StopInDebugger

Stop in a C debugger (like GDB or LLDB) when a Ruby method is called.

Useful to debug the Ruby VM itself and learn how it works, as the Ruby VM is implemented in C.

# -- test/main.rb --
require 'stop_in_debugger'

def hello
  puts 'Hello, world!'
end

# Execution will halt here if a debugger is attached, or
# the program will exit if a debugger is not attached.
StopInDebugger.stop_in_debugger

hello

A sample debugger session looks like this:

❯ bundle exec lldb -- $(rbenv which ruby) test/main.rb

Or with colors:

From there, you can add whatever breakpoints you want. This works best when you've built Ruby with debug symbols and no optimizations.

This gem is on RubyGems.org, so you can make your Gemfile look like this:

# -- Gemfile --
source 'https://rubygems.org'
gem 'stop_in_debugger'

and then install with:

bundle install

bundle install
bundle exec rake

# to generate a compile_commands.json file for clangd
bundle exec rake compile_commands

# to release a version
# -- edit version in stop_in_debugger.gemspec --
git commit -am 'Bump version'
git tag <version>
git push --tags origin master
gem build stop_in_debugger
gem push stop_in_debugger-*.gem