1326938Sdim//===-- WebAssemblyLowerGlobalDtors.cpp - Lower @llvm.global_dtors --------===// 2326938Sdim// 3353358Sdim// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4353358Sdim// See https://llvm.org/LICENSE.txt for license information. 5353358Sdim// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6326938Sdim// 7326938Sdim//===----------------------------------------------------------------------===// 8326938Sdim/// 9326938Sdim/// \file 10341825Sdim/// Lower @llvm.global_dtors. 11326938Sdim/// 12326938Sdim/// WebAssembly doesn't have a builtin way to invoke static destructors. 13326938Sdim/// Implement @llvm.global_dtors by creating wrapper functions that are 14326938Sdim/// registered in @llvm.global_ctors and which contain a call to 15326938Sdim/// `__cxa_atexit` to register their destructor functions. 16326938Sdim/// 17326938Sdim//===----------------------------------------------------------------------===// 18326938Sdim 19326938Sdim#include "WebAssembly.h" 20344779Sdim#include "llvm/ADT/MapVector.h" 21326938Sdim#include "llvm/IR/Constants.h" 22326938Sdim#include "llvm/IR/Instructions.h" 23326938Sdim#include "llvm/IR/Intrinsics.h" 24326938Sdim#include "llvm/IR/Module.h" 25326938Sdim#include "llvm/Pass.h" 26326938Sdim#include "llvm/Support/Debug.h" 27326938Sdim#include "llvm/Support/raw_ostream.h" 28344779Sdim#include "llvm/Transforms/Utils/ModuleUtils.h" 29326938Sdimusing namespace llvm; 30326938Sdim 31326938Sdim#define DEBUG_TYPE "wasm-lower-global-dtors" 32326938Sdim 33326938Sdimnamespace { 34326938Sdimclass LowerGlobalDtors final : public ModulePass { 35326938Sdim StringRef getPassName() const override { 36326938Sdim return "WebAssembly Lower @llvm.global_dtors"; 37326938Sdim } 38326938Sdim 39326938Sdim void getAnalysisUsage(AnalysisUsage &AU) const override { 40326938Sdim AU.setPreservesCFG(); 41326938Sdim ModulePass::getAnalysisUsage(AU); 42326938Sdim } 43326938Sdim 44326938Sdim bool runOnModule(Module &M) override; 45326938Sdim 46326938Sdimpublic: 47326938Sdim static char ID; 48326938Sdim LowerGlobalDtors() : ModulePass(ID) {} 49326938Sdim}; 50326938Sdim} // End anonymous namespace 51326938Sdim 52326938Sdimchar LowerGlobalDtors::ID = 0; 53341825SdimINITIALIZE_PASS(LowerGlobalDtors, DEBUG_TYPE, 54341825Sdim "Lower @llvm.global_dtors for WebAssembly", false, false) 55341825Sdim 56326938SdimModulePass *llvm::createWebAssemblyLowerGlobalDtors() { 57326938Sdim return new LowerGlobalDtors(); 58326938Sdim} 59326938Sdim 60326938Sdimbool LowerGlobalDtors::runOnModule(Module &M) { 61344779Sdim LLVM_DEBUG(dbgs() << "********** Lower Global Destructors **********\n"); 62344779Sdim 63326938Sdim GlobalVariable *GV = M.getGlobalVariable("llvm.global_dtors"); 64353358Sdim if (!GV || !GV->hasInitializer()) 65326938Sdim return false; 66326938Sdim 67326938Sdim const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer()); 68326938Sdim if (!InitList) 69326938Sdim return false; 70326938Sdim 71326938Sdim // Sanity-check @llvm.global_dtor's type. 72353358Sdim auto *ETy = dyn_cast<StructType>(InitList->getType()->getElementType()); 73326938Sdim if (!ETy || ETy->getNumElements() != 3 || 74326938Sdim !ETy->getTypeAtIndex(0U)->isIntegerTy() || 75326938Sdim !ETy->getTypeAtIndex(1U)->isPointerTy() || 76326938Sdim !ETy->getTypeAtIndex(2U)->isPointerTy()) 77326938Sdim return false; // Not (int, ptr, ptr). 78326938Sdim 79326938Sdim // Collect the contents of @llvm.global_dtors, collated by priority and 80326938Sdim // associated symbol. 81344779Sdim std::map<uint16_t, MapVector<Constant *, std::vector<Constant *>>> DtorFuncs; 82326938Sdim for (Value *O : InitList->operands()) { 83353358Sdim auto *CS = dyn_cast<ConstantStruct>(O); 84344779Sdim if (!CS) 85344779Sdim continue; // Malformed. 86326938Sdim 87353358Sdim auto *Priority = dyn_cast<ConstantInt>(CS->getOperand(0)); 88344779Sdim if (!Priority) 89344779Sdim continue; // Malformed. 90326938Sdim uint16_t PriorityValue = Priority->getLimitedValue(UINT16_MAX); 91326938Sdim 92326938Sdim Constant *DtorFunc = CS->getOperand(1); 93326938Sdim if (DtorFunc->isNullValue()) 94344779Sdim break; // Found a null terminator, skip the rest. 95326938Sdim 96326938Sdim Constant *Associated = CS->getOperand(2); 97360784Sdim Associated = cast<Constant>(Associated->stripPointerCasts()); 98326938Sdim 99326938Sdim DtorFuncs[PriorityValue][Associated].push_back(DtorFunc); 100326938Sdim } 101326938Sdim if (DtorFuncs.empty()) 102326938Sdim return false; 103326938Sdim 104326938Sdim // extern "C" int __cxa_atexit(void (*f)(void *), void *p, void *d); 105326938Sdim LLVMContext &C = M.getContext(); 106326938Sdim PointerType *VoidStar = Type::getInt8PtrTy(C); 107344779Sdim Type *AtExitFuncArgs[] = {VoidStar}; 108344779Sdim FunctionType *AtExitFuncTy = 109344779Sdim FunctionType::get(Type::getVoidTy(C), AtExitFuncArgs, 110344779Sdim /*isVarArg=*/false); 111326938Sdim 112353358Sdim FunctionCallee AtExit = M.getOrInsertFunction( 113353358Sdim "__cxa_atexit", 114353358Sdim FunctionType::get(Type::getInt32Ty(C), 115353358Sdim {PointerType::get(AtExitFuncTy, 0), VoidStar, VoidStar}, 116353358Sdim /*isVarArg=*/false)); 117326938Sdim 118326938Sdim // Declare __dso_local. 119326938Sdim Constant *DsoHandle = M.getNamedValue("__dso_handle"); 120326938Sdim if (!DsoHandle) { 121326938Sdim Type *DsoHandleTy = Type::getInt8Ty(C); 122344779Sdim GlobalVariable *Handle = new GlobalVariable( 123344779Sdim M, DsoHandleTy, /*isConstant=*/true, 124344779Sdim GlobalVariable::ExternalWeakLinkage, nullptr, "__dso_handle"); 125326938Sdim Handle->setVisibility(GlobalVariable::HiddenVisibility); 126326938Sdim DsoHandle = Handle; 127326938Sdim } 128326938Sdim 129326938Sdim // For each unique priority level and associated symbol, generate a function 130326938Sdim // to call all the destructors at that level, and a function to register the 131326938Sdim // first function with __cxa_atexit. 132326938Sdim for (auto &PriorityAndMore : DtorFuncs) { 133326938Sdim uint16_t Priority = PriorityAndMore.first; 134326938Sdim for (auto &AssociatedAndMore : PriorityAndMore.second) { 135326938Sdim Constant *Associated = AssociatedAndMore.first; 136326938Sdim 137326938Sdim Function *CallDtors = Function::Create( 138344779Sdim AtExitFuncTy, Function::PrivateLinkage, 139344779Sdim "call_dtors" + 140344779Sdim (Priority != UINT16_MAX ? (Twine(".") + Twine(Priority)) 141344779Sdim : Twine()) + 142344779Sdim (!Associated->isNullValue() ? (Twine(".") + Associated->getName()) 143344779Sdim : Twine()), 144344779Sdim &M); 145326938Sdim BasicBlock *BB = BasicBlock::Create(C, "body", CallDtors); 146353358Sdim FunctionType *VoidVoid = FunctionType::get(Type::getVoidTy(C), 147353358Sdim /*isVarArg=*/false); 148326938Sdim 149326938Sdim for (auto Dtor : AssociatedAndMore.second) 150353358Sdim CallInst::Create(VoidVoid, Dtor, "", BB); 151326938Sdim ReturnInst::Create(C, BB); 152326938Sdim 153326938Sdim Function *RegisterCallDtors = Function::Create( 154344779Sdim VoidVoid, Function::PrivateLinkage, 155344779Sdim "register_call_dtors" + 156344779Sdim (Priority != UINT16_MAX ? (Twine(".") + Twine(Priority)) 157344779Sdim : Twine()) + 158344779Sdim (!Associated->isNullValue() ? (Twine(".") + Associated->getName()) 159344779Sdim : Twine()), 160344779Sdim &M); 161326938Sdim BasicBlock *EntryBB = BasicBlock::Create(C, "entry", RegisterCallDtors); 162326938Sdim BasicBlock *FailBB = BasicBlock::Create(C, "fail", RegisterCallDtors); 163326938Sdim BasicBlock *RetBB = BasicBlock::Create(C, "return", RegisterCallDtors); 164326938Sdim 165326938Sdim Value *Null = ConstantPointerNull::get(VoidStar); 166344779Sdim Value *Args[] = {CallDtors, Null, DsoHandle}; 167326938Sdim Value *Res = CallInst::Create(AtExit, Args, "call", EntryBB); 168326938Sdim Value *Cmp = new ICmpInst(*EntryBB, ICmpInst::ICMP_NE, Res, 169326938Sdim Constant::getNullValue(Res->getType())); 170326938Sdim BranchInst::Create(FailBB, RetBB, Cmp, EntryBB); 171326938Sdim 172326938Sdim // If `__cxa_atexit` hits out-of-memory, trap, so that we don't misbehave. 173344779Sdim // This should be very rare, because if the process is running out of 174344779Sdim // memory before main has even started, something is wrong. 175344779Sdim CallInst::Create(Intrinsic::getDeclaration(&M, Intrinsic::trap), "", 176344779Sdim FailBB); 177326938Sdim new UnreachableInst(C, FailBB); 178326938Sdim 179326938Sdim ReturnInst::Create(C, RetBB); 180326938Sdim 181326938Sdim // Now register the registration function with @llvm.global_ctors. 182326938Sdim appendToGlobalCtors(M, RegisterCallDtors, Priority, Associated); 183326938Sdim } 184326938Sdim } 185326938Sdim 186326938Sdim // Now that we've lowered everything, remove @llvm.global_dtors. 187326938Sdim GV->eraseFromParent(); 188326938Sdim 189326938Sdim return true; 190326938Sdim} 191