Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1562317

[PATCH perf/core 1/6] tools lib bpf: Fix map offsets in relocation

Show all headers | View raw

Commit 4708bbda5cb2 ("tools lib bpf: Fix maps resolution") attempted to
fix map resolution by identifying the number of symbols that point to
maps, and using this number to resolve each of the maps.

However, during relocation the original definition of the map size was
still in use. For up to two maps, the calculation was correct if there
was a small difference in size between the map definition in libbpf and
the one that the client library uses. However if the difference was
large, particularly if more than two maps were used in the BPF program,
the relocation would fail.

For example, when using a map definition with size 28, with three maps,
map relocation would count
    (sym_offset / sizeof(struct bpf_map_def) => map_idx)
    (0 / 16 => 0), ie map_idx = 0
    (28 / 16 => 1), ie map_idx = 1
    (56 / 16 => 3), ie map_idx = 3

So, libbpf reports:
    libbpf: bpf relocation: map_idx 3 large than 2

Fix map relocation by tracking the size of the map definition during
map counting, then reuse this instead of the size of the libbpf map
structure. With this patch applied, libbpf will accept such ELFs.

Fixes: 4708bbda5cb2 ("tools lib bpf: Fix maps resolution")
Signed-off-by: Joe Stringer <joe@ovn.org>
---
 tools/lib/bpf/libbpf.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 84e6b35da4bd..350ee4c59f85 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -201,6 +201,7 @@ struct bpf_object {
 	size_t nr_programs;
 	struct bpf_map *maps;
 	size_t nr_maps;
+	size_t map_len;
 
 	bool loaded;
 
@@ -379,6 +380,7 @@ static struct bpf_object *bpf_object__new(const char *path,
 	obj->efile.maps_shndx = -1;
 
 	obj->loaded = false;
+	obj->map_len = sizeof(struct bpf_map_def);
 
 	INIT_LIST_HEAD(&obj->list);
 	list_add(&obj->list, &bpf_objects_list);
@@ -602,6 +604,7 @@ bpf_object__init_maps(struct bpf_object *obj)
 		return -ENOMEM;
 	}
 	obj->nr_maps = nr_maps;
+	obj->map_len = data->d_size / nr_maps;
 
 	/*
 	 * fill all fd with -1 so won't close incorrect
@@ -829,7 +832,7 @@ bpf_program__collect_reloc(struct bpf_program *prog,
 			return -LIBBPF_ERRNO__RELOC;
 		}
 
-		map_idx = sym.st_value / sizeof(struct bpf_map_def);
+		map_idx = sym.st_value / prog->obj->map_len;
 		if (map_idx >= nr_maps) {
 			pr_warning("bpf relocation: map_idx %d large than %d\n",
 				   (int)map_idx, (int)nr_maps - 1);
-- 
2.11.0

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH perf/core 0/6] Libbpf improvements Joe Stringer <joe@ovn.org> - 2017-01-19 01:00 +0100
  [PATCH perf/core 2/6] tools lib bpf: Fix grammar in map_idx warning Joe Stringer <joe@ovn.org> - 2017-01-19 01:00 +0100
    Re: [PATCH perf/core 2/6] tools lib bpf: Fix grammar in map_idx  warning "Wangnan (F)" <wangnan0@huawei.com> - 2017-01-19 11:20 +0100
  [PATCH perf/core 4/6] tools lib bpf: Add set/is helpers for all prog types Joe Stringer <joe@ovn.org> - 2017-01-19 01:00 +0100
  [PATCH perf/core 5/6] tools lib bpf: Add libbpf_get_error() Joe Stringer <joe@ovn.org> - 2017-01-19 01:10 +0100
  [PATCH perf/core 1/6] tools lib bpf: Fix map offsets in relocation Joe Stringer <joe@ovn.org> - 2017-01-19 01:10 +0100
    Re: [PATCH perf/core 1/6] tools lib bpf: Fix map offsets in  relocation "Wangnan (F)" <wangnan0@huawei.com> - 2017-01-19 07:10 +0100
    [PATCH -improve] tools lib bpf: Fix map offsets in relocation Wang Nan <wangnan0@huawei.com> - 2017-01-19 11:00 +0100
  [PATCH perf/core 3/6] tools lib bpf: Define prog_type fns with macro Joe Stringer <joe@ovn.org> - 2017-01-19 01:10 +0100
  [PATCH perf/core 6/6] tools lib bpf: Add bpf_object__pin() Joe Stringer <joe@ovn.org> - 2017-01-19 01:10 +0100
    Re: [PATCH perf/core 6/6] tools lib bpf: Add bpf_object__pin() "Wangnan (F)" <wangnan0@huawei.com> - 2017-01-19 11:30 +0100
      Re: [PATCH perf/core 6/6] tools lib bpf: Add bpf_object__pin() Joe Stringer <joe@ovn.org> - 2017-01-20 01:00 +0100
  Re: [PATCH perf/core 0/6] Libbpf improvements "Wangnan (F)" <wangnan0@huawei.com> - 2017-01-19 11:30 +0100
    Re: [PATCH perf/core 0/6] Libbpf improvements Joe Stringer <joe@ovn.org> - 2017-01-23 02:20 +0100

csiph-web