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Diffstat (limited to 'llvm/lib/Target/WebAssembly/WebAssemblyLowerGlobalDtors.cpp')
| -rw-r--r-- | llvm/lib/Target/WebAssembly/WebAssemblyLowerGlobalDtors.cpp | 190 |
1 files changed, 190 insertions, 0 deletions
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyLowerGlobalDtors.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyLowerGlobalDtors.cpp new file mode 100644 index 000000000000..750b2233e67a --- /dev/null +++ b/llvm/lib/Target/WebAssembly/WebAssemblyLowerGlobalDtors.cpp @@ -0,0 +1,190 @@ +//===-- WebAssemblyLowerGlobalDtors.cpp - Lower @llvm.global_dtors --------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +/// +/// \file +/// Lower @llvm.global_dtors. +/// +/// WebAssembly doesn't have a builtin way to invoke static destructors. +/// Implement @llvm.global_dtors by creating wrapper functions that are +/// registered in @llvm.global_ctors and which contain a call to +/// `__cxa_atexit` to register their destructor functions. +/// +//===----------------------------------------------------------------------===// + +#include "WebAssembly.h" +#include "llvm/ADT/MapVector.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/Module.h" +#include "llvm/Pass.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Utils/ModuleUtils.h" +using namespace llvm; + +#define DEBUG_TYPE "wasm-lower-global-dtors" + +namespace { +class LowerGlobalDtors final : public ModulePass { + StringRef getPassName() const override { + return "WebAssembly Lower @llvm.global_dtors"; + } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.setPreservesCFG(); + ModulePass::getAnalysisUsage(AU); + } + + bool runOnModule(Module &M) override; + +public: + static char ID; + LowerGlobalDtors() : ModulePass(ID) {} +}; +} // End anonymous namespace + +char LowerGlobalDtors::ID = 0; +INITIALIZE_PASS(LowerGlobalDtors, DEBUG_TYPE, + "Lower @llvm.global_dtors for WebAssembly", false, false) + +ModulePass *llvm::createWebAssemblyLowerGlobalDtors() { + return new LowerGlobalDtors(); +} + +bool LowerGlobalDtors::runOnModule(Module &M) { + LLVM_DEBUG(dbgs() << "********** Lower Global Destructors **********\n"); + + GlobalVariable *GV = M.getGlobalVariable("llvm.global_dtors"); + if (!GV || !GV->hasInitializer()) + return false; + + const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer()); + if (!InitList) + return false; + + // Sanity-check @llvm.global_dtor's type. + auto *ETy = dyn_cast<StructType>(InitList->getType()->getElementType()); + if (!ETy || ETy->getNumElements() != 3 || + !ETy->getTypeAtIndex(0U)->isIntegerTy() || + !ETy->getTypeAtIndex(1U)->isPointerTy() || + !ETy->getTypeAtIndex(2U)->isPointerTy()) + return false; // Not (int, ptr, ptr). + + // Collect the contents of @llvm.global_dtors, collated by priority and + // associated symbol. + std::map<uint16_t, MapVector<Constant *, std::vector<Constant *>>> DtorFuncs; + for (Value *O : InitList->operands()) { + auto *CS = dyn_cast<ConstantStruct>(O); + if (!CS) + continue; // Malformed. + + auto *Priority = dyn_cast<ConstantInt>(CS->getOperand(0)); + if (!Priority) + continue; // Malformed. + uint16_t PriorityValue = Priority->getLimitedValue(UINT16_MAX); + + Constant *DtorFunc = CS->getOperand(1); + if (DtorFunc->isNullValue()) + break; // Found a null terminator, skip the rest. + + Constant *Associated = CS->getOperand(2); + Associated = cast<Constant>(Associated->stripPointerCasts()); + + DtorFuncs[PriorityValue][Associated].push_back(DtorFunc); + } + if (DtorFuncs.empty()) + return false; + + // extern "C" int __cxa_atexit(void (*f)(void *), void *p, void *d); + LLVMContext &C = M.getContext(); + PointerType *VoidStar = Type::getInt8PtrTy(C); + Type *AtExitFuncArgs[] = {VoidStar}; + FunctionType *AtExitFuncTy = + FunctionType::get(Type::getVoidTy(C), AtExitFuncArgs, + /*isVarArg=*/false); + + FunctionCallee AtExit = M.getOrInsertFunction( + "__cxa_atexit", + FunctionType::get(Type::getInt32Ty(C), + {PointerType::get(AtExitFuncTy, 0), VoidStar, VoidStar}, + /*isVarArg=*/false)); + + // Declare __dso_local. + Constant *DsoHandle = M.getNamedValue("__dso_handle"); + if (!DsoHandle) { + Type *DsoHandleTy = Type::getInt8Ty(C); + GlobalVariable *Handle = new GlobalVariable( + M, DsoHandleTy, /*isConstant=*/true, + GlobalVariable::ExternalWeakLinkage, nullptr, "__dso_handle"); + Handle->setVisibility(GlobalVariable::HiddenVisibility); + DsoHandle = Handle; + } + + // For each unique priority level and associated symbol, generate a function + // to call all the destructors at that level, and a function to register the + // first function with __cxa_atexit. + for (auto &PriorityAndMore : DtorFuncs) { + uint16_t Priority = PriorityAndMore.first; + for (auto &AssociatedAndMore : PriorityAndMore.second) { + Constant *Associated = AssociatedAndMore.first; + + Function *CallDtors = Function::Create( + AtExitFuncTy, Function::PrivateLinkage, + "call_dtors" + + (Priority != UINT16_MAX ? (Twine(".") + Twine(Priority)) + : Twine()) + + (!Associated->isNullValue() ? (Twine(".") + Associated->getName()) + : Twine()), + &M); + BasicBlock *BB = BasicBlock::Create(C, "body", CallDtors); + FunctionType *VoidVoid = FunctionType::get(Type::getVoidTy(C), + /*isVarArg=*/false); + + for (auto Dtor : AssociatedAndMore.second) + CallInst::Create(VoidVoid, Dtor, "", BB); + ReturnInst::Create(C, BB); + + Function *RegisterCallDtors = Function::Create( + VoidVoid, Function::PrivateLinkage, + "register_call_dtors" + + (Priority != UINT16_MAX ? (Twine(".") + Twine(Priority)) + : Twine()) + + (!Associated->isNullValue() ? (Twine(".") + Associated->getName()) + : Twine()), + &M); + BasicBlock *EntryBB = BasicBlock::Create(C, "entry", RegisterCallDtors); + BasicBlock *FailBB = BasicBlock::Create(C, "fail", RegisterCallDtors); + BasicBlock *RetBB = BasicBlock::Create(C, "return", RegisterCallDtors); + + Value *Null = ConstantPointerNull::get(VoidStar); + Value *Args[] = {CallDtors, Null, DsoHandle}; + Value *Res = CallInst::Create(AtExit, Args, "call", EntryBB); + Value *Cmp = new ICmpInst(*EntryBB, ICmpInst::ICMP_NE, Res, + Constant::getNullValue(Res->getType())); + BranchInst::Create(FailBB, RetBB, Cmp, EntryBB); + + // If `__cxa_atexit` hits out-of-memory, trap, so that we don't misbehave. + // This should be very rare, because if the process is running out of + // memory before main has even started, something is wrong. + CallInst::Create(Intrinsic::getDeclaration(&M, Intrinsic::trap), "", + FailBB); + new UnreachableInst(C, FailBB); + + ReturnInst::Create(C, RetBB); + + // Now register the registration function with @llvm.global_ctors. + appendToGlobalCtors(M, RegisterCallDtors, Priority, Associated); + } + } + + // Now that we've lowered everything, remove @llvm.global_dtors. + GV->eraseFromParent(); + + return true; +} |