Class: Fisk::UnresolvedJumpInstruction

Inherits:
Object
  • Object
show all
Includes:
InstructionPredicates
Defined in:
lib/fisk.rb

Instance Method Summary collapse

Methods included from InstructionPredicates

#comment?, #has_temp_registers?, #label?, #lazy?

Constructor Details

#initialize(insn, form, operand) ⇒ UnresolvedJumpInstruction

Returns a new instance of UnresolvedJumpInstruction.



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# File 'lib/fisk.rb', line 448

def initialize insn, form, operand
  @insn       = insn
  @form       = form
  @operand    = operand
  @must_retry = false
end

Instance Method Details

#encode(buffer, labels) ⇒ Object 



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# File 'lib/fisk.rb', line 467

def encode buffer, labels
  # Estimate by using a rel32 offset
  form              = find_form "rel32"
  encoding          = form.encodings.first
  operand_klass     = Rel32

  if labels.key? target
    unless @must_retry
      estimated_offset = labels[target] - (buffer.pos + 6) # 6 seems like a good length

      if estimated_offset >= -128 && estimated_offset <= 127
        # fits in a rel8
        operand_klass     = Rel8
        form              = find_form "rel8"
        encoding          = form.encodings.first
      end
    end

    # We don't know what the size of the jump will be, so just write
    # it out with some dummy data and keep track of the buffer position.
    # Calculate the real jump offset, then rewind and patch the jump with
    # the right location. 😩
    pos = buffer.pos
    encoding.encode buffer, [operand_klass.new(0xFE)]
    jump_len = -(buffer.pos - labels[target])
    buffer.seek pos, IO::SEEK_SET
    encoding.encode buffer, [operand_klass.new(jump_len)]
  else
    if @must_retry
      # We retried once, but the label wasn't defined
      raise Errors::MissingLabel, "Label `#{target}` was used, but not defined"
    end
    @must_retry = true
    encoding.encode buffer, [operand_klass.new(0x0CAFE)]
  end
end

#jump? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/fisk.rb', line 455

def jump?
  true
end

#retry? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/fisk.rb', line 463

def retry?
  true
end

#target ⇒ Object 



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# File 'lib/fisk.rb', line 459

def target
  @operand.name
end