xform_inst.py

   1 # ScratchABlock - Program analysis and decompilation framework
   2 #
   3 # Copyright (c) 2015-2018 Paul Sokolovsky
   4 #
   5 # This program is free software: you can redistribute it and/or modify
   6 # it under the terms of the GNU General Public License as published by
   7 # the Free Software Foundation, either version 3 of the License, or
   8 # (at your option) any later version.
   9 #
  10 # This program is distributed in the hope that it will be useful,
  11 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 # GNU General Public License for more details.
  14 #
  15 # You should have received a copy of the GNU General Public License
  16 # along with this program. If not, see <http://www.gnu.org/licenses/>.
  17
  18 """Transformation passes on instructions"""
  19
  20 from xform_expr import *
  21 import arch
  22
  23
  24 def normalize_cond(inst):
  25     "Normalize conditions so constants are on the right side."
  26     if inst.op == "if":
  27         inst.args[0].normalize()
  28
  29
  30 def booleanize_cond(inst):
  31     "Make conditions be of bool type (have bool operation)."
  32     if inst.op == "if":
  33         cond = inst.args[0]
  34         if not cond.is_relation():
  35             e = cond.expr
  36             if is_expr(e) and e.op == "!":
  37                 new = EXPR("==", e.args[0], VALUE(0, 0))
  38             else:
  39                 new = EXPR("!=", e, VALUE(0, 0))
  40             cond.expr = new
  41
  42
  43 def sub_const_to_add(inst):
  44     "Replace subtractions of constant with adds."
  45
  46     inst.dest = expr_xform(inst.dest, expr_sub_const_to_add)
  47     for i, a in enumerate(inst.args):
  48         inst.args[i] = expr_xform(a, expr_sub_const_to_add)
  49
  50
  51 def simplify_inst(inst):
  52     if not (inst.dest and inst.op == "="):
  53         return
  54     assert len(inst.args) == 1
  55     inst.args[0] = simplify_expr(inst.args[0])
  56
  57
  58 def struct_access_inst(inst):
  59     if not (inst.dest and inst.op == "="):
  60         return
  61     assert len(inst.args) == 1
  62     inst.args[0] = struct_access_expr(inst.args[0])
  63
  64
  65 def rewrite_complex_dest(inst):
  66     "Rewrite casts and bitfield() on the left hand side of assignment."
  67
  68     dest = inst.dest
  69     if not (inst.dest and inst.op == "="):
  70         return
  71     if not is_expr(inst.dest):
  72         return
  73     if dest.op == "CAST":
  74         lsb = 0
  75         size = dest.args[0].bitsize()
  76     elif dest.op == "SFUNC" and dest.args[0].name == "bitfield":
  77         assert is_value(dest.args[2]) and is_value(dest.args[3])
  78         lsb = dest.args[2].val
  79         size = dest.args[3].val
  80     else:
  81         assert 0
  82
  83     inst.dest = dest.args[1]
  84     if lsb == 0 and size == arch.BITNESS:
  85         return
  86
  87     all_ones = (1 << arch.BITNESS) - 1
  88     mask = (1 << size) - 1
  89     mask <<= lsb
  90     if lsb == 0:
  91         new_rhs = EXPR("&", inst.args[0], VALUE(mask))
  92     else:
  93         new_rhs = EXPR("&",
  94             EXPR("<<", inst.args[0], VALUE(lsb, 10)),
  95             VALUE(mask))
  96
  97     inst.args[0] = EXPR("|",
  98         EXPR("&", inst.dest, VALUE(all_ones ^ mask)),
  99         new_rhs)
 100
 101
 102 def rewrite_stack_vars(inst, rewrite_to=CVAR):
 103     "Rewrite memory references relative to sp0 to local variables."
 104     def mem2loc(m):
 105         if is_mem(m) and is_expr(m.expr) and set(m.expr.regs()) == {REG("sp_0")}:
 106             name = "loc" + str(m.expr.args[1].val).replace("-", "_") + "_" + str(m.type)
 107             return rewrite_to(name)
 108
 109     if inst.dest:
 110         inst.dest = expr_xform(inst.dest, mem2loc)
 111
 112     for arg_no, arg in enumerate(inst.args):
 113         inst.args[arg_no] = expr_xform(arg, mem2loc)