Code coverage is broken

[Nala Ginrut]

Hi folks!
I'm trying to add code coverage for certain program.
However, the function callings are always unrecorded.
--------------------------------------------------------------------------------------
(use-modules (system vm coverage)
                         (system vm vm))
   (call-with-values
        (lambda ()
           (with-code-coverage
             (lambda () (display "hello\n"))))
        (lambda (data result)
          (let ((port (open-output-file "1.info")))
            (coverage-data->lcov data port)
            (close port))))
---------------------------------------------------------------------------------------

(To someone who uses old 2.0, with-code-coverage interface has been
changed to accept only one thunk)

When I use lcov to generate coverage graph, it always complains that
--------------------------------------------
 lines......: 0.0% (0 of 36447 lines)
  functions..: no data found
  branches...: no data found
--------------------------------------------
I found the FN tag in info file is always missing.

Then I found in 581a4eb82b1534970060e3cbd79b9a96d351edf9

-------------------------------------------------
+      #;
         (for-each dump-function procs)
-------------------------------------------------
It seems that FN printing was skipped intended.

Is it a bug?
Anyone who has tried code coverage?

Thanks!