[PATCH] Improve Android tracing instructions

Wed Apr 10 08:29:17 PDT 2013

Thanks. I don't use Android, so can't comment on the correctness of
the updated instructions, but given I heard no objection I'll commit
it.

That said, I'd prefer that _all_ Android instructions (including
non-Java) are the Android.markdown, otherwise a first reader might
miss the Android section in README.

Alternatively, if you prefer to only discuss Java apps as you have
now, then Android.markdown should be renamed to something less
abragent like Dalvik.markdown, Zygote.markdown, or something like
that.

Jose

On Fri, Apr 5, 2013 at 6:53 PM, Alexander Monakov <amonakov at ispras.ru> wrote:
> Tracing of Java applications on Android is quite different from tracing native
> executables, so move it to a separate file.
>
> Add instructions on using wrapping support that appeared in Android 4.0, which
> simplifies usage of apitrace on Android.
>
> Add a reference to adjust-child-env tool that allows to inject tracing library
> on Android without rebuilding and reflashing recovery image.
> ---
>  Android.markdown | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  README.markdown  | 65 +++------------------------------------------------
>  2 files changed, 74 insertions(+), 62 deletions(-)
>  create mode 100644 Android.markdown
>
> diff --git a/Android.markdown b/Android.markdown
> new file mode 100644
> index 0000000..0cbf4de
> --- /dev/null
> +++ b/Android.markdown
> @@ -0,0 +1,71 @@
> +Tracing Dalvik VM (Java) applications on Android
> +================================================
> +
> +Android's Java machine, DalvikVM, 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.
> diff --git a/README.markdown b/README.markdown
> index 5fa3ab9..eeaaee7 100644
> --- a/README.markdown
> +++ b/README.markdown
> @@ -151,68 +151,9 @@ To trace the application inside gdb, invoke gdb as:
>
>  ### Android ###
>
> -The following instructions should work at least for Android Ice Scream
> -Sandwitch.
> -
> -To trace applications started from within the Android VM process
> -(`app_process` aka zygote) you'll have to wrap this process and enable
> -tracing dynamically for the application to be traced.
> -
> -- Wrapping the android main VM process:
> -
> -  In the Android root /init.rc add the `LD_PRELOAD` setting to zygote's
> -  environment in the 'service zygote' section:
> -
> -        service zygote ...
> -           setenv LD_PRELOAD /data/egltrace.so
> -           ...
> -
> -  Note that ICS will overwrite the /init.rc during each boot with the
> -  version in the recovery image. So you'll have to change the file in
> -  your ICS source tree, rebuild and reflash the device.
> -  Rebuilding/reflashing only the recovery image should be sufficient.
> -
> -- Copy egltrace.so to /data
> -
> -  On the host:
> -
> -        adb push /path/to/apitrace/build/wrappers/egltrace.so /data
> -
> -- Adjust file permissions to store the trace file:
> -
> -  By default egltrace.so will store the trace in
> -  `/data/app_process.trace`. For this to work for applications running
> -  with a uid other than 0, you have to allow writes to the `/data`
> -  directory on the device:
> -
> -        chmod 0777 /data
> -
> -- Enable tracing for a specific process name:
> -
> -  To trace for example the Settings application:
> -
> -        setprop debug.apitrace.procname com.android.settings
> -
> -  In general this name will match what `ps` reports.
> -
> -- Start the application:
> -
> -  If the application was already running, for example due to ICS's way
> -  of pre-starting the apps, you might have to kill the application
> -  first:
> -
> -        kill <pid of app>
> -
> -  Launch the application for example from the application menu.
> -
> -To trace standalone applications do:
> -
> -    adb push /path/to/apitrace/build/wrappers/egltrace.so /data
> -    adb shell
> -    # cd /data/local/tmp
> -    # LD_PRELOAD=/data/egltrace.so test-opengl-gl2_basic
> -    adb pull /data/local/tmp/test-opengl-gl2_basic.trace
> -    apitrace replay test-opengl-gl2_basic.trace
> +To trace standalone native OpenGL ES applications, use
> +`LD_PRELOAD=/path/to/egltrace.so /path/to/application` like described in the
> +previous section.  To trace Java applications, refer to Android.markdown.
>
>  ### Mac OS X ###
>
> --
> 1.8.1.2
>
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