bpftool: Enable libbpf's strict mode by default

Otherwise, attaching with bpftool doesn't work with strict section names.

Also:

  - Add --legacy option to switch back to pre-1.0 behavior
  - Print a warning when program fails to load in strict mode to
    point to --legacy flag
  - By default, don't append / to the section name; in strict
    mode it's relevant only for a small subset of prog types

+ bpftool --legacy prog loadall tools/testing/selftests/bpf/test_cgroup_link.o /sys/fs/bpf/kprobe type kprobe
libbpf: failed to pin program: File exists
Error: failed to pin all programs
+ bpftool prog loadall tools/testing/selftests/bpf/test_cgroup_link.o /sys/fs/bpf/kprobe type kprobe

v1 -> v2:
  - strict by default (Quentin Monnet)
  - add more info to --legacy description (Quentin Monnet)
  - add bash completion (Quentin Monnet)

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20211110192324.920934-1-sdf@google.com

1 files changed, 12 insertions, 1 deletions

diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 28237d7cef67..473791e87f7d 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -31,6 +31,7 @@ bool block_mount;
 bool verifier_logs;
 bool relaxed_maps;
 bool use_loader;
+bool legacy_libbpf;
 struct btf *base_btf;
 struct hashmap *refs_table;
 
@@ -396,6 +397,7 @@ int main(int argc, char **argv)
 		{ "debug",	no_argument,	NULL,	'd' },
 		{ "use-loader",	no_argument,	NULL,	'L' },
 		{ "base-btf",	required_argument, NULL, 'B' },
+		{ "legacy",	no_argument,	NULL,	'l' },
 		{ 0 }
 	};
 	int opt, ret;
@@ -408,7 +410,7 @@ int main(int argc, char **argv)
 	bin_name = argv[0];
 
 	opterr = 0;
-	while ((opt = getopt_long(argc, argv, "VhpjfLmndB:",
+	while ((opt = getopt_long(argc, argv, "VhpjfLmndB:l",
 				  options, NULL)) >= 0) {
 		switch (opt) {
 		case 'V':
@@ -454,6 +456,9 @@ int main(int argc, char **argv)
 		case 'L':
 			use_loader = true;
 			break;
+		case 'l':
+			legacy_libbpf = true;
+			break;
 		default:
 			p_err("unrecognized option '%s'", argv[optind - 1]);
 			if (json_output)
@@ -463,6 +468,12 @@ int main(int argc, char **argv)
 		}
 	}
 
+	if (!legacy_libbpf) {
+		ret = libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
+		if (ret)
+			p_err("failed to enable libbpf strict mode: %d", ret);
+	}
+
 	argc -= optind;
 	argv += optind;
 	if (argc < 0)