[PATCHv2 bpf-next 13/24] libbpf: Add uprobe multi link detection

Jiri Olsa
2023-06-20T08:38:02Z

Adding uprobe-multi link detection. It will be used later in
bpf_program__attach_usdt function to check and use uprobe_multi
link over standard uprobe links.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/lib/bpf/libbpf.c | 29 +++++++++++++++++++++++++++++
tools/lib/bpf/libbpf_internal.h | 2 ++
2 files changed, 31 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e42080258ec7..3d570898459e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4815,6 +4815,32 @@ static int probe_perf_link(void)
return link_fd < 0 && err == -EBADF;
}

+static int probe_uprobe_multi_link(void)
+{
+ struct bpf_insn insns[] = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ };
+ int prog_fd, link_fd, err;
+
+ prog_fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL",
+ insns, ARRAY_SIZE(insns), NULL);
+ if (prog_fd < 0)
+ return -errno;
+
+ /* No need to specify attach function. If the link is not supported
+ * we will get -EOPNOTSUPP error before any other check is performed.
+ */
+ link_fd = bpf_link_create(prog_fd, -1, BPF_TRACE_UPROBE_MULTI, NULL);
+ err = -errno; /* close() can clobber errno */
+
+ if (link_fd >= 0)
+ close(link_fd);
+ close(prog_fd);
+
+ return link_fd < 0 && err != -EOPNOTSUPP;
+}
+
static int probe_kern_bpf_cookie(void)
{
struct bpf_insn insns[] = {
@@ -4911,6 +4937,9 @@ static struct kern_feature_desc {
[FEAT_SYSCALL_WRAPPER] = {
"Kernel using syscall wrapper", probe_kern_syscall_wrapper,
},
+ [FEAT_UPROBE_LINK] = {
+ "BPF uprobe multi link support", probe_uprobe_multi_link,
+ },
};

bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 22b0834e7fe1..a257eb81af25 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -354,6 +354,8 @@ enum kern_feature_id {
FEAT_BTF_ENUM64,
/* Kernel uses syscall wrapper (CONFIG_ARCH_HAS_SYSCALL_WRAPPER) */
FEAT_SYSCALL_WRAPPER,
+ /* BPF uprobe_multi link support */
+ FEAT_UPROBE_LINK,
__FEAT_CNT,
};

--
2.41.0