#    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/ia32/opcodes'
require 'metasm/encode'

module Metasm
class Ia32
	class InvalidModRM < Exception ; end
	class ModRM
		# returns the byte representing the register encoded as modrm
		# works with Reg/SimdReg
		def self.encode_reg(reg, mregval = 0)
			0xc0 | (mregval << 3) | reg.val
		end

		# The argument is an integer representing the 'reg' field of the mrm
		#
		# caller is responsible for setting the adsz
		# returns an array, 1 element per possible immediate size (for un-reduce()able Expression)
		def encode(reg = 0, endianness = :little)
			reg = reg.val if reg.kind_of? Argument
			case @adsz
			when 16; encode16(reg, endianness)
			when 32; encode32(reg, endianness)
			end
		end

		private
		def encode16(reg, endianness)
			if not b
				# imm only
				return [EncodedData.new << (6 | (reg << 3)) << @imm.encode(:u16, endianness)]
			end

			imm = @imm.reduce if self.imm
			imm = nil if imm == 0
			ret = EncodedData.new
			ret <<
			case [@b.val, (@i.val if i)]
			when [3, 6], [6, 3]; 0
			when [3, 7], [7, 3]; 1
			when [5, 6], [6, 5]; 2
			when [5, 7], [7, 5]; 3
			when [6, nil]; 4
			when [7, nil]; 5
			when [5, nil]
				imm ||= 0
				6
			when [3, nil]; 7
			else raise InvalidModRM, 'invalid modrm16'
			end

			# add bits in the first octet of ret.data (1.9 compatibility layer)
			or_bits = lambda { |v|	# rape me
				if ret.data[0].kind_of? Integer
					ret.data[0] |= v
				else
					ret.data[0] = (ret.data[0].unpack('C').first | v).chr
				end
			}

			or_bits[reg << 3]

			if imm
				case Expression.in_range?(imm, :i8)
				when true
					or_bits[1 << 6]
					[ret << Expression.encode_imm(imm, :i8, endianness)]
				when false
					or_bits[2 << 6]
					[ret << Expression.encode_imm(imm, :a16, endianness)]
				when nil
					rets = ret.dup
					or_bits[1<<6]
					ret << @imm.encode(:i8, endianness)
					ret, rets = rets, ret	# or_bits uses ret
					or_bits[2<<6]
					ret << @imm.encode(:a16, endianness)
					[ret, rets]
				end
			else
				[ret]
			end
		end

		def encode32(reg, endianness)
			# 0 => [ [0      ], [1      ], [2      ], [3      ], [:sib      ], [:i32   ], [6      ], [7      ] ], \
			# 1 => [ [0, :i8 ], [1, :i8 ], [2, :i8 ], [3, :i8 ], [:sib, :i8 ], [5, :i8 ], [6, :i8 ], [7, :i8 ] ], \
			# 2 => [ [0, :i32], [1, :i32], [2, :i32], [3, :i32], [:sib, :i32], [5, :i32], [6, :i32], [7, :i32] ]
			#
			# b => 0  1  2  3  4  5+i|i 6  7
			# i => 0  1  2  3 nil   5   6  7

			ret = EncodedData.new << (reg << 3)

			# add bits in the first octet of ret.data (1.9 compatibility layer)
			or_bits = lambda { |v|	# rape me
				if ret.data[0].kind_of? Integer
					ret.data[0] |= v
				else
					ret.data[0] = (ret.data[0].unpack('C').first | v).chr
				end
			}

			if not self.b and not self.i
				or_bits[5]
				[ret << @imm.encode(:a32, endianness)]

			elsif not self.b and self.s != 1
				# sib with no b
				raise EncodeError, "Invalid ModRM #{self}" if @i.val == 4
				or_bits[4]
				s = {8=>3, 4=>2, 2=>1}[@s]
				imm = self.imm || Expression[0]
				fu = (s << 6) | (@i.val << 3) | 5
				fu = fu.chr if s >= 2	# rb1.9 encoding fix
				[ret << fu << imm.encode(:a32, endianness)]
			else
				imm = @imm.reduce if self.imm
				imm = nil if imm == 0

				if not self.i or (not self.b and self.s == 1)
					# no sib byte (except for [esp])
					b = self.b || self.i

					or_bits[b.val]
					ret << 0x24 if b.val == 4
				else
					# sib
					or_bits[4]

					i, b = @i, @b
					b, i = i, b if @s == 1 and (i.val == 4 or b.val == 5)

					raise EncodeError, "Invalid ModRM #{self}" if i.val == 4

					s = {8=>3, 4=>2, 2=>1, 1=>0}[@s]
					fu = (s << 6) | (i.val << 3) | b.val
					fu = fu.chr if s >= 2	# rb1.9 encoding fix
					ret << fu
				end

				imm ||= 0 if b.val == 5
				if imm
					case Expression.in_range?(imm, :i8)
					when true
						or_bits[1<<6]
						[ret << Expression.encode_imm(imm, :i8, endianness)]
					when false
						or_bits[2<<6]
						[ret << Expression.encode_imm(imm, :a32, endianness)]
					when nil
						rets = ret.dup
						or_bits[1<<6]
						ret << @imm.encode(:i8, endianness)
						rets, ret = ret, rets	# or_bits[] modifies ret directly
						or_bits[2<<6]
						ret << @imm.encode(:a32, endianness)
						[ret, rets]
					end
				else
					[ret]
				end
			end
		end
	end

	class Farptr
		def encode(endianness, atype)
			@addr.encode(atype, endianness) << @seg.encode(:u16, endianness)
		end
	end

	# returns all forms of the encoding of instruction i using opcode op
	# program may be used to create a new label for relative jump/call
	def encode_instr_op(program, i, op)
		base      = op.bin.dup
		oi        = op.args.zip(i.args)
		set_field = lambda { |f, v|
			v ||= 0		# ST => ST(0)
			fld = op.fields[f]
			base[fld[0]] |= v << fld[1]
		}

		size = i.prefix[:sz] || @size

		#
		# handle prefixes and bit fields
		#
		pfx = i.prefix.map { |k, v|
			case k
			when :jmp;  {:jmp => 0x3e, :nojmp => 0x2e}[v]
			when :lock; 0xf0
			when :rep;  {'repnz' => 0xf2, 'repz' => 0xf3, 'rep' => 0xf2}[v] # TODO
			end
		}.compact.pack 'C*'
		pfx << op.props[:needpfx] if op.props[:needpfx]

		if op.name == 'movsx' or op.name == 'movzx'
			pfx << 0x66 if size == 48-i.args[0].sz
		else
			opsz = op.props[:argsz]
			oi.each { |oa, ia|
				case oa
				when :reg, :reg_eax, :modrm, :modrmA, :mrm_imm
					raise EncodeError, "Incompatible arg size in #{i}" if ia.sz and opsz and opsz != ia.sz
					opsz = ia.sz
				end
			}
			pfx << 0x66 if (not op.props[:argsz] or opsz != op.props[:argsz]) and (
				(opsz and size == 48 - opsz) or (op.props[:opsz] and op.props[:opsz] != size))
			if op.props[:opsz] and size == 48 - op.props[:opsz]
				opsz = op.props[:opsz]
			end
		end
		opsz ||= size

		if op.props[:adsz] and size == 48 - op.props[:adsz]
			pfx << 0x67
			adsz = 48 - size
		end
		adsz ||= size
		# addrsize override / segment override
		if mrm = i.args.grep(ModRM).first
			if not op.props[:adsz] and ((mrm.b and mrm.b.sz != adsz) or (mrm.i and mrm.i.sz != adsz))
				pfx << 0x67
				adsz = 48 - adsz
			end
			pfx << [0x26, 0x2E, 0x36, 0x3E, 0x64, 0x65][mrm.seg.val] if mrm.seg
		end


		#
		# encode embedded arguments
		#
		postponed = []
		oi.each { |oa, ia|
			case oa
			when :reg, :seg3, :seg3A, :seg2, :seg2A, :eeec, :eeed, :regfp, :regmmx, :regxmm
				# field arg
				set_field[oa, ia.val]
				pfx << 0x66 if oa == :regmmx and op.props[:xmmx] and ia.sz == 128
			when :imm_val1, :imm_val3, :reg_cl, :reg_eax, :reg_dx, :regfp0
				# implicit
			else
				postponed << [oa, ia]
			end
		}

		if !(op.args & [:modrm, :modrmA, :modrmxmm, :modrmmmx]).empty?
			# reg field of modrm
			regval = (base[-1] >> 3) & 7
			base.pop
		end

		# convert label name for jmp/call/loop to relative offset
		if op.props[:setip] and op.name[0, 3] != 'ret' and i.args.first.kind_of? Expression
			postlabel = program.new_label('post'+op.name)
			target = postponed.first[1]
			target = target.rexpr if target.kind_of? Expression and target.op == :+ and not target.lexpr
			postponed.first[1] = Expression[target, :-, postlabel]
		end

		#
		# append other arguments
		#
		ret = EncodedData.new(pfx + base.pack('C*'))

		postponed.each { |oa, ia|
			case oa
			when :farptr; ed = ia.encode(@endianness, "a#{opsz}".to_sym)
			when :modrm, :modrmA, :modrmmmx, :modrmxmm
				if ia.kind_of? ModRM
					ed = ia.encode(regval, @endianness)
					if ed.kind_of?(::Array)
						if ed.length > 1
							# we know that no opcode can have more than 1 modrm
							ary = []
							ed.each { |m|
								ary << (ret.dup << m)
							}
							ret = ary
							next
						else
							ed = ed.first
						end
					end
				else
					ed = ModRM.encode_reg(ia, regval)
				end
			when :mrm_imm; ed = ia.imm.encode("a#{adsz}".to_sym, @endianness)
			when :i8, :u8, :u16; ed = ia.encode(oa, @endianness)
			when :i; ed = ia.encode("a#{opsz}".to_sym, @endianness)
			else raise SyntaxError, "Internal error: want to encode field #{oa.inspect} as arg in #{i}"
			end

			if ret.kind_of?(::Array)
				ret.each { |e| e << ed }
			else
				ret << ed
			end
		}

		# we know that no opcode with setip accept both modrm and immediate arg, so ret is not an ::Array
		ret.add_export(postlabel, ret.virtsize) if postlabel

		ret
	end
end
end
