细说dex2oat(3)

dex2oat是如何在makefile中落地的

在Android的mk系统中，调用dex2oat中有几处，但是真正被调用来生成目标系统上的oat的是下面这个，位于/build/core/dex_preopt_libart.mk中:

 # For a single jar or APK

 # $(1): the input .jar or .apk file
 # $(2): the output .odex file
define dex2oat-one-file
$(hide) rm -f $(2)
$(hide) mkdir -p $(dir $(2))
$(hide) $(DEX2OAT) \
    --runtime-arg -Xms$(DEX2OAT_XMS) --runtime-arg -Xmx$(DEX2OAT_XMX) \
    --boot-image=$(PRIVATE_DEX_PREOPT_IMAGE_LOCATION) \
    --dex-file=$(1) \
    --dex-location=$(PRIVATE_DEX_LOCATION) \
    --oat-file=$(2) \
    --android-root=$(PRODUCT_OUT)/system \
    --instruction-set=$($(PRIVATE_2ND_ARCH_VAR_PREFIX)DEX2OAT_TARGET_ARCH) \
    --instruction-set-variant=$($(PRIVATE_2ND_ARCH_VAR_PREFIX)DEX2OAT_TARGET_CPU_VARIANT) \
    --instruction-set-features=$($(PRIVATE_2ND_ARCH_VAR_PREFIX)DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES) \
    --include-patch-information --runtime-arg -Xnorelocate --no-generate-debug-info \
    --abort-on-hard-verifier-error \
    $(PRIVATE_DEX_PREOPT_FLAGS)
endef

这个dex2oat-one-file，是被dexpreopt-one-file调用，位于/build/core/dex_preopt.mk中：

include $(BUILD_SYSTEM)/dex_preopt_libart.mk

 # Define dexpreopt-one-file based on current default runtime.
 # $(1): the input .jar or .apk file
 # $(2): the output .odex file
define dexpreopt-one-file
$(call dex2oat-one-file,$(1),$(2))
endef

以下根据生成的类型不同，包、库、预先编译好的应用有不同的路径。

Build package中的odex生成

/build/core/package_internal.mk

 ###############################
 ## Rule to build the odex file
ifdef LOCAL_DEX_PREOPT
$(built_odex): PRIVATE_DEX_FILE := $(built_dex)
 # Use pattern rule - we may have multiple built odex files.
$(built_odex) : $(dir $(LOCAL_BUILT_MODULE))% : $(built_dex)
    $(hide) mkdir -p $(dir $@) && rm -f $@
    $(add-dex-to-package)
    $(hide) mv $@ $@.input
    $(call dexpreopt-one-file,$@.input,$@)
    $(hide) rm $@.input
endif

Build java library中的odex生成

/build/core/java_library.mk

$(built_odex): PRIVATE_MODULE := $(LOCAL_MODULE)
 # Use pattern rule - we may have multiple built odex files.
$(built_odex) : $(dir $(LOCAL_BUILT_MODULE))% : $(common_javalib.jar)
    @echo "Dexpreopt Jar: $(PRIVATE_MODULE) ($@)"
    $(call dexpreopt-one-file,$<,$@)

Prebuild的odex生成

 ###############################
 ## Rule to build the odex file
ifdef LOCAL_DEX_PREOPT
$(built_odex) : $(my_prebuilt_src_file)
    $(call dexpreopt-one-file,$<,$@)
endif

install odex

我们再来看看，odex是如何被install到system分区下面的。

 # Use pattern rule - we may have multiple installed odex files.
 # Ugly syntax - See the definition get-odex-file-path.
$(installed_odex) : $(dir $(LOCAL_INSTALLED_MODULE))%$(notdir $(word 1,$(installed_odex))) \
                  : $(dir $(LOCAL_BUILT_MODULE))%$(notdir $(word 1,$(built_odex))) \
    | $(ACP)
    @echo "Install: $@"
    $(copy-file-to-target)
endif

我们看一个实际的例子：

Install: out/target/product/6753_64_m/system/app/Note/oat/arm64/Note.odex
mkdir -p out/target/product/6753_64_m/system/app/Note/oat/arm64/
out/host/linux-x86/bin/acp -fp out/target/product/6753_64_m/obj/APPS/Note_intermediates/oat/arm64/package.odex out/target/product/6753_64_m/system/app/Note/oat/arm64/Note.odex

Install: out/target/product/6753_64_m/system/priv-app/Settings/oat/arm64/Settings.odex
mkdir -p out/target/product/6753_64_m/system/priv-app/Settings/oat/arm64/
out/host/linux-x86/bin/acp -fp out/target/product/6753_64_m/obj/APPS/Settings_intermediates/oat/arm64/package.odex out/target/product/6753_64_m/system/priv-app/Settings/oat/arm64/Settings.odex

definitions.mk中预定义的一些函数

除了编译之外，我们得先看一些预先定义好的函数。它们定义于/build/core/definitions.mk中。

add-dex-to-package

将class文件压缩成classes*.dex

define add-dex-to-package
$(hide) zip -qj $@ $(dir $(PRIVATE_DEX_FILE))classes*.dex
endef

copy-file-to-target

将依赖文件复制到目标文件

define copy-file-to-target
@mkdir -p $(dir $@)
$(hide) $(ACP) -fp $< $@
endef