linux-kernel - Re: [PATCH v3 1/4] perf tool: Change fields type in perf_record_time

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Message-ID: <a3bcac42-f268-fe65-b871-3d5e3718a30b@intel.com>
Date:   Wed, 28 Apr 2021 16:16:45 +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>,
        "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-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/4] perf tool: Change fields type in
 perf_record_time_conv

On 28/04/21 3:09 pm, Leo Yan wrote:
> C standard claims "An object declared as type _Bool is large enough to
> store the values 0 and 1", bool type size can be 1 byte or larger than
> 1 byte.  Thus it's uncertian for bool type size with different
> compilers.
> 
> This patch changes the bool type in structure perf_record_time_conv to
> __u8 type, and pads extra bytes for 8-byte alignment; this can give
> reliable structure size.
> 
> Suggested-by: Adrian Hunter <adrian.hunter@...el.com>
> Fixes: d110162cafc8 ("perf tsc: Support cap_user_time_short for event TIME_CONV")
> Signed-off-by: Leo Yan <leo.yan@...aro.org>

Acked-by: Adrian Hunter <adrian.hunter@...el.com>

> ---
>  tools/lib/perf/include/perf/event.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
> index d82054225fcc..48583e441d9b 100644
> --- a/tools/lib/perf/include/perf/event.h
> +++ b/tools/lib/perf/include/perf/event.h
> @@ -346,8 +346,9 @@ struct perf_record_time_conv {
>  	__u64			 time_zero;
>  	__u64			 time_cycles;
>  	__u64			 time_mask;
> -	bool			 cap_user_time_zero;
> -	bool			 cap_user_time_short;
> +	__u8			 cap_user_time_zero;
> +	__u8			 cap_user_time_short;
> +	__u8			 reserved[6];	/* For alignment */
>  };
>  
>  struct perf_record_header_feature {
>