linux-kernel - Re: [PATCH v2] perf: Fix display of kernel symbols

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Message-ID: <Z36Ra23US_zC3n2v@x1>
Date: Wed, 8 Jan 2025 11:53:31 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	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>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-perf-users@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH v2] perf: Fix display of kernel symbols

On Wed, Jan 08, 2025 at 10:54:20AM +0100, Christophe Leroy wrote:
> Since commit 659ad3492b91 ("perf maps: Switch from rbtree to lazily
> sorted array for addresses"), perf doesn't display anymore kernel
> symbols on powerpc, allthough it still detects them as kernel addresses.
> 
> 	# Overhead  Command     Shared Object  Symbol
> 	# ........  ..........  ............. ......................................
> 	#
> 	    80.49%  Coeur main  [unknown]      [k] 0xc005f0f8
> 	     3.91%  Coeur main  gau            [.] engine_loop.constprop.0.isra.0
> 	     1.72%  Coeur main  [unknown]      [k] 0xc005f11c
> 	     1.09%  Coeur main  [unknown]      [k] 0xc01f82c8
> 	     0.44%  Coeur main  libc.so.6      [.] epoll_wait
> 	     0.38%  Coeur main  [unknown]      [k] 0xc0011718
> 	     0.36%  Coeur main  [unknown]      [k] 0xc01f45c0
> 
> This is because function maps__find_next_entry() now returns current
> entry instead of next entry, leading to kernel map end address
> getting mis-configured with its own start address instead of the
> start address of the following map.
> 
> Fix it by really taking the next entry, also make sure that entry
> follows current one by making sure entries are sorted.
> 
> Fixes: 659ad3492b91 ("perf maps: Switch from rbtree to lazily sorted array for addresses")
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> Reviewed-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
> v2: Make sure the entries are sorted, if not sort them.

Since you have changed what I reviewed I'll have to re-review :-) Will
try to do it after some calls.

- Arnaldo

> ---
>  tools/perf/util/maps.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/maps.c b/tools/perf/util/maps.c
> index 432399cbe5dd..09c9cc326c08 100644
> --- a/tools/perf/util/maps.c
> +++ b/tools/perf/util/maps.c
> @@ -1136,8 +1136,13 @@ struct map *maps__find_next_entry(struct maps *maps, struct map *map)
>  	struct map *result = NULL;
>  
>  	down_read(maps__lock(maps));
> +	while (!maps__maps_by_address_sorted(maps)) {
> +		up_read(maps__lock(maps));
> +		maps__sort_by_address(maps);
> +		down_read(maps__lock(maps));
> +	}
>  	i = maps__by_address_index(maps, map);
> -	if (i < maps__nr_maps(maps))
> +	if (++i < maps__nr_maps(maps))
>  		result = map__get(maps__maps_by_address(maps)[i]);
>  
>  	up_read(maps__lock(maps));
> -- 
> 2.47.0