// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/* Copyright (c) 2018 Facebook */

#include <byteswap.h>
#include <endian.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <sys/utsname.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <linux/kernel.h>
#include <linux/err.h>
#include <linux/btf.h>
#include <gelf.h>
#include "btf.h"
#include "bpf.h"
#include "libbpf.h"
#include "libbpf_internal.h"
#include "hashmap.h"
#include "strset.h"

#define BTF_MAX_NR_TYPES 0x7fffffffU
#define BTF_MAX_STR_OFFSET 0x7fffffffU

static struct btf_type btf_void;

struct btf {
        /* raw BTF data in native endianness */
        void *raw_data;
        /* raw BTF data in non-native endianness */
        void *raw_data_swapped;
        __u32 raw_size;
        /* whether target endianness differs from the native one */
        bool swapped_endian;

        /*
         * 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
         * point inside that memory region to their respective parts of BTF
         * representation:
         *
         * +--------------------------------+
         * |  Header  |  Types  |  Strings  |
         * +--------------------------------+
         * ^          ^         ^
         * |          |         |
         * hdr        |         |
         * types_data-+         |
         * strs_data------------+
         *
         * 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.
         * raw_data is nulled out at that point, but can be later allocated
         * and cached again if user calls btf__get_raw_data(), at which point
         * raw_data will contain a contiguous copy of header, types, and
         * strings:
         *
         * +----------+  +---------+  +-----------+
         * |  Header  |  |  Types  |  |  Strings  |
         * +----------+  +---------+  +-----------+
         * ^             ^            ^
         * |             |            |
         * hdr           |            |
         * types_data----+            |
         * strset__data(strs_set)-----+
         *
         *               +----------+---------+-----------+
         *               |  Header  |  Types  |  Strings  |
         * raw_data----->+----------+---------+-----------+
         */
        struct btf_header *hdr;

        void *types_data;
        size_t types_data_cap; /* used size stored in hdr->type_len */

        /* 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;

        /* only one of strs_data or strs_set can be non-NULL, depending on
         * whether BTF is in a modifiable state (strs_set is used) or not
         * (strs_data points inside raw_data)
         */
        void *strs_data;
        /* a set of unique strings */
        struct strset *strs_set;
        /* whether strings are already deduplicated */
        bool strs_deduped;

        /* BTF object FD, if loaded into kernel */
        int fd;

        /* Pointer size (in bytes) for a target architecture of this BTF */
        int ptr_sz;
};

static inline __u64 ptr_to_u64(const void *ptr)
{
        return (__u64) (unsigned long) ptr;
}

/* Ensure given dynamically allocated memory region pointed to by *data* with
 * capacity of *cap_cnt* elements each taking *elem_sz* bytes has enough
 * memory to accomodate *add_cnt* new elements, assuming *cur_cnt* elements
 * are already used. At most *max_cnt* elements can be ever allocated.
 * If necessary, memory is reallocated and all existing data is copied over,
 * new pointer to the memory region is stored at *data, new memory region
 * capacity (in number of elements) is stored in *cap.
 * On success, memory pointer to the beginning of unused memory is returned.
 * On error, NULL is returned.
 */
void *libbpf_add_mem(void **data, size_t *cap_cnt, size_t elem_sz,
                     size_t cur_cnt, size_t max_cnt, size_t add_cnt)
{
        size_t new_cnt;
        void *new_data;

        if (cur_cnt + add_cnt <= *cap_cnt)
                return *data + cur_cnt * elem_sz;

        /* requested more than the set limit */
        if (cur_cnt + add_cnt > max_cnt)
                return NULL;

        new_cnt = *cap_cnt;
        new_cnt += new_cnt / 4;           /* expand by 25% */
        if (new_cnt < 16)                 /* but at least 16 elements */
                new_cnt = 16;
        if (new_cnt > max_cnt)            /* but not exceeding a set limit */
                new_cnt = max_cnt;
        if (new_cnt < cur_cnt + add_cnt)  /* also ensure we have enough memory */
                new_cnt = cur_cnt + add_cnt;

        new_data = libbpf_reallocarray(*data, new_cnt, elem_sz);
        if (!new_data)
                return NULL;

        /* zero out newly allocated portion of memory */
        memset(new_data + (*cap_cnt) * elem_sz, 0, (new_cnt - *cap_cnt) * elem_sz);

        *data = new_data;
        *cap_cnt = new_cnt;
        return new_data + cur_cnt * elem_sz;
}

/* Ensure given dynamically allocated memory region has enough allocated space
 * to accommodate *need_cnt* elements of size *elem_sz* bytes each
 */
int libbpf_ensure_mem(void **data, size_t *cap_cnt, size_t elem_sz, size_t need_cnt)
{
        void *p;

        if (need_cnt <= *cap_cnt)
                return 0;

        p = libbpf_add_mem(data, cap_cnt, elem_sz, *cap_cnt, SIZE_MAX, need_cnt - *cap_cnt);
        if (!p)
                return -ENOMEM;

        return 0;
}

static int btf_add_type_idx_entry(struct btf *btf, __u32 type_off)
{
        __u32 *p;

        p = libbpf_add_mem((void **)&btf->type_offs, &btf->type_offs_cap, sizeof(__u32),
                           btf->nr_types, BTF_MAX_NR_TYPES, 1);
        if (!p)
                return -ENOMEM;

        *p = type_off;
        return 0;
}

static void btf_bswap_hdr(struct btf_header *h)
{
        h->magic = bswap_16(h->magic);
        h->hdr_len = bswap_32(h->hdr_len);
        h->type_off = bswap_32(h->type_off);
        h->type_len = bswap_32(h->type_len);
        h->str_off = bswap_32(h->str_off);
        h->str_len = bswap_32(h->str_len);
}

static int btf_parse_hdr(struct btf *btf)
{
        struct btf_header *hdr = btf->hdr;
        __u32 meta_left;

        if (btf->raw_size < sizeof(struct btf_header)) {
                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)) {
                        pr_warn("Can't load BTF with non-native endianness due to unsupported header length %u\n",
                                bswap_32(hdr->hdr_len));
                        return -ENOTSUP;
                }
                btf_bswap_hdr(hdr);
        } else if (hdr->magic != BTF_MAGIC) {
                pr_debug("Invalid BTF magic:%x\n", hdr->magic);
                return -EINVAL;
        }

        meta_left = btf->raw_size - sizeof(*hdr);
        if (meta_left < hdr->str_off + hdr->str_len) {
                pr_debug("Invalid BTF total size:%u\n", btf->raw_size);
                return -EINVAL;
        }

        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 % 4) {
                pr_debug("BTF type section is not aligned to 4 bytes\n");
                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;

        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;
}

static int btf_type_size(const struct btf_type *t)
{
        const int base_size = sizeof(struct btf_type);
        __u16 vlen = btf_vlen(t);

        switch (btf_kind(t)) {
        case BTF_KIND_FWD:
        case BTF_KIND_CONST:
        case BTF_KIND_VOLATILE:
        case BTF_KIND_RESTRICT:
        case BTF_KIND_PTR:
        case BTF_KIND_TYPEDEF:
        case BTF_KIND_FUNC:
        case BTF_KIND_FLOAT:
                return base_size;
        case BTF_KIND_INT:
                return base_size + sizeof(__u32);
        case BTF_KIND_ENUM:
                return base_size + vlen * sizeof(struct btf_enum);
        case BTF_KIND_ARRAY:
                return base_size + sizeof(struct btf_array);
        case BTF_KIND_STRUCT:
        case BTF_KIND_UNION:
                return base_size + vlen * sizeof(struct btf_member);
        case BTF_KIND_FUNC_PROTO:
                return base_size + vlen * sizeof(struct btf_param);
        case BTF_KIND_VAR:
                return base_size + sizeof(struct btf_var);
        case BTF_KIND_DATASEC:
                return base_size + vlen * sizeof(struct btf_var_secinfo);
        default:
                pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
                return -EINVAL;
        }
}

static void btf_bswap_type_base(struct btf_type *t)
{
        t->name_off = bswap_32(t->name_off);
        t->info = bswap_32(t->info);
        t->type = bswap_32(t->type);
}

static int btf_bswap_type_rest(struct btf_type *t)
{
        struct btf_var_secinfo *v;
        struct btf_member *m;
        struct btf_array *a;
        struct btf_param *p;
        struct btf_enum *e;
        __u16 vlen = btf_vlen(t);
        int i;

        switch (btf_kind(t)) {
        case BTF_KIND_FWD:
        case BTF_KIND_CONST:
        case BTF_KIND_VOLATILE:
        case BTF_KIND_RESTRICT:
        case BTF_KIND_PTR:
        case BTF_KIND_TYPEDEF:
        case BTF_KIND_FUNC:
        case BTF_KIND_FLOAT:
                return 0;
        case BTF_KIND_INT:
                *(__u32 *)(t + 1) = bswap_32(*(__u32 *)(t + 1));
                return 0;
        case BTF_KIND_ENUM:
                for (i = 0, e = btf_enum(t); i < vlen; i++, e++) {
                        e->name_off = bswap_32(e->name_off);
                        e->val = bswap_32(e->val);
                }
                return 0;
        case BTF_KIND_ARRAY:
                a = btf_array(t);
                a->type = bswap_32(a->type);
                a->index_type = bswap_32(a->index_type);
                a->nelems = bswap_32(a->nelems);
                return 0;
        case BTF_KIND_STRUCT:
        case BTF_KIND_UNION:
                for (i = 0, m = btf_members(t); i < vlen; i++, m++) {
                        m->name_off = bswap_32(m->name_off);
                        m->type = bswap_32(m->type);
                        m->offset = bswap_32(m->offset);
                }
                return 0;
        case BTF_KIND_FUNC_PROTO:
                for (i = 0, p = btf_params(t); i < vlen; i++, p++) {
                        p->name_off = bswap_32(p->name_off);
                        p->type = bswap_32(p->type);
                }
                return 0;
        case BTF_KIND_VAR:
                btf_var(t)->linkage = bswap_32(btf_var(t)->linkage);
                return 0;
        case BTF_KIND_DATASEC:
                for (i = 0, v = btf_var_secinfos(t); i < vlen; i++, v++) {
                        v->type = bswap_32(v->type);
                        v->offset = bswap_32(v->offset);
                        v->size = bswap_32(v->size);
                }
                return 0;
        default:
                pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
                return -EINVAL;
        }
}

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, type_size;

        while (next_type + sizeof(struct btf_type) <= end_type) {
                if (btf->swapped_endian)
                        btf_bswap_type_base(next_type);

                type_size = btf_type_size(next_type);
                if (type_size < 0)
                        return type_size;
                if (next_type + type_size > end_type) {
                        pr_warn("BTF type [%d] is malformed\n", btf->start_id + btf->nr_types);
                        return -EINVAL;
                }

                if (btf->swapped_endian && btf_bswap_type_rest(next_type))
                        return -EINVAL;

                err = btf_add_type_idx_entry(btf, next_type - btf->types_data);
                if (err)
                        return err;

                next_type += type_size;
                btf->nr_types++;
        }

        if (next_type != end_type) {
                pr_warn("BTF types data is malformed\n");
                return -EINVAL;
        }

        return 0;
}

__u32 btf__get_nr_types(const struct btf *btf)
{
        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 */
struct btf_type *btf_type_by_id(struct btf *btf, __u32 type_id)
{
        if (type_id == 0)
                return &btf_void;
        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->start_id + btf->nr_types)
                return errno = EINVAL, NULL;
        return btf_type_by_id((struct btf *)btf, type_id);
}

static int determine_ptr_size(const struct btf *btf)
{
        const struct btf_type *t;
        const char *name;
        int i, n;

        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;

                name = btf__name_by_offset(btf, t->name_off);
                if (!name)
                        continue;

                if (strcmp(name, "long int") == 0 ||
                    strcmp(name, "long unsigned int") == 0) {
                        if (t->size != 4 && t->size != 8)
                                continue;
                        return t->size;
                }
        }

        return -1;
}

static size_t btf_ptr_sz(const struct btf *btf)
{
        if (!btf->ptr_sz)
                ((struct btf *)btf)->ptr_sz = determine_ptr_size(btf);
        return btf->ptr_sz < 0 ? sizeof(void *) : btf->ptr_sz;
}

/* Return pointer size this BTF instance assumes. The size is heuristically
 * determined by looking for 'long' or 'unsigned long' integer type and
 * recording its size in bytes. If BTF type information doesn't have any such
 * type, this function returns 0. In the latter case, native architecture's
 * pointer size is assumed, so will be either 4 or 8, depending on
 * architecture that libbpf was compiled for. It's possible to override
 * guessed value by using btf__set_pointer_size() API.
 */
size_t btf__pointer_size(const struct btf *btf)
{
        if (!btf->ptr_sz)
                ((struct btf *)btf)->ptr_sz = determine_ptr_size(btf);

        if (btf->ptr_sz < 0)
                /* not enough BTF type info to guess */
                return 0;

        return btf->ptr_sz;
}

/* Override or set pointer size in bytes. Only values of 4 and 8 are
 * supported.
 */
int btf__set_pointer_size(struct btf *btf, size_t ptr_sz)
{
        if (ptr_sz != 4 && ptr_sz != 8)
                return libbpf_err(-EINVAL);
        btf->ptr_sz = ptr_sz;
        return 0;
}

static bool is_host_big_endian(void)
{
#if __BYTE_ORDER == __LITTLE_ENDIAN
        return false;
#elif __BYTE_ORDER == __BIG_ENDIAN
        return true;
#else
# error "Unrecognized __BYTE_ORDER__"
#endif
}

enum btf_endianness btf__endianness(const struct btf *btf)
{
        if (is_host_big_endian())
                return btf->swapped_endian ? BTF_LITTLE_ENDIAN : BTF_BIG_ENDIAN;
        else
                return btf->swapped_endian ? BTF_BIG_ENDIAN : BTF_LITTLE_ENDIAN;
}

int btf__set_endianness(struct btf *btf, enum btf_endianness endian)
{
        if (endian != BTF_LITTLE_ENDIAN && endian != BTF_BIG_ENDIAN)
                return libbpf_err(-EINVAL);

        btf->swapped_endian = is_host_big_endian() != (endian == BTF_BIG_ENDIAN);
        if (!btf->swapped_endian) {
                free(btf->raw_data_swapped);
                btf->raw_data_swapped = NULL;
        }
        return 0;
}

static bool btf_type_is_void(const struct btf_type *t)
{
        return t == &btf_void || btf_is_fwd(t);
}

static bool btf_type_is_void_or_null(const struct btf_type *t)
{
        return !t || btf_type_is_void(t);
}

#define MAX_RESOLVE_DEPTH 32

__s64 btf__resolve_size(const struct btf *btf, __u32 type_id)
{
        const struct btf_array *array;
        const struct btf_type *t;
        __u32 nelems = 1;
        __s64 size = -1;
        int i;

        t = btf__type_by_id(btf, type_id);
        for (i = 0; i < MAX_RESOLVE_DEPTH && !btf_type_is_void_or_null(t); i++) {
                switch (btf_kind(t)) {
                case BTF_KIND_INT:
                case BTF_KIND_STRUCT:
                case BTF_KIND_UNION:
                case BTF_KIND_ENUM:
                case BTF_KIND_DATASEC:
                case BTF_KIND_FLOAT:
                        size = t->size;
                        goto done;
                case BTF_KIND_PTR:
                        size = btf_ptr_sz(btf);
                        goto done;
                case BTF_KIND_TYPEDEF:
                case BTF_KIND_VOLATILE:
                case BTF_KIND_CONST:
                case BTF_KIND_RESTRICT:
                case BTF_KIND_VAR:
                        type_id = t->type;
                        break;
                case BTF_KIND_ARRAY:
                        array = btf_array(t);
                        if (nelems && array->nelems > UINT32_MAX / nelems)
                                return libbpf_err(-E2BIG);
                        nelems *= array->nelems;
                        type_id = array->type;
                        break;
                default:
                        return libbpf_err(-EINVAL);
                }

                t = btf__type_by_id(btf, type_id);
        }

done:
        if (size < 0)
                return libbpf_err(-EINVAL);
        if (nelems && size > UINT32_MAX / nelems)
                return libbpf_err(-E2BIG);

        return nelems * size;
}

int btf__align_of(const struct btf *btf, __u32 id)
{
        const struct btf_type *t = btf__type_by_id(btf, id);
        __u16 kind = btf_kind(t);

        switch (kind) {
        case BTF_KIND_INT:
        case BTF_KIND_ENUM:
        case BTF_KIND_FLOAT:
                return min(btf_ptr_sz(btf), (size_t)t->size);
        case BTF_KIND_PTR:
                return btf_ptr_sz(btf);
        case BTF_KIND_TYPEDEF:
        case BTF_KIND_VOLATILE:
        case BTF_KIND_CONST:
        case BTF_KIND_RESTRICT:
                return btf__align_of(btf, t->type);
        case BTF_KIND_ARRAY:
                return btf__align_of(btf, btf_array(t)->type);
        case BTF_KIND_STRUCT:
        case BTF_KIND_UNION: {
                const struct btf_member *m = btf_members(t);
                __u16 vlen = btf_vlen(t);
                int i, max_align = 1, align;

                for (i = 0; i < vlen; i++, m++) {
                        align = btf__align_of(btf, m->type);
                        if (align <= 0)
                                return libbpf_err(align);
                        max_align = max(max_align, align);
                }

                return max_align;
        }
        default:
                pr_warn("unsupported BTF_KIND:%u\n", btf_kind(t));
                return errno = EINVAL, 0;
        }
}

int btf__resolve_type(const struct btf *btf, __u32 type_id)
{
        const struct btf_type *t;
        int depth = 0;

        t = btf__type_by_id(btf, type_id);
        while (depth < MAX_RESOLVE_DEPTH &&
               !btf_type_is_void_or_null(t) &&
               (btf_is_mod(t) || btf_is_typedef(t) || btf_is_var(t))) {
                type_id = t->type;
                t = btf__type_by_id(btf, type_id);
                depth++;
        }

        if (depth == MAX_RESOLVE_DEPTH || btf_type_is_void_or_null(t))
                return libbpf_err(-EINVAL);

        return type_id;
}

__s32 btf__find_by_name(const struct btf *btf, const char *type_name)
{
        __u32 i, nr_types = btf__get_nr_types(btf);

        if (!strcmp(type_name, "void"))
                return 0;

        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);

                if (name && !strcmp(type_name, name))
                        return i;
        }

        return libbpf_err(-ENOENT);
}

__s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
                             __u32 kind)
{
        __u32 i, nr_types = btf__get_nr_types(btf);

        if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
                return 0;

        for (i = 1; i <= nr_types; i++) {
                const struct btf_type *t = btf__type_by_id(btf, i);
                const char *name;

                if (btf_kind(t) != kind)
                        continue;
                name = btf__name_by_offset(btf, t->name_off);
                if (name && !strcmp(type_name, name))
                        return i;
        }

        return libbpf_err(-ENOENT);
}

static bool btf_is_modifiable(const struct btf *btf)
{
        return (void *)btf->hdr != btf->raw_data;
}

void btf__free(struct btf *btf)
{
        if (IS_ERR_OR_NULL(btf))
                return;

        if (btf->fd >= 0)
                close(btf->fd);

        if (btf_is_modifiable(btf)) {
                /* if BTF was modified after loading, it will have a split
                 * in-memory representation for header, types, and strings
                 * 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->raw_data);
        free(btf->raw_data_swapped);
        free(btf->type_offs);
        free(btf);
}

static struct btf *btf_new_empty(struct btf *base_btf)
{
        struct btf *btf;

        btf = calloc(1, sizeof(*btf));
        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) + (base_btf ? 0 : 1);
        btf->raw_data = calloc(1, btf->raw_size);
        if (!btf->raw_data) {
                free(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;

        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 */

        return btf;
}

struct btf *btf__new_empty(void)
{
        return libbpf_ptr(btf_new_empty(NULL));
}

struct btf *btf__new_empty_split(struct btf *base_btf)
{
        return libbpf_ptr(btf_new_empty(base_btf));
}

static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
{
        struct btf *btf;
        int err;

        btf = calloc(1, sizeof(struct btf));
        if (!btf)
                return ERR_PTR(-ENOMEM);

        btf->nr_types = 0;
        btf->start_id = 1;
        btf->start_str_off = 0;
        btf->fd = -1;

        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;
                goto done;
        }
        memcpy(btf->raw_data, data, size);
        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;

        err = btf_parse_str_sec(btf);
        err = err ?: btf_parse_type_sec(btf);
        if (err)
                goto done;

done:
        if (err) {
                btf__free(btf);
                return ERR_PTR(err);
        }

        return btf;
}

struct btf *btf__new(const void *data, __u32 size)
{
        return libbpf_ptr(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;
        struct btf *btf = NULL;
        Elf_Scn *scn = NULL;
        Elf *elf = NULL;
        GElf_Ehdr ehdr;
        size_t shstrndx;

        if (elf_version(EV_CURRENT) == EV_NONE) {
                pr_warn("failed to init libelf for %s\n", path);
                return ERR_PTR(-LIBBPF_ERRNO__LIBELF);
        }

        fd = open(path, O_RDONLY);
        if (fd < 0) {
                err = -errno;
                pr_warn("failed to open %s: %s\n", path, strerror(errno));
                return ERR_PTR(err);
        }

        err = -LIBBPF_ERRNO__FORMAT;

        elf = elf_begin(fd, ELF_C_READ, NULL);
        if (!elf) {
                pr_warn("failed to open %s as ELF file\n", path);
                goto done;
        }
        if (!gelf_getehdr(elf, &ehdr)) {
                pr_warn("failed to get EHDR from %s\n", path);
                goto done;
        }

        if (elf_getshdrstrndx(elf, &shstrndx)) {
                pr_warn("failed to get section names section index for %s\n",
                        path);
                goto done;
        }

        if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) {
                pr_warn("failed to get e_shstrndx from %s\n", path);
                goto done;
        }

        while ((scn = elf_nextscn(elf, scn)) != NULL) {
                GElf_Shdr sh;
                char *name;

                idx++;
                if (gelf_getshdr(scn, &sh) != &sh) {
                        pr_warn("failed to get section(%d) header from %s\n",
                                idx, path);
                        goto done;
                }
                name = elf_strptr(elf, shstrndx, sh.sh_name);
                if (!name) {
                        pr_warn("failed to get section(%d) name from %s\n",
                                idx, path);
                        goto done;
                }
                if (strcmp(name, BTF_ELF_SEC) == 0) {
                        btf_data = elf_getdata(scn, 0);
                        if (!btf_data) {
                                pr_warn("failed to get section(%d, %s) data from %s\n",
                                        idx, name, path);
                                goto done;
                        }
                        continue;
                } else if (btf_ext && strcmp(name, BTF_EXT_ELF_SEC) == 0) {
                        btf_ext_data = elf_getdata(scn, 0);
                        if (!btf_ext_data) {
                                pr_warn("failed to get section(%d, %s) data from %s\n",
                                        idx, name, path);
                                goto done;
                        }
                        continue;
                }
        }

        err = 0;

        if (!btf_data) {
                err = -ENOENT;
                goto done;
        }
        btf = btf_new(btf_data->d_buf, btf_data->d_size, base_btf);
        err = libbpf_get_error(btf);
        if (err)
                goto done;

        switch (gelf_getclass(elf)) {
        case ELFCLASS32:
                btf__set_pointer_size(btf, 4);
                break;
        case ELFCLASS64:
                btf__set_pointer_size(btf, 8);
                break;
        default:
                pr_warn("failed to get ELF class (bitness) for %s\n", path);
                break;
        }

        if (btf_ext && btf_ext_data) {
                *btf_ext = btf_ext__new(btf_ext_data->d_buf, btf_ext_data->d_size);
                err = libbpf_get_error(*btf_ext);
                if (err)
                        goto done;
        } else if (btf_ext) {
                *btf_ext = NULL;
        }
done:
        if (elf)
                elf_end(elf);
        close(fd);

        if (!err)
                return btf;

        if (btf_ext)
                btf_ext__free(*btf_ext);
        btf__free(btf);

        return ERR_PTR(err);
}

struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)
{
        return libbpf_ptr(btf_parse_elf(path, NULL, btf_ext));
}

struct btf *btf__parse_elf_split(const char *path, struct btf *base_btf)
{
        return libbpf_ptr(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;
        FILE *f = NULL;
        __u16 magic;
        int err = 0;
        long sz;

        f = fopen(path, "rb");
        if (!f) {
                err = -errno;
                goto err_out;
        }

        /* check BTF magic */
        if (fread(&magic, 1, sizeof(magic), f) < sizeof(magic)) {
                err = -EIO;
                goto err_out;
        }
        if (magic != BTF_MAGIC && magic != bswap_16(BTF_MAGIC)) {
                /* definitely not a raw BTF */
                err = -EPROTO;
                goto err_out;
        }

        /* get file size */
        if (fseek(f, 0, SEEK_END)) {
                err = -errno;
                goto err_out;
        }
        sz = ftell(f);
        if (sz < 0) {
                err = -errno;
                goto err_out;
        }
        /* rewind to the start */
        if (fseek(f, 0, SEEK_SET)) {
                err = -errno;
                goto err_out;
        }

        /* pre-alloc memory and read all of BTF data */
        data = malloc(sz);
        if (!data) {
                err = -ENOMEM;
                goto err_out;
        }
        if (fread(data, 1, sz, f) < sz) {
                err = -EIO;
                goto err_out;
        }

        /* finally parse BTF data */
        btf = btf_new(data, sz, base_btf);

err_out:
        free(data);
        if (f)
                fclose(f);
        return err ? ERR_PTR(err) : btf;
}

struct btf *btf__parse_raw(const char *path)
{
        return libbpf_ptr(btf_parse_raw(path, NULL));
}

struct btf *btf__parse_raw_split(const char *path, struct btf *base_btf)
{
        return libbpf_ptr(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;
        int err;

        if (btf_ext)
                *btf_ext = NULL;

        btf = btf_parse_raw(path, base_btf);
        err = libbpf_get_error(btf);
        if (!err)
                return btf;
        if (err != -EPROTO)
                return ERR_PTR(err);
        return btf_parse_elf(path, base_btf, btf_ext);
}

struct btf *btf__parse(const char *path, struct btf_ext **btf_ext)
{
        return libbpf_ptr(btf_parse(path, NULL, btf_ext));
}

struct btf *btf__parse_split(const char *path, struct btf *base_btf)
{
        return libbpf_ptr(btf_parse(path, base_btf, NULL));
}

static int compare_vsi_off(const void *_a, const void *_b)
{
        const struct btf_var_secinfo *a = _a;
        const struct btf_var_secinfo *b = _b;

        return a->offset - b->offset;
}

static int btf_fixup_datasec(struct bpf_object *obj, struct btf *btf,
                             struct btf_type *t)
{
        __u32 size = 0, off = 0, i, vars = btf_vlen(t);
        const char *name = btf__name_by_offset(btf, t->name_off);
        const struct btf_type *t_var;
        struct btf_var_secinfo *vsi;
        const struct btf_var *var;
        int ret;

        if (!name) {
                pr_debug("No name found in string section for DATASEC kind.\n");
                return -ENOENT;
        }

        /* .extern datasec size and var offsets were set correctly during
         * extern collection step, so just skip straight to sorting variables
         */
        if (t->size)
                goto sort_vars;

        ret = bpf_object__section_size(obj, name, &size);
        if (ret || !size || (t->size && t->size != size)) {
                pr_debug("Invalid size for section %s: %u bytes\n", name, size);
                return -ENOENT;
        }

        t->size = size;

        for (i = 0, vsi = btf_var_secinfos(t); i < vars; i++, vsi++) {
                t_var = btf__type_by_id(btf, vsi->type);
                var = btf_var(t_var);

                if (!btf_is_var(t_var)) {
                        pr_debug("Non-VAR type seen in section %s\n", name);
                        return -EINVAL;
                }

                if (var->linkage == BTF_VAR_STATIC)
                        continue;

                name = btf__name_by_offset(btf, t_var->name_off);
                if (!name) {
                        pr_debug("No name found in string section for VAR kind\n");
                        return -ENOENT;
                }

                ret = bpf_object__variable_offset(obj, name, &off);
                if (ret) {
                        pr_debug("No offset found in symbol table for VAR %s\n",
                                 name);
                        return -ENOENT;
                }

                vsi->offset = off;
        }

sort_vars:
        qsort(btf_var_secinfos(t), vars, sizeof(*vsi), compare_vsi_off);
        return 0;
}

int btf__finalize_data(struct bpf_object *obj, struct btf *btf)
{
        int err = 0;
        __u32 i;

        for (i = 1; i <= btf->nr_types; i++) {
                struct btf_type *t = btf_type_by_id(btf, i);

                /* Loader needs to fix up some of the things compiler
                 * couldn't get its hands on while emitting BTF. This
                 * is section size and global variable offset. We use
                 * the info from the ELF itself for this purpose.
                 */
                if (btf_is_datasec(t)) {
                        err = btf_fixup_datasec(obj, btf, t);
                        if (err)
                                break;
                }
        }

        return libbpf_err(err);
}

static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian);

int btf__load_into_kernel(struct btf *btf)
{
        __u32 log_buf_size = 0, raw_size;
        char *log_buf = NULL;
        void *raw_data;
        int err = 0;

        if (btf->fd >= 0)
                return libbpf_err(-EEXIST);

retry_load:
        if (log_buf_size) {
                log_buf = malloc(log_buf_size);
                if (!log_buf)
                        return libbpf_err(-ENOMEM);

                *log_buf = 0;
        }

        raw_data = btf_get_raw_data(btf, &raw_size, false);
        if (!raw_data) {
                err = -ENOMEM;
                goto done;
        }
        /* cache native raw data representation */
        btf->raw_size = raw_size;
        btf->raw_data = raw_data;

        btf->fd = bpf_load_btf(raw_data, raw_size, log_buf, log_buf_size, false);
        if (btf->fd < 0) {
                if (!log_buf || errno == ENOSPC) {
                        log_buf_size = max((__u32)BPF_LOG_BUF_SIZE,
                                           log_buf_size << 1);
                        free(log_buf);
                        goto retry_load;
                }

                err = -errno;
                pr_warn("Error loading BTF: %s(%d)\n", strerror(errno), errno);
                if (*log_buf)
                        pr_warn("%s\n", log_buf);
                goto done;
        }

done:
        free(log_buf);
        return libbpf_err(err);
}
int btf__load(struct btf *) __attribute__((alias("btf__load_into_kernel")));

int btf__fd(const struct btf *btf)
{
        return btf->fd;
}

void btf__set_fd(struct btf *btf, int fd)
{
        btf->fd = fd;
}

static const void *btf_strs_data(const struct btf *btf)
{
        return btf->strs_data ? btf->strs_data : strset__data(btf->strs_set);
}

static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian)
{
        struct btf_header *hdr = btf->hdr;
        struct btf_type *t;
        void *data, *p;
        __u32 data_sz;
        int i;

        data = swap_endian ? btf->raw_data_swapped : btf->raw_data;
        if (data) {
                *size = btf->raw_size;
                return data;
        }

        data_sz = hdr->hdr_len + hdr->type_len + hdr->str_len;
        data = calloc(1, data_sz);
        if (!data)
                return NULL;
        p = data;

        memcpy(p, hdr, hdr->hdr_len);
        if (swap_endian)
                btf_bswap_hdr(p);
        p += hdr->hdr_len;

        memcpy(p, btf->types_data, hdr->type_len);
        if (swap_endian) {
                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
                         */
                        if (btf_bswap_type_rest(t))
                                goto err_out;
                        btf_bswap_type_base(t);
                }
        }
        p += hdr->type_len;

        memcpy(p, btf_strs_data(btf), hdr->str_len);
        p += hdr->str_len;

        *size = data_sz;
        return data;
err_out:
        free(data);
        return NULL;
}

const void *btf__get_raw_data(const struct btf *btf_ro, __u32 *size)
{
        struct btf *btf = (struct btf *)btf_ro;
        __u32 data_sz;
        void *data;

        data = btf_get_raw_data(btf, &data_sz, btf->swapped_endian);
        if (!data)
                return errno = -ENOMEM, NULL;

        btf->raw_size = data_sz;
        if (btf->swapped_endian)
                btf->raw_data_swapped = data;
        else
                btf->raw_data = data;
        *size = data_sz;
        return data;
}

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)
                return btf_strs_data(btf) + (offset - btf->start_str_off);
        else
                return errno = EINVAL, NULL;
}

const char *btf__name_by_offset(const struct btf *btf, __u32 offset)
{
        return btf__str_by_offset(btf, offset);
}

struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
{
        struct bpf_btf_info btf_info;
        __u32 len = sizeof(btf_info);
        __u32 last_size;
        struct btf *btf;
        void *ptr;
        int err;

        /* 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.
         */
        last_size = 4096;
        ptr = malloc(last_size);
        if (!ptr)
                return ERR_PTR(-ENOMEM);

        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) {
                void *temp_ptr;

                last_size = btf_info.btf_size;
                temp_ptr = realloc(ptr, last_size);
                if (!temp_ptr) {
                        btf = ERR_PTR(-ENOMEM);
                        goto exit_free;
                }
                ptr = temp_ptr;

                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) {
                btf = err ? ERR_PTR(-errno) : ERR_PTR(-E2BIG);
                goto exit_free;
        }

        btf = btf_new(ptr, btf_info.btf_size, base_btf);

exit_free:
        free(ptr);
        return btf;
}

struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
{
        struct btf *btf;
        int btf_fd;

        btf_fd = bpf_btf_get_fd_by_id(id);
        if (btf_fd < 0)
                return libbpf_err_ptr(-errno);

        btf = btf_get_from_fd(btf_fd, base_btf);
        close(btf_fd);

        return libbpf_ptr(btf);
}

struct btf *btf__load_from_kernel_by_id(__u32 id)
{
        return btf__load_from_kernel_by_id_split(id, NULL);
}

int btf__get_from_id(__u32 id, struct btf **btf)
{
        struct btf *res;
        int err;

        *btf = NULL;
        res = btf__load_from_kernel_by_id(id);
        err = libbpf_get_error(res);

        if (err)
                return libbpf_err(err);

        *btf = res;
        return 0;
}

int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
                         __u32 expected_key_size, __u32 expected_value_size,
                         __u32 *key_type_id, __u32 *value_type_id)
{
        const struct btf_type *container_type;
        const struct btf_member *key, *value;
        const size_t max_name = 256;
        char container_name[max_name];
        __s64 key_size, value_size;
        __s32 container_id;

        if (snprintf(container_name, max_name, "____btf_map_%s", map_name) == max_name) {
                pr_warn("map:%s length of '____btf_map_%s' is too long\n",
                        map_name, map_name);
                return libbpf_err(-EINVAL);
        }

        container_id = btf__find_by_name(btf, container_name);
        if (container_id < 0) {
                pr_debug("map:%s container_name:%s cannot be found in BTF. Missing BPF_ANNOTATE_KV_PAIR?\n",
                         map_name, container_name);
                return libbpf_err(container_id);
        }

        container_type = btf__type_by_id(btf, container_id);
        if (!container_type) {
                pr_warn("map:%s cannot find BTF type for container_id:%u\n",
                        map_name, container_id);
                return libbpf_err(-EINVAL);
        }

        if (!btf_is_struct(container_type) || btf_vlen(container_type) < 2) {
                pr_warn("map:%s container_name:%s is an invalid container struct\n",
                        map_name, container_name);
                return libbpf_err(-EINVAL);
        }

        key = btf_members(container_type);
        value = key + 1;

        key_size = btf__resolve_size(btf, key->type);
        if (key_size < 0) {
                pr_warn("map:%s invalid BTF key_type_size\n", map_name);
                return libbpf_err(key_size);
        }

        if (expected_key_size != key_size) {
                pr_warn("map:%s btf_key_type_size:%u != map_def_key_size:%u\n",
                        map_name, (__u32)key_size, expected_key_size);
                return libbpf_err(-EINVAL);
        }

        value_size = btf__resolve_size(btf, value->type);
        if (value_size < 0) {
                pr_warn("map:%s invalid BTF value_type_size\n", map_name);
                return libbpf_err(value_size);
        }

        if (expected_value_size != value_size) {
                pr_warn("map:%s btf_value_type_size:%u != map_def_value_size:%u\n",
                        map_name, (__u32)value_size, expected_value_size);
                return libbpf_err(-EINVAL);
        }

        *key_type_id = key->type;
        *value_type_id = value->type;

        return 0;
}

static void btf_invalidate_raw_data(struct btf *btf)
{
        if (btf->raw_data) {
                free(btf->raw_data);
                btf->raw_data = NULL;
        }
        if (btf->raw_data_swapped) {
                free(btf->raw_data_swapped);
                btf->raw_data_swapped = NULL;
        }
}

/* Ensure BTF is ready to be modified (by splitting into a three memory
 * regions for header, types, and strings). Also invalidate cached
 * raw_data, if any.
 */
static int btf_ensure_modifiable(struct btf *btf)
{
        void *hdr, *types;
        struct strset *set = NULL;
        int err = -ENOMEM;

        if (btf_is_modifiable(btf)) {
                /* any BTF modification invalidates raw_data */
                btf_invalidate_raw_data(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)
                goto err_out;

        memcpy(hdr, btf->hdr, btf->hdr->hdr_len);
        memcpy(types, btf->types_data, btf->hdr->type_len);

        /* build lookup index for all strings */
        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->strs_data = NULL;
        btf->strs_set = set;
        /* if BTF was created from scratch, all strings are guaranteed to be
         * unique and deduplicated
         */
        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);

        return 0;

err_out:
        strset__free(set);
        free(hdr);
        free(types);
        return err;
}

/* Find an offset in BTF string section that corresponds to a given string *s*.
 * Returns:
 *   - >0 offset into string section, if string is found;
 *   - -ENOENT, if string is not in the string section;
 *   - <0, on any other error.
 */
int btf__find_str(struct btf *btf, const char *s)
{
        int off;

        if (btf->base_btf) {
                off = btf__find_str(btf->base_btf, s);
                if (off != -ENOENT)
                        return off;
        }

        /* BTF needs to be in a modifiable state to build string lookup index */
        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        off = strset__find_str(btf->strs_set, s);
        if (off < 0)
                return libbpf_err(off);

        return btf->start_str_off + off;
}

/* Add a string s to the BTF string section.
 * Returns:
 *   - > 0 offset into string section, on success;
 *   - < 0, on error.
 */
int btf__add_str(struct btf *btf, const char *s)
{
        int off;

        if (btf->base_btf) {
                off = btf__find_str(btf->base_btf, s);
                if (off != -ENOENT)
                        return off;
        }

        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        off = strset__add_str(btf->strs_set, s);
        if (off < 0)
                return libbpf_err(off);

        btf->hdr->str_len = strset__data_size(btf->strs_set);

        return btf->start_str_off + off;
}

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);
}

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 libbpf_err(err);

        btf->hdr->type_len += data_sz;
        btf->hdr->str_off += data_sz;
        btf->nr_types++;
        return btf->start_id + btf->nr_types - 1;
}

struct btf_pipe {
        const struct btf *src;
        struct btf *dst;
};

static int btf_rewrite_str(__u32 *str_off, void *ctx)
{
        struct btf_pipe *p = ctx;
        int off;

        if (!*str_off) /* nothing to do for empty strings */
                return 0;

        off = btf__add_str(p->dst, btf__str_by_offset(p->src, *str_off));
        if (off < 0)
                return off;

        *str_off = off;
        return 0;
}

int btf__add_type(struct btf *btf, const struct btf *src_btf, const struct btf_type *src_type)
{
        struct btf_pipe p = { .src = src_btf, .dst = btf };
        struct btf_type *t;
        int sz, err;

        sz = btf_type_size(src_type);
        if (sz < 0)
                return libbpf_err(sz);

        /* deconstruct BTF, if necessary, and invalidate raw_data */
        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        memcpy(t, src_type, sz);

        err = btf_type_visit_str_offs(t, btf_rewrite_str, &p);
        if (err)
                return libbpf_err(err);

        return btf_commit_type(btf, sz);
}

/*
 * Append new BTF_KIND_INT type with:
 *   - *name* - non-empty, non-NULL type name;
 *   - *sz* - power-of-2 (1, 2, 4, ..) size of the type, in bytes;
 *   - encoding is a combination of BTF_INT_SIGNED, BTF_INT_CHAR, BTF_INT_BOOL.
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_int(struct btf *btf, const char *name, size_t byte_sz, int encoding)
{
        struct btf_type *t;
        int sz, name_off;

        /* non-empty name */
        if (!name || !name[0])
                return libbpf_err(-EINVAL);
        /* byte_sz must be power of 2 */
        if (!byte_sz || (byte_sz & (byte_sz - 1)) || byte_sz > 16)
                return libbpf_err(-EINVAL);
        if (encoding & ~(BTF_INT_SIGNED | BTF_INT_CHAR | BTF_INT_BOOL))
                return libbpf_err(-EINVAL);

        /* deconstruct BTF, if necessary, and invalidate raw_data */
        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_type) + sizeof(int);
        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        /* if something goes wrong later, we might end up with an extra string,
         * but that shouldn't be a problem, because BTF can't be constructed
         * completely anyway and will most probably be just discarded
         */
        name_off = btf__add_str(btf, name);
        if (name_off < 0)
                return name_off;

        t->name_off = name_off;
        t->info = btf_type_info(BTF_KIND_INT, 0, 0);
        t->size = byte_sz;
        /* set INT info, we don't allow setting legacy bit offset/size */
        *(__u32 *)(t + 1) = (encoding << 24) | (byte_sz * 8);

        return btf_commit_type(btf, sz);
}

/*
 * Append new BTF_KIND_FLOAT type with:
 *   - *name* - non-empty, non-NULL type name;
 *   - *sz* - size of the type, in bytes;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_float(struct btf *btf, const char *name, size_t byte_sz)
{
        struct btf_type *t;
        int sz, name_off;

        /* non-empty name */
        if (!name || !name[0])
                return libbpf_err(-EINVAL);

        /* byte_sz must be one of the explicitly allowed values */
        if (byte_sz != 2 && byte_sz != 4 && byte_sz != 8 && byte_sz != 12 &&
            byte_sz != 16)
                return libbpf_err(-EINVAL);

        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_type);
        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        name_off = btf__add_str(btf, name);
        if (name_off < 0)
                return name_off;

        t->name_off = name_off;
        t->info = btf_type_info(BTF_KIND_FLOAT, 0, 0);
        t->size = byte_sz;

        return btf_commit_type(btf, sz);
}

/* it's completely legal to append BTF types with type IDs pointing forward to
 * types that haven't been appended yet, so we only make sure that id looks
 * sane, we can't guarantee that ID will always be valid
 */
static int validate_type_id(int id)
{
        if (id < 0 || id > BTF_MAX_NR_TYPES)
                return -EINVAL;
        return 0;
}

/* generic append function for PTR, TYPEDEF, CONST/VOLATILE/RESTRICT */
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;

        if (validate_type_id(ref_type_id))
                return libbpf_err(-EINVAL);

        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_type);
        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        if (name && name[0]) {
                name_off = btf__add_str(btf, name);
                if (name_off < 0)
                        return name_off;
        }

        t->name_off = name_off;
        t->info = btf_type_info(kind, 0, 0);
        t->type = ref_type_id;

        return btf_commit_type(btf, sz);
}

/*
 * Append new BTF_KIND_PTR type with:
 *   - *ref_type_id* - referenced type ID, it might not exist yet;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_ptr(struct btf *btf, int ref_type_id)
{
        return btf_add_ref_kind(btf, BTF_KIND_PTR, NULL, ref_type_id);
}

/*
 * Append new BTF_KIND_ARRAY type with:
 *   - *index_type_id* - type ID of the type describing array index;
 *   - *elem_type_id* - type ID of the type describing array element;
 *   - *nr_elems* - the size of the array;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_array(struct btf *btf, int index_type_id, int elem_type_id, __u32 nr_elems)
{
        struct btf_type *t;
        struct btf_array *a;
        int sz;

        if (validate_type_id(index_type_id) || validate_type_id(elem_type_id))
                return libbpf_err(-EINVAL);

        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_type) + sizeof(struct btf_array);
        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        t->name_off = 0;
        t->info = btf_type_info(BTF_KIND_ARRAY, 0, 0);
        t->size = 0;

        a = btf_array(t);
        a->type = elem_type_id;
        a->index_type = index_type_id;
        a->nelems = nr_elems;

        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, name_off = 0;

        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_type);
        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        if (name && name[0]) {
                name_off = btf__add_str(btf, name);
                if (name_off < 0)
                        return name_off;
        }

        /* start out with vlen=0 and no kflag; this will be adjusted when
         * adding each member
         */
        t->name_off = name_off;
        t->info = btf_type_info(kind, 0, 0);
        t->size = bytes_sz;

        return btf_commit_type(btf, sz);
}

/*
 * Append new BTF_KIND_STRUCT type with:
 *   - *name* - name of the struct, can be NULL or empty for anonymous structs;
 *   - *byte_sz* - size of the struct, in bytes;
 *
 * Struct initially has no fields in it. Fields can be added by
 * btf__add_field() right after btf__add_struct() succeeds.
 *
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_struct(struct btf *btf, const char *name, __u32 byte_sz)
{
        return btf_add_composite(btf, BTF_KIND_STRUCT, name, byte_sz);
}

/*
 * Append new BTF_KIND_UNION type with:
 *   - *name* - name of the union, can be NULL or empty for anonymous union;
 *   - *byte_sz* - size of the union, in bytes;
 *
 * Union initially has no fields in it. Fields can be added by
 * btf__add_field() right after btf__add_union() succeeds. All fields
 * should have *bit_offset* of 0.
 *
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
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;
 *   - *type_id* - type ID for the type describing field type;
 *   - *bit_offset* - bit offset of the start of the field within struct/union;
 *   - *bit_size* - bit size of a bitfield, 0 for non-bitfield fields;
 * Returns:
 *   -  0, on success;
 *   - <0, on error.
 */
int btf__add_field(struct btf *btf, const char *name, int type_id,
                   __u32 bit_offset, __u32 bit_size)
{
        struct btf_type *t;
        struct btf_member *m;
        bool is_bitfield;
        int sz, name_off = 0;

        /* last type should be union/struct */
        if (btf->nr_types == 0)
                return libbpf_err(-EINVAL);
        t = btf_last_type(btf);
        if (!btf_is_composite(t))
                return libbpf_err(-EINVAL);

        if (validate_type_id(type_id))
                return libbpf_err(-EINVAL);
        /* best-effort bit field offset/size enforcement */
        is_bitfield = bit_size || (bit_offset % 8 != 0);
        if (is_bitfield && (bit_size == 0 || bit_size > 255 || bit_offset > 0xffffff))
                return libbpf_err(-EINVAL);

        /* only offset 0 is allowed for unions */
        if (btf_is_union(t) && bit_offset)
                return libbpf_err(-EINVAL);

        /* decompose and invalidate raw data */
        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_member);
        m = btf_add_type_mem(btf, sz);
        if (!m)
                return libbpf_err(-ENOMEM);

        if (name && name[0]) {
                name_off = btf__add_str(btf, name);
                if (name_off < 0)
                        return name_off;
        }

        m->name_off = name_off;
        m->type = type_id;
        m->offset = bit_offset | (bit_size << 24);

        /* btf_add_type_mem can invalidate t pointer */
        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));

        btf->hdr->type_len += sz;
        btf->hdr->str_off += sz;

        return 0;
}

/*
 * Append new BTF_KIND_ENUM type with:
 *   - *name* - name of the enum, can be NULL or empty for anonymous enums;
 *   - *byte_sz* - size of the enum, in bytes.
 *
 * Enum initially has no enum values in it (and corresponds to enum forward
 * declaration). Enumerator values can be added by btf__add_enum_value()
 * immediately after btf__add_enum() succeeds.
 *
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_enum(struct btf *btf, const char *name, __u32 byte_sz)
{
        struct btf_type *t;
        int sz, name_off = 0;

        /* byte_sz must be power of 2 */
        if (!byte_sz || (byte_sz & (byte_sz - 1)) || byte_sz > 8)
                return libbpf_err(-EINVAL);

        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_type);
        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        if (name && name[0]) {
                name_off = btf__add_str(btf, name);
                if (name_off < 0)
                        return name_off;
        }

        /* start out with vlen=0; it will be adjusted when adding enum values */
        t->name_off = name_off;
        t->info = btf_type_info(BTF_KIND_ENUM, 0, 0);
        t->size = byte_sz;

        return btf_commit_type(btf, sz);
}

/*
 * Append new enum value for the current ENUM type with:
 *   - *name* - name of the enumerator value, can't be NULL or empty;
 *   - *value* - integer value corresponding to enum value *name*;
 * Returns:
 *   -  0, on success;
 *   - <0, on error.
 */
int btf__add_enum_value(struct btf *btf, const char *name, __s64 value)
{
        struct btf_type *t;
        struct btf_enum *v;
        int sz, name_off;

        /* last type should be BTF_KIND_ENUM */
        if (btf->nr_types == 0)
                return libbpf_err(-EINVAL);
        t = btf_last_type(btf);
        if (!btf_is_enum(t))
                return libbpf_err(-EINVAL);

        /* non-empty name */
        if (!name || !name[0])
                return libbpf_err(-EINVAL);
        if (value < INT_MIN || value > UINT_MAX)
                return libbpf_err(-E2BIG);

        /* decompose and invalidate raw data */
        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_enum);
        v = btf_add_type_mem(btf, sz);
        if (!v)
                return libbpf_err(-ENOMEM);

        name_off = btf__add_str(btf, name);
        if (name_off < 0)
                return name_off;

        v->name_off = name_off;
        v->val = value;

        /* update parent type's vlen */
        t = btf_last_type(btf);
        btf_type_inc_vlen(t);

        btf->hdr->type_len += sz;
        btf->hdr->str_off += sz;
        return 0;
}

/*
 * Append new BTF_KIND_FWD type with:
 *   - *name*, non-empty/non-NULL name;
 *   - *fwd_kind*, kind of forward declaration, one of BTF_FWD_STRUCT,
 *     BTF_FWD_UNION, or BTF_FWD_ENUM;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_fwd(struct btf *btf, const char *name, enum btf_fwd_kind fwd_kind)
{
        if (!name || !name[0])
                return libbpf_err(-EINVAL);

        switch (fwd_kind) {
        case BTF_FWD_STRUCT:
        case BTF_FWD_UNION: {
                struct btf_type *t;
                int id;

                id = btf_add_ref_kind(btf, BTF_KIND_FWD, name, 0);
                if (id <= 0)
                        return id;
                t = btf_type_by_id(btf, id);
                t->info = btf_type_info(BTF_KIND_FWD, 0, fwd_kind == BTF_FWD_UNION);
                return id;
        }
        case BTF_FWD_ENUM:
                /* enum forward in BTF currently is just an enum with no enum
                 * values; we also assume a standard 4-byte size for it
                 */
                return btf__add_enum(btf, name, sizeof(int));
        default:
                return libbpf_err(-EINVAL);
        }
}

/*
 * Append new BTF_KING_TYPEDEF type with:
 *   - *name*, non-empty/non-NULL name;
 *   - *ref_type_id* - referenced type ID, it might not exist yet;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_typedef(struct btf *btf, const char *name, int ref_type_id)
{
        if (!name || !name[0])
                return libbpf_err(-EINVAL);

        return btf_add_ref_kind(btf, BTF_KIND_TYPEDEF, name, ref_type_id);
}

/*
 * Append new BTF_KIND_VOLATILE type with:
 *   - *ref_type_id* - referenced type ID, it might not exist yet;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_volatile(struct btf *btf, int ref_type_id)
{
        return btf_add_ref_kind(btf, BTF_KIND_VOLATILE, NULL, ref_type_id);
}

/*
 * Append new BTF_KIND_CONST type with:
 *   - *ref_type_id* - referenced type ID, it might not exist yet;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_const(struct btf *btf, int ref_type_id)
{
        return btf_add_ref_kind(btf, BTF_KIND_CONST, NULL, ref_type_id);
}

/*
 * Append new BTF_KIND_RESTRICT type with:
 *   - *ref_type_id* - referenced type ID, it might not exist yet;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_restrict(struct btf *btf, int ref_type_id)
{
        return btf_add_ref_kind(btf, BTF_KIND_RESTRICT, NULL, ref_type_id);
}

/*
 * Append new BTF_KIND_FUNC type with:
 *   - *name*, non-empty/non-NULL name;
 *   - *proto_type_id* - FUNC_PROTO's type ID, it might not exist yet;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_func(struct btf *btf, const char *name,
                  enum btf_func_linkage linkage, int proto_type_id)
{
        int id;

        if (!name || !name[0])
                return libbpf_err(-EINVAL);
        if (linkage != BTF_FUNC_STATIC && linkage != BTF_FUNC_GLOBAL &&
            linkage != BTF_FUNC_EXTERN)
                return libbpf_err(-EINVAL);

        id = btf_add_ref_kind(btf, BTF_KIND_FUNC, name, proto_type_id);
        if (id > 0) {
                struct btf_type *t = btf_type_by_id(btf, id);

                t->info = btf_type_info(BTF_KIND_FUNC, linkage, 0);
        }
        return libbpf_err(id);
}

/*
 * Append new BTF_KIND_FUNC_PROTO with:
 *   - *ret_type_id* - type ID for return result of a function.
 *
 * Function prototype initially has no arguments, but they can be added by
 * btf__add_func_param() one by one, immediately after
 * btf__add_func_proto() succeeded.
 *
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_func_proto(struct btf *btf, int ret_type_id)
{
        struct btf_type *t;
        int sz;

        if (validate_type_id(ret_type_id))
                return libbpf_err(-EINVAL);

        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_type);
        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        /* start out with vlen=0; this will be adjusted when adding enum
         * values, if necessary
         */
        t->name_off = 0;
        t->info = btf_type_info(BTF_KIND_FUNC_PROTO, 0, 0);
        t->type = ret_type_id;

        return btf_commit_type(btf, sz);
}

/*
 * Append new function parameter for current FUNC_PROTO type with:
 *   - *name* - parameter name, can be NULL or empty;
 *   - *type_id* - type ID describing the type of the parameter.
 * Returns:
 *   -  0, on success;
 *   - <0, on error.
 */
int btf__add_func_param(struct btf *btf, const char *name, int type_id)
{
        struct btf_type *t;
        struct btf_param *p;
        int sz, name_off = 0;

        if (validate_type_id(type_id))
                return libbpf_err(-EINVAL);

        /* last type should be BTF_KIND_FUNC_PROTO */
        if (btf->nr_types == 0)
                return libbpf_err(-EINVAL);
        t = btf_last_type(btf);
        if (!btf_is_func_proto(t))
                return libbpf_err(-EINVAL);

        /* decompose and invalidate raw data */
        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_param);
        p = btf_add_type_mem(btf, sz);
        if (!p)
                return libbpf_err(-ENOMEM);

        if (name && name[0]) {
                name_off = btf__add_str(btf, name);
                if (name_off < 0)
                        return name_off;
        }

        p->name_off = name_off;
        p->type = type_id;

        /* update parent type's vlen */
        t = btf_last_type(btf);
        btf_type_inc_vlen(t);

        btf->hdr->type_len += sz;
        btf->hdr->str_off += sz;
        return 0;
}

/*
 * Append new BTF_KIND_VAR type with:
 *   - *name* - non-empty/non-NULL name;
 *   - *linkage* - variable linkage, one of BTF_VAR_STATIC,
 *     BTF_VAR_GLOBAL_ALLOCATED, or BTF_VAR_GLOBAL_EXTERN;
 *   - *type_id* - type ID of the type describing the type of the variable.
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
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, name_off;

        /* non-empty name */
        if (!name || !name[0])
                return libbpf_err(-EINVAL);
        if (linkage != BTF_VAR_STATIC && linkage != BTF_VAR_GLOBAL_ALLOCATED &&
            linkage != BTF_VAR_GLOBAL_EXTERN)
                return libbpf_err(-EINVAL);
        if (validate_type_id(type_id))
                return libbpf_err(-EINVAL);

        /* deconstruct BTF, if necessary, and invalidate raw_data */
        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_type) + sizeof(struct btf_var);
        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        name_off = btf__add_str(btf, name);
        if (name_off < 0)
                return name_off;

        t->name_off = name_off;
        t->info = btf_type_info(BTF_KIND_VAR, 0, 0);
        t->type = type_id;

        v = btf_var(t);
        v->linkage = linkage;

        return btf_commit_type(btf, sz);
}

/*
 * Append new BTF_KIND_DATASEC type with:
 *   - *name* - non-empty/non-NULL name;
 *   - *byte_sz* - data section size, in bytes.
 *
 * Data section is initially empty. Variables info can be added with
 * btf__add_datasec_var_info() calls, after btf__add_datasec() succeeds.
 *
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_datasec(struct btf *btf, const char *name, __u32 byte_sz)
{
        struct btf_type *t;
        int sz, name_off;

        /* non-empty name */
        if (!name || !name[0])
                return libbpf_err(-EINVAL);

        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_type);
        t = btf_add_type_mem(btf, sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        name_off = btf__add_str(btf, name);
        if (name_off < 0)
                return name_off;

        /* start with vlen=0, which will be update as var_secinfos are added */
        t->name_off = name_off;
        t->info = btf_type_info(BTF_KIND_DATASEC, 0, 0);
        t->size = byte_sz;

        return btf_commit_type(btf, sz);
}

/*
 * Append new data section variable information entry for current DATASEC type:
 *   - *var_type_id* - type ID, describing type of the variable;
 *   - *offset* - variable offset within data section, in bytes;
 *   - *byte_sz* - variable size, in bytes.
 *
 * Returns:
 *   -  0, on success;
 *   - <0, on error.
 */
int btf__add_datasec_var_info(struct btf *btf, int var_type_id, __u32 offset, __u32 byte_sz)
{
        struct btf_type *t;
        struct btf_var_secinfo *v;
        int sz;

        /* last type should be BTF_KIND_DATASEC */
        if (btf->nr_types == 0)
                return libbpf_err(-EINVAL);
        t = btf_last_type(btf);
        if (!btf_is_datasec(t))
                return libbpf_err(-EINVAL);

        if (validate_type_id(var_type_id))
                return libbpf_err(-EINVAL);

        /* decompose and invalidate raw data */
        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        sz = sizeof(struct btf_var_secinfo);
        v = btf_add_type_mem(btf, sz);
        if (!v)
                return libbpf_err(-ENOMEM);

        v->type = var_type_id;
        v->offset = offset;
        v->size = byte_sz;

        /* update parent type's vlen */
        t = btf_last_type(btf);
        btf_type_inc_vlen(t);

        btf->hdr->type_len += sz;
        btf->hdr->str_off += sz;
        return 0;
}

struct btf_ext_sec_setup_param {
        __u32 off;
        __u32 len;
        __u32 min_rec_size;
        struct btf_ext_info *ext_info;
        const char *desc;
};

static int btf_ext_setup_info(struct btf_ext *btf_ext,
                              struct btf_ext_sec_setup_param *ext_sec)
{
        const struct btf_ext_info_sec *sinfo;
        struct btf_ext_info *ext_info;
        __u32 info_left, record_size;
        /* The start of the info sec (including the __u32 record_size). */
        void *info;

        if (ext_sec->len == 0)
                return 0;

        if (ext_sec->off & 0x03) {
                pr_debug(".BTF.ext %s section is not aligned to 4 bytes\n",
                     ext_sec->desc);
                return -EINVAL;
        }

        info = btf_ext->data + btf_ext->hdr->hdr_len + ext_sec->off;
        info_left = ext_sec->len;

        if (btf_ext->data + btf_ext->data_size < info + ext_sec->len) {
                pr_debug("%s section (off:%u len:%u) is beyond the end of the ELF section .BTF.ext\n",
                         ext_sec->desc, ext_sec->off, ext_sec->len);
                return -EINVAL;
        }

        /* At least a record size */
        if (info_left < sizeof(__u32)) {
                pr_debug(".BTF.ext %s record size not found\n", ext_sec->desc);
                return -EINVAL;
        }

        /* The record size needs to meet the minimum standard */
        record_size = *(__u32 *)info;
        if (record_size < ext_sec->min_rec_size ||
            record_size & 0x03) {
                pr_debug("%s section in .BTF.ext has invalid record size %u\n",
                         ext_sec->desc, record_size);
                return -EINVAL;
        }

        sinfo = info + sizeof(__u32);
        info_left -= sizeof(__u32);

        /* If no records, return failure now so .BTF.ext won't be used. */
        if (!info_left) {
                pr_debug("%s section in .BTF.ext has no records", ext_sec->desc);
                return -EINVAL;
        }

        while (info_left) {
                unsigned int sec_hdrlen = sizeof(struct btf_ext_info_sec);
                __u64 total_record_size;
                __u32 num_records;

                if (info_left < sec_hdrlen) {
                        pr_debug("%s section header is not found in .BTF.ext\n",
                             ext_sec->desc);
                        return -EINVAL;
                }

                num_records = sinfo->num_info;
                if (num_records == 0) {
                        pr_debug("%s section has incorrect num_records in .BTF.ext\n",
                             ext_sec->desc);
                        return -EINVAL;
                }

                total_record_size = sec_hdrlen +
                                    (__u64)num_records * record_size;
                if (info_left < total_record_size) {
                        pr_debug("%s section has incorrect num_records in .BTF.ext\n",
                             ext_sec->desc);
                        return -EINVAL;
                }

                info_left -= total_record_size;
                sinfo = (void *)sinfo + total_record_size;
        }

        ext_info = ext_sec->ext_info;
        ext_info->len = ext_sec->len - sizeof(__u32);
        ext_info->rec_size = record_size;
        ext_info->info = info + sizeof(__u32);

        return 0;
}

static int btf_ext_setup_func_info(struct btf_ext *btf_ext)
{
        struct btf_ext_sec_setup_param param = {
                .off = btf_ext->hdr->func_info_off,
                .len = btf_ext->hdr->func_info_len,
                .min_rec_size = sizeof(struct bpf_func_info_min),
                .ext_info = &btf_ext->func_info,
                .desc = "func_info"
        };

        return btf_ext_setup_info(btf_ext, &param);
}

static int btf_ext_setup_line_info(struct btf_ext *btf_ext)
{
        struct btf_ext_sec_setup_param param = {
                .off = btf_ext->hdr->line_info_off,
                .len = btf_ext->hdr->line_info_len,
                .min_rec_size = sizeof(struct bpf_line_info_min),
                .ext_info = &btf_ext->line_info,
                .desc = "line_info",
        };

        return btf_ext_setup_info(btf_ext, &param);
}

static int btf_ext_setup_core_relos(struct btf_ext *btf_ext)
{
        struct btf_ext_sec_setup_param param = {
                .off = btf_ext->hdr->core_relo_off,
                .len = btf_ext->hdr->core_relo_len,
                .min_rec_size = sizeof(struct bpf_core_relo),
                .ext_info = &btf_ext->core_relo_info,
                .desc = "core_relo",
        };

        return btf_ext_setup_info(btf_ext, &param);
}

static int btf_ext_parse_hdr(__u8 *data, __u32 data_size)
{
        const struct btf_ext_header *hdr = (struct btf_ext_header *)data;

        if (data_size < offsetofend(struct btf_ext_header, hdr_len) ||
            data_size < hdr->hdr_len) {
                pr_debug("BTF.ext header not found");
                return -EINVAL;
        }

        if (hdr->magic == bswap_16(BTF_MAGIC)) {
                pr_warn("BTF.ext in non-native endianness is not supported\n");
                return -ENOTSUP;
        } else if (hdr->magic != BTF_MAGIC) {
                pr_debug("Invalid BTF.ext magic:%x\n", hdr->magic);
                return -EINVAL;
        }

        if (hdr->version != BTF_VERSION) {
                pr_debug("Unsupported BTF.ext version:%u\n", hdr->version);
                return -ENOTSUP;
        }

        if (hdr->flags) {
                pr_debug("Unsupported BTF.ext flags:%x\n", hdr->flags);
                return -ENOTSUP;
        }

        if (data_size == hdr->hdr_len) {
                pr_debug("BTF.ext has no data\n");
                return -EINVAL;
        }

        return 0;
}

void btf_ext__free(struct btf_ext *btf_ext)
{
        if (IS_ERR_OR_NULL(btf_ext))
                return;
        free(btf_ext->data);
        free(btf_ext);
}

struct btf_ext *btf_ext__new(__u8 *data, __u32 size)
{
        struct btf_ext *btf_ext;
        int err;

        err = btf_ext_parse_hdr(data, size);
        if (err)
                return libbpf_err_ptr(err);

        btf_ext = calloc(1, sizeof(struct btf_ext));
        if (!btf_ext)
                return libbpf_err_ptr(-ENOMEM);

        btf_ext->data_size = size;
        btf_ext->data = malloc(size);
        if (!btf_ext->data) {
                err = -ENOMEM;
                goto done;
        }
        memcpy(btf_ext->data, data, size);

        if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, line_info_len)) {
                err = -EINVAL;
                goto done;
        }

        err = btf_ext_setup_func_info(btf_ext);
        if (err)
                goto done;

        err = btf_ext_setup_line_info(btf_ext);
        if (err)
                goto done;

        if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len)) {
                err = -EINVAL;
                goto done;
        }

        err = btf_ext_setup_core_relos(btf_ext);
        if (err)
                goto done;

done:
        if (err) {
                btf_ext__free(btf_ext);
                return libbpf_err_ptr(err);
        }

        return btf_ext;
}

const void *btf_ext__get_raw_data(const struct btf_ext *btf_ext, __u32 *size)
{
        *size = btf_ext->data_size;
        return btf_ext->data;
}

static int btf_ext_reloc_info(const struct btf *btf,
                              const struct btf_ext_info *ext_info,
                              const char *sec_name, __u32 insns_cnt,
                              void **info, __u32 *cnt)
{
        __u32 sec_hdrlen = sizeof(struct btf_ext_info_sec);
        __u32 i, record_size, existing_len, records_len;
        struct btf_ext_info_sec *sinfo;
        const char *info_sec_name;
        __u64 remain_len;
        void *data;

        record_size = ext_info->rec_size;
        sinfo = ext_info->info;
        remain_len = ext_info->len;
        while (remain_len > 0) {
                records_len = sinfo->num_info * record_size;
                info_sec_name = btf__name_by_offset(btf, sinfo->sec_name_off);
                if (strcmp(info_sec_name, sec_name)) {
                        remain_len -= sec_hdrlen + records_len;
                        sinfo = (void *)sinfo + sec_hdrlen + records_len;
                        continue;
                }

                existing_len = (*cnt) * record_size;
                data = realloc(*info, existing_len + records_len);
                if (!data)
                        return libbpf_err(-ENOMEM);

                memcpy(data + existing_len, sinfo->data, records_len);
                /* adjust insn_off only, the rest data will be passed
                 * to the kernel.
                 */
                for (i = 0; i < sinfo->num_info; i++) {
                        __u32 *insn_off;

                        insn_off = data + existing_len + (i * record_size);
                        *insn_off = *insn_off / sizeof(struct bpf_insn) + insns_cnt;
                }
                *info = data;
                *cnt += sinfo->num_info;
                return 0;
        }

        return libbpf_err(-ENOENT);
}

int btf_ext__reloc_func_info(const struct btf *btf,
                             const struct btf_ext *btf_ext,
                             const char *sec_name, __u32 insns_cnt,
                             void **func_info, __u32 *cnt)
{
        return btf_ext_reloc_info(btf, &btf_ext->func_info, sec_name,
                                  insns_cnt, func_info, cnt);
}

int btf_ext__reloc_line_info(const struct btf *btf,
                             const struct btf_ext *btf_ext,
                             const char *sec_name, __u32 insns_cnt,
                             void **line_info, __u32 *cnt)
{
        return btf_ext_reloc_info(btf, &btf_ext->line_info, sec_name,
                                  insns_cnt, line_info, cnt);
}

__u32 btf_ext__func_info_rec_size(const struct btf_ext *btf_ext)
{
        return btf_ext->func_info.rec_size;
}

__u32 btf_ext__line_info_rec_size(const struct btf_ext *btf_ext)
{
        return btf_ext->line_info.rec_size;
}

struct btf_dedup;

static struct btf_dedup *btf_dedup_new(struct btf *btf, struct btf_ext *btf_ext,
                                       const struct btf_dedup_opts *opts);
static void btf_dedup_free(struct btf_dedup *d);
static int btf_dedup_prep(struct btf_dedup *d);
static int btf_dedup_strings(struct btf_dedup *d);
static int btf_dedup_prim_types(struct btf_dedup *d);
static int btf_dedup_struct_types(struct btf_dedup *d);
static int btf_dedup_ref_types(struct btf_dedup *d);
static int btf_dedup_compact_types(struct btf_dedup *d);
static int btf_dedup_remap_types(struct btf_dedup *d);

/*
 * Deduplicate BTF types and strings.
 *
 * BTF dedup algorithm takes as an input `struct btf` representing `.BTF` ELF
 * section with all BTF type descriptors and string data. It overwrites that
 * memory in-place with deduplicated types and strings without any loss of
 * information. If optional `struct btf_ext` representing '.BTF.ext' ELF section
 * is provided, all the strings referenced from .BTF.ext section are honored
 * and updated to point to the right offsets after deduplication.
 *
 * If function returns with error, type/string data might be garbled and should
 * be discarded.
 *
 * More verbose and detailed description of both problem btf_dedup is solving,
 * as well as solution could be found at:
 * https://facebookmicrosites.github.io/bpf/blog/2018/11/14/btf-enhancement.html
 *
 * Problem description and justification
 * =====================================
 *
 * BTF type information is typically emitted either as a result of conversion
 * from DWARF to BTF or directly by compiler. In both cases, each compilation
 * unit contains information about a subset of all the types that are used
 * in an application. These subsets are frequently overlapping and contain a lot
 * of duplicated information when later concatenated together into a single
 * binary. This algorithm ensures that each unique type is represented by single
 * BTF type descriptor, greatly reducing resulting size of BTF data.
 *
 * Compilation unit isolation and subsequent duplication of data is not the only
 * problem. The same type hierarchy (e.g., struct and all the type that struct
 * references) in different compilation units can be represented in BTF to
 * various degrees of completeness (or, rather, incompleteness) due to
 * struct/union forward declarations.
 *
 * Let's take a look at an example, that we'll use to better understand the
 * problem (and solution). Suppose we have two compilation units, each using
 * same `struct S`, but each of them having incomplete type information about
 * struct's fields:
 *
 * // CU #1:
 * struct S;
 * struct A {
 *      int a;
 *      struct A* self;
 *      struct S* parent;
 * };
 * struct B;
 * struct S {
 *      struct A* a_ptr;
 *      struct B* b_ptr;
 * };
 *
 * // CU #2:
 * struct S;
 * struct A;
 * struct B {
 *      int b;
 *      struct B* self;
 *      struct S* parent;
 * };
 * struct S {
 *      struct A* a_ptr;
 *      struct B* b_ptr;
 * };
 *
 * In case of CU #1, BTF data will know only that `struct B` exist (but no
 * more), but will know the complete type information about `struct A`. While
 * for CU #2, it will know full type information about `struct B`, but will
 * only know about forward declaration of `struct A` (in BTF terms, it will
 * have `BTF_KIND_FWD` type descriptor with name `B`).
 *
 * This compilation unit isolation means that it's possible that there is no
 * single CU with complete type information describing structs `S`, `A`, and
 * `B`. Also, we might get tons of duplicated and redundant type information.
 *
 * Additional complication we need to keep in mind comes from the fact that
 * types, in general, can form graphs containing cycles, not just DAGs.
 *
 * While algorithm does deduplication, it also merges and resolves type
 * information (unless disabled throught `struct btf_opts`), whenever possible.
 * E.g., in the example above with two compilation units having partial type
 * information for structs `A` and `B`, the output of algorithm will emit
 * a single copy of each BTF type that describes structs `A`, `B`, and `S`
 * (as well as type information for `int` and pointers), as if they were defined
 * in a single compilation unit as:
 *
 * struct A {
 *      int a;
 *      struct A* self;
 *      struct S* parent;
 * };
 * struct B {
 *      int b;
 *      struct B* self;
 *      struct S* parent;
 * };
 * struct S {
 *      struct A* a_ptr;
 *      struct B* b_ptr;
 * };
 *
 * Algorithm summary
 * =================
 *
 * Algorithm completes its work in 6 separate passes:
 *
 * 1. Strings deduplication.
 * 2. Primitive types deduplication (int, enum, fwd).
 * 3. Struct/union types deduplication.
 * 4. Reference types deduplication (pointers, typedefs, arrays, funcs, func
 *    protos, and const/volatile/restrict modifiers).
 * 5. Types compaction.
 * 6. Types remapping.
 *
 * Algorithm determines canonical type descriptor, which is a single
 * representative type for each truly unique type. This canonical type is the
 * one that will go into final deduplicated BTF type information. For
 * struct/unions, it is also the type that algorithm will merge additional type
 * information into (while resolving FWDs), as it discovers it from data in
 * other CUs. Each input BTF type eventually gets either mapped to itself, if
 * that type is canonical, or to some other type, if that type is equivalent
 * and was chosen as canonical representative. This mapping is stored in
 * `btf_dedup->map` array. This map is also used to record STRUCT/UNION that
 * FWD type got resolved to.
 *
 * To facilitate fast discovery of canonical types, we also maintain canonical
 * index (`btf_dedup->dedup_table`), which maps type descriptor's signature hash
 * (i.e., hashed kind, name, size, fields, etc) into a list of canonical types
 * that match that signature. With sufficiently good choice of type signature
 * hashing function, we can limit number of canonical types for each unique type
 * signature to a very small number, allowing to find canonical type for any
 * duplicated type very quickly.
 *
 * Struct/union deduplication is the most critical part and algorithm for
 * deduplicating structs/unions is described in greater details in comments for
 * `btf_dedup_is_equiv` function.
 */
int btf__dedup(struct btf *btf, struct btf_ext *btf_ext,
               const struct btf_dedup_opts *opts)
{
        struct btf_dedup *d = btf_dedup_new(btf, btf_ext, opts);
        int err;

        if (IS_ERR(d)) {
                pr_debug("btf_dedup_new failed: %ld", PTR_ERR(d));
                return libbpf_err(-EINVAL);
        }

        if (btf_ensure_modifiable(btf))
                return libbpf_err(-ENOMEM);

        err = btf_dedup_prep(d);
        if (err) {
                pr_debug("btf_dedup_prep failed:%d\n", err);
                goto done;
        }
        err = btf_dedup_strings(d);
        if (err < 0) {
                pr_debug("btf_dedup_strings failed:%d\n", err);
                goto done;
        }
        err = btf_dedup_prim_types(d);
        if (err < 0) {
                pr_debug("btf_dedup_prim_types failed:%d\n", err);
                goto done;
        }
        err = btf_dedup_struct_types(d);
        if (err < 0) {
                pr_debug("btf_dedup_struct_types failed:%d\n", err);
                goto done;
        }
        err = btf_dedup_ref_types(d);
        if (err < 0) {
                pr_debug("btf_dedup_ref_types failed:%d\n", err);
                goto done;
        }
        err = btf_dedup_compact_types(d);
        if (err < 0) {
                pr_debug("btf_dedup_compact_types failed:%d\n", err);
                goto done;
        }
        err = btf_dedup_remap_types(d);
        if (err < 0) {
                pr_debug("btf_dedup_remap_types failed:%d\n", err);
                goto done;
        }

done:
        btf_dedup_free(d);
        return libbpf_err(err);
}

#define BTF_UNPROCESSED_ID ((__u32)-1)
#define BTF_IN_PROGRESS_ID ((__u32)-2)

struct btf_dedup {
        /* .BTF section to be deduped in-place */
        struct btf *btf;
        /*
         * Optional .BTF.ext section. When provided, any strings referenced
         * from it will be taken into account when deduping strings
         */
        struct btf_ext *btf_ext;
        /*
         * This is a map from any type's signature hash to a list of possible
         * canonical representative type candidates. Hash collisions are
         * ignored, so even types of various kinds can share same list of
         * candidates, which is fine because we rely on subsequent
         * btf_xxx_equal() checks to authoritatively verify type equality.
         */
        struct hashmap *dedup_table;
        /* Canonical types map */
        __u32 *map;
        /* Hypothetical mapping, used during type graph equivalence checks */
        __u32 *hypot_map;
        __u32 *hypot_list;
        size_t hypot_cnt;
        size_t hypot_cap;
        /* Whether hypothetical mapping, if successful, would need to adjust
         * already canonicalized types (due to a new forward declaration to
         * concrete type resolution). In such case, during split BTF dedup
         * candidate type would still be considered as different, because base
         * BTF is considered to be immutable.
         */
        bool hypot_adjust_canon;
        /* Various option modifying behavior of algorithm */
        struct btf_dedup_opts opts;
        /* temporary strings deduplication state */
        struct strset *strs_set;
};

static long hash_combine(long h, long value)

{
        return h * 31 + value;
}

#define for_each_dedup_cand(d, node, hash) \
        hashmap__for_each_key_entry(d->dedup_table, node, (void *)hash)

static int btf_dedup_table_add(struct btf_dedup *d, long hash, __u32 type_id)
{
        return hashmap__append(d->dedup_table,
                               (void *)hash, (void *)(long)type_id);
}

static int btf_dedup_hypot_map_add(struct btf_dedup *d,
                                   __u32 from_id, __u32 to_id)
{
        if (d->hypot_cnt == d->hypot_cap) {
                __u32 *new_list;

                d->hypot_cap += max((size_t)16, d->hypot_cap / 2);
                new_list = libbpf_reallocarray(d->hypot_list, d->hypot_cap, sizeof(__u32));
                if (!new_list)
                        return -ENOMEM;
                d->hypot_list = new_list;
        }
        d->hypot_list[d->hypot_cnt++] = from_id;
        d->hypot_map[from_id] = to_id;
        return 0;
}

static void btf_dedup_clear_hypot_map(struct btf_dedup *d)
{
        int i;

        for (i = 0; i < d->hypot_cnt; i++)
                d->hypot_map[d->hypot_list[i]] = BTF_UNPROCESSED_ID;
        d->hypot_cnt = 0;
        d->hypot_adjust_canon = false;
}

static void btf_dedup_free(struct btf_dedup *d)
{
        hashmap__free(d->dedup_table);
        d->dedup_table = NULL;

        free(d->map);
        d->map = NULL;

        free(d->hypot_map);
        d->hypot_map = NULL;

        free(d->hypot_list);
        d->hypot_list = NULL;

        free(d);
}

static size_t btf_dedup_identity_hash_fn(const void *key, void *ctx)
{
        return (size_t)key;
}

static size_t btf_dedup_collision_hash_fn(const void *key, void *ctx)
{
        return 0;
}

static bool btf_dedup_equal_fn(const void *k1, const void *k2, void *ctx)
{
        return k1 == k2;
}

static struct btf_dedup *btf_dedup_new(struct btf *btf, struct btf_ext *btf_ext,
                                       const struct btf_dedup_opts *opts)
{
        struct btf_dedup *d = calloc(1, sizeof(struct btf_dedup));
        hashmap_hash_fn hash_fn = btf_dedup_identity_hash_fn;
        int i, err = 0, type_cnt;

        if (!d)
                return ERR_PTR(-ENOMEM);

        d->opts.dont_resolve_fwds = opts && opts->dont_resolve_fwds;
        /* dedup_table_size is now used only to force collisions in tests */
        if (opts && opts->dedup_table_size == 1)
                hash_fn = btf_dedup_collision_hash_fn;

        d->btf = btf;
        d->btf_ext = btf_ext;

        d->dedup_table = hashmap__new(hash_fn, btf_dedup_equal_fn, NULL);
        if (IS_ERR(d->dedup_table)) {
                err = PTR_ERR(d->dedup_table);
                d->dedup_table = NULL;
                goto done;
        }

        type_cnt = btf__get_nr_types(btf) + 1;
        d->map = malloc(sizeof(__u32) * type_cnt);
        if (!d->map) {
                err = -ENOMEM;
                goto done;
        }
        /* special BTF "void" type is made canonical immediately */
        d->map[0] = 0;
        for (i = 1; i < type_cnt; i++) {
                struct btf_type *t = btf_type_by_id(d->btf, i);

                /* VAR and DATASEC are never deduped and are self-canonical */
                if (btf_is_var(t) || btf_is_datasec(t))
                        d->map[i] = i;
                else
                        d->map[i] = BTF_UNPROCESSED_ID;
        }

        d->hypot_map = malloc(sizeof(__u32) * type_cnt);
        if (!d->hypot_map) {
                err = -ENOMEM;
                goto done;
        }
        for (i = 0; i < type_cnt; i++)
                d->hypot_map[i] = BTF_UNPROCESSED_ID;

done:
        if (err) {
                btf_dedup_free(d);
                return ERR_PTR(err);
        }

        return d;
}

/*
 * Iterate over all possible places in .BTF and .BTF.ext that can reference
 * string and pass pointer to it to a provided callback `fn`.
 */
static int btf_for_each_str_off(struct btf_dedup *d, str_off_visit_fn fn, void *ctx)
{
        int i, r;

        for (i = 0; i < d->btf->nr_types; i++) {
                struct btf_type *t = btf_type_by_id(d->btf, d->btf->start_id + i);

                r = btf_type_visit_str_offs(t, fn, ctx);
                if (r)
                        return r;
        }

        if (!d->btf_ext)
                return 0;

        r = btf_ext_visit_str_offs(d->btf_ext, fn, ctx);
        if (r)
                return r;

        return 0;
}

static int strs_dedup_remap_str_off(__u32 *str_off_ptr, void *ctx)
{
        struct btf_dedup *d = ctx;
        __u32 str_off = *str_off_ptr;
        const char *s;
        int off, err;

        /* don't touch empty string or string in main BTF */
        if (str_off == 0 || str_off < d->btf->start_str_off)
                return 0;

        s = btf__str_by_offset(d->btf, str_off);
        if (d->btf->base_btf) {
                err = btf__find_str(d->btf->base_btf, s);
                if (err >= 0) {
                        *str_off_ptr = err;
                        return 0;
                }
                if (err != -ENOENT)
                        return err;
        }

        off = strset__add_str(d->strs_set, s);
        if (off < 0)
                return off;

        *str_off_ptr = d->btf->start_str_off + off;
        return 0;
}

/*
 * Dedup string and filter out those that are not referenced from either .BTF
 * or .BTF.ext (if provided) sections.
 *
 * This is done by building index of all strings in BTF's string section,
 * then iterating over all entities that can reference strings (e.g., type
 * names, struct field names, .BTF.ext line info, etc) and marking corresponding
 * strings as used. After that all used strings are deduped and compacted into
 * sequential blob of memory and new offsets are calculated. Then all the string
 * references are iterated again and rewritten using new offsets.
 */
static int btf_dedup_strings(struct btf_dedup *d)
{
        int err;

        if (d->btf->strs_deduped)
                return 0;

        d->strs_set = strset__new(BTF_MAX_STR_OFFSET, NULL, 0);
        if (IS_ERR(d->strs_set)) {
                err = PTR_ERR(d->strs_set);
                goto err_out;
        }

        if (!d->btf->base_btf) {
                /* insert empty string; we won't be looking it up during strings
                 * dedup, but it's good to have it for generic BTF string lookups
                 */
                err = strset__add_str(d->strs_set, "");
                if (err < 0)
                        goto err_out;
        }

        /* remap string offsets */
        err = btf_for_each_str_off(d, strs_dedup_remap_str_off, d);
        if (err)
                goto err_out;

        /* 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);
        d->btf->strs_set = d->strs_set;
        d->strs_set = NULL;
        d->btf->strs_deduped = true;
        return 0;

err_out:
        strset__free(d->strs_set);
        d->strs_set = NULL;

        return err;
}

static long btf_hash_common(struct btf_type *t)
{
        long h;

        h = hash_combine(0, t->name_off);
        h = hash_combine(h, t->info);
        h = hash_combine(h, t->size);
        return h;
}

static bool btf_equal_common(struct btf_type *t1, struct btf_type *t2)
{
        return t1->name_off == t2->name_off &&
               t1->info == t2->info &&
               t1->size == t2->size;
}

/* Calculate type signature hash of INT. */
static long btf_hash_int(struct btf_type *t)
{
        __u32 info = *(__u32 *)(t + 1);
        long h;

        h = btf_hash_common(t);
        h = hash_combine(h, info);
        return h;
}

/* Check structural equality of two INTs. */
static bool btf_equal_int(struct btf_type *t1, struct btf_type *t2)
{
        __u32 info1, info2;

        if (!btf_equal_common(t1, t2))
                return false;
        info1 = *(__u32 *)(t1 + 1);
        info2 = *(__u32 *)(t2 + 1);
        return info1 == info2;
}

/* Calculate type signature hash of ENUM. */
static long btf_hash_enum(struct btf_type *t)
{
        long h;

        /* don't hash vlen and enum members to support enum fwd resolving */
        h = hash_combine(0, t->name_off);
        h = hash_combine(h, t->info & ~0xffff);
        h = hash_combine(h, t->size);
        return h;
}

/* Check structural equality of two ENUMs. */
static bool btf_equal_enum(struct btf_type *t1, struct btf_type *t2)
{
        const struct btf_enum *m1, *m2;
        __u16 vlen;
        int i;

        if (!btf_equal_common(t1, t2))
                return false;

        vlen = btf_vlen(t1);
        m1 = btf_enum(t1);
        m2 = btf_enum(t2);
        for (i = 0; i < vlen; i++) {
                if (m1->name_off != m2->name_off || m1->val != m2->val)
                        return false;
                m1++;
                m2++;
        }
        return true;
}

static inline bool btf_is_enum_fwd(struct btf_type *t)
{
        return btf_is_enum(t) && btf_vlen(t) == 0;
}

static bool btf_compat_enum(struct btf_type *t1, struct btf_type *t2)
{
        if (!btf_is_enum_fwd(t1) && !btf_is_enum_fwd(t2))
                return btf_equal_enum(t1, t2);
        /* ignore vlen when comparing */
        return t1->name_off == t2->name_off &&
               (t1->info & ~0xffff) == (t2->info & ~0xffff) &&
               t1->size == t2->size;
}

/*
 * Calculate type signature hash of STRUCT/UNION, ignoring referenced type IDs,
 * as referenced type IDs equivalence is established separately during type
 * graph equivalence check algorithm.
 */
static long btf_hash_struct(struct btf_type *t)
{
        const struct btf_member *member = btf_members(t);
        __u32 vlen = btf_vlen(t);
        long h = btf_hash_common(t);
        int i;

        for (i = 0; i < vlen; i++) {
                h = hash_combine(h, member->name_off);
                h = hash_combine(h, member->offset);
                /* no hashing of referenced type ID, it can be unresolved yet */
                member++;
        }
        return h;
}

/*
 * Check structural compatibility of two FUNC_PROTOs, ignoring referenced type
 * IDs. This check is performed during type graph equivalence check and
 * referenced types equivalence is checked separately.
 */
static bool btf_shallow_equal_struct(struct btf_type *t1, struct btf_type *t2)
{
        const struct btf_member *m1, *m2;
        __u16 vlen;
        int i;

        if (!btf_equal_common(t1, t2))
                return false;

        vlen = btf_vlen(t1);
        m1 = btf_members(t1);
        m2 = btf_members(t2);
        for (i = 0; i < vlen; i++) {
                if (m1->name_off != m2->name_off || m1->offset != m2->offset)
                        return false;
                m1++;
                m2++;
        }
        return true;
}

/*
 * Calculate type signature hash of ARRAY, including referenced type IDs,
 * under assumption that they were already resolved to canonical type IDs and
 * are not going to change.
 */
static long btf_hash_array(struct btf_type *t)
{
        const struct btf_array *info = btf_array(t);
        long h = btf_hash_common(t);

        h = hash_combine(h, info->type);
        h = hash_combine(h, info->index_type);
        h = hash_combine(h, info->nelems);
        return h;
}

/*
 * Check exact equality of two ARRAYs, taking into account referenced
 * type IDs, under assumption that they were already resolved to canonical
 * type IDs and are not going to change.
 * This function is called during reference types deduplication to compare
 * ARRAY to potential canonical representative.
 */
static bool btf_equal_array(struct btf_type *t1, struct btf_type *t2)
{
        const struct btf_array *info1, *info2;

        if (!btf_equal_common(t1, t2))
                return false;

        info1 = btf_array(t1);
        info2 = btf_array(t2);
        return info1->type == info2->type &&
               info1->index_type == info2->index_type &&
               info1->nelems == info2->nelems;
}

/*
 * Check structural compatibility of two ARRAYs, ignoring referenced type
 * IDs. This check is performed during type graph equivalence check and
 * referenced types equivalence is checked separately.
 */
static bool btf_compat_array(struct btf_type *t1, struct btf_type *t2)
{
        if (!btf_equal_common(t1, t2))
                return false;

        return btf_array(t1)->nelems == btf_array(t2)->nelems;
}

/*
 * Calculate type signature hash of FUNC_PROTO, including referenced type IDs,
 * under assumption that they were already resolved to canonical type IDs and
 * are not going to change.
 */
static long btf_hash_fnproto(struct btf_type *t)
{
        const struct btf_param *member = btf_params(t);
        __u16 vlen = btf_vlen(t);
        long h = btf_hash_common(t);
        int i;

        for (i = 0; i < vlen; i++) {
                h = hash_combine(h, member->name_off);
                h = hash_combine(h, member->type);
                member++;
        }
        return h;
}

/*
 * Check exact equality of two FUNC_PROTOs, taking into account referenced
 * type IDs, under assumption that they were already resolved to canonical
 * type IDs and are not going to change.
 * This function is called during reference types deduplication to compare
 * FUNC_PROTO to potential canonical representative.
 */
static bool btf_equal_fnproto(struct btf_type *t1, struct btf_type *t2)
{
        const struct btf_param *m1, *m2;
        __u16 vlen;
        int i;

        if (!btf_equal_common(t1, t2))
                return false;

        vlen = btf_vlen(t1);
        m1 = btf_params(t1);
        m2 = btf_params(t2);
        for (i = 0; i < vlen; i++) {
                if (m1->name_off != m2->name_off || m1->type != m2->type)
                        return false;
                m1++;
                m2++;
        }
        return true;
}

/*
 * Check structural compatibility of two FUNC_PROTOs, ignoring referenced type
 * IDs. This check is performed during type graph equivalence check and
 * referenced types equivalence is checked separately.
 */
static bool btf_compat_fnproto(struct btf_type *t1, struct btf_type *t2)
{
        const struct btf_param *m1, *m2;
        __u16 vlen;
        int i;

        /* skip return type ID */
        if (t1->name_off != t2->name_off || t1->info != t2->info)
                return false;

        vlen = btf_vlen(t1);
        m1 = btf_params(t1);
        m2 = btf_params(t2);
        for (i = 0; i < vlen; i++) {
                if (m1->name_off != m2->name_off)
                        return false;
                m1++;
                m2++;
        }
        return true;
}

/* Prepare split BTF for deduplication by calculating hashes of base BTF's
 * types and initializing the rest of the state (canonical type mapping) for
 * the fixed base BTF part.
 */
static int btf_dedup_prep(struct btf_dedup *d)
{
        struct btf_type *t;
        int type_id;
        long h;

        if (!d->btf->base_btf)
                return 0;

        for (type_id = 1; type_id < d->btf->start_id; type_id++) {
                t = btf_type_by_id(d->btf, type_id);

                /* all base BTF types are self-canonical by definition */
                d->map[type_id] = type_id;

                switch (btf_kind(t)) {
                case BTF_KIND_VAR:
                case BTF_KIND_DATASEC:
                        /* VAR and DATASEC are never hash/deduplicated */
                        continue;
                case BTF_KIND_CONST:
                case BTF_KIND_VOLATILE:
                case BTF_KIND_RESTRICT:
                case BTF_KIND_PTR:
                case BTF_KIND_FWD:
                case BTF_KIND_TYPEDEF:
                case BTF_KIND_FUNC:
                case BTF_KIND_FLOAT:
                        h = btf_hash_common(t);
                        break;
                case BTF_KIND_INT:
                        h = btf_hash_int(t);
                        break;
                case BTF_KIND_ENUM:
                        h = btf_hash_enum(t);
                        break;
                case BTF_KIND_STRUCT:
                case BTF_KIND_UNION:
                        h = btf_hash_struct(t);
                        break;
                case BTF_KIND_ARRAY:
                        h = btf_hash_array(t);
                        break;
                case BTF_KIND_FUNC_PROTO:
                        h = btf_hash_fnproto(t);
                        break;
                default:
                        pr_debug("unknown kind %d for type [%d]\n", btf_kind(t), type_id);
                        return -EINVAL;
                }
                if (btf_dedup_table_add(d, h, type_id))
                        return -ENOMEM;
        }

        return 0;
}

/*
 * Deduplicate primitive types, that can't reference other types, by calculating
 * their type signature hash and comparing them with any possible canonical
 * candidate. If no canonical candidate matches, type itself is marked as
 * canonical and is added into `btf_dedup->dedup_table` as another candidate.
 */
static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
{
        struct btf_type *t = btf_type_by_id(d->btf, type_id);
        struct hashmap_entry *hash_entry;
        struct btf_type *cand;
        /* if we don't find equivalent type, then we are canonical */
        __u32 new_id = type_id;
        __u32 cand_id;
        long h;

        switch (btf_kind(t)) {
        case BTF_KIND_CONST:
        case BTF_KIND_VOLATILE:
        case BTF_KIND_RESTRICT:
        case BTF_KIND_PTR:
        case BTF_KIND_TYPEDEF:
        case BTF_KIND_ARRAY:
        case BTF_KIND_STRUCT:
        case BTF_KIND_UNION:
        case BTF_KIND_FUNC:
        case BTF_KIND_FUNC_PROTO:
        case BTF_KIND_VAR:
        case BTF_KIND_DATASEC:
                return 0;

        case BTF_KIND_INT:
                h = btf_hash_int(t);
                for_each_dedup_cand(d, hash_entry, h) {
                        cand_id = (__u32)(long)hash_entry->value;
                        cand = btf_type_by_id(d->btf, cand_id);
                        if (btf_equal_int(t, cand)) {
                                new_id = cand_id;
                                break;
                        }
                }
                break;

        case BTF_KIND_ENUM:
                h = btf_hash_enum(t);
                for_each_dedup_cand(d, hash_entry, h) {
                        cand_id = (__u32)(long)hash_entry->value;
                        cand = btf_type_by_id(d->btf, cand_id);
                        if (btf_equal_enum(t, cand)) {
                                new_id = cand_id;
                                break;
                        }
                        if (d->opts.dont_resolve_fwds)
                                continue;
                        if (btf_compat_enum(t, cand)) {
                                if (btf_is_enum_fwd(t)) {
                                        /* resolve fwd to full enum */
                                        new_id = cand_id;
                                        break;
                                }
                                /* resolve canonical enum fwd to full enum */
                                d->map[cand_id] = type_id;
                        }
                }
                break;

        case BTF_KIND_FWD:
        case BTF_KIND_FLOAT:
                h = btf_hash_common(t);
                for_each_dedup_cand(d, hash_entry, h) {
                        cand_id = (__u32)(long)hash_entry->value;
                        cand = btf_type_by_id(d->btf, cand_id);
                        if (btf_equal_common(t, cand)) {
                                new_id = cand_id;
                                break;
                        }
                }
                break;

        default:
                return -EINVAL;
        }

        d->map[type_id] = new_id;
        if (type_id == new_id && btf_dedup_table_add(d, h, type_id))
                return -ENOMEM;

        return 0;
}

static int btf_dedup_prim_types(struct btf_dedup *d)
{
        int i, err;

        for (i = 0; i < d->btf->nr_types; i++) {
                err = btf_dedup_prim_type(d, d->btf->start_id + i);
                if (err)
                        return err;
        }
        return 0;
}

/*
 * Check whether type is already mapped into canonical one (could be to itself).
 */
static inline bool is_type_mapped(struct btf_dedup *d, uint32_t type_id)
{
        return d->map[type_id] <= BTF_MAX_NR_TYPES;
}

/*
 * Resolve type ID into its canonical type ID, if any; otherwise return original
 * type ID. If type is FWD and is resolved into STRUCT/UNION already, follow
 * STRUCT/UNION link and resolve it into canonical type ID as well.
 */
static inline __u32 resolve_type_id(struct btf_dedup *d, __u32 type_id)
{
        while (is_type_mapped(d, type_id) && d->map[type_id] != type_id)
                type_id = d->map[type_id];
        return type_id;
}

/*
 * Resolve FWD to underlying STRUCT/UNION, if any; otherwise return original
 * type ID.
 */
static uint32_t resolve_fwd_id(struct btf_dedup *d, uint32_t type_id)
{
        __u32 orig_type_id = type_id;

        if (!btf_is_fwd(btf__type_by_id(d->btf, type_id)))
                return type_id;

        while (is_type_mapped(d, type_id) && d->map[type_id] != type_id)
                type_id = d->map[type_id];

        if (!btf_is_fwd(btf__type_by_id(d->btf, type_id)))
                return type_id;

        return orig_type_id;
}


static inline __u16 btf_fwd_kind(struct btf_type *t)
{
        return btf_kflag(t) ? BTF_KIND_UNION : BTF_KIND_STRUCT;
}

/* Check if given two types are identical ARRAY definitions */
static int btf_dedup_identical_arrays(struct btf_dedup *d, __u32 id1, __u32 id2)
{
        struct btf_type *t1, *t2;

        t1 = btf_type_by_id(d->btf, id1);
        t2 = btf_type_by_id(d->btf, id2);
        if (!btf_is_array(t1) || !btf_is_array(t2))
                return 0;

        return btf_equal_array(t1, t2);
}

/*
 * Check equivalence of BTF type graph formed by candidate struct/union (we'll
 * call it "candidate graph" in this description for brevity) to a type graph
 * formed by (potential) canonical struct/union ("canonical graph" for brevity
 * here, though keep in mind that not all types in canonical graph are
 * necessarily canonical representatives themselves, some of them might be
 * duplicates or its uniqueness might not have been established yet).
 * Returns:
 *  - >0, if type graphs are equivalent;
 *  -  0, if not equivalent;
 *  - <0, on error.
 *
 * Algorithm performs side-by-side DFS traversal of both type graphs and checks
 * equivalence of BTF types at each step. If at any point BTF types in candidate
 * and canonical graphs are not compatible structurally, whole graphs are
 * incompatible. If types are structurally equivalent (i.e., all information
 * except referenced type IDs is exactly the same), a mapping from `canon_id` to
 * a `cand_id` is recored in hypothetical mapping (`btf_dedup->hypot_map`).
 * If a type references other types, then those referenced types are checked
 * for equivalence recursively.
 *
 * During DFS traversal, if we find that for current `canon_id` type we
 * already have some mapping in hypothetical map, we check for two possible
 * situations:
 *   - `canon_id` is mapped to exactly the same type as `cand_id`. This will
 *     happen when type graphs have cycles. In this case we assume those two
 *     types are equivalent.
 *   - `canon_id` is mapped to different type. This is contradiction in our
 *     hypothetical mapping, because same graph in canonical graph corresponds
 *     to two different types in candidate graph, which for equivalent type
 *     graphs shouldn't happen. This condition terminates equivalence check
 *     with negative result.
 *
 * If type graphs traversal exhausts types to check and find no contradiction,
 * then type graphs are equivalent.
 *
 * When checking types for equivalence, there is one special case: FWD types.
 * If FWD type resolution is allowed and one of the types (either from canonical
 * or candidate graph) is FWD and other is STRUCT/UNION (depending on FWD's kind
 * flag) and their names match, hypothetical mapping is updated to point from
 * FWD to STRUCT/UNION. If graphs will be determined as equivalent successfully,
 * this mapping will be used to record FWD -> STRUCT/UNION mapping permanently.
 *
 * Technically, this could lead to incorrect FWD to STRUCT/UNION resolution,
 * if there are two exactly named (or anonymous) structs/unions that are
 * compatible structurally, one of which has FWD field, while other is concrete
 * STRUCT/UNION, but according to C sources they are different structs/unions
 * that are referencing different types with the same name. This is extremely
 * unlikely to happen, but btf_dedup API allows to disable FWD resolution if
 * this logic is causing problems.
 *
 * Doing FWD resolution means that both candidate and/or canonical graphs can
 * consists of portions of the graph that come from multiple compilation units.
 * This is due to the fact that types within single compilation unit are always
 * deduplicated and FWDs are already resolved, if referenced struct/union
 * definiton is available. So, if we had unresolved FWD and found corresponding
 * STRUCT/UNION, they will be from different compilation units. This
 * consequently means that when we "link" FWD to corresponding STRUCT/UNION,
 * type graph will likely have at least two different BTF types that describe
 * same type (e.g., most probably there will be two different BTF types for the
 * same 'int' primitive type) and could even have "overlapping" parts of type
 * graph that describe same subset of types.
 *
 * This in turn means that our assumption that each type in canonical graph
 * must correspond to exactly one type in candidate graph might not hold
 * anymore and will make it harder to detect contradictions using hypothetical
 * map. To handle this problem, we allow to follow FWD -> STRUCT/UNION
 * resolution only in canonical graph. FWDs in candidate graphs are never
 * resolved. To see why it's OK, let's check all possible situations w.r.t. FWDs
 * that can occur:
 *   - Both types in canonical and candidate graphs are FWDs. If they are
 *     structurally equivalent, then they can either be both resolved to the
 *     same STRUCT/UNION or not resolved at all. In both cases they are
 *     equivalent and there is no need to resolve FWD on candidate side.
 *   - Both types in canonical and candidate graphs are concrete STRUCT/UNION,
 *     so nothing to resolve as well, algorithm will check equivalence anyway.
 *   - Type in canonical graph is FWD, while type in candidate is concrete
 *     STRUCT/UNION. In this case candidate graph comes from single compilation
 *     unit, so there is exactly one BTF type for each unique C type. After
 *     resolving FWD into STRUCT/UNION, there might be more than one BTF type
 *     in canonical graph mapping to single BTF type in candidate graph, but
 *     because hypothetical mapping maps from canonical to candidate types, it's
 *     alright, and we still maintain the property of having single `canon_id`
 *     mapping to single `cand_id` (there could be two different `canon_id`
 *     mapped to the same `cand_id`, but it's not contradictory).
 *   - Type in canonical graph is concrete STRUCT/UNION, while type in candidate
 *     graph is FWD. In this case we are just going to check compatibility of
 *     STRUCT/UNION and corresponding FWD, and if they are compatible, we'll
 *     assume that whatever STRUCT/UNION FWD resolves to must be equivalent to
 *     a concrete STRUCT/UNION from canonical graph. If the rest of type graphs
 *     turn out equivalent, we'll re-resolve FWD to concrete STRUCT/UNION from
 *     canonical graph.
 */
static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
                              __u32 canon_id)
{
        struct btf_type *cand_type;
        struct btf_type *canon_type;
        __u32 hypot_type_id;
        __u16 cand_kind;
        __u16 canon_kind;
        int i, eq;

        /* if both resolve to the same canonical, they must be equivalent */
        if (resolve_type_id(d, cand_id) == resolve_type_id(d, canon_id))
                return 1;

        canon_id = resolve_fwd_id(d, canon_id);

        hypot_type_id = d->hypot_map[canon_id];
        if (hypot_type_id <= BTF_MAX_NR_TYPES) {
                /* In some cases compiler will generate different DWARF types
                 * for *identical* array type definitions and use them for
                 * different fields within the *same* struct. This breaks type
                 * equivalence check, which makes an assumption that candidate
                 * types sub-graph has a consistent and deduped-by-compiler
                 * types within a single CU. So work around that by explicitly
                 * allowing identical array types here.
                 */
                return hypot_type_id == cand_id ||
                       btf_dedup_identical_arrays(d, hypot_type_id, cand_id);
        }

        if (btf_dedup_hypot_map_add(d, canon_id, cand_id))
                return -ENOMEM;

        cand_type = btf_type_by_id(d->btf, cand_id);
        canon_type = btf_type_by_id(d->btf, canon_id);
        cand_kind = btf_kind(cand_type);
        canon_kind = btf_kind(canon_type);

        if (cand_type->name_off != canon_type->name_off)
                return 0;

        /* FWD <--> STRUCT/UNION equivalence check, if enabled */
        if (!d->opts.dont_resolve_fwds
            && (cand_kind == BTF_KIND_FWD || canon_kind == BTF_KIND_FWD)
            && cand_kind != canon_kind) {
                __u16 real_kind;
                __u16 fwd_kind;

                if (cand_kind == BTF_KIND_FWD) {
                        real_kind = canon_kind;
                        fwd_kind = btf_fwd_kind(cand_type);
                } else {
                        real_kind = cand_kind;
                        fwd_kind = btf_fwd_kind(canon_type);
                        /* we'd need to resolve base FWD to STRUCT/UNION */
                        if (fwd_kind == real_kind && canon_id < d->btf->start_id)
                                d->hypot_adjust_canon = true;
                }
                return fwd_kind == real_kind;
        }

        if (cand_kind != canon_kind)
                return 0;

        switch (cand_kind) {
        case BTF_KIND_INT:
                return btf_equal_int(cand_type, canon_type);

        case BTF_KIND_ENUM:
                if (d->opts.dont_resolve_fwds)
                        return btf_equal_enum(cand_type, canon_type);
                else
                        return btf_compat_enum(cand_type, canon_type);

        case BTF_KIND_FWD:
        case BTF_KIND_FLOAT:
                return btf_equal_common(cand_type, canon_type);

        case BTF_KIND_CONST:
        case BTF_KIND_VOLATILE:
        case BTF_KIND_RESTRICT:
        case BTF_KIND_PTR:
        case BTF_KIND_TYPEDEF:
        case BTF_KIND_FUNC:
                if (cand_type->info != canon_type->info)
                        return 0;
                return btf_dedup_is_equiv(d, cand_type->type, canon_type->type);

        case BTF_KIND_ARRAY: {
                const struct btf_array *cand_arr, *canon_arr;

                if (!btf_compat_array(cand_type, canon_type))
                        return 0;
                cand_arr = btf_array(cand_type);
                canon_arr = btf_array(canon_type);
                eq = btf_dedup_is_equiv(d, cand_arr->index_type, canon_arr->index_type);
                if (eq <= 0)
                        return eq;
                return btf_dedup_is_equiv(d, cand_arr->type, canon_arr->type);
        }

        case BTF_KIND_STRUCT:
        case BTF_KIND_UNION: {
                const struct btf_member *cand_m, *canon_m;
                __u16 vlen;

                if (!btf_shallow_equal_struct(cand_type, canon_type))
                        return 0;
                vlen = btf_vlen(cand_type);
                cand_m = btf_members(cand_type);
                canon_m = btf_members(canon_type);
                for (i = 0; i < vlen; i++) {
                        eq = btf_dedup_is_equiv(d, cand_m->type, canon_m->type);
                        if (eq <= 0)
                                return eq;
                        cand_m++;
                        canon_m++;
                }

                return 1;
        }

        case BTF_KIND_FUNC_PROTO: {
                const struct btf_param *cand_p, *canon_p;
                __u16 vlen;

                if (!btf_compat_fnproto(cand_type, canon_type))
                        return 0;
                eq = btf_dedup_is_equiv(d, cand_type->type, canon_type->type);
                if (eq <= 0)
                        return eq;
                vlen = btf_vlen(cand_type);
                cand_p = btf_params(cand_type);
                canon_p = btf_params(canon_type);
                for (i = 0; i < vlen; i++) {
                        eq = btf_dedup_is_equiv(d, cand_p->type, canon_p->type);
                        if (eq <= 0)
                                return eq;
                        cand_p++;
                        canon_p++;
                }
                return 1;
        }

        default:
                return -EINVAL;
        }
        return 0;
}

/*
 * Use hypothetical mapping, produced by successful type graph equivalence
 * check, to augment existing struct/union canonical mapping, where possible.
 *
 * If BTF_KIND_FWD resolution is allowed, this mapping is also used to record
 * FWD -> STRUCT/UNION correspondence as well. FWD resolution is bidirectional:
 * it doesn't matter if FWD type was part of canonical graph or candidate one,
 * we are recording the mapping anyway. As opposed to carefulness required
 * for struct/union correspondence mapping (described below), for FWD resolution
 * it's not important, as by the time that FWD type (reference type) will be
 * deduplicated all structs/unions will be deduped already anyway.
 *
 * Recording STRUCT/UNION mapping is purely a performance optimization and is
 * not required for correctness. It needs to be done carefully to ensure that
 * struct/union from candidate's type graph is not mapped into corresponding
 * struct/union from canonical type graph that itself hasn't been resolved into
 * canonical representative. The only guarantee we have is that canonical
 * struct/union was determined as canonical and that won't change. But any
 * types referenced through that struct/union fields could have been not yet
 * resolved, so in case like that it's too early to establish any kind of
 * correspondence between structs/unions.
 *
 * No canonical correspondence is derived for primitive types (they are already
 * deduplicated completely already anyway) or reference types (they rely on
 * stability of struct/union canonical relationship for equivalence checks).
 */
static void btf_dedup_merge_hypot_map(struct btf_dedup *d)
{
        __u32 canon_type_id, targ_type_id;
        __u16 t_kind, c_kind;
        __u32 t_id, c_id;
        int i;