linux-kernel - Re: [PATCH 01/14] perf/x86: Introduce PERF_RECORD

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Date:   Wed, 23 Nov 2016 21:11:05 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...el.com
Cc:     mingo@...hat.com, acme@...nel.org, linux-kernel@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, tglx@...utronix.de,
        namhyung@...nel.org, jolsa@...nel.org, adrian.hunter@...el.com,
        wangnan0@...wei.com, mark.rutland@....com, andi@...stfloor.org
Subject: Re: [PATCH 01/14] perf/x86: Introduce PERF_RECORD_OVERHEAD

On Wed, Nov 23, 2016 at 04:44:39AM -0500, kan.liang@...el.com wrote:
> +struct perf_overhead_entry {
> +	__u32	cpu;
> +	__u64	nr;
> +	__u64	time;
> +};

> +void perf_log_overhead(struct perf_event *event, u32 type,
> +		       struct perf_overhead_entry *entry)
> +{
> +	struct perf_output_handle handle;
> +	struct perf_sample_data sample;
> +	int ret;
> +
> +	struct {
> +		struct perf_event_header	header;
> +		u32				type;

There's two u32 sized holes here.

> +		struct perf_overhead_entry	overhead;
> +	} overhead_event = {
> +		.header = {
> +			.type = PERF_RECORD_OVERHEAD,
> +			.misc = 0,
> +			.size = sizeof(overhead_event),
> +		},
		.type = type,
		.overhead = *event,
> +	};

> +	overhead_event.type = type;
> +	memcpy(&overhead_event.overhead, entry, sizeof(overhead_event.overhead));

Do the above named initialization instead.

> +
> +	perf_event_header__init_id(&overhead_event.header, &sample, event);
> +	ret = perf_output_begin(&handle, event, overhead_event.header.size);
> +
> +	if (ret)
> +		return;
> +
> +	perf_output_put(&handle, overhead_event);
> +	perf_event__output_id_sample(event, &handle, &sample);
> +
> +	perf_output_end(&handle);
> +	memset(entry, 0, sizeof(*entry));
> +}