构建内核
# shell 执行如下指令
make zImage
全局变量
srctree := $(if $(KBUILD_SRC),$(KBUILD_SRC),$(CURDIR))
objtree := $(CURDIR)
src := $(srctree)
obj := $(objtree)
VPATH := $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))
export srctree objtree VPATH
体系架构相关变量
ARCH ?= arm
CROSS_COMPILE ?= arm-linux-gnueabi-
# Architecture as present in compile.h
UTS_MACHINE := $(ARCH)
SRCARCH := $(ARCH)
编译会用到的通用定义
# Look for make include files relative to root of kernel src
MAKEFLAGS += --include-dir=$(srctree)
# We need some generic definitions (do not try to remake the file).
$(srctree)/scripts/Kbuild.include: ;
include $(srctree)/scripts/Kbuild.include
引入体系结构相关 Makefile
# Read arch specific Makefile to set KBUILD_DEFCONFIG as needed.
# KBUILD_DEFCONFIG may point out an alternative default configuration
# used for 'make defconfig'
include $(srctree)/arch/$(SRCARCH)/Makefile
export KBUILD_DEFCONFIG KBUILD_KCONFIG
内核 vmlinux 镜像布局
用于处理用户直接在 shell 中输入 make 这类操作，真正的目标是 all，此时仅生成 vmlinux
# That's our default target when none is given on the command line
PHONY := _all
_all:
vmlinux 依赖项
# 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
# 真正的目标
all: vmlinux
vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o $(kallsyms.o) FORCE
# head-y 对应的值 arch/arm/kernel/head.o arch/arm/kernel/init_task.o
vmlinux-init := $(head-y) $(init-y)
vmlinux-main := $(core-y) $(libs-y) $(drivers-y) $(net-y)
vmlinux-all := $(vmlinux-init) $(vmlinux-main)
vmlinux-lds := arch/$(SRCARCH)/kernel/vmlinux.lds
export KBUILD_VMLINUX_OBJS := $(vmlinux-all)
core-y += kernel/ mm/ fs/ ipc/ security/ crypto/ block/
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)
vmlinux-dirs := $(patsubst %/,%,$(filter %/, $(init-y) $(init-m) \
$(core-y) $(core-m) $(drivers-y) $(drivers-m) \
$(net-y) $(net-m) $(libs-y) $(libs-m)))
vmlinux-alldirs := $(sort $(vmlinux-dirs) $(patsubst %/,%,$(filter %/, \
$(init-n) $(init-) \
$(core-n) $(core-) $(drivers-n) $(drivers-) \
$(net-n) $(net-) $(libs-n) $(libs-))))
# 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
生成 zImage
这其中给出了 make zImage 目标及其依赖
zImage Image xipImage bootpImage uImage: vmlinux
$(Q)$(MAKE) $(build)=$(boot) MACHINE=$(MACHINE) $(boot)/$@
其作用是执行 arch/$(SRCARCH)/Makefile，传入 MACHINE 参数，执行目标是 $(boot)/$@ --> arch/$(SRCARCH)/boot/zImage，查看 arch/arm/boot/Makefile
$(obj)/zImage: $(obj)/compressed/vmlinux FORCE
$(call if_changed,objcopy)
@echo ' Kernel: $@ is ready'
$(obj)/Image: vmlinux FORCE
$(call if_changed,objcopy)
@echo ' Kernel: $@ is ready'
$(obj)/compressed/vmlinux: $(obj)/Image FORCE
$(Q)$(MAKE) $(build)=$(obj)/compressed $@
该目标生成需要进入到 arch/arm/boot/compressed 下执行 make，使用 $(obj)/vmlinux.lds 链接脚本链接，head.o, piggy.o misc.o
$(obj)/vmlinux: $(obj)/vmlinux.lds $(obj)/$(HEAD) $(obj)/piggy.o \
$(addprefix $(obj)/, $(OBJS)) FORCE
$(call if_changed,ld)
@:
(obj)/vmlinux 的依赖目标，压缩 boot 目录下的 vmlinux 文件生成 piggy.gz，if_changed 执行的命令为 cmd_* 形式，定义在 Makefile.lib 中
$(obj)/piggy.gz: $(obj)/../Image FORCE
$(call if_changed,gzip)
$(obj)/piggy.o: $(obj)/piggy.gz FORCE
CFLAGS_font.o := -Dstatic=
$(obj)/font.c: $(FONTC)
$(call cmd,shipped)
# 生成链接脚本
$(obj)/vmlinux.lds: $(obj)/vmlinux.lds.in arch/arm/boot/Makefile .config
@sed "$(SEDFLAGS)" < $< > $@
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############# 最终，arch/arm/boot 目录下生成 zImage...... ##############
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