Em Tue, Jul 26, 2022 at 03:09:21PM -0700, Ian Rogers escreveu:
> bpf_perf_object__next folded the last element in the list test with the
> empty list test. However, this meant that offsets were computed against
> null and that a struct list_head was compared against a struct
> bpf_perf_object. Working around this with clang's undefined behavior
> sanitizer required -fno-sanitize=null and -fno-sanitize=object-size.
> in
> Remove the undefined behav(ior by using the regular Linux list APIs and
> handling the starting case separately from the end testing case. Looking
> at uses like bpf_perf_object__for_each, as the constant NULL or non-NULL
> argument can be constant propagated the code is no less efficient.
Nicely spotted!
In some places people solve this with list_first_entry_or_null(), like
in cs_etm__queue_aux_records().
Applied.
- Arnado
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
> tools/perf/util/bpf-loader.c | 18 +++++++-----------
> 1 file changed, 7 insertions(+), 11 deletions(-)
>
> diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
> indelx f8ad581ea247..cdd6463a5b68 100644
> --- a/tools/perf/util/bpf-loader.c
> +++ b/tools/perf/util/bpf-loader.c
> @@ -63,20 +63,16 @@ static struct hashmap *bpf_map_hash;
> static struct bpf_perf_object *
> bpf_perf_object__next(struct bpf_perf_object *prev)
> {
> - struct bpf_perf_object *next;
> -
> - if (!prev)
> - next = list_first_entry(&bpf_objects_list,
> - struct bpf_perf_object,
> - list);
> - else
> - next = list_next_entry(prev, list);
> + if (!prev) {
> + if (list_empty(&bpf_objects_list))
> + return NULL;
>
> - /* Empty list is noticed here so don't need checking on entry. */
> - if (&next->list == &bpf_objects_list)
> + return list_first_entry(&bpf_objects_list, struct bpf_perf_object, list);
> + }
> + if (list_is_last(&prev->list, &bpf_objects_list))
> return NULL;
>
> - return next;
> + return list_next_entry(prev, list);
> }
>
> #define bpf_perf_object__for_each(perf_obj, tmp) \
> --
> 2.37.1.359.gd136c6c3e2-goog
--
- Arnaldo
