[PATCH 08/12] perf tools: Preserve eBPF maps when loading kcore

Jiri Olsa
2019-05-08T13:20:45Z

We need to preserve eBPF maps even if they are
covered by kcore, because we need to access
eBPF dso for source data.

Adding map_groups__merge_in function to do that.
It merges map into map_groups by splitting the
new map within the existing map regions.

Suggested-by: Adrian Hunter <adrian.hunter@intel.com>
Link: http://lkml.kernel.org/n/tip-mlu13e9zl6rbsz4fa00x7mfa@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/perf/util/symbol.c | 97 ++++++++++++++++++++++++++++++++++++++--
1 file changed, 93 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 5cbad55cd99d..29780fcd049c 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1166,6 +1166,85 @@ static int kcore_mapfn(u64 start, u64 len, u64 pgoff, void *data)
return 0;
}

+/*
+ * Merges map into map_groups by splitting the new map
+ * within the existing map regions.
+ */
+static int map_groups__merge_in(struct map_groups *kmaps, struct map *new_map)
+{
+ struct map *old_map;
+ LIST_HEAD(merged);
+
+ for (old_map = map_groups__first(kmaps); old_map;
+ old_map = map_groups__next(old_map)) {
+
+ /* no overload with this one */
+ if (new_map->end < old_map->start ||
+ new_map->start >= old_map->end)
+ continue;
+
+ if (new_map->start < old_map->start) {
+ /*
+ * |new......
+ * |old....
+ */
+ if (new_map->end < old_map->end) {
+ /*
+ * |new......| -> |new..|
+ * |old....| -> |old....|
+ */
+ new_map->end = old_map->start;
+ } else {
+ /*
+ * |new.............| -> |new..| |new..|
+ * |old....| -> |old....|
+ */
+ struct map *m = map__clone(new_map);
+
+ if (!m)
+ return -ENOMEM;
+
+ m->end = old_map->start;
+ list_add_tail(&m->node, &merged);
+ new_map->start = old_map->end;
+ }
+ } else {
+ /*
+ * |new......
+ * |old....
+ */
+ if (new_map->end < old_map->end) {
+ /*
+ * |new..| -> x
+ * |old.........| -> |old.........|
+ */
+ map__put(new_map);
+ new_map = NULL;
+ break;
+ } else {
+ /*
+ * |new......| -> |new...|
+ * |old....| -> |old....|
+ */
+ new_map->start = old_map->end;
+ }
+ }
+ }
+
+ while (!list_empty(&merged)) {
+ old_map = list_entry(merged.next, struct map, node);
+ list_del_init(&old_map->node);
+ map_groups__insert(kmaps, old_map);
+ map__put(old_map);
+ }
+
+ if (new_map) {
+ map_groups__insert(kmaps, new_map);
+ map__put(new_map);
+ }
+ return 0;
+}
+
static int dso__load_kcore(struct dso *dso, struct map *map,
const char *kallsyms_filename)
{
@@ -1222,7 +1301,12 @@ 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)
+ /*
+ * We need to preserve eBPF maps even if they are
+ * covered by kcore, because we need to access
+ * eBPF dso for source data.
+ */
+ if (old_map != map && !__map__is_bpf_prog(old_map))
map_groups__remove(kmaps, old_map);
old_map = next;
}
@@ -1256,11 +1340,16 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
map_groups__remove(kmaps, map);
map_groups__insert(kmaps, map);
map__put(map);
+ map__put(new_map);
} else {
- map_groups__insert(kmaps, new_map);
+ /*
+ * Merge kcore map into existing maps,
+ * and ensure that current maps (eBPF)
+ * stay intact.
+ */
+ if (map_groups__merge_in(kmaps, new_map))
+ goto out_err;
}
-
- map__put(new_map);
}

if (machine__is(machine, "x86_64")) {
--
2.20.1