Add fallback to an old attaching method

src/libbpf.c

@@ -620,6 +620,93 @@ bpf_object__init_prog_names(struct bpf_object *obj)
 	return 0;
 }
 
+static __u32 choose_specific_version0(int fd, __u32 current)
+{
+	char ver[256];
+	__u32 v_major, v_minor, v_patch;
+	ssize_t len = read(fd, ver, sizeof(ver));
+	if (len < 0) {
+		return 0;
+	}
+	ver[len] = '\0';
+
+	char *first = strchr(ver, ' ');
+	if (!first) {
+		return 0;
+	}
+
+	first++;
+	char *version = strchr(first, ' ');
+	if (!version) {
+		return 0;
+	}
+
+	version++;
+	if (sscanf(version, "%u.%u.%u", &v_major, &v_minor, &v_patch) != 3)
+		return current;
+
+	return KERNEL_VERSION(v_major, v_minor, v_patch);
+}
+
+static __u32 choose_kernel_version(__u32 current)
+{
+	FILE *fp_d = fopen("/etc/debian_version","r");
+	int fp_u = open("/proc/version_signature", O_RDONLY);
+	FILE *fp_rh = fopen("/etc/redhat-release","r");
+	char tmp[32];
+	int de = 0;
+	__u32 ret;
+
+	if (!fp_d && !fp_rh && fp_u == -1)
+		return current;
+
+	struct utsname u;
+	uname(&u);
+
+	if (fp_d) {
+		fclose(fp_d);
+		de = 1;
+	}
+
+	if (fp_rh) {
+		fclose(fp_rh);
+		de = 0;
+	}
+
+	if ( fp_u > 0 ) {
+		ret = choose_specific_version0(fp_u, current);
+		close(fp_u);
+		return (!ret)?current:ret;
+	}
+
+	__u32 v_kernel,v_major, v_minor, v_patch;
+	__u32 r_kernel,r_major, r_minor, r_patch;
+
+	if (sscanf(u.release, "%u.%u.%u-%u", &v_kernel, &v_major, &v_minor, &v_patch) != 4)
+		return current;
+
+	int length = snprintf(tmp, 31, "%u.%u", v_kernel, v_major);
+	tmp[length] = '\0';
+
+	char *parse = strstr(u.version, tmp);
+	if (!parse) {
+		return current;
+	}
+
+	char *space = strchr(parse, ' ');
+	if(space) {
+		length = (int)(space - parse);
+		strncpy(tmp, parse, (size_t)length);
+		tmp[length] = '\0';
+	}
+
+	if (sscanf(tmp, "%u.%u.%u-%u", &r_kernel, &r_major, &r_minor, &r_patch) != 4)
+		return current;
+
+	ret = (de)?KERNEL_VERSION(r_kernel, r_major, r_minor):KERNEL_VERSION(r_kernel, r_major, r_minor) + r_patch;
+	return (ret > current)?ret:current;
+}
+
 static __u32 get_kernel_version(void)
 {
 	__u32 major, minor, patch;
@@ -628,7 +715,11 @@ static __u32 get_kernel_version(void)
 	uname(&info);
 	if (sscanf(info.release, "%u.%u.%u", &major, &minor, &patch) != 3)
 		return 0;
-	return KERNEL_VERSION(major, minor, patch);
+
+	if (major < 5)
+		return choose_kernel_version(KERNEL_VERSION(major, minor, patch));
+	else
+		return KERNEL_VERSION(major, minor, patch);
 }
 
 static const struct btf_member *
@@ -3239,6 +3330,10 @@ int bpf_map__resize(struct bpf_map *map, __u32 max_entries)
 static int
 bpf_object__probe_loading(struct bpf_object *obj)
 {
+	// Don't probe loading for very old kernels. CentOS 7 can't load this probe.
+	if (obj->kern_version <= KERNEL_VERSION(3, 10, 0))
+		return 0;
+
 	struct bpf_load_program_attr attr;
 	char *cp, errmsg[STRERR_BUFSIZE];
 	struct bpf_insn insns[] = {
@@ -7612,6 +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)
@@ -7623,11 +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)) {