119 lines
5.2 KiB
Ruby
119 lines
5.2 KiB
Ruby
module Vm
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# Our virtual c-machine has a number of registers of a given size and uses a stack
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# So much so standard
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# But our machine is oo, meaning that the register contents is typed.
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# Off course current hardware does not have that (a perceived issue), but for our machine we pretend.
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# So internally we have at least 8 word registers, one of which is used to keep track of types*
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# and any number of scratch registers
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# but externally it's all Values (see there)
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# * Note that register content is typed externally. Not as in mri, where int's are tagged. Floats can's
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# be tagged and lambda should be it's own type, so tagging does not work
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# A Machines main responsibility in the framework is to instantiate Instruction
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# Value functions are mapped to machines by concatenating the values class name + the methd name
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# Example: IntegerValue.plus( value ) -> Machine.signed_plus (value )
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# Also, shortcuts are created to easily instantiate Instruction objects. The "standard" set of instructions
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# (arm-influenced) provides for normal operations on a register machine,
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# Example: pop -> StackInstruction.new( {:opcode => :pop}.merge(options) )
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# Instructions work with options, so you can pass anything in, and the only thing the functions does
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# is save you typing the clazz.new. It passes the function name as the :opcode
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class CMachine
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# hmm, not pretty but for now
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@@instance = nil
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attr_reader :registers
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attr_reader :scratch
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attr_reader :pc
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attr_reader :stack
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# is often a pseudo register (ie doesn't support move or other operations).
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# Still, using if to express tests makes sense, not just for
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# consistency in this code, but also because that is what is actually done
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attr_reader :status
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# conditions specify all the possibilities for branches. Branches are b + condition
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# Example: beq means brach if equal.
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# :al means always, so bal is an unconditional branch (but b() also works)
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CONDITIONS = [ :al , :eq , :ne , :lt , :le, :ge, :gt , :cs , :mi , :hi , :cc , :pl, :ls , :vc , :vs ]
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# here we create the shortcuts for the "standard" instructions, see above
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# Derived machines may use own instructions and define functions for them if so desired
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def initialize
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[:push, :pop].each do |inst|
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define_instruction_for(inst , StackInstruction)
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end
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[:adc, :add, :and, :bic, :eor, :orr, :rsb, :rsc, :sbc, :sub].each do |inst|
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define_instruction_for(inst , LogicInstruction)
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end
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[:mov, :mvn].each do |inst|
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define_instruction_for(inst , MoveInstruction)
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end
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[:cmn, :cmp, :teq, :tst].each do |inst|
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define_instruction_for(inst , CompareInstruction)
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end
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[:strb, :str , :ldrb, :ldr].each do |inst|
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define_instruction_for(inst , MemoryInstruction)
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end
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[:b, :call , :swi].each do |inst|
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define_instruction_for(inst , CallInstruction)
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end
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# create all possible brach instructions, but the CallInstruction demangles the
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# code, and has opcode set to :b and :condition_code set to the condition
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CONDITIONS.each do |suffix|
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define_instruction_for("b#{suffix}".to_sym , CallInstruction)
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end
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end
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def create_method(name, &block)
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self.class.send(:define_method, name , &block)
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end
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# define the instruction inst (given as a symbol) on this class as a methods
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# As we define a standard set of instructions (or memnonics) , this turns this class into a kind of
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# Assembler, in that you can write .mov() or .pop() and those functions mean the same as if they
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# were in an assembler file (also options are the same)
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# defaults gets merged into the instructions options hash, ie passed on to the (machine specific)
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# Instruction constructor and as such can be used to influence that classes behaviour
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def define_instruction(inst , clazz , defaults = {} )
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create_method(inst) do |options|
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options = {} if options == nil
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options.merge defaults
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options[:opcode] = inst
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clazz.new(options)
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end
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end
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def self.instance
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@@instance
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end
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def self.instance= machine
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@@instance = machine
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end
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private
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#defining the instruction (opcode, symbol) as an given class.
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# the class is a Vm::Instruction derived base class and to create machine specific function
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# an actual machine must create derived classes (from this base class)
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# These instruction classes must follow a naming pattern and take a hash in the contructor
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# Example, a mov() opcode instantiates a Vm::MoveInstruction
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# for an Arm machine, a class Arm::MoveInstruction < Vm::MoveInstruction exists, and it will
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# be used to define the mov on an arm machine.
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# This methods picks up that derived class and calls a define_instruction methods that can
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# be overriden in subclasses
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def define_instruction_for(inst , clazz )
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c_name = clazz.name
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my_module = self.class.name.split("::").first
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clazz_name = clazz.name.split("::").last
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if(my_module != Vm )
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module_class = eval("#{my_module}::#{clazz_name}") rescue nil
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clazz = module_class if module_class
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end
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define_instruction(inst , clazz )
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end
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end
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end
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