[PATCH bpf-next v4] libbpf: Fix expected_attach_type set when kernel not support

[PATCH bpf-next v4] libbpf: Fix expected_attach_type set when kernel not support

[Tao Chen]

The commit "5902da6d8a52" set expected_attach_type again with
field of bpf_program after libbpf_prepare_prog_load, which makes
expected_attach_type = 0 no sense when kernel not support the
attach_type feature, so fix it.

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>
---
 tools/lib/bpf/libbpf.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

Change list:
- v3 -> v4:
    - fix some typo
- v2 -> v3:
    - update BPF_TRACE_UPROBE_MULTI both in prog and opts suggested by
      Andrri
- v1 -> v2:
    - restore the original initialization way suggested by Jiri

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 219facd0e66e..a78e24ff354b 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7352,8 +7352,14 @@ 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;
@@ -7443,6 +7449,7 @@ 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)) {
@@ -7474,9 +7481,6 @@ 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,
-- 
2.25.1

Re: [PATCH bpf-next v4] libbpf: Fix expected_attach_type set when kernel not support

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Wed, 25 Sep 2024 23:30:12 +0800 you wrote:
> The commit "5902da6d8a52" set expected_attach_type again with
> field of bpf_program after libbpf_prepare_prog_load, which makes
> expected_attach_type = 0 no sense when kernel not support the
> attach_type feature, so fix it.
> 
> 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>
> 
> [...]

Here is the summary with links:
  - [bpf-next,v4] libbpf: Fix expected_attach_type set when kernel not support
    https://git.kernel.org/bpf/bpf-next/c/c51003e23373

You are awesome, thank you!
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