[Bounds-Safety] Add sized_by, counted_by_or_null & sized_by_or_null

The attributes `sized_by`, `counted_by_or_null` and `sized_by_or_null`
have been added as variants on `counted_by`, each with slightly
different semantics.  `sized_by` takes a byte size parameter instead of
an element count, allowing pointees with unknown size. The
`counted_by_or_null` and `sized_by_or_null` variants are equivalent to
their base variants, except the pointer can be null regardless of
count/size value.  If the pointer is null the size is effectively 0.

rdar://125400354

Author: hnrklssn

clang/docs/ReleaseNotes.rst

@@ -451,6 +451,12 @@ Attribute Changes in Clang
        size_t count;
      };
 
+- The attributes ``sized_by``, ``counted_by_or_null`` and ``sized_by_or_null```
+  have been added as variants on ``counted_by``, each with slightly different semantics.
+  ``sized_by`` takes a byte size parameter instead of an element count, allowing pointees
+  with unknown size. The ``counted_by_or_null`` and ``sized_by_or_null`` variants are equivalent
+  to their base variants, except the pointer can be null regardless of count/size value.
+  If the pointer is null the size is effectively 0.
 
 Improvements to Clang's diagnostics
 -----------------------------------

clang/include/clang/Basic/Attr.td

@@ -2265,6 +2265,36 @@ def CountedBy : DeclOrTypeAttr {
   let LangOpts = [COnly];
 }
 
+def CountedByOrNull : DeclOrTypeAttr {
+  let Spellings = [Clang<"counted_by_or_null">];
+  let Subjects = SubjectList<[Field], ErrorDiag>;
+  let Args = [ExprArgument<"Count">, IntArgument<"NestedLevel", 1>];
+  let LateParsed = LateAttrParseExperimentalExt;
+  let ParseArgumentsAsUnevaluated = 1;
+  let Documentation = [CountedByDocs];
+  let LangOpts = [COnly];
+}
+
+def SizedBy : DeclOrTypeAttr {
+  let Spellings = [Clang<"sized_by">];
+  let Subjects = SubjectList<[Field], ErrorDiag>;
+  let Args = [ExprArgument<"Size">, IntArgument<"NestedLevel", 1>];
+  let LateParsed = LateAttrParseExperimentalExt;
+  let ParseArgumentsAsUnevaluated = 1;
+  let Documentation = [CountedByDocs];
+  let LangOpts = [COnly];
+}
+
+def SizedByOrNull : DeclOrTypeAttr {
+  let Spellings = [Clang<"sized_by_or_null">];
+  let Subjects = SubjectList<[Field], ErrorDiag>;
+  let Args = [ExprArgument<"Size">, IntArgument<"NestedLevel", 1>];
+  let LateParsed = LateAttrParseExperimentalExt;
+  let ParseArgumentsAsUnevaluated = 1;
+  let Documentation = [CountedByDocs];
+  let LangOpts = [COnly];
+}
+
 // This is a marker used to indicate that an __unsafe_unretained qualifier was
 // ignored because ARC is not enabled. The usual representation for this
 // qualifier is as an ObjCOwnership attribute with Kind == "none".

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -6543,27 +6543,27 @@ def warn_superclass_variable_sized_type_not_at_end : Warning<
   " in superclass %3">, InGroup<ObjCFlexibleArray>;
 
 def err_flexible_array_count_not_in_same_struct : Error<
-  "'counted_by' field %0 isn't within the same struct as the flexible array">;
+  "'%select{counted_by|sized_by|counted_by_or_null|sized_by_or_null}1' field %0 isn't within the same struct as the flexible array">;
 def err_counted_by_attr_not_on_ptr_or_flexible_array_member : Error<
-  "'counted_by' only applies to pointers or C99 flexible array members">;
+  "'%select{counted_by|sized_by|counted_by_or_null|sized_by_or_null}0' only applies to pointers%select{ or C99 flexible array members|||}0">;
 def err_counted_by_attr_on_array_not_flexible_array_member : Error<
   "'counted_by' on arrays only applies to C99 flexible array members">;
 def err_counted_by_attr_refer_to_itself : Error<
   "'counted_by' cannot refer to the flexible array member %0">;
 def err_counted_by_must_be_in_structure : Error<
-  "field %0 in 'counted_by' not inside structure">;
+  "field %0 in '%select{counted_by|sized_by|counted_by_or_null|sized_by_or_null}1' not inside structure">;
 def err_counted_by_attr_argument_not_integer : Error<
-  "'counted_by' requires a non-boolean integer type argument">;
+  "'%select{counted_by|sized_by|counted_by_or_null|sized_by_or_null}0' requires a non-boolean integer type argument">;
 def err_counted_by_attr_only_support_simple_decl_reference : Error<
-  "'counted_by' argument must be a simple declaration reference">;
+  "'%select{counted_by|sized_by|counted_by_or_null|sized_by_or_null}0' argument must be a simple declaration reference">;
 def err_counted_by_attr_in_union : Error<
-  "'counted_by' cannot be applied to a union member">;
+  "'%select{counted_by|sized_by|counted_by_or_null|sized_by_or_null}0' cannot be applied to a union member">;
 def err_counted_by_attr_refer_to_union : Error<
-  "'counted_by' argument cannot refer to a union member">;
+  "'%select{counted_by|sized_by|counted_by_or_null|sized_by_or_null}0' argument cannot refer to a union member">;
 def note_flexible_array_counted_by_attr_field : Note<
   "field %0 declared here">;
 def err_counted_by_attr_pointee_unknown_size : Error<
-  "'counted_by' %select{cannot|should not}3 be applied to %select{"
+  "'%select{counted_by|counted_by_or_null}4' %select{cannot|should not}3 be applied to %select{"
     "a pointer with pointee|" // pointer
     "an array with element}0" // array
   " of unknown size because %1 is %select{"

clang/include/clang/Sema/Sema.h

@@ -11432,7 +11432,9 @@ class Sema final : public SemaBase {
                            SourceLocation AttrLoc);
 
   QualType BuildCountAttributedArrayOrPointerType(QualType WrappedTy,
-                                                  Expr *CountExpr);
+                                                  Expr *CountExpr,
+                                                  bool CountInBytes,
+                                                  bool OrNull);
 
   QualType BuildAddressSpaceAttr(QualType &T, LangAS ASIdx, Expr *AddrSpace,
                                  SourceLocation AttrLoc);

clang/lib/AST/TypePrinter.cpp

@@ -1905,6 +1905,9 @@ void TypePrinter::printAttributedAfter(const AttributedType *T,
     break;
 
   case attr::CountedBy:
+  case attr::CountedByOrNull:
+  case attr::SizedBy:
+  case attr::SizedByOrNull:
   case attr::LifetimeBound:
   case attr::TypeNonNull:
   case attr::TypeNullable:

clang/lib/Parse/ParseDecl.cpp

@@ -667,7 +667,10 @@ void Parser::ParseGNUAttributeArgs(
     ParseAttributeWithTypeArg(*AttrName, AttrNameLoc, Attrs, ScopeName,
                               ScopeLoc, Form);
     return;
-  } else if (AttrKind == ParsedAttr::AT_CountedBy) {
+  } else if (AttrKind == ParsedAttr::AT_CountedBy ||
+             AttrKind == ParsedAttr::AT_CountedByOrNull ||
+             AttrKind == ParsedAttr::AT_SizedBy ||
+             AttrKind == ParsedAttr::AT_SizedByOrNull) {
     ParseBoundsAttribute(*AttrName, AttrNameLoc, Attrs, ScopeName, ScopeLoc,
                          Form);
     return;
@@ -4835,7 +4838,7 @@ static void DiagnoseCountAttributedTypeInUnnamedAnon(ParsingDeclSpec &DS,
       if (!RD->containsDecl(DD.getDecl())) {
         P.Diag(VD->getBeginLoc(),
                diag::err_flexible_array_count_not_in_same_struct)
-            << DD.getDecl();
+            << DD.getDecl() << CAT->getKind();
         P.Diag(DD.getDecl()->getBeginLoc(),
                diag::note_flexible_array_counted_by_attr_field)
             << DD.getDecl();

clang/lib/Sema/SemaDeclAttr.cpp

@@ -8328,22 +8328,33 @@ enum class CountedByInvalidPointeeTypeKind {
   VALID,
 };
 
-static bool CheckCountedByAttrOnField(
-    Sema &S, FieldDecl *FD, Expr *E,
-    llvm::SmallVectorImpl<TypeCoupledDeclRefInfo> &Decls) {
+static bool
+CheckCountedByAttrOnField(Sema &S, FieldDecl *FD, Expr *E,
+                          llvm::SmallVectorImpl<TypeCoupledDeclRefInfo> &Decls,
+                          bool CountInBytes, bool OrNull) {
   // Check the context the attribute is used in
 
+  unsigned Kind = CountInBytes;
+  if (OrNull)
+    Kind += 2;
+
   if (FD->getParent()->isUnion()) {
     S.Diag(FD->getBeginLoc(), diag::err_counted_by_attr_in_union)
-        << FD->getSourceRange();
+        << Kind << FD->getSourceRange();
     return true;
   }
 
   const auto FieldTy = FD->getType();
+  if (FieldTy->isArrayType() && (CountInBytes || OrNull)) {
+    S.Diag(FD->getBeginLoc(),
+           diag::err_counted_by_attr_not_on_ptr_or_flexible_array_member)
+        << Kind << FD->getLocation();
+    return true;
+  }
   if (!FieldTy->isArrayType() && !FieldTy->isPointerType()) {
     S.Diag(FD->getBeginLoc(),
            diag::err_counted_by_attr_not_on_ptr_or_flexible_array_member)
-        << FD->getLocation();
+        << Kind << FD->getLocation();
     return true;
   }
 
@@ -8354,7 +8365,7 @@ static bool CheckCountedByAttrOnField(
                                        StrictFlexArraysLevel, true)) {
     S.Diag(FD->getBeginLoc(),
            diag::err_counted_by_attr_on_array_not_flexible_array_member)
-        << FD->getLocation();
+        << Kind << FD->getLocation();
     return true;
   }
 
@@ -8394,29 +8405,30 @@ static bool CheckCountedByAttrOnField(
     InvalidTypeKind = CountedByInvalidPointeeTypeKind::FLEXIBLE_ARRAY_MEMBER;
   }
 
-  if (InvalidTypeKind != CountedByInvalidPointeeTypeKind::VALID) {
+  if (InvalidTypeKind != CountedByInvalidPointeeTypeKind::VALID &&
+      !CountInBytes) {
     unsigned DiagID = ShouldWarn
                           ? diag::warn_counted_by_attr_elt_type_unknown_size
                           : diag::err_counted_by_attr_pointee_unknown_size;
     S.Diag(FD->getBeginLoc(), DiagID)
         << SelectPtrOrArr << PointeeTy << (int)InvalidTypeKind
-        << (ShouldWarn ? 1 : 0) << FD->getSourceRange();
+        << (ShouldWarn ? 1 : 0) << OrNull << FD->getSourceRange();
     return true;
   }
 
   // Check the expression
 
   if (!E->getType()->isIntegerType() || E->getType()->isBooleanType()) {
     S.Diag(E->getBeginLoc(), diag::err_counted_by_attr_argument_not_integer)
-        << E->getSourceRange();
+        << Kind << E->getSourceRange();
     return true;
   }
 
   auto *DRE = dyn_cast<DeclRefExpr>(E);
   if (!DRE) {
     S.Diag(E->getBeginLoc(),
            diag::err_counted_by_attr_only_support_simple_decl_reference)
-        << E->getSourceRange();
+        << Kind << E->getSourceRange();
     return true;
   }
 
@@ -8427,7 +8439,7 @@ static bool CheckCountedByAttrOnField(
   }
   if (!CountFD) {
     S.Diag(E->getBeginLoc(), diag::err_counted_by_must_be_in_structure)
-        << CountDecl << E->getSourceRange();
+        << CountDecl << Kind << E->getSourceRange();
 
     S.Diag(CountDecl->getBeginLoc(),
            diag::note_flexible_array_counted_by_attr_field)
@@ -8438,7 +8450,7 @@ static bool CheckCountedByAttrOnField(
   if (FD->getParent() != CountFD->getParent()) {
     if (CountFD->getParent()->isUnion()) {
       S.Diag(CountFD->getBeginLoc(), diag::err_counted_by_attr_refer_to_union)
-          << CountFD->getSourceRange();
+          << Kind << CountFD->getSourceRange();
       return true;
     }
     // Whether CountRD is an anonymous struct is not determined at this
@@ -8450,7 +8462,7 @@ static bool CheckCountedByAttrOnField(
     if (RD != CountRD) {
       S.Diag(E->getBeginLoc(),
              diag::err_flexible_array_count_not_in_same_struct)
-          << CountFD << E->getSourceRange();
+          << CountFD << Kind << E->getSourceRange();
       S.Diag(CountFD->getBeginLoc(),
              diag::note_flexible_array_counted_by_attr_field)
           << CountFD << CountFD->getSourceRange();
@@ -8470,12 +8482,35 @@ static void handleCountedByAttrField(Sema &S, Decl *D, const ParsedAttr &AL) {
   if (!CountExpr)
     return;
 
+  bool CountInBytes;
+  bool OrNull;
+  switch (AL.getKind()) {
+  case ParsedAttr::AT_CountedBy:
+    CountInBytes = false;
+    OrNull = false;
+    break;
+  case ParsedAttr::AT_CountedByOrNull:
+    CountInBytes = false;
+    OrNull = true;
+    break;
+  case ParsedAttr::AT_SizedBy:
+    CountInBytes = true;
+    OrNull = false;
+    break;
+  case ParsedAttr::AT_SizedByOrNull:
+    CountInBytes = true;
+    OrNull = true;
+    break;
+  default:
+    llvm_unreachable("unexpected counted_by family attribute");
+  }
+
   llvm::SmallVector<TypeCoupledDeclRefInfo, 1> Decls;
-  if (CheckCountedByAttrOnField(S, FD, CountExpr, Decls))
+  if (CheckCountedByAttrOnField(S, FD, CountExpr, Decls, CountInBytes, OrNull))
     return;
 
-  QualType CAT =
-      S.BuildCountAttributedArrayOrPointerType(FD->getType(), CountExpr);
+  QualType CAT = S.BuildCountAttributedArrayOrPointerType(
+      FD->getType(), CountExpr, CountInBytes, OrNull);
   FD->setType(CAT);
 }
 
@@ -9502,6 +9537,9 @@ ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D, const ParsedAttr &AL,
     break;
 
   case ParsedAttr::AT_CountedBy:
+  case ParsedAttr::AT_CountedByOrNull:
+  case ParsedAttr::AT_SizedBy:
+  case ParsedAttr::AT_SizedByOrNull:
     handleCountedByAttrField(S, D, AL);
     break;
 

clang/lib/Sema/SemaType.cpp

@@ -9350,15 +9350,17 @@ BuildTypeCoupledDecls(Expr *E,
 }
 
 QualType Sema::BuildCountAttributedArrayOrPointerType(QualType WrappedTy,
-                                                      Expr *CountExpr) {
+                                                      Expr *CountExpr,
+                                                      bool CountInBytes,
+                                                      bool OrNull) {
   assert(WrappedTy->isIncompleteArrayType() || WrappedTy->isPointerType());
 
   llvm::SmallVector<TypeCoupledDeclRefInfo, 1> Decls;
   BuildTypeCoupledDecls(CountExpr, Decls);
   /// When the resulting expression is invalid, we still create the AST using
   /// the original count expression for the sake of AST dump.
-  return Context.getCountAttributedType(
-      WrappedTy, CountExpr, /*CountInBytes*/ false, /*OrNull*/ false, Decls);
+  return Context.getCountAttributedType(WrappedTy, CountExpr, CountInBytes,
+                                        OrNull, Decls);
 }
 
 /// getDecltypeForExpr - Given an expr, will return the decltype for

clang/lib/Sema/TreeTransform.h

@@ -7336,7 +7336,8 @@ QualType TreeTransform<Derived>::TransformCountAttributedType(
   if (getDerived().AlwaysRebuild() || InnerTy != OldTy->desugar() ||
       OldCount != NewCount) {
     // Currently, CountAttributedType can only wrap incomplete array types.
-    Result = SemaRef.BuildCountAttributedArrayOrPointerType(InnerTy, NewCount);
+    Result = SemaRef.BuildCountAttributedArrayOrPointerType(
+        InnerTy, NewCount, OldTy->isCountInBytes(), OldTy->isOrNull());
   }
 
   TLB.push<CountAttributedTypeLoc>(Result);

clang/test/AST/attr-counted-by-or-null-late-parsed-struct-ptrs.c

@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -fexperimental-late-parse-attributes %s -ast-dump | FileCheck %s
+
+#define __counted_by_or_null(f)  __attribute__((counted_by_or_null(f)))
+
+struct size_known {
+  int field;
+};
+
+//==============================================================================
+// __counted_by_or_null on struct member pointer in decl attribute position
+//==============================================================================
+
+struct on_member_pointer_complete_ty {
+  struct size_known *buf __counted_by_or_null(count);
+  int count;
+};
+// CHECK-LABEL: struct on_member_pointer_complete_ty definition
+// CHECK-NEXT: |-FieldDecl {{.*}} buf 'struct size_known * __counted_by_or_null(count)':'struct size_known *'
+// CHECK-NEXT: `-FieldDecl {{.*}} referenced count 'int'
+
+struct on_pointer_anon_count {
+  struct size_known *buf __counted_by_or_null(count);
+  struct {
+    int count;
+  };
+};
+
+// CHECK-LABEL: struct on_pointer_anon_count definition
+// CHECK-NEXT:  |-FieldDecl {{.*}} buf 'struct size_known * __counted_by_or_null(count)':'struct size_known *'
+// CHECK-NEXT:  |-RecordDecl {{.*}} struct definition
+// CHECK-NEXT:  | `-FieldDecl {{.*}} count 'int'
+// CHECK-NEXT:  |-FieldDecl {{.*}} implicit 'struct on_pointer_anon_count::(anonymous at {{.*}})'
+// CHECK-NEXT:  `-IndirectFieldDecl {{.*}} implicit referenced count 'int'
+// CHECK-NEXT:    |-Field {{.*}} '' 'struct on_pointer_anon_count::(anonymous at {{.*}})'
+// CHECK-NEXT:    `-Field {{.*}} 'count' 'int'
+
+//==============================================================================
+// __counted_by_or_null on struct member pointer in type attribute position
+//==============================================================================
+// TODO: Correctly parse counted_by_or_null as a type attribute. Currently it is parsed
+// as a declaration attribute and is **not** late parsed resulting in the `count`
+// field being unavailable.
+//
+// See `clang/test/Sema/attr-counted-by-late-parsed-struct-ptrs.c` for test
+// cases.