Index: test/wasm/Inputs/comdat2.ll
===================================================================
--- test/wasm/Inputs/comdat2.ll
+++ test/wasm/Inputs/comdat2.ll
@@ -9,5 +9,5 @@
 
 define i32 @callInline2() {
 entry:
-    ret i32 ptrtoint (i32 ()* @inlineFn to i32)
+  ret i32 ptrtoint (i32 ()* @inlineFn to i32)
 }
Index: test/wasm/entry-signature.ll
===================================================================
--- /dev/null
+++ test/wasm/entry-signature.ll
@@ -0,0 +1,11 @@
+; Verify that the entry point signauture can be flexible.
+; RUN: llc -filetype=obj %s -o %t.o
+; RUN: wasm-ld -o %t1.wasm %t.o
+
+target triple = "wasm32-unknown-unknown-wasm"
+
+define hidden i32 @_start(i32, i64) local_unnamed_addr #0 {
+entry:
+  ret i32 0
+}
+
Index: test/wasm/entry.ll
===================================================================
--- test/wasm/entry.ll
+++ test/wasm/entry.ll
@@ -28,8 +28,8 @@
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:   - Type:
 
-; The __wasm_call_ctors is somewhat special.  Make sure we can use it
-; as the entry point if we choose
+; The __wasm_call_ctors is somewhat special since its created by the linker.
+; Make sure we can use it as the entry point if we choose
 ; RUN: wasm-ld --entry=__wasm_call_ctors -o %t3.wasm %t.o
 ; RUN: obj2yaml %t3.wasm | FileCheck %s -check-prefix=CHECK-CTOR
 
Index: test/wasm/fatal-warnings.ll
===================================================================
--- test/wasm/fatal-warnings.ll
+++ test/wasm/fatal-warnings.ll
@@ -1,14 +1,17 @@
 ; RUN: llc -filetype=obj %s -o %t.main.o
-; RUN: lld -flavor wasm -o %t.wasm %t.main.o 2>&1 | FileCheck %s -check-prefix=CHECK-WARN
-; RUN: not lld -flavor wasm --fatal-warnings -o %t.wasm %t.main.o 2>&1 | FileCheck %s -check-prefix=CHECK-FATAL
+; RUN: llc -filetype=obj %p/Inputs/ret32.ll -o %t.ret32.o
+; RUN: lld -flavor wasm -o %t.wasm %t.main.o %t.ret32.o 2>&1 | FileCheck %s -check-prefix=CHECK-WARN
+; RUN: not lld -flavor wasm --fatal-warnings -o %t.wasm %t.main.o %t.ret32.o 2>&1 | FileCheck %s -check-prefix=CHECK-FATAL
 
-; CHECK-WARN: warning: Function type mismatch: _start
-; CHECK-FATAL: error: Function type mismatch: _start
+; CHECK-WARN: warning: Function type mismatch: ret32
+; CHECK-FATAL: error: Function type mismatch: ret32
 
 target triple = "wasm32-unknown-unknown-wasm"
 
-define hidden i32 @_start(i32 %arg) local_unnamed_addr {
+define hidden void @_start() local_unnamed_addr #0 {
 entry:
-  ret i32 %arg
+  %call = tail call i32 @ret32(i32 1, i64 2, i32 3) #2
+  ret void
 }
 
+declare i32 @ret32(i32, i64, i32) local_unnamed_addr #1
Index: wasm/Driver.cpp
===================================================================
--- wasm/Driver.cpp
+++ wasm/Driver.cpp
@@ -358,9 +358,11 @@
         "__dso_handle", WASM_SYMBOL_VISIBILITY_HIDDEN);
     WasmSym::DataEnd = Symtab->addSyntheticDataSymbol("__data_end", 0);
 
+    // For now, since we don't actually use the start function as the
+    // wasm start symbol, we don't need to care about it signature.
     if (!Config->Entry.empty())
-      EntrySym = Symtab->addUndefinedFunction(Config->Entry, 0, nullptr,
-                                              &NullSignature);
+      EntrySym =
+          Symtab->addUndefinedFunction(Config->Entry, 0, nullptr, nullptr);
 
     // Handle the `--undefined <sym>` options.
     for (auto *Arg : Args.filtered(OPT_undefined))
Index: wasm/SymbolTable.cpp
===================================================================
--- wasm/SymbolTable.cpp
+++ wasm/SymbolTable.cpp
@@ -78,14 +78,14 @@
 
 static void checkFunctionType(const Symbol *Existing, const InputFile *File,
                               const WasmSignature *NewSig) {
-  if (!isa<FunctionSymbol>(Existing)) {
+  auto ExistingFunction = dyn_cast<FunctionSymbol>(Existing);
+  if (!ExistingFunction) {
     reportTypeError(Existing, File, "Function");
     return;
   }
 
-  const WasmSignature *OldSig =
-      cast<FunctionSymbol>(Existing)->getFunctionType();
-  if (OldSig && *NewSig != *OldSig) {
+  const WasmSignature *OldSig = ExistingFunction->getFunctionType();
+  if (OldSig && NewSig && *NewSig != *OldSig) {
     warn("Function type mismatch: " + Existing->getName() +
          "\n>>> defined as " + toString(*OldSig) + " in " +
          toString(Existing->getFile()) + "\n>>> defined as " +
Index: wasm/Writer.cpp
===================================================================
--- wasm/Writer.cpp
+++ wasm/Writer.cpp
@@ -742,12 +742,18 @@
     if (!Sym->isLive())
       continue;
 
-    DEBUG(dbgs() << "import: " << Sym->getName() << "\n");
-    ImportedSymbols.emplace_back(Sym);
-    if (auto *F = dyn_cast<FunctionSymbol>(Sym))
+    if (auto *F = dyn_cast<FunctionSymbol>(Sym)) {
+      if (F->getFunctionType() == nullptr) {
+        assert(Config->AllowUndefined);
+        continue;
+      }
       F->setFunctionIndex(NumImportedFunctions++);
-    else
+    } else {
       cast<GlobalSymbol>(Sym)->setGlobalIndex(NumImportedGlobals++);
+    }
+
+    ImportedSymbols.emplace_back(Sym);
+    DEBUG(dbgs() << "import: " << Sym->getName() << "\n");
   }
 }