samples: bpf: Refactor kprobe tracing programs with libbpf

For the problem of increasing fragmentation of the bpf loader programs,
instead of using bpf_loader.o, which is used in samples/bpf, this
commit refactors the existing kprobe tracing programs with libbbpf
bpf loader.

    - For kprobe events pointing to system calls, the SYSCALL() macro in
    trace_common.h was used.
    - Adding a kprobe event and attaching a bpf program to it was done
    through bpf_program_attach().
    - Instead of using the existing BPF MAP definition, MAP definition
    has been refactored with the new BTF-defined MAP format.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200823085334.9413-3-danieltimlee@gmail.com

samples/bpf/trace_output_user.c

@@ -1,23 +1,10 @@
 // SPDX-License-Identifier: GPL-2.0-only
 #include <stdio.h>
-#include <unistd.h>
-#include <stdlib.h>
-#include <stdbool.h>
-#include <string.h>
 #include <fcntl.h>
 #include <poll.h>
-#include <linux/perf_event.h>
-#include <linux/bpf.h>
-#include <errno.h>
-#include <assert.h>
-#include <sys/syscall.h>
-#include <sys/ioctl.h>
-#include <sys/mman.h>
 #include <time.h>
 #include <signal.h>
 #include <bpf/libbpf.h>
-#include "bpf_load.h"
-#include "perf-sys.h"
 
 static __u64 time_get_ns(void)
 {
@@ -57,20 +44,48 @@ static void print_bpf_output(void *ctx, int cpu, void *data, __u32 size)
 int main(int argc, char **argv)
 {
 	struct perf_buffer_opts pb_opts = {};
+	struct bpf_link *link = NULL;
+	struct bpf_program *prog;
 	struct perf_buffer *pb;
+	struct bpf_object *obj;
+	int map_fd, ret = 0;
 	char filename[256];
 	FILE *f;
-	int ret;
 
 	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;
+	}
 
-	if (load_bpf_file(filename)) {
-		printf("%s", bpf_log_buf);
-		return 1;
+	/* load BPF program */
+	if (bpf_object__load(obj)) {
+		fprintf(stderr, "ERROR: loading BPF object file failed\n");
+		goto cleanup;
+	}
+
+	map_fd = bpf_object__find_map_fd_by_name(obj, "my_map");
+	if (map_fd < 0) {
+		fprintf(stderr, "ERROR: finding a map in obj file failed\n");
+		goto cleanup;
+	}
+
+	prog = bpf_object__find_program_by_name(obj, "bpf_prog1");
+	if (libbpf_get_error(prog)) {
+		fprintf(stderr, "ERROR: finding a prog in obj file failed\n");
+		goto cleanup;
+	}
+
+	link = bpf_program__attach(prog);
+	if (libbpf_get_error(link)) {
+		fprintf(stderr, "ERROR: bpf_program__attach failed\n");
+		link = NULL;
+		goto cleanup;
 	}
 
 	pb_opts.sample_cb = print_bpf_output;
-	pb = perf_buffer__new(map_fd[0], 8, &pb_opts);
+	pb = perf_buffer__new(map_fd, 8, &pb_opts);
 	ret = libbpf_get_error(pb);
 	if (ret) {
 		printf("failed to setup perf_buffer: %d\n", ret);
@@ -84,5 +99,9 @@ int main(int argc, char **argv)
 	while ((ret = perf_buffer__poll(pb, 1000)) >= 0 && cnt < MAX_CNT) {
 	}
 	kill(0, SIGINT);
+
+cleanup:
+	bpf_link__destroy(link);
+	bpf_object__close(obj);
 	return ret;
 }