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https://github.com/iovisor/ply

Dynamic Tracing in Linux
https://github.com/iovisor/ply

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Dynamic Tracing in Linux

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README 

        
ply

===



Documentation and language reference is available at

[wkz.github.io/ply][3].



A light-weight dynamic tracer for Linux that leverages the kernel's

BPF VM in concert with kprobes and tracepoints to attach probes to

arbitrary points in the kernel. Most tracers that generate BPF

bytecode are based on the LLVM based BCC toolchain. ply on the other

hand has no required external dependencies except for `libc`. In

addition to `x86_64`, ply also runs on `aarch64`, `arm`, `riscv64`,

`riscv32`, and `powerpc`. Adding support for more ISAs is easy.



`ply` follows the [Little Language][1] approach of yore, compiling ply

scripts into Linux [BPF][2] programs that are attached to kprobes and

tracepoints in the kernel. The scripts have a C-like syntax, heavily

inspired by `dtrace(1)` and, by extension, `awk(1)`.



The primary goals of `ply` are:



   * Expose most of the BPF tracing feature-set in such a way that new

     scripts can be whipped up very quickly to test different

     hypotheses.



   * Keep dependencies to a minimum. Right now Flex and Bison are

     required at build-time, leaving `libc` as the only runtime

     dependency. Thus, `ply` is well suited for embedded targets.



If you need more fine-grained control over the kernel/userspace

interaction in your tracing, checkout the [bcc][4] project which

compiles C programs to BPF using LLVM in combination with a python

userspace recipient to give you the full six degrees of freedom.



Examples

--------



Here are some one-liner examples to show the kinds of questions that

`ply` can help answer.



**What is the distribution of the returned sizes from `read(2)`s to the VFS?**

```

ply 'kretprobe:vfs_read { @["size"] = quantize(retval); }'

```



**Which processes are receiving errors when reading from the VFS?**

```

ply 'kretprobe:vfs_read if (retval < 0) { @[pid, comm, retval] = count(); }'

```



**Which files are being opened, by who?**

```

ply 'kprobe:do_sys_open { printf("%v(%v): %s\n", comm, uid, str(arg1)); }'

```



**When sending packets, where are we coming from?**

```

ply 'kprobe:dev_queue_xmit { @[stack] = count(); }'

```



**From which hosts and ports are we receiving TCP resets?**

```

ply 'tracepoint:tcp/tcp_receive_reset {

	printf("saddr:%v port:%v->%v\n",

		data->saddr, data->sport, data->dport);

}'

```



Build and Installation

----------------------



`ply` uses GNU's autotools as its build system. When building from

a Git clone, use the following steps:



```

./autogen.sh   # to generate the configure script

./configure

make

make install   # you probably need to be root for this

```



Contributing

------------



Contributions are welcome! To help you on your way, the [test/](test/)

directory contains ready-made infrastructure to:



- Test cross-compilation on all supported architectures.

- Run a simple test suite on a range of machines using QEMU system

  emulation.

- Run interactive sessions on QEMU machines.



A GitHub Action is setup to run these jobs. Please make sure to test

your changes locally before opening a PR to avoid unnecessary review

cycles.



Maintainers

-----------



`ply` is developed and maintained by [Tobias Waldekranz][5]. Please

direct all bug reports and pull requests towards the official

[Github][6] repo.



[1]: http://c2.com/cgi/wiki?LittleLanguage

[2]: https://www.kernel.org/doc/Documentation/networking/filter.txt

[3]: https://wkz.github.io/ply

[4]: https://github.com/iovisor/bcc

[5]: mailto://[email protected]

[6]: https://github.com/iovisor/ply