libbpf: Add elf_open/elf_close functions

Adding elf_open/elf_close functions and using it in
elf_find_func_offset_from_file function. It will be
used in following changes to save some common code.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230809083440.3209381-10-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: olsajiri

tools/lib/bpf/elf.c

@@ -10,6 +10,42 @@
 
 #define STRERR_BUFSIZE  128
 
+int elf_open(const char *binary_path, struct elf_fd *elf_fd)
+{
+	char errmsg[STRERR_BUFSIZE];
+	int fd, ret;
+	Elf *elf;
+
+	if (elf_version(EV_CURRENT) == EV_NONE) {
+		pr_warn("elf: failed to init libelf for %s\n", binary_path);
+		return -LIBBPF_ERRNO__LIBELF;
+	}
+	fd = open(binary_path, O_RDONLY | O_CLOEXEC);
+	if (fd < 0) {
+		ret = -errno;
+		pr_warn("elf: failed to open %s: %s\n", binary_path,
+			libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
+		return ret;
+	}
+	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+	if (!elf) {
+		pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
+		close(fd);
+		return -LIBBPF_ERRNO__FORMAT;
+	}
+	elf_fd->fd = fd;
+	elf_fd->elf = elf;
+	return 0;
+}
+
+void elf_close(struct elf_fd *elf_fd)
+{
+	if (!elf_fd)
+		return;
+	elf_end(elf_fd->elf);
+	close(elf_fd->fd);
+}
+
 /* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
 static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
 {
@@ -170,28 +206,13 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
  */
 long elf_find_func_offset_from_file(const char *binary_path, const char *name)
 {
-	char errmsg[STRERR_BUFSIZE];
+	struct elf_fd elf_fd;
 	long ret = -ENOENT;
-	Elf *elf;
-	int fd;
 
-	fd = open(binary_path, O_RDONLY | O_CLOEXEC);
-	if (fd < 0) {
-		ret = -errno;
-		pr_warn("failed to open %s: %s\n", binary_path,
-			libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
+	ret = elf_open(binary_path, &elf_fd);
+	if (ret)
 		return ret;
-	}
-	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
-	if (!elf) {
-		pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
-		close(fd);
-		return -LIBBPF_ERRNO__FORMAT;
-	}
-
-	ret = elf_find_func_offset(elf, binary_path, name);
-	elf_end(elf);
-	close(fd);
+	ret = elf_find_func_offset(elf_fd.elf, binary_path, name);
+	elf_close(&elf_fd);
 	return ret;
 }
-

tools/lib/bpf/libbpf_internal.h

@@ -581,4 +581,12 @@ int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size, int attempts);
 long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name);
 long elf_find_func_offset_from_file(const char *binary_path, const char *name);
 
+struct elf_fd {
+	Elf *elf;
+	int fd;
+};
+
+int elf_open(const char *binary_path, struct elf_fd *elf_fd);
+void elf_close(struct elf_fd *elf_fd);
+
 #endif /* __LIBBPF_LIBBPF_INTERNAL_H */

tools/lib/bpf/usdt.c

@@ -946,32 +946,22 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct
 					  const char *usdt_provider, const char *usdt_name,
 					  __u64 usdt_cookie)
 {
-	int i, fd, err, spec_map_fd, ip_map_fd;
+	int i, err, spec_map_fd, ip_map_fd;
 	LIBBPF_OPTS(bpf_uprobe_opts, opts);
 	struct hashmap *specs_hash = NULL;
 	struct bpf_link_usdt *link = NULL;
 	struct usdt_target *targets = NULL;
+	struct elf_fd elf_fd;
 	size_t target_cnt;
-	Elf *elf;
 
 	spec_map_fd = bpf_map__fd(man->specs_map);
 	ip_map_fd = bpf_map__fd(man->ip_to_spec_id_map);
 
-	fd = open(path, O_RDONLY | O_CLOEXEC);
-	if (fd < 0) {
-		err = -errno;
-		pr_warn("usdt: failed to open ELF binary '%s': %d\n", path, err);
+	err = elf_open(path, &elf_fd);
+	if (err)
 		return libbpf_err_ptr(err);
-	}
 
-	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
-	if (!elf) {
-		err = -EBADF;
-		pr_warn("usdt: failed to parse ELF binary '%s': %s\n", path, elf_errmsg(-1));
-		goto err_out;
-	}
-
-	err = sanity_check_usdt_elf(elf, path);
+	err = sanity_check_usdt_elf(elf_fd.elf, path);
 	if (err)
 		goto err_out;
 
@@ -984,7 +974,7 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct
 	/* discover USDT in given binary, optionally limiting
 	 * activations to a given PID, if pid > 0
 	 */
-	err = collect_usdt_targets(man, elf, path, pid, usdt_provider, usdt_name,
+	err = collect_usdt_targets(man, elf_fd.elf, path, pid, usdt_provider, usdt_name,
 				   usdt_cookie, &targets, &target_cnt);
 	if (err <= 0) {
 		err = (err == 0) ? -ENOENT : err;
@@ -1069,19 +1059,15 @@ struct bpf_link *usdt_manager_attach_usdt(struct usdt_manager *man, const struct
 
 	free(targets);
 	hashmap__free(specs_hash);
-	elf_end(elf);
-	close(fd);
-
+	elf_close(&elf_fd);
 	return &link->link;
 
 err_out:
 	if (link)
 		bpf_link__destroy(&link->link);
 	free(targets);
 	hashmap__free(specs_hash);
-	if (elf)
-		elf_end(elf);
-	close(fd);
+	elf_close(&elf_fd);
 	return libbpf_err_ptr(err);
 }