Minimal C Debugger in Python

The goal of this project is to make a c debugger, similar to gdb, in python. This is exclusively for educational purposes :)

This debugger works by using the ptrace system call. A good chunk of the theory is here.

Features

• Read function names from binaries
• Set breakpoints
• Read registers
• Continue to next breakpoint
• Read/Set Memory

Setup

• Install Vagrant
• git clone https://github.com/theicfire/pygdb
• cd pygdb
• vagrant up -- will take a bit of time
• vagrant ssh

Now run these commands in the VM:

• cd /vagrant
• make test

All the tests should pass!

Example Usage

• cd /vagrant
• make
• objdump -d hello
• Find somewhere to break. In this case we'll pick the start of the program: 8048080
• Start the debugger: make interactive
• Load the hello binary: exec-file hello
• Set a breakpoint: b 0x8048080
• Run the binary: run. Nothing will seem to happen, but the program has started to run and hit a breakpoint.
• Get the registers. You'll notice eip is one after our breakpoint. regs
• Step one instruction. s.
• Get the registers again. regs. Notice that edx == 0x7, just like the assembly said it should have been.
• Continue (Should finish): c
• Quit: q

Future Priorities

• Get this to run on 64 bit machines
• Add any number of features that GDB has