11 files changed, 1197 insertions, 554 deletions

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index d27e34133973..bba48ff4c5c0 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -67,11 +67,12 @@ static inline int sys_bpf(enum bpf_cmd cmd, union bpf_attr *attr,
 
 static inline int sys_bpf_prog_load(union bpf_attr *attr, unsigned int size)
 {
+	int retries = 5;
 	int fd;
 
 	do {
 		fd = sys_bpf(BPF_PROG_LOAD, attr, size);
-	} while (fd < 0 && errno == EAGAIN);
+	} while (fd < 0 && errno == EAGAIN && retries-- > 0);
 
 	return fd;
 }
@@ -214,59 +215,55 @@ alloc_zero_tailing_info(const void *orecord, __u32 cnt,
 	return info;
 }
 
-int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
-			   char *log_buf, size_t log_buf_sz)
+int libbpf__bpf_prog_load(const struct bpf_prog_load_params *load_attr)
 {
 	void *finfo = NULL, *linfo = NULL;
 	union bpf_attr attr;
-	__u32 log_level;
 	int fd;
 
-	if (!load_attr || !log_buf != !log_buf_sz)
+	if (!load_attr->log_buf != !load_attr->log_buf_sz)
 		return -EINVAL;
 
-	log_level = load_attr->log_level;
-	if (log_level > (4 | 2 | 1) || (log_level && !log_buf))
+	if (load_attr->log_level > (4 | 2 | 1) || (load_attr->log_level && !load_attr->log_buf))
 		return -EINVAL;
 
 	memset(&attr, 0, sizeof(attr));
 	attr.prog_type = load_attr->prog_type;
 	attr.expected_attach_type = load_attr->expected_attach_type;
-	if (attr.prog_type == BPF_PROG_TYPE_STRUCT_OPS ||
-	    attr.prog_type == BPF_PROG_TYPE_LSM) {
-		attr.attach_btf_id = load_attr->attach_btf_id;
-	} else if (attr.prog_type == BPF_PROG_TYPE_TRACING ||
-		   attr.prog_type == BPF_PROG_TYPE_EXT) {
-		attr.attach_btf_id = load_attr->attach_btf_id;
+
+	if (load_attr->attach_prog_fd)
 		attr.attach_prog_fd = load_attr->attach_prog_fd;
-	} else {
-		attr.prog_ifindex = load_attr->prog_ifindex;
-		attr.kern_version = load_attr->kern_version;
-	}
-	attr.insn_cnt = (__u32)load_attr->insns_cnt;
+	else
+		attr.attach_btf_obj_fd = load_attr->attach_btf_obj_fd;
+	attr.attach_btf_id = load_attr->attach_btf_id;
+
+	attr.prog_ifindex = load_attr->prog_ifindex;
+	attr.kern_version = load_attr->kern_version;
+
+	attr.insn_cnt = (__u32)load_attr->insn_cnt;
 	attr.insns = ptr_to_u64(load_attr->insns);
 	attr.license = ptr_to_u64(load_attr->license);
 
-	attr.log_level = log_level;
-	if (log_level) {
-		attr.log_buf = ptr_to_u64(log_buf);
-		attr.log_size = log_buf_sz;
-	} else {
-		attr.log_buf = ptr_to_u64(NULL);
-		attr.log_size = 0;
+	attr.log_level = load_attr->log_level;
+	if (attr.log_level) {
+		attr.log_buf = ptr_to_u64(load_attr->log_buf);
+		attr.log_size = load_attr->log_buf_sz;
 	}
 
 	attr.prog_btf_fd = load_attr->prog_btf_fd;
+	attr.prog_flags = load_attr->prog_flags;
+
 	attr.func_info_rec_size = load_attr->func_info_rec_size;
 	attr.func_info_cnt = load_attr->func_info_cnt;
 	attr.func_info = ptr_to_u64(load_attr->func_info);
+
 	attr.line_info_rec_size = load_attr->line_info_rec_size;
 	attr.line_info_cnt = load_attr->line_info_cnt;
 	attr.line_info = ptr_to_u64(load_attr->line_info);
+
 	if (load_attr->name)
 		memcpy(attr.prog_name, load_attr->name,
-		       min(strlen(load_attr->name), BPF_OBJ_NAME_LEN - 1));
-	attr.prog_flags = load_attr->prog_flags;
+		       min(strlen(load_attr->name), (size_t)BPF_OBJ_NAME_LEN - 1));
 
 	fd = sys_bpf_prog_load(&attr, sizeof(attr));
 	if (fd >= 0)
@@ -306,19 +303,19 @@ int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
 		}
 
 		fd = sys_bpf_prog_load(&attr, sizeof(attr));
-
 		if (fd >= 0)
 			goto done;
 	}
 
-	if (log_level || !log_buf)
+	if (load_attr->log_level || !load_attr->log_buf)
 		goto done;
 
 	/* Try again with log */
-	attr.log_buf = ptr_to_u64(log_buf);
-	attr.log_size = log_buf_sz;
+	attr.log_buf = ptr_to_u64(load_attr->log_buf);
+	attr.log_size = load_attr->log_buf_sz;
 	attr.log_level = 1;
-	log_buf[0] = 0;
+	load_attr->log_buf[0] = 0;
+
 	fd = sys_bpf_prog_load(&attr, sizeof(attr));
 done:
 	free(finfo);
@@ -326,6 +323,49 @@ done:
 	return fd;
 }
 
+int bpf_load_program_xattr(const struct bpf_load_program_attr *load_attr,
+			   char *log_buf, size_t log_buf_sz)
+{
+	struct bpf_prog_load_params p = {};
+
+	if (!load_attr || !log_buf != !log_buf_sz)
+		return -EINVAL;
+
+	p.prog_type = load_attr->prog_type;
+	p.expected_attach_type = load_attr->expected_attach_type;
+	switch (p.prog_type) {
+	case BPF_PROG_TYPE_STRUCT_OPS:
+	case BPF_PROG_TYPE_LSM:
+		p.attach_btf_id = load_attr->attach_btf_id;
+		break;
+	case BPF_PROG_TYPE_TRACING:
+	case BPF_PROG_TYPE_EXT:
+		p.attach_btf_id = load_attr->attach_btf_id;
+		p.attach_prog_fd = load_attr->attach_prog_fd;
+		break;
+	default:
+		p.prog_ifindex = load_attr->prog_ifindex;
+		p.kern_version = load_attr->kern_version;
+	}
+	p.insn_cnt = load_attr->insns_cnt;
+	p.insns = load_attr->insns;
+	p.license = load_attr->license;
+	p.log_level = load_attr->log_level;
+	p.log_buf = log_buf;
+	p.log_buf_sz = log_buf_sz;
+	p.prog_btf_fd = load_attr->prog_btf_fd;
+	p.func_info_rec_size = load_attr->func_info_rec_size;
+	p.func_info_cnt = load_attr->func_info_cnt;
+	p.func_info = load_attr->func_info;
+	p.line_info_rec_size = load_attr->line_info_rec_size;
+	p.line_info_cnt = load_attr->line_info_cnt;
+	p.line_info = load_attr->line_info;
+	p.name = load_attr->name;
+	p.prog_flags = load_attr->prog_flags;
+
+	return libbpf__bpf_prog_load(&p);
+}
+
 int bpf_load_program(enum bpf_prog_type type, const struct bpf_insn *insns,
 		     size_t insns_cnt, const char *license,
 		     __u32 kern_version, char *log_buf,
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 231b07203e3d..3c3f2bc6c652 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -78,10 +78,32 @@ struct btf {
 	void *types_data;
 	size_t types_data_cap; /* used size stored in hdr->type_len */
 
-	/* type ID to `struct btf_type *` lookup index */
+	/* type ID to `struct btf_type *` lookup index
+	 * type_offs[0] corresponds to the first non-VOID type:
+	 *   - for base BTF it's type [1];
+	 *   - for split BTF it's the first non-base BTF type.
+	 */
 	__u32 *type_offs;
 	size_t type_offs_cap;
+	/* number of types in this BTF instance:
+	 *   - doesn't include special [0] void type;
+	 *   - for split BTF counts number of types added on top of base BTF.
+	 */
 	__u32 nr_types;
+	/* if not NULL, points to the base BTF on top of which the current
+	 * split BTF is based
+	 */
+	struct btf *base_btf;
+	/* BTF type ID of the first type in this BTF instance:
+	 *   - for base BTF it's equal to 1;
+	 *   - for split BTF it's equal to biggest type ID of base BTF plus 1.
+	 */
+	int start_id;
+	/* logical string offset of this BTF instance:
+	 *   - for base BTF it's equal to 0;
+	 *   - for split BTF it's equal to total size of base BTF's string section size.
+	 */
+	int start_str_off;
 
 	void *strs_data;
 	size_t strs_data_cap; /* used size stored in hdr->str_len */
@@ -90,6 +112,14 @@ struct btf {
 	struct hashmap *strs_hash;
 	/* whether strings are already deduplicated */
 	bool strs_deduped;
+	/* extra indirection layer to make strings hashmap work with stable
+	 * string offsets and ability to transparently choose between
+	 * btf->strs_data or btf_dedup->strs_data as a source of strings.
+	 * This is used for BTF strings dedup to transfer deduplicated strings
+	 * data back to struct btf without re-building strings index.
+	 */
+	void **strs_data_ptr;
+
 	/* BTF object FD, if loaded into kernel */
 	int fd;
 
@@ -168,7 +198,7 @@ static int btf_add_type_idx_entry(struct btf *btf, __u32 type_off)
 	__u32 *p;
 
 	p = btf_add_mem((void **)&btf->type_offs, &btf->type_offs_cap, sizeof(__u32),
-			btf->nr_types + 1, BTF_MAX_NR_TYPES, 1);
+			btf->nr_types, BTF_MAX_NR_TYPES, 1);
 	if (!p)
 		return -ENOMEM;
 
@@ -215,22 +245,18 @@ static int btf_parse_hdr(struct btf *btf)
 		return -EINVAL;
 	}
 
-	if (meta_left < hdr->type_off) {
-		pr_debug("Invalid BTF type section offset:%u\n", hdr->type_off);
+	if (meta_left < hdr->str_off + hdr->str_len) {
+		pr_debug("Invalid BTF total size:%u\n", btf->raw_size);
 		return -EINVAL;
 	}
 
-	if (meta_left < hdr->str_off) {
-		pr_debug("Invalid BTF string section offset:%u\n", hdr->str_off);
+	if (hdr->type_off + hdr->type_len > hdr->str_off) {
+		pr_debug("Invalid BTF data sections layout: type data at %u + %u, strings data at %u + %u\n",
+			 hdr->type_off, hdr->type_len, hdr->str_off, hdr->str_len);
 		return -EINVAL;
 	}
 
-	if (hdr->type_off >= hdr->str_off) {
-		pr_debug("BTF type section offset >= string section offset. No type?\n");
-		return -EINVAL;
-	}
-
-	if (hdr->type_off & 0x02) {
+	if (hdr->type_off % 4) {
 		pr_debug("BTF type section is not aligned to 4 bytes\n");
 		return -EINVAL;
 	}
@@ -244,12 +270,16 @@ static int btf_parse_str_sec(struct btf *btf)
 	const char *start = btf->strs_data;
 	const char *end = start + btf->hdr->str_len;
 
-	if (!hdr->str_len || hdr->str_len - 1 > BTF_MAX_STR_OFFSET ||
-	    start[0] || end[-1]) {
+	if (btf->base_btf && hdr->str_len == 0)
+		return 0;
+	if (!hdr->str_len || hdr->str_len - 1 > BTF_MAX_STR_OFFSET || end[-1]) {
+		pr_debug("Invalid BTF string section\n");
+		return -EINVAL;
+	}
+	if (!btf->base_btf && start[0]) {
 		pr_debug("Invalid BTF string section\n");
 		return -EINVAL;
 	}
-
 	return 0;
 }
 
@@ -364,19 +394,9 @@ static int btf_parse_type_sec(struct btf *btf)
 	struct btf_header *hdr = btf->hdr;
 	void *next_type = btf->types_data;
 	void *end_type = next_type + hdr->type_len;
-	int err, i = 0, type_size;
-
-	/* VOID (type_id == 0) is specially handled by btf__get_type_by_id(),
-	 * so ensure we can never properly use its offset from index by
-	 * setting it to a large value
-	 */
-	err = btf_add_type_idx_entry(btf, UINT_MAX);
-	if (err)
-		return err;
+	int err, type_size;
 
 	while (next_type + sizeof(struct btf_type) <= end_type) {
-		i++;
-
 		if (btf->swapped_endian)
 			btf_bswap_type_base(next_type);
 
@@ -384,7 +404,7 @@ static int btf_parse_type_sec(struct btf *btf)
 		if (type_size < 0)
 			return type_size;
 		if (next_type + type_size > end_type) {
-			pr_warn("BTF type [%d] is malformed\n", i);
+			pr_warn("BTF type [%d] is malformed\n", btf->start_id + btf->nr_types);
 			return -EINVAL;
 		}
 
@@ -409,7 +429,12 @@ static int btf_parse_type_sec(struct btf *btf)
 
 __u32 btf__get_nr_types(const struct btf *btf)
 {
-	return btf->nr_types;
+	return btf->start_id + btf->nr_types - 1;
+}
+
+const struct btf *btf__base_btf(const struct btf *btf)
+{
+	return btf->base_btf;
 }
 
 /* internal helper returning non-const pointer to a type */
@@ -417,13 +442,14 @@ static struct btf_type *btf_type_by_id(struct btf *btf, __u32 type_id)
 {
 	if (type_id == 0)
 		return &btf_void;
-
-	return btf->types_data + btf->type_offs[type_id];
+	if (type_id < btf->start_id)
+		return btf_type_by_id(btf->base_btf, type_id);
+	return btf->types_data + btf->type_offs[type_id - btf->start_id];
 }
 
 const struct btf_type *btf__type_by_id(const struct btf *btf, __u32 type_id)
 {
-	if (type_id > btf->nr_types)
+	if (type_id >= btf->start_id + btf->nr_types)
 		return NULL;
 	return btf_type_by_id((struct btf *)btf, type_id);
 }
@@ -432,9 +458,13 @@ static int determine_ptr_size(const struct btf *btf)
 {
 	const struct btf_type *t;
 	const char *name;
-	int i;
+	int i, n;
 
-	for (i = 1; i <= btf->nr_types; i++) {
+	if (btf->base_btf && btf->base_btf->ptr_sz > 0)
+		return btf->base_btf->ptr_sz;
+
+	n = btf__get_nr_types(btf);
+	for (i = 1; i <= n; i++) {
 		t = btf__type_by_id(btf, i);
 		if (!btf_is_int(t))
 			continue;
@@ -649,12 +679,12 @@ int btf__resolve_type(const struct btf *btf, __u32 type_id)
 
 __s32 btf__find_by_name(const struct btf *btf, const char *type_name)
 {
-	__u32 i;
+	__u32 i, nr_types = btf__get_nr_types(btf);
 
 	if (!strcmp(type_name, "void"))
 		return 0;
 
-	for (i = 1; i <= btf->nr_types; i++) {
+	for (i = 1; i <= nr_types; i++) {
 		const struct btf_type *t = btf__type_by_id(btf, i);
 		const char *name = btf__name_by_offset(btf, t->name_off);
 
@@ -668,12 +698,12 @@ __s32 btf__find_by_name(const struct btf *btf, const char *type_name)
 __s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
 			     __u32 kind)
 {
-	__u32 i;
+	__u32 i, nr_types = btf__get_nr_types(btf);
 
 	if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
 		return 0;
 
-	for (i = 1; i <= btf->nr_types; i++) {
+	for (i = 1; i <= nr_types; i++) {
 		const struct btf_type *t = btf__type_by_id(btf, i);
 		const char *name;
 
@@ -717,7 +747,7 @@ void btf__free(struct btf *btf)
 	free(btf);
 }
 
-struct btf *btf__new_empty(void)
+static struct btf *btf_new_empty(struct btf *base_btf)
 {
 	struct btf *btf;
 
@@ -725,12 +755,21 @@ struct btf *btf__new_empty(void)
 	if (!btf)
 		return ERR_PTR(-ENOMEM);
 
+	btf->nr_types = 0;
+	btf->start_id = 1;
+	btf->start_str_off = 0;
 	btf->fd = -1;
 	btf->ptr_sz = sizeof(void *);
 	btf->swapped_endian = false;
 
+	if (base_btf) {
+		btf->base_btf = base_btf;
+		btf->start_id = btf__get_nr_types(base_btf) + 1;
+		btf->start_str_off = base_btf->hdr->str_len;
+	}
+
 	/* +1 for empty string at offset 0 */
-	btf->raw_size = sizeof(struct btf_header) + 1;
+	btf->raw_size = sizeof(struct btf_header) + (base_btf ? 0 : 1);
 	btf->raw_data = calloc(1, btf->raw_size);
 	if (!btf->raw_data) {
 		free(btf);
@@ -744,12 +783,22 @@ struct btf *btf__new_empty(void)
 
 	btf->types_data = btf->raw_data + btf->hdr->hdr_len;
 	btf->strs_data = btf->raw_data + btf->hdr->hdr_len;
-	btf->hdr->str_len = 1; /* empty string at offset 0 */
+	btf->hdr->str_len = base_btf ? 0 : 1; /* empty string at offset 0 */
 
 	return btf;
 }
 
-struct btf *btf__new(const void *data, __u32 size)
+struct btf *btf__new_empty(void)
+{
+	return btf_new_empty(NULL);
+}
+
+struct btf *btf__new_empty_split(struct btf *base_btf)
+{
+	return btf_new_empty(base_btf);
+}
+
+static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
 {
 	struct btf *btf;
 	int err;
@@ -758,6 +807,16 @@ struct btf *btf__new(const void *data, __u32 size)
 	if (!btf)
 		return ERR_PTR(-ENOMEM);
 
+	btf->nr_types = 0;
+	btf->start_id = 1;
+	btf->start_str_off = 0;
+
+	if (base_btf) {
+		btf->base_btf = base_btf;
+		btf->start_id = btf__get_nr_types(base_btf) + 1;
+		btf->start_str_off = base_btf->hdr->str_len;
+	}
+
 	btf->raw_data = malloc(size);
 	if (!btf->raw_data) {
 		err = -ENOMEM;
@@ -790,7 +849,13 @@ done:
 	return btf;
 }
 
-struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)
+struct btf *btf__new(const void *data, __u32 size)
+{
+	return btf_new(data, size, NULL);
+}
+
+static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
+				 struct btf_ext **btf_ext)
 {
 	Elf_Data *btf_data = NULL, *btf_ext_data = NULL;
 	int err = 0, fd = -1, idx = 0;
@@ -868,7 +933,7 @@ struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)
 		err = -ENOENT;
 		goto done;
 	}
-	btf = btf__new(btf_data->d_buf, btf_data->d_size);
+	btf = btf_new(btf_data->d_buf, btf_data->d_size, base_btf);
 	if (IS_ERR(btf))
 		goto done;
 
@@ -913,7 +978,17 @@ done:
 	return btf;
 }
 
-struct btf *btf__parse_raw(const char *path)
+struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)
+{
+	return btf_parse_elf(path, NULL, btf_ext);
+}
+
+struct btf *btf__parse_elf_split(const char *path, struct btf *base_btf)
+{
+	return btf_parse_elf(path, base_btf, NULL);
+}
+
+static struct btf *btf_parse_raw(const char *path, struct btf *base_btf)
 {
 	struct btf *btf = NULL;
 	void *data = NULL;
@@ -967,7 +1042,7 @@ struct btf *btf__parse_raw(const char *path)
 	}
 
 	/* finally parse BTF data */
-	btf = btf__new(data, sz);
+	btf = btf_new(data, sz, base_btf);
 
 err_out:
 	free(data);
@@ -976,18 +1051,38 @@ err_out:
 	return err ? ERR_PTR(err) : btf;
 }
 
-struct btf *btf__parse(const char *path, struct btf_ext **btf_ext)
+struct btf *btf__parse_raw(const char *path)
+{
+	return btf_parse_raw(path, NULL);
+}
+
+struct btf *btf__parse_raw_split(const char *path, struct btf *base_btf)
+{
+	return btf_parse_raw(path, base_btf);
+}
+
+static struct btf *btf_parse(const char *path, struct btf *base_btf, struct btf_ext **btf_ext)
 {
 	struct btf *btf;
 
 	if (btf_ext)
 		*btf_ext = NULL;
 
-	btf = btf__parse_raw(path);
+	btf = btf_parse_raw(path, base_btf);
 	if (!IS_ERR(btf) || PTR_ERR(btf) != -EPROTO)
 		return btf;
 
-	return btf__parse_elf(path, btf_ext);
+	return btf_parse_elf(path, base_btf, btf_ext);
+}
+
+struct btf *btf__parse(const char *path, struct btf_ext **btf_ext)
+{
+	return btf_parse(path, NULL, btf_ext);
+}
+
+struct btf *btf__parse_split(const char *path, struct btf *base_btf)
+{
+	return btf_parse(path, base_btf, NULL);
 }
 
 static int compare_vsi_off(const void *_a, const void *_b)
@@ -1171,8 +1266,8 @@ static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endi
 
 	memcpy(p, btf->types_data, hdr->type_len);
 	if (swap_endian) {
-		for (i = 1; i <= btf->nr_types; i++) {
-			t = p  + btf->type_offs[i];
+		for (i = 0; i < btf->nr_types; i++) {
+			t = p + btf->type_offs[i];
 			/* btf_bswap_type_rest() relies on native t->info, so
 			 * we swap base type info after we swapped all the
 			 * additional information
@@ -1215,8 +1310,10 @@ const void *btf__get_raw_data(const struct btf *btf_ro, __u32 *size)
 
 const char *btf__str_by_offset(const struct btf *btf, __u32 offset)
 {
-	if (offset < btf->hdr->str_len)
-		return btf->strs_data + offset;
+	if (offset < btf->start_str_off)
+		return btf__str_by_offset(btf->base_btf, offset);
+	else if (offset - btf->start_str_off < btf->hdr->str_len)
+		return btf->strs_data + (offset - btf->start_str_off);
 	else
 		return NULL;
 }
@@ -1226,35 +1323,27 @@ const char *btf__name_by_offset(const struct btf *btf, __u32 offset)
 	return btf__str_by_offset(btf, offset);
 }
 
-int btf__get_from_id(__u32 id, struct btf **btf)
+struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
 {
-	struct bpf_btf_info btf_info = { 0 };
+	struct bpf_btf_info btf_info;
 	__u32 len = sizeof(btf_info);
 	__u32 last_size;
-	int btf_fd;
+	struct btf *btf;
 	void *ptr;
 	int err;
 
-	err = 0;
-	*btf = NULL;
-	btf_fd = bpf_btf_get_fd_by_id(id);
-	if (btf_fd < 0)
-		return 0;
-
 	/* we won't know btf_size until we call bpf_obj_get_info_by_fd(). so
 	 * let's start with a sane default - 4KiB here - and resize it only if
 	 * bpf_obj_get_info_by_fd() needs a bigger buffer.
 	 */
-	btf_info.btf_size = 4096;
-	last_size = btf_info.btf_size;
+	last_size = 4096;
 	ptr = malloc(last_size);
-	if (!ptr) {
-		err = -ENOMEM;
-		goto exit_free;
-	}
+	if (!ptr)
+		return ERR_PTR(-ENOMEM);
 
-	memset(ptr, 0, last_size);
+	memset(&btf_info, 0, sizeof(btf_info));
 	btf_info.btf = ptr_to_u64(ptr);
+	btf_info.btf_size = last_size;
 	err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
 
 	if (!err && btf_info.btf_size > last_size) {
@@ -1263,31 +1352,48 @@ int btf__get_from_id(__u32 id, struct btf **btf)
 		last_size = btf_info.btf_size;
 		temp_ptr = realloc(ptr, last_size);
 		if (!temp_ptr) {
-			err = -ENOMEM;
+			btf = ERR_PTR(-ENOMEM);
 			goto exit_free;
 		}
 		ptr = temp_ptr;
-		memset(ptr, 0, last_size);
+
+		len = sizeof(btf_info);
+		memset(&btf_info, 0, sizeof(btf_info));
 		btf_info.btf = ptr_to_u64(ptr);
+		btf_info.btf_size = last_size;
+
 		err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
 	}
 
 	if (err || btf_info.btf_size > last_size) {
-		err = errno;
+		btf = err ? ERR_PTR(-errno) : ERR_PTR(-E2BIG);
 		goto exit_free;
 	}
 
-	*btf = btf__new((__u8 *)(long)btf_info.btf, btf_info.btf_size);
-	if (IS_ERR(*btf)) {
-		err = PTR_ERR(*btf);
-		*btf = NULL;
-	}
+	btf = btf_new(ptr, btf_info.btf_size, base_btf);
 
 exit_free:
-	close(btf_fd);
 	free(ptr);
+	return btf;
+}
 
-	return err;
+int btf__get_from_id(__u32 id, struct btf **btf)
+{
+	struct btf *res;
+	int btf_fd;
+
+	*btf = NULL;
+	btf_fd = bpf_btf_get_fd_by_id(id);
+	if (btf_fd < 0)
+		return -errno;
+
+	res = btf_get_from_fd(btf_fd, NULL);
+	close(btf_fd);
+	if (IS_ERR(res))
+		return PTR_ERR(res);
+
+	*btf = res;
+	return 0;
 }
 
 int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
@@ -1363,17 +1469,19 @@ int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
 
 static size_t strs_hash_fn(const void *key, void *ctx)
 {
-	struct btf *btf = ctx;
-	const char *str = btf->strs_data + (long)key;
+	const struct btf *btf = ctx;
+	const char *strs = *btf->strs_data_ptr;
+	const char *str = strs + (long)key;
 
 	return str_hash(str);
 }
 
 static bool strs_hash_equal_fn(const void *key1, const void *key2, void *ctx)
 {
-	struct btf *btf = ctx;
-	const char *str1 = btf->strs_data + (long)key1;
-	const char *str2 = btf->strs_data + (long)key2;
+	const struct btf *btf = ctx;
+	const char *strs = *btf->strs_data_ptr;
+	const char *str1 = strs + (long)key1;
+	const char *str2 = strs + (long)key2;
 
 	return strcmp(str1, str2) == 0;
 }
@@ -1418,6 +1526,9 @@ static int btf_ensure_modifiable(struct btf *btf)
 	memcpy(types, btf->types_data, btf->hdr->type_len);
 	memcpy(strs, btf->strs_data, btf->hdr->str_len);
 
+	/* make hashmap below use btf->strs_data as a source of strings */
+	btf->strs_data_ptr = &btf->strs_data;
+
 	/* build lookup index for all strings */
 	hash = hashmap__new(strs_hash_fn, strs_hash_equal_fn, btf);
 	if (IS_ERR(hash)) {
@@ -1448,7 +1559,10 @@ static int btf_ensure_modifiable(struct btf *btf)
 	/* if BTF was created from scratch, all strings are guaranteed to be
 	 * unique and deduplicated
 	 */
-	btf->strs_deduped = btf->hdr->str_len <= 1;
+	if (btf->hdr->str_len == 0)
+		btf->strs_deduped = true;
+	if (!btf->base_btf && btf->hdr->str_len == 1)
+		btf->strs_deduped = true;
 
 	/* invalidate raw_data representation */
 	btf_invalidate_raw_data(btf);
@@ -1480,6 +1594,14 @@ int btf__find_str(struct btf *btf, const char *s)
 	long old_off, new_off, len;
 	void *p;
 
+	if (btf->base_btf) {
+		int ret;
+
+		ret = btf__find_str(btf->base_btf, s);
+		if (ret != -ENOENT)
+			return ret;
+	}
+
 	/* BTF needs to be in a modifiable state to build string lookup index */
 	if (btf_ensure_modifiable(btf))
 		return -ENOMEM;
@@ -1494,7 +1616,7 @@ int btf__find_str(struct btf *btf, const char *s)
 	memcpy(p, s, len);
 
 	if (hashmap__find(btf->strs_hash, (void *)new_off, (void **)&old_off))
-		return old_off;
+		return btf->start_str_off + old_off;
 
 	return -ENOENT;
 }
@@ -1510,6 +1632,14 @@ int btf__add_str(struct btf *btf, const char *s)
 	void *p;
 	int err;
 
+	if (btf->base_btf) {
+		int ret;
+
+		ret = btf__find_str(btf->base_btf, s);
+		if (ret != -ENOENT)
+			return ret;
+	}
+
 	if (btf_ensure_modifiable(btf))
 		return -ENOMEM;
 
@@ -1536,12 +1666,12 @@ int btf__add_str(struct btf *btf, const char *s)
 	err = hashmap__insert(btf->strs_hash, (void *)new_off, (void *)new_off,
 			      HASHMAP_ADD, (const void **)&old_off, NULL);
 	if (err == -EEXIST)
-		return old_off; /* duplicated string, return existing offset */
+		return btf->start_str_off + old_off; /* duplicated string, return existing offset */
 	if (err)
 		return err;
 
 	btf->hdr->str_len += len; /* new unique string, adjust data length */
-	return new_off;
+	return btf->start_str_off + new_off;
 }
 
 static void *btf_add_type_mem(struct btf *btf, size_t add_sz)
@@ -1560,6 +1690,20 @@ static void btf_type_inc_vlen(struct btf_type *t)
 	t->info = btf_type_info(btf_kind(t), btf_vlen(t) + 1, btf_kflag(t));
 }
 
+static int btf_commit_type(struct btf *btf, int data_sz)
+{
+	int err;
+
+	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
+	if (err)
+		return err;
+
+	btf->hdr->type_len += data_sz;
+	btf->hdr->str_off += data_sz;
+	btf->nr_types++;
+	return btf->start_id + btf->nr_types - 1;
+}
+
 /*
  * Append new BTF_KIND_INT type with:
  *   - *name* - non-empty, non-NULL type name;
@@ -1572,7 +1716,7 @@ static void btf_type_inc_vlen(struct btf_type *t)
 int btf__add_int(struct btf *btf, const char *name, size_t byte_sz, int encoding)
 {
 	struct btf_type *t;
-	int sz, err, name_off;
+	int sz, name_off;
 
 	/* non-empty name */
 	if (!name || !name[0])
@@ -1606,14 +1750,7 @@ int btf__add_int(struct btf *btf, const char *name, size_t byte_sz, int encoding
 	/* set INT info, we don't allow setting legacy bit offset/size */
 	*(__u32 *)(t + 1) = (encoding << 24) | (byte_sz * 8);
 
-	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
-	if (err)
-		return err;
-
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
-	btf->nr_types++;
-	return btf->nr_types;
+	return btf_commit_type(btf, sz);
 }
 
 /* it's completely legal to append BTF types with type IDs pointing forward to
@@ -1631,7 +1768,7 @@ static int validate_type_id(int id)
 static int btf_add_ref_kind(struct btf *btf, int kind, const char *name, int ref_type_id)
 {
 	struct btf_type *t;
-	int sz, name_off = 0, err;
+	int sz, name_off = 0;
 
 	if (validate_type_id(ref_type_id))
 		return -EINVAL;
@@ -1654,14 +1791,7 @@ static int btf_add_ref_kind(struct btf *btf, int kind, const char *name, int ref
 	t->info = btf_type_info(kind, 0, 0);
 	t->type = ref_type_id;
 
-	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
-	if (err)
-		return err;
-
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
-	btf->nr_types++;
-	return btf->nr_types;
+	return btf_commit_type(btf, sz);
 }
 
 /*
@@ -1689,7 +1819,7 @@ int btf__add_array(struct btf *btf, int index_type_id, int elem_type_id, __u32 n
 {
 	struct btf_type *t;
 	struct btf_array *a;
-	int sz, err;
+	int sz;
 
 	if (validate_type_id(index_type_id) || validate_type_id(elem_type_id))
 		return -EINVAL;
@@ -1711,21 +1841,14 @@ int btf__add_array(struct btf *btf, int index_type_id, int elem_type_id, __u32 n
 	a->index_type = index_type_id;
 	a->nelems = nr_elems;
 
-	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
-	if (err)
-		return err;
-
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
-	btf->nr_types++;
-	return btf->nr_types;
+	return btf_commit_type(btf, sz);
 }
 
 /* generic STRUCT/UNION append function */
 static int btf_add_composite(struct btf *btf, int kind, const char *name, __u32 bytes_sz)
 {
 	struct btf_type *t;
-	int sz, err, name_off = 0;
+	int sz, name_off = 0;
 
 	if (btf_ensure_modifiable(btf))
 		return -ENOMEM;
@@ -1748,14 +1871,7 @@ static int btf_add_composite(struct btf *btf, int kind, const char *name, __u32
 	t->info = btf_type_info(kind, 0, 0);
 	t->size = bytes_sz;
 
-	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
-	if (err)
-		return err;
-
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
-	btf->nr_types++;
-	return btf->nr_types;
+	return btf_commit_type(btf, sz);
 }
 
 /*
@@ -1793,6 +1909,11 @@ int btf__add_union(struct btf *btf, const char *name, __u32 byte_sz)
 	return btf_add_composite(btf, BTF_KIND_UNION, name, byte_sz);
 }
 
+static struct btf_type *btf_last_type(struct btf *btf)
+{
+	return btf_type_by_id(btf, btf__get_nr_types(btf));
+}
+
 /*
  * Append new field for the current STRUCT/UNION type with:
  *   - *name* - name of the field, can be NULL or empty for anonymous field;
@@ -1814,7 +1935,7 @@ int btf__add_field(struct btf *btf, const char *name, int type_id,
 	/* last type should be union/struct */
 	if (btf->nr_types == 0)
 		return -EINVAL;
-	t = btf_type_by_id(btf, btf->nr_types);
+	t = btf_last_type(btf);
 	if (!btf_is_composite(t))
 		return -EINVAL;
 
@@ -1849,7 +1970,7 @@ int btf__add_field(struct btf *btf, const char *name, int type_id,
 	m->offset = bit_offset | (bit_size << 24);
 
 	/* btf_add_type_mem can invalidate t pointer */
-	t = btf_type_by_id(btf, btf->nr_types);
+	t = btf_last_type(btf);
 	/* update parent type's vlen and kflag */
 	t->info = btf_type_info(btf_kind(t), btf_vlen(t) + 1, is_bitfield || btf_kflag(t));
 
@@ -1874,7 +1995,7 @@ int btf__add_field(struct btf *btf, const char *name, int type_id,
 int btf__add_enum(struct btf *btf, const char *name, __u32 byte_sz)
 {
 	struct btf_type *t;
-	int sz, err, name_off = 0;
+	int sz, name_off = 0;
 
 	/* byte_sz must be power of 2 */
 	if (!byte_sz || (byte_sz & (byte_sz - 1)) || byte_sz > 8)
@@ -1899,14 +2020,7 @@ int btf__add_enum(struct btf *btf, const char *name, __u32 byte_sz)
 	t->info = btf_type_info(BTF_KIND_ENUM, 0, 0);
 	t->size = byte_sz;
 
-	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
-	if (err)
-		return err;
-
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
-	btf->nr_types++;
-	return btf->nr_types;
+	return btf_commit_type(btf, sz);
 }
 
 /*
@@ -1926,7 +2040,7 @@ int btf__add_enum_value(struct btf *btf, const char *name, __s64 value)
 	/* last type should be BTF_KIND_ENUM */
 	if (btf->nr_types == 0)
 		return -EINVAL;
-	t = btf_type_by_id(btf, btf->nr_types);
+	t = btf_last_type(btf);
 	if (!btf_is_enum(t))
 		return -EINVAL;
 
@@ -1953,7 +2067,7 @@ int btf__add_enum_value(struct btf *btf, const char *name, __s64 value)
 	v->val = value;
 
 	/* update parent type's vlen */
-	t = btf_type_by_id(btf, btf->nr_types);
+	t = btf_last_type(btf);
 	btf_type_inc_vlen(t);
 
 	btf->hdr->type_len += sz;
@@ -2093,7 +2207,7 @@ int btf__add_func(struct btf *btf, const char *name,
 int btf__add_func_proto(struct btf *btf, int ret_type_id)
 {
 	struct btf_type *t;
-	int sz, err;
+	int sz;
 
 	if (validate_type_id(ret_type_id))
 		return -EINVAL;
@@ -2113,14 +2227,7 @@ int btf__add_func_proto(struct btf *btf, int ret_type_id)
 	t->info = btf_type_info(BTF_KIND_FUNC_PROTO, 0, 0);
 	t->type = ret_type_id;
 
-	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
-	if (err)
-		return err;
-
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
-	btf->nr_types++;
-	return btf->nr_types;
+	return btf_commit_type(btf, sz);
 }
 
 /*
@@ -2143,7 +2250,7 @@ int btf__add_func_param(struct btf *btf, const char *name, int type_id)
 	/* last type should be BTF_KIND_FUNC_PROTO */
 	if (btf->nr_types == 0)
 		return -EINVAL;
-	t = btf_type_by_id(btf, btf->nr_types);
+	t = btf_last_type(btf);
 	if (!btf_is_func_proto(t))
 		return -EINVAL;
 
@@ -2166,7 +2273,7 @@ int btf__add_func_param(struct btf *btf, const char *name, int type_id)
 	p->type = type_id;
 
 	/* update parent type's vlen */
-	t = btf_type_by_id(btf, btf->nr_types);
+	t = btf_last_type(btf);
 	btf_type_inc_vlen(t);
 
 	btf->hdr->type_len += sz;
@@ -2188,7 +2295,7 @@ int btf__add_var(struct btf *btf, const char *name, int linkage, int type_id)
 {
 	struct btf_type *t;
 	struct btf_var *v;
-	int sz, err, name_off;
+	int sz, name_off;
 
 	/* non-empty name */
 	if (!name || !name[0])
@@ -2219,14 +2326,7 @@ int btf__add_var(struct btf *btf, const char *name, int linkage, int type_id)
 	v = btf_var(t);
 	v->linkage = linkage;
 
-	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
-	if (err)
-		return err;
-
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
-	btf->nr_types++;
-	return btf->nr_types;
+	return btf_commit_type(btf, sz);
 }
 
 /*
@@ -2244,7 +2344,7 @@ int btf__add_var(struct btf *btf, const char *name, int linkage, int type_id)
 int btf__add_datasec(struct btf *btf, const char *name, __u32 byte_sz)
 {
 	struct btf_type *t;
-	int sz, err, name_off;
+	int sz, name_off;
 
 	/* non-empty name */
 	if (!name || !name[0])
@@ -2267,14 +2367,7 @@ int btf__add_datasec(struct btf *btf, const char *name, __u32 byte_sz)
 	t->info = btf_type_info(BTF_KIND_DATASEC, 0, 0);
 	t->size = byte_sz;
 
-	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
-	if (err)
-		return err;
-
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
-	btf->nr_types++;
-