Class: Pf2::Reporter::StackWeaver

Inherits:
Object
  • Object
show all
Defined in:
lib/pf2/reporter/stack_weaver.rb

Overview

“Weaves” the native stack into the Ruby stack.

Strategy:

  • Split the stack into Ruby and Native parts

  • Start from the root of the Native stack

  • Dig in to the native stack until we hit a rb_vm_exec(), which marks a call into Ruby code

  • Switch to Ruby stack. Keep digging until we hit a Cfunc call, then switch back to Native stack

  • Repeat until we consume the entire stack

Instance Method Summary collapse

Constructor Details

#initialize(profile) ⇒ StackWeaver

Returns a new instance of StackWeaver.



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# File 'lib/pf2/reporter/stack_weaver.rb', line 14

def initialize(profile)
  @profile = profile
end

Instance Method Details

#should_switch_to_native?(location_index, native_stack_remainder) ⇒ Boolean

Parameters:

  • location_index (Integer)
  • native_stack_remainder (Array<Integer>)

Returns:

  • (Boolean) 


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# File 'lib/pf2/reporter/stack_weaver.rb', line 57

def should_switch_to_native?(location_index, native_stack_remainder)
  location = @profile[:locations][location_index]
  function = @profile[:functions][location[:function_index]]
  raise if function[:implementation] != :ruby # assert

  # Is the current Ruby function a cfunc?
  return false if function[:start_address] == nil

  # Does a corresponding native function exist in the remainder of the native stack?
  loop do
    break if native_stack_remainder.size == 0
    n_location_index = native_stack_remainder.pop
    n_location = @profile[:locations][n_location_index]
    n_function = @profile[:functions][n_location[:function_index]]

    return true if function[:start_address] == n_function[:start_address]
  end

  false
end

#should_switch_to_ruby?(location_index) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/pf2/reporter/stack_weaver.rb', line 78

def should_switch_to_ruby?(location_index)
  location = @profile[:locations][location_index]
  function = @profile[:functions][location[:function_index]]
  raise if function[:implementation] != :native # assert

  # If the next function is a vm_exec_core() (= VM_EXEC in vm_exec.h),
  # we switch to the Ruby stack.
  function[:name] == 'vm_exec_core'
end

#weave(ruby_stack, native_stack) ⇒ Object 



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# File 'lib/pf2/reporter/stack_weaver.rb', line 18

def weave(ruby_stack, native_stack)
  ruby_stack = ruby_stack.dup
  native_stack = native_stack.dup

  weaved_stack = []

  current_stack = :native
  loop do
    break if ruby_stack.size == 0 && native_stack.size == 0
    case current_stack
    when :ruby
      if ruby_stack.size == 0 # We've reached the end of the Ruby stack
        current_stack = :native
        next
      end

      location_index = ruby_stack.pop
      weaved_stack.unshift(location_index)

      current_stack = :native if should_switch_to_native?(location_index, native_stack.dup)

    when :native
      if native_stack.size == 0 # We've reached the end of the native stack
        current_stack = :ruby
        next
      end

      location_index = native_stack.pop
      weaved_stack.unshift(location_index)

      current_stack = :ruby if should_switch_to_ruby?(location_index)
    end
  end

  weaved_stack
end