115 lines
4.6 KiB
Ruby
115 lines
4.6 KiB
Ruby
module Arm
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class MoveInstruction < Instruction
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include Arm::Constants
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def initialize to , from , options = {}
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super(options)
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if( from.is_a?(Symbol) and Register::RegisterReference.look_like_reg(from) )
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from = Register::RegisterReference.new(from)
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end
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@from = from
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@to = to
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raise "move must have from set #{inspect}" unless from
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@attributes[:update_status] = 0 if @attributes[:update_status] == nil
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@attributes[:condition_code] = :al if @attributes[:condition_code] == nil
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@attributes[:opcode] = attributes[:opcode]
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@operand = 0
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@immediate = 0
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@rn = :r0 # register zero = zero bit pattern
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@extra = nil
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end
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attr_accessor :to , :from
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# arm intructions are pretty sensible, and always 4 bytes (thumb not supported)
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# but not all constants fit into the part of the instruction that is left after the instruction
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# code, so large moves have to be split into two instructions.
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# we handle this "transparently", just this instruction looks longer
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# alas, full transparency is not achieved as we only know when to use 2 instruction once we
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# know where the other object is, and that position is only set after code positions have been
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# determined (in link) and so see below in assemble
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def byte_length
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@extra ? 8 : 4
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end
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def assemble(io)
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# don't overwrite instance variables, to make assembly repeatable
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rn = @rn
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operand = @operand
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immediate = @immediate
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right = @from
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if (right.is_a?(Numeric))
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if (right.fits_u8?)
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# no shifting needed
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operand = right
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immediate = 1
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elsif (op_with_rot = calculate_u8_with_rr(right))
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operand = op_with_rot
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immediate = 1
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else
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# unfortunately i was wrong in thinking the pi is armv7. The good news is the code
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# below implements the movw instruction (armv7 for moving a word) and works
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#armv7 raise "Too big #{right} " if (right >> 16) > 0
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#armv7 operand = (right & 0xFFF)
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#armv7 immediate = 1
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#armv7 rn = (right >> 12)
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# a little STRANGE, that the armv7 movw (move a 2 byte word) is an old test opcode,
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# but there it is
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#armv7 @attributes[:opcode] = :tst
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raise "No negatives implemented #{right} " if right < 0
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# and so it continues: when we notice that the const doesn't fit, first time we raise an
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# error,but set the extra flag, to say the instruction is now 8 bytes
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# then on subsequent assemblies we can assemble
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unless @extra
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@extra = 1
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#puts "RELINK M at #{self.position.to_s(16)}"
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raise ::Register::LinkException.new("cannot fit numeric literal argument in operand #{right.inspect}")
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end
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# now we can do the actual breaking of instruction, by splitting the operand
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first = right & 0xFFFFFF00
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operand = calculate_u8_with_rr( first )
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raise "no fit for #{right}" unless operand
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immediate = 1
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@extra = ArmMachine.add( to , to , (right & 0xFF) )
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#TODO: this is still a hack, as it does not encode all possible values.
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# The way it _should_ be done
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# is to check that the first part is doabe with u8_with_rr AND leaves a u8 remainder
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end
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elsif( right.is_a? Register::RegisterReference)
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operand = reg_code(right)
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immediate = 0 # ie not immediate is register
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else
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raise "invalid operand argument #{right.class} , #{self.class}"
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end
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op = shift_handling
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instuction_class = 0b00 # OPC_DATA_PROCESSING
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val = shift(operand , 0)
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val |= shift(op , 0) # any barrel action, is already shifted
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val |= shift(reg_code(@to) , 12)
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val |= shift(reg_code(rn) , 12+4)
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val |= shift(@attributes[:update_status] , 12+4+4)#20
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val |= shift(op_bit_code , 12+4+4 + 1)
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val |= shift(immediate , 12+4+4 + 1+4)
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val |= shift(instuction_class , 12+4+4 + 1+4+1)
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val |= shift(cond_bit_code , 12+4+4 + 1+4+1+2)
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io.write_uint32 val
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# by now we have the extra add so assemble that
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if(@extra)
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@extra.assemble(io)
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#puts "Assemble extra at #{val.to_s(16)}"
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end
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end
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def shift val , by
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raise "Not integer #{val}:#{val.class} in #{inspect}" unless val.is_a? Fixnum
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val << by
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end
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def uses
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@from.is_a?(Constant) ? [] : [@from.register]
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end
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def assigns
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[@to.register]
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end
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end
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end
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