Exemplo n.º 1
0
void goto_checkt::bounds_check(
  const index_exprt &expr,
  const guardt &guard)
{
  if(!enable_bounds_check)
    return;

  if(expr.find("bounds_check").is_not_nil() &&
     !expr.get_bool("bounds_check"))
    return;

  typet array_type=ns.follow(expr.array().type());

  if(array_type.id()==ID_pointer)
    return; // done by the pointer code
  else if(array_type.id()==ID_incomplete_array)
    throw "index got incomplete array";
  else if(array_type.id()!=ID_array && array_type.id()!=ID_vector)
    throw "bounds check expected array or vector type, got "
      +array_type.id_string();

  std::string name=array_name(expr.array());

  const exprt &index=expr.index();
  object_descriptor_exprt ode;
  ode.build(expr, ns);

  if(index.type().id()!=ID_unsignedbv)
  {
    // we undo typecasts to signedbv
    if(index.id()==ID_typecast &&
       index.operands().size()==1 &&
       index.op0().type().id()==ID_unsignedbv)
    {
      // ok
    }
    else
    {
      mp_integer i;

      if(!to_integer(index, i) && i>=0)
      {
        // ok
      }
      else
      {
        exprt effective_offset=ode.offset();

        if(ode.root_object().id()==ID_dereference)
        {
          exprt p_offset=pointer_offset(
            to_dereference_expr(ode.root_object()).pointer());
          assert(p_offset.type()==effective_offset.type());

          effective_offset=plus_exprt(p_offset, effective_offset);
        }

        exprt zero=gen_zero(ode.offset().type());
        assert(zero.is_not_nil());

        // the final offset must not be negative
        binary_relation_exprt inequality(effective_offset, ID_ge, zero);

        add_guarded_claim(
          inequality,
          name+" lower bound",
          "array bounds",
          expr.find_source_location(),
          expr,
          guard);
      }
    }
  }

  if(ode.root_object().id()==ID_dereference)
  {
    const exprt &pointer=
      to_dereference_expr(ode.root_object()).pointer();

    if_exprt size(
      dynamic_object(pointer),
      typecast_exprt(dynamic_size(ns), object_size(pointer).type()),
      object_size(pointer));

    plus_exprt effective_offset(ode.offset(), pointer_offset(pointer));

    assert(effective_offset.op0().type()==effective_offset.op1().type());
    assert(effective_offset.type()==size.type());

    binary_relation_exprt inequality(effective_offset, ID_lt, size);

    or_exprt precond(
      and_exprt(
        dynamic_object(pointer),
        not_exprt(malloc_object(pointer, ns))),
      inequality);

    add_guarded_claim(
      precond,
      name+" upper bound",
      "array bounds",
      expr.find_source_location(),
      expr,
      guard);

    return;
  }

  const exprt &size=array_type.id()==ID_array ?
                    to_array_type(array_type).size() :
                    to_vector_type(array_type).size();

  if(size.is_nil())
  {
    // Linking didn't complete, we don't have a size.
    // Not clear what to do.
  }
  else if(size.id()==ID_infinity)
  {
  }
  else if(size.is_zero() &&
          expr.array().id()==ID_member)
  {
    // a variable sized struct member
  }
  else
  {
    binary_relation_exprt inequality(index, ID_lt, size);

    // typecast size
    if(inequality.op1().type()!=inequality.op0().type())
      inequality.op1().make_typecast(inequality.op0().type());

    // typecast size
    if(inequality.op1().type()!=inequality.op0().type())
      inequality.op1().make_typecast(inequality.op0().type());

    add_guarded_claim(
      inequality,
      name+" upper bound",
      "array bounds",
      expr.find_source_location(),
      expr,
      guard);
  }
}
Exemplo n.º 2
0
void value_set_dereferencet::bounds_check(
  const index_exprt &expr,
  const guardt &guard)
{
  if(!options.get_bool_option("pointer-check"))
    return;

  if(!options.get_bool_option("bounds-check"))
    return;

  const typet &array_type=ns.follow(expr.op0().type());

  if(array_type.id()!=ID_array)
    throw "bounds check expected array type";

  std::string name=array_name(ns, expr.array());

  {
    mp_integer i;
    if(!to_integer(expr.index(), i) &&
       i>=0)
    {
    }
    else
    {
      exprt zero=from_integer(0, expr.index().type());

      if(zero.is_nil())
        throw "no zero constant of index type "+
          expr.index().type().pretty();

      binary_relation_exprt
        inequality(expr.index(), ID_lt, zero);

      guardt tmp_guard(guard);
      tmp_guard.add(inequality);
      dereference_callback.dereference_failure(
        "array bounds",
        name+" lower bound", tmp_guard);
    }
  }

  const exprt &size_expr=
    to_array_type(array_type).size();

  if(size_expr.id()==ID_infinity)
  {
  }
  else if(size_expr.is_zero() && expr.array().id()==ID_member)
  {
    // this is a variable-sized struct field
  }
  else
  {
    if(size_expr.is_nil())
      throw "index array operand of wrong type";

    binary_relation_exprt inequality(expr.index(), ID_ge, size_expr);

    if(c_implicit_typecast(
      inequality.op0(),
      inequality.op1().type(),
      ns))
      throw "index address of wrong type";

    guardt tmp_guard(guard);
    tmp_guard.add(inequality);
    dereference_callback.dereference_failure(
      "array bounds",
      name+" upper bound", tmp_guard);
  }
}
Exemplo n.º 3
0
void arrayst::record_array_index(const index_exprt &index)
{
  unsigned number=arrays.number(index.array());
  if(number>=index_map.size()) index_map.resize(number+1);
  index_map[number].insert(index.index());
}
Exemplo n.º 4
0
void boolbvt::convert_index(const index_exprt &expr, bvt &bv)
{
  if(expr.id()!=ID_index)
    throw "expected index expression";

  if(expr.operands().size()!=2)
    throw "index takes two operands";
    
  const exprt &array=expr.array();
  const exprt &index=expr.index();
  
  const array_typet &array_type=
    to_array_type(ns.follow(array.type()));

  // see if the array size is constant

  if(is_unbounded_array(array_type))
  {
    // use array decision procedure
  
    unsigned width=boolbv_width(expr.type());
    
    if(width==0)
      return conversion_failed(expr, bv);

    // free variables

    bv.resize(width);
    for(unsigned i=0; i<width; i++)
      bv[i]=prop.new_variable();

    record_array_index(expr);

    // record type if array is a symbol

    if(array.id()==ID_symbol)
      map.get_map_entry(
        to_symbol_expr(array).get_identifier(), array_type);

    // make sure we have the index in the cache
    convert_bv(index);
    
    return;
  }

  // see if the index address is constant

  mp_integer index_value;
  if(!to_integer(index, index_value))
    return convert_index(array, index_value, bv);

  unsigned width=boolbv_width(expr.type());
  
  if(width==0)
    return conversion_failed(expr, bv);

  mp_integer array_size;
  if(to_integer(array_type.size(), array_size))
  {
    std::cout << to_array_type(array.type()).size().pretty() << std::endl;
    throw "failed to convert array size";
  }

  // get literals for the whole array

  const bvt &array_bv=convert_bv(array);

  if(array_size*width!=array_bv.size())
    throw "unexpected array size";
    
  // TODO: maybe a shifter-like construction would be better

  if(prop.has_set_to())
  {
    // free variables

    bv.resize(width);
    for(unsigned i=0; i<width; i++)
      bv[i]=prop.new_variable();

    // add implications

    equal_exprt index_equality;
    index_equality.lhs()=index; // index operand

    bvt equal_bv;
    equal_bv.resize(width);

    for(mp_integer i=0; i<array_size; i=i+1)
    {
      index_equality.rhs()=from_integer(i, index_equality.lhs().type());

      if(index_equality.rhs().is_nil())
        throw "number conversion failed (1)";

      mp_integer offset=i*width;

      for(unsigned j=0; j<width; j++)
        equal_bv[j]=prop.lequal(bv[j],
                           array_bv[integer2long(offset+j)]);

      prop.l_set_to_true(
        prop.limplies(convert(index_equality), prop.land(equal_bv)));
    }
  }
  else
  {
    bv.resize(width);

    equal_exprt equality;
    equality.lhs()=index; // index operand

    typet constant_type=index.type(); // type of index operand
    
    assert(array_size>0);

    for(mp_integer i=0; i<array_size; i=i+1)
    {
      equality.op1()=from_integer(i, constant_type);
        
      literalt e=convert(equality);

      mp_integer offset=i*width;

      for(unsigned j=0; j<width; j++)
      {
        literalt l=array_bv[integer2long(offset+j)];

        if(i==0) // this initializes bv
          bv[j]=l;
        else
          bv[j]=prop.lselect(e, l, bv[j]);
      }
    }    
  }
}
bool remove_const_function_pointerst::try_resolve_index_of(
  const index_exprt &index_expr,
  expressionst &out_expressions,
  bool &out_is_const)
{
  // Get the array(s) it belongs to
  expressionst potential_array_exprs;
  bool array_const=false;
  bool resolved_array=
    try_resolve_expression(
      index_expr.array(),
      potential_array_exprs,
      array_const);

  if(resolved_array)
  {
    bool all_possible_const=true;
    for(const exprt &potential_array_expr : potential_array_exprs)
    {
      all_possible_const=
        all_possible_const &&
        is_const_type(potential_array_expr.type().subtype());

      if(potential_array_expr.id()==ID_array)
      {
        // Get the index if we can
        mp_integer value;
        if(try_resolve_index_value(index_expr.index(), value))
        {
          expressionst array_out_functions;
          const exprt &func_expr=
            potential_array_expr.operands()[integer2size_t(value)];
          bool value_const=false;
          bool resolved_value=
            try_resolve_expression(func_expr, array_out_functions, value_const);

          if(resolved_value)
          {
            out_expressions.insert(
              out_expressions.end(),
              array_out_functions.begin(),
              array_out_functions.end());
          }
          else
          {
            LOG("Failed to resolve array value", func_expr);
            return false;
          }
        }
        else
        {
          // We don't know what index it is,
          // but we know the value is from the array
          for(const exprt &array_entry : potential_array_expr.operands())
          {
            expressionst array_contents;
            bool is_entry_const;
            bool resolved_value=
              try_resolve_expression(
                array_entry, array_contents, is_entry_const);

            if(!resolved_value)
            {
              LOG("Failed to resolve array value", array_entry);
              return false;
            }

            for(const exprt &resolved_array_entry : array_contents)
            {
              if(!resolved_array_entry.is_zero())
              {
                out_expressions.push_back(resolved_array_entry);
              }
            }
          }
        }
      }
      else
      {
        LOG(
          "Squashing index of did not result in an array",
          potential_array_expr);
        return false;
      }
    }

    out_is_const=all_possible_const || array_const;
    return true;
  }
  else
  {
    LOG("Failed to squash index of to array expression", index_expr);
    return false;
  }
}