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 * 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 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 } 116 117 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 } 141 142 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 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