Re: [PATCH v3 09/15] replay: implement replay-seek command

[Alex Bennée]

Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru> writes:

> On 07.09.2020 15:58, Alex Bennée wrote:
>> 
>> Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru> writes:
>> 
>>> From: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
>>>
>>> This patch adds hmp/qmp commands replay_seek/replay-seek that proceed
>>> the execution to the specified instruction count.
>>> The command automatically loads nearest snapshot and replays the execution
>>> to find the desired instruction count.
>> 
>> Should there be an initial snapshot created at instruction 0? Using a
>> separate monitor channel:
>
> Right, you can't go to the prior state, when there is no preceding 
> snapshot available.

It seems creating an initial snapshot automatically would be more user
friendly? What can you do to trigger a snapshot, say for example on a
gdb connect?

>
>> 
>>    (qemu) replay_break 190505
>>    replay_break 190505
>>    (qemu) c
>>    (qemu) info replay
>>    info replay
>>    Replaying execution 'record.out': instruction count = 190505
>>    (qemu) replay_seek 190000
>>    replay_seek 190000
>>    snapshotting is disabled
>> 
>> And then the guest dies with a sigabort:
>
> This could be a bug, thanks.
>
>> 
>>    ./qemu-system-aarch64 -cpu cortex-a53 -display none -serial stdio 
>> -machine virt -kernel zephyr.elf -net none -icount 
>> shift=6,align=off,sleep=off,rr=replay,rrfile=record.out -drive 
>> file=record.qcow2,if=none,snapshot,id=rr -monitor telnet:127.0.0.1:4444 -S
>>    *** Booting Zephyr OS build zephyr-v2.3.0-1183-ge5628ad0faf3  ***
>>    Hello World! qemu_cortex_a53
>>    double free or corruption (out)
>>    fish: “./qemu-system-aarch64 -cpu cort…” terminated by signal SIGABRT 
>> (Abort)
>> 
>>>
>>> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
>>> Acked-by: Markus Armbruster <armbru@redhat.com>
>>> ---
>>>   hmp-commands.hx           |   18 +++++++++
>>>   include/monitor/hmp.h     |    1
>>>   qapi/replay.json          |   20 ++++++++++
>>>   replay/replay-debugging.c |   92 
>>> +++++++++++++++++++++++++++++++++++++++++++++
>>>   4 files changed, 131 insertions(+)
>>>
>>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>>> index e8ce385879..4288274c4e 100644
>>> --- a/hmp-commands.hx
>>> +++ b/hmp-commands.hx
>>> @@ -1851,6 +1851,24 @@ SRST
>>>     The command is ignored when there are no replay breakpoints.
>>>   ERST
>>>   
>>> +    {
>>> +        .name       = "replay_seek",
>>> +        .args_type  = "icount:i",
>>> +        .params     = "icount",
>>> +        .help       = "replay execution to the specified instruction 
>>> count",
>>> +        .cmd        = hmp_replay_seek,
>>> +    },
>>> +
>>> +SRST
>>> +``replay_seek`` *icount*
>>> +Automatically proceed to the instruction count *icount*, when
>>> +replaying the execution. The command automatically loads nearest
>>> +snapshot and replays the execution to find the desired instruction.
>>> +When there is no preceding snapshot or the execution is not replayed,
>>> +then the command fails.
>>> +*icount* for the reference may be observed with ``info replay`` command.
>>> +ERST
>>> +
>>>       {
>>>           .name       = "info",
>>>           .args_type  = "item:s?",
>>> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
>>> index 21849bdda5..655eb81a4c 100644
>>> --- a/include/monitor/hmp.h
>>> +++ b/include/monitor/hmp.h
>>> @@ -133,5 +133,6 @@ void hmp_info_sev(Monitor *mon, const QDict *qdict);
>>>   void hmp_info_replay(Monitor *mon, const QDict *qdict);
>>>   void hmp_replay_break(Monitor *mon, const QDict *qdict);
>>>   void hmp_replay_delete_break(Monitor *mon, const QDict *qdict);
>>> +void hmp_replay_seek(Monitor *mon, const QDict *qdict);
>>>   
>>>   #endif
>>> diff --git a/qapi/replay.json b/qapi/replay.json
>>> index 173ba76107..bfd83d7591 100644
>>> --- a/qapi/replay.json
>>> +++ b/qapi/replay.json
>>> @@ -99,3 +99,23 @@
>>>   #
>>>   ##
>>>   { 'command': 'replay-delete-break' }
>>> +
>>> +##
>>> +# @replay-seek:
>>> +#
>>> +# Automatically proceed to the instruction count @icount, when
>>> +# replaying the execution. The command automatically loads nearest
>>> +# snapshot and replays the execution to find the desired instruction.
>>> +# When there is no preceding snapshot or the execution is not replayed,
>>> +# then the command fails.
>>> +# icount for the reference may be obtained with @query-replay command.
>>> +#
>>> +# @icount: target instruction count
>>> +#
>>> +# Since: 5.2
>>> +#
>>> +# Example:
>>> +#
>>> +# -> { "execute": "replay-seek", "data": { "icount": 220414 } }
>>> +##
>>> +{ 'command': 'replay-seek', 'data': { 'icount': 'int' } }
>>> diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
>>> index 86e19bb217..cfd0221692 100644
>>> --- a/replay/replay-debugging.c
>>> +++ b/replay/replay-debugging.c
>>> @@ -19,6 +19,8 @@
>>>   #include "qapi/qapi-commands-replay.h"
>>>   #include "qapi/qmp/qdict.h"
>>>   #include "qemu/timer.h"
>>> +#include "block/snapshot.h"
>>> +#include "migration/snapshot.h"
>>>   
>>>   void hmp_info_replay(Monitor *mon, const QDict *qdict)
>>>   {
>>> @@ -127,3 +129,93 @@ void hmp_replay_delete_break(Monitor *mon, const QDict 
>>> *qdict)
>>>           return;
>>>       }
>>>   }
>>> +
>>> +static char *replay_find_nearest_snapshot(int64_t icount,
>>> +                                          int64_t *snapshot_icount)
>>> +{
>>> +    BlockDriverState *bs;
>>> +    QEMUSnapshotInfo *sn_tab;
>>> +    QEMUSnapshotInfo *nearest = NULL;
>>> +    char *ret = NULL;
>>> +    int nb_sns, i;
>>> +    AioContext *aio_context;
>>> +
>>> +    *snapshot_icount = -1;
>>> +
>>> +    bs = bdrv_all_find_vmstate_bs();
>>> +    if (!bs) {
>>> +        goto fail;
>>> +    }
>>> +    aio_context = bdrv_get_aio_context(bs);
>>> +
>>> +    aio_context_acquire(aio_context);
>>> +    nb_sns = bdrv_snapshot_list(bs, &sn_tab);
>>> +    aio_context_release(aio_context);
>>> +
>>> +    for (i = 0; i < nb_sns; i++) {
>>> +        if (bdrv_all_find_snapshot(sn_tab[i].name, &bs) == 0) {
>>> +            if (sn_tab[i].icount != -1ULL
>>> +                && sn_tab[i].icount <= icount
>>> +                && (!nearest || nearest->icount < sn_tab[i].icount)) {
>>> +                nearest = &sn_tab[i];
>>> +            }
>>> +        }
>>> +    }
>>> +    if (nearest) {
>>> +        ret = g_strdup(nearest->name);
>>> +        *snapshot_icount = nearest->icount;
>>> +    }
>>> +    g_free(sn_tab);
>>> +
>>> +fail:
>>> +    return ret;
>>> +}
>>> +
>>> +static void replay_seek(int64_t icount, QEMUTimerCB callback, Error **errp)
>>> +{
>>> +    char *snapshot = NULL;
>>> +    int64_t snapshot_icount;
>>> +
>>> +    if (replay_mode != REPLAY_MODE_PLAY) {
>>> +        error_setg(errp, "replay must be enabled to seek");
>>> +        return;
>>> +    }
>>> +    if (!replay_snapshot) {
>>> +        error_setg(errp, "snapshotting is disabled");
>>> +        return;
>>> +    }
>>> +
>>> +    snapshot = replay_find_nearest_snapshot(icount, &snapshot_icount);
>>> +    if (snapshot) {
>>> +        if (icount < replay_get_current_icount()
>>> +            || replay_get_current_icount() < snapshot_icount) {
>>> +            vm_stop(RUN_STATE_RESTORE_VM);
>>> +            load_snapshot(snapshot, errp);
>>> +        }
>>> +        g_free(snapshot);
>>> +    }
>>> +    if (replay_get_current_icount() <= icount) {
>>> +        replay_break(icount, callback, NULL);
>>> +        vm_start();
>>> +    } else {
>>> +        error_setg(errp, "cannot seek to the specified instruction count");
>>> +    }
>>> +}
>>> +
>>> +void qmp_replay_seek(int64_t icount, Error **errp)
>>> +{
>>> +    replay_seek(icount, replay_stop_vm, errp);
>>> +}
>>> +
>>> +void hmp_replay_seek(Monitor *mon, const QDict *qdict)
>>> +{
>>> +    int64_t icount = qdict_get_try_int(qdict, "icount", -1LL);
>>> +    Error *err = NULL;
>>> +
>>> +    qmp_replay_seek(icount, &err);
>>> +    if (err) {
>>> +        error_report_err(err);
>>> +        error_free(err);
>>> +        return;
>>> +    }
>>> +}
>> 
>> 


-- 
Alex Bennée