Getting building and profiling Firefox for Android or GeckoView_example is relatively easy if you know how, so here's my quickstart guide.
See also, the official GeckoView documentation.
First, ensure you run ./mach boostrap, and select "4. GeckoView/Firefox for Android".
Here's the mozconfig I'm using (Ubuntu 18.04):
# With the following compiler toolchain:
export CC="/home/chris/.mozbuild/clang/bin/clang -fcolor-diagnostics"
export CXX="/home/chris/.mozbuild/clang/bin/clang++ -fcolor-diagnostics"
mk_add_options 'export RUSTC_WRAPPER=sccache'
# Build GeckoView/Firefox for Android:
# Work around issues with mozbuild not finding the exact JDK that works.
# See also https://bugzilla.mozilla.org/show_bug.cgi?id=1451447#c7
# With the following Android NDK:
A noteworthy item in there is "--with-java-bin-path". I've had trouble on Ubuntu with the system default Java not being the right version. This helps.
Note that if you're profiling, you really want to be doing a release build. The behaviour of release is different from an optimized build.
If you're debuging, you probably need --enable-debug. For details of how to debug, see GeckoView Debugging Native Code in Android Studio.
To build, package, and install Firefox for Android (Fennec) on your Android device, run:
./mach build && ./mach package && ./mach install
Note that you need to do the package step after every build. Once you've installed, you can start Firefox on a given URL with:
./mach run --url https://www.youtube.com/watch?v=dQw4w9WgXcQ
For testing and profiling GeckoView, the easiest option is to run the GeckoView_example app. To build and install this, run:
./mach build && ./mach package && ./mach android build-geckoview_example && ./mach android install-geckoview_example
To run GeckoView_example, opening a URL:
adb shell am start -a android.intent.action.MAIN -c android.intent.category.LAUNCHER -n org.mozilla.geckoview_example/org.mozilla.geckoview_example.GeckoViewActivity -d 'https://www.youtube.com/watch?v=dQw4w9WgXcQ'
If you want to set environment variables, for example to turn on MOZ_LOGs, run like so:
adb shell am start -a android.intent.action.MAIN -c android.intent.category.LAUNCHER -n org.mozilla.geckoview_example/org.mozilla.geckoview_example.GeckoViewActivity -d 'https://www.youtube.com/watch?v=dQw4w9WgXcQ' --es env0 MOZ_LOG=MediaSource:5
Note if you want to create more than one environment variable, each one needs to be numberd, i.e. `--es env0 FOO=BAR env1 BAZ=FUZ`, and so on. Also note that you do not put quotes around environment variables here. That is, use `--es env0 FOO=BAR`, do not use `--es env0 FOO="BAR"`.
MOZ_LOGs go to adb logcat. To setup an output stream that reads specific MOZ_LOGs:
adb logcat | grep MediaSource
This stays open, printing logs until you terminate with CTRL+C. If you want to exit at the end of the logs buffered, pass -d. i.e.:
adb logcat -d > log_file.txt
Apparently you can pass a logtag filterspec to `adb logcat` to have it filter for you, but I never figured the syntax out.
To clear logcat's buffered logs:
adb logcat --clear
This is useful if you're prinf-debugging something via logcat, and want to clear the decks before each run.
Other useful commands...
To terminate a running GeckoView_example:
adb shell am force-stop org.mozilla.geckoview_example
To list all packages on your device related to Mozilla:
adb shell pm list packages mozilla
To uninstall a GeckoView_example:
adb uninstall org.mozilla.geckoview_example && adb uninstall org.mozilla.geckoview_example.test
Note that this also uninstalls the GeckoView test app. Sometimes you may find you need to uninstall both apps before you can re-install. I think this is related to different versions of adb interacting.
To get the Android version on your device:
adb shell getprop ro.build.version.release
To simulate typing text:
adb shell input text "your text"
To profile a GeckoView_example session, you need to download the latest Firefox Desktop Nightly build, and install the Firefox Profiler add-on. Note that the Firefox Profiler Documentation is pretty good, so I'll only cover the highlights.
Once you've got Firefox Desktop Nightly and the Firefox Profiler add-on installed, start up your GeckoView_example app and URL you want to profile, and in Firefox Nightly Desktop open about:debugging. Click "Connect" to attach to the device you want to profile on, and then click "Profile Performance".
If you're profiling media playback, you want to add "Media" to the custom thread names under the "Threads" settings.
Since you're profiling a local build, you want to open the "Local build" settings, and ensure you add the path to your object directory.
Once you're configured, press "Start recording", do the thing in GeckoView_example you're profiling, and then hit "Stop and grab the recording".
The profile will open in a new tab in the browser. Sometimes I've noticed that the profiler hangs at "Waiting for symbol tables for library libxul.so". Just reloading the page seems to resovle this normally.
I find the Firefox Profiler very straightforward to use. The Flame Graph view can be particularly enlightening to see where threads are spending time.
Unfortunately the Firefox profiler can't symbollocate Java call stacks. Java calls usually show up as hex addresses, sometimes on the far side of an AndroidBridge C++ call.