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A library for ptrace-based tracing of Python programs

Home Page: https://ptracer.readthedocs.io/

License: Apache License 2.0

Python 94.73% C 5.27%

python ptrace syscalls

ptracer's Introduction

ptracer -- a library for ptrace-based tracing of Python programs

Ptracer is a library providing on-demand system call tracing in Python programs.

Basic Usage

import traceback
import ptracer

def callback(syscall):
    print('{}({}) -> {}'.format(
        syscall.name,
        ', '.join(repr(arg.value) for arg in syscall.args),
        syscall.result.text))
    print('Traceback: ')
    print(''.join(traceback.format_list(syscall.traceback)))

with ptracer.context(callback):
    open('/dev/null', 'wb')

Filtering

Ptracer allows elaborate syscall filtering via the filter argument:

flt = [
    ptracer.SysCallPattern(
        name='open',
        args=[
            re.compile(b'/tmp/.*'),
            lambda arg: arg.value & os.O_WRONLY
        ],
        result=lambda res: res.value > 0
    )
]

with ptracer.context(callback, filter=flt):
    # traced code
    ...

In the above example, ptracer will invoke the callback only for successful attempts to open files in the "/tmp" directory for writing.

Documentation

The documentation is available on ptracer.readthedocs.io.

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ptracer's Issues

ImportError: .../_lltraceback.cpython-38-x86_64-linux-gnu.so: undefined symbol: _PyThreadState_GetFrame

Hello,

I am not sure, if this repository is actively maintained, because the last changes are some time ago.

I tried to use ptracer and installed it in a Python 3.8 environment.
The import failed in Python 3.8:

>>> import ptracer
...
ImportError: .../ptracer/_lltraceback.cpython-38-x86_64-linux-gnu.so: undefined symbol: _PyThreadState_GetFrame

Then I tried it in an older environment with Python 3.6 on another computer and ptracer worked.

I found https://bugs.python.org/issue39946 and from the comments there, it looks like _PyThreadState_GetFrame was removed in Python 3.7.

Fix thread-safety (or document its absence)

Because ptracer uses a context manager, it's easy to use it in a multi-threaded context where the context can be entered and exited from multiple threads concurrently. However it seems to deal rather badly with doing that: because ptracer.context works with an unprotected global (_context), that object can be in a completely inconsistent state because there's a TOCTOU bug on self.enabled.

An easy fix would be to replace enabled with a regular lock (and acquire it in non-blocking, raising if it was not acquired).

It would be nice if ptracer could handle the situation better by having each context "subscribe" to the tracing process, but the asynchronous nature of the reporting likely makes that complicated.

TypeError: cannot use a bytes pattern on a string-like object

The following snippet crashes with the above error when it comes across a system call that passes the filter.

import traceback
import ptracer
import re
import os

def callback(syscall):
    print(syscall.name, syscall.result.raw_value)

flt = [
    ptracer.SysCallPattern(
        name='openat',
        args=[
            re.compile(b'/tmp/.*'),
            lambda arg: arg.value & os.O_WRONLY
        ],
        result=lambda res: res.value > 0
    )
]

with ptracer.context(callback, filter=flt):
    open('/tmp/domf', mode='w')

Here's the error stack.

$ py a.py 
Traceback (most recent call last):
  File "/home/shubham/workspace/tracer/a.py", line 21, in <module>
    open('/tmp/domf', mode='w')
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/__init__.py", line 106, in __exit__
    _context.disable()
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/__init__.py", line 92, in disable
    raise error
ptracer._ptracer.PtracerError: Unhandled exception in ptrace process
Traceback (most recent call last):
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_ptracer.py", line 276, in _debugger_thread
    _debugger_thread_inner(main_pid, dbgproc_started, dbgthread_stop,
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_ptracer.py", line 405, in _debugger_thread_inner
    elif filter_ is None or filter_(syscall):
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_ptracer.py", line 294, in <lambda>
    filter_ = lambda sc: any(m.match(sc) for m in syscall_filter)
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_ptracer.py", line 294, in <genexpr>
    filter_ = lambda sc: any(m.match(sc) for m in syscall_filter)
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_syscall.py", line 52, in match
    return all(m[1](m[0](syscall)) for m in self.matcher)
  File "/home/shubham/workspace/tracer/venv/lib/python3.9/site-packages/ptracer/_syscall.py", line 52, in <genexpr>
    return all(m[1](m[0](syscall)) for m in self.matcher)
TypeError: cannot use a bytes pattern on a string-like object

pinterest / ptracer Goto Github PK

ptracer's Introduction

ptracer -- a library for ptrace-based tracing of Python programs

Basic Usage

Filtering

Documentation

ptracer's People

Contributors

Stargazers

Watchers

Forkers

ptracer's Issues

ImportError: .../_lltraceback.cpython-38-x86_64-linux-gnu.so: undefined symbol: _PyThreadState_GetFrame

Fix thread-safety (or document its absence)

TypeError: cannot use a bytes pattern on a string-like object

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