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"
17 using namespace clang;
18 using namespace CodeGen;
19
20 static llvm::GlobalVariable *
GetAddrOfVTTVTable(CodeGenVTables & CGVT,CodeGenModule & CGM,const CXXRecordDecl * MostDerivedClass,const VTTVTable & VTable,llvm::GlobalVariable::LinkageTypes Linkage,VTableLayout::AddressPointsMapTy & AddressPoints)21 GetAddrOfVTTVTable(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(MostDerivedClass, CharUnits());
31 }
32
33 return CGVT.GenerateConstructionVTable(MostDerivedClass,
34 VTable.getBaseSubobject(),
35 VTable.isVirtual(),
36 Linkage,
37 AddressPoints);
38 }
39
40 void
EmitVTTDefinition(llvm::GlobalVariable * VTT,llvm::GlobalVariable::LinkageTypes Linkage,const CXXRecordDecl * RD)41 CodeGenVTables::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 CGM.GlobalsInt8PtrTy, 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(VTableAddressPointsMapTy());
53 VTables.push_back(GetAddrOfVTTVTable(*this, CGM, RD, *i, Linkage,
54 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 i->VTableBase);
68 } else {
69 AddressPoint = VTableAddressPoints[i->VTableIndex].lookup(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(CGM.Int32Ty, 0),
76 llvm::ConstantInt::get(CGM.Int32Ty, AddressPoint.VTableIndex),
77 llvm::ConstantInt::get(CGM.Int32Ty, 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(getVTableComponentType());
84 unsigned VTableSize = CGM.getDataLayout().getTypeAllocSize(
85 cast<llvm::StructType>(VTable->getValueType())
86 ->getElementType(AddressPoint.VTableIndex));
87 unsigned Offset = ComponentSize * AddressPoint.AddressPointIndex;
88 llvm::ConstantRange InRange(llvm::APInt(32, -Offset, true),
89 llvm::APInt(32, VTableSize - Offset, true));
90 llvm::Constant *Init = llvm::ConstantExpr::getGetElementPtr(
91 VTable->getValueType(), VTable, Idxs, /*InBounds=*/true, InRange);
92
93 if (const auto &Schema =
94 CGM.getCodeGenOpts().PointerAuth.CXXVTTVTablePointers)
95 Init = CGM.getConstantSignedPointer(Init, Schema, nullptr, GlobalDecl(),
96 QualType());
97
98 VTTComponents.push_back(Init);
99 }
100
101 llvm::Constant *Init = llvm::ConstantArray::get(ArrayType, VTTComponents);
102
103 VTT->setInitializer(Init);
104
105 // Set the correct linkage.
106 VTT->setLinkage(Linkage);
107
108 if (CGM.supportsCOMDAT() && VTT->isWeakForLinker())
109 VTT->setComdat(CGM.getModule().getOrInsertComdat(VTT->getName()));
110
111 // Set the visibility. This will already have been set on the VTT declaration.
112 // Set it again, now that we have a definition, as the implicit visibility can
113 // apply differently to definitions.
114 CGM.setGVProperties(VTT, RD);
115 }
116
GetAddrOfVTT(const CXXRecordDecl * RD)117 llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
118 assert(RD->getNumVBases() && "Only classes with virtual bases need a VTT");
119
120 SmallString<256> OutName;
121 llvm::raw_svector_ostream Out(OutName);
122 cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
123 .mangleCXXVTT(RD, Out);
124 StringRef Name = OutName.str();
125
126 // This will also defer the definition of the VTT.
127 (void) CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
128
129 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
130
131 llvm::ArrayType *ArrayType = llvm::ArrayType::get(
132 CGM.GlobalsInt8PtrTy, Builder.getVTTComponents().size());
133 llvm::Align Align = CGM.getDataLayout().getABITypeAlign(CGM.GlobalsInt8PtrTy);
134
135 llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
136 Name, ArrayType, llvm::GlobalValue::ExternalLinkage, Align);
137 GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
138 CGM.setGVProperties(GV, RD);
139 return GV;
140 }
141
getSubVTTIndex(const CXXRecordDecl * RD,BaseSubobject Base)142 uint64_t CodeGenVTables::getSubVTTIndex(const CXXRecordDecl *RD,
143 BaseSubobject Base) {
144 BaseSubobjectPairTy ClassSubobjectPair(RD, Base);
145
146 SubVTTIndicesMapTy::iterator I = SubVTTIndices.find(ClassSubobjectPair);
147 if (I != SubVTTIndices.end())
148 return I->second;
149
150 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
151
152 for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator
153 I = Builder.getSubVTTIndices().begin(),
154 E = Builder.getSubVTTIndices().end();
155 I != E; ++I) {
156 // Insert all indices.
157 BaseSubobjectPairTy ClassSubobjectPair(RD, I->first);
158
159 SubVTTIndices.insert(std::make_pair(ClassSubobjectPair, I->second));
160 }
161
162 I = SubVTTIndices.find(ClassSubobjectPair);
163 assert(I != SubVTTIndices.end() && "Did not find index!");
164
165 return I->second;
166 }
167
168 uint64_t
getSecondaryVirtualPointerIndex(const CXXRecordDecl * RD,BaseSubobject Base)169 CodeGenVTables::getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD,
170 BaseSubobject Base) {
171 SecondaryVirtualPointerIndicesMapTy::iterator I =
172 SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
173
174 if (I != SecondaryVirtualPointerIndices.end())
175 return I->second;
176
177 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
178
179 // Insert all secondary vpointer indices.
180 for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
181 Builder.getSecondaryVirtualPointerIndices().begin(),
182 E = Builder.getSecondaryVirtualPointerIndices().end(); I != E; ++I) {
183 std::pair<const CXXRecordDecl *, BaseSubobject> Pair =
184 std::make_pair(RD, I->first);
185
186 SecondaryVirtualPointerIndices.insert(std::make_pair(Pair, I->second));
187 }
188
189 I = SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
190 assert(I != SecondaryVirtualPointerIndices.end() && "Did not find index!");
191
192 return I->second;
193 }
194