Re: [PATCH v5 14/15] replay: create temporary snapshot at debugger connection

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 9/22/20 2:55 PM, Philippe Mathieu-Daudé wrote:
> Hi Pavel,
> 
> On 9/22/20 2:16 PM, Pavel Dovgalyuk wrote:
>> When record/replay does not uses overlays for storing the snapshots,
>> user is not capable of issuing reverse debugging commands.
>> This patch adds creation of the VM snapshot on the temporary
>> overlay image, when the debugger connects to QEMU.
>> Therefore the execution can be rewind to the moment
>> of the debugger connection while debugging the virtual machine.
>>
>> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
>> ---
>>  gdbstub.c                 |    1 +
>>  include/sysemu/replay.h   |    2 ++
>>  replay/replay-debugging.c |   16 ++++++++++++++++
>>  3 files changed, 19 insertions(+)
>>
>> diff --git a/gdbstub.c b/gdbstub.c
>> index ac92273018..f19f98ab1a 100644
>> --- a/gdbstub.c
>> +++ b/gdbstub.c
>> @@ -3321,6 +3321,7 @@ static void gdb_chr_event(void *opaque, QEMUChrEvent event)
>>          s->g_cpu = s->c_cpu;
>>  
>>          vm_stop(RUN_STATE_PAUSED);
>> +        replay_gdb_attached();
>>          gdb_has_xml = false;
>>          break;
>>      default:
>> diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
>> index b6cac175c4..2aa34b8919 100644
>> --- a/include/sysemu/replay.h
>> +++ b/include/sysemu/replay.h
>> @@ -94,6 +94,8 @@ bool replay_reverse_continue(void);
>>  bool replay_running_debug(void);
>>  /* Called in reverse debugging mode to collect breakpoint information */
>>  void replay_breakpoint(void);
>> +/* Called when gdb is attached to gdbstub */
>> +void replay_gdb_attached(void);
>>  
>>  /* Processing the instructions */
>>  
>> diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
>> index d02d4e0766..bb9110707a 100644
>> --- a/replay/replay-debugging.c
>> +++ b/replay/replay-debugging.c
>> @@ -316,3 +316,19 @@ void replay_breakpoint(void)
>>      assert(replay_mode == REPLAY_MODE_PLAY);
>>      replay_last_breakpoint = replay_get_current_icount();
>>  }
>> +
>> +void replay_gdb_attached(void)
>> +{
>> +    /*
>> +     * Create VM snapshot on temporary overlay to allow reverse
>> +     * debugging even if snapshots were not enabled.
>> +     */
>> +    if (replay_mode == REPLAY_MODE_PLAY
>> +        && !replay_snapshot) {
>> +        Error *err = NULL;
>> +        if (save_snapshot("start_debugging", &err) != 0) {
>> +            /* Can't create the snapshot. Continue conventional debugging. */
> 
> If you deliberately ignore the error, then use NULL;
> else display the error.

Can be cleaned on top, if Paolo is already OK with this series.

> 
>> +            error_free(err);
>> +        }
>> +    }
>> +}
>>
>