linux-kernel - Re: [PATCH v1 1/3] perf synthetic-events: Ensure features are aligned

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Message-ID: <CAP-5=fWtxkt_kFCF8G=Dp4Fj+=m1M7Fv6Ep4RvJmH_k-k53rNw@mail.gmail.com>
Date: Sat, 14 Dec 2024 11:32:27 -0800
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, Sun Haiyong <sunhaiyong@...ngson.cn>, 
	Yanteng Si <siyanteng@...ngson.cn>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/3] perf synthetic-events: Ensure features are aligned

On Thu, Dec 12, 2024 at 12:05 AM Ian Rogers <irogers@...gle.com> wrote:
>
> Features like hostname have arbitrary size and break the assumed
> 8-byte alignment of perf events. Pad all feature events until 8-byte
> alignment is restored.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

This change breaks pipe mode tests for me on ARM. I've not investigated why yet.

Thanks,
Ian

> ---
>  tools/perf/util/synthetic-events.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index f8ac2ac2da45..5b14244253b5 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -2401,6 +2401,11 @@ int perf_event__synthesize_features(const struct perf_tool *tool, struct perf_se
>                         pr_debug("Error writing feature\n");
>                         continue;
>                 }
> +               while (PERF_ALIGN(ff.offset, sizeof(u64)) != ff.offset) {
> +                       char c = 0;
> +
> +                       do_write(&ff, &c, 1);
> +               }
>                 /* ff.buf may have changed due to realloc in do_write() */
>                 fe = ff.buf;
>                 memset(fe, 0, sizeof(*fe));
> --
> 2.47.1.613.gc27f4b7a9f-goog
>