From 673424c56127bb556e64095f41fd60c26f9083ec Mon Sep 17 00:00:00 2001
From: Vladimir Kobal <vlad@prokk.net>
Date: Thu, 30 Jul 2020 13:38:27 +0300
Subject: [PATCH] Add fallback to an old attaching method

---
 src/libbpf.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 90 insertions(+), 5 deletions(-)

diff --git a/src/libbpf.c b/src/libbpf.c
index 79c6607..5f792a0 100644
--- a/src/libbpf.c
+++ b/src/libbpf.c
@@ -7707,6 +7707,88 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
 	return pfd;
 }
 
+static int perf_event_open_old_kprobe(bool retprobe, const char *name)
+{
+#define DEBUG_FS "/sys/kernel/debug/tracing/"
+	struct perf_event_attr attr = {};
+	char errmsg[STRERR_BUFSIZE];
+	int kfd = -1, ret = -1, err;
+	char event_alias[256], buf[PATH_MAX];
+	const char *event_prefix = "";
+	bool event_was_written = false;
+
+	kfd = open(DEBUG_FS "kprobe_events", O_WRONLY | O_APPEND, 0);
+	if (kfd < 0) {
+		pr_warn("failed to open '%s%s': %s\n",
+			DEBUG_FS,
+			"kprobe_events",
+			libbpf_strerror_r(kfd, errmsg, sizeof(errmsg)));
+		return kfd;
+	}
+
+	char type = retprobe ? 'r' : 'p';
+	snprintf(event_alias, sizeof(event_alias), "%c_netdata_%s_%d", type, name, getpid());
+
+#ifdef __x86_64__
+	if (strncmp(name, "sys_", 4) == 0) {
+		snprintf(buf, sizeof(buf), "%c:__x64_%s __x64_%s",
+			type, event_alias, name);
+		ret = write(kfd, buf, strlen(buf));
+
+		if (ret >= 0) {
+			event_was_written = true;
+			event_prefix = "__x64_";
+		}
+	}
+#endif
+
+	if (!event_was_written) {
+		snprintf(buf, sizeof(buf), "%c:%s %s",
+			type, event_alias, name);
+		ret = write(kfd, buf, strlen(buf));
+		if (ret < 0) {
+			pr_warn("failed to create kprobe '%s': %s\n",
+				name,
+				libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
+			close(kfd);
+			return ret;
+		}
+	}
+
+	close(kfd);
+
+	snprintf(buf, sizeof(buf), DEBUG_FS "events/kprobes/%s%s/id",
+		event_prefix,
+		event_alias);
+
+	ret = parse_uint_from_file(buf, "%d\n");
+	if (ret < 0) {
+		pr_warn("failed to determine event id: %s\n",
+			libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
+		return ret;
+	}
+	attr.config = ret;
+
+	attr.size = sizeof(attr);
+	attr.type = PERF_TYPE_TRACEPOINT;
+	attr.config1 = ptr_to_u64(name); /* kprobe_func */
+	attr.config2 = 0;		 /* kprobe_addr */
+
+	/* pid filter is meaningful only for uprobes */
+	kfd = syscall(__NR_perf_event_open, &attr,
+		      -1 /* pid */,
+		      0 /* cpu */,
+		      -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
+	if (kfd < 0) {
+		err = -errno;
+		pr_warn("%s perf_event_open_old_kprobe() failed: %s\n",
+			"kprobe",
+			libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+		return err;
+	}
+	return kfd;
+}
+
 struct bpf_link *bpf_program__attach_kprobe(struct bpf_program *prog,
 					    bool retprobe,
 					    const char *func_name)
@@ -7718,11 +7800,14 @@ struct bpf_link *bpf_program__attach_kprobe(struct bpf_program *prog,
 	pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,
 				    0 /* offset */, -1 /* pid */);
 	if (pfd < 0) {
-		pr_warn("program '%s': failed to create %s '%s' perf event: %s\n",
-			bpf_program__title(prog, false),
-			retprobe ? "kretprobe" : "kprobe", func_name,
-			libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
-		return ERR_PTR(pfd);
+		pfd = perf_event_open_old_kprobe(retprobe, func_name);
+		if (pfd < 0) {
+			pr_warn("program '%s': failed to create %s '%s' perf event: %s\n",
+				bpf_program__title(prog, false),
+				retprobe ? "kretprobe" : "kprobe", func_name,
+				libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
+			return ERR_PTR(pfd);
+		}
 	}
 	link = bpf_program__attach_perf_event(prog, pfd);
 	if (IS_ERR(link)) {