[wasm] Fix crash serializing modules w/ big frames

When a wasm function has a large stack frame, the x64 code generator
performs the stack overflow check before constructing the frame. This
requires using the `address_of_real_stack_limit` external reference, as
well as the `ThrowWasmStackOverflow` runtime function.

`ThrowWasmStackOverflow` is called via a generated trampoline, but it is
not a builtin, so the serializer adds it to the `stub_lookup_` map. This
map is encoded by using a monotonically increasing `stub_id` that starts
at 0.

When the function is serialized, a stub is differentiated from a builtin
by which half of the `i32` bits is used, upper or lower. A stub only
uses the lower 16 bits and a builtin only uses the upper 16 bits.

The deserializer checks whether the lower 16 bits are 0; if so, it is
determined to be a builtin. But if the `stub_id` is 0, then it will be
confused with builtin 0 (`RecordWrite`). Calling the builtin instead of
the stub causes a crash.

This CL starts all `stub_id`s at 1, which prevents the builtin/stub
confusion.

There is an additional bug that is not fixed by this CL:
`ThrowWasmStackOverflow` shouldn't be called at all. Currently it is
called because `address_of_real_stack_limit` is a thread-local value
that is not properly relocated.

Bug: chromium:808848
Change-Id: I06b3e650ea58ad717dcc47a3716443e16582e711
Reviewed-on: https://chromium-review.googlesource.com/981687
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52252}

src/wasm/wasm-serialization.cc

@@ -100,6 +100,9 @@ class Reader {
 
 constexpr size_t kVersionSize = 4 * sizeof(uint32_t);
 
+// Start from 1 so an encoded stub id is not confused with an encoded builtin.
+constexpr int kFirstStubId = 1;
+
 void WriteVersion(Isolate* isolate, Vector<byte> buffer) {
   DCHECK_GE(buffer.size(), kVersionSize);
   Writer writer(buffer);
@@ -304,7 +307,7 @@ void NativeModuleSerializer::BufferCopiedStubs() {
   Writer writer(remaining_);
   writer.Write(
       static_cast<uint32_t>((buff_size - sizeof(uint32_t)) / sizeof(uint32_t)));
-  uint32_t stub_id = 0;
+  uint32_t stub_id = kFirstStubId;
 
   for (auto pair : native_module_->stubs_) {
     uint32_t key = pair.first;
@@ -615,7 +618,7 @@ Address NativeModuleDeserializer::GetTrampolineOrStubFromTag(uint32_t tag) {
     return native_module_->GetLocalAddressFor(handle(builtin));
   } else {
     DCHECK_EQ(tag & 0xFFFF0000, 0);
-    return stubs_[tag];
+    return stubs_[tag - kFirstStubId];
   }
 }
 

test/mjsunit/regress/wasm/regress-808848.js

@@ -0,0 +1,71 @@
+// Copyright 2018 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.
+
+// Flags: --allow-natives-syntax
+
+load('test/mjsunit/wasm/wasm-constants.js');
+load('test/mjsunit/wasm/wasm-module-builder.js');
+
+// The number of locals must be greater than the constant defined here:
+// https://cs.chromium.org/chromium/src/v8/src/compiler/x64/code-generator-x64.cc?l=3146
+const kNumLocals = 128;
+
+function varuint32(val) {
+  let bytes = [];
+  for (let i = 0; i < 4; ++i) {
+    bytes.push(0x80 | ((val >> (7 * i)) & 0x7f));
+  }
+  bytes.push((val >> (7 * 4)) & 0x7f);
+  return bytes;
+}
+
+// Generate a function that calls the "get" import `kNumLocals` times, and
+// stores each result in a local, then calls the "call" import `kNumLocals`
+// times with the stored local values.
+//
+// The intention is to create a function that has a large stack frame.
+let body = [];
+
+for (let i = 0; i < kNumLocals; ++i) {
+  body.push(kExprCallFunction, 0, kExprSetLocal, ...varuint32(i));
+}
+
+for (let i = 0; i < kNumLocals; ++i) {
+  body.push(kExprGetLocal, ...varuint32(i), kExprCallFunction, 1);
+}
+
+let builder = new WasmModuleBuilder();
+builder.addImport('mod', 'get', kSig_i_v);
+builder.addImport('mod', 'call', kSig_v_i);
+builder.
+  addFunction('main', kSig_v_v).
+  addLocals({i32_count: kNumLocals}).
+  addBody(body).
+  exportAs('main');
+let m1_bytes = builder.toBuffer();
+let m1 = new WebAssembly.Module(m1_bytes);
+
+// Serialize the module and postMessage it to another thread.
+let serialized_m1 = %SerializeWasmModule(m1);
+
+let workerScript =
+  `onmessage = function(msg) {
+    let {serialized_m1, m1_bytes} = msg;
+
+    try {
+      let m1_clone = %DeserializeWasmModule(serialized_m1, m1_bytes);
+      let imports = {mod: {get: () => 3, call: () => {}}};
+      let i2 = new WebAssembly.Instance(m1_clone, imports);
+      i2.exports.main();
+      postMessage('done');
+    } catch(e) {
+      postMessage('done w/ exception');
+    }
+  }`;
+
+let worker = new Worker(workerScript);
+worker.postMessage({serialized_m1, m1_bytes});
+
+// Wait for worker to finish.
+print(worker.getMessage());