[wasm] Initial signal handler

src/trap-handler/trap-handler-internal.h

+// 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.
+
+#ifndef TRAP_HANDLER_INTERNAL_H_
+#define TRAP_HANDLER_INTERNAL_H_
+
+// This file should not be included (even transitively) by files outside of
+// src/trap-handler.
+
+#include "src/trap-handler/trap-handler.h"
+
+#include <atomic>
+
+namespace v8 {
+namespace internal {
+namespace trap_handler {
+
+// This describes a chunk of code that the signal handler will be able to handle
+// faults in. {base} points to the beginning of the chunk, and {size} is the
+// number of bytes in the code chunk. The remainder of the struct is a list of
+// protected memory access instructions and an offset to a landing pad to handle
+// faults on that instruction.
+struct CodeProtectionInfo {
+  void* base;
+  size_t size;
+  size_t num_protected_instructions;
+  ProtectedInstructionData instructions[1];
+};
+
+class MetadataLock {
+  static std::atomic_flag spinlock_;
+
+ public:
+  MetadataLock();
+  ~MetadataLock();
+
+  // We'd normally use DISALLOW_COPY_AND_ASSIGN, but we're avoiding a dependency
+  // on base/macros.h
+  MetadataLock(const MetadataLock&) = delete;
+  void operator=(const MetadataLock&) = delete;
+};
+
+#if V8_TRAP_HANDLER_SUPPORTED
+void HandleSignal(int signum, siginfo_t* info, void* context);
+#endif
+
+// To enable constant time registration of handler data, we keep a free list of
+// entries in the gCodeObjects table. Each entry contains a {next_free} field,
+// which can be used to figure out where the next entry should be inserted.
+// In order to avoid having to initialize all the links to start with, we use
+// 0 to indicate that this is a fresh, never-used list entry and that therefore
+// the next entry is known to be free. If {next_entry} is greater than zero,
+// then {next_entry - 1} is the index that we should insert into next.
+struct CodeProtectionInfoListEntry {
+  CodeProtectionInfo* code_info;
+  size_t next_free;
+};
+
+extern size_t gNumCodeObjects;
+extern CodeProtectionInfoListEntry* gCodeObjects;
+
+}  // namespace trap_handler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // TRAP_HANDLER_INTERNAL_H_