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

Jiri Olsa
2019-04-23T14:55:14Z

On Tue, Apr 23, 2019 at 12:32:12PM +0300, Adrian Hunter wrote:
> 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.

I haven't considered it could get in between modules,
I think you're right and we need to cut kcore maps
in case bpf is mapped within.. I'll submit new version

thanks,
jirka

>
> >
> > 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;
> > }
> >
>