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to reflect the new license. We understand that people may be surprised that we're moving the header entirely to discuss the new license. We checked this carefully with the Foundation's lawyer and we believe this is the correct approach. Essentially, all code in the project is now made available by the LLVM project under our new license, so you will see that the license headers include that license only. Some of our contributors have contributed code under our old license, and accordingly, we have retained a copy of our old license notice in the top-level files in each project and repository. llvm-svn: 351636
97 lines
4.1 KiB
C++
97 lines
4.1 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/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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// This is the symbol used in 'throw' and 'if_except' instruction to denote
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// this is a C++ exception. This symbol has to be emitted somewhere once in
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// the module. Check if the symbol has already been created, i.e., we have at
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// least one 'throw' or 'if_except' instruction in the module, and emit the
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// symbol only if so.
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SmallString<60> NameStr;
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Mangler::getNameWithPrefix(NameStr, "__cpp_exception", Asm->getDataLayout());
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if (Asm->OutContext.lookupSymbol(NameStr)) {
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MCSymbol *ExceptionSym = Asm->GetExternalSymbolSymbol("__cpp_exception");
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Asm->OutStreamer->EmitLabel(ExceptionSym);
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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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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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