EnforceCompatibility: Stub out void pointers

CodeGen v1 does not record anything for pointers to incomplete types.
Not even the address, as is done for other pointers.

Introduce a new Primitive type "Incomplete". This behaves identically to
"Void", but allows us to tell whether a type was defined as void or if
it ended up like that because of incomplete DWARF information.

.circleci/config.yml

@@ -20,7 +20,7 @@ workflows:
             - build-gcc
           oid_test_args: "-ftype-graph"
           tests_regex: "OidIntegration\\..*"
-          exclude_regex: ".*inheritance_polymorphic.*|.*pointers_incomplete_containing_struct|.*arrays_member_int0"
+          exclude_regex: ".*inheritance_polymorphic.*|.*arrays_member_int0"
       - test:
           name: test-typed-data-segment-gcc
           requires:
@@ -68,7 +68,7 @@ workflows:
           oid_test_args: "-ftype-graph"
           tests_regex: "OidIntegration\\..*"
           # Tests disabled due to bad DWARF generated by the old clang compiler in CI
-          exclude_regex: ".*inheritance_polymorphic.*|.*pointers_incomplete_containing_struct|.*arrays_member_int0|.*fbstring.*|.*std_string_*|.*multi_arg_tb_.*|.*ignored_a"
+          exclude_regex: ".*inheritance_polymorphic.*|.*arrays_member_int0|.*fbstring.*|.*std_string_*|.*multi_arg_tb_.*|.*ignored_a"
 
 executors:
   ubuntu-docker:

oi/type_graph/DrgnParser.cpp

@@ -83,8 +83,9 @@ Type& DrgnParser::enumerateType(struct drgn_type* type) {
   if (auto it = drgn_types_.find(type); it != drgn_types_.end())
     return it->second;
 
-  if (!drgn_utils::isSizeComplete(type)) {
-    return makeType<Primitive>(nullptr, Primitive::Kind::Void);
+  if (!drgn_utils::isSizeComplete(type) &&
+      drgn_type_kind(type) != DRGN_TYPE_VOID) {
+    return makeType<Primitive>(nullptr, Primitive::Kind::Incomplete);
   }
 
   enum drgn_type_kind kind = drgn_type_kind(type);

oi/type_graph/EnforceCompatibility.cpp

@@ -72,9 +72,22 @@ void EnforceCompatibility::visit(Class& c) {
     accept(child);
   }
 
-  // CodeGen v1 replaces parent containers with padding
   std::erase_if(c.members, [](Member member) {
-    return member.name.starts_with(Flattener::ParentPrefix);
+    // CodeGen v1 replaces parent containers with padding
+    if (member.name.starts_with(Flattener::ParentPrefix))
+      return true;
+
+    if (auto* ptr = dynamic_cast<Pointer*>(&member.type())) {
+      if (auto* primitive = dynamic_cast<Primitive*>(&ptr->pointeeType())) {
+        if (primitive->kind() == Primitive::Kind::Incomplete) {
+          // This is a pointer to an incomplete type. CodeGen v1 does not record
+          // the pointer's address in this case.
+          return true;
+        }
+      }
+    }
+
+    return false;
   });
 }
 

oi/type_graph/Printer.cpp

@@ -87,7 +87,10 @@ void Printer::visit(const Container& c) {
 
 void Printer::visit(const Primitive& p) {
   prefix();
-  out_ << "Primitive: " << p.name() << std::endl;
+  out_ << "Primitive: " << p.name();
+  if (p.kind() == Primitive::Kind::Incomplete)
+    out_ << " (incomplete)";
+  out_ << std::endl;
 }
 
 void Printer::visit(const Enum& e) {

oi/type_graph/TypeGraph.cpp

@@ -71,6 +71,9 @@ Primitive& TypeGraph::makeType<Primitive>(Primitive::Kind kind) {
     case Primitive::Kind::Void:
       static Primitive pVoid{kind};
       return pVoid;
+    case Primitive::Kind::Incomplete:
+      static Primitive pIncomplete{kind};
+      return pIncomplete;
   }
 }
 

oi/type_graph/Types.cpp

@@ -60,6 +60,7 @@ std::string Primitive::name() const {
     case Kind::UIntPtr:
       return "uintptr_t";
     case Kind::Void:
+    case Kind::Incomplete:
       return "void";
   }
 }
@@ -95,6 +96,7 @@ std::size_t Primitive::size() const {
     case Kind::UIntPtr:
       return sizeof(uintptr_t);
     case Kind::Void:
+    case Kind::Incomplete:
       return 0;
   }
 }

oi/type_graph/Types.h

@@ -411,6 +411,8 @@ class Primitive : public Type {
     UIntPtr,  // Really an alias, but useful to have as its own primitive
 
     Void,
+    Incomplete,  // Behaves the same as Void, but alerts us that the type was
+                 // stubbed out due to incomplete DWARF
   };
 
   explicit Primitive(Kind kind) : kind_(kind) {
@@ -428,6 +430,9 @@ class Primitive : public Type {
   virtual NodeId id() const override {
     return -1;
   }
+  Kind kind() const {
+    return kind_;
+  }
 
  private:
   Kind kind_;

test/TypeGraphParser.cpp

@@ -49,6 +49,8 @@ Primitive::Kind getKind(std::string_view kindStr) {
     return Primitive::Kind::UIntPtr;
   if (kindStr == "void")
     return Primitive::Kind::Void;
+  if (kindStr == "void (incomplete)")
+    return Primitive::Kind::Incomplete;
   throw TypeGraphParserError{"Invalid Primitive::Kind: " +
                              std::string{kindStr}};
 }

test/test_drgn_parser.cpp

@@ -330,7 +330,7 @@ TEST_F(DrgnParserTest, PointerNoFollow) {
 TEST_F(DrgnParserTest, PointerIncomplete) {
   test("oid_test_case_pointers_incomplete_raw", R"(
 [0] Pointer
-      Primitive: void
+      Primitive: void (incomplete)
 )");
 }
 

test/test_enforce_compatibility.cpp

@@ -30,3 +30,15 @@ TEST(EnforceCompatibilityTest, TypesToStub) {
 [0] Class: EnumMap (size: 8)
 )");
 }
+
+TEST(EnforceCompatibilityTest, VoidPointer) {
+  test(EnforceCompatibility::createPass(), R"(
+[0] Class: MyClass (size: 8)
+      Member: p (offset: 0)
+[1]     Pointer
+          Primitive: void (incomplete)
+)",
+       R"(
+[0] Class: MyClass (size: 8)
+)");
+}