Question

i am trying to listen to ETW kernel events.

• Step 1: Call OpenTrace, specifying the EventCallback and optional BufferCallback functions that will be called during my call to ProcessTrace:

  var
      logFile: EVENT_TRACE_LOGFILE;
      currentTrace: TRACEHANDLE;
  begin
      ZeroMemory(@logFile, sizeof(logFile));
  
      logFile.LoggerName := KERNEL_LOGGER_NAME;
      logFile.LogFileName := 'C:\Users\Ian\foo.etl';
      logFile.ProcessTraceMode := 0;
      logFile.EventCallback := RealtimeEventCallback;
      logFile.BufferCallback := BufferCallback; //optional
  
      currentTrace := OpenTrace(@logFile);
      if (currentTrace = INVALID_PROCESSTRACE_HANDLE) or (currentTrace = -1) then
             RaiseLastWin32Error();
  

• Step 2: Enable kernel events. This is done by calling StartTrace. In my case i want to trace kernel interrupts (EVENT_TRACE_FLAG_INTERRUPT) and deferred procedure calls (EVENT_TRACE_FLAG_DPC):

  var
      sessionProperties: PEVENT_TRACE_PROPERTIES;
      bufferSize: Int64;
      th: TRACEHANDLE;
      loggerName: string;
      logFilePath: string;
  begin
      loggerName := KERNEL_LOGGER_NAME;
      logFilePath := 'C:\Users\Ian\foo.etl';
  
      bufferSize := sizeof(EVENT_TRACE_PROPERTIES)
          + 1024 //maximum session name is 1024 characters
          + 1024; //maximum log file name is 1024 characters
  
      sessionProperties := AllocMem(bufferSize);
      ZeroMemory(sessionProperties, bufferSize);
  
      sessionProperties.Wnode.BufferSize := bufferSize;
      sessionProperties.Wnode.ClientContext := 1; //QPC clock resolution
      sessionProperties.Wnode.Flags := WNODE_FLAG_TRACED_GUID;
      sessionProperties.Wnode.Guid := SystemTraceControlGuid;
      sessionProperties.EnableFlags := EVENT_TRACE_FLAG_INTERRUPT or EVENT_TRACE_FLAG_DPC;
      sessionProperties.LogFileMode := EVENT_TRACE_FILE_MODE_CIRCULAR;
      sessionProperties.MaximumFileSize := 5;  // 5 MB
      sessionProperties.LoggerNameOffset := sizeof(EVENT_TRACE_PROPERTIES);
      sessionProperties.LogFileNameOffset := sizeof(EVENT_TRACE_PROPERTIES)+1024;
  
      //Copy LoggerName to the offset address
      MoveMemory(Pointer(Cardinal(sessionProperties)+sessionProperties.LoggerNameOffset), PChar(loggerName), Length(loggerName)+1);
  
      //Copy LogFilePath to the offset address
      MoveMemory(Pointer(Cardinal(sessionProperties)+sessionProperties.LogFileNameOffset), PChar(logFilePath), Length(logFilePath)+1);
  
      hr := StartTrace({var}th, PChar(loggerName), sessionProperties);
      if (hr <> ERROR_SUCCESS) then
            raise EWin32Error.Create(SysErrorMessage(hr));
  

  And the log is started sucessfully (i can see foo.etl begin to grow to its 5 MB circuluar limit).

• Step 3: Call ProcessTrace, which blocks until it has delivered all pending events to the EventCallback handler specified in Step 1:

  var
     res: LongWord;
  begin
     res := EventTrace.ProcessTrace(@currentTrace, 1, nil, nil);
     if (res <> ERROR_SUCCESS) then
        raise EWin32Error.Create(SysErrorMessage(res));
  

Except that ProcessTrace repeatedly returns immediately, and no callback is called – even though the etl file is present and growing.

---

If i change the logging from File Based to Realtime logging:

• Step 1 – OpenTrace changes to support realtime:

  logFile.ProcessTraceMode := PROCESS_TRACE_MODE_REAL_TIME;
  

• Step 2 – StartTrace changes to support realtime:

  sessionProperties.LogFileMode := EVENT_TRACE_REAL_TIME_MODE;
  

In this case ProcessTrace never returns, but neither EventCallback or BufferCallback are ever called.

What am i doing wrong?

---

Update: My callback functions:

function BufferCallback(Logfile: PEVENT_TRACE_LOGFILE): LongWord; stdcall;
begin
   ShowMessage('BufferCallback');
   Result := 1; //return true to keep processing rows
end;

procedure RealtimeEventCallback(pEvent: PEVENT_TRACE); stdcall;
begin
   ShowMessage('EventCallback');
   nEvents := nEvents+1;
end;

Answer 1

i found the problem.

The headers i was using were not quad-word aligned.

In Delphi parlance, the keyword packed was being used.