BTF kind layouts provide information to parse BTF kinds. By separating
parsing BTF from using all the information it provides, we allow BTF
to encode new features even if they cannot be used by readers. This
will be helpful in particular for cases where older tools are used
to parse newer BTF with kinds the older tools do not recognize;
the BTF can still be parsed in such cases using kind layout.

The intent is to support encoding of kind layouts optionally so that
tools like pahole can add this information. For each kind, we record

- length of singular element following struct btf_type
- length of each of the btf_vlen() elements following
- a (currently unused) flags field

The ideas here were discussed at [1], [2]; hence

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

[1] https://lore.kernel.org/bpf/CAEf4BzYjWHRdNNw4B=eOXOs_ONrDwrgX4bn=Nuc1g8JPFC34MA@mail.gmail.com/
[2] https://lore.kernel.org/bpf/20230531201936.1992188-1-alan.maguire@oracle.com/
---
 include/uapi/linux/btf.h       | 12 ++++++++++++
 tools/include/uapi/linux/btf.h | 12 ++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h
index 266d4ffa6c07..638615ebddc2 100644
--- a/include/uapi/linux/btf.h
+++ b/include/uapi/linux/btf.h
@@ -8,6 +8,16 @@
 #define BTF_MAGIC	0xeB9F
 #define BTF_VERSION	1
 
+/*
+ * BTF layout section consists of a struct btf_layout for each known
+ * kind at BTF encoding time.
+ */
+struct btf_layout {
+	__u8 info_sz;		/* size of singular element after btf_type */
+	__u8 elem_sz;		/* size of each of btf_vlen(t) elements */
+	__u16 flags;		/* currently unused */
+};
+
 struct btf_header {
 	__u16	magic;
 	__u8	version;
@@ -19,6 +29,8 @@ struct btf_header {
 	__u32	type_len;	/* length of type section	*/
 	__u32	str_off;	/* offset of string section	*/
 	__u32	str_len;	/* length of string section	*/
+	__u32	layout_off;	/* offset of layout section	*/
+	__u32	layout_len;	/* length of layout section	*/
 };
 
 /* Max # of type identifier */
diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
index 266d4ffa6c07..638615ebddc2 100644
--- a/tools/include/uapi/linux/btf.h
+++ b/tools/include/uapi/linux/btf.h
@@ -8,6 +8,16 @@
 #define BTF_MAGIC	0xeB9F
 #define BTF_VERSION	1
 
+/*
+ * BTF layout section consists of a struct btf_layout for each known
+ * kind at BTF encoding time.
+ */
+struct btf_layout {
+	__u8 info_sz;		/* size of singular element after btf_type */
+	__u8 elem_sz;		/* size of each of btf_vlen(t) elements */
+	__u16 flags;		/* currently unused */
+};
+
 struct btf_header {
 	__u16	magic;
 	__u8	version;
@@ -19,6 +29,8 @@ struct btf_header {
 	__u32	type_len;	/* length of type section	*/
 	__u32	str_off;	/* offset of string section	*/
 	__u32	str_len;	/* length of string section	*/
+	__u32	layout_off;	/* offset of layout section	*/
+	__u32	layout_len;	/* length of layout section	*/
 };
 
 /* Max # of type identifier */
-- 
2.39.3

Support reading in layout fixing endian issues on reading;
also support writing layout section to raw BTF object.
There is not yet an API to populate the layout with meaningful
information.

As part of this, we need to consider multiple valid BTF header
sizes; the original or the layout-extended headers.
So to support this, the "struct btf" representation is modified
to contain a "struct btf_header" and we copy the valid
portion from the raw data to it; this means we can always safely
check fields like btf->hdr.layout_len

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/btf.c | 304 ++++++++++++++++++++++++++++----------------
 1 file changed, 197 insertions(+), 107 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 83fe79ffcb8f..3438cc15bb7a 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -40,42 +40,53 @@ struct btf {
 
 	/*
 	 * When BTF is loaded from an ELF or raw memory it is stored
-	 * in a contiguous memory block. The hdr, type_data, and, strs_data
+	 * in a contiguous memory block. The type_data, layout and strs_data
 	 * point inside that memory region to their respective parts of BTF
 	 * representation:
 	 *
-	 * +--------------------------------+
-	 * |  Header  |  Types  |  Strings  |
-	 * +--------------------------------+
-	 * ^          ^         ^
-	 * |          |         |
-	 * hdr        |         |
-	 * types_data-+         |
-	 * strs_data------------+
+	 * +----------------------------------------+---------------+
+	 * |  Header  |  Types  |  Optional layout  |  Strings      |
+	 * +--------------------------------------------------------+
+	 * ^          ^         ^                   ^
+	 * |          |         |                   |
+	 * raw_data   |         |                   |
+	 * types_data-+         |                   |
+	 * layout---------------+                   |
+	 * strs_data--------------------------------+
+	 *
+	 * A separate struct btf_header is embedded as btf->hdr,
+	 * and header information is copied into it.  This allows us
+	 * to handle header data for various header formats; the original,
+	 * the extended header with layout info, etc.
 	 *
 	 * If BTF data is later modified, e.g., due to types added or
 	 * removed, BTF deduplication performed, etc, this contiguous
-	 * representation is broken up into three independently allocated
-	 * memory regions to be able to modify them independently.
+	 * representation is broken up into four independent memory
+	 * regions.
+	 *
 	 * raw_data is nulled out at that point, but can be later allocated
 	 * and cached again if user calls btf__raw_data(), at which point
-	 * raw_data will contain a contiguous copy of header, types, and
-	 * strings:
+	 * raw_data will contain a contiguous copy of header, types, optional
+	 * layout and strings.  layout optionally points to a
+	 * btf_layout array - this allows us to encode information about
+	 * the kinds known at encoding time.  If layout is NULL no
+	 * layout information is encoded.
 	 *
-	 * +----------+  +---------+  +-----------+
-	 * |  Header  |  |  Types  |  |  Strings  |
-	 * +----------+  +---------+  +-----------+
-	 * ^             ^            ^
-	 * |             |            |
-	 * hdr           |            |
-	 * types_data----+            |
-	 * strset__data(strs_set)-----+
+	 * +----------+  +---------+  +-----------+   +-----------+
+	 * |  Header  |  |  Types  |  |  Layout   |   |  Strings  |
+	 * +----------+  +---------+  +-----------+   +-----------+
+	 * ^             ^            ^               ^
+	 * |             |            |               |
+	 * hdr           |            |               |
+	 * types_data----+            |               |
+	 * layout---------------------+               |
+	 * strset__data(strs_set)---------------------+
 	 *
-	 *               +----------+---------+-----------+
-	 *               |  Header  |  Types  |  Strings  |
-	 * raw_data----->+----------+---------+-----------+
+	 *               +----------+---------+-------------------+-----------+
+	 *               |  Header  |  Types  |  Optional Layout  |  Strings  |
+	 * raw_data----->+----------+---------+-------------------+-----------+
 	 */
-	struct btf_header *hdr;
+	struct btf_header hdr;
 
 	void *types_data;
 	size_t types_data_cap; /* used size stored in hdr->type_len */
@@ -125,6 +136,13 @@ struct btf {
 	/* whether raw_data is a (read-only) mmap */
 	bool raw_data_is_mmap;
 
+	/* is BTF modifiable? i.e. is it split into separate sections as described above? */
+	bool modifiable;
+	/* Points either at raw kind layout data in parsed BTF (if present), or
+	 * at an allocated kind layout array when BTF is modifiable.
+	 */
+	void *layout;
+
 	/* BTF object FD, if loaded into kernel */
 	int fd;
 
@@ -216,7 +234,7 @@ static int btf_add_type_idx_entry(struct btf *btf, __u32 type_off)
 	return 0;
 }
 
-static void btf_bswap_hdr(struct btf_header *h)
+static void btf_bswap_hdr(struct btf_header *h, __u32 hdr_len)
 {
 	h->magic = bswap_16(h->magic);
 	h->hdr_len = bswap_32(h->hdr_len);
@@ -224,66 +242,95 @@ static void btf_bswap_hdr(struct btf_header *h)
 	h->type_len = bswap_32(h->type_len);
 	h->str_off = bswap_32(h->str_off);
 	h->str_len = bswap_32(h->str_len);
+	/* May be operating on raw data with hdr_len that does not include below fields */
+	if (hdr_len >= sizeof(struct btf_header)) {
+		h->layout_off = bswap_32(h->layout_off);
+		h->layout_len = bswap_32(h->layout_len);
+	}
 }
 
 static int btf_parse_hdr(struct btf *btf)
 {
-	struct btf_header *hdr = btf->hdr;
+	struct btf_header *hdr = btf->raw_data;
+	__u32 hdr_len = hdr->hdr_len;
 	__u32 meta_left;
 
-	if (btf->raw_size < sizeof(struct btf_header)) {
+	if (btf->raw_size < offsetofend(struct btf_header, str_len)) {
 		pr_debug("BTF header not found\n");
 		return -EINVAL;
 	}
 
 	if (hdr->magic == bswap_16(BTF_MAGIC)) {
 		btf->swapped_endian = true;
-		if (bswap_32(hdr->hdr_len) != sizeof(struct btf_header)) {
+		hdr_len = bswap_32(hdr->hdr_len);
+		if (hdr_len < offsetofend(struct btf_header, str_len)) {
 			pr_warn("Can't load BTF with non-native endianness due to unsupported header length %u\n",
-				bswap_32(hdr->hdr_len));
+				hdr_len);
 			return -ENOTSUP;
 		}
-		btf_bswap_hdr(hdr);
+		btf_bswap_hdr(hdr, hdr_len);
 	} else if (hdr->magic != BTF_MAGIC) {
 		pr_debug("Invalid BTF magic: %x\n", hdr->magic);
 		return -EINVAL;
 	}
 
-	if (btf->raw_size < hdr->hdr_len) {
+	if (btf->raw_size < hdr_len) {
 		pr_debug("BTF header len %u larger than data size %u\n",
-			 hdr->hdr_len, btf->raw_size);
+			 hdr_len, btf->raw_size);
 		return -EINVAL;
 	}
 
-	meta_left = btf->raw_size - hdr->hdr_len;
-	if (meta_left < (long long)hdr->str_off + hdr->str_len) {
+	memcpy(&btf->hdr, hdr, min((size_t)hdr_len, sizeof(struct btf_header)));
+
+	meta_left = btf->raw_size - hdr_len;
+	if (meta_left < (long long)btf->hdr.str_off + btf->hdr.str_len) {
 		pr_debug("Invalid BTF total size: %u\n", btf->raw_size);
 		return -EINVAL;
 	}
 
-	if ((long long)hdr->type_off + hdr->type_len > hdr->str_off) {
+	if ((long long)btf->hdr.type_off + btf->hdr.type_len > btf->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);
+			 btf->hdr.type_off, btf->hdr.type_len, btf->hdr.str_off,
+			 btf->hdr.str_len);
 		return -EINVAL;
 	}
 
-	if (hdr->type_off % 4) {
+	if (btf->hdr.type_off % 4) {
 		pr_debug("BTF type section is not aligned to 4 bytes\n");
 		return -EINVAL;
 	}
 
+	if (btf->hdr.layout_len == 0)
+		return 0;
+
+	/* optional layout section sits between types and strings */
+	if (btf->hdr.layout_off % 4) {
+		pr_debug("BTF layout section is not aligned to 4 bytes\n");
+		return -EINVAL;
+	}
+	if (btf->hdr.layout_off < (long long)btf->hdr.type_off + btf->hdr.type_len) {
+		pr_debug("Invalid BTF data sections layout: type data at %u + %u,  layout data at %u + %u\n",
+			 btf->hdr.type_off, btf->hdr.type_len,
+			 btf->hdr.layout_off, btf->hdr.layout_len);
+		return -EINVAL;
+	}
+	if ((long long)btf->hdr.layout_off + btf->hdr.layout_len > btf->hdr.str_off ||
+	    btf->hdr.layout_off > btf->hdr.str_off) {
+		pr_debug("Invalid BTF data sections layout: layout data at %u + %u, strings data at %u\n",
+			 btf->hdr.layout_off, btf->hdr.layout_len, btf->hdr.str_off);
+		return -EINVAL;
+	}
 	return 0;
 }
 
 static int btf_parse_str_sec(struct btf *btf)
 {
-	const struct btf_header *hdr = btf->hdr;
 	const char *start = btf->strs_data;
-	const char *end = start + btf->hdr->str_len;
+	const char *end = start + btf->hdr.str_len;
 
-	if (btf->base_btf && hdr->str_len == 0)
+	if (btf->base_btf && btf->hdr.str_len == 0)
 		return 0;
-	if (!hdr->str_len || hdr->str_len - 1 > BTF_MAX_STR_OFFSET || end[-1]) {
+	if (!btf->hdr.str_len || btf->hdr.str_len - 1 > BTF_MAX_STR_OFFSET || end[-1]) {
 		pr_debug("Invalid BTF string section\n");
 		return -EINVAL;
 	}
@@ -294,6 +341,20 @@ static int btf_parse_str_sec(struct btf *btf)
 	return 0;
 }
 
+static int btf_parse_layout_sec(struct btf *btf)
+{
+	if (!btf->hdr.layout_len)
+		return 0;
+
+	if (btf->hdr.layout_len % sizeof(struct btf_layout) != 0) {
+		pr_debug("Invalid BTF kind layout section\n");
+		return -EINVAL;
+	}
+	btf->layout = btf->raw_data + btf->hdr.hdr_len + btf->hdr.layout_off;
+
+	return 0;
+}
+
 static int btf_type_size(const struct btf_type *t)
 {
 	const int base_size = sizeof(struct btf_type);
@@ -421,9 +482,8 @@ static int btf_bswap_type_rest(struct btf_type *t)
 
 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;
+	void *end_type = next_type + btf->hdr.type_len;
 	int err, type_size;
 
 	while (next_type + sizeof(struct btf_type) <= end_type) {
@@ -1012,7 +1072,8 @@ __s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
 
 static bool btf_is_modifiable(const struct btf *btf)
 {
-	return (void *)btf->hdr != btf->raw_data;
+	/* BTF is modifiable if split into multiple sections */
+	return btf->modifiable;
 }
 
 static void btf_free_raw_data(struct btf *btf)
@@ -1036,14 +1097,14 @@ void btf__free(struct btf *btf)
 
 	if (btf_is_modifiable(btf)) {
 		/* if BTF was modified after loading, it will have a split
-		 * in-memory representation for header, types, and strings
+		 * in-memory representation for types, strings and layout
 		 * sections, so we need to free all of them individually. It
 		 * might still have a cached contiguous raw data present,
 		 * which will be unconditionally freed below.
 		 */
-		free(btf->hdr);
 		free(btf->types_data);
 		strset__free(btf->strs_set);
+		free(btf->layout);
 	}
 	btf_free_raw_data(btf);
 	free(btf->raw_data_swapped);
@@ -1055,6 +1116,7 @@ void btf__free(struct btf *btf)
 
 static struct btf *btf_new_empty(struct btf *base_btf)
 {
+	struct btf_header *hdr;
 	struct btf *btf;
 
 	btf = calloc(1, sizeof(*btf));
@@ -1072,7 +1134,7 @@ static struct btf *btf_new_empty(struct btf *base_btf)
 	if (base_btf) {
 		btf->base_btf = base_btf;
 		btf->start_id = btf__type_cnt(base_btf);
-		btf->start_str_off = base_btf->hdr->str_len + base_btf->start_str_off;
+		btf->start_str_off = base_btf->hdr.str_len + base_btf->start_str_off;
 		btf->swapped_endian = base_btf->swapped_endian;
 	}
 
@@ -1084,14 +1146,15 @@ static struct btf *btf_new_empty(struct btf *base_btf)
 		return ERR_PTR(-ENOMEM);
 	}
 
-	btf->hdr = btf->raw_data;
-	btf->hdr->hdr_len = sizeof(struct btf_header);
-	btf->hdr->magic = BTF_MAGIC;
-	btf->hdr->version = BTF_VERSION;
+	hdr = btf->raw_data;
+	hdr->hdr_len = sizeof(struct btf_header);
+	hdr->magic = BTF_MAGIC;
+	hdr->version = BTF_VERSION;
 
-	btf->types_data = btf->raw_data + btf->hdr->hdr_len;
-	btf->strs_data = btf->raw_data + btf->hdr->hdr_len;
-	btf->hdr->str_len = base_btf ? 0 : 1; /* empty string at offset 0 */
+	btf->types_data = btf->raw_data + hdr->hdr_len;
+	btf->strs_data = btf->raw_data + hdr->hdr_len;
+	hdr->str_len = base_btf ? 0 : 1; /* empty string at offset 0 */
+	memcpy(&btf->hdr, hdr, sizeof(*hdr));
 
 	return btf;
 }
@@ -1124,7 +1187,7 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf, b
 	if (base_btf) {
 		btf->base_btf = base_btf;
 		btf->start_id = btf__type_cnt(base_btf);
-		btf->start_str_off = base_btf->hdr->str_len + base_btf->start_str_off;
+		btf->start_str_off = base_btf->hdr.str_len + base_btf->start_str_off;
 	}
 
 	if (is_mmap) {
@@ -1141,15 +1204,15 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf, b
 
 	btf->raw_size = size;
 
-	btf->hdr = btf->raw_data;
 	err = btf_parse_hdr(btf);
 	if (err)
 		goto done;
 
-	btf->strs_data = btf->raw_data + btf->hdr->hdr_len + btf->hdr->str_off;
-	btf->types_data = btf->raw_data + btf->hdr->hdr_len + btf->hdr->type_off;
+	btf->strs_data = btf->raw_data + btf->hdr.hdr_len + btf->hdr.str_off;
+	btf->types_data = btf->raw_data + btf->hdr.hdr_len + btf->hdr.type_off;
 
 	err = btf_parse_str_sec(btf);
+	err = err ?: btf_parse_layout_sec(btf);
 	err = err ?: btf_parse_type_sec(btf);
 	err = err ?: btf_sanity_check(btf);
 	if (err)
@@ -1601,7 +1664,7 @@ static const void *btf_strs_data(const struct btf *btf)
 
 static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian)
 {
-	struct btf_header *hdr = btf->hdr;
+	const struct btf_header *hdr = &btf->hdr;
 	struct btf_type *t;
 	void *data, *p;
 	__u32 data_sz;
@@ -1614,6 +1677,9 @@ static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endi
 	}
 
 	data_sz = hdr->hdr_len + hdr->type_len + hdr->str_len;
+	if (btf->layout)
+		data_sz += hdr->layout_len;
+
 	data = calloc(1, data_sz);
 	if (!data)
 		return NULL;
@@ -1621,7 +1687,7 @@ static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endi
 
 	memcpy(p, hdr, hdr->hdr_len);
 	if (swap_endian)
-		btf_bswap_hdr(p);
+		btf_bswap_hdr(p, hdr->hdr_len);
 	p += hdr->hdr_len;
 
 	memcpy(p, btf->types_data, hdr->type_len);
@@ -1639,8 +1705,12 @@ static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endi
 	}
 	p += hdr->type_len;
 
+	if (btf->layout) {
+		memcpy(p, btf->layout, hdr->layout_len);
+		p += hdr->layout_len;
+	}
+
 	memcpy(p, btf_strs_data(btf), hdr->str_len);
-	p += hdr->str_len;
 
 	*size = data_sz;
 	return data;
@@ -1675,7 +1745,7 @@ const char *btf__str_by_offset(const struct btf *btf, __u32 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)
+	else if (offset - btf->start_str_off < btf->hdr.str_len)
 		return btf_strs_data(btf) + (offset - btf->start_str_off);
 	else
 		return errno = EINVAL, NULL;
@@ -1783,12 +1853,12 @@ static void btf_invalidate_raw_data(struct btf *btf)
 }
 
 /* Ensure BTF is ready to be modified (by splitting into a three memory
- * regions for header, types, and strings). Also invalidate cached
+ * regions for types, strings and layout. Also invalidate cached
  * raw_data, if any.
  */
 static int btf_ensure_modifiable(struct btf *btf)
 {
-	void *hdr, *types;
+	void *types, *layout = NULL;
 	struct strset *set = NULL;
 	int err = -ENOMEM;
 
@@ -1798,45 +1868,53 @@ static int btf_ensure_modifiable(struct btf *btf)
 		return 0;
 	}
 
-	/* split raw data into three memory regions */
-	hdr = malloc(btf->hdr->hdr_len);
-	types = malloc(btf->hdr->type_len);
-	if (!hdr || !types)
+	/* split raw data into memory regions; btf->hdr is done already. */
+	types = malloc(btf->hdr.type_len);
+	if (!types)
 		goto err_out;
+	memcpy(types, btf->types_data, btf->hdr.type_len);
 
-	memcpy(hdr, btf->hdr, btf->hdr->hdr_len);
-	memcpy(types, btf->types_data, btf->hdr->type_len);
+	if (btf->hdr.layout_len) {
+		layout = malloc(btf->hdr.layout_len);
+		if (!layout)
+			goto err_out;
+		memcpy(layout, btf->raw_data + btf->hdr.hdr_len + btf->hdr.layout_off,
+		       btf->hdr.layout_len);
+	}
 
 	/* build lookup index for all strings */
-	set = strset__new(BTF_MAX_STR_OFFSET, btf->strs_data, btf->hdr->str_len);
+	set = strset__new(BTF_MAX_STR_OFFSET, btf->strs_data, btf->hdr.str_len);
 	if (IS_ERR(set)) {
 		err = PTR_ERR(set);
 		goto err_out;
 	}
 
 	/* only when everything was successful, update internal state */
-	btf->hdr = hdr;
 	btf->types_data = types;
-	btf->types_data_cap = btf->hdr->type_len;
+	btf->types_data_cap = btf->hdr.type_len;
 	btf->strs_data = NULL;
 	btf->strs_set = set;
+	if (layout)
+		btf->layout = layout;
 	/* if BTF was created from scratch, all strings are guaranteed to be
 	 * unique and deduplicated
 	 */
-	if (btf->hdr->str_len == 0)
+	if (btf->hdr.str_len == 0)
 		btf->strs_deduped = true;
-	if (!btf->base_btf && btf->hdr->str_len == 1)
+	if (!btf->base_btf && btf->hdr.str_len == 1)
 		btf->strs_deduped = true;
 
 	/* invalidate raw_data representation */
 	btf_invalidate_raw_data(btf);
 
+	btf->modifiable = true;
+
 	return 0;
 
 err_out:
 	strset__free(set);
-	free(hdr);
 	free(types);
+	free(layout);
 	return err;
 }
 
@@ -1889,7 +1967,7 @@ int btf__add_str(struct btf *btf, const char *s)
 	if (off < 0)
 		return libbpf_err(off);
 
-	btf->hdr->str_len = strset__data_size(btf->strs_set);
+	btf->hdr.str_len = strset__data_size(btf->strs_set);
 
 	return btf->start_str_off + off;
 }
@@ -1897,7 +1975,7 @@ int btf__add_str(struct btf *btf, const char *s)
 static void *btf_add_type_mem(struct btf *btf, size_t add_sz)
 {
 	return libbpf_add_mem(&btf->types_data, &btf->types_data_cap, 1,
-			      btf->hdr->type_len, UINT_MAX, add_sz);
+			      btf->hdr.type_len, UINT_MAX, add_sz);
 }
 
 static void btf_type_inc_vlen(struct btf_type *t)
@@ -1905,16 +1983,31 @@ 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 void btf_hdr_update_type_len(struct btf *btf, int new_len)
+{
+	btf->hdr.type_len = new_len;
+	if (btf->layout) {
+		btf->hdr.layout_off = new_len;
+		btf->hdr.str_off = btf->hdr.layout_off + btf->hdr.layout_len;
+	} else {
+		btf->hdr.str_off = new_len;
+	}
+}
+
+static void btf_hdr_update_str_len(struct btf *btf, int new_len)
+{
+	btf->hdr.str_len = new_len;
+}
+
 static int btf_commit_type(struct btf *btf, int data_sz)
 {
 	int err;
 
-	err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
+	err = btf_add_type_idx_entry(btf, btf->hdr.type_len);
 	if (err)
 		return libbpf_err(err);
 
-	btf->hdr->type_len += data_sz;
-	btf->hdr->str_off += data_sz;
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + data_sz);
 	btf->nr_types++;
 	return btf->start_id + btf->nr_types - 1;
 }
@@ -2018,9 +2111,9 @@ int btf__add_btf(struct btf *btf, const struct btf *src_btf)
 	/* remember original strings section size if we have to roll back
 	 * partial strings section changes
 	 */
-	old_strs_len = btf->hdr->str_len;
+	old_strs_len = btf->hdr.str_len;
 
-	data_sz = src_btf->hdr->type_len;
+	data_sz = src_btf->hdr.type_len;
 	cnt = btf__type_cnt(src_btf) - 1;
 
 	/* pre-allocate enough memory for new types */
@@ -2094,8 +2187,7 @@ int btf__add_btf(struct btf *btf, const struct btf *src_btf)
 	 * update type count and various internal offsets and sizes to
 	 * "commit" the changes and made them visible to the outside world.
 	 */
-	btf->hdr->type_len += data_sz;
-	btf->hdr->str_off += data_sz;
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + data_sz);
 	btf->nr_types += cnt;
 
 	hashmap__free(p.str_off_map);
@@ -2106,13 +2198,13 @@ int btf__add_btf(struct btf *btf, const struct btf *src_btf)
 	/* zero out preallocated memory as if it was just allocated with
 	 * libbpf_add_mem()
 	 */
-	memset(btf->types_data + btf->hdr->type_len, 0, data_sz);
-	memset(btf->strs_data + old_strs_len, 0, btf->hdr->str_len - old_strs_len);
+	memset(btf->types_data + btf->hdr.type_len, 0, data_sz);
+	memset(btf->strs_data + old_strs_len, 0, btf->hdr.str_len - old_strs_len);
 
 	/* and now restore original strings section size; types data size
 	 * wasn't modified, so doesn't need restoring, see big comment above
 	 */
-	btf->hdr->str_len = old_strs_len;
+	btf_hdr_update_str_len(btf, old_strs_len);
 
 	hashmap__free(p.str_off_map);
 
@@ -2430,8 +2522,7 @@ int btf__add_field(struct btf *btf, const char *name, int type_id,
 	/* update parent type's vlen and kflag */
 	t->info = btf_type_info(btf_kind(t), btf_vlen(t) + 1, is_bitfield || btf_kflag(t));
 
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -2540,8 +2631,7 @@ int btf__add_enum_value(struct btf *btf, const char *name, __s64 value)
 	if (value < 0)
 		t->info = btf_type_info(btf_kind(t), btf_vlen(t), true);
 
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -2612,8 +2702,7 @@ int btf__add_enum64_value(struct btf *btf, const char *name, __u64 value)
 	t = btf_last_type(btf);
 	btf_type_inc_vlen(t);
 
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -2851,8 +2940,7 @@ int btf__add_func_param(struct btf *btf, const char *name, int type_id)
 	t = btf_last_type(btf);
 	btf_type_inc_vlen(t);
 
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -2988,8 +3076,7 @@ int btf__add_datasec_var_info(struct btf *btf, int var_type_id, __u32 offset, __
 	t = btf_last_type(btf);
 	btf_type_inc_vlen(t);
 
-	btf->hdr->type_len += sz;
-	btf->hdr->str_off += sz;
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -3953,7 +4040,7 @@ static int btf_dedup_strings(struct btf_dedup *d)
 
 	/* replace BTF string data and hash with deduped ones */
 	strset__free(d->btf->strs_set);
-	d->btf->hdr->str_len = strset__data_size(d->strs_set);
+	btf_hdr_update_str_len(d->btf, strset__data_size(d->strs_set));
 	d->btf->strs_set = d->strs_set;
 	d->strs_set = NULL;
 	d->btf->strs_deduped = true;
@@ -5400,14 +5487,17 @@ static int btf_dedup_compact_types(struct btf_dedup *d)
 	/* shrink struct btf's internal types index and update btf_header */
 	d->btf->nr_types = next_type_id - d->btf->start_id;
 	d->btf->type_offs_cap = d->btf->nr_types;
-	d->btf->hdr->type_len = p - d->btf->types_data;
+	d->btf->hdr.type_len = p - d->btf->types_data;
 	new_offs = libbpf_reallocarray(d->btf->type_offs, d->btf->type_offs_cap,
 				       sizeof(*new_offs));
 	if (d->btf->type_offs_cap && !new_offs)
 		return -ENOMEM;
 	d->btf->type_offs = new_offs;
-	d->btf->hdr->str_off = d->btf->hdr->type_len;
-	d->btf->raw_size = d->btf->hdr->hdr_len + d->btf->hdr->type_len + d->btf->hdr->str_len;
+	if (d->btf->layout)
+		d->btf->hdr.layout_off = d->btf->hdr.type_len;
+	d->btf->hdr.str_off = d->btf->hdr.type_len + d->btf->hdr.layout_len;
+	d->btf->raw_size = d->btf->hdr.hdr_len + d->btf->hdr.type_len + d->btf->hdr.layout_len +
+			   d->btf->hdr.str_len;
 	return 0;
 }
 
@@ -5865,7 +5955,7 @@ int btf__distill_base(const struct btf *src_btf, struct btf **new_base_btf,
 		goto done;
 	}
 	dist.split_start_id = btf__type_cnt(old_base);
-	dist.split_start_str = old_base->hdr->str_len;
+	dist.split_start_str = old_base->hdr.str_len;
 
 	/* Pass over src split BTF; generate the list of base BTF type ids it
 	 * references; these will constitute our distilled BTF set to be
@@ -5934,14 +6024,14 @@ int btf__distill_base(const struct btf *src_btf, struct btf **new_base_btf,
 
 const struct btf_header *btf_header(const struct btf *btf)
 {
-	return btf->hdr;
+	return &btf->hdr;
 }
 
 void btf_set_base_btf(struct btf *btf, const struct btf *base_btf)
 {
 	btf->base_btf = (struct btf *)base_btf;
 	btf->start_id = btf__type_cnt(base_btf);
-	btf->start_str_off = base_btf->hdr->str_len + base_btf->start_str_off;
+	btf->start_str_off = base_btf->hdr.str_len + base_btf->start_str_off;
 }
 
 int btf__relocate(struct btf *btf, const struct btf *base_btf)
@@ -6008,7 +6098,7 @@ int btf__permute(struct btf *btf, __u32 *id_map, __u32 id_map_cnt,
 		goto done;
 	}
 
-	new_types = calloc(btf->hdr->type_len, 1);
+	new_types = calloc(btf->hdr.type_len, 1);
 	if (!new_types) {
 		err = -ENOMEM;
 		goto done;
-- 
2.39.3

This allows BTF parsing to proceed even if we do not know the
kind.  Fall back to base BTF layout if layout information is
not in split BTF.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/btf.c | 46 ++++++++++++++++++++++++++++++++++++---------
 1 file changed, 37 insertions(+), 9 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 3438cc15bb7a..c0603a8f8533 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -355,7 +355,36 @@ static int btf_parse_layout_sec(struct btf *btf)
 	return 0;
 }
 
-static int btf_type_size(const struct btf_type *t)
+/* for unknown kinds, consult kind layout. */
+static int btf_type_size_unknown(const struct btf *btf, const struct btf_type *t)
+{
+	__u32 layout_kinds = btf->hdr.layout_len / sizeof(struct btf_layout);
+	int size = sizeof(struct btf_type);
+	struct btf_layout *l = btf->layout;
+	__u16 vlen = btf_vlen(t);
+	__u32 kind = btf_kind(t);
+
+	/* Fall back to base BTF if needed as they share layout information */
+	if (!l) {
+		struct btf *base_btf = btf->base_btf;
+
+		if (base_btf) {
+			l = base_btf->layout;
+			layout_kinds = base_btf->hdr.layout_len / sizeof(struct btf_layout);
+		}
+	}
+	if (!l || kind >= layout_kinds) {
+		pr_debug("Unsupported BTF_KIND: %u\n", btf_kind(t));
+		return -EINVAL;
+	}
+
+	size += l[kind].info_sz;
+	size += vlen * l[kind].elem_sz;
+
+	return size;
+}
+
+static int btf_type_size(const struct btf *btf, const struct btf_type *t)
 {
 	const int base_size = sizeof(struct btf_type);
 	__u16 vlen = btf_vlen(t);
@@ -391,8 +420,7 @@ static int btf_type_size(const struct btf_type *t)
 	case BTF_KIND_DECL_TAG:
 		return base_size + sizeof(struct btf_decl_tag);
 	default:
-		pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
-		return -EINVAL;
+		return btf_type_size_unknown(btf, t);
 	}
 }
 
@@ -490,7 +518,7 @@ static int btf_parse_type_sec(struct btf *btf)
 		if (btf->swapped_endian)
 			btf_bswap_type_base(next_type);
 
-		type_size = btf_type_size(next_type);
+		type_size = btf_type_size(btf, next_type);
 		if (type_size < 0)
 			return type_size;
 		if (next_type + type_size > end_type) {
@@ -2056,7 +2084,7 @@ static int btf_add_type(struct btf_pipe *p, const struct btf_type *src_type)
 	__u32 *str_off;
 	int sz, err;
 
-	sz = btf_type_size(src_type);
+	sz = btf_type_size(p->src, src_type);
 	if (sz < 0)
 		return libbpf_err(sz);
 
@@ -2138,7 +2166,7 @@ int btf__add_btf(struct btf *btf, const struct btf *src_btf)
 		struct btf_field_iter it;
 		__u32 *type_id, *str_off;
 
-		sz = btf_type_size(t);
+		sz = btf_type_size(src_btf, t);
 		if (sz < 0) {
 			/* unlikely, has to be corrupted src_btf */
 			err = sz;
@@ -5473,7 +5501,7 @@ static int btf_dedup_compact_types(struct btf_dedup *d)
 			continue;
 
 		t = btf__type_by_id(d->btf, id);
-		len = btf_type_size(t);
+		len = btf_type_size(d->btf, t);
 		if (len < 0)
 			return len;
 
@@ -6136,7 +6164,7 @@ int btf__permute(struct btf *btf, __u32 *id_map, __u32 id_map_cnt,
 
 		id = order_map[i];
 		t = btf__type_by_id(btf, id);
-		type_size = btf_type_size(t);
+		type_size = btf_type_size(btf, t);
 		memcpy(nt, t, type_size);
 
 		/* fix up referenced IDs for BTF */
@@ -6162,7 +6190,7 @@ int btf__permute(struct btf *btf, __u32 *id_map, __u32 id_map_cnt,
 
 	for (nt = new_types, i = 0; i < id_map_cnt - start_offs; i++) {
 		btf->type_offs[i] = nt - new_types;
-		nt += btf_type_size(nt);
+		nt += btf_type_size(btf, nt);
 	}
 
 	free(order_map);
-- 
2.39.3

Support encoding of BTF layout data via btf__new_empty_opts().

Current supported opts are base_btf and add_layout.

Layout information is maintained in btf.c in the layouts[] array;
when BTF is created with the add_layout option in represents the
current view of supported BTF kinds.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/btf.c      | 62 ++++++++++++++++++++++++++++++++++++++--
 tools/lib/bpf/btf.h      | 20 +++++++++++++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 80 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index c0603a8f8533..348dd5047556 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -29,6 +29,35 @@
 
 static struct btf_type btf_void;
 
+/* Describe how kinds are laid out; some have a singular element following the "struct btf_type",
+ * some have BTF_INFO_VLEN(t->info) elements.  Specify sizes for both.  Flags are currently unused.
+ * Kind layout can be optionally added to the BTF representation in a dedicated section to
+ * facilitate parsing.  New kinds must be added here.
+ */
+static struct btf_layout layouts[NR_BTF_KINDS] = {
+/*				singular element size		vlen element(s) size		flags */
+[BTF_KIND_UNKN] =	{	0,				0,				0 },
+[BTF_KIND_INT] =	{	sizeof(__u32),			0,				0 },
+[BTF_KIND_PTR] =	{	0,				0,				0 },
+[BTF_KIND_ARRAY] =	{	sizeof(struct btf_array),	0,				0 },
+[BTF_KIND_STRUCT] =	{	0,				sizeof(struct btf_member),	0 },
+[BTF_KIND_UNION] =	{	0,				sizeof(struct btf_member),	0 },
+[BTF_KIND_ENUM] =	{	0,				sizeof(struct btf_enum),	0 },
+[BTF_KIND_FWD] =	{	0,				0,				0 },
+[BTF_KIND_TYPEDEF] =	{	0,				0,				0 },
+[BTF_KIND_VOLATILE] =	{	0,				0,				0 },
+[BTF_KIND_CONST] =	{	0,				0,				0 },
+[BTF_KIND_RESTRICT] =	{	0,				0,				0 },
+[BTF_KIND_FUNC] =	{	0,				0,				0 },
+[BTF_KIND_FUNC_PROTO] =	{	0,				sizeof(struct btf_param),	0 },
+[BTF_KIND_VAR] =	{	sizeof(struct btf_var),		0,				0 },
+[BTF_KIND_DATASEC] =	{	0,				sizeof(struct btf_var_secinfo),	0 },
+[BTF_KIND_FLOAT] =	{	0,				0,				0 },
+[BTF_KIND_DECL_TAG] =	{	sizeof(struct btf_decl_tag),	0,				0 },
+[BTF_KIND_TYPE_TAG] =	{	0,				0,				0 },
+[BTF_KIND_ENUM64] =	{	0,				sizeof(struct btf_enum64),	0 },
+};
+
 struct btf {
 	/* raw BTF data in native endianness */
 	void *raw_data;
@@ -1142,8 +1171,10 @@ void btf__free(struct btf *btf)
 	free(btf);
 }
 
-static struct btf *btf_new_empty(struct btf *base_btf)
+static struct btf *btf_new_empty(struct btf_new_opts *opts)
 {
+	bool add_layout = OPTS_GET(opts, add_layout, false);
+	struct btf *base_btf = OPTS_GET(opts, base_btf, NULL);
 	struct btf_header *hdr;
 	struct btf *btf;
 
@@ -1168,6 +1199,8 @@ static struct btf *btf_new_empty(struct btf *base_btf)
 
 	/* +1 for empty string at offset 0 */
 	btf->raw_size = sizeof(struct btf_header) + (base_btf ? 0 : 1);
+	if (add_layout)
+		btf->raw_size += sizeof(layouts);
 	btf->raw_data = calloc(1, btf->raw_size);
 	if (!btf->raw_data) {
 		free(btf);
@@ -1182,6 +1215,15 @@ static struct btf *btf_new_empty(struct btf *base_btf)
 	btf->types_data = btf->raw_data + hdr->hdr_len;
 	btf->strs_data = btf->raw_data + hdr->hdr_len;
 	hdr->str_len = base_btf ? 0 : 1; /* empty string at offset 0 */
+
+	if (add_layout) {
+		hdr->layout_len = sizeof(layouts);
+		btf->layout = btf->raw_data + hdr->hdr_len;
+		memcpy(btf->layout, layouts, sizeof(layouts));
+		btf->strs_data += sizeof(layouts);
+		hdr->str_off += sizeof(layouts);
+	}
+
 	memcpy(&btf->hdr, hdr, sizeof(*hdr));
 
 	return btf;
@@ -1189,12 +1231,26 @@ static struct btf *btf_new_empty(struct btf *base_btf)
 
 struct btf *btf__new_empty(void)
 {
-	return libbpf_ptr(btf_new_empty(NULL));
+	LIBBPF_OPTS(btf_new_opts, opts);
+
+	return libbpf_ptr(btf_new_empty(&opts));
 }
 
 struct btf *btf__new_empty_split(struct btf *base_btf)
 {
-	return libbpf_ptr(btf_new_empty(base_btf));
+	LIBBPF_OPTS(btf_new_opts, opts);
+
+	opts.base_btf = base_btf;
+
+	return libbpf_ptr(btf_new_empty(&opts));
+}
+
+struct btf *btf__new_empty_opts(struct btf_new_opts *opts)
+{
+	if (!OPTS_VALID(opts, btf_new_opts))
+		return libbpf_err_ptr(-EINVAL);
+
+	return libbpf_ptr(btf_new_empty(opts));
 }
 
 static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf, bool is_mmap)
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index b30008c267c0..a1f8deca2603 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -109,6 +109,26 @@ LIBBPF_API struct btf *btf__new_empty(void);
  */
 LIBBPF_API struct btf *btf__new_empty_split(struct btf *base_btf);
 
+struct btf_new_opts {
+	size_t sz;
+	struct btf *base_btf;	/* optional base BTF */
+	bool add_layout;	/* add BTF layout information */
+	size_t:0;
+};
+#define btf_new_opts__last_field add_layout
+
+/**
+ * @brief **btf__new_empty_opts()** creates an unpopulated BTF object with
+ * optional *base_btf* and BTF kind layout description if *add_layout*
+ * is set
+ * @return new BTF object instance which has to be eventually freed with
+ * **btf__free()**
+ *
+ * On error, NULL is returned and the thread-local `errno` variable is
+ * set to the error code.
+ */
+LIBBPF_API struct btf *btf__new_empty_opts(struct btf_new_opts *opts);
+
 /**
  * @brief **btf__distill_base()** creates new versions of the split BTF
  * *src_btf* and its base BTF. The new base BTF will only contain the types
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index d18fbcea7578..0f740fb27a12 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -453,5 +453,6 @@ LIBBPF_1.7.0 {
 		bpf_map__exclusive_program;
 		bpf_prog_assoc_struct_ops;
 		bpf_program__assoc_struct_ops;
+		btf__new_empty_opts;
 		btf__permute;
 } LIBBPF_1.6.0;
-- 
2.39.3

BTF parsing can use layout to navigate unknown kinds, so
btf_validate_type() should take layout information into
account to avoid failure when an unrecognized kind is met.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/btf.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 348dd5047556..b98785967fc9 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -708,8 +708,12 @@ static int btf_validate_type(const struct btf *btf, const struct btf_type *t, __
 		break;
 	}
 	default:
-		pr_warn("btf: type [%u]: unrecognized kind %u\n", id, kind);
-		return -EINVAL;
+		/* Kind may be represented in kind layout information. */
+		if (btf_type_size_unknown(btf, t) < 0) {
+			pr_warn("btf: type [%u]: unrecognized kind %u\n", id, kind);
+			return -EINVAL;
+		}
+		break;
 	}
 	return 0;
 }
-- 
2.39.3

Validate layout if present, but because the kernel must be
strict in what it accepts, reject BTF with unsupported kinds,
even if they are in the layout information.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 kernel/bpf/btf.c | 96 ++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 76 insertions(+), 20 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 4872d2a6c42d..852403bab520 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -270,6 +270,7 @@ struct btf {
 	struct btf_id_dtor_kfunc_tab *dtor_kfunc_tab;
 	struct btf_struct_metas *struct_meta_tab;
 	struct btf_struct_ops_tab *struct_ops_tab;
+	struct btf_layout *layout;
 
 	/* split BTF support */
 	struct btf *base_btf;
@@ -5327,23 +5328,36 @@ static s32 btf_check_meta(struct btf_verifier_env *env,
 		return -EINVAL;
 	}
 
-	if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX ||
-	    BTF_INFO_KIND(t->info) == BTF_KIND_UNKN) {
+	if (!btf_name_offset_valid(env->btf, t->name_off)) {
+		btf_verifier_log(env, "[%u] Invalid name_offset:%u",
+				 env->log_type_id, t->name_off);
+		return -EINVAL;
+	}
+
+	if (BTF_INFO_KIND(t->info) == BTF_KIND_UNKN) {
 		btf_verifier_log(env, "[%u] Invalid kind:%u",
 				 env->log_type_id, BTF_INFO_KIND(t->info));
 		return -EINVAL;
 	}
 
-	if (!btf_name_offset_valid(env->btf, t->name_off)) {
-		btf_verifier_log(env, "[%u] Invalid name_offset:%u",
-				 env->log_type_id, t->name_off);
+	if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX && env->btf->layout &&
+	    ((BTF_INFO_KIND(t->info) + 1) * sizeof(struct btf_layout)) <
+	     env->btf->hdr.layout_len) {
+		btf_verifier_log(env, "[%u] unknown but required kind %u",
+				 env->log_type_id,
+				 BTF_INFO_KIND(t->info));
 		return -EINVAL;
+	} else {
+		if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX) {
+			btf_verifier_log(env, "[%u] Invalid kind:%u",
+					 env->log_type_id, BTF_INFO_KIND(t->info));
+			return -EINVAL;
+		}
+		var_meta_size = btf_type_ops(t)->check_meta(env, t, meta_left);
+		if (var_meta_size < 0)
+			return var_meta_size;
 	}
 
-	var_meta_size = btf_type_ops(t)->check_meta(env, t, meta_left);
-	if (var_meta_size < 0)
-		return var_meta_size;
-
 	meta_left -= var_meta_size;
 
 	return saved_meta_left - meta_left;
@@ -5517,7 +5531,8 @@ static int btf_parse_str_sec(struct btf_verifier_env *env)
 	start = btf->nohdr_data + hdr->str_off;
 	end = start + hdr->str_len;
 
-	if (end != btf->data + btf->data_size) {
+	if (hdr->hdr_len < sizeof(struct btf_header) &&
+	    end != btf->data + btf->data_size) {
 		btf_verifier_log(env, "String section is not at the end");
 		return -EINVAL;
 	}
@@ -5538,9 +5553,41 @@ static int btf_parse_str_sec(struct btf_verifier_env *env)
 	return 0;
 }
 
+static int btf_parse_layout_sec(struct btf_verifier_env *env)
+{
+	const struct btf_header *hdr = &env->btf->hdr;
+	struct btf *btf = env->btf;
+	void *start, *end;
+
+	if (hdr->hdr_len < sizeof(struct btf_header) ||
+	    hdr->layout_len == 0)
+		return 0;
+
+	/* Llayout section must align to 4 bytes */
+	if (hdr->layout_off & (sizeof(u32) - 1)) {
+		btf_verifier_log(env, "Unaligned layout_off");
+		return -EINVAL;
+	}
+	start = btf->nohdr_data + hdr->layout_off;
+	end = start + hdr->layout_len;
+
+	if (hdr->layout_len < sizeof(struct btf_layout)) {
+		btf_verifier_log(env, "Layout section is too small");
+		return -EINVAL;
+	}
+	if (end > btf->data + btf->data_size) {
+		btf_verifier_log(env, "Layout section is too big");
+		return -EINVAL;
+	}
+	btf->layout = start;
+
+	return 0;
+}
+
 static const size_t btf_sec_info_offset[] = {
 	offsetof(struct btf_header, type_off),
 	offsetof(struct btf_header, str_off),
+	offsetof(struct btf_header, layout_off)
 };
 
 static int btf_sec_info_cmp(const void *a, const void *b)
@@ -5555,44 +5602,49 @@ static int btf_check_sec_info(struct btf_verifier_env *env,
 			      u32 btf_data_size)
 {
 	struct btf_sec_info secs[ARRAY_SIZE(btf_sec_info_offset)];
-	u32 total, expected_total, i;
+	u32 nr_secs = ARRAY_SIZE(btf_sec_info_offset);
+	u32 total, expected_total, gap, i;
 	const struct btf_header *hdr;
 	const struct btf *btf;
 
 	btf = env->btf;
 	hdr = &btf->hdr;
 
+	if (hdr->hdr_len < sizeof(struct btf_header) || hdr->layout_len == 0)
+		nr_secs--;
+
 	/* Populate the secs from hdr */
-	for (i = 0; i < ARRAY_SIZE(btf_sec_info_offset); i++)
+	for (i = 0; i < nr_secs; i++)
 		secs[i] = *(struct btf_sec_info *)((void *)hdr +
 						   btf_sec_info_offset[i]);
 
-	sort(secs, ARRAY_SIZE(btf_sec_info_offset),
+	sort(secs, nr_secs,
 	     sizeof(struct btf_sec_info), btf_sec_info_cmp, NULL);
 
 	/* Check for gaps and overlap among sections */
 	total = 0;
 	expected_total = btf_data_size - hdr->hdr_len;
-	for (i = 0; i < ARRAY_SIZE(btf_sec_info_offset); i++) {
+	for (i = 0; i < nr_secs; i++) {
 		if (expected_total < secs[i].off) {
 			btf_verifier_log(env, "Invalid section offset");
 			return -EINVAL;
 		}
-		if (total < secs[i].off) {
-			/* gap */
-			btf_verifier_log(env, "Unsupported section found");
-			return -EINVAL;
-		}
 		if (total > secs[i].off) {
 			btf_verifier_log(env, "Section overlap found");
 			return -EINVAL;
 		}
+		gap = secs[i].off - total;
+		if (gap >= 4) {
+			/* gap larger than alignment gap */
+			btf_verifier_log(env, "Unsupported section found");
+			return -EINVAL;
+		}
 		if (expected_total - total < secs[i].len) {
 			btf_verifier_log(env,
 					 "Total section length too long");
 			return -EINVAL;
 		}
-		total += secs[i].len;
+		total += secs[i].len + gap;
 	}
 
 	/* There is data other than hdr and known sections */
@@ -5929,6 +5981,10 @@ static struct btf *btf_parse(const union bpf_attr *attr, bpfptr_t uattr, u32 uat
 	if (err)
 		goto errout;
 
+	err = btf_parse_layout_sec(env);
+	if (err)
+		goto errout;
+
 	err = btf_parse_type_sec(env);
 	if (err)
 		goto errout;
-- 
2.39.3

verify btf__new_empty_opts() adds layouts for all kinds supported,
and after adding kind-related types for an unknown kind, ensure that
parsing uses this info when that kind is encountered rather than
giving up.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 .../selftests/bpf/prog_tests/btf_kind.c       | 206 ++++++++++++++++++
 1 file changed, 206 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/btf_kind.c

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_kind.c b/tools/testing/selftests/bpf/prog_tests/btf_kind.c
new file mode 100644
index 000000000000..09246dc61f5a
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/btf_kind.c
@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026, Oracle and/or its affiliates. */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+#include <bpf/libbpf.h>
+
+/* verify kind encoding exists for each kind */
+static void test_btf_kind_encoding(void)
+{
+	LIBBPF_OPTS(btf_new_opts, opts);
+	const struct btf_header *hdr;
+	const void *raw_btf;
+	struct btf *btf;
+	__u32 raw_size;
+
+	opts.add_layout = true;
+	btf = btf__new_empty_opts(&opts);
+	if (!ASSERT_OK_PTR(btf, "btf_new"))
+		return;
+
+	raw_btf = btf__raw_data(btf, &raw_size);
+	if (!ASSERT_OK_PTR(raw_btf, "btf__raw_data"))
+		return;
+
+	hdr = raw_btf;
+
+	ASSERT_EQ(hdr->layout_off % 4, 0, "layout_aligned");
+	ASSERT_EQ(hdr->layout_len, sizeof(struct btf_layout) * NR_BTF_KINDS,
+		  "layout_len");
+	ASSERT_EQ(hdr->str_off, hdr->layout_off + hdr->layout_len, "str_after_layout");
+	btf__free(btf);
+
+	opts.add_layout = false;
+	btf = btf__new_empty_opts(&opts);
+	if (!ASSERT_OK_PTR(btf, "btf_new"))
+		return;
+
+	raw_btf = btf__raw_data(btf, &raw_size);
+	if (!ASSERT_OK_PTR(raw_btf, "btf__raw_data"))
+		return;
+
+	hdr = raw_btf;
+
+	ASSERT_EQ(hdr->layout_off, 0, "no_layout_off");
+	ASSERT_EQ(hdr->layout_len, 0, "no_layout_len");
+	ASSERT_EQ(hdr->str_off, hdr->type_off + hdr->type_len, "strs_after_types");
+	btf__free(btf);
+}
+
+static void write_raw_btf(const char *btf_path, void *raw_btf, size_t raw_size)
+{
+	int fd = open(btf_path, O_WRONLY | O_CREAT);
+
+	write(fd, raw_btf, raw_size);
+	close(fd);
+}
+
+/* fabricate an unrecognized kind at BTF_KIND_MAX + 1, and after adding
+ * the appropriate struct/typedefs to the BTF such that it recognizes
+ * this kind, ensure that parsing of BTF containing the unrecognized kind
+ * can succeed.
+ */
+void test_btf_kind_decoding(void)
+{
+	__s32 int_id, unrec_id, id, id2;
+	LIBBPF_OPTS(btf_new_opts, opts);
+	struct btf *btf, *new_btf;
+	struct btf_layout *l;
+	struct btf_header *hdr;
+	const void *raw_btf;
+	struct btf_type *t;
+	char btf_path[64];
+	void *new_raw_btf;
+	void *str_data;
+	__u32 raw_size;
+
+	opts.add_layout = true;
+	btf = btf__new_empty_opts(&opts);
+	if (!ASSERT_OK_PTR(btf, "btf_new"))
+		return;
+
+	int_id = btf__add_int(btf, "test_char", 1, BTF_INT_CHAR);
+	if (!ASSERT_GT(int_id, 0, "add_int_id"))
+		return;
+
+	/* now create our type with unrecognized kind by adding a typedef kind
+	 * we will overwrite it with our unrecognized kind value.
+	 */
+	unrec_id = btf__add_typedef(btf, "unrec_kind", int_id);
+	if (!ASSERT_GT(unrec_id, 0, "add_unrec_id"))
+		return;
+
+	/* add an id after it that we will look up to verify we can parse
+	 * beyond unrecognized kinds.
+	 */
+	id = btf__add_typedef(btf, "test_lookup", int_id);
+	if (!ASSERT_GT(id, 0, "add_test_lookup_id"))
+		return;
+	id2 = btf__add_typedef(btf, "test_lookup2", int_id);
+	if (!ASSERT_GT(id2, 0, "add_test_lookup_id2"))
+		return;
+
+	raw_btf = (void *)btf__raw_data(btf, &raw_size);
+	if (!ASSERT_OK_PTR(raw_btf, "btf__raw_data"))
+		return;
+
+	new_raw_btf = calloc(1, raw_size + sizeof(*l));
+	if (!ASSERT_OK_PTR(new_raw_btf, "calloc_raw_btf"))
+		return;
+	memcpy(new_raw_btf, raw_btf, raw_size);
+
+	hdr = new_raw_btf;
+
+	/* move strings to make space for one new layout description */
+	raw_size += sizeof(*l);
+	str_data = new_raw_btf + hdr->hdr_len + hdr->str_off;
+	memmove(str_data + sizeof(*l), str_data, hdr->str_len);
+	hdr->str_off += sizeof(*l);
+
+	/* add new layout description */
+	hdr->layout_len += sizeof(*l);
+	l = new_raw_btf + hdr->hdr_len + hdr->layout_off;
+	l[NR_BTF_KINDS].info_sz = 0;
+	l[NR_BTF_KINDS].elem_sz = 0;
+	l[NR_BTF_KINDS].flags = 0;
+
+	/* now modify our typedef added above to be an unrecognized kind. */
+	t = (void *)hdr + hdr->hdr_len + hdr->type_off + sizeof(struct btf_type) +
+		sizeof(__u32);
+	t->info = (NR_BTF_KINDS << 24);
+
+	/* now write our BTF to a raw file, ready for parsing. */
+	snprintf(btf_path, sizeof(btf_path), "/tmp/btf_kind.%d", getpid());
+
+	write_raw_btf(btf_path, new_raw_btf, raw_size);
+
+	/* verify parsing succeeds, and that we can read type info past
+	 * the unrecognized kind.
+	 */
+	new_btf = btf__parse_raw(btf_path);
+	if (ASSERT_OK_PTR(new_btf, "btf__parse_raw")) {
+		ASSERT_EQ(btf__find_by_name(new_btf, "unrec_kind"), unrec_id,
+			  "unrec_kind_found");
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup",
+						 BTF_KIND_TYPEDEF), id,
+			  "verify_id_lookup");
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup2",
+						 BTF_KIND_TYPEDEF), id2,
+			  "verify_id2_lookup");
+	}
+	btf__free(new_btf);
+
+	/* next, change info_sz to equal sizeof(struct btf_type); this means the
+	 * "test_lookup" kind will be reinterpreted as a singular info element
+	 * following the unrecognized kind.
+	 */
+	l[NR_BTF_KINDS].info_sz = sizeof(struct btf_type);
+	write_raw_btf(btf_path, new_raw_btf, raw_size);
+
+	new_btf = btf__parse_raw(btf_path);
+	if (ASSERT_OK_PTR(new_btf, "btf__parse_raw")) {
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup",
+						 BTF_KIND_TYPEDEF), -ENOENT,
+			  "verify_id_not_found");
+		/* id of "test_lookup2" will be id2 -1 as we have removed one type */
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup2",
+						 BTF_KIND_TYPEDEF), id2 - 1,
+			  "verify_id_lookup2");
+
+	}
+	btf__free(new_btf);
+
+	/* next, change elem_sz to equal sizeof(struct btf_type)/2 and set
+	 * vlen associated with unrecognized type to 2; this allows us to verify
+	 * vlen-specified BTF can still be parsed.
+	 */
+	l[NR_BTF_KINDS].info_sz = 0;
+	l[NR_BTF_KINDS].elem_sz = sizeof(struct btf_type)/2;
+	t->info |= 2;
+	write_raw_btf(btf_path, new_raw_btf, raw_size);
+
+	new_btf = btf__parse_raw(btf_path);
+	if (ASSERT_OK_PTR(new_btf, "btf__parse_raw")) {
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup",
+						 BTF_KIND_TYPEDEF), -ENOENT,
+			  "verify_id_not_found");
+		/* id of "test_lookup2" will be id2 -1 as we have removed one type */
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup2",
+						 BTF_KIND_TYPEDEF), id2 - 1,
+			  "verify_id_lookup2");
+
+	}
+	btf__free(new_btf);
+	free(new_raw_btf);
+	unlink(btf_path);
+	btf__free(btf);
+}
+
+void test_btf_kind(void)
+{
+	if (test__start_subtest("btf_kind_encoding"))
+		test_btf_kind_encoding();
+	if (test__start_subtest("btf_kind_decoding"))
+		test_btf_kind_decoding();
+}
-- 
2.39.3

Provide a way to dump BTF metadata info via bpftool; this
consists of BTF size, header fields and layout info
(if available); for example

$ bpftool btf dump file vmlinux format meta
size 6516862
magic 0xeb9f
version 1
flags 0x0
hdr_len 32
type_len 3929096
type_off 0
str_len 2587654
str_off 3929176
layout_len 80
layout_off 3929096
kind 0    UNKNOWN    info_sz 0    elem_sz 0    flags 0
kind 1    INT        info_sz 4    elem_sz 0    flags 0
kind 2    PTR        info_sz 0    elem_sz 0    flags 0
kind 3    ARRAY      info_sz 12   elem_sz 0    flags 0
kind 4    STRUCT     info_sz 0    elem_sz 12   flags 0
kind 5    UNION      info_sz 0    elem_sz 12   flags 0
kind 6    ENUM       info_sz 0    elem_sz 8    flags 0
kind 7    FWD        info_sz 0    elem_sz 0    flags 0
kind 8    TYPEDEF    info_sz 0    elem_sz 0    flags 0
kind 9    VOLATILE   info_sz 0    elem_sz 0    flags 0
kind 10   CONST      info_sz 0    elem_sz 0    flags 0
kind 11   RESTRICT   info_sz 0    elem_sz 0    flags 0
kind 12   FUNC       info_sz 0    elem_sz 0    flags 0
kind 13   FUNC_PROTO info_sz 0    elem_sz 8    flags 0
kind 14   VAR        info_sz 4    elem_sz 0    flags 0
kind 15   DATASEC    info_sz 0    elem_sz 12   flags 0
kind 16   FLOAT      info_sz 0    elem_sz 0    flags 0
kind 17   DECL_TAG   info_sz 4    elem_sz 0    flags 0
kind 18   TYPE_TAG   info_sz 0    elem_sz 0    flags 0
kind 19   ENUM64     info_sz 0    elem_sz 12   flags 0

JSON output is also supported:

$ bpftool -p btf dump file /var/tmp/vmlinux.kind_layout format meta
{
    "size": 6516862,
    "header": {
        "magic": 60319,
        "version": 1,
        "flags": 0,
        "hdr_len": 32,
        "type_len": 3929096,
        "type_off": 0,
        "str_len": 2587654,
        "str_off": 3929176,
        "layout_len": 80,
        "layout_offset": 3929096
    },
    "layouts": [{
            "kind": 0,
            "name": "UNKNOWN",
            "info_sz": 0,
            "elem_sz": 0,
            "flags": 0
        },{
            "kind": 1,
            "name": "INT",
            "info_sz": 4,
            "elem_sz": 0,
            "flags": 0
        },{
            "kind": 2,
            "name": "PTR",
            "info_sz": 0,
            "elem_sz": 0,
            "flags": 0
        },{
...

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/bpf/bpftool/bash-completion/bpftool |  2 +-
 tools/bpf/bpftool/btf.c                   | 94 ++++++++++++++++++++++-
 2 files changed, 92 insertions(+), 4 deletions(-)

diff --git a/tools/bpf/bpftool/bash-completion/bpftool b/tools/bpf/bpftool/bash-completion/bpftool
index a28f0cc522e4..d49d6a70cb74 100644
--- a/tools/bpf/bpftool/bash-completion/bpftool
+++ b/tools/bpf/bpftool/bash-completion/bpftool
@@ -950,7 +950,7 @@ _bpftool()
                             return 0
                             ;;
                         format)
-                            COMPREPLY=( $( compgen -W "c raw" -- "$cur" ) )
+                            COMPREPLY=( $( compgen -W "c raw meta" -- "$cur" ) )
                             ;;
                         root_id)
                             return 0;
diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 946612029dee..02f6ca4b3a51 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -835,6 +835,90 @@ static int dump_btf_c(const struct btf *btf,
 	return err;
 }
 
+static int dump_btf_meta(const struct btf *btf)
+{
+	__u32 data_sz, i, nr_kinds = 0;
+	const struct btf_header *hdr;
+	const struct btf_layout *l;
+	const void *data;
+
+	data = btf__raw_data(btf, &data_sz);
+	if (!data)
+		return -ENOMEM;
+	hdr = data;
+	if (json_output) {
+		jsonw_start_object(json_wtr);		/* metadata object */
+		jsonw_uint_field(json_wtr, "size", data_sz);
+		jsonw_name(json_wtr, "header");
+		jsonw_start_object(json_wtr);		/* header object */
+		jsonw_uint_field(json_wtr, "magic", hdr->magic);
+		jsonw_uint_field(json_wtr, "version", hdr->version);
+		jsonw_uint_field(json_wtr, "flags", hdr->flags);
+		jsonw_uint_field(json_wtr, "hdr_len", hdr->hdr_len);
+		jsonw_uint_field(json_wtr, "type_len", hdr->type_len);
+		jsonw_uint_field(json_wtr, "type_off", hdr->type_off);
+		jsonw_uint_field(json_wtr, "str_len", hdr->str_len);
+		jsonw_uint_field(json_wtr, "str_off", hdr->str_off);
+	} else {
+		printf("size %-10u\n", data_sz);
+		printf("magic 0x%-10x\nversion %-10d\nflags 0x%-10x\nhdr_len %-10u\n",
+		       hdr->magic, hdr->version, hdr->flags, hdr->hdr_len);
+		printf("type_len %-10u\ntype_off %-10u\n", hdr->type_len, hdr->type_off);
+		printf("str_len %-10u\nstr_off %-10u\n", hdr->str_len, hdr->str_off);
+	}
+
+	if (hdr->hdr_len < sizeof(struct btf_header) || data_sz <= hdr->hdr_len) {
+		if (json_output) {
+			jsonw_end_object(json_wtr);	/* end header object */
+			jsonw_end_object(json_wtr);	/* end metadata object */
+		}
+		return 0;
+	}
+
+	data_sz -= hdr->hdr_len;
+
+	if (hdr->layout_len > 0 && hdr->layout_off > 0) {
+		if ((long long)hdr->layout_off + hdr->layout_len <= data_sz) {
+			l = (void *)hdr + hdr->hdr_len + hdr->layout_off;
+			nr_kinds = hdr->layout_len / sizeof(*l);
+		}
+	}
+	if (json_output) {
+		jsonw_uint_field(json_wtr, "layout_len", hdr->layout_len);
+		jsonw_uint_field(json_wtr, "layout_offset", hdr->layout_off);
+		jsonw_end_object(json_wtr);		/* end header object */
+
+		if (nr_kinds > 0) {
+			jsonw_name(json_wtr, "layouts");
+			jsonw_start_array(json_wtr);
+			for (i = 0; i < nr_kinds; i++) {
+				jsonw_start_object(json_wtr);
+				jsonw_uint_field(json_wtr, "kind", i);
+				if (i < NR_BTF_KINDS)
+					jsonw_string_field(json_wtr, "name", btf_kind_str[i]);
+				else
+					jsonw_null_field(json_wtr, "name");
+				jsonw_uint_field(json_wtr, "info_sz", l[i].info_sz);
+				jsonw_uint_field(json_wtr, "elem_sz", l[i].elem_sz);
+				jsonw_uint_field(json_wtr, "flags", l[i].flags);
+				jsonw_end_object(json_wtr);
+			}
+			jsonw_end_array(json_wtr);
+		}
+		jsonw_end_object(json_wtr);		/* end metadata object */
+	} else {
+		printf("layout_len %-10u\nlayout_off %-10u\n",
+		       hdr->layout_len, hdr->layout_off);
+		for (i = 0; i < nr_kinds; i++) {
+			printf("kind %-4u %-10s info_sz %-4d elem_sz %-4d flags %-4d\n",
+			       i, i < NR_BTF_KINDS ? btf_kind_str[i] : "?",
+			       l[i].info_sz, l[i].elem_sz, l[i].flags);
+		}
+	}
+
+	return 0;
+}
+
 static const char sysfs_vmlinux[] = "/sys/kernel/btf/vmlinux";
 
 static struct btf *get_vmlinux_btf_from_sysfs(void)
@@ -880,7 +964,7 @@ static bool btf_is_kernel_module(__u32 btf_id)
 
 static int do_dump(int argc, char **argv)
 {
-	bool dump_c = false, sort_dump_c = true;
+	bool dump_c = false, sort_dump_c = true, dump_meta = false;
 	struct btf *btf = NULL, *base = NULL;
 	__u32 root_type_ids[MAX_ROOT_IDS];
 	bool have_id_filtering;
@@ -990,10 +1074,12 @@ static int do_dump(int argc, char **argv)
 			}
 			if (strcmp(*argv, "c") == 0) {
 				dump_c = true;
+			} else if (is_prefix(*argv, "meta")) {
+				dump_meta = true;
 			} else if (strcmp(*argv, "raw") == 0) {
 				dump_c = false;
 			} else {
-				p_err("unrecognized format specifier: '%s', possible values: raw, c",
+				p_err("unrecognized format specifier: '%s', possible values: raw, c, meta",
 				      *argv);
 				err = -EINVAL;
 				goto done;
@@ -1072,6 +1158,8 @@ static int do_dump(int argc, char **argv)
 			goto done;
 		}
 		err = dump_btf_c(btf, root_type_ids, root_type_cnt, sort_dump_c);
+	} else if (dump_meta) {
+		err = dump_btf_meta(btf);
 	} else {
 		err = dump_btf_raw(btf, root_type_ids, root_type_cnt);
 	}
@@ -1446,7 +1534,7 @@ static int do_help(int argc, char **argv)
 		"       %1$s %2$s help\n"
 		"\n"
 		"       BTF_SRC := { id BTF_ID | prog PROG | map MAP [{key | value | kv | all}] | file FILE }\n"
-		"       FORMAT  := { raw | c [unsorted] }\n"
+		"       FORMAT  := { raw | c [unsorted] | meta }\n"
 		"       " HELP_SPEC_MAP "\n"
 		"       " HELP_SPEC_PROGRAM "\n"
 		"       " HELP_SPEC_OPTIONS " |\n"
-- 
2.39.3

...and provide an example of output.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 .../bpf/bpftool/Documentation/bpftool-btf.rst | 28 +++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/Documentation/bpftool-btf.rst b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
index d47dddc2b4ee..ea1b5cdecd0a 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-btf.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
@@ -28,7 +28,7 @@ BTF COMMANDS
 | **bpftool** **btf help**
 |
 | *BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
-| *FORMAT* := { **raw** | **c** [**unsorted**] }
+| *FORMAT* := { **raw** | **c** [**unsorted**] | **meta** }
 | *MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
 | *PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* | **name** *PROG_NAME* }
 
@@ -65,7 +65,8 @@ bpftool btf dump *BTF_SRC* [format *FORMAT*] [root_id *ROOT_ID*]
     **format** option can be used to override default (raw) output format. Raw
     (**raw**) or C-syntax (**c**) output formats are supported. With C-style
     formatting, the output is sorted by default. Use the **unsorted** option
-    to avoid sorting the output.
+    to avoid sorting the output.  BTF metadata can be displayed with the
+    **meta** option.
 
     **root_id** option can be used to filter a dump to a single type and all
     its dependent types. It cannot be used with any other types of filtering
@@ -267,3 +268,26 @@ All the standard ways to specify map or program are supported:
   [104859] FUNC 'smbalert_work' type_id=9695 linkage=static
   [104860] FUNC 'smbus_alert' type_id=71367 linkage=static
   [104861] FUNC 'smbus_do_alert' type_id=84827 linkage=static
+
+Display BTF metadata from file vmlinux
+
+**# bpftool btf dump file vmlinux format meta**
+
+::
+
+  size 5161076
+  magic 0xeb9f
+  version 1
+  flags 0x1
+  hdr_len 40
+  type_len 3036368
+  type_off 0
+  str_len 2124588
+  str_off 3036368
+  layout_len 80
+  layout_off 5160956
+  kind 0    UNKNOWN    info_sz 0    elem_sz 0
+  kind 1    INT        info_sz 0    elem_sz 0
+  kind 2    PTR        info_sz 0    elem_sz 0
+  kind 3    ARRAY      info_sz 0    elem_sz 0
+  kind 4    STRUCT     info_sz 0    elem_sz 0
-- 
2.39.3

The "layout" feature will add metadata about BTF kinds to the
generated BTF; its absence in pahole will not trigger an error so it
is safe to add unconditionally as it will simply be ignored if pahole
does not support it.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 scripts/Makefile.btf | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
index 562a04b40e06..e66e13e79653 100644
--- a/scripts/Makefile.btf
+++ b/scripts/Makefile.btf
@@ -18,6 +18,8 @@ pahole-flags-$(call test-ge, $(pahole-ver), 126)  = -j$(JOBS) --btf_features=enc
 
 pahole-flags-$(call test-ge, $(pahole-ver), 130) += --btf_features=attributes
 
+pahole-flags-$(call test-ge, $(pahole-ver), 131) += --btf_features=layout
+
 endif
 
 pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)		+= --lang_exclude=rust
-- 
2.39.3