[wasm] Support undefined indirect table entries, behind a flag.

test/mjsunit/wasm/wasm-module-builder.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 function WasmFunctionBuilder(name, sig_index) {
     this.name = name;
     this.sig_index = sig_index;
     this.exports = [];
 }
 
@@ skipping 18 matching lines @@
 }
 
 function WasmModuleBuilder() {
     this.signatures = [];
     this.imports = [];
     this.functions = [];
     this.exports = [];
     this.function_table = [];
     this.data_segments = [];
     this.explicit = [];
+    this.pad = null;
     return this;
 }
 
 WasmModuleBuilder.prototype.addStart = function(start_index) {
     this.start_index = start_index;
 }
 
 WasmModuleBuilder.prototype.addMemory = function(min, max, exp) {
     this.memory = {min: min, max: max, exp: exp};
     return this;
 }
 
+WasmModuleBuilder.prototype.addPadFunctionTable = function(size) {
+    this.pad = size;
+    return this;
+}
+
 WasmModuleBuilder.prototype.addExplicitSection = function(bytes) {
   this.explicit.push(bytes);
   return this;
 }
 
 // Add a signature; format is [param_count, param0, param1, ..., retcount, ret0]
 WasmModuleBuilder.prototype.addSignature = function(sig) {
     // TODO: canonicalize signatures?
     this.signatures.push(sig);
     return this.signatures.length - 1;
@@ skipping 255 matching lines @@
         emit_section(bytes, kDeclNames, function(bytes) {
             emit_varint(bytes, wasm.functions.length);
             for (func of wasm.functions) {
                 var name = func.name == undefined ? "" : func.name;
                 emit_string(bytes, name);
                 emit_u8(bytes, 0);  // local names count == 0
             }
         });
     }
 
+    // Add an indirect function table pad section.
+    if (wasm.pad !== null) {
+        if (debug)
+          print("emitting indirect function table pad @ " + bytes.length);
+        emit_section(bytes, kDeclFunctionTablePad, function(bytes) {
+            emit_varint(bytes, wasm.pad);
+        });
+    }
+
     // End the module.
     if (debug) print("emitting end @ " + bytes.length);
     emit_section(bytes, kDeclEnd, function(bytes) {});
 
     return bytes;
 }
 
 WasmModuleBuilder.prototype.toBuffer = function(debug) {
     var bytes = this.toArray(debug);
     var buffer = new ArrayBuffer(bytes.length);
     var view = new Uint8Array(buffer);
     for (var i = 0; i < bytes.length; i++) {
         var val = bytes[i];
         if ((typeof val) == "string") val = val.charCodeAt(0);
         view[i] = val | 0;
     }
     return buffer;
 }
 
 WasmModuleBuilder.prototype.instantiate = function(ffi, memory) {
     var buffer = this.toBuffer();
     if (memory != undefined) {
       return Wasm.instantiateModule(buffer, ffi, memory);
     } else {
       return Wasm.instantiateModule(buffer, ffi);
     }
 }