109 lines
4.6 KiB
C++
109 lines
4.6 KiB
C++
//===-- CodeGen/AsmPrinter/WasmException.cpp - Wasm Exception Impl --------===//
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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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// This file contains support for writing WebAssembly exception info into asm
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// files.
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//
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//===----------------------------------------------------------------------===//
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#include "WasmException.h"
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#include "llvm/CodeGen/AsmPrinter.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/IR/Mangler.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCStreamer.h"
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using namespace llvm;
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void WasmException::endModule() {
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// These are symbols used to throw/catch C++ exceptions and C longjmps. These
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// symbols have to be emitted somewhere once in the module. Check if each of
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// the symbols has already been created, i.e., we have at least one 'throw' or
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// 'catch' instruction with the symbol in the module, and emit the symbol only
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// if so.
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//
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// But in dynamic linking, it is in general not possible to come up with a
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// module instantiating order in which tag-defining modules are loaded before
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// the importing modules. So we make them undefined symbols here, define tags
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// in the JS side, and feed them to each importing module.
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if (!Asm->isPositionIndependent()) {
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for (const char *SymName : {"__cpp_exception", "__c_longjmp"}) {
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SmallString<60> NameStr;
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Mangler::getNameWithPrefix(NameStr, SymName, Asm->getDataLayout());
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if (Asm->OutContext.lookupSymbol(NameStr)) {
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MCSymbol *ExceptionSym = Asm->GetExternalSymbolSymbol(SymName);
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Asm->OutStreamer->emitLabel(ExceptionSym);
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}
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}
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}
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}
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void WasmException::markFunctionEnd() {
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// Get rid of any dead landing pads.
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if (!Asm->MF->getLandingPads().empty()) {
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auto *NonConstMF = const_cast<MachineFunction *>(Asm->MF);
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// Wasm does not set BeginLabel and EndLabel information for landing pads,
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// so we should set the second argument false.
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NonConstMF->tidyLandingPads(nullptr, /* TidyIfNoBeginLabels */ false);
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}
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}
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void WasmException::endFunction(const MachineFunction *MF) {
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bool ShouldEmitExceptionTable = false;
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for (const LandingPadInfo &Info : MF->getLandingPads()) {
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if (MF->hasWasmLandingPadIndex(Info.LandingPadBlock)) {
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ShouldEmitExceptionTable = true;
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break;
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}
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}
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if (!ShouldEmitExceptionTable)
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return;
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MCSymbol *LSDALabel = emitExceptionTable();
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assert(LSDALabel && ".GCC_exception_table has not been emitted!");
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// Wasm requires every data section symbol to have a .size set. So we emit an
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// end marker and set the size as the difference between the start end the end
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// marker.
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MCSymbol *LSDAEndLabel = Asm->createTempSymbol("GCC_except_table_end");
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Asm->OutStreamer->emitLabel(LSDAEndLabel);
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MCContext &OutContext = Asm->OutStreamer->getContext();
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const MCExpr *SizeExp = MCBinaryExpr::createSub(
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MCSymbolRefExpr::create(LSDAEndLabel, OutContext),
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MCSymbolRefExpr::create(LSDALabel, OutContext), OutContext);
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Asm->OutStreamer->emitELFSize(LSDALabel, SizeExp);
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}
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// Compute the call-site table for wasm EH. Even though we use the same function
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// name to share the common routines, a call site entry in the table corresponds
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// to not a call site for possibly-throwing functions but a landing pad. In wasm
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// EH the VM is responsible for stack unwinding. After an exception occurs and
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// the stack is unwound, the control flow is transferred to wasm 'catch'
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// instruction by the VM, after which the personality function is called from
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// the compiler-generated code. Refer to WasmEHPrepare pass for more
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// information.
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void WasmException::computeCallSiteTable(
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SmallVectorImpl<CallSiteEntry> &CallSites,
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SmallVectorImpl<CallSiteRange> &CallSiteRanges,
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const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
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const SmallVectorImpl<unsigned> &FirstActions) {
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MachineFunction &MF = *Asm->MF;
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for (unsigned I = 0, N = LandingPads.size(); I < N; ++I) {
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const LandingPadInfo *Info = LandingPads[I];
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MachineBasicBlock *LPad = Info->LandingPadBlock;
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// We don't emit LSDA for single catch (...).
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if (!MF.hasWasmLandingPadIndex(LPad))
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continue;
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// Wasm EH must maintain the EH pads in the order assigned to them by the
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// WasmEHPrepare pass.
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unsigned LPadIndex = MF.getWasmLandingPadIndex(LPad);
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CallSiteEntry Site = {nullptr, nullptr, Info, FirstActions[I]};
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if (CallSites.size() < LPadIndex + 1)
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CallSites.resize(LPadIndex + 1);
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CallSites[LPadIndex] = Site;
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}
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}
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