[PATCH bpf-next] libbpf: use original struct sizes for skeleton iterations

[Mykyta Yatsenko mykyta.yatsenko5@gmail.com]

From: Mykyta Yatsenko <yatsenko@meta.com>

BPF skeletons can be created by previous or newer versions of libbpf,
for which sizeof(bpf_map_skeleton) or bpf_prog_skeleton may differ.
Libbpf should not rely on array indexing, but instead use original
sizes via map_skel_sz/prog_skel_sz for iterating over the
arrays of maps/progs.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
---
 tools/lib/bpf/libbpf.c | 52 +++++++++++++++++++++++++++---------------
 1 file changed, 33 insertions(+), 19 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 4a28fac4908a..b46cf29d74b6 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -13712,14 +13712,16 @@ int libbpf_num_possible_cpus(void)
 
 static int populate_skeleton_maps(const struct bpf_object *obj,
 				  struct bpf_map_skeleton *maps,
-				  size_t map_cnt)
+				  size_t map_cnt, size_t map_sz)
 {
 	int i;
 
 	for (i = 0; i < map_cnt; i++) {
-		struct bpf_map **map = maps[i].map;
-		const char *name = maps[i].name;
-		void **mmaped = maps[i].mmaped;
+		struct bpf_map_skeleton *map_skel = (struct bpf_map_skeleton *)
+			((char *)maps + map_sz * i);
+		struct bpf_map **map = map_skel->map;
+		const char *name = map_skel->name;
+		void **mmaped = map_skel->mmaped;
 
 		*map = bpf_object__find_map_by_name(obj, name);
 		if (!*map) {
@@ -13736,13 +13738,15 @@ static int populate_skeleton_maps(const struct bpf_object *obj,
 
 static int populate_skeleton_progs(const struct bpf_object *obj,
 				   struct bpf_prog_skeleton *progs,
-				   size_t prog_cnt)
+				   size_t prog_cnt, size_t prog_sz)
 {
 	int i;
 
 	for (i = 0; i < prog_cnt; i++) {
-		struct bpf_program **prog = progs[i].prog;
-		const char *name = progs[i].name;
+		struct bpf_prog_skeleton *cur_prog = (struct bpf_prog_skeleton *)
+			((char *)progs + prog_sz * i);
+		struct bpf_program **prog = cur_prog->prog;
+		const char *name = cur_prog->name;
 
 		*prog = bpf_object__find_program_by_name(obj, name);
 		if (!*prog) {
@@ -13783,13 +13787,13 @@ int bpf_object__open_skeleton(struct bpf_object_skeleton *s,
 	}
 
 	*s->obj = obj;
-	err = populate_skeleton_maps(obj, s->maps, s->map_cnt);
+	err = populate_skeleton_maps(obj, s->maps, s->map_cnt, s->map_skel_sz);
 	if (err) {
 		pr_warn("failed to populate skeleton maps for '%s': %d\n", s->name, err);
 		return libbpf_err(err);
 	}
 
-	err = populate_skeleton_progs(obj, s->progs, s->prog_cnt);
+	err = populate_skeleton_progs(obj, s->progs, s->prog_cnt, s->prog_skel_sz);
 	if (err) {
 		pr_warn("failed to populate skeleton progs for '%s': %d\n", s->name, err);
 		return libbpf_err(err);
@@ -13819,13 +13823,13 @@ int bpf_object__open_subskeleton(struct bpf_object_subskeleton *s)
 		return libbpf_err(-errno);
 	}
 
-	err = populate_skeleton_maps(s->obj, s->maps, s->map_cnt);
+	err = populate_skeleton_maps(s->obj, s->maps, s->map_cnt, s->map_skel_sz);
 	if (err) {
 		pr_warn("failed to populate subskeleton maps: %d\n", err);
 		return libbpf_err(err);
 	}
 
-	err = populate_skeleton_progs(s->obj, s->progs, s->prog_cnt);
+	err = populate_skeleton_progs(s->obj, s->progs, s->prog_cnt, s->prog_skel_sz);
 	if (err) {
 		pr_warn("failed to populate subskeleton maps: %d\n", err);
 		return libbpf_err(err);
@@ -13879,10 +13883,12 @@ int bpf_object__load_skeleton(struct bpf_object_skeleton *s)
 	}
 
 	for (i = 0; i < s->map_cnt; i++) {
-		struct bpf_map *map = *s->maps[i].map;
+		struct bpf_map_skeleton *map_skel = (struct bpf_map_skeleton *)
+			((char *)s->maps + s->map_skel_sz * i);
+		struct bpf_map *map = *map_skel->map;
 		size_t mmap_sz = bpf_map_mmap_sz(map);
 		int prot, map_fd = map->fd;
-		void **mmaped = s->maps[i].mmaped;
+		void **mmaped = map_skel->mmaped;
 
 		if (!mmaped)
 			continue;
@@ -13930,8 +13936,10 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s)
 	int i, err;
 
 	for (i = 0; i < s->prog_cnt; i++) {
-		struct bpf_program *prog = *s->progs[i].prog;
-		struct bpf_link **link = s->progs[i].link;
+		struct bpf_prog_skeleton *prog_skel = (struct bpf_prog_skeleton *)
+			((char *)s->progs + s->prog_skel_sz * i);
+		struct bpf_program *prog = *prog_skel->prog;
+		struct bpf_link **link = prog_skel->link;
 
 		if (!prog->autoload || !prog->autoattach)
 			continue;
@@ -13970,8 +13978,10 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s)
 		return 0;
 
 	for (i = 0; i < s->map_cnt; i++) {
-		struct bpf_map *map = *s->maps[i].map;
-		struct bpf_link **link = s->maps[i].link;
+		struct bpf_map_skeleton *map_skel = (struct bpf_map_skeleton *)
+			((char *)s->maps + s->map_skel_sz * i);
+		struct bpf_map *map = *map_skel->map;
+		struct bpf_link **link = map_skel->link;
 
 		if (!map->autocreate || !map->autoattach)
 			continue;
@@ -14000,7 +14010,9 @@ void bpf_object__detach_skeleton(struct bpf_object_skeleton *s)
 	int i;
 
 	for (i = 0; i < s->prog_cnt; i++) {
-		struct bpf_link **link = s->progs[i].link;
+		struct bpf_prog_skeleton *prog_skel = (struct bpf_prog_skeleton *)
+			((char *)s->progs + s->prog_skel_sz * i);
+		struct bpf_link **link = prog_skel->link;
 
 		bpf_link__destroy(*link);
 		*link = NULL;
@@ -14010,7 +14022,9 @@ void bpf_object__detach_skeleton(struct bpf_object_skeleton *s)
 		return;
 
 	for (i = 0; i < s->map_cnt; i++) {
-		struct bpf_link **link = s->maps[i].link;
+		struct bpf_map_skeleton *map_skel = (struct bpf_map_skeleton *)
+			((char *)s->maps + s->map_skel_sz * i);
+		struct bpf_link **link = map_skel->link;
 
 		if (link) {
 			bpf_link__destroy(*link);
-- 
2.45.2