[PATCHv5 bpf-next 16/28] libbpf: Add uprobe multi link detection

Jiri Olsa
2023-07-30T13:45:09Z

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 | 36 +++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf_internal.h | 2 ++
2 files changed, 38 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index d7b1a159d001..d1bb6eb7cde2 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4819,6 +4819,39 @@ static int probe_perf_link(void)
return link_fd < 0 && err == -EBADF;
}

+static int probe_uprobe_multi_link(void)
+{
+ LIBBPF_OPTS(bpf_prog_load_opts, load_opts,
+ .expected_attach_type = BPF_TRACE_UPROBE_MULTI,
+ );
+ LIBBPF_OPTS(bpf_link_create_opts, link_opts);
+ struct bpf_insn insns[] = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ };
+ int prog_fd, link_fd, err;
+ unsigned long offset = 0;
+
+ prog_fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL",
+ insns, ARRAY_SIZE(insns), &load_opts);
+ if (prog_fd < 0)
+ return -errno;
+
+ /* Creating uprobe in '/' binary should fail with -EBADF. */
+ link_opts.uprobe_multi.path = "/";
+ link_opts.uprobe_multi.offsets = &offset;
+ link_opts.uprobe_multi.cnt = 1;
+
+ link_fd = bpf_link_create(prog_fd, -1, BPF_TRACE_UPROBE_MULTI, &link_opts);
+ err = -errno; /* close() can clobber errno */
+
+ if (link_fd >= 0)
+ close(link_fd);
+ close(prog_fd);
+
+ return link_fd < 0 && err == -EBADF;
+}
+
static int probe_kern_bpf_cookie(void)
{
struct bpf_insn insns[] = {
@@ -4915,6 +4948,9 @@ static struct kern_feature_desc {
[FEAT_SYSCALL_WRAPPER] = {
"Kernel using syscall wrapper", probe_kern_syscall_wrapper,
},
+ [FEAT_UPROBE_MULTI_LINK] = {
+ "BPF multi-uprobe 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 ead551318fec..f0f08635adb0 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -355,6 +355,8 @@ enum kern_feature_id {
FEAT_BTF_ENUM64,
/* Kernel uses syscall wrapper (CONFIG_ARCH_HAS_SYSCALL_WRAPPER) */
FEAT_SYSCALL_WRAPPER,
+ /* BPF multi-uprobe link support */
+ FEAT_UPROBE_MULTI_LINK,
__FEAT_CNT,
};

--
2.41.0