[PATCHv2 bpf-next 14/24] libbpf: Add uprobe multi link support to bpf_program__attach_usdt

Jiri Olsa
2023-06-20T08:38:11Z

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_opts to
create all needed uprobes.

If uprobe_multi support is not detected the old behaviour stays.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/lib/bpf/libbpf.c | 12 ++++-
tools/lib/bpf/usdt.c | 120 ++++++++++++++++++++++++++++++-----------
2 files changed, 99 insertions(+), 33 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 3d570898459e..9c7a67c5cbe8 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -363,6 +363,8 @@ 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 {
@@ -6799,6 +6801,10 @@ 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(NULL, FEAT_UPROBE_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;
@@ -6867,7 +6873,6 @@ 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;
@@ -6903,6 +6908,9 @@ 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,
@@ -8703,7 +8711,7 @@ 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("tc", SCHED_CLS, 0, SEC_NONE),
SEC_DEF("classifier", SCHED_CLS, 0, SEC_NONE),
SEC_DEF("action", SCHED_ACT, 0, SEC_NONE),
diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
index f1a141555f08..33f0a2b4cc1c 100644
--- a/tools/lib/bpf/usdt.c
+++ b/tools/lib/bpf/usdt.c
@@ -808,6 +808,16 @@ struct bpf_link_usdt {
long abs_ip;
struct bpf_link *link;
} *uprobes;
+
+ bool has_uprobe_multi;
+
+ struct {
+ char *path;
+ unsigned long *offsets;
+ unsigned long *ref_ctr_offsets;
+ __u64 *cookies;
+ struct bpf_link *link;
+ } uprobe_multi;
};

static int bpf_link_usdt_detach(struct bpf_link *link)
@@ -816,19 +826,23 @@ static int bpf_link_usdt_detach(struct bpf_link *link)
struct usdt_manager *man = usdt_link->usdt_man;
int i;

- for (i = 0; i < usdt_link->uprobe_cnt; i++) {
- /* detach underlying uprobe link */
- bpf_link__destroy(usdt_link->uprobes[i].link);
- /* there is no need to update specs map because it will be
- * unconditionally overwritten on subsequent USDT attaches,
- * but if BPF cookies are not used we need to remove entry
- * from ip_to_spec_id map, otherwise we'll run into false
- * conflicting IP errors
- */
- if (!man->has_bpf_cookie) {
- /* not much we can do about errors here */
- (void)bpf_map_delete_elem(bpf_map__fd(man->ip_to_spec_id_map),
- &usdt_link->uprobes[i].abs_ip);
+ if (usdt_link->has_uprobe_multi) {
+ bpf_link__destroy(usdt_link->uprobe_multi.link);
+ } else {
+ for (i = 0; i < usdt_link->uprobe_cnt; i++) {
+ /* detach underlying uprobe link */
+ bpf_link__destroy(usdt_link->uprobes[i].link);
+ /* there is no need to update specs map because it will be
+ * unconditionally overwritten on subsequent USDT attaches,
+ * but if BPF cookies are not used we need to remove entry
+ * from ip_to_spec_id map, otherwise we'll run into false
+ * conflicting IP errors
+ */
+ if (!man->has_bpf_cookie) {
+ /* not much we can do about errors here */
+ (void)bpf_map_delete_elem(bpf_map__fd(man->ip_to_spec_id_map),
+ &usdt_link->uprobes[i].abs_ip);
+ }
}
}

@@ -868,9 +882,15 @@ static void bpf_link_usdt_dealloc(struct bpf_link *link)
{
struct bpf_link_usdt *usdt_link = container_of(link, struct bpf_link_usdt, link);

- free(usdt_link->spec_ids);
- free(usdt_link->uprobes);
- free(usdt_link);
+ if (usdt_link->has_uprobe_multi) {
+ free(usdt_link->uprobe_multi.offsets);
+ free(usdt_link->uprobe_multi.ref_ctr_offsets);
+ free(usdt_link->uprobe_multi.cookies);
+ } else {
+ free(usdt_link->spec_ids);
+ free(usdt_link->uprobes);
+ free(usdt_link);
+ }
}

static size_t specs_hash_fn(long key, void *ctx)
@@ -943,11 +963,13 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct
const char *usdt_provider, const char *usdt_name,
__u64 usdt_cookie)
{
+ LIBBPF_OPTS(bpf_uprobe_multi_opts, opts_multi);
int i, fd, 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;
+ struct bpf_link *uprobe_link;
size_t target_cnt;
Elf *elf;

@@ -1003,16 +1025,29 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct
link->usdt_man = man;
link->link.detach = &bpf_link_usdt_detach;
link->link.dealloc = &bpf_link_usdt_dealloc;
+ link->has_uprobe_multi = bpf_program__expected_attach_type(prog) == BPF_TRACE_UPROBE_MULTI;

- link->uprobes = calloc(target_cnt, sizeof(*link->uprobes));
- if (!link->uprobes) {
- err = -ENOMEM;
- goto err_out;
+ if (link->has_uprobe_multi) {
+ link->uprobe_multi.offsets = calloc(target_cnt, sizeof(*link->uprobe_multi.offsets));
+ link->uprobe_multi.ref_ctr_offsets = calloc(target_cnt, sizeof(*link->uprobe_multi.ref_ctr_offsets));
+ link->uprobe_multi.cookies = calloc(target_cnt, sizeof(*link->uprobe_multi.cookies));
+
+ if (!link->uprobe_multi.offsets ||
+ !link->uprobe_multi.ref_ctr_offsets ||
+ !link->uprobe_multi.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++) {
struct usdt_target *target = &targets[i];
- struct bpf_link *uprobe_link;
bool is_new;
int spec_id;

@@ -1048,20 +1083,43 @@ 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);
+ if (link->has_uprobe_multi) {
+ link->uprobe_multi.offsets[i] = target->rel_ip;
+ link->uprobe_multi.ref_ctr_offsets[i] = target->sema_off;
+ link->uprobe_multi.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 (link->has_uprobe_multi) {
+ opts_multi.cnt = target_cnt;
+ opts_multi.path = path;
+ opts_multi.offsets = link->uprobe_multi.offsets;
+ opts_multi.ref_ctr_offsets = link->uprobe_multi.ref_ctr_offsets;
+ opts_multi.cookies = link->uprobe_multi.cookies;
+
+ uprobe_link = bpf_program__attach_uprobe_multi_opts(prog, pid, NULL, NULL, &opts_multi);
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);
+ 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++;
+ link->uprobe_multi.link = uprobe_link;
}

free(targets);
--
2.41.0