[PATCHv5 bpf-next 17/28] libbpf: Add uprobe multi link support to bpf_program__attach_usdt

Jiri Olsa
2023-07-30T13:45:19Z

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 <jolsa@kernel.org>
---
tools/lib/bpf/libbpf.c | 13 ++++++-
tools/lib/bpf/usdt.c | 86 ++++++++++++++++++++++++++++++++++--------
2 files changed, 82 insertions(+), 17 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index d1bb6eb7cde2..e0463e050192 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -367,6 +367,8 @@ enum sec_def_flags {
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 {
@@ -6818,6 +6820,10 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
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;
@@ -6886,7 +6892,6 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
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;
@@ -6922,6 +6927,9 @@ 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,
@@ -8741,7 +8749,8 @@ static const struct bpf_sec_def section_defs[] = {
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),
diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
index 8322337ab65b..93794f01bb67 100644
--- a/tools/lib/bpf/usdt.c
+++ b/tools/lib/bpf/usdt.c
@@ -250,6 +250,7 @@ struct usdt_manager {

bool has_bpf_cookie;
bool has_sema_refcnt;
+ bool has_uprobe_multi;
};

struct usdt_manager *usdt_manager_new(struct bpf_object *obj)
@@ -284,6 +285,11 @@ 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;
}

@@ -808,6 +814,8 @@ struct bpf_link_usdt {
long abs_ip;
struct bpf_link *link;
} *uprobes;
+
+ struct bpf_link *multi_link;
};

static int bpf_link_usdt_detach(struct bpf_link *link)
@@ -816,6 +824,9 @@ 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);
@@ -946,11 +957,13 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct
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;

@@ -997,10 +1010,21 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct
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++) {
@@ -1041,20 +1065,48 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct
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);
@@ -1063,6 +1115,10 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct
return &link->link;

err_out:
+ free(offsets);
+ free(ref_ctr_offsets);
+ free(cookies);
+
if (link)
bpf_link__destroy(&link->link);
free(targets);
--
2.41.0