1 //===------- MicrosoftCXXABI.cpp - AST support for the Microsoft C++ ABI --===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This provides C++ AST support targeting the Microsoft Visual C++ 11 // ABI. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "CXXABI.h" 16 #include "clang/AST/Attr.h" 17 #include "clang/AST/ASTContext.h" 18 #include "clang/AST/DeclCXX.h" 19 #include "clang/AST/RecordLayout.h" 20 #include "clang/AST/Type.h" 21 #include "clang/Basic/TargetInfo.h" 22 23 using namespace clang; 24 25 namespace { 26 class MicrosoftCXXABI : public CXXABI { 27 ASTContext &Context; 28 public: 29 MicrosoftCXXABI(ASTContext &Ctx) : Context(Ctx) { } 30 31 std::pair<uint64_t, unsigned> 32 getMemberPointerWidthAndAlign(const MemberPointerType *MPT) const; 33 34 CallingConv getDefaultMethodCallConv(bool isVariadic) const { 35 if (!isVariadic && 36 Context.getTargetInfo().getTriple().getArch() == llvm::Triple::x86) 37 return CC_X86ThisCall; 38 return CC_C; 39 } 40 41 bool isNearlyEmpty(const CXXRecordDecl *RD) const { 42 // FIXME: Audit the corners 43 if (!RD->isDynamicClass()) 44 return false; 45 46 const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD); 47 48 // In the Microsoft ABI, classes can have one or two vtable pointers. 49 CharUnits PointerSize = 50 Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0)); 51 return Layout.getNonVirtualSize() == PointerSize || 52 Layout.getNonVirtualSize() == PointerSize * 2; 53 } 54 }; 55 } 56 57 // getNumBases() seems to only give us the number of direct bases, and not the 58 // total. This function tells us if we inherit from anybody that uses MI, or if 59 // we have a non-primary base class, which uses the multiple inheritance model. 60 static bool usesMultipleInheritanceModel(const CXXRecordDecl *RD) { 61 while (RD->getNumBases() > 0) { 62 if (RD->getNumBases() > 1) 63 return true; 64 assert(RD->getNumBases() == 1); 65 const CXXRecordDecl *Base = 66 RD->bases_begin()->getType()->getAsCXXRecordDecl(); 67 if (RD->isPolymorphic() && !Base->isPolymorphic()) 68 return true; 69 RD = Base; 70 } 71 return false; 72 } 73 74 static MSInheritanceModel MSInheritanceAttrToModel(attr::Kind Kind) { 75 switch (Kind) { 76 default: llvm_unreachable("expected MS inheritance attribute"); 77 case attr::SingleInheritance: return MSIM_Single; 78 case attr::MultipleInheritance: return MSIM_Multiple; 79 case attr::VirtualInheritance: return MSIM_Virtual; 80 case attr::UnspecifiedInheritance: return MSIM_Unspecified; 81 } 82 } 83 84 MSInheritanceModel CXXRecordDecl::getMSInheritanceModel() const { 85 if (Attr *IA = this->getAttr<MSInheritanceAttr>()) 86 return MSInheritanceAttrToModel(IA->getKind()); 87 // If there was no explicit attribute, the record must be defined already, and 88 // we can figure out the inheritance model from its other properties. 89 if (this->getNumVBases() > 0) 90 return MSIM_Virtual; 91 if (usesMultipleInheritanceModel(this)) 92 return this->isPolymorphic() ? MSIM_MultiplePolymorphic : MSIM_Multiple; 93 return this->isPolymorphic() ? MSIM_SinglePolymorphic : MSIM_Single; 94 } 95 96 // Returns the number of pointer and integer slots used to represent a member 97 // pointer in the MS C++ ABI. 98 // 99 // Member function pointers have the following general form; however, fields 100 // are dropped as permitted (under the MSVC interpretation) by the inheritance 101 // model of the actual class. 102 // 103 // struct { 104 // // A pointer to the member function to call. If the member function is 105 // // virtual, this will be a thunk that forwards to the appropriate vftable 106 // // slot. 107 // void *FunctionPointerOrVirtualThunk; 108 // 109 // // An offset to add to the address of the vbtable pointer after (possibly) 110 // // selecting the virtual base but before resolving and calling the function. 111 // // Only needed if the class has any virtual bases or bases at a non-zero 112 // // offset. 113 // int NonVirtualBaseAdjustment; 114 // 115 // // An offset within the vb-table that selects the virtual base containing 116 // // the member. Loading from this offset produces a new offset that is 117 // // added to the address of the vb-table pointer to produce the base. 118 // int VirtualBaseAdjustmentOffset; 119 // 120 // // The offset of the vb-table pointer within the object. Only needed for 121 // // incomplete types. 122 // int VBPtrOffset; 123 // }; 124 static std::pair<unsigned, unsigned> 125 getMSMemberPointerSlots(const MemberPointerType *MPT) { 126 const CXXRecordDecl *RD = MPT->getClass()->getAsCXXRecordDecl(); 127 MSInheritanceModel Inheritance = RD->getMSInheritanceModel(); 128 unsigned Ptrs; 129 unsigned Ints = 0; 130 if (MPT->isMemberFunctionPointer()) { 131 // Member function pointers are a struct of a function pointer followed by a 132 // variable number of ints depending on the inheritance model used. The 133 // function pointer is a real function if it is non-virtual and a vftable 134 // slot thunk if it is virtual. The ints select the object base passed for 135 // the 'this' pointer. 136 Ptrs = 1; // First slot is always a function pointer. 137 switch (Inheritance) { 138 case MSIM_Unspecified: ++Ints; // VBTableOffset 139 case MSIM_Virtual: ++Ints; // VirtualBaseAdjustmentOffset 140 case MSIM_MultiplePolymorphic: 141 case MSIM_Multiple: ++Ints; // NonVirtualBaseAdjustment 142 case MSIM_SinglePolymorphic: 143 case MSIM_Single: break; // Nothing 144 } 145 } else { 146 // Data pointers are an aggregate of ints. The first int is an offset 147 // followed by vbtable-related offsets. 148 Ptrs = 0; 149 switch (Inheritance) { 150 case MSIM_Unspecified: ++Ints; // VBTableOffset 151 case MSIM_Virtual: ++Ints; // VirtualBaseAdjustmentOffset 152 case MSIM_MultiplePolymorphic: 153 case MSIM_Multiple: // Nothing 154 case MSIM_SinglePolymorphic: 155 case MSIM_Single: ++Ints; // Field offset 156 } 157 } 158 return std::make_pair(Ptrs, Ints); 159 } 160 161 std::pair<uint64_t, unsigned> MicrosoftCXXABI::getMemberPointerWidthAndAlign( 162 const MemberPointerType *MPT) const { 163 const TargetInfo &Target = Context.getTargetInfo(); 164 assert(Target.getTriple().getArch() == llvm::Triple::x86 || 165 Target.getTriple().getArch() == llvm::Triple::x86_64); 166 unsigned Ptrs, Ints; 167 llvm::tie(Ptrs, Ints) = getMSMemberPointerSlots(MPT); 168 // The nominal struct is laid out with pointers followed by ints and aligned 169 // to a pointer width if any are present and an int width otherwise. 170 unsigned PtrSize = Target.getPointerWidth(0); 171 unsigned IntSize = Target.getIntWidth(); 172 uint64_t Width = Ptrs * PtrSize + Ints * IntSize; 173 unsigned Align = Ptrs > 0 ? Target.getPointerAlign(0) : Target.getIntAlign(); 174 Width = llvm::RoundUpToAlignment(Width, Align); 175 return std::make_pair(Width, Align); 176 } 177 178 CXXABI *clang::CreateMicrosoftCXXABI(ASTContext &Ctx) { 179 return new MicrosoftCXXABI(Ctx); 180 } 181 182
