[wasm] Add a magic word and a version number to the binary.

src/wasm/encoder.cc

 // Copyright 2015 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.
 
 #include "src/signature.h"
 
 #include "src/handles.h"
 #include "src/v8.h"
 #include "src/zone-containers.h"
 
@@ skipping 443 matching lines @@
         size = size >> 7;
       }
     }
   }
 };
 
 
 WasmModuleIndex* WasmModuleWriter::WriteTo(Zone* zone) const {
   Sizes sizes = {0, 0};
 
+  sizes.Add(2 * sizeof(uint32_t), 0);  // header
+
   sizes.Add(1, 0);
   sizes.Add(kDeclMemorySize, 0);
 
   sizes.AddSection(signatures_.size());
   for (auto sig : signatures_) {
     sizes.Add(2 + sig->parameter_count(), 0);
   }
 
   sizes.AddSection(globals_.size());
   if (globals_.size() > 0) {
@@ skipping 14 matching lines @@
   sizes.AddSection(indirect_functions_.size());
   sizes.Add(2 * static_cast<uint32_t>(indirect_functions_.size()), 0);
 
   if (sizes.body_size > 0) sizes.Add(1, 0);
 
   ZoneVector<uint8_t> buffer_vector(sizes.total(), zone);
   byte* buffer = &buffer_vector[0];
   byte* header = buffer;
   byte* body = buffer + sizes.header_size;
 
+  // -- emit magic -------------------------------------------------------------
+  EmitUint32(&header, kWasmMagic);
+  EmitUint32(&header, kWasmVersion);
+
   // -- emit memory declaration ------------------------------------------------
   EmitUint8(&header, kDeclMemory);
   EmitUint8(&header, 16);  // min memory size
   EmitUint8(&header, 16);  // max memory size
   EmitUint8(&header, 0);   // memory export
 
   // -- emit globals -----------------------------------------------------------
   if (globals_.size() > 0) {
     EmitUint8(&header, kDeclGlobals);
     EmitVarInt(&header, globals_.size());
@@ skipping 69 matching lines @@
       next = next | 0x80;
     }
     output.push_back(next);
     shift += 7;
   } while ((next & 0x80) != 0);
   return output;
 }
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8