[wasm] Add a JavaScript utility to make it easier to build WASM modules from JavaScript.

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

Index: test/mjsunit/wasm/wasm-module-builder.js
diff --git a/test/mjsunit/wasm/wasm-module-builder.js b/test/mjsunit/wasm/wasm-module-builder.js
new file mode 100644
index 0000000000000000000000000000000000000000..faec8fe738612680151095d175806e6e10e5fd69
--- /dev/null
+++ b/test/mjsunit/wasm/wasm-module-builder.js
@@ -0,0 +1,311 @@
+// 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 StringRef(string) {
+  this.pos = -1;
+  this.string = string;
+}
+
+function DataRef(data) {
+  this.pos = -1;
+  this.data = data;
+}
+
+function WasmFunctionBuilder(name, sig_index) {
+  this.name = name;
+  this.sig_index = sig_index;
+  this.exports = [];
+}
+
+WasmFunctionBuilder.prototype.ExportAs =

[binji, 2016/03/04 05:13:26]

isn't JavaScript style lowerCamelCase?

+    function(name) {
+  this.exports.push(name);
+  return this;
+}
+
+WasmFunctionBuilder.prototype.AddBody = function(body) {
+  this.body = body;
+  return this;
+}
+
+WasmFunctionBuilder.prototype.AddLocals = function(locals) {
+  this.locals = locals;
+  return this;
+}
+
+function WasmModuleBuilder() {
+    this.signatures = new Array();

[binji, 2016/03/04 05:13:26]

this.memory = null;

Otherwise it just magically appears. :)

[binji, 2016/03/04 05:13:26]

why not []?

[titzer, 2016/03/05 01:26:22]

That's the JS way; M-O-O-N spells undefined!

+    this.imports = new Array();
+    this.functions = new Array();
+    this.exports = new Array();
+    this.function_table = new Array();
+    this.data_segments = new Array();
+    return this;
+}
+
+WasmModuleBuilder.prototype.AddMemory = function(min, max, exp) {
+  this.memory = {min: min, max: max, exp: exp};
+  return this;
+}
+
+WasmModuleBuilder.prototype.AddSignature = function(sig) {

[binji, 2016/03/04 05:13:26]

mention the expected type/format of sig?

[titzer, 2016/03/05 01:26:22]

Done.

+  // TODO: canonicalize signatures?
+  this.signatures.push(sig);
+  return this.signatures.length - 1;
+}
+
+WasmModuleBuilder.prototype.AddFunction = function(name, sig) {
+  var sig_index = (typeof sig) == "number" ? sig : this.AddSignature(sig);
+  var func = new WasmFunctionBuilder(name, sig_index);
+  func.index = this.functions.length;
+  this.functions.push(func);
+  return func;
+}
+
+WasmModuleBuilder.prototype.AddImport = function(name, sig) {
+  var sig_index = (typeof sig) == "number" ? sig : this.AddSignature(sig);
+  this.imports.push({name: name, sig_index: sig_index});
+  return this.imports.length - 1;
+}
+
+WasmModuleBuilder.prototype.AddDataSegment = function(addr, data, init) {
+  this.data_segments.push({addr: addr, data: data, init: init});
+  return this.data_segments.length - 1;
+}
+
+WasmModuleBuilder.prototype.AppendToFunctionTable = function(array) {
+  this.function_table = this.function_table.concat(array);
+  return this;
+}
+
+function emit_u8(bytes, val) {
+    bytes.push(val & 0xff);
+}
+
+function emit_u16(bytes, val) {
+    bytes.push(val & 0xff);
+    bytes.push((val >> 8) & 0xff);
+}
+
+function emit_u32(bytes, val) {
+    bytes.push(val & 0xff);
+    bytes.push((val >> 8) & 0xff);
+    bytes.push((val >> 16) & 0xff);
+    bytes.push((val >> 24) & 0xff);
+}
+
+function emit_string(bytes, string) {
+    bytes.push(new StringRef(string));
+    bytes.push(0);
+    bytes.push(0);
+    bytes.push(0);
+}
+
+function emit_data_ref(bytes, string) {
+    bytes.push(new DataRef(string));

[binji, 2016/03/04 05:13:26]

Neat trick, but why not just store the Ref in a separate list that you fix up
afterward? That way you don't have to iterate over bytes that you know aren't
StringRef or DataRefs.

[titzer, 2016/03/05 01:26:22]

I started doing that but it was getting unwieldy with four different lists and a
map for canonicalization, with the lists having positions, etc. Can do that in a
followup CL if necessary.

+    bytes.push(0);
+    bytes.push(0);
+    bytes.push(0);
+}
+
+function emit_varint(bytes, val) {
+    while (true) {
+        var v = val & 0xff;
+        val = val >>> 7;
+        if (val == 0) {
+            bytes.push(v);
+            break;
+        }
+        bytes.push(v | 0x80);
+    }
+}
+
+WasmModuleBuilder.prototype.ToArray = function(debug) {
+    // Add header bytes
+    var bytes = new Array();
+    bytes = bytes.concat([kWasmH0, kWasmH1, kWasmH2, kWasmH3, kWasmV0, kWasmV1, kWasmV2, kWasmV3]);
+
+    // Add memory section
+    if (this.memory != undefined) {
+    if (debug) print("emiting memory @ " + bytes.length);

[binji, 2016/03/04 05:13:26]

sp: emitting

[titzer, 2016/03/05 01:26:22]

Done.

+    emit_u8(bytes, kDeclMemory);
+    emit_varint(bytes, this.memory.min);
+    emit_varint(bytes, this.memory.max);
+    emit_u8(bytes, this.memory.exp ? 1 : 0);
+  }
+
+  // Add signatures section
+  if (this.signatures.length > 0) {
+    if (debug) print("emiting signatures @ " + bytes.length);
+    emit_u8(bytes, kDeclSignatures);
+    emit_varint(bytes, this.signatures.length);
+    for (var i = 0; i < this.signatures.length; i++) {

[binji, 2016/03/04 05:13:26]

for-of here too?

[titzer, 2016/03/05 01:26:22]

Done.

+      var sig = this.signatures[i];
+      var params = sig.length - 1;
+      emit_u8(bytes, params);
+      for (var j = 0; j < sig.length; j++) {
+        emit_u8(bytes, sig[j]);
+      }
+    }
+  }
+
+  // Add imports section
+  if (this.imports.length > 0) {
+    if (debug) print("emiting imports @ " + bytes.length);
+    emit_u8(bytes, kDeclImportTable);
+    emit_varint(bytes, this.imports.length);
+    for (imp of this.imports) {
+      emit_u16(bytes, imp.sig_index);
+      emit_string(bytes, "");
+      emit_string(bytes, imp.name);
+    }
+  }
+
+  // Add functions section
+  var names = false;
+  var exports = 0;
+  if (this.functions.length > 0) {
+    if (debug) print("emiting functions @ " + bytes.length);
+    emit_u8(bytes, kDeclFunctions);
+    emit_varint(bytes, this.functions.length);
+    var index = 0;
+    for (func of this.functions) {
+      var flags = 0;
+      var hasName = func.name != undefined && func.name.length > 0;
+      names = names || hasName;
+      if (hasName) flags |= kDeclFunctionName;
+      if (func.locals != undefined) flags |= kDeclFunctionLocals;
+      exports += func.exports.length;
+
+      emit_u8(bytes, flags);
+      emit_u16(bytes, func.sig_index);
+
+      if (hasName) {
+        emit_string(bytes, func.name);
+      }
+      if (func.locals != undefined) {
+        emit_u16(bytes, func.locals.i32_count);
+        emit_u16(bytes, func.locals.i64_count);
+        emit_u16(bytes, func.locals.f32_count);
+        emit_u16(bytes, func.locals.f64_count);
+      }
+      emit_u16(bytes, func.body.length);
+      for (var i = 0; i < func.body.length; i++) {
+        emit_u8(bytes, func.body[i]);
+      }
+
+      index++;
+    }
+  }
+
+  if (this.function_table.length > 0) {
+    if (debug) print("emiting function table @ " + bytes.length);
+    emit_u8(bytes, kDeclFunctionTable);
+    emit_varint(bytes, this.function_table.length);
+    for (index of this.function_table) {
+      emit_u16(bytes, index);
+    }
+  }
+
+  if (exports > 0) {
+    if (debug) print("emiting exports @ " + bytes.length);
+    emit_u8(bytes, kDeclExportTable);
+    emit_varint(bytes, exports);
+    for (func of this.functions) {
+      for (exp of func.exports) {
+        emit_u16(bytes, func.index);
+        emit_string(bytes, exp);
+      }
+    }
+  }
+
+  if (this.data_segments.length > 0) {
+    if (debug) print("emiting data segments @ " + bytes.length);
+    emit_u8(bytes, kDeclDataSegments);
+    emit_varint(bytes, this.data_segments.length);
+    for (seg of this.data_segments) {
+      emit_u32(bytes, seg.addr);
+      emit_data_ref(bytes, seg.data);
+      emit_u32(bytes, seg.data.length);
+      emit_u8(bytes, seg.init ? 1 : 0);
+    }
+  }
+
+  // End the module.
+  if (debug) print("emiting end @ " + bytes.length);
+  emit_u8(bytes, kDeclEnd);
+
+  // Collect references and canonicalize strings.
+  var strings = new Object();
+  var data_segments = new Array();
+  var count = 0;
+  for (var i = 0; i < bytes.length; i++) {
+    var b = bytes[i];
+    if (b instanceof StringRef) {
+      count++;
+      var prev = strings[b.string];
+      if (prev) {
+        bytes[i] = prev;
+      } else {
+        strings[b.string] = b;
+      }
+    }
+    if (b instanceof DataRef) {
+      data_segments.push(b);
+      count++;
+    }
+  }
+
+  if (count > 0) {
+    // Emit strings.
+    if (debug) print("emiting strings @ " + bytes.length);
+    for (str in strings) {
+      var ref = strings[str];
+      if (!(ref instanceof StringRef)) continue;
+      if (debug) print("  \"" + str + "\" @ " + bytes.length);
+      ref.pos = bytes.length;
+      for (var i = 0; i < str.length; i++) {
+        emit_u8(bytes, str.charCodeAt(i));
+      }
+      emit_u8(bytes, 0);  // null terminator.
+    }
+    // Emit data.
+    if (debug) print("emiting data @ " + bytes.length);
+    for (ref of data_segments) {
+      ref.pos = bytes.length;
+      for (var i = 0; i < ref.data.length; i++) {
+        emit_u8(bytes, ref.data[i]);
+      }
+    }
+    // Update references to strings and data.
+    for (var i = 0; i < bytes.length; i++) {
+      var b = bytes[i];
+      if (b instanceof StringRef || b instanceof DataRef) {
+        bytes[i] = b.pos & 0xFF;
+        bytes[i + 1] = (b.pos >> 8) & 0xFF;
+        bytes[i + 2] = (b.pos >> 16) & 0xFF;
+        bytes[i + 3] = (b.pos >> 24) & 0xFF;
+      }
+    }
+  }
+
+  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) {
+  var buffer = this.ToBuffer();
+  return _WASMEXP_.instantiateModule(buffer, ffi);
+}