On Mon, Jan 6, 2025 at 11:38 AM Christophe Leroy
<christophe.le...@csgroup.eu> 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.
>
> Fixes: 659ad3492b91 ("perf maps: Switch from rbtree to lazily sorted array
> for addresses")
> Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
> Reviewed-by: Arnaldo Carvalho de Melo <a...@redhat.com>
> ---
> tools/perf/util/maps.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/maps.c b/tools/perf/util/maps.c
> index 432399cbe5dd..d39bf27a5fdd 100644
> --- a/tools/perf/util/maps.c
> +++ b/tools/perf/util/maps.c
> @@ -1137,7 +1137,7 @@ struct map *maps__find_next_entry(struct maps *maps,
> struct map *map)
>
> 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]);
Thanks for diagnosing this and sorry for the bug! Using the next entry
in this way won't work if the entries aren't sorted. I think the code
needs to be a little more complex, something like:
```
while (1) {
down_read(maps__lock(maps));
if (!maps__maps_by_address_sorted(maps)) {
up_read(maps__lock(maps));
maps__sort_by_address(maps);
continue;
}
i = maps__by_address_index(maps, map) + 1;
if (i < maps__nr_maps(maps))
result = map__get(maps__maps_by_address(maps)[i]);
up_read(maps__lock(maps));
break;
}
```
We could also implement the code similar to maps__by_address_index but
with some kind of best next value in the unsorted case. Given the
function has a single caller then this is probably overkill, but we've
seen performance issues in this code before.
Thanks,
Ian
