[wasm] Initial signal handler

src/trap-handler/handler-shared.cc

Index: src/trap-handler/handler-shared.cc
diff --git a/src/trap-handler/handler-shared.cc b/src/trap-handler/handler-shared.cc
new file mode 100644
index 0000000000000000000000000000000000000000..88984c6978b72eed1d71ef4a300d8db15bc577d7
--- /dev/null
+++ b/src/trap-handler/handler-shared.cc
@@ -0,0 +1,52 @@
+// Copyright 2017 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.
+
+// PLEASE READ BEFORE CHANGING THIS FILE!
+//
+// This file contains code that is used both inside and outside the out of
+// bounds signal handler. Because this code runs in a signal handler context,
+// use extra care when modifying this file. Here are some rules to follow.
+//
+// 1. Do not introduce any new external dependencies. This file needs
+//    to be self contained so it is easy to audit everything that a
+//    signal handler might do.
+//
+// 2. Any changes must be reviewed by someone from the crash reporting
+//    or security team. See OWNERS for suggested reviewers.
+//
+// For more information, see https://goo.gl/yMeyUY.
+
+#include "src/trap-handler/trap-handler-internal.h"
+
+namespace v8 {
+namespace internal {
+namespace trap_handler {
+
+THREAD_LOCAL bool g_thread_in_wasm_code = false;
+
+size_t gNumCodeObjects = 0;
+CodeProtectionInfo** gCodeObjects = nullptr;
+
+std::atomic_flag MetadataLock::spinlock_ = ATOMIC_FLAG_INIT;
+
+MetadataLock::MetadataLock() {
+  if (g_thread_in_wasm_code) {

[ahaas, 2017/02/20 09:27:24]

CHECK(!g_thread_in_wasm_code)?

[Eric Holk, 2017/02/23 02:16:57]

This code can run within a signal handler, which means there are only a handful
of functions that are safe to call. CHECK potentially pulls in a bunch of unseen
dependencies that are not safe to call from signal handlers, so it's safer not
to use it.

https://www.securecoding.cert.org/confluence/display/c/SIG30-C.+Call+only+asy...

+    abort();
+  }
+
+  while (spinlock_.test_and_set(std::memory_order::memory_order_acquire)) {
+  }
+}
+
+MetadataLock::~MetadataLock() {
+  if (g_thread_in_wasm_code) {

[ahaas, 2017/02/20 09:27:24]

same here

[Eric Holk, 2017/02/23 02:16:57]

See above comment.

+    abort();
+  }
+
+  spinlock_.clear(std::memory_order::memory_order_release);
+}
+
+}  // namespace trap_handler
+}  // namespace internal
+}  // namespace v8