上一篇学习了make的相关东西，这里结合android.mk这个makefile文件讲讲安卓是怎么通过android.mk编译的（不用多想，android.mk就是个makefile）。
本文还是转载的前辈的文章，学习。
1. android系统源码的编译流程
来回顾一下常见的编译步骤：
source build/envsetup.sh lunch xxx make -j8 2>&1 | tee build.log
这三步究竟做了什么呢？我们来逐步分析一下。
1.1 source build/envsetup.sh
build/envsetup.sh这个文件中定义了一些变量和函数，执行source build/envsetup.sh之后，envsetup.sh中的变量成了全局变量，而其中的函数也可以直接在当前终端命令行中使用了。
这些函数可以帮助我们切换目录，查找文件，可以使我们在编译源码时更方便。这些函数可通过hmm函数来查看，下面列出了一些常用的函数：
lunch: lunch <product_name>-<build_variant> (选择要编译的目标产品和版本) tapas: tapas [<App1> <App2> ...] [arm|x86|mips|armv5] [eng|userdebug|user] croot: Changes directory to the top of the tree.(切换到源码的顶层目录) m: Makes from the top of the tree.(从顶层目录build整个系统) mm: Builds all of the modules in the current directory, but not their dependencies.(构建当前目录下所有的模块，但不包括它们的依赖) mmm: Builds all of the modules in the supplied directories, but not their dependencies.(构建指定目录下所有的模块，但不包括它们的依赖) mma: Builds all of the modules in the current directory, and their dependencies.(构建当前目录下所有的模块以及它们所依赖的模块) mmma: Builds all of the modules in the supplied directories, and their dependencies.(构建指定目录下所有的模块以及它们所依赖的模块) provision: Flash device with all required partitions. Options will be passed on to fastboot.(将设备所有需要的分区刷入，选项将传递给fastboot) cgrep: Greps on all local C/C++ files.(在C，C++文件中搜索指定关键字) ggrep: Greps on all local Gradle files.(在gradle文件中搜索指定关键字) jgrep: Greps on all local Java files.(在java文件中搜索指定关键字) resgrep: Greps on all local res/*.xml files.(在资源xml文件中搜索指定关键字) mangrep: Greps on all local AndroidManifest.xml files.(在AndroidManifest.xml文件中搜索指定关键字) mgrep: Greps on all local Makefiles files.(在Makefiles和android.mk文件中搜索指定关键字) sepgrep: Greps on all local sepolicy files.(在sepolicy文件中搜索指定关键字) sgrep: Greps on all local source files.(在所有本地文件中搜索指定关键字) godir: Go to the directory containing a file.(切换到包含某个文件的目录下)
除了hmm提示的这些，还有一些方法，具体可以直接查看build/envsetup.sh文件（话说用来这么久，我竟然没有打开看过，真是羞愧）：
cproj: 向上切换到最近包含Android.mk的目录下 findmakefile: 打印当前目录所在工程的Android.mk的文件路径 getsdcardpath: 获取Sd卡路径 getscreenshotpath: 获取屏幕截图的路径 getlastscreenshot: 获取最后一张截图,导出到当前目录下 getbugreports: 将bug报告从设备上导出到本地，bug报告存放于目录/sdcard/bugreports gettop: 获取Android源码根目录 pid: pid processname 查看某个可执行程序对应的进程id key_back: 模拟按返回键 key_home: 模拟按Home键 key_menu: 模拟按菜单键
envsetup.sh中还定义了add_lunch_combo函数，并且多次执行了add_lunch_combo函数，将自身定义的所有product添加到LUNCH_MENU_CHOICES中：
# Clear this variable. It will be built up again when the vendorsetup.sh # files are included at the end of this file. unset LUNCH_MENU_CHOICES function add_lunch_combo() { local new_combo=$1 local c for c in ${LUNCH_MENU_CHOICES[@]} ; do if [ "$new_combo" = "$c" ] ; then return fi done LUNCH_MENU_CHOICES=(${LUNCH_MENU_CHOICES[@]} $new_combo) } # add the default one here add_lunch_combo aosp_arm-eng add_lunch_combo aosp_arm64-eng add_lunch_combo aosp_mips-eng add_lunch_combo aosp_mips64-eng add_lunch_combo aosp_x86-eng add_lunch_combo aosp_x86_64-eng
最后，envsetup.sh中还遍历并执行vendor和device目录下的所有vendorsetup.sh文件：
# Execute the contents of any vendorsetup.sh files we can find. for f in `test -d device && find -L device -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort` \ `test -d vendor && find -L vendor -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort` \ `test -d product && find -L product -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort` do echo "including $f" . $f done unset f
这些vendorsetup.sh中也定义了的一些product，执行这些vendorsetup.sh后，也会将它们当中定义的product添加到LUNCH_MENU_CHOICES中：
add_lunch_combo full_k63v2_64_bsp-eng add_lunch_combo full_k63v2_64_bsp-user add_lunch_combo full_k63v2_64_bsp-userdebug
在此之后，我们就可以在命令行用lunch函数从LUNCH_MENU_CHOICES中选择需要编译的product。
1.2 lunch
执行lunch函数时，如果用户指定了product，获取指定的product。
如果用户未指定product，调用print_lunch_menu函数输出上一步生成的lunch menu choices让用户选择。
如用户指定了product或者提示后选择了product，会获取用户指定的product，并提取p r o d u c t 和 product和product和variant。
然后检查是否支持product，如不支持，提示不支持并退出。如支持，接着会调用set_stuff_for_environment函数设置一系列环境变量，还会调用printconfig输出相关变量和配置信息。
function lunch() { local answer if [ "$1" ] ; then answer=$1 else print_lunch_menu echo -n "Which would you like? [aosp_arm-eng] " read answer fi local selection= if [ -z "$answer" ] then selection=aosp_arm-eng elif (echo -n $answer | grep -q -e "^[0-9][0-9]*$") then if [ $answer -le ${#LUNCH_MENU_CHOICES[@]} ] then selection=${LUNCH_MENU_CHOICES[$(($answer-1))]} fi else selection=$answer fi export TARGET_BUILD_APPS= local product variant_and_version variant version product=${selection%%-*} # Trim everything after first dash variant_and_version=${selection#*-} # Trim everything up to first dash if [ "$variant_and_version" != "$selection" ]; then variant=${variant_and_version%%-*} if [ "$variant" != "$variant_and_version" ]; then version=${variant_and_version#*-} fi fi if [ -z "$product" ] then echo echo "Invalid lunch combo: $selection" return 1 fi TARGET_PRODUCT=$product \ TARGET_BUILD_VARIANT=$variant \ TARGET_PLATFORM_VERSION=$version \ build_build_var_cache if [ $? -ne 0 ] then return 1 fi export TARGET_PRODUCT=$(get_build_var TARGET_PRODUCT) export TARGET_BUILD_VARIANT=$(get_build_var TARGET_BUILD_VARIANT) if [ -n "$version" ]; then export TARGET_PLATFORM_VERSION=$(get_build_var TARGET_PLATFORM_VERSION) else unset TARGET_PLATFORM_VERSION fi export TARGET_BUILD_TYPE=release echo set_stuff_for_environment printconfig destroy_build_var_cache }
1.3 make -j8 2>&1 | tee build.log
- -j8是用于指定编译的cpu核心，如果编译服务器配置好，可以略为改大一些。
- 2>&1 | tee build.log则是同时输出编译的提示、异常信息到终端和build.log文件中。
- 具体可以看一下：
每个程序在运行后，都会至少打开三个文件描述符，分别是0：标准输入;1：标准输出;2：标准错误。 1、程序运行后会打开三个文件描述符，分别是标准输入，标准输出和标准错误输出。 2、在调用脚本时，可使用2>&1来将标准错误输出重定向。 3、只需要查看脚本的错误时，可将标准输出重定向到文件，而标准错误会打印在控制台，便于查看。 4、>>log.txt会将重定向内容追加到log.txt文件末尾。 5、通过查看/proc/进程id/fd下的内容，可了解进程打开的文件描述符信息。
- make则是执行make命令，寻找源码根目录下的Makefile，解析Makefile并开始整个源码的编译。
接下来我们就从源码根目录下的Makefile开始逐步解析。
2. android的Makefile和android.mk
执行make之后，从源码根目录下的Makefile开始逐步解析。该Makefile的内容很少，只是导入了build/make/core/main.mk。
Makefile：
### DO NOT EDIT THIS FILE ### include build/make/core/main.mk ### DO NOT EDIT THIS FILE ###
main.mk中有两个最重要的部分，一个是导入build/make/core/config.mk和build/make/core/definitions.mk。
main.mk：
...... BUILD_SYSTEM := $(TOPDIR)build/make/core ...... # Set up various standard variables based on configuration # and host information. include $(BUILD_SYSTEM)/config.mk ...... # Bring in standard build system definitions. include $(BUILD_SYSTEM)/definitions.mk ......
config.mk中定义了一系列编译需要用到的变量，比如常用的CLEAR_VARS、BUILD_PACKAGE。这些变量实际上是每一个变量导入另一个.mk文件。
每一个被导入的.mk完成一个基本功能，比如，CLEAR_VARS对应的build/make/core/clear_vars.mk是清除编译的临时变量，BUILD_PACKAGE对应的build/make/core/package.mk是编译APK。
config.mk：
# Set up efficient math functions which are used in make. # Here since this file is included by envsetup as well as during build. include $(BUILD_SYSTEM)/math.mk # Various mappings to avoid hard-coding paths all over the place include $(BUILD_SYSTEM)/pathmap.mk # Allow projects to define their own globally-available variables include $(BUILD_SYSTEM)/project_definitions.mk # ############################################################### # Build system internal files # ############################################################### BUILD_COMBOS:= $(BUILD_SYSTEM)/combo CLEAR_VARS:= $(BUILD_SYSTEM)/clear_vars.mk BUILD_HOST_STATIC_LIBRARY:= $(BUILD_SYSTEM)/host_static_library.mk BUILD_HOST_SHARED_LIBRARY:= $(BUILD_SYSTEM)/host_shared_library.mk BUILD_STATIC_LIBRARY:= $(BUILD_SYSTEM)/static_library.mk BUILD_HEADER_LIBRARY:= $(BUILD_SYSTEM)/header_library.mk BUILD_AUX_STATIC_LIBRARY:= $(BUILD_SYSTEM)/aux_static_library.mk BUILD_AUX_EXECUTABLE:= $(BUILD_SYSTEM)/aux_executable.mk BUILD_SHARED_LIBRARY:= $(BUILD_SYSTEM)/shared_library.mk BUILD_EXECUTABLE:= $(BUILD_SYSTEM)/executable.mk BUILD_HOST_EXECUTABLE:= $(BUILD_SYSTEM)/host_executable.mk BUILD_PACKAGE:= $(BUILD_SYSTEM)/package.mk BUILD_PHONY_PACKAGE:= $(BUILD_SYSTEM)/phony_package.mk BUILD_RRO_PACKAGE:= $(BUILD_SYSTEM)/build_rro_package.mk BUILD_HOST_PREBUILT:= $(BUILD_SYSTEM)/host_prebuilt.mk BUILD_PREBUILT:= $(BUILD_SYSTEM)/prebuilt.mk BUILD_MULTI_PREBUILT:= $(BUILD_SYSTEM)/multi_prebuilt.mk BUILD_JAVA_LIBRARY:= $(BUILD_SYSTEM)/java_library.mk BUILD_STATIC_JAVA_LIBRARY:= $(BUILD_SYSTEM)/static_java_library.mk BUILD_HOST_JAVA_LIBRARY:= $(BUILD_SYSTEM)/host_java_library.mk BUILD_DROIDDOC:= $(BUILD_SYSTEM)/droiddoc.mk BUILD_APIDIFF:= $(BUILD_SYSTEM)/apidiff.mk BUILD_COPY_HEADERS := $(BUILD_SYSTEM)/copy_headers.mk BUILD_NATIVE_TEST := $(BUILD_SYSTEM)/native_test.mk BUILD_NATIVE_BENCHMARK := $(BUILD_SYSTEM)/native_benchmark.mk BUILD_HOST_NATIVE_TEST := $(BUILD_SYSTEM)/host_native_test.mk BUILD_FUZZ_TEST := $(BUILD_SYSTEM)/fuzz_test.mk BUILD_HOST_FUZZ_TEST := $(BUILD_SYSTEM)/host_fuzz_test.mk BUILD_SHARED_TEST_LIBRARY := $(BUILD_SYSTEM)/shared_test_lib.mk BUILD_HOST_SHARED_TEST_LIBRARY := $(BUILD_SYSTEM)/host_shared_test_lib.mk BUILD_STATIC_TEST_LIBRARY := $(BUILD_SYSTEM)/static_test_lib.mk BUILD_HOST_STATIC_TEST_LIBRARY := $(BUILD_SYSTEM)/host_static_test_lib.mk BUILD_NOTICE_FILE := $(BUILD_SYSTEM)/notice_files.mk BUILD_HOST_DALVIK_JAVA_LIBRARY := $(BUILD_SYSTEM)/host_dalvik_java_library.mk BUILD_HOST_DALVIK_STATIC_JAVA_LIBRARY := $(BUILD_SYSTEM)/host_dalvik_static_java_library.mk BUILD_HOST_TEST_CONFIG := $(BUILD_SYSTEM)/host_test_config.mk BUILD_TARGET_TEST_CONFIG := $(BUILD_SYSTEM)/target_test_config.mk
而definitions.mk中用define也定义了一系列变量，比如常用的my-dir、all-subdir-makefiles、all-subdir-java-files等等。
这些编译主要用于处理目录相关的功能，比如my-dir是获取当前目录路径，all-subdir-makefiles 调用所有子目录的android.mk 。
definitions.mk中有很多变量，列举如下：
definitions.mk：
define print-vars define true-or-empty define gcno-touch-rule define my-dir define all-makefiles-under define first-makefiles-under define all-subdir-makefiles define all-named-subdir-makefiles define all-named-dirs-under define all-subdir-named-dirs define all-named-files-under define all-subdir-named-files define all-java-files-under define all-subdir-java-files define all-c-files-under define all-subdir-c-files define all-cpp-files-under define all-subdir-cpp-files define all-Iaidl-files-under define all-subdir-Iaidl-files define all-vts-files-under define all-subdir-vts-files define all-logtags-files-under define all-proto-files-under define all-renderscript-files-under define all-S-files-under define all-html-files-under define all-subdir-html-files define find-subdir-files define find-subdir-subdir-files define find-subdir-assets define find-other-java-files define find-other-html-files define find-files-in-subdirs define find-parent-file define find-test-data-in-subdirs define add-dependency define reverse-list define def-host-aux-target define find-idf-prefix define intermediates-dir-for define local-intermediates-dir define generated-sources-dir-for define local-generated-sources-dir define module-built-files define module-installed-files define module-stubs-files define doc-timestamp-for define java-lib-files define java-lib-header-files define java-lib-header-files define java-lib-deps define app-lib-files define app-lib-header-files define app-lib-header-files define streq define normalize-path-list define normalize-comma-list define word-colon define collapse-pairs define uniq-pairs-by-first-component define modules-for-tag-list define module-names-for-tag-list define get-tagged-modules define append-path define echo-warning define echo-error define pretty-warning define pretty-error define _get-package-overrides define get-package-overrides define pretty define pretty define include-depfile define include-depfiles-for-objs define track-src-file-obj define _track-src-file-obj define track-src-file-gen define _track-src-file-gen define track-gen-file-obj define transform-l-to-c-or-cpp define transform-y-to-c-or-cpp define _merge-renderscript-d define transform-renderscripts-to-java-and-bc define transform-bc-to-so define transform-renderscripts-to-cpp-and-bc define transform-aidl-to-java define transform-aidl-to-cpp define define-aidl-java-rule define define-aidl-java-rule define-aidl-java-rule-src define define-aidl-cpp-rule define define-aidl-cpp-rule define-aidl-cpp-rule-src define transform-vts-to-cpp define define-vts-cpp-rule define define-vts-cpp-rule define-vts-cpp-rule-src define transform-logtags-to-java define transform-proto-to-java define transform-proto-to-cc define c-includes define transform-cpp-to-o-compiler-args define clang-tidy-cpp define transform-cpp-to-o define transform-cpp-to-o define transform-c-or-s-to-o-compiler-args define transform-c-to-o-compiler-args define clang-tidy-c define transform-c-to-o define transform-c-to-o define transform-s-to-o define transform-asm-to-o define transform-m-to-o define transform-host-cpp-to-o-compiler-args define clang-tidy-host-cpp define transform-host-cpp-to-o define transform-host-cpp-to-o define transform-host-c-or-s-to-o-common-args define transform-host-c-or-s-to-o define transform-host-c-to-o-compiler-args define clang-tidy-host-c define transform-host-c-to-o define transform-host-c-to-o define transform-host-s-to-o define transform-host-m-to-o define transform-host-mm-to-o define compile-dotdot-cpp-file define compile-dotdot-c-file define compile-dotdot-s-file define compile-dotdot-s-file-no-deps define _concat-if-arg2-not-empty define split-long-arguments define _extract-and-include-single-target-whole-static-lib define extract-and-include-whole-static-libs-first define extract-and-include-target-whole-static-libs define transform-o-to-static-lib define _extract-and-include-single-aux-whole-static-lib define extract-and-include-aux-whole-static-libs define transform-o-to-aux-static-lib define transform-o-to-aux-executable-inner define transform-o-to-aux-executable define transform-o-to-aux-static-executable-inner define transform-o-to-aux-static-executable define _extract-and-include-single-host-whole-static-lib define extract-and-include-host-whole-static-libs define create-dummy.o-if-no-objs define get-dummy.o-if-no-objs define delete-dummy.o-if-no-objs define transform-host-o-to-static-lib define transform-host-o-to-shared-lib-inner define transform-host-o-to-shared-lib define transform-host-o-to-package define transform-o-to-shared-lib-inner define transform-o-to-shared-lib define transform-to-stripped define transform-to-stripped-keep-mini-debug-info define transform-to-stripped-keep-symbols define pack-elf-relocations define transform-o-to-executable-inner define transform-o-to-executable define transform-o-to-static-executable-inner define transform-o-to-static-executable define transform-host-o-to-executable-inner define transform-host-o-to-executable define create-resource-java-files define find-generated-R.java define aapt2-compile-one-resource-file define aapt2-compile-resource-dirs define aapt2-compile-resource-zips define aapt2-compile-one-resource-file-rule define aapt2-compiled-resource-out-file define aapt2-link define emit-line define dump-words-to-file define unzip-jar-files define jar-args-sorted-files-in-directory define fetch-additional-java-source define write-java-source-list define compile-java define transform-java-to-header.jar define commit-change-for-toc define _transform-dex-to-toc define define-dex-to-toc-rule define define-dex-to-toc-rule define define-dex-to-toc-rule define define-dex-to-toc-rule define codename-or-sdk-to-sdk define desugar-classes-jar define transform-classes.jar-to-dex define transform-classes-d8.jar-to-dex define create-empty-package-at define create-empty-package define initialize-package-file define add-assets-to-package define _add-jni-shared-libs-to-package-per-abi define add-jni-shared-libs-to-package define add-dex-to-package define add-dex-to-package-arg define add-java-resources-to define add-jar-resources-to-package define sign-package define sign-package-arg define align-package define compress-package define remove-timestamps-from-package define uncompress-dexs define uncompress-shared-libs define transform-host-java-to-package define transform-host-java-to-dalvik-package define copy-one-header define copy-one-file define copy-and-uncompress-dexs define copy-many-files define copy-xml-file-checked define copy-file-to-target define copy-file-to-target-with-cp define copy-file-to-target-strip-comments define copy-file-to-new-target define copy-file-to-new-target-with-cp define transform-prebuilt-to-target define transform-prebuilt-to-target-strip-comments define copy-files-with-structure define symlink-file define _symlink-file define dexpreopt-copy-jar define dexpreopt-remove-classes.dex define hiddenapi-copy-dex-files define hiddenapi-copy-soong-jar define transform-jar-to-proguard define transform-jar-to-proguard define transform-jar-to-dex-r8 define transform-generated-source define assert-max-image-size define add-radio-file define add-radio-file-internal define add-radio-file-checked define add-radio-file-checked-internal define inherit-package define inherit-package-internal define set-inherited-package-variables define keep-or-override define set-inherited-package-variables-internal define check-api define if-build-from-source define if-build-from-source define include-if-build-from-source define get-prebuilt-src-arch define record-module-type define compatibility_suite_dirs define create-suite-dependencies define _clean-path-strip-dotdot define _clean-path-strip-root-dotdots define _clean-path-expanded define clean-path define my_test define try-validate-path-is-subdir define validate-path-is-subdir define try-validate-paths-are-subdirs define validate-paths-are-subdirs define test-validate-paths-are-subdirs define jacoco-class-filter-to-file-args define jacoco-validate-file-args define append_enforce_rro_sources define generate_all_enforce_rro_packages define has-system-sdk-version define get-numeric-sdk-version
main.mk中另一个重要的部分就是定义了一系列的规则，这些规则的目标就是编译要生成的目标文件：
# This is the default target. It must be the first declared target. .PHONY: droid DEFAULT_GOAL := droid $(DEFAULT_GOAL): droid_targets ...... .PHONY: ramdisk ramdisk: $(INSTALLED_RAMDISK_TARGET) .PHONY: systemtarball systemtarball: $(INSTALLED_SYSTEMTARBALL_TARGET) .PHONY: boottarball boottarball: $(INSTALLED_BOOTTARBALL_TARGET) .PHONY: userdataimage userdataimage: $(INSTALLED_USERDATAIMAGE_TARGET) ifneq (,$(filter userdataimage, $(MAKECMDGOALS))) $(call dist-for-goals, userdataimage, $(BUILT_USERDATAIMAGE_TARGET)) endif .PHONY: userdatatarball userdatatarball: $(INSTALLED_USERDATATARBALL_TARGET) .PHONY: cacheimage cacheimage: $(INSTALLED_CACHEIMAGE_TARGET) .PHONY: bptimage bptimage: $(INSTALLED_BPTIMAGE_TARGET) .PHONY: vendorimage vendorimage: $(INSTALLED_VENDORIMAGE_TARGET) .PHONY: productimage productimage: $(INSTALLED_PRODUCTIMAGE_TARGET) .PHONY: systemotherimage systemotherimage: $(INSTALLED_SYSTEMOTHERIMAGE_TARGET) .PHONY: bootimage bootimage: $(MTK_BOOTIMAGE_TARGET)
而编译的默认目标，也就是终极目标droid，逐级依赖，依赖到各个image文件，也就是各个分区imge文件：
# Building a full system-- the default is to build droidcore droid_targets: droidcore dist_files ...... # Build files and then package it into the rom formats .PHONY: droidcore droidcore: files \ systemimage \ $(INSTALLED_BOOTIMAGE_TARGET) \ $(MTK_BOOTIMAGE_TARGET) \ $(INSTALLED_RECOVERYIMAGE_TARGET) \ $(INSTALLED_VBMETAIMAGE_TARGET) \ $(INSTALLED_USERDATAIMAGE_TARGET) \ $(INSTALLED_CACHEIMAGE_TARGET) \ $(INSTALLED_BPTIMAGE_TARGET) \ $(INSTALLED_VENDORIMAGE_TARGET) \ $(INSTALLED_PRODUCTIMAGE_TARGET) \ $(INSTALLED_SYSTEMOTHERIMAGE_TARGET) \ $(INSTALLED_FILES_FILE) \ $(INSTALLED_FILES_FILE_VENDOR) \ $(INSTALLED_FILES_FILE_PRODUCT) \ $(INSTALLED_FILES_FILE_SYSTEMOTHER) \ soong_docs
根据make的编译原理，编译时，先编译终极目标的各个依赖文件，如image文件、bin文件等等，而image文件又依赖许多的库文件、APK文件、资源文件等等，也就会递归触发库文件、APK文件、资源文件等模块的编译。
递归编译完依赖文件，最后完成终极目标，这样就完成了整个android源码的构建。
当然，main.mk中为了完成整个android的编译，还导入了一系列的mk等等，这里就不一一介绍了，有兴趣的可以自行查看源码。
同样，根据make的编译原理，我们也可以通过make指定的目标来单独编译某个模块，这样可以加快编译速度。例如: make systemimage。
当然，为了进一步加快编译速度，我们还可以**利用envsetup.sh中的mm或者mmm函数，在仅需要编译模块自身，**不需要编译模块的依赖的情况下，用mm或者mmm编译更快。
我们可以看到，实际上android.mk和Makefile没有明显差别。
android.mk实际上只是多了一些方便编译android源码的内置变量和内置函数。
android.mk完全遵循Makefile的语法规则，并且它的内置变量和内置函数也是按照Makefile语法进行导入的。
最关键的，构建android系统时也是从一个Makefile开始的。
所以，我们可以认为android.mk实际上是一种扩展的Makefile，就像GNU make扩展了原始make一样。
接下来我们介绍android.mk的使用实例。
3. android.mk的使用实例
3.1 编译APK
LOCAL_PATH:= $(call my-dir) include $(CLEAR_VARS) # 源文件，可包含java、aidl文件 LOCAL_SRC_FILES := $(call all-java-files-under, src) LOCAL_SRC_FILES += src/com/sprd/gallery3d/aidl/IFloatWindowController.aidl # resource资源文件 LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/res # AndroidManifest.xml文件 LOCAL_MANIFEST_FILE := $(LOCAL_PATH)/AndroidManifest.xml # 是否启用AAPT2 LOCAL_USE_AAPT2 := true LOCAL_MODULE_TAGS := optional # 目标APK文件名称 LOCAL_PACKAGE_NAME := DreamCamera2 # 需要override的名称 LOCAL_OVERRIDES_PACKAGES := Camera2 # APK的签名 LOCAL_CERTIFICATE := platform # 是否启用odex优化 LOCAL_DEX_PREOPT := false # SDK版本 LOCAL_SDK_VERSION := current # 混淆配置文件 LOCAL_PROGUARD_FLAG_FILES := proguard.flags # 依赖的java共享库 LOCAL_JAVA_LIBRARIES := android.test.runner # 依赖的java静态库 LOCAL_STATIC_JAVA_LIBRARIES := zxing # 依赖的共享库 LOCAL_SHARED_LIBRARIES := libjpeg # 依赖的静态库 LOCAL_STATIC_LIBRARIES := libjpeg_static_ndk # 版本号 LOCAL_AAPT_FLAGS := \ --auto-add-overlay \ --version-name "$(version_name_package)" \ --version-code $(version_code_package) \ # 构建APK include $(BUILD_PACKAGE)
3.2 编译java静态库
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) # 源文件，可包含java、aidl文件 LOCAL_SRC_FILES := $(call all-subdir-java-files) # 依赖的java静态库 LOCAL_STATIC_JAVA_LIBRARIES := zxing # 依赖的java动态库 LOCAL_JAVA_LIBRARIES := android.test.runner # 目标java静态库的名称 LOCAL_MODULE := scan # 构建java静态库 include $(BUILD_STATIC_JAVA_LIBRARY)
3.3 编译java共享库
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) # 源文件，可包含java、aidl文件 LOCAL_SRC_FILES := $(call all-subdir-java-files) # 依赖的java共享库 LOCAL_JAVA_LIBRARIES := bouncycastle core-libart ext services.core LOCAL_MODULE_TAGS := optional LOCAL_JACK_ENABLED := disabled # 目标java共享库的名称 LOCAL_MODULE:= security # 构建java共享库 include $(BUILD_JAVA_LIBRARY)
3.4 编译C/C++静态库
LOCAL_PATH:= $(call my-dir) include $(CLEAR_VARS) # 目标静态库的名称 LOCAL_MODULE := libgif-ex # C/C++源文件 LOCAL_SRC_FILES := \ dgif_lib.c \ egif_lib.c \ gifalloc.c \ gif_err.c \ gif_hash.c \ openbsd-reallocarray.c \ quantize.c LOCAL_CFLAGS += -Wno-format -Wno-sign-compare -Wno-unused-parameter -DHAVE_CONFIG_H LOCAL_SDK_VERSION := 8 LOCAL_NDK_STL_VARIANT := c++_static # 构建C/C++静态库 include $(BUILD_STATIC_LIBRARY)
3.5 编译C/C++共享库
LOCAL_PATH:= $(call my-dir) include $(CLEAR_VARS) # C/C++头文件 LOCAL_C_INCLUDES := \ $(LOCAL_PATH)/include \ $(TOPDIR)system/core/include # C FLAG LOCAL_CFLAGS := -O3 -DNDEBUG # LDFLAG LOCAL_LDFLAGS := -llog # 依赖的共享库 LOCAL_SHARED_LIBRARIES := \ libutils \ myutils # 依赖的静态库 LOCAL_STATIC_LIBRARIES := libjpeg_static_ndk # C/C++源文件 LOCAL_SRC_FILES := \ main.cpp \ utils.cpp # 目标共享库的名称 LOCAL_MODULE := mylib LOCAL_MODULE_TAGS := optional # 构建共享库 include $(BUILD_SHARED_LIBRARY)
4. 用于预置的android.mk
4.1 预置jar
方法一：
LOCAL_PATH:= $(call my-dir) # 预置 include $(CLEAR_VARS) LOCAL_PREBUILT_STATIC_JAVA_LIBRARIES := zxing:libs/core.jar \ gson:libs/gson-2.8.0.jar \ android-support-v7:libs/android-support-v7-recyclerview.jar include $(BUILD_MULTI_PREBUILT) # 引用 include $(CLEAR_VARS) ...... LOCAL_STATIC_JAVA_LIBRARIES += zxing LOCAL_STATIC_JAVA_LIBRARIES += gson LOCAL_STATIC_JAVA_LIBRARIES += android-support-v7 ...... include $(BUILD_PACKAGE)
方法二：
LOCAL_PATH := $(call my-dir) # 预置 include $(CLEAR_VARS) LOCAL_MODULE_CLASS := JAVA_LIBRARIES LOCAL_MODULE := commons-io LOCAL_SDK_VERSION := current LOCAL_SRC_FILES := ../../../../../../../../prebuilts/tools/common/m2/repository/commons-io/commons-io/2.4/commons-io-2.4.jar LOCAL_UNINSTALLABLE_MODULE := true include $(BUILD_PREBUILT) # 引用 include $(CLEAR_VARS) ...... LOCAL_STATIC_JAVA_LIBRARIES += commons-io ...... include $(BUILD_PACKAGE)
4.2 预置so
方法一：
LOCAL_PATH:= $(call my-dir) # 预置 include $(CLEAR_VARS) LOCAL_MODULE := mylib2 LOCAL_SRC_FILES_32 := lib/armeabi-v7a/mylib2.so LOCAL_SRC_FILES_64 := lib/arm64-v8a/mylib2.so LOCAL_MODULE_TAGS := optional LOCAL_MODULE_CLASS := SHARED_LIBRARIES LOCAL_MODULE_SUFFIX := .so LOCAL_PROPRIETARY_MODULE := true LOCAL_MULTILIB := both include $(BUILD_PREBUILT) ...... # 引用 include $(CLEAR_VARS) LOCAL_SHARED_LIBRARIES += mylib2 include $(BUILD_PACKAGE) ......
方法二：
LOCAL_PATH:= $(call my-dir) # 预置 include $(CLEAR_VARS) ...... ifeq ($(strip $(TARGET_ARCH)), arm64) LOCAL_PREBUILT_JNI_LIBS := libs/arm64-v8a/mylib3.so else ifeq ($(strip $(TARGET_ARCH)), x86_64) LOCAL_PREBUILT_JNI_LIBS := libs/x86_64/mylib3.so else ifeq ($(strip $(TARGET_ARCH)),arm) LOCAL_PREBUILT_JNI_LIBS := libs/armeabi-v7a/mylib3.so else LOCAL_PREBUILT_JNI_LIBS := libs/x86/mylib3.so endif ...... include $(BUILD_PACKAGE)
4.3 预置APK
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) # 模块名称 LOCAL_MODULE := NewGallery2 # 要覆盖掉的模块名称 LOCAL_OVERRIDES_PACKAGES := Gallery Gallery3D GalleryNew3D Gallery2 DreamGallery2 # 模块类型为APPS LOCAL_MODULE_CLASS := APPS # 允许使用系统隐藏接口 LOCAL_PRIVATE_PLATFORM_APIS := true # 签名，如无需重签名，则直接设置为PRESIGNED使用已有签名；需要重签，则设置为对应签名的值。 LOCAL_CERTIFICATE := platform # 目标编译后的输出目录 LOCAL_MODULE_PATH := $(TARGET_OUT)/priv-app # APK文件 LOCAL_SRC_FILES := apk/NewGallery2.apk # APK预置的so ifeq ($(strip $(TARGET_ARCH)), arm64) LOCAL_PREBUILT_JNI_LIBS := libs/arm64-v8a/libjni_jpeg.so else ifeq ($(strip $(TARGET_ARCH)), x86_64) LOCAL_PREBUILT_JNI_LIBS := libs/x86_64/libjni_jpeg.so else ifeq ($(strip $(TARGET_ARCH)),arm) LOCAL_PREBUILT_JNI_LIBS := libs/armeabi-v7a/libjni_jpeg.so else LOCAL_PREBUILT_JNI_LIBS := libs/x86/libjni_jpeg.so endif include $(BUILD_PREBUILT)
5、结语
在掌握了Makefile基础知识以及结合源码理清楚了android.mk之后，就不会觉得.mk文件那么陌生了。
尤其是在理解了android.mk的内置变量和内置函数之后，我们在编写.mk文件就基本可以得心应手了。
由于make在编译android系统源码时表现出效率不够高的问题，google后来在7.0及以上版本引进了速度更快的Soong，Soong对应的配置文件是android.bp。
但google即便引进了Soong，源码中还是保留了部分android.mk。
并且android.mk也可以通过kati工具转换成ninja构建清单文件，也就是说android.mk还可以继续使用。
所以，make仍然是android开发者的必备技能。
