fuzz update/node/lib/metasm/metasm/cpu/z80/decode.rb
#    This file is part of Metasm, the Ruby assembly manipulation suite
#    Copyright (C) 2006-2009 Yoann GUILLOT
#
#    Licence is LGPL, see LICENCE in the top-level directory


require 'metasm/cpu/z80/opcodes'
require 'metasm/decode'

module Metasm
class Z80
	def build_opcode_bin_mask(op)
		# bit = 0 if can be mutated by an field value, 1 if fixed by opcode
		op.bin_mask = Array.new(op.bin.length, 0)
		op.fields.each { |f, (oct, off)|
			op.bin_mask[oct] |= (@fields_mask[f] << off)
		}
		op.bin_mask.map! { |v| 255 ^ v }
	end

	def build_bin_lookaside
		# sets up a hash byte value => list of opcodes that may match
		# opcode.bin_mask is built here
		lookaside = Array.new(256) { [] }
		opcode_list.each { |op|
			build_opcode_bin_mask op
			b   = op.bin[0]
			msk = op.bin_mask[0]
			next @unknown_opcode = op if not b
			for i in b..(b | (255^msk))
				lookaside[i] << op if i & msk == b & msk
			end
		}
		lookaside
	end

	def decode_prefix(instr, byte)
		case byte
		when 0xDD; instr.prefix = 0xDD
		when 0xFD; instr.prefix = 0xFD
		# implicit 'else return false'
		end
	end

	# tries to find the opcode encoded at edata.ptr
	# if no match, tries to match a prefix (update di.instruction.prefix)
	# on match, edata.ptr points to the first byte of the opcode (after prefixes)
	def decode_findopcode(edata)
		di = DecodedInstruction.new self
		while edata.ptr < edata.data.length
			byte = edata.data[edata.ptr]
			byte = byte.unpack('C').first if byte.kind_of?(::String)
			return di if di.opcode = @bin_lookaside[byte].find { |op|
				# fetch the relevant bytes from edata
				bseq = edata.data[edata.ptr, op.bin.length].unpack('C*')
				# check against full opcode mask
				op.bin.zip(bseq, op.bin_mask).all? { |b1, b2, m| b2 and ((b1 & m) == (b2 & m)) }
			}

			if decode_prefix(di.instruction, edata.get_byte)
				nb = edata.data[edata.ptr]
				nb = nb.unpack('C').first if nb.kind_of?(::String)
				case nb
				when 0xCB
					# DD CB <disp8> <opcode_pfxCB> [<args>]
					di.instruction.prefix |= edata.get_byte	<< 8
					di.bin_length += 2
					opc = edata.data[edata.ptr+1]
					opc = opc.unpack('C').first if opc.kind_of?(::String)
					bseq = [0xCB, opc]
					# XXX in decode_instr_op, byte[0] is the immediate displacement instead of cb
					return di if di.opcode = @bin_lookaside[nb].find { |op|
						op.bin.zip(bseq, op.bin_mask).all? { |b1, b2, m| b2 and ((b1 & m) == (b2 & m)) }
					}
				when 0xED
					di.instruction.prefix = nil
				end
			else
				di.opcode = @unknown_opcode
				return di
			end
			di.bin_length += 1
		end
	end


	def decode_instr_op(edata, di)
		before_ptr = edata.ptr
		op = di.opcode
		di.instruction.opname = op.name
		bseq = edata.read(op.bin.length).unpack('C*')		# decode_findopcode ensures that data >= op.length
		pfx = di.instruction.prefix

		field_val = lambda { |f|
			if fld = op.fields[f]
				(bseq[fld[0]] >> fld[1]) & @fields_mask[f]
			end
		}

		op.args.each { |a|
			di.instruction.args << case a
			when :i8, :u8, :i16, :u16; Expression[edata.decode_imm(a, @endianness)]
			when :iy; Expression[field_val[a]]
			when :iy8; Expression[field_val[a]*8]

			when :rp
				v = field_val[a]
				Reg.new(16, v)
			when :rp2
				v = field_val[a]
				v = 4 if v == 3
				Reg.new(16, v)
			when :ry, :rz
				v = field_val[a]
				if v == 6
					Memref.new(Reg.from_str('HL'), nil, 1)
				else
					Reg.new(8, v)
				end

			when :r_a;   Reg.from_str('A')
			when :r_af;  Reg.from_str('AF')
			when :r_hl;  Reg.from_str('HL')
			when :r_de;  Reg.from_str('DE')
			when :r_sp;  Reg.from_str('SP')
			when :r_i;   Reg.from_str('I')

			when :m16;  Memref.new(nil, edata.decode_imm(:u16, @endianness), nil)
			when :m_bc; Memref.new(Reg.from_str('BC'), nil, 1)
			when :m_de; Memref.new(Reg.from_str('DE'), nil, 1)
			when :m_sp; Memref.new(Reg.from_str('SP'), nil, 2)
			when :m_hl; Memref.new(Reg.from_str('HL'), nil, 1)
			when :mf8;  Memref.new(nil, 0xff00 + edata.decode_imm(:u8, @endianness), 1)
			when :mfc;  Memref.new(Reg.from_str('C'), 0xff00, 1)

			else raise SyntaxError, "Internal error: invalid argument #{a} in #{op.name}"
			end
		}

		case pfx
		when 0xDD
		when 0xFD
		when 0xCBDD
		when 0xCBFD
		end

		di.bin_length += edata.ptr - before_ptr

		return if edata.ptr > edata.length

		di
	end

	# hash opcode_name => lambda { |dasm, di, *symbolic_args| instr_binding }
	def backtrace_binding
		@backtrace_binding ||= init_backtrace_binding
	end
	def backtrace_binding=(b) @backtrace_binding = b end

	# populate the @backtrace_binding hash with default values
	def init_backtrace_binding
		@backtrace_binding ||= {}

		mask = 0xffff

		opcode_list.map { |ol| ol.basename }.uniq.sort.each { |op|
			binding = case op
			when 'ld'; lambda { |di, a0, a1, *aa| a2 = aa[0] ; a2 ? { a0 => Expression[a1, :+, a2] } : { a0 => Expression[a1] } }
			when 'ldi'; lambda { |di, a0, a1| hl = (a0 == :a ? a1 : a0) ; { a0 => Expression[a1], hl => Expression[hl, :+, 1] } }
			when 'ldd'; lambda { |di, a0, a1| hl = (a0 == :a ? a1 : a0) ; { a0 => Expression[a1], hl => Expression[hl, :-, 1] } }
			when 'add', 'adc', 'sub', 'sbc', 'and', 'xor', 'or'
				lambda { |di, a0, a1|
					e_op = { 'add' => :+, 'adc' => :+, 'sub' => :-, 'sbc' => :-, 'and' => :&, 'xor' => :^, 'or' => :| }[op]
					ret = Expression[a0, e_op, a1]
					ret = Expression[ret, e_op, :flag_c] if op == 'adc' or op == 'sbc'
					ret = Expression[ret.reduce] if not a0.kind_of? Indirection
					{ a0 => ret }
				}
			when 'cp', 'cmp'; lambda { |di, *a| {} }
			when 'inc'; lambda { |di, a0| { a0 => Expression[a0, :+, 1] } }
			when 'dec'; lambda { |di, a0| { a0 => Expression[a0, :-, 1] } }
			when 'not'; lambda { |di, a0| { a0 => Expression[a0, :^, mask] } }
			when 'push'
				lambda { |di, a0| { :sp => Expression[:sp, :-, 2],
					Indirection[:sp, 2, di.address] => Expression[a0] } }
			when 'pop'
				lambda { |di, a0| { :sp => Expression[:sp, :+, 2],
					a0 => Indirection[:sp, 2, di.address] } }
			when 'call'
				lambda { |di, a0| { :sp => Expression[:sp, :-, 2],
					  Indirection[:sp, 2, di.address] => Expression[di.next_addr] }
				}
			when 'ret', 'reti'; lambda { |di, *a| { :sp => Expression[:sp, :+, 2] } }
			# TODO callCC, retCC ...
			when 'bswap'
				lambda { |di, a0| { a0 => Expression[
						[[a0, :&, 0xff00], :>>,  8], :|,
						[[a0, :&, 0x00ff], :<<,  8]] } }
			when 'nop', /^j/; lambda { |di, *a| {} }
			end

			# TODO flags ?

			@backtrace_binding[op] ||= binding if binding
		}
		@backtrace_binding
	end

	def get_backtrace_binding(di)
		a = di.instruction.args.map { |arg|
			case arg
			when Memref, Reg; arg.symbolic(di)
			else arg
			end
		}

		if binding = backtrace_binding[di.opcode.basename]
			binding[di, *a]
		else
			puts "unhandled instruction to backtrace: #{di}" if $VERBOSE
			# assume nothing except the 1st arg is modified
			case a[0]
			when Indirection, Symbol; { a[0] => Expression::Unknown }
			when Expression; (x = a[0].externals.first) ? { x => Expression::Unknown } : {}
			else {}
			end.update(:incomplete_binding => Expression[1])
		end
	end

	# patch a forward binding from the backtrace binding
	def fix_fwdemu_binding(di, fbd)
		case di.opcode.name
		when 'push', 'call'; fbd[Indirection[[:sp, :-, 2], 2]] = fbd.delete(Indirection[:sp, 2])
		end
		fbd
	end

	def get_xrefs_x(dasm, di)
		return [] if not di.opcode.props[:setip]

		case di.opcode.basename
		when 'ret', 'reti'
			return [Indirection[:sp, 2, di.address]]
		when /^jr|^djnz/
			# jmp/call are absolute addrs, only jr/djnz are relative
			# also, the asm source should display the relative offset
			return [Expression[[di.address, :+, di.bin_length], :+, di.instruction.args.first]]
		end

		case tg = di.instruction.args.first
		when Memref; [Expression[tg.symbolic(di)]]
		when Reg; [Expression[tg.symbolic(di)]]
		when Expression, ::Integer; [Expression[tg]]
		else
			puts "unhandled setip at #{di.address} #{di.instruction}" if $DEBUG
			[]
		end
	end

	# checks if expr is a valid return expression matching the :saveip instruction
	def backtrace_is_function_return(expr, di=nil)
		expr = Expression[expr].reduce_rec
		expr.kind_of?(Indirection) and expr.len == 2 and expr.target == Expression[:sp]
	end

	# updates the function backtrace_binding
	# if the function is big and no specific register is given, do nothing (the binding will be lazily updated later, on demand)
	def backtrace_update_function_binding(dasm, faddr, f, retaddrlist, *wantregs)
		b = f.backtrace_binding

		bt_val = lambda { |r|
			next if not retaddrlist
			b[r] = Expression::Unknown
			bt = []
			retaddrlist.each { |retaddr|
				bt |= dasm.backtrace(Expression[r], retaddr, :include_start => true,
					     :snapshot_addr => faddr, :origin => retaddr)
			}
			if bt.length != 1
				b[r] = Expression::Unknown
			else
				b[r] = bt.first
			end
		}

		if not wantregs.empty?
			wantregs.each(&bt_val)
		else
			bt_val[:sp]
		end

		b
	end

	# returns true if the expression is an address on the stack
	def backtrace_is_stack_address(expr)
		Expression[expr].expr_externals.include?(:sp)
	end

	# updates an instruction's argument replacing an expression with another (eg label renamed)
	def replace_instr_arg_immediate(i, old, new)
		i.args.map! { |a|
			case a
			when Expression; a == old ? new : Expression[a.bind(old => new).reduce]
			when Memref
				a.offset = (a.offset == old ? new : Expression[a.offset.bind(old => new).reduce]) if a.offset
				a
			else a
			end
		}
	end
end
end
