1 //===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===// 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. 10 // 11 //===----------------------------------------------------------------------===// 12 13 // We might split this into multiple files if it gets too unwieldy 14 15 #include "CGCXXABI.h" 16 #include "CodeGenFunction.h" 17 #include "CodeGenModule.h" 18 #include "clang/AST/ASTContext.h" 19 #include "clang/AST/Attr.h" 20 #include "clang/AST/Decl.h" 21 #include "clang/AST/DeclCXX.h" 22 #include "clang/AST/DeclObjC.h" 23 #include "clang/AST/Mangle.h" 24 #include "clang/AST/RecordLayout.h" 25 #include "clang/AST/StmtCXX.h" 26 #include "clang/Basic/CodeGenOptions.h" 27 #include "llvm/ADT/StringExtras.h" 28 using namespace clang; 29 using namespace CodeGen; 30 31 32 /// Try to emit a base destructor as an alias to its primary 33 /// base-class destructor. 34 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) { 35 if (!getCodeGenOpts().CXXCtorDtorAliases) 36 return true; 37 38 // Producing an alias to a base class ctor/dtor can degrade debug quality 39 // as the debugger cannot tell them apart. 40 if (getCodeGenOpts().OptimizationLevel == 0) 41 return true; 42 43 // Disable this optimization for ARM64EC. FIXME: This probably should work, 44 // but getting the symbol table correct is complicated. 45 if (getTarget().getTriple().isWindowsArm64EC()) 46 return true; 47 48 // If sanitizing memory to check for use-after-dtor, do not emit as 49 // an alias, unless this class owns no members. 50 if (getCodeGenOpts().SanitizeMemoryUseAfterDtor && 51 !D->getParent()->field_empty()) 52 return true; 53 54 // If the destructor doesn't have a trivial body, we have to emit it 55 // separately. 56 if (!D->hasTrivialBody()) 57 return true; 58 59 const CXXRecordDecl *Class = D->getParent(); 60 61 // We are going to instrument this destructor, so give up even if it is 62 // currently empty. 63 if (Class->mayInsertExtraPadding()) 64 return true; 65 66 // If we need to manipulate a VTT parameter, give up. 67 if (Class->getNumVBases()) { 68 // Extra Credit: passing extra parameters is perfectly safe 69 // in many calling conventions, so only bail out if the ctor's 70 // calling convention is nonstandard. 71 return true; 72 } 73 74 // If any field has a non-trivial destructor, we have to emit the 75 // destructor separately. 76 for (const auto *I : Class->fields()) 77 if (I->getType().isDestructedType()) 78 return true; 79 80 // Try to find a unique base class with a non-trivial destructor. 81 const CXXRecordDecl *UniqueBase = nullptr; 82 for (const auto &I : Class->bases()) { 83 84 // We're in the base destructor, so skip virtual bases. 85 if (I.isVirtual()) continue; 86 87 // Skip base classes with trivial destructors. 88 const auto *Base = 89 cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl()); 90 if (Base->hasTrivialDestructor()) continue; 91 92 // If we've already found a base class with a non-trivial 93 // destructor, give up. 94 if (UniqueBase) return true; 95 UniqueBase = Base; 96 } 97 98 // If we didn't find any bases with a non-trivial destructor, then 99 // the base destructor is actually effectively trivial, which can 100 // happen if it was needlessly user-defined or if there are virtual 101 // bases with non-trivial destructors. 102 if (!UniqueBase) 103 return true; 104 105 // If the base is at a non-zero offset, give up. 106 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class); 107 if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero()) 108 return true; 109 110 // Give up if the calling conventions don't match. We could update the call, 111 // but it is probably not worth it. 112 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor(); 113 if (BaseD->getType()->castAs<FunctionType>()->getCallConv() != 114 D->getType()->castAs<FunctionType>()->getCallConv()) 115 return true; 116 117 GlobalDecl AliasDecl(D, Dtor_Base); 118 GlobalDecl TargetDecl(BaseD, Dtor_Base); 119 120 // The alias will use the linkage of the referent. If we can't 121 // support aliases with that linkage, fail. 122 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl); 123 124 // We can't use an alias if the linkage is not valid for one. 125 if (!llvm::GlobalAlias::isValidLinkage(Linkage)) 126 return true; 127 128 llvm::GlobalValue::LinkageTypes TargetLinkage = 129 getFunctionLinkage(TargetDecl); 130 131 // Check if we have it already. 132 StringRef MangledName = getMangledName(AliasDecl); 133 llvm::GlobalValue *Entry = GetGlobalValue(MangledName); 134 if (Entry && !Entry->isDeclaration()) 135 return false; 136 if (Replacements.count(MangledName)) 137 return false; 138 139 llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl); 140 141 // Find the referent. 142 auto *Aliasee = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl)); 143 144 // Instead of creating as alias to a linkonce_odr, replace all of the uses 145 // of the aliasee. 146 if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) && 147 !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage && 148 TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) { 149 // FIXME: An extern template instantiation will create functions with 150 // linkage "AvailableExternally". In libc++, some classes also define 151 // members with attribute "AlwaysInline" and expect no reference to 152 // be generated. It is desirable to reenable this optimisation after 153 // corresponding LLVM changes. 154 addReplacement(MangledName, Aliasee); 155 return false; 156 } 157 158 // If we have a weak, non-discardable alias (weak, weak_odr), like an extern 159 // template instantiation or a dllexported class, avoid forming it on COFF. 160 // A COFF weak external alias cannot satisfy a normal undefined symbol 161 // reference from another TU. The other TU must also mark the referenced 162 // symbol as weak, which we cannot rely on. 163 if (llvm::GlobalValue::isWeakForLinker(Linkage) && 164 getTriple().isOSBinFormatCOFF()) { 165 return true; 166 } 167 168 // If we don't have a definition for the destructor yet or the definition is 169 // avaialable_externally, don't emit an alias. We can't emit aliases to 170 // declarations; that's just not how aliases work. 171 if (Aliasee->isDeclarationForLinker()) 172 return true; 173 174 // Don't create an alias to a linker weak symbol. This avoids producing 175 // different COMDATs in different TUs. Another option would be to 176 // output the alias both for weak_odr and linkonce_odr, but that 177 // requires explicit comdat support in the IL. 178 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) 179 return true; 180 181 // Create the alias with no name. 182 auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "", 183 Aliasee, &getModule()); 184 185 // Destructors are always unnamed_addr. 186 Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global); 187 188 // Switch any previous uses to the alias. 189 if (Entry) { 190 assert(Entry->getValueType() == AliasValueType && 191 Entry->getAddressSpace() == Alias->getAddressSpace() && 192 "declaration exists with different type"); 193 Alias->takeName(Entry); 194 Entry->replaceAllUsesWith(Alias); 195 Entry->eraseFromParent(); 196 } else { 197 Alias->setName(MangledName); 198 } 199 200 // Finally, set up the alias with its proper name and attributes. 201 SetCommonAttributes(AliasDecl, Alias); 202 203 return false; 204 } 205 206 llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) { 207 const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD); 208 auto *Fn = cast<llvm::Function>( 209 getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr, 210 /*DontDefer=*/true, ForDefinition)); 211 212 setFunctionLinkage(GD, Fn); 213 214 CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo); 215 setNonAliasAttributes(GD, Fn); 216 SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn); 217 return Fn; 218 } 219 220 llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor( 221 GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType, 222 bool DontDefer, ForDefinition_t IsForDefinition) { 223 auto *MD = cast<CXXMethodDecl>(GD.getDecl()); 224 225 if (isa<CXXDestructorDecl>(MD)) { 226 // Always alias equivalent complete destructors to base destructors in the 227 // MS ABI. 228 if (getTarget().getCXXABI().isMicrosoft() && 229 GD.getDtorType() == Dtor_Complete && 230 MD->getParent()->getNumVBases() == 0) 231 GD = GD.getWithDtorType(Dtor_Base); 232 } 233 234 if (!FnType) { 235 if (!FnInfo) 236 FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD); 237 FnType = getTypes().GetFunctionType(*FnInfo); 238 } 239 240 llvm::Constant *Ptr = GetOrCreateLLVMFunction( 241 getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer, 242 /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition); 243 return {FnType, Ptr}; 244 } 245 246 static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF, 247 GlobalDecl GD, 248 llvm::Type *Ty, 249 const CXXRecordDecl *RD) { 250 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() && 251 "No kext in Microsoft ABI"); 252 CodeGenModule &CGM = CGF.CGM; 253 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits()); 254 Ty = llvm::PointerType::getUnqual(CGM.getLLVMContext()); 255 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null"); 256 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD); 257 const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD); 258 VTableLayout::AddressPointLocation AddressPoint = 259 VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero())); 260 VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) + 261 AddressPoint.AddressPointIndex; 262 llvm::Value *VFuncPtr = 263 CGF.Builder.CreateConstInBoundsGEP1_64(Ty, VTable, VTableIndex, "vfnkxt"); 264 llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad( 265 Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes)); 266 CGCallee Callee(GD, VFunc); 267 return Callee; 268 } 269 270 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making 271 /// indirect call to virtual functions. It makes the call through indexing 272 /// into the vtable. 273 CGCallee 274 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD, 275 NestedNameSpecifier *Qual, 276 llvm::Type *Ty) { 277 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) && 278 "BuildAppleKextVirtualCall - bad Qual kind"); 279 280 const Type *QTy = Qual->getAsType(); 281 QualType T = QualType(QTy, 0); 282 const RecordType *RT = T->getAs<RecordType>(); 283 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record"); 284 const auto *RD = cast<CXXRecordDecl>(RT->getDecl()); 285 286 if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD)) 287 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD); 288 289 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD); 290 } 291 292 /// BuildVirtualCall - This routine makes indirect vtable call for 293 /// call to virtual destructors. It returns 0 if it could not do it. 294 CGCallee 295 CodeGenFunction::BuildAppleKextVirtualDestructorCall( 296 const CXXDestructorDecl *DD, 297 CXXDtorType Type, 298 const CXXRecordDecl *RD) { 299 assert(DD->isVirtual() && Type != Dtor_Base); 300 // Compute the function type we're calling. 301 const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration( 302 GlobalDecl(DD, Dtor_Complete)); 303 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo); 304 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD); 305 } 306