Windows corrupt minidump

Question

When my program crashes it creates a minidump, from the unhandled exception handler. The issue I'm having is that people are sending me crash dumps, but when I try to open them in Visual Studio 2010 it says they're corrupt ("The dump file has an invalid format"). I'm not distributing dbghelp.dll with my program, do I need to? I assume that if it's a version issue, Visual Studio would let me know and not output the above message.

The code I use to generate the logs is

LONG WINAPI OnUnhandledException(PEXCEPTION_POINTERS pExceptionInfo)
    {
        MINIDUMP_EXCEPTION_INFORMATION ei;
        ei.ExceptionPointers = pExceptionInfo;
        ei.ThreadId = GetCurrentThreadId();
        ei.ClientPointers = FALSE;

        DWORD dwProcessId = GetCurrentProcessId();
        SYSTEMTIME stLocalTime;
        GetLocalTime(&stLocalTime);
        wchar_t CrashDumpW[1024];
        swprintf_s(CrashDumpW, NELEMS(CrashDumpW), 
                L"%s\\%s-%s-%04X-%04d%02d%02d-%02d%02d%02d-%ld-%ld.dmp", 
                g_CrashDirectory.c_str(), L"Program", MAJOR_VERSION_STR, 
                INTERNAL_VERSION, stLocalTime.wYear, stLocalTime.wMonth,
                stLocalTime.wDay, stLocalTime.wHour, stLocalTime.wMinute, 
                stLocalTime.wSecond, dwProcessId, ei.ThreadId);

        HANDLE hFile = CreateFileW(CrashDumpW, GENERIC_READ | GENERIC_WRITE,
            NULL, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
        MiniDumpWriteDump(GetCurrentProcess(), dwProcessId, hFile, 
            MiniDumpScanMemory, &ei, NULL, NULL);
        CloseHandle(hFile);

        return EXCEPTION_EXECUTE_HANDLER;
    }

Answer 1

This can be caused by someone debugging your process. I have noticed that if a process has a debugger attached, the minidumps it produces are often corrupted exactly the same way. They are less in size than the ones produced normally.

Since you return EXCEPTION_EXECUTE_HANDLER from your handler, the default unhandled exception handler is executed after yours, which may cause DrWatson come into play and attach to your process as a debugger.