对linux内核makefile的一点点研究

对linux内核makefile的一点点研究

包含CONFIG_EXT3_FS=y
等数据的文件include/config/auto.conf

---- include/linux/version.h ----
include $(srctree)/arch/$(SRCARCH)/Makefile
我们的ARCH为arm,所以
将包含进arch/arm/Makefile
而archprepare在这里有了第1依赖文件
archprepare: maketools
maketools: include/linux/version.h FORCE


然后将根据如下顺序,依次执行依赖检查[luther.gliethttp]
prepare3: include/config/kernel.release
prepare2: prepare3 outputmakefile
prepare1: prepare2 include/linux/version.h include/linux/utsrelease.h \
                   include/asm include/config/auto.conf
可以看到prepare1将依次检查依赖prepare2,
include/linux/version.h,include/linux/utsrelease.h
然后include/asm,最后是include/config/auto.conf
当prepare1执行完毕之后,随即archprepare的另一个依赖scripts_basic将被继续执行.
当archprepare所有依赖执行完毕之后,随即prepare0的命令将被执行

archprepare: prepare1 scripts_basic
prepare0: archprepare FORCE
    $(Q)$(MAKE) $(build)=.
    $(Q)$(MAKE) $(build)=. missing-syscalls
prepare: prepare0

而scripts/Makefile.build首先清除所有变量,然后include Kbuild
而我们可以看到$(builtin-target) $(lib-target) $(extra-y)全为空
同时$(obj-m) $(modorder-target)将因为$(obj-m),而只剩下$(modorder-target)
__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \
     $(if $(KBUILD_MODULES),$(obj-m) $(modorder-target)) \
     $(subdir-ym) $(always)
所以翻译后为
__build: $(modorder-target) $(always)

$(modorder-target): $(subdir-ym) FORCE
    $(Q)(cat /dev/null; $(modorder-cmds)) > $@

又因为./Kbuild包含内容为
bounds-file := include/linux/bounds.h

always  := $(bounds-file)
targets := $(bounds-file) kernel/bounds.s
offsets-file := include/asm/asm-offsets.h
always  += $(offsets-file)
targets += $(offsets-file)
targets += arch/$(SRCARCH)/kernel/asm-offsets.s

kernel/bounds.s: kernel/bounds.c FORCE
    $(Q)mkdir -p $(dir $@)
    $(call if_changed_dep,cc_s_c)

$(obj)/$(bounds-file): kernel/bounds.s Kbuild
    $(Q)mkdir -p $(dir $@)
    $(call cmd,bounds)

arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c \
                                      $(obj)/$(bounds-file) FORCE
    $(Q)mkdir -p $(dir $@)
    $(call if_changed_dep,cc_s_c)

$(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s Kbuild
    $(call cmd,offsets)


接下来就是检查依赖scripts的具体实现了
scripts: scripts_basic include/config/auto.conf
    $(Q)$(MAKE) $(build)=$(@)

因为scripts/Makefile
包含了subdir-y += mod
同时kernel/scripts/Makefile.lib
subdir-ym := $(sort $(subdir-y) $(subdir-m))
又被添加到了subdir-ym变量中
在scripts/Makefile.build中就有定义了处理目标的规则了
$(subdir-ym):
    $(Q)$(MAKE) $(build)=$@

而最终目标__build又依赖$(subdir-ym)
__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \
     $(if $(KBUILD_MODULES),$(obj-m) $(modorder-target)) \
     $(subdir-ym) $(always)
所以可以看到
make $(build)=mod
将被执行

ok上面的所有事情都做完之后,下面是vmlinux包含的所有dirs编译规则统一处理入口[luher.gliehtttp]
$(vmlinux-dirs): prepare scripts
    $(Q)$(MAKE) $(build)=$@

比如
1. ARCH=arm make s3c6400_defconfig
2. ARCH=arm CROSS_COMPILE=arm-eabi- make
他默认的$(vmlinux-dirs)内容如下[luther.gliethttp]
init usr arch/arm/kernel arch/arm/mm arch/arm/common arch/arm/mach-s3c6400 arch/arm/mach-s3c6410 arch/arm/plat-s3c64xx arch/arm/plat-s3c arch/arm/vfp kernel mm fs ipc security crypto block drivers sound firmware net arch/arm/lib lib


include $(srctree)/arch/$(SRCARCH)/Makefile
即arch/arm/Makefile
zImage Image xipImage bootpImage uImage: vmlinux
    $(Q)$(MAKE) $(build)=$(boot) MACHINE=$(MACHINE) $(boot)/$@
我们看看./Makefile
# 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: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o $(kallsyms.o) FORCE

vmlinux.o: $(modpost-init) $(vmlinux-main) FORCE
    $(call if_changed_rule,vmlinux-modpost)