Re: [RFC 3/4] perf tool: Introduce PERF_RECORD_KMOD_SEC_MAP

[Adrian Hunter]

On 10/01/23 07:58, Ravi Bangoria wrote:
> Introduce, perf tool only, synthetic event type PERF_RECORD_KMOD_SEC_MAP.
> Also add stub code for it. This event will be used to save/restore kernel
> module section maps to/from perf.data file. This is needed because kernel
> module elfs does not contain program header table and thus there is no
> easy way to find out how kernel would have loaded module sections in the
> memory.

Currently machine__addnew_module_map() adds a map for a
module, and then perf_event__synthesize_modules() creates
an MMAP/MMAP2 event for it.  Why can't we do that for the
sections?

> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxx>
> ---
>  tools/lib/perf/Documentation/libperf.txt |  1 +
>  tools/lib/perf/include/perf/event.h      | 25 ++++++++++++++++++++++++
>  tools/perf/util/event.c                  |  1 +
>  tools/perf/util/session.c                | 12 ++++++++++++
>  tools/perf/util/tool.h                   |  3 ++-
>  5 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/perf/Documentation/libperf.txt b/tools/lib/perf/Documentation/libperf.txt
> index a8f1a237931b..b62730b84cc5 100644
> --- a/tools/lib/perf/Documentation/libperf.txt
> +++ b/tools/lib/perf/Documentation/libperf.txt
> @@ -211,6 +211,7 @@ SYNOPSIS
>    struct perf_record_time_conv;
>    struct perf_record_header_feature;
>    struct perf_record_compressed;
> +  struct perf_record_kmod_sec_maps;
>  --
>  
>  DESCRIPTION
> diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
> index ad47d7b31046..404b23b6902b 100644
> --- a/tools/lib/perf/include/perf/event.h
> +++ b/tools/lib/perf/include/perf/event.h
> @@ -438,6 +438,29 @@ struct perf_record_compressed {
>  	char			 data[];
>  };
>  
> +/* Kernel module elf section maps */
> +struct perf_record_kmod_sec_map {
> +	struct perf_event_header header;
> +	/* Machine id. Same as synthesized PERF_RECORD_MMAP */
> +	__u32			 pid;
> +	/* Section start ip address */
> +	__u64			 start;
> +	/* Section length */
> +	__u64			 len;
> +	/* Section page offset in kernel module elf file */
> +	__u64			 pgoff;
> +	/* Section name length, including '\0' */
> +	__u16			 sec_name_len;
> +	/* Kernel module filename(path) length, including '\0' */
> +	__u16			 filename_len;
> +	/*
> +	 * Section name and filename stored as: "sec_name\0filename\0". i.e:
> +	 * data[0]: Section name
> +	 * data[sec_name_len + 1]: File name
> +	 */
> +	char			 data[];
> +};
> +
>  enum perf_user_event_type { /* above any possible kernel type */
>  	PERF_RECORD_USER_TYPE_START		= 64,
>  	PERF_RECORD_HEADER_ATTR			= 64,
> @@ -459,6 +482,7 @@ enum perf_user_event_type { /* above any possible kernel type */
>  	PERF_RECORD_HEADER_FEATURE		= 80,
>  	PERF_RECORD_COMPRESSED			= 81,
>  	PERF_RECORD_FINISHED_INIT		= 82,
> +	PERF_RECORD_KMOD_SEC_MAP		= 83,
>  	PERF_RECORD_HEADER_MAX
>  };
>  
> @@ -499,6 +523,7 @@ union perf_event {
>  	struct perf_record_time_conv		time_conv;
>  	struct perf_record_header_feature	feat;
>  	struct perf_record_compressed		pack;
> +	struct perf_record_kmod_sec_map		kmod_sec_map;
>  };
>  
>  #endif /* __LIBPERF_EVENT_H */
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index 1fa14598b916..1b03061440bc 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -77,6 +77,7 @@ static const char *perf_event__names[] = {
>  	[PERF_RECORD_HEADER_FEATURE]		= "FEATURE",
>  	[PERF_RECORD_COMPRESSED]		= "COMPRESSED",
>  	[PERF_RECORD_FINISHED_INIT]		= "FINISHED_INIT",
> +	[PERF_RECORD_KMOD_SEC_MAP]		= "KMOD_SEC_MAP",
>  };
>  
>  const char *perf_event__name(unsigned int id)
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index 7c021c6cedb9..4f5165cd58de 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -563,6 +563,8 @@ void perf_tool__fill_defaults(struct perf_tool *tool)
>  		tool->compressed = perf_session__process_compressed_event;
>  	if (tool->finished_init == NULL)
>  		tool->finished_init = process_event_op2_stub;
> +	if (tool->kmod_sec_map == NULL)
> +		tool->kmod_sec_map = process_event_stub;
>  }
>  
>  static void swap_sample_id_all(union perf_event *event, void *data)
> @@ -997,6 +999,12 @@ static void perf_event__time_conv_swap(union perf_event *event,
>  	}
>  }
>  
> +static void perf_event_kmod_sec_map_swap(union perf_event *event __maybe_unused,
> +					  bool sample_id_all __maybe_unused)
> +{
> +	/* FIXME */
> +}
> +
>  typedef void (*perf_event__swap_op)(union perf_event *event,
>  				    bool sample_id_all);
>  
> @@ -1035,6 +1043,7 @@ static perf_event__swap_op perf_event__swap_ops[] = {
>  	[PERF_RECORD_STAT_ROUND]	  = perf_event__stat_round_swap,
>  	[PERF_RECORD_EVENT_UPDATE]	  = perf_event__event_update_swap,
>  	[PERF_RECORD_TIME_CONV]		  = perf_event__time_conv_swap,
> +	[PERF_RECORD_KMOD_SEC_MAP]	  = perf_event_kmod_sec_map_swap,
>  	[PERF_RECORD_HEADER_MAX]	  = NULL,
>  };
>  
> @@ -1727,6 +1736,9 @@ static s64 perf_session__process_user_event(struct perf_session *session,
>  		return err;
>  	case PERF_RECORD_FINISHED_INIT:
>  		return tool->finished_init(session, event);
> +	case PERF_RECORD_KMOD_SEC_MAP:
> +		/* Currently PERF_RECORD_KMOD_SEC_MAP is supported only for host */
> +		return tool->kmod_sec_map(tool, event, &sample, &session->machines.host);
>  	default:
>  		return -EINVAL;
>  	}
> diff --git a/tools/perf/util/tool.h b/tools/perf/util/tool.h
> index c957fb849ac6..8ea7fb85c196 100644
> --- a/tools/perf/util/tool.h
> +++ b/tools/perf/util/tool.h
> @@ -60,7 +60,8 @@ struct perf_tool {
>  			unthrottle,
>  			ksymbol,
>  			bpf,
> -			text_poke;
> +			text_poke,
> +			kmod_sec_map;
>  
>  	event_attr_op	attr;
>  	event_attr_op	event_update;