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