Crashing with style on Vista (18 Jun 2007)

ReportFault() is a great one-stop shopping API: A one-liner will display all required dialogs, ask the user if he wants to contact Microsoft, create report data (including minidumps) if required, and send the whole report off to Microsoft.

The new WER APIs in Vista are slightly more complex, but also provide more control for the details of error reporting. Well, if you know how to handle the APIs, that is. Apparently, I do not know how to handle them since I still haven't solved all the problems around them.

More on this in a moment. Let's first take a look at the core of a test application I wrote:

static bool report_crash(_EXCEPTION_POINTERS *inExceptionPointer)
{
  // Set up parameters for WerReportCreate()
  WER_REPORT_INFORMATION werReportInfo;
  memset(&werReportInfo, 0, sizeof(werReportInfo));
  werReportInfo.dwSize = sizeof(werReportInfo);
  wcscpy_s(werReportInfo.wzFriendlyEventName,
    _countof(werReportInfo.wzFriendlyEventName),
        L"werapitest (friendly event name)");
  wcscpy_s(werReportInfo.wzApplicationName,
    _countof(werReportInfo.wzApplicationName), L"");
  wcscpy_s(werReportInfo.wzDescription,
    _countof(werReportInfo.wzDescription), L"Critical runtime problem");

  PCWSTR eventType = L"werapitest (eventType)"; // APPCRASH
  HREPORT hReportHandle;
  if (FAILED(pWerReportCreate(eventType, WerReportCritical,
    &werReportInfo, &hReportHandle)) || !hReportHandle) {
      return false;
  }

  bool ret = false;

  WER_EXCEPTION_INFORMATION werExceptionInformation;
  werExceptionInformation.bClientPointers = FALSE;
  werExceptionInformation.pExceptionPointers = inExceptionPointer;
  bool dumpAdded = SUCCEEDED(pWerReportAddDump(hReportHandle, ::GetCurrentProcess(),
    ::GetCurrentThread(), WerDumpTypeMiniDump, &werExceptionInformation, NULL, 0));
  if (!dumpAdded) {
    FATAL_ERROR("Minidump generation failed.\n");
  }

  DWORD submitOptions = WER_SUBMIT_OUTOFPROCESS | WER_SUBMIT_NO_CLOSE_UI;
  WER_SUBMIT_RESULT submitResult;
  if (SUCCEEDED(pWerReportSubmit(hReportHandle, WerConsentNotAsked,
    submitOptions, &submitResult))) {
      switch(submitResult)
      {
        // ... decode result ...

      }
  }
  pWerReportCloseHandle(hReportHandle);

  return ret;
}

static int filter_exception(EXCEPTION_POINTERS *exc_ptr)
{
  report_crash(exc_ptr);
  return EXCEPTION_EXECUTE_HANDLER;
}

static void wedding_crasher(void)
{
  __try {
    int *foo = (int *)0;
    *foo = 42;
  } __except(filter_exception(GetExceptionInformation())) {
    printf("Now in exception handler, process is still alive!\n");
  }
  Sleep(5000);
}

int main()
{
  HMODULE hWer = LoadLibrary("Wer.dll");
  if (hWer) {
    pWerReportCreate =
      (pfn_WERREPORTCREATE)GetProcAddress(hWer, "WerReportCreate");
    pWerReportSubmit =
      (pfn_WERREPORTSUBMIT)GetProcAddress(hWer, "WerReportSubmit");
    pWerReportCloseHandle =
      (pfn_WERREPORTCLOSEHANDLE)GetProcAddress(hWer, "WerReportCloseHandle");
    pWerReportAddDump =
      (pfn_WERREPORTADDDUMP)GetProcAddress(hWer, "WerReportAddDump");
  }

  if (!pWerReportCreate || !pWerReportSubmit ||
    !pWerReportCloseHandle || !pWerReportAddDump) {
      printf("Cannot initialize WER API.\n");
      return 1;
  }

  wedding_crasher();
  return 0;
}

The fundamental approach is still the same as for the ReportFault test program presented recently:

• A structured exception block is established using __try and __except.
• Code provokes an access violation.
• The exception filter filter_exception is consulted by the exception handling infrastructure to find out how to proceed with the exception.
• The filter calls the WER APIs to display the crash dialog(s), and to give the user options to debug the problem, ignore it, or report it to Microsoft.
• The exception filter returns EXCEPTION_EXECUTE_HANDLER to indicate that its associated exception handler should be called.

The following WER APIs are used to create and send a crash report:

• WerReportCreate to open a handle for a new crash report
• WerReportAddDump to add minidump data to the report
• WerReportSubmit to display the WER dialogs and (if the user chooses this option) to send the report to Microsoft
• WerReportCloseHandle to release resources associated with the crash report.

The WER APIs do indeed solve a problem that I found with ReportFault on Vista: They don't force the calling process to be terminated, and allow me to proceed as I see fit. That's really good news.

The problem I haven't resolved yet is this: Even though I call WerReportAddDump, I have no idea whether minidump data are actually generated and sent. In fact, from the feedback provided by the system, it seems likely that those data are not generated.

To illustrate my uncertainties, I wrote a test program called werapitest. The code is attached as a ZIP file; unpack it into a directory, open a Visual Studio command prompt window, and build the code as follows:

  cl werapitest.cpp

Run the resulting executable, then open up the "Problem Reports and Solutions" control panel and click on "View problem history". On my system, I get something like this:

Double-clicking on the report entry leads to this:

The problem history entry does not mention any attached files, such as minidump data!

When a crash occurs, the system also writes entries into the event log; those log entries claim there are additional data in paths such as C:\Users\clausb\AppData\Local\Microsoft\Windows\WER\ReportArchive\Report0f8918ad, and indeed, such directories exist and each contain a file called Report.wer, which holds data such as:

Version=1
EventType=werapitest (eventType)
EventTime=128266502225896608
ReportType=1
Consent=1
UploadTime=128266502257542112
Response.BucketId=8
Response.BucketTable=5
Response.type=4
DynamicSig[1].Name=OS Version
DynamicSig[1].Value=6.0.6000.2.0.0.256.16
DynamicSig[2].Name=Locale ID
DynamicSig[2].Value=1033
UI[3]=werapitest.exe has stopped working
UI[4]=Windows can check online for a solution to the problem.
UI[5]=Check online for a solution and close the program
UI[6]=Check online for a solution later and close the program
UI[7]=Close the program
State[0].Key=Transport.DoneStage1
State[0].Value=1
State[1].Key=DataRequest
State[1].Value=Bucket=8/nBucketTable=5/nResponse=1/n
FriendlyEventName=werapitest (friendly event name)
ConsentKey=werapitest (eventType)
AppName=werapitest.exe
AppPath=C:\tmp\werapitest.exe
ReportDescription=Critical runtime problem

So again, the minidump is not mentioned anywhere.

Now let's try some minimal code which uses neither ReportFault nor the new WER API:

  int main(void)
  {
    int *p = (int *)0;
    *p = 42;
    return 0;
  }

After running this code and letting it crash and report to Microsoft, I get the following problem history entry:

This problem report contains a lot more data than the one for werapitest, and it even refers to a minidump file which was apparently generated by the system and probably also sent to Microsoft.

So the lazy code which doesn't do anything about crashes gets full and proper service from the OS, while the application which tries to deal with a crash in an orderly manner and elaborately goes through all the trouble of using the proper APIs doesn't get its message across to Microsoft. I call this unfair

Oh, and in case you're wondering: Yes, we've registered with Microsoft's Winqual site where the crash reports are supposed to be sent to, and we established "product mappings" there, and the whole process seems to work for XP clients just fine.

I'm pretty sure that I'm just missing a couple of details with the new APIs, or maybe I'm misinterpreting the feedback from the system. I ran numerous experiments and umpteen variations, I've searched the web high and low, read the docs, consulted newsgroups here and there - and now I'm running out of ideas. Any hints most welcome...

PS: I did indeed receive some hints. For updated WER code, along with an explanation on why the above failed, see Crashing with style on Vista, part II.