[WebAssembly] Handle event exports

Summary: This handles exports of events, which was missing.

Reviewers: sbc100

Subscribers: dschuff, jgravelle-google, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77566

Author: aheejin

lld/test/wasm/event-section.ll

@@ -2,7 +2,9 @@
 ; RUN: llc -filetype=obj -exception-model=wasm -mattr=+exception-handling %p/Inputs/event-section2.ll -o %t2.o
 ; RUN: llc -filetype=obj -exception-model=wasm -mattr=+exception-handling %s -o %t.o
 ; RUN: wasm-ld -o %t.wasm %t.o %t1.o %t2.o
+; RUN: wasm-ld --export-all -o %t-export-all.wasm %t.o %t1.o %t2.o
 ; RUN: obj2yaml %t.wasm | FileCheck %s
+; RUN: obj2yaml %t-export-all.wasm | FileCheck %s --check-prefix=EXPORT-ALL
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
@@ -35,3 +37,9 @@ define void @_start() {
 
 ; Global section has to come after event section
 ; CHECK:        - Type:            GLOBAL
+
+; EXPORT-ALL:   - Type:            EXPORT
+; EXPORT-ALL-NEXT Exports:
+; EXPORT-ALL:       - Name:            __cpp_exception
+; EXPORT-ALL:         Kind:            EVENT
+; EXPORT-ALL:         Index:           0

lld/wasm/WriterUtils.cpp

@@ -217,6 +217,9 @@ void writeExport(raw_ostream &os, const WasmExport &export_) {
   case WASM_EXTERNAL_GLOBAL:
     writeUleb128(os, export_.Index, "global index");
     break;
+  case WASM_EXTERNAL_EVENT:
+    writeUleb128(os, export_.Index, "event index");
+    break;
   case WASM_EXTERNAL_MEMORY:
     writeUleb128(os, export_.Index, "memory index");
     break;