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author | Jesper Dangaard Brouer <brouer@redhat.com> | 2019-12-02 15:37:31 +0300 |
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committer | Alexei Starovoitov <ast@kernel.org> | 2019-12-05 04:54:15 +0300 |
commit | edbca120a8cdfa5a5793707e33497aa5185875ca (patch) | |
tree | 0503e0d8d7acdf7ccac3a62e123e232a956c5b17 /samples/bpf/xdp_rxq_info_user.c | |
parent | 099ffd7eddfe03b9b5b43e1f4ffece99121dd7ba (diff) | |
download | linux-edbca120a8cdfa5a5793707e33497aa5185875ca.tar.xz |
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')
-rw-r--r-- | samples/bpf/xdp_rxq_info_user.c | 6 |
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; |