[RFC PATCH bpf-next 1/1] libbpf: Auto-upgrade uprobes to multi-uprobes when supported

[Varun R Mallya <varunrmallya@gmail.com>]

This patch modifies libbpf to automatically "upgrade" standard
SEC("uprobe") and SEC("uretprobe") programs to use the multi-uprobe
infrastructure (BPF_TRACE_UPROBE_MULTI) at load time if the kernel
supports it, making them compatible with BPF tokens.

To maintain backward compatibility and handle rare cases where singular
uprobes are required, new SEC("uprobe.single") and SEC("uretprobe.single")
section types are introduced. These force libbpf to use the legacy
perf_event_open() attachment path.

Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
---
 tools/lib/bpf/libbpf.c | 42 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0c8bf0b5cce4..a32f221d3245 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8265,6 +8265,22 @@ static int bpf_object_init_progs(struct bpf_object *obj, const struct bpf_object
 		prog->type = prog->sec_def->prog_type;
 		prog->expected_attach_type = prog->sec_def->expected_attach_type;
 
+		/* set BPF_TRACE_UPROBE_MULTI if sec_name matches "u[ret]probe"
+		 * otherwise, leave alone.
+		 */
+		if (kernel_supports(obj, FEAT_UPROBE_MULTI_LINK)) {
+			char *probe_type = NULL;
+			int n;
+
+			n = sscanf(prog->sec_name, "%m[^/]", &probe_type);
+			if (n >= 1)
+				if (!strcmp(probe_type, "uprobe") ||
+				    !strcmp(probe_type, "uretprobe"))
+					prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
+
+			free(probe_type);
+		}
+
 		/* sec_def can have custom callback which should be called
 		 * after bpf_program is initialized to adjust its properties
 		 */
@@ -9822,9 +9838,11 @@ static const struct bpf_sec_def section_defs[] = {
 	SEC_DEF("kprobe+",		KPROBE,	0, SEC_NONE, attach_kprobe),
 	SEC_DEF("uprobe+",		KPROBE,	0, SEC_NONE, attach_uprobe),
 	SEC_DEF("uprobe.s+",		KPROBE,	0, SEC_SLEEPABLE, attach_uprobe),
+	SEC_DEF("uprobe.single+",	KPROBE,	0, SEC_NONE, attach_uprobe),
 	SEC_DEF("kretprobe+",		KPROBE, 0, SEC_NONE, attach_kprobe),
 	SEC_DEF("uretprobe+",		KPROBE, 0, SEC_NONE, attach_uprobe),
 	SEC_DEF("uretprobe.s+",		KPROBE, 0, SEC_SLEEPABLE, attach_uprobe),
+	SEC_DEF("uretprobe.single+",	KPROBE,	0, SEC_NONE, attach_uprobe),
 	SEC_DEF("kprobe.multi+",	KPROBE,	BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
 	SEC_DEF("kretprobe.multi+",	KPROBE,	BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
 	SEC_DEF("kprobe.session+",	KPROBE,	BPF_TRACE_KPROBE_SESSION, SEC_NONE, attach_kprobe_session),
@@ -12722,10 +12740,10 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
  */
 static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
 {
-	DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
 	char *probe_type = NULL, *binary_path = NULL, *func_name = NULL, *func_off;
 	int n, c, ret = -EINVAL;
 	long offset = 0;
+	bool is_retprobe;
 
 	*link = NULL;
 
@@ -12752,15 +12770,27 @@ static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf
 			else
 				offset = 0;
 		}
-		opts.retprobe = strcmp(probe_type, "uretprobe") == 0 ||
-				strcmp(probe_type, "uretprobe.s") == 0;
-		if (opts.retprobe && offset != 0) {
+		is_retprobe = strcmp(probe_type, "uretprobe") == 0 ||
+			      strcmp(probe_type, "uretprobe.s") == 0;
+		if (is_retprobe && offset != 0) {
 			pr_warn("prog '%s': uretprobes do not support offset specification\n",
 				prog->name);
 			break;
 		}
-		opts.func_name = func_name;
-		*link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
+		if (prog->expected_attach_type == BPF_TRACE_UPROBE_MULTI) {
+			DECLARE_LIBBPF_OPTS(bpf_uprobe_multi_opts, opts);
+
+			opts.retprobe = is_retprobe;
+			*link = bpf_program__attach_uprobe_multi(prog, -1, binary_path,
+								 func_name, &opts);
+		} else {
+			DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
+
+			opts.retprobe = is_retprobe;
+			opts.func_name = func_name;
+			*link = bpf_program__attach_uprobe_opts(prog, -1, binary_path,
+								offset, &opts);
+		}
 		ret = libbpf_get_error(*link);
 		break;
 	default:
-- 
2.52.0