When debugging and profiling apps with native code, it’s often useful to use debugging tools that need to be enabled at process startup. This requires that you run your app in a fresh process rather than cloning from the zygote. Examples include:
- Tracing system calls with strace.
- Finding memory bugs with malloc debug or Address Sanitizer (ASan).
- Profiling with Simpleperf.
Using the wrap shell script
wrap.sh is easy:
- Compile a custom debuggable APK that packages the following:
- Install the debuggable APK on a device.
- Launch the app.
Creating the wrap shell script
When you launch a debuggable APK that contains
wrap.sh, the system executes
the script and passes the command to start the app as arguments. The script is
responsible for starting the app, but can make any environment or argument
changes. The script should follow
MirBSD Korn shell (mksh) syntax.
The following snippet shows how to write a simple
wrap.sh file that just
starts the app:
#!/system/bin/sh exec "$@"
wrap.sh, you would include the following line:
#!/system/bin/sh LIBC_DEBUG_MALLOC_OPTIONS=backtrace logwrapper "$@"
There's an example of how to do this for ASan in the ASan documentation.
To take advantage of
wrap.sh, your APK must be debuggable. Make sure that the
android:debuggable=”true”setting is configured in the
element in your Android manifest.
It's also necessary to set
This is the default, but if you explicitly set it to
script will not work.
You must package the
wrap.sh script with the native libraries of the app. If
your app does not contain native libraries, add the lib directory manually to
your project directory. For each architecture that your app supports, you must
provide a copy of the wrap shell script under that native library directory.
The following example shows the file layout to support both the ARMv8 and x86-64 architectures:
# App Directory |- AndroidManifest.xml |- … |- lib |- arm64-v8a |- ... |- wrap.sh |- x86_64 |- ... |- wrap.sh
Android Studio only packages
.so files from the
lib/ directories, so if
you're an Android Studio user, you'll need to place your
wrap.sh files in the
src/main/resources/lib/* directories instead, so that they'll be packaged
resources/lib/x86 will be displayed in the UI as
lib.x86, but it should actually be a subdirectory:
Debugging when using wrap.sh
If you want to attach a debugger when using
wrap.sh, your shell script will
need to manually enable debugging. How to do this has varied between releases,
so this example shows how to add the appropriate options for all releases that
#!/system/bin/sh cmd=$1 shift os_version=$(getprop ro.build.version.sdk) if [ "$os_version" -eq "27" ]; then cmd="$cmd -Xrunjdwp:transport=dt_android_adb,suspend=n,server=y -Xcompiler-option --debuggable $@" elif [ "$os_version" -eq "28" ]; then cmd="$cmd -XjdwpProvider:adbconnection -XjdwpOptions:suspend=n,server=y -Xcompiler-option --debuggable $@" else cmd="$cmd -XjdwpProvider:adbconnection $@" fi exec $cmd