xref: /openbsd/gnu/llvm/clang/lib/CodeGen/CGVTables.cpp (revision 12c85518)
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 "CodeGenFunction.h"
15 #include "CodeGenModule.h"
16 #include "clang/AST/Attr.h"
17 #include "clang/AST/CXXInheritance.h"
18 #include "clang/AST/RecordLayout.h"
19 #include "clang/Basic/CodeGenOptions.h"
20 #include "clang/CodeGen/CGFunctionInfo.h"
21 #include "clang/CodeGen/ConstantInitBuilder.h"
22 #include "llvm/IR/IntrinsicInst.h"
23 #include "llvm/Support/Format.h"
24 #include "llvm/Transforms/Utils/Cloning.h"
25 #include <algorithm>
26 #include <cstdio>
27 
28 using namespace clang;
29 using namespace CodeGen;
30 
CodeGenVTables(CodeGenModule & CGM)31 CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
32     : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
33 
GetAddrOfThunk(StringRef Name,llvm::Type * FnTy,GlobalDecl GD)34 llvm::Constant *CodeGenModule::GetAddrOfThunk(StringRef Name, llvm::Type *FnTy,
35                                               GlobalDecl GD) {
36   return GetOrCreateLLVMFunction(Name, FnTy, GD, /*ForVTable=*/true,
37                                  /*DontDefer=*/true, /*IsThunk=*/true);
38 }
39 
setThunkProperties(CodeGenModule & CGM,const ThunkInfo & Thunk,llvm::Function * ThunkFn,bool ForVTable,GlobalDecl GD)40 static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,
41                                llvm::Function *ThunkFn, bool ForVTable,
42                                GlobalDecl GD) {
43   CGM.setFunctionLinkage(GD, ThunkFn);
44   CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
45                                   !Thunk.Return.isEmpty());
46 
47   // Set the right visibility.
48   CGM.setGVProperties(ThunkFn, GD);
49 
50   if (!CGM.getCXXABI().exportThunk()) {
51     ThunkFn->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
52     ThunkFn->setDSOLocal(true);
53   }
54 
55   if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())
56     ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(ThunkFn->getName()));
57 }
58 
59 #ifndef NDEBUG
similar(const ABIArgInfo & infoL,CanQualType typeL,const ABIArgInfo & infoR,CanQualType typeR)60 static bool similar(const ABIArgInfo &infoL, CanQualType typeL,
61                     const ABIArgInfo &infoR, CanQualType typeR) {
62   return (infoL.getKind() == infoR.getKind() &&
63           (typeL == typeR ||
64            (isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||
65            (isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));
66 }
67 #endif
68 
PerformReturnAdjustment(CodeGenFunction & CGF,QualType ResultType,RValue RV,const ThunkInfo & Thunk)69 static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
70                                       QualType ResultType, RValue RV,
71                                       const ThunkInfo &Thunk) {
72   // Emit the return adjustment.
73   bool NullCheckValue = !ResultType->isReferenceType();
74 
75   llvm::BasicBlock *AdjustNull = nullptr;
76   llvm::BasicBlock *AdjustNotNull = nullptr;
77   llvm::BasicBlock *AdjustEnd = nullptr;
78 
79   llvm::Value *ReturnValue = RV.getScalarVal();
80 
81   if (NullCheckValue) {
82     AdjustNull = CGF.createBasicBlock("adjust.null");
83     AdjustNotNull = CGF.createBasicBlock("adjust.notnull");
84     AdjustEnd = CGF.createBasicBlock("adjust.end");
85 
86     llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);
87     CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
88     CGF.EmitBlock(AdjustNotNull);
89   }
90 
91   auto ClassDecl = ResultType->getPointeeType()->getAsCXXRecordDecl();
92   auto ClassAlign = CGF.CGM.getClassPointerAlignment(ClassDecl);
93   ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(
94       CGF,
95       Address(ReturnValue, CGF.ConvertTypeForMem(ResultType->getPointeeType()),
96               ClassAlign),
97       Thunk.Return);
98 
99   if (NullCheckValue) {
100     CGF.Builder.CreateBr(AdjustEnd);
101     CGF.EmitBlock(AdjustNull);
102     CGF.Builder.CreateBr(AdjustEnd);
103     CGF.EmitBlock(AdjustEnd);
104 
105     llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
106     PHI->addIncoming(ReturnValue, AdjustNotNull);
107     PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
108                      AdjustNull);
109     ReturnValue = PHI;
110   }
111 
112   return RValue::get(ReturnValue);
113 }
114 
115 /// This function clones a function's DISubprogram node and enters it into
116 /// a value map with the intent that the map can be utilized by the cloner
117 /// to short-circuit Metadata node mapping.
118 /// Furthermore, the function resolves any DILocalVariable nodes referenced
119 /// by dbg.value intrinsics so they can be properly mapped during cloning.
resolveTopLevelMetadata(llvm::Function * Fn,llvm::ValueToValueMapTy & VMap)120 static void resolveTopLevelMetadata(llvm::Function *Fn,
121                                     llvm::ValueToValueMapTy &VMap) {
122   // Clone the DISubprogram node and put it into the Value map.
123   auto *DIS = Fn->getSubprogram();
124   if (!DIS)
125     return;
126   auto *NewDIS = DIS->replaceWithDistinct(DIS->clone());
127   VMap.MD()[DIS].reset(NewDIS);
128 
129   // Find all llvm.dbg.declare intrinsics and resolve the DILocalVariable nodes
130   // they are referencing.
131   for (auto &BB : *Fn) {
132     for (auto &I : BB) {
133       if (auto *DII = dyn_cast<llvm::DbgVariableIntrinsic>(&I)) {
134         auto *DILocal = DII->getVariable();
135         if (!DILocal->isResolved())
136           DILocal->resolve();
137       }
138     }
139   }
140 }
141 
142 // This function does roughly the same thing as GenerateThunk, but in a
143 // very different way, so that va_start and va_end work correctly.
144 // FIXME: This function assumes "this" is the first non-sret LLVM argument of
145 //        a function, and that there is an alloca built in the entry block
146 //        for all accesses to "this".
147 // FIXME: This function assumes there is only one "ret" statement per function.
148 // FIXME: Cloning isn't correct in the presence of indirect goto!
149 // FIXME: This implementation of thunks bloats codesize by duplicating the
150 //        function definition.  There are alternatives:
151 //        1. Add some sort of stub support to LLVM for cases where we can
152 //           do a this adjustment, then a sibcall.
153 //        2. We could transform the definition to take a va_list instead of an
154 //           actual variable argument list, then have the thunks (including a
155 //           no-op thunk for the regular definition) call va_start/va_end.
156 //           There's a bit of per-call overhead for this solution, but it's
157 //           better for codesize if the definition is long.
158 llvm::Function *
GenerateVarArgsThunk(llvm::Function * Fn,const CGFunctionInfo & FnInfo,GlobalDecl GD,const ThunkInfo & Thunk)159 CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,
160                                       const CGFunctionInfo &FnInfo,
161                                       GlobalDecl GD, const ThunkInfo &Thunk) {
162   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
163   const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
164   QualType ResultType = FPT->getReturnType();
165 
166   // Get the original function
167   assert(FnInfo.isVariadic());
168   llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
169   llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
170   llvm::Function *BaseFn = cast<llvm::Function>(Callee);
171 
172   // Cloning can't work if we don't have a definition. The Microsoft ABI may
173   // require thunks when a definition is not available. Emit an error in these
174   // cases.
175   if (!MD->isDefined()) {
176     CGM.ErrorUnsupported(MD, "return-adjusting thunk with variadic arguments");
177     return Fn;
178   }
179   assert(!BaseFn->isDeclaration() && "cannot clone undefined variadic method");
180 
181   // Clone to thunk.
182   llvm::ValueToValueMapTy VMap;
183 
184   // We are cloning a function while some Metadata nodes are still unresolved.
185   // Ensure that the value mapper does not encounter any of them.
186   resolveTopLevelMetadata(BaseFn, VMap);
187   llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap);
188   Fn->replaceAllUsesWith(NewFn);
189   NewFn->takeName(Fn);
190   Fn->eraseFromParent();
191   Fn = NewFn;
192 
193   // "Initialize" CGF (minimally).
194   CurFn = Fn;
195 
196   // Get the "this" value
197   llvm::Function::arg_iterator AI = Fn->arg_begin();
198   if (CGM.ReturnTypeUsesSRet(FnInfo))
199     ++AI;
200 
201   // Find the first store of "this", which will be to the alloca associated
202   // with "this".
203   Address ThisPtr =
204       Address(&*AI, ConvertTypeForMem(MD->getThisType()->getPointeeType()),
205               CGM.getClassPointerAlignment(MD->getParent()));
206   llvm::BasicBlock *EntryBB = &Fn->front();
207   llvm::BasicBlock::iterator ThisStore =
208       llvm::find_if(*EntryBB, [&](llvm::Instruction &I) {
209         return isa<llvm::StoreInst>(I) &&
210                I.getOperand(0) == ThisPtr.getPointer();
211       });
212   assert(ThisStore != EntryBB->end() &&
213          "Store of this should be in entry block?");
214   // Adjust "this", if necessary.
215   Builder.SetInsertPoint(&*ThisStore);
216   llvm::Value *AdjustedThisPtr =
217       CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
218   AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr,
219                                           ThisStore->getOperand(0)->getType());
220   ThisStore->setOperand(0, AdjustedThisPtr);
221 
222   if (!Thunk.Return.isEmpty()) {
223     // Fix up the returned value, if necessary.
224     for (llvm::BasicBlock &BB : *Fn) {
225       llvm::Instruction *T = BB.getTerminator();
226       if (isa<llvm::ReturnInst>(T)) {
227         RValue RV = RValue::get(T->getOperand(0));
228         T->eraseFromParent();
229         Builder.SetInsertPoint(&BB);
230         RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
231         Builder.CreateRet(RV.getScalarVal());
232         break;
233       }
234     }
235   }
236 
237   return Fn;
238 }
239 
StartThunk(llvm::Function * Fn,GlobalDecl GD,const CGFunctionInfo & FnInfo,bool IsUnprototyped)240 void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
241                                  const CGFunctionInfo &FnInfo,
242                                  bool IsUnprototyped) {
243   assert(!CurGD.getDecl() && "CurGD was already set!");
244   CurGD = GD;
245   CurFuncIsThunk = true;
246 
247   // Build FunctionArgs.
248   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
249   QualType ThisType = MD->getThisType();
250   QualType ResultType;
251   if (IsUnprototyped)
252     ResultType = CGM.getContext().VoidTy;
253   else if (CGM.getCXXABI().HasThisReturn(GD))
254     ResultType = ThisType;
255   else if (CGM.getCXXABI().hasMostDerivedReturn(GD))
256     ResultType = CGM.getContext().VoidPtrTy;
257   else
258     ResultType = MD->getType()->castAs<FunctionProtoType>()->getReturnType();
259   FunctionArgList FunctionArgs;
260 
261   // Create the implicit 'this' parameter declaration.
262   CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
263 
264   // Add the rest of the parameters, if we have a prototype to work with.
265   if (!IsUnprototyped) {
266     FunctionArgs.append(MD->param_begin(), MD->param_end());
267 
268     if (isa<CXXDestructorDecl>(MD))
269       CGM.getCXXABI().addImplicitStructorParams(*this, ResultType,
270                                                 FunctionArgs);
271   }
272 
273   // Start defining the function.
274   auto NL = ApplyDebugLocation::CreateEmpty(*this);
275   StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
276                 MD->getLocation());
277   // Create a scope with an artificial location for the body of this function.
278   auto AL = ApplyDebugLocation::CreateArtificial(*this);
279 
280   // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
281   CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
282   CXXThisValue = CXXABIThisValue;
283   CurCodeDecl = MD;
284   CurFuncDecl = MD;
285 }
286 
FinishThunk()287 void CodeGenFunction::FinishThunk() {
288   // Clear these to restore the invariants expected by
289   // StartFunction/FinishFunction.
290   CurCodeDecl = nullptr;
291   CurFuncDecl = nullptr;
292 
293   FinishFunction();
294 }
295 
EmitCallAndReturnForThunk(llvm::FunctionCallee Callee,const ThunkInfo * Thunk,bool IsUnprototyped)296 void CodeGenFunction::EmitCallAndReturnForThunk(llvm::FunctionCallee Callee,
297                                                 const ThunkInfo *Thunk,
298                                                 bool IsUnprototyped) {
299   assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
300          "Please use a new CGF for this thunk");
301   const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());
302 
303   // Adjust the 'this' pointer if necessary
304   llvm::Value *AdjustedThisPtr =
305     Thunk ? CGM.getCXXABI().performThisAdjustment(
306                           *this, LoadCXXThisAddress(), Thunk->This)
307           : LoadCXXThis();
308 
309   // If perfect forwarding is required a variadic method, a method using
310   // inalloca, or an unprototyped thunk, use musttail. Emit an error if this
311   // thunk requires a return adjustment, since that is impossible with musttail.
312   if (CurFnInfo->usesInAlloca() || CurFnInfo->isVariadic() || IsUnprototyped) {
313     if (Thunk && !Thunk->Return.isEmpty()) {
314       if (IsUnprototyped)
315         CGM.ErrorUnsupported(
316             MD, "return-adjusting thunk with incomplete parameter type");
317       else if (CurFnInfo->isVariadic())
318         llvm_unreachable("shouldn't try to emit musttail return-adjusting "
319                          "thunks for variadic functions");
320       else
321         CGM.ErrorUnsupported(
322             MD, "non-trivial argument copy for return-adjusting thunk");
323     }
324     EmitMustTailThunk(CurGD, AdjustedThisPtr, Callee);
325     return;
326   }
327 
328   // Start building CallArgs.
329   CallArgList CallArgs;
330   QualType ThisType = MD->getThisType();
331   CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
332 
333   if (isa<CXXDestructorDecl>(MD))
334     CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
335 
336 #ifndef NDEBUG
337   unsigned PrefixArgs = CallArgs.size() - 1;
338 #endif
339   // Add the rest of the arguments.
340   for (const ParmVarDecl *PD : MD->parameters())
341     EmitDelegateCallArg(CallArgs, PD, SourceLocation());
342 
343   const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
344 
345 #ifndef NDEBUG
346   const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(
347       CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1), PrefixArgs);
348   assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
349          CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
350          CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
351   assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
352          similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
353                  CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
354   assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
355   for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
356     assert(similar(CallFnInfo.arg_begin()[i].info,
357                    CallFnInfo.arg_begin()[i].type,
358                    CurFnInfo->arg_begin()[i].info,
359                    CurFnInfo->arg_begin()[i].type));
360 #endif
361 
362   // Determine whether we have a return value slot to use.
363   QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)
364                             ? ThisType
365                             : CGM.getCXXABI().hasMostDerivedReturn(CurGD)
366                                   ? CGM.getContext().VoidPtrTy
367                                   : FPT->getReturnType();
368   ReturnValueSlot Slot;
369   if (!ResultType->isVoidType() &&
370       (CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect ||
371        hasAggregateEvaluationKind(ResultType)))
372     Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified(),
373                            /*IsUnused=*/false, /*IsExternallyDestructed=*/true);
374 
375   // Now emit our call.
376   llvm::CallBase *CallOrInvoke;
377   RValue RV = EmitCall(*CurFnInfo, CGCallee::forDirect(Callee, CurGD), Slot,
378                        CallArgs, &CallOrInvoke);
379 
380   // Consider return adjustment if we have ThunkInfo.
381   if (Thunk && !Thunk->Return.isEmpty())
382     RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
383   else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))
384     Call->setTailCallKind(llvm::CallInst::TCK_Tail);
385 
386   // Emit return.
387   if (!ResultType->isVoidType() && Slot.isNull())
388     CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
389 
390   // Disable the final ARC autorelease.
391   AutoreleaseResult = false;
392 
393   FinishThunk();
394 }
395 
EmitMustTailThunk(GlobalDecl GD,llvm::Value * AdjustedThisPtr,llvm::FunctionCallee Callee)396 void CodeGenFunction::EmitMustTailThunk(GlobalDecl GD,
397                                         llvm::Value *AdjustedThisPtr,
398                                         llvm::FunctionCallee Callee) {
399   // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
400   // to translate AST arguments into LLVM IR arguments.  For thunks, we know
401   // that the caller prototype more or less matches the callee prototype with
402   // the exception of 'this'.
403   SmallVector<llvm::Value *, 8> Args(llvm::make_pointer_range(CurFn->args()));
404 
405   // Set the adjusted 'this' pointer.
406   const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
407   if (ThisAI.isDirect()) {
408     const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
409     int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
410     llvm::Type *ThisType = Args[ThisArgNo]->getType();
411     if (ThisType != AdjustedThisPtr->getType())
412       AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
413     Args[ThisArgNo] = AdjustedThisPtr;
414   } else {
415     assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
416     Address ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
417     llvm::Type *ThisType = ThisAddr.getElementType();
418     if (ThisType != AdjustedThisPtr->getType())
419       AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
420     Builder.CreateStore(AdjustedThisPtr, ThisAddr);
421   }
422 
423   // Emit the musttail call manually.  Even if the prologue pushed cleanups, we
424   // don't actually want to run them.
425   llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
426   Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
427 
428   // Apply the standard set of call attributes.
429   unsigned CallingConv;
430   llvm::AttributeList Attrs;
431   CGM.ConstructAttributeList(Callee.getCallee()->getName(), *CurFnInfo, GD,
432                              Attrs, CallingConv, /*AttrOnCallSite=*/true,
433                              /*IsThunk=*/false);
434   Call->setAttributes(Attrs);
435   Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
436 
437   if (Call->getType()->isVoidTy())
438     Builder.CreateRetVoid();
439   else
440     Builder.CreateRet(Call);
441 
442   // Finish the function to maintain CodeGenFunction invariants.
443   // FIXME: Don't emit unreachable code.
444   EmitBlock(createBasicBlock());
445 
446   FinishThunk();
447 }
448 
generateThunk(llvm::Function * Fn,const CGFunctionInfo & FnInfo,GlobalDecl GD,const ThunkInfo & Thunk,bool IsUnprototyped)449 void CodeGenFunction::generateThunk(llvm::Function *Fn,
450                                     const CGFunctionInfo &FnInfo, GlobalDecl GD,
451                                     const ThunkInfo &Thunk,
452                                     bool IsUnprototyped) {
453   StartThunk(Fn, GD, FnInfo, IsUnprototyped);
454   // Create a scope with an artificial location for the body of this function.
455   auto AL = ApplyDebugLocation::CreateArtificial(*this);
456 
457   // Get our callee. Use a placeholder type if this method is unprototyped so
458   // that CodeGenModule doesn't try to set attributes.
459   llvm::Type *Ty;
460   if (IsUnprototyped)
461     Ty = llvm::StructType::get(getLLVMContext());
462   else
463     Ty = CGM.getTypes().GetFunctionType(FnInfo);
464 
465   llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
466 
467   // Fix up the function type for an unprototyped musttail call.
468   if (IsUnprototyped)
469     Callee = llvm::ConstantExpr::getBitCast(Callee, Fn->getType());
470 
471   // Make the call and return the result.
472   EmitCallAndReturnForThunk(llvm::FunctionCallee(Fn->getFunctionType(), Callee),
473                             &Thunk, IsUnprototyped);
474 }
475 
shouldEmitVTableThunk(CodeGenModule & CGM,const CXXMethodDecl * MD,bool IsUnprototyped,bool ForVTable)476 static bool shouldEmitVTableThunk(CodeGenModule &CGM, const CXXMethodDecl *MD,
477                                   bool IsUnprototyped, bool ForVTable) {
478   // Always emit thunks in the MS C++ ABI. We cannot rely on other TUs to
479   // provide thunks for us.
480   if (CGM.getTarget().getCXXABI().isMicrosoft())
481     return true;
482 
483   // In the Itanium C++ ABI, vtable thunks are provided by TUs that provide
484   // definitions of the main method. Therefore, emitting thunks with the vtable
485   // is purely an optimization. Emit the thunk if optimizations are enabled and
486   // all of the parameter types are complete.
487   if (ForVTable)
488     return CGM.getCodeGenOpts().OptimizationLevel && !IsUnprototyped;
489 
490   // Always emit thunks along with the method definition.
491   return true;
492 }
493 
maybeEmitThunk(GlobalDecl GD,const ThunkInfo & TI,bool ForVTable)494 llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,
495                                                const ThunkInfo &TI,
496                                                bool ForVTable) {
497   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
498 
499   // First, get a declaration. Compute the mangled name. Don't worry about
500   // getting the function prototype right, since we may only need this
501   // declaration to fill in a vtable slot.
502   SmallString<256> Name;
503   MangleContext &MCtx = CGM.getCXXABI().getMangleContext();
504   llvm::raw_svector_ostream Out(Name);
505   if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
506     MCtx.mangleCXXDtorThunk(DD, GD.getDtorType(), TI.This, Out);
507   else
508     MCtx.mangleThunk(MD, TI, Out);
509   llvm::Type *ThunkVTableTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
510   llvm::Constant *Thunk = CGM.GetAddrOfThunk(Name, ThunkVTableTy, GD);
511 
512   // If we don't need to emit a definition, return this declaration as is.
513   bool IsUnprototyped = !CGM.getTypes().isFuncTypeConvertible(
514       MD->getType()->castAs<FunctionType>());
515   if (!shouldEmitVTableThunk(CGM, MD, IsUnprototyped, ForVTable))
516     return Thunk;
517 
518   // Arrange a function prototype appropriate for a function definition. In some
519   // cases in the MS ABI, we may need to build an unprototyped musttail thunk.
520   const CGFunctionInfo &FnInfo =
521       IsUnprototyped ? CGM.getTypes().arrangeUnprototypedMustTailThunk(MD)
522                      : CGM.getTypes().arrangeGlobalDeclaration(GD);
523   llvm::FunctionType *ThunkFnTy = CGM.getTypes().GetFunctionType(FnInfo);
524 
525   // If the type of the underlying GlobalValue is wrong, we'll have to replace
526   // it. It should be a declaration.
527   llvm::Function *ThunkFn = cast<llvm::Function>(Thunk->stripPointerCasts());
528   if (ThunkFn->getFunctionType() != ThunkFnTy) {
529     llvm::GlobalValue *OldThunkFn = ThunkFn;
530 
531     assert(OldThunkFn->isDeclaration() && "Shouldn't replace non-declaration");
532 
533     // Remove the name from the old thunk function and get a new thunk.
534     OldThunkFn->setName(StringRef());
535     ThunkFn = llvm::Function::Create(ThunkFnTy, llvm::Function::ExternalLinkage,
536                                      Name.str(), &CGM.getModule());
537     CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn, /*IsThunk=*/false);
538 
539     // If needed, replace the old thunk with a bitcast.
540     if (!OldThunkFn->use_empty()) {
541       llvm::Constant *NewPtrForOldDecl =
542           llvm::ConstantExpr::getBitCast(ThunkFn, OldThunkFn->getType());
543       OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
544     }
545 
546     // Remove the old thunk.
547     OldThunkFn->eraseFromParent();
548   }
549 
550   bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
551   bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
552 
553   if (!ThunkFn->isDeclaration()) {
554     if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
555       // There is already a thunk emitted for this function, do nothing.
556       return ThunkFn;
557     }
558 
559     setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
560     return ThunkFn;
561   }
562 
563   // If this will be unprototyped, add the "thunk" attribute so that LLVM knows
564   // that the return type is meaningless. These thunks can be used to call
565   // functions with differing return types, and the caller is required to cast
566   // the prototype appropriately to extract the correct value.
567   if (IsUnprototyped)
568     ThunkFn->addFnAttr("thunk");
569 
570   CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
571 
572   // Thunks for variadic methods are special because in general variadic
573   // arguments cannot be perfectly forwarded. In the general case, clang
574   // implements such thunks by cloning the original function body. However, for
575   // thunks with no return adjustment on targets that support musttail, we can
576   // use musttail to perfectly forward the variadic arguments.
577   bool ShouldCloneVarArgs = false;
578   if (!IsUnprototyped && ThunkFn->isVarArg()) {
579     ShouldCloneVarArgs = true;
580     if (TI.Return.isEmpty()) {
581       switch (CGM.getTriple().getArch()) {
582       case llvm::Triple::x86_64:
583       case llvm::Triple::x86:
584       case llvm::Triple::aarch64:
585         ShouldCloneVarArgs = false;
586         break;
587       default:
588         break;
589       }
590     }
591   }
592 
593   if (ShouldCloneVarArgs) {
594     if (UseAvailableExternallyLinkage)
595       return ThunkFn;
596     ThunkFn =
597         CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, TI);
598   } else {
599     // Normal thunk body generation.
600     CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, TI, IsUnprototyped);
601   }
602 
603   setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
604   return ThunkFn;
605 }
606 
EmitThunks(GlobalDecl GD)607 void CodeGenVTables::EmitThunks(GlobalDecl GD) {
608   const CXXMethodDecl *MD =
609     cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
610 
611   // We don't need to generate thunks for the base destructor.
612   if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
613     return;
614 
615   const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
616       VTContext->getThunkInfo(GD);
617 
618   if (!ThunkInfoVector)
619     return;
620 
621   for (const ThunkInfo& Thunk : *ThunkInfoVector)
622     maybeEmitThunk(GD, Thunk, /*ForVTable=*/false);
623 }
624 
addRelativeComponent(ConstantArrayBuilder & builder,llvm::Constant * component,unsigned vtableAddressPoint,bool vtableHasLocalLinkage,bool isCompleteDtor) const625 void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,
626                                           llvm::Constant *component,
627                                           unsigned vtableAddressPoint,
628                                           bool vtableHasLocalLinkage,
629                                           bool isCompleteDtor) const {
630   // No need to get the offset of a nullptr.
631   if (component->isNullValue())
632     return builder.add(llvm::ConstantInt::get(CGM.Int32Ty, 0));
633 
634   auto *globalVal =
635       cast<llvm::GlobalValue>(component->stripPointerCastsAndAliases());
636   llvm::Module &module = CGM.getModule();
637 
638   // We don't want to copy the linkage of the vtable exactly because we still
639   // want the stub/proxy to be emitted for properly calculating the offset.
640   // Examples where there would be no symbol emitted are available_externally
641   // and private linkages.
642   auto stubLinkage = vtableHasLocalLinkage ? llvm::GlobalValue::InternalLinkage
643                                            : llvm::GlobalValue::ExternalLinkage;
644 
645   llvm::Constant *target;
646   if (auto *func = dyn_cast<llvm::Function>(globalVal)) {
647     target = llvm::DSOLocalEquivalent::get(func);
648   } else {
649     llvm::SmallString<16> rttiProxyName(globalVal->getName());
650     rttiProxyName.append(".rtti_proxy");
651 
652     // The RTTI component may not always be emitted in the same linkage unit as
653     // the vtable. As a general case, we can make a dso_local proxy to the RTTI
654     // that points to the actual RTTI struct somewhere. This will result in a
655     // GOTPCREL relocation when taking the relative offset to the proxy.
656     llvm::GlobalVariable *proxy = module.getNamedGlobal(rttiProxyName);
657     if (!proxy) {
658       proxy = new llvm::GlobalVariable(module, globalVal->getType(),
659                                        /*isConstant=*/true, stubLinkage,
660                                        globalVal, rttiProxyName);
661       proxy->setDSOLocal(true);
662       proxy->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
663       if (!proxy->hasLocalLinkage()) {
664         proxy->setVisibility(llvm::GlobalValue::HiddenVisibility);
665         proxy->setComdat(module.getOrInsertComdat(rttiProxyName));
666       }
667       // Do not instrument the rtti proxies with hwasan to avoid a duplicate
668       // symbol error. Aliases generated by hwasan will retain the same namebut
669       // the addresses they are set to may have different tags from different
670       // compilation units. We don't run into this without hwasan because the
671       // proxies are in comdat groups, but those aren't propagated to the alias.
672       RemoveHwasanMetadata(proxy);
673     }
674     target = proxy;
675   }
676 
677   builder.addRelativeOffsetToPosition(CGM.Int32Ty, target,
678                                       /*position=*/vtableAddressPoint);
679 }
680 
UseRelativeLayout(const CodeGenModule & CGM)681 static bool UseRelativeLayout(const CodeGenModule &CGM) {
682   return CGM.getTarget().getCXXABI().isItaniumFamily() &&
683          CGM.getItaniumVTableContext().isRelativeLayout();
684 }
685 
useRelativeLayout() const686 bool CodeGenVTables::useRelativeLayout() const {
687   return UseRelativeLayout(CGM);
688 }
689 
getVTableComponentType() const690 llvm::Type *CodeGenModule::getVTableComponentType() const {
691   if (UseRelativeLayout(*this))
692     return Int32Ty;
693   return Int8PtrTy;
694 }
695 
getVTableComponentType() const696 llvm::Type *CodeGenVTables::getVTableComponentType() const {
697   return CGM.getVTableComponentType();
698 }
699 
AddPointerLayoutOffset(const CodeGenModule & CGM,ConstantArrayBuilder & builder,CharUnits offset)700 static void AddPointerLayoutOffset(const CodeGenModule &CGM,
701                                    ConstantArrayBuilder &builder,
702                                    CharUnits offset) {
703   builder.add(llvm::ConstantExpr::getIntToPtr(
704       llvm::ConstantInt::get(CGM.PtrDiffTy, offset.getQuantity()),
705       CGM.Int8PtrTy));
706 }
707 
AddRelativeLayoutOffset(const CodeGenModule & CGM,ConstantArrayBuilder & builder,CharUnits offset)708 static void AddRelativeLayoutOffset(const CodeGenModule &CGM,
709                                     ConstantArrayBuilder &builder,
710                                     CharUnits offset) {
711   builder.add(llvm::ConstantInt::get(CGM.Int32Ty, offset.getQuantity()));
712 }
713 
addVTableComponent(ConstantArrayBuilder & builder,const VTableLayout & layout,unsigned componentIndex,llvm::Constant * rtti,unsigned & nextVTableThunkIndex,unsigned vtableAddressPoint,bool vtableHasLocalLinkage)714 void CodeGenVTables::addVTableComponent(ConstantArrayBuilder &builder,
715                                         const VTableLayout &layout,
716                                         unsigned componentIndex,
717                                         llvm::Constant *rtti,
718                                         unsigned &nextVTableThunkIndex,
719                                         unsigned vtableAddressPoint,
720                                         bool vtableHasLocalLinkage) {
721   auto &component = layout.vtable_components()[componentIndex];
722 
723   auto addOffsetConstant =
724       useRelativeLayout() ? AddRelativeLayoutOffset : AddPointerLayoutOffset;
725 
726   switch (component.getKind()) {
727   case VTableComponent::CK_VCallOffset:
728     return addOffsetConstant(CGM, builder, component.getVCallOffset());
729 
730   case VTableComponent::CK_VBaseOffset:
731     return addOffsetConstant(CGM, builder, component.getVBaseOffset());
732 
733   case VTableComponent::CK_OffsetToTop:
734     return addOffsetConstant(CGM, builder, component.getOffsetToTop());
735 
736   case VTableComponent::CK_RTTI:
737     if (useRelativeLayout())
738       return addRelativeComponent(builder, rtti, vtableAddressPoint,
739                                   vtableHasLocalLinkage,
740                                   /*isCompleteDtor=*/false);
741     else
742       return builder.add(llvm::ConstantExpr::getBitCast(rtti, CGM.Int8PtrTy));
743 
744   case VTableComponent::CK_FunctionPointer:
745   case VTableComponent::CK_CompleteDtorPointer:
746   case VTableComponent::CK_DeletingDtorPointer: {
747     GlobalDecl GD = component.getGlobalDecl();
748 
749     if (CGM.getLangOpts().CUDA) {
750       // Emit NULL for methods we can't codegen on this
751       // side. Otherwise we'd end up with vtable with unresolved
752       // references.
753       const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
754       // OK on device side: functions w/ __device__ attribute
755       // OK on host side: anything except __device__-only functions.
756       bool CanEmitMethod =
757           CGM.getLangOpts().CUDAIsDevice
758               ? MD->hasAttr<CUDADeviceAttr>()
759               : (MD->hasAttr<CUDAHostAttr>() || !MD->hasAttr<CUDADeviceAttr>());
760       if (!CanEmitMethod)
761         return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int8PtrTy));
762       // Method is acceptable, continue processing as usual.
763     }
764 
765     auto getSpecialVirtualFn = [&](StringRef name) -> llvm::Constant * {
766       // FIXME(PR43094): When merging comdat groups, lld can select a local
767       // symbol as the signature symbol even though it cannot be accessed
768       // outside that symbol's TU. The relative vtables ABI would make
769       // __cxa_pure_virtual and __cxa_deleted_virtual local symbols, and
770       // depending on link order, the comdat groups could resolve to the one
771       // with the local symbol. As a temporary solution, fill these components
772       // with zero. We shouldn't be calling these in the first place anyway.
773       if (useRelativeLayout())
774         return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
775 
776       // For NVPTX devices in OpenMP emit special functon as null pointers,
777       // otherwise linking ends up with unresolved references.
778       if (CGM.getLangOpts().OpenMP && CGM.getLangOpts().OpenMPIsDevice &&
779           CGM.getTriple().isNVPTX())
780         return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
781       llvm::FunctionType *fnTy =
782           llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
783       llvm::Constant *fn = cast<llvm::Constant>(
784           CGM.CreateRuntimeFunction(fnTy, name).getCallee());
785       if (auto f = dyn_cast<llvm::Function>(fn))
786         f->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
787       return llvm::ConstantExpr::getBitCast(fn, CGM.Int8PtrTy);
788     };
789 
790     llvm::Constant *fnPtr;
791 
792     // Pure virtual member functions.
793     if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
794       if (!PureVirtualFn)
795         PureVirtualFn =
796             getSpecialVirtualFn(CGM.getCXXABI().GetPureVirtualCallName());
797       fnPtr = PureVirtualFn;
798 
799     // Deleted virtual member functions.
800     } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
801       if (!DeletedVirtualFn)
802         DeletedVirtualFn =
803             getSpecialVirtualFn(CGM.getCXXABI().GetDeletedVirtualCallName());
804       fnPtr = DeletedVirtualFn;
805 
806     // Thunks.
807     } else if (nextVTableThunkIndex < layout.vtable_thunks().size() &&
808                layout.vtable_thunks()[nextVTableThunkIndex].first ==
809                    componentIndex) {
810       auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
811 
812       nextVTableThunkIndex++;
813       fnPtr = maybeEmitThunk(GD, thunkInfo, /*ForVTable=*/true);
814 
815     // Otherwise we can use the method definition directly.
816     } else {
817       llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
818       fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);
819     }
820 
821     if (useRelativeLayout()) {
822       return addRelativeComponent(
823           builder, fnPtr, vtableAddressPoint, vtableHasLocalLinkage,
824           component.getKind() == VTableComponent::CK_CompleteDtorPointer);
825     } else
826       return builder.add(llvm::ConstantExpr::getBitCast(fnPtr, CGM.Int8PtrTy));
827   }
828 
829   case VTableComponent::CK_UnusedFunctionPointer:
830     if (useRelativeLayout())
831       return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int32Ty));
832     else
833       return builder.addNullPointer(CGM.Int8PtrTy);
834   }
835 
836   llvm_unreachable("Unexpected vtable component kind");
837 }
838 
getVTableType(const VTableLayout & layout)839 llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {
840   SmallVector<llvm::Type *, 4> tys;
841   llvm::Type *componentType = getVTableComponentType();
842   for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i)
843     tys.push_back(llvm::ArrayType::get(componentType, layout.getVTableSize(i)));
844 
845   return llvm::StructType::get(CGM.getLLVMContext(), tys);
846 }
847 
createVTableInitializer(ConstantStructBuilder & builder,const VTableLayout & layout,llvm::Constant * rtti,bool vtableHasLocalLinkage)848 void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,
849                                              const VTableLayout &layout,
850                                              llvm::Constant *rtti,
851                                              bool vtableHasLocalLinkage) {
852   llvm::Type *componentType = getVTableComponentType();
853 
854   const auto &addressPoints = layout.getAddressPointIndices();
855   unsigned nextVTableThunkIndex = 0;
856   for (unsigned vtableIndex = 0, endIndex = layout.getNumVTables();
857        vtableIndex != endIndex; ++vtableIndex) {
858     auto vtableElem = builder.beginArray(componentType);
859 
860     size_t vtableStart = layout.getVTableOffset(vtableIndex);
861     size_t vtableEnd = vtableStart + layout.getVTableSize(vtableIndex);
862     for (size_t componentIndex = vtableStart; componentIndex < vtableEnd;
863          ++componentIndex) {
864       addVTableComponent(vtableElem, layout, componentIndex, rtti,
865                          nextVTableThunkIndex, addressPoints[vtableIndex],
866                          vtableHasLocalLinkage);
867     }
868     vtableElem.finishAndAddTo(builder);
869   }
870 }
871 
GenerateConstructionVTable(const CXXRecordDecl * RD,const BaseSubobject & Base,bool BaseIsVirtual,llvm::GlobalVariable::LinkageTypes Linkage,VTableAddressPointsMapTy & AddressPoints)872 llvm::GlobalVariable *CodeGenVTables::GenerateConstructionVTable(
873     const CXXRecordDecl *RD, const BaseSubobject &Base, bool BaseIsVirtual,
874     llvm::GlobalVariable::LinkageTypes Linkage,
875     VTableAddressPointsMapTy &AddressPoints) {
876   if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
877     DI->completeClassData(Base.getBase());
878 
879   std::unique_ptr<VTableLayout> VTLayout(
880       getItaniumVTableContext().createConstructionVTableLayout(
881           Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
882 
883   // Add the address points.
884   AddressPoints = VTLayout->getAddressPoints();
885 
886   // Get the mangled construction vtable name.
887   SmallString<256> OutName;
888   llvm::raw_svector_ostream Out(OutName);
889   cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
890       .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
891                            Base.getBase(), Out);
892   SmallString<256> Name(OutName);
893 
894   bool UsingRelativeLayout = getItaniumVTableContext().isRelativeLayout();
895   bool VTableAliasExists =
896       UsingRelativeLayout && CGM.getModule().getNamedAlias(Name);
897   if (VTableAliasExists) {
898     // We previously made the vtable hidden and changed its name.
899     Name.append(".local");
900   }
901 
902   llvm::Type *VTType = getVTableType(*VTLayout);
903 
904   // Construction vtable symbols are not part of the Itanium ABI, so we cannot
905   // guarantee that they actually will be available externally. Instead, when
906   // emitting an available_externally VTT, we provide references to an internal
907   // linkage construction vtable. The ABI only requires complete-object vtables
908   // to be the same for all instances of a type, not construction vtables.
909   if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
910     Linkage = llvm::GlobalVariable::InternalLinkage;
911 
912   llvm::Align Align = CGM.getDataLayout().getABITypeAlign(VTType);
913 
914   // Create the variable that will hold the construction vtable.
915   llvm::GlobalVariable *VTable =
916       CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage, Align);
917 
918   // V-tables are always unnamed_addr.
919   VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
920 
921   llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
922       CGM.getContext().getTagDeclType(Base.getBase()));
923 
924   // Create and set the initializer.
925   ConstantInitBuilder builder(CGM);
926   auto components = builder.beginStruct();
927   createVTableInitializer(components, *VTLayout, RTTI,
928                           VTable->hasLocalLinkage());
929   components.finishAndSetAsInitializer(VTable);
930 
931   // Set properties only after the initializer has been set to ensure that the
932   // GV is treated as definition and not declaration.
933   assert(!VTable->isDeclaration() && "Shouldn't set properties on declaration");
934   CGM.setGVProperties(VTable, RD);
935 
936   CGM.EmitVTableTypeMetadata(RD, VTable, *VTLayout.get());
937 
938   if (UsingRelativeLayout) {
939     RemoveHwasanMetadata(VTable);
940     if (!VTable->isDSOLocal())
941       GenerateRelativeVTableAlias(VTable, OutName);
942   }
943 
944   return VTable;
945 }
946 
947 // Ensure this vtable is not instrumented by hwasan. That is, a global alias is
948 // not generated for it. This is mainly used by the relative-vtables ABI where
949 // vtables instead contain 32-bit offsets between the vtable and function
950 // pointers. Hwasan is disabled for these vtables for now because the tag in a
951 // vtable pointer may fail the overflow check when resolving 32-bit PLT
952 // relocations. A future alternative for this would be finding which usages of
953 // the vtable can continue to use the untagged hwasan value without any loss of
954 // value in hwasan.
RemoveHwasanMetadata(llvm::GlobalValue * GV) const955 void CodeGenVTables::RemoveHwasanMetadata(llvm::GlobalValue *GV) const {
956   if (CGM.getLangOpts().Sanitize.has(SanitizerKind::HWAddress)) {
957     llvm::GlobalValue::SanitizerMetadata Meta;
958     if (GV->hasSanitizerMetadata())
959       Meta = GV->getSanitizerMetadata();
960     Meta.NoHWAddress = true;
961     GV->setSanitizerMetadata(Meta);
962   }
963 }
964 
965 // If the VTable is not dso_local, then we will not be able to indicate that
966 // the VTable does not need a relocation and move into rodata. A frequent
967 // time this can occur is for classes that should be made public from a DSO
968 // (like in libc++). For cases like these, we can make the vtable hidden or
969 // private and create a public alias with the same visibility and linkage as
970 // the original vtable type.
GenerateRelativeVTableAlias(llvm::GlobalVariable * VTable,llvm::StringRef AliasNameRef)971 void CodeGenVTables::GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
972                                                  llvm::StringRef AliasNameRef) {
973   assert(getItaniumVTableContext().isRelativeLayout() &&
974          "Can only use this if the relative vtable ABI is used");
975   assert(!VTable->isDSOLocal() && "This should be called only if the vtable is "
976                                   "not guaranteed to be dso_local");
977 
978   // If the vtable is available_externally, we shouldn't (or need to) generate
979   // an alias for it in the first place since the vtable won't actually by
980   // emitted in this compilation unit.
981   if (VTable->hasAvailableExternallyLinkage())
982     return;
983 
984   // Create a new string in the event the alias is already the name of the
985   // vtable. Using the reference directly could lead to use of an inititialized
986   // value in the module's StringMap.
987   llvm::SmallString<256> AliasName(AliasNameRef);
988   VTable->setName(AliasName + ".local");
989 
990   auto Linkage = VTable->getLinkage();
991   assert(llvm::GlobalAlias::isValidLinkage(Linkage) &&
992          "Invalid vtable alias linkage");
993 
994   llvm::GlobalAlias *VTableAlias = CGM.getModule().getNamedAlias(AliasName);
995   if (!VTableAlias) {
996     VTableAlias = llvm::GlobalAlias::create(VTable->getValueType(),
997                                             VTable->getAddressSpace(), Linkage,
998                                             AliasName, &CGM.getModule());
999   } else {
1000     assert(VTableAlias->getValueType() == VTable->getValueType());
1001     assert(VTableAlias->getLinkage() == Linkage);
1002   }
1003   VTableAlias->setVisibility(VTable->getVisibility());
1004   VTableAlias->setUnnamedAddr(VTable->getUnnamedAddr());
1005 
1006   // Both of these imply dso_local for the vtable.
1007   if (!VTable->hasComdat()) {
1008     // If this is in a comdat, then we shouldn't make the linkage private due to
1009     // an issue in lld where private symbols can be used as the key symbol when
1010     // choosing the prevelant group. This leads to "relocation refers to a
1011     // symbol in a discarded section".
1012     VTable->setLinkage(llvm::GlobalValue::PrivateLinkage);
1013   } else {
1014     // We should at least make this hidden since we don't want to expose it.
1015     VTable->setVisibility(llvm::GlobalValue::HiddenVisibility);
1016   }
1017 
1018   VTableAlias->setAliasee(VTable);
1019 }
1020 
shouldEmitAvailableExternallyVTable(const CodeGenModule & CGM,const CXXRecordDecl * RD)1021 static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,
1022                                                 const CXXRecordDecl *RD) {
1023   return CGM.getCodeGenOpts().OptimizationLevel > 0 &&
1024          CGM.getCXXABI().canSpeculativelyEmitVTable(RD);
1025 }
1026 
1027 /// Compute the required linkage of the vtable for the given class.
1028 ///
1029 /// Note that we only call this at the end of the translation unit.
1030 llvm::GlobalVariable::LinkageTypes
getVTableLinkage(const CXXRecordDecl * RD)1031 CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
1032   if (!RD->isExternallyVisible())
1033     return llvm::GlobalVariable::InternalLinkage;
1034 
1035   // We're at the end of the translation unit, so the current key
1036   // function is fully correct.
1037   const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
1038   if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
1039     // If this class has a key function, use that to determine the
1040     // linkage of the vtable.
1041     const FunctionDecl *def = nullptr;
1042     if (keyFunction->hasBody(def))
1043       keyFunction = cast<CXXMethodDecl>(def);
1044 
1045     switch (keyFunction->getTemplateSpecializationKind()) {
1046       case TSK_Undeclared:
1047       case TSK_ExplicitSpecialization:
1048         assert((def || CodeGenOpts.OptimizationLevel > 0 ||
1049                 CodeGenOpts.getDebugInfo() != codegenoptions::NoDebugInfo) &&
1050                "Shouldn't query vtable linkage without key function, "
1051                "optimizations, or debug info");
1052         if (!def && CodeGenOpts.OptimizationLevel > 0)
1053           return llvm::GlobalVariable::AvailableExternallyLinkage;
1054 
1055         if (keyFunction->isInlined())
1056           return !Context.getLangOpts().AppleKext ?
1057                    llvm::GlobalVariable::LinkOnceODRLinkage :
1058                    llvm::Function::InternalLinkage;
1059 
1060         return llvm::GlobalVariable::ExternalLinkage;
1061 
1062       case TSK_ImplicitInstantiation:
1063         return !Context.getLangOpts().AppleKext ?
1064                  llvm::GlobalVariable::LinkOnceODRLinkage :
1065                  llvm::Function::InternalLinkage;
1066 
1067       case TSK_ExplicitInstantiationDefinition:
1068         return !Context.getLangOpts().AppleKext ?
1069                  llvm::GlobalVariable::WeakODRLinkage :
1070                  llvm::Function::InternalLinkage;
1071 
1072       case TSK_ExplicitInstantiationDeclaration:
1073         llvm_unreachable("Should not have been asked to emit this");
1074     }
1075   }
1076 
1077   // -fapple-kext mode does not support weak linkage, so we must use
1078   // internal linkage.
1079   if (Context.getLangOpts().AppleKext)
1080     return llvm::Function::InternalLinkage;
1081 
1082   llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
1083       llvm::GlobalValue::LinkOnceODRLinkage;
1084   llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
1085       llvm::GlobalValue::WeakODRLinkage;
1086   if (RD->hasAttr<DLLExportAttr>()) {
1087     // Cannot discard exported vtables.
1088     DiscardableODRLinkage = NonDiscardableODRLinkage;
1089   } else if (RD->hasAttr<DLLImportAttr>()) {
1090     // Imported vtables are available externally.
1091     DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1092     NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1093   }
1094 
1095   switch (RD->getTemplateSpecializationKind()) {
1096     case TSK_Undeclared:
1097     case TSK_ExplicitSpecialization:
1098     case TSK_ImplicitInstantiation:
1099       return DiscardableODRLinkage;
1100 
1101     case TSK_ExplicitInstantiationDeclaration:
1102       // Explicit instantiations in MSVC do not provide vtables, so we must emit
1103       // our own.
1104       if (getTarget().getCXXABI().isMicrosoft())
1105         return DiscardableODRLinkage;
1106       return shouldEmitAvailableExternallyVTable(*this, RD)
1107                  ? llvm::GlobalVariable::AvailableExternallyLinkage
1108                  : llvm::GlobalVariable::ExternalLinkage;
1109 
1110     case TSK_ExplicitInstantiationDefinition:
1111       return NonDiscardableODRLinkage;
1112   }
1113 
1114   llvm_unreachable("Invalid TemplateSpecializationKind!");
1115 }
1116 
1117 /// This is a callback from Sema to tell us that a particular vtable is
1118 /// required to be emitted in this translation unit.
1119 ///
1120 /// This is only called for vtables that _must_ be emitted (mainly due to key
1121 /// functions).  For weak vtables, CodeGen tracks when they are needed and
1122 /// emits them as-needed.
EmitVTable(CXXRecordDecl * theClass)1123 void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
1124   VTables.GenerateClassData(theClass);
1125 }
1126 
1127 void
GenerateClassData(const CXXRecordDecl * RD)1128 CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
1129   if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
1130     DI->completeClassData(RD);
1131 
1132   if (RD->getNumVBases())
1133     CGM.getCXXABI().emitVirtualInheritanceTables(RD);
1134 
1135   CGM.getCXXABI().emitVTableDefinitions(*this, RD);
1136 }
1137 
1138 /// At this point in the translation unit, does it appear that can we
1139 /// rely on the vtable being defined elsewhere in the program?
1140 ///
1141 /// The response is really only definitive when called at the end of
1142 /// the translation unit.
1143 ///
1144 /// The only semantic restriction here is that the object file should
1145 /// not contain a vtable definition when that vtable is defined
1146 /// strongly elsewhere.  Otherwise, we'd just like to avoid emitting
1147 /// vtables when unnecessary.
isVTableExternal(const CXXRecordDecl * RD)1148 bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
1149   assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
1150 
1151   // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
1152   // emit them even if there is an explicit template instantiation.
1153   if (CGM.getTarget().getCXXABI().isMicrosoft())
1154     return false;
1155 
1156   // If we have an explicit instantiation declaration (and not a
1157   // definition), the vtable is defined elsewhere.
1158   TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
1159   if (TSK == TSK_ExplicitInstantiationDeclaration)
1160     return true;
1161 
1162   // Otherwise, if the class is an instantiated template, the
1163   // vtable must be defined here.
1164   if (TSK == TSK_ImplicitInstantiation ||
1165       TSK == TSK_ExplicitInstantiationDefinition)
1166     return false;
1167 
1168   // Otherwise, if the class doesn't have a key function (possibly
1169   // anymore), the vtable must be defined here.
1170   const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
1171   if (!keyFunction)
1172     return false;
1173 
1174   // Otherwise, if we don't have a definition of the key function, the
1175   // vtable must be defined somewhere else.
1176   return !keyFunction->hasBody();
1177 }
1178 
1179 /// Given that we're currently at the end of the translation unit, and
1180 /// we've emitted a reference to the vtable for this class, should
1181 /// we define that vtable?
shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule & CGM,const CXXRecordDecl * RD)1182 static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
1183                                                    const CXXRecordDecl *RD) {
1184   // If vtable is internal then it has to be done.
1185   if (!CGM.getVTables().isVTableExternal(RD))
1186     return true;
1187 
1188   // If it's external then maybe we will need it as available_externally.
1189   return shouldEmitAvailableExternallyVTable(CGM, RD);
1190 }
1191 
1192 /// Given that at some point we emitted a reference to one or more
1193 /// vtables, and that we are now at the end of the translation unit,
1194 /// decide whether we should emit them.
EmitDeferredVTables()1195 void CodeGenModule::EmitDeferredVTables() {
1196 #ifndef NDEBUG
1197   // Remember the size of DeferredVTables, because we're going to assume
1198   // that this entire operation doesn't modify it.
1199   size_t savedSize = DeferredVTables.size();
1200 #endif
1201 
1202   for (const CXXRecordDecl *RD : DeferredVTables)
1203     if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
1204       VTables.GenerateClassData(RD);
1205     else if (shouldOpportunisticallyEmitVTables())
1206       OpportunisticVTables.push_back(RD);
1207 
1208   assert(savedSize == DeferredVTables.size() &&
1209          "deferred extra vtables during vtable emission?");
1210   DeferredVTables.clear();
1211 }
1212 
AlwaysHasLTOVisibilityPublic(const CXXRecordDecl * RD)1213 bool CodeGenModule::AlwaysHasLTOVisibilityPublic(const CXXRecordDecl *RD) {
1214   if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
1215     return true;
1216 
1217   if (!getCodeGenOpts().LTOVisibilityPublicStd)
1218     return false;
1219 
1220   const DeclContext *DC = RD;
1221   while (true) {
1222     auto *D = cast<Decl>(DC);
1223     DC = DC->getParent();
1224     if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
1225       if (auto *ND = dyn_cast<NamespaceDecl>(D))
1226         if (const IdentifierInfo *II = ND->getIdentifier())
1227           if (II->isStr("std") || II->isStr("stdext"))
1228             return true;
1229       break;
1230     }
1231   }
1232 
1233   return false;
1234 }
1235 
HasHiddenLTOVisibility(const CXXRecordDecl * RD)1236 bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
1237   LinkageInfo LV = RD->getLinkageAndVisibility();
1238   if (!isExternallyVisible(LV.getLinkage()))
1239     return true;
1240 
1241   if (getTriple().isOSBinFormatCOFF()) {
1242     if (RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
1243       return false;
1244   } else {
1245     if (LV.getVisibility() != HiddenVisibility)
1246       return false;
1247   }
1248 
1249   return !AlwaysHasLTOVisibilityPublic(RD);
1250 }
1251 
GetVCallVisibilityLevel(const CXXRecordDecl * RD,llvm::DenseSet<const CXXRecordDecl * > & Visited)1252 llvm::GlobalObject::VCallVisibility CodeGenModule::GetVCallVisibilityLevel(
1253     const CXXRecordDecl *RD, llvm::DenseSet<const CXXRecordDecl *> &Visited) {
1254   // If we have already visited this RD (which means this is a recursive call
1255   // since the initial call should have an empty Visited set), return the max
1256   // visibility. The recursive calls below compute the min between the result
1257   // of the recursive call and the current TypeVis, so returning the max here
1258   // ensures that it will have no effect on the current TypeVis.
1259   if (!Visited.insert(RD).second)
1260     return llvm::GlobalObject::VCallVisibilityTranslationUnit;
1261 
1262   LinkageInfo LV = RD->getLinkageAndVisibility();
1263   llvm::GlobalObject::VCallVisibility TypeVis;
1264   if (!isExternallyVisible(LV.getLinkage()))
1265     TypeVis = llvm::GlobalObject::VCallVisibilityTranslationUnit;
1266   else if (HasHiddenLTOVisibility(RD))
1267     TypeVis = llvm::GlobalObject::VCallVisibilityLinkageUnit;
1268   else
1269     TypeVis = llvm::GlobalObject::VCallVisibilityPublic;
1270 
1271   for (auto B : RD->bases())
1272     if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1273       TypeVis = std::min(
1274           TypeVis,
1275           GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
1276 
1277   for (auto B : RD->vbases())
1278     if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1279       TypeVis = std::min(
1280           TypeVis,
1281           GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
1282 
1283   return TypeVis;
1284 }
1285 
EmitVTableTypeMetadata(const CXXRecordDecl * RD,llvm::GlobalVariable * VTable,const VTableLayout & VTLayout)1286 void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
1287                                            llvm::GlobalVariable *VTable,
1288                                            const VTableLayout &VTLayout) {
1289   if (!getCodeGenOpts().LTOUnit)
1290     return;
1291 
1292   CharUnits ComponentWidth = GetTargetTypeStoreSize(getVTableComponentType());
1293 
1294   typedef std::pair<const CXXRecordDecl *, unsigned> AddressPoint;
1295   std::vector<AddressPoint> AddressPoints;
1296   for (auto &&AP : VTLayout.getAddressPoints())
1297     AddressPoints.push_back(std::make_pair(
1298         AP.first.getBase(), VTLayout.getVTableOffset(AP.second.VTableIndex) +
1299                                 AP.second.AddressPointIndex));
1300 
1301   // Sort the address points for determinism.
1302   llvm::sort(AddressPoints, [this](const AddressPoint &AP1,
1303                                    const AddressPoint &AP2) {
1304     if (&AP1 == &AP2)
1305       return false;
1306 
1307     std::string S1;
1308     llvm::raw_string_ostream O1(S1);
1309     getCXXABI().getMangleContext().mangleTypeName(
1310         QualType(AP1.first->getTypeForDecl(), 0), O1);
1311     O1.flush();
1312 
1313     std::string S2;
1314     llvm::raw_string_ostream O2(S2);
1315     getCXXABI().getMangleContext().mangleTypeName(
1316         QualType(AP2.first->getTypeForDecl(), 0), O2);
1317     O2.flush();
1318 
1319     if (S1 < S2)
1320       return true;
1321     if (S1 != S2)
1322       return false;
1323 
1324     return AP1.second < AP2.second;
1325   });
1326 
1327   ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
1328   for (auto AP : AddressPoints) {
1329     // Create type metadata for the address point.
1330     AddVTableTypeMetadata(VTable, ComponentWidth * AP.second, AP.first);
1331 
1332     // The class associated with each address point could also potentially be
1333     // used for indirect calls via a member function pointer, so we need to
1334     // annotate the address of each function pointer with the appropriate member
1335     // function pointer type.
1336     for (unsigned I = 0; I != Comps.size(); ++I) {
1337       if (Comps[I].getKind() != VTableComponent::CK_FunctionPointer)
1338         continue;
1339       llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
1340           Context.getMemberPointerType(
1341               Comps[I].getFunctionDecl()->getType(),
1342               Context.getRecordType(AP.first).getTypePtr()));
1343       VTable->addTypeMetadata((ComponentWidth * I).getQuantity(), MD);
1344     }
1345   }
1346 
1347   if (getCodeGenOpts().VirtualFunctionElimination ||
1348       getCodeGenOpts().WholeProgramVTables) {
1349     llvm::DenseSet<const CXXRecordDecl *> Visited;
1350     llvm::GlobalObject::VCallVisibility TypeVis =
1351         GetVCallVisibilityLevel(RD, Visited);
1352     if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
1353       VTable->setVCallVisibilityMetadata(TypeVis);
1354   }
1355 }
1356