// 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.

// PLEASE READ BEFORE CHANGING THIS FILE!
//
// This file implements the out of bounds trap handler for
// WebAssembly. Exception handlers are notoriously difficult to get
// right, and getting it wrong can lead to security
// vulnerabilities. In order to minimize this risk, 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
//    trap 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.
//
// This file contains most of the code that actually runs in an exception
// handler context. Some additional code is used both inside and outside the
// trap handler. This code can be found in handler-shared.cc.

#include "src/trap-handler/handler-inside-win.h"

#include <windows.h>

#include "src/trap-handler/trap-handler-internal.h"
#include "src/trap-handler/trap-handler.h"

namespace v8 {
namespace internal {
namespace trap_handler {

bool TryHandleWasmTrap(EXCEPTION_POINTERS* exception) {
  // Ensure the faulting thread was actually running Wasm code.
  if (!IsThreadInWasm()) {
    return false;
  }

  // Clear g_thread_in_wasm_code, primarily to protect against nested faults.
  g_thread_in_wasm_code = false;

  const EXCEPTION_RECORD* record = exception->ExceptionRecord;

  if (record->ExceptionCode != EXCEPTION_ACCESS_VIOLATION) {
    return false;
  }

  uintptr_t fault_addr = reinterpret_cast<uintptr_t>(record->ExceptionAddress);
  uintptr_t landing_pad = 0;

  if (TryFindLandingPad(fault_addr, &landing_pad)) {
    exception->ContextRecord->Rip = landing_pad;
    // We will return to wasm code, so restore the g_thread_in_wasm_code flag.
    g_thread_in_wasm_code = true;
    return true;
  }

  // If we get here, it's not a recoverable wasm fault, so we go to the next
  // handler. Leave the g_thread_in_wasm_code flag unset since we do not return
  // to wasm code.
  return false;
}

LONG HandleWasmTrap(EXCEPTION_POINTERS* exception) {
  if (TryHandleWasmTrap(exception)) {
    return EXCEPTION_CONTINUE_EXECUTION;
  }
  return EXCEPTION_CONTINUE_SEARCH;
}

}  // namespace trap_handler
}  // namespace internal
}  // namespace v8