Android定义的途径全局变量

对Android定义的路径全局变量，可以查看如下代码：

ifeq?(,$(strip?$(OUT_DIR)))?
OUT_DIR?:=?$(TOPDIR)out?
endif?
?
DEBUG_OUT_DIR?:=?$(OUT_DIR)/debug?
?
#?Move?the?host?or?target?under?the?debug/?directory?
#?if?necessary.?
TARGET_OUT_ROOT_release?:=?$(OUT_DIR)/target?
TARGET_OUT_ROOT_debug?:=?$(DEBUG_OUT_DIR)/target?
TARGET_OUT_ROOT?:=?$(TARGET_OUT_ROOT_$(TARGET_BUILD_TYPE))?
?
HOST_OUT_ROOT_release?:=?$(OUT_DIR)/host?
HOST_OUT_ROOT_debug?:=?$(DEBUG_OUT_DIR)/host?
HOST_OUT_ROOT?:=?$(HOST_OUT_ROOT_$(HOST_BUILD_TYPE))?
?
HOST_OUT_release?:=?$(HOST_OUT_ROOT_release)/$(HOST_OS)-$(HOST_ARCH)?
HOST_OUT_debug?:=?$(HOST_OUT_ROOT_debug)/$(HOST_OS)-$(HOST_ARCH)?
HOST_OUT?:=?$(HOST_OUT_$(HOST_BUILD_TYPE))?
?
ifeq?($(TARGET_SIMULATOR),true)?
??#?Any?arch-?or?os-specific?parts?of?the?simulator?(everything?
??#?under?product/)?are?actually?host-dependent.?
??#?But,?the?debug?type?is?controlled?by?TARGET_BUILD_TYPE?and?not?
??#?HOST_BUILD_TYPE.?
??TARGET_PRODUCT_OUT_ROOT?:=?$(HOST_OUT_$(TARGET_BUILD_TYPE))/product?
else?
??TARGET_PRODUCT_OUT_ROOT?:=?$(TARGET_OUT_ROOT)/product?
endif?
?
TARGET_COMMON_OUT_ROOT?:=?$(TARGET_OUT_ROOT)/common?
HOST_COMMON_OUT_ROOT?:=?$(HOST_OUT_ROOT)/common?
?
PRODUCT_OUT?:=?$(TARGET_PRODUCT_OUT_ROOT)/$(TARGET_DEVICE)?
?
OUT_DOCS?:=?$(TARGET_COMMON_OUT_ROOT)/docs?
?
HOST_OUT_EXECUTABLES:=?$(HOST_OUT)/bin?
HOST_OUT_SHARED_LIBRARIES:=?$(HOST_OUT)/lib?
HOST_OUT_JAVA_LIBRARIES:=?$(HOST_OUT)/framework?
HOST_OUT_SDK_ADDON?:=?$(HOST_OUT)/sdk_addon?
?
HOST_OUT_INTERMEDIATES?:=?$(HOST_OUT)/obj?
HOST_OUT_HEADERS:=?$(HOST_OUT_INTERMEDIATES)/include?
HOST_OUT_INTERMEDIATE_LIBRARIES?:=?$(HOST_OUT_INTERMEDIATES)/lib?
HOST_OUT_STATIC_LIBRARIES?:=?$(HOST_OUT_INTERMEDIATE_LIBRARIES)?
HOST_OUT_NOTICE_FILES:=$(HOST_OUT_INTERMEDIATES)/NOTICE_FILES?
HOST_OUT_COMMON_INTERMEDIATES?:=?$(HOST_COMMON_OUT_ROOT)/obj?
?
TARGET_OUT_INTERMEDIATES?:=?$(PRODUCT_OUT)/obj?
TARGET_OUT_HEADERS:=?$(TARGET_OUT_INTERMEDIATES)/include?
TARGET_OUT_INTERMEDIATE_LIBRARIES?:=?$(TARGET_OUT_INTERMEDIATES)/lib?
TARGET_OUT_COMMON_INTERMEDIATES?:=?$(TARGET_COMMON_OUT_ROOT)/obj?
?
TARGET_OUT?:=?$(PRODUCT_OUT)/system?
TARGET_OUT_EXECUTABLES:=?$(TARGET_OUT)/bin?
TARGET_OUT_OPTIONAL_EXECUTABLES:=?$(TARGET_OUT)/xbin?
TARGET_OUT_SHARED_LIBRARIES:=?$(TARGET_OUT)/lib?
TARGET_OUT_JAVA_LIBRARIES:=?$(TARGET_OUT)/framework?
TARGET_OUT_APPS:=?$(TARGET_OUT)/app?
TARGET_OUT_KEYLAYOUT?:=?$(TARGET_OUT)/usr/keylayout?
TARGET_OUT_KEYCHARS?:=?$(TARGET_OUT)/usr/keychars?
TARGET_OUT_ETC?:=?$(TARGET_OUT)/etc?
TARGET_OUT_STATIC_LIBRARIES:=?$(TARGET_OUT_INTERMEDIATES)/lib?
TARGET_OUT_NOTICE_FILES:=$(TARGET_OUT_INTERMEDIATES)/NOTICE_FILES?
?
TARGET_OUT_DATA?:=?$(PRODUCT_OUT)/data?
TARGET_OUT_DATA_EXECUTABLES:=?$(TARGET_OUT_EXECUTABLES)?
TARGET_OUT_DATA_SHARED_LIBRARIES:=?$(TARGET_OUT_SHARED_LIBRARIES)?
TARGET_OUT_DATA_JAVA_LIBRARIES:=?$(TARGET_OUT_JAVA_LIBRARIES)?
TARGET_OUT_DATA_APPS:=?$(TARGET_OUT_DATA)/app?
TARGET_OUT_DATA_KEYLAYOUT?:=?$(TARGET_OUT_KEYLAYOUT)?
TARGET_OUT_DATA_KEYCHARS?:=?$(TARGET_OUT_KEYCHARS)?
TARGET_OUT_DATA_ETC?:=?$(TARGET_OUT_ETC)?
TARGET_OUT_DATA_STATIC_LIBRARIES:=?$(TARGET_OUT_STATIC_LIBRARIES)?
?
TARGET_OUT_UNSTRIPPED?:=?$(PRODUCT_OUT)/symbols?
TARGET_OUT_EXECUTABLES_UNSTRIPPED?:=?$(TARGET_OUT_UNSTRIPPED)/system/bin?
TARGET_OUT_SHARED_LIBRARIES_UNSTRIPPED?:=?$(TARGET_OUT_UNSTRIPPED)/system/lib?
TARGET_ROOT_OUT_UNSTRIPPED?:=?$(TARGET_OUT_UNSTRIPPED)?
TARGET_ROOT_OUT_SBIN_UNSTRIPPED?:=?$(TARGET_OUT_UNSTRIPPED)/sbin?
TARGET_ROOT_OUT_BIN_UNSTRIPPED?:=?$(TARGET_OUT_UNSTRIPPED)/bin?
?
TARGET_ROOT_OUT?:=?$(PRODUCT_OUT)/root?
TARGET_ROOT_OUT_BIN?:=?$(TARGET_ROOT_OUT)/bin?
TARGET_ROOT_OUT_SBIN?:=?$(TARGET_ROOT_OUT)/sbin?
TARGET_ROOT_OUT_ETC?:=?$(TARGET_ROOT_OUT)/etc?
TARGET_ROOT_OUT_USR?:=?$(TARGET_ROOT_OUT)/usr?
?
TARGET_RECOVERY_OUT?:=?$(PRODUCT_OUT)/recovery?
TARGET_RECOVERY_ROOT_OUT?:=?$(TARGET_RECOVERY_OUT)/root?
?
TARGET_SYSLOADER_OUT?:=?$(PRODUCT_OUT)/sysloader?
TARGET_SYSLOADER_ROOT_OUT?:=?$(TARGET_SYSLOADER_OUT)/root?
TARGET_SYSLOADER_SYSTEM_OUT?:=?$(TARGET_SYSLOADER_OUT)/root/system?
?
TARGET_INSTALLER_OUT?:=?$(PRODUCT_OUT)/installer?
TARGET_INSTALLER_DATA_OUT?:=?$(TARGET_INSTALLER_OUT)/data?
TARGET_INSTALLER_ROOT_OUT?:=?$(TARGET_INSTALLER_OUT)/root?
TARGET_INSTALLER_SYSTEM_OUT?:=?$(TARGET_INSTALLER_OUT)/root/system?
?
COMMON_MODULE_CLASSES?:=?JAVA_LIBRARIES?NOTICE_FILES