//===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This contains code dealing with C++ code generation. // //===----------------------------------------------------------------------===// // We might split this into multiple files if it gets too unwieldy #include "CGCXXABI.h" #include "CodeGenFunction.h" #include "CodeGenModule.h" #include "clang/AST/ASTContext.h" #include "clang/AST/Attr.h" #include "clang/AST/Decl.h" #include "clang/AST/DeclCXX.h" #include "clang/AST/DeclObjC.h" #include "clang/AST/Mangle.h" #include "clang/AST/RecordLayout.h" #include "clang/AST/StmtCXX.h" #include "clang/Basic/CodeGenOptions.h" #include "llvm/ADT/StringExtras.h" using namespace clang; using namespace CodeGen; /// Try to emit a base destructor as an alias to its primary /// base-class destructor. bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) { if (!getCodeGenOpts().CXXCtorDtorAliases) return true; // Producing an alias to a base class ctor/dtor can degrade debug quality // as the debugger cannot tell them apart. if (getCodeGenOpts().OptimizationLevel == 0) return true; // If sanitizing memory to check for use-after-dtor, do not emit as // an alias, unless this class owns no members. if (getCodeGenOpts().SanitizeMemoryUseAfterDtor && !D->getParent()->field_empty()) return true; // If the destructor doesn't have a trivial body, we have to emit it // separately. if (!D->hasTrivialBody()) return true; const CXXRecordDecl *Class = D->getParent(); // We are going to instrument this destructor, so give up even if it is // currently empty. if (Class->mayInsertExtraPadding()) return true; // If we need to manipulate a VTT parameter, give up. if (Class->getNumVBases()) { // Extra Credit: passing extra parameters is perfectly safe // in many calling conventions, so only bail out if the ctor's // calling convention is nonstandard. return true; } // If any field has a non-trivial destructor, we have to emit the // destructor separately. for (const auto *I : Class->fields()) if (I->getType().isDestructedType()) return true; // Try to find a unique base class with a non-trivial destructor. const CXXRecordDecl *UniqueBase = nullptr; for (const auto &I : Class->bases()) { // We're in the base destructor, so skip virtual bases. if (I.isVirtual()) continue; // Skip base classes with trivial destructors. const auto *Base = cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl()); if (Base->hasTrivialDestructor()) continue; // If we've already found a base class with a non-trivial // destructor, give up. if (UniqueBase) return true; UniqueBase = Base; } // If we didn't find any bases with a non-trivial destructor, then // the base destructor is actually effectively trivial, which can // happen if it was needlessly user-defined or if there are virtual // bases with non-trivial destructors. if (!UniqueBase) return true; // If the base is at a non-zero offset, give up. const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class); if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero()) return true; // Give up if the calling conventions don't match. We could update the call, // but it is probably not worth it. const CXXDestructorDecl *BaseD = UniqueBase->getDestructor(); if (BaseD->getType()->castAs<FunctionType>()->getCallConv() != D->getType()->castAs<FunctionType>()->getCallConv()) return true; GlobalDecl AliasDecl(D, Dtor_Base); GlobalDecl TargetDecl(BaseD, Dtor_Base); // The alias will use the linkage of the referent. If we can't // support aliases with that linkage, fail. llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl); // We can't use an alias if the linkage is not valid for one. if (!llvm::GlobalAlias::isValidLinkage(Linkage)) return true; llvm::GlobalValue::LinkageTypes TargetLinkage = getFunctionLinkage(TargetDecl); // Check if we have it already. StringRef MangledName = getMangledName(AliasDecl); llvm::GlobalValue *Entry = GetGlobalValue(MangledName); if (Entry && !Entry->isDeclaration()) return false; if (Replacements.count(MangledName)) return false; // Derive the type for the alias. llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl); llvm::PointerType *AliasType = AliasValueType->getPointerTo(); // Find the referent. Some aliases might require a bitcast, in // which case the caller is responsible for ensuring the soundness // of these semantics. auto *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl)); llvm::Constant *Aliasee = Ref; if (Ref->getType() != AliasType) Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType); // Instead of creating as alias to a linkonce_odr, replace all of the uses // of the aliasee. if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) && !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage && TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) { // FIXME: An extern template instantiation will create functions with // linkage "AvailableExternally". In libc++, some classes also define // members with attribute "AlwaysInline" and expect no reference to // be generated. It is desirable to reenable this optimisation after // corresponding LLVM changes. addReplacement(MangledName, Aliasee); return false; } // If we have a weak, non-discardable alias (weak, weak_odr), like an extern // template instantiation or a dllexported class, avoid forming it on COFF. // A COFF weak external alias cannot satisfy a normal undefined symbol // reference from another TU. The other TU must also mark the referenced // symbol as weak, which we cannot rely on. if (llvm::GlobalValue::isWeakForLinker(Linkage) && getTriple().isOSBinFormatCOFF()) { return true; } // If we don't have a definition for the destructor yet or the definition is // avaialable_externally, don't emit an alias. We can't emit aliases to // declarations; that's just not how aliases work. if (Ref->isDeclarationForLinker()) return true; // Don't create an alias to a linker weak symbol. This avoids producing // different COMDATs in different TUs. Another option would be to // output the alias both for weak_odr and linkonce_odr, but that // requires explicit comdat support in the IL. if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) return true; // Create the alias with no name. auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "", Aliasee, &getModule()); // Destructors are always unnamed_addr. Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global); // Switch any previous uses to the alias. if (Entry) { assert(Entry->getType() == AliasType && "declaration exists with different type"); Alias->takeName(Entry); Entry->replaceAllUsesWith(Alias); Entry->eraseFromParent(); } else { Alias->setName(MangledName); } // Finally, set up the alias with its proper name and attributes. SetCommonAttributes(AliasDecl, Alias); return false; } llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) { const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD); auto *Fn = cast<llvm::Function>( getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr, /*DontDefer=*/true, ForDefinition)); setFunctionLinkage(GD, Fn); CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo); setNonAliasAttributes(GD, Fn); SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn); return Fn; } llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor( GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType, bool DontDefer, ForDefinition_t IsForDefinition) { auto *MD = cast<CXXMethodDecl>(GD.getDecl()); if (isa<CXXDestructorDecl>(MD)) { // Always alias equivalent complete destructors to base destructors in the // MS ABI. if (getTarget().getCXXABI().isMicrosoft() && GD.getDtorType() == Dtor_Complete && MD->getParent()->getNumVBases() == 0) GD = GD.getWithDtorType(Dtor_Base); } if (!FnType) { if (!FnInfo) FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD); FnType = getTypes().GetFunctionType(*FnInfo); } llvm::Constant *Ptr = GetOrCreateLLVMFunction( getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer, /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition); return {FnType, Ptr}; } static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF, GlobalDecl GD, llvm::Type *Ty, const CXXRecordDecl *RD) { assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() && "No kext in Microsoft ABI"); CodeGenModule &CGM = CGF.CGM; llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits()); Ty = Ty->getPointerTo(); VTable = CGF.Builder.CreateBitCast(VTable, Ty->getPointerTo()); assert(VTable && "BuildVirtualCall = kext vtbl pointer is null"); uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD); const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD); VTableLayout::AddressPointLocation AddressPoint = VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero())); VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) + AddressPoint.AddressPointIndex; llvm::Value *VFuncPtr = CGF.Builder.CreateConstInBoundsGEP1_64(Ty, VTable, VTableIndex, "vfnkxt"); llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad( Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes)); CGCallee Callee(GD, VFunc); return Callee; } /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making /// indirect call to virtual functions. It makes the call through indexing /// into the vtable. CGCallee CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD, NestedNameSpecifier *Qual, llvm::Type *Ty) { assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) && "BuildAppleKextVirtualCall - bad Qual kind"); const Type *QTy = Qual->getAsType(); QualType T = QualType(QTy, 0); const RecordType *RT = T->getAs<RecordType>(); assert(RT && "BuildAppleKextVirtualCall - Qual type must be record"); const auto *RD = cast<CXXRecordDecl>(RT->getDecl()); if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD)) return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD); return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD); } /// BuildVirtualCall - This routine makes indirect vtable call for /// call to virtual destructors. It returns 0 if it could not do it. CGCallee CodeGenFunction::BuildAppleKextVirtualDestructorCall( const CXXDestructorDecl *DD, CXXDtorType Type, const CXXRecordDecl *RD) { assert(DD->isVirtual() && Type != Dtor_Base); // Compute the function type we're calling. const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration( GlobalDecl(DD, Dtor_Complete)); llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo); return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD); }