1//===--- CGVTT.cpp - Emit LLVM Code for C++ VTTs --------------------------===//
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 contains code dealing with C++ code generation of VTTs (vtable tables).
10//
11//===----------------------------------------------------------------------===//
12
13#include "CodeGenModule.h"
14#include "CGCXXABI.h"
15#include "clang/AST/RecordLayout.h"
16#include "clang/AST/VTTBuilder.h"
17using namespace clang;
18using namespace CodeGen;
19
20static llvm::GlobalVariable *
21GetAddrOfVTTVTable(CodeGenVTables &CGVT, CodeGenModule &CGM,
22 const CXXRecordDecl *MostDerivedClass,
23 const VTTVTable &VTable,
24 llvm::GlobalVariable::LinkageTypes Linkage,
25 VTableLayout::AddressPointsMapTy &AddressPoints) {
26 if (VTable.getBase() == MostDerivedClass) {
27 assert(VTable.getBaseOffset().isZero() &&
28 "Most derived class vtable must have a zero offset!");
29 // This is a regular vtable.
30 return CGM.getCXXABI().getAddrOfVTable(RD: MostDerivedClass, VPtrOffset: CharUnits());
31 }
32
33 return CGVT.GenerateConstructionVTable(RD: MostDerivedClass,
34 Base: VTable.getBaseSubobject(),
35 BaseIsVirtual: VTable.isVirtual(),
36 Linkage,
37 AddressPoints);
38}
39
40void
41CodeGenVTables::EmitVTTDefinition(llvm::GlobalVariable *VTT,
42 llvm::GlobalVariable::LinkageTypes Linkage,
43 const CXXRecordDecl *RD) {
44 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/true);
45 llvm::ArrayType *ArrayType = llvm::ArrayType::get(
46 ElementType: CGM.GlobalsInt8PtrTy, NumElements: Builder.getVTTComponents().size());
47
48 SmallVector<llvm::GlobalVariable *, 8> VTables;
49 SmallVector<VTableAddressPointsMapTy, 8> VTableAddressPoints;
50 for (const VTTVTable *i = Builder.getVTTVTables().begin(),
51 *e = Builder.getVTTVTables().end(); i != e; ++i) {
52 VTableAddressPoints.push_back(Elt: VTableAddressPointsMapTy());
53 VTables.push_back(Elt: GetAddrOfVTTVTable(CGVT&: *this, CGM, MostDerivedClass: RD, VTable: *i, Linkage,
54 AddressPoints&: VTableAddressPoints.back()));
55 }
56
57 SmallVector<llvm::Constant *, 8> VTTComponents;
58 for (const VTTComponent *i = Builder.getVTTComponents().begin(),
59 *e = Builder.getVTTComponents().end(); i != e; ++i) {
60 const VTTVTable &VTTVT = Builder.getVTTVTables()[i->VTableIndex];
61 llvm::GlobalVariable *VTable = VTables[i->VTableIndex];
62 VTableLayout::AddressPointLocation AddressPoint;
63 if (VTTVT.getBase() == RD) {
64 // Just get the address point for the regular vtable.
65 AddressPoint =
66 getItaniumVTableContext().getVTableLayout(RD).getAddressPoint(
67 Base: i->VTableBase);
68 } else {
69 AddressPoint = VTableAddressPoints[i->VTableIndex].lookup(Val: i->VTableBase);
70 assert(AddressPoint.AddressPointIndex != 0 &&
71 "Did not find ctor vtable address point!");
72 }
73
74 llvm::Value *Idxs[] = {
75 llvm::ConstantInt::get(Ty: CGM.Int32Ty, V: 0),
76 llvm::ConstantInt::get(Ty: CGM.Int32Ty, V: AddressPoint.VTableIndex),
77 llvm::ConstantInt::get(Ty: CGM.Int32Ty, V: AddressPoint.AddressPointIndex),
78 };
79
80 // Add inrange attribute to indicate that only the VTableIndex can be
81 // accessed.
82 unsigned ComponentSize =
83 CGM.getDataLayout().getTypeAllocSize(Ty: getVTableComponentType());
84 unsigned VTableSize = CGM.getDataLayout().getTypeAllocSize(
85 Ty: cast<llvm::StructType>(Val: VTable->getValueType())
86 ->getElementType(N: AddressPoint.VTableIndex));
87 unsigned Offset = ComponentSize * AddressPoint.AddressPointIndex;
88 llvm::ConstantRange InRange(
89 llvm::APInt(32, (int)-Offset, true),
90 llvm::APInt(32, (int)(VTableSize - Offset), true));
91 llvm::Constant *Init = llvm::ConstantExpr::getGetElementPtr(
92 Ty: VTable->getValueType(), C: VTable, IdxList: Idxs, /*InBounds=*/NW: true, InRange);
93
94 if (const auto &Schema =
95 CGM.getCodeGenOpts().PointerAuth.CXXVTTVTablePointers)
96 Init = CGM.getConstantSignedPointer(Pointer: Init, Schema, StorageAddress: nullptr, SchemaDecl: GlobalDecl(),
97 SchemaType: QualType());
98
99 VTTComponents.push_back(Elt: Init);
100 }
101
102 llvm::Constant *Init = llvm::ConstantArray::get(T: ArrayType, V: VTTComponents);
103
104 VTT->setInitializer(Init);
105
106 // Set the correct linkage.
107 VTT->setLinkage(Linkage);
108
109 if (CGM.supportsCOMDAT() && VTT->isWeakForLinker())
110 VTT->setComdat(CGM.getModule().getOrInsertComdat(Name: VTT->getName()));
111
112 // Set the visibility. This will already have been set on the VTT declaration.
113 // Set it again, now that we have a definition, as the implicit visibility can
114 // apply differently to definitions.
115 CGM.setGVProperties(GV: VTT, D: RD);
116}
117
118llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
119 assert(RD->getNumVBases() && "Only classes with virtual bases need a VTT");
120
121 SmallString<256> OutName;
122 llvm::raw_svector_ostream Out(OutName);
123 cast<ItaniumMangleContext>(Val&: CGM.getCXXABI().getMangleContext())
124 .mangleCXXVTT(RD, Out);
125 StringRef Name = OutName.str();
126
127 // This will also defer the definition of the VTT.
128 (void) CGM.getCXXABI().getAddrOfVTable(RD, VPtrOffset: CharUnits());
129
130 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
131
132 llvm::ArrayType *ArrayType = llvm::ArrayType::get(
133 ElementType: CGM.GlobalsInt8PtrTy, NumElements: Builder.getVTTComponents().size());
134 llvm::Align Align = CGM.getDataLayout().getABITypeAlign(Ty: CGM.GlobalsInt8PtrTy);
135
136 llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
137 Name, Ty: ArrayType, Linkage: llvm::GlobalValue::ExternalLinkage, Alignment: Align);
138 GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
139 CGM.setGVProperties(GV, D: RD);
140 return GV;
141}
142
143uint64_t CodeGenVTables::getSubVTTIndex(const CXXRecordDecl *RD,
144 BaseSubobject Base) {
145 BaseSubobjectPairTy ClassSubobjectPair(RD, Base);
146
147 SubVTTIndicesMapTy::iterator I = SubVTTIndices.find(Val: ClassSubobjectPair);
148 if (I != SubVTTIndices.end())
149 return I->second;
150
151 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
152
153 for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator
154 I = Builder.getSubVTTIndices().begin(),
155 E = Builder.getSubVTTIndices().end();
156 I != E; ++I) {
157 // Insert all indices.
158 BaseSubobjectPairTy ClassSubobjectPair(RD, I->first);
159
160 SubVTTIndices.insert(KV: std::make_pair(x&: ClassSubobjectPair, y: I->second));
161 }
162
163 I = SubVTTIndices.find(Val: ClassSubobjectPair);
164 assert(I != SubVTTIndices.end() && "Did not find index!");
165
166 return I->second;
167}
168
169uint64_t
170CodeGenVTables::getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD,
171 BaseSubobject Base) {
172 SecondaryVirtualPointerIndicesMapTy::iterator I =
173 SecondaryVirtualPointerIndices.find(Val: std::make_pair(x&: RD, y&: Base));
174
175 if (I != SecondaryVirtualPointerIndices.end())
176 return I->second;
177
178 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
179
180 // Insert all secondary vpointer indices.
181 for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
182 Builder.getSecondaryVirtualPointerIndices().begin(),
183 E = Builder.getSecondaryVirtualPointerIndices().end(); I != E; ++I) {
184 std::pair<const CXXRecordDecl *, BaseSubobject> Pair =
185 std::make_pair(x&: RD, y: I->first);
186
187 SecondaryVirtualPointerIndices.insert(KV: std::make_pair(x&: Pair, y: I->second));
188 }
189
190 I = SecondaryVirtualPointerIndices.find(Val: std::make_pair(x&: RD, y&: Base));
191 assert(I != SecondaryVirtualPointerIndices.end() && "Did not find index!");
192
193 return I->second;
194}
195