libbpf: Add uprobe multi link support to bpf_program__attach_usdt

Adding support for usdt_manager_attach_usdt to use uprobe_multi
link to attach to usdt probes.

The uprobe_multi support is detected before the usdt program is
loaded and its expected_attach_type is set accordingly.

If uprobe_multi support is detected the usdt_manager_attach_usdt
gathers uprobes info and calls bpf_program__attach_uprobe to
create all needed uprobes.

If uprobe_multi support is not detected the old behaviour stays.

Also adding usdt.s program section for sleepable usdt probes.

Signed-off-by: Jiri Olsa <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/lib/bpf/libbpf.c

···
 	SEC_SLEEPABLE = 8,
 	/* BPF program support non-linear XDP buffer */
 	SEC_XDP_FRAGS = 16,
+	/* Setup proper attach type for usdt probes. */
+	SEC_USDT = 32,
 };
 
 struct bpf_sec_def {
···
 	if (prog->type == BPF_PROG_TYPE_XDP && (def & SEC_XDP_FRAGS))
 		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))
+		prog->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;
 		const char *attach_name;
···
 	if (!insns || !insns_cnt)
 		return -EINVAL;
 
-	load_attr.expected_attach_type = prog->expected_attach_type;
 	if (kernel_supports(obj, FEAT_PROG_NAME))
 		prog_name = prog->name;
 	load_attr.attach_prog_fd = prog->attach_prog_fd;
···
 		insns = prog->insns;
 		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,
···
 	SEC_DEF("uretprobe.multi.s+",	KPROBE,	BPF_TRACE_UPROBE_MULTI, SEC_SLEEPABLE, attach_uprobe_multi),
 	SEC_DEF("ksyscall+",		KPROBE,	0, SEC_NONE, attach_ksyscall),
 	SEC_DEF("kretsyscall+",		KPROBE, 0, SEC_NONE, attach_ksyscall),
-	SEC_DEF("usdt+",		KPROBE,	0, SEC_NONE, attach_usdt),
+	SEC_DEF("usdt+",		KPROBE,	0, SEC_USDT, attach_usdt),
+	SEC_DEF("usdt.s+",		KPROBE,	0, SEC_USDT | SEC_SLEEPABLE, attach_usdt),
 	SEC_DEF("tc/ingress",		SCHED_CLS, BPF_TCX_INGRESS, SEC_NONE), /* alias for tcx */
 	SEC_DEF("tc/egress",		SCHED_CLS, BPF_TCX_EGRESS, SEC_NONE),  /* alias for tcx */
 	SEC_DEF("tcx/ingress",		SCHED_CLS, BPF_TCX_INGRESS, SEC_NONE),

tools/lib/bpf/usdt.c

···
 
 	bool has_bpf_cookie;
 	bool has_sema_refcnt;
+	bool has_uprobe_multi;
 };
 
 struct usdt_manager *usdt_manager_new(struct bpf_object *obj)
···
 	 */
 	man->has_sema_refcnt = faccessat(AT_FDCWD, ref_ctr_sysfs_path, F_OK, AT_EACCESS) == 0;
 
+	/*
+	 * Detect kernel support for uprobe multi link to be used for attaching
+	 * usdt probes.
+	 */
+	man->has_uprobe_multi = kernel_supports(obj, FEAT_UPROBE_MULTI_LINK);
 	return man;
 }
 
···
 		long abs_ip;
 		struct bpf_link *link;
 	} *uprobes;
+
+	struct bpf_link *multi_link;
 };
 
 static int bpf_link_usdt_detach(struct bpf_link *link)
···
 	struct usdt_manager *man = usdt_link->usdt_man;
 	int i;
 
+	bpf_link__destroy(usdt_link->multi_link);
+
+	/* When having multi_link, uprobe_cnt is 0 */
 	for (i = 0; i < usdt_link->uprobe_cnt; i++) {
 		/* detach underlying uprobe link */
 		bpf_link__destroy(usdt_link->uprobes[i].link);
···
 					  const char *usdt_provider, const char *usdt_name,
 					  __u64 usdt_cookie)
 {
+	unsigned long *offsets = NULL, *ref_ctr_offsets = NULL;
 	int i, err, spec_map_fd, ip_map_fd;
 	LIBBPF_OPTS(bpf_uprobe_opts, opts);
 	struct hashmap *specs_hash = NULL;
 	struct bpf_link_usdt *link = NULL;
 	struct usdt_target *targets = NULL;
+	__u64 *cookies = NULL;
 	struct elf_fd elf_fd;
 	size_t target_cnt;
 
···
 	link->link.detach = &bpf_link_usdt_detach;
 	link->link.dealloc = &bpf_link_usdt_dealloc;
 
-	link->uprobes = calloc(target_cnt, sizeof(*link->uprobes));
-	if (!link->uprobes) {
-		err = -ENOMEM;
-		goto err_out;
+	if (man->has_uprobe_multi) {
+		offsets = calloc(target_cnt, sizeof(*offsets));
+		cookies = calloc(target_cnt, sizeof(*cookies));
+		ref_ctr_offsets = calloc(target_cnt, sizeof(*ref_ctr_offsets));
+
+		if (!offsets || !ref_ctr_offsets || !cookies) {
+			err = -ENOMEM;
+			goto err_out;
+		}
+	} else {
+		link->uprobes = calloc(target_cnt, sizeof(*link->uprobes));
+		if (!link->uprobes) {
+			err = -ENOMEM;
+			goto err_out;
+		}
 	}
 
 	for (i = 0; i < target_cnt; i++) {
···
 			goto err_out;
 		}
 
-		opts.ref_ctr_offset = target->sema_off;
-		opts.bpf_cookie = man->has_bpf_cookie ? spec_id : 0;
-		uprobe_link = bpf_program__attach_uprobe_opts(prog, pid, path,
-							      target->rel_ip, &opts);
-		err = libbpf_get_error(uprobe_link);
-		if (err) {
-			pr_warn("usdt: failed to attach uprobe #%d for '%s:%s' in '%s': %d\n",
-				i, usdt_provider, usdt_name, path, err);
+		if (man->has_uprobe_multi) {
+			offsets[i] = target->rel_ip;
+			ref_ctr_offsets[i] = target->sema_off;
+			cookies[i] = spec_id;
+		} else {
+			opts.ref_ctr_offset = target->sema_off;
+			opts.bpf_cookie = man->has_bpf_cookie ? spec_id : 0;
+			uprobe_link = bpf_program__attach_uprobe_opts(prog, pid, path,
+								      target->rel_ip, &opts);
+			err = libbpf_get_error(uprobe_link);
+			if (err) {
+				pr_warn("usdt: failed to attach uprobe #%d for '%s:%s' in '%s': %d\n",
+					i, usdt_provider, usdt_name, path, err);
+				goto err_out;
+			}
+
+			link->uprobes[i].link = uprobe_link;
+			link->uprobes[i].abs_ip = target->abs_ip;
+			link->uprobe_cnt++;
+		}
+	}
+
+	if (man->has_uprobe_multi) {
+		LIBBPF_OPTS(bpf_uprobe_multi_opts, opts_multi,
+			.ref_ctr_offsets = ref_ctr_offsets,
+			.offsets = offsets,
+			.cookies = cookies,
+			.cnt = target_cnt,
+		);
+
+		link->multi_link = bpf_program__attach_uprobe_multi(prog, pid, path,
+								    NULL, &opts_multi);
+		if (!link->multi_link) {
+			err = -errno;
+			pr_warn("usdt: failed to attach uprobe multi for '%s:%s' in '%s': %d\n",
+				usdt_provider, usdt_name, path, err);
 			goto err_out;
 		}
 
-		link->uprobes[i].link = uprobe_link;
-		link->uprobes[i].abs_ip = target->abs_ip;
-		link->uprobe_cnt++;
+		free(offsets);
+		free(ref_ctr_offsets);
+		free(cookies);
 	}
 
 	free(targets);
···
 	return &link->link;
 
 err_out:
+	free(offsets);
+	free(ref_ctr_offsets);
+	free(cookies);
+
 	if (link)
 		bpf_link__destroy(&link->link);
 	free(targets);