Kbuild两个target

1.各个子目录相应的build-in.o链接为vmlinux

vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o $(kallsyms.o) FORCE vmlinux.o: $(modpost-init) $(vmlinux-main) FORCE modpost-init := $(filter-out init/built-in.o, $(vmlinux-init)) vmlinux-init := $(head-y) $(init-y) vmlinux-main := $(core-y) $(libs-y) $(drivers-y) $(net-y) 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) init-y := init/ drivers-y := drivers/ sound/ firmware/ net-y := net/ libs-y := lib/ core-y := usr/

2.编译各个子目录生成build-in.o

$(vmlinux-dirs): prepare scripts ## make -f scripts/Makefile.build obj=$@ ## Makefile.build会进行处理并递归到相应的子目录生成build-in.o $(Q)$(MAKE) $(build)=$@

注意：只有head-y比较特殊，和机器有关的变量，定义在arch内的Makefile里(顶层Makefile包含此Makefile，此Makefile还扩展了core-y、libs-y等目录变量)，而且直接就是.o的形式，比如head-y := arch/x86/kernel/head_32.o arch/x86/kernel/init_task.o