how to trace VirtualAlloc + CallStack?

[chena1982]

void kernel_trace_004::start()
{
    krabs::kernel_trace trace(L"Memory Trace");


    krabs::kernel::virtual_alloc_provider provider;

    // Kernel providers accept all the typical callback mechanisms.
    provider.add_on_event_callback([](const EVENT_RECORD& record, const krabs::trace_context& trace_context) {
        krabs::schema schema(record, trace_context.schema_locator);

        for (int i = 0; i < record.ExtendedDataCount; i++) {
            //auto extended_data_item = &record.ExtendedData[i];

        }
    });

    CLASSIC_EVENT_ID StackTracingEvents[2];

    StackTracingEvents[0].EventGuid = krabs::guids::page_fault;
    StackTracingEvents[0].Type = 98;                 // VirtualAlloc
    memset(StackTracingEvents[0].Reserved, 0, sizeof(StackTracingEvents[0].Reserved));

    StackTracingEvents[1].EventGuid = krabs::guids::page_fault;
    StackTracingEvents[1].Type = 99;                 // VirtualFree
    memset(StackTracingEvents[1].Reserved, 0, sizeof(StackTracingEvents[1].Reserved));

    trace.set_trace_information(TraceStackTracingInfo, &StackTracingEvents, sizeof(StackTracingEvents));

    trace.enable(provider);
    trace.start();
}

virtual alloc trace is easy, but record.ExtendedDataCount is 0, how to get call stack?
Thanks.