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

[Jiri Olsa <jolsa@kernel.org>]

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