Re: [PATCH v8 bpf-next 02/10] libbpf: Support kind layout section handling in BTF

[Eduard Zingerman <eddyz87@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 5789 bytes --]

On Mon, 2025-12-15 at 09:17 +0000, Alan Maguire wrote:

Hi Alan,

Overall makes sense, please fine one suggestion below.

> Support reading in kind layout fixing endian issues on reading;
> also support writing kind layout section to raw BTF object.
> There is not yet an API to populate the kind layout with meaningful
> information.
> 
> As part of this, we need to consider multiple valid BTF header
> sizes; the original or the kind layout-extended headers.
> So to support this, the "struct btf" representation is modified
> to always allocate a "struct btf_header" and copy the valid
> portion from the raw data to it; this means we can always safely
> check fields like btf->hdr->kind_layout_len.
> 
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  tools/lib/bpf/btf.c | 260 +++++++++++++++++++++++++++++++-------------
>  1 file changed, 183 insertions(+), 77 deletions(-)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index b136572e889a..8835aee6ee84 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, 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  |  Strings  |Optional kind layout |
> +	 * +--------------------------------+---------------------+
> +	 * ^          ^         ^           ^
> +	 * |          |         |           |
> +	 * raw_data   |         |           |
> +	 * types_data-+         |           |
> +	 * strs_data------------+           |
> +	 * kind_layout----------------------+
> +	 *
> +	 * A separate struct btf_header is allocated for 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 kind layout, 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, strings
> +	 * and optionally kind_layout.  kind_layout optionally points to a
> +	 * kind_layout array - this allows us to encode information about
> +	 * the kinds known at encoding time.  If kind_layout is NULL no
> +	 * kind information is encoded.
>  	 *
> -	 * +----------+  +---------+  +-----------+
> -	 * |  Header  |  |  Types  |  |  Strings  |
> -	 * +----------+  +---------+  +-----------+
> -	 * ^             ^            ^
> -	 * |             |            |
> -	 * hdr           |            |
> -	 * types_data----+            |
> -	 * strset__data(strs_set)-----+
> +	 * +----------+  +---------+  +-----------+   +-----------+
> +	 * |  Header  |  |  Types  |  |  Strings  |   |kind_layout|
> +	 * +----------+  +---------+  +-----------+   +-----------+
> +	 * ^             ^            ^               ^
> +	 * |             |            |               |
> +	 * hdr           |            |               |
> +	 * types_data----+            |               |
> +	 * strset__data(strs_set)-----+               |
> +	 * kind_layout--------------------------------+
>  	 *
> -	 *               +----------+---------+-----------+
> -	 *               |  Header  |  Types  |  Strings  |
> -	 * raw_data----->+----------+---------+-----------+
> +	 *               +----------+---------+-----------+---------------------+
> +	 *               |  Header  |  Types  |  Strings  | Optional kind layout|
> +	 * raw_data----->+----------+---------+-----------+---------------------+
>  	 */
> -	struct btf_header *hdr;
> +	struct btf_header *hdr; /* separately-allocated header data */

Do we want to directly embed this structure?
E.g. as in the diff attached.
No need to bother with calloc/free in such case.

>  
>  	void *types_data;
>  	size_t types_data_cap; /* used size stored in hdr->type_len */
> @@ -123,6 +134,13 @@ 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 *kind_layout;
> +
>  	/* BTF object FD, if loaded into kernel */
>  	int fd;
>  
> @@ -214,7 +232,7 @@ 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);

[...]

Thanks,
Eduard

[-- Attachment #2: embed-hdr.diff --]
[-- Type: text/x-patch, Size: 16269 bytes --]

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 6098c8d1e26a..af4eb27d2f54 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -115,7 +115,7 @@ struct btf {
 	 *               |  Header  |  Types  |  Strings  | Optional kind layout|
 	 * raw_data----->+----------+---------+-----------+---------------------+
 	 */
-	struct btf_header *hdr; /* separately-allocated header data */
+	struct btf_header hdr; /* copy of the header data */
 
 	void *types_data;
 	size_t types_data_cap; /* used size stored in hdr->type_len */
@@ -307,46 +307,41 @@ static int btf_parse_hdr(struct btf *btf)
 		return -EINVAL;
 	}
 
-	/* At this point, we have basic header information, so allocate btf->hdr */
-	btf->hdr = calloc(1, sizeof(struct btf_header));
-	if (!btf->hdr) {
-		pr_debug("BTF header allocation failed\n");
-		return -ENOMEM;
-	}
-	memcpy(btf->hdr, hdr, min((size_t)hdr_len, sizeof(struct btf_header)));
+	/* At this point, we have basic header information, so copy to btf->hdr */
+	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) {
+	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)btf->hdr->type_off + btf->hdr->type_len > btf->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",
-			 btf->hdr->type_off, btf->hdr->type_len, btf->hdr->str_off,
-			 btf->hdr->str_len);
+			 btf->hdr.type_off, btf->hdr.type_len, btf->hdr.str_off,
+			 btf->hdr.str_len);
 		return -EINVAL;
 	}
 
-	if (btf->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->kind_layout_len == 0)
+	if (btf->hdr.kind_layout_len == 0)
 		return 0;
 
-	if (btf->hdr->kind_layout_off % 4) {
+	if (btf->hdr.kind_layout_off % 4) {
 		pr_debug("BTF kind_layout section is not aligned to 4 bytes\n");
 		return -EINVAL;
 	}
-	if (btf->hdr->kind_layout_off < btf->hdr->str_off + btf->hdr->str_len) {
+	if (btf->hdr.kind_layout_off < btf->hdr.str_off + btf->hdr.str_len) {
 		pr_debug("Invalid BTF data sections layout: strings data at %u + %u, kind layout data at %u + %u\n",
-			 btf->hdr->str_off, btf->hdr->str_len,
-			 btf->hdr->kind_layout_off, btf->hdr->kind_layout_len);
+			 btf->hdr.str_off, btf->hdr.str_len,
+			 btf->hdr.kind_layout_off, btf->hdr.kind_layout_len);
 		return -EINVAL;
 	}
-	if (btf->hdr->kind_layout_off + btf->hdr->kind_layout_len > meta_left) {
+	if (btf->hdr.kind_layout_off + btf->hdr.kind_layout_len > meta_left) {
 		pr_debug("Invalid BTF total size: %u\n", btf->raw_size);
 		return -EINVAL;
 	}
@@ -355,9 +350,9 @@ static int btf_parse_hdr(struct btf *btf)
 
 static int btf_parse_str_sec(struct btf *btf)
 {
-	const struct btf_header *hdr = btf->hdr;
+	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)
 		return 0;
@@ -374,7 +369,7 @@ static int btf_parse_str_sec(struct btf *btf)
 
 static int btf_parse_kind_layout_sec(struct btf *btf)
 {
-	const struct btf_header *hdr = btf->hdr;
+	const struct btf_header *hdr = &btf->hdr;
 
 	if (!hdr->kind_layout_len)
 		return 0;
@@ -383,7 +378,7 @@ static int btf_parse_kind_layout_sec(struct btf *btf)
 		pr_debug("Invalid BTF kind layout section\n");
 		return -EINVAL;
 	}
-	btf->kind_layout = btf->raw_data + btf->hdr->hdr_len + btf->hdr->kind_layout_off;
+	btf->kind_layout = btf->raw_data + btf->hdr.hdr_len + btf->hdr.kind_layout_off;
 
 	return 0;
 }
@@ -397,7 +392,7 @@ static int btf_type_size_unknown(const struct btf *btf, const struct btf_type *t
 	__u8 kind = btf_kind(t);
 	__u32 off = kind * sizeof(struct btf_kind_layout);
 
-	if (!btf->kind_layout || off >= btf->hdr->kind_layout_len) {
+	if (!btf->kind_layout || off >= btf->hdr.kind_layout_len) {
 		pr_debug("Unsupported BTF_KIND: %u\n", btf_kind(t));
 		return -EINVAL;
 	}
@@ -535,7 +530,7 @@ 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;
+	struct btf_header *hdr = &btf->hdr;
 	void *next_type = btf->types_data;
 	void *end_type = next_type + hdr->type_len;
 	int err, type_size;
@@ -1105,7 +1100,6 @@ void btf__free(struct btf *btf)
 		strset__free(btf->strs_set);
 		free(btf->kind_layout);
 	}
-	free(btf->hdr);
 	btf_free_raw_data(btf);
 	free(btf->raw_data_swapped);
 	free(btf->type_offs);
@@ -1135,7 +1129,7 @@ static struct btf *btf_new_empty(struct btf_new_opts *opts)
 	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;
 	}
 
@@ -1157,20 +1151,13 @@ static struct btf *btf_new_empty(struct btf_new_opts *opts)
 	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 */
-	btf->hdr = calloc(1, sizeof(struct btf_header));
-	if (!btf->hdr) {
-		free(btf->raw_data);
-		free(btf);
-		return ERR_PTR(-ENOMEM);
-	}
-
 	if (add_kind_layout) {
 		hdr->kind_layout_len = sizeof(kind_layouts);
 		hdr->kind_layout_off = roundup(hdr->str_len, 4);
 		btf->kind_layout = btf->raw_data + hdr->hdr_len + hdr->kind_layout_off;
 		memcpy(btf->kind_layout, kind_layouts, sizeof(kind_layouts));
 	}
-	memcpy(btf->hdr, hdr, sizeof(*hdr));
+	memcpy(&btf->hdr, hdr, sizeof(*hdr));
 
 	return btf;
 }
@@ -1216,7 +1203,7 @@ 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) {
@@ -1237,8 +1224,8 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf, b
 	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_kind_layout_sec(btf);
@@ -1692,7 +1679,7 @@ 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;
@@ -1774,7 +1761,7 @@ 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;
@@ -1897,21 +1884,21 @@ static int btf_ensure_modifiable(struct btf *btf)
 	}
 
 	/* split raw data into memory regions; btf->hdr is done already. */
-	types = malloc(btf->hdr->type_len);
+	types = malloc(btf->hdr.type_len);
 	if (!types)
 		goto err_out;
-	memcpy(types, btf->types_data, btf->hdr->type_len);
+	memcpy(types, btf->types_data, btf->hdr.type_len);
 
-	if (btf->hdr->kind_layout_len) {
-		kind_layout = malloc(btf->hdr->kind_layout_len);
+	if (btf->hdr.kind_layout_len) {
+		kind_layout = malloc(btf->hdr.kind_layout_len);
 		if (!kind_layout)
 			goto err_out;
-		memcpy(kind_layout, btf->raw_data + btf->hdr->hdr_len + btf->hdr->kind_layout_off,
-		       btf->hdr->kind_layout_len);
+		memcpy(kind_layout, btf->raw_data + btf->hdr.hdr_len + btf->hdr.kind_layout_off,
+		       btf->hdr.kind_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;
@@ -1919,7 +1906,7 @@ static int btf_ensure_modifiable(struct btf *btf)
 
 	/* only when everything was successful, update internal state */
 	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 (kind_layout)
@@ -1927,9 +1914,9 @@ static int btf_ensure_modifiable(struct btf *btf)
 	/* 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 */
@@ -1995,7 +1982,7 @@ 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;
 }
@@ -2003,7 +1990,7 @@ 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)
@@ -2013,28 +2000,28 @@ static void btf_type_inc_vlen(struct btf_type *t)
 
 static void btf_hdr_update_type_len(struct btf *btf, int new_len)
 {
-	btf->hdr->type_len = new_len;
-	btf->hdr->str_off = new_len;
+	btf->hdr.type_len = new_len;
+	btf->hdr.str_off = new_len;
 	if (btf->kind_layout)
-		btf->hdr->kind_layout_off = btf->hdr->type_len + roundup(btf->hdr->str_len, 4);
+		btf->hdr.kind_layout_off = btf->hdr.type_len + roundup(btf->hdr.str_len, 4);
 }
 
 static void btf_hdr_update_str_len(struct btf *btf, int new_len)
 {
-	btf->hdr->str_len = new_len;
+	btf->hdr.str_len = new_len;
 	if (btf->kind_layout)
-		btf->hdr->kind_layout_off = btf->hdr->type_len + roundup(new_len, 4);
+		btf->hdr.kind_layout_off = btf->hdr.type_len + roundup(new_len, 4);
 }
 
 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_update_type_len(btf, btf->hdr->type_len + 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;
 }
@@ -2138,9 +2125,9 @@ 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 */
@@ -2214,7 +2201,7 @@ 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_update_type_len(btf, btf->hdr->type_len + data_sz);
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + data_sz);
 	btf->nr_types += cnt;
 
 	hashmap__free(p.str_off_map);
@@ -2225,8 +2212,8 @@ 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
@@ -2549,7 +2536,7 @@ 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_update_type_len(btf, btf->hdr->type_len + sz);
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -2658,7 +2645,7 @@ 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_update_type_len(btf, btf->hdr->type_len + sz);
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -2729,7 +2716,7 @@ 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_update_type_len(btf, btf->hdr->type_len + sz);
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -2967,7 +2954,7 @@ 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_update_type_len(btf, btf->hdr->type_len + sz);
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -3103,7 +3090,7 @@ 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_update_type_len(btf, btf->hdr->type_len + sz);
+	btf_hdr_update_type_len(btf, btf->hdr.type_len + sz);
 	return 0;
 }
 
@@ -5514,18 +5501,18 @@ 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;
+	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->kind_layout) {
-		d->btf->hdr->kind_layout_off = d->btf->hdr->str_off + roundup(d->btf->hdr->str_len,
+		d->btf->hdr.kind_layout_off = d->btf->hdr.str_off + roundup(d->btf->hdr.str_len,
 									      4);
-		d->btf->raw_size = roundup(d->btf->raw_size, 4) + d->btf->hdr->kind_layout_len;
+		d->btf->raw_size = roundup(d->btf->raw_size, 4) + d->btf->hdr.kind_layout_len;
 	}
 	return 0;
 }
@@ -5984,7 +5971,7 @@ 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
@@ -6053,14 +6040,14 @@ 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)