samples, bpf: Refactor kprobe tracing user progs with libbpf

Currently, the kprobe BPF program attachment method for bpf_load is
quite old. The implementation of bpf_load "directly" controls and
manages(create, delete) the kprobe events of DEBUGFS. On the other hand,
using using the libbpf automatically manages the kprobe event.
(under bpf_link interface)

By calling bpf_program__attach(_kprobe) in libbpf, the corresponding
kprobe is created and the BPF program will be attached to this kprobe.
To remove this, by simply invoking bpf_link__destroy will clean up the
event.

This commit refactors kprobe tracing programs (tracex{1~7}_user.c) with
libbpf using bpf_link interface and bpf_program__attach.

tracex2_kern.c, which tracks system calls (sys_*), has been modified to
append prefix depending on architecture.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200516040608.1377876-3-danieltimlee@gmail.com

samples/bpf/tracex6_user.c

@@ -4,7 +4,6 @@
 #include <assert.h>
 #include <fcntl.h>
 #include <linux/perf_event.h>
-#include <linux/bpf.h>
 #include <sched.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -15,12 +14,15 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
-#include "bpf_load.h"
 #include <bpf/bpf.h>
+#include <bpf/libbpf.h>
 #include "perf-sys.h"
 
 #define SAMPLE_PERIOD  0x7fffffffffffffffULL
 
+/* counters, values, values2 */
+static int map_fd[3];
+
 static void check_on_cpu(int cpu, struct perf_event_attr *attr)
 {
 	struct bpf_perf_event_value value2;
@@ -174,16 +176,51 @@ static void test_bpf_perf_event(void)
 int main(int argc, char **argv)
 {
 	struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
+	struct bpf_link *links[2];
+	struct bpf_program *prog;
+	struct bpf_object *obj;
 	char filename[256];
-
-	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+	int i = 0;
 
 	setrlimit(RLIMIT_MEMLOCK, &r);
-	if (load_bpf_file(filename)) {
-		printf("%s", bpf_log_buf);
-		return 1;
+
+	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+	obj = bpf_object__open_file(filename, NULL);
+	if (libbpf_get_error(obj)) {
+		fprintf(stderr, "ERROR: opening BPF object file failed\n");
+		return 0;
+	}
+
+	/* load BPF program */
+	if (bpf_object__load(obj)) {
+		fprintf(stderr, "ERROR: loading BPF object file failed\n");
+		goto cleanup;
+	}
+
+	map_fd[0] = bpf_object__find_map_fd_by_name(obj, "counters");
+	map_fd[1] = bpf_object__find_map_fd_by_name(obj, "values");
+	map_fd[2] = bpf_object__find_map_fd_by_name(obj, "values2");
+	if (map_fd[0] < 0 || map_fd[1] < 0 || map_fd[2] < 0) {
+		fprintf(stderr, "ERROR: finding a map in obj file failed\n");
+		goto cleanup;
+	}
+
+	bpf_object__for_each_program(prog, obj) {
+		links[i] = bpf_program__attach(prog);
+		if (libbpf_get_error(links[i])) {
+			fprintf(stderr, "ERROR: bpf_program__attach failed\n");
+			links[i] = NULL;
+			goto cleanup;
+		}
+		i++;
 	}
 
 	test_bpf_perf_event();
+
+cleanup:
+	for (i--; i >= 0; i--)
+		bpf_link__destroy(links[i]);
+
+	bpf_object__close(obj);
 	return 0;
 }