rubyx/lib/risc/instructions/label.rb

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module Risc
# A label is a placeholder for it's next Instruction
# It's function is not to turn into code, but to be a valid branch target
# Labels have the same position as their next instruction (See positioning code)
#
# So branches and Labels are pairs, fan out, fan in
#
# For a return, the address (position) of the label has to be loaded.
# So a Label carries the ReturnAddress constant that holds the address (it's own
# position, again see positioning code).
# But currently the label is used in the Risc abstraction layer, and in the
# arm/interpreter layer. The integer is only used in the lower layer, but needs
# to be created (and positioned)
class Label < Instruction
# See class description. also factory method Risc.label below
def initialize( source , name , addr , nekst = nil)
super(source , nekst)
@name = name
@address = addr
raise "Not address #{addr}" unless addr.is_a?(Parfait::ReturnAddress)
end
attr_reader :name , :address
def to_cpu(translator)
@cpu_label ||= super
end
def to_s
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class_source "#{@name} (next: #{self.next.class.name.split("::").last})"
end
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def rxf_reference_name
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@name
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end
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# a method start has a label of the form Class.method , test for that
def is_method
@name.split(".").length == 2
end
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def assemble_all( io )
self.each {|ins| ins.assemble(io)}
end
def assemble io
end
def total_byte_length
ret = 0
self.each{|ins| ret += ins.byte_length}
ret
end
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# shame we need this, just for logging
def byte_length
0
end
alias :padded_length :byte_length
end
# Labels carry what is esentially an integer constant
# The int holds the labels position for use at runtime (return address)
# An integer is plucked from object_space abd added to the machine constant pool
# if none was given
def self.label( source , name , position = nil , nekst = nil)
position = Parfait.object_space.get_next_for(:ReturnAddress) unless position
Label.new( source , name , position, nekst )
end
end