304 lines · cpp
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-exception6//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 unwieldy14 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/Basic/CodeGenOptions.h"26using namespace clang;27using namespace CodeGen;28 29 30/// Try to emit a base destructor as an alias to its primary31/// base-class destructor.32bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {33 if (!getCodeGenOpts().CXXCtorDtorAliases)34 return true;35 36 // Producing an alias to a base class ctor/dtor can degrade debug quality37 // as the debugger cannot tell them apart.38 if (getCodeGenOpts().OptimizationLevel == 0)39 return true;40 41 // Disable this optimization for ARM64EC. FIXME: This probably should work,42 // but getting the symbol table correct is complicated.43 if (getTarget().getTriple().isWindowsArm64EC())44 return true;45 46 // If sanitizing memory to check for use-after-dtor, do not emit as47 // an alias, unless this class owns no members.48 if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&49 !D->getParent()->field_empty())50 return true;51 52 // If the destructor doesn't have a trivial body, we have to emit it53 // separately.54 if (!D->hasTrivialBody())55 return true;56 57 const CXXRecordDecl *Class = D->getParent();58 59 // We are going to instrument this destructor, so give up even if it is60 // currently empty.61 if (Class->mayInsertExtraPadding())62 return true;63 64 // If we need to manipulate a VTT parameter, give up.65 if (Class->getNumVBases()) {66 // Extra Credit: passing extra parameters is perfectly safe67 // in many calling conventions, so only bail out if the ctor's68 // calling convention is nonstandard.69 return true;70 }71 72 // If any field has a non-trivial destructor, we have to emit the73 // destructor separately.74 for (const auto *I : Class->fields())75 if (I->getType().isDestructedType())76 return true;77 78 // Try to find a unique base class with a non-trivial destructor.79 const CXXRecordDecl *UniqueBase = nullptr;80 for (const auto &I : Class->bases()) {81 82 // We're in the base destructor, so skip virtual bases.83 if (I.isVirtual()) continue;84 85 // Skip base classes with trivial destructors.86 const auto *Base = I.getType()->castAsCXXRecordDecl();87 if (Base->hasTrivialDestructor()) continue;88 89 // If we've already found a base class with a non-trivial90 // destructor, give up.91 if (UniqueBase) return true;92 UniqueBase = Base;93 }94 95 // If we didn't find any bases with a non-trivial destructor, then96 // the base destructor is actually effectively trivial, which can97 // happen if it was needlessly user-defined or if there are virtual98 // bases with non-trivial destructors.99 if (!UniqueBase)100 return true;101 102 // If the base is at a non-zero offset, give up.103 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);104 if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())105 return true;106 107 // Give up if the calling conventions don't match. We could update the call,108 // but it is probably not worth it.109 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();110 if (BaseD->getType()->castAs<FunctionType>()->getCallConv() !=111 D->getType()->castAs<FunctionType>()->getCallConv())112 return true;113 114 GlobalDecl AliasDecl(D, Dtor_Base);115 GlobalDecl TargetDecl(BaseD, Dtor_Base);116 117 // The alias will use the linkage of the referent. If we can't118 // support aliases with that linkage, fail.119 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);120 121 // We can't use an alias if the linkage is not valid for one.122 if (!llvm::GlobalAlias::isValidLinkage(Linkage))123 return true;124 125 llvm::GlobalValue::LinkageTypes TargetLinkage =126 getFunctionLinkage(TargetDecl);127 128 // Check if we have it already.129 StringRef MangledName = getMangledName(AliasDecl);130 llvm::GlobalValue *Entry = GetGlobalValue(MangledName);131 if (Entry && !Entry->isDeclaration())132 return false;133 if (Replacements.count(MangledName))134 return false;135 136 llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);137 138 // Find the referent.139 auto *Aliasee = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));140 141 // Instead of creating as alias to a linkonce_odr, replace all of the uses142 // of the aliasee.143 if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&144 !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&145 TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {146 // FIXME: An extern template instantiation will create functions with147 // linkage "AvailableExternally". In libc++, some classes also define148 // members with attribute "AlwaysInline" and expect no reference to149 // be generated. It is desirable to reenable this optimisation after150 // corresponding LLVM changes.151 addReplacement(MangledName, Aliasee);152 return false;153 }154 155 // If we have a weak, non-discardable alias (weak, weak_odr), like an extern156 // template instantiation or a dllexported class, avoid forming it on COFF.157 // A COFF weak external alias cannot satisfy a normal undefined symbol158 // reference from another TU. The other TU must also mark the referenced159 // symbol as weak, which we cannot rely on.160 if (llvm::GlobalValue::isWeakForLinker(Linkage) &&161 getTriple().isOSBinFormatCOFF()) {162 return true;163 }164 165 // If we don't have a definition for the destructor yet or the definition is166 // avaialable_externally, don't emit an alias. We can't emit aliases to167 // declarations; that's just not how aliases work.168 if (Aliasee->isDeclarationForLinker())169 return true;170 171 // Don't create an alias to a linker weak symbol. This avoids producing172 // different COMDATs in different TUs. Another option would be to173 // output the alias both for weak_odr and linkonce_odr, but that174 // requires explicit comdat support in the IL.175 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))176 return true;177 178 // Create the alias with no name.179 auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",180 Aliasee, &getModule());181 182 // Destructors are always unnamed_addr.183 Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);184 185 // Switch any previous uses to the alias.186 if (Entry) {187 assert(Entry->getValueType() == AliasValueType &&188 Entry->getAddressSpace() == Alias->getAddressSpace() &&189 "declaration exists with different type");190 Alias->takeName(Entry);191 Entry->replaceAllUsesWith(Alias);192 Entry->eraseFromParent();193 } else {194 Alias->setName(MangledName);195 }196 197 // Finally, set up the alias with its proper name and attributes.198 SetCommonAttributes(AliasDecl, Alias);199 200 return false;201}202 203llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {204 const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);205 auto *Fn = cast<llvm::Function>(206 getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr,207 /*DontDefer=*/true, ForDefinition));208 209 setFunctionLinkage(GD, Fn);210 211 CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);212 setNonAliasAttributes(GD, Fn);213 SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn);214 return Fn;215}216 217llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor(218 GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType,219 bool DontDefer, ForDefinition_t IsForDefinition) {220 auto *MD = cast<CXXMethodDecl>(GD.getDecl());221 222 if (isa<CXXDestructorDecl>(MD)) {223 // Always alias equivalent complete destructors to base destructors in the224 // MS ABI.225 if (getTarget().getCXXABI().isMicrosoft() &&226 GD.getDtorType() == Dtor_Complete &&227 MD->getParent()->getNumVBases() == 0)228 GD = GD.getWithDtorType(Dtor_Base);229 }230 231 if (!FnType) {232 if (!FnInfo)233 FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD);234 FnType = getTypes().GetFunctionType(*FnInfo);235 }236 237 llvm::Constant *Ptr = GetOrCreateLLVMFunction(238 getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,239 /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);240 return {FnType, Ptr};241}242 243static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,244 GlobalDecl GD,245 llvm::Type *Ty,246 const CXXRecordDecl *RD) {247 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&248 "No kext in Microsoft ABI");249 CodeGenModule &CGM = CGF.CGM;250 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());251 Ty = llvm::PointerType::getUnqual(CGM.getLLVMContext());252 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");253 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);254 const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);255 VTableLayout::AddressPointLocation AddressPoint =256 VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));257 VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +258 AddressPoint.AddressPointIndex;259 llvm::Value *VFuncPtr =260 CGF.Builder.CreateConstInBoundsGEP1_64(Ty, VTable, VTableIndex, "vfnkxt");261 llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(262 Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes));263 264 CGPointerAuthInfo PointerAuth;265 if (auto &Schema =266 CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers) {267 GlobalDecl OrigMD =268 CGM.getItaniumVTableContext().findOriginalMethod(GD.getCanonicalDecl());269 PointerAuth = CGF.EmitPointerAuthInfo(Schema, VFuncPtr, OrigMD, QualType());270 }271 272 CGCallee Callee(GD, VFunc, PointerAuth);273 return Callee;274}275 276/// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making277/// indirect call to virtual functions. It makes the call through indexing278/// into the vtable.279CGCallee CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,280 NestedNameSpecifier Qual,281 llvm::Type *Ty) {282 const CXXRecordDecl *RD = Qual.getAsRecordDecl();283 assert(RD && "BuildAppleKextVirtualCall - Qual must be record");284 if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))285 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);286 287 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);288}289 290/// BuildVirtualCall - This routine makes indirect vtable call for291/// call to virtual destructors. It returns 0 if it could not do it.292CGCallee293CodeGenFunction::BuildAppleKextVirtualDestructorCall(294 const CXXDestructorDecl *DD,295 CXXDtorType Type,296 const CXXRecordDecl *RD) {297 assert(DD->isVirtual() && Type != Dtor_Base);298 // Compute the function type we're calling.299 const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(300 GlobalDecl(DD, Dtor_Complete));301 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);302 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);303}304