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