Experimenting with MRI internals in FFI

evil.rb

require 'ffi'

class Object
  def memory_location
    object_id * 2
  end

  def to_pointer
    FFI::Pointer.new(memory_location)
  end

  def class=(klass)
    to_pointer.put_ulong(8, klass.memory_location)
  end

  def unfreeze
    to_pointer.tap do |p|
      p.put_ulong(0, p.get_ulong(0) &~ (1<<11))
    end
    self
  end
end

if $0 == __FILE__
  a = Object.new
  a.class = Array
  p a.class

  a.freeze
  p a.frozen?
  a.unfreeze
  p a.frozen?
end