exprt ssa_alias_value(
const exprt &e1,
const exprt &e2,
const namespacet &ns)
{
const typet &e1_type=ns.follow(e1.type());
const typet &e2_type=ns.follow(e2.type());
// type matches?
if(e1_type==e2_type)
return e2;
exprt a1=address_canonizer(address_of_exprt(e1), ns);
exprt a2=address_canonizer(address_of_exprt(e2), ns);
exprt offset1=pointer_offset(a1);
// array index possible?
if(e2_type.id()==ID_array &&
e1_type==ns.follow(e2_type.subtype()))
{
// this assumes well-alignedness
mp_integer element_size=pointer_offset_size(e2_type.subtype(), ns);
if(element_size==1)
return index_exprt(e2, offset1, e1.type());
else if(element_size>1)
{
exprt index=
div_exprt(offset1, from_integer(element_size, offset1.type()));
return index_exprt(e2, index, e1.type());
}
}
byte_extract_exprt byte_extract(byte_extract_id(), e1.type());
byte_extract.op()=e2;
byte_extract.offset()=offset1;
return byte_extract;
}
void test_extract(void)
{
int i;
u_int32_t ret;
u_int8_t value1[2];
u_int8_t value2[2];
u_int8_t value3[4];
value1[0] = 0;
value1[1] = 0xff;
value2[0] = 0xff;
value2[1] = 0x01;
value3[0] = 0xff;
value3[1] = 0xff;
value3[2] = 0x00;
value3[3] = 0x00;
if(byte_extract(BIG, 2, value1, value1, value1 + 2, &ret))
{
printf("test 1 failed\n");
}
else
{
printf("test 1: value: %x %u\n", ret, ret);
}
if(byte_extract(LITTLE, 2, value1, value1, value1 + 2, &ret))
{
printf("test 2 failed\n");
}
else
{
printf("test 2: value: %x %u\n", ret, ret);
}
if(byte_extract(LITTLE, 2, value1 + 2, value1, value1 + 2, &ret))
{
printf("test 3 failed correctly\n");
}
else
{
printf("test 3: value: %x %u\n", ret, ret);
}
if(byte_extract(BIG, 2, value2, value2, value2 + 2, &ret))
{
printf("test 1 failed\n");
}
else
{
printf("test 1: value: %x %u\n", ret, ret);
}
if(byte_extract(LITTLE, 2, value2, value2, value2 + 2, &ret))
{
printf("test 2 failed\n");
}
else
{
printf("test 2: value: %x %u\n", ret, ret);
}
if(byte_extract(LITTLE, 2, value2 + 2, value2, value2 + 2, &ret))
{
printf("test 3 failed correctly\n");
}
else
{
printf("test 3: value: %x %u\n", ret, ret);
}
if(byte_extract(BIG, 4, value3, value3, value3 + 4, &ret))
{
printf("test 1 failed\n");
}
else
{
printf("test 1: value: %x %u\n", ret, ret);
}
if(byte_extract(LITTLE, 4, value3, value3, value3 + 4, &ret))
{
printf("test 2 failed\n");
}
else
{
printf("test 2: value: %x %u\n", ret, ret);
}
if(byte_extract(LITTLE, 4, value3 + 2, value3, value3 + 4, &ret))
{
printf("test 3 failed correctly\n");
}
else
{
printf("test 3: value: %x %u\n", ret, ret);
}
printf("-----------------------------\n");
for(i=0;i<10;i++)
{
if(byte_extract(LITTLE, 4, value3 + i, value3, value3 + 4, &ret))
{
printf("[loop] %d failed correctly\n", i);
}
else
{
printf("[loop] value: %x %x\n", ret, *(u_int32_t *) &value3);
}
}
}
value_set_dereferencet::valuet value_set_dereferencet::build_reference_to(
const exprt &what,
const modet mode,
const exprt &pointer_expr,
const guardt &guard)
{
const typet &dereference_type=
ns.follow(pointer_expr.type()).subtype();
if(what.id()==ID_unknown ||
what.id()==ID_invalid)
{
invalid_pointer(pointer_expr, guard);
return valuet();
}
if(what.id()!=ID_object_descriptor)
throw "unknown points-to: "+what.id_string();
const object_descriptor_exprt &o=to_object_descriptor_expr(what);
const exprt &root_object=o.root_object();
const exprt &object=o.object();
#if 0
std::cout << "O: " << from_expr(ns, "", root_object) << '\n';
#endif
valuet result;
if(root_object.id()=="NULL-object")
{
if(options.get_bool_option("pointer-check"))
{
guardt tmp_guard(guard);
if(o.offset().is_zero())
{
tmp_guard.add(null_pointer(pointer_expr));
dereference_callback.dereference_failure(
"pointer dereference",
"NULL pointer", tmp_guard);
}
else
{
tmp_guard.add(null_object(pointer_expr));
dereference_callback.dereference_failure(
"pointer dereference",
"NULL plus offset pointer", tmp_guard);
}
}
}
else if(root_object.id()==ID_dynamic_object)
{
// const dynamic_object_exprt &dynamic_object=
// to_dynamic_object_expr(root_object);
// the object produced by malloc
exprt malloc_object=
ns.lookup(CPROVER_PREFIX "malloc_object").symbol_expr();
exprt is_malloc_object=same_object(pointer_expr, malloc_object);
// constraint that it actually is a dynamic object
exprt dynamic_object_expr(ID_dynamic_object, bool_typet());
dynamic_object_expr.copy_to_operands(pointer_expr);
// this is also our guard
result.pointer_guard=dynamic_object_expr;
// can't remove here, turn into *p
result.value=dereference_exprt(pointer_expr, dereference_type);
if(options.get_bool_option("pointer-check"))
{
// if(!dynamic_object.valid().is_true())
{
// check if it is still alive
guardt tmp_guard(guard);
tmp_guard.add(deallocated(pointer_expr, ns));
dereference_callback.dereference_failure(
"pointer dereference",
"dynamic object deallocated",
tmp_guard);
}
if(options.get_bool_option("bounds-check"))
{
if(!o.offset().is_zero())
{
// check lower bound
guardt tmp_guard(guard);
tmp_guard.add(is_malloc_object);
tmp_guard.add(
dynamic_object_lower_bound(
pointer_expr,
ns,
nil_exprt()));
dereference_callback.dereference_failure(
"pointer dereference",
"dynamic object lower bound", tmp_guard);
}
{
// check upper bound
// we check SAME_OBJECT(__CPROVER_malloc_object, p) &&
// POINTER_OFFSET(p)+size>__CPROVER_malloc_size
guardt tmp_guard(guard);
tmp_guard.add(is_malloc_object);
tmp_guard.add(
dynamic_object_upper_bound(
pointer_expr,
dereference_type,
ns,
size_of_expr(dereference_type, ns)));
dereference_callback.dereference_failure(
"pointer dereference",
"dynamic object upper bound", tmp_guard);
}
}
}
}
else if(root_object.id()==ID_integer_address)
{
// This is stuff like *((char *)5).
// This is turned into an access to __CPROVER_memory[...].
if(language_mode==ID_java)
{
result.value=nil_exprt();
return result;
}
const symbolt &memory_symbol=ns.lookup(CPROVER_PREFIX "memory");
exprt symbol_expr=symbol_exprt(memory_symbol.name, memory_symbol.type);
if(base_type_eq(
ns.follow(memory_symbol.type).subtype(),
dereference_type, ns))
{
// Types match already, what a coincidence!
// We can use an index expression.
exprt index_expr=index_exprt(symbol_expr, pointer_offset(pointer_expr));
index_expr.type()=ns.follow(memory_symbol.type).subtype();
result.value=index_expr;
}
else if(dereference_type_compare(
ns.follow(memory_symbol.type).subtype(),
dereference_type))
{
exprt index_expr=index_exprt(symbol_expr, pointer_offset(pointer_expr));
index_expr.type()=ns.follow(memory_symbol.type).subtype();
result.value=typecast_exprt(index_expr, dereference_type);
}
else
{
// We need to use byte_extract.
// Won't do this without a commitment to an endianness.
if(config.ansi_c.endianness==configt::ansi_ct::endiannesst::NO_ENDIANNESS)
{
}
else
{
exprt byte_extract(byte_extract_id(), dereference_type);
byte_extract.copy_to_operands(
symbol_expr, pointer_offset(pointer_expr));
result.value=byte_extract;
}
}
}
else
{
// something generic -- really has to be a symbol
address_of_exprt object_pointer(object);
if(o.offset().is_zero())
{
equal_exprt equality(pointer_expr, object_pointer);
if(ns.follow(equality.lhs().type())!=ns.follow(equality.rhs().type()))
equality.lhs().make_typecast(equality.rhs().type());
result.pointer_guard=equality;
}
else
{
result.pointer_guard=same_object(pointer_expr, object_pointer);
}
guardt tmp_guard(guard);
tmp_guard.add(result.pointer_guard);
valid_check(object, tmp_guard, mode);
const typet &object_type=ns.follow(object.type());
const exprt &root_object=o.root_object();
const typet &root_object_type=ns.follow(root_object.type());
exprt root_object_subexpression=root_object;
if(dereference_type_compare(object_type, dereference_type) &&
o.offset().is_zero())
{
// The simplest case: types match, and offset is zero!
// This is great, we are almost done.
result.value=object;
if(object_type!=ns.follow(dereference_type))
result.value.make_typecast(dereference_type);
}
else if(root_object_type.id()==ID_array &&
dereference_type_compare(
root_object_type.subtype(),
dereference_type))
{
// We have an array with a subtype that matches
// the dereferencing type.
// We will require well-alignedness!
exprt offset;
// this should work as the object is essentially the root object
if(o.offset().is_constant())
offset=o.offset();
else
offset=pointer_offset(pointer_expr);
exprt adjusted_offset;
// are we doing a byte?
mp_integer element_size=
dereference_type.id()==ID_empty?
pointer_offset_size(char_type(), ns):
pointer_offset_size(dereference_type, ns);
if(element_size==1)
{
// no need to adjust offset
adjusted_offset=offset;
}
else if(element_size<=0)
{
throw "unknown or invalid type size of:\n"+dereference_type.pretty();
}
else
{
exprt element_size_expr=
from_integer(element_size, offset.type());
adjusted_offset=binary_exprt(
offset, ID_div, element_size_expr, offset.type());
// TODO: need to assert well-alignedness
}
index_exprt index_expr=
index_exprt(root_object, adjusted_offset, root_object_type.subtype());
bounds_check(index_expr, tmp_guard);
result.value=index_expr;
if(ns.follow(result.value.type())!=ns.follow(dereference_type))
result.value.make_typecast(dereference_type);
}
else if(get_subexpression_at_offset(
root_object_subexpression,
o.offset(),
dereference_type,
ns))
{
// Successfully found a member, array index, or combination thereof
// that matches the desired type and offset:
result.value=root_object_subexpression;
}
else
{
// we extract something from the root object
result.value=o.root_object();
// this is relative to the root object
const exprt offset=pointer_offset(pointer_expr);
if(memory_model(result.value, dereference_type, tmp_guard, offset))
{
// ok, done
}
else
{
if(options.get_bool_option("pointer-check"))
{
std::string msg="memory model not applicable (got `";
msg+=from_type(ns, "", result.value.type());
msg+="', expected `";
msg+=from_type(ns, "", dereference_type);
msg+="')";
dereference_callback.dereference_failure(
"pointer dereference",
msg, tmp_guard);
}
return valuet(); // give up, no way that this is ok
}
}
}
return result;
}
