Re: [PATCH 06/12] perf tools: Do not erase uncovered maps by kcore

Adrian Hunter
2019-04-23T09:33:42Z

On 16/04/19 7:01 PM, Jiri Olsa wrote:
> Maps in kcore do not cover bpf maps, so we can't just
> remove everything. Keeping all kernel maps, which are
> not covered by kcore maps.

Memory for jited-bpf is allocated from the same area that is used for
modules. In the case of /proc/kcore, that entire area is mapped, so there
won't be any bpf-maps that are not covered. For copies of kcore made by
'perf buildid-cache' the same would be true for any bpf that got allocated
in between modules.

But shouldn't the bpf map supersede the kcore map for the address range that
it maps? I guess that would mean splitting the kcore map, truncating the
first piece and inserting the bpf map in between.

>
> Link: http://lkml.kernel.org/n/tip-9eytka8wofp0a047ul6lmejk@git.kernel.org
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> tools/perf/util/symbol.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 5cbad55cd99d..96738a7a8c14 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -1166,6 +1166,18 @@ static int kcore_mapfn(u64 start, u64 len, u64 pgoff, void *data)
> return 0;
> }
>
> +static bool in_kcore(struct kcore_mapfn_data *md, struct map *map)
> +{
> + struct map *iter;
> +
> + list_for_each_entry(iter, &md->maps, node) {
> + if ((map->start >= iter->start) && (map->start < iter->end))
> + return true;
> + }
> +
> + return false;
> +}
> +
> static int dso__load_kcore(struct dso *dso, struct map *map,
> const char *kallsyms_filename)
> {
> @@ -1222,7 +1234,7 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
> while (old_map) {
> struct map *next = map_groups__next(old_map);
>
> - if (old_map != map)
> + if (old_map != map && !in_kcore(&md, old_map))
> map_groups__remove(kmaps, old_map);
> old_map = next;
> }
>