Re: [PATCH 15/19] libbpf: Add support to link multi func tracing program

On Sun, Jun 06, 2021 at 10:49:16PM -0700, Yonghong Song wrote:

On 6/5/21 4:10 AM, Jiri Olsa wrote:

quoted

Adding support to link multi func tracing program
through link_create interface.

Adding special types for multi func programs:

   fentry.multi
   fexit.multi

so you can define multi func programs like:

   SEC("fentry.multi/bpf_fentry_test*")
   int BPF_PROG(test1, unsigned long ip, __u64 a, __u64 b, __u64 c, __u64 d, __u64 e, __u64 f)

that defines test1 to be attached to bpf_fentry_test* functions,
and able to attach ip and 6 arguments.

If functions are not specified the program needs to be attached
manually.

Adding new btf id related fields to bpf_link_create_opts and
bpf_link_create to use them.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
  tools/lib/bpf/bpf.c    | 11 ++++++-
  tools/lib/bpf/bpf.h    |  4 ++-
  tools/lib/bpf/libbpf.c | 72 ++++++++++++++++++++++++++++++++++++++++++
  3 files changed, 85 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 86dcac44f32f..da892737b522 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c

@@ -674,7 +674,8 @@ int bpf_link_create(int prog_fd, int target_fd,
  		    enum bpf_attach_type attach_type,
  		    const struct bpf_link_create_opts *opts)
  {
-	__u32 target_btf_id, iter_info_len;
+	__u32 target_btf_id, iter_info_len, multi_btf_ids_cnt;
+	__s32 *multi_btf_ids;
  	union bpf_attr attr;
  	int fd;

[...]

quoted

@@ -9584,6 +9597,9 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog, int *btf_obj_fd,
  	if (!name)
  		return -EINVAL;
+	if (prog->prog_flags & BPF_F_MULTI_FUNC)
+		return 0;
+
  	for (i = 0; i < ARRAY_SIZE(section_defs); i++) {
  		if (!section_defs[i].is_attach_btf)
  			continue;

@@ -10537,6 +10553,62 @@ static struct bpf_link *bpf_program__attach_btf_id(struct bpf_program *prog)
  	return (struct bpf_link *)link;
  }
+static struct bpf_link *bpf_program__attach_multi(struct bpf_program *prog)
+{
+	char *pattern = prog->sec_name + prog->sec_def->len;
+	DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts);
+	enum bpf_attach_type attach_type;
+	int prog_fd, link_fd, cnt, err;
+	struct bpf_link *link = NULL;
+	__s32 *ids = NULL;
+
+	prog_fd = bpf_program__fd(prog);
+	if (prog_fd < 0) {
+		pr_warn("prog '%s': can't attach before loaded\n", prog->name);
+		return ERR_PTR(-EINVAL);
+	}
+
+	err = bpf_object__load_vmlinux_btf(prog->obj, true);
+	if (err)
+		return ERR_PTR(err);
+
+	cnt = btf__find_by_pattern_kind(prog->obj->btf_vmlinux, pattern,
+					BTF_KIND_FUNC, &ids);
+	if (cnt <= 0)
+		return ERR_PTR(-EINVAL);

In kernel, looks like we support cnt = 0, here we error out.
Should we also error out in the kernel if cnt == 0?

hum, I'm not what you mean.. what kernel code are you referring to?

thanks,
jirka