WebAssemblyLowerGlobalDtors.cpp revision 341825
1326938Sdim//===-- WebAssemblyLowerGlobalDtors.cpp - Lower @llvm.global_dtors --------===// 2326938Sdim// 3326938Sdim// The LLVM Compiler Infrastructure 4326938Sdim// 5326938Sdim// This file is distributed under the University of Illinois Open Source 6326938Sdim// License. See LICENSE.TXT for details. 7326938Sdim// 8326938Sdim//===----------------------------------------------------------------------===// 9326938Sdim/// 10326938Sdim/// \file 11341825Sdim/// Lower @llvm.global_dtors. 12326938Sdim/// 13326938Sdim/// WebAssembly doesn't have a builtin way to invoke static destructors. 14326938Sdim/// Implement @llvm.global_dtors by creating wrapper functions that are 15326938Sdim/// registered in @llvm.global_ctors and which contain a call to 16326938Sdim/// `__cxa_atexit` to register their destructor functions. 17326938Sdim/// 18326938Sdim//===----------------------------------------------------------------------===// 19326938Sdim 20326938Sdim#include "WebAssembly.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/Transforms/Utils/ModuleUtils.h" 26326938Sdim#include "llvm/Pass.h" 27326938Sdim#include "llvm/ADT/MapVector.h" 28326938Sdim#include "llvm/Support/Debug.h" 29326938Sdim#include "llvm/Support/raw_ostream.h" 30326938Sdimusing namespace llvm; 31326938Sdim 32326938Sdim#define DEBUG_TYPE "wasm-lower-global-dtors" 33326938Sdim 34326938Sdimnamespace { 35326938Sdimclass LowerGlobalDtors final : public ModulePass { 36326938Sdim StringRef getPassName() const override { 37326938Sdim return "WebAssembly Lower @llvm.global_dtors"; 38326938Sdim } 39326938Sdim 40326938Sdim void getAnalysisUsage(AnalysisUsage &AU) const override { 41326938Sdim AU.setPreservesCFG(); 42326938Sdim ModulePass::getAnalysisUsage(AU); 43326938Sdim } 44326938Sdim 45326938Sdim bool runOnModule(Module &M) override; 46326938Sdim 47326938Sdimpublic: 48326938Sdim static char ID; 49326938Sdim LowerGlobalDtors() : ModulePass(ID) {} 50326938Sdim}; 51326938Sdim} // End anonymous namespace 52326938Sdim 53326938Sdimchar LowerGlobalDtors::ID = 0; 54341825SdimINITIALIZE_PASS(LowerGlobalDtors, DEBUG_TYPE, 55341825Sdim "Lower @llvm.global_dtors for WebAssembly", false, false) 56341825Sdim 57326938SdimModulePass *llvm::createWebAssemblyLowerGlobalDtors() { 58326938Sdim return new LowerGlobalDtors(); 59326938Sdim} 60326938Sdim 61326938Sdimbool LowerGlobalDtors::runOnModule(Module &M) { 62326938Sdim GlobalVariable *GV = M.getGlobalVariable("llvm.global_dtors"); 63326938Sdim if (!GV) 64326938Sdim return false; 65326938Sdim 66326938Sdim const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer()); 67326938Sdim if (!InitList) 68326938Sdim return false; 69326938Sdim 70326938Sdim // Sanity-check @llvm.global_dtor's type. 71326938Sdim StructType *ETy = dyn_cast<StructType>(InitList->getType()->getElementType()); 72326938Sdim if (!ETy || ETy->getNumElements() != 3 || 73326938Sdim !ETy->getTypeAtIndex(0U)->isIntegerTy() || 74326938Sdim !ETy->getTypeAtIndex(1U)->isPointerTy() || 75326938Sdim !ETy->getTypeAtIndex(2U)->isPointerTy()) 76326938Sdim return false; // Not (int, ptr, ptr). 77326938Sdim 78326938Sdim // Collect the contents of @llvm.global_dtors, collated by priority and 79326938Sdim // associated symbol. 80326938Sdim std::map<uint16_t, MapVector<Constant *, std::vector<Constant *> > > DtorFuncs; 81326938Sdim for (Value *O : InitList->operands()) { 82326938Sdim ConstantStruct *CS = dyn_cast<ConstantStruct>(O); 83326938Sdim if (!CS) continue; // Malformed. 84326938Sdim 85326938Sdim ConstantInt *Priority = dyn_cast<ConstantInt>(CS->getOperand(0)); 86326938Sdim if (!Priority) continue; // Malformed. 87326938Sdim uint16_t PriorityValue = Priority->getLimitedValue(UINT16_MAX); 88326938Sdim 89326938Sdim Constant *DtorFunc = CS->getOperand(1); 90326938Sdim if (DtorFunc->isNullValue()) 91326938Sdim break; // Found a null terminator, skip the rest. 92326938Sdim 93326938Sdim Constant *Associated = CS->getOperand(2); 94326938Sdim Associated = cast<Constant>(Associated->stripPointerCastsNoFollowAliases()); 95326938Sdim 96326938Sdim DtorFuncs[PriorityValue][Associated].push_back(DtorFunc); 97326938Sdim } 98326938Sdim if (DtorFuncs.empty()) 99326938Sdim return false; 100326938Sdim 101326938Sdim // extern "C" int __cxa_atexit(void (*f)(void *), void *p, void *d); 102326938Sdim LLVMContext &C = M.getContext(); 103326938Sdim PointerType *VoidStar = Type::getInt8PtrTy(C); 104326938Sdim Type *AtExitFuncArgs[] = { VoidStar }; 105326938Sdim FunctionType *AtExitFuncTy = FunctionType::get( 106326938Sdim Type::getVoidTy(C), 107326938Sdim AtExitFuncArgs, 108326938Sdim /*isVarArg=*/false); 109326938Sdim 110326938Sdim Type *AtExitArgs[] = { 111326938Sdim PointerType::get(AtExitFuncTy, 0), 112326938Sdim VoidStar, 113326938Sdim VoidStar 114326938Sdim }; 115326938Sdim FunctionType *AtExitTy = FunctionType::get( 116326938Sdim Type::getInt32Ty(C), 117326938Sdim AtExitArgs, 118326938Sdim /*isVarArg=*/false); 119326938Sdim Constant *AtExit = M.getOrInsertFunction("__cxa_atexit", AtExitTy); 120326938Sdim 121326938Sdim // Declare __dso_local. 122326938Sdim Constant *DsoHandle = M.getNamedValue("__dso_handle"); 123326938Sdim if (!DsoHandle) { 124326938Sdim Type *DsoHandleTy = Type::getInt8Ty(C); 125326938Sdim GlobalVariable *Handle = 126326938Sdim new GlobalVariable(M, DsoHandleTy, /*isConstant=*/true, 127326938Sdim GlobalVariable::ExternalWeakLinkage, 128326938Sdim nullptr, "__dso_handle"); 129326938Sdim Handle->setVisibility(GlobalVariable::HiddenVisibility); 130326938Sdim DsoHandle = Handle; 131326938Sdim } 132326938Sdim 133326938Sdim // For each unique priority level and associated symbol, generate a function 134326938Sdim // to call all the destructors at that level, and a function to register the 135326938Sdim // first function with __cxa_atexit. 136326938Sdim for (auto &PriorityAndMore : DtorFuncs) { 137326938Sdim uint16_t Priority = PriorityAndMore.first; 138326938Sdim for (auto &AssociatedAndMore : PriorityAndMore.second) { 139326938Sdim Constant *Associated = AssociatedAndMore.first; 140326938Sdim 141326938Sdim Function *CallDtors = Function::Create( 142326938Sdim AtExitFuncTy, Function::PrivateLinkage, 143326938Sdim "call_dtors" + 144326938Sdim (Priority != UINT16_MAX ? 145326938Sdim (Twine(".") + Twine(Priority)) : Twine()) + 146326938Sdim (!Associated->isNullValue() ? 147326938Sdim (Twine(".") + Associated->getName()) : Twine()), 148326938Sdim &M); 149326938Sdim BasicBlock *BB = BasicBlock::Create(C, "body", CallDtors); 150326938Sdim 151326938Sdim for (auto Dtor : AssociatedAndMore.second) 152326938Sdim CallInst::Create(Dtor, "", BB); 153326938Sdim ReturnInst::Create(C, BB); 154326938Sdim 155326938Sdim FunctionType *VoidVoid = FunctionType::get(Type::getVoidTy(C), 156326938Sdim /*isVarArg=*/false); 157326938Sdim Function *RegisterCallDtors = Function::Create( 158326938Sdim VoidVoid, Function::PrivateLinkage, 159326938Sdim "register_call_dtors" + 160326938Sdim (Priority != UINT16_MAX ? 161326938Sdim (Twine(".") + Twine(Priority)) : Twine()) + 162326938Sdim (!Associated->isNullValue() ? 163326938Sdim (Twine(".") + Associated->getName()) : Twine()), 164326938Sdim &M); 165326938Sdim BasicBlock *EntryBB = BasicBlock::Create(C, "entry", RegisterCallDtors); 166326938Sdim BasicBlock *FailBB = BasicBlock::Create(C, "fail", RegisterCallDtors); 167326938Sdim BasicBlock *RetBB = BasicBlock::Create(C, "return", RegisterCallDtors); 168326938Sdim 169326938Sdim Value *Null = ConstantPointerNull::get(VoidStar); 170326938Sdim Value *Args[] = { CallDtors, Null, DsoHandle }; 171326938Sdim Value *Res = CallInst::Create(AtExit, Args, "call", EntryBB); 172326938Sdim Value *Cmp = new ICmpInst(*EntryBB, ICmpInst::ICMP_NE, Res, 173326938Sdim Constant::getNullValue(Res->getType())); 174326938Sdim BranchInst::Create(FailBB, RetBB, Cmp, EntryBB); 175326938Sdim 176326938Sdim // If `__cxa_atexit` hits out-of-memory, trap, so that we don't misbehave. 177326938Sdim // This should be very rare, because if the process is running out of memory 178326938Sdim // before main has even started, something is wrong. 179326938Sdim CallInst::Create(Intrinsic::getDeclaration(&M, Intrinsic::trap), 180326938Sdim "", FailBB); 181326938Sdim new UnreachableInst(C, FailBB); 182326938Sdim 183326938Sdim ReturnInst::Create(C, RetBB); 184326938Sdim 185326938Sdim // Now register the registration function with @llvm.global_ctors. 186326938Sdim appendToGlobalCtors(M, RegisterCallDtors, Priority, Associated); 187326938Sdim } 188326938Sdim } 189326938Sdim 190326938Sdim // Now that we've lowered everything, remove @llvm.global_dtors. 191326938Sdim GV->eraseFromParent(); 192326938Sdim 193326938Sdim return true; 194326938Sdim} 195