在平台源码中找到需要的以下文件：
build/target/product/security/platform.pk8
build/target/product/security/platform.x509.pem
prebuilts/sdk/tools/lib/signapk.jar
在windows命令行运行命令：
java -jar signapk.jar platform.x509.pem platform.pk8 xxx.apk xxx_sign.apk