Rename Android.markdown to Dalvik.markdown.

[apitrace] / Dalvik.markdown

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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](https://github.com/amonakov/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.