Userspace stack missing detail

here is my golang demo

```
package main

import (
"log"
"time"
)`

func main() {
for {
log.Printf("hello world")
add(1, 1)
del(1, 1)
time.Sleep(time.Millisecond * 100)
}
}

func add(x int, y int) int {
return x + y
}

func del(x int, y int) int {
return x - y
}
```
I compile it like that
`gccgo -O0 -fno-omit-frameointer -o main main.go`

I run it and use the offcputime tool to mesurement it. However， the userspace stack seems not correct
`./offcputime -U -p 3303`
And get the result is
````
write
[unknown]
- main (3372)
1915

select
- main (3371)
11303

syscall
- main (3371)
3824106

syscall
- main (3372)
3829608

syscall
- main (3373)
3836335
````
It looks like -O0 and -fno-omit-frameointer makes no sense. I just get a main stack what I expect get should contains add function and del function's stack. Is there any idea about it?