Create Systemtap's USDT probes at runtime
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README.md

libstapsdt

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libstapsdt is a library which allows creating and firing Systemtap's USDT probes at runtime. It's inspired on chrisa/libusdt. The goal of this library is to add USDT probes functionality to dynamic languages.

Table of Contents

How it works

Systemtap's USDT implementation allows only statically defined probes because they are set as ELF notes by the compiler. To create probes at runtime, libstapsdt takes advantage of shared libraries: it creates a small library with an ELF note and links it at runtime. This way, most existing tools will keep working as expected.

Dependencies

libstapsdt currently requires the following dependencies:

  • libelf (from elfutils)

Ubuntu 16.04

sudo apt install libelf1 libelf-dev

Install

To build and install libstapsdt, just run:

make
sudo make install
sudo ldconfig

Demo

There's a demo program available. To build it, run:

make demo  # Executable will be available at ./demo

Usage:

./demo PROVIDER_NAME PROBE_NAME

After running the demo program, it can be instrumented with proper tools.

Here's an example using eBPF/bcc trace tool (built from source):

sudo /usr/share/bcc/tools/trace -p $(pgrep demo) 'u::PROBE_NAME'

Run tests

To run tests, just run the command below. Please be aware that there are only a few tests for now, but more will be added in the future.

make test

Wrappers

Here is a list of wrappers for other languages:

Write your own wrapper

libstapsdt is written in C, which makes it very portable to almost any language. Most dynamic languages provide a way to wrap C code. Feel free to develop a wrapper in your language of choice. If you do, please let us know to update our wrappers list!