[Qemu-devel] [Bug 1783422] [NEW] qemu_clock_get_ns does not take into account icount_time_shift

[SilverOnemi]

Public bug reported:

Hello,

If you check the qemu/util/qemu-timer.c you will find the following
function:

597: int64_t qemu_clock_get_ns(QEMUClockType type)
598: {
....
602:    switch (type) {
....
606:    case QEMU_CLOCK_VIRTUAL:
607:        if (use_icount) {
608:            return cpu_get_icount(); 


Now on line 606, in case we requested QEMU_CLOCK_VIRTUAL, and we are using 
icount, the value of cpu_get_icount(); will be returned.

However if I understand correctly, in order to convert icount to ns, you
must use take into account the icount shift -- as defined in the
documentation: "The virtual cpu will execute one instruction every 2^N
ns of virtual time.".

Therefor, the correct value to return would be
cpu_icount_to_ns(cpu_get_icount()), where cpu_icount_to_ns is defined in
cpus.c:

296: int64_t cpu_icount_to_ns(int64_t icount)
297: {
298:    return icount << icount_time_shift;
299: }

Best Regards,
Humberto "SilverOne" Carvalho

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1783422

Title:
  qemu_clock_get_ns does not take into account icount_time_shift

Status in QEMU:
  New

Bug description:
  Hello,

  If you check the qemu/util/qemu-timer.c you will find the following
  function:

  597: int64_t qemu_clock_get_ns(QEMUClockType type)
  598: {
  ....
  602:    switch (type) {
  ....
  606:    case QEMU_CLOCK_VIRTUAL:
  607:        if (use_icount) {
  608:            return cpu_get_icount(); 

  
  Now on line 606, in case we requested QEMU_CLOCK_VIRTUAL, and we are using 
icount, the value of cpu_get_icount(); will be returned.

  However if I understand correctly, in order to convert icount to ns,
  you must use take into account the icount shift -- as defined in the
  documentation: "The virtual cpu will execute one instruction every 2^N
  ns of virtual time.".

  Therefor, the correct value to return would be
  cpu_icount_to_ns(cpu_get_icount()), where cpu_icount_to_ns is defined
  in cpus.c:

  296: int64_t cpu_icount_to_ns(int64_t icount)
  297: {
  298:    return icount << icount_time_shift;
  299: }

  Best Regards,
  Humberto "SilverOne" Carvalho

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