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Android平台实现开机调试system_process

2014-07-25 15:57 309 查看

from:http://blog.csdn.net/i2cbus/article/details/21476401

1 首先要理清一下什么是system_process

1.1 system_process是我们在DDMS可以看到的名称。设置的地方在ActivityThread.java:

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private void attach(boolean system) {        sThreadLocal.set(this);        mSystemThread = system;        if (!system) {             ...        } else {            // Don't set application object here -- if the system crashes,            // we can't display an alert, we just want to die die die.            android.ddm.DdmHandleAppName.setAppName("system_process",                                                    UserHandle.myUserId());              ...          }          ...    }

来自CODE的代码片
ActivityThread.java

1.2 system_process不是进程的名称，它是DDM用于区别不同的Java App的标识，对于一般Android程序来说会被设置成包名

1.3 system_process的进程名称是system_server，就是我们通过ps可以看到的

1.4 system_server进程是zygote进程孵化的第一个Java进程

1.5 zygote进程的程序名称叫app_process。

它的代码在frameworks\base\cmds\app_process\app_main.cpp

在init.rc中可以看到它是怎样启动起来的：

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service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server    class main    socket zygote stream 660 root system    onrestart write /sys/android_power/request_state wake    onrestart write /sys/power/state on    onrestart restart media    onrestart restart netd

来自CODE的代码片
init.rc

1.6 system_server的启动过程如下：

在app_main.cpp的main函数中，有如下的代码：

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if (zygote) {        runtime.start("com.android.internal.os.ZygoteInit",                startSystemServer ? "start-system-server" : "");    }

来自CODE的代码片
app_main.cpp

runtime.start在正常情况下不会返回

在frameworks\base\core\java\com\android\internal\os\ZygoteInit.java的main中：

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if (argv[1].equals("start-system-server")) {                startSystemServer();            }

来自CODE的代码片
ZygoteInit.java

startSystemServer中：

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private static boolean startSystemServer()            throws MethodAndArgsCaller, RuntimeException {        /* Hardcoded command line to start the system server */        String args[] = {            "--setuid=1000",            "--setgid=1000",            "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,3001,3002,3003,3006,3007",            "--capabilities=130104352,130104352",            "--runtime-init",            "--nice-name=system_server",            "com.android.server.SystemServer",        };
ZygoteConnection.Arguments parsedArgs = null;
int pid;
try {            parsedArgs = new ZygoteConnection.Arguments(args);            ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);            ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);
/* Request to fork the system server process */            pid = Zygote.forkSystemServer(                    parsedArgs.uid, parsedArgs.gid,                    parsedArgs.gids,                    parsedArgs.debugFlags,                    null,                    parsedArgs.permittedCapabilities,                    parsedArgs.effectiveCapabilities);        } catch (IllegalArgumentException ex) {            throw new RuntimeException(ex);        }。。。}

来自CODE的代码片
startSystemServer.java

args中，有：--nice-name=system_server，这就是进程名system_server的由来

2 接下来我们来看看怎么去调试这个Android里Java层的最重要的进程，一般调试和开机调试

3 一般调试：

3.1 这种调试方法就是在Android启动完后，用adb连接Android，再调试system_process进程，实现起来是比较简单的，

3.2 无非就是在eclipse里创建一个名叫system_process的Android程序，然后在DDMS里选择system_process即可开始调试。

4 开机调试

4.1 有时我们需要调试一下system_process的初始化过程，因为上面的方法是在system_process已经初始化完之后开始调试的，用上面的方法是无能为力的，这就得另想办法。

4.2 搜索了下网络，没有找到比较实用的资源，于是自己研究了下。

4.3 其实也不是很麻烦：

找到SystemServer.java里的main函数，在函数的最开始加上几行代码：

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java.io.File f = new java.io.File("/system/debug");        if(f.exists()){            android.ddm.DdmHandleAppName.setAppName("system_process",                                                    UserHandle.myUserId());       android.os.Debug.waitForDebugger();        }

来自CODE的代码片
SysemServer.java

4.4 解析下：

首先通过判断/system/debug是否存在来判断是否要等待调试器连接

android.os.Debug.waitForDebugger()就是等待调试器来连接，在调试器连接上之前代码不会往下执行

但是第一行代码就比较费解了，先来解析下什么叫ddm,ddm就是Dalvik Debug Monitor的缩写

android.ddm.DdmHandleAppName.setAppName就是要设置Java App在ddm里的名称。

如果不设置的话，你在DDMS里看到的Name一栏就会有一个“？”，这个时候，eclipse找不到对应的工程，所以就没法调试了。

所以这一行代码很重要

4.5 接下来就是重新编译代码并烧录了，这个看自己使用的是什么平台。

4.6 呵呵，是不是可以开机后用adb连接,再通过eclipse调试了？

5 这种方式的唯一缺陷就是要修改源代码，这个留着以后再研究，现在要做的是好好享受一下这种调试方法。

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