fuzz update/node/lib/metasm/metasm/cpu/ppc/decompile.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/ppc/main'

module Metasm
class PowerPC
	# temporarily setup dasm.address_binding so that backtracking
	# stack-related offsets resolve in :frameptr (relative to func start)
	def decompile_makestackvars(dasm, funcstart, blocks)
		oldfuncbd = dasm.address_binding[funcstart]
		dasm.address_binding[funcstart] = { :sp => :frameptr }	# this would suffice, the rest here is just optimisation

		blocks.each { |block|
			yield block
		}

		dasm.address_binding[funcstart] = oldfuncbd if oldfuncbd
	end

	# list variable dependency for each block, remove useless writes
	# returns { blockaddr => [list of vars that are needed by a following block] }
	def decompile_func_finddeps(dcmp, blocks, func)
		deps_r = {} ; deps_w = {} ; deps_to = {}
		deps_subfunc = {}	# things read/written by subfuncs

		# find read/writes by each block
		blocks.each { |b, to|
			deps_r[b] = [] ; deps_w[b] = [] ; deps_to[b] = to
			deps_subfunc[b] = []

			blk = dcmp.dasm.decoded[b].block
			blk.list.each { |di|
				a = di.backtrace_binding.values
				w = []
				di.backtrace_binding.keys.each { |k|
					case k
					when ::Symbol; w |= [k]
					else a |= Expression[k].externals	# if dword [eax] <- 42, eax is read
					end
				}
				#a << :eax if di.opcode.name == 'ret'		# standard ABI

				deps_r[b] |= a.map { |ee| Expression[ee].externals.grep(::Symbol) }.flatten - [:unknown] - deps_w[b]
				deps_w[b] |= w.map { |ee| Expression[ee].externals.grep(::Symbol) }.flatten - [:unknown]
			}
			stackoff = nil
			blk.each_to_normal { |t|
				t = dcmp.backtrace_target(t, blk.list.last.address)
				next if not t = dcmp.c_parser.toplevel.symbol[t]
				t.type = C::Function.new(C::BaseType.new(:int)) if not t.type.kind_of? C::Function	# XXX this may seem a bit extreme, and yes, it is.
				stackoff ||= Expression[dcmp.dasm.backtrace(:sp, blk.list.last.address, :snapshot_addr => blocks.first[0]).first, :-, :sp].reduce
			}
			if stackoff	# last block instr == subfunction call
				deps_r[b] |= deps_subfunc[b] - deps_w[b]
				#deps_w[b] |= [:eax, :ecx, :edx]			# standard ABI
			end
		}



		# find regs read and never written (must have been set by caller and are part of the func ABI)
		uninitialized = lambda { |b, r, done|
			from = deps_to.keys.find_all { |f| deps_to[f].include? b } - done
			from.empty? or from.find { |f|
				!deps_w[f].include?(r) and uninitialized[f, r, done + [b]]
			}
		}

		# remove writes from a block if no following block read the value
		dw = {}
		deps_w.each { |b, deps|
			dw[b] = deps.reject { |dep|
				ret = true
				done = []
				todo = deps_to[b].dup
				while a = todo.pop
					next if done.include? a
					done << a
					if not deps_r[a] or deps_r[a].include? dep
						ret = false
						break
					elsif not deps_w[a].include? dep
						todo.concat deps_to[a]
					end
				end
				ret
			}
		}

		dw
	end

	def decompile_blocks(dcmp, myblocks, deps, func, nextaddr = nil)
		scope = func.initializer
		func.type.args.each { |a| scope.symbol[a.name] = a }
		stmts = scope.statements
		func_entry = myblocks.first[0]
		until myblocks.empty?
			b, to = myblocks.shift
			if l = dcmp.dasm.get_label_at(b)
				stmts << C::Label.new(l)
			end

			# list of assignments [[dest reg, expr assigned]]
			ops = []
			# reg binding (reg => value, values.externals = regs at block start)
			binding = {}
			# Expr => CExpr
			ce  = lambda { |*e| dcmp.decompile_cexpr(Expression[Expression[*e].reduce], scope) }
			# Expr => Expr.bind(binding) => CExpr
			ceb = lambda { |*e| ce[Expression[*e].bind(binding)] }

			# dumps a CExprs that implements an assignment to a reg (uses ops[], patches op => [reg, nil])
			commit = lambda {
				deps[b].map { |k|
					[k, ops.rindex(ops.reverse.find { |r, v| r == k })]
				}.sort_by { |k, i| i.to_i }.each { |k, i|
					next if not i or not binding[k]
					e = k
					final = []
					ops[0..i].reverse_each { |r, v|
						final << r if not v
						e = Expression[e].bind(r => v).reduce if not final.include? r
					}
					ops[i][1] = nil
					binding.delete k
					stmts << ce[k, :'=', e] if k != e
				}
			}

			# go !
			dcmp.dasm.decoded[b].block.list.each_with_index { |di, didx|
				a = di.instruction.args
				if di.opcode.props[:setip] and not di.opcode.props[:stopexec]
					# conditional jump
					commit[]
					n = dcmp.backtrace_target(get_xrefs_x(dcmp.dasm, di).first, di.address)
					#cc = ceb[decode_cc_to_expr(di.opcode.name[1..-1])]
					cc = ceb[:condjmp]
					stmts << C::If.new(C::CExpression[cc], C::Goto.new(n))
					to.delete dcmp.dasm.normalize(n)
					next
				end

				case di.opcode.name
				when 'blr'
					commit[]
					stmts << C::Return.new(nil)
				when 'bl'	# :saveip
					n = dcmp.backtrace_target(get_xrefs_x(dcmp.dasm, di).first, di.address)
					args = []
					if t = dcmp.c_parser.toplevel.symbol[n] and t.type.args
						stackoff = Expression[dcmp.dasm.backtrace(:sp, di.address, :snapshot_addr => func_entry), :-, :sp].bind(:sp => :frameptr).reduce rescue nil
						args_todo = t.type.args.dup
						args = []
						args_todo.each {
							if stackoff.kind_of? Integer
								var = Indirection[[:frameptr, :+, stackoff], @size/8]
								stackoff += @size/8
							else
								var = 0
							end
							args << ceb[var]
							binding.delete var
						}
					end
					commit[]
					#next if not di.block.to_subfuncret

					if n.kind_of? ::String
						if not f = dcmp.c_parser.toplevel.symbol[n]
							# internal functions are predeclared, so this one is extern
							f = dcmp.c_parser.toplevel.symbol[n] = C::Variable.new
							f.name = n
							f.type = C::Function.new(C::BaseType.new(:int))
							dcmp.c_parser.toplevel.statements << C::Declaration.new(f)
						end
						commit[]
					else
						# indirect funcall
						fptr = ceb[n]
						binding.delete n
						commit[]
						proto = C::Function.new(C::BaseType.new(:int))
						f = C::CExpression[[fptr], proto]
					end
					binding.delete :eax
					e = C::CExpression[f, :funcall, args]
					e = C::CExpression[ce[:eax], :'=', e, f.type.type] if deps[b].include? :eax and f.type.type != C::BaseType.new(:void)
					stmts << e
				when 'b'
					a = di.instruction.args.first
					if a.kind_of? Expression
					else
						# indirect jmp, convert to return (*fptr)();
						n = di.instruction.args.first.symbolic
						fptr = ceb[n]
						binding.delete n
						commit[]
						proto = C::Function.new(C::BaseType.new(:void))
						ret = C::Return.new(C::CExpression[[[fptr], C::Pointer.new(proto)], :funcall, []])
						class << ret ; attr_accessor :from_instr end
						ret.from_instr = di
						stmts << ret
						to = []
					end
				else
					bd = get_fwdemu_binding(di)
					if di.backtrace_binding[:incomplete_binding]
						commit[]
						stmts << C::Asm.new(di.instruction.to_s, nil, nil, nil, nil, nil)
					else
						bd.each { |k, v|
							if k.kind_of? ::Symbol
								ops << [k, v]
							else	# memory
								stmts << ceb[k, :'=', v]
								binding.delete k
							end
						}
						update = {}
						bd.each { |k, v|
							next if not k.kind_of? ::Symbol
							update[k] = Expression[Expression[v].bind(binding).reduce]
						}
						binding.update update
					end
				end
			}
			commit[]

			case to.length
			when 0
				if not myblocks.empty? and not %w[ret jmp].include? dcmp.dasm.decoded[b].block.list.last.instruction.opname
					puts "  block #{Expression[b]} has no to and don't end in ret"
				end
			when 1
				if (myblocks.empty? ? nextaddr != to[0] : myblocks.first.first != to[0])
					stmts << C::Goto.new(dcmp.dasm.auto_label_at(to[0], 'unknown_goto'))
				end
			else
				puts "  block #{Expression[b]} with multiple to"
			end
		end
	end
end
end
