fix a bug in accessing union fields

GCC and MSVC and Clang pack structs with bit-fields differently. So if a union has a field of packed struct type, and the struct has a bit-field, writing to a field after the bit-field has non-deterministic effect, thus makes all the union fields non-readable.

src/FactUnion.cpp

@@ -135,7 +135,7 @@ FactUnion::abstract_fact_for_assign(const std::vector<const Fact*>& facts, const
 		const FactUnion* fu = 0;
 		if (v->is_union_field()) { 
 			fu = make_fact(v->field_var_of, v->get_field_id());
-		} else if (v->is_inside_union_field() && v->type->has_padding()) {
+		} else if (v->is_inside_union_field() && (v->type->has_padding() || v->is_packed_after_bitfield())) {
 			fu = make_fact(v->get_container_union(), BOTTOM);
 		}
 

src/Type.cpp

@@ -1207,10 +1207,13 @@ Type::is_bitfield(size_t index) const
 bool
 Type::has_bitfields() const
 {
-	size_t i;
-	for (i = 0; i < bitfields_length_.size(); ++i) {
-		if (bitfields_length_[i] >= 0)
+	for (size_t i=0; i<fields.size(); i++) { 
+		if (bitfields_length_[i] >= 0) {
 			return true;
+		}
+		if (fields[i]->eType == eStruct && fields[i]->has_bitfields()) {
+			return true;
+		}
 	}
 	return false;
 }

src/Variable.cpp

@@ -1360,6 +1360,25 @@ Variable::find_pointer_fields(vector<const Variable*>& ptr_fields) const
 	}
 }
 
+/* a struct field packed after a bit-field could has nondeterministic offset due to incompatible packings between compilers */
+bool
+Variable::is_packed_after_bitfield(void) const 
+{ 
+	const Variable* parent = this->field_var_of; 
+	if (parent == NULL) return false;
+	if (parent->type->eType == eStruct && parent->type->packed_) {
+		for (size_t i=0; i<parent->field_vars.size(); i++) {
+			if (parent->field_vars[i] == this) {
+				break;
+			}
+			if (parent->type->is_bitfield(i) || parent->field_vars[i]->type->has_bitfields()) {
+				return true;
+			} 
+		}
+	} 
+	return parent->is_packed_after_bitfield();
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 // Local Variables:

src/Variable.h

@@ -94,6 +94,7 @@ class Variable
 	int  get_field_id(void) const;
 	bool is_union_field(void) const { return field_var_of != 0 && field_var_of->type->eType == eUnion; };
 	bool is_inside_union_field(void) const { return is_union_field() || (field_var_of && field_var_of->is_inside_union_field()); }
+	bool is_packed_after_bitfield(void) const;
 	bool is_array_field(void) const;
 	bool is_virtual(void) const;
 	bool is_aggregate(void) const { return type && type->is_aggregate(); }