// 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__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 void *btf_add_type_offs_mem(struct btf *btf, size_t add_cnt)
{
        return libbpf_add_mem((void **)&btf->type_offs, &btf->type_offs_cap, sizeof(__u32),
                              btf->nr_types, BTF_MAX_NR_TYPES, add_cnt);
}

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

        p = btf_add_type_offs_mem(btf, 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;
        }

        if (btf->raw_size < hdr->hdr_len) {
                pr_debug("BTF header len %u larger than data size %u\n",
                         hdr->hdr_len, btf->raw_size);
                return -EINVAL;
        }

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

        if ((long long)hdr->type_off + hdr->type_len > hdr->str_off) {
                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:
        case BTF_KIND_TYPE_TAG:
                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);
        case BTF_KIND_DECL_TAG:
                return base_size + sizeof(struct btf_decl_tag);
        default:
                pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
                return -EINVAL;
        }
}

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:
        case BTF_KIND_TYPE_TAG:
                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;
        case BTF_KIND_DECL_TAG:
                btf_decl_tag(t)->component_idx = bswap_32(btf_decl_tag(t)->component_idx);
                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;
}

__u32 btf__type_cnt(const struct btf *btf)
{
        return btf->start_id + btf->nr_types;
}

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(const 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__type_cnt(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__ == __ORDER_LITTLE_ENDIAN__
        return false;
#elif __BYTE_ORDER__ == __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:
                case BTF_KIND_DECL_TAG:
                case BTF_KIND_TYPE_TAG:
                        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:
        case BTF_KIND_TYPE_TAG:
                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__type_cnt(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);
}

static __s32 btf_find_by_name_kind(const struct btf *btf, int start_id,
                                   const char *type_name, __u32 kind)
{
        __u32 i, nr_types = btf__type_cnt(btf);

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

        for (i = start_id; 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);
}

__s32 btf__find_by_name_kind_own(const struct btf *btf, const char *type_name,
                                 __u32 kind)
{
        return btf_find_by_name_kind(btf, btf->start_id, type_name, kind);
}

__s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
                             __u32 kind)
{
        return btf_find_by_name_kind(btf, 1, type_name, kind);
}

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__type_cnt(base_btf);
                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__type_cnt(base_btf);
                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 | O_CLOEXEC);
        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 void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian);

int btf_load_into_kernel(struct btf *btf, char *log_buf, size_t log_sz, __u32 log_level)
{
        LIBBPF_OPTS(bpf_btf_load_opts, opts);
        __u32 buf_sz = 0, raw_size;
        char *buf = NULL, *tmp;
        void *raw_data;
        int err = 0;

        if (btf->fd >= 0)
                return libbpf_err(-EEXIST);
        if (log_sz && !log_buf)
                return libbpf_err(-EINVAL);

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

retry_load:
        /* if log_level is 0, we won't provide log_buf/log_size to the kernel,
         * initially. Only if BTF loading fails, we bump log_level to 1 and
         * retry, using either auto-allocated or custom log_buf. This way
         * non-NULL custom log_buf provides a buffer just in case, but hopes
         * for successful load and no need for log_buf.
         */
        if (log_level) {
                /* if caller didn't provide custom log_buf, we'll keep
                 * allocating our own progressively bigger buffers for BTF
                 * verification log
                 */
                if (!log_buf) {
                        buf_sz = max((__u32)BPF_LOG_BUF_SIZE, buf_sz * 2);
                        tmp = realloc(buf, buf_sz);
                        if (!tmp) {
                                err = -ENOMEM;
                                goto done;
                        }
                        buf = tmp;
                        buf[0] = '\0';
                }

                opts.log_buf = log_buf ? log_buf : buf;
                opts.log_size = log_buf ? log_sz : buf_sz;
                opts.log_level = log_level;
        }

        btf->fd = bpf_btf_load(raw_data, raw_size, &opts);
        if (btf->fd < 0) {
                /* time to turn on verbose mode and try again */
                if (log_level == 0) {
                        log_level = 1;
                        goto retry_load;
                }
                /* only retry if caller didn't provide custom log_buf, but
                 * make sure we can never overflow buf_sz
                 */
                if (!log_buf && errno == ENOSPC && buf_sz <= UINT_MAX / 2)
                        goto retry_load;

                err = -errno;
                pr_warn("BTF loading error: %d\n", err);
                /* don't print out contents of custom log_buf */
                if (!log_buf && buf[0])
                        pr_warn("-- BEGIN BTF LOAD LOG ---\n%s\n-- END BTF LOAD LOG --\n", buf);
        }

done:
        free(buf);
        return libbpf_err(err);
}

int btf__load_into_kernel(struct btf *btf)
{
        return btf_load_into_kernel(btf, NULL, 0, 0);
}

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__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;
}

__attribute__((alias("btf__raw_data")))
const void *btf__get_raw_data(const struct btf *btf, __u32 *size);

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);
}

static int btf_rewrite_type_ids(__u32 *type_id, void *ctx)
{
        struct btf *btf = ctx;

        if (!*type_id) /* nothing to do for VOID references */
                return 0;

        /* we haven't updated btf's type count yet, so
         * btf->start_id + btf->nr_types - 1 is the type ID offset we should
         * add to all newly added BTF types
         */
        *type_id += btf->start_id + btf->nr_types - 1;
        return 0;
}

int btf__add_btf(struct btf *btf, const struct btf *src_btf)
{
        struct btf_pipe p = { .src = src_btf, .dst = btf };
        int data_sz, sz, cnt, i, err, old_strs_len;
        __u32 *off;
        void *t;

        /* appending split BTF isn't supported yet */
        if (src_btf->base_btf)
                return libbpf_err(-ENOTSUP);

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

        /* remember original strings section size if we have to roll back
         * partial strings section changes
         */
        old_strs_len = btf->hdr->str_len;

        data_sz = src_btf->hdr->type_len;
        cnt = btf__type_cnt(src_btf) - 1;

        /* pre-allocate enough memory for new types */
        t = btf_add_type_mem(btf, data_sz);
        if (!t)
                return libbpf_err(-ENOMEM);

        /* pre-allocate enough memory for type offset index for new types */
        off = btf_add_type_offs_mem(btf, cnt);
        if (!off)
                return libbpf_err(-ENOMEM);

        /* bulk copy types data for all types from src_btf */
        memcpy(t, src_btf->types_data, data_sz);

        for (i = 0; i < cnt; i++) {
                sz = btf_type_size(t);
                if (sz < 0) {
                        /* unlikely, has to be corrupted src_btf */
                        err = sz;
                        goto err_out;
                }

                /* fill out type ID to type offset mapping for lookups by type ID */
                *off = t - btf->types_data;

                /* add, dedup, and remap strings referenced by this BTF type */
                err = btf_type_visit_str_offs(t, btf_rewrite_str, &p);
                if (err)
                        goto err_out;

                /* remap all type IDs referenced from this BTF type */
                err = btf_type_visit_type_ids(t, btf_rewrite_type_ids, btf);
                if (err)
                        goto err_out;

                /* go to next type data and type offset index entry */
                t += sz;
                off++;
        }

        /* Up until now any of the copied type data was effectively invisible,
         * so if we exited early before this point due to error, BTF would be
         * effectively unmodified. There would be extra internal memory
         * pre-allocated, but it would not be available for querying.  But now
         * that we've copied and rewritten all the data successfully, we can
         * update type count and various internal offsets and sizes to
         * "commit" the changes and made them visible to the outside world.
         */
        btf->hdr->type_len += data_sz;
        btf->hdr->str_off += data_sz;
        btf->nr_types += cnt;

        /* return type ID of the first added BTF type */
        return btf->start_id + btf->nr_types - cnt;
err_out:
        /* zero out preallocated memory as if it was just allocated with
         * libbpf_add_mem()
         */
        memset(btf->types_data + btf->hdr->type_len, 0, data_sz);
        memset(btf->strs_data + old_strs_len, 0, btf->hdr->str_len - old_strs_len);

        /* and now restore original strings section size; types data size
         * wasn't modified, so doesn't need restoring, see big comment above */
        btf->hdr->str_len = old_strs_len;

        return libbpf_err(err);
}

/*
 * 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__type_cnt(btf) - 1);
}

/*
 * 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_TYPE_TAG type with:
 *   - *value*, non-empty/non-NULL tag value;
 *   - *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_type_tag(struct btf *btf, const char *value, int ref_type_id)
{
        if (!value|| !value[0])
                return libbpf_err(-EINVAL);

        return btf_add_ref_kind(btf, BTF_KIND_TYPE_TAG, value, 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;
}

/*
 * Append new BTF_KIND_DECL_TAG type with:
 *   - *value* - non-empty/non-NULL string;
 *   - *ref_type_id* - referenced type ID, it might not exist yet;
 *   - *component_idx* - -1 for tagging reference type, otherwise struct/union
 *     member or function argument index;
 * Returns:
 *   - >0, type ID of newly added BTF type;
 *   - <0, on error.
 */
int btf__add_decl_tag(struct btf *btf, const char *value, int ref_type_id,
                 int component_idx)
{
        struct btf_type *t;
        int sz, value_off;

        if (!value || !value[0] || component_idx < -1)
                return libbpf_err(-EINVAL);

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

        value_off = btf__add_str(btf, value);
        if (value_off < 0)
                return value_off;

        t->name_off = value_off;
        t->info = btf_type_info(BTF_KIND_DECL_TAG, 0, false);
        t->type = ref_type_id;
        btf_decl_tag(t)->component_idx = component_idx;

        return btf_commit_type(btf, sz);
}

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

        err = btf_ext_parse_hdr(btf_ext->data, size);
        if (err)
                goto done;

        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, 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;