exprt ssa_alias_guard( const exprt &e1, const exprt &e2, const namespacet &ns) { exprt a1=address_canonizer(address_of_exprt(e1), ns); // TODO: We should compare 'base' pointers here because // we have a higher chance that there was no pointer arithmetic // on the base pointer than that the result of the pointer // arithmetic points to a base pointer. // The following hack does that: if(a1.id()==ID_plus) a1=a1.op0(); exprt a2=address_canonizer(address_of_exprt(e2), ns); // in some cases, we can use plain address equality, // as we assume well-aligned-ness mp_integer size1=pointer_offset_size(e1.type(), ns); mp_integer size2=pointer_offset_size(e2.type(), ns); if(size1>=size2) { exprt lhs=a1; exprt rhs=a2; if(ns.follow(rhs.type())!=ns.follow(lhs.type())) rhs=typecast_exprt(rhs, lhs.type()); return equal_exprt(lhs, rhs); } return same_object(a1, a2); }
exprt ssa_alias_guard( const exprt &e1, const exprt &e2, const namespacet &ns) { exprt a1=address_canonizer(address_of_exprt(e1), ns); exprt a2=address_canonizer(address_of_exprt(e2), ns); // in some cases, we can use plain address equality, // as we assume well-aligned-ness mp_integer size1=pointer_offset_size(e1.type(), ns); mp_integer size2=pointer_offset_size(e2.type(), ns); if(size1>=size2) { exprt lhs=a1; exprt rhs=a2; if(ns.follow(rhs.type())!=ns.follow(lhs.type())) rhs=typecast_exprt(rhs, lhs.type()); return equal_exprt(lhs, rhs); } return same_object(a1, a2); }
void goto_checkt::pointer_rel_check(const exprt &expr, const guardt &guard) { if (expr.operands().size() != 2) throw expr.id_string() + " takes one argument"; if (expr.op0().type().id() == "pointer" && expr.op1().type().id() == "pointer") { // add same-object subgoal if (!options.get_bool_option("no-pointer-check")) { exprt same_object("same-object", bool_typet()); same_object.copy_to_operands(expr.op0(), expr.op1()); add_guarded_claim(same_object, "same object violation", "pointer", expr.find_location(), guard); } } }
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; }