MS ABI: Implement support for throwing a C++ exception
Throwing a C++ exception, under the MS ABI, is implemented using three
components:
- ThrowInfo structure which contains information like CV qualifiers,
what destructor to call and a pointer to the CatchableTypeArray.
- In a significant departure from the Itanium ABI, copying by-value
occurs in the runtime and not at the catch site. This means we need
to enumerate all possible types that this exception could be caught as
and encode the necessary information to convert from the exception
object's type to the catch handler's type. This includes complicated
derived to base conversions and the execution of copy-constructors.
N.B. This implementation doesn't support the execution of a
copy-constructor from within the runtime for now. Adding support for
that functionality is quite difficult due to things like default
argument expressions which may evaluate arbitrary code hiding in the
copy-constructor's parameters.
Differential Revision: http://reviews.llvm.org/D8066
llvm-svn: 231328
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 399a6e4..dd4c274 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -43,7 +43,8 @@
MicrosoftCXXABI(CodeGenModule &CGM)
: CGCXXABI(CGM), BaseClassDescriptorType(nullptr),
ClassHierarchyDescriptorType(nullptr),
- CompleteObjectLocatorType(nullptr) {}
+ CompleteObjectLocatorType(nullptr), CatchableTypeType(nullptr),
+ ThrowInfoType(nullptr) {}
bool HasThisReturn(GlobalDecl GD) const override;
bool hasMostDerivedReturn(GlobalDecl GD) const override;
@@ -74,6 +75,7 @@
const CXXDestructorDecl *Dtor) override;
void emitRethrow(CodeGenFunction &CGF, bool isNoReturn) override;
+ void emitThrow(CodeGenFunction &CGF, const CXXThrowExpr *E) override;
void emitBeginCatch(CodeGenFunction &CGF, const CXXCatchStmt *C) override;
@@ -415,6 +417,9 @@
if (!isImageRelative())
return PtrVal;
+ if (PtrVal->isNullValue())
+ return llvm::Constant::getNullValue(CGM.IntTy);
+
llvm::Constant *ImageBaseAsInt =
llvm::ConstantExpr::getPtrToInt(getImageBase(), CGM.IntPtrTy);
llvm::Constant *PtrValAsInt =
@@ -565,6 +570,79 @@
void emitCXXStructor(const CXXMethodDecl *MD, StructorType Type) override;
+ llvm::StructType *getCatchableTypeType() {
+ if (CatchableTypeType)
+ return CatchableTypeType;
+ llvm::Type *FieldTypes[] = {
+ CGM.IntTy, // Flags
+ getImageRelativeType(CGM.Int8PtrTy), // TypeDescriptor
+ CGM.IntTy, // NonVirtualAdjustment
+ CGM.IntTy, // OffsetToVBPtr
+ CGM.IntTy, // VBTableIndex
+ CGM.IntTy, // Size
+ getImageRelativeType(CGM.Int8PtrTy) // CopyCtor
+ };
+ CatchableTypeType = llvm::StructType::create(
+ CGM.getLLVMContext(), FieldTypes, "eh.CatchableType");
+ return CatchableTypeType;
+ }
+
+ llvm::StructType *getCatchableTypeArrayType(uint32_t NumEntries) {
+ llvm::StructType *&CatchableTypeArrayType =
+ CatchableTypeArrayTypeMap[NumEntries];
+ if (CatchableTypeArrayType)
+ return CatchableTypeArrayType;
+
+ llvm::SmallString<23> CTATypeName("eh.CatchableTypeArray.");
+ CTATypeName += llvm::utostr(NumEntries);
+ llvm::Type *CTType =
+ getImageRelativeType(getCatchableTypeType()->getPointerTo());
+ llvm::Type *FieldTypes[] = {
+ CGM.IntTy, // NumEntries
+ llvm::ArrayType::get(CTType, NumEntries) // CatchableTypes
+ };
+ CatchableTypeArrayType =
+ llvm::StructType::create(CGM.getLLVMContext(), FieldTypes, CTATypeName);
+ return CatchableTypeArrayType;
+ }
+
+ llvm::StructType *getThrowInfoType() {
+ if (ThrowInfoType)
+ return ThrowInfoType;
+ llvm::Type *FieldTypes[] = {
+ CGM.IntTy, // Flags
+ getImageRelativeType(CGM.Int8PtrTy), // CleanupFn
+ getImageRelativeType(CGM.Int8PtrTy), // ForwardCompat
+ getImageRelativeType(CGM.Int8PtrTy) // CatchableTypeArray
+ };
+ ThrowInfoType = llvm::StructType::create(CGM.getLLVMContext(), FieldTypes,
+ "eh.ThrowInfo");
+ return ThrowInfoType;
+ }
+
+ llvm::Constant *getThrowFn() {
+ // _CxxThrowException is passed an exception object and a ThrowInfo object
+ // which describes the exception.
+ llvm::Type *Args[] = {CGM.Int8PtrTy, getThrowInfoType()->getPointerTo()};
+ llvm::FunctionType *FTy =
+ llvm::FunctionType::get(CGM.VoidTy, Args, /*IsVarArgs=*/false);
+ auto *Fn = cast<llvm::Function>(
+ CGM.CreateRuntimeFunction(FTy, "_CxxThrowException"));
+ // _CxxThrowException is stdcall on 32-bit x86 platforms.
+ if (CGM.getTarget().getTriple().getArch() == llvm::Triple::x86)
+ Fn->setCallingConv(llvm::CallingConv::X86_StdCall);
+ return Fn;
+ }
+
+ llvm::Constant *getCatchableType(QualType T,
+ uint32_t NVOffset = 0,
+ int32_t VBPtrOffset = -1,
+ uint32_t VBIndex = 0);
+
+ llvm::GlobalVariable *getCatchableTypeArray(QualType T);
+
+ llvm::GlobalVariable *getThrowInfo(QualType T);
+
private:
typedef std::pair<const CXXRecordDecl *, CharUnits> VFTableIdTy;
typedef llvm::DenseMap<VFTableIdTy, llvm::GlobalVariable *> VTablesMapTy;
@@ -596,6 +674,12 @@
llvm::StructType *BaseClassDescriptorType;
llvm::StructType *ClassHierarchyDescriptorType;
llvm::StructType *CompleteObjectLocatorType;
+
+ llvm::DenseMap<QualType, llvm::GlobalVariable *> CatchableTypeArrays;
+
+ llvm::StructType *CatchableTypeType;
+ llvm::DenseMap<uint32_t, llvm::StructType *> CatchableTypeArrayTypeMap;
+ llvm::StructType *ThrowInfoType;
};
}
@@ -676,24 +760,11 @@
CGF.EmitDeleteCall(DE->getOperatorDelete(), MDThis, ElementType);
}
-static llvm::Function *getRethrowFn(CodeGenModule &CGM) {
- // _CxxThrowException takes two pointer width arguments: a value and a context
- // object which points to a TypeInfo object.
- llvm::Type *ArgTypes[] = {CGM.Int8PtrTy, CGM.Int8PtrTy};
- llvm::FunctionType *FTy =
- llvm::FunctionType::get(CGM.VoidTy, ArgTypes, false);
- auto *Fn = cast<llvm::Function>(
- CGM.CreateRuntimeFunction(FTy, "_CxxThrowException"));
- // _CxxThrowException is stdcall on 32-bit x86 platforms.
- if (CGM.getTarget().getTriple().getArch() == llvm::Triple::x86)
- Fn->setCallingConv(llvm::CallingConv::X86_StdCall);
- return Fn;
-}
-
void MicrosoftCXXABI::emitRethrow(CodeGenFunction &CGF, bool isNoReturn) {
- llvm::Value *Args[] = {llvm::ConstantPointerNull::get(CGM.Int8PtrTy),
- llvm::ConstantPointerNull::get(CGM.Int8PtrTy)};
- auto *Fn = getRethrowFn(CGM);
+ llvm::Value *Args[] = {
+ llvm::ConstantPointerNull::get(CGM.Int8PtrTy),
+ llvm::ConstantPointerNull::get(getThrowInfoType()->getPointerTo())};
+ auto *Fn = getThrowFn();
if (isNoReturn)
CGF.EmitNoreturnRuntimeCallOrInvoke(Fn, Args);
else
@@ -2913,7 +2984,7 @@
auto Type = ABI.getClassHierarchyDescriptorType();
auto CHD = new llvm::GlobalVariable(Module, Type, /*Constant=*/true, Linkage,
/*Initializer=*/nullptr,
- MangledName.c_str());
+ StringRef(MangledName));
if (CHD->isWeakForLinker())
CHD->setComdat(CGM.getModule().getOrInsertComdat(CHD->getName()));
@@ -2946,9 +3017,10 @@
llvm::Type *PtrType = ABI.getImageRelativeType(
ABI.getBaseClassDescriptorType()->getPointerTo());
auto *ArrType = llvm::ArrayType::get(PtrType, Classes.size() + 1);
- auto *BCA = new llvm::GlobalVariable(
- Module, ArrType,
- /*Constant=*/true, Linkage, /*Initializer=*/nullptr, MangledName.c_str());
+ auto *BCA =
+ new llvm::GlobalVariable(Module, ArrType,
+ /*Constant=*/true, Linkage,
+ /*Initializer=*/nullptr, StringRef(MangledName));
if (BCA->isWeakForLinker())
BCA->setComdat(CGM.getModule().getOrInsertComdat(BCA->getName()));
@@ -2988,9 +3060,9 @@
// Forward-declare the base class descriptor.
auto Type = ABI.getBaseClassDescriptorType();
- auto BCD = new llvm::GlobalVariable(Module, Type, /*Constant=*/true, Linkage,
- /*Initializer=*/nullptr,
- MangledName.c_str());
+ auto BCD =
+ new llvm::GlobalVariable(Module, Type, /*Constant=*/true, Linkage,
+ /*Initializer=*/nullptr, StringRef(MangledName));
if (BCD->isWeakForLinker())
BCD->setComdat(CGM.getModule().getOrInsertComdat(BCD->getName()));
@@ -3036,7 +3108,7 @@
// Forward-declare the complete object locator.
llvm::StructType *Type = ABI.getCompleteObjectLocatorType();
auto COL = new llvm::GlobalVariable(Module, Type, /*Constant=*/true, Linkage,
- /*Initializer=*/nullptr, MangledName.c_str());
+ /*Initializer=*/nullptr, StringRef(MangledName));
// Initialize the CompleteObjectLocator.
llvm::Constant *Fields[] = {
@@ -3089,7 +3161,7 @@
CGM.getModule(), TypeDescriptorType, /*Constant=*/false,
getLinkageForRTTI(Type),
llvm::ConstantStruct::get(TypeDescriptorType, Fields),
- MangledName.c_str());
+ StringRef(MangledName));
if (Var->isWeakForLinker())
Var->setComdat(CGM.getModule().getOrInsertComdat(Var->getName()));
return llvm::ConstantExpr::getBitCast(Var, CGM.Int8PtrTy);
@@ -3146,3 +3218,272 @@
}
emitCXXDestructor(CGM, cast<CXXDestructorDecl>(MD), Type);
}
+
+llvm::Constant *MicrosoftCXXABI::getCatchableType(QualType T,
+ uint32_t NVOffset,
+ int32_t VBPtrOffset,
+ uint32_t VBIndex) {
+ assert(!T->isReferenceType());
+
+ uint32_t Size = getContext().getTypeSizeInChars(T).getQuantity();
+ SmallString<256> MangledName;
+ {
+ llvm::raw_svector_ostream Out(MangledName);
+ getMangleContext().mangleCXXCatchableType(T, Size, Out);
+ }
+ if (llvm::GlobalVariable *GV = CGM.getModule().getNamedGlobal(MangledName))
+ return getImageRelativeConstant(GV);
+
+ // The TypeDescriptor is used by the runtime to determine of a catch handler
+ // is appropriate for the exception object.
+ llvm::Constant *TD = getImageRelativeConstant(getAddrOfRTTIDescriptor(T));
+
+ // The runtime is responsible for calling the copy constructor if the
+ // exception is caught by value.
+ llvm::Constant *CopyCtor =
+ getImageRelativeConstant(llvm::Constant::getNullValue(CGM.Int8PtrTy));
+
+ bool IsScalar = true;
+ bool HasVirtualBases = false;
+ bool IsStdBadAlloc = false; // std::bad_alloc is special for some reason.
+ if (T->getAsCXXRecordDecl()) {
+ IsScalar = false;
+ // TODO: Fill in the CopyCtor here! This is not trivial due to
+ // copy-constructors possessing things like default arguments.
+ }
+ QualType PointeeType = T;
+ if (T->isPointerType())
+ PointeeType = T->getPointeeType();
+ if (const CXXRecordDecl *RD = PointeeType->getAsCXXRecordDecl()) {
+ HasVirtualBases = RD->getNumVBases() > 0;
+ if (IdentifierInfo *II = RD->getIdentifier())
+ IsStdBadAlloc = II->isStr("bad_alloc") && RD->isInStdNamespace();
+ }
+
+ // Encode the relevant CatchableType properties into the Flags bitfield.
+ // FIXME: Figure out how bits 2 or 8 can get set.
+ uint32_t Flags = 0;
+ if (IsScalar)
+ Flags |= 1;
+ if (HasVirtualBases)
+ Flags |= 4;
+ if (IsStdBadAlloc)
+ Flags |= 16;
+
+ llvm::Constant *Fields[] = {
+ llvm::ConstantInt::get(CGM.IntTy, Flags), // Flags
+ TD, // TypeDescriptor
+ llvm::ConstantInt::get(CGM.IntTy, NVOffset), // NonVirtualAdjustment
+ llvm::ConstantInt::get(CGM.IntTy, VBPtrOffset), // OffsetToVBPtr
+ llvm::ConstantInt::get(CGM.IntTy, VBIndex), // VBTableIndex
+ llvm::ConstantInt::get(CGM.IntTy, Size), // Size
+ CopyCtor // CopyCtor
+ };
+ llvm::StructType *CTType = getCatchableTypeType();
+ auto *GV = new llvm::GlobalVariable(
+ CGM.getModule(), CTType, /*Constant=*/true, getLinkageForRTTI(T),
+ llvm::ConstantStruct::get(CTType, Fields), StringRef(MangledName));
+ if (GV->isWeakForLinker())
+ GV->setComdat(CGM.getModule().getOrInsertComdat(GV->getName()));
+ GV->setUnnamedAddr(true);
+ return getImageRelativeConstant(GV);
+}
+
+llvm::GlobalVariable *MicrosoftCXXABI::getCatchableTypeArray(QualType T) {
+ assert(!T->isReferenceType());
+
+ // See if we've already generated a CatchableTypeArray for this type before.
+ llvm::GlobalVariable *&CTA = CatchableTypeArrays[T];
+ if (CTA)
+ return CTA;
+
+ // Ensure that we don't have duplicate entries in our CatchableTypeArray by
+ // using a SmallSetVector. Duplicates may arise due to virtual bases
+ // occurring more than once in the hierarchy.
+ llvm::SmallSetVector<llvm::Constant *, 2> CatchableTypes;
+
+ // C++14 [except.handle]p3:
+ // A handler is a match for an exception object of type E if [...]
+ // - the handler is of type cv T or cv T& and T is an unambiguous public
+ // base class of E, or
+ // - the handler is of type cv T or const T& where T is a pointer type and
+ // E is a pointer type that can be converted to T by [...]
+ // - a standard pointer conversion (4.10) not involving conversions to
+ // pointers to private or protected or ambiguous classes
+ const CXXRecordDecl *MostDerivedClass = nullptr;
+ bool IsPointer = T->isPointerType();
+ if (IsPointer)
+ MostDerivedClass = T->getPointeeType()->getAsCXXRecordDecl();
+ else
+ MostDerivedClass = T->getAsCXXRecordDecl();
+
+ // Collect all the unambiguous public bases of the MostDerivedClass.
+ if (MostDerivedClass) {
+ const ASTContext &Context = CGM.getContext();
+ const ASTRecordLayout &MostDerivedLayout =
+ Context.getASTRecordLayout(MostDerivedClass);
+ MicrosoftVTableContext &VTableContext = CGM.getMicrosoftVTableContext();
+ SmallVector<MSRTTIClass, 8> Classes;
+ serializeClassHierarchy(Classes, MostDerivedClass);
+ Classes.front().initialize(/*Parent=*/nullptr, /*Specifier=*/nullptr);
+ detectAmbiguousBases(Classes);
+ for (const MSRTTIClass &Class : Classes) {
+ // Skip any ambiguous or private bases.
+ if (Class.Flags &
+ (MSRTTIClass::IsPrivateOnPath | MSRTTIClass::IsAmbiguous))
+ continue;
+ // Write down how to convert from a derived pointer to a base pointer.
+ uint32_t OffsetInVBTable = 0;
+ int32_t VBPtrOffset = -1;
+ if (Class.VirtualRoot) {
+ OffsetInVBTable =
+ VTableContext.getVBTableIndex(MostDerivedClass, Class.VirtualRoot)*4;
+ VBPtrOffset = MostDerivedLayout.getVBPtrOffset().getQuantity();
+ }
+
+ // Turn our record back into a pointer if the exception object is a
+ // pointer.
+ QualType RTTITy = QualType(Class.RD->getTypeForDecl(), 0);
+ if (IsPointer)
+ RTTITy = Context.getPointerType(RTTITy);
+ CatchableTypes.insert(getCatchableType(RTTITy, Class.OffsetInVBase,
+ VBPtrOffset, OffsetInVBTable));
+ }
+ }
+
+ // C++14 [except.handle]p3:
+ // A handler is a match for an exception object of type E if
+ // - The handler is of type cv T or cv T& and E and T are the same type
+ // (ignoring the top-level cv-qualifiers)
+ CatchableTypes.insert(getCatchableType(T));
+
+ // C++14 [except.handle]p3:
+ // A handler is a match for an exception object of type E if
+ // - the handler is of type cv T or const T& where T is a pointer type and
+ // E is a pointer type that can be converted to T by [...]
+ // - a standard pointer conversion (4.10) not involving conversions to
+ // pointers to private or protected or ambiguous classes
+ //
+ // All pointers are convertible to void so ensure that it is in the
+ // CatchableTypeArray.
+ if (IsPointer)
+ CatchableTypes.insert(getCatchableType(getContext().VoidPtrTy));
+
+ uint32_t NumEntries = CatchableTypes.size();
+ llvm::Type *CTType =
+ getImageRelativeType(getCatchableTypeType()->getPointerTo());
+ llvm::ArrayType *AT = llvm::ArrayType::get(CTType, NumEntries);
+ llvm::StructType *CTAType = getCatchableTypeArrayType(NumEntries);
+ llvm::Constant *Fields[] = {
+ llvm::ConstantInt::get(CGM.IntTy, NumEntries), // NumEntries
+ llvm::ConstantArray::get(
+ AT, llvm::makeArrayRef(CatchableTypes.begin(),
+ CatchableTypes.end())) // CatchableTypes
+ };
+ SmallString<256> MangledName;
+ {
+ llvm::raw_svector_ostream Out(MangledName);
+ getMangleContext().mangleCXXCatchableTypeArray(T, NumEntries, Out);
+ }
+ CTA = new llvm::GlobalVariable(
+ CGM.getModule(), CTAType, /*Constant=*/true, getLinkageForRTTI(T),
+ llvm::ConstantStruct::get(CTAType, Fields), StringRef(MangledName));
+ if (CTA->isWeakForLinker())
+ CTA->setComdat(CGM.getModule().getOrInsertComdat(CTA->getName()));
+ CTA->setUnnamedAddr(true);
+ return CTA;
+}
+
+llvm::GlobalVariable *MicrosoftCXXABI::getThrowInfo(QualType T) {
+ // C++14 [except.handle]p3:
+ // A handler is a match for an exception object of type E if [...]
+ // - the handler is of type cv T or const T& where T is a pointer type and
+ // E is a pointer type that can be converted to T by [...]
+ // - a qualification conversion
+ bool IsConst = false, IsVolatile = false;
+ QualType PointeeType = T->getPointeeType();
+ if (!PointeeType.isNull()) {
+ IsConst = PointeeType.isConstQualified();
+ IsVolatile = PointeeType.isVolatileQualified();
+ }
+ T = getContext().getExceptionObjectType(T);
+
+ // The CatchableTypeArray enumerates the various (CV-unqualified) types that
+ // the exception object may be caught as.
+ llvm::GlobalVariable *CTA = getCatchableTypeArray(T);
+ // The first field in a CatchableTypeArray is the number of CatchableTypes.
+ // This is used as a component of the mangled name which means that we need to
+ // know what it is in order to see if we have previously generated the
+ // ThrowInfo.
+ uint32_t NumEntries =
+ cast<llvm::ConstantInt>(CTA->getInitializer()->getAggregateElement(0U))
+ ->getLimitedValue();
+
+ SmallString<256> MangledName;
+ {
+ llvm::raw_svector_ostream Out(MangledName);
+ getMangleContext().mangleCXXThrowInfo(T, IsConst, IsVolatile, NumEntries,
+ Out);
+ }
+
+ // Reuse a previously generated ThrowInfo if we have generated an appropriate
+ // one before.
+ if (llvm::GlobalVariable *GV = CGM.getModule().getNamedGlobal(MangledName))
+ return GV;
+
+ // The RTTI TypeDescriptor uses an unqualified type but catch clauses must
+ // be at least as CV qualified. Encode this requirement into the Flags
+ // bitfield.
+ uint32_t Flags = 0;
+ if (IsConst)
+ Flags |= 1;
+ if (IsVolatile)
+ Flags |= 2;
+
+ // The cleanup-function (a destructor) must be called when the exception
+ // object's lifetime ends.
+ llvm::Constant *CleanupFn = llvm::Constant::getNullValue(CGM.Int8PtrTy);
+ if (const CXXRecordDecl *RD = T->getAsCXXRecordDecl())
+ if (CXXDestructorDecl *DtorD = RD->getDestructor())
+ if (!DtorD->isTrivial())
+ CleanupFn = llvm::ConstantExpr::getBitCast(
+ CGM.getAddrOfCXXStructor(DtorD, StructorType::Complete),
+ CGM.Int8PtrTy);
+ // This is unused as far as we can tell, initialize it to null.
+ llvm::Constant *ForwardCompat =
+ getImageRelativeConstant(llvm::Constant::getNullValue(CGM.Int8PtrTy));
+ llvm::Constant *PointerToCatchableTypes = getImageRelativeConstant(
+ llvm::ConstantExpr::getBitCast(CTA, CGM.Int8PtrTy));
+ llvm::StructType *TIType = getThrowInfoType();
+ llvm::Constant *Fields[] = {
+ llvm::ConstantInt::get(CGM.IntTy, Flags), // Flags
+ getImageRelativeConstant(CleanupFn), // CleanupFn
+ ForwardCompat, // ForwardCompat
+ PointerToCatchableTypes // CatchableTypeArray
+ };
+ auto *GV = new llvm::GlobalVariable(
+ CGM.getModule(), TIType, /*Constant=*/true, getLinkageForRTTI(T),
+ llvm::ConstantStruct::get(TIType, Fields), StringRef(MangledName));
+ if (GV->isWeakForLinker())
+ GV->setComdat(CGM.getModule().getOrInsertComdat(GV->getName()));
+ GV->setUnnamedAddr(true);
+ return GV;
+}
+
+void MicrosoftCXXABI::emitThrow(CodeGenFunction &CGF, const CXXThrowExpr *E) {
+ const Expr *SubExpr = E->getSubExpr();
+ QualType ThrowType = SubExpr->getType();
+ // The exception object lives on the stack and it's address is passed to the
+ // runtime function.
+ llvm::AllocaInst *AI = CGF.CreateMemTemp(ThrowType);
+ CGF.EmitAnyExprToMem(SubExpr, AI, ThrowType.getQualifiers(),
+ /*IsInit=*/true);
+
+ // The so-called ThrowInfo is used to describe how the exception object may be
+ // caught.
+ llvm::GlobalVariable *TI = getThrowInfo(ThrowType);
+
+ // Call into the runtime to throw the exception.
+ llvm::Value *Args[] = {CGF.Builder.CreateBitCast(AI, CGM.Int8PtrTy), TI};
+ CGF.EmitNoreturnRuntimeCallOrInvoke(getThrowFn(), Args);
+}