makefile-5.3.12

构建顺序

make menuconfig

menuconfig

代码分析

版本号等的定义，并将默认目标定义好，即_all，最后通过_all的依赖项决定到编译哪个目标。

VERSION = 5
PATCHLEVEL = 3
SUBLEVEL = 12
EXTRAVERSION =
NAME = Bobtail Squid

PHONY := _all
_all:

linux的编译可以指定输出路径的，如果自行指定输出路径，则会在对应路径再次运行make。所以会分为两步进行。同样的，即使不指定输出路径，也会进行两步。分别为make和sub-make。make是用户自行调用的，sub-make是由make调用的在输出路径下的make。

路径确定

# sub_make_done表示当前是否正在进行sub-make
# need-sub-make表示当前make是否需要进行sub-make
ifneq ($(sub_make_done),1)
# 不让make使用隐式规则，这样避免一些难以确定的问题。
MAKEFLAGS += -rR

# 字符集定义
unexport LC_ALL
LC_COLLATE=C
LC_NUMERIC=C
export LC_COLLATE LC_NUMERIC

# 避免环境变量的影响
unexport GREP_OPTIONS

# 通过一些小手段来控制输出的详细程度
ifeq ("$(origin V)", "command line")
  KBUILD_VERBOSE = $(V)
endif
ifndef KBUILD_VERBOSE
  KBUILD_VERBOSE = 0
endif

ifeq ($(KBUILD_VERBOSE),1)
  quiet =
  Q =
else
  quiet=quiet_
  Q = @
endif

ifneq ($(findstring s,$(filter-out --%,$(MAKEFLAGS))),)
  quiet=silent_
endif
export quiet Q KBUILD_VERBOSE

# 指定的输出目录，通过make O=...传入
ifeq ("$(origin O)", "command line")
  KBUILD_OUTPUT := $(O)
endif

ifneq ($(KBUILD_OUTPUT),)
# 保证输出目录存在
abs_objtree := $(shell mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) && pwd)
$(if $(abs_objtree),, \
     $(error failed to create output directory "$(KBUILD_OUTPUT)"))

abs_objtree := $(realpath $(abs_objtree))
else
abs_objtree := $(CURDIR)
endif # ifneq ($(KBUILD_OUTPUT),)

ifeq ($(abs_objtree),$(CURDIR))
MAKEFLAGS += --no-print-directory
else
need-sub-make := 1
endif
# 通过Makefile的路径来确定源码目录，并保证目录没有":"和空格
abs_srctree := $(realpath $(dir $(lastword $(MAKEFILE_LIST))))
ifneq ($(words $(subst :, ,$(abs_srctree))), 1)
$(error source directory cannot contain spaces or colons)
endif
# 如果源码目录跟输出目录不同，则需要sub-make
ifneq ($(abs_srctree),$(abs_objtree))
MAKEFLAGS += --include-dir=$(abs_srctree)
need-sub-make := 1
endif
# make 3.x的'MAKEFLAGS += -rR'并不是立马生效 ，所以需要sub-make来屏蔽隐式规则，同时屏蔽当前makefile的隐式规则
ifneq ($(filter 3.%,$(MAKE_VERSION)),)
need-sub-make := 1
$(lastword $(MAKEFILE_LIST)): ;
endif

取消回显没有别的export abs_srctree abs_objtree
export sub_make_done := 1

ifeq ($(need-sub-make),1)

PHONY += $(MAKECMDGOALS) sub-make
$(filter-out _all sub-make $(lastword $(MAKEFILE_LIST)), $(MAKECMDGOALS)) _all: sub-make
	@:
# 在输出目录下调用make
sub-make:
	$(Q)$(MAKE) -C $(abs_objtree) -f $(abs_srctree)/Makefile $(MAKECMDGOALS)

endif # need-sub-make
endif # sub_make_done

正式编译

如果不需要sub-make，则当前的make调用需要进行真正的编译操作。

ifeq ($(need-sub-make),)
...
endif   # need-sub-make

MAKEFLAGS += --no-print-directory
# C=1只检查需要重新编译的文件
# C=2 检查所有的文件
ifeq ("$(origin C)", "command line")
  KBUILD_CHECKSRC = $(C)
endif
ifndef KBUILD_CHECKSRC
  KBUILD_CHECKSRC = 0
endif

确定M的值，确定需要编译的外部模块

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

确定源码路径

ifeq ($(abs_srctree),$(abs_objtree))
        # building in the source tree
        srctree := .
	building_out_of_srctree :=
else
        ifeq ($(abs_srctree)/,$(dir $(abs_objtree)))
                # building in a subdirectory of the source tree
                srctree := ..
        else
                srctree := $(abs_srctree)
        endif
	building_out_of_srctree := 1
endif

ifneq ($(KBUILD_ABS_SRCTREE),)
srctree := $(abs_srctree)
endif

objtree		:= .
VPATH		:= $(srctree)

export building_out_of_srctree srctree objtree VPATH

version_h := include/generated/uapi/linux/version.h
old_version_h := include/linux/version.h
# 清理用的target
clean-targets := %clean mrproper cleandocs
# 不需要依赖.config的target
no-dot-config-targets := $(clean-targets) \
			 cscope gtags TAGS tags help% %docs check% coccicheck \
			 $(version_h) headers headers_% archheaders archscripts \
			 %asm-generic kernelversion %src-pkg
# 不需要同步config的target
no-sync-config-targets := $(no-dot-config-targets) install %install \
			   kernelrelease

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

# 确定是否需要依赖.config
ifneq ($(filter $(no-dot-config-targets), $(MAKECMDGOALS)),)
	ifeq ($(filter-out $(no-dot-config-targets), $(MAKECMDGOALS)),)
		dot-config := 0
	endif
endif
# 确定是否需要同步config
ifneq ($(filter $(no-sync-config-targets), $(MAKECMDGOALS)),)
	ifeq ($(filter-out $(no-sync-config-targets), $(MAKECMDGOALS)),)
		may-sync-config := 0
	endif
endif
# 如果是构建外部模块，则不需要同步config
ifneq ($(KBUILD_EXTMOD),)
	may-sync-config := 0
endif
# 确定是不是config 与build的混合目标
ifeq ($(KBUILD_EXTMOD),)
        ifneq ($(filter config %config,$(MAKECMDGOALS)),)
                config-targets := 1
                ifneq ($(words $(MAKECMDGOALS)),1)
                        mixed-targets := 1
                endif
        endif
endif
# 如 "make -j clean all", "make -j mrproper defconfig all"等，清理target与非清理target也是混合目标
ifneq ($(filter $(clean-targets),$(MAKECMDGOALS)),)
        ifneq ($(filter-out $(clean-targets),$(MAKECMDGOALS)),)
                mixed-targets := 1
        endif
endif

# install和modules_install也需要按顺序进行
ifneq ($(filter install,$(MAKECMDGOALS)),)
        ifneq ($(filter modules_install,$(MAKECMDGOALS)),)
	        mixed-targets := 1
        endif
endif

如果是混合目标，则需要一个一个处理

ifeq ($(mixed-targets),1)
PHONY += $(MAKECMDGOALS) __build_one_by_one

$(filter-out __build_one_by_one, $(MAKECMDGOALS)): __build_one_by_one
	@:

__build_one_by_one:
	$(Q)set -e; \
	for i in $(MAKECMDGOALS); do \
		$(MAKE) -f $(srctree)/Makefile $$i; \
	done
else

# 引入kbuild工具包
include scripts/Kbuild.include
#获取版本信息，通常是在config的过程中生成的kernel.release文件。
KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)
export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
# 引入架构解析相关的工具包
include scripts/subarch.include

# 确定目标架构
ARCH		?= $(SUBARCH)

# 使用对应架构的源码
UTS_MACHINE 	:= $(ARCH)
SRCARCH 	:= $(ARCH)

ifeq ($(ARCH),i386)
        SRCARCH := x86
endif
ifeq ($(ARCH),x86_64)
        SRCARCH := x86
endif

ifeq ($(ARCH),sparc32)
       SRCARCH := sparc
endif
ifeq ($(ARCH),sparc64)
       SRCARCH := sparc
endif

ifeq ($(ARCH),sh64)
       SRCARCH := sh
endif
# 内核编译使用的配置文件
KCONFIG_CONFIG	?= .config
export KCONFIG_CONFIG

# 内核编译使用的shell
CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
	  else if [ -x /bin/bash ]; then echo /bin/bash; \
	  else echo sh; fi ; fi)

HOST_LFS_CFLAGS := $(shell getconf LFS_CFLAGS 2>/dev/null)
HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS 2>/dev/null)
HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null)

# 本机使用的编译器及其参数
HOSTCC       = gcc
HOSTCXX      = g++
KBUILD_HOSTCFLAGS   := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \
		-fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS) \
		$(HOSTCFLAGS)
KBUILD_HOSTCXXFLAGS := -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)
KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)

# 交叉编译使用的工具链
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
OBJSIZE		= $(CROSS_COMPILE)size
PAHOLE		= pahole
LEX		= flex
YACC		= bison
AWK		= awk
INSTALLKERNEL  := installkernel
DEPMOD		= /sbin/depmod
PERL		= perl
PYTHON		= python
PYTHON2		= python2
PYTHON3		= python3
CHECK		= sparse

CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
		  -Wbitwise -Wno-return-void -Wno-unknown-attribute $(CF)
NOSTDINC_FLAGS :=
CFLAGS_MODULE   =
AFLAGS_MODULE   =
LDFLAGS_MODULE  =
CFLAGS_KERNEL	=
AFLAGS_KERNEL	=
LDFLAGS_vmlinux =

# 用户空间API路径
USERINCLUDE    := \
		-I$(srctree)/arch/$(SRCARCH)/include/uapi \
		-I$(objtree)/arch/$(SRCARCH)/include/generated/uapi \
		-I$(srctree)/include/uapi \
		-I$(objtree)/include/generated/uapi \
                -include $(srctree)/include/linux/kconfig.h

# 系统空间头文件路径
LINUXINCLUDE    := \
		-I$(srctree)/arch/$(SRCARCH)/include \
		-I$(objtree)/arch/$(SRCARCH)/include/generated \
		$(if $(building_out_of_srctree),-I$(srctree)/include) \
		-I$(objtree)/include \
		$(USERINCLUDE)

KBUILD_AFLAGS   := -D__ASSEMBLY__ -fno-PIE
KBUILD_CFLAGS   := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \
		   -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \
		   -Werror=implicit-function-declaration -Werror=implicit-int \
		   -Wno-format-security \
		   -std=gnu89
KBUILD_CPPFLAGS := -D__KERNEL__
KBUILD_AFLAGS_KERNEL :=
KBUILD_CFLAGS_KERNEL :=
KBUILD_AFLAGS_MODULE  := -DMODULE
KBUILD_CFLAGS_MODULE  := -DMODULE
KBUILD_LDFLAGS_MODULE := -T $(srctree)/scripts/module-common.lds
KBUILD_LDFLAGS :=
GCC_PLUGINS_CFLAGS :=
CLANG_FLAGS :=

export ARCH SRCARCH CONFIG_SHELL HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE PAHOLE LEX YACC AWK INSTALLKERNEL
export PERL PYTHON PYTHON2 PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE

export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN
export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
export KBUILD_ARFLAGS

# find 命令需要忽略的文件名

export RCS_FIND_IGNORE := \( -name SCCS -o -name BitKeeper -o -name .svn -o    \
			  -name CVS -o -name .pc -o -name .hg -o -name .git \) \
			  -prune -o
export RCS_TAR_IGNORE := --exclude SCCS --exclude BitKeeper --exclude .svn \
			 --exclude CVS --exclude .pc --exclude .hg --exclude .git

config目标与build目标的共用规则

# 引入基本的脚本工具包
PHONY += scripts_basic
scripts_basic:
	$(Q)$(MAKE) $(build)=scripts/basic
	$(Q)rm -f .tmp_quiet_recordmcount

# 如果build路径下有.gitignore，则将该目录直接加入忽略列表。
PHONY += outputmakefile
outputmakefile:
ifdef building_out_of_srctree
	$(Q)ln -fsn $(srctree) source
	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile $(srctree)
	$(Q)test -e .gitignore || \
	{ echo "# this is build directory, ignore it"; echo "*"; } > .gitignore
endif

ifneq ($(shell $(CC) --version 2>&1 | head -n 1 | grep clang),)
ifneq ($(CROSS_COMPILE),)
CLANG_FLAGS	+= --target=$(notdir $(CROSS_COMPILE:%-=%))
GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
CLANG_FLAGS	+= --prefix=$(GCC_TOOLCHAIN_DIR)
GCC_TOOLCHAIN	:= $(realpath $(GCC_TOOLCHAIN_DIR)/..)
endif
ifneq ($(GCC_TOOLCHAIN),)
CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
endif
ifeq ($(shell $(AS) --version 2>&1 | head -n 1 | grep clang),)
CLANG_FLAGS	+= -no-integrated-as
endif
CLANG_FLAGS	+= -Werror=unknown-warning-option
KBUILD_CFLAGS	+= $(CLANG_FLAGS)
KBUILD_AFLAGS	+= $(CLANG_FLAGS)
export CLANG_FLAGS
endif

CC_VERSION_TEXT = $(shell $(CC) --version 2>/dev/null | head -n 1)

config目标

ifeq ($(config-targets),1)
# 直接使用Kconfig来进行配置
include arch/$(SRCARCH)/Makefile
export KBUILD_DEFCONFIG KBUILD_KCONFIG CC_VERSION_TEXT

config: scripts_basic outputmakefile FORCE
	$(Q)$(MAKE) $(build)=scripts/kconfig $@

%config: scripts_basic outputmakefile FORCE
	$(Q)$(MAKE) $(build)=scripts/kconfig $@

else

build目标

5.x版本的编译过程，每次make调用都只处理一个target，极大减小make目标之间的耦合度。

# 指定默认的target
PHONY += all
ifeq ($(KBUILD_EXTMOD),)
_all: all
else
_all: modules
endif

判断是否编译内部模块，是否编译外部模块。通常情况下只编译内部模块

KBUILD_MODULES :=
KBUILD_BUILTIN := 1

# 如果在编译modules时，指定了MODVERSIONS，那就需要考虑内部对象，所以需要重构内部模块，保证校验和是相等的
# 这是官方注释，不太明白，等遇到对应案例时再说。
ifeq ($(MAKECMDGOALS),modules)
  KBUILD_BUILTIN := $(if $(CONFIG_MODVERSIONS),1)
endif

ifneq ($(filter all _all modules,$(MAKECMDGOALS)),)
  KBUILD_MODULES := 1
endif

ifeq ($(MAKECMDGOALS),)
  KBUILD_MODULES := 1
endif

export KBUILD_MODULES KBUILD_BUILTIN

ifeq ($(dot-config),1)
include include/config/auto.conf
endif

需要编译的文件夹，旧版本应该是叫子目录

ifeq ($(KBUILD_EXTMOD),)
init-y		:= init/								# 初始化
drivers-y	:= drivers/ sound/						# 驱动和声音
drivers-$(CONFIG_SAMPLES) += samples/				
drivers-$(CONFIG_KERNEL_HEADER_TEST) += include/	# 头文件
net-y		:= net/									# 网络
libs-y		:= lib/									# 基础库
core-y		:= usr/									
virt-y		:= virt/								# 虚拟化
endif # KBUILD_EXTMOD

all: vmlinux

CFLAGS_GCOV	:= -fprofile-arcs -ftest-coverage \
	$(call cc-option,-fno-tree-loop-im) \
	$(call cc-disable-warning,maybe-uninitialized,)
export CFLAGS_GCOV

# The arch Makefiles can override CC_FLAGS_FTRACE. We may also append it later.
ifdef CONFIG_FUNCTION_TRACER
  CC_FLAGS_FTRACE := -pg
endif

RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register
RETPOLINE_VDSO_CFLAGS_GCC := -mindirect-branch=thunk-inline -mindirect-branch-register
RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
RETPOLINE_VDSO_CFLAGS_CLANG := -mretpoline
RETPOLINE_CFLAGS := $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
RETPOLINE_VDSO_CFLAGS := $(call cc-option,$(RETPOLINE_VDSO_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_VDSO_CFLAGS_CLANG)))
export RETPOLINE_CFLAGS
export RETPOLINE_VDSO_CFLAGS

# 由不同架构的Makefile自行决定以下编译参数
ARCH_CPPFLAGS :=
ARCH_AFLAGS :=
ARCH_CFLAGS :=
include arch/$(SRCARCH)/Makefile

对配置文件的检查，这里涉及到一个规则，那就是include时，会检查文件是否存在，而这个目标同样是由Makefile中的目标处理的。也就是说这个过程是make执行时处理的，即，解析时，会告知用户这个文件不存在，而后在运行时，调用对应的目标来处理。

ifeq ($(dot-config),1)
ifeq ($(may-sync-config),1)

#如果需要同步配置，则需要这个文件
include include/config/auto.conf.cmd

$(KCONFIG_CONFIG):
	@echo >&2 '***'
	@echo >&2 '*** Configuration file "$@" not found!'
	@echo >&2 '***'
	@echo >&2 '*** Please run some configurator (e.g. "make oldconfig" or'
	@echo >&2 '*** "make menuconfig" or "make xconfig").'
	@echo >&2 '***'
	@/bin/false

# 如果$(KCONFIG_CONFIG)比这几个文件要新，则syncconfig.
%/auto.conf %/auto.conf.cmd %/tristate.conf: $(KCONFIG_CONFIG)
	$(Q)$(MAKE) -f $(srctree)/Makefile syncconfig
else
# External modules and some install targets need include/generated/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
# 有些目标并不关心 auto.conf文件是否是最新，就不需要同步配置文件，则只需要这几个文件存在就行。
include/config/auto.conf:
	$(Q)test -e include/generated/autoconf.h -a -e $@ || (		\
	echo >&2;							\
	echo >&2 "  ERROR: Kernel configuration is invalid.";		\
	echo >&2 "         include/generated/autoconf.h or $@ are missing.";\
	echo >&2 "         Run 'make oldconfig && make prepare' on kernel src to fix it.";	\
	echo >&2 ;							\
	/bin/false)

endif # may-sync-config
endif # $(dot-config)

很多编译选项跟优化选项，要不要一条条看呢。。。(待）

#
KBUILD_CFLAGS	+= $(call cc-option,-fno-delete-null-pointer-checks,)
KBUILD_CFLAGS	+= $(call cc-disable-warning,frame-address,)
KBUILD_CFLAGS	+= $(call cc-disable-warning, format-truncation)
KBUILD_CFLAGS	+= $(call cc-disable-warning, format-overflow)
KBUILD_CFLAGS	+= $(call cc-disable-warning, address-of-packed-member)

ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
KBUILD_CFLAGS	+= -Os
else
KBUILD_CFLAGS   += -O2
endif

ifdef CONFIG_CC_DISABLE_WARN_MAYBE_UNINITIALIZED
KBUILD_CFLAGS   += -Wno-maybe-uninitialized
endif

# Tell gcc to never replace conditional load with a non-conditional one
KBUILD_CFLAGS	+= $(call cc-option,--param=allow-store-data-races=0)

include scripts/Makefile.kcov
include scripts/Makefile.gcc-plugins

ifdef CONFIG_READABLE_ASM
# Disable optimizations that make assembler listings hard to read.
# reorder blocks reorders the control in the function
# ipa clone creates specialized cloned functions
# partial inlining inlines only parts of functions
KBUILD_CFLAGS += $(call cc-option,-fno-reorder-blocks,) \
                 $(call cc-option,-fno-ipa-cp-clone,) \
                 $(call cc-option,-fno-partial-inlining)
endif

ifneq ($(CONFIG_FRAME_WARN),0)
KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
endif

stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong

KBUILD_CFLAGS += $(stackp-flags-y)

ifdef CONFIG_CC_IS_CLANG
KBUILD_CPPFLAGS += -Qunused-arguments
KBUILD_CFLAGS += -Wno-format-invalid-specifier
KBUILD_CFLAGS += -Wno-gnu
# Quiet clang warning: comparison of unsigned expression < 0 is always false
KBUILD_CFLAGS += -Wno-tautological-compare
# CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
# source of a reference will be _MergedGlobals and not on of the whitelisted names.
# See modpost pattern 2
KBUILD_CFLAGS += -mno-global-merge
else

# These warnings generated too much noise in a regular build.
# Use make W=1 to enable them (see scripts/Makefile.extrawarn)
KBUILD_CFLAGS += -Wno-unused-but-set-variable

# Warn about unmarked fall-throughs in switch statement.
# Disabled for clang while comment to attribute conversion happens and
# https://github.com/ClangBuiltLinux/linux/issues/636 is discussed.
KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,)
endif

KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
ifdef CONFIG_FRAME_POINTER
KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
else
# Some targets (ARM with Thumb2, for example), can't be built with frame
# pointers.  For those, we don't have FUNCTION_TRACER automatically
# select FRAME_POINTER.  However, FUNCTION_TRACER adds -pg, and this is
# incompatible with -fomit-frame-pointer with current GCC, so we don't use
# -fomit-frame-pointer with FUNCTION_TRACER.
ifndef CONFIG_FUNCTION_TRACER
KBUILD_CFLAGS	+= -fomit-frame-pointer
endif
endif

# Initialize all stack variables with a pattern, if desired.
ifdef CONFIG_INIT_STACK_ALL
KBUILD_CFLAGS	+= -ftrivial-auto-var-init=pattern
endif

DEBUG_CFLAGS	:= $(call cc-option, -fno-var-tracking-assignments)

ifdef CONFIG_DEBUG_INFO
ifdef CONFIG_DEBUG_INFO_SPLIT
DEBUG_CFLAGS	+= -gsplit-dwarf
else
DEBUG_CFLAGS	+= -g
endif
KBUILD_AFLAGS	+= -Wa,-gdwarf-2
endif
ifdef CONFIG_DEBUG_INFO_DWARF4
DEBUG_CFLAGS	+= -gdwarf-4
endif

ifdef CONFIG_DEBUG_INFO_REDUCED
DEBUG_CFLAGS	+= $(call cc-option, -femit-struct-debug-baseonly) \
		   $(call cc-option,-fno-var-tracking)
endif

KBUILD_CFLAGS += $(DEBUG_CFLAGS)
export DEBUG_CFLAGS

ifdef CONFIG_FUNCTION_TRACER
ifdef CONFIG_FTRACE_MCOUNT_RECORD
  # gcc 5 supports generating the mcount tables directly
  ifeq ($(call cc-option-yn,-mrecord-mcount),y)
    CC_FLAGS_FTRACE	+= -mrecord-mcount
    export CC_USING_RECORD_MCOUNT := 1
  endif
  ifdef CONFIG_HAVE_NOP_MCOUNT
    ifeq ($(call cc-option-yn, -mnop-mcount),y)
      CC_FLAGS_FTRACE	+= -mnop-mcount
      CC_FLAGS_USING	+= -DCC_USING_NOP_MCOUNT
    endif
  endif
endif
ifdef CONFIG_HAVE_FENTRY
  ifeq ($(call cc-option-yn, -mfentry),y)
    CC_FLAGS_FTRACE	+= -mfentry
    CC_FLAGS_USING	+= -DCC_USING_FENTRY
  endif
endif
export CC_FLAGS_FTRACE
KBUILD_CFLAGS	+= $(CC_FLAGS_FTRACE) $(CC_FLAGS_USING)
KBUILD_AFLAGS	+= $(CC_FLAGS_USING)
ifdef CONFIG_DYNAMIC_FTRACE
	ifdef CONFIG_HAVE_C_RECORDMCOUNT
		BUILD_C_RECORDMCOUNT := y
		export BUILD_C_RECORDMCOUNT
	endif
endif
endif

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

ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
KBUILD_CFLAGS_KERNEL += -ffunction-sections -fdata-sections
LDFLAGS_vmlinux += --gc-sections
endif

ifdef CONFIG_LIVEPATCH
KBUILD_CFLAGS += $(call cc-option, -flive-patching=inline-clone)
endif

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

# warn about C99 declaration after statement
KBUILD_CFLAGS += -Wdeclaration-after-statement

# Variable Length Arrays (VLAs) should not be used anywhere in the kernel
KBUILD_CFLAGS += -Wvla

# disable pointer signed / unsigned warnings in gcc 4.0
KBUILD_CFLAGS += -Wno-pointer-sign

# disable stringop warnings in gcc 8+
KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)

# disable invalid "can't wrap" optimizations for signed / pointers
KBUILD_CFLAGS	+= $(call cc-option,-fno-strict-overflow)

# clang sets -fmerge-all-constants by default as optimization, but this
# is non-conforming behavior for C and in fact breaks the kernel, so we
# need to disable it here generally.
KBUILD_CFLAGS	+= $(call cc-option,-fno-merge-all-constants)

# for gcc -fno-merge-all-constants disables everything, but it is fine
# to have actual conforming behavior enabled.
KBUILD_CFLAGS	+= $(call cc-option,-fmerge-constants)

# Make sure -fstack-check isn't enabled (like gentoo apparently did)
KBUILD_CFLAGS  += $(call cc-option,-fno-stack-check,)

# conserve stack if available
KBUILD_CFLAGS   += $(call cc-option,-fconserve-stack)

# Prohibit date/time macros, which would make the build non-deterministic
KBUILD_CFLAGS   += $(call cc-option,-Werror=date-time)

# enforce correct pointer usage
KBUILD_CFLAGS   += $(call cc-option,-Werror=incompatible-pointer-types)

# Require designated initializers for all marked structures
KBUILD_CFLAGS   += $(call cc-option,-Werror=designated-init)

# change __FILE__ to the relative path from the srctree
KBUILD_CFLAGS	+= $(call cc-option,-fmacro-prefix-map=$(srctree)/=)

# ensure -fcf-protection is disabled when using retpoline as it is
# incompatible with -mindirect-branch=thunk-extern
ifdef CONFIG_RETPOLINE
KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)
endif

# use the deterministic mode of AR if available
KBUILD_ARFLAGS := $(call ar-option,D)

include scripts/Makefile.kasan
include scripts/Makefile.extrawarn
include scripts/Makefile.ubsan

# Add any arch overrides and user supplied CPPFLAGS, AFLAGS and CFLAGS as the
# last assignments
KBUILD_CPPFLAGS += $(ARCH_CPPFLAGS) $(KCPPFLAGS)
KBUILD_AFLAGS   += $(ARCH_AFLAGS)   $(KAFLAGS)
KBUILD_CFLAGS   += $(ARCH_CFLAGS)   $(KCFLAGS)

KBUILD_LDFLAGS_MODULE += --build-id
LDFLAGS_vmlinux += --build-id

ifeq ($(CONFIG_STRIP_ASM_SYMS),y)
LDFLAGS_vmlinux	+= $(call ld-option, -X,)
endif

# insure the checker run with the right endianness
CHECKFLAGS += $(if $(CONFIG_CPU_BIG_ENDIAN),-mbig-endian,-mlittle-endian)

# the checker needs the correct machine size
CHECKFLAGS += $(if $(CONFIG_64BIT),-m64,-m32)

（待）

export KBUILD_IMAGE ?= vmlinux
export	INSTALL_PATH ?= /boot

# device tree binary, device tree script，设备树相关的安装地址
export INSTALL_DTBS_PATH ?= $(INSTALL_PATH)/dtbs/$(KERNELRELEASE)

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

# 在安装模块之后对其进行strip
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

# 安装模块之后进行压缩
mod_compress_cmd = true
ifdef CONFIG_MODULE_COMPRESS
  ifdef CONFIG_MODULE_COMPRESS_GZIP
    mod_compress_cmd = gzip -n -f
  endif # CONFIG_MODULE_COMPRESS_GZIP
  ifdef CONFIG_MODULE_COMPRESS_XZ
    mod_compress_cmd = xz -f
  endif # CONFIG_MODULE_COMPRESS_XZ
endif # CONFIG_MODULE_COMPRESS
export mod_compress_cmd

ifdef CONFIG_MODULE_SIG_ALL
$(eval $(call config_filename,MODULE_SIG_KEY))

mod_sign_cmd = scripts/sign-file $(CONFIG_MODULE_SIG_HASH) $(MODULE_SIG_KEY_SRCPREFIX)$(CONFIG_MODULE_SIG_KEY) certs/signing_key.x509
else
mod_sign_cmd = true
endif
export mod_sign_cmd

HOST_LIBELF_LIBS = $(shell pkg-config libelf --libs 2>/dev/null || echo -lelf)

ifdef CONFIG_STACK_VALIDATION
  has_libelf := $(call try-run,\
		echo "int main() {}" | $(HOSTCC) -xc -o /dev/null $(HOST_LIBELF_LIBS) -,1,0)
  ifeq ($(has_libelf),1)
    objtool_target := tools/objtool FORCE
  else
    SKIP_STACK_VALIDATION := 1
    export SKIP_STACK_VALIDATION
  endif
endif

PHONY += prepare0
export MODORDER := $(if $(KBUILD_EXTMOD),$(KBUILD_EXTMOD)/)modules.order

接下来是内核编译部分

ifeq ($(KBUILD_EXTMOD),)

根据配置决定处理文件夹路径

# linux内核对应文件夹
core-y		+= kernel/ certs/ mm/ fs/ ipc/ security/ crypto/ block/
# vmlinux构建所需的文件夹
vmlinux-dirs	:= $(patsubst %/,%,$(filter %/, $(init-y) $(init-m) \
		     $(core-y) $(core-m) $(drivers-y) $(drivers-m) \
		     $(net-y) $(net-m) $(libs-y) $(libs-m) $(virt-y)))

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

init-y		:= $(patsubst %/, %/built-in.a, $(init-y))
core-y		:= $(patsubst %/, %/built-in.a, $(core-y))
drivers-y	:= $(patsubst %/, %/built-in.a, $(drivers-y))
net-y		:= $(patsubst %/, %/built-in.a, $(net-y))
libs-y1		:= $(patsubst %/, %/lib.a, $(libs-y))
libs-y2		:= $(patsubst %/, %/built-in.a, $(filter-out %.a, $(libs-y)))
virt-y		:= $(patsubst %/, %/built-in.a, $(virt-y))

链接vmlinux所需的依赖项

# Externally visible symbols (used by link-vmlinux.sh)
export KBUILD_VMLINUX_OBJS := $(head-y) $(init-y) $(core-y) $(libs-y2) \
			      $(drivers-y) $(net-y) $(virt-y)
export KBUILD_VMLINUX_LIBS := $(libs-y1)
export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
export LDFLAGS_vmlinux
# used by scripts/package/Makefile
export KBUILD_ALLDIRS := $(sort $(filter-out arch/%,$(vmlinux-alldirs)) LICENSES arch include scripts tools)

vmlinux-deps := $(KBUILD_LDS) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS)

这部分估计是去除不需要export的符号（待）

# Recurse until adjust_autoksyms.sh is satisfied
PHONY += autoksyms_recursive
ifdef CONFIG_TRIM_UNUSED_KSYMS
autoksyms_recursive: $(vmlinux-deps) modules.order
	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh \
	  "$(MAKE) -f $(srctree)/Makefile vmlinux"
endif

# For the kernel to actually contain only the needed exported symbols,
# we have to build modules as well to determine what those symbols are.
# (this can be evaluated only once include/config/auto.conf has been included)
ifdef CONFIG_TRIM_UNUSED_KSYMS
  KBUILD_MODULES := 1
endif

autoksyms_h := $(if $(CONFIG_TRIM_UNUSED_KSYMS), include/generated/autoksyms.h)

$(autoksyms_h):
	$(Q)mkdir -p $(dir $@)
	$(Q)touch $@

link vmlinux时的target及相关命令

ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)

# vmlinux链接命令
cmd_link-vmlinux =                                                 \
	$(CONFIG_SHELL) $< $(LD) $(KBUILD_LDFLAGS) $(LDFLAGS_vmlinux) ;    \
	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)

vmlinux: scripts/link-vmlinux.sh autoksyms_recursive $(vmlinux-deps) FORCE
	+$(call if_changed,link-vmlinux)

targets := vmlinux

# The actual objects are generated when descending,
# make sure no implicit rule kicks in
$(sort $(vmlinux-deps)): $(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
	$(Q)$(MAKE) $(build)=$@ need-builtin=1 need-modorder=1

filechk_kernel.release = \
	echo "$(KERNELVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))"

# Store (new) KERNELRELEASE string in include/config/kernel.release
include/config/kernel.release: FORCE
	$(call filechk,kernel.release)

# Additional helpers built in scripts/
# Carefully list dependencies so we do not try to build scripts twice
# in parallel
PHONY += scripts
scripts: scripts_basic scripts_dtc
	$(Q)$(MAKE) $(build)=$(@)

# 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.

PHONY += prepare archprepare prepare3

# prepare3 is used to check if we are building in a separate output directory,
# and if so do:
# 1) Check that make has not been executed in the kernel src $(srctree)
prepare3: include/config/kernel.release
ifdef building_out_of_srctree
	@$(kecho) '  Using $(srctree) as source for kernel'
	$(Q)if [ -f $(srctree)/.config -o \
		 -d $(srctree)/include/config -o \
		 -d $(srctree)/arch/$(SRCARCH)/include/generated ]; then \
		echo >&2 "  $(srctree) is not clean, please run 'make ARCH=$(ARCH) mrproper'"; \
		echo >&2 "  in the '$(srctree)' directory.";\
		/bin/false; \
	fi;
endif

archprepare: archheaders archscripts scripts prepare3 outputmakefile \
	asm-generic $(version_h) $(autoksyms_h) include/generated/utsrelease.h

prepare0: archprepare
	$(Q)$(MAKE) $(build)=scripts/mod
	$(Q)$(MAKE) $(build)=.

# All the preparing..
prepare: prepare0 prepare-objtool

# Support for using generic headers in asm-generic
asm-generic := -f $(srctree)/scripts/Makefile.asm-generic obj

PHONY += asm-generic uapi-asm-generic
asm-generic: uapi-asm-generic
	$(Q)$(MAKE) $(asm-generic)=arch/$(SRCARCH)/include/generated/asm \
	generic=include/asm-generic
uapi-asm-generic:
	$(Q)$(MAKE) $(asm-generic)=arch/$(SRCARCH)/include/generated/uapi/asm \
	generic=include/uapi/asm-generic

PHONY += prepare-objtool
prepare-objtool: $(objtool_target)
ifeq ($(SKIP_STACK_VALIDATION),1)
ifdef CONFIG_UNWINDER_ORC
	@echo "error: Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
	@false
else
	@echo "warning: Cannot use CONFIG_STACK_VALIDATION=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel" >&2
endif
endif

# 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

define filechk_version.h
	echo \#define LINUX_VERSION_CODE $(shell                         \
	expr $(VERSION) \* 65536 + 0$(PATCHLEVEL) \* 256 + 0$(SUBLEVEL)); \
	echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))'
endef

$(version_h): FORCE
	$(call filechk,version.h)
	$(Q)rm -f $(old_version_h)

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

PHONY += headerdep
headerdep:
	$(Q)find $(srctree)/include/ -name '*.h' | xargs --max-args 1 \
	$(srctree)/scripts/headerdep.pl -I$(srctree)/include

# ---------------------------------------------------------------------------
# Kernel headers

#Default location for installed headers
export INSTALL_HDR_PATH = $(objtree)/usr

quiet_cmd_headers_install = INSTALL $(INSTALL_HDR_PATH)/include
      cmd_headers_install = \
	mkdir -p $(INSTALL_HDR_PATH); \
	rsync -mrl --include='*/' --include='*\.h' --exclude='*' \
	usr/include $(INSTALL_HDR_PATH)

PHONY += headers_install
headers_install: headers
	$(call cmd,headers_install)

PHONY += archheaders archscripts

hdr-inst := -f $(srctree)/scripts/Makefile.headersinst obj

PHONY += headers
headers: $(version_h) scripts_unifdef uapi-asm-generic archheaders archscripts
	$(if $(wildcard $(srctree)/arch/$(SRCARCH)/include/uapi/asm/Kbuild),, \
	  $(error Headers not exportable for the $(SRCARCH) architecture))
	$(Q)$(MAKE) $(hdr-inst)=include/uapi
	$(Q)$(MAKE) $(hdr-inst)=arch/$(SRCARCH)/include/uapi

PHONY += headers_check
headers_check: headers
	$(Q)$(MAKE) $(hdr-inst)=include/uapi HDRCHECK=1
	$(Q)$(MAKE) $(hdr-inst)=arch/$(SRCARCH)/include/uapi HDRCHECK=1

ifdef CONFIG_HEADERS_INSTALL
prepare: headers
endif

ifdef CONFIG_HEADERS_CHECK
all: headers_check
endif

PHONY += scripts_unifdef
scripts_unifdef: scripts_basic
	$(Q)$(MAKE) $(build)=scripts scripts/unifdef

# ---------------------------------------------------------------------------
# Kernel selftest

PHONY += kselftest
kselftest:
	$(Q)$(MAKE) -C $(srctree)/tools/testing/selftests run_tests

PHONY += kselftest-clean
kselftest-clean:
	$(Q)$(MAKE) -C $(srctree)/tools/testing/selftests clean

PHONY += kselftest-merge
kselftest-merge:
	$(if $(wildcard $(objtree)/.config),, $(error No .config exists, config your kernel first!))
	$(Q)find $(srctree)/tools/testing/selftests -name config | \
		xargs $(srctree)/scripts/kconfig/merge_config.sh -m $(objtree)/.config
	+$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig

# ---------------------------------------------------------------------------
# Devicetree files

ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
dtstree := arch/$(SRCARCH)/boot/dts
endif

ifneq ($(dtstree),)

%.dtb: prepare3 scripts_dtc
	$(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@

PHONY += dtbs dtbs_install dt_binding_check
dtbs dtbs_check: prepare3 scripts_dtc
	$(Q)$(MAKE) $(build)=$(dtstree)

dtbs_check: export CHECK_DTBS=1
dtbs_check: dt_binding_check

dtbs_install:
	$(Q)$(MAKE) $(dtbinst)=$(dtstree)

ifdef CONFIG_OF_EARLY_FLATTREE
all: dtbs
endif

endif

PHONY += scripts_dtc
scripts_dtc: scripts_basic
	$(Q)$(MAKE) $(build)=scripts/dtc

dt_binding_check: scripts_dtc
	$(Q)$(MAKE) $(build)=Documentation/devicetree/bindings

# ---------------------------------------------------------------------------
# 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: $(if $(KBUILD_BUILTIN),vmlinux) modules.order modules.builtin
	@$(kecho) '  Building modules, stage 2.';
	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/modules-check.sh

modules.order: $(vmlinux-dirs)
	$(Q)$(AWK) '!x[$$0]++' $(addsuffix /$@, $(vmlinux-dirs)) > $@

modbuiltin-dirs := $(addprefix _modbuiltin_, $(vmlinux-dirs))

modules.builtin: $(modbuiltin-dirs)
	$(Q)$(AWK) '!x[$$0]++' $(addsuffix /$@, $(vmlinux-dirs)) > $@

PHONY += $(modbuiltin-dirs)
# tristate.conf is not included from this Makefile. Add it as a prerequisite
# here to make it self-healing in case somebody accidentally removes it.
$(modbuiltin-dirs): include/config/tristate.conf
	$(Q)$(MAKE) $(modbuiltin)=$(patsubst _modbuiltin_%,%,$@)

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

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

PHONY += _modinst_
_modinst_:
	@rm -rf $(MODLIB)/kernel
	@rm -f $(MODLIB)/source
	@mkdir -p $(MODLIB)/kernel
	@ln -s $(abspath $(srctree)) $(MODLIB)/source
	@if [ ! $(objtree) -ef  $(MODLIB)/build ]; then \
		rm -f $(MODLIB)/build ; \
		ln -s $(CURDIR) $(MODLIB)/build ; \
	fi
	@sed 's:^:kernel/:' modules.order > $(MODLIB)/modules.order
	@sed 's:^:kernel/:' modules.builtin > $(MODLIB)/modules.builtin
	@cp -f $(objtree)/modules.builtin.modinfo $(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)

ifeq ($(CONFIG_MODULE_SIG), y)
PHONY += modules_sign
modules_sign:
	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modsign
endif

else # CONFIG_MODULES

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

PHONY += modules modules_install
modules modules_install:
	@echo >&2
	@echo >&2 "The present kernel configuration has modules disabled."
	@echo >&2 "Type 'make config' and enable loadable module support."
	@echo >&2 "Then build a kernel with module support enabled."
	@echo >&2
	@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_DIRS  += include/ksym
CLEAN_FILES += modules.builtin.modinfo

# Directories & files removed with 'make mrproper'
MRPROPER_DIRS  += include/config include/generated          \
		  arch/$(SRCARCH)/include/generated .tmp_objdiff
MRPROPER_FILES += .config .config.old .version \
		  Module.symvers \
		  signing_key.pem signing_key.priv signing_key.x509	\
		  x509.genkey extra_certificates signing_key.x509.keyid	\
		  signing_key.x509.signer vmlinux-gdb.py

# Directories & files removed with 'make distclean'
DISTCLEAN_DIRS  +=
DISTCLEAN_FILES += tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS

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

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

vmlinuxclean:
	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean
	$(Q)$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) clean)

clean: archclean vmlinuxclean

# mrproper - Delete all generated files, including .config
#
mrproper: rm-dirs  := $(wildcard $(MRPROPER_DIRS))
mrproper: rm-files := $(wildcard $(MRPROPER_FILES))
mrproper-dirs      := $(addprefix _mrproper_,scripts)

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

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

# distclean
#
distclean: rm-dirs  := $(wildcard $(DISTCLEAN_DIRS))
distclean: rm-files := $(wildcard $(DISTCLEAN_FILES))

PHONY += distclean

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


# Packaging of the kernel to various formats
# ---------------------------------------------------------------------------
package-dir	:= scripts/package

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


# Brief documentation of the typical targets used
# ---------------------------------------------------------------------------

boards := $(wildcard $(srctree)/arch/$(SRCARCH)/configs/*_defconfig)
boards := $(sort $(notdir $(boards)))
board-dirs := $(dir $(wildcard $(srctree)/arch/$(SRCARCH)/configs/*/*_defconfig))
board-dirs := $(sort $(notdir $(board-dirs:/=)))

PHONY += help
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.ll     - Build the LLVM assembly file'
	@echo  '                    (requires compiler support for LLVM assembly generation)'
	@echo  '  dir/file.lst    - Build specified mixed source/assembly target only'
	@echo  '                    (requires a recent binutils and recent build (System.map))'
	@echo  '  dir/file.ko     - Build module including final link'
	@echo  '  modules_prepare - Set up for building external modules'
	@echo  '  tags/TAGS	  - Generate tags file for editors'
	@echo  '  cscope	  - Generate cscope index'
	@echo  '  gtags           - Generate GNU GLOBAL index'
	@echo  '  kernelrelease	  - Output the release version string (use with make -s)'
	@echo  '  kernelversion	  - Output the version stored in Makefile (use with make -s)'
	@echo  '  image_name	  - Output the image name (use with make -s)'
	@echo  '  headers_install - Install sanitised kernel headers to INSTALL_HDR_PATH'; \
	 echo  '                    (default: $(INSTALL_HDR_PATH))'; \
	 echo  ''
	@echo  'Static analysers:'
	@echo  '  checkstack      - Generate a list of stack hogs'
	@echo  '  namespacecheck  - Name space analysis on compiled kernel'
	@echo  '  versioncheck    - Sanity check on version.h usage'
	@echo  '  includecheck    - Check for duplicate included header files'
	@echo  '  export_report   - List the usages of all exported symbols'
	@echo  '  headers_check   - Sanity check on exported headers'
	@echo  '  headerdep       - Detect inclusion cycles in headers'
	@echo  '  coccicheck      - Check with Coccinelle'
	@echo  ''
	@echo  'Kernel selftest:'
	@echo  '  kselftest       - Build and run kernel selftest (run as root)'
	@echo  '                    Build, install, and boot kernel before'
	@echo  '                    running kselftest on it'
	@echo  '  kselftest-clean - Remove all generated kselftest files'
	@echo  '  kselftest-merge - Merge all the config dependencies of kselftest to existing'
	@echo  '                    .config.'
	@echo  ''
	@$(if $(dtstree), \
		echo 'Devicetree:'; \
		echo '* dtbs            - Build device tree blobs for enabled boards'; \
		echo '  dtbs_install    - Install dtbs to $(INSTALL_DTBS_PATH)'; \
		echo '')

	@echo 'Userspace tools targets:'
	@echo '  use "make tools/help"'
	@echo '  or  "cd tools; make help"'
	@echo  ''
	@echo  'Kernel packaging:'
	@$(MAKE) $(build)=$(package-dir) help
	@echo  ''
	@echo  'Documentation targets:'
	@$(MAKE) -f $(srctree)/Documentation/Makefile dochelp
	@echo  ''
	@echo  'Architecture specific targets ($(SRCARCH)):'
	@$(if $(archhelp),$(archhelp),\
		echo '  No architecture specific help defined for $(SRCARCH)')
	@echo  ''
	@$(if $(boards), \
		$(foreach b, $(boards), \
		printf "  %-24s - Build for %s\\n" $(b) $(subst _defconfig,,$(b));) \
		echo '')
	@$(if $(board-dirs), \
		$(foreach b, $(board-dirs), \
		printf "  %-16s - Show %s-specific targets\\n" help-$(b) $(b);) \
		printf "  %-16s - Show all of the above\\n" help-boards; \
		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 re-compiled c source with $$CHECK (sparse by default)'
	@echo  '  make C=2   [targets] Force check of all c source with $$CHECK'
	@echo  '  make RECORDMCOUNT_WARN=1 [targets] Warn about ignored mcount sections'
	@echo  '  make W=n   [targets] Enable extra gcc checks, n=1,2,3 where'
	@echo  '		1: warnings which may be relevant and do not occur too often'
	@echo  '		2: warnings which occur quite often but may still be relevant'
	@echo  '		3: more obscure warnings, can most likely be ignored'
	@echo  '		Multiple levels can be combined with W=12 or W=123'
	@echo  ''
	@echo  'Execute "make" or "make all" to build all targets marked with [*] '
	@echo  'For further info see the ./README file'


help-board-dirs := $(addprefix help-,$(board-dirs))

help-boards: $(help-board-dirs)

boards-per-dir = $(sort $(notdir $(wildcard $(srctree)/arch/$(SRCARCH)/configs/$*/*_defconfig)))

$(help-board-dirs): help-%:
	@echo  'Architecture specific targets ($(SRCARCH) $*):'
	@$(if $(boards-per-dir), \
		$(foreach b, $(boards-per-dir), \
		printf "  %-24s - Build for %s\\n" $*/$(b) $(subst _defconfig,,$(b));) \
		echo '')


# Documentation targets
# ---------------------------------------------------------------------------
DOC_TARGETS := xmldocs latexdocs pdfdocs htmldocs epubdocs cleandocs \
	       linkcheckdocs dochelp refcheckdocs
PHONY += $(DOC_TARGETS)
$(DOC_TARGETS): scripts_basic FORCE
	$(Q)$(MAKE) $(build)=Documentation $@

# Misc
# ---------------------------------------------------------------------------

PHONY += scripts_gdb
scripts_gdb: prepare0
	$(Q)$(MAKE) $(build)=scripts/gdb
	$(Q)ln -fsn $(abspath $(srctree)/scripts/gdb/vmlinux-gdb.py)

ifdef CONFIG_GDB_SCRIPTS
all: scripts_gdb
endif

内核编译部分结束

else # KBUILD_EXTMOD

模块编译部分开始

###
# 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 += $(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): prepare $(objtree)/Module.symvers
	$(Q)$(MAKE) $(build)=$(patsubst _module_%,%,$@) need-modorder=1

modules: $(module-dirs)
	@$(kecho) '  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-files := $(KBUILD_EXTMOD)/Module.symvers

PHONY += help
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  ''

PHONY += prepare
endif # KBUILD_EXTMOD

clean: $(clean-dirs)
	$(call cmd,rmdirs)
	$(call cmd,rmfiles)
	@find $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \
		\( -name '*.[aios]' -o -name '*.ko' -o -name '.*.cmd' \
		-o -name '*.ko.*' \
		-o -name '*.dtb' -o -name '*.dtb.S' -o -name '*.dt.yaml' \
		-o -name '*.dwo' -o -name '*.lst' \
		-o -name '*.su' -o -name '*.mod' \
		-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
		-o -name '*.lex.c' -o -name '*.tab.[ch]' \
		-o -name '*.asn1.[ch]' \
		-o -name '*.symtypes' -o -name 'modules.order' \
		-o -name modules.builtin -o -name '.tmp_*.o.*' \
		-o -name '*.c.[012]*.*' \
		-o -name '*.ll' \
		-o -name '*.gcno' \) -type f -print | xargs rm -f

# Generate tags for editors
# ---------------------------------------------------------------------------
quiet_cmd_tags = GEN     $@
      cmd_tags = $(CONFIG_SHELL) $(srctree)/scripts/tags.sh $@

tags TAGS cscope gtags: FORCE
	$(call cmd,tags)

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

PHONY += includecheck versioncheck coccicheck namespacecheck export_report

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

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

coccicheck:
	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/$@

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

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

PHONY += checkstack kernelrelease kernelversion image_name

# 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) $(srctree)/scripts/checkstack.pl $(CHECKSTACK_ARCH)

kernelrelease:
	@echo "$(KERNELVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))"

kernelversion:
	@echo $(KERNELVERSION)

image_name:
	@echo $(KBUILD_IMAGE)

# Clear a bunch of variables before executing the submake

ifeq ($(quiet),silent_)
tools_silent=s
endif

tools/: FORCE
	$(Q)mkdir -p $(objtree)/tools
	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/

tools/%: FORCE
	$(Q)mkdir -p $(objtree)/tools
	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*

# 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

build-target = $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD)/)$@
build-dir = $(patsubst %/,%,$(dir $(build-target)))

%.i: prepare FORCE
	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
%.ll: prepare FORCE
	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
%.lst: prepare FORCE
	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
%.o: prepare FORCE
	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
%.s: prepare FORCE
	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
%.symtypes: prepare FORCE
	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target)
ifeq ($(KBUILD_EXTMOD),)
# For the single build of an in-tree module, use a temporary file to avoid
# the situation of modules_install installing an invalid modules.order.
%.ko: MODORDER := .modules.tmp
endif
%.ko: prepare FORCE
	$(Q)$(MAKE) $(build)=$(build-dir) $(build-target:.ko=.mod)
	$(Q)echo $(build-target) > $(MODORDER)
	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost

# Modules
PHONY += /
/: ./

%/: prepare FORCE
	$(Q)$(MAKE) KBUILD_MODULES=1 $(build)=$(build-dir) need-modorder=1

# 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 if we have System.map and depmod is executable
quiet_cmd_depmod = DEPMOD  $(KERNELRELEASE)
      cmd_depmod = $(CONFIG_SHELL) $(srctree)/scripts/depmod.sh $(DEPMOD) \
                   $(KERNELRELEASE)

# read saved command lines for existing targets
existing-targets := $(wildcard $(sort $(targets)))

-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)

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