181ad6265SDimitry Andric //===-- LowerGlobalDtors.cpp - Lower @llvm.global_dtors -------------------===// 281ad6265SDimitry Andric // 381ad6265SDimitry Andric // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 481ad6265SDimitry Andric // See https://llvm.org/LICENSE.txt for license information. 581ad6265SDimitry Andric // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 681ad6265SDimitry Andric // 781ad6265SDimitry Andric //===----------------------------------------------------------------------===// 881ad6265SDimitry Andric /// 981ad6265SDimitry Andric /// \file 1081ad6265SDimitry Andric /// Lower @llvm.global_dtors. 1181ad6265SDimitry Andric /// 1281ad6265SDimitry Andric /// Implement @llvm.global_dtors by creating wrapper functions that are 1381ad6265SDimitry Andric /// registered in @llvm.global_ctors and which contain a call to 1481ad6265SDimitry Andric /// `__cxa_atexit` to register their destructor functions. 1581ad6265SDimitry Andric /// 1681ad6265SDimitry Andric //===----------------------------------------------------------------------===// 1781ad6265SDimitry Andric 1881ad6265SDimitry Andric #include "llvm/Transforms/Utils/LowerGlobalDtors.h" 1981ad6265SDimitry Andric 2081ad6265SDimitry Andric #include "llvm/IR/Constants.h" 2181ad6265SDimitry Andric #include "llvm/IR/Instructions.h" 2281ad6265SDimitry Andric #include "llvm/IR/Intrinsics.h" 23*0fca6ea1SDimitry Andric #include "llvm/IR/Module.h" 2481ad6265SDimitry Andric #include "llvm/InitializePasses.h" 2581ad6265SDimitry Andric #include "llvm/Pass.h" 2681ad6265SDimitry Andric #include "llvm/Transforms/Utils.h" 2781ad6265SDimitry Andric #include "llvm/Transforms/Utils/ModuleUtils.h" 2881ad6265SDimitry Andric #include <map> 2981ad6265SDimitry Andric 3081ad6265SDimitry Andric using namespace llvm; 3181ad6265SDimitry Andric 3281ad6265SDimitry Andric #define DEBUG_TYPE "lower-global-dtors" 3381ad6265SDimitry Andric 3481ad6265SDimitry Andric namespace { 3581ad6265SDimitry Andric class LowerGlobalDtorsLegacyPass final : public ModulePass { 3681ad6265SDimitry Andric StringRef getPassName() const override { 3781ad6265SDimitry Andric return "Lower @llvm.global_dtors via `__cxa_atexit`"; 3881ad6265SDimitry Andric } 3981ad6265SDimitry Andric 4081ad6265SDimitry Andric void getAnalysisUsage(AnalysisUsage &AU) const override { 4181ad6265SDimitry Andric AU.setPreservesCFG(); 4281ad6265SDimitry Andric ModulePass::getAnalysisUsage(AU); 4381ad6265SDimitry Andric } 4481ad6265SDimitry Andric 4581ad6265SDimitry Andric bool runOnModule(Module &M) override; 4681ad6265SDimitry Andric 4781ad6265SDimitry Andric public: 4881ad6265SDimitry Andric static char ID; 4981ad6265SDimitry Andric LowerGlobalDtorsLegacyPass() : ModulePass(ID) { 5081ad6265SDimitry Andric initializeLowerGlobalDtorsLegacyPassPass(*PassRegistry::getPassRegistry()); 5181ad6265SDimitry Andric } 5281ad6265SDimitry Andric }; 5381ad6265SDimitry Andric } // End anonymous namespace 5481ad6265SDimitry Andric 5581ad6265SDimitry Andric char LowerGlobalDtorsLegacyPass::ID = 0; 5681ad6265SDimitry Andric INITIALIZE_PASS(LowerGlobalDtorsLegacyPass, DEBUG_TYPE, 5781ad6265SDimitry Andric "Lower @llvm.global_dtors via `__cxa_atexit`", false, false) 5881ad6265SDimitry Andric 5981ad6265SDimitry Andric ModulePass *llvm::createLowerGlobalDtorsLegacyPass() { 6081ad6265SDimitry Andric return new LowerGlobalDtorsLegacyPass(); 6181ad6265SDimitry Andric } 6281ad6265SDimitry Andric 6381ad6265SDimitry Andric static bool runImpl(Module &M); 6481ad6265SDimitry Andric bool LowerGlobalDtorsLegacyPass::runOnModule(Module &M) { return runImpl(M); } 6581ad6265SDimitry Andric 6681ad6265SDimitry Andric PreservedAnalyses LowerGlobalDtorsPass::run(Module &M, 6781ad6265SDimitry Andric ModuleAnalysisManager &AM) { 6881ad6265SDimitry Andric bool Changed = runImpl(M); 6981ad6265SDimitry Andric if (!Changed) 7081ad6265SDimitry Andric return PreservedAnalyses::all(); 7181ad6265SDimitry Andric 7281ad6265SDimitry Andric PreservedAnalyses PA; 7381ad6265SDimitry Andric PA.preserveSet<CFGAnalyses>(); 7481ad6265SDimitry Andric return PA; 7581ad6265SDimitry Andric } 7681ad6265SDimitry Andric 7781ad6265SDimitry Andric static bool runImpl(Module &M) { 7881ad6265SDimitry Andric GlobalVariable *GV = M.getGlobalVariable("llvm.global_dtors"); 7981ad6265SDimitry Andric if (!GV || !GV->hasInitializer()) 8081ad6265SDimitry Andric return false; 8181ad6265SDimitry Andric 8281ad6265SDimitry Andric const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer()); 8381ad6265SDimitry Andric if (!InitList) 8481ad6265SDimitry Andric return false; 8581ad6265SDimitry Andric 8681ad6265SDimitry Andric // Validate @llvm.global_dtor's type. 8781ad6265SDimitry Andric auto *ETy = dyn_cast<StructType>(InitList->getType()->getElementType()); 8881ad6265SDimitry Andric if (!ETy || ETy->getNumElements() != 3 || 8981ad6265SDimitry Andric !ETy->getTypeAtIndex(0U)->isIntegerTy() || 9081ad6265SDimitry Andric !ETy->getTypeAtIndex(1U)->isPointerTy() || 9181ad6265SDimitry Andric !ETy->getTypeAtIndex(2U)->isPointerTy()) 9281ad6265SDimitry Andric return false; // Not (int, ptr, ptr). 9381ad6265SDimitry Andric 9481ad6265SDimitry Andric // Collect the contents of @llvm.global_dtors, ordered by priority. Within a 9581ad6265SDimitry Andric // priority, sequences of destructors with the same associated object are 9681ad6265SDimitry Andric // recorded so that we can register them as a group. 9781ad6265SDimitry Andric std::map< 9881ad6265SDimitry Andric uint16_t, 9981ad6265SDimitry Andric std::vector<std::pair<Constant *, std::vector<Constant *>>> 10081ad6265SDimitry Andric > DtorFuncs; 10181ad6265SDimitry Andric for (Value *O : InitList->operands()) { 10281ad6265SDimitry Andric auto *CS = dyn_cast<ConstantStruct>(O); 10381ad6265SDimitry Andric if (!CS) 10481ad6265SDimitry Andric continue; // Malformed. 10581ad6265SDimitry Andric 10681ad6265SDimitry Andric auto *Priority = dyn_cast<ConstantInt>(CS->getOperand(0)); 10781ad6265SDimitry Andric if (!Priority) 10881ad6265SDimitry Andric continue; // Malformed. 10981ad6265SDimitry Andric uint16_t PriorityValue = Priority->getLimitedValue(UINT16_MAX); 11081ad6265SDimitry Andric 11181ad6265SDimitry Andric Constant *DtorFunc = CS->getOperand(1); 11281ad6265SDimitry Andric if (DtorFunc->isNullValue()) 11381ad6265SDimitry Andric break; // Found a null terminator, skip the rest. 11481ad6265SDimitry Andric 11581ad6265SDimitry Andric Constant *Associated = CS->getOperand(2); 11681ad6265SDimitry Andric Associated = cast<Constant>(Associated->stripPointerCasts()); 11781ad6265SDimitry Andric 11881ad6265SDimitry Andric auto &AtThisPriority = DtorFuncs[PriorityValue]; 11981ad6265SDimitry Andric if (AtThisPriority.empty() || AtThisPriority.back().first != Associated) { 12081ad6265SDimitry Andric std::vector<Constant *> NewList; 12181ad6265SDimitry Andric NewList.push_back(DtorFunc); 12281ad6265SDimitry Andric AtThisPriority.push_back(std::make_pair(Associated, NewList)); 12381ad6265SDimitry Andric } else { 12481ad6265SDimitry Andric AtThisPriority.back().second.push_back(DtorFunc); 12581ad6265SDimitry Andric } 12681ad6265SDimitry Andric } 12781ad6265SDimitry Andric if (DtorFuncs.empty()) 12881ad6265SDimitry Andric return false; 12981ad6265SDimitry Andric 13081ad6265SDimitry Andric // extern "C" int __cxa_atexit(void (*f)(void *), void *p, void *d); 13181ad6265SDimitry Andric LLVMContext &C = M.getContext(); 1325f757f3fSDimitry Andric PointerType *VoidStar = PointerType::getUnqual(C); 13381ad6265SDimitry Andric Type *AtExitFuncArgs[] = {VoidStar}; 13481ad6265SDimitry Andric FunctionType *AtExitFuncTy = 13581ad6265SDimitry Andric FunctionType::get(Type::getVoidTy(C), AtExitFuncArgs, 13681ad6265SDimitry Andric /*isVarArg=*/false); 13781ad6265SDimitry Andric 13881ad6265SDimitry Andric FunctionCallee AtExit = M.getOrInsertFunction( 13981ad6265SDimitry Andric "__cxa_atexit", 14081ad6265SDimitry Andric FunctionType::get(Type::getInt32Ty(C), 14181ad6265SDimitry Andric {PointerType::get(AtExitFuncTy, 0), VoidStar, VoidStar}, 14281ad6265SDimitry Andric /*isVarArg=*/false)); 14381ad6265SDimitry Andric 1445f757f3fSDimitry Andric // If __cxa_atexit is defined (e.g. in the case of LTO) and arg0 is not 1455f757f3fSDimitry Andric // actually used (i.e. it's dummy/stub function as used in emscripten when 1465f757f3fSDimitry Andric // the program never exits) we can simply return early and clear out 1475f757f3fSDimitry Andric // @llvm.global_dtors. 1485f757f3fSDimitry Andric if (auto F = dyn_cast<Function>(AtExit.getCallee())) { 1495f757f3fSDimitry Andric if (F && F->hasExactDefinition() && F->getArg(0)->getNumUses() == 0) { 1505f757f3fSDimitry Andric GV->eraseFromParent(); 1515f757f3fSDimitry Andric return true; 1525f757f3fSDimitry Andric } 1535f757f3fSDimitry Andric } 1545f757f3fSDimitry Andric 15581ad6265SDimitry Andric // Declare __dso_local. 15681ad6265SDimitry Andric Type *DsoHandleTy = Type::getInt8Ty(C); 15781ad6265SDimitry Andric Constant *DsoHandle = M.getOrInsertGlobal("__dso_handle", DsoHandleTy, [&] { 15881ad6265SDimitry Andric auto *GV = new GlobalVariable(M, DsoHandleTy, /*isConstant=*/true, 15981ad6265SDimitry Andric GlobalVariable::ExternalWeakLinkage, nullptr, 16081ad6265SDimitry Andric "__dso_handle"); 16181ad6265SDimitry Andric GV->setVisibility(GlobalVariable::HiddenVisibility); 16281ad6265SDimitry Andric return GV; 16381ad6265SDimitry Andric }); 16481ad6265SDimitry Andric 16581ad6265SDimitry Andric // For each unique priority level and associated symbol, generate a function 16681ad6265SDimitry Andric // to call all the destructors at that level, and a function to register the 16781ad6265SDimitry Andric // first function with __cxa_atexit. 16881ad6265SDimitry Andric for (auto &PriorityAndMore : DtorFuncs) { 16981ad6265SDimitry Andric uint16_t Priority = PriorityAndMore.first; 17081ad6265SDimitry Andric uint64_t Id = 0; 17181ad6265SDimitry Andric auto &AtThisPriority = PriorityAndMore.second; 17281ad6265SDimitry Andric for (auto &AssociatedAndMore : AtThisPriority) { 17381ad6265SDimitry Andric Constant *Associated = AssociatedAndMore.first; 17481ad6265SDimitry Andric auto ThisId = Id++; 17581ad6265SDimitry Andric 17681ad6265SDimitry Andric Function *CallDtors = Function::Create( 17781ad6265SDimitry Andric AtExitFuncTy, Function::PrivateLinkage, 17881ad6265SDimitry Andric "call_dtors" + 17981ad6265SDimitry Andric (Priority != UINT16_MAX ? (Twine(".") + Twine(Priority)) 18081ad6265SDimitry Andric : Twine()) + 18181ad6265SDimitry Andric (AtThisPriority.size() > 1 ? Twine("$") + Twine(ThisId) 18281ad6265SDimitry Andric : Twine()) + 18381ad6265SDimitry Andric (!Associated->isNullValue() ? (Twine(".") + Associated->getName()) 18481ad6265SDimitry Andric : Twine()), 18581ad6265SDimitry Andric &M); 18681ad6265SDimitry Andric BasicBlock *BB = BasicBlock::Create(C, "body", CallDtors); 18781ad6265SDimitry Andric FunctionType *VoidVoid = FunctionType::get(Type::getVoidTy(C), 18881ad6265SDimitry Andric /*isVarArg=*/false); 18981ad6265SDimitry Andric 190bdd1243dSDimitry Andric for (auto *Dtor : reverse(AssociatedAndMore.second)) 19181ad6265SDimitry Andric CallInst::Create(VoidVoid, Dtor, "", BB); 19281ad6265SDimitry Andric ReturnInst::Create(C, BB); 19381ad6265SDimitry Andric 19481ad6265SDimitry Andric Function *RegisterCallDtors = Function::Create( 19581ad6265SDimitry Andric VoidVoid, Function::PrivateLinkage, 19681ad6265SDimitry Andric "register_call_dtors" + 19781ad6265SDimitry Andric (Priority != UINT16_MAX ? (Twine(".") + Twine(Priority)) 19881ad6265SDimitry Andric : Twine()) + 19981ad6265SDimitry Andric (AtThisPriority.size() > 1 ? Twine("$") + Twine(ThisId) 20081ad6265SDimitry Andric : Twine()) + 20181ad6265SDimitry Andric (!Associated->isNullValue() ? (Twine(".") + Associated->getName()) 20281ad6265SDimitry Andric : Twine()), 20381ad6265SDimitry Andric &M); 20481ad6265SDimitry Andric BasicBlock *EntryBB = BasicBlock::Create(C, "entry", RegisterCallDtors); 20581ad6265SDimitry Andric BasicBlock *FailBB = BasicBlock::Create(C, "fail", RegisterCallDtors); 20681ad6265SDimitry Andric BasicBlock *RetBB = BasicBlock::Create(C, "return", RegisterCallDtors); 20781ad6265SDimitry Andric 20881ad6265SDimitry Andric Value *Null = ConstantPointerNull::get(VoidStar); 20981ad6265SDimitry Andric Value *Args[] = {CallDtors, Null, DsoHandle}; 21081ad6265SDimitry Andric Value *Res = CallInst::Create(AtExit, Args, "call", EntryBB); 211*0fca6ea1SDimitry Andric Value *Cmp = new ICmpInst(EntryBB, ICmpInst::ICMP_NE, Res, 21281ad6265SDimitry Andric Constant::getNullValue(Res->getType())); 21381ad6265SDimitry Andric BranchInst::Create(FailBB, RetBB, Cmp, EntryBB); 21481ad6265SDimitry Andric 21581ad6265SDimitry Andric // If `__cxa_atexit` hits out-of-memory, trap, so that we don't misbehave. 21681ad6265SDimitry Andric // This should be very rare, because if the process is running out of 21781ad6265SDimitry Andric // memory before main has even started, something is wrong. 21881ad6265SDimitry Andric CallInst::Create(Intrinsic::getDeclaration(&M, Intrinsic::trap), "", 21981ad6265SDimitry Andric FailBB); 22081ad6265SDimitry Andric new UnreachableInst(C, FailBB); 22181ad6265SDimitry Andric 22281ad6265SDimitry Andric ReturnInst::Create(C, RetBB); 22381ad6265SDimitry Andric 22481ad6265SDimitry Andric // Now register the registration function with @llvm.global_ctors. 22581ad6265SDimitry Andric appendToGlobalCtors(M, RegisterCallDtors, Priority, Associated); 22681ad6265SDimitry Andric } 22781ad6265SDimitry Andric } 22881ad6265SDimitry Andric 22981ad6265SDimitry Andric // Now that we've lowered everything, remove @llvm.global_dtors. 23081ad6265SDimitry Andric GV->eraseFromParent(); 23181ad6265SDimitry Andric 23281ad6265SDimitry Andric return true; 23381ad6265SDimitry Andric } 234