1//===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===//
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.
10//
11//===----------------------------------------------------------------------===//
12
13// We might split this into multiple files if it gets too unwieldy
14
15#include "CGCXXABI.h"
16#include "CodeGenFunction.h"
17#include "CodeGenModule.h"
18#include "clang/AST/ASTContext.h"
19#include "clang/AST/Attr.h"
20#include "clang/AST/Decl.h"
21#include "clang/AST/DeclCXX.h"
22#include "clang/AST/DeclObjC.h"
23#include "clang/AST/Mangle.h"
24#include "clang/AST/RecordLayout.h"
25#include "clang/Basic/CodeGenOptions.h"
26using namespace clang;
27using namespace CodeGen;
28
29
30/// Try to emit a base destructor as an alias to its primary
31/// base-class destructor.
32bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
33 if (!getCodeGenOpts().CXXCtorDtorAliases)
34 return true;
35
36 // Producing an alias to a base class ctor/dtor can degrade debug quality
37 // as the debugger cannot tell them apart.
38 if (getCodeGenOpts().OptimizationLevel == 0)
39 return true;
40
41 // Disable this optimization for ARM64EC. FIXME: This probably should work,
42 // but getting the symbol table correct is complicated.
43 if (getTarget().getTriple().isWindowsArm64EC())
44 return true;
45
46 // If sanitizing memory to check for use-after-dtor, do not emit as
47 // an alias, unless this class owns no members.
48 if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&
49 !D->getParent()->field_empty())
50 return true;
51
52 // If the destructor doesn't have a trivial body, we have to emit it
53 // separately.
54 if (!D->hasTrivialBody())
55 return true;
56
57 const CXXRecordDecl *Class = D->getParent();
58
59 // We are going to instrument this destructor, so give up even if it is
60 // currently empty.
61 if (Class->mayInsertExtraPadding())
62 return true;
63
64 // If we need to manipulate a VTT parameter, give up.
65 if (Class->getNumVBases()) {
66 // Extra Credit: passing extra parameters is perfectly safe
67 // in many calling conventions, so only bail out if the ctor's
68 // calling convention is nonstandard.
69 return true;
70 }
71
72 // If any field has a non-trivial destructor, we have to emit the
73 // destructor separately.
74 for (const auto *I : Class->fields())
75 if (I->getType().isDestructedType())
76 return true;
77
78 // Try to find a unique base class with a non-trivial destructor.
79 const CXXRecordDecl *UniqueBase = nullptr;
80 for (const auto &I : Class->bases()) {
81
82 // We're in the base destructor, so skip virtual bases.
83 if (I.isVirtual()) continue;
84
85 // Skip base classes with trivial destructors.
86 const auto *Base =
87 cast<CXXRecordDecl>(Val: I.getType()->castAs<RecordType>()->getDecl());
88 if (Base->hasTrivialDestructor()) continue;
89
90 // If we've already found a base class with a non-trivial
91 // destructor, give up.
92 if (UniqueBase) return true;
93 UniqueBase = Base;
94 }
95
96 // If we didn't find any bases with a non-trivial destructor, then
97 // the base destructor is actually effectively trivial, which can
98 // happen if it was needlessly user-defined or if there are virtual
99 // bases with non-trivial destructors.
100 if (!UniqueBase)
101 return true;
102
103 // If the base is at a non-zero offset, give up.
104 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(D: Class);
105 if (!ClassLayout.getBaseClassOffset(Base: UniqueBase).isZero())
106 return true;
107
108 // Give up if the calling conventions don't match. We could update the call,
109 // but it is probably not worth it.
110 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
111 if (BaseD->getType()->castAs<FunctionType>()->getCallConv() !=
112 D->getType()->castAs<FunctionType>()->getCallConv())
113 return true;
114
115 GlobalDecl AliasDecl(D, Dtor_Base);
116 GlobalDecl TargetDecl(BaseD, Dtor_Base);
117
118 // The alias will use the linkage of the referent. If we can't
119 // support aliases with that linkage, fail.
120 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(GD: AliasDecl);
121
122 // We can't use an alias if the linkage is not valid for one.
123 if (!llvm::GlobalAlias::isValidLinkage(L: Linkage))
124 return true;
125
126 llvm::GlobalValue::LinkageTypes TargetLinkage =
127 getFunctionLinkage(GD: TargetDecl);
128
129 // Check if we have it already.
130 StringRef MangledName = getMangledName(GD: AliasDecl);
131 llvm::GlobalValue *Entry = GetGlobalValue(Ref: MangledName);
132 if (Entry && !Entry->isDeclaration())
133 return false;
134 if (Replacements.count(Key: MangledName))
135 return false;
136
137 llvm::Type *AliasValueType = getTypes().GetFunctionType(GD: AliasDecl);
138
139 // Find the referent.
140 auto *Aliasee = cast<llvm::GlobalValue>(Val: GetAddrOfGlobal(GD: TargetDecl));
141
142 // Instead of creating as alias to a linkonce_odr, replace all of the uses
143 // of the aliasee.
144 if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
145 !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&
146 TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
147 // FIXME: An extern template instantiation will create functions with
148 // linkage "AvailableExternally". In libc++, some classes also define
149 // members with attribute "AlwaysInline" and expect no reference to
150 // be generated. It is desirable to reenable this optimisation after
151 // corresponding LLVM changes.
152 addReplacement(Name: MangledName, C: Aliasee);
153 return false;
154 }
155
156 // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
157 // template instantiation or a dllexported class, avoid forming it on COFF.
158 // A COFF weak external alias cannot satisfy a normal undefined symbol
159 // reference from another TU. The other TU must also mark the referenced
160 // symbol as weak, which we cannot rely on.
161 if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
162 getTriple().isOSBinFormatCOFF()) {
163 return true;
164 }
165
166 // If we don't have a definition for the destructor yet or the definition is
167 // avaialable_externally, don't emit an alias. We can't emit aliases to
168 // declarations; that's just not how aliases work.
169 if (Aliasee->isDeclarationForLinker())
170 return true;
171
172 // Don't create an alias to a linker weak symbol. This avoids producing
173 // different COMDATs in different TUs. Another option would be to
174 // output the alias both for weak_odr and linkonce_odr, but that
175 // requires explicit comdat support in the IL.
176 if (llvm::GlobalValue::isWeakForLinker(Linkage: TargetLinkage))
177 return true;
178
179 // Create the alias with no name.
180 auto *Alias = llvm::GlobalAlias::create(Ty: AliasValueType, AddressSpace: 0, Linkage, Name: "",
181 Aliasee, Parent: &getModule());
182
183 // Destructors are always unnamed_addr.
184 Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
185
186 // Switch any previous uses to the alias.
187 if (Entry) {
188 assert(Entry->getValueType() == AliasValueType &&
189 Entry->getAddressSpace() == Alias->getAddressSpace() &&
190 "declaration exists with different type");
191 Alias->takeName(V: Entry);
192 Entry->replaceAllUsesWith(V: Alias);
193 Entry->eraseFromParent();
194 } else {
195 Alias->setName(MangledName);
196 }
197
198 // Finally, set up the alias with its proper name and attributes.
199 SetCommonAttributes(GD: AliasDecl, GV: Alias);
200
201 return false;
202}
203
204llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {
205 const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);
206 auto *Fn = cast<llvm::Function>(
207 Val: getAddrOfCXXStructor(GD, FnInfo: &FnInfo, /*FnType=*/nullptr,
208 /*DontDefer=*/true, IsForDefinition: ForDefinition));
209
210 setFunctionLinkage(GD, F: Fn);
211
212 CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
213 setNonAliasAttributes(GD, GO: Fn);
214 SetLLVMFunctionAttributesForDefinition(D: cast<CXXMethodDecl>(Val: GD.getDecl()), F: Fn);
215 return Fn;
216}
217
218llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor(
219 GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType,
220 bool DontDefer, ForDefinition_t IsForDefinition) {
221 auto *MD = cast<CXXMethodDecl>(Val: GD.getDecl());
222
223 if (isa<CXXDestructorDecl>(Val: MD)) {
224 // Always alias equivalent complete destructors to base destructors in the
225 // MS ABI.
226 if (getTarget().getCXXABI().isMicrosoft() &&
227 GD.getDtorType() == Dtor_Complete &&
228 MD->getParent()->getNumVBases() == 0)
229 GD = GD.getWithDtorType(Type: Dtor_Base);
230 }
231
232 if (!FnType) {
233 if (!FnInfo)
234 FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD);
235 FnType = getTypes().GetFunctionType(Info: *FnInfo);
236 }
237
238 llvm::Constant *Ptr = GetOrCreateLLVMFunction(
239 MangledName: getMangledName(GD), Ty: FnType, D: GD, /*ForVTable=*/false, DontDefer,
240 /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
241 return {FnType, Ptr};
242}
243
244static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,
245 GlobalDecl GD,
246 llvm::Type *Ty,
247 const CXXRecordDecl *RD) {
248 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
249 "No kext in Microsoft ABI");
250 CodeGenModule &CGM = CGF.CGM;
251 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, VPtrOffset: CharUnits());
252 Ty = llvm::PointerType::getUnqual(C&: CGM.getLLVMContext());
253 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
254 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
255 const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
256 VTableLayout::AddressPointLocation AddressPoint =
257 VTLayout.getAddressPoint(Base: BaseSubobject(RD, CharUnits::Zero()));
258 VTableIndex += VTLayout.getVTableOffset(i: AddressPoint.VTableIndex) +
259 AddressPoint.AddressPointIndex;
260 llvm::Value *VFuncPtr =
261 CGF.Builder.CreateConstInBoundsGEP1_64(Ty, Ptr: VTable, Idx0: VTableIndex, Name: "vfnkxt");
262 llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(
263 Ty, Ptr: VFuncPtr, Align: llvm::Align(CGF.PointerAlignInBytes));
264
265 CGPointerAuthInfo PointerAuth;
266 if (auto &Schema =
267 CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers) {
268 GlobalDecl OrigMD =
269 CGM.getItaniumVTableContext().findOriginalMethod(GD: GD.getCanonicalDecl());
270 PointerAuth = CGF.EmitPointerAuthInfo(Schema, StorageAddress: VFuncPtr, SchemaDecl: OrigMD, SchemaType: QualType());
271 }
272
273 CGCallee Callee(GD, VFunc, PointerAuth);
274 return Callee;
275}
276
277/// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
278/// indirect call to virtual functions. It makes the call through indexing
279/// into the vtable.
280CGCallee
281CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
282 NestedNameSpecifier *Qual,
283 llvm::Type *Ty) {
284 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
285 "BuildAppleKextVirtualCall - bad Qual kind");
286
287 const Type *QTy = Qual->getAsType();
288 QualType T = QualType(QTy, 0);
289 const RecordType *RT = T->getAs<RecordType>();
290 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
291 const auto *RD = cast<CXXRecordDecl>(Val: RT->getDecl());
292
293 if (const auto *DD = dyn_cast<CXXDestructorDecl>(Val: MD))
294 return BuildAppleKextVirtualDestructorCall(DD, Type: Dtor_Complete, RD);
295
296 return ::BuildAppleKextVirtualCall(CGF&: *this, GD: MD, Ty, RD);
297}
298
299/// BuildVirtualCall - This routine makes indirect vtable call for
300/// call to virtual destructors. It returns 0 if it could not do it.
301CGCallee
302CodeGenFunction::BuildAppleKextVirtualDestructorCall(
303 const CXXDestructorDecl *DD,
304 CXXDtorType Type,
305 const CXXRecordDecl *RD) {
306 assert(DD->isVirtual() && Type != Dtor_Base);
307 // Compute the function type we're calling.
308 const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
309 GD: GlobalDecl(DD, Dtor_Complete));
310 llvm::Type *Ty = CGM.getTypes().GetFunctionType(Info: FInfo);
311 return ::BuildAppleKextVirtualCall(CGF&: *this, GD: GlobalDecl(DD, Type), Ty, RD);
312}
313