Xperf does not display full stack - or maybe I am doing something wrong

Hello,

I am new in using XPerf. I tried to see the performance problem spot by Xperf for a bad program like this:

int func()
{
    FILE * f = fopen("lala.txt", "w+");
    int c = 10;
    while(1)
    {
        fwrite(&c, sizeof(int), 1, f);
        fflush(f);
        fseek(f, 0, SEEK_SET);
        fread(&c, sizeof(int), 1, f);
        fseek(f, 0, SEEK_SET);
    }
    return 0;

}
int main()
{
    return func();
}

I've started xperf like this:

xperf -start perf!GeneralProfiles.InSequentialFile

started my bad program named MoreCPU.exe, let it run for a while, and stop it. After that, i've stopped also xperf with:

xperf -stop perf!GeneralProfiles.InSequentialFile trace_disk2.etl

I've started to look at the etl file with Windows Performance Analyzer, it spot me that there is a CPU problem, but when I try to see the stack it looks like this:

So, it shows me that the problem is the number of the calls to fread, fwrite, fflush but is does not show me who call them - I would expect a stack like this:

MoreCPU.exe -> Root -> MoreCPU.exe!main -> MoreCPU.exe!func -> MSVCR90.DLL!fread and so on

As you can see in the table above it is able to display MoreCPU.exe!func so most probably the symbols are loaded also for my bad program.

So, what can I change to see from where are called the three functions fread, fwrite, fflush from my bad program?

Thank you - any help will be much appreciated.

Mihai