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

#include <endian.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.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"

#define BTF_MAX_NR_TYPES 0x7fffffff
#define BTF_MAX_STR_OFFSET 0x7fffffff

static struct btf_type btf_void;

struct btf {
        union {
                struct btf_header *hdr;
                void *data;
        };
        struct btf_type **types;
        const char *strings;
        void *nohdr_data;
        __u32 nr_types;
        __u32 types_size;
        __u32 data_size;
        int fd;
};

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

static int btf_add_type(struct btf *btf, struct btf_type *t)
{
        if (btf->types_size - btf->nr_types < 2) {
                struct btf_type **new_types;
                __u32 expand_by, new_size;

                if (btf->types_size == BTF_MAX_NR_TYPES)
                        return -E2BIG;

                expand_by = max(btf->types_size >> 2, 16);
                new_size = min(BTF_MAX_NR_TYPES, btf->types_size + expand_by);

                new_types = realloc(btf->types, sizeof(*new_types) * new_size);
                if (!new_types)
                        return -ENOMEM;

                if (btf->nr_types == 0)
                        new_types[0] = &btf_void;

                btf->types = new_types;
                btf->types_size = new_size;
        }

        btf->types[++(btf->nr_types)] = t;

        return 0;
}

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

        if (btf->data_size < sizeof(struct btf_header)) {
                pr_debug("BTF header not found\n");
                return -EINVAL;
        }

        if (hdr->magic != BTF_MAGIC) {
                pr_debug("Invalid BTF magic:%x\n", hdr->magic);
                return -EINVAL;
        }

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

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

        meta_left = btf->data_size - sizeof(*hdr);
        if (!meta_left) {
                pr_debug("BTF has no data\n");
                return -EINVAL;
        }

        if (meta_left < hdr->type_off) {
                pr_debug("Invalid BTF type section offset:%u\n", hdr->type_off);
                return -EINVAL;
        }

        if (meta_left < hdr->str_off) {
                pr_debug("Invalid BTF string section offset:%u\n", hdr->str_off);
                return -EINVAL;
        }

        if (hdr->type_off >= hdr->str_off) {
                pr_debug("BTF type section offset >= string section offset. No type?\n");
                return -EINVAL;
        }

        if (hdr->type_off & 0x02) {
                pr_debug("BTF type section is not aligned to 4 bytes\n");
                return -EINVAL;
        }

        btf->nohdr_data = btf->hdr + 1;

        return 0;
}

static int btf_parse_str_sec(struct btf *btf)
{
        const struct btf_header *hdr = btf->hdr;
        const char *start = btf->nohdr_data + hdr->str_off;
        const char *end = start + btf->hdr->str_len;

        if (!hdr->str_len || hdr->str_len - 1 > BTF_MAX_STR_OFFSET ||
            start[0] || end[-1]) {
                pr_debug("Invalid BTF string section\n");
                return -EINVAL;
        }

        btf->strings = start;

        return 0;
}

static int btf_type_size(struct btf_type *t)
{
        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:
                return base_size;
        case BTF_KIND_INT:
                return base_size + sizeof(__u32);
        case BTF_KIND_ENUM:
                return base_size + vlen * sizeof(struct btf_enum);
        case BTF_KIND_ARRAY:
                return base_size + sizeof(struct btf_array);
        case BTF_KIND_STRUCT:
        case BTF_KIND_UNION:
                return base_size + vlen * sizeof(struct btf_member);
        case BTF_KIND_FUNC_PROTO:
                return base_size + vlen * sizeof(struct btf_param);
        case BTF_KIND_VAR:
                return base_size + sizeof(struct btf_var);
        case BTF_KIND_DATASEC:
                return base_size + vlen * sizeof(struct btf_var_secinfo);
        default:
                pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
                return -EINVAL;
        }
}

static int btf_parse_type_sec(struct btf *btf)
{
        struct btf_header *hdr = btf->hdr;
        void *nohdr_data = btf->nohdr_data;
        void *next_type = nohdr_data + hdr->type_off;
        void *end_type = nohdr_data + hdr->str_off;

        while (next_type < end_type) {
                struct btf_type *t = next_type;
                int type_size;
                int err;

                type_size = btf_type_size(t);
                if (type_size < 0)
                        return type_size;
                next_type += type_size;
                err = btf_add_type(btf, t);
                if (err)
                        return err;
        }

        return 0;
}

__u32 btf__get_nr_types(const struct btf *btf)
{
        return btf->nr_types;
}

const struct btf_type *btf__type_by_id(const struct btf *btf, __u32 type_id)
{
        if (type_id > btf->nr_types)
                return NULL;

        return btf->types[type_id];
}

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:
                        size = t->size;
                        goto done;
                case BTF_KIND_PTR:
                        size = sizeof(void *);
                        goto done;
                case BTF_KIND_TYPEDEF:
                case BTF_KIND_VOLATILE:
                case BTF_KIND_CONST:
                case BTF_KIND_RESTRICT:
                case BTF_KIND_VAR:
                        type_id = t->type;
                        break;
                case BTF_KIND_ARRAY:
                        array = btf_array(t);
                        if (nelems && array->nelems > UINT32_MAX / nelems)
                                return -E2BIG;
                        nelems *= array->nelems;
                        type_id = array->type;
                        break;
                default:
                        return -EINVAL;
                }

                t = btf__type_by_id(btf, type_id);
        }

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

        return nelems * size;
}

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 -EINVAL;

        return type_id;
}

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

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

        for (i = 1; i <= btf->nr_types; i++) {
                const struct btf_type *t = btf->types[i];
                const char *name = btf__name_by_offset(btf, t->name_off);

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

        return -ENOENT;
}

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

        if (btf->fd != -1)
                close(btf->fd);

        free(btf->data);
        free(btf->types);
        free(btf);
}

struct btf *btf__new(__u8 *data, __u32 size)
{
        struct btf *btf;
        int err;

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

        btf->fd = -1;

        btf->data = malloc(size);
        if (!btf->data) {
                err = -ENOMEM;
                goto done;
        }

        memcpy(btf->data, data, size);
        btf->data_size = size;

        err = btf_parse_hdr(btf);
        if (err)
                goto done;

        err = btf_parse_str_sec(btf);
        if (err)
                goto done;

        err = btf_parse_type_sec(btf);

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

        return btf;
}

static bool btf_check_endianness(const GElf_Ehdr *ehdr)
{
#if __BYTE_ORDER == __LITTLE_ENDIAN
        return ehdr->e_ident[EI_DATA] == ELFDATA2LSB;
#elif __BYTE_ORDER == __BIG_ENDIAN
        return ehdr->e_ident[EI_DATA] == ELFDATA2MSB;
#else
# error "Unrecognized __BYTE_ORDER__"
#endif
}

struct btf *btf__parse_elf(const char *path, 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;

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

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

        err = -LIBBPF_ERRNO__FORMAT;

        elf = elf_begin(fd, ELF_C_READ, NULL);
        if (!elf) {
                pr_warn("failed to open %s as ELF file\n", path);
                goto done;
        }
        if (!gelf_getehdr(elf, &ehdr)) {
                pr_warn("failed to get EHDR from %s\n", path);
                goto done;
        }
        if (!btf_check_endianness(&ehdr)) {
                pr_warn("non-native ELF endianness is not supported\n");
                goto done;
        }
        if (!elf_rawdata(elf_getscn(elf, ehdr.e_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, ehdr.e_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);
        if (IS_ERR(btf))
                goto done;

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

        if (err)
                return ERR_PTR(err);
        /*
         * btf is always parsed before btf_ext, so no need to clean up
         * btf_ext, if btf loading failed
         */
        if (IS_ERR(btf))
                return btf;
        if (btf_ext && IS_ERR(*btf_ext)) {
                btf__free(btf);
                err = PTR_ERR(*btf_ext);
                return ERR_PTR(err);
        }
        return btf;
}

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

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

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

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

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

        t->size = size;

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

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

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

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

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

                vsi->offset = off;
        }

        qsort(t + 1, vars, sizeof(*vsi), compare_vsi_off);
        return 0;
}

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

        for (i = 1; i <= btf->nr_types; i++) {
                struct btf_type *t = btf->types[i];

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

        return err;
}

int btf__load(struct btf *btf)
{
        __u32 log_buf_size = BPF_LOG_BUF_SIZE;
        char *log_buf = NULL;
        int err = 0;

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

        log_buf = malloc(log_buf_size);
        if (!log_buf)
                return -ENOMEM;

        *log_buf = 0;

        btf->fd = bpf_load_btf(btf->data, btf->data_size,
                               log_buf, log_buf_size, false);
        if (btf->fd < 0) {
                err = -errno;
                pr_warn("Error loading BTF: %s(%d)\n", strerror(errno), errno);
                if (*log_buf)
                        pr_warn("%s\n", log_buf);
                goto done;
        }

done:
        free(log_buf);
        return err;
}

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

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

const char *btf__name_by_offset(const struct btf *btf, __u32 offset)
{
        if (offset < btf->hdr->str_len)
                return &btf->strings[offset];
        else
                return NULL;
}

int btf__get_from_id(__u32 id, struct btf **btf)
{
        struct bpf_btf_info btf_info = { 0 };
        __u32 len = sizeof(btf_info);
        __u32 last_size;
        int btf_fd;
        void *ptr;
        int err;

        err = 0;
        *btf = NULL;
        btf_fd = bpf_btf_get_fd_by_id(id);
        if (btf_fd < 0)
                return 0;

        /* we won't know btf_size until we call bpf_obj_get_info_by_fd(). so
         * let's start with a sane default - 4KiB here - and resize it only if
         * bpf_obj_get_info_by_fd() needs a bigger buffer.
         */
        btf_info.btf_size = 4096;
        last_size = btf_info.btf_size;
        ptr = malloc(last_size);
        if (!ptr) {
                err = -ENOMEM;
                goto exit_free;
        }

        memset(ptr, 0, last_size);
        btf_info.btf = ptr_to_u64(ptr);
        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) {
                        err = -ENOMEM;
                        goto exit_free;
                }
                ptr = temp_ptr;
                memset(ptr, 0, last_size);
                btf_info.btf = ptr_to_u64(ptr);
                err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
        }

        if (err || btf_info.btf_size > last_size) {
                err = errno;
                goto exit_free;
        }

        *btf = btf__new((__u8 *)(long)btf_info.btf, btf_info.btf_size);
        if (IS_ERR(*btf)) {
                err = PTR_ERR(*btf);
                *btf = NULL;
        }

exit_free:
        close(btf_fd);
        free(ptr);

        return err;
}

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 -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 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 -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 -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 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 -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 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 -EINVAL;
        }

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

        return 0;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        return 0;
}

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

        return btf_ext_setup_info(btf_ext, &param);
}

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

        return btf_ext_setup_info(btf_ext, &param);
}

static int btf_ext_setup_field_reloc(struct btf_ext *btf_ext)
{
        struct btf_ext_sec_setup_param param = {
                .off = btf_ext->hdr->field_reloc_off,
                .len = btf_ext->hdr->field_reloc_len,
                .min_rec_size = sizeof(struct bpf_field_reloc),
                .ext_info = &btf_ext->field_reloc_info,
                .desc = "field_reloc",
        };

        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 != 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 (!btf_ext)
                return;
        free(btf_ext->data);
        free(btf_ext);
}

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

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

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

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

        if (btf_ext->hdr->hdr_len <
            offsetofend(struct btf_ext_header, line_info_len))
                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, field_reloc_len))
                goto done;
        err = btf_ext_setup_field_reloc(btf_ext);
        if (err)
                goto done;

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

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

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

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

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

struct btf_dedup;

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

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

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

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

done:
        btf_dedup_free(d);
        return err;
}

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

struct btf_dedup {
        /* .BTF section to be deduped in-place */
        struct btf *btf;
        /*
         * Optional .BTF.ext section. When provided, any strings referenced
         * from it will be taken into account when deduping strings
         */
        struct btf_ext *btf_ext;
        /*
         * This is a map from any type's signature hash to a list of possible
         * canonical representative type candidates. Hash collisions are
         * ignored, so even types of various kinds can share same list of
         * candidates, which is fine because we rely on subsequent
         * btf_xxx_equal() checks to authoritatively verify type equality.
         */
        struct hashmap *dedup_table;
        /* Canonical types map */
        __u32 *map;
        /* Hypothetical mapping, used during type graph equivalence checks */
        __u32 *hypot_map;
        __u32 *hypot_list;
        size_t hypot_cnt;
        size_t hypot_cap;
        /* Various option modifying behavior of algorithm */
        struct btf_dedup_opts opts;
};

struct btf_str_ptr {
        const char *str;
        __u32 new_off;
        bool used;
};

struct btf_str_ptrs {
        struct btf_str_ptr *ptrs;
        const char *data;
        __u32 cnt;
        __u32 cap;
};

static long hash_combine(long h, long value)
{
        return h * 31 + value;
}

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

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

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

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

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

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

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

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

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

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

        free(d);
}

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

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

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

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

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

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

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

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

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

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

        d->hypot_map = malloc(sizeof(__u32) * (1 + btf->nr_types));
        if (!d->hypot_map) {
                err = -ENOMEM;
                goto done;
        }
        for (i = 0; i <= btf->nr_types; i++)
                d->hypot_map[i] = BTF_UNPROCESSED_ID;

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

        return d;
}

typedef int (*str_off_fn_t)(__u32 *str_off_ptr, void *ctx);

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

        for (i = 1; i <= d->btf->nr_types; i++) {
                t = d->btf->types[i];
                r = fn(&t->name_off, ctx);
                if (r)
                        return r;

                switch (btf_kind(t)) {
                case BTF_KIND_STRUCT:
                case BTF_KIND_UNION: {
                        struct btf_member *m = btf_members(t);
                        __u16 vlen = btf_vlen(t);

                        for (j = 0; j < vlen; j++) {
                                r = fn(&m->name_off, ctx);
                                if (r)
                                        return r;
                                m++;
                        }
                        break;
                }
                case BTF_KIND_ENUM: {
                        struct btf_enum *m = btf_enum(t);
                        __u16 vlen = btf_vlen(t);

                        for (j = 0; j < vlen; j++) {
                                r = fn(&m->name_off, ctx);
                                if (r)
                                        return r;
                                m++;
                        }
                        break;
                }
                case BTF_KIND_FUNC_PROTO: {
                        struct btf_param *m = btf_params(t);
                        __u16 vlen = btf_vlen(t);

                        for (j = 0; j < vlen; j++) {
                                r = fn(&m->name_off, ctx);
                                if (r)
                                        return r;
                                m++;
                        }
                        break;
                }
                default:
                        break;
                }
        }

        if (!d->btf_ext)
                return 0;

        line_data_cur = d->btf_ext->line_info.info;
        line_data_end = d->btf_ext->line_info.info + d->btf_ext->line_info.len;
        rec_size = d->btf_ext->line_info.rec_size;

        while (line_data_cur < line_data_end) {
                struct btf_ext_info_sec *sec = line_data_cur;
                struct bpf_line_info_min *line_info;
                __u32 num_info = sec->num_info;

                r = fn(&sec->sec_name_off, ctx);
                if (r)
                        return r;

                line_data_cur += sizeof(struct btf_ext_info_sec);
                for (i = 0; i < num_info; i++) {
                        line_info = line_data_cur;
                        r = fn(&line_info->file_name_off, ctx);
                        if (r)
                                return r;
                        r = fn(&line_info->line_off, ctx);
                        if (r)
                                return r;
                        line_data_cur += rec_size;
                }
        }

        return 0;
}

static int str_sort_by_content(const void *a1, const void *a2)
{
        const struct btf_str_ptr *p1 = a1;
        const struct btf_str_ptr *p2 = a2;

        return strcmp(p1->str, p2->str);
}

static int str_sort_by_offset(const void *a1, const void *a2)
{
        const struct btf_str_ptr *p1 = a1;
        const struct btf_str_ptr *p2 = a2;

        if (p1->str != p2->str)
                return p1->str < p2->str ? -1 : 1;
        return 0;
}

static int btf_dedup_str_ptr_cmp(const void *str_ptr, const void *pelem)
{
        const struct btf_str_ptr *p = pelem;

        if (str_ptr != p->str)
                return (const char *)str_ptr < p->str ? -1 : 1;
        return 0;
}

static int btf_str_mark_as_used(__u32 *str_off_ptr, void *ctx)
{
        struct btf_str_ptrs *strs;
        struct btf_str_ptr *s;

        if (*str_off_ptr == 0)
                return 0;

        strs = ctx;
        s = bsearch(strs->data + *str_off_ptr, strs->ptrs, strs->cnt,
                    sizeof(struct btf_str_ptr), btf_dedup_str_ptr_cmp);
        if (!s)
                return -EINVAL;
        s->used = true;
        return 0;
}

static int btf_str_remap_offset(__u32 *str_off_ptr, void *ctx)
{
        struct btf_str_ptrs *strs;
        struct btf_str_ptr *s;

        if (*str_off_ptr == 0)
                return 0;

        strs = ctx;
        s = bsearch(strs->data + *str_off_ptr, strs->ptrs, strs->cnt,
                    sizeof(struct btf_str_ptr), btf_dedup_str_ptr_cmp);
        if (!s)
                return -EINVAL;
        *str_off_ptr = s->new_off;
        return 0;
}

/*
 * Dedup string and filter out those that are not referenced from either .BTF
 * or .BTF.ext (if provided) sections.
 *
 * This is done by building index of all strings in BTF's string section,
 * then iterating over all entities that can reference strings (e.g., type
 * names, struct field names, .BTF.ext line info, etc) and marking corresponding
 * strings as used. After that all used strings are deduped and compacted into
 * sequential blob of memory and new offsets are calculated. Then all the string
 * references are iterated again and rewritten using new offsets.
 */
static int btf_dedup_strings(struct btf_dedup *d)
{
        const struct btf_header *hdr = d->btf->hdr;
        char *start = (char *)d->btf->nohdr_data + hdr->str_off;
        char *end = start + d->btf->hdr->str_len;
        char *p = start, *tmp_strs = NULL;
        struct btf_str_ptrs strs = {
                .cnt = 0,
                .cap = 0,
                .ptrs = NULL,
                .data = start,
        };
        int i, j, err = 0, grp_idx;
        bool grp_used;

        /* build index of all strings */
        while (p < end) {
                if (strs.cnt + 1 > strs.cap) {
                        struct btf_str_ptr *new_ptrs;

                        strs.cap += max(strs.cnt / 2, 16);
                        new_ptrs = realloc(strs.ptrs,
                                           sizeof(strs.ptrs[0]) * strs.cap);
                        if (!new_ptrs) {
                                err = -ENOMEM;
                                goto done;
                        }
                        strs.ptrs = new_ptrs;
                }

                strs.ptrs[strs.cnt].str = p;
                strs.ptrs[strs.cnt].used = false;

                p += strlen(p) + 1;
                strs.cnt++;
        }

        /* temporary storage for deduplicated strings */
        tmp_strs = malloc(d->btf->hdr->str_len);
        if (!tmp_strs) {
                err = -ENOMEM;
                goto done;
        }

        /* mark all used strings */
        strs.ptrs[0].used = true;
        err = btf_for_each_str_off(d, btf_str_mark_as_used, &strs);
        if (err)
                goto done;

        /* sort strings by context, so that we can identify duplicates */
        qsort(strs.ptrs, strs.cnt, sizeof(strs.ptrs[0]), str_sort_by_content);

        /*
         * iterate groups of equal strings and if any instance in a group was
         * referenced, emit single instance and remember new offset
         */
        p = tmp_strs;
        grp_idx = 0;
        grp_used = strs.ptrs[0].used;
        /* iterate past end to avoid code duplication after loop */
        for (i = 1; i <= strs.cnt; i++) {
                /*
                 * when i == strs.cnt, we want to skip string comparison and go
                 * straight to handling last group of strings (otherwise we'd
                 * need to handle last group after the loop w/ duplicated code)
                 */
                if (i < strs.cnt &&
                    !strcmp(strs.ptrs[i].str, strs.ptrs[grp_idx].str)) {
                        grp_used = grp_used || strs.ptrs[i].used;
                        continue;
                }

                /*
                 * this check would have been required after the loop to handle
                 * last group of strings, but due to <= condition in a loop
                 * we avoid that duplication
                 */
                if (grp_used) {
                        int new_off = p - tmp_strs;
                        __u32 len = strlen(strs.ptrs[grp_idx].str);

                        memmove(p, strs.ptrs[grp_idx].str, len + 1);
                        for (j = grp_idx; j < i; j++)
                                strs.ptrs[j].new_off = new_off;
                        p += len + 1;
                }

                if (i < strs.cnt) {
                        grp_idx = i;
                        grp_used = strs.ptrs[i].used;
                }
        }

        /* replace original strings with deduped ones */
        d->btf->hdr->str_len = p - tmp_strs;
        memmove(start, tmp_strs, d->btf->hdr->str_len);
        end = start + d->btf->hdr->str_len;

        /* restore original order for further binary search lookups */
        qsort(strs.ptrs, strs.cnt, sizeof(strs.ptrs[0]), str_sort_by_offset);

        /* remap string offsets */
        err = btf_for_each_str_off(d, btf_str_remap_offset, &strs);
        if (err)
                goto done;

        d->btf->hdr->str_len = end - start;

done:
        free(tmp_strs);
        free(strs.ptrs);
        return err;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        default:
                return -EINVAL;
        }

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

        return 0;
}

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

        for (i = 1; i <= d->btf->nr_types; i++) {
                err = btf_dedup_prim_type(d, i);
                if (err)
                        return err;
        }
        return 0;
}

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

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

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

        if (!btf_is_fwd(d->btf->types[type_id]))
                return type_id;

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

        if (!btf_is_fwd(d->btf->types[type_id]))
                return type_id;

        return orig_type_id;
}


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

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

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

        canon_id = resolve_fwd_id(d, canon_id);

        hypot_type_id = d->hypot_map[canon_id];
        if (hypot_type_id <= BTF_MAX_NR_TYPES)
                return hypot_type_id == cand_id;

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

        cand_type = d->btf->types[cand_id];
        canon_type = d->btf->types[canon_id];
        cand_kind = btf_kind(cand_type);
        canon_kind = btf_kind(canon_type);

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

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

                if (cand_kind == BTF_KIND_FWD) {
                        real_kind = canon_kind;
                        fwd_kind = btf_fwd_kind(cand_type);
                } else {
                        real_kind = cand_kind;
                        fwd_kind = btf_fwd_kind(canon_type);
                }
                return fwd_kind == real_kind;
        }

        if (cand_kind != canon_kind)
                return 0;

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

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

        case BTF_KIND_FWD:
                return btf_equal_common(cand_type, canon_type);

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

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

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

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

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

                return 1;
        }

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

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

        default:
                return -EINVAL;
        }
        return 0;
}

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

        for (i = 0; i < d->hypot_cnt; i++) {
                cand_type_id = d->hypot_list[i];
                targ_type_id = d->hypot_map[cand_type_id];
                t_id = resolve_type_id(d, targ_type_id);
                c_id = resolve_type_id(d, cand_type_id);
                t_kind = btf_kind(d->btf->types[t_id]);
                c_kind = btf_kind(d->btf->types[c_id]);
                /*
                 * Resolve FWD into STRUCT/UNION.
                 * It's ok to resolve FWD into STRUCT/UNION that's not yet
                 * mapped to canonical representative (as opposed to
                 * STRUCT/UNION <--> STRUCT/UNION mapping logic below), because
                 * eventually that struct is going to be mapped and all resolved
                 * FWDs will automatically resolve to correct canonical
                 * representative. This will happen before ref type deduping,
                 * which critically depends on stability of these mapping. This
                 * stability is not a requirement for STRUCT/UNION equivalence
                 * checks, though.
                 */
                if (t_kind != BTF_KIND_FWD && c_kind == BTF_KIND_FWD)
                        d->map[c_id] = t_id;
                else if (t_kind == BTF_KIND_FWD && c_kind != BTF_KIND_FWD)
                        d->map[t_id] = c_id;

                if ((t_kind == BTF_KIND_STRUCT || t_kind == BTF_KIND_UNION) &&
                    c_kind != BTF_KIND_FWD &&
                    is_type_mapped(d, c_id) &&
                    !is_type_mapped(d, t_id)) {
                        /*
                         * as a perf optimization, we can map struct/union
                         * that's part of type graph we just verified for
                         * equivalence. We can do that for struct/union that has
                         * canonical representative only, though.
                         */
                        d->map[t_id] = c_id;
                }
        }
}

/*
 * Deduplicate struct/union types.
 *
 * For each struct/union type its type signature hash is calculated, taking
 * into account type's name, size, number, order and names of fields, but
 * ignoring type ID's referenced from fields, because they might not be deduped
 * completely until after reference types deduplication phase. This type hash
 * is used to iterate over all potential canonical types, sharing same hash.
 * For each canonical candidate we check whether type graphs that they form
 * (through referenced types in fields and so on) are equivalent using algorithm
 * implemented in `btf_dedup_is_equiv`. If such equivalence is found and
 * BTF_KIND_FWD resolution is allowed, then hypothetical mapping
 * (btf_dedup->hypot_map) produced by aforementioned type graph equivalence
 * algorithm is used to record FWD -> STRUCT/UNION mapping. It's also used to
 * potentially map other structs/unions to their canonical representatives,
 * if such relationship hasn't yet been established. This speeds up algorithm
 * by eliminating some of the duplicate work.
 *
 * If no matching canonical representative was found, struct/union is marked
 * as canonical for itself and is added into btf_dedup->dedup_table hash map
 * for further look ups.
 */
static int btf_dedup_struct_type(struct btf_dedup *d, __u32 type_id)
{
        struct btf_type *cand_type, *t;
        struct hashmap_entry *hash_entry;
        /* if we don't find equivalent type, then we are canonical */
        __u32 new_id = type_id;
        __u16 kind;
        long h;

        /* already deduped or is in process of deduping (loop detected) */
        if (d->map[type_id] <= BTF_MAX_NR_TYPES)
                return 0;

        t = d->btf->types[type_id];
        kind = btf_kind(t);

        if (kind != BTF_KIND_STRUCT && kind != BTF_KIND_UNION)
                return 0;

        h = btf_hash_struct(t);
        for_each_dedup_cand(d, hash_entry, h) {
                __u32 cand_id = (__u32)(long)hash_entry->value;
                int eq;

                /*
                 * Even though btf_dedup_is_equiv() checks for
                 * btf_shallow_equal_struct() internally when checking two
                 * structs (unions) for equivalence, we need to guard here
                 * from picking matching FWD type as a dedup candidate.
                 * This can happen due to hash collision. In such case just
                 * relying on btf_dedup_is_equiv() would lead to potentially
                 * creating a loop (FWD -> STRUCT and STRUCT -> FWD), because
                 * FWD and compatible STRUCT/UNION are considered equivalent.
                 */
                cand_type = d->btf->types[cand_id];
                if (!btf_shallow_equal_struct(t, cand_type))
                        continue;

                btf_dedup_clear_hypot_map(d);
                eq = btf_dedup_is_equiv(d, type_id, cand_id);
                if (eq < 0)
                        return eq;
                if (!eq)
                        continue;
                new_id = cand_id;
                btf_dedup_merge_hypot_map(d);
                break;
        }

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

        return 0;
}

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

        for (i = 1; i <= d->btf->nr_types; i++) {
                err = btf_dedup_struct_type(d, i);
                if (err)
                        return err;
        }
        return 0;
}

/*
 * Deduplicate reference type.
 *
 * Once all primitive and struct/union types got deduplicated, we can easily
 * deduplicate all other (reference) BTF types. This is done in two steps:
 *
 * 1. Resolve all referenced type IDs into their canonical type IDs. This
 * resolution can be done either immediately for primitive or struct/union types
 * (because they were deduped in previous two phases) or recursively for
 * reference types. Recursion will always terminate at either primitive or
 * struct/union type, at which point we can "unwind" chain of reference types
 * one by one. There is no danger of encountering cycles because in C type
 * system the only way to form type cycle is through struct/union, so any chain
 * of reference types, even those taking part in a type cycle, will inevitably
 * reach struct/union at some point.
 *
 * 2. Once all referenced type IDs are resolved into canonical ones, BTF type
 * becomes "stable", in the sense that no further deduplication will cause
 * any changes to it. With that, it's now possible to calculate type's signature
 * hash (this time taking into account referenced type IDs) and loop over all
 * potential canonical representatives. If no match was found, current type
 * will become canonical representative of itself and will be added into
 * btf_dedup->dedup_table as another possible canonical representative.
 */
static int btf_dedup_ref_type(struct btf_dedup *d, __u32 type_id)
{
        struct hashmap_entry *hash_entry;
        __u32 new_id = type_id, cand_id;
        struct btf_type *t, *cand;
        /* if we don't find equivalent type, then we are representative type */
        int ref_type_id;
        long h;

        if (d->map[type_id] == BTF_IN_PROGRESS_ID)
                return -ELOOP;
        if (d->map[type_id] <= BTF_MAX_NR_TYPES)
                return resolve_type_id(d, type_id);

        t = d->btf->types[type_id];
        d->map[type_id] = BTF_IN_PROGRESS_ID;

        switch (btf_kind(t)) {
        case BTF_KIND_CONST:
        case BTF_KIND_VOLATILE:
        case BTF_KIND_RESTRICT:
        case BTF_KIND_PTR:
        case BTF_KIND_TYPEDEF:
        case BTF_KIND_FUNC:
                ref_type_id = btf_dedup_ref_type(d, t->type);
                if (ref_type_id < 0)
                        return ref_type_id;
                t->type = ref_type_id;

                h = btf_hash_common(t);
                for_each_dedup_cand(d, hash_entry, h) {
                        cand_id = (__u32)(long)hash_entry->value;
                        cand = d->btf->types[cand_id];
                        if (btf_equal_common(t, cand)) {
                                new_id = cand_id;
                                break;
                        }
                }
                break;

        case BTF_KIND_ARRAY: {
                struct btf_array *info = btf_array(t);

                ref_type_id = btf_dedup_ref_type(d, info->type);
                if (ref_type_id < 0)
                        return ref_type_id;
                info->type = ref_type_id;

                ref_type_id = btf_dedup_ref_type(d, info->index_type);
                if (ref_type_id < 0)
                        return ref_type_id;
                info->index_type = ref_type_id;

                h = btf_hash_array(t);
                for_each_dedup_cand(d, hash_entry, h) {
                        cand_id = (__u32)(long)hash_entry->value;
                        cand = d->btf->types[cand_id];
                        if (btf_equal_array(t, cand)) {
                                new_id = cand_id;
                                break;
                        }
                }
                break;
        }

        case BTF_KIND_FUNC_PROTO: {
                struct btf_param *param;
                __u16 vlen;
                int i;

                ref_type_id = btf_dedup_ref_type(d, t->type);
                if (ref_type_id < 0)
                        return ref_type_id;
                t->type = ref_type_id;

                vlen = btf_vlen(t);
                param = btf_params(t);
                for (i = 0; i < vlen; i++) {
                        ref_type_id = btf_dedup_ref_type(d, param->type);
                        if (ref_type_id < 0)
                                return ref_type_id;
                        param->type = ref_type_id;
                        param++;
                }

                h = btf_hash_fnproto(t);
                for_each_dedup_cand(d, hash_entry, h) {
                        cand_id = (__u32)(long)hash_entry->value;
                        cand = d->btf->types[cand_id];
                        if (btf_equal_fnproto(t, cand)) {
                                new_id = cand_id;
                                break;
                        }
                }
                break;
        }

        default:
                return -EINVAL;
        }

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

        return new_id;
}

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

        for (i = 1; i <= d->btf->nr_types; i++) {
                err = btf_dedup_ref_type(d, i);
                if (err < 0)
                        return err;
        }
        /* we won't need d->dedup_table anymore */
        hashmap__free(d->dedup_table);
        d->dedup_table = NULL;
        return 0;
}

/*
 * Compact types.
 *
 * After we established for each type its corresponding canonical representative
 * type, we now can eliminate types that are not canonical and leave only
 * canonical ones layed out sequentially in memory by copying them over
 * duplicates. During compaction btf_dedup->hypot_map array is reused to store
 * a map from original type ID to a new compacted type ID, which will be used
 * during next phase to "fix up" type IDs, referenced from struct/union and
 * reference types.
 */
static int btf_dedup_compact_types(struct btf_dedup *d)
{
        struct btf_type **new_types;
        __u32 next_type_id = 1;
        char *types_start, *p;
        int i, len;

        /* we are going to reuse hypot_map to store compaction remapping */
        d->hypot_map[0] = 0;
        for (i = 1; i <= d->btf->nr_types; i++)
                d->hypot_map[i] = BTF_UNPROCESSED_ID;

        types_start = d->btf->nohdr_data + d->btf->hdr->type_off;
        p = types_start;

        for (i = 1; i <= d->btf->nr_types; i++) {
                if (d->map[i] != i)
                        continue;

                len = btf_type_size(d->btf->types[i]);
                if (len < 0)
                        return len;

                memmove(p, d->btf->types[i], len);
                d->hypot_map[i] = next_type_id;
                d->btf->types[next_type_id] = (struct btf_type *)p;
                p += len;
                next_type_id++;
        }

        /* shrink struct btf's internal types index and update btf_header */
        d->btf->nr_types = next_type_id - 1;
        d->btf->types_size = d->btf->nr_types;
        d->btf->hdr->type_len = p - types_start;
        new_types = realloc(d->btf->types,
                            (1 + d->btf->nr_types) * sizeof(struct btf_type *));
        if (!new_types)
                return -ENOMEM;
        d->btf->types = new_types;

        /* make sure string section follows type information without gaps */
        d->btf->hdr->str_off = p - (char *)d->btf->nohdr_data;
        memmove(p, d->btf->strings, d->btf->hdr->str_len);
        d->btf->strings = p;
        p += d->btf->hdr->str_len;

        d->btf->data_size = p - (char *)d->btf->data;
        return 0;
}

/*
 * Figure out final (deduplicated and compacted) type ID for provided original
 * `type_id` by first resolving it into corresponding canonical type ID and
 * then mapping it to a deduplicated type ID, stored in btf_dedup->hypot_map,
 * which is populated during compaction phase.
 */
static int btf_dedup_remap_type_id(struct btf_dedup *d, __u32 type_id)
{
        __u32 resolved_type_id, new_type_id;

        resolved_type_id = resolve_type_id(d, type_id);
        new_type_id = d->hypot_map[resolved_type_id];
        if (new_type_id > BTF_MAX_NR_TYPES)
                return -EINVAL;
        return new_type_id;
}

/*
 * Remap referenced type IDs into deduped type IDs.
 *
 * After BTF types are deduplicated and compacted, their final type IDs may
 * differ from original ones. The map from original to a corresponding
 * deduped type ID is stored in btf_dedup->hypot_map and is populated during
 * compaction phase. During remapping phase we are rewriting all type IDs
 * referenced from any BTF type (e.g., struct fields, func proto args, etc) to
 * their final deduped type IDs.
 */
static int btf_dedup_remap_type(struct btf_dedup *d, __u32 type_id)
{
        struct btf_type *t = d->btf->types[type_id];
        int i, r;

        switch (btf_kind(t)) {
        case BTF_KIND_INT:
        case BTF_KIND_ENUM:
                break;

        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_VAR:
                r = btf_dedup_remap_type_id(d, t->type);
                if (r < 0)
                        return r;
                t->type = r;
                break;

        case BTF_KIND_ARRAY: {
                struct btf_array *arr_info = btf_array(t);

                r = btf_dedup_remap_type_id(d, arr_info->type);
                if (r < 0)
                        return r;
                arr_info->type = r;
                r = btf_dedup_remap_type_id(d, arr_info->index_type);
                if (r < 0)
                        return r;
                arr_info->index_type = r;
                break;
        }

        case BTF_KIND_STRUCT:
        case BTF_KIND_UNION: {
                struct btf_member *member = btf_members(t);
                __u16 vlen = btf_vlen(t);

                for (i = 0; i < vlen; i++) {
                        r = btf_dedup_remap_type_id(d, member->type);
                        if (r < 0)
                                return r;
                        member->type = r;
                        member++;
                }
                break;
        }

        case BTF_KIND_FUNC_PROTO: {
                struct btf_param *param = btf_params(t);
                __u16 vlen = btf_vlen(t);

                r = btf_dedup_remap_type_id(d, t->type);
                if (r < 0)
                        return r;
                t->type = r;

                for (i = 0; i < vlen; i++) {
                        r = btf_dedup_remap_type_id(d, param->type);
                        if (r < 0)
                                return r;
                        param->type = r;
                        param++;
                }
                break;
        }

        case BTF_KIND_DATASEC: {
                struct btf_var_secinfo *var = btf_var_secinfos(t);
                __u16 vlen = btf_vlen(t);

                for (i = 0; i < vlen; i++) {
                        r = btf_dedup_remap_type_id(d, var->type);
                        if (r < 0)
                                return r;
                        var->type = r;
                        var++;
                }
                break;
        }

        default:
                return -EINVAL;
        }

        return 0;
}

static int btf_dedup_remap_types(struct btf_dedup *d)
{
        int i, r;

        for (i = 1; i <= d->btf->nr_types; i++) {
                r = btf_dedup_remap_type(d, i);
                if (r < 0)
                        return r;
        }
        return 0;
}