| From 669c48aec1ca81101191b7b50ee30a6dd877c6a1 Mon Sep 17 00:00:00 2001 |
| From: Jesper Dangaard Brouer <brouer@redhat.com> |
| Date: Mon, 2 Dec 2019 13:37:31 +0100 |
| Subject: [PATCH] samples/bpf: Fix broken xdp_rxq_info due to map order |
| assumptions |
| MIME-Version: 1.0 |
| Content-Type: text/plain; charset=UTF-8 |
| Content-Transfer-Encoding: 8bit |
| |
| commit edbca120a8cdfa5a5793707e33497aa5185875ca upstream. |
| |
| 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 |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/samples/bpf/xdp_rxq_info_user.c b/samples/bpf/xdp_rxq_info_user.c |
| index 1210f3b170f0..7e2e858f140a 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; |
| -- |
| 2.7.4 |
| |