[bpf-next,v2,2/2] libbpf: add getters for BTF.ext func and line info

Commit Message

Mykyta Yatsenko March 31, 2025, 2:48 p.m. UTC

From: Mykyta Yatsenko <[e-mail]>

Introducing new libbpf API getters for BTF.ext func and line info,
namely:
  bpf_program__func_info
  bpf_program__func_info_cnt
  bpf_program__line_info
  bpf_program__line_info_cnt

This change enables scenarios, when user needs to load bpf_program
directly using `bpf_prog_load`, instead of higher-level
`bpf_object__load`. Line and func info are required for checking BTF
info in verifier; verification may fail without these fields if, for
example, program calls `bpf_obj_new`.

Signed-off-by: Mykyta Yatsenko <[e-mail]>
---
 tools/lib/bpf/libbpf.c   | 20 ++++++++++++++++++++
 tools/lib/bpf/libbpf.h   |  6 ++++++
 tools/lib/bpf/libbpf.map |  4 ++++
 3 files changed, 30 insertions(+)

Comments

Andrii Nakryiko March 31, 2025, 8:09 p.m. UTC | #1

On Mon, Mar 31, 2025 at 7:48 AM Mykyta Yatsenko
<[e-mail]> wrote:
>
> From: Mykyta Yatsenko <[e-mail]>
>
> Introducing new libbpf API getters for BTF.ext func and line info,
> namely:
>   bpf_program__func_info
>   bpf_program__func_info_cnt
>   bpf_program__line_info
>   bpf_program__line_info_cnt
>
> This change enables scenarios, when user needs to load bpf_program
> directly using `bpf_prog_load`, instead of higher-level
> `bpf_object__load`. Line and func info are required for checking BTF
> info in verifier; verification may fail without these fields if, for
> example, program calls `bpf_obj_new`.
>
> Signed-off-by: Mykyta Yatsenko <[e-mail]>
> ---
>  tools/lib/bpf/libbpf.c   | 20 ++++++++++++++++++++
>  tools/lib/bpf/libbpf.h   |  6 ++++++
>  tools/lib/bpf/libbpf.map |  4 ++++
>  3 files changed, 30 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6b85060f07b3..86f6aff76ef2 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9455,6 +9455,26 @@ int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log
>         return 0;
>  }
>
> +struct bpf_func_info_min *bpf_program__func_info(const struct bpf_program *prog)
> +{
> +       return prog->func_info;
> +}
> +
> +__u32 bpf_program__func_info_cnt(const struct bpf_program *prog)
> +{
> +       return prog->func_info_cnt;
> +}
> +
> +struct bpf_line_info_min *bpf_program__line_info(const struct bpf_program *prog)
> +{
> +       return prog->line_info;
> +}
> +
> +__u32 bpf_program__line_info_cnt(const struct bpf_program *prog)
> +{
> +       return prog->line_info_cnt;
> +}
> +

I didn't realize that we already have bpf_line_info/bpf_func_info as
part of Linux UAPI. If that's the case, let's keep _min variants where
they are (internal), and use public types. No need for patch #1.

Let's just add:

if (prog->func_info_rec_size != sizeof(struct bpf_func_info_min))
    return libbpf_err_ptr(-EOPNOTSUPP);

everywhere so we don't accidentally return invalid data, ok?


Also, let's do a bit of testing here. I think it would be nice to have
a selftests that loads some simple BPF program (perhaps with
non-inlined subprog to test func/line info with subprogs) first
through normal skeleton load approach. Capture its func_info/line_info
from kernel. Then use these new APIs you are adding and do
bpf_prog_load(), and then compare that we got identical
func_info/line_info (as reported by the kernel). Can you please add
that?

>  #define SEC_DEF(sec_pfx, ptype, atype, flags, ...) {                       \
>         .sec = (char *)sec_pfx,                                             \
>         .prog_type = BPF_PROG_TYPE_##ptype,                                 \
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index e0605403f977..a6ec87fb0fb9 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -940,6 +940,12 @@ LIBBPF_API int bpf_program__set_log_level(struct bpf_program *prog, __u32 log_le
>  LIBBPF_API const char *bpf_program__log_buf(const struct bpf_program *prog, size_t *log_size);
>  LIBBPF_API int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log_size);
>
> +LIBBPF_API struct bpf_func_info_min *bpf_program__func_info(const struct bpf_program *prog);
> +LIBBPF_API __u32 bpf_program__func_info_cnt(const struct bpf_program *prog);
> +
> +LIBBPF_API struct bpf_line_info_min *bpf_program__line_info(const struct bpf_program *prog);
> +LIBBPF_API __u32 bpf_program__line_info_cnt(const struct bpf_program *prog);
> +
>  /**
>   * @brief **bpf_program__set_attach_target()** sets BTF-based attach target
>   * for supported BPF program types:
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index d8b71f22f197..1205f9a4fe04 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -437,6 +437,10 @@ LIBBPF_1.6.0 {
>                 bpf_linker__add_fd;
>                 bpf_linker__new_fd;
>                 bpf_object__prepare;
> +               bpf_program__func_info;
> +               bpf_program__func_info_cnt;
> +               bpf_program__line_info;
> +               bpf_program__line_info_cnt;
>                 btf__add_decl_attr;
>                 btf__add_type_attr;
>  } LIBBPF_1.5.0;
> --
> 2.49.0
>

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 6b85060f07b3..86f6aff76ef2 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9455,6 +9455,26 @@  int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log
 	return 0;
 }
 
+struct bpf_func_info_min *bpf_program__func_info(const struct bpf_program *prog)
+{
+	return prog->func_info;
+}
+
+__u32 bpf_program__func_info_cnt(const struct bpf_program *prog)
+{
+	return prog->func_info_cnt;
+}
+
+struct bpf_line_info_min *bpf_program__line_info(const struct bpf_program *prog)
+{
+	return prog->line_info;
+}
+
+__u32 bpf_program__line_info_cnt(const struct bpf_program *prog)
+{
+	return prog->line_info_cnt;
+}
+
 #define SEC_DEF(sec_pfx, ptype, atype, flags, ...) {			    \
 	.sec = (char *)sec_pfx,						    \
 	.prog_type = BPF_PROG_TYPE_##ptype,				    \
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index e0605403f977..a6ec87fb0fb9 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -940,6 +940,12 @@  LIBBPF_API int bpf_program__set_log_level(struct bpf_program *prog, __u32 log_le
 LIBBPF_API const char *bpf_program__log_buf(const struct bpf_program *prog, size_t *log_size);
 LIBBPF_API int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log_size);
 
+LIBBPF_API struct bpf_func_info_min *bpf_program__func_info(const struct bpf_program *prog);
+LIBBPF_API __u32 bpf_program__func_info_cnt(const struct bpf_program *prog);
+
+LIBBPF_API struct bpf_line_info_min *bpf_program__line_info(const struct bpf_program *prog);
+LIBBPF_API __u32 bpf_program__line_info_cnt(const struct bpf_program *prog);
+
 /**
  * @brief **bpf_program__set_attach_target()** sets BTF-based attach target
  * for supported BPF program types:
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index d8b71f22f197..1205f9a4fe04 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -437,6 +437,10 @@  LIBBPF_1.6.0 {
 		bpf_linker__add_fd;
 		bpf_linker__new_fd;
 		bpf_object__prepare;
+		bpf_program__func_info;
+		bpf_program__func_info_cnt;
+		bpf_program__line_info;
+		bpf_program__line_info_cnt;
 		btf__add_decl_attr;
 		btf__add_type_attr;
 } LIBBPF_1.5.0;