linux-kernel - Re: [PATCH v1 2/3] perf session: Add swap operation for event TIME

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Date:   Mon, 26 Apr 2021 08:40:00 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Leo Yan <leo.yan@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Steve MacLean <Steve.MacLean@...rosoft.com>,
        Yonatan Goldschmidt <yonatan.goldschmidt@...nulate.io>,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/3] perf session: Add swap operation for event
 TIME_CONV

On 12/04/21 11:34 am, Leo Yan wrote:
> Since commit d110162cafc8 ("perf tsc: Support cap_user_time_short for
> event TIME_CONV"), the event PERF_RECORD_TIME_CONV has extended the data
> structure for clock parameters.
> 
> To be backwards-compatible, this patch adds a dedicated swap operation
> for the event PERF_RECORD_TIME_CONV, based on checking the event size,
> it can support both for the old and new event formats.
> 
> Fixes: d110162cafc8 ("perf tsc: Support cap_user_time_short for event TIME_CONV")
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  tools/perf/util/session.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index 9a8808507bd9..afca3d5fc851 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -949,6 +949,26 @@ static void perf_event__stat_round_swap(union perf_event *event,
>  	event->stat_round.time = bswap_64(event->stat_round.time);
>  }
>  
> +static void perf_event__time_conv_swap(union perf_event *event,
> +				       bool sample_id_all __maybe_unused)
> +{
> +	size_t time_zero_size;
> +
> +	event->time_conv.time_shift = bswap_64(event->time_conv.time_shift);
> +	event->time_conv.time_mult  = bswap_64(event->time_conv.time_mult);
> +	event->time_conv.time_zero  = bswap_64(event->time_conv.time_zero);
> +
> +	time_zero_size = (void *)&event->time_conv.time_cycles - (void *)event;
> +	if (event->header.size > time_zero_size) {

I wonder if we could have a helper for this e.g. (untested)

#define event_contains(obj, mem) (obj.header.size > offsetof(typeof(obj), mem))

	if (event_contains(event->time_conv, time_cycles)) {


> +		event->time_conv.time_cycles = bswap_64(event->time_conv.time_cycles);
> +		event->time_conv.time_mask = bswap_64(event->time_conv.time_mask);
> +		event->time_conv.cap_user_time_zero =
> +			bswap_32(event->time_conv.cap_user_time_zero);
> +		event->time_conv.cap_user_time_short =
> +			bswap_32(event->time_conv.cap_user_time_short);

'struct perf_record_time_conv' contains bool, the sizeof which, AFAIK, is not defined.
Is it really 4 bytes on your implementation?  It is only 1 byte with gcc on x86.

Either way, you should change 'struct perf_record_time_conv' so it uses a type of known size.
Since you are the only one using it, it should match your implementation.

> +	}
> +}
> +
>  typedef void (*perf_event__swap_op)(union perf_event *event,
>  				    bool sample_id_all);
>  
> @@ -985,7 +1005,7 @@ static perf_event__swap_op perf_event__swap_ops[] = {
>  	[PERF_RECORD_STAT]		  = perf_event__stat_swap,
>  	[PERF_RECORD_STAT_ROUND]	  = perf_event__stat_round_swap,
>  	[PERF_RECORD_EVENT_UPDATE]	  = perf_event__event_update_swap,
> -	[PERF_RECORD_TIME_CONV]		  = perf_event__all64_swap,
> +	[PERF_RECORD_TIME_CONV]		  = perf_event__time_conv_swap,
>  	[PERF_RECORD_HEADER_MAX]	  = NULL,
>  };
>  
>