libbpf: Add support for uprobe multi session attach

Adding support to attach program in uprobe session mode
with bpf_program__attach_uprobe_multi function.

Adding session bool to bpf_uprobe_multi_opts struct that allows
to load and attach the bpf program via uprobe session.
the attachment to create uprobe multi session.

Also adding new program loader section that allows:
  SEC("uprobe.session/bpf_fentry_test*")

and loads/attaches uprobe program as uprobe session.

Adding sleepable hook (uprobe.session.s) as well.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241108134544.480660-6-jolsa@kernel.org

src/libbpf.h

@@ -577,10 +577,12 @@ struct bpf_uprobe_multi_opts {
 	size_t cnt;
 	/* create return uprobes */
 	bool retprobe;
+	/* create session kprobes */
+	bool session;
 	size_t :0;
 };
 
-#define bpf_uprobe_multi_opts__last_field retprobe
+#define bpf_uprobe_multi_opts__last_field session
 
 /**
  * @brief **bpf_program__attach_uprobe_multi()** attaches a BPF program