libbpf: Fix expected_attach_type set handling in program load callback

Referenced commit broke the logic of resetting expected_attach_type to
zero for allowed program types if kernel doesn't yet support such field.
We do need to overwrite and preserve expected_attach_type for
multi-uprobe though, but that can be done explicitly in
libbpf_prepare_prog_load().

Fixes: 5902da6d8a52 ("libbpf: Add uprobe multi link support to bpf_program__attach_usdt")
Suggested-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Tao Chen <chen.dylane@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240925153012.212866-1-chen.dylane@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b8d72b5fbc7905cafac295c457368e0249fdcdd3..1ef221df0541a9ed151781ba15cd1e131d0a4847 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7353,8 +7353,14 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
                opts->prog_flags |= BPF_F_XDP_HAS_FRAGS;
 
        /* special check for usdt to use uprobe_multi link */
-       if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK))
+       if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK)) {
+               /* for BPF_TRACE_UPROBE_MULTI, user might want to query expected_attach_type
+                * in prog, and expected_attach_type we set in kernel is from opts, so we
+                * update both.
+                */
                prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
+               opts->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
+       }
 
        if ((def & SEC_ATTACH_BTF) && !prog->attach_btf_id) {
                int btf_obj_fd = 0, btf_type_id = 0, err;
@@ -7444,6 +7450,7 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
        load_attr.attach_btf_id = prog->attach_btf_id;
        load_attr.kern_version = kern_version;
        load_attr.prog_ifindex = prog->prog_ifindex;
+       load_attr.expected_attach_type = prog->expected_attach_type;
 
        /* specify func_info/line_info only if kernel supports them */
        if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
@@ -7475,9 +7482,6 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
                insns_cnt = prog->insns_cnt;
        }
 
-       /* allow prog_prepare_load_fn to change expected_attach_type */
-       load_attr.expected_attach_type = prog->expected_attach_type;
-
        if (obj->gen_loader) {
                bpf_gen__prog_load(obj->gen_loader, prog->type, prog->name,
                                   license, insns, insns_cnt, &load_attr,