C++ Reference

src/ast/passes/codegen_llvm.cpp

@@ -1800,7 +1800,8 @@ void CodegenLLVM::unop_ptr(Unop &unop)
   switch (unop.op) {
     case Operator::MUL: {
       if (unop.type.IsIntegerTy() || unop.type.IsPtrTy()) {
-        auto *et = type.GetPointeeTy();
+        auto *et = type.IsRefTy() ? type.GetDereferencedType()
+                                  : type.GetPointeeTy();
         AllocaInst *dst = b_.CreateAllocaBPF(*et, "deref");
         b_.CreateProbeRead(ctx_, dst, *et, expr_, unop.loc, type.GetAS());
         expr_ = b_.CreateLoad(b_.GetType(*et), dst);
@@ -1826,7 +1827,10 @@ void CodegenLLVM::visit(Unop &unop)
   SizedType &type = unop.expr->type;
   if (type.IsIntegerTy()) {
     unop_int(unop);
-  } else if (type.IsPtrTy() || type.IsCtxAccess()) // allow dereferencing args
+  } else if (type.IsPtrTy() || type.IsRefTy() ||
+             type.IsCtxAccess()) // allow
+                                 // dereferencing
+                                 // args
   {
     unop_ptr(unop);
   } else {
@@ -3791,7 +3795,7 @@ void CodegenLLVM::readDatastructElemFromStack(Value *src_data,
   if (src->getType() != dst_type->getPointerTo())
     src = b_.CreatePointerCast(src, dst_type->getPointerTo());
 
-  if (elem_type.IsIntegerTy() || elem_type.IsPtrTy()) {
+  if (elem_type.IsIntegerTy() || elem_type.IsPtrTy() || elem_type.IsRefTy()) {
     // Load the correct type from src
     expr_ = b_.CreateDatastructElemLoad(
         elem_type, src, true, elem_type.GetAS());

src/ast/passes/field_analyser.cpp

@@ -159,8 +159,10 @@ void FieldAnalyser::visit(AssignVarStatement &assignment)
 void FieldAnalyser::visit(Unop &unop)
 {
   Visit(*unop.expr);
-  if (unop.op == Operator::MUL && sized_type_.IsPtrTy()) {
-    sized_type_ = *sized_type_.GetPointeeTy();
+  if (unop.op == Operator::MUL &&
+      (sized_type_.IsPtrTy() || sized_type_.IsRefTy())) {
+    sized_type_ = sized_type_.IsPtrTy() ? *sized_type_.GetPointeeTy()
+                                        : *sized_type_.GetDereferencedType();
     resolve_fields(sized_type_);
   }
 }

src/ast/passes/semantic_analyser.cpp

@@ -531,6 +531,7 @@ void SemanticAnalyser::visit(Call &call)
       }
 
       expr.accept(*this);
+      dereference_if_needed((*call.vargs)[i]);
     }
   }
 
@@ -1324,6 +1325,7 @@ void SemanticAnalyser::visit(Sizeof &szof)
   szof.type = CreateUInt64();
   if (szof.expr) {
     szof.expr->accept(*this);
+    dereference_if_needed(szof.expr);
     szof.argtype = szof.expr->type;
   }
   resolve_struct_type(szof.argtype, szof.loc);
@@ -1334,6 +1336,7 @@ void SemanticAnalyser::visit(Offsetof &ofof)
   ofof.type = CreateUInt64();
   if (ofof.expr) {
     ofof.expr->accept(*this);
+    dereference_if_needed(ofof.expr);
     ofof.record = ofof.expr->type;
   }
   resolve_struct_type(ofof.record, ofof.loc);
@@ -1440,6 +1443,7 @@ void SemanticAnalyser::visit(Map &map)
     for (unsigned int i = 0; i < map.vargs->size(); i++) {
       Expression *expr = map.vargs->at(i);
       expr->accept(*this);
+      dereference_if_needed(map.vargs->at(i));
 
       // Insert a cast to 64 bits if needed by injecting
       // a cast into the ast.
@@ -1508,7 +1512,9 @@ void SemanticAnalyser::visit(Variable &var)
 void SemanticAnalyser::visit(ArrayAccess &arr)
 {
   arr.expr->accept(*this);
+  dereference_if_needed(arr.expr);
   arr.indexpr->accept(*this);
+  dereference_if_needed(arr.indexpr);
 
   SizedType &type = arr.expr->type;
   SizedType &indextype = arr.indexpr->type;
@@ -1749,7 +1755,10 @@ void SemanticAnalyser::binop_ptr(Binop &binop)
 void SemanticAnalyser::visit(Binop &binop)
 {
   binop.left->accept(*this);
+  dereference_if_needed(binop.left);
+
   binop.right->accept(*this);
+  dereference_if_needed(binop.right);
 
   auto &lht = binop.left->type;
   auto &rht = binop.right->type;
@@ -1852,6 +1861,10 @@ void SemanticAnalyser::visit(Unop &unop)
   }
 
   unop.expr->accept(*this);
+  if (!(unop.op == Operator::MUL && unop.expr->type.IsRefTy())) {
+    // Prevent dereferencing a deref
+    dereference_if_needed(unop.expr);
+  }
 
   auto valid_ptr_op = false;
   switch (unop.op) {
@@ -1865,10 +1878,11 @@ void SemanticAnalyser::visit(Unop &unop)
 
   SizedType &type = unop.expr->type;
   if (is_final_pass()) {
-    // Unops are only allowed on ints (e.g. ~$x), dereference only on pointers
-    // and context (we allow args->field for backwards compatibility)
+    // Unops are only allowed on ints (e.g. ~$x), dereference only on pointers,
+    // references and context (we allow args->field for backwards compatibility)
     if (!type.IsIntegerTy() &&
-        !((type.IsPtrTy() || type.IsCtxAccess()) && valid_ptr_op)) {
+        !((type.IsPtrTy() || type.IsRefTy() || type.IsCtxAccess()) &&
+          valid_ptr_op)) {
       LOG(ERROR, unop.loc, err_)
           << "The " << opstr(unop)
           << " operator can not be used on expressions of type '" << type
@@ -1920,8 +1934,11 @@ void SemanticAnalyser::visit(Unop &unop)
 void SemanticAnalyser::visit(Ternary &ternary)
 {
   ternary.cond->accept(*this);
+  dereference_if_needed(ternary.cond);
   ternary.left->accept(*this);
+  dereference_if_needed(ternary.left);
   ternary.right->accept(*this);
+  dereference_if_needed(ternary.right);
   const Type &cond = ternary.cond->type.GetTy();
   const Type &lhs = ternary.left->type.GetTy();
   const Type &rhs = ternary.right->type.GetTy();
@@ -1949,6 +1966,7 @@ void SemanticAnalyser::visit(Ternary &ternary)
 void SemanticAnalyser::visit(If &if_block)
 {
   if_block.cond->accept(*this);
+  dereference_if_needed(if_block.cond);
 
   if (is_final_pass()) {
     const Type &cond = if_block.cond->type.GetTy();
@@ -1965,6 +1983,7 @@ void SemanticAnalyser::visit(If &if_block)
 void SemanticAnalyser::visit(Unroll &unroll)
 {
   unroll.expr->accept(*this);
+  dereference_if_needed(unroll.expr);
 
   auto unroll_value = bpftrace_.get_int_literal(unroll.expr);
   if (!unroll_value.has_value()) {
@@ -1987,8 +2006,10 @@ void SemanticAnalyser::visit(Jump &jump)
 {
   switch (jump.ident) {
     case JumpType::RETURN:
-      if (jump.return_value)
+      if (jump.return_value) {
         jump.return_value->accept(*this);
+        dereference_if_needed(jump.return_value);
+      }
       if (auto subprog = dynamic_cast<Subprog *>(scope_)) {
         if ((subprog->return_type.IsVoidTy() !=
              (jump.return_value == nullptr)) ||
@@ -2020,6 +2041,7 @@ void SemanticAnalyser::visit(While &while_block)
   }
 
   while_block.cond->accept(*this);
+  dereference_if_needed(while_block.cond);
 
   loop_depth_++;
   accept_statements(while_block.stmts);
@@ -2148,6 +2170,7 @@ void SemanticAnalyser::visit(FieldAccess &acc)
   assert((acc.field.size() > 0) != (acc.index >= 0));
 
   acc.expr->accept(*this);
+  dereference_if_needed(acc.expr);
 
   SizedType &type = acc.expr->type;
 
@@ -2285,6 +2308,7 @@ void SemanticAnalyser::visit(FieldAccess &acc)
 void SemanticAnalyser::visit(Cast &cast)
 {
   cast.expr->accept(*this);
+  dereference_if_needed(cast.expr);
 
   // cast type is synthesised in parser, if it is a struct, it needs resolving
   resolve_struct_type(cast.type, cast.loc);
@@ -2365,6 +2389,7 @@ void SemanticAnalyser::visit(Tuple &tuple)
   for (size_t i = 0; i < tuple.elems->size(); ++i) {
     Expression *elem = tuple.elems->at(i);
     elem->accept(*this);
+    dereference_if_needed(tuple.elems->at(i));
 
     // If elem type is none that means that the tuple contains some
     // invalid cast (e.g., (0, (aaa)0)). In this case, skip the tuple
@@ -2380,12 +2405,14 @@ void SemanticAnalyser::visit(Tuple &tuple)
 void SemanticAnalyser::visit(ExprStatement &expr)
 {
   expr.expr->accept(*this);
+  dereference_if_needed(expr.expr);
 }
 
 void SemanticAnalyser::visit(AssignMapStatement &assignment)
 {
   assignment.map->accept(*this);
   assignment.expr->accept(*this);
+  dereference_if_needed(assignment.expr);
 
   assign_map_type(*assignment.map, assignment.expr->type);
 
@@ -2462,6 +2489,7 @@ void SemanticAnalyser::visit(AssignMapStatement &assignment)
 void SemanticAnalyser::visit(AssignVarStatement &assignment)
 {
   assignment.expr->accept(*this);
+  dereference_if_needed(assignment.expr);
 
   std::string var_ident = assignment.var->ident;
   auto search = variable_val_[scope_].find(var_ident);
@@ -2542,11 +2570,13 @@ void SemanticAnalyser::visit(AssignVarStatement &assignment)
 void SemanticAnalyser::visit(AssignConfigVarStatement &assignment)
 {
   assignment.expr->accept(*this);
+  dereference_if_needed(assignment.expr);
 }
 
 void SemanticAnalyser::visit(Predicate &pred)
 {
   pred.expr->accept(*this);
+  dereference_if_needed(pred.expr);
   if (is_final_pass()) {
     SizedType &ty = pred.expr->type;
     if (!ty.IsIntTy() && !ty.IsPtrTy()) {
@@ -3324,5 +3354,18 @@ Pass CreateSemanticPass()
   return Pass("Semantic", fn);
 };
 
+void SemanticAnalyser::dereference_if_needed(Expression *&expr)
+{
+  const auto &type = expr->type;
+  if (type.IsRefTy()) {
+    expr = new Unop(Operator::MUL, expr, expr->loc);
+    expr->type = *type.GetDereferencedType();
+    expr->type.is_internal = type.is_internal;
+    expr->type.SetAS(type.GetAS());
+    if (type.IsCtxAccess())
+      expr->type.MarkCtxAccess();
+  }
+}
+
 } // namespace ast
 } // namespace bpftrace

src/ast/passes/semantic_analyser.h

@@ -123,6 +123,7 @@ class SemanticAnalyser : public Visitor {
   void binop_ptr(Binop &op);
   void binop_int(Binop &op);
   void binop_array(Binop &op);
+  void dereference_if_needed(Expression *&expr);
 
   bool has_error() const;
   bool in_loop(void)

src/dwarf_parser.cpp

@@ -184,7 +184,7 @@ SizedType Dwarf::get_stype(lldb::SBType type, bool resolve_structs)
     case lldb::eTypeClassPointer:
       return CreatePointer(get_stype(type.GetPointeeType(), false));
     case lldb::eTypeClassReference:
-      return CreatePointer(get_stype(type.GetDereferencedType(), false));
+      return CreateReference(get_stype(type.GetDereferencedType(), false));
     case lldb::eTypeClassClass:
     case lldb::eTypeClassStruct:
     case lldb::eTypeClassUnion: {

src/types.cpp

@@ -148,6 +148,7 @@ std::string typestr(Type t)
     case Type::voidtype: return "void";     break;
     case Type::integer:  return "integer";  break;
     case Type::pointer:  return "pointer";  break;
+    case Type::reference:return "reference";break;
     case Type::record:   return "record";   break;
     case Type::hist:     return "hist";     break;
     case Type::lhist:    return "lhist";    break;
@@ -354,6 +355,15 @@ SizedType CreatePointer(const SizedType &pointee_type, AddrSpace as)
   return ty;
 }
 
+SizedType CreateReference(const SizedType &referred_type, AddrSpace as)
+{
+  // Pointer itself is always an uint64
+  auto ty = SizedType(Type::reference, 8);
+  ty.element_type_ = std::make_shared<SizedType>(referred_type);
+  ty.SetAS(as);
+  return ty;
+}
+
 SizedType CreateRecord(const std::string &name, std::weak_ptr<Struct> record)
 {
   auto ty = SizedType(Type::record, record.expired() ? 0 : record.lock()->size);
@@ -584,6 +594,9 @@ size_t hash<bpftrace::SizedType>::operator()(
     case bpftrace::Type::pointer:
       bpftrace::hash_combine(hash, *type.GetPointeeTy());
       break;
+    case bpftrace::Type::reference:
+      bpftrace::hash_combine(hash, *type.GetDereferencedType());
+      break;
     case bpftrace::Type::record:
       bpftrace::hash_combine(hash, type.GetName());
       break;

src/types.h

@@ -25,6 +25,7 @@ enum class Type : uint8_t {
   voidtype,
   integer,
   pointer,
+  reference,
   record, // struct/union, as struct is a protected keyword
   hist,
   lhist,
@@ -284,6 +285,12 @@ class SizedType {
     return element_type_.get();
   }
 
+  const SizedType *GetDereferencedType() const
+  {
+    assert(IsRefTy());
+    return element_type_.get();
+  }
+
   bool IsBoolTy() const
   {
     return type_ == Type::integer && size_bits_ == 1;
@@ -292,6 +299,10 @@ class SizedType {
   {
     return type_ == Type::pointer;
   };
+  bool IsRefTy() const
+  {
+    return type_ == Type::reference;
+  };
   bool IsIntTy() const
   {
     return type_ == Type::integer;
@@ -422,6 +433,7 @@ class SizedType {
                                const SizedType &element_type);
 
   friend SizedType CreatePointer(const SizedType &pointee_type, AddrSpace as);
+  friend SizedType CreateReference(const SizedType &pointee_type, AddrSpace as);
   friend SizedType CreateRecord(const std::string &name,
                                 std::weak_ptr<Struct> record);
   friend SizedType CreateInteger(size_t bits, bool is_signed);
@@ -448,6 +460,8 @@ SizedType CreateString(size_t size);
 SizedType CreateArray(size_t num_elements, const SizedType &element_type);
 SizedType CreatePointer(const SizedType &pointee_type,
                         AddrSpace as = AddrSpace::none);
+SizedType CreateReference(const SizedType &referred_type,
+                          AddrSpace as = AddrSpace::none);
 
 SizedType CreateRecord(const std::string &name, std::weak_ptr<Struct> record);
 SizedType CreateTuple(std::weak_ptr<Struct> tuple);

tests/data/data_source_cxx.cpp

@@ -54,9 +54,10 @@ struct Bottom : public Left, public Right {
 
 struct Multi : public Parent, public Top {
   int abc;
+  int &rabc;
 
   Multi(int a, int b, int c, int d, int e)
-      : Parent{ a, b, c, d }, Top{ e }, abc{ e + 1 }
+      : Parent{ a, b, c, d }, Top{ e }, abc{ e + 1 }, rabc{ abc }
   {
   }
 };

tests/field_analyser.cpp

@@ -610,8 +610,8 @@ TEST_F(field_analyser_dwarf, parse_inheritance_multi)
   }
 
   ASSERT_TRUE(cls->HasFields());
-  ASSERT_EQ(cls->fields.size(), 6);
-  ASSERT_EQ(cls->size, 24);
+  ASSERT_EQ(cls->fields.size(), 7);
+  ASSERT_EQ(cls->size, 32);
 
   CheckParentFields(cls);
 
@@ -624,6 +624,11 @@ TEST_F(field_analyser_dwarf, parse_inheritance_multi)
   EXPECT_TRUE(cls->GetField("abc").type.IsIntTy());
   EXPECT_EQ(cls->GetField("abc").type.GetSize(), 4);
   EXPECT_EQ(cls->GetField("abc").offset, 20);
+
+  EXPECT_TRUE(cls->HasField("rabc"));
+  EXPECT_TRUE(cls->GetField("rabc").type.IsRefTy());
+  EXPECT_EQ(cls->GetField("rabc").type.GetSize(), 8);
+  EXPECT_EQ(cls->GetField("rabc").offset, 24);
 }
 
 TEST_F(field_analyser_dwarf, parse_struct_anonymous_fields)