1//===--- CGVTables.cpp - Emit LLVM Code for C++ vtables -------------------===//
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 of virtual tables.
10//
11//===----------------------------------------------------------------------===//
12
13#include "CGCXXABI.h"
14#include "CGDebugInfo.h"
15#include "CodeGenFunction.h"
16#include "CodeGenModule.h"
17#include "clang/AST/Attr.h"
18#include "clang/AST/CXXInheritance.h"
19#include "clang/AST/RecordLayout.h"
20#include "clang/Basic/CodeGenOptions.h"
21#include "clang/CodeGen/CGFunctionInfo.h"
22#include "clang/CodeGen/ConstantInitBuilder.h"
23#include "llvm/IR/IRBuilder.h"
24#include "llvm/IR/IntrinsicInst.h"
25#include "llvm/IR/Intrinsics.h"
26#include "llvm/Transforms/Utils/Cloning.h"
27#include <algorithm>
28#include <cstdio>
29#include <utility>
30
31using namespace clang;
32using namespace CodeGen;
33
34CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
35 : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
36
37llvm::Constant *CodeGenModule::GetAddrOfThunk(StringRef Name, llvm::Type *FnTy,
38 GlobalDecl GD) {
39 return GetOrCreateLLVMFunction(MangledName: Name, Ty: FnTy, D: GD, /*ForVTable=*/true,
40 /*DontDefer=*/true, /*IsThunk=*/true);
41}
42
43llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTable(const CXXRecordDecl *RD) {
44 llvm::GlobalVariable *VTable =
45 CGM.getCXXABI().getAddrOfVTable(RD, VPtrOffset: CharUnits());
46 return VTable;
47}
48
49static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,
50 llvm::Function *ThunkFn, bool ForVTable,
51 GlobalDecl GD) {
52 CGM.setFunctionLinkage(GD, F: ThunkFn);
53 CGM.getCXXABI().setThunkLinkage(Thunk: ThunkFn, ForVTable, GD,
54 ReturnAdjustment: !Thunk.Return.isEmpty());
55
56 // Set the right visibility.
57 CGM.setGVProperties(GV: ThunkFn, GD);
58
59 if (!CGM.getCXXABI().exportThunk()) {
60 ThunkFn->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
61 ThunkFn->setDSOLocal(true);
62 }
63
64 if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())
65 ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(Name: ThunkFn->getName()));
66}
67
68#ifndef NDEBUG
69static bool similar(const ABIArgInfo &infoL, CanQualType typeL,
70 const ABIArgInfo &infoR, CanQualType typeR) {
71 return (infoL.getKind() == infoR.getKind() &&
72 (typeL == typeR ||
73 (isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||
74 (isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));
75}
76#endif
77
78static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
79 QualType ResultType, RValue RV,
80 const ThunkInfo &Thunk) {
81 // Emit the return adjustment.
82 bool NullCheckValue = !ResultType->isReferenceType();
83
84 llvm::BasicBlock *AdjustNull = nullptr;
85 llvm::BasicBlock *AdjustNotNull = nullptr;
86 llvm::BasicBlock *AdjustEnd = nullptr;
87
88 llvm::Value *ReturnValue = RV.getScalarVal();
89
90 if (NullCheckValue) {
91 AdjustNull = CGF.createBasicBlock(name: "adjust.null");
92 AdjustNotNull = CGF.createBasicBlock(name: "adjust.notnull");
93 AdjustEnd = CGF.createBasicBlock(name: "adjust.end");
94
95 llvm::Value *IsNull = CGF.Builder.CreateIsNull(Arg: ReturnValue);
96 CGF.Builder.CreateCondBr(Cond: IsNull, True: AdjustNull, False: AdjustNotNull);
97 CGF.EmitBlock(BB: AdjustNotNull);
98 }
99
100 auto ClassDecl = ResultType->getPointeeType()->getAsCXXRecordDecl();
101 auto ClassAlign = CGF.CGM.getClassPointerAlignment(CD: ClassDecl);
102 ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(
103 CGF,
104 Ret: Address(ReturnValue, CGF.ConvertTypeForMem(T: ResultType->getPointeeType()),
105 ClassAlign),
106 UnadjustedClass: ClassDecl, RA: Thunk.Return);
107
108 if (NullCheckValue) {
109 CGF.Builder.CreateBr(Dest: AdjustEnd);
110 CGF.EmitBlock(BB: AdjustNull);
111 CGF.Builder.CreateBr(Dest: AdjustEnd);
112 CGF.EmitBlock(BB: AdjustEnd);
113
114 llvm::PHINode *PHI = CGF.Builder.CreatePHI(Ty: ReturnValue->getType(), NumReservedValues: 2);
115 PHI->addIncoming(V: ReturnValue, BB: AdjustNotNull);
116 PHI->addIncoming(V: llvm::Constant::getNullValue(Ty: ReturnValue->getType()),
117 BB: AdjustNull);
118 ReturnValue = PHI;
119 }
120
121 return RValue::get(V: ReturnValue);
122}
123
124/// This function clones a function's DISubprogram node and enters it into
125/// a value map with the intent that the map can be utilized by the cloner
126/// to short-circuit Metadata node mapping.
127/// Furthermore, the function resolves any DILocalVariable nodes referenced
128/// by dbg.value intrinsics so they can be properly mapped during cloning.
129static void resolveTopLevelMetadata(llvm::Function *Fn,
130 llvm::ValueToValueMapTy &VMap) {
131 // Clone the DISubprogram node and put it into the Value map.
132 auto *DIS = Fn->getSubprogram();
133 if (!DIS)
134 return;
135 auto *NewDIS = llvm::MDNode::replaceWithDistinct(N: DIS->clone());
136 // As DISubprogram remapping is avoided, clear retained nodes list of
137 // cloned DISubprogram from retained nodes local to original DISubprogram.
138 // FIXME: Thunk function signature is produced wrong in DWARF, as retained
139 // nodes are not remapped.
140 NewDIS->replaceRetainedNodes(N: llvm::MDTuple::get(Context&: Fn->getContext(), MDs: {}));
141 VMap.MD()[DIS].reset(MD: NewDIS);
142
143 // Find all llvm.dbg.declare intrinsics and resolve the DILocalVariable nodes
144 // they are referencing.
145 //
146 // DIDerivedTypes referring to incomplete Clang types, or
147 // LLVM enumeration types representing complete enums with no definition
148 // may be still unresolved. As they can't be cloned, keep references
149 // to the types from the base subprogram.
150 // FIXME: As a result, variables of cloned subprogram may refer to local types
151 // from base subprogram. In such case, type locality information is damaged.
152 // Find a way to enable cloning of all local types.
153 auto PrepareVariableMapping = [&VMap](llvm::DILocalVariable *DILocal) {
154 if (DILocal->isResolved())
155 return;
156
157 if (llvm::DIType *Ty = DILocal->getType(); Ty && !Ty->isResolved())
158 VMap.MD()[Ty].reset(MD: Ty);
159
160 DILocal->resolve();
161 };
162
163 for (auto &BB : *Fn) {
164 for (auto &I : BB) {
165 for (llvm::DbgVariableRecord &DVR :
166 llvm::filterDbgVars(R: I.getDbgRecordRange()))
167 PrepareVariableMapping(DVR.getVariable());
168
169 if (auto *DII = dyn_cast<llvm::DbgVariableIntrinsic>(Val: &I))
170 PrepareVariableMapping(DII->getVariable());
171 }
172 }
173}
174
175// This function does roughly the same thing as GenerateThunk, but in a
176// very different way, so that va_start and va_end work correctly.
177// FIXME: This function assumes "this" is the first non-sret LLVM argument of
178// a function, and that there is an alloca built in the entry block
179// for all accesses to "this".
180// FIXME: This function assumes there is only one "ret" statement per function.
181// FIXME: Cloning isn't correct in the presence of indirect goto!
182// FIXME: This implementation of thunks bloats codesize by duplicating the
183// function definition. There are alternatives:
184// 1. Add some sort of stub support to LLVM for cases where we can
185// do a this adjustment, then a sibcall.
186// 2. We could transform the definition to take a va_list instead of an
187// actual variable argument list, then have the thunks (including a
188// no-op thunk for the regular definition) call va_start/va_end.
189// There's a bit of per-call overhead for this solution, but it's
190// better for codesize if the definition is long.
191llvm::Function *
192CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,
193 const CGFunctionInfo &FnInfo,
194 GlobalDecl GD, const ThunkInfo &Thunk) {
195 const CXXMethodDecl *MD = cast<CXXMethodDecl>(Val: GD.getDecl());
196 const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
197 QualType ResultType = FPT->getReturnType();
198
199 // Get the original function
200 assert(FnInfo.isVariadic());
201 llvm::Type *Ty = CGM.getTypes().GetFunctionType(Info: FnInfo);
202 llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
203 llvm::Function *BaseFn = cast<llvm::Function>(Val: Callee);
204
205 // Cloning can't work if we don't have a definition. The Microsoft ABI may
206 // require thunks when a definition is not available. Emit an error in these
207 // cases.
208 if (!MD->isDefined()) {
209 CGM.ErrorUnsupported(D: MD, Type: "return-adjusting thunk with variadic arguments");
210 return Fn;
211 }
212 assert(!BaseFn->isDeclaration() && "cannot clone undefined variadic method");
213
214 // Clone to thunk.
215 llvm::ValueToValueMapTy VMap;
216
217 // We are cloning a function while some Metadata nodes are still unresolved.
218 // Ensure that the value mapper does not encounter any of them.
219 resolveTopLevelMetadata(Fn: BaseFn, VMap);
220 llvm::Function *NewFn = llvm::CloneFunction(F: BaseFn, VMap);
221 Fn->replaceAllUsesWith(V: NewFn);
222 NewFn->takeName(V: Fn);
223 Fn->eraseFromParent();
224 Fn = NewFn;
225
226 // "Initialize" CGF (minimally).
227 CurFn = Fn;
228
229 // Get the "this" value
230 llvm::Function::arg_iterator AI = Fn->arg_begin();
231 if (CGM.ReturnTypeUsesSRet(FI: FnInfo))
232 ++AI;
233
234 // Find the first store of "this", which will be to the alloca associated
235 // with "this".
236 Address ThisPtr = makeNaturalAddressForPointer(
237 Ptr: &*AI, T: MD->getFunctionObjectParameterType(),
238 Alignment: CGM.getClassPointerAlignment(CD: MD->getParent()));
239 llvm::BasicBlock *EntryBB = &Fn->front();
240 llvm::BasicBlock::iterator ThisStore =
241 llvm::find_if(Range&: *EntryBB, P: [&](llvm::Instruction &I) {
242 return isa<llvm::StoreInst>(Val: I) && I.getOperand(i: 0) == &*AI;
243 });
244 assert(ThisStore != EntryBB->end() &&
245 "Store of this should be in entry block?");
246 // Adjust "this", if necessary.
247 Builder.SetInsertPoint(&*ThisStore);
248
249 const CXXRecordDecl *ThisValueClass = Thunk.ThisType->getPointeeCXXRecordDecl();
250 llvm::Value *AdjustedThisPtr = CGM.getCXXABI().performThisAdjustment(
251 CGF&: *this, This: ThisPtr, UnadjustedClass: ThisValueClass, TI: Thunk);
252 AdjustedThisPtr = Builder.CreateBitCast(V: AdjustedThisPtr,
253 DestTy: ThisStore->getOperand(i: 0)->getType());
254 ThisStore->setOperand(i: 0, Val: AdjustedThisPtr);
255
256 if (!Thunk.Return.isEmpty()) {
257 // Fix up the returned value, if necessary.
258 for (llvm::BasicBlock &BB : *Fn) {
259 llvm::Instruction *T = BB.getTerminator();
260 if (isa<llvm::ReturnInst>(Val: T)) {
261 RValue RV = RValue::get(V: T->getOperand(i: 0));
262 T->eraseFromParent();
263 Builder.SetInsertPoint(&BB);
264 RV = PerformReturnAdjustment(CGF&: *this, ResultType, RV, Thunk);
265 Builder.CreateRet(V: RV.getScalarVal());
266 break;
267 }
268 }
269 }
270
271 return Fn;
272}
273
274void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
275 const CGFunctionInfo &FnInfo,
276 bool IsUnprototyped) {
277 assert(!CurGD.getDecl() && "CurGD was already set!");
278 CurGD = GD;
279 CurFuncIsThunk = true;
280
281 // Build FunctionArgs.
282 const CXXMethodDecl *MD = cast<CXXMethodDecl>(Val: GD.getDecl());
283 QualType ThisType = MD->getThisType();
284 QualType ResultType;
285 if (IsUnprototyped)
286 ResultType = CGM.getContext().VoidTy;
287 else if (CGM.getCXXABI().HasThisReturn(GD))
288 ResultType = ThisType;
289 else if (CGM.getCXXABI().hasMostDerivedReturn(GD))
290 ResultType = CGM.getContext().VoidPtrTy;
291 else
292 ResultType = MD->getType()->castAs<FunctionProtoType>()->getReturnType();
293 FunctionArgList FunctionArgs;
294
295 // Create the implicit 'this' parameter declaration.
296 CGM.getCXXABI().buildThisParam(CGF&: *this, Params&: FunctionArgs);
297
298 // Add the rest of the parameters, if we have a prototype to work with.
299 if (!IsUnprototyped) {
300 FunctionArgs.append(in_start: MD->param_begin(), in_end: MD->param_end());
301
302 if (isa<CXXDestructorDecl>(Val: MD))
303 CGM.getCXXABI().addImplicitStructorParams(CGF&: *this, ResTy&: ResultType,
304 Params&: FunctionArgs);
305 }
306
307 // Start defining the function.
308 auto NL = ApplyDebugLocation::CreateEmpty(CGF&: *this);
309 StartFunction(GD: GlobalDecl(), RetTy: ResultType, Fn, FnInfo, Args: FunctionArgs,
310 Loc: MD->getLocation());
311 // Create a scope with an artificial location for the body of this function.
312 auto AL = ApplyDebugLocation::CreateArtificial(CGF&: *this);
313
314 // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
315 CGM.getCXXABI().EmitInstanceFunctionProlog(CGF&: *this);
316 CXXThisValue = CXXABIThisValue;
317 CurCodeDecl = MD;
318 CurFuncDecl = MD;
319}
320
321void CodeGenFunction::FinishThunk() {
322 // Clear these to restore the invariants expected by
323 // StartFunction/FinishFunction.
324 CurCodeDecl = nullptr;
325 CurFuncDecl = nullptr;
326
327 FinishFunction();
328}
329
330void CodeGenFunction::EmitCallAndReturnForThunk(llvm::FunctionCallee Callee,
331 const ThunkInfo *Thunk,
332 bool IsUnprototyped) {
333 assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
334 "Please use a new CGF for this thunk");
335 const CXXMethodDecl *MD = cast<CXXMethodDecl>(Val: CurGD.getDecl());
336
337 // Adjust the 'this' pointer if necessary
338 const CXXRecordDecl *ThisValueClass =
339 MD->getThisType()->getPointeeCXXRecordDecl();
340 if (Thunk)
341 ThisValueClass = Thunk->ThisType->getPointeeCXXRecordDecl();
342
343 llvm::Value *AdjustedThisPtr =
344 Thunk ? CGM.getCXXABI().performThisAdjustment(CGF&: *this, This: LoadCXXThisAddress(),
345 UnadjustedClass: ThisValueClass, TI: *Thunk)
346 : LoadCXXThis();
347
348 // If perfect forwarding is required a variadic method, a method using
349 // inalloca, or an unprototyped thunk, use musttail. Emit an error if this
350 // thunk requires a return adjustment, since that is impossible with musttail.
351 if (CurFnInfo->usesInAlloca() || CurFnInfo->isVariadic() || IsUnprototyped) {
352 if (Thunk && !Thunk->Return.isEmpty()) {
353 if (IsUnprototyped)
354 CGM.ErrorUnsupported(
355 D: MD, Type: "return-adjusting thunk with incomplete parameter type");
356 else if (CurFnInfo->isVariadic())
357 llvm_unreachable("shouldn't try to emit musttail return-adjusting "
358 "thunks for variadic functions");
359 else
360 CGM.ErrorUnsupported(
361 D: MD, Type: "non-trivial argument copy for return-adjusting thunk");
362 }
363 EmitMustTailThunk(GD: CurGD, AdjustedThisPtr, Callee);
364 return;
365 }
366
367 // Start building CallArgs.
368 CallArgList CallArgs;
369 QualType ThisType = MD->getThisType();
370 CallArgs.add(rvalue: RValue::get(V: AdjustedThisPtr), type: ThisType);
371
372 if (isa<CXXDestructorDecl>(Val: MD))
373 CGM.getCXXABI().adjustCallArgsForDestructorThunk(CGF&: *this, GD: CurGD, CallArgs);
374
375#ifndef NDEBUG
376 unsigned PrefixArgs = CallArgs.size() - 1;
377#endif
378 // Add the rest of the arguments.
379 for (const ParmVarDecl *PD : MD->parameters())
380 EmitDelegateCallArg(args&: CallArgs, param: PD, loc: SourceLocation());
381
382 const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
383
384#ifndef NDEBUG
385 const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(
386 CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1), PrefixArgs);
387 assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
388 CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
389 CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
390 assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
391 similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
392 CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
393 assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
394 for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
395 assert(similar(CallFnInfo.arg_begin()[i].info,
396 CallFnInfo.arg_begin()[i].type,
397 CurFnInfo->arg_begin()[i].info,
398 CurFnInfo->arg_begin()[i].type));
399#endif
400
401 // Determine whether we have a return value slot to use.
402 QualType ResultType = CGM.getCXXABI().HasThisReturn(GD: CurGD)
403 ? ThisType
404 : CGM.getCXXABI().hasMostDerivedReturn(GD: CurGD)
405 ? CGM.getContext().VoidPtrTy
406 : FPT->getReturnType();
407 ReturnValueSlot Slot;
408 if (!ResultType->isVoidType() &&
409 (CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect ||
410 hasAggregateEvaluationKind(T: ResultType)))
411 Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified(),
412 /*IsUnused=*/false, /*IsExternallyDestructed=*/true);
413
414 // Now emit our call.
415 llvm::CallBase *CallOrInvoke;
416 RValue RV = EmitCall(CallInfo: *CurFnInfo, Callee: CGCallee::forDirect(functionPtr: Callee, abstractInfo: CurGD), ReturnValue: Slot,
417 Args: CallArgs, CallOrInvoke: &CallOrInvoke);
418
419 // Consider return adjustment if we have ThunkInfo.
420 if (Thunk && !Thunk->Return.isEmpty())
421 RV = PerformReturnAdjustment(CGF&: *this, ResultType, RV, Thunk: *Thunk);
422 else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(Val: CallOrInvoke))
423 Call->setTailCallKind(llvm::CallInst::TCK_Tail);
424
425 // Emit return.
426 if (!ResultType->isVoidType() && Slot.isNull())
427 CGM.getCXXABI().EmitReturnFromThunk(CGF&: *this, RV, ResultType);
428
429 // Disable the final ARC autorelease.
430 AutoreleaseResult = false;
431
432 FinishThunk();
433}
434
435void CodeGenFunction::EmitMustTailThunk(GlobalDecl GD,
436 llvm::Value *AdjustedThisPtr,
437 llvm::FunctionCallee Callee) {
438 // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
439 // to translate AST arguments into LLVM IR arguments. For thunks, we know
440 // that the caller prototype more or less matches the callee prototype with
441 // the exception of 'this'.
442 SmallVector<llvm::Value *, 8> Args(llvm::make_pointer_range(Range: CurFn->args()));
443
444 // Set the adjusted 'this' pointer.
445 const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
446 if (ThisAI.isDirect()) {
447 const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
448 int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
449 llvm::Type *ThisType = Args[ThisArgNo]->getType();
450 if (ThisType != AdjustedThisPtr->getType())
451 AdjustedThisPtr = Builder.CreateBitCast(V: AdjustedThisPtr, DestTy: ThisType);
452 Args[ThisArgNo] = AdjustedThisPtr;
453 } else {
454 assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
455 Address ThisAddr = GetAddrOfLocalVar(VD: CXXABIThisDecl);
456 llvm::Type *ThisType = ThisAddr.getElementType();
457 if (ThisType != AdjustedThisPtr->getType())
458 AdjustedThisPtr = Builder.CreateBitCast(V: AdjustedThisPtr, DestTy: ThisType);
459 Builder.CreateStore(Val: AdjustedThisPtr, Addr: ThisAddr);
460 }
461
462 // Emit the musttail call manually. Even if the prologue pushed cleanups, we
463 // don't actually want to run them.
464 llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
465 Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
466
467 // Apply the standard set of call attributes.
468 unsigned CallingConv;
469 llvm::AttributeList Attrs;
470 CGM.ConstructAttributeList(Name: Callee.getCallee()->getName(), Info: *CurFnInfo, CalleeInfo: GD,
471 Attrs, CallingConv, /*AttrOnCallSite=*/true,
472 /*IsThunk=*/false);
473 Call->setAttributes(Attrs);
474 Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
475
476 if (Call->getType()->isVoidTy())
477 Builder.CreateRetVoid();
478 else
479 Builder.CreateRet(V: Call);
480
481 // Finish the function to maintain CodeGenFunction invariants.
482 // FIXME: Don't emit unreachable code.
483 EmitBlock(BB: createBasicBlock());
484
485 FinishThunk();
486}
487
488void CodeGenFunction::generateThunk(llvm::Function *Fn,
489 const CGFunctionInfo &FnInfo, GlobalDecl GD,
490 const ThunkInfo &Thunk,
491 bool IsUnprototyped) {
492 StartThunk(Fn, GD, FnInfo, IsUnprototyped);
493 // Create a scope with an artificial location for the body of this function.
494 auto AL = ApplyDebugLocation::CreateArtificial(CGF&: *this);
495
496 // Get our callee. Use a placeholder type if this method is unprototyped so
497 // that CodeGenModule doesn't try to set attributes.
498 llvm::Type *Ty;
499 if (IsUnprototyped)
500 Ty = llvm::StructType::get(Context&: getLLVMContext());
501 else
502 Ty = CGM.getTypes().GetFunctionType(Info: FnInfo);
503
504 llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
505
506 // Make the call and return the result.
507 EmitCallAndReturnForThunk(Callee: llvm::FunctionCallee(Fn->getFunctionType(), Callee),
508 Thunk: &Thunk, IsUnprototyped);
509}
510
511static bool shouldEmitVTableThunk(CodeGenModule &CGM, const CXXMethodDecl *MD,
512 bool IsUnprototyped, bool ForVTable) {
513 // Always emit thunks in the MS C++ ABI. We cannot rely on other TUs to
514 // provide thunks for us.
515 if (CGM.getTarget().getCXXABI().isMicrosoft())
516 return true;
517
518 // In the Itanium C++ ABI, vtable thunks are provided by TUs that provide
519 // definitions of the main method. Therefore, emitting thunks with the vtable
520 // is purely an optimization. Emit the thunk if optimizations are enabled and
521 // all of the parameter types are complete.
522 if (ForVTable)
523 return CGM.getCodeGenOpts().OptimizationLevel && !IsUnprototyped;
524
525 // Always emit thunks along with the method definition.
526 return true;
527}
528
529llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,
530 const ThunkInfo &TI,
531 bool ForVTable) {
532 const CXXMethodDecl *MD = cast<CXXMethodDecl>(Val: GD.getDecl());
533
534 // First, get a declaration. Compute the mangled name. Don't worry about
535 // getting the function prototype right, since we may only need this
536 // declaration to fill in a vtable slot.
537 SmallString<256> Name;
538 MangleContext &MCtx = CGM.getCXXABI().getMangleContext();
539 llvm::raw_svector_ostream Out(Name);
540
541 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(Val: MD)) {
542 MCtx.mangleCXXDtorThunk(DD, Type: GD.getDtorType(), Thunk: TI,
543 /* elideOverrideInfo */ ElideOverrideInfo: false, Out);
544 } else
545 MCtx.mangleThunk(MD, Thunk: TI, /* elideOverrideInfo */ ElideOverrideInfo: false, Out);
546
547 if (CGM.getContext().useAbbreviatedThunkName(VirtualMethodDecl: GD, MangledName: Name.str())) {
548 Name = "";
549 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(Val: MD))
550 MCtx.mangleCXXDtorThunk(DD, Type: GD.getDtorType(), Thunk: TI,
551 /* elideOverrideInfo */ ElideOverrideInfo: true, Out);
552 else
553 MCtx.mangleThunk(MD, Thunk: TI, /* elideOverrideInfo */ ElideOverrideInfo: true, Out);
554 }
555
556 llvm::Type *ThunkVTableTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
557 llvm::Constant *Thunk = CGM.GetAddrOfThunk(Name, FnTy: ThunkVTableTy, GD);
558
559 // If we don't need to emit a definition, return this declaration as is.
560 bool IsUnprototyped = !CGM.getTypes().isFuncTypeConvertible(
561 FT: MD->getType()->castAs<FunctionType>());
562 if (!shouldEmitVTableThunk(CGM, MD, IsUnprototyped, ForVTable))
563 return Thunk;
564
565 // Arrange a function prototype appropriate for a function definition. In some
566 // cases in the MS ABI, we may need to build an unprototyped musttail thunk.
567 const CGFunctionInfo &FnInfo =
568 IsUnprototyped ? CGM.getTypes().arrangeUnprototypedMustTailThunk(MD)
569 : CGM.getTypes().arrangeGlobalDeclaration(GD);
570 llvm::FunctionType *ThunkFnTy = CGM.getTypes().GetFunctionType(Info: FnInfo);
571
572 // If the type of the underlying GlobalValue is wrong, we'll have to replace
573 // it. It should be a declaration.
574 llvm::Function *ThunkFn = cast<llvm::Function>(Val: Thunk->stripPointerCasts());
575 if (ThunkFn->getFunctionType() != ThunkFnTy) {
576 llvm::GlobalValue *OldThunkFn = ThunkFn;
577
578 assert(OldThunkFn->isDeclaration() && "Shouldn't replace non-declaration");
579
580 // Remove the name from the old thunk function and get a new thunk.
581 OldThunkFn->setName(StringRef());
582 ThunkFn = llvm::Function::Create(Ty: ThunkFnTy, Linkage: llvm::Function::ExternalLinkage,
583 N: Name.str(), M: &CGM.getModule());
584 CGM.SetLLVMFunctionAttributes(GD: MD, Info: FnInfo, F: ThunkFn, /*IsThunk=*/false);
585
586 if (!OldThunkFn->use_empty()) {
587 OldThunkFn->replaceAllUsesWith(V: ThunkFn);
588 }
589
590 // Remove the old thunk.
591 OldThunkFn->eraseFromParent();
592 }
593
594 bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
595 bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
596
597 if (!ThunkFn->isDeclaration()) {
598 if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
599 // There is already a thunk emitted for this function, do nothing.
600 return ThunkFn;
601 }
602
603 setThunkProperties(CGM, Thunk: TI, ThunkFn, ForVTable, GD);
604 return ThunkFn;
605 }
606
607 // If this will be unprototyped, add the "thunk" attribute so that LLVM knows
608 // that the return type is meaningless. These thunks can be used to call
609 // functions with differing return types, and the caller is required to cast
610 // the prototype appropriately to extract the correct value.
611 if (IsUnprototyped)
612 ThunkFn->addFnAttr(Kind: "thunk");
613
614 CGM.SetLLVMFunctionAttributesForDefinition(D: GD.getDecl(), F: ThunkFn);
615
616 // Thunks for variadic methods are special because in general variadic
617 // arguments cannot be perfectly forwarded. In the general case, clang
618 // implements such thunks by cloning the original function body. However, for
619 // thunks with no return adjustment on targets that support musttail, we can
620 // use musttail to perfectly forward the variadic arguments.
621 bool ShouldCloneVarArgs = false;
622 if (!IsUnprototyped && ThunkFn->isVarArg()) {
623 ShouldCloneVarArgs = true;
624 if (TI.Return.isEmpty()) {
625 switch (CGM.getTriple().getArch()) {
626 case llvm::Triple::x86_64:
627 case llvm::Triple::x86:
628 case llvm::Triple::aarch64:
629 ShouldCloneVarArgs = false;
630 break;
631 default:
632 break;
633 }
634 }
635 }
636
637 if (ShouldCloneVarArgs) {
638 if (UseAvailableExternallyLinkage)
639 return ThunkFn;
640 ThunkFn =
641 CodeGenFunction(CGM).GenerateVarArgsThunk(Fn: ThunkFn, FnInfo, GD, Thunk: TI);
642 } else {
643 // Normal thunk body generation.
644 CodeGenFunction(CGM).generateThunk(Fn: ThunkFn, FnInfo, GD, Thunk: TI, IsUnprototyped);
645 }
646
647 setThunkProperties(CGM, Thunk: TI, ThunkFn, ForVTable, GD);
648 return ThunkFn;
649}
650
651void CodeGenVTables::EmitThunks(GlobalDecl GD) {
652 const CXXMethodDecl *MD =
653 cast<CXXMethodDecl>(Val: GD.getDecl())->getCanonicalDecl();
654
655 // We don't need to generate thunks for the base destructor.
656 if (isa<CXXDestructorDecl>(Val: MD) && GD.getDtorType() == Dtor_Base)
657 return;
658
659 const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
660 VTContext->getThunkInfo(GD);
661
662 if (!ThunkInfoVector)
663 return;
664
665 for (const ThunkInfo& Thunk : *ThunkInfoVector)
666 maybeEmitThunk(GD, TI: Thunk, /*ForVTable=*/false);
667}
668
669void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,
670 llvm::Constant *component,
671 unsigned vtableAddressPoint,
672 bool vtableHasLocalLinkage,
673 bool isCompleteDtor) const {
674 // No need to get the offset of a nullptr.
675 if (component->isNullValue())
676 return builder.add(value: llvm::ConstantInt::get(Ty: CGM.Int32Ty, V: 0));
677
678 auto *globalVal =
679 cast<llvm::GlobalValue>(Val: component->stripPointerCastsAndAliases());
680 llvm::Module &module = CGM.getModule();
681
682 // We don't want to copy the linkage of the vtable exactly because we still
683 // want the stub/proxy to be emitted for properly calculating the offset.
684 // Examples where there would be no symbol emitted are available_externally
685 // and private linkages.
686 //
687 // `internal` linkage results in STB_LOCAL Elf binding while still manifesting a
688 // local symbol.
689 //
690 // `linkonce_odr` linkage results in a STB_DEFAULT Elf binding but also allows for
691 // the rtti_proxy to be transparently replaced with a GOTPCREL reloc by a
692 // target that supports this replacement.
693 auto stubLinkage = vtableHasLocalLinkage
694 ? llvm::GlobalValue::InternalLinkage
695 : llvm::GlobalValue::LinkOnceODRLinkage;
696
697 llvm::Constant *target;
698 if (auto *func = dyn_cast<llvm::Function>(Val: globalVal)) {
699 target = llvm::DSOLocalEquivalent::get(GV: func);
700 } else {
701 llvm::SmallString<16> rttiProxyName(globalVal->getName());
702 rttiProxyName.append(RHS: ".rtti_proxy");
703
704 // The RTTI component may not always be emitted in the same linkage unit as
705 // the vtable. As a general case, we can make a dso_local proxy to the RTTI
706 // that points to the actual RTTI struct somewhere. This will result in a
707 // GOTPCREL relocation when taking the relative offset to the proxy.
708 llvm::GlobalVariable *proxy = module.getNamedGlobal(Name: rttiProxyName);
709 if (!proxy) {
710 proxy = new llvm::GlobalVariable(module, globalVal->getType(),
711 /*isConstant=*/true, stubLinkage,
712 globalVal, rttiProxyName);
713 proxy->setDSOLocal(true);
714 proxy->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
715 if (!proxy->hasLocalLinkage()) {
716 proxy->setVisibility(llvm::GlobalValue::HiddenVisibility);
717 proxy->setComdat(module.getOrInsertComdat(Name: rttiProxyName));
718 }
719 // Do not instrument the rtti proxies with hwasan to avoid a duplicate
720 // symbol error. Aliases generated by hwasan will retain the same namebut
721 // the addresses they are set to may have different tags from different
722 // compilation units. We don't run into this without hwasan because the
723 // proxies are in comdat groups, but those aren't propagated to the alias.
724 RemoveHwasanMetadata(GV: proxy);
725 }
726 target = proxy;
727 }
728
729 builder.addRelativeOffsetToPosition(type: CGM.Int32Ty, target,
730 /*position=*/vtableAddressPoint);
731}
732
733llvm::Type *CodeGenModule::getVTableComponentType() const {
734 if (getLangOpts().RelativeCXXABIVTables)
735 return Int32Ty;
736 return GlobalsInt8PtrTy;
737}
738
739llvm::Type *CodeGenVTables::getVTableComponentType() const {
740 return CGM.getVTableComponentType();
741}
742
743static void AddPointerLayoutOffset(const CodeGenModule &CGM,
744 ConstantArrayBuilder &builder,
745 CharUnits offset) {
746 builder.add(value: llvm::ConstantExpr::getIntToPtr(
747 C: llvm::ConstantInt::getSigned(Ty: CGM.PtrDiffTy, V: offset.getQuantity()),
748 Ty: CGM.GlobalsInt8PtrTy));
749}
750
751static void AddRelativeLayoutOffset(const CodeGenModule &CGM,
752 ConstantArrayBuilder &builder,
753 CharUnits offset) {
754 builder.add(value: llvm::ConstantInt::getSigned(Ty: CGM.Int32Ty, V: offset.getQuantity()));
755}
756
757void CodeGenVTables::addVTableComponent(ConstantArrayBuilder &builder,
758 const VTableLayout &layout,
759 unsigned componentIndex,
760 llvm::Constant *rtti,
761 unsigned &nextVTableThunkIndex,
762 unsigned vtableAddressPoint,
763 bool vtableHasLocalLinkage) {
764 auto &component = layout.vtable_components()[componentIndex];
765
766 bool RelativeCXXABIVTables = CGM.getLangOpts().RelativeCXXABIVTables;
767 auto addOffsetConstant =
768 RelativeCXXABIVTables ? AddRelativeLayoutOffset : AddPointerLayoutOffset;
769
770 switch (component.getKind()) {
771 case VTableComponent::CK_VCallOffset:
772 return addOffsetConstant(CGM, builder, component.getVCallOffset());
773
774 case VTableComponent::CK_VBaseOffset:
775 return addOffsetConstant(CGM, builder, component.getVBaseOffset());
776
777 case VTableComponent::CK_OffsetToTop:
778 return addOffsetConstant(CGM, builder, component.getOffsetToTop());
779
780 case VTableComponent::CK_RTTI:
781 if (RelativeCXXABIVTables)
782 return addRelativeComponent(builder, component: rtti, vtableAddressPoint,
783 vtableHasLocalLinkage,
784 /*isCompleteDtor=*/false);
785 else
786 return builder.add(value: rtti);
787
788 case VTableComponent::CK_FunctionPointer:
789 case VTableComponent::CK_CompleteDtorPointer:
790 case VTableComponent::CK_DeletingDtorPointer: {
791 GlobalDecl GD = component.getGlobalDecl(
792 HasVectorDeletingDtors: CGM.getContext().getTargetInfo().emitVectorDeletingDtors(
793 CGM.getContext().getLangOpts()));
794
795 const bool IsThunk =
796 nextVTableThunkIndex < layout.vtable_thunks().size() &&
797 layout.vtable_thunks()[nextVTableThunkIndex].first == componentIndex;
798
799 if (CGM.getLangOpts().CUDA) {
800 // Emit NULL for methods we can't codegen on this
801 // side. Otherwise we'd end up with vtable with unresolved
802 // references.
803 const CXXMethodDecl *MD = cast<CXXMethodDecl>(Val: GD.getDecl());
804 // OK on device side: functions w/ __device__ attribute
805 // OK on host side: anything except __device__-only functions.
806 bool CanEmitMethod =
807 CGM.getLangOpts().CUDAIsDevice
808 ? MD->hasAttr<CUDADeviceAttr>()
809 : (MD->hasAttr<CUDAHostAttr>() || !MD->hasAttr<CUDADeviceAttr>());
810 if (!CanEmitMethod) {
811 if (IsThunk)
812 nextVTableThunkIndex++;
813 return builder.add(
814 value: llvm::ConstantExpr::getNullValue(Ty: CGM.GlobalsInt8PtrTy));
815 }
816 // Method is acceptable, continue processing as usual.
817 }
818
819 auto getSpecialVirtualFn = [&](StringRef name) -> llvm::Constant * {
820 // FIXME(PR43094): When merging comdat groups, lld can select a local
821 // symbol as the signature symbol even though it cannot be accessed
822 // outside that symbol's TU. The relative vtables ABI would make
823 // __cxa_pure_virtual and __cxa_deleted_virtual local symbols, and
824 // depending on link order, the comdat groups could resolve to the one
825 // with the local symbol. As a temporary solution, fill these components
826 // with zero. We shouldn't be calling these in the first place anyway.
827 if (RelativeCXXABIVTables)
828 return llvm::ConstantPointerNull::get(T: CGM.GlobalsInt8PtrTy);
829
830 // For NVPTX devices in OpenMP emit special functon as null pointers,
831 // otherwise linking ends up with unresolved references.
832 if (CGM.getLangOpts().OpenMP && CGM.getLangOpts().OpenMPIsTargetDevice &&
833 CGM.getTriple().isNVPTX())
834 return llvm::ConstantPointerNull::get(T: CGM.GlobalsInt8PtrTy);
835 llvm::FunctionType *fnTy =
836 llvm::FunctionType::get(Result: CGM.VoidTy, /*isVarArg=*/false);
837 llvm::Constant *fn = cast<llvm::Constant>(
838 Val: CGM.CreateRuntimeFunction(Ty: fnTy, Name: name).getCallee());
839 if (auto f = dyn_cast<llvm::Function>(Val: fn))
840 f->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
841 return fn;
842 };
843
844 llvm::Constant *fnPtr;
845
846 // Pure virtual member functions.
847 if (cast<CXXMethodDecl>(Val: GD.getDecl())->isPureVirtual()) {
848 if (!PureVirtualFn)
849 PureVirtualFn =
850 getSpecialVirtualFn(CGM.getCXXABI().GetPureVirtualCallName());
851 fnPtr = PureVirtualFn;
852
853 // Deleted virtual member functions.
854 } else if (cast<CXXMethodDecl>(Val: GD.getDecl())->isDeleted()) {
855 if (!DeletedVirtualFn)
856 DeletedVirtualFn =
857 getSpecialVirtualFn(CGM.getCXXABI().GetDeletedVirtualCallName());
858 fnPtr = DeletedVirtualFn;
859
860 // Thunks.
861 } else if (IsThunk) {
862 auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
863
864 nextVTableThunkIndex++;
865 fnPtr = maybeEmitThunk(GD, TI: thunkInfo, /*ForVTable=*/true);
866 if (CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers) {
867 assert(thunkInfo.Method && "Method not set");
868 GD = GD.getWithDecl(D: thunkInfo.Method);
869 }
870
871 // Otherwise we can use the method definition directly.
872 } else {
873 llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
874 fnPtr = CGM.GetAddrOfFunction(GD, Ty: fnTy, /*ForVTable=*/true);
875 if (CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers)
876 GD = getItaniumVTableContext().findOriginalMethod(GD);
877 }
878
879 if (RelativeCXXABIVTables) {
880 return addRelativeComponent(
881 builder, component: fnPtr, vtableAddressPoint, vtableHasLocalLinkage,
882 isCompleteDtor: component.getKind() == VTableComponent::CK_CompleteDtorPointer);
883 } else {
884 // TODO: this icky and only exists due to functions being in the generic
885 // address space, rather than the global one, even though they are
886 // globals; fixing said issue might be intrusive, and will be done
887 // later.
888 unsigned FnAS = fnPtr->getType()->getPointerAddressSpace();
889 unsigned GVAS = CGM.GlobalsInt8PtrTy->getPointerAddressSpace();
890
891 if (FnAS != GVAS)
892 fnPtr =
893 llvm::ConstantExpr::getAddrSpaceCast(C: fnPtr, Ty: CGM.GlobalsInt8PtrTy);
894 if (const auto &Schema =
895 CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers)
896 return builder.addSignedPointer(Pointer: fnPtr, Schema, CalleeDecl: GD, CalleeType: QualType());
897 return builder.add(value: fnPtr);
898 }
899 }
900
901 case VTableComponent::CK_UnusedFunctionPointer:
902 if (RelativeCXXABIVTables)
903 return builder.add(value: llvm::ConstantExpr::getNullValue(Ty: CGM.Int32Ty));
904 else
905 return builder.addNullPointer(ptrTy: CGM.GlobalsInt8PtrTy);
906 }
907
908 llvm_unreachable("Unexpected vtable component kind");
909}
910
911llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {
912 SmallVector<llvm::Type *, 4> tys;
913 llvm::Type *componentType = getVTableComponentType();
914 for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i)
915 tys.push_back(Elt: llvm::ArrayType::get(ElementType: componentType, NumElements: layout.getVTableSize(i)));
916
917 return llvm::StructType::get(Context&: CGM.getLLVMContext(), Elements: tys);
918}
919
920void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,
921 const VTableLayout &layout,
922 llvm::Constant *rtti,
923 bool vtableHasLocalLinkage) {
924 llvm::Type *componentType = getVTableComponentType();
925
926 const auto &addressPoints = layout.getAddressPointIndices();
927 unsigned nextVTableThunkIndex = 0;
928 for (unsigned vtableIndex = 0, endIndex = layout.getNumVTables();
929 vtableIndex != endIndex; ++vtableIndex) {
930 auto vtableElem = builder.beginArray(eltTy: componentType);
931
932 size_t vtableStart = layout.getVTableOffset(i: vtableIndex);
933 size_t vtableEnd = vtableStart + layout.getVTableSize(i: vtableIndex);
934 for (size_t componentIndex = vtableStart; componentIndex < vtableEnd;
935 ++componentIndex) {
936 addVTableComponent(builder&: vtableElem, layout, componentIndex, rtti,
937 nextVTableThunkIndex, vtableAddressPoint: addressPoints[vtableIndex],
938 vtableHasLocalLinkage);
939 }
940 vtableElem.finishAndAddTo(parent&: builder);
941 }
942}
943
944llvm::GlobalVariable *CodeGenVTables::GenerateConstructionVTable(
945 const CXXRecordDecl *RD, const BaseSubobject &Base, bool BaseIsVirtual,
946 llvm::GlobalVariable::LinkageTypes Linkage,
947 VTableAddressPointsMapTy &AddressPoints) {
948 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
949 DI->completeClassData(RD: Base.getBase());
950
951 std::unique_ptr<VTableLayout> VTLayout(
952 getItaniumVTableContext().createConstructionVTableLayout(
953 MostDerivedClass: Base.getBase(), MostDerivedClassOffset: Base.getBaseOffset(), MostDerivedClassIsVirtual: BaseIsVirtual, LayoutClass: RD));
954
955 // Add the address points.
956 AddressPoints = VTLayout->getAddressPoints();
957
958 // Get the mangled construction vtable name.
959 SmallString<256> OutName;
960 llvm::raw_svector_ostream Out(OutName);
961 cast<ItaniumMangleContext>(Val&: CGM.getCXXABI().getMangleContext())
962 .mangleCXXCtorVTable(RD, Offset: Base.getBaseOffset().getQuantity(),
963 Type: Base.getBase(), Out);
964 SmallString<256> Name(OutName);
965
966 bool UsingRelativeLayout = CGM.getLangOpts().RelativeCXXABIVTables;
967 bool VTableAliasExists =
968 UsingRelativeLayout && CGM.getModule().getNamedAlias(Name);
969 if (VTableAliasExists) {
970 // We previously made the vtable hidden and changed its name.
971 Name.append(RHS: ".local");
972 }
973
974 llvm::Type *VTType = getVTableType(layout: *VTLayout);
975
976 // Construction vtable symbols are not part of the Itanium ABI, so we cannot
977 // guarantee that they actually will be available externally. Instead, when
978 // emitting an available_externally VTT, we provide references to an internal
979 // linkage construction vtable. The ABI only requires complete-object vtables
980 // to be the same for all instances of a type, not construction vtables.
981 if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
982 Linkage = llvm::GlobalVariable::InternalLinkage;
983
984 llvm::Align Align = CGM.getDataLayout().getABITypeAlign(Ty: VTType);
985
986 // Create the variable that will hold the construction vtable.
987 llvm::GlobalVariable *VTable =
988 CGM.CreateOrReplaceCXXRuntimeVariable(Name, Ty: VTType, Linkage, Alignment: Align);
989
990 // dynamic_cast assumes the vtable address is unique; see
991 // https://github.com/llvm/llvm-project/pull/200108
992 if (!CGM.shouldEmitRTTI())
993 VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
994
995 llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
996 Ty: CGM.getContext().getCanonicalTagType(TD: Base.getBase()));
997
998 // Create and set the initializer.
999 ConstantInitBuilder builder(CGM);
1000 auto components = builder.beginStruct();
1001 createVTableInitializer(builder&: components, layout: *VTLayout, rtti: RTTI,
1002 vtableHasLocalLinkage: VTable->hasLocalLinkage());
1003 components.finishAndSetAsInitializer(global: VTable);
1004
1005 // Set properties only after the initializer has been set to ensure that the
1006 // GV is treated as definition and not declaration.
1007 assert(!VTable->isDeclaration() && "Shouldn't set properties on declaration");
1008 CGM.setGVProperties(GV: VTable, D: RD);
1009
1010 CGM.EmitVTableTypeMetadata(RD, VTable, VTLayout: *VTLayout);
1011
1012 if (UsingRelativeLayout) {
1013 RemoveHwasanMetadata(GV: VTable);
1014 if (!VTable->isDSOLocal())
1015 GenerateRelativeVTableAlias(VTable, AliasNameRef: OutName);
1016 }
1017
1018 return VTable;
1019}
1020
1021// Ensure this vtable is not instrumented by hwasan. That is, a global alias is
1022// not generated for it. This is mainly used by the relative-vtables ABI where
1023// vtables instead contain 32-bit offsets between the vtable and function
1024// pointers. Hwasan is disabled for these vtables for now because the tag in a
1025// vtable pointer may fail the overflow check when resolving 32-bit PLT
1026// relocations. A future alternative for this would be finding which usages of
1027// the vtable can continue to use the untagged hwasan value without any loss of
1028// value in hwasan.
1029void CodeGenVTables::RemoveHwasanMetadata(llvm::GlobalValue *GV) const {
1030 if (CGM.getLangOpts().Sanitize.has(K: SanitizerKind::HWAddress)) {
1031 llvm::GlobalValue::SanitizerMetadata Meta;
1032 if (GV->hasSanitizerMetadata())
1033 Meta = GV->getSanitizerMetadata();
1034 Meta.NoHWAddress = true;
1035 GV->setSanitizerMetadata(Meta);
1036 }
1037}
1038
1039// If the VTable is not dso_local, then we will not be able to indicate that
1040// the VTable does not need a relocation and move into rodata. A frequent
1041// time this can occur is for classes that should be made public from a DSO
1042// (like in libc++). For cases like these, we can make the vtable hidden or
1043// internal and create a public alias with the same visibility and linkage as
1044// the original vtable type.
1045void CodeGenVTables::GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
1046 llvm::StringRef AliasNameRef) {
1047 assert(CGM.getLangOpts().RelativeCXXABIVTables &&
1048 "Can only use this if the relative vtable ABI is used");
1049 assert(!VTable->isDSOLocal() && "This should be called only if the vtable is "
1050 "not guaranteed to be dso_local");
1051
1052 // If the vtable is available_externally, we shouldn't (or need to) generate
1053 // an alias for it in the first place since the vtable won't actually by
1054 // emitted in this compilation unit.
1055 if (VTable->hasAvailableExternallyLinkage())
1056 return;
1057
1058 // Create a new string in the event the alias is already the name of the
1059 // vtable. Using the reference directly could lead to use of an inititialized
1060 // value in the module's StringMap.
1061 llvm::SmallString<256> AliasName(AliasNameRef);
1062 VTable->setName(AliasName + ".local");
1063
1064 auto Linkage = VTable->getLinkage();
1065 assert(llvm::GlobalAlias::isValidLinkage(Linkage) &&
1066 "Invalid vtable alias linkage");
1067
1068 llvm::GlobalAlias *VTableAlias = CGM.getModule().getNamedAlias(Name: AliasName);
1069 if (!VTableAlias) {
1070 VTableAlias = llvm::GlobalAlias::create(Ty: VTable->getValueType(),
1071 AddressSpace: VTable->getAddressSpace(), Linkage,
1072 Name: AliasName, Parent: &CGM.getModule());
1073 } else {
1074 assert(VTableAlias->getValueType() == VTable->getValueType());
1075 assert(VTableAlias->getLinkage() == Linkage);
1076 }
1077 VTableAlias->setVisibility(VTable->getVisibility());
1078 VTableAlias->setUnnamedAddr(VTable->getUnnamedAddr());
1079
1080 // Both of these will now imply dso_local for the vtable.
1081 if (!VTable->hasComdat()) {
1082 VTable->setLinkage(llvm::GlobalValue::InternalLinkage);
1083 } else {
1084 // If a relocation targets an internal linkage symbol, MC will generate the
1085 // relocation against the symbol's section instead of the symbol itself
1086 // (see ELFObjectWriter::shouldRelocateWithSymbol). If an internal symbol is
1087 // in a COMDAT section group, that section might be discarded, and then the
1088 // relocation to that section will generate a linker error. We therefore
1089 // make COMDAT vtables hidden instead of internal: they'll still not be
1090 // public, but relocations will reference the symbol instead of the section
1091 // and COMDAT deduplication will thus work as expected.
1092 VTable->setVisibility(llvm::GlobalValue::HiddenVisibility);
1093 }
1094
1095 VTableAlias->setAliasee(VTable);
1096}
1097
1098static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,
1099 const CXXRecordDecl *RD) {
1100 return CGM.getCodeGenOpts().OptimizationLevel > 0 &&
1101 CGM.getCXXABI().canSpeculativelyEmitVTable(RD);
1102}
1103
1104/// Compute the required linkage of the vtable for the given class.
1105///
1106/// Note that we only call this at the end of the translation unit.
1107llvm::GlobalVariable::LinkageTypes
1108CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
1109 if (!RD->isExternallyVisible())
1110 return llvm::GlobalVariable::InternalLinkage;
1111
1112 // In windows, the linkage of vtable is not related to modules.
1113 bool IsInNamedModule = !getTarget().getCXXABI().isMicrosoft() &&
1114 RD->isInNamedModule();
1115 // If the CXXRecordDecl is not in a module unit, we need to get
1116 // its key function. We're at the end of the translation unit, so the current
1117 // key function is fully correct.
1118 const CXXMethodDecl *keyFunction =
1119 IsInNamedModule ? nullptr : Context.getCurrentKeyFunction(RD);
1120 if (IsInNamedModule || (keyFunction && !RD->hasAttr<DLLImportAttr>())) {
1121 // If this class has a key function, use that to determine the
1122 // linkage of the vtable.
1123 const FunctionDecl *def = nullptr;
1124 if (keyFunction && keyFunction->hasBody(Definition&: def))
1125 keyFunction = cast<CXXMethodDecl>(Val: def);
1126
1127 bool IsExternalDefinition =
1128 IsInNamedModule ? RD->shouldEmitInExternalSource() : !def;
1129
1130 TemplateSpecializationKind Kind =
1131 IsInNamedModule ? RD->getTemplateSpecializationKind()
1132 : keyFunction->getTemplateSpecializationKind();
1133
1134 switch (Kind) {
1135 case TSK_Undeclared:
1136 case TSK_ExplicitSpecialization:
1137 assert(
1138 (IsInNamedModule || def || CodeGenOpts.OptimizationLevel > 0 ||
1139 CodeGenOpts.getDebugInfo() != llvm::codegenoptions::NoDebugInfo) &&
1140 "Shouldn't query vtable linkage without the class in module units, "
1141 "key function, optimizations, or debug info");
1142 if (IsExternalDefinition && CodeGenOpts.OptimizationLevel > 0)
1143 return llvm::GlobalVariable::AvailableExternallyLinkage;
1144
1145 if (keyFunction && keyFunction->isInlined())
1146 return !Context.getLangOpts().AppleKext
1147 ? llvm::GlobalVariable::LinkOnceODRLinkage
1148 : llvm::Function::InternalLinkage;
1149
1150 return llvm::GlobalVariable::ExternalLinkage;
1151
1152 case TSK_ImplicitInstantiation:
1153 return !Context.getLangOpts().AppleKext ?
1154 llvm::GlobalVariable::LinkOnceODRLinkage :
1155 llvm::Function::InternalLinkage;
1156
1157 case TSK_ExplicitInstantiationDefinition:
1158 return !Context.getLangOpts().AppleKext ?
1159 llvm::GlobalVariable::WeakODRLinkage :
1160 llvm::Function::InternalLinkage;
1161
1162 case TSK_ExplicitInstantiationDeclaration:
1163 return IsExternalDefinition
1164 ? llvm::GlobalVariable::AvailableExternallyLinkage
1165 : llvm::GlobalVariable::ExternalLinkage;
1166 }
1167 }
1168
1169 // -fapple-kext mode does not support weak linkage, so we must use
1170 // internal linkage.
1171 if (Context.getLangOpts().AppleKext)
1172 return llvm::Function::InternalLinkage;
1173
1174 llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
1175 llvm::GlobalValue::LinkOnceODRLinkage;
1176 llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
1177 llvm::GlobalValue::WeakODRLinkage;
1178 if (RD->hasAttr<DLLExportAttr>()) {
1179 // Cannot discard exported vtables.
1180 DiscardableODRLinkage = NonDiscardableODRLinkage;
1181 } else if (RD->hasAttr<DLLImportAttr>()) {
1182 // Imported vtables are available externally.
1183 DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1184 NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1185 }
1186
1187 switch (RD->getTemplateSpecializationKind()) {
1188 case TSK_Undeclared:
1189 case TSK_ExplicitSpecialization:
1190 case TSK_ImplicitInstantiation:
1191 return DiscardableODRLinkage;
1192
1193 case TSK_ExplicitInstantiationDeclaration:
1194 // Explicit instantiations in MSVC do not provide vtables, so we must emit
1195 // our own.
1196 if (getTarget().getCXXABI().isMicrosoft())
1197 return DiscardableODRLinkage;
1198 return shouldEmitAvailableExternallyVTable(CGM: *this, RD)
1199 ? llvm::GlobalVariable::AvailableExternallyLinkage
1200 : llvm::GlobalVariable::ExternalLinkage;
1201
1202 case TSK_ExplicitInstantiationDefinition:
1203 return NonDiscardableODRLinkage;
1204 }
1205
1206 llvm_unreachable("Invalid TemplateSpecializationKind!");
1207}
1208
1209/// This is a callback from Sema to tell us that a particular vtable is
1210/// required to be emitted in this translation unit.
1211///
1212/// This is only called for vtables that _must_ be emitted (mainly due to key
1213/// functions). For weak vtables, CodeGen tracks when they are needed and
1214/// emits them as-needed.
1215void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
1216 VTables.GenerateClassData(RD: theClass);
1217 EmittedVTables.insert(Ptr: theClass);
1218}
1219
1220void
1221CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
1222 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
1223 DI->completeClassData(RD);
1224
1225 if (RD->getNumVBases())
1226 CGM.getCXXABI().emitVirtualInheritanceTables(RD);
1227
1228 CGM.getCXXABI().emitVTableDefinitions(CGVT&: *this, RD);
1229}
1230
1231/// At this point in the translation unit, does it appear that can we
1232/// rely on the vtable being defined elsewhere in the program?
1233///
1234/// The response is really only definitive when called at the end of
1235/// the translation unit.
1236///
1237/// The only semantic restriction here is that the object file should
1238/// not contain a vtable definition when that vtable is defined
1239/// strongly elsewhere. Otherwise, we'd just like to avoid emitting
1240/// vtables when unnecessary.
1241bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
1242 assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
1243
1244 // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
1245 // emit them even if there is an explicit template instantiation.
1246 if (CGM.getTarget().getCXXABI().isMicrosoft())
1247 return false;
1248
1249 // If we have an explicit instantiation declaration (and not a
1250 // definition), the vtable is defined elsewhere.
1251 TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
1252 if (TSK == TSK_ExplicitInstantiationDeclaration)
1253 return true;
1254
1255 // Otherwise, if the class is an instantiated template, the
1256 // vtable must be defined here.
1257 if (TSK == TSK_ImplicitInstantiation ||
1258 TSK == TSK_ExplicitInstantiationDefinition)
1259 return false;
1260
1261 // Otherwise, if the class is attached to a module, the tables are uniquely
1262 // emitted in the object for the module unit in which it is defined.
1263 if (RD->isInNamedModule())
1264 return RD->shouldEmitInExternalSource();
1265
1266 // Otherwise, if the class doesn't have a key function (possibly
1267 // anymore), the vtable must be defined here.
1268 const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
1269 if (!keyFunction)
1270 return false;
1271
1272 // Otherwise, if we don't have a definition of the key function, the
1273 // vtable must be defined somewhere else.
1274 return !keyFunction->hasBody();
1275}
1276
1277/// Given that we're currently at the end of the translation unit, and
1278/// we've emitted a reference to the vtable for this class, should
1279/// we define that vtable?
1280static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
1281 const CXXRecordDecl *RD) {
1282 // If vtable is internal then it has to be done.
1283 if (!CGM.getVTables().isVTableExternal(RD))
1284 return true;
1285
1286 // If it's external then maybe we will need it as available_externally.
1287 return shouldEmitAvailableExternallyVTable(CGM, RD);
1288}
1289
1290/// Given that at some point we emitted a reference to one or more
1291/// vtables, and that we are now at the end of the translation unit,
1292/// decide whether we should emit them.
1293void CodeGenModule::EmitDeferredVTables() {
1294#ifndef NDEBUG
1295 // Remember the size of DeferredVTables, because we're going to assume
1296 // that this entire operation doesn't modify it.
1297 size_t savedSize = DeferredVTables.size();
1298#endif
1299
1300 for (const CXXRecordDecl *RD : DeferredVTables) {
1301 // if a table has been emitted in an earlier PTU, but was also marked
1302 // deferred, we should skip if the linkage is external
1303 if (EmittedVTables.count(Ptr: RD) &&
1304 getVTableLinkage(RD) == llvm::GlobalValue::ExternalLinkage)
1305 continue;
1306
1307 if (shouldEmitVTableAtEndOfTranslationUnit(CGM&: *this, RD))
1308 VTables.GenerateClassData(RD);
1309 else if (shouldOpportunisticallyEmitVTables())
1310 OpportunisticVTables.push_back(x: RD);
1311 }
1312
1313 assert(savedSize == DeferredVTables.size() &&
1314 "deferred extra vtables during vtable emission?");
1315 DeferredVTables.clear();
1316}
1317
1318bool CodeGenModule::AlwaysHasLTOVisibilityPublic(const CXXRecordDecl *RD) {
1319 if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>() ||
1320 RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
1321 return true;
1322
1323 if (!getCodeGenOpts().LTOVisibilityPublicStd)
1324 return false;
1325
1326 const DeclContext *DC = RD;
1327 while (true) {
1328 auto *D = cast<Decl>(Val: DC);
1329 DC = DC->getParent();
1330 if (isa<TranslationUnitDecl>(Val: DC->getRedeclContext())) {
1331 if (auto *ND = dyn_cast<NamespaceDecl>(Val: D))
1332 if (const IdentifierInfo *II = ND->getIdentifier())
1333 if (II->isStr(Str: "std") || II->isStr(Str: "stdext"))
1334 return true;
1335 break;
1336 }
1337 }
1338
1339 return false;
1340}
1341
1342bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
1343 LinkageInfo LV = RD->getLinkageAndVisibility();
1344 if (!isExternallyVisible(L: LV.getLinkage()))
1345 return true;
1346
1347 if (!getTriple().isOSBinFormatCOFF() &&
1348 LV.getVisibility() != HiddenVisibility)
1349 return false;
1350
1351 return !AlwaysHasLTOVisibilityPublic(RD);
1352}
1353
1354llvm::GlobalObject::VCallVisibility CodeGenModule::GetVCallVisibilityLevel(
1355 const CXXRecordDecl *RD, llvm::DenseSet<const CXXRecordDecl *> &Visited) {
1356 // If we have already visited this RD (which means this is a recursive call
1357 // since the initial call should have an empty Visited set), return the max
1358 // visibility. The recursive calls below compute the min between the result
1359 // of the recursive call and the current TypeVis, so returning the max here
1360 // ensures that it will have no effect on the current TypeVis.
1361 if (!Visited.insert(V: RD).second)
1362 return llvm::GlobalObject::VCallVisibilityTranslationUnit;
1363
1364 LinkageInfo LV = RD->getLinkageAndVisibility();
1365 llvm::GlobalObject::VCallVisibility TypeVis;
1366 if (!isExternallyVisible(L: LV.getLinkage()))
1367 TypeVis = llvm::GlobalObject::VCallVisibilityTranslationUnit;
1368 else if (HasHiddenLTOVisibility(RD))
1369 TypeVis = llvm::GlobalObject::VCallVisibilityLinkageUnit;
1370 else
1371 TypeVis = llvm::GlobalObject::VCallVisibilityPublic;
1372
1373 for (const auto &B : RD->bases())
1374 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1375 TypeVis = std::min(
1376 a: TypeVis,
1377 b: GetVCallVisibilityLevel(RD: B.getType()->getAsCXXRecordDecl(), Visited));
1378
1379 for (const auto &B : RD->vbases())
1380 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1381 TypeVis = std::min(
1382 a: TypeVis,
1383 b: GetVCallVisibilityLevel(RD: B.getType()->getAsCXXRecordDecl(), Visited));
1384
1385 return TypeVis;
1386}
1387
1388void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
1389 llvm::GlobalVariable *VTable,
1390 const VTableLayout &VTLayout) {
1391 // Emit type metadata on vtables with LTO or IR instrumentation or
1392 // speculative devirtualization.
1393 // In IR instrumentation, the type metadata is used to find out vtable
1394 // definitions (for type profiling) among all global variables.
1395 if (!getCodeGenOpts().LTOUnit && !getCodeGenOpts().hasProfileIRInstr() &&
1396 !getCodeGenOpts().DevirtualizeSpeculatively)
1397 return;
1398
1399 CharUnits ComponentWidth = GetTargetTypeStoreSize(Ty: getVTableComponentType());
1400
1401 struct AddressPoint {
1402 const CXXRecordDecl *Base;
1403 size_t Offset;
1404 std::string TypeName;
1405 bool operator<(const AddressPoint &RHS) const {
1406 int D = TypeName.compare(str: RHS.TypeName);
1407 return D < 0 || (D == 0 && Offset < RHS.Offset);
1408 }
1409 };
1410 std::vector<AddressPoint> AddressPoints;
1411 for (auto &&AP : VTLayout.getAddressPoints()) {
1412 AddressPoint N{.Base: AP.first.getBase(),
1413 .Offset: VTLayout.getVTableOffset(i: AP.second.VTableIndex) +
1414 AP.second.AddressPointIndex,
1415 .TypeName: {}};
1416 llvm::raw_string_ostream Stream(N.TypeName);
1417 CanQualType T = getContext().getCanonicalTagType(TD: N.Base);
1418 getCXXABI().getMangleContext().mangleCanonicalTypeName(T, Stream);
1419 AddressPoints.push_back(x: std::move(N));
1420 }
1421
1422 // Sort the address points for determinism.
1423 llvm::sort(C&: AddressPoints);
1424
1425 ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
1426 for (auto AP : AddressPoints) {
1427 // Create type metadata for the address point.
1428 AddVTableTypeMetadata(VTable, Offset: ComponentWidth * AP.Offset, RD: AP.Base);
1429
1430 // The class associated with each address point could also potentially be
1431 // used for indirect calls via a member function pointer, so we need to
1432 // annotate the address of each function pointer with the appropriate member
1433 // function pointer type.
1434 for (unsigned I = 0; I != Comps.size(); ++I) {
1435 if (Comps[I].getKind() != VTableComponent::CK_FunctionPointer)
1436 continue;
1437 llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
1438 T: Context.getMemberPointerType(T: Comps[I].getFunctionDecl()->getType(),
1439 /*Qualifier=*/std::nullopt, Cls: AP.Base));
1440 VTable->addTypeMetadata(Offset: (ComponentWidth * I).getQuantity(), TypeID: MD);
1441 }
1442 }
1443
1444 if (getCodeGenOpts().VirtualFunctionElimination ||
1445 getCodeGenOpts().WholeProgramVTables) {
1446 llvm::DenseSet<const CXXRecordDecl *> Visited;
1447 llvm::GlobalObject::VCallVisibility TypeVis =
1448 GetVCallVisibilityLevel(RD, Visited);
1449 if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
1450 VTable->setVCallVisibilityMetadata(TypeVis);
1451 }
1452}
1453