linux-kernel - Re: [RFC] perf record: missing buildid for callstack modules

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Date:	Thu, 14 Jan 2016 12:27:34 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Namhyung Kim <namhyung@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [RFC] perf record: missing buildid for callstack modules


* Peter Zijlstra <peterz@...radead.org> wrote:

> The current problem with that is that we use the 'remaining' size as
> the length field for a string (with the PERF_RECORD_MMAP* records).
> 
> We could of course fix that no problem.
> 
> 
> ---
>  include/uapi/linux/perf_event.h | 27 ++++++++++++++++++++++++++-
>  kernel/events/core.c            | 35 ++++++++++++++++++++++++-----------
>  2 files changed, 50 insertions(+), 12 deletions(-)
> 
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 1afe9623c1a7..b7b673387581 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -340,7 +340,8 @@ struct perf_event_attr {
>  				comm_exec      :  1, /* flag comm events that are due to an exec */
>  				use_clockid    :  1, /* use @clockid for time fields */
>  				context_switch :  1, /* context switch data */
> -				__reserved_1   : 37;
> +				mmap3          :  1, /* include mmap with mtime */
> +				__reserved_1   : 36;
>  
>  	union {
>  		__u32		wakeup_events;	  /* wakeup every n events */
> @@ -856,6 +857,30 @@ enum perf_event_type {
>  	 */
>  	PERF_RECORD_SWITCH_CPU_WIDE		= 15,
>  
> +	/*
> +	 * The MMAP3 records are an augmented version of MMAP2, they add
> +	 * mtime and filename_len, allowing for size based extensions.
> +	 *
> +	 * struct {
> +	 *	struct perf_event_header	header;
> +	 *
> +	 *	u32				pid, tid;
> +	 *	u64				addr;
> +	 *	u64				len;
> +	 *	u64				pgoff;
> +	 *	u32				maj;
> +	 *	u32				min;
> +	 *	u64				ino;
> +	 *	u64				ino_generation;
> +	 *	u32				prot, flags;
> +	 *	u64				mtime;
> +	 *	u32				filename_len;
> +	 *	char				filename[2+];
> +	 *	struct sample_id		sample_id;
> +	 * }
> +	 */
> +	PERF_RECORD_MMAP3			= 16,
> +
>  	PERF_RECORD_MAX,			/* non-ABI */
>  };

Yeah, very nice!

And this means v3 should be the last ever version - all future extensions can 
happen via the length field.

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo