Android编译系统参考手册

http://android.cloudchou.com/build/core/tasks/kernel.php

build/core/tasks/kernel.mk

定义生成内核的规则

TARGET_AUTO_KDIR

TARGET_AUTO_KDIR := $(shell echo $(TARGET_DEVICE_DIR) | sed -e 's/^device/kernel/g')
自动设置的内核目录
比如i9100，那么自动设置的内核目录是
kernel/samsung/i9100

TARGET_KERNEL_SOURCE

TARGET_KERNEL_SOURCE ?= $(TARGET_AUTO_KDIR)
内核源码目录
默认 kernel//
一般在BoardConfig.mk里配置

KERNEL_SRC

KERNEL_SRC := $(TARGET_KERNEL_SOURCE)
内核源码目录

KERNEL_DEFCONFIG

KERNEL_DEFCONFIG := $(TARGET_KERNEL_CONFIG)
编译内核用的配置文件
一般在BoardConfig.mk里配置

VARIANT_DEFCONFIG

VARIANT_DEFCONFIG := $(TARGET_KERNEL_VARIANT_CONFIG)
变量配置
一般在BoardConfig.mk里配置

KERNEL_OUT

KERNEL_OUT := $(TARGET_OUT_INTERMEDIATES)/KERNEL_OBJ
示例：
out/target/product/i9100/obj/KERNEL_OBJ

KERNEL_CONFIG

生成的编译内核的配置文件
KERNEL_CONFIG := $(KERNEL_OUT)/.config
示例：
out/target/product/i9100/obj/KERNEL_OBJ/.config

ifeq ($(BOARD_USES_UBOOT),true)
   TARGET_PREBUILT_INT_KERNEL := $(KERNEL_OUT)/arch/$(TARGET_ARCH)/boot/uImage
   TARGET_PREBUILT_INT_KERNEL_TYPE := uImage
else ifeq ($(BOARD_USES_UNCOMPRESSED_BOOT),true)
   TARGET_PREBUILT_INT_KERNEL := $(KERNEL_OUT)/arch/$(TARGET_ARCH)/boot/Image
   TARGET_PREBUILT_INT_KERNEL_TYPE := Image
else
   TARGET_PREBUILT_INT_KERNEL := $(KERNEL_OUT)/arch/$(TARGET_ARCH)/boot/zImage
   TARGET_PREBUILT_INT_KERNEL_TYPE := zImage
endif
示例：
    out/target/product/i9100/obj/KERNEL_OBJ/arch/arm/boot/zImage

TARGET_PREBUILT_INT_KERNEL_TYPE

见TARGET_PREBUILT_INT_KERNEL

TARGET_PREBUILT_KERNEL

预编译的内核
一般在BoardConfig.mk里配置
在Recovery适配时经常需要设置该项
示例：
TARGET_PREBUILT_KERNEL := $(LOCAL_DIR)/kernel

HAS_PREBUILT_KERNEL

是否有预编译的内核

NEEDS_KERNEL_COPY

是否需要拷贝内核

FULL_KERNEL_BUILD

是否需要编译内核源代码

KERNEL_BIN

内核文件
ifeq "$(wildcard $(KERNEL_SRC) )" ""
   ifneq ($(HAS_PREBUILT_KERNEL),)
KERNEL_BIN := $(TARGET_PREBUILT_KERNEL)
  endif
     else
  ifeq ($(TARGET_KERNEL_CONFIG),)
     ....
  else
     ifeq ($(TARGET_USES_UNCOMPRESSED_KERNEL),true)
    KERNEL_BIN := $(KERNEL_OUT)/piggy
     else
KERNEL_BIN := $(TARGET_PREBUILT_INT_KERNEL)
     endif
  endif
     endif
     示例：
out/target/product/i9100/obj/KERNEL_OBJ/arch/arm/boot/zImage

KERNEL_HEADERS_INSTALL

KERNEL_HEADERS_INSTALL := $(KERNEL_OUT)/usr
示例：
out/target/product/i9100/obj/KERNEL_OBJ/usr

KERNEL_MODULES_INSTALL

KERNEL_MODULES_INSTALL := system
内核模块的安装目录

KERNEL_MODULES_OUT

KERNEL_MODULES_OUT := $(TARGET_OUT)/lib/modules
内核模块的的实际安装目录
out/target/product/i9100/system/lib/modules

Function: mv-modules

移动模块
在system/lib/modules找到modules.order文件，
然后找到该文件所在目录下的kernel目录的ko模块文件
对这些文件用arm-eabi-strip进行strip处理
然后将其移至system/lib/modules

Function: clean-module-folder

在system/lib/modules找到modules.order文件
然后删除该文件所在的目录

ccache

ccache程序
ifneq ($(USE_CCACHE),)
  # search executable
   ccache =
   ifneq ($(strip $(wildcard $(ANDROID_BUILD_TOP)/prebuilts/misc/$(HOST_PREBUILT_EXTRA_TAG)/ccache/ccache)),)
     ccache := $(ANDROID_BUILD_TOP)/prebuilts/misc/$(HOST_PREBUILT_EXTRA_TAG)/ccache/ccache
   else
     ifneq ($(strip $(wildcard $(ANDROID_BUILD_TOP)/prebuilts/misc/$(HOST_PREBUILT_TAG)/ccache/ccache)),)
ccache := $(ANDROID_BUILD_TOP)/prebuilts/misc/$(HOST_PREBUILT_TAG)/ccache/ccache
     endif
   endif
endif

ARM_CROSS_COMPILE

交叉编译工具链所在目录
ifneq ($(TARGET_KERNEL_CUSTOM_TOOLCHAIN),)
  ifeq ($(HOST_OS),darwin)
ARM_CROSS_COMPILE:=CROSS_COMPILE="$(ccache) $(ANDROID_BUILD_TOP)/prebuilt/darwin-x86/toolchain/$(TARGET_KERNEL_CUSTOM_TOOLCHAIN)/bin/arm-eabi-"
  else
ARM_CROSS_COMPILE:=CROSS_COMPILE="$(ccache) $(ANDROID_BUILD_TOP)/prebuilt/linux-x86/toolchain/$(TARGET_KERNEL_CUSTOM_TOOLCHAIN)/bin/arm-eabi-"
  endif
    else
  ARM_CROSS_COMPILE:=CROSS_COMPILE="$(ccache) $(ARM_EABI_TOOLCHAIN)/arm-eabi-"
    endif

MAKE_FLAGS

ifeq ($(HOST_OS),darwin)
MAKE_FLAGS := C_INCLUDE_PATH=$(ANDROID_BUILD_TOP)/external/elfutils/libelf
endif

TARGET_KERNEL_MODULES

ifeq ($(TARGET_KERNEL_MODULES),)
TARGET_KERNEL_MODULES := no-external-modules
endif

Target: $(KERNEL_OUT)

创建$(KERNEL_OUT)目录
即目录out/target/product/i9100/obj/KERNEL_OBJ

Target: $(KERNEL_CONFIG)

生成编译内核源代码用的配置文件
$(KERNEL_CONFIG): $(KERNEL_OUT)
$(MAKE) $(MAKE_FLAGS) -C $(KERNEL_SRC) O=$(KERNEL_OUT) ARCH=$(TARGET_ARCH) $(ARM_CROSS_COMPILE) VARIANT_DEFCONFIG=$(VARIANT_DEFCONFIG) SELINUX_DEFCONFIG=$(SELINUX_DEFCONFIG) $(KERNEL_DEFCONFIG)

Target: $(KERNEL_OUT)/piggy

生成piggy内核
$(KERNEL_OUT)/piggy : $(TARGET_PREBUILT_INT_KERNEL)
$(hide) gunzip -c $(KERNEL_OUT)/arch/$(TARGET_ARCH)/boot/compressed/piggy.gzip > $(KERNEL_OUT)/piggy

TARGET_KERNEL_BINARIES

生成内核，并安装好模块
TARGET_KERNEL_BINARIES: $(KERNEL_OUT) $(KERNEL_CONFIG) $(KERNEL_HEADERS_INSTALL)
#生成内核
$(MAKE) $(MAKE_FLAGS) -C $(KERNEL_SRC) O=$(KERNEL_OUT) ARCH=$(TARGET_ARCH) $(ARM_CROSS_COMPILE) $(TARGET_PREBUILT_INT_KERNEL_TYPE)
#生成模块
-$(MAKE) $(MAKE_FLAGS) -C $(KERNEL_SRC) O=$(KERNEL_OUT) ARCH=$(TARGET_ARCH) $(ARM_CROSS_COMPILE) modules
#安装模块至system/lib/modules目录，但是还需strip处理
-$(MAKE) $(MAKE_FLAGS) -C $(KERNEL_SRC) O=$(KERNEL_OUT) INSTALL_MOD_PATH=../../$(KERNEL_MODULES_INSTALL) ARCH=$(TARGET_ARCH) $(ARM_CROSS_COMPILE) modules_install
$(mv-modules)
$(clean-module-folder)

Target: $(TARGET_PREBUILT_INT_KERNEL)

安装模块，并清除先前不用的模块所在目录

ALL_PREBUILT

ALL_PREBUILT += $(file)
$(file) : $(KERNEL_BIN) | $(ACP)
$(transform-prebuilt-to-target)
ALL_PREBUILT += $(INSTALLED_KERNEL_TARGET)