[WebAssembly] Add support for the event section

Summary:
This adds support for the 'event section' specified in the exception
handling proposal. (This was named 'exception section' first, but later
renamed to 'event section' to take possibilities of other kinds of
events into consideration. But currently we only store exception info in
this section.)

The event section is added between the global section and the export
section. This is for ease of validation per request of the V8 team.

This patch:
- Creates the event symbol type, which is a weak symbol
- Makes 'throw' instruction take the event symbol '__cpp_exception'
- Adds relocation support for events
- Adds WasmObjectWriter / WasmObjectFile (Reader) support
- Adds obj2yaml / yaml2obj support
- Adds '.eventtype' printing support

Reviewers: dschuff, sbc100, aardappel

Subscribers: jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D54096

llvm-svn: 346825

13 files changed, 150 insertions, 31 deletions

diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
index 53b69eaf005..490c00aa9ec 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
@@ -86,6 +86,7 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
     const MCOperand &MO = MI.getOperand(i);
     if (MO.isReg()) {
       /* nothing to encode */
+
     } else if (MO.isImm()) {
       if (i < Desc.getNumOperands()) {
         assert(Desc.TSFlags == 0 &&
@@ -128,6 +129,7 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
                                 WebAssemblyII::VariableOpImmediateIsLabel));
         encodeULEB128(uint64_t(MO.getImm()), OS);
       }
+
     } else if (MO.isFPImm()) {
       assert(i < Desc.getNumOperands() &&
              "Unexpected floating-point immediate as a non-fixed operand");
@@ -144,22 +146,27 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
         double d = MO.getFPImm();
         support::endian::write<double>(OS, d, support::little);
       }
+
     } else if (MO.isExpr()) {
       const MCOperandInfo &Info = Desc.OpInfo[i];
       llvm::MCFixupKind FixupKind;
       size_t PaddedSize = 5;
-      if (Info.OperandType == WebAssembly::OPERAND_I32IMM) {
+      switch (Info.OperandType) {
+      case WebAssembly::OPERAND_I32IMM:
         FixupKind = MCFixupKind(WebAssembly::fixup_code_sleb128_i32);
-      } else if (Info.OperandType == WebAssembly::OPERAND_I64IMM) {
+        break;
+      case WebAssembly::OPERAND_I64IMM:
         FixupKind = MCFixupKind(WebAssembly::fixup_code_sleb128_i64);
         PaddedSize = 10;
-      } else if (Info.OperandType == WebAssembly::OPERAND_FUNCTION32 ||
-                 Info.OperandType == WebAssembly::OPERAND_OFFSET32 ||
-                 Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
+        break;
+      case WebAssembly::OPERAND_FUNCTION32:
+      case WebAssembly::OPERAND_OFFSET32:
+      case WebAssembly::OPERAND_TYPEINDEX:
+      case WebAssembly::OPERAND_GLOBAL:
+      case WebAssembly::OPERAND_EVENT:
         FixupKind = MCFixupKind(WebAssembly::fixup_code_uleb128_i32);
-      } else if (Info.OperandType == WebAssembly::OPERAND_GLOBAL) {
-        FixupKind = MCFixupKind(WebAssembly::fixup_code_uleb128_i32);
-      } else {
+        break;
+      default:
         llvm_unreachable("unexpected symbolic operand kind");
       }
       Fixups.push_back(MCFixup::create(OS.tell() - Start, MO.getExpr(),
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h
index 730bb8d6c79..69d4db96323 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h
@@ -77,6 +77,8 @@ enum OperandType {
   OPERAND_SIGNATURE,
   /// type signature immediate for call_indirect.
   OPERAND_TYPEINDEX,
+  /// Event index.
+  OPERAND_EVENT,
 };
 } // end namespace WebAssembly
 
@@ -97,7 +99,8 @@ enum TOF {
   // Flags to indicate the type of the symbol being referenced
   MO_SYMBOL_FUNCTION = 0x1,
   MO_SYMBOL_GLOBAL = 0x2,
-  MO_SYMBOL_MASK = 0x3,
+  MO_SYMBOL_EVENT = 0x4,
+  MO_SYMBOL_MASK = 0x7,
 };
 } // end namespace WebAssemblyII
 
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
index 4c4ca4e599c..ada687e20e1 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
@@ -100,12 +100,28 @@ void WebAssemblyTargetAsmStreamer::emitIndirectFunctionType(
 }
 
 void WebAssemblyTargetAsmStreamer::emitGlobalType(MCSymbolWasm *Sym) {
+  assert(Sym->isGlobal());
   OS << "\t.globaltype\t" << Sym->getName() << ", " <<
         WebAssembly::TypeToString(
           static_cast<wasm::ValType>(Sym->getGlobalType().Type)) <<
         '\n';
 }
 
+void WebAssemblyTargetAsmStreamer::emitEventType(MCSymbolWasm *Sym) {
+  assert(Sym->isEvent());
+  OS << "\t.eventtype\t" << Sym->getName();
+  if (Sym->getSignature()->Returns.empty())
+    OS << ", void";
+  else {
+    assert(Sym->getSignature()->Returns.size() == 1);
+    OS << ", "
+       << WebAssembly::TypeToString(Sym->getSignature()->Returns.front());
+  }
+  for (auto Ty : Sym->getSignature()->Params)
+    OS << ", " << WebAssembly::TypeToString(Ty);
+  OS << '\n';
+}
+
 void WebAssemblyTargetAsmStreamer::emitImportModule(MCSymbolWasm *Sym,
                                                     StringRef ModuleName) {
   OS << "\t.import_module\t" << Sym->getName() << ", " << ModuleName << '\n';
@@ -159,6 +175,9 @@ void WebAssemblyTargetWasmStreamer::emitGlobalType(MCSymbolWasm *Sym) {
   // Not needed.
 }
 
+void WebAssemblyTargetWasmStreamer::emitEventType(MCSymbolWasm *Sym) {
+  // Not needed.
+}
 void WebAssemblyTargetWasmStreamer::emitImportModule(MCSymbolWasm *Sym,
                                                      StringRef ModuleName) {
   Sym->setModuleName(ModuleName);
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h
index e60158b5def..68527542e3e 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h
@@ -45,6 +45,8 @@ public:
   virtual void emitIndIdx(const MCExpr *Value) = 0;
   /// .globaltype
   virtual void emitGlobalType(MCSymbolWasm *Sym) = 0;
+  /// .eventtype
+  virtual void emitEventType(MCSymbolWasm *Sym) = 0;
   /// .import_module
   virtual void emitImportModule(MCSymbolWasm *Sym, StringRef ModuleName) = 0;
 
@@ -66,6 +68,7 @@ public:
   void emitIndirectFunctionType(MCSymbolWasm *Symbol) override;
   void emitIndIdx(const MCExpr *Value) override;
   void emitGlobalType(MCSymbolWasm *Sym) override;
+  void emitEventType(MCSymbolWasm *Sym) override;
   void emitImportModule(MCSymbolWasm *Sym, StringRef ModuleName) override;
 };
 
@@ -81,6 +84,7 @@ public:
   void emitIndirectFunctionType(MCSymbolWasm *Symbol) override;
   void emitIndIdx(const MCExpr *Value) override;
   void emitGlobalType(MCSymbolWasm *Sym) override;
+  void emitEventType(MCSymbolWasm *Sym) override;
   void emitImportModule(MCSymbolWasm *Sym, StringRef ModuleName) override;
 };
 
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp
index d9ed146ede7..763e30be8e0 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp
@@ -86,6 +86,11 @@ static bool IsGlobalType(const MCValue &Target) {
   return RefA && RefA->getKind() == MCSymbolRefExpr::VK_WebAssembly_GLOBAL;
 }
 
+static bool IsEventType(const MCValue &Target) {
+  const MCSymbolRefExpr *RefA = Target.getSymA();
+  return RefA && RefA->getKind() == MCSymbolRefExpr::VK_WebAssembly_EVENT;
+}
+
 unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
                                                    const MCFixup &Fixup) const {
   // WebAssembly functions are not allocated in the data address space. To
@@ -106,6 +111,8 @@ unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
       return wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB;
     if (IsFunction)
       return wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB;
+    if (IsEventType(Target))
+      return wasm::R_WEBASSEMBLY_EVENT_INDEX_LEB;
     return wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB;
   case FK_Data_4:
     if (IsFunction)
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
index 1e21ab92b62..66fa91bd4d9 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
@@ -79,11 +79,12 @@ WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
 
 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
   for (auto &It : OutContext.getSymbols()) {
-    // Emit a .globaltype declaration.
+    // Emit a .globaltype and .eventtype declaration.
     auto Sym = cast<MCSymbolWasm>(It.getValue());
-    if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_GLOBAL) {
+    if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_GLOBAL)
       getTargetStreamer()->emitGlobalType(Sym);
-    }
+    else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_EVENT)
+      getTargetStreamer()->emitEventType(Sym);
   }
 
   for (const auto &F : M) {
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISD.def b/llvm/lib/Target/WebAssembly/WebAssemblyISD.def
index 444a087605e..e987d7f7f43 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISD.def
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISD.def
@@ -25,5 +25,6 @@ HANDLE_NODETYPE(SHUFFLE)
 HANDLE_NODETYPE(VEC_SHL)
 HANDLE_NODETYPE(VEC_SHR_S)
 HANDLE_NODETYPE(VEC_SHR_U)
+HANDLE_NODETYPE(THROW)
 
 // add memory opcodes starting at ISD::FIRST_TARGET_MEMORY_OPCODE here...
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
index 46f8877198c..418ceca5713 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -24,6 +24,7 @@
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/SelectionDAG.h"
+#include "llvm/CodeGen/WasmEHFuncInfo.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/DiagnosticPrinter.h"
 #include "llvm/IR/Function.h"
@@ -234,6 +235,7 @@ WebAssemblyTargetLowering::WebAssemblyTargetLowering(
 
   // Exception handling intrinsics
   setOperationAction(ISD::INTRINSIC_WO_CHAIN, MVT::Other, Custom);
+  setOperationAction(ISD::INTRINSIC_VOID, MVT::Other, Custom);
 
   setMaxAtomicSizeInBitsSupported(64);
 }
@@ -882,6 +884,8 @@ SDValue WebAssemblyTargetLowering::LowerOperation(SDValue Op,
   case ISD::EXTRACT_VECTOR_ELT:
   case ISD::INSERT_VECTOR_ELT:
     return LowerAccessVectorElement(Op, DAG);
+  case ISD::INTRINSIC_VOID:
+    return LowerINTRINSIC_VOID(Op, DAG);
   case ISD::VECTOR_SHUFFLE:
     return LowerVECTOR_SHUFFLE(Op, DAG);
   case ISD::SHL:
@@ -1046,6 +1050,44 @@ WebAssemblyTargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
 }
 
 SDValue
+WebAssemblyTargetLowering::LowerINTRINSIC_VOID(SDValue Op,
+                                               SelectionDAG &DAG) const {
+  MachineFunction &MF = DAG.getMachineFunction();
+  unsigned IntNo = cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
+  SDLoc DL(Op);
+
+  switch (IntNo) {
+  default:
+    return {}; // Don't custom lower most intrinsics.
+
+  case Intrinsic::wasm_throw: {
+    int Tag = cast<ConstantSDNode>(Op.getOperand(2).getNode())->getZExtValue();
+    switch (Tag) {
+    case CPP_EXCEPTION: {
+      const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+      MVT PtrVT = TLI.getPointerTy(DAG.getDataLayout());
+      const char *SymName = MF.createExternalSymbolName("__cpp_exception");
+      SDValue SymNode =
+          DAG.getNode(WebAssemblyISD::Wrapper, DL, PtrVT,
+                      DAG.getTargetExternalSymbol(
+                          SymName, PtrVT, WebAssemblyII::MO_SYMBOL_EVENT));
+      return DAG.getNode(WebAssemblyISD::THROW, DL,
+                         MVT::Other, // outchain type
+                         {
+                             Op.getOperand(0), // inchain
+                             SymNode,          // exception symbol
+                             Op.getOperand(3)  // thrown value
+                         });
+    }
+    default:
+      llvm_unreachable("Invalid tag!");
+    }
+    break;
+  }
+  }
+}
+
+SDValue
 WebAssemblyTargetLowering::LowerVECTOR_SHUFFLE(SDValue Op,
                                                SelectionDAG &DAG) const {
   SDLoc DL(Op);
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h
index 5182a58efc7..80076818de7 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h
@@ -98,6 +98,7 @@ private:
   SDValue LowerVASTART(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerCopyToReg(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerINTRINSIC_WO_CHAIN(SDValue Op, SelectionDAG &DAG) const;
+  SDValue LowerINTRINSIC_VOID(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVECTOR_SHUFFLE(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerAccessVectorElement(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerShift(SDValue Op, SelectionDAG &DAG) const;
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
index 0af94ef8755..718bbfa54b9 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
@@ -146,14 +146,16 @@ let Predicates = [HasExceptionHandling] in {
 
 // Throwing an exception: throw / rethrow
 let isTerminator = 1, hasCtrlDep = 1, isBarrier = 1 in {
-defm THROW_I32 : I<(outs), (ins i32imm:$tag, I32:$val),
-                   (outs), (ins i32imm:$tag),
-                   [(int_wasm_throw imm:$tag, I32:$val)],
+defm THROW_I32 : I<(outs), (ins event_op:$tag, I32:$val),
+                   (outs), (ins event_op:$tag),
+                   [(WebAssemblythrow (WebAssemblywrapper texternalsym:$tag),
+                                      I32:$val)],
                    "throw   \t$tag, $val", "throw   \t$tag",
                    0x08>;
-defm THROW_I64 : I<(outs), (ins i32imm:$tag, I64:$val),
-                   (outs), (ins i32imm:$tag),
-                   [(int_wasm_throw imm:$tag, I64:$val)],
+defm THROW_I64 : I<(outs), (ins event_op:$tag, I64:$val),
+                   (outs), (ins event_op:$tag),
+                   [(WebAssemblythrow (WebAssemblywrapper texternalsym:$tag),
+                                      I64:$val)],
                    "throw   \t$tag, $val", "throw   \t$tag",
                    0x08>;
 defm RETHROW : NRI<(outs), (ins bb_op:$dst), [], "rethrow \t$dst", 0x09>;
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
index 8fff924265f..085c5a77e68 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
@@ -64,6 +64,7 @@ def SDT_WebAssemblyArgument : SDTypeProfile<1, 1, [SDTCisVT<1, i32>]>;
 def SDT_WebAssemblyReturn   : SDTypeProfile<0, -1, []>;
 def SDT_WebAssemblyWrapper  : SDTypeProfile<1, 1, [SDTCisSameAs<0, 1>,
                                                    SDTCisPtrTy<0>]>;
+def SDT_WebAssemblyThrow    : SDTypeProfile<0, 2, [SDTCisPtrTy<0>]>;
 
 //===----------------------------------------------------------------------===//
 // WebAssembly-specific DAG Nodes.
@@ -90,6 +91,8 @@ def WebAssemblyreturn   : SDNode<"WebAssemblyISD::RETURN",
                                  SDT_WebAssemblyReturn, [SDNPHasChain]>;
 def WebAssemblywrapper  : SDNode<"WebAssemblyISD::Wrapper",
                                  SDT_WebAssemblyWrapper>;
+def WebAssemblythrow : SDNode<"WebAssemblyISD::THROW", SDT_WebAssemblyThrow,
+                              [SDNPHasChain]>;
 
 //===----------------------------------------------------------------------===//
 // WebAssembly-specific Operands.
@@ -140,6 +143,10 @@ let OperandType = "OPERAND_P2ALIGN" in {
 def P2Align : Operand<i32> {
   let PrintMethod = "printWebAssemblyP2AlignOperand";
 }
+
+let OperandType = "OPERAND_EVENT" in
+def event_op : Operand<i32>;
+
 } // OperandType = "OPERAND_P2ALIGN"
 
 let OperandType = "OPERAND_SIGNATURE" in {
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
index 1dad7b8a289..fa862fbaa63 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
@@ -75,10 +75,10 @@ MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
       cast<MCSymbolWasm>(Printer.GetExternalSymbolSymbol(Name));
   const WebAssemblySubtarget &Subtarget = Printer.getSubtarget();
 
-  // __stack_pointer is a global variable; all other external symbols used by
-  // CodeGen are functions.  It's OK to hardcode knowledge of specific symbols
-  // here; this method is precisely there for fetching the signatures of known
-  // Clang-provided symbols.
+  // Except for the two exceptions (__stack_pointer and __cpp_exception), all
+  // other external symbols used by CodeGen are functions. It's OK to hardcode
+  // knowledge of specific symbols here; this method is precisely there for
+  // fetching the signatures of known Clang-provided symbols.
   if (strcmp(Name, "__stack_pointer") == 0) {
     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
     WasmSym->setGlobalType(wasm::WasmGlobalType{
@@ -90,24 +90,45 @@ MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
 
   SmallVector<wasm::ValType, 4> Returns;
   SmallVector<wasm::ValType, 4> Params;
-  GetLibcallSignature(Subtarget, Name, Returns, Params);
+  if (strcmp(Name, "__cpp_exception") == 0) {
+    WasmSym->setType(wasm::WASM_SYMBOL_TYPE_EVENT);
+    // We can't confirm its signature index for now because there can be
+    // imported exceptions. Set it to be 0 for now.
+    WasmSym->setEventType(
+        {wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION, /* SigIndex */ 0});
+    // We may have multiple C++ compilation units to be linked together, each of
+    // which defines the exception symbol. To resolve them, we declare them as
+    // weak.
+    WasmSym->setWeak(true);
+    WasmSym->setExternal(true);
+
+    // All C++ exceptions are assumed to have a single i32 (for wasm32) or i64
+    // (for wasm64) param type and void return type. The reaon is, all C++
+    // exception values are pointers, and to share the type section with
+    // functions, exceptions are assumed to have void return type.
+    Params.push_back(Subtarget.hasAddr64() ? wasm::ValType::I64
+                                           : wasm::ValType::I32);
+  } else { // Function symbols
+    WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
+    GetLibcallSignature(Subtarget, Name, Returns, Params);
+  }
   auto Signature =
       make_unique<wasm::WasmSignature>(std::move(Returns), std::move(Params));
   WasmSym->setSignature(Signature.get());
   Printer.addSignature(std::move(Signature));
-  WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
 
   return WasmSym;
 }
 
 MCOperand WebAssemblyMCInstLower::LowerSymbolOperand(MCSymbol *Sym,
                                                      int64_t Offset,
-                                                     bool IsFunc,
-                                                     bool IsGlob) const {
+                                                     bool IsFunc, bool IsGlob,
+                                                     bool IsEvent) const {
   MCSymbolRefExpr::VariantKind VK =
       IsFunc ? MCSymbolRefExpr::VK_WebAssembly_FUNCTION
              : IsGlob ? MCSymbolRefExpr::VK_WebAssembly_GLOBAL
-                      : MCSymbolRefExpr::VK_None;
+                      : IsEvent ? MCSymbolRefExpr::VK_WebAssembly_EVENT
+                                : MCSymbolRefExpr::VK_None;
 
   const MCExpr *Expr = MCSymbolRefExpr::create(Sym, VK, Ctx);
 
@@ -116,6 +137,8 @@ MCOperand WebAssemblyMCInstLower::LowerSymbolOperand(MCSymbol *Sym,
       report_fatal_error("Function addresses with offsets not supported");
     if (IsGlob)
       report_fatal_error("Global indexes with offsets not supported");
+    if (IsEvent)
+      report_fatal_error("Event indexes with offsets not supported");
     Expr =
         MCBinaryExpr::createAdd(Expr, MCConstantExpr::create(Offset, Ctx), Ctx);
   }
@@ -218,7 +241,7 @@ void WebAssemblyMCInstLower::Lower(const MachineInstr *MI,
              "WebAssembly does not use target flags on GlobalAddresses");
       MCOp = LowerSymbolOperand(GetGlobalAddressSymbol(MO), MO.getOffset(),
                                 MO.getGlobal()->getValueType()->isFunctionTy(),
-                                false);
+                                false, false);
       break;
     case MachineOperand::MO_ExternalSymbol:
       // The target flag indicates whether this is a symbol for a
@@ -228,14 +251,16 @@ void WebAssemblyMCInstLower::Lower(const MachineInstr *MI,
       MCOp = LowerSymbolOperand(
           GetExternalSymbolSymbol(MO), /*Offset=*/0,
           (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_FUNCTION) != 0,
-          (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_GLOBAL) != 0);
+          (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_GLOBAL) != 0,
+          (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_EVENT) != 0);
       break;
     case MachineOperand::MO_MCSymbol:
       // This is currently used only for LSDA symbols (GCC_except_table),
       // because global addresses or other external symbols are handled above.
       assert(MO.getTargetFlags() == 0 &&
              "WebAssembly does not use target flags on MCSymbol");
-      MCOp = LowerSymbolOperand(MO.getMCSymbol(), /*Offset=*/0, false, false);
+      MCOp = LowerSymbolOperand(MO.getMCSymbol(), /*Offset=*/0, false, false,
+                                false);
       break;
     }
 
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.h b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.h
index 54a55796415..fa7a0ea61b3 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.h
@@ -34,7 +34,7 @@ class LLVM_LIBRARY_VISIBILITY WebAssemblyMCInstLower {
   MCSymbol *GetGlobalAddressSymbol(const MachineOperand &MO) const;
   MCSymbol *GetExternalSymbolSymbol(const MachineOperand &MO) const;
   MCOperand LowerSymbolOperand(MCSymbol *Sym, int64_t Offset, bool IsFunc,
-                               bool IsGlob) const;
+                               bool IsGlob, bool IsEvent) const;
 
 public:
   WebAssemblyMCInstLower(MCContext &ctx, WebAssemblyAsmPrinter &printer)