69 lines
2.3 KiB
Ruby
69 lines
2.3 KiB
Ruby
require_relative "nodes"
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module Arm
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# There are only three call instructions in arm branch (b), call (bl) and syscall (swi)
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# A branch could be called a jump as it has no notion of returning
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# The pc is put into the link register to make a return possible
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# a return is affected by moving the stored link register into the pc, effectively a branch
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# swi (SoftWareInterrupt) or system call is how we call the kernel.
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# in Arm the register layout is different and so we have to place the syscall code into register 7
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# Registers 0-6 hold the call values as for a normal c call
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class CallInstruction < Vm::CallInstruction
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include Arm::Constants
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# arm intrucioons are pretty sensible, and always 4 bytes (thumb not supported)
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def length
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4
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end
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def initialize(attributes)
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super(attributes)
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@attributes[:update_status_flag] = 0
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@attributes[:condition_code] = :al if @attributes[:condition_code] == nil
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end
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def assemble(io)
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case @attributes[:opcode]
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when :b, :call
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arg = @attributes[:left]
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#puts "BLAB #{arg.inspect}"
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if( arg.is_a? Fixnum ) #HACK to not have to change the code just now
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arg = Arm::NumLiteral.new( arg )
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end
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if arg.is_a? Vm::Code
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diff = arg.position - self.position - 8
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arg = Arm::NumLiteral.new(diff)
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end
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if (arg.is_a?(Arm::NumLiteral))
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jmp_val = arg.value >> 2
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packed = [jmp_val].pack('l')
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# signed 32-bit, condense to 24-bit
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# TODO add check that the value fits into 24 bits
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io << packed[0,3]
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else
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raise "else not coded arg =#{arg}: #{inspect}"
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end
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io.write_uint8 op_bit_code | (COND_CODES[@attributes[:condition_code]] << 4)
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when :swi
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arg = @attributes[:left]
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if( arg.is_a? Fixnum ) #HACK to not have to change the code just now
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arg = Arm::NumLiteral.new( arg )
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end
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if (arg.is_a?(Arm::NumLiteral))
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packed = [arg.value].pack('L')[0,3]
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io << packed
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io.write_uint8 0b1111 | (COND_CODES[@attributes[:condition_code]] << 4)
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else
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raise "invalid operand argument expected literal not #{arg} #{inspect}"
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end
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else
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raise "Should not be the case #{inspect}"
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end
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end
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end#class
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end |