高通kernel顶层目录下的AndroidKernel.mk文件

高通kernel顶层目录下的AndroidKernel.mk文件是Android的编译系统的一部分，用来编译kernel。

它的位置是在aosp/kernel目录下。

文件层级结构

定义变量【第一处】ifeq ($(TARGET_PREBUILT_KERNEL),)    定义变量【第二处】    ifeq ($(KERNEL_DEFCONFIG)$(wildcard $(KERNEL_CONFIG)),)        $(error Kernel configuration not defined, cannot build kernel)    else        定义变量【第三处】        定义一些目标和依赖    endifendif

文件具体内容（带注释）

定义变量【第一处】

PERL变量

#Android makefile to build kernel as a part of Android BuildPERL        = perl

KERNEL_TARGET 和 INSTALLED_KERNEL_TARGET 变量

KERNEL_TARGET := $(strip $(INSTALLED_KERNEL_TARGET))ifeq ($(KERNEL_TARGET),)INSTALLED_KERNEL_TARGET := $(PRODUCT_OUT)/kernelendif

在build/core/Makefile文件中，定义了INSTALLED_KERNEL_TARGET变量

ifneq ($(strip $(TARGET_NO_KERNEL)),true)  INSTALLED_KERNEL_TARGET := $(PRODUCT_OUT)/kernelelse  INSTALLED_KERNEL_TARGET :=endif

TARGET_NO_KERNEL是在device/厂商/产品名/BoardConfig.mk中定义的

TARGET_NO_KERNEL := false

Makefile中，
ifeq关键字用来判断参数是否相等，
ifneq的关键字是用来判断参数是否不相等，
格式为：

ifneq (ARG1, ARG2) / ifneq (ARG1, ARG2)ifneq 'ARG1' 'ARG2' / ifneq 'ARG1' 'ARG2'ifneq "ARG1" "ARG2" / ifneq "ARG1" "ARG2"ifneq "ARG1" 'ARG2' / ifneq "ARG1" 'ARG2'ifneq 'ARG1' "ARG2" / ifneq 'ARG1' "ARG2"

综上所述可知，不论TARGET_NO_KERNEL为false还是true，则KERNEL_TARGET和INSTALLED_KERNEL_TARGET的值都为$(PRODUCT_OUT)/kernel。

TARGET_KERNEL_ARCH 和 KERNEL_ARCH 变量

TARGET_KERNEL_ARCH := $(strip $(TARGET_KERNEL_ARCH))ifeq ($(TARGET_KERNEL_ARCH),)KERNEL_ARCH := armelseKERNEL_ARCH := $(TARGET_KERNEL_ARCH)endif

TARGET_KERNEL_ARCH是在device/厂商/产品名/BoardConfig.mk中定义的。
如果已经定义为某值（如arm64），KERNEL_ARCH就设定为该值（如arm64）。
反之，则设定为默认值arm

TARGET_KERNEL_HEADER_ARCH 和 KERNEL_HEADER_ARCH 变量

TARGET_KERNEL_HEADER_ARCH := $(strip $(TARGET_KERNEL_HEADER_ARCH))ifeq ($(TARGET_KERNEL_HEADER_ARCH),)KERNEL_HEADER_ARCH := $(KERNEL_ARCH)else$(warning Forcing kernel header generation only for '$(TARGET_KERNEL_HEADER_ARCH)')KERNEL_HEADER_ARCH := $(TARGET_KERNEL_HEADER_ARCH)endif

TARGET_KERNEL_ARCH是在device/厂商/产品名/BoardConfig.mk中定义的。
如果TARGET_KERNEL_HEADER_ARCH为空，KERNEL_HEADER_ARCH就设定为KERNEL_ARCH的值。
反之，则警告并将KERNEL_HEADER_ARCH设定为TARGET_KERNEL_HEADER_ARCH

KERNEL_HEADER_DEFCONFIG 变量

KERNEL_HEADER_DEFCONFIG := $(strip $(KERNEL_HEADER_DEFCONFIG))ifeq ($(KERNEL_HEADER_DEFCONFIG),)KERNEL_HEADER_DEFCONFIG := $(KERNEL_DEFCONFIG)endif

KERNEL_DEFCONFIG是在device/厂商/产品名/AndroidBoard.mk中定义的。
KERNEL_HEADER_DEFCONFIG未找到定义的地方。
当KERNEL_HEADER_DEFCONFIG为空，则被赋值为KERNEL_DEFCONFIG。

binder

# Force 32-bit binder IPC for 64bit kernel with 32bit userspaceifeq ($(KERNEL_ARCH),arm64)ifeq ($(TARGET_ARCH),arm)KERNEL_CONFIG_OVERRIDE := CONFIG_ANDROID_BINDER_IPC_32BIT=yendifendif

通过条件判断，是否让32-bit的binder IPC（进程间通信机制） 强制运行于64bit的kernel的32bit用户空间。

TARGET_KERNEL_CROSS_COMPILE_PREFIX 和 KERNEL_CROSS_COMPILE 变量

TARGET_KERNEL_CROSS_COMPILE_PREFIX := $(strip $(TARGET_KERNEL_CROSS_COMPILE_PREFIX))ifeq ($(TARGET_KERNEL_CROSS_COMPILE_PREFIX),)KERNEL_CROSS_COMPILE := arm-eabi-elseKERNEL_CROSS_COMPILE := $(TARGET_KERNEL_CROSS_COMPILE_PREFIX)endif

TARGET_KERNEL_CROSS_COMPILE_PREFIX是在device/厂商/产品名/AndroidBoard.mk中定义的。
例：TARGET_KERNEL_CROSS_COMPILE_PREFIX := aarch64-linux-android-

定义变量【第二处】

KERNEL_CFLAGS变量

KERNEL_GCC_NOANDROID_CHK := $(shell (echo "int main() {return 0;}" | $(KERNEL_CROSS_COMPILE)gcc -E -mno-android - > /dev/null 2>&1 ; echo $$?))ifeq ($(strip $(KERNEL_GCC_NOANDROID_CHK)),0)KERNEL_CFLAGS := KCFLAGS=-mno-androidendif

KERNEL_GCC_NOANDROID_CHK 变量如果为0，则定义KERNEL_CFLAGS为KCFLAGS=-mno-android

mkfile_path变量

mkfile_path := $(abspath $(lastword $(MAKEFILE_LIST)))

获得mk文件路径

current_dir变量

current_dir := $(notdir $(patsubst %/,%,$(dir $(mkfile_path))))

TARGET_KERNEL_VERSION变量

ifeq ($(TARGET_KERNEL_VERSION),)    TARGET_KERNEL_VERSION := 3.18endif

TARGET_KERNEL变量

TARGET_KERNEL := msm-$(TARGET_KERNEL_VERSION)

通过TARGET_KERNEL变量，定义KERNEL_OUT等变量

ifeq ($(TARGET_KERNEL),$(current_dir))    # New style, kernel/msm-version    BUILD_ROOT_LOC := ../../    TARGET_KERNEL_SOURCE := kernel/$(TARGET_KERNEL)    KERNEL_OUT := $(TARGET_OUT_INTERMEDIATES)/kernel/$(TARGET_KERNEL)    KERNEL_SYMLINK := $(TARGET_OUT_INTERMEDIATES)/KERNEL_OBJ    KERNEL_USR := $(KERNEL_SYMLINK)/usrelse    # Legacy style, kernel source directly under kernel    KERNEL_LEGACY_DIR := true    BUILD_ROOT_LOC := ../    TARGET_KERNEL_SOURCE := kernel    KERNEL_OUT := $(TARGET_OUT_INTERMEDIATES)/KERNEL_OBJendif

KERNEL_CONFIG变量

KERNEL_CONFIG := $(KERNEL_OUT)/.config

定义变量【第三处】

TARGET_PREBUILT_INT_KERNEL变量

ifeq ($(TARGET_USES_UNCOMPRESSED_KERNEL),true)$(info Using uncompressed kernel)TARGET_PREBUILT_INT_KERNEL := $(KERNEL_OUT)/arch/$(KERNEL_ARCH)/boot/Imageelseifeq ($(KERNEL_ARCH),arm64)TARGET_PREBUILT_INT_KERNEL := $(KERNEL_OUT)/arch/$(KERNEL_ARCH)/boot/Image.gzelseTARGET_PREBUILT_INT_KERNEL := $(KERNEL_OUT)/arch/$(KERNEL_ARCH)/boot/zImageendifendif

依据TARGET_KERNEL_APPEND_DTB变量，定义TARGET_PREBUILT_INT_KERNEL变量

ifeq ($(TARGET_KERNEL_APPEND_DTB), true)$(info Using appended DTB)TARGET_PREBUILT_INT_KERNEL := $(TARGET_PREBUILT_INT_KERNEL)-dtbendif

KERNEL_HEADERS_INSTALL变量

KERNEL_HEADERS_INSTALL := $(KERNEL_OUT)/usr

KERNEL_MODULES_INSTALL变量

KERNEL_MODULES_INSTALL := system

KERNEL_MODULES_OUT变量

KERNEL_MODULES_OUT := $(TARGET_OUT)/lib/modules

TARGET_PREBUILT_KERNEL变量

TARGET_PREBUILT_KERNEL := $(TARGET_PREBUILT_INT_KERNEL)

宏mv-modules

define mv-modulesmdpath=`find $(KERNEL_MODULES_OUT) -type f -name modules.dep`;\if [ "$$mdpath" != "" ];then\mpath=`dirname $$mdpath`;\ko=`find $$mpath/kernel -type f -name *.ko`;\for i in $$ko; do mv $$i $(KERNEL_MODULES_OUT)/; done;\fiendef

宏clean-module-folder

define clean-module-foldermdpath=`find $(KERNEL_MODULES_OUT) -type f -name modules.dep`;\if [ "$$mdpath" != "" ];then\mpath=`dirname $$mdpath`; rm -rf $$mpath;\fiendef

目标和依赖

ifneq ($(KERNEL_LEGACY_DIR),true)$(KERNEL_USR): $(KERNEL_HEADERS_INSTALL)    rm -rf $(KERNEL_SYMLINK)    ln -s kernel/$(TARGET_KERNEL) $(KERNEL_SYMLINK)$(TARGET_PREBUILT_INT_KERNEL): $(KERNEL_USR)endif$(KERNEL_OUT):    mkdir -p $(KERNEL_OUT)$(KERNEL_CONFIG): $(KERNEL_OUT)    $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_DEFCONFIG)    $(hide) if [ ! -z "$(KERNEL_CONFIG_OVERRIDE)" ]; then \            echo "Overriding kernel config with '$(KERNEL_CONFIG_OVERRIDE)'"; \            echo $(KERNEL_CONFIG_OVERRIDE) >> $(KERNEL_OUT)/.config; \            $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) oldconfig; fi$(TARGET_PREBUILT_INT_KERNEL): $(KERNEL_OUT) $(KERNEL_HEADERS_INSTALL)    $(hide) echo "Building kernel..."    $(hide) rm -rf $(KERNEL_OUT)/arch/$(KERNEL_ARCH)/boot/dts    $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_CFLAGS)    $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_CFLAGS) modules    $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) INSTALL_MOD_PATH=$(BUILD_ROOT_LOC)../$(KERNEL_MODULES_INSTALL) INSTALL_MOD_STRIP=1 ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) modules_install    $(mv-modules)    $(clean-module-folder)$(KERNEL_HEADERS_INSTALL): $(KERNEL_OUT)    $(hide) if [ ! -z "$(KERNEL_HEADER_DEFCONFIG)" ]; then \            rm -f $(BUILD_ROOT_LOC)$(KERNEL_CONFIG); \            $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_HEADER_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_HEADER_DEFCONFIG); \            $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_HEADER_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) headers_install; fi    $(hide) if [ "$(KERNEL_HEADER_DEFCONFIG)" != "$(KERNEL_DEFCONFIG)" ]; then \            echo "Used a different defconfig for header generation"; \            rm -f $(BUILD_ROOT_LOC)$(KERNEL_CONFIG); \            $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_DEFCONFIG); fi    $(hide) if [ ! -z "$(KERNEL_CONFIG_OVERRIDE)" ]; then \            echo "Overriding kernel config with '$(KERNEL_CONFIG_OVERRIDE)'"; \            echo $(KERNEL_CONFIG_OVERRIDE) >> $(KERNEL_OUT)/.config; \            $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) oldconfig; fikerneltags: $(KERNEL_OUT) $(KERNEL_CONFIG)    $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) tagskernelconfig: $(KERNEL_OUT) $(KERNEL_CONFIG)    env KCONFIG_NOTIMESTAMP=true \         $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) menuconfig    env KCONFIG_NOTIMESTAMP=true \         $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) savedefconfig    cp $(KERNEL_OUT)/defconfig $(TARGET_KERNEL_SOURCE)/arch/$(KERNEL_ARCH)/configs/$(KERNEL_DEFCONFIG)