libdumpcoverage.so is a JVMTI agent designed to dump coverage information for a process, where the binaries have been instrumented by JaCoCo. JaCoCo automatically starts recording data on process start, and we need a way to trigger the resetting or dumping of this data.
The JVMTI agent is used to make the calls to JaCoCo in its process.
Note that these examples assume you have an instrumented build (userdebug_coverage). Here is, for example, how to dump coverage information regarding the default clock app. First some setup is necessary:
adb root # necessary to copy files in/out of the /data/data/{package} folder
adb shell 'mkdir /data/data/com.android.deskclock/folder-to-use'
Then we can run the command to dump the data:
adb shell 'am attach-agent com.android.deskclock /system/lib/libdumpcoverage.so=dump:/data/data/com.android.deskclock/folder-to-use'
We can also reset the coverage information with
adb shell 'am attach-agent com.android.deskclock /system/lib/libdumpcoverage.so=reset'
then perform more actions, then dump the data again. To get the files, we can get
adb pull /data/data/com.android.deskclock/folder-to-use ~/path-on-your-computer
And you should have timestamped .exec files on your machine under the folder ~/path-on-your-computer
In dump mode, the agent makes JNI calls equivalent to
Agent.getInstance().getExecutionData(/*reset = */ false);
and then saves the result to a file specified by the passed in directory
In reset mode, it makes a JNI call equivalent to
Agent.getInstance().reset();