In this post I want to try and find out more stuff about theAndroid software framework initialises. Ipreviouslylooked a little bit at the boot process. Now I really want to get abetter idea of what is actually happening with the system runtime.
The important processes in the system appear to be zygote(which is theapp_process binary), and runtime.These are both started up by theinit process. The followingfragment of init.rc is relevant. It is important to note thatthese services have theautostart 1 attribute, indicating theyare restarted if they quit.
zygote {
exec /system/bin/app_process
args {
0 -Xzygote
1 /system/bin
2 --zygote
}
autostart 1
}
runtime {
exec /system/bin/runtime
autostart 1
}
If we go and kill either the zygote, orruntime process something interesting happens. Firstlythe other process seems to kill itself, and then the whole systemseems to restart.
Changing the ramdisk image
I want to get a bit more control of what things are starting up when.To do this I need to modify theinit.rc file. To do thisI first extracted the the ramdisk to the fileystem so that I can modifyit (gnucpio -iz -F ramdisk.img).
After this I simply commented out the line from init.rc. Thenwe can recreate it: (gnucpio -i -t -F ../ramdisk.img | gnucpio -o -H newc -O ../rootfs.img).
Note if you are using Mac OS X, you will need to download and installgnucpio, becuase the built-in cpio doesn't supportnewc.
We can then use the emulator -ramdisk option to loadour new ramdisk.
Manual startup
Now we can start things up manually. First we start up the zygote process.As # app_process -Xzygote /system/bin --zygote. When we do that thereis no output either on the console, or on the LCD. Next we start the runtime process( # runtime), and now things start to happen!
Once both processes start we get the cylon image, and we also end upwith some console output:
Prepping: /system/app/AlarmProvider.apk:/system/app/Browser.apk:/system/app/Ca lendar.apk:/system/app/Camera.apk:/system/app/Contacts.apk:/system/app/Developm ent.apk:/system/app/GDataFeedsProvider.apk:/system/app/Gmail.apk:/system/app/Gm ailProvider.apk:/system/app/GoogleApps.apk:/system/app/GoogleAppsProvider.apk:/ system/app/Home.apk:/system/app/ImProvider.apk:/system/app/Maps.apk:/system/app /MediaPickerActivity.apk:/system/app/MediaProvider.apk:/system/app/Phone.apk:/s ystem/app/PimProvider.apk:/system/app/ApiDemos.apk:/system/app/SettingsProvider .apk:/system/app/Sms.apk:/system/app/SyncProvider.apk:/system/app/TelephonyProv ider.apk:/system/app/XmppService.apk:/system/app/YouTube.apk File not found: /system/app/AlarmProvider.apk File not found: /system/app/Calendar.apk File not found: /system/app/Camera.apk File not found: /system/app/GDataFeedsProvider.apk File not found: /system/app/Gmail.apk File not found: /system/app/GmailProvider.apk File not found: /system/app/MediaPickerActivity.apk File not found: /system/app/PimProvider.apk File not found: /system/app/ApiDemos.apk File not found: /system/app/Sms.apk File not found: /system/app/SyncProvider.apk File not found: /system/app/YouTube.apk Prep complete
It might give some clue of which Google applications will be available in the future. :)
The output from runtime looks like this:
+++ post-zygote
There is also some interesting output from the kernel. Inparticular the binder_open log. We can look at these inmore detail later.
binder_open(c086f300 c0832160) (pid 462) got c5cea000 binder_open(c086f300 c095ec40) (pid 475) got c4e8b000 binder_open(c086f300 c095ef40) (pid 476) got c46f8000 android_power: auto off timeout set to 604800 seconds Descriptor2Node failed secondary: desc=4, max=32, node=c4e8c350, weak=0 binder_open(c086f300 c4008d60) (pid 513) got c473a000 binder_open(c086f300 c4008760) (pid 512) got c39fc000 binder_open(c086f300 c4008260) (pid 531) got c35e3000
That is about enough detail for this entry, next time I'll be usingstrace to try and get a bit more information about theseprocesses.