PYTHON-PTRACE(1)

python-ptrace

PYTHON-PTRACE(1)

NAME

python-ptrace - python-ptrace Documentation No Maintenance Intended

This project is no longer maintained and is looking for a new maintainer.

python-ptrace is a debugger using ptrace (Linux, BSD and Darwin system call to trace processes) written in Python.

python-ptrace documentation
python-ptrace at GitHub
python-ptrace at the Python Cheeseshop (PyPI)

python-ptrace is an opensource project written in Python under GNU GPLv2 license. It supports Python 3.6 and newer.

FEATURES

High level Python object API : PtraceDebugger and PtraceProcess
Able to control multiple processes: catch fork events on Linux
Read/write bytes to arbitrary address: take care of memory alignment and split bytes to cpu word
Execution step by step using ptrace_singlestep() or hardware interruption 3
Can use distorm disassembler
Dump registers, memory mappings, stack, etc.
Syscall tracer and parser (strace.py command)

Status:

Supported operating systems: Linux, FreeBSD, OpenBSD
Supported architectures: x86, x86_64 (Linux), PPC (Linux), ARM (Linux EAPI)

Missing features:

Symbols: it's not possible to break on a function or read a variable value
No C language support: debugger shows assembler code, not your C (C++ or other language) code!
No thread support

Install python-ptrace

python-ptrace supports Python 3.6 and newer.

Linux packages

Debian: python-ptrace Debian package.
Mandriva: python-ptrace Mandriva package
OpenEmbedded: python-ptrace recipe
Arch Linux: python-ptrace Arch Linux package
Gentoo: dev-python/python-ptrace

See also python-ptrace on Python Package Index (PyPI)

Install from source

Download tarball

Get the latest tarball at the Python Package Index (PyPI).

Download development version

Download the development version using Git:

git clone https://github.com/vstinner/python-ptrace.git

Browse python-ptrace source code.

Option dependency

•: distorm disassembler (optional) http://www.ragestorm.net/distorm/

Installation

Note: pip is strongly recommanded.

Type as root:

python3 setup.py install

Or using sudo program:

sudo python3 setup.py install

cptrace

For faster debug and to avoid ctypes, you can also install cptrace: Python binding of the ptrace() function written in C:

python3 setup_cptrace.py install

Run tests

Run tests with tox

To run all tests, just type:

tox

The tox project creates a clean virtual environment to run tests.

Run tests manually

Type:

python3 runtests.py
python3 test_doc.py

It's also possible to run a specific test:

PYTHONPATH=$PWD python3 tests/test_strace.py

python-ptrace usage

Hello World

Short example attaching a running process. It gets the instruction pointer, executes a single step, and gets the new instruction pointer:

import ptrace.debugger
import signal
import subprocess
import sys
def debugger_example(pid):
    debugger = ptrace.debugger.PtraceDebugger()
    print("Attach the running process %s" % pid)
    process = debugger.addProcess(pid, False)
    # process is a PtraceProcess instance
    print("IP before: %#x" % process.getInstrPointer())
    print("Execute a single step")
    process.singleStep()
    # singleStep() gives back control to the process. We have to wait
    # until the process is trapped again to retrieve the control on the
    # process.
    process.waitSignals(signal.SIGTRAP)
    print("IP after: %#x" % process.getInstrPointer())
    process.detach()
    debugger.quit()
def main():
    args = [sys.executable, '-c', 'import time; time.sleep(60)']
    child_popen = subprocess.Popen(args)
    debugger_example(child_popen.pid)
    child_popen.kill()
    child_popen.wait()
if __name__ == "__main__":
    main()

API

PtraceProcess

The PtraceProcess class is an helper to manipulate a traced process.

Example:

tracer = PtraceProcess(pid)              # attach the process
tracer.singleStep()                      # execute one instruction
tracer.cont()                            # continue execution
tracer.syscall()                         # break at next syscall
tracer.detach()                          # detach process
# Get status
tracer.getreg('al')                      # get AL register value
regs = tracer.getregs()                  # read all registers
bytes = tracer.readBytes(regs.ax, 10)    # read 10 bytes
tracer.dumpCode()                        # dump code (as assembler or hexa is the disassembler is missing)
tracer.dumpStack()                       # dump stack (memory words around ESP)
# Modify the process
shellcode = '...'
ip = tracer.getInstrPointer()            # get EIP/RIP register
bytes = tracer.writeBytes(ip, shellcode) # write some bytes
tracer.setreg('ebx', 0)                  # set EBX register value to zero

Read ptrace/debugger/process.py source code to see more methods.

Trace system calls (syscalls)

python-ptrace can trace system calls using PTRACE_SYSCALL.

PtraceSyscall

ptrace.syscall module contains PtraceSyscall class: it's a parser of Linux syscalls similar to strace program.

Example:

connect(5, <sockaddr_in sin_family=AF_INET, sin_port=53, sin_addr=212.27.54.252>, 28) = 0
open('/usr/lib/i686/cmov/libcrypto.so.0.9.8', 0, 0 <read only>) = 4
mmap2(0xb7e87000, 81920, 3, 2066, 4, 297) = 0xb7e87000
rt_sigaction(SIGWINCH, 0xbfb7d4a8, 0xbfb7d41c, 8) = 0

You can get more information: result type, value address, argument types, and argument names.

Examples:

long open(const char* filename='/usr/lib/i686/cmov/libcrypto.so.0.9.8' at 0xb7efc027, int flags=0, int mode=0 <read only>) = 4
long fstat64(unsigned long fd=4, struct stat* buf=0xbfa46e2c) = 0
long set_robust_list(struct robust_list_head* head=0xb7be5710, size_t len_ptr=12) = 0

strace.py

Program strace.py is very close to strace program: display syscalls of a program. Example:

Features

Nice output of signal: see [[signal|python-ptrace signal handling]]
Supports multiple processes
Can trace running process
Can display arguments name, type and address
Option --filename to show only syscall using file names
Option --socketcall to show only syscall related to network (socket usage)
Option --syscalls to list all known syscalls

Example

$ ./strace.py /bin/ls
execve(/bin/ls, [['/bin/ls'],|[/* 40 vars */]]) = 756
brk(0)                                   = 0x0805c000
access('/etc/ld.so.nohwcap', 0)          = -2 (No such file or directory)
mmap2(NULL, 8192, 3, 34, -1, 0)          = 0xb7f56000
access('/etc/ld.so.preload', 4)          = -2 (No such file or directory)
(...)
close(1)                                 = 0
munmap(0xb7c5c000, 4096)                 = 0
exit_group(0)
---done---

Options

The program has many options. Example with --socketcall (display only network functions):

$ ./strace.py --socketcall nc localhost 8080
execve(/bin/nc, [['/bin/nc',|'localhost', '8080']], [[/*|40 vars */]]) = 12948
socket(AF_FILE, SOCK_STREAM, 0)          = 3
connect(3, <sockaddr_un sun_family=AF_FILE, sun_path=/var/run/nscd/socket>, 110) = -2 (No such file or directory)
socket(AF_FILE, SOCK_STREAM, 0)          = 3
connect(3, <sockaddr_un sun_family=AF_FILE, sun_path=/var/run/nscd/socket>, 110) = -2 (No such file or directory)
socket(AF_INET, SOCK_STREAM, 6)          = 3
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, 3217455272L, 4) = 0
connect(3, <sockaddr_in sin_family=AF_INET, sin_port=8080, sin_addr=127.0.0.1>, 16) = -111 (Connection refused)
(...)

gdb.py

gdb.py is a command line debugger similar to gdb, but with fewer features: no symbol support, no C language support, no thread support, etc.

Some commands

cont: continue execution
stepi: execute one instruction
step: execute one instruction, but don't enter into calls

Type help to list all available commands.

Features

•: print command displays value as decimal and hexadecimal, but also the related memory mapping (if any):

(gdb) print $eip
Decimal: 3086383120
Hexadecimal: 0xb7f67810
Address is part of mapping: 0xb7f67000-0xb7f81000 => /lib/ld-2.6.1.so (r-xp)

Nice output of signal: see [[signal|python-ptrace signal handling]]
Syscall tracer with command "sys": see python-ptrace system call tracer <syscall>. Short example:

(gdb) sys
long access(char* filename='/etc/ld.so.nohwcap' at 0xb7f7f35b, int mode=F_OK) = -2 (No such file or directory)

•: Supports multiple processes:

(gdb) proclist
<PtraceProcess #24187> (active)
<PtraceProcess #24188>
(gdb) proc
Process ID: 24187 (parent: 24182)
Process state: T (traced)
Process command line: [['tests/fork_execve']
(...)
(gdb)|switch; proc
Switch to <PtraceProcess #24188>
Process ID: 24188 (parent: 24187)
Process state: T (traced)
Process command line: ['/bin/ls']]
(...)

•: Allow multiple commands on the same line using ";" separator:

(gdb) print $eax; set $ax=0xdead; print $eax
Decimal: 0
Hexadecimal: 0x00000000
Set $ax to 57005
Decimal: 57005
Hexadecimal: 0x0000dead

Only written in pure Python code, so it's easy to extend
Expression parser supports all arithmetic operator (a+b, a/b, a<<b, a&b, ...), parenthesis, use of registers, etc. and pointer dereference (ex: print *($ebx+0xc)).

Screenshot

$ ./gdb.py ls
execve(/bin/ls, [['/bin/ls'],|[/* 40 vars */]]) = 16182
(gdb) where
ASM 0xb7f47810: MOV EAX, ESP <==
ASM 0xb7f47812: CALL 0xb7f47a60
ASM 0xb7f47817: MOV EDI, EAX
ASM 0xb7f47819: CALL 0xb7f47800
(gdb) regs
     EBX = 0xb7f4781e
     ECX = 0x0001d2f4
     EDX = 0xb7f61ff4
     ESI = 0x00000000
     (...)
(gdb) proc
Process ID: 16182
Process command line: [['/bin/ls']
Process|environment: ['TERM=xterm', 'SHELL=/bin/bash', (...)]]
Process working directory: /home/vstinner/prog/fusil/ptrace/trunk
(gdb) stack
STACK: 0xbfc58000..0xbfc6e000
STACK -8: 0x00000000
STACK -4: 0xb7f4781e
STACK +0: 0x00000001
STACK +4: 0xbfc6c6bb
STACK +8: 0x00000000
(gdb) maps
MAPS: 08048000-0805b000 r-xp 00000000 08:03 2588939    /bin/ls
MAPS: 0805b000-0805c000 rw-p 00012000 08:03 2588939    /bin/ls
(...)
MAPS: b7f61000-b7f63000 rw-p 00019000 08:03 1540553    /lib/ld-2.6.1.so
MAPS: bfc58000-bfc6e000 rw-p bfc58000 00:00 0          [[stack]
MAPS:|ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]]
(gdb) quit
Quit.
Terminate <PtraceProcess pid=16182>
Quit gdb.

python-ptrace process events

Process events

All process events are based on ProcessEvent class.

ProcessExit: process exited with an exitcode, killed by a signal or exited abnormally
ProcessSignal: process received a signal
NewProcessEvent: new process created, e.g. after a fork() syscall

Attributes:

All events have a "process" attribute
ProcessExit has "exitcode" and "signum" attributes (both can be None)
ProcessSignal has "signum" and "name" attributes

For NewProcessEvent, use process.parent attribute to get the parent process.

Note: ProcessSignal has a display() method to display its content. Use it just after receiving the message because it reads process memory to analyze the reasons why the signal was sent.

Wait for any process event

The most generic function is waitProcessEvent(): it waits for any process event (exit, signal or new process):

event = debugger.waitProcessEvent()

To wait one or more signals, use waitSignals() methods. With no argument, it waits for any signal. Events different than signal are raised as Python exception. Examples:

signal = debugger.waitSignals()
signal = debugger.waitSignals(SIGTRAP)
signal = debugger.waitSignals(SIGINT, SIGTERM)

Note: signal is a ProcessSignal object, use signal.signum to get the signal number.

Wait for a specific process events

To wait any event from a process, use waitEvent() method:

event = process.waitEvent()

To wait one or more signals, use waitSignals() method. With no argument, it waits for any signal. Other process events are raised as Python exception. Examples:

signal = process.waitSignals()
signal = process.waitSignals(SIGTRAP)
signal = process.waitSignals(SIGINT, SIGTERM)

Note: As debugger.waitSignals(), signal is a ProcessSignal object.

python-ptrace signal handling

Introduction

PtraceSignal tries to display useful information when a signal is received. Depending on the signal number, it shows different information.

It uses the current instruction decoded as assembler code to understand why the signal is raised.

Only Intel x86 (i386, maybe x86_64) is supported now.

When a process receives a signal, python-ptrace tries to explain why the signal was emitted.

General information (not shown for all signals, e.g. not for SIGABRT):

CPU instruction causing the crash
CPU registers related to the crash
Memory mappings of the memory addresses

Categorize signals:

•: SIGFPE

•: Division by zero

•: SIGSEGV, SIGBUS

Invalid memory read
Invalid memory write
Stack overflow
Invalid memory access

•: SIGABRT

•: Program abort

•: SIGCHLD

•: Child process exit

Examples

Division by zero (SIGFPE)

Signal: SIGFPE
Division by zero
- instruction: IDIV DWORD [[EBP-0x8]
- register ebp=0xbfdc4a98

Invalid memory read/write (SIGSEGV)

Signal: SIGSEGV
Invalid read from 0x00000008
- instruction: MOV EAX, [EAX+0x8]]
- mapping: 0x00000008 is not mapped in memory
- register eax=0x00000000

PID: 23766
Signal: SIGSEGV
Invalid write to 0x00000008 (size=4 bytes)
- instruction: MOV DWORD [[EAX+0x8],|0x2a
- mapping: 0x00000008..0x0000000b is not mapped in memory
- register eax=0x00000000

Given information:

Address of the segmentation fault
(if possible) Size of the invalid memory read/write
CPU instruction causing the crash
CPU registers related to the crash
Memory mappings of the related memory address

Stack overflow (SIGSEGV)

Signal: SIGSEGV
STACK OVERFLOW! Stack pointer is in 0xbf534000-0xbfd34000 => [stack]] (rw-p)
- instruction: MOV BYTE [[EBP-0x1004],|0x0
- mapping: 0xbf533430 is not mapped in memory
- register <stack ptr>=0xbf533430
- register ebp=0xbf534448

Child exit (SIGCHLD)

PID: 24008
Signal: SIGCHLD
Child process 24009 exited normally
Signal sent by user 1000

Information:

Child process identifier
Child process user identifier

Examples

Invalid read:

Signal: SIGSEGV
Invalid read from 0x00000008
- instruction: MOV EAX, [EAX+0x8]
- mapping: (no memory mapping)
- register eax=0x00000000

Invalid write (MOV):

Signal: SIGSEGV
Invalid write to 0x00000008 (size=4 bytes)
- instruction: MOV DWORD [EAX+0x8], 0x2a
- mapping: (no memory mapping)
- register eax=0x00000000

abort():

Signal: SIGABRT
Program received signal SIGABRT, Aborted.

Source code

See:

ptrace/debugger/ptrace_signal.py
ptrace/debugger/signal_reason.py

cptrace Python module

Python binding for ptrace written in C.

Example

Dummy example:

>>> import cptrace
>>> cptrace.ptrace(1, 1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: ptrace(request=1, pid=1, 0x(nil), 0x(nil)) error #1: Operation not permitted

Authors

Contributors

Anthony Gelibert <anthony.gelibert AT me.com> - fix cptrace on Apple
Dimitris Glynos <dimitris AT census-labs.com> - follow gdb.py commands
Jakub Wilk <jwilk AT debian.org> - fix for GNU/kFreeBSD
Mark Seaborn <mrs AT mythic-beasts.com> - Create -i option for strace
Mickaël Guérin aka KAeL <mickael.guerin AT crocobox.org> - OpenBSD port
teythoon - convert all classes to new-style classes

T.: Bursztyka aka Tuna <tuna AT lyua.org> - x86_64 port

•: Victor Stinner <victor.stinner AT gmail.com> - python-ptrace author and maintainer

Thanks

•: procps authors (top and uptime programs)

Changelog

python-ptrace 0.9.9 (2024-03-13)

Fix arguments of pipe/pipe2 system calls for proper display in call format. Patch by José Pereira.
Introduced support for three-digit minor device IDs in PROC_MAP_REGEX. Patch by fab1ano.
Added RISCV (riscv32/riscv64) support. Patch by Andreas Schwab and vimer/yuzibo.
Fix stray exception raised by child processes terminating with exit code 255. Patch by Duane Voth/duanev.
Removed usage of the imp module. Collaboration between Mario Haustein/hamarituc and Stephen Kitt/skitt.

python-ptrace 0.9.8 (2021-03-17)

Added Arm 64bit (AArch64) support.
Implemented PTRACE_GETREGSET and PTRACE_SETREGSET required on AArch64 and available on Linux.
Issue #66: Fix SIGTRAP|0x80 or SIGTRAP wait in syscall_state.exit (PTRACE_O_TRACESYSGOOD).
The development branch master was renamed to main. See https://sfconservancy.org/news/2020/jun/23/gitbranchname/ for the rationale.

python-ptrace 0.9.7 (2020-08-10)

Add missing module to install directives
Update README.rst
Project back in beta and maintenance

python-ptrace 0.9.6 (2020-08-10)

Remove RUNNING_WINDOWS constant: python-ptrace doesn't not support Windows.
Drop Python 2.7 support. six dependency is no longer needed.
Add close_fds and pass_fds to createChild() function. Patch by Jean-Baptiste Skutnik.
Enhance strace.py output for open flags and open optional parameters. Patch by Jean-Baptiste Skutnik.
Add support for PowerPC 64-bit (ppc64). Patch by Jean-Baptiste Skutnik.

python-ptrace 0.9.5 (2020-04-13)

Fix readProcessMappings() for device id on 3 digits. Patch by Cat Stevens.
Drop Python 2 support.

python-ptrace 0.9.4 (2019-07-30)

Issue #36: Fix detaching from process object created without is_attached=True
The project now requires the six module.
Project moved to: https://github.com/vstinner/python-ptrace

python-ptrace 0.9.3 (2017-09-19)

•: Issue #42: Fix test_strace.py: tolerate the openat() syscall.

python-ptrace 0.9.2 (2017-02-12)

•: Issue #35: Fix strace.py when tracing multiple processes: use the correct process. Fix suggested by Daniel Trnka.

python-ptrace 0.9.1 (2016-10-12)

Added tracing of processes created with the clone syscall (commonly known as threads).
gdb.py: add gcore command, dump the process memory.
Allow command names without absolute path.
Fix ptrace binding: clear errno before calling ptrace().
Fix PtraceSyscall.exit() for unknown error code
Project moved to GitHub: https://github.com/haypo/python-ptrace
Remove the ptrace.ctypes_errno module: use directly the ctypes.get_errno() function
Remove the ptrace.ctypes_errno module: use directly ctypes.c_int8, ctypes.c_uint32, ... types

python-ptrace 0.9 (2016-04-23)

Add all Linux syscall prototypes
Add error symbols (e.g. ENOENT), in addition to error text, for strace
Fix open mode so O_RDONLY shows if it's the only file access mode
Python 3: fix formatting of string syscall arguments (ex: filenames), decode bytes from the locale encoding
Issue #17: syscall parser now supports O_CLOEXEC and SOCK_CLOEXEC, fix unit tests on Python 3.4 and newer

python-ptrace 0.8.1 (2014-10-30)

Update MANIFEST.in to include all files
Fix to support Python 3.5

python-ptrace 0.8 (2014-10-05)

Issue #9: Rewrite waitProcessEvent() and waitSignals() methods of PtraceProcess to not call waitpid() with pid=-1. There is a race condition with waitpid(-1) and fork, the status of the child process may be returned before the debugger is noticed of the creation of the new child process.
Issue #10: Fix PtraceProcess.readBytes() for processes not created by the debugger (ex: fork) if the kernel blocks access to private mappings of /proc/pid/mem. Fallback to PTRACE_PEEKTEXT which is slower but a debugger tracing the process is always allowed to use it.

python-ptrace 0.7 (2013-03-05)

Experimental support of Python 3.3 in the same code base
Drop support of Python 2.5
Remove the ptrace.compatibility module
Fix Process.readStruct() and Process.readArray() on x86_64
Experimental support of ARM architecture (Linux EAPI), strace.py has been tested on Raspberry Pi (armv6l)

python-ptrace 0.6.6 (2013-12-16)

Fix os_tools.RUNNING_LINUX for Python 2.x compiled on Linux kernel 3.x
Support FreeBSD on x86_64
Add missing prototype of the unlinkat() system call. Patch written by Matthew Fernandez.

python-ptrace 0.6.5 (2013-06-06)

syscall: fix parsing socketcall on Linux x86
syscall: fix prototype of socket()

python-ptrace 0.6.4 (2012-02-26)

Convert all classes to new-style classes, patch written by teythoon
Fix compilation on Apple, patch written by Anthony Gelibert
Support GNU/kFreeBSD, patch written by Jakub Wilk
Support sockaddr_in6 (IPv6 address)

python-ptrace 0.6.3 (2011-02-16)

Support distrom3
Support Python 3
Rename strace.py option --socketcall to --socket, and fix this option for FreeBSD and Linux/64 bits
Add MANIFEST.in: include all files in source distribution (tests, cptrace module, ...)

python-ptrace 0.6.2 (2009-11-09)

•: Fix 64 bits sub registers (set mask for eax, ebx, ecx, edx)

python-ptrace 0.6.1 (2009-11-07)

Create follow, showfollow, resetfollow, xray commands in gdb.py. Patch written by Dimitris Glynos
Project website moved to: http://bitbucket.org/haypo/python-ptrace/
Replace types (u)intXX_t by c_(u)intXX
Create MemoryMapping.search() method and MemoryMapping now keeps a weak reference to the process

python-ptrace 0.6 (2009-02-13)

User visible changes:

python-ptrace now depends on Python 2.5
Invalid memory access: add fault address in the name
Update Python 3.0 conversion patch
Create -i (--show-ip) option to strace.py: show instruction pointer
Add a new example (itrace.py) written by Mark Seaborn and based on strace.py

API changes:

PtraceSyscall: store the instruction pointer at syscall enter (if the option instr_pointer=True, disabled by default)
Remove PROC_DIRNAME and procFilename() from ptrace.linux_proc

Bugfixes:

Fix locateProgram() for relative path
Fix interpretation of memory fault on MOSVW instruction (source is ESI and destination is EDI, and not the inverse!)

python-ptrace 0.5 (2008-09-13)

Visible changes:

Write an example (the most simple debugger) and begin to document the code
gdb.py: create "dbginfo" command
Parse socket syscalls on FreeBSD
On invalid memory access (SIGSEGV), eval the dereference expression to get the fault address on OS without siginfo (e.g. FreeBSD)
Fixes to get minimal Windows support: fix imports, fix locateProgram()

Other changes:

Break the API: - Rename PtraceDebugger.traceSysgood() to PtraceDebugger.enableSysgood() - Rename PtraceDebugger.trace_sysgood to PtraceDebugger.use_sysgood - Remove PtraceProcess.readCode()
Create createChild() function which close all files except stdin, stdout and stderr
On FreeBSD, on process exit recalls waitpid(pid) to avoid zombi process

python-ptrace 0.4.2 (2008-08-28)

BUGFIX: Fix typo in gdb.py (commands => command_str), it wasn't possible to write more than one command...
BUGFIX: Fix typo in SignalInfo class (remove "self."). When a process received a signal SIGCHLD (because of a fork), the debugger exited because of this bug.
BUGFIX: Debugger._wait() return abnormal process exit as a normal event, the event is not raised as an exception
PtraceSignal: don't clear preformatted arguments (e.g. arguments of execve)

python-ptrace 0.4.1 (2008-08-23)

The project has a new dedicated website: http://python-ptrace.hachoir.org/
Create cptrace: optional Python binding of ptrace written in C (faster than ptrace, the Python binding written in Python with ctypes)
Add name attribute to SignalInfo classes
Fixes to help Python 3.0 compatibility: don't use sys.exc_clear() (was useless) in writeBacktrace()
ProcessState: create utime, stime, starttime attributes

python-ptrace 0.4.0 (2008-08-19)