android编译分析【一】
最近以CM7为基础移植android到某个机型，简单的说编译步骤如下：
1，在device/zte/blade/目录下运行unzip-files.sh，这步的主要目的是将某些硬件相关的库直接复制到vendor目录（因为拿不到厂家的源码只能这样做了）;
2，在source目录运行. build/envsetup.sh;
3，lunch，选取适当的编译目标;
4，make -jx，开跑。
一切从envsetup.sh开始，在运行了build/envsetup.sh之后，将会多出一堆有用的函数来帮助我们更好的编译或者分析android，在输入help之后会显示：
Invoke ". build/envsetup.sh" from your shell to add the following functions to your environment: - croot: Changes directory to the top of the tree. - m: Makes from the top of the tree. - mm: Builds all of the modules in the current directory. - mmm: Builds all of the modules in the supplied directories. - cgrep: Greps on all local C/C++ files. - jgrep: Greps on all local Java files. - resgrep: Greps on all local res/*.xml files. - godir: Go to the directory containing a file. Look at the source to view more functions. The complete list is: add_lunch_combo cgrep check_product check_variant choosecombo chooseproduct choosetype choosevariant cproj croot findmakefile gdbclient get_abs_build_var getbugreports get_build_var getprebuilt gettop godir help isviewserverstarted jgrep lunch m mm mmm pid printconfig print_lunch_menu resgrep runhat runtest set_java_home setpaths set_sequence_number set_stuff_for_environment settitle smoketest startviewserver stopviewserver systemstack tapas tracedmdump其中的各项功能可以参照英文解说，croot可以从各种目录下随时回到source目录，mm根据当前路径的Makefile编译出模块，mmm根据后面跟着的path来寻找makefile，然后把makefile里面定义了的LOCAL_MODULE编译出来。
build/envsetup.sh的工作大部分就是定义上述的一些helper函数，最后运行的就是这一段：
# add the default one here
add_lunch_combo generic-eng
# if we're on linux, add the simulator. There is a special case
# in lunch to deal with the simulator
if [ "$(uname)" = "Linux" ] ; then
add_lunch_combo simulator
fi
...
# Execute the contents of any vendorsetup.sh files we can find.
for f in `/bin/ls vendor/*/vendorsetup.sh vendor/*/build/vendorsetup.sh device/*/*/vendorsetup.sh 2> /dev/null`
do
echo "including $f"
. $f
done
unset f
因此，在默认情况下会有generic-eng这个选项，在linux下编译的话会再有simulator选项，然后就会到vendor和device目录中寻找vendorsetup.sh然后执行，以ZTE blade的CM7为例，在device/zte/blade中有vendorsetup.sh文件，内容如下：
add_lunch_combo zte_blade-eng add_lunch_combo zte_blade-userdebug它会再增加zte_blade-eng和zte_blade-userdebug两个目标。
随后的lunch根据上述的目标生成菜单供选择，lunch与choosecombo达到的效果一样，只不过choosecombo是把选择细化成几个步骤。
通过lunch完成选择后输出如下信息：
============================================ PLATFORM_VERSION_CODENAME=REL PLATFORM_VERSION=2.3.5 TARGET_PRODUCT=zte_blade TARGET_BUILD_VARIANT=eng TARGET_SIMULATOR=false TARGET_BUILD_TYPE=release TARGET_BUILD_APPS= TARGET_ARCH=arm HOST_ARCH=x86 HOST_OS=linux HOST_BUILD_TYPE=release BUILD_ID=GINGERBREAD ============================================其中记录了本次编译的主要配置，此后可以通过printconfig命令显示。