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tiallocsample

tiallocsample is a JVMTI agent designed to track the call stacks of allocations in the heap.

Usage

Build

m libtiallocsample

The libraries will be built for 32-bit, 64-bit, host and target. Below examples assume you want to use the 64-bit version.

Use libtiallocsamples if you wish to build a version without non-NDK dynamic dependencies.

Command Line

The agent is loaded using -agentpath like normal. It takes arguments in the following format:

`sample_rate,stack_depth_limit,log_path`

sample_rate is an integer specifying how frequently an event is reported. E.g., 10 means every tenth call to new will be logged.
stack_depth_limit is an integer that determines the number of frames the deepest stack trace can contain. It returns just the top portion if the limit is exceeded.
log_path is an absolute file path specifying where the log is to be written.

Output Format

The resulting file is a sequence of object allocations, with a limited form of text compression. For example a single stack frame might look like:

+0,jthread[main], jclass[[I file: <UNKNOWN_FILE>], size[24, hex: 0x18]
+1,main([Ljava/lang/String;)V
+2,run()V
+3,invoke(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;
+4,loop()V
+5,dispatchMessage(Landroid/os/Message;)V
+6,handleMessage(Landroid/os/Message;)V
+7,onDisplayChanged(I)V
+8,getState()I
+9,updateDisplayInfoLocked()V
+10,getDisplayInfo(I)Landroid/view/DisplayInfo;
+11,createFromParcel(Landroid/os/Parcel;)Ljava/lang/Object;
+12,createFromParcel(Landroid/os/Parcel;)Landroid/view/DisplayInfo;
+13,<init>(Landroid/os/Parcel;Landroid/view/DisplayInfo$1;)V
+14,<init>(Landroid/os/Parcel;)V
+15,readFromParcel(Landroid/os/Parcel;)V
=16,0;1;2;3;1;4;5;6;7;8;9;10;10;11;12;13;14;15
16

Lines starting with a + are key, value pairs. So, for instance, key 2 stands for

run()V

The line starting with 0 is the thread, type, and size (TTS) of an allocation. The remaining lines starting with + are stack frames (SFs), containing function signatures. Lines starting with = are stack traces (STs), and are again key, value pairs. In the example above, an ST called 16 is the TTS plus sequence of SFs. Any line not starting with + or = is a sample. It is a reference to an ST. Hence repeated samples are represented as just numbers.

ART

art -Xplugin:$ANDROID_HOST_OUT/lib64/libopenjdkjvmti.so '-agentpath:libtiallocsample.so=100' -cp tmp/java/helloworld.dex -Xint helloworld

-Xplugin and -agentpath need to be used, otherwise the agent will fail during init.
If using libartd.so, make sure to use the debug version of jvmti.

adb shell setenforce 0

adb push $ANDROID_PRODUCT_OUT/system/lib64/libtiallocsample.so /data/local/tmp/

adb shell am start-activity --attach-agent /data/local/tmp/libtiallocsample.so=100 some.debuggable.apps/.the.app.MainActivity

RI

java '-agentpath:libtiallocsample.so=MethodEntry' -cp tmp/helloworld/classes helloworld

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