SemaBoundsSafety.cpp

//===-- 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