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/tracex2_user.c

@@ -3,17 +3,19 @@
 #include <unistd.h>
 #include <stdlib.h>
 #include <signal.h>
-#include <linux/bpf.h>
 #include <string.h>
 #include <sys/resource.h>
 
 #include <bpf/bpf.h>
-#include "bpf_load.h"
+#include <bpf/libbpf.h>
 #include "bpf_util.h"
 
 #define MAX_INDEX	64
 #define MAX_STARS	38
 
+/* my_map, my_hist_map */
+static int map_fd[2];
+
 static void stars(char *str, long val, long max, int width)
 {
 	int i;
@@ -115,18 +117,39 @@ static void int_exit(int sig)
 int main(int ac, char **argv)
 {
 	struct rlimit r = {1024*1024, RLIM_INFINITY};
-	char filename[256];
 	long key, next_key, value;
+	struct bpf_link *links[2];
+	struct bpf_program *prog;
+	struct bpf_object *obj;
+	char filename[256];
+	int i, j = 0;
 	FILE *f;
-	int i;
-
-	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
 
 	if (setrlimit(RLIMIT_MEMLOCK, &r)) {
 		perror("setrlimit(RLIMIT_MEMLOCK)");
 		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, "my_map");
+	map_fd[1] = bpf_object__find_map_fd_by_name(obj, "my_hist_map");
+	if (map_fd[0] < 0 || map_fd[1] < 0) {
+		fprintf(stderr, "ERROR: finding a map in obj file failed\n");
+		goto cleanup;
+	}
+
 	signal(SIGINT, int_exit);
 	signal(SIGTERM, int_exit);
 
@@ -138,9 +161,14 @@ int main(int ac, char **argv)
 	f = popen("dd if=/dev/zero of=/dev/null count=5000000", "r");
 	(void) f;
 
-	if (load_bpf_file(filename)) {
-		printf("%s", bpf_log_buf);
-		return 1;
+	bpf_object__for_each_program(prog, obj) {
+		links[j] = bpf_program__attach(prog);
+		if (libbpf_get_error(links[j])) {
+			fprintf(stderr, "ERROR: bpf_program__attach failed\n");
+			links[j] = NULL;
+			goto cleanup;
+		}
+		j++;
 	}
 
 	for (i = 0; i < 5; i++) {
@@ -156,5 +184,10 @@ int main(int ac, char **argv)
 	}
 	print_hist(map_fd[1]);
 
+cleanup:
+	for (j--; j >= 0; j--)
+		bpf_link__destroy(links[j]);
+
+	bpf_object__close(obj);
 	return 0;
 }