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Tracing Dalvik VM (Java) applications on Android

Android's Java virtual machine, Dalvik, runs as a system service (started at bootup by init) and Java applications are run by forks of the initial resident process. Thus, injecting apitrace's tracing library is different from other operating systems.

The following discussion assumes that tracing library is copied to '/data':

adb push /path/to/apitrace/build/wrappers/egltrace.so /data

Tracing on Android 4.0 and newer

Starting from Android 4.0 (Ice Cream Sandwich) release, Dalvik supports running designated processes with wrappers, in which case a new Java VM is started with 'system()' library call for that process.

Obtain the process name of the application to be traced (the one reported in ps output, such as com.android.settings), and set two system properties:

PROCNAME=com.android.settings
adb shell setprop wrap.$PROCNAME LD_PRELOAD=/data/egltrace.so
adb shell setprop debug.apitrace.procname $PROCNAME

(the former is read by Dalvik and specifies wrapping prefix, the latter is read by apitrace itself and used in case apitrace is preloaded into Java VM globally to specify which process should be traced).

Make sure the process is not loaded before starting to trace it, for example use -S flag to am start:

adb shell am start -S $PROCNAME

Use adb logcat \*:S apitrace to examine apitrace debug output. Trace files are saved into '/data/' directory by default:

adb pull /data/$PROCNAME.trace
adb shell rm /data/$PROCNAME.trace

(you need to chmod 0777 /data beforehand).

Injecting tracing library globally

If LD_PRELOAD is supported (Android 2.3 "Gingerbread" and newer), it is possible to inject egltrace.so into the resident Java VM, in which case debug.apitrace.procname system propery is used to control for which process tracing will be active.

Restarting 'zygote' (Java VM) service is not straightforward, since '/init.rc' is read only once at system bootup, and restored from the recovery image on reboots. Thus, you either need to augment '/init.rc' in the recovery image with setenv LD_PRELOAD /data/egltrace.so in service zygote section, or you can use a tool such as adjust-child-env to restart the service with modified environment.

Put adjust-child-env and a script with the following contents into /data:

stop zygote
/data/adjust-child-env 1 /system/bin/app_process LD_PRELOAD=/data/egltrace.so &
sleep 1
start zygote

The scripts restarts the Java VM ('zygote') with modified environment.

Invoke the script with adb shell to prepare for tracing, and then follow the Android 4.0 directions.