InferAlloc.cpp

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//===--- InferAlloc.cpp - Allocation type inference -----------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements allocation-related type inference.
//
//===----------------------------------------------------------------------===//
 
#include "clang/AST/InferAlloc.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/Expr.h"
#include "clang/AST/Type.h"
#include "clang/Basic/IdentifierTable.h"
#include "llvm/ADT/SmallPtrSet.h"
 
using namespace clang;
using namespace infer_alloc;
 
static bool
typeContainsPointer(QualType T,
                    llvm::SmallPtrSet<const RecordDecl *, 4> &VisitedRD,
                    bool &IncompleteType) {
  QualType CanonicalType = T.getCanonicalType();
  if (CanonicalType->isPointerType())
    return true; // base case
 
  // Look through typedef chain to check for special types.
  for (QualType CurrentT = T; const auto *TT = CurrentT->getAs<TypedefType>();
       CurrentT = TT->getDecl()->getUnderlyingType()) {
    const IdentifierInfo *II = TT->getDecl()->getIdentifier();
    // Special Case: Syntactically uintptr_t is not a pointer; semantically,
    // however, very likely used as such. Therefore, classify uintptr_t as a
    // pointer, too.
    if (II && II->isStr("uintptr_t"))
      return true;
  }
 
  // The type is an array; check the element type.
  if (const ArrayType *AT = dyn_cast<ArrayType>(CanonicalType))
    return typeContainsPointer(AT->getElementType(), VisitedRD, IncompleteType);
  // The type is a struct, class, or union.
  if (const RecordDecl *RD = CanonicalType->getAsRecordDecl()) {
    if (!RD->isCompleteDefinition()) {
      IncompleteType = true;
      return false;
    }
    if (!VisitedRD.insert(RD).second)
      return false; // already visited
    // Check all fields.
    for (const FieldDecl *Field : RD->fields()) {
      if (typeContainsPointer(Field->getType(), VisitedRD, IncompleteType))
        return true;
    }
    // For C++ classes, also check base classes.
    if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
      // Polymorphic types require a vptr.
      if (CXXRD->isDynamicClass())
        return true;
      for (const CXXBaseSpecifier &Base : CXXRD->bases()) {
        if (typeContainsPointer(Base.getType(), VisitedRD, IncompleteType))
          return true;
      }
    }
  }
  return false;
}
 
/// Infer type from a simple sizeof expression.
static QualType inferTypeFromSizeofExpr(const Expr *E) {
  const Expr *Arg = E->IgnoreParenImpCasts();
  if (const auto *UET = dyn_cast<UnaryExprOrTypeTraitExpr>(Arg)) {
    if (UET->getKind() == UETT_SizeOf) {
      if (UET->isArgumentType())
        return UET->getArgumentTypeInfo()->getType();
      else
        return UET->getArgumentExpr()->getType();
    }
  }
  return QualType();
}
 
/// Infer type from an arithmetic expression involving a sizeof. For example:
///
///   malloc(sizeof(MyType) + padding);  // infers 'MyType'
///   malloc(sizeof(MyType) * 32);       // infers 'MyType'
///   malloc(32 * sizeof(MyType));       // infers 'MyType'
///   malloc(sizeof(MyType) << 1);       // infers 'MyType'
///   ...
///
/// More complex arithmetic expressions are supported, but are a heuristic, e.g.
/// when considering allocations for structs with flexible array members:
///
///   malloc(sizeof(HasFlexArray) + sizeof(int) * 32);  // infers 'HasFlexArray'
///
static QualType inferPossibleTypeFromArithSizeofExpr(const Expr *E) {
  const Expr *Arg = E->IgnoreParenImpCasts();
  // The argument is a lone sizeof expression.
  if (QualType T = inferTypeFromSizeofExpr(Arg); !T.isNull())
    return T;
  if (const auto *BO = dyn_cast<BinaryOperator>(Arg)) {
    // Argument is an arithmetic expression. Cover common arithmetic patterns
    // involving sizeof.
    switch (BO->getOpcode()) {
    case BO_Add:
    case BO_Div:
    case BO_Mul:
    case BO_Shl:
    case BO_Shr:
    case BO_Sub:
      if (QualType T = inferPossibleTypeFromArithSizeofExpr(BO->getLHS());
          !T.isNull())
        return T;
      if (QualType T = inferPossibleTypeFromArithSizeofExpr(BO->getRHS());
          !T.isNull())
        return T;
      break;
    default:
      break;
    }
  }
  return QualType();
}
 
/// If the expression E is a reference to a variable, infer the type from a
/// variable's initializer if it contains a sizeof. Beware, this is a heuristic
/// and ignores if a variable is later reassigned. For example:
///
///   size_t my_size = sizeof(MyType);
///   void *x = malloc(my_size);  // infers 'MyType'
///
static QualType inferPossibleTypeFromVarInitSizeofExpr(const Expr *E) {
  const Expr *Arg = E->IgnoreParenImpCasts();
  if (const auto *DRE = dyn_cast<DeclRefExpr>(Arg)) {
    if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl())) {
      if (const Expr *Init = VD->getInit())
        return inferPossibleTypeFromArithSizeofExpr(Init);
    }
  }
  return QualType();
}
 
/// Deduces the allocated type by checking if the allocation call's result
/// is immediately used in a cast expression. For example:
///
///   MyType *x = (MyType *)malloc(4096);  // infers 'MyType'
///
static QualType inferPossibleTypeFromCastExpr(const CallExpr *CallE,
                                              const CastExpr *CastE) {
  if (!CastE)
    return QualType();
  QualType PtrType = CastE->getType();
  if (PtrType->isPointerType())
    return PtrType->getPointeeType();
  return QualType();
}
 
QualType infer_alloc::inferPossibleType(const CallExpr *E,
                                        const ASTContext &Ctx,
                                        const CastExpr *CastE) {
  QualType AllocType;
  // First check arguments.
  for (const Expr *Arg : E->arguments()) {
    AllocType = inferPossibleTypeFromArithSizeofExpr(Arg);
    if (AllocType.isNull())
      AllocType = inferPossibleTypeFromVarInitSizeofExpr(Arg);
    if (!AllocType.isNull())
      break;
  }
  // Then check later casts.
  if (AllocType.isNull())
    AllocType = inferPossibleTypeFromCastExpr(E, CastE);
  return AllocType;
}
 
std::optional<llvm::AllocTokenMetadata>
infer_alloc::getAllocTokenMetadata(QualType T, const ASTContext &Ctx) {
  llvm::AllocTokenMetadata ATMD;
 
  // Get unique type name.
  PrintingPolicy Policy(Ctx.getLangOpts());
  Policy.SuppressTagKeyword = true;
  Policy.FullyQualifiedName = true;
  llvm::raw_svector_ostream TypeNameOS(ATMD.TypeName);
  T.getCanonicalType().print(TypeNameOS, Policy);
 
  // Check if QualType contains a pointer. Implements a simple DFS to
  // recursively check if a type contains a pointer type.
  llvm::SmallPtrSet<const RecordDecl *, 4> VisitedRD;
  bool IncompleteType = false;
  ATMD.ContainsPointer = typeContainsPointer(T, VisitedRD, IncompleteType);
  if (!ATMD.ContainsPointer && IncompleteType)
    return std::nullopt;
 
  return ATMD;
}