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| 1 | +//===--- InferAlloc.cpp - Allocation type inference -----------------------===// |
| 2 | +// |
| 3 | +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | +// See https://llvm.org/LICENSE.txt for license information. |
| 5 | +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | +// |
| 7 | +//===----------------------------------------------------------------------===// |
| 8 | +// |
| 9 | +// This file implements allocation-related type inference. |
| 10 | +// |
| 11 | +//===----------------------------------------------------------------------===// |
| 12 | + |
| 13 | +#include "clang/AST/InferAlloc.h" |
| 14 | +#include "clang/AST/ASTContext.h" |
| 15 | +#include "clang/AST/Decl.h" |
| 16 | +#include "clang/AST/DeclCXX.h" |
| 17 | +#include "clang/AST/Expr.h" |
| 18 | +#include "clang/AST/Type.h" |
| 19 | +#include "clang/Basic/IdentifierTable.h" |
| 20 | +#include "llvm/ADT/SmallPtrSet.h" |
| 21 | + |
| 22 | +namespace clang { |
| 23 | +namespace { |
| 24 | +bool typeContainsPointer(QualType T, |
| 25 | + llvm::SmallPtrSet<const RecordDecl *, 4> &VisitedRD, |
| 26 | + bool &IncompleteType) { |
| 27 | + QualType CanonicalType = T.getCanonicalType(); |
| 28 | + if (CanonicalType->isPointerType()) |
| 29 | + return true; // base case |
| 30 | + |
| 31 | + // Look through typedef chain to check for special types. |
| 32 | + for (QualType CurrentT = T; const auto *TT = CurrentT->getAs<TypedefType>(); |
| 33 | + CurrentT = TT->getDecl()->getUnderlyingType()) { |
| 34 | + const IdentifierInfo *II = TT->getDecl()->getIdentifier(); |
| 35 | + // Special Case: Syntactically uintptr_t is not a pointer; semantically, |
| 36 | + // however, very likely used as such. Therefore, classify uintptr_t as a |
| 37 | + // pointer, too. |
| 38 | + if (II && II->isStr("uintptr_t")) |
| 39 | + return true; |
| 40 | + } |
| 41 | + |
| 42 | + // The type is an array; check the element type. |
| 43 | + if ( const ArrayType *AT = dyn_cast<ArrayType>(CanonicalType)) |
| 44 | + return typeContainsPointer(AT->getElementType(), VisitedRD, IncompleteType); |
| 45 | + // The type is a struct, class, or union. |
| 46 | + if (const RecordDecl *RD = CanonicalType->getAsRecordDecl()) { |
| 47 | + if (!RD->isCompleteDefinition()) { |
| 48 | + IncompleteType = true; |
| 49 | + return false; |
| 50 | + } |
| 51 | + if (!VisitedRD.insert(RD).second) |
| 52 | + return false; // already visited |
| 53 | + // Check all fields. |
| 54 | + for (const FieldDecl *Field : RD->fields()) { |
| 55 | + if (typeContainsPointer(Field->getType(), VisitedRD, IncompleteType)) |
| 56 | + return true; |
| 57 | + } |
| 58 | + // For C++ classes, also check base classes. |
| 59 | + if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) { |
| 60 | + // Polymorphic types require a vptr. |
| 61 | + if (CXXRD->isDynamicClass()) |
| 62 | + return true; |
| 63 | + for (const CXXBaseSpecifier &Base : CXXRD->bases()) { |
| 64 | + if (typeContainsPointer(Base.getType(), VisitedRD, IncompleteType)) |
| 65 | + return true; |
| 66 | + } |
| 67 | + } |
| 68 | + } |
| 69 | + return false; |
| 70 | +} |
| 71 | + |
| 72 | +/// Infer type from a simple sizeof expression. |
| 73 | +QualType inferTypeFromSizeofExpr(const Expr *E) { |
| 74 | + const Expr *Arg = E->IgnoreParenImpCasts(); |
| 75 | + if (const auto *UET = dyn_cast<UnaryExprOrTypeTraitExpr>(Arg)) { |
| 76 | + if (UET->getKind() == UETT_SizeOf) { |
| 77 | + if (UET->isArgumentType()) |
| 78 | + return UET->getArgumentTypeInfo()->getType(); |
| 79 | + else |
| 80 | + return UET->getArgumentExpr()->getType(); |
| 81 | + } |
| 82 | + } |
| 83 | + return QualType(); |
| 84 | +} |
| 85 | + |
| 86 | +/// Infer type from an arithmetic expression involving a sizeof. For example: |
| 87 | +/// |
| 88 | +/// malloc(sizeof(MyType) + padding); // infers 'MyType' |
| 89 | +/// malloc(sizeof(MyType) * 32); // infers 'MyType' |
| 90 | +/// malloc(32 * sizeof(MyType)); // infers 'MyType' |
| 91 | +/// malloc(sizeof(MyType) << 1); // infers 'MyType' |
| 92 | +/// ... |
| 93 | +/// |
| 94 | +/// More complex arithmetic expressions are supported, but are a heuristic, e.g. |
| 95 | +/// when considering allocations for structs with flexible array members: |
| 96 | +/// |
| 97 | +/// malloc(sizeof(HasFlexArray) + sizeof(int) * 32); // infers 'HasFlexArray' |
| 98 | +/// |
| 99 | +QualType inferPossibleTypeFromArithSizeofExpr(const Expr *E) { |
| 100 | + const Expr *Arg = E->IgnoreParenImpCasts(); |
| 101 | + // The argument is a lone sizeof expression. |
| 102 | + if (QualType T = inferTypeFromSizeofExpr(Arg); !T.isNull()) |
| 103 | + return T; |
| 104 | + if (const auto *BO = dyn_cast<BinaryOperator>(Arg)) { |
| 105 | + // Argument is an arithmetic expression. Cover common arithmetic patterns |
| 106 | + // involving sizeof. |
| 107 | + switch (BO->getOpcode()) { |
| 108 | + case BO_Add: |
| 109 | + case BO_Div: |
| 110 | + case BO_Mul: |
| 111 | + case BO_Shl: |
| 112 | + case BO_Shr: |
| 113 | + case BO_Sub: |
| 114 | + if (QualType T = inferPossibleTypeFromArithSizeofExpr(BO->getLHS()); |
| 115 | + !T.isNull()) |
| 116 | + return T; |
| 117 | + if (QualType T = inferPossibleTypeFromArithSizeofExpr(BO->getRHS()); |
| 118 | + !T.isNull()) |
| 119 | + return T; |
| 120 | + break; |
| 121 | + default: |
| 122 | + break; |
| 123 | + } |
| 124 | + } |
| 125 | + return QualType(); |
| 126 | +} |
| 127 | + |
| 128 | +/// If the expression E is a reference to a variable, infer the type from a |
| 129 | +/// variable's initializer if it contains a sizeof. Beware, this is a heuristic |
| 130 | +/// and ignores if a variable is later reassigned. For example: |
| 131 | +/// |
| 132 | +/// size_t my_size = sizeof(MyType); |
| 133 | +/// void *x = malloc(my_size); // infers 'MyType' |
| 134 | +/// |
| 135 | +QualType inferPossibleTypeFromVarInitSizeofExpr(const Expr *E) { |
| 136 | + const Expr *Arg = E->IgnoreParenImpCasts(); |
| 137 | + if (const auto *DRE = dyn_cast<DeclRefExpr>(Arg)) { |
| 138 | + if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl())) { |
| 139 | + if (const Expr *Init = VD->getInit()) |
| 140 | + return inferPossibleTypeFromArithSizeofExpr(Init); |
| 141 | + } |
| 142 | + } |
| 143 | + return QualType(); |
| 144 | +} |
| 145 | + |
| 146 | +/// Deduces the allocated type by checking if the allocation call's result |
| 147 | +/// is immediately used in a cast expression. For example: |
| 148 | +/// |
| 149 | +/// MyType *x = (MyType *)malloc(4096); // infers 'MyType' |
| 150 | +/// |
| 151 | +QualType inferPossibleTypeFromCastExpr(const CallExpr *CallE, |
| 152 | + const CastExpr *CastE) { |
| 153 | + if (!CastE) |
| 154 | + return QualType(); |
| 155 | + QualType PtrType = CastE->getType(); |
| 156 | + if (PtrType->isPointerType()) |
| 157 | + return PtrType->getPointeeType(); |
| 158 | + return QualType(); |
| 159 | +} |
| 160 | +} // anonymous namespace |
| 161 | + |
| 162 | +namespace infer_alloc { |
| 163 | + |
| 164 | +QualType inferPossibleType(const CallExpr *E, const ASTContext &Ctx, |
| 165 | + const CastExpr *CastE) { |
| 166 | + QualType AllocType; |
| 167 | + // First check arguments. |
| 168 | + for (const Expr *Arg : E->arguments()) { |
| 169 | + AllocType = inferPossibleTypeFromArithSizeofExpr(Arg); |
| 170 | + if (AllocType.isNull()) |
| 171 | + AllocType = inferPossibleTypeFromVarInitSizeofExpr(Arg); |
| 172 | + if (!AllocType.isNull()) |
| 173 | + break; |
| 174 | + } |
| 175 | + // Then check later casts. |
| 176 | + if (AllocType.isNull()) |
| 177 | + AllocType = inferPossibleTypeFromCastExpr(E, CastE); |
| 178 | + return AllocType; |
| 179 | +} |
| 180 | + |
| 181 | +std::optional<llvm::AllocTokenMetadata> |
| 182 | +getAllocTokenMetadata(QualType T, const ASTContext &Ctx) { |
| 183 | + llvm::AllocTokenMetadata ATMD; |
| 184 | + |
| 185 | + // Get unique type name. |
| 186 | + PrintingPolicy Policy(Ctx.getLangOpts()); |
| 187 | + Policy.SuppressTagKeyword = true; |
| 188 | + Policy.FullyQualifiedName = true; |
| 189 | + llvm::raw_svector_ostream TypeNameOS(ATMD.TypeName); |
| 190 | + T.getCanonicalType().print(TypeNameOS, Policy); |
| 191 | + |
| 192 | + // Check if QualType contains a pointer. Implements a simple DFS to |
| 193 | + // recursively check if a type contains a pointer type. |
| 194 | + llvm::SmallPtrSet<const RecordDecl *, 4> VisitedRD; |
| 195 | + bool IncompleteType = false; |
| 196 | + ATMD.ContainsPointer = typeContainsPointer(T, VisitedRD, IncompleteType); |
| 197 | + if (!ATMD.ContainsPointer && IncompleteType) |
| 198 | + return std::nullopt; |
| 199 | + |
| 200 | + return ATMD; |
| 201 | +} |
| 202 | + |
| 203 | +} // namespace infer_alloc |
| 204 | +} // namespace clang |
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