Basicdbg

For learning purposes built myself a very basic debugger in an effort to refresh my understanding of C++. Code heavily based on the following blog posts.

Getting started

Ubuntu

$ git clone --recursive git@github.com:davidkdickson/basicdbg.git
$ sudo apt install build-essential      # installs gcc, tested on version 9.3
$ cd basicdbg
$ make
$ ./basicdbg examples/hello

Docker

$ docker build -t basicdbg .
$ docker run -it basicdbg /bin/bash
$ ./basicdbg examples/hello

Usage

basicdbg <program>

• s step in, note cannot step in to shared library dependencies
• n next / step over
• f finish / step out
• b address break at hex address, e.g. b 0x11b5
• b file:line_number break at line number, e.g. b examples/hello.cc:9
• c continue
• q quit

Useful articles

• http://www.alexonlinux.com/how-debugger-works
• https://www.linuxjournal.com/article/6100
• https://www.linuxjournal.com/article/6210
• https://jvns.ca/blog/2018/01/09/resolving-symbol-addresses/
• https://amir.rachum.com/blog/2016/09/17/shared-libraries/

Useful supporting commands

objdump -f examples/hello       # outputs start address
objdump -d examples/hello       # assembler sections of executable
nm examples/hello               # another way at identifying address of main function