func PanicTrace(kb int) []byte {
  s := []byte("/src/runtime/panic.go")
  e := []byte("\ngoroutine ")
  line := []byte("\n")
  stack := make([]byte, kb<<10) //4KB
  length := runtime.Stack(stack, true)
  start := bytes.Index(stack, s)
  stack = stack[start:length]
  start = bytes.Index(stack, line) + 1
  stack = stack[start:]
  end := bytes.LastIndex(stack, line)
  if end != -1 {
    stack = stack[:end]
  }
  end = bytes.Index(stack, e)
  if end != -1 {
    stack = stack[:end]
  }
  stack = bytes.TrimRight(stack, "\n")
  return stack
}