bpf: libbpf: Refactor and bug fix on the bpf_func_info loading logic

This patch refactor and fix a bug in the libbpf's bpf_func_info loading
logic. The bug fix and refactoring are targeting the same
commit 2993e0515bb4 ("tools/bpf: add support to read .BTF.ext sections")
which is in the bpf-next branch.

1) In bpf_load_program_xattr(), it should retry when errno == E2BIG
regardless of log_buf and log_buf_sz. This patch fixes it.

2) btf_ext__reloc_init() and btf_ext__reloc() are essentially
the same except btf_ext__reloc_init() always has insns_cnt == 0.
Hence, btf_ext__reloc_init() is removed.

btf_ext__reloc() is also renamed to btf_ext__reloc_func_info()
to get ready for the line_info support in the next patch.

3) Consolidate func_info section logic from "btf_ext_parse_hdr()",
"btf_ext_validate_func_info()" and "btf_ext__new()" to
a new function "btf_ext_copy_func_info()" such that similar
logic can be reused by the later libbpf's line_info patch.

4) The next line_info patch will store line_info_cnt instead of
line_info_len in the bpf_program because the kernel is taking
line_info_cnt also. It will save a few "len" to "cnt" conversions
and will also save some function args.

Hence, this patch also makes bpf_program to store func_info_cnt
instead of func_info_len.

5) btf_ext depends on btf. e.g. the func_info's type_id
in ".BTF.ext" is not useful when ".BTF" is absent.
This patch only init the obj->btf_ext pointer after
it has successfully init the obj->btf pointer.

This can avoid always checking "obj->btf && obj->btf_ext"
together for accessing ".BTF.ext". Checking "obj->btf_ext"
alone will do.

6) Move "struct btf_sec_func_info" from btf.h to btf.c.
There is no external usage outside btf.c.

Fixes: 2993e0515bb4 ("tools/bpf: add support to read .BTF.ext sections")
Signed-off-by: Martin KaFai Lau <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/lib/bpf/bpf.c

···
 	       min(name_len, BPF_OBJ_NAME_LEN - 1));
 
 	fd = sys_bpf(BPF_PROG_LOAD, &attr, sizeof(attr));
-	if (fd >= 0 || !log_buf || !log_buf_sz)
+	if (fd >= 0)
 		return fd;
 
 	/* After bpf_prog_load, the kernel may modify certain attributes
···
 
 		fd = sys_bpf(BPF_PROG_LOAD, &attr, sizeof(attr));
 
-		if (fd >= 0 || !log_buf || !log_buf_sz)
+		if (fd >= 0)
 			goto done;
 	}
+
+	if (!log_buf || !log_buf_sz)
+		goto done;
 
 	/* Try again with log */
 	attr.log_buf = ptr_to_u64(log_buf);

tools/lib/bpf/btf.c

···
 	__u32 func_info_len;
 };
 
+struct btf_sec_func_info {
+	__u32	sec_name_off;
+	__u32	num_func_info;
+	/* Followed by num_func_info number of bpf func_info records */
+	__u8	data[0];
+};
+
 /* The minimum bpf_func_info checked by the loader */
 struct bpf_func_info_min {
 	__u32   insn_off;
···
 	return err;
 }
 
-static int btf_ext_validate_func_info(const void *finfo, __u32 size,
-				      btf_print_fn_t err_log)
+static int btf_ext_copy_func_info(struct btf_ext *btf_ext,
+				  __u8 *data, __u32 data_size,
+				  btf_print_fn_t err_log)
 {
-	int sec_hdrlen = sizeof(struct btf_sec_func_info);
-	__u32 size_left, num_records, record_size;
+	const struct btf_ext_header *hdr = (struct btf_ext_header *)data;
 	const struct btf_sec_func_info *sinfo;
-	__u64 total_record_size;
+	__u32 info_left, record_size;
+	/* The start of the info sec (including the __u32 record_size). */
+	const void *info;
+
+	/* data and data_size do not include btf_ext_header from now on */
+	data = data + hdr->hdr_len;
+	data_size -= hdr->hdr_len;
+
+	if (hdr->func_info_off & 0x03) {
+		elog("BTF.ext func_info section is not aligned to 4 bytes\n");
+		return -EINVAL;
+	}
+
+	if (data_size < hdr->func_info_off ||
+	    hdr->func_info_len > data_size - hdr->func_info_off) {
+		elog("func_info section (off:%u len:%u) is beyond the end of the ELF section .BTF.ext\n",
+		     hdr->func_info_off, hdr->func_info_len);
+		return -EINVAL;
+	}
+
+	info = data + hdr->func_info_off;
+	info_left = hdr->func_info_len;
 
 	/* At least a func_info record size */
-	if (size < sizeof(__u32)) {
+	if (info_left < sizeof(__u32)) {
 		elog("BTF.ext func_info record size not found");
 		return -EINVAL;
 	}
 
-	/* The record size needs to meet below minimum standard */
-	record_size = *(__u32 *)finfo;
+	/* The record size needs to meet the minimum standard */
+	record_size = *(__u32 *)info;
 	if (record_size < sizeof(struct bpf_func_info_min) ||
-	    record_size % sizeof(__u32)) {
+	    record_size & 0x03) {
 		elog("BTF.ext func_info invalid record size");
 		return -EINVAL;
 	}
 
-	sinfo = finfo + sizeof(__u32);
-	size_left = size - sizeof(__u32);
+	sinfo = info + sizeof(__u32);
+	info_left -= sizeof(__u32);
 
 	/* If no func_info records, return failure now so .BTF.ext
 	 * won't be used.
 	 */
-	if (!size_left) {
+	if (!info_left) {
 		elog("BTF.ext no func info records");
 		return -EINVAL;
 	}
 
-	while (size_left) {
-		if (size_left < sec_hdrlen) {
+	while (info_left) {
+		unsigned int sec_hdrlen = sizeof(struct btf_sec_func_info);
+		__u64 total_record_size;
+		__u32 num_records;
+
+		if (info_left < sec_hdrlen) {
 			elog("BTF.ext func_info header not found");
 			return -EINVAL;
 		}
···
 
 		total_record_size = sec_hdrlen +
 				    (__u64)num_records * record_size;
-		if (size_left < total_record_size) {
+		if (info_left < total_record_size) {
 			elog("incorrect BTF.ext num_func_info");
 			return -EINVAL;
 		}
 
-		size_left -= total_record_size;
+		info_left -= total_record_size;
 		sinfo = (void *)sinfo + total_record_size;
 	}
+
+	btf_ext->func_info_len = hdr->func_info_len - sizeof(__u32);
+	btf_ext->func_info_rec_size = record_size;
+	btf_ext->func_info = malloc(btf_ext->func_info_len);
+	if (!btf_ext->func_info)
+		return -ENOMEM;
+	memcpy(btf_ext->func_info, info + sizeof(__u32),
+	       btf_ext->func_info_len);
 
 	return 0;
 }
···
 			     btf_print_fn_t err_log)
 {
 	const struct btf_ext_header *hdr = (struct btf_ext_header *)data;
-	__u32 meta_left, last_func_info_pos;
-	void *finfo;
 
 	if (data_size < offsetof(struct btf_ext_header, func_info_off) ||
 	    data_size < hdr->hdr_len) {
···
 		return -ENOTSUP;
 	}
 
-	meta_left = data_size - hdr->hdr_len;
-	if (!meta_left) {
+	if (data_size == hdr->hdr_len) {
 		elog("BTF.ext has no data\n");
 		return -EINVAL;
 	}
 
-	if (meta_left < hdr->func_info_off) {
-		elog("Invalid BTF.ext func_info section offset:%u\n",
-		     hdr->func_info_off);
-		return -EINVAL;
-	}
-
-	if (hdr->func_info_off & 0x03) {
-		elog("BTF.ext func_info section is not aligned to 4 bytes\n");
-		return -EINVAL;
-	}
-
-	last_func_info_pos = hdr->hdr_len + hdr->func_info_off +
-			     hdr->func_info_len;
-	if (last_func_info_pos > data_size) {
-		elog("Invalid BTF.ext func_info section size:%u\n",
-		     hdr->func_info_len);
-		return -EINVAL;
-	}
-
-	finfo = data + hdr->hdr_len + hdr->func_info_off;
-	return btf_ext_validate_func_info(finfo, hdr->func_info_len,
-					  err_log);
+	return 0;
 }
 
 void btf_ext__free(struct btf_ext *btf_ext)
···
 
 struct btf_ext *btf_ext__new(__u8 *data, __u32 size, btf_print_fn_t err_log)
 {
-	const struct btf_ext_header *hdr;
 	struct btf_ext *btf_ext;
-	void *org_fdata, *fdata;
-	__u32 hdrlen, size_u32;
 	int err;
 
 	err = btf_ext_parse_hdr(data, size, err_log);
···
 	if (!btf_ext)
 		return ERR_PTR(-ENOMEM);
 
-	hdr = (const struct btf_ext_header *)data;
-	hdrlen = hdr->hdr_len;
-	size_u32 = sizeof(__u32);
-	fdata = malloc(hdr->func_info_len - size_u32);
-	if (!fdata) {
-		free(btf_ext);
-		return ERR_PTR(-ENOMEM);
+	err = btf_ext_copy_func_info(btf_ext, data, size, err_log);
+	if (err) {
+		btf_ext__free(btf_ext);
+		return ERR_PTR(err);
 	}
-
-	/* remember record size and copy rest of func_info data */
-	org_fdata = data + hdrlen + hdr->func_info_off;
-	btf_ext->func_info_rec_size = *(__u32 *)org_fdata;
-	memcpy(fdata, org_fdata + size_u32, hdr->func_info_len - size_u32);
-	btf_ext->func_info = fdata;
-	btf_ext->func_info_len = hdr->func_info_len - size_u32;
 
 	return btf_ext;
 }
 
-int btf_ext__reloc_init(struct btf *btf, struct btf_ext *btf_ext,
-			const char *sec_name, void **func_info,
-			__u32 *func_info_rec_size, __u32 *func_info_len)
-{
-	__u32 sec_hdrlen = sizeof(struct btf_sec_func_info);
-	__u32 i, record_size, records_len;
-	struct btf_sec_func_info *sinfo;
-	const char *info_sec_name;
-	__s64 remain_len;
-	void *data;
-
-	record_size = btf_ext->func_info_rec_size;
-	sinfo = btf_ext->func_info;
-	remain_len = btf_ext->func_info_len;
-
-	while (remain_len > 0) {
-		records_len = sinfo->num_func_info * record_size;
-		info_sec_name = btf__name_by_offset(btf, sinfo->sec_name_off);
-		if (strcmp(info_sec_name, sec_name)) {
-			remain_len -= sec_hdrlen + records_len;
-			sinfo = (void *)sinfo + sec_hdrlen + records_len;
-			continue;
-		}
-
-		data = malloc(records_len);
-		if (!data)
-			return -ENOMEM;
-
-		memcpy(data, sinfo->data, records_len);
-
-		/* adjust the insn_off, the data in .BTF.ext is
-		 * the actual byte offset, and the kernel expects
-		 * the offset in term of bpf_insn.
-		 *
-		 * adjust the insn offset only, the rest data will
-		 * be passed to kernel.
-		 */
-		for (i = 0; i < sinfo->num_func_info; i++) {
-			struct bpf_func_info_min *record;
-
-			record = data + i * record_size;
-			record->insn_off /= sizeof(struct bpf_insn);
-		}
-
-		*func_info = data;
-		*func_info_len = records_len;
-		*func_info_rec_size = record_size;
-		return 0;
-	}
-
-	return -EINVAL;
-}
-
-int btf_ext__reloc(struct btf *btf, struct btf_ext *btf_ext,
-		   const char *sec_name, __u32 insns_cnt,
-		   void **func_info, __u32 *func_info_len)
+int btf_ext__reloc_func_info(struct btf *btf, struct btf_ext *btf_ext,
+			     const char *sec_name, __u32 insns_cnt,
+			     void **func_info, __u32 *cnt)
 {
 	__u32 sec_hdrlen = sizeof(struct btf_sec_func_info);
 	__u32 i, record_size, existing_flen, records_len;
···
 			continue;
 		}
 
-		existing_flen = *func_info_len;
+		existing_flen = (*cnt) * record_size;
 		data = realloc(*func_info, existing_flen + records_len);
 		if (!data)
 			return -ENOMEM;
···
 				insns_cnt;
 		}
 		*func_info = data;
-		*func_info_len = existing_flen + records_len;
+		*cnt += sinfo->num_func_info;
 		return 0;
 	}
 
-	return -EINVAL;
+	return -ENOENT;
+}
+
+__u32 btf_ext__func_info_rec_size(const struct btf_ext *btf_ext)
+{
+	return btf_ext->func_info_rec_size;
 }

tools/lib/bpf/btf.h

···
 	__u32	func_info_len;
 };
 
-struct btf_sec_func_info {
-	__u32	sec_name_off;
-	__u32	num_func_info;
-	/* Followed by num_func_info number of bpf func_info records */
-	__u8	data[0];
-};
-
 typedef int (*btf_print_fn_t)(const char *, ...)
 	__attribute__((format(printf, 1, 2)));
 
···
 
 struct btf_ext *btf_ext__new(__u8 *data, __u32 size, btf_print_fn_t err_log);
 void btf_ext__free(struct btf_ext *btf_ext);
-int btf_ext__reloc_init(struct btf *btf, struct btf_ext *btf_ext,
-			const char *sec_name, void **func_info,
-			__u32 *func_info_rec_size, __u32 *func_info_len);
-int btf_ext__reloc(struct btf *btf, struct btf_ext *btf_ext,
-		   const char *sec_name, __u32 insns_cnt, void **func_info,
-		   __u32 *func_info_len);
+int btf_ext__reloc_func_info(struct btf *btf, struct btf_ext *btf_ext,
+			     const char *sec_name, __u32 insns_cnt,
+			     void **func_info, __u32 *func_info_len);
+__u32 btf_ext__func_info_rec_size(const struct btf_ext *btf_ext);
 
 #ifdef __cplusplus
 } /* extern "C" */

tools/lib/bpf/libbpf.c

···
 	int btf_fd;
 	void *func_info;
 	__u32 func_info_rec_size;
-	__u32 func_info_len;
+	__u32 func_info_cnt;
 
 	struct bpf_capabilities *caps;
 };
···
 {
 	Elf *elf = obj->efile.elf;
 	GElf_Ehdr *ep = &obj->efile.ehdr;
+	Elf_Data *btf_ext_data = NULL;
 	Elf_Scn *scn = NULL;
 	int idx = 0, err = 0;
 
···
 				obj->btf = NULL;
 			}
 		} else if (strcmp(name, BTF_EXT_ELF_SEC) == 0) {
-			obj->btf_ext = btf_ext__new(data->d_buf, data->d_size,
-						    __pr_debug);
-			if (IS_ERR(obj->btf_ext)) {
-				pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
-					   BTF_EXT_ELF_SEC,
-					   PTR_ERR(obj->btf_ext));
-				obj->btf_ext = NULL;
-			}
+			btf_ext_data = data;
 		} else if (sh.sh_type == SHT_SYMTAB) {
 			if (obj->efile.symbols) {
 				pr_warning("bpf: multiple SYMTAB in %s\n",
···
 	if (!obj->efile.strtabidx || obj->efile.strtabidx >= idx) {
 		pr_warning("Corrupted ELF file: index of strtab invalid\n");
 		return LIBBPF_ERRNO__FORMAT;
+	}
+	if (btf_ext_data) {
+		if (!obj->btf) {
+			pr_debug("Ignore ELF section %s because its depending ELF section %s is not found.\n",
+				 BTF_EXT_ELF_SEC, BTF_ELF_SEC);
+		} else {
+			obj->btf_ext = btf_ext__new(btf_ext_data->d_buf,
+						    btf_ext_data->d_size,
+						    __pr_debug);
+			if (IS_ERR(obj->btf_ext)) {
+				pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
+					   BTF_EXT_ELF_SEC,
+					   PTR_ERR(obj->btf_ext));
+				obj->btf_ext = NULL;
+			}
+		}
 	}
 	if (obj->efile.maps_shndx >= 0) {
 		err = bpf_object__init_maps(obj, flags);
···
 }
 
 static int
+check_btf_ext_reloc_err(struct bpf_program *prog, int err,
+			void *btf_prog_info, const char *info_name)
+{
+	if (err != -ENOENT) {
+		pr_warning("Error in loading %s for sec %s.\n",
+			   info_name, prog->section_name);
+		return err;
+	}
+
+	/* err == -ENOENT (i.e. prog->section_name not found in btf_ext) */
+
+	if (btf_prog_info) {
+		/*
+		 * Some info has already been found but has problem
+		 * in the last btf_ext reloc.  Must have to error
+		 * out.
+		 */
+		pr_warning("Error in relocating %s for sec %s.\n",
+			   info_name, prog->section_name);
+		return err;
+	}
+
+	/*
+	 * Have problem loading the very first info.  Ignore
+	 * the rest.
+	 */
+	pr_warning("Cannot find %s for main program sec %s. Ignore all %s.\n",
+		   info_name, prog->section_name, info_name);
+	return 0;
+}
+
+static int
+bpf_program_reloc_btf_ext(struct bpf_program *prog, struct bpf_object *obj,
+			  const char *section_name,  __u32 insn_offset)
+{
+	int err;
+
+	if (!insn_offset || prog->func_info) {
+		/*
+		 * !insn_offset => main program
+		 *
+		 * For sub prog, the main program's func_info has to
+		 * be loaded first (i.e. prog->func_info != NULL)
+		 */
+		err = btf_ext__reloc_func_info(obj->btf, obj->btf_ext,
+					       section_name, insn_offset,
+					       &prog->func_info,
+					       &prog->func_info_cnt);
+		if (err)
+			return check_btf_ext_reloc_err(prog, err,
+						       prog->func_info,
+						       "bpf_func_info");
+
+		prog->func_info_rec_size = btf_ext__func_info_rec_size(obj->btf_ext);
+	}
+
+	if (!insn_offset)
+		prog->btf_fd = btf__fd(obj->btf);
+
+	return 0;
+}
+
+static int
 bpf_program__reloc_text(struct bpf_program *prog, struct bpf_object *obj,
 			struct reloc_desc *relo)
 {
···
 			return -ENOMEM;
 		}
 
-		if (obj->btf && obj->btf_ext) {
-			err = btf_ext__reloc(obj->btf, obj->btf_ext,
-					     text->section_name,
-					     prog->insns_cnt,
-					     &prog->func_info,
-					     &prog->func_info_len);
-			if (err) {
-				pr_warning("error in btf_ext__reloc for sec %s\n",
-					   text->section_name);
+		if (obj->btf_ext) {
+			err = bpf_program_reloc_btf_ext(prog, obj,
+							text->section_name,
+							prog->insns_cnt);
+			if (err)
 				return err;
-			}
 		}
 
 		memcpy(new_insn + prog->insns_cnt, text->insns,
···
 	if (!prog)
 		return 0;
 
-	if (obj->btf && obj->btf_ext) {
-		err = btf_ext__reloc_init(obj->btf, obj->btf_ext,
-					  prog->section_name,
-					  &prog->func_info,
-					  &prog->func_info_rec_size,
-					  &prog->func_info_len);
-		if (err) {
-			pr_warning("err in btf_ext__reloc_init for sec %s\n",
-				   prog->section_name);
+	if (obj->btf_ext) {
+		err = bpf_program_reloc_btf_ext(prog, obj,
+						prog->section_name, 0);
+		if (err)
 			return err;
-		}
-		prog->btf_fd = btf__fd(obj->btf);
 	}
 
 	if (!prog->reloc_desc)
···
 
 static int
 load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
-	     char *license, __u32 kern_version, int *pfd,
-	     __u32 func_info_cnt)
+	     char *license, __u32 kern_version, int *pfd)
 {
 	struct bpf_load_program_attr load_attr;
 	char *cp, errmsg[STRERR_BUFSIZE];
···
 	load_attr.prog_btf_fd = prog->btf_fd >= 0 ? prog->btf_fd : 0;
 	load_attr.func_info = prog->func_info;
 	load_attr.func_info_rec_size = prog->func_info_rec_size;
-	load_attr.func_info_cnt = func_info_cnt;
-
+	load_attr.func_info_cnt = prog->func_info_cnt;
 	if (!load_attr.insns || !load_attr.insns_cnt)
 		return -EINVAL;
 
···
 bpf_program__load(struct bpf_program *prog,
 		  char *license, __u32 kern_version)
 {
-	__u32 func_info_cnt;
 	int err = 0, fd, i;
-
-	if (prog->func_info_len == 0)
-		func_info_cnt = 0;
-	else
-		func_info_cnt = prog->func_info_len / prog->func_info_rec_size;
 
 	if (prog->instances.nr < 0 || !prog->instances.fds) {
 		if (prog->preprocessor) {
···
 				   prog->section_name, prog->instances.nr);
 		}
 		err = load_program(prog, prog->insns, prog->insns_cnt,
-				   license, kern_version, &fd,
-				   func_info_cnt);
+				   license, kern_version, &fd);
 		if (!err)
 			prog->instances.fds[0] = fd;
 		goto out;
···
 
 		err = load_program(prog, result.new_insn_ptr,
 				   result.new_insn_cnt,
-				   license, kern_version, &fd,
-				   func_info_cnt);
+				   license, kern_version, &fd);
 
 		if (err) {
 			pr_warning("Loading the %dth instance of program '%s' failed\n",