76 lines · cpp
1//===-- CodeGen/AsmPrinter/WasmException.cpp - Wasm Exception Impl --------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// This file contains support for writing WebAssembly exception info into asm10// files.11//12//===----------------------------------------------------------------------===//13 14#include "WasmException.h"15#include "llvm/CodeGen/AsmPrinter.h"16#include "llvm/CodeGen/MachineFunction.h"17#include "llvm/IR/Mangler.h"18#include "llvm/MC/MCContext.h"19#include "llvm/MC/MCStreamer.h"20using namespace llvm;21 22void WasmException::endFunction(const MachineFunction *MF) {23 bool ShouldEmitExceptionTable = false;24 for (const LandingPadInfo &Info : MF->getLandingPads()) {25 if (MF->hasWasmLandingPadIndex(Info.LandingPadBlock)) {26 ShouldEmitExceptionTable = true;27 break;28 }29 }30 if (!ShouldEmitExceptionTable)31 return;32 MCSymbol *LSDALabel = emitExceptionTable();33 assert(LSDALabel && ".GCC_exception_table has not been emitted!");34 35 // Wasm requires every data section symbol to have a .size set. So we emit an36 // end marker and set the size as the difference between the start end the end37 // marker.38 MCSymbol *LSDAEndLabel = Asm->createTempSymbol("GCC_except_table_end");39 Asm->OutStreamer->emitLabel(LSDAEndLabel);40 MCContext &OutContext = Asm->OutStreamer->getContext();41 const MCExpr *SizeExp = MCBinaryExpr::createSub(42 MCSymbolRefExpr::create(LSDAEndLabel, OutContext),43 MCSymbolRefExpr::create(LSDALabel, OutContext), OutContext);44 Asm->OutStreamer->emitELFSize(LSDALabel, SizeExp);45}46 47// Compute the call-site table for wasm EH. Even though we use the same function48// name to share the common routines, a call site entry in the table corresponds49// to not a call site for possibly-throwing functions but a landing pad. In wasm50// EH the VM is responsible for stack unwinding. After an exception occurs and51// the stack is unwound, the control flow is transferred to wasm 'catch'52// instruction by the VM, after which the personality function is called from53// the compiler-generated code. Refer to WasmEHPrepare pass for more54// information.55void WasmException::computeCallSiteTable(56 SmallVectorImpl<CallSiteEntry> &CallSites,57 SmallVectorImpl<CallSiteRange> &CallSiteRanges,58 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,59 const SmallVectorImpl<unsigned> &FirstActions) {60 MachineFunction &MF = *Asm->MF;61 for (unsigned I = 0, N = LandingPads.size(); I < N; ++I) {62 const LandingPadInfo *Info = LandingPads[I];63 MachineBasicBlock *LPad = Info->LandingPadBlock;64 // We don't emit LSDA for single catch (...).65 if (!MF.hasWasmLandingPadIndex(LPad))66 continue;67 // Wasm EH must maintain the EH pads in the order assigned to them by the68 // WasmEHPrepare pass.69 unsigned LPadIndex = MF.getWasmLandingPadIndex(LPad);70 CallSiteEntry Site = {nullptr, nullptr, Info, FirstActions[I]};71 if (CallSites.size() < LPadIndex + 1)72 CallSites.resize(LPadIndex + 1);73 CallSites[LPadIndex] = Site;74 }75}76