bpftool: Adding support for BTF program names

`bpftool prog list` and other bpftool subcommands that show
BPF program names currently get them from bpf_prog_info.name.
That field is limited to 16 (BPF_OBJ_NAME_LEN) chars which leads
to truncated names since many progs have much longer names.

The idea of this change is to improve all bpftool commands that
output prog name so that bpftool uses info from BTF to print
program names if available.

It tries bpf_prog_info.name first and fall back to btf only if
the name is suspected to be truncated (has 15 chars length).

Right now `bpftool p show id <id>` returns capped prog name

<id>: kprobe  name example_cap_cap  tag 712e...
...

With this change it would return

<id>: kprobe  name example_cap_capable  tag 712e...
...

Note, other commands that print prog names (e.g. "bpftool
cgroup tree") are also addressed in this change.
Signed-off-by: Raman Shukhau <ramasha@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220119100255.1068997-1-ramasha@fb.com

tools/bpf/bpftool/cgroup.c

@@ -50,6 +50,7 @@ static int show_bpf_prog(int id, enum bpf_attach_type attach_type,
 			 const char *attach_flags_str,
 			 int level)
 {
+	char prog_name[MAX_PROG_FULL_NAME];
 	struct bpf_prog_info info = {};
 	__u32 info_len = sizeof(info);
 	int prog_fd;
@@ -63,6 +64,7 @@ static int show_bpf_prog(int id, enum bpf_attach_type attach_type,
 		return -1;
 	}
 
+	get_prog_full_name(&info, prog_fd, prog_name, sizeof(prog_name));
 	if (json_output) {
 		jsonw_start_object(json_wtr);
 		jsonw_uint_field(json_wtr, "id", info.id);
@@ -73,7 +75,7 @@ static int show_bpf_prog(int id, enum bpf_attach_type attach_type,
 			jsonw_uint_field(json_wtr, "attach_type", attach_type);
 		jsonw_string_field(json_wtr, "attach_flags",
 				   attach_flags_str);
-		jsonw_string_field(json_wtr, "name", info.name);
+		jsonw_string_field(json_wtr, "name", prog_name);
 		jsonw_end_object(json_wtr);
 	} else {
 		printf("%s%-8u ", level ? "    " : "", info.id);
@@ -81,7 +83,7 @@ static int show_bpf_prog(int id, enum bpf_attach_type attach_type,
 			printf("%-15s", attach_type_name[attach_type]);
 		else
 			printf("type %-10u", attach_type);
-		printf(" %-15s %-15s\n", attach_flags_str, info.name);
+		printf(" %-15s %-15s\n", attach_flags_str, prog_name);
 	}
 
 	close(prog_fd);

tools/bpf/bpftool/common.c

@@ -24,6 +24,7 @@
 #include <bpf/bpf.h>
 #include <bpf/hashmap.h>
 #include <bpf/libbpf.h> /* libbpf_num_possible_cpus */
+#include <bpf/btf.h>
 
 #include "main.h"
 
@@ -304,6 +305,49 @@ const char *get_fd_type_name(enum bpf_obj_type type)
 	return names[type];
 }
 
+void get_prog_full_name(const struct bpf_prog_info *prog_info, int prog_fd,
+			char *name_buff, size_t buff_len)
+{
+	const char *prog_name = prog_info->name;
+	const struct btf_type *func_type;
+	const struct bpf_func_info finfo;
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
+	struct btf *prog_btf = NULL;
+
+	if (buff_len <= BPF_OBJ_NAME_LEN ||
+	    strlen(prog_info->name) < BPF_OBJ_NAME_LEN - 1)
+		goto copy_name;
+
+	if (!prog_info->btf_id || prog_info->nr_func_info == 0)
+		goto copy_name;
+
+	info.nr_func_info = 1;
+	info.func_info_rec_size = prog_info->func_info_rec_size;
+	if (info.func_info_rec_size > sizeof(finfo))
+		info.func_info_rec_size = sizeof(finfo);
+	info.func_info = ptr_to_u64(&finfo);
+
+	if (bpf_obj_get_info_by_fd(prog_fd, &info, &info_len))
+		goto copy_name;
+
+	prog_btf = btf__load_from_kernel_by_id(info.btf_id);
+	if (!prog_btf)
+		goto copy_name;
+
+	func_type = btf__type_by_id(prog_btf, finfo.type_id);
+	if (!func_type || !btf_is_func(func_type))
+		goto copy_name;
+
+	prog_name = btf__name_by_offset(prog_btf, func_type->name_off);
+
+copy_name:
+	snprintf(name_buff, buff_len, "%s", prog_name);
+
+	if (prog_btf)
+		btf__free(prog_btf);
+}
+
 int get_fd_type(int fd)
 {
 	char path[PATH_MAX];

tools/bpf/bpftool/main.h

@@ -140,6 +140,10 @@ struct cmd {
 int cmd_select(const struct cmd *cmds, int argc, char **argv,
 	       int (*help)(int argc, char **argv));
 
+#define MAX_PROG_FULL_NAME 128
+void get_prog_full_name(const struct bpf_prog_info *prog_info, int prog_fd,
+			char *name_buff, size_t buff_len);
+
 int get_fd_type(int fd);
 const char *get_fd_type_name(enum bpf_obj_type type);
 char *get_fdinfo(int fd, const char *key);

tools/bpf/bpftool/prog.c

@@ -424,8 +424,10 @@ static void show_prog_metadata(int fd, __u32 num_maps)
 	free(value);
 }
 
-static void print_prog_header_json(struct bpf_prog_info *info)
+static void print_prog_header_json(struct bpf_prog_info *info, int fd)
 {
+	char prog_name[MAX_PROG_FULL_NAME];
+
 	jsonw_uint_field(json_wtr, "id", info->id);
 	if (info->type < ARRAY_SIZE(prog_type_name))
 		jsonw_string_field(json_wtr, "type",
@@ -433,8 +435,10 @@ static void print_prog_header_json(struct bpf_prog_info *info)
 	else
 		jsonw_uint_field(json_wtr, "type", info->type);
 
-	if (*info->name)
-		jsonw_string_field(json_wtr, "name", info->name);
+	if (*info->name) {
+		get_prog_full_name(info, fd, prog_name, sizeof(prog_name));
+		jsonw_string_field(json_wtr, "name", prog_name);
+	}
 
 	jsonw_name(json_wtr, "tag");
 	jsonw_printf(json_wtr, "\"" BPF_TAG_FMT "\"",
@@ -455,7 +459,7 @@ static void print_prog_json(struct bpf_prog_info *info, int fd)
 	char *memlock;
 
 	jsonw_start_object(json_wtr);
-	print_prog_header_json(info);
+	print_prog_header_json(info, fd);
 	print_dev_json(info->ifindex, info->netns_dev, info->netns_ino);
 
 	if (info->load_time) {
@@ -507,16 +511,20 @@ static void print_prog_json(struct bpf_prog_info *info, int fd)
 	jsonw_end_object(json_wtr);
 }
 
-static void print_prog_header_plain(struct bpf_prog_info *info)
+static void print_prog_header_plain(struct bpf_prog_info *info, int fd)
 {
+	char prog_name[MAX_PROG_FULL_NAME];
+
 	printf("%u: ", info->id);
 	if (info->type < ARRAY_SIZE(prog_type_name))
 		printf("%s  ", prog_type_name[info->type]);
 	else
 		printf("type %u  ", info->type);
 
-	if (*info->name)
-		printf("name %s  ", info->name);
+	if (*info->name) {
+		get_prog_full_name(info, fd, prog_name, sizeof(prog_name));
+		printf("name %s  ", prog_name);
+	}
 
 	printf("tag ");
 	fprint_hex(stdout, info->tag, BPF_TAG_SIZE, "");
@@ -534,7 +542,7 @@ static void print_prog_plain(struct bpf_prog_info *info, int fd)
 {
 	char *memlock;
 
-	print_prog_header_plain(info);
+	print_prog_header_plain(info, fd);
 
 	if (info->load_time) {
 		char buf[32];
@@ -972,10 +980,10 @@ static int do_dump(int argc, char **argv)
 
 		if (json_output && nb_fds > 1) {
 			jsonw_start_object(json_wtr);	/* prog object */
-			print_prog_header_json(&info);
+			print_prog_header_json(&info, fds[i]);
 			jsonw_name(json_wtr, "insns");
 		} else if (nb_fds > 1) {
-			print_prog_header_plain(&info);
+			print_prog_header_plain(&info, fds[i]);
 		}
 
 		err = prog_dump(&info, mode, filepath, opcodes, visual, linum);