utils/KillTheDoctor/KillTheDoctor.cpp

   1 //===- KillTheDoctor - Prevent Dr. Watson from stopping tests ---*- C++ -*-===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This program provides an extremely hacky way to stop Dr. Watson from starting
  11 // due to unhandled exceptions in child processes.
  12 //
  13 // This simply starts the program named in the first positional argument with
  14 // the arguments following it under a debugger. All this debugger does is catch
  15 // any unhandled exceptions thrown in the child process and close the program
  16 // (and hopefully tells someone about it).
  17 //
  18 // This also provides another really hacky method to prevent assert dialog boxes
  19 // from popping up. When --no-user32 is passed, if any process loads user32.dll,
  20 // we assume it is trying to call MessageBoxEx and terminate it. The proper way
  21 // to do this would be to actually set a break point, but there's quite a bit
  22 // of code involved to get the address of MessageBoxEx in the remote process's
  23 // address space due to Address space layout randomization (ASLR). This can be
  24 // added if it's ever actually needed.
  25 //
  26 // If the subprocess exits for any reason other than successful termination, -1
  27 // is returned. If the process exits normally the value it returned is returned.
  28 //
  29 // I hate Windows.
  30 //
  31 //===----------------------------------------------------------------------===//
  32
  33 #include "llvm/ADT/STLExtras.h"
  34 #include "llvm/ADT/SmallString.h"
  35 #include "llvm/ADT/SmallVector.h"
  36 #include "llvm/ADT/StringExtras.h"
  37 #include "llvm/ADT/StringRef.h"
  38 #include "llvm/ADT/Twine.h"
  39 #include "llvm/Support/CommandLine.h"
  40 #include "llvm/Support/ManagedStatic.h"
  41 #include "llvm/Support/PrettyStackTrace.h"
  42 #include "llvm/Support/raw_ostream.h"
  43 #include "llvm/Support/type_traits.h"
  44 #include "llvm/Support/Signals.h"
  45 #include "llvm/Support/system_error.h"
  46 #include <algorithm>
  47 #include <cerrno>
  48 #include <cstdlib>
  49 #include <map>
  50 #include <string>
  51 #include <Windows.h>
  52 #include <WinError.h>
  53 #include <Dbghelp.h>
  54 #include <psapi.h>
  55 using namespace llvm;
  56
  57 #undef max
  58
  59 namespace {
  60   cl::opt<std::string> ProgramToRun(cl::Positional,
  61     cl::desc("<program to run>"));
  62   cl::list<std::string>  Argv(cl::ConsumeAfter,
  63     cl::desc("<program arguments>..."));
  64   cl::opt<bool> TraceExecution("x",
  65     cl::desc("Print detailed output about what is being run to stderr."));
  66   cl::opt<unsigned> Timeout("t", cl::init(0),
  67     cl::desc("Set maximum runtime in seconds. Defaults to infinite."));
  68   cl::opt<bool> NoUser32("no-user32",
  69     cl::desc("Terminate process if it loads user32.dll."));
  70
  71   StringRef ToolName;
  72
  73   template <typename HandleType>
  74   class ScopedHandle {
  75     typedef typename HandleType::handle_type handle_type;
  76
  77     handle_type Handle;
  78
  79   public:
  80     ScopedHandle()
  81       : Handle(HandleType::GetInvalidHandle()) {}
  82
  83     explicit ScopedHandle(handle_type handle)
  84       : Handle(handle) {}
  85
  86     ~ScopedHandle() {
  87       HandleType::Destruct(Handle);
  88     }
  89
  90     ScopedHandle& operator=(handle_type handle) {
  91       // Cleanup current handle.
  92       if (!HandleType::isValid(Handle))
  93         HandleType::Destruct(Handle);
  94       Handle = handle;
  95       return *this;
  96     }
  97
  98     operator bool() const {
  99       return HandleType::isValid(Handle);
 100     }
 101
 102     operator handle_type() {
 103       return Handle;
 104     }
 105   };
 106
 107   // This implements the most common handle in the Windows API.
 108   struct CommonHandle {
 109     typedef HANDLE handle_type;
 110
 111     static handle_type GetInvalidHandle() {
 112       return INVALID_HANDLE_VALUE;
 113     }
 114
 115     static void Destruct(handle_type Handle) {
 116       ::CloseHandle(Handle);
 117     }
 118
 119     static bool isValid(handle_type Handle) {
 120       return Handle != GetInvalidHandle();
 121     }
 122   };
 123
 124   struct FileMappingHandle {
 125     typedef HANDLE handle_type;
 126
 127     static handle_type GetInvalidHandle() {
 128       return NULL;
 129     }
 130
 131     static void Destruct(handle_type Handle) {
 132       ::CloseHandle(Handle);
 133     }
 134
 135     static bool isValid(handle_type Handle) {
 136       return Handle != GetInvalidHandle();
 137     }
 138   };
 139
 140   struct MappedViewOfFileHandle {
 141     typedef LPVOID handle_type;
 142
 143     static handle_type GetInvalidHandle() {
 144       return NULL;
 145     }
 146
 147     static void Destruct(handle_type Handle) {
 148       ::UnmapViewOfFile(Handle);
 149     }
 150
 151     static bool isValid(handle_type Handle) {
 152       return Handle != GetInvalidHandle();
 153     }
 154   };
 155
 156   struct ProcessHandle : CommonHandle {};
 157   struct ThreadHandle  : CommonHandle {};
 158   struct TokenHandle   : CommonHandle {};
 159   struct FileHandle    : CommonHandle {};
 160
 161   typedef ScopedHandle<FileMappingHandle>       FileMappingScopedHandle;
 162   typedef ScopedHandle<MappedViewOfFileHandle>  MappedViewOfFileScopedHandle;
 163   typedef ScopedHandle<ProcessHandle>           ProcessScopedHandle;
 164   typedef ScopedHandle<ThreadHandle>            ThreadScopedHandle;
 165   typedef ScopedHandle<TokenHandle>             TokenScopedHandle;
 166   typedef ScopedHandle<FileHandle>              FileScopedHandle;
 167 }
 168
 169 static error_code GetFileNameFromHandle(HANDLE FileHandle,
 170                                         std::string& Name) {
 171   char Filename[MAX_PATH+1];
 172   bool Success = false;
 173   Name.clear();
 174
 175   // Get the file size.
 176   LARGE_INTEGER FileSize;
 177   Success = ::GetFileSizeEx(FileHandle, &FileSize);
 178
 179   if (!Success)
 180     return windows_error(::GetLastError());
 181
 182   // Create a file mapping object.
 183   FileMappingScopedHandle FileMapping(
 184     ::CreateFileMappingA(FileHandle,
 185                          NULL,
 186                          PAGE_READONLY,
 187                          0,
 188                          1,
 189                          NULL));
 190
 191   if (!FileMapping)
 192     return windows_error(::GetLastError());
 193
 194   // Create a file mapping to get the file name.
 195   MappedViewOfFileScopedHandle MappedFile(
 196     ::MapViewOfFile(FileMapping, FILE_MAP_READ, 0, 0, 1));
 197
 198   if (!MappedFile)
 199     return windows_error(::GetLastError());
 200
 201   Success = ::GetMappedFileNameA(::GetCurrentProcess(),
 202                                 MappedFile,
 203                                 Filename,
 204                                 array_lengthof(Filename) - 1);
 205
 206   if (!Success)
 207     return windows_error(::GetLastError());
 208   else {
 209     Name = Filename;
 210     return windows_error::success;
 211   }
 212 }
 213
 214 static std::string QuoteProgramPathIfNeeded(StringRef Command) {
 215   if (Command.find_first_of(' ') == StringRef::npos)
 216     return Command;
 217   else {
 218     std::string ret;
 219     ret.reserve(Command.size() + 3);
 220     ret.push_back('"');
 221     ret.append(Command.begin(), Command.end());
 222     ret.push_back('"');
 223     return ret;
 224   }
 225 }
 226
 227 /// @brief Find program using shell lookup rules.
 228 /// @param Program This is either an absolute path, relative path, or simple a
 229 ///        program name. Look in PATH for any programs that match. If no
 230 ///        extension is present, try all extensions in PATHEXT.
 231 /// @return If ec == errc::success, The absolute path to the program. Otherwise
 232 ///         the return value is undefined.
 233 static std::string FindProgram(const std::string &Program, error_code &ec) {
 234   char PathName[MAX_PATH + 1];
 235   typedef SmallVector<StringRef, 12> pathext_t;
 236   pathext_t pathext;
 237   // Check for the program without an extension (in case it already has one).
 238   pathext.push_back("");
 239   SplitString(std::getenv("PATHEXT"), pathext, ";");
 240
 241   for (pathext_t::iterator i = pathext.begin(), e = pathext.end(); i != e; ++i){
 242     SmallString<5> ext;
 243     for (std::size_t ii = 0, e = i->size(); ii != e; ++ii)
 244       ext.push_back(::tolower((*i)[ii]));
 245     LPCSTR Extension = NULL;
 246     if (ext.size() && ext[0] == '.')
 247       Extension = ext.c_str();
 248     DWORD length = ::SearchPathA(NULL,
 249                                  Program.c_str(),
 250                                  Extension,
 251                                  array_lengthof(PathName),
 252                                  PathName,
 253                                  NULL);
 254     if (length == 0)
 255       ec = windows_error(::GetLastError());
 256     else if (length > array_lengthof(PathName)) {
 257       // This may have been the file, return with error.
 258       ec = windows_error::buffer_overflow;
 259       break;
 260     } else {
 261       // We found the path! Return it.
 262       ec = windows_error::success;
 263       break;
 264     }
 265   }
 266
 267   // Make sure PathName is valid.
 268   PathName[MAX_PATH] = 0;
 269   return PathName;
 270 }
 271
 272 static error_code EnableDebugPrivileges() {
 273   HANDLE TokenHandle;
 274   BOOL success = ::OpenProcessToken(::GetCurrentProcess(),
 275                                     TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY,
 276                                     &TokenHandle);
 277   if (!success)
 278     return windows_error(::GetLastError());
 279
 280   TokenScopedHandle Token(TokenHandle);
 281   TOKEN_PRIVILEGES  TokenPrivileges;
 282   LUID              LocallyUniqueID;
 283
 284   success = ::LookupPrivilegeValueA(NULL,
 285                                     SE_DEBUG_NAME,
 286                                     &LocallyUniqueID);
 287   if (!success)
 288     return windows_error(::GetLastError());
 289
 290   TokenPrivileges.PrivilegeCount = 1;
 291   TokenPrivileges.Privileges[0].Luid = LocallyUniqueID;
 292   TokenPrivileges.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
 293
 294   success = ::AdjustTokenPrivileges(Token,
 295                                     FALSE,
 296                                     &TokenPrivileges,
 297                                     sizeof(TOKEN_PRIVILEGES),
 298                                     NULL,
 299                                     NULL);
 300   // The value of success is basically useless. Either way we are just returning
 301   // the value of ::GetLastError().
 302   return windows_error(::GetLastError());
 303 }
 304
 305 static StringRef ExceptionCodeToString(DWORD ExceptionCode) {
 306   switch(ExceptionCode) {
 307   case EXCEPTION_ACCESS_VIOLATION: return "EXCEPTION_ACCESS_VIOLATION";
 308   case EXCEPTION_ARRAY_BOUNDS_EXCEEDED:
 309     return "EXCEPTION_ARRAY_BOUNDS_EXCEEDED";
 310   case EXCEPTION_BREAKPOINT: return "EXCEPTION_BREAKPOINT";
 311   case EXCEPTION_DATATYPE_MISALIGNMENT:
 312     return "EXCEPTION_DATATYPE_MISALIGNMENT";
 313   case EXCEPTION_FLT_DENORMAL_OPERAND: return "EXCEPTION_FLT_DENORMAL_OPERAND";
 314   case EXCEPTION_FLT_DIVIDE_BY_ZERO: return "EXCEPTION_FLT_DIVIDE_BY_ZERO";
 315   case EXCEPTION_FLT_INEXACT_RESULT: return "EXCEPTION_FLT_INEXACT_RESULT";
 316   case EXCEPTION_FLT_INVALID_OPERATION:
 317     return "EXCEPTION_FLT_INVALID_OPERATION";
 318   case EXCEPTION_FLT_OVERFLOW: return "EXCEPTION_FLT_OVERFLOW";
 319   case EXCEPTION_FLT_STACK_CHECK: return "EXCEPTION_FLT_STACK_CHECK";
 320   case EXCEPTION_FLT_UNDERFLOW: return "EXCEPTION_FLT_UNDERFLOW";
 321   case EXCEPTION_ILLEGAL_INSTRUCTION: return "EXCEPTION_ILLEGAL_INSTRUCTION";
 322   case EXCEPTION_IN_PAGE_ERROR: return "EXCEPTION_IN_PAGE_ERROR";
 323   case EXCEPTION_INT_DIVIDE_BY_ZERO: return "EXCEPTION_INT_DIVIDE_BY_ZERO";
 324   case EXCEPTION_INT_OVERFLOW: return "EXCEPTION_INT_OVERFLOW";
 325   case EXCEPTION_INVALID_DISPOSITION: return "EXCEPTION_INVALID_DISPOSITION";
 326   case EXCEPTION_NONCONTINUABLE_EXCEPTION:
 327     return "EXCEPTION_NONCONTINUABLE_EXCEPTION";
 328   case EXCEPTION_PRIV_INSTRUCTION: return "EXCEPTION_PRIV_INSTRUCTION";
 329   case EXCEPTION_SINGLE_STEP: return "EXCEPTION_SINGLE_STEP";
 330   case EXCEPTION_STACK_OVERFLOW: return "EXCEPTION_STACK_OVERFLOW";
 331   default: return "<unknown>";
 332   }
 333 }
 334
 335 int main(int argc, char **argv) {
 336   // Print a stack trace if we signal out.
 337   sys::PrintStackTraceOnErrorSignal();
 338   PrettyStackTraceProgram X(argc, argv);
 339   llvm_shutdown_obj Y;  // Call llvm_shutdown() on exit.
 340
 341   ToolName = argv[0];
 342
 343   cl::ParseCommandLineOptions(argc, argv, "Dr. Watson Assassin.\n");
 344   if (ProgramToRun.size() == 0) {
 345     cl::PrintHelpMessage();
 346     return -1;
 347   }
 348
 349   if (Timeout > std::numeric_limits<uint32_t>::max() / 1000) {
 350     errs() << ToolName << ": Timeout value too large, must be less than: "
 351                        << std::numeric_limits<uint32_t>::max() / 1000
 352                        << '\n';
 353     return -1;
 354   }
 355
 356   std::string CommandLine(ProgramToRun);
 357
 358   error_code ec;
 359   ProgramToRun = FindProgram(ProgramToRun, ec);
 360   if (ec) {
 361     errs() << ToolName << ": Failed to find program: '" << CommandLine
 362            << "': " << ec.message() << '\n';
 363     return -1;
 364   }
 365
 366   if (TraceExecution)
 367     errs() << ToolName << ": Found Program: " << ProgramToRun << '\n';
 368
 369   for (std::vector<std::string>::iterator i = Argv.begin(),
 370                                           e = Argv.end();
 371                                           i != e; ++i) {
 372     CommandLine.push_back(' ');
 373     CommandLine.append(*i);
 374   }
 375
 376   if (TraceExecution)
 377     errs() << ToolName << ": Program Image Path: " << ProgramToRun << '\n'
 378            << ToolName << ": Command Line: " << CommandLine << '\n';
 379
 380   STARTUPINFO StartupInfo;
 381   PROCESS_INFORMATION ProcessInfo;
 382   std::memset(&StartupInfo, 0, sizeof(StartupInfo));
 383   StartupInfo.cb = sizeof(StartupInfo);
 384   std::memset(&ProcessInfo, 0, sizeof(ProcessInfo));
 385
 386   // Set error mode to not display any message boxes. The child process inherits
 387   // this.
 388   ::SetErrorMode(SEM_FAILCRITICALERRORS | SEM_NOGPFAULTERRORBOX);
 389   ::_set_error_mode(_OUT_TO_STDERR);
 390
 391   BOOL success = ::CreateProcessA(ProgramToRun.c_str(),
 392                             LPSTR(CommandLine.c_str()),
 393                                   NULL,
 394                                   NULL,
 395                                   FALSE,
 396                                   DEBUG_PROCESS,
 397                                   NULL,
 398                                   NULL,
 399                                   &StartupInfo,
 400                                   &ProcessInfo);
 401   if (!success) {
 402     errs() << ToolName << ": Failed to run program: '" << ProgramToRun
 403            << "': " << error_code(windows_error(::GetLastError())).message()
 404            << '\n';
 405     return -1;
 406   }
 407
 408   // Make sure ::CloseHandle is called on exit.
 409   std::map<DWORD, HANDLE> ProcessIDToHandle;
 410
 411   DEBUG_EVENT DebugEvent;
 412   std::memset(&DebugEvent, 0, sizeof(DebugEvent));
 413   DWORD dwContinueStatus = DBG_CONTINUE;
 414
 415   // Run the program under the debugger until either it exits, or throws an
 416   // exception.
 417   if (TraceExecution)
 418     errs() << ToolName << ": Debugging...\n";
 419
 420   while(true) {
 421     DWORD TimeLeft = INFINITE;
 422     if (Timeout > 0) {
 423       FILETIME CreationTime, ExitTime, KernelTime, UserTime;
 424       ULARGE_INTEGER a, b;
 425       success = ::GetProcessTimes(ProcessInfo.hProcess,
 426                                   &CreationTime,
 427                                   &ExitTime,
 428                                   &KernelTime,
 429                                   &UserTime);
 430       if (!success) {
 431         ec = windows_error(::GetLastError());
 432
 433         errs() << ToolName << ": Failed to get process times: "
 434                << ec.message() << '\n';
 435         return -1;
 436       }
 437       a.LowPart = KernelTime.dwLowDateTime;
 438       a.HighPart = KernelTime.dwHighDateTime;
 439       b.LowPart = UserTime.dwLowDateTime;
 440       b.HighPart = UserTime.dwHighDateTime;
 441       // Convert 100-nanosecond units to milliseconds.
 442       uint64_t TotalTimeMiliseconds = (a.QuadPart + b.QuadPart) / 10000;
 443       // Handle the case where the process has been running for more than 49
 444       // days.
 445       if (TotalTimeMiliseconds > std::numeric_limits<uint32_t>::max()) {
 446         errs() << ToolName << ": Timeout Failed: Process has been running for"
 447                               "more than 49 days.\n";
 448         return -1;
 449       }
 450
 451       // We check with > instead of using Timeleft because if
 452       // TotalTimeMiliseconds is greater than Timeout * 1000, TimeLeft would
 453       // underflow.
 454       if (TotalTimeMiliseconds > (Timeout * 1000)) {
 455         errs() << ToolName << ": Process timed out.\n";
 456         ::TerminateProcess(ProcessInfo.hProcess, -1);
 457         // Otherwise other stuff starts failing...
 458         return -1;
 459       }
 460
 461       TimeLeft = (Timeout * 1000) - static_cast<uint32_t>(TotalTimeMiliseconds);
 462     }
 463     success = WaitForDebugEvent(&DebugEvent, TimeLeft);
 464
 465     if (!success) {
 466       ec = windows_error(::GetLastError());
 467
 468       if (ec == errc::timed_out) {
 469         errs() << ToolName << ": Process timed out.\n";
 470         ::TerminateProcess(ProcessInfo.hProcess, -1);
 471         // Otherwise other stuff starts failing...
 472         return -1;
 473       }
 474
 475       errs() << ToolName << ": Failed to wait for debug event in program: '"
 476              << ProgramToRun << "': " << ec.message() << '\n';
 477       return -1;
 478     }
 479
 480     switch(DebugEvent.dwDebugEventCode) {
 481     case CREATE_PROCESS_DEBUG_EVENT:
 482       // Make sure we remove the handle on exit.
 483       if (TraceExecution)
 484         errs() << ToolName << ": Debug Event: CREATE_PROCESS_DEBUG_EVENT\n";
 485       ProcessIDToHandle[DebugEvent.dwProcessId] =
 486         DebugEvent.u.CreateProcessInfo.hProcess;
 487       ::CloseHandle(DebugEvent.u.CreateProcessInfo.hFile);
 488       break;
 489     case EXIT_PROCESS_DEBUG_EVENT: {
 490         if (TraceExecution)
 491           errs() << ToolName << ": Debug Event: EXIT_PROCESS_DEBUG_EVENT\n";
 492
 493         // If this is the process we originally created, exit with its exit
 494         // code.
 495         if (DebugEvent.dwProcessId == ProcessInfo.dwProcessId)
 496           return DebugEvent.u.ExitProcess.dwExitCode;
 497
 498         // Otherwise cleanup any resources we have for it.
 499         std::map<DWORD, HANDLE>::iterator ExitingProcess =
 500           ProcessIDToHandle.find(DebugEvent.dwProcessId);
 501         if (ExitingProcess == ProcessIDToHandle.end()) {
 502           errs() << ToolName << ": Got unknown process id!\n";
 503           return -1;
 504         }
 505         ::CloseHandle(ExitingProcess->second);
 506         ProcessIDToHandle.erase(ExitingProcess);
 507       }
 508       break;
 509     case CREATE_THREAD_DEBUG_EVENT:
 510       ::CloseHandle(DebugEvent.u.CreateThread.hThread);
 511       break;
 512     case LOAD_DLL_DEBUG_EVENT: {
 513         // Cleanup the file handle.
 514         FileScopedHandle DLLFile(DebugEvent.u.LoadDll.hFile);
 515         std::string DLLName;
 516         ec = GetFileNameFromHandle(DLLFile, DLLName);
 517         if (ec) {
 518           DLLName = "<failed to get file name from file handle> : ";
 519           DLLName += ec.message();
 520         }
 521         if (TraceExecution) {
 522           errs() << ToolName << ": Debug Event: LOAD_DLL_DEBUG_EVENT\n";
 523           errs().indent(ToolName.size()) << ": DLL Name : " << DLLName << '\n';
 524         }
 525
 526         if (NoUser32 && sys::path::stem(DLLName) == "user32") {
 527           // Program is loading user32.dll, in the applications we are testing,
 528           // this only happens if an assert has fired. By now the message has
 529           // already been printed, so simply close the program.
 530           errs() << ToolName << ": user32.dll loaded!\n";
 531           errs().indent(ToolName.size())
 532                  << ": This probably means that assert was called. Closing "
 533                     "program to prevent message box from popping up.\n";
 534           dwContinueStatus = DBG_CONTINUE;
 535           ::TerminateProcess(ProcessIDToHandle[DebugEvent.dwProcessId], -1);
 536           return -1;
 537         }
 538       }
 539       break;
 540     case EXCEPTION_DEBUG_EVENT: {
 541         // Close the application if this exception will not be handled by the
 542         // child application.
 543         if (TraceExecution)
 544           errs() << ToolName << ": Debug Event: EXCEPTION_DEBUG_EVENT\n";
 545
 546         EXCEPTION_DEBUG_INFO  &Exception = DebugEvent.u.Exception;
 547         if (Exception.dwFirstChance > 0) {
 548           if (TraceExecution) {
 549             errs().indent(ToolName.size()) << ": Debug Info : ";
 550             errs() << "First chance exception at "
 551                    << Exception.ExceptionRecord.ExceptionAddress
 552                    << ", exception code: "
 553                    << ExceptionCodeToString(
 554                         Exception.ExceptionRecord.ExceptionCode)
 555                    << " (" << Exception.ExceptionRecord.ExceptionCode << ")\n";
 556           }
 557           dwContinueStatus = DBG_EXCEPTION_NOT_HANDLED;
 558         } else {
 559           errs() << ToolName << ": Unhandled exception in: " << ProgramToRun
 560                  << "!\n";
 561                  errs().indent(ToolName.size()) << ": location: ";
 562                  errs() << Exception.ExceptionRecord.ExceptionAddress
 563                         << ", exception code: "
 564                         << ExceptionCodeToString(
 565                             Exception.ExceptionRecord.ExceptionCode)
 566                         << " (" << Exception.ExceptionRecord.ExceptionCode
 567                         << ")\n";
 568           dwContinueStatus = DBG_CONTINUE;
 569           ::TerminateProcess(ProcessIDToHandle[DebugEvent.dwProcessId], -1);
 570           return -1;
 571         }
 572       }
 573       break;
 574     default:
 575       // Do nothing.
 576       if (TraceExecution)
 577         errs() << ToolName << ": Debug Event: <unknown>\n";
 578       break;
 579     }
 580
 581     success = ContinueDebugEvent(DebugEvent.dwProcessId,
 582                                  DebugEvent.dwThreadId,
 583                                  dwContinueStatus);
 584     if (!success) {
 585       ec = windows_error(::GetLastError());
 586       errs() << ToolName << ": Failed to continue debugging program: '"
 587              << ProgramToRun << "': " << ec.message() << '\n';
 588       return -1;
 589     }
 590
 591     dwContinueStatus = DBG_CONTINUE;
 592   }
 593
 594   assert(0 && "Fell out of debug loop. This shouldn't be possible!");
 595   return -1;
 596 }