root/base/debug/debugger_win.cc

DEFINITIONS

1. RegReadString
2. StringReplace
3. SpawnDebuggerOnProcess
4. BeingDebugged
5. BreakDebugger

// Copyright (c) 2010 The Chromium 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 "base/debug/debugger.h"

#include <windows.h>
#include <dbghelp.h>

#include "base/basictypes.h"
#include "base/logging.h"

namespace base {
namespace debug {

namespace {

// Minimalist key reader.
// Note: Does not use the CRT.
bool RegReadString(HKEY root, const wchar_t* subkey,
                   const wchar_t* value_name, wchar_t* buffer, int* len) {
  HKEY key = NULL;
  DWORD res = RegOpenKeyEx(root, subkey, 0, KEY_READ, &key);
  if (ERROR_SUCCESS != res || key == NULL)
    return false;

  DWORD type = 0;
  DWORD buffer_size = *len * sizeof(wchar_t);
  // We don't support REG_EXPAND_SZ.
  res = RegQueryValueEx(key, value_name, NULL, &type,
                        reinterpret_cast<BYTE*>(buffer), &buffer_size);
  if (ERROR_SUCCESS == res && buffer_size != 0 && type == REG_SZ) {
    // Make sure the buffer is NULL terminated.
    buffer[*len - 1] = 0;
    *len = lstrlen(buffer);
    RegCloseKey(key);
    return true;
  }
  RegCloseKey(key);
  return false;
}

// Replaces each "%ld" in input per a value. Not efficient but it works.
// Note: Does not use the CRT.
bool StringReplace(const wchar_t* input, int value, wchar_t* output,
                   int output_len) {
  memset(output, 0, output_len*sizeof(wchar_t));
  int input_len = lstrlen(input);

  for (int i = 0; i < input_len; ++i) {
    int current_output_len = lstrlen(output);

    if (input[i] == L'%' && input[i + 1] == L'l' && input[i + 2] == L'd') {
      // Make sure we have enough place left.
      if ((current_output_len + 12) >= output_len)
        return false;

      // Cheap _itow().
      wsprintf(output+current_output_len, L"%d", value);
      i += 2;
    } else {
      if (current_output_len >= output_len)
        return false;
      output[current_output_len] = input[i];
    }
  }
  return true;
}

}  // namespace

// Note: Does not use the CRT.
bool SpawnDebuggerOnProcess(unsigned process_id) {
  wchar_t reg_value[1026];
  int len = arraysize(reg_value);
  if (RegReadString(HKEY_LOCAL_MACHINE,
      L"SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug",
      L"Debugger", reg_value, &len)) {
    wchar_t command_line[1026];
    if (StringReplace(reg_value, process_id, command_line,
                      arraysize(command_line))) {
      // We don't mind if the debugger is present because it will simply fail
      // to attach to this process.
      STARTUPINFO startup_info = {0};
      startup_info.cb = sizeof(startup_info);
      PROCESS_INFORMATION process_info = {0};

      if (CreateProcess(NULL, command_line, NULL, NULL, FALSE, 0, NULL, NULL,
                        &startup_info, &process_info)) {
        CloseHandle(process_info.hThread);
        WaitForInputIdle(process_info.hProcess, 10000);
        CloseHandle(process_info.hProcess);
        return true;
      }
    }
  }
  return false;
}

bool BeingDebugged() {
  return ::IsDebuggerPresent() != 0;
}

void BreakDebugger() {
  if (IsDebugUISuppressed())
    _exit(1);
  __debugbreak();
#if defined(NDEBUG)
  _exit(1);
#endif
}

}  // namespace debug
}  // namespace base