path: root/samples/bpf/xdp_rxq_info_user.c
diff options
authorJesper Dangaard Brouer <brouer@redhat.com>2019-12-02 13:37:31 +0100
committerAlexei Starovoitov <ast@kernel.org>2019-12-04 17:54:15 -0800
commitedbca120a8cdfa5a5793707e33497aa5185875ca (patch)
tree0503e0d8d7acdf7ccac3a62e123e232a956c5b17 /samples/bpf/xdp_rxq_info_user.c
parent099ffd7eddfe03b9b5b43e1f4ffece99121dd7ba (diff)
samples/bpf: Fix broken xdp_rxq_info due to map order assumptions
In the days of using bpf_load.c the order in which the 'maps' sections were defines in BPF side (*_kern.c) file, were used by userspace side to identify the map via using the map order as an index. In effect the order-index is created based on the order the maps sections are stored in the ELF-object file, by the LLVM compiler. This have also carried over in libbpf via API bpf_map__next(NULL, obj) to extract maps in the order libbpf parsed the ELF-object file. When BTF based maps were introduced a new section type ".maps" were created. I found that the LLVM compiler doesn't create the ".maps" sections in the order they are defined in the C-file. The order in the ELF file is based on the order the map pointer is referenced in the code. This combination of changes lead to xdp_rxq_info mixing up the map file-descriptors in userspace, resulting in very broken behaviour, but without warning the user. This patch fix issue by instead using bpf_object__find_map_by_name() to find maps via their names. (Note, this is the ELF name, which can be longer than the name the kernel retains). Fixes: be5bca44aa6b ("samples: bpf: convert some XDP samples from bpf_load to libbpf") Fixes: 451d1dc886b5 ("samples: bpf: update map definition to new syntax BTF-defined map") Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Toke Høiland-Jørgensen <toke@redhat.com> Acked-by: Andrii Nakryiko <andriin@fb.com> Link: https://lore.kernel.org/bpf/157529025128.29832.5953245340679936909.stgit@firesoul
Diffstat (limited to 'samples/bpf/xdp_rxq_info_user.c')
1 files changed, 3 insertions, 3 deletions
diff --git a/samples/bpf/xdp_rxq_info_user.c b/samples/bpf/xdp_rxq_info_user.c
index 51e0d810e070..8fc3ad01de72 100644
--- a/samples/bpf/xdp_rxq_info_user.c
+++ b/samples/bpf/xdp_rxq_info_user.c
@@ -489,9 +489,9 @@ int main(int argc, char **argv)
if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))
return EXIT_FAIL;
- map = bpf_map__next(NULL, obj);
- stats_global_map = bpf_map__next(map, obj);
- rx_queue_index_map = bpf_map__next(stats_global_map, obj);
+ map = bpf_object__find_map_by_name(obj, "config_map");
+ stats_global_map = bpf_object__find_map_by_name(obj, "stats_global_map");
+ rx_queue_index_map = bpf_object__find_map_by_name(obj, "rx_queue_index_map");
if (!map || !stats_global_map || !rx_queue_index_map) {
printf("finding a map in obj file failed\n");
return EXIT_FAIL;