[clang][NFC] Move Bounds Safety Sema code to SemaBoundsSafety.cpp (l…

…lvm#99330)

This patch adds a new `SemaBoundsSafety.cpp` source file and moves the
existing `CheckCountedByAttrOnField` function and related helper
functions and types from `SemaDeclAttr.cpp` into the new source file.
The `CheckCountedByAttrOnField` function is now a method on the Sema
class and now has doxygen comments.

The goal behind this refactor is to clearly separate the
`-fbounds-safety` Sema code from everything else.

Although `counted_by(_or_null)` and `sized_by(_or_null)` attributes have
a meaning outside of `-fbounds-safety` it seems reasonable to also have
the Sema logic live in `SemaBoundsSafety.cpp` since the intention is
that the attributes will have the same semantics (but not necessarily
the same enforcement).

As `-fbounds-safety` is upstreamed additional Sema checks will be added
to `SemaBoundsSafety.cpp`.

rdar://131777237

clang/include/clang/Sema/Sema.h

@@ -15051,6 +15051,44 @@ class Sema final : public SemaBase {
   void ProcessAPINotes(Decl *D);
 
   ///@}
+
+  //
+  //
+  // -------------------------------------------------------------------------
+  //
+  //
+
+  /// \name Bounds Safety
+  /// Implementations are in SemaBoundsSafety.cpp
+  ///@{
+public:
+  /// Check if applying the specified attribute variant from the "counted by"
+  /// family of attributes to FieldDecl \p FD is semantically valid. If
+  /// semantically invalid diagnostics will be emitted explaining the problems.
+  ///
+  /// \param FD The FieldDecl to apply the attribute to
+  /// \param E The count expression on the attribute
+  /// \param[out] Decls If the attribute is semantically valid \p Decls
+  ///             is populated with TypeCoupledDeclRefInfo objects, each
+  ///             describing Decls referred to in \p E.
+  /// \param CountInBytes If true the attribute is from the "sized_by" family of
+  ///                     attributes. If the false the attribute is from
+  ///                     "counted_by" family of attributes.
+  /// \param OrNull If true the attribute is from the "_or_null" suffixed family
+  ///               of attributes. If false the attribute does not have the
+  ///               suffix.
+  ///
+  /// Together \p CountInBytes and \p OrNull decide the attribute variant. E.g.
+  /// \p CountInBytes and \p OrNull both being true indicates the
+  /// `counted_by_or_null` attribute.
+  ///
+  /// \returns false iff semantically valid.
+  bool CheckCountedByAttrOnField(
+      FieldDecl *FD, Expr *E,
+      llvm::SmallVectorImpl<TypeCoupledDeclRefInfo> &Decls, bool CountInBytes,
+      bool OrNull);
+
+  ///@}
 };
 
 DeductionFailureInfo

clang/lib/Sema/CMakeLists.txt

@@ -36,6 +36,7 @@ add_clang_library(clangSema
   SemaAvailability.cpp
   SemaBPF.cpp
   SemaBase.cpp
+  SemaBoundsSafety.cpp
   SemaCXXScopeSpec.cpp
   SemaCast.cpp
   SemaChecking.cpp

clang/lib/Sema/SemaBoundsSafety.cpp

@@ -0,0 +1,193 @@
+//===-- SemaBoundsSafety.cpp - Bounds Safety specific routines-*- C++ -*---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file declares semantic analysis functions specific to `-fbounds-safety`
+/// (Bounds Safety) and also its attributes when used without `-fbounds-safety`
+/// (e.g. `counted_by`)
+///
+//===----------------------------------------------------------------------===//
+#include "clang/Sema/Sema.h"
+
+namespace clang {
+
+static CountAttributedType::DynamicCountPointerKind
+getCountAttrKind(bool CountInBytes, bool OrNull) {
+  if (CountInBytes)
+    return OrNull ? CountAttributedType::SizedByOrNull
+                  : CountAttributedType::SizedBy;
+  return OrNull ? CountAttributedType::CountedByOrNull
+                : CountAttributedType::CountedBy;
+}
+
+static const RecordDecl *GetEnclosingNamedOrTopAnonRecord(const FieldDecl *FD) {
+  const auto *RD = FD->getParent();
+  // An unnamed struct is anonymous struct only if it's not instantiated.
+  // However, the struct may not be fully processed yet to determine
+  // whether it's anonymous or not. In that case, this function treats it as
+  // an anonymous struct and tries to find a named parent.
+  while (RD && (RD->isAnonymousStructOrUnion() ||
+                (!RD->isCompleteDefinition() && RD->getName().empty()))) {
+    const auto *Parent = dyn_cast<RecordDecl>(RD->getParent());
+    if (!Parent)
+      break;
+    RD = Parent;
+  }
+  return RD;
+}
+
+enum class CountedByInvalidPointeeTypeKind {
+  INCOMPLETE,
+  SIZELESS,
+  FUNCTION,
+  FLEXIBLE_ARRAY_MEMBER,
+  VALID,
+};
+
+bool Sema::CheckCountedByAttrOnField(
+    FieldDecl *FD, Expr *E,
+    llvm::SmallVectorImpl<TypeCoupledDeclRefInfo> &Decls, bool CountInBytes,
+    bool OrNull) {
+  // Check the context the attribute is used in
+
+  unsigned Kind = getCountAttrKind(CountInBytes, OrNull);
+
+  if (FD->getParent()->isUnion()) {
+    Diag(FD->getBeginLoc(), diag::err_count_attr_in_union)
+        << Kind << FD->getSourceRange();
+    return true;
+  }
+
+  const auto FieldTy = FD->getType();
+  if (FieldTy->isArrayType() && (CountInBytes || OrNull)) {
+    Diag(FD->getBeginLoc(),
+         diag::err_count_attr_not_on_ptr_or_flexible_array_member)
+        << Kind << FD->getLocation() << /* suggest counted_by */ 1;
+    return true;
+  }
+  if (!FieldTy->isArrayType() && !FieldTy->isPointerType()) {
+    Diag(FD->getBeginLoc(),
+         diag::err_count_attr_not_on_ptr_or_flexible_array_member)
+        << Kind << FD->getLocation() << /* do not suggest counted_by */ 0;
+    return true;
+  }
+
+  LangOptions::StrictFlexArraysLevelKind StrictFlexArraysLevel =
+      LangOptions::StrictFlexArraysLevelKind::IncompleteOnly;
+  if (FieldTy->isArrayType() &&
+      !Decl::isFlexibleArrayMemberLike(getASTContext(), FD, FieldTy,
+                                       StrictFlexArraysLevel, true)) {
+    Diag(FD->getBeginLoc(),
+         diag::err_counted_by_attr_on_array_not_flexible_array_member)
+        << Kind << FD->getLocation();
+    return true;
+  }
+
+  CountedByInvalidPointeeTypeKind InvalidTypeKind =
+      CountedByInvalidPointeeTypeKind::VALID;
+  QualType PointeeTy;
+  int SelectPtrOrArr = 0;
+  if (FieldTy->isPointerType()) {
+    PointeeTy = FieldTy->getPointeeType();
+    SelectPtrOrArr = 0;
+  } else {
+    assert(FieldTy->isArrayType());
+    const ArrayType *AT = getASTContext().getAsArrayType(FieldTy);
+    PointeeTy = AT->getElementType();
+    SelectPtrOrArr = 1;
+  }
+  // Note: The `Decl::isFlexibleArrayMemberLike` check earlier on means
+  // only `PointeeTy->isStructureTypeWithFlexibleArrayMember()` is reachable
+  // when `FieldTy->isArrayType()`.
+  bool ShouldWarn = false;
+  if (PointeeTy->isIncompleteType() && !CountInBytes) {
+    InvalidTypeKind = CountedByInvalidPointeeTypeKind::INCOMPLETE;
+  } else if (PointeeTy->isSizelessType()) {
+    InvalidTypeKind = CountedByInvalidPointeeTypeKind::SIZELESS;
+  } else if (PointeeTy->isFunctionType()) {
+    InvalidTypeKind = CountedByInvalidPointeeTypeKind::FUNCTION;
+  } else if (PointeeTy->isStructureTypeWithFlexibleArrayMember()) {
+    if (FieldTy->isArrayType() && !getLangOpts().BoundsSafety) {
+      // This is a workaround for the Linux kernel that has already adopted
+      // `counted_by` on a FAM where the pointee is a struct with a FAM. This
+      // should be an error because computing the bounds of the array cannot be
+      // done correctly without manually traversing every struct object in the
+      // array at runtime. To allow the code to be built this error is
+      // downgraded to a warning.
+      ShouldWarn = true;
+    }
+    InvalidTypeKind = CountedByInvalidPointeeTypeKind::FLEXIBLE_ARRAY_MEMBER;
+  }
+
+  if (InvalidTypeKind != CountedByInvalidPointeeTypeKind::VALID) {
+    unsigned DiagID = ShouldWarn
+                          ? diag::warn_counted_by_attr_elt_type_unknown_size
+                          : diag::err_counted_by_attr_pointee_unknown_size;
+    Diag(FD->getBeginLoc(), DiagID)
+        << SelectPtrOrArr << PointeeTy << (int)InvalidTypeKind
+        << (ShouldWarn ? 1 : 0) << Kind << FD->getSourceRange();
+    return true;
+  }
+
+  // Check the expression
+
+  if (!E->getType()->isIntegerType() || E->getType()->isBooleanType()) {
+    Diag(E->getBeginLoc(), diag::err_count_attr_argument_not_integer)
+        << Kind << E->getSourceRange();
+    return true;
+  }
+
+  auto *DRE = dyn_cast<DeclRefExpr>(E);
+  if (!DRE) {
+    Diag(E->getBeginLoc(),
+         diag::err_count_attr_only_support_simple_decl_reference)
+        << Kind << E->getSourceRange();
+    return true;
+  }
+
+  auto *CountDecl = DRE->getDecl();
+  FieldDecl *CountFD = dyn_cast<FieldDecl>(CountDecl);
+  if (auto *IFD = dyn_cast<IndirectFieldDecl>(CountDecl)) {
+    CountFD = IFD->getAnonField();
+  }
+  if (!CountFD) {
+    Diag(E->getBeginLoc(), diag::err_count_attr_must_be_in_structure)
+        << CountDecl << Kind << E->getSourceRange();
+
+    Diag(CountDecl->getBeginLoc(),
+         diag::note_flexible_array_counted_by_attr_field)
+        << CountDecl << CountDecl->getSourceRange();
+    return true;
+  }
+
+  if (FD->getParent() != CountFD->getParent()) {
+    if (CountFD->getParent()->isUnion()) {
+      Diag(CountFD->getBeginLoc(), diag::err_count_attr_refer_to_union)
+          << Kind << CountFD->getSourceRange();
+      return true;
+    }
+    // Whether CountRD is an anonymous struct is not determined at this
+    // point. Thus, an additional diagnostic in case it's not anonymous struct
+    // is done later in `Parser::ParseStructDeclaration`.
+    auto *RD = GetEnclosingNamedOrTopAnonRecord(FD);
+    auto *CountRD = GetEnclosingNamedOrTopAnonRecord(CountFD);
+
+    if (RD != CountRD) {
+      Diag(E->getBeginLoc(), diag::err_count_attr_param_not_in_same_struct)
+          << CountFD << Kind << FieldTy->isArrayType() << E->getSourceRange();
+      Diag(CountFD->getBeginLoc(),
+           diag::note_flexible_array_counted_by_attr_field)
+          << CountFD << CountFD->getSourceRange();
+      return true;
+    }
+  }
+
+  Decls.push_back(TypeCoupledDeclRefInfo(CountFD, /*IsDref*/ false));
+  return false;
+}
+
+} // namespace clang