selftests/bpf: Add BPF program dump in veristat

Add the ability to dump BPF program instructions directly from veristat.
Previously, inspecting a program required separate bpftool invocations:
one to load and another to dump it, which meant running multiple
commands.
During active development, it's common for developers to use veristat
for testing verification. Integrating instruction dumping into veristat
reduces the need to switch tools and simplifies the workflow.
By making this information more readily accessible, this change aims
to streamline the BPF development cycle and improve usability for
developers.
This implementation leverages bpftool, by running it directly via popen
to avoid any code duplication and keep veristat simple.

Signed-off-by: Mykyta Yatsenko <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/veristat.c

···
 	bool applied;
 };
 
+enum dump_mode {
+	DUMP_NONE = 0,
+	DUMP_XLATED = 1,
+	DUMP_JITED = 2,
+};
+
 static struct env {
 	char **filenames;
 	int filename_cnt;
···
 	char orig_cgroup[PATH_MAX];
 	char stat_cgroup[PATH_MAX];
 	int memory_peak_fd;
+	__u32 dump_mode;
 } env;
 
 static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
···
 enum {
 	OPT_LOG_FIXED = 1000,
 	OPT_LOG_SIZE = 1001,
+	OPT_DUMP = 1002,
 };
 
 static const struct argp_option opts[] = {
···
 	  "Force BPF verifier failure on register invariant violation (BPF_F_TEST_REG_INVARIANTS program flag)" },
 	{ "top-src-lines", 'S', "N", 0, "Emit N most frequent source code lines" },
 	{ "set-global-vars", 'G', "GLOBAL", 0, "Set global variables provided in the expression, for example \"var1 = 1\"" },
+	{ "dump", OPT_DUMP, "DUMP_MODE", OPTION_ARG_OPTIONAL, "Print BPF program dump (xlated, jited)" },
 	{},
 };
 
···
 		if (err) {
 			fprintf(stderr, "Failed to collect BPF object files: %d\n", err);
 			return err;
+		}
+		break;
+	case OPT_DUMP:
+		if (!arg || strcasecmp(arg, "xlated") == 0) {
+			env.dump_mode |= DUMP_XLATED;
+		} else if (strcasecmp(arg, "jited") == 0) {
+			env.dump_mode |= DUMP_JITED;
+		} else {
+			fprintf(stderr, "Unrecognized dump mode '%s'\n", arg);
+			return -EINVAL;
 		}
 		break;
 	default:
···
 	return 0;
 }
 
+static void dump(__u32 prog_id, enum dump_mode mode, const char *file_name, const char *prog_name)
+{
+	char command[64], buf[4096];
+	FILE *fp;
+	int status;
+
+	status = system("command -v bpftool > /dev/null 2>&1");
+	if (status != 0) {
+		fprintf(stderr, "bpftool is not available, can't print program dump\n");
+		return;
+	}
+	snprintf(command, sizeof(command), "bpftool prog dump %s id %u",
+		 mode == DUMP_JITED ? "jited" : "xlated", prog_id);
+	fp = popen(command, "r");
+	if (!fp) {
+		fprintf(stderr, "bpftool failed with error: %d\n", errno);
+		return;
+	}
+
+	printf("DUMP (%s) %s/%s:\n", mode == DUMP_JITED ? "JITED" : "XLATED", file_name, prog_name);
+	while (fgets(buf, sizeof(buf), fp))
+		fputs(buf, stdout);
+	fprintf(stdout, "\n");
+
+	if (ferror(fp))
+		fprintf(stderr, "Failed to dump BPF prog with error: %d\n", errno);
+
+	pclose(fp);
+}
+
 static int process_prog(const char *filename, struct bpf_object *obj, struct bpf_program *prog)
 {
 	const char *base_filename = basename(strdupa(filename));
···
 
 	memset(&info, 0, info_len);
 	fd = bpf_program__fd(prog);
-	if (fd > 0 && bpf_prog_get_info_by_fd(fd, &info, &info_len) == 0)
+	if (fd > 0 && bpf_prog_get_info_by_fd(fd, &info, &info_len) == 0) {
 		stats->stats[JITED_SIZE] = info.jited_prog_len;
+		if (env.dump_mode & DUMP_JITED)
+			dump(info.id, DUMP_JITED, base_filename, prog_name);
+		if (env.dump_mode & DUMP_XLATED)
+			dump(info.id, DUMP_XLATED, base_filename, prog_name);
+	}
 
 	parse_verif_log(buf, buf_sz, stats);