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

src/wasm/module-decoder.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/macro-assembler.h"
 #include "src/objects.h"
 #include "src/v8.h"
 
 #include "src/wasm/decoder.h"
 #include "src/wasm/module-decoder.h"
@@ skipping 42 matching lines @@
     module->signatures = new std::vector<FunctionSig*>();
     module->functions = new std::vector<WasmFunction>();
     module->data_segments = new std::vector<WasmDataSegment>();
     module->function_table = new std::vector<uint16_t>();
     module->import_table = new std::vector<WasmImport>();
     module->export_table = new std::vector<WasmExport>();
 
     bool sections[kMaxModuleSectionCode];
     memset(sections, 0, sizeof(sections));
 
+    const byte* pos = pc_;
+    uint32_t magic_number = consume_u32("wasm magic");
+    if (magic_number != kWasmMagic) {
+      error(pos, pos, "expected magic bytes 0 a s m");

[JF, 2016/02/27 19:43:04]

"0 a s m" will be incorrect if we change kWasmMagic. Can you %02x %02x %02x %02x
kWasmMagic in as below instead?

Also, can you print out magic_number?

[titzer, 2016/02/27 23:05:09]

Done.

+      return toResult(module);
+    }
+
+    pos = pc_;
+    uint32_t magic_version = consume_u32("wasm version");
+    if (magic_version != kWasmVersion) {
+      error(pos, pos, "expected version %02x %02x %02x %02x",
+            (kWasmVersion & 0xff), (kWasmVersion >> 8) & 0xff,
+            (kWasmVersion >> 16) & 0xff, (kWasmVersion >> 24) & 0xff);

[JF, 2016/02/27 19:43:04]

Same here, print magic_version.

[titzer, 2016/02/27 23:05:09]

Done.

+      return toResult(module);
+    }
+
     // Decode the module sections.
     while (pc_ < limit_) {
       TRACE("DecodeSection\n");
       WasmSectionDeclCode section =
           static_cast<WasmSectionDeclCode>(consume_u8("section"));
       // Each section should appear at most once.
       if (section < kMaxModuleSectionCode) {
         CheckForPreviousSection(sections, section, false);
         sections[section] = true;
       }
@@ skipping 563 matching lines @@
   if (function_start > function_end) return FunctionError("start > end");
   if (size > kMaxFunctionSize)
     return FunctionError("size > maximum function size");
   WasmFunction* function = new WasmFunction();
   ModuleDecoder decoder(zone, function_start, function_end, false);
   return decoder.DecodeSingleFunction(module_env, function);
 }
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8