Re: [PATCH 13/24] perf tools: Allow mmap2 event to synthesize kernel image

From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ingo Molnar <mingo@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Michael Petlan <mpetlan@redhat.com>,
	Song Liu <songliubraving@fb.com>, Ian Rogers <irogers@google.com>,
	Stephane Eranian <eranian@google.com>,
	Alexey Budankov <alexey.budankov@linux.intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCH 13/24] perf tools: Allow mmap2 event to synthesize kernel image
Date: Tue, 17 Nov 2020 09:44:37 -0300	[thread overview]
Message-ID: <20201117124437.GO614220@kernel.org> (raw)
In-Reply-To: <20201117110053.1303113-14-jolsa@kernel.org>

Em Tue, Nov 17, 2020 at 12:00:42PM +0100, Jiri Olsa escreveu:
> Allow mmap2 event to synthesize kernel image,
> so we can synthesize kernel build id data in
> following changes.
> 
> It's enabled by new symbol_conf.buildid_mmap2
> bool, which will be switched in following
> changes.

Why make this an option? MMAP2 goes back years:

13d7a2410fa637f45 (Stephane Eranian         2013-08-21 12:10:24 +0200  904)      * The MMAP2 records are an augmented version of MMAP, they add
13d7a2410fa637f45 (Stephane Eranian         2013-08-21 12:10:24 +0200  905)      * maj, min, ino numbers to be used to uniquely identify each mapping

Also we unconditionally generate MMAP2 events if the kernel supports it,
from evsel__config():

  attr->mmap  = track;
  attr->mmap2 = track && !perf_missing_features.mmap2;

So perhaps we should reuse that logic? I.e. use mmap2 if the kernel
supports it?

- Arnaldo

> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  tools/perf/util/symbol_conf.h      |  3 ++-
>  tools/perf/util/synthetic-events.c | 40 ++++++++++++++++++++----------
>  2 files changed, 29 insertions(+), 14 deletions(-)
> 
> diff --git a/tools/perf/util/symbol_conf.h b/tools/perf/util/symbol_conf.h
> index b916afb95ec5..b18f9c8dbb75 100644
> --- a/tools/perf/util/symbol_conf.h
> +++ b/tools/perf/util/symbol_conf.h
> @@ -42,7 +42,8 @@ struct symbol_conf {
>  			report_block,
>  			report_individual_block,
>  			inline_name,
> -			disable_add2line_warn;
> +			disable_add2line_warn,
> +			buildid_mmap2;
>  	const char	*vmlinux_name,
>  			*kallsyms_name,
>  			*source_prefix,
> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 8a23391558cf..872df6d6dbef 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -988,11 +988,12 @@ static int __perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
>  						perf_event__handler_t process,
>  						struct machine *machine)
>  {
> -	size_t size;
> +	union perf_event *event;
> +	size_t size = symbol_conf.buildid_mmap2 ?
> +			sizeof(event->mmap2) : sizeof(event->mmap);
>  	struct map *map = machine__kernel_map(machine);
>  	struct kmap *kmap;
>  	int err;
> -	union perf_event *event;
>  
>  	if (map == NULL)
>  		return -1;
> @@ -1006,7 +1007,7 @@ static int __perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
>  	 * available use this, and after it is use this as a fallback for older
>  	 * kernels.
>  	 */
> -	event = zalloc((sizeof(event->mmap) + machine->id_hdr_size));
> +	event = zalloc(size + machine->id_hdr_size);
>  	if (event == NULL) {
>  		pr_debug("Not enough memory synthesizing mmap event "
>  			 "for kernel modules\n");
> @@ -1023,16 +1024,29 @@ static int __perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
>  		event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
>  	}
>  
> -	size = snprintf(event->mmap.filename, sizeof(event->mmap.filename),
> -			"%s%s", machine->mmap_name, kmap->ref_reloc_sym->name) + 1;
> -	size = PERF_ALIGN(size, sizeof(u64));
> -	event->mmap.header.type = PERF_RECORD_MMAP;
> -	event->mmap.header.size = (sizeof(event->mmap) -
> -			(sizeof(event->mmap.filename) - size) + machine->id_hdr_size);
> -	event->mmap.pgoff = kmap->ref_reloc_sym->addr;
> -	event->mmap.start = map->start;
> -	event->mmap.len   = map->end - event->mmap.start;
> -	event->mmap.pid   = machine->pid;
> +	if (symbol_conf.buildid_mmap2) {
> +		size = snprintf(event->mmap2.filename, sizeof(event->mmap2.filename),
> +				"%s%s", machine->mmap_name, kmap->ref_reloc_sym->name) + 1;
> +		size = PERF_ALIGN(size, sizeof(u64));
> +		event->mmap2.header.type = PERF_RECORD_MMAP2;
> +		event->mmap2.header.size = (sizeof(event->mmap2) -
> +				(sizeof(event->mmap2.filename) - size) + machine->id_hdr_size);
> +		event->mmap2.pgoff = kmap->ref_reloc_sym->addr;
> +		event->mmap2.start = map->start;
> +		event->mmap2.len   = map->end - event->mmap.start;
> +		event->mmap2.pid   = machine->pid;
> +	} else {
> +		size = snprintf(event->mmap.filename, sizeof(event->mmap.filename),
> +				"%s%s", machine->mmap_name, kmap->ref_reloc_sym->name) + 1;
> +		size = PERF_ALIGN(size, sizeof(u64));
> +		event->mmap.header.type = PERF_RECORD_MMAP;
> +		event->mmap.header.size = (sizeof(event->mmap) -
> +				(sizeof(event->mmap.filename) - size) + machine->id_hdr_size);
> +		event->mmap.pgoff = kmap->ref_reloc_sym->addr;
> +		event->mmap.start = map->start;
> +		event->mmap.len   = map->end - event->mmap.start;
> +		event->mmap.pid   = machine->pid;
> +	}
>  
>  	err = perf_tool__process_synth_event(tool, event, machine, process);
>  	free(event);
> -- 
> 2.26.2
> 

-- 

- Arnaldo