_post: _modinst_
if [ -r System.map -a -x $(DEPMOD) ]; then $(DEPMOD) -ae -F System.map $(depmod_opts) $(KERNELRELEASE); fi
# strip是Makefile中的用于去掉空格的函数。其语法是：$(strip
# 第二四行分别在不同的情况下给变量depmod_opts赋值。
# 第六行给变量PHONY追加值。
# 第七行定义了一个规则，目标是_modinst_post，依赖文件是_modinst_
else # CONFIG_MODULES
# 上面这个else与ifdef CONFIG_MODULES对应。
# 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
# 定义了一个规则，目标是modules modules_install，依赖文件是FORCE
# 当“@”字符在命令行前，那么这个命令将不被make显示出来。
endif # CONFIG_MODULES
# 上面这个endif与ifdef CONFIG_MODULES对应。
###
# 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)
CLEAN_FILES += vmlinux System.map \
.tmp_kallsyms* .tmp_version .tmp_vmlinux* .tmp_System.map
# 第一行将变量MODVERDIR的值追加给变量CLEAN_DIRS
# 第二行给变量CLEAN_FILES追加值。
# Directories & files removed with 'make mrproper'
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*
# 上面的是给变量MRPROPER_DIRS和MRPROPER_FILES追加值，
# 字符“\”有两个功能：一是：续行；二是：转义。
# 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))
# 第一二行分别定义了一个规则，每个规则的命令都是给依赖文件赋值。
# 第三行定义了一个依赖关系。
PHONY += $(clean-dirs) clean archclean
$(clean-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)
# 第一行给变量PHONY追加值。
# 第二行定义了一个伪目标$(clean-dirs)。
clean: archclean $(clean-dirs)
$(call cmd,rmdirs)
$(call cmd,rmfiles)
@find . $(RCS_FIND_IGNORE) \
\( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
-o -name '*.symtypes' \) \
-type f -print | xargs rm -f
# 第一行定义了一个规则，目标是clean，依赖文件是archclean和$(clean-dirs)
# 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)
# 第一二行分别定义了一个规则，它们的命令分别是给依赖文件赋值。
# 第三行给变量mrproper-dirs 赋值。
PHONY += $(mrproper-dirs) mrproper archmrproper
$(mrproper-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _mrproper_%,%,$@)
# 第一行给变量PHONY赋值。
# 第二行定义了一个伪目标$(mrproper-dirs)。
mrproper: clean archmrproper $(mrproper-dirs)
$(call cmd,rmdirs)
$(call cmd,rmfiles)
# 定义了一个规则，目标是mrproper。
# distclean
#
PHONY += distclean
# 给变量PHONY追加值
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
# 上面定义了一个规则，目标是distclean，依赖文件是mrproper。
# Packaging of the kernel to various formats
# ---------------------------------------------------------------------------
# rpm target kept for backward compatibility
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) $@
# 上面定义了两个规则，目标分别是%pkg和rpm。
@ $@是Makefile的自动化变量，表示当前规则的目标集。
# Brief documentation of the typical targets used
# ---------------------------------------------------------------------------
boards := $(wildcard $(srctree)/arch/$(ARCH)/configs/*_defconfig)
boards := $(notdir $(boards))
# 上面两行分别给变量boards赋值。
# wildcard是Makefile中的关键字，用于让通配符在变量中展开。
# notdir是Makefile中的取文件函数，其语法是：$(notdir
# 功能：从文件名序列
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 ' rpm - Build a kernel as an RPM package'
@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 $(srctree)/include/asm-$(ARCH)/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'
@if [ -r $(srctree)/include/asm-$(ARCH)/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'
# 第一行定义了一个伪目标help。
# 当“@”字符在命令行前，那么这个命令将不被make显示出来。
#
# Documentation targets
# ---------------------------------------------------------------------------
%docs: scripts_basic FORCE
$(Q)$(MAKE) $(build)=Documentation/DocBook $@
# 定义了一个规则，目标是%docs，依赖关系是scripts_basic FORCE
# $@是Makefile的自动化变量，表示当前规则的目标集。
else # KBUILD_EXTMOD
###
# 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:
$(Q)mkdir -p $(MODVERDIR)
$(Q)rm -f $(MODVERDIR)/*
# 第一行给变量KBUILD_MODULES赋值1.
# 第二行给变量PHONY追加值。
# 第三行定义了一个伪目标crmodverdir
# mkdir是linux shell下创建文件夹的命令，其语法是：mkdir [-p] dirName
# rm是linux shell下删除文件或文件夹的命令，其语法是：rm [选项]... 文件...
PHONY += $(objtree)/Module.symvers
$(objtree)/Module.symvers:
@test -e $(objtree)/Module.symvers || ( \
echo; \
echo " WARNING: Symbol version dump $(objtree)/Module.symvers"; \
echo " is missing; modules will have no dependencies and modversions."; \
echo )
# 第一行给变量PHONY追加值。
# 第二行定义了一个为目标$(objtree)/Module.symvers。
# 当“@”字符在命令行前，那么这个命令将不被make显示出来。
# echo是Makefile中的一个将输入的字符串送往标准输出关键字，其语法是：echo [-ne][字符串]
# test是linux shell下的一个对档案侦测、判定的函数，其语法是：test [选项] string
module-dirs := $(addprefix _module_,$(KBUILD_EXTMOD))
PHONY += $(module-dirs) modules
$(module-dirs): crmodverdir $(objtree)/Module.symvers
$(Q)$(MAKE) $(build)=$(patsubst _module_%,%,$@)
# 第一行将函数addprefix的返回值展开后赋给变量module-dirs。
# 第二行给变量PHONY追加值。
# 第三行定义了一个规则，目标是$(module-dirs)，依赖文件是crmodverdir $(objtree)/Module.symvers
# addprefix是Makefile中的一个加前缀函数函数，其语法是：$(addprefix
modules: $(module-dirs)
@echo ' Building modules, stage 2.';
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
# 上面定义了一个规则，目标是modules，依赖文件是$(module-dirs)。
# 当“@”字符在命令行前，那么这个命令将不被make显示出来。
# echo是Makefile中的一个将输入的字符串送往标准输出关键字，其语法是：echo [-ne][字符串]
PHONY += modules_install
modules_install: _emodinst_ _emodinst_post
# 第一行给变量PHONY追加值
# 第二行定义了一个依赖关系，目标是modules_install，依赖文件是_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
# 第一行将if函数的返回值展开后赋给变量install-dir。
# 第二行给变量PHONY追加值。
# 第三行定义了一个伪目标_emodinst_
# mkdir是linux shell下的一个创建文件夹的命令，其语法是：mkdir [-p] dirName
# Run depmod only is we have System.map and depmod is executable
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) \
$(KERNELRELEASE); \
fi
# 第一二行分别给变量quiet_cmd_depmod和cmd_depmod赋值。
# strip是Makefile中的去空格函数，其语法是：$(strip
# 字符“\”有两个功能：一是：续行；二是：转义。
PHONY += _emodinst_post
_emodinst_post: _emodinst_
$(call cmd,depmod)
# 第一行给变量PHONY追加值。
# 第二行定义了一个规则，目标是_emodinst_post，依赖文件是_emodinst_
clean-dirs := $(addprefix _clean_,$(KBUILD_EXTMOD))
# 上面将函数addprefix的返回值展开后赋给变量clean-dirs。
PHONY += $(clean-dirs) clean
$(clean-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)
# 第一行给变量PHONY追加值。
# 第二行定义了一个为目标$(clean-dirs)，
clean: rm-dirs := $(MODVERDIR)
clean: $(clean-dirs)
$(call cmd,rmdirs)
@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
# 第一行定义了一个规则，目标是clean，依赖文件是rm-dirs，命令是给依赖文件rm-dirs赋值
help:
@echo ' Building external modules.'
@echo ' Syntax: make -C path/to/kernel/src M=$$PWD target'
@echo ''
@echo ' modules - default target, build the module(s)'
@echo ' modules_install - install the module'
@echo ' clean - remove generated files in module directory only'
@echo ''
# 上面定义了一个伪目标help。
# Dummies...
PHONY += prepare scripts
prepare: ;
scripts: ;
endif # KBUILD_EXTMOD
# 第一行给变量PHONY追加值
# 第二三行分别定义了一个为目标，命令为空命令。
# Generate tags for editors
# ---------------------------------------------------------------------------
#We want __srctree to totally vanish out when KBUILD_OUTPUT is not set
#(which is the most common case IMHO) to avoid unneeded clutter in the big tags file.
#Adding $(srctree) adds about 20M on i386 to the size of the output file!
ifeq ($(src),$(obj))
__srctree =
else
__srctree = $(srctree)/
endif
ifeq ($(ALLSOURCE_ARCHS),)
ifeq ($(ARCH),um)
ALLINCLUDE_ARCHS := $(ARCH) $(SUBARCH)
else # 这个else与ifeq ($(ARCH),um)对应。
ALLINCLUDE_ARCHS := $(ARCH)
endif # 这个endif与ifeq ($(ARCH),um)对应。
else # 这个else与外层的ifeq ($(ALLSOURCE_ARCHS),)对应
#Allow user to specify only ALLSOURCE_PATHS on the command line, keeping existing behavour.
ALLINCLUDE_ARCHS := $(ALLSOURCE_ARCHS)
endif # 这个endif与外层的ifeq ($(ALLSOURCE_ARCHS),)对应
# ifeq是Makefile中的一个条件关键字，其语法是：ifeq (
# 功能：比较参数“arg1”和“arg2”的值是否相同。
# 上面在ifeq ($(ALLSOURCE_ARCHS),)里面嵌入了一个ifeq ($(ARCH),um)。
ALLSOURCE_ARCHS := $(ARCH)
# 给变量ALLSOURCE_ARCHS赋值
define find-sources
( for ARCH in $(ALLSOURCE_ARCHS) ; do \
find $(__srctree)arch/$${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) \
\( -name include -o -name arch \) -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 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
# define是Makefile中的一个定义命令包（相同的命令序列）的关键字，
# 字符“\”有两个功能：一是：续行；二是：转义。
# 字符“|”是管道的标志，它的作用是：将上一个命令的stdout重定向到下一个命令的stdin。
# grep是linux shell中一个在文件中查找字符串的命令。其语法是：grep 字符串 文件名
# xargs是linux shell中的一个对输出执行其他某些命令的命令。
quiet_cmd_cscope-file = FILELST cscope.files
cmd_cscope-file = (echo \-k; echo \-q; $(all-sources)) > cscope.files
# 第一二行分别给变量quiet_cmd_cscope-file、cmd_cscope-file 赋值。
# echo是Makefile中的一个将输入的字符串送往标准输出关键字，其语法是：echo [-ne][字符串]
# 字符“\”有两个功能：一是：续行；二是：转义。
# 字符“>”是重定向标志，功能将前一个命令的stdou重定向到档案（文件等）。
quiet_cmd_cscope = MAKE cscope.out
cmd_cscope = cscope -b
# 分别给变量quiet_cmd_cscope和cmd_cscope赋值。
cscope: FORCE
$(call cmd,cscope-file)
$(call cmd,cscope)
# 上面定义了一个规则，目标是cscope，依赖文件是FORCE。
quiet_cmd_TAGS = MAKE $@
define cmd_TAGS
rm -f $@; \
$(call xtags,etags)
endef
# 第一行给变量quiet_cmd_TAGS赋值。
# $@是Makefile的自动化变量，它代表当前规则的目标文件集。
TAGS: FORCE
$(call cmd,TAGS)
# 上面定义了一个规则，目标是TAGS，依赖文件是FORCE。
quiet_cmd_tags = MAKE $@
define cmd_tags
rm -f $@; \
$(call xtags,ctags)
endef
# 第一行给变量quiet_cmd_tags赋值。
tags: FORCE
$(call cmd,tags)
# 上面定义了一个规则，目标是tags，依赖文件是FORCE
includecheck:
find * $(RCS_FIND_IGNORE) \
-name '*.[hcS]' -type f -print | sort \
| xargs $(PERL) -w scripts/checkincludes.pl
# 第一行定义了一个伪目标includecheck
versioncheck:
find * $(RCS_FIND_IGNORE) \
-name '*.[hcS]' -type f -print | sort \
| xargs $(PERL) -w scripts/checkversion.pl
# 第一行定义了一个伪目标versioncheck
namespacecheck:
$(PERL) $(srctree)/scripts/namespace.pl
# 上面定义了一个伪目标namespacecheck
endif #ifeq ($(config-targets),1)
endif #ifeq ($(mixed-targets),1)
# 上面第一个endif与ifeq ($(config-targets),1)对应
# 上面第二个endif与ifeq ($(mixed-targets),1)对应
PHONY += checkstack kernelrelease kernelversion
# 给变量PHONY追加值
# 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 $(KERNELVERSION)
# Single targets
# ---------------------------------------------------------------------------
# Single targets are compatible with:
# - build whith mixed source and output
# - build with separate output dir 'make O=...'
# - external modules
#
# target-dir => where to store outputfile
# build-dir => directory in kernel source tree to use
ifeq ($(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 $@)
# 上面定义了一系列的规则。
# Modules
/ %/: prepare scripts FORCE
$(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
$(build)=$(build-dir)
%.ko: prepare scripts FORCE
$(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
$(build)=$(build-dir)
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
# 上面第一四行分别定义了一个规则。
# 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)
# 上面两行分别给变量quiet_cmd_rmdirs和cmd_rmdirs赋值
quiet_cmd_rmfiles = $(if $(wildcard $(rm-files)),CLEAN $(wildcard $(rm-files)))
cmd_rmfiles = rm -f $(rm-files)
# 上面两行分别给变量quiet_cmd_rmfiles和cmd_rmfiles赋值
a_flags = -Wp,-MD,$(depfile) $(AFLAGS) $(AFLAGS_KERNEL) \
$(NOSTDINC_FLAGS) $(CPPFLAGS) \
$(modkern_aflags) $(EXTRA_AFLAGS) $(AFLAGS_$(basetarget).o)
# 第一行给变量a_flags赋值
# 第二三行是命令，命令都是以tab开头的。
quiet_cmd_as_o_S = AS $@
cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $<
# 上面两行分别给变量quiet_cmd_as_o_S和cmd_as_o_S赋值。
# $@和$<都是Makefile中的自动化变量，$@表示当前规则中的目标文件集，$<表示依赖目标中的第一个目标名字。
# read all saved command lines
targets := $(wildcard $(sort $(targets)))
cmd_files := $(wildcard .*.cmd $(foreach f,$(targets),$(dir $(f)).$(notdir $(f)).cmd))
# 上面两行分别给变量targets和cmd_files赋值
# sort是Makefile中的一个排序（升序）函数，其语法是：$(sort ;)
# wildcard是Makefile中的关键字，它的作用是让通配符在变量中展开。
# foreach是Makefile中的循环函数，其语法是：$(foreach ;,;,
# dir是Makefile中的取目录函数，其语法是：$(dir
# 功能：从文件名序列
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
# 上面这一行是给变量clean赋值
endif # skip-makefile
PHONY += FORCE
FORCE:
# 第一行给变量PHONY追加值
# 第二行定义了一个伪目标FORCE
# Cancel implicit rules on top Makefile, `-rR' will apply to sub-makes.
Makefile: ;
# 上面这一行定义了一个伪目标Makefile，命令为空
# 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)
# 上面这一行定义了一个依赖关系。
总结的一点基础：
1）在script/kbuild.include中定义了一些常用函数
# echo command.
# Short version is used, if $(quiet) equals `quiet_', otherwise full one.
echo-cmd = $(if $($(quiet)cmd_$(1)),\
echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
# printing commands
cmd = @$(echo-cmd) $(cmd_$(1))
用于打印命令，并且执行命令。
2）
###
# if_changed - execute command if any prerequisite is newer than
# target, or command line has changed
# if_changed_dep - as if_changed, but uses fixdep to reveal dependencies
# including used config symbols
# if_changed_rule - as if_changed but execute rule instead
# See Documentation/kbuild/makefiles.txt for more info
当以来条件有更新时执行command。
3）
# 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
ifdef SUBDIRS
KBUILD_EXTMOD ?= $(SUBDIRS)
endif
ifeq ("$(origin M)", "command line")
KBUILD_EXTMOD := $(M)
endif
使用M=dir来指定模块的编译目录，传统的通过SUBIDRS的方法仍然支持。
4）产生符号：
# Generate System.map
quiet_cmd_sysmap = SYSMAP
cmd_sysmap = $(CONFIG_SHELL) $(srctree)/scripts/mksysmap
其中mksysmap只是简单的一句话：
$NM -n $1 | grep -v '\( [aNUw] \)\|\(__crc_\)\|\( \$[adt]\)' > $2
5）Makefile.modpost
Step 1), find all modules listed in $(MODVERDIR)
modules 变量是 $(MODVERDIR) 下的所有 <模块>.ko 。
对于 kernel 模块来说, MODVERDIR=
对于外部变量而言, MODVERDIR=
step2)调用modpost产生从.o变为mod.c文件，之后再编译成.mod.o,最后结合.o和mod.o生成.ko
把 module 中的 EXPORT_SYMBOL 符号写入 Module.symvers。
mod.c是这个样子的：
