63 lines
2.0 KiB
Ruby
63 lines
2.0 KiB
Ruby
module Risc
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# Little glue class to get the assembled binary from the Arm Instructions into
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# the BinaryCode instances. Arm code originally uses io, but slightly modified
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# really only uses write_unsigned_int_32 , which converts
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# to an set_internal_word on the BinaryCode
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#
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# Machine instantiates and the writer reads from the arm Instructions
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# and writes to the BinaryCode
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class BinaryWriter
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def initialize( code )
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@code = code
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end
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# write into the given BinaryCode instance
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# LinkException may be thrown, possibly several times
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# So repeat until it works
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def assemble( instruction )
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not_ok = 1
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while(not_ok)
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begin
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#puts "Not ok #{not_ok}"
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#FIXME really need to reposition here, so jumps go right
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assemble_all(instruction)
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not_ok = false
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rescue LinkException
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not_ok += 1
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end
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end
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end
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# Go through and assemble all instructions.
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# Assembly may cause LinkException, which is caught by caller
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def assemble_all( instruction )
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@index = 1
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while(instruction)
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instruction.assemble(self)
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instruction = instruction.next
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end
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end
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def write_unsigned_int_32( bin )
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@code.set_word( @index , bin )
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@index += 1
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end
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end
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# A LinkException is raised when the arm code can't fit a constant into _one_
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# instruction. This is kind of unavoidable with arm.
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#
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# Off course the problem could be fixed without the exception, but the exception
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# means all subsequent Instructions, including labels/jump targets move.
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# Thus changing jump instructions to those labels.
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# So the whole method has to be reassembled and (at least) the instructions beyond
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# repositioned. Ie a non-local problem, and so the Exception.
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#
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# Note: In the future i hope to have a more flexible system, possibly with position
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# listeners and change events. Because positions chaning is normal, not exceptional.
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#
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class LinkException < Exception
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end
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end
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