1- adroid 演进过程
Android编译演进过程：
Android7.0之前 使用GNU Make
Android7.0 引入ninja、kati、Android.bp和soong构建系统
Android8.0 默认打开Android.bp
Android9.0 强制使用Android.bp
Make 构建系统得到了广泛的支持和使用，但在 Android 层面变得缓慢、容易出错、无法扩展且难以测试。Soong 构建系统正好提供了 Android build 所需的灵活性。
2- android build 流程
build/ 目录下
blueprint：用于处理Android.bp，编译生成*.ninja文件，用于做ninja的处理
kati：用于处理Android.mk，编译生成*.ninja文件，用于做ninja的处理
make：文件夹还是原始的make那一套流程，比如envsetup.sh
soong：构建系统，核心编译为soong_ui.bash
build 流程
3 编译环境初始化
source build/envsetup.sh
输入指令hmm 就可以查看信息
Run “m help” for help with the build system itself.
Invoke “. build/envsetup.sh” from your shell to add the following functions to your environment:
– lunch: lunch –
Selects as the product to build, and as the variant to
build, and stores those selections in the environment to be read by subsequent
invocations of ‘m’ etc.
– tapas: tapas [ …] [arm|x86|mips|arm64|x86_64|mips64] [eng|userdebug|user]
– croot: Changes directory to the top of the tree, or a subdirectory thereof.
– m: Makes from the top of the tree.
– mm: Builds all of the modules in the current directory, but not their dependencies.
– mmm: Builds all of the modules in the supplied directories, but not their dependencies.
To limit the modules being built use the syntax: mmm dir/:target1,target2.
– mma: Builds all of the modules in the current directory, and their dependencies.
– mmma: Builds all of the modules in the supplied directories, and their dependencies.
– provision: Flash device with all required partitions. Options will be passed on to fastboot.
– cgrep: Greps on all local C/C++ files.
– ggrep: Greps on all local Gradle files.
– jgrep: Greps on all local Java files.
– resgrep: Greps on all local res/*.xml files.
– mangrep: Greps on all local AndroidManifest.xml files.
– mgrep: Greps on all local Makefiles files.
– sepgrep: Greps on all local sepolicy files.
– sgrep: Greps on all local source files.
– godir: Go to the directory containing a file.
– allmod: List all modules.
– gomod: Go to the directory containing a module.
– pathmod: Get the directory containing a module.
– refreshmod: Refresh list of modules for allmod/gomod.
Environment options:
– SANITIZE_HOST: Set to ‘true’ to use ASAN for all host modules. Note that
ASAN_OPTIONS=detect_leaks=0 will be set by default until the
build is leak-check clean.
– ANDROID_QUIET_BUILD: set to ‘true’ to display only the essential messages.
lunch 2
PLATFORM_VERSION_CODENAME=REL
PLATFORM_VERSION=10
TARGET_PRODUCT=aosp_arm64
TARGET_BUILD_VARIANT=eng
TARGET_BUILD_TYPE=release
TARGET_ARCH=arm64
TARGET_ARCH_VARIANT=armv8-a
TARGET_CPU_VARIANT=generic
TARGET_2ND_ARCH=arm
TARGET_2ND_ARCH_VARIANT=armv8-a
TARGET_2ND_CPU_VARIANT=generic
HOST_ARCH=x86_64
HOST_2ND_ARCH=x86
HOST_OS=linux
HOST_OS_EXTRA=Linux-4.15.0-137-generic-x86_64-Ubuntu-16.04.7-LTS
HOST_CROSS_OS=windows
HOST_CROSS_ARCH=x86
HOST_CROSS_2ND_ARCH=x86_64
HOST_BUILD_TYPE=release
BUILD_ID=QD4A.200805.003
OUT_DIR=out
4-make 说明
通过soong执行编译构建，这里执行make命令时，main.mk文件把一些环境变量和目标都配置好后，会执行envsetup.sh中的make()进行编译。
function make()
{
_wrap_build $(get_make_command “$@”) “$@”
}
function get_make_command()
{
# If we’re in the top of an Android tree, use soong_ui.bash instead of make
if [ -f build/soong/soong_ui.bash ]; then
# Always use the real make if -C is passed in
for arg in “$@”; do
if [[ $arg == -C* ]]; then
echo command make
return
fi
done
echo build/soong/soong_ui.bash –make-mode
else
echo command make
fi
}
build/soong/soong_ui.bash –make-mode
——->
[build/soong/soong_ui.bash] ——-》 下面说明
# Save the current PWD for use in soong_ui
export ORIGINAL_PWD=${PWD}
export TOP=$(gettop)
source ${TOP}/build/soong/scripts/microfactory.bash
soong_build_go soong_ui android/soong/cmd/soong_ui –>生成soog_ui
cd ${TOP} —>return root
exec “$(getoutdir)/soong_ui” “$@”——>exec out/soong_ui –make-mode build
“echo build/soong/soong_ui.bash –make-mode ”
soong的编译过程:
soong_ui.bash 调用流程：
可以看到include 了main.mk文件，从main.mk开始，将通过include命令将其所有需要的.mk文件包含进来，最终在内存中形成一个包括所有编译脚本的集合，这个相当于一个巨大Makefile文件。Makefile文件看上去很庞大，其实主要由三种内容构成: 变量定义、函数定义和目标依赖规则，此外mk文件之间的包含也很重要。
文件
作用
build/make/core/main.mk
Build的主控文件，主要作用是包含其他mk，以及定义几个最重要的编译目标，同时检查编译工具的版本，例如如gcc、clang、java等
build/make/core/config.mk
Build的配置文件，主要是区分各个产品的配置，并将这些编译器参数引入产品配置 BoardConfig.mk,同时也配置了一些编译器的路径等
build/make/core/definitions.mk
最重要的 Make 文件之一，在其中定义了大量的函数。这些函数都是 Build 系统的其他文件将用到的。例如：my-dir，all-subdir-makefiles，find-subdir-files，sign-package 等，关于这些函数的说明请参见每个函数的代码注释。
build/make/core/dex_preopt.mk
定义了dex优化相关的路径和参数
5.工具链的关系
Android.bp –> Blueprint –> Soong –> Ninja
Makefile or Android.mk –> kati –> Ninja
(Android.mk –> Soong –> Blueprint –> Android.bp)