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 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
 /* Copyright (c) 2018 Facebook */
 
 #include <byteswap.h>
 #include <endian.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
 #include <sys/utsname.h>
 #include <sys/param.h>
 #include <sys/stat.h>
 #include <linux/kernel.h>
 #include <linux/err.h>
 #include <linux/btf.h>
 #include <gelf.h>
 #include "btf.h"
 #include "bpf.h"
 #include "libbpf.h"
 #include "libbpf_internal.h"
 #include "hashmap.h"
 #include "strset.h"
 
 #define BTF_MAX_NR_TYPES 0x7fffffffU
 #define BTF_MAX_STR_OFFSET 0x7fffffffU
 
 static struct btf_type btf_void;
 
 struct btf {
     /* raw BTF data in native endianness */
     void *raw_data;
     /* raw BTF data in non-native endianness */
     void *raw_data_swapped;
     __u32 raw_size;
     /* whether target endianness differs from the native one */
     bool swapped_endian;
 
     /*
      * When BTF is loaded from an ELF or raw memory it is stored
      * in a contiguous memory block. The hdr, type_data, and, strs_data
      * point inside that memory region to their respective parts of BTF
      * representation:
      *
      * +--------------------------------+
      * |  Header  |  Types  |  Strings  |
      * +--------------------------------+
      * ^          ^         ^
      * |          |         |
      * hdr        |         |
      * types_data-+         |
      * strs_data------------+
      *
      * If BTF data is later modified, e.g., due to types added or
      * removed, BTF deduplication performed, etc, this contiguous
      * representation is broken up into three independently allocated
      * memory regions to be able to modify them independently.
      * raw_data is nulled out at that point, but can be later allocated
      * and cached again if user calls btf__raw_data(), at which point
      * raw_data will contain a contiguous copy of header, types, and
      * strings:
      *
      * +----------+  +---------+  +-----------+
      * |  Header  |  |  Types  |  |  Strings  |
      * +----------+  +---------+  +-----------+
      * ^             ^            ^
      * |             |            |
      * hdr           |            |
      * types_data----+            |
      * strset__data(strs_set)-----+
      *
      *               +----------+---------+-----------+
      *               |  Header  |  Types  |  Strings  |
      * raw_data----->+----------+---------+-----------+
      */
     struct btf_header *hdr;
 
     void *types_data;
     size_t types_data_cap; /* used size stored in hdr->type_len */
 
     /* type ID to `struct btf_type *` lookup index
      * type_offs[0] corresponds to the first non-VOID type:
      *   - for base BTF it's type [1];
      *   - for split BTF it's the first non-base BTF type.
      */
     __u32 *type_offs;
     size_t type_offs_cap;
     /* number of types in this BTF instance:
      *   - doesn't include special [0] void type;
      *   - for split BTF counts number of types added on top of base BTF.
      */
     __u32 nr_types;
     /* if not NULL, points to the base BTF on top of which the current
      * split BTF is based
      */
     struct btf *base_btf;
     /* BTF type ID of the first type in this BTF instance:
      *   - for base BTF it's equal to 1;
      *   - for split BTF it's equal to biggest type ID of base BTF plus 1.
      */
     int start_id;
     /* logical string offset of this BTF instance:
      *   - for base BTF it's equal to 0;
      *   - for split BTF it's equal to total size of base BTF's string section size.
      */
     int start_str_off;
 
     /* only one of strs_data or strs_set can be non-NULL, depending on
      * whether BTF is in a modifiable state (strs_set is used) or not
      * (strs_data points inside raw_data)
      */
     void *strs_data;
     /* a set of unique strings */
     struct strset *strs_set;
     /* whether strings are already deduplicated */
     bool strs_deduped;
 
     /* BTF object FD, if loaded into kernel */
     int fd;
 
     /* Pointer size (in bytes) for a target architecture of this BTF */
     int ptr_sz;
 };
 
 static inline __u64 ptr_to_u64(const void *ptr)
 {
     return (__u64) (unsigned long) ptr;
 }
 
 /* Ensure given dynamically allocated memory region pointed to by *data* with
  * capacity of *cap_cnt* elements each taking *elem_sz* bytes has enough
  * memory to accommodate *add_cnt* new elements, assuming *cur_cnt* elements
  * are already used. At most *max_cnt* elements can be ever allocated.
  * If necessary, memory is reallocated and all existing data is copied over,
  * new pointer to the memory region is stored at *data, new memory region
  * capacity (in number of elements) is stored in *cap.
  * On success, memory pointer to the beginning of unused memory is returned.
  * On error, NULL is returned.
  */
 void *libbpf_add_mem(void **data, size_t *cap_cnt, size_t elem_sz,
              size_t cur_cnt, size_t max_cnt, size_t add_cnt)
 {
     size_t new_cnt;
     void *new_data;
 
     if (cur_cnt + add_cnt <= *cap_cnt)
         return *data + cur_cnt * elem_sz;
 
     /* requested more than the set limit */
     if (cur_cnt + add_cnt > max_cnt)
         return NULL;
 
     new_cnt = *cap_cnt;
     new_cnt += new_cnt / 4;       /* expand by 25% */
     if (new_cnt < 16)         /* but at least 16 elements */
         new_cnt = 16;
     if (new_cnt > max_cnt)        /* but not exceeding a set limit */
         new_cnt = max_cnt;
     if (new_cnt < cur_cnt + add_cnt)  /* also ensure we have enough memory */
         new_cnt = cur_cnt + add_cnt;
 
     new_data = libbpf_reallocarray(*data, new_cnt, elem_sz);
     if (!new_data)
         return NULL;
 
     /* zero out newly allocated portion of memory */
     memset(new_data + (*cap_cnt) * elem_sz, 0, (new_cnt - *cap_cnt) * elem_sz);
 
     *data = new_data;
     *cap_cnt = new_cnt;
     return new_data + cur_cnt * elem_sz;
 }
 
 /* Ensure given dynamically allocated memory region has enough allocated space
  * to accommodate *need_cnt* elements of size *elem_sz* bytes each
  */
 int libbpf_ensure_mem(void **data, size_t *cap_cnt, size_t elem_sz, size_t need_cnt)
 {
     void *p;
 
     if (need_cnt <= *cap_cnt)
         return 0;
 
     p = libbpf_add_mem(data, cap_cnt, elem_sz, *cap_cnt, SIZE_MAX, need_cnt - *cap_cnt);
     if (!p)
         return -ENOMEM;
 
     return 0;
 }
 
 static void *btf_add_type_offs_mem(struct btf *btf, size_t add_cnt)
 {
     return libbpf_add_mem((void **)&btf->type_offs, &btf->type_offs_cap, sizeof(__u32),
                   btf->nr_types, BTF_MAX_NR_TYPES, add_cnt);
 }
 
 static int btf_add_type_idx_entry(struct btf *btf, __u32 type_off)
 {
     __u32 *p;
 
     p = btf_add_type_offs_mem(btf, 1);
     if (!p)
         return -ENOMEM;
 
     *p = type_off;
     return 0;
 }
 
 static void btf_bswap_hdr(struct btf_header *h)
 {
     h->magic = bswap_16(h->magic);
     h->hdr_len = bswap_32(h->hdr_len);
     h->type_off = bswap_32(h->type_off);
     h->type_len = bswap_32(h->type_len);
     h->str_off = bswap_32(h->str_off);
     h->str_len = bswap_32(h->str_len);
 }
 
 static int btf_parse_hdr(struct btf *btf)
 {
     struct btf_header *hdr = btf->hdr;
     __u32 meta_left;
 
     if (btf->raw_size < sizeof(struct btf_header)) {
         pr_debug("BTF header not found\n");
         return -EINVAL;
     }
 
     if (hdr->magic == bswap_16(BTF_MAGIC)) {
         btf->swapped_endian = true;
         if (bswap_32(hdr->hdr_len) != sizeof(struct btf_header)) {
             pr_warn("Can't load BTF with non-native endianness due to unsupported header length %u\n",
                 bswap_32(hdr->hdr_len));
             return -ENOTSUP;
         }
         btf_bswap_hdr(hdr);
     } else if (hdr->magic != BTF_MAGIC) {
         pr_debug("Invalid BTF magic: %x\n", hdr->magic);
         return -EINVAL;
     }
 
     if (btf->raw_size < hdr->hdr_len) {
         pr_debug("BTF header len %u larger than data size %u\n",
              hdr->hdr_len, btf->raw_size);
         return -EINVAL;
     }
 
     meta_left = btf->raw_size - hdr->hdr_len;
     if (meta_left < (long long)hdr->str_off + hdr->str_len) {
         pr_debug("Invalid BTF total size: %u\n", btf->raw_size);
         return -EINVAL;
     }
 
     if ((long long)hdr->type_off + hdr->type_len > hdr->str_off) {
         pr_debug("Invalid BTF data sections layout: type data at %u + %u, strings data at %u + %u\n",
              hdr->type_off, hdr->type_len, hdr->str_off, hdr->str_len);
         return -EINVAL;
     }
 
     if (hdr->type_off % 4) {
         pr_debug("BTF type section is not aligned to 4 bytes\n");
         return -EINVAL;
     }
 
     return 0;
 }
 
 static int btf_parse_str_sec(struct btf *btf)
 {
     const struct btf_header *hdr = btf->hdr;
     const char *start = btf->strs_data;
     const char *end = start + btf->hdr->str_len;
 
     if (btf->base_btf && hdr->str_len == 0)
         return 0;
     if (!hdr->str_len || hdr->str_len - 1 > BTF_MAX_STR_OFFSET || end[-1]) {
         pr_debug("Invalid BTF string section\n");
         return -EINVAL;
     }
     if (!btf->base_btf && start[0]) {
         pr_debug("Invalid BTF string section\n");
         return -EINVAL;
     }
     return 0;
 }
 
 static int btf_type_size(const struct btf_type *t)
 {
     const int base_size = sizeof(struct btf_type);
     __u16 vlen = btf_vlen(t);
 
     switch (btf_kind(t)) {
     case BTF_KIND_FWD:
     case BTF_KIND_CONST:
     case BTF_KIND_VOLATILE:
     case BTF_KIND_RESTRICT:
     case BTF_KIND_PTR:
     case BTF_KIND_TYPEDEF:
     case BTF_KIND_FUNC:
     case BTF_KIND_FLOAT:
     case BTF_KIND_TYPE_TAG:
         return base_size;
     case BTF_KIND_INT:
         return base_size + sizeof(__u32);
     case BTF_KIND_ENUM:
         return base_size + vlen * sizeof(struct btf_enum);
     case BTF_KIND_ENUM64:
         return base_size + vlen * sizeof(struct btf_enum64);
     case BTF_KIND_ARRAY:
         return base_size + sizeof(struct btf_array);
     case BTF_KIND_STRUCT:
     case BTF_KIND_UNION:
         return base_size + vlen * sizeof(struct btf_member);
     case BTF_KIND_FUNC_PROTO:
         return base_size + vlen * sizeof(struct btf_param);
     case BTF_KIND_VAR:
         return base_size + sizeof(struct btf_var);
     case BTF_KIND_DATASEC:
         return base_size + vlen * sizeof(struct btf_var_secinfo);
     case BTF_KIND_DECL_TAG:
         return base_size + sizeof(struct btf_decl_tag);
     default:
         pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
         return -EINVAL;
     }
 }
 
 static void btf_bswap_type_base(struct btf_type *t)
 {
     t->name_off = bswap_32(t->name_off);
     t->info = bswap_32(t->info);
     t->type = bswap_32(t->type);
 }
 
 static int btf_bswap_type_rest(struct btf_type *t)
 {
     struct btf_var_secinfo *v;
     struct btf_enum64 *e64;
     struct btf_member *m;
     struct btf_array *a;
     struct btf_param *p;
     struct btf_enum *e;
     __u16 vlen = btf_vlen(t);
     int i;
 
     switch (btf_kind(t)) {
     case BTF_KIND_FWD:
     case BTF_KIND_CONST:
     case BTF_KIND_VOLATILE:
     case BTF_KIND_RESTRICT:
     case BTF_KIND_PTR:
     case BTF_KIND_TYPEDEF:
     case BTF_KIND_FUNC:
     case BTF_KIND_FLOAT:
     case BTF_KIND_TYPE_TAG:
         return 0;
     case BTF_KIND_INT:
         *(__u32 *)(t + 1) = bswap_32(*(__u32 *)(t + 1));
         return 0;
     case BTF_KIND_ENUM:
         for (i = 0, e = btf_enum(t); i < vlen; i++, e++) {
             e->name_off = bswap_32(e->name_off);
             e->val = bswap_32(e->val);
         }
         return 0;
     case BTF_KIND_ENUM64:
         for (i = 0, e64 = btf_enum64(t); i < vlen; i++, e64++) {
             e64->name_off = bswap_32(e64->name_off);
             e64->val_lo32 = bswap_32(e64->val_lo32);
             e64->val_hi32 = bswap_32(e64->val_hi32);
         }
         return 0;
     case BTF_KIND_ARRAY:
         a = btf_array(t);
         a->type = bswap_32(a->type);
         a->index_type = bswap_32(a->index_type);
         a->nelems = bswap_32(a->nelems);
         return 0;
     case BTF_KIND_STRUCT:
     case BTF_KIND_UNION:
         for (i = 0, m = btf_members(t); i < vlen; i++, m++) {
             m->name_off = bswap_32(m->name_off);
             m->type = bswap_32(m->type);
             m->offset = bswap_32(m->offset);
         }
         return 0;
     case BTF_KIND_FUNC_PROTO:
         for (i = 0, p = btf_params(t); i < vlen; i++, p++) {
             p->name_off = bswap_32(p->name_off);
             p->type = bswap_32(p->type);
         }
         return 0;
     case BTF_KIND_VAR:
         btf_var(t)->linkage = bswap_32(btf_var(t)->linkage);
         return 0;
     case BTF_KIND_DATASEC:
         for (i = 0, v = btf_var_secinfos(t); i < vlen; i++, v++) {
             v->type = bswap_32(v->type);
             v->offset = bswap_32(v->offset);
             v->size = bswap_32(v->size);
         }
         return 0;
     case BTF_KIND_DECL_TAG:
         btf_decl_tag(t)->component_idx = bswap_32(btf_decl_tag(t)->component_idx);
         return 0;
     default:
         pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
         return -EINVAL;
     }
 }
 
 static int btf_parse_type_sec(struct btf *btf)
 {
     struct btf_header *hdr = btf->hdr;
     void *next_type = btf->types_data;
     void *end_type = next_type + hdr->type_len;
     int err, type_size;
 
     while (next_type + sizeof(struct btf_type) <= end_type) {
         if (btf->swapped_endian)
             btf_bswap_type_base(next_type);
 
         type_size = btf_type_size(next_type);
         if (type_size < 0)
             return type_size;
         if (next_type + type_size > end_type) {
             pr_warn("BTF type [%d] is malformed\n", btf->start_id + btf->nr_types);
             return -EINVAL;
         }
 
         if (btf->swapped_endian && btf_bswap_type_rest(next_type))
             return -EINVAL;
 
         err = btf_add_type_idx_entry(btf, next_type - btf->types_data);
         if (err)
             return err;
 
         next_type += type_size;
         btf->nr_types++;
     }
 
     if (next_type != end_type) {
         pr_warn("BTF types data is malformed\n");
         return -EINVAL;
     }
 
     return 0;
 }
 
 __u32 btf__type_cnt(const struct btf *btf)
 {
     return btf->start_id + btf->nr_types;
 }
 
 const struct btf *btf__base_btf(const struct btf *btf)
 {
     return btf->base_btf;
 }
 
 /* internal helper returning non-const pointer to a type */
 struct btf_type *btf_type_by_id(const struct btf *btf, __u32 type_id)
 {
     if (type_id == 0)
         return &btf_void;
     if (type_id < btf->start_id)
         return btf_type_by_id(btf->base_btf, type_id);
     return btf->types_data + btf->type_offs[type_id - btf->start_id];
 }
 
 const struct btf_type *btf__type_by_id(const struct btf *btf, __u32 type_id)
 {
     if (type_id >= btf->start_id + btf->nr_types)
         return errno = EINVAL, NULL;
     return btf_type_by_id((struct btf *)btf, type_id);
 }
 
 static int determine_ptr_size(const struct btf *btf)
 {
     static const char * const long_aliases[] = {
         "long",
         "long int",
         "int long",
         "unsigned long",
         "long unsigned",
         "unsigned long int",
         "unsigned int long",
         "long unsigned int",
         "long int unsigned",
         "int unsigned long",
         "int long unsigned",
     };
     const struct btf_type *t;
     const char *name;
     int i, j, n;
 
     if (btf->base_btf && btf->base_btf->ptr_sz > 0)
         return btf->base_btf->ptr_sz;
 
     n = btf__type_cnt(btf);
     for (i = 1; i < n; i++) {
         t = btf__type_by_id(btf, i);
         if (!btf_is_int(t))
             continue;
 
         if (t->size != 4 && t->size != 8)
             continue;
 
         name = btf__name_by_offset(btf, t->name_off);
         if (!name)
             continue;
 
         for (j = 0; j < ARRAY_SIZE(long_aliases); j++) {
             if (strcmp(name, long_aliases[j]) == 0)
                 return t->size;
         }
     }
 
     return -1;
 }
 
 static size_t btf_ptr_sz(const struct btf *btf)
 {
     if (!btf->ptr_sz)
         ((struct btf *)btf)->ptr_sz = determine_ptr_size(btf);
     return btf->ptr_sz < 0 ? sizeof(void *) : btf->ptr_sz;
 }
 
 /* Return pointer size this BTF instance assumes. The size is heuristically
  * determined by looking for 'long' or 'unsigned long' integer type and
  * recording its size in bytes. If BTF type information doesn't have any such
  * type, this function returns 0. In the latter case, native architecture's
  * pointer size is assumed, so will be either 4 or 8, depending on
  * architecture that libbpf was compiled for. It's possible to override
  * guessed value by using btf__set_pointer_size() API.
  */
 size_t btf__pointer_size(const struct btf *btf)
 {
     if (!btf->ptr_sz)
         ((struct btf *)btf)->ptr_sz = determine_ptr_size(btf);
 
     if (btf->ptr_sz < 0)
         /* not enough BTF type info to guess */
         return 0;
 
     return btf->ptr_sz;
 }
 
 /* Override or set pointer size in bytes. Only values of 4 and 8 are
  * supported.
  */
 int btf__set_pointer_size(struct btf *btf, size_t ptr_sz)
 {
     if (ptr_sz != 4 && ptr_sz != 8)
         return libbpf_err(-EINVAL);
     btf->ptr_sz = ptr_sz;
     return 0;
 }
 
 static bool is_host_big_endian(void)
 {
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     return false;
 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
     return true;
 #else
 # error "Unrecognized __BYTE_ORDER__"
 #endif
 }
 
 enum btf_endianness btf__endianness(const struct btf *btf)
 {
     if (is_host_big_endian())
         return btf->swapped_endian ? BTF_LITTLE_ENDIAN : BTF_BIG_ENDIAN;
     else
         return btf->swapped_endian ? BTF_BIG_ENDIAN : BTF_LITTLE_ENDIAN;
 }
 
 int btf__set_endianness(struct btf *btf, enum btf_endianness endian)
 {
     if (endian != BTF_LITTLE_ENDIAN && endian != BTF_BIG_ENDIAN)
         return libbpf_err(-EINVAL);
 
     btf->swapped_endian = is_host_big_endian() != (endian == BTF_BIG_ENDIAN);
     if (!btf->swapped_endian) {
         free(btf->raw_data_swapped);
         btf->raw_data_swapped = NULL;
     }
     return 0;
 }
 
 static bool btf_type_is_void(const struct btf_type *t)
 {
     return t == &btf_void || btf_is_fwd(t);
 }
 
 static bool btf_type_is_void_or_null(const struct btf_type *t)
 {
     return !t || btf_type_is_void(t);
 }
 
 #define MAX_RESOLVE_DEPTH 32
 
 __s64 btf__resolve_size(const struct btf *btf, __u32 type_id)
 {
     const struct btf_array *array;
     const struct btf_type *t;
     __u32 nelems = 1;
     __s64 size = -1;
     int i;
 
     t = btf__type_by_id(btf, type_id);
     for (i = 0; i < MAX_RESOLVE_DEPTH && !btf_type_is_void_or_null(t); i++) {
         switch (btf_kind(t)) {
         case BTF_KIND_INT:
         case BTF_KIND_STRUCT:
         case BTF_KIND_UNION:
         case BTF_KIND_ENUM:
         case BTF_KIND_ENUM64:
         case BTF_KIND_DATASEC:
         case BTF_KIND_FLOAT:
             size = t->size;
             goto done;
         case BTF_KIND_PTR:
             size = btf_ptr_sz(btf);
             goto done;
         case BTF_KIND_TYPEDEF:
         case BTF_KIND_VOLATILE:
         case BTF_KIND_CONST:
         case BTF_KIND_RESTRICT:
         case BTF_KIND_VAR:
         case BTF_KIND_DECL_TAG:
         case BTF_KIND_TYPE_TAG:
             type_id = t->type;
             break;
         case BTF_KIND_ARRAY:
             array = btf_array(t);
             if (nelems && array->nelems > UINT32_MAX / nelems)
                 return libbpf_err(-E2BIG);
             nelems *= array->nelems;
             type_id = array->type;
             break;
         default:
             return libbpf_err(-EINVAL);
         }
 
         t = btf__type_by_id(btf, type_id);
     }
 
 done:
     if (size < 0)
         return libbpf_err(-EINVAL);
     if (nelems && size > UINT32_MAX / nelems)
         return libbpf_err(-E2BIG);
 
     return nelems * size;
 }
 
 int btf__align_of(const struct btf *btf, __u32 id)
 {
     const struct btf_type *t = btf__type_by_id(btf, id);
     __u16 kind = btf_kind(t);
 
     switch (kind) {
     case BTF_KIND_INT:
     case BTF_KIND_ENUM:
     case BTF_KIND_ENUM64:
     case BTF_KIND_FLOAT:
         return min(btf_ptr_sz(btf), (size_t)t->size);
     case BTF_KIND_PTR:
         return btf_ptr_sz(btf);
     case BTF_KIND_TYPEDEF:
     case BTF_KIND_VOLATILE:
     case BTF_KIND_CONST:
     case BTF_KIND_RESTRICT:
     case BTF_KIND_TYPE_TAG:
         return btf__align_of(btf, t->type);
     case BTF_KIND_ARRAY:
         return btf__align_of(btf, btf_array(t)->type);
     case BTF_KIND_STRUCT:
     case BTF_KIND_UNION: {
         const struct btf_member *m = btf_members(t);
         __u16 vlen = btf_vlen(t);
         int i, max_align = 1, align;
 
         for (i = 0; i < vlen; i++, m++) {
             align = btf__align_of(btf, m->type);
             if (align <= 0)
                 return libbpf_err(align);
             max_align = max(max_align, align);
         }
 
         return max_align;
     }
     default:
         pr_warn("unsupported BTF_KIND:%u\n", btf_kind(t));
         return errno = EINVAL, 0;
     }
 }
 
 int btf__resolve_type(const struct btf *btf, __u32 type_id)
 {
     const struct btf_type *t;
     int depth = 0;
 
     t = btf__type_by_id(btf, type_id);
     while (depth < MAX_RESOLVE_DEPTH &&
            !btf_type_is_void_or_null(t) &&
            (btf_is_mod(t) || btf_is_typedef(t) || btf_is_var(t))) {
         type_id = t->type;
         t = btf__type_by_id(btf, type_id);
         depth++;
     }
 
     if (depth == MAX_RESOLVE_DEPTH || btf_type_is_void_or_null(t))
         return libbpf_err(-EINVAL);
 
     return type_id;
 }
 
 __s32 btf__find_by_name(const struct btf *btf, const char *type_name)
 {
     __u32 i, nr_types = btf__type_cnt(btf);
 
     if (!strcmp(type_name, "void"))
         return 0;
 
     for (i = 1; i < nr_types; i++) {
         const struct btf_type *t = btf__type_by_id(btf, i);
         const char *name = btf__name_by_offset(btf, t->name_off);
 
         if (name && !strcmp(type_name, name))
             return i;
     }
 
     return libbpf_err(-ENOENT);
 }
 
 static __s32 btf_find_by_name_kind(const struct btf *btf, int start_id,
                    const char *type_name, __u32 kind)
 {
     __u32 i, nr_types = btf__type_cnt(btf);
 
     if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
         return 0;
 
     for (i = start_id; i < nr_types; i++) {
         const struct btf_type *t = btf__type_by_id(btf, i);
         const char *name;
 
         if (btf_kind(t) != kind)
             continue;
         name = btf__name_by_offset(btf, t->name_off);
         if (name && !strcmp(type_name, name))
             return i;
     }
 
     return libbpf_err(-ENOENT);
 }
 
 __s32 btf__find_by_name_kind_own(const struct btf *btf, const char *type_name,
                  __u32 kind)
 {
     return btf_find_by_name_kind(btf, btf->start_id, type_name, kind);
 }
 
 __s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
                  __u32 kind)
 {
     return btf_find_by_name_kind(btf, 1, type_name, kind);
 }
 
 static bool btf_is_modifiable(const struct btf *btf)
 {
     return (void *)btf->hdr != btf->raw_data;
 }
 
 void btf__free(struct btf *btf)
 {
     if (IS_ERR_OR_NULL(btf))
         return;
 
     if (btf->fd >= 0)
         close(btf->fd);
 
     if (btf_is_modifiable(btf)) {
         /* if BTF was modified after loading, it will have a split
          * in-memory representation for header, types, and strings
          * sections, so we need to free all of them individually. It
          * might still have a cached contiguous raw data present,
          * which will be unconditionally freed below.
          */
         free(btf->hdr);
         free(btf->types_data);
         strset__free(btf->strs_set);
     }
     free(btf->raw_data);
     free(btf->raw_data_swapped);
     free(btf->type_offs);
     free(btf);
 }
 
 static struct btf *btf_new_empty(struct btf *base_btf)
 {
     struct btf *btf;
 
     btf = calloc(1, sizeof(*btf));
     if (!btf)
         return ERR_PTR(-ENOMEM);
 
     btf->nr_types = 0;
     btf->start_id = 1;
     btf->start_str_off = 0;
     btf->fd = -1;
     btf->ptr_sz = sizeof(void *);
     btf->swapped_endian = false;
 
     if (base_btf) {
         btf->base_btf = base_btf;
         btf->start_id = btf__type_cnt(base_btf);
         btf->start_str_off = base_btf->hdr->str_len;
     }
 
     /* +1 for empty string at offset 0 */
     btf->raw_size = sizeof(struct btf_header) + (base_btf ? 0 : 1);
     btf->raw_data = calloc(1, btf->raw_size);
     if (!btf->raw_data) {
         free(btf);
         return ERR_PTR(-ENOMEM);
     }
 
     btf->hdr = btf->raw_data;
     btf->hdr->hdr_len = sizeof(struct btf_header);
     btf->hdr->magic = BTF_MAGIC;
     btf->hdr->version = BTF_VERSION;
 
     btf->types_data = btf->raw_data + btf->hdr->hdr_len;
     btf->strs_data = btf->raw_data + btf->hdr->hdr_len;
     btf->hdr->str_len = base_btf ? 0 : 1; /* empty string at offset 0 */
 
     return btf;
 }
 
 struct btf *btf__new_empty(void)
 {
     return libbpf_ptr(btf_new_empty(NULL));
 }
 
 struct btf *btf__new_empty_split(struct btf *base_btf)
 {
     return libbpf_ptr(btf_new_empty(base_btf));
 }
 
 static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
 {
     struct btf *btf;
     int err;
 
     btf = calloc(1, sizeof(struct btf));
     if (!btf)
         return ERR_PTR(-ENOMEM);
 
     btf->nr_types = 0;
     btf->start_id = 1;
     btf->start_str_off = 0;
     btf->fd = -1;
 
     if (base_btf) {
         btf->base_btf = base_btf;
         btf->start_id = btf__type_cnt(base_btf);
         btf->start_str_off = base_btf->hdr->str_len;
     }
 
     btf->raw_data = malloc(size);
     if (!btf->raw_data) {
         err = -ENOMEM;
         goto done;
     }
     memcpy(btf->raw_data, data, size);
     btf->raw_size = size;
 
     btf->hdr = btf->raw_data;
     err = btf_parse_hdr(btf);
     if (err)
         goto done;
 
     btf->strs_data = btf->raw_data + btf->hdr->hdr_len + btf->hdr->str_off;
     btf->types_data = btf->raw_data + btf->hdr->hdr_len + btf->hdr->type_off;
 
     err = btf_parse_str_sec(btf);
     err = err ?: btf_parse_type_sec(btf);
     if (err)
         goto done;
 
 done:
     if (err) {
         btf__free(btf);
         return ERR_PTR(err);
     }
 
     return btf;
 }
 
 struct btf *btf__new(const void *data, __u32 size)
 {
     return libbpf_ptr(btf_new(data, size, NULL));
 }
 
 static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
                  struct btf_ext **btf_ext)
 {
     Elf_Data *btf_data = NULL, *btf_ext_data = NULL;
     int err = 0, fd = -1, idx = 0;
     struct btf *btf = NULL;
     Elf_Scn *scn = NULL;
     Elf *elf = NULL;
     GElf_Ehdr ehdr;
     size_t shstrndx;
 
     if (elf_version(EV_CURRENT) == EV_NONE) {
         pr_warn("failed to init libelf for %s\n", path);
         return ERR_PTR(-LIBBPF_ERRNO__LIBELF);
     }
 
     fd = open(path, O_RDONLY | O_CLOEXEC);
     if (fd < 0) {
         err = -errno;
         pr_warn("failed to open %s: %s\n", path, strerror(errno));
         return ERR_PTR(err);
     }
 
     err = -LIBBPF_ERRNO__FORMAT;
 
     elf = elf_begin(fd, ELF_C_READ, NULL);
     if (!elf) {
         pr_warn("failed to open %s as ELF file\n", path);
         goto done;
     }
     if (!gelf_getehdr(elf, &ehdr)) {
         pr_warn("failed to get EHDR from %s\n", path);
         goto done;
     }
 
     if (elf_getshdrstrndx(elf, &shstrndx)) {
         pr_warn("failed to get section names section index for %s\n",
             path);
         goto done;
     }
 
     if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) {
         pr_warn("failed to get e_shstrndx from %s\n", path);
         goto done;
     }
 
     while ((scn = elf_nextscn(elf, scn)) != NULL) {
         GElf_Shdr sh;
         char *name;
 
         idx++;
         if (gelf_getshdr(scn, &sh) != &sh) {
             pr_warn("failed to get section(%d) header from %s\n",
                 idx, path);
             goto done;
         }
         name = elf_strptr(elf, shstrndx, sh.sh_name);
         if (!name) {
             pr_warn("failed to get section(%d) name from %s\n",
                 idx, path);
             goto done;
         }
         if (strcmp(name, BTF_ELF_SEC) == 0) {
             btf_data = elf_getdata(scn, 0);
             if (!btf_data) {
                 pr_warn("failed to get section(%d, %s) data from %s\n",
                     idx, name, path);
                 goto done;
             }
             continue;
         } else if (btf_ext && strcmp(name, BTF_EXT_ELF_SEC) == 0) {
             btf_ext_data = elf_getdata(scn, 0);
             if (!btf_ext_data) {
                 pr_warn("failed to get section(%d, %s) data from %s\n",
                     idx, name, path);
                 goto done;
             }
             continue;
         }
     }
 
     err = 0;
 
     if (!btf_data) {
         err = -ENOENT;
         goto done;
     }
     btf = btf_new(btf_data->d_buf, btf_data->d_size, base_btf);
     err = libbpf_get_error(btf);
     if (err)
         goto done;
 
     switch (gelf_getclass(elf)) {
     case ELFCLASS32:
         btf__set_pointer_size(btf, 4);
         break;
     case ELFCLASS64:
         btf__set_pointer_size(btf, 8);
         break;
     default:
         pr_warn("failed to get ELF class (bitness) for %s\n", path);
         break;
     }
 
     if (btf_ext && btf_ext_data) {
         *btf_ext = btf_ext__new(btf_ext_data->d_buf, btf_ext_data->d_size);
         err = libbpf_get_error(*btf_ext);
         if (err)
             goto done;
     } else if (btf_ext) {
         *btf_ext = NULL;
     }
 done:
     if (elf)
         elf_end(elf);
     close(fd);
 
     if (!err)
         return btf;
 
     if (btf_ext)
         btf_ext__free(*btf_ext);
     btf__free(btf);
 
     return ERR_PTR(err);
 }
 
 struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)
 {
     return libbpf_ptr(btf_parse_elf(path, NULL, btf_ext));
 }
 
 struct btf *btf__parse_elf_split(const char *path, struct btf *base_btf)
 {
     return libbpf_ptr(btf_parse_elf(path, base_btf, NULL));
 }
 
 static struct btf *btf_parse_raw(const char *path, struct btf *base_btf)
 {
     struct btf *btf = NULL;
     void *data = NULL;
     FILE *f = NULL;
     __u16 magic;
     int err = 0;
     long sz;
 
     f = fopen(path, "rb");
     if (!f) {
         err = -errno;
         goto err_out;
     }
 
     /* check BTF magic */
     if (fread(&magic, 1, sizeof(magic), f) < sizeof(magic)) {
         err = -EIO;
         goto err_out;
     }
     if (magic != BTF_MAGIC && magic != bswap_16(BTF_MAGIC)) {
         /* definitely not a raw BTF */
         err = -EPROTO;
         goto err_out;
     }
 
     /* get file size */
     if (fseek(f, 0, SEEK_END)) {
         err = -errno;
         goto err_out;
     }
     sz = ftell(f);
     if (sz < 0) {
         err = -errno;
         goto err_out;
     }
     /* rewind to the start */
     if (fseek(f, 0, SEEK_SET)) {
         err = -errno;
         goto err_out;
     }
 
     /* pre-alloc memory and read all of BTF data */
     data = malloc(sz);
     if (!data) {
         err = -ENOMEM;
         goto err_out;
     }
     if (fread(data, 1, sz, f) < sz) {
         err = -EIO;
         goto err_out;
     }
 
     /* finally parse BTF data */
     btf = btf_new(data, sz, base_btf);
 
 err_out:
     free(data);
     if (f)
         fclose(f);
     return err ? ERR_PTR(err) : btf;
 }
 
 struct btf *btf__parse_raw(const char *path)
 {
     return libbpf_ptr(btf_parse_raw(path, NULL));
 }
 
 struct btf *btf__parse_raw_split(const char *path, struct btf *base_btf)
 {
     return libbpf_ptr(btf_parse_raw(path, base_btf));
 }
 
 static struct btf *btf_parse(const char *path, struct btf *base_btf, struct btf_ext **btf_ext)
 {
     struct btf *btf;
     int err;
 
     if (btf_ext)
         *btf_ext = NULL;
 
     btf = btf_parse_raw(path, base_btf);
     err = libbpf_get_error(btf);
     if (!err)
         return btf;
     if (err != -EPROTO)
         return ERR_PTR(err);
     return btf_parse_elf(path, base_btf, btf_ext);
 }
 
 struct btf *btf__parse(const char *path, struct btf_ext **btf_ext)
 {
     return libbpf_ptr(btf_parse(path, NULL, btf_ext));
 }
 
 struct btf *btf__parse_split(const char *path, struct btf *base_btf)
 {
     return libbpf_ptr(btf_parse(path, base_btf, NULL));
 }
 
 static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian);
 
 int btf_load_into_kernel(struct btf *btf, char *log_buf, size_t log_sz, __u32 log_level)
 {
     LIBBPF_OPTS(bpf_btf_load_opts, opts);
     __u32 buf_sz = 0, raw_size;
     char *buf = NULL, *tmp;
     void *raw_data;
     int err = 0;
 
     if (btf->fd >= 0)
         return libbpf_err(-EEXIST);
     if (log_sz && !log_buf)
         return libbpf_err(-EINVAL);
 
     /* cache native raw data representation */
     raw_data = btf_get_raw_data(btf, &raw_size, false);
     if (!raw_data) {
         err = -ENOMEM;
         goto done;
     }
     btf->raw_size = raw_size;
     btf->raw_data = raw_data;
 
 retry_load:
     /* if log_level is 0, we won't provide log_buf/log_size to the kernel,
      * initially. Only if BTF loading fails, we bump log_level to 1 and
      * retry, using either auto-allocated or custom log_buf. This way
      * non-NULL custom log_buf provides a buffer just in case, but hopes
      * for successful load and no need for log_buf.
      */
     if (log_level) {
         /* if caller didn't provide custom log_buf, we'll keep
          * allocating our own progressively bigger buffers for BTF
          * verification log
          */
         if (!log_buf) {
             buf_sz = max((__u32)BPF_LOG_BUF_SIZE, buf_sz * 2);
             tmp = realloc(buf, buf_sz);
             if (!tmp) {
                 err = -ENOMEM;
                 goto done;
             }
             buf = tmp;
             buf[0] = '\0';
         }
 
         opts.log_buf = log_buf ? log_buf : buf;
         opts.log_size = log_buf ? log_sz : buf_sz;
         opts.log_level = log_level;
     }
 
     btf->fd = bpf_btf_load(raw_data, raw_size, &opts);
     if (btf->fd < 0) {
         /* time to turn on verbose mode and try again */
         if (log_level == 0) {
             log_level = 1;
             goto retry_load;
         }
         /* only retry if caller didn't provide custom log_buf, but
          * make sure we can never overflow buf_sz
          */
         if (!log_buf && errno == ENOSPC && buf_sz <= UINT_MAX / 2)
             goto retry_load;
 
         err = -errno;
         pr_warn("BTF loading error: %d\n", err);
         /* don't print out contents of custom log_buf */
         if (!log_buf && buf[0])
             pr_warn("-- BEGIN BTF LOAD LOG ---\n%s\n-- END BTF LOAD LOG --\n", buf);
     }
 
 done:
     free(buf);
     return libbpf_err(err);
 }
 
 int btf__load_into_kernel(struct btf *btf)
 {
     return btf_load_into_kernel(btf, NULL, 0, 0);
 }
 
 int btf__load(struct btf *) __attribute__((alias("btf__load_into_kernel")));
 
 int btf__fd(const struct btf *btf)
 {
     return btf->fd;
 }
 
 void btf__set_fd(struct btf *btf, int fd)
 {
     btf->fd = fd;
 }
 
 static const void *btf_strs_data(const struct btf *btf)
 {
     return btf->strs_data ? btf->strs_data : strset__data(btf->strs_set);
 }
 
 static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian)
 {
     struct btf_header *hdr = btf->hdr;
     struct btf_type *t;
     void *data, *p;
     __u32 data_sz;
     int i;
 
     data = swap_endian ? btf->raw_data_swapped : btf->raw_data;
     if (data) {
         *size = btf->raw_size;
         return data;
     }
 
     data_sz = hdr->hdr_len + hdr->type_len + hdr->str_len;
     data = calloc(1, data_sz);
     if (!data)
         return NULL;
     p = data;
 
     memcpy(p, hdr, hdr->hdr_len);
     if (swap_endian)
         btf_bswap_hdr(p);
     p += hdr->hdr_len;
 
     memcpy(p, btf->types_data, hdr->type_len);
     if (swap_endian) {
         for (i = 0; i < btf->nr_types; i++) {
             t = p + btf->type_offs[i];
             /* btf_bswap_type_rest() relies on native t->info, so
              * we swap base type info after we swapped all the
              * additional information
              */
             if (btf_bswap_type_rest(t))
                 goto err_out;
             btf_bswap_type_base(t);
         }
     }
     p += hdr->type_len;
 
     memcpy(p, btf_strs_data(btf), hdr->str_len);
     p += hdr->str_len;
 
     *size = data_sz;
     return data;
 err_out:
     free(data);
     return NULL;
 }
 
 const void *btf__raw_data(const struct btf *btf_ro, __u32 *size)
 {
     struct btf *btf = (struct btf *)btf_ro;
     __u32 data_sz;
     void *data;
 
     data = btf_get_raw_data(btf, &data_sz, btf->swapped_endian);
     if (!data)
         return errno = ENOMEM, NULL;
 
     btf->raw_size = data_sz;
     if (btf->swapped_endian)
         btf->raw_data_swapped = data;
     else
         btf->raw_data = data;
     *size = data_sz;
     return data;
 }
 
 __attribute__((alias("btf__raw_data")))
 const void *btf__get_raw_data(const struct btf *btf, __u32 *size);
 
 const char *btf__str_by_offset(const struct btf *btf, __u32 offset)
 {
     if (offset < btf->start_str_off)
         return btf__str_by_offset(btf->base_btf, offset);
     else if (offset - btf->start_str_off < btf->hdr->str_len)
         return btf_strs_data(btf) + (offset - btf->start_str_off);
     else
         return errno = EINVAL, NULL;
 }
 
 const char *btf__name_by_offset(const struct btf *btf, __u32 offset)
 {
     return btf__str_by_offset(btf, offset);
 }
 
 struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
 {
     struct bpf_btf_info btf_info;
     __u32 len = sizeof(btf_info);
     __u32 last_size;
     struct btf *btf;
     void *ptr;
     int err;
 
     /* we won't know btf_size until we call bpf_obj_get_info_by_fd(). so
      * let's start with a sane default - 4KiB here - and resize it only if
      * bpf_obj_get_info_by_fd() needs a bigger buffer.
      */
     last_size = 4096;
     ptr = malloc(last_size);
     if (!ptr)
         return ERR_PTR(-ENOMEM);
 
     memset(&btf_info, 0, sizeof(btf_info));
     btf_info.btf = ptr_to_u64(ptr);
     btf_info.btf_size = last_size;
     err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
 
     if (!err && btf_info.btf_size > last_size) {
         void *temp_ptr;
 
         last_size = btf_info.btf_size;
         temp_ptr = realloc(ptr, last_size);
         if (!temp_ptr) {
             btf = ERR_PTR(-ENOMEM);
             goto exit_free;
         }
         ptr = temp_ptr;
 
         len = sizeof(btf_info);
         memset(&btf_info, 0, sizeof(btf_info));
         btf_info.btf = ptr_to_u64(ptr);
         btf_info.btf_size = last_size;
 
         err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
     }
 
     if (err || btf_info.btf_size > last_size) {
         btf = err ? ERR_PTR(-errno) : ERR_PTR(-E2BIG);
         goto exit_free;
     }
 
     btf = btf_new(ptr, btf_info.btf_size, base_btf);
 
 exit_free:
     free(ptr);
     return btf;
 }
 
 struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
 {
     struct btf *btf;
     int btf_fd;
 
     btf_fd = bpf_btf_get_fd_by_id(id);
     if (btf_fd < 0)
         return libbpf_err_ptr(-errno);
 
     btf = btf_get_from_fd(btf_fd, base_btf);
     close(btf_fd);
 
     return libbpf_ptr(btf);
 }
 
 struct btf *btf__load_from_kernel_by_id(__u32 id)
 {
     return btf__load_from_kernel_by_id_split(id, NULL);
 }
 
 static void btf_invalidate_raw_data(struct btf *btf)
 {
     if (btf->raw_data) {
         free(btf->raw_data);
         btf->raw_data = NULL;
     }
     if (btf->raw_data_swapped) {
         free(btf->raw_data_swapped);
         btf->raw_data_swapped = NULL;
     }
 }
 
 /* Ensure BTF is ready to be modified (by splitting into a three memory
  * regions for header, types, and strings). Also invalidate cached
  * raw_data, if any.
  */
 static int btf_ensure_modifiable(struct btf *btf)
 {
     void *hdr, *types;
     struct strset *set = NULL;
     int err = -ENOMEM;
 
     if (btf_is_modifiable(btf)) {
         /* any BTF modification invalidates raw_data */
         btf_invalidate_raw_data(btf);
         return 0;
     }
 
     /* split raw data into three memory regions */
     hdr = malloc(btf->hdr->hdr_len);
     types = malloc(btf->hdr->type_len);
     if (!hdr || !types)
         goto err_out;
 
     memcpy(hdr, btf->hdr, btf->hdr->hdr_len);
     memcpy(types, btf->types_data, btf->hdr->type_len);
 
     /* build lookup index for all strings */
     set = strset__new(BTF_MAX_STR_OFFSET, btf->strs_data, btf->hdr->str_len);
     if (IS_ERR(set)) {
         err = PTR_ERR(set);
         goto err_out;
     }
 
     /* only when everything was successful, update internal state */
     btf->hdr = hdr;
     btf->types_data = types;
     btf->types_data_cap = btf->hdr->type_len;
     btf->strs_data = NULL;
     btf->strs_set = set;
     /* if BTF was created from scratch, all strings are guaranteed to be
      * unique and deduplicated
      */
     if (btf->hdr->str_len == 0)
         btf->strs_deduped = true;
     if (!btf->base_btf && btf->hdr->str_len == 1)
         btf->strs_deduped = true;
 
     /* invalidate raw_data representation */
     btf_invalidate_raw_data(btf);
 
     return 0;
 
 err_out:
     strset__free(set);
     free(hdr);
     free(types);
     return err;
 }
 
 /* Find an offset in BTF string section that corresponds to a given string *s*.
  * Returns:
  *   - >0 offset into string section, if string is found;
  *   - -ENOENT, if string is not in the string section;
  *   - <0, on any other error.
  */
 int btf__find_str(struct btf *btf, const char *s)
 {
     int off;
 
     if (btf->base_btf) {
         off = btf__find_str(btf->base_btf, s);
         if (off != -ENOENT)
             return off;
     }
 
     /* BTF needs to be in a modifiable state to build string lookup index */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     off = strset__find_str(btf->strs_set, s);
     if (off < 0)
         return libbpf_err(off);
 
     return btf->start_str_off + off;
 }
 
 /* Add a string s to the BTF string section.
  * Returns:
  *   - > 0 offset into string section, on success;
  *   - < 0, on error.
  */
 int btf__add_str(struct btf *btf, const char *s)
 {
     int off;
 
     if (btf->base_btf) {
         off = btf__find_str(btf->base_btf, s);
         if (off != -ENOENT)
             return off;
     }
 
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     off = strset__add_str(btf->strs_set, s);
     if (off < 0)
         return libbpf_err(off);
 
     btf->hdr->str_len = strset__data_size(btf->strs_set);
 
     return btf->start_str_off + off;
 }
 
 static void *btf_add_type_mem(struct btf *btf, size_t add_sz)
 {
     return libbpf_add_mem(&btf->types_data, &btf->types_data_cap, 1,
                   btf->hdr->type_len, UINT_MAX, add_sz);
 }
 
 static void btf_type_inc_vlen(struct btf_type *t)
 {
     t->info = btf_type_info(btf_kind(t), btf_vlen(t) + 1, btf_kflag(t));
 }
 
 static int btf_commit_type(struct btf *btf, int data_sz)
 {
     int err;
 
     err = btf_add_type_idx_entry(btf, btf->hdr->type_len);
     if (err)
         return libbpf_err(err);
 
     btf->hdr->type_len += data_sz;
     btf->hdr->str_off += data_sz;
     btf->nr_types++;
     return btf->start_id + btf->nr_types - 1;
 }
 
 struct btf_pipe {
     const struct btf *src;
     struct btf *dst;
     struct hashmap *str_off_map; /* map string offsets from src to dst */
 };
 
 static int btf_rewrite_str(__u32 *str_off, void *ctx)
 {
     struct btf_pipe *p = ctx;
     void *mapped_off;
     int off, err;
 
     if (!*str_off) /* nothing to do for empty strings */
         return 0;
 
     if (p->str_off_map &&
         hashmap__find(p->str_off_map, (void *)(long)*str_off, &mapped_off)) {
         *str_off = (__u32)(long)mapped_off;
         return 0;
     }
 
     off = btf__add_str(p->dst, btf__str_by_offset(p->src, *str_off));
     if (off < 0)
         return off;
 
     /* Remember string mapping from src to dst.  It avoids
      * performing expensive string comparisons.
      */
     if (p->str_off_map) {
         err = hashmap__append(p->str_off_map, (void *)(long)*str_off, (void *)(long)off);
         if (err)
             return err;
     }
 
     *str_off = off;
     return 0;
 }
 
 int btf__add_type(struct btf *btf, const struct btf *src_btf, const struct btf_type *src_type)
 {
     struct btf_pipe p = { .src = src_btf, .dst = btf };
     struct btf_type *t;
     int sz, err;
 
     sz = btf_type_size(src_type);
     if (sz < 0)
         return libbpf_err(sz);
 
     /* deconstruct BTF, if necessary, and invalidate raw_data */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     memcpy(t, src_type, sz);
 
     err = btf_type_visit_str_offs(t, btf_rewrite_str, &p);
     if (err)
         return libbpf_err(err);
 
     return btf_commit_type(btf, sz);
 }
 
 static int btf_rewrite_type_ids(__u32 *type_id, void *ctx)
 {
     struct btf *btf = ctx;
 
     if (!*type_id) /* nothing to do for VOID references */
         return 0;
 
     /* we haven't updated btf's type count yet, so
      * btf->start_id + btf->nr_types - 1 is the type ID offset we should
      * add to all newly added BTF types
      */
     *type_id += btf->start_id + btf->nr_types - 1;
     return 0;
 }
 
 static size_t btf_dedup_identity_hash_fn(const void *key, void *ctx);
 static bool btf_dedup_equal_fn(const void *k1, const void *k2, void *ctx);
 
 int btf__add_btf(struct btf *btf, const struct btf *src_btf)
 {
     struct btf_pipe p = { .src = src_btf, .dst = btf };
     int data_sz, sz, cnt, i, err, old_strs_len;
     __u32 *off;
     void *t;
 
     /* appending split BTF isn't supported yet */
     if (src_btf->base_btf)
         return libbpf_err(-ENOTSUP);
 
     /* deconstruct BTF, if necessary, and invalidate raw_data */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     /* remember original strings section size if we have to roll back
      * partial strings section changes
      */
     old_strs_len = btf->hdr->str_len;
 
     data_sz = src_btf->hdr->type_len;
     cnt = btf__type_cnt(src_btf) - 1;
 
     /* pre-allocate enough memory for new types */
     t = btf_add_type_mem(btf, data_sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     /* pre-allocate enough memory for type offset index for new types */
     off = btf_add_type_offs_mem(btf, cnt);
     if (!off)
         return libbpf_err(-ENOMEM);
 
     /* Map the string offsets from src_btf to the offsets from btf to improve performance */
     p.str_off_map = hashmap__new(btf_dedup_identity_hash_fn, btf_dedup_equal_fn, NULL);
     if (IS_ERR(p.str_off_map))
         return libbpf_err(-ENOMEM);
 
     /* bulk copy types data for all types from src_btf */
     memcpy(t, src_btf->types_data, data_sz);
 
     for (i = 0; i < cnt; i++) {
         sz = btf_type_size(t);
         if (sz < 0) {
             /* unlikely, has to be corrupted src_btf */
             err = sz;
             goto err_out;
         }
 
         /* fill out type ID to type offset mapping for lookups by type ID */
         *off = t - btf->types_data;
 
         /* add, dedup, and remap strings referenced by this BTF type */
         err = btf_type_visit_str_offs(t, btf_rewrite_str, &p);
         if (err)
             goto err_out;
 
         /* remap all type IDs referenced from this BTF type */
         err = btf_type_visit_type_ids(t, btf_rewrite_type_ids, btf);
         if (err)
             goto err_out;
 
         /* go to next type data and type offset index entry */
         t += sz;
         off++;
     }
 
     /* Up until now any of the copied type data was effectively invisible,
      * so if we exited early before this point due to error, BTF would be
      * effectively unmodified. There would be extra internal memory
      * pre-allocated, but it would not be available for querying.  But now
      * that we've copied and rewritten all the data successfully, we can
      * update type count and various internal offsets and sizes to
      * "commit" the changes and made them visible to the outside world.
      */
     btf->hdr->type_len += data_sz;
     btf->hdr->str_off += data_sz;
     btf->nr_types += cnt;
 
     hashmap__free(p.str_off_map);
 
     /* return type ID of the first added BTF type */
     return btf->start_id + btf->nr_types - cnt;
 err_out:
     /* zero out preallocated memory as if it was just allocated with
      * libbpf_add_mem()
      */
     memset(btf->types_data + btf->hdr->type_len, 0, data_sz);
     memset(btf->strs_data + old_strs_len, 0, btf->hdr->str_len - old_strs_len);
 
     /* and now restore original strings section size; types data size
      * wasn't modified, so doesn't need restoring, see big comment above */
     btf->hdr->str_len = old_strs_len;
 
     hashmap__free(p.str_off_map);
 
     return libbpf_err(err);
 }
 
 /*
  * Append new BTF_KIND_INT type with:
  *   - *name* - non-empty, non-NULL type name;
  *   - *sz* - power-of-2 (1, 2, 4, ..) size of the type, in bytes;
  *   - encoding is a combination of BTF_INT_SIGNED, BTF_INT_CHAR, BTF_INT_BOOL.
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_int(struct btf *btf, const char *name, size_t byte_sz, int encoding)
 {
     struct btf_type *t;
     int sz, name_off;
 
     /* non-empty name */
     if (!name || !name[0])
         return libbpf_err(-EINVAL);
     /* byte_sz must be power of 2 */
     if (!byte_sz || (byte_sz & (byte_sz - 1)) || byte_sz > 16)
         return libbpf_err(-EINVAL);
     if (encoding & ~(BTF_INT_SIGNED | BTF_INT_CHAR | BTF_INT_BOOL))
         return libbpf_err(-EINVAL);
 
     /* deconstruct BTF, if necessary, and invalidate raw_data */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type) + sizeof(int);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     /* if something goes wrong later, we might end up with an extra string,
      * but that shouldn't be a problem, because BTF can't be constructed
      * completely anyway and will most probably be just discarded
      */
     name_off = btf__add_str(btf, name);
     if (name_off < 0)
         return name_off;
 
     t->name_off = name_off;
     t->info = btf_type_info(BTF_KIND_INT, 0, 0);
     t->size = byte_sz;
     /* set INT info, we don't allow setting legacy bit offset/size */
     *(__u32 *)(t + 1) = (encoding << 24) | (byte_sz * 8);
 
     return btf_commit_type(btf, sz);
 }
 
 /*
  * Append new BTF_KIND_FLOAT type with:
  *   - *name* - non-empty, non-NULL type name;
  *   - *sz* - size of the type, in bytes;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_float(struct btf *btf, const char *name, size_t byte_sz)
 {
     struct btf_type *t;
     int sz, name_off;
 
     /* non-empty name */
     if (!name || !name[0])
         return libbpf_err(-EINVAL);
 
     /* byte_sz must be one of the explicitly allowed values */
     if (byte_sz != 2 && byte_sz != 4 && byte_sz != 8 && byte_sz != 12 &&
         byte_sz != 16)
         return libbpf_err(-EINVAL);
 
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     name_off = btf__add_str(btf, name);
     if (name_off < 0)
         return name_off;
 
     t->name_off = name_off;
     t->info = btf_type_info(BTF_KIND_FLOAT, 0, 0);
     t->size = byte_sz;
 
     return btf_commit_type(btf, sz);
 }
 
 /* it's completely legal to append BTF types with type IDs pointing forward to
  * types that haven't been appended yet, so we only make sure that id looks
  * sane, we can't guarantee that ID will always be valid
  */
 static int validate_type_id(int id)
 {
     if (id < 0 || id > BTF_MAX_NR_TYPES)
         return -EINVAL;
     return 0;
 }
 
 /* generic append function for PTR, TYPEDEF, CONST/VOLATILE/RESTRICT */
 static int btf_add_ref_kind(struct btf *btf, int kind, const char *name, int ref_type_id)
 {
     struct btf_type *t;
     int sz, name_off = 0;
 
     if (validate_type_id(ref_type_id))
         return libbpf_err(-EINVAL);
 
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     if (name && name[0]) {
         name_off = btf__add_str(btf, name);
         if (name_off < 0)
             return name_off;
     }
 
     t->name_off = name_off;
     t->info = btf_type_info(kind, 0, 0);
     t->type = ref_type_id;
 
     return btf_commit_type(btf, sz);
 }
 
 /*
  * Append new BTF_KIND_PTR type with:
  *   - *ref_type_id* - referenced type ID, it might not exist yet;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_ptr(struct btf *btf, int ref_type_id)
 {
     return btf_add_ref_kind(btf, BTF_KIND_PTR, NULL, ref_type_id);
 }
 
 /*
  * Append new BTF_KIND_ARRAY type with:
  *   - *index_type_id* - type ID of the type describing array index;
  *   - *elem_type_id* - type ID of the type describing array element;
  *   - *nr_elems* - the size of the array;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_array(struct btf *btf, int index_type_id, int elem_type_id, __u32 nr_elems)
 {
     struct btf_type *t;
     struct btf_array *a;
     int sz;
 
     if (validate_type_id(index_type_id) || validate_type_id(elem_type_id))
         return libbpf_err(-EINVAL);
 
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type) + sizeof(struct btf_array);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     t->name_off = 0;
     t->info = btf_type_info(BTF_KIND_ARRAY, 0, 0);
     t->size = 0;
 
     a = btf_array(t);
     a->type = elem_type_id;
     a->index_type = index_type_id;
     a->nelems = nr_elems;
 
     return btf_commit_type(btf, sz);
 }
 
 /* generic STRUCT/UNION append function */
 static int btf_add_composite(struct btf *btf, int kind, const char *name, __u32 bytes_sz)
 {
     struct btf_type *t;
     int sz, name_off = 0;
 
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     if (name && name[0]) {
         name_off = btf__add_str(btf, name);
         if (name_off < 0)
             return name_off;
     }
 
     /* start out with vlen=0 and no kflag; this will be adjusted when
      * adding each member
      */
     t->name_off = name_off;
     t->info = btf_type_info(kind, 0, 0);
     t->size = bytes_sz;
 
     return btf_commit_type(btf, sz);
 }
 
 /*
  * Append new BTF_KIND_STRUCT type with:
  *   - *name* - name of the struct, can be NULL or empty for anonymous structs;
  *   - *byte_sz* - size of the struct, in bytes;
  *
  * Struct initially has no fields in it. Fields can be added by
  * btf__add_field() right after btf__add_struct() succeeds.
  *
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_struct(struct btf *btf, const char *name, __u32 byte_sz)
 {
     return btf_add_composite(btf, BTF_KIND_STRUCT, name, byte_sz);
 }
 
 /*
  * Append new BTF_KIND_UNION type with:
  *   - *name* - name of the union, can be NULL or empty for anonymous union;
  *   - *byte_sz* - size of the union, in bytes;
  *
  * Union initially has no fields in it. Fields can be added by
  * btf__add_field() right after btf__add_union() succeeds. All fields
  * should have *bit_offset* of 0.
  *
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_union(struct btf *btf, const char *name, __u32 byte_sz)
 {
     return btf_add_composite(btf, BTF_KIND_UNION, name, byte_sz);
 }
 
 static struct btf_type *btf_last_type(struct btf *btf)
 {
     return btf_type_by_id(btf, btf__type_cnt(btf) - 1);
 }
 
 /*
  * Append new field for the current STRUCT/UNION type with:
  *   - *name* - name of the field, can be NULL or empty for anonymous field;
  *   - *type_id* - type ID for the type describing field type;
  *   - *bit_offset* - bit offset of the start of the field within struct/union;
  *   - *bit_size* - bit size of a bitfield, 0 for non-bitfield fields;
  * Returns:
  *   -  0, on success;
  *   - <0, on error.
  */
 int btf__add_field(struct btf *btf, const char *name, int type_id,
            __u32 bit_offset, __u32 bit_size)
 {
     struct btf_type *t;
     struct btf_member *m;
     bool is_bitfield;
     int sz, name_off = 0;
 
     /* last type should be union/struct */
     if (btf->nr_types == 0)
         return libbpf_err(-EINVAL);
     t = btf_last_type(btf);
     if (!btf_is_composite(t))
         return libbpf_err(-EINVAL);
 
     if (validate_type_id(type_id))
         return libbpf_err(-EINVAL);
     /* best-effort bit field offset/size enforcement */
     is_bitfield = bit_size || (bit_offset % 8 != 0);
     if (is_bitfield && (bit_size == 0 || bit_size > 255 || bit_offset > 0xffffff))
         return libbpf_err(-EINVAL);
 
     /* only offset 0 is allowed for unions */
     if (btf_is_union(t) && bit_offset)
         return libbpf_err(-EINVAL);
 
     /* decompose and invalidate raw data */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_member);
     m = btf_add_type_mem(btf, sz);
     if (!m)
         return libbpf_err(-ENOMEM);
 
     if (name && name[0]) {
         name_off = btf__add_str(btf, name);
         if (name_off < 0)
             return name_off;
     }
 
     m->name_off = name_off;
     m->type = type_id;
     m->offset = bit_offset | (bit_size << 24);
 
     /* btf_add_type_mem can invalidate t pointer */
     t = btf_last_type(btf);
     /* update parent type's vlen and kflag */
     t->info = btf_type_info(btf_kind(t), btf_vlen(t) + 1, is_bitfield || btf_kflag(t));
 
     btf->hdr->type_len += sz;
     btf->hdr->str_off += sz;
     return 0;
 }
 
 static int btf_add_enum_common(struct btf *btf, const char *name, __u32 byte_sz,
                    bool is_signed, __u8 kind)
 {
     struct btf_type *t;
     int sz, name_off = 0;
 
     /* byte_sz must be power of 2 */
     if (!byte_sz || (byte_sz & (byte_sz - 1)) || byte_sz > 8)
         return libbpf_err(-EINVAL);
 
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     if (name && name[0]) {
         name_off = btf__add_str(btf, name);
         if (name_off < 0)
             return name_off;
     }
 
     /* start out with vlen=0; it will be adjusted when adding enum values */
     t->name_off = name_off;
     t->info = btf_type_info(kind, 0, is_signed);
     t->size = byte_sz;
 
     return btf_commit_type(btf, sz);
 }
 
 /*
  * Append new BTF_KIND_ENUM type with:
  *   - *name* - name of the enum, can be NULL or empty for anonymous enums;
  *   - *byte_sz* - size of the enum, in bytes.
  *
  * Enum initially has no enum values in it (and corresponds to enum forward
  * declaration). Enumerator values can be added by btf__add_enum_value()
  * immediately after btf__add_enum() succeeds.
  *
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_enum(struct btf *btf, const char *name, __u32 byte_sz)
 {
     /*
      * set the signedness to be unsigned, it will change to signed
      * if any later enumerator is negative.
      */
     return btf_add_enum_common(btf, name, byte_sz, false, BTF_KIND_ENUM);
 }
 
 /*
  * Append new enum value for the current ENUM type with:
  *   - *name* - name of the enumerator value, can't be NULL or empty;
  *   - *value* - integer value corresponding to enum value *name*;
  * Returns:
  *   -  0, on success;
  *   - <0, on error.
  */
 int btf__add_enum_value(struct btf *btf, const char *name, __s64 value)
 {
     struct btf_type *t;
     struct btf_enum *v;
     int sz, name_off;
 
     /* last type should be BTF_KIND_ENUM */
     if (btf->nr_types == 0)
         return libbpf_err(-EINVAL);
     t = btf_last_type(btf);
     if (!btf_is_enum(t))
         return libbpf_err(-EINVAL);
 
     /* non-empty name */
     if (!name || !name[0])
         return libbpf_err(-EINVAL);
     if (value < INT_MIN || value > UINT_MAX)
         return libbpf_err(-E2BIG);
 
     /* decompose and invalidate raw data */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_enum);
     v = btf_add_type_mem(btf, sz);
     if (!v)
         return libbpf_err(-ENOMEM);
 
     name_off = btf__add_str(btf, name);
     if (name_off < 0)
         return name_off;
 
     v->name_off = name_off;
     v->val = value;
 
     /* update parent type's vlen */
     t = btf_last_type(btf);
     btf_type_inc_vlen(t);
 
     /* if negative value, set signedness to signed */
     if (value < 0)
         t->info = btf_type_info(btf_kind(t), btf_vlen(t), true);
 
     btf->hdr->type_len += sz;
     btf->hdr->str_off += sz;
     return 0;
 }
 
 /*
  * Append new BTF_KIND_ENUM64 type with:
  *   - *name* - name of the enum, can be NULL or empty for anonymous enums;
  *   - *byte_sz* - size of the enum, in bytes.
  *   - *is_signed* - whether the enum values are signed or not;
  *
  * Enum initially has no enum values in it (and corresponds to enum forward
  * declaration). Enumerator values can be added by btf__add_enum64_value()
  * immediately after btf__add_enum64() succeeds.
  *
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_enum64(struct btf *btf, const char *name, __u32 byte_sz,
             bool is_signed)
 {
     return btf_add_enum_common(btf, name, byte_sz, is_signed,
                    BTF_KIND_ENUM64);
 }
 
 /*
  * Append new enum value for the current ENUM64 type with:
  *   - *name* - name of the enumerator value, can't be NULL or empty;
  *   - *value* - integer value corresponding to enum value *name*;
  * Returns:
  *   -  0, on success;
  *   - <0, on error.
  */
 int btf__add_enum64_value(struct btf *btf, const char *name, __u64 value)
 {
     struct btf_enum64 *v;
     struct btf_type *t;
     int sz, name_off;
 
     /* last type should be BTF_KIND_ENUM64 */
     if (btf->nr_types == 0)
         return libbpf_err(-EINVAL);
     t = btf_last_type(btf);
     if (!btf_is_enum64(t))
         return libbpf_err(-EINVAL);
 
     /* non-empty name */
     if (!name || !name[0])
         return libbpf_err(-EINVAL);
 
     /* decompose and invalidate raw data */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_enum64);
     v = btf_add_type_mem(btf, sz);
     if (!v)
         return libbpf_err(-ENOMEM);
 
     name_off = btf__add_str(btf, name);
     if (name_off < 0)
         return name_off;
 
     v->name_off = name_off;
     v->val_lo32 = (__u32)value;
     v->val_hi32 = value >> 32;
 
     /* update parent type's vlen */
     t = btf_last_type(btf);
     btf_type_inc_vlen(t);
 
     btf->hdr->type_len += sz;
     btf->hdr->str_off += sz;
     return 0;
 }
 
 /*
  * Append new BTF_KIND_FWD type with:
  *   - *name*, non-empty/non-NULL name;
  *   - *fwd_kind*, kind of forward declaration, one of BTF_FWD_STRUCT,
  *     BTF_FWD_UNION, or BTF_FWD_ENUM;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_fwd(struct btf *btf, const char *name, enum btf_fwd_kind fwd_kind)
 {
     if (!name || !name[0])
         return libbpf_err(-EINVAL);
 
     switch (fwd_kind) {
     case BTF_FWD_STRUCT:
     case BTF_FWD_UNION: {
         struct btf_type *t;
         int id;
 
         id = btf_add_ref_kind(btf, BTF_KIND_FWD, name, 0);
         if (id <= 0)
             return id;
         t = btf_type_by_id(btf, id);
         t->info = btf_type_info(BTF_KIND_FWD, 0, fwd_kind == BTF_FWD_UNION);
         return id;
     }
     case BTF_FWD_ENUM:
         /* enum forward in BTF currently is just an enum with no enum
          * values; we also assume a standard 4-byte size for it
          */
         return btf__add_enum(btf, name, sizeof(int));
     default:
         return libbpf_err(-EINVAL);
     }
 }
 
 /*
  * Append new BTF_KING_TYPEDEF type with:
  *   - *name*, non-empty/non-NULL name;
  *   - *ref_type_id* - referenced type ID, it might not exist yet;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_typedef(struct btf *btf, const char *name, int ref_type_id)
 {
     if (!name || !name[0])
         return libbpf_err(-EINVAL);
 
     return btf_add_ref_kind(btf, BTF_KIND_TYPEDEF, name, ref_type_id);
 }
 
 /*
  * Append new BTF_KIND_VOLATILE type with:
  *   - *ref_type_id* - referenced type ID, it might not exist yet;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_volatile(struct btf *btf, int ref_type_id)
 {
     return btf_add_ref_kind(btf, BTF_KIND_VOLATILE, NULL, ref_type_id);
 }
 
 /*
  * Append new BTF_KIND_CONST type with:
  *   - *ref_type_id* - referenced type ID, it might not exist yet;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_const(struct btf *btf, int ref_type_id)
 {
     return btf_add_ref_kind(btf, BTF_KIND_CONST, NULL, ref_type_id);
 }
 
 /*
  * Append new BTF_KIND_RESTRICT type with:
  *   - *ref_type_id* - referenced type ID, it might not exist yet;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_restrict(struct btf *btf, int ref_type_id)
 {
     return btf_add_ref_kind(btf, BTF_KIND_RESTRICT, NULL, ref_type_id);
 }
 
 /*
  * Append new BTF_KIND_TYPE_TAG type with:
  *   - *value*, non-empty/non-NULL tag value;
  *   - *ref_type_id* - referenced type ID, it might not exist yet;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_type_tag(struct btf *btf, const char *value, int ref_type_id)
 {
     if (!value|| !value[0])
         return libbpf_err(-EINVAL);
 
     return btf_add_ref_kind(btf, BTF_KIND_TYPE_TAG, value, ref_type_id);
 }
 
 /*
  * Append new BTF_KIND_FUNC type with:
  *   - *name*, non-empty/non-NULL name;
  *   - *proto_type_id* - FUNC_PROTO's type ID, it might not exist yet;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_func(struct btf *btf, const char *name,
           enum btf_func_linkage linkage, int proto_type_id)
 {
     int id;
 
     if (!name || !name[0])
         return libbpf_err(-EINVAL);
     if (linkage != BTF_FUNC_STATIC && linkage != BTF_FUNC_GLOBAL &&
         linkage != BTF_FUNC_EXTERN)
         return libbpf_err(-EINVAL);
 
     id = btf_add_ref_kind(btf, BTF_KIND_FUNC, name, proto_type_id);
     if (id > 0) {
         struct btf_type *t = btf_type_by_id(btf, id);
 
         t->info = btf_type_info(BTF_KIND_FUNC, linkage, 0);
     }
     return libbpf_err(id);
 }
 
 /*
  * Append new BTF_KIND_FUNC_PROTO with:
  *   - *ret_type_id* - type ID for return result of a function.
  *
  * Function prototype initially has no arguments, but they can be added by
  * btf__add_func_param() one by one, immediately after
  * btf__add_func_proto() succeeded.
  *
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_func_proto(struct btf *btf, int ret_type_id)
 {
     struct btf_type *t;
     int sz;
 
     if (validate_type_id(ret_type_id))
         return libbpf_err(-EINVAL);
 
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     /* start out with vlen=0; this will be adjusted when adding enum
      * values, if necessary
      */
     t->name_off = 0;
     t->info = btf_type_info(BTF_KIND_FUNC_PROTO, 0, 0);
     t->type = ret_type_id;
 
     return btf_commit_type(btf, sz);
 }
 
 /*
  * Append new function parameter for current FUNC_PROTO type with:
  *   - *name* - parameter name, can be NULL or empty;
  *   - *type_id* - type ID describing the type of the parameter.
  * Returns:
  *   -  0, on success;
  *   - <0, on error.
  */
 int btf__add_func_param(struct btf *btf, const char *name, int type_id)
 {
     struct btf_type *t;
     struct btf_param *p;
     int sz, name_off = 0;
 
     if (validate_type_id(type_id))
         return libbpf_err(-EINVAL);
 
     /* last type should be BTF_KIND_FUNC_PROTO */
     if (btf->nr_types == 0)
         return libbpf_err(-EINVAL);
     t = btf_last_type(btf);
     if (!btf_is_func_proto(t))
         return libbpf_err(-EINVAL);
 
     /* decompose and invalidate raw data */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_param);
     p = btf_add_type_mem(btf, sz);
     if (!p)
         return libbpf_err(-ENOMEM);
 
     if (name && name[0]) {
         name_off = btf__add_str(btf, name);
         if (name_off < 0)
             return name_off;
     }
 
     p->name_off = name_off;
     p->type = type_id;
 
     /* update parent type's vlen */
     t = btf_last_type(btf);
     btf_type_inc_vlen(t);
 
     btf->hdr->type_len += sz;
     btf->hdr->str_off += sz;
     return 0;
 }
 
 /*
  * Append new BTF_KIND_VAR type with:
  *   - *name* - non-empty/non-NULL name;
  *   - *linkage* - variable linkage, one of BTF_VAR_STATIC,
  *     BTF_VAR_GLOBAL_ALLOCATED, or BTF_VAR_GLOBAL_EXTERN;
  *   - *type_id* - type ID of the type describing the type of the variable.
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_var(struct btf *btf, const char *name, int linkage, int type_id)
 {
     struct btf_type *t;
     struct btf_var *v;
     int sz, name_off;
 
     /* non-empty name */
     if (!name || !name[0])
         return libbpf_err(-EINVAL);
     if (linkage != BTF_VAR_STATIC && linkage != BTF_VAR_GLOBAL_ALLOCATED &&
         linkage != BTF_VAR_GLOBAL_EXTERN)
         return libbpf_err(-EINVAL);
     if (validate_type_id(type_id))
         return libbpf_err(-EINVAL);
 
     /* deconstruct BTF, if necessary, and invalidate raw_data */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type) + sizeof(struct btf_var);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     name_off = btf__add_str(btf, name);
     if (name_off < 0)
         return name_off;
 
     t->name_off = name_off;
     t->info = btf_type_info(BTF_KIND_VAR, 0, 0);
     t->type = type_id;
 
     v = btf_var(t);
     v->linkage = linkage;
 
     return btf_commit_type(btf, sz);
 }
 
 /*
  * Append new BTF_KIND_DATASEC type with:
  *   - *name* - non-empty/non-NULL name;
  *   - *byte_sz* - data section size, in bytes.
  *
  * Data section is initially empty. Variables info can be added with
  * btf__add_datasec_var_info() calls, after btf__add_datasec() succeeds.
  *
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_datasec(struct btf *btf, const char *name, __u32 byte_sz)
 {
     struct btf_type *t;
     int sz, name_off;
 
     /* non-empty name */
     if (!name || !name[0])
         return libbpf_err(-EINVAL);
 
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     name_off = btf__add_str(btf, name);
     if (name_off < 0)
         return name_off;
 
     /* start with vlen=0, which will be update as var_secinfos are added */
     t->name_off = name_off;
     t->info = btf_type_info(BTF_KIND_DATASEC, 0, 0);
     t->size = byte_sz;
 
     return btf_commit_type(btf, sz);
 }
 
 /*
  * Append new data section variable information entry for current DATASEC type:
  *   - *var_type_id* - type ID, describing type of the variable;
  *   - *offset* - variable offset within data section, in bytes;
  *   - *byte_sz* - variable size, in bytes.
  *
  * Returns:
  *   -  0, on success;
  *   - <0, on error.
  */
 int btf__add_datasec_var_info(struct btf *btf, int var_type_id, __u32 offset, __u32 byte_sz)
 {
     struct btf_type *t;
     struct btf_var_secinfo *v;
     int sz;
 
     /* last type should be BTF_KIND_DATASEC */
     if (btf->nr_types == 0)
         return libbpf_err(-EINVAL);
     t = btf_last_type(btf);
     if (!btf_is_datasec(t))
         return libbpf_err(-EINVAL);
 
     if (validate_type_id(var_type_id))
         return libbpf_err(-EINVAL);
 
     /* decompose and invalidate raw data */
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_var_secinfo);
     v = btf_add_type_mem(btf, sz);
     if (!v)
         return libbpf_err(-ENOMEM);
 
     v->type = var_type_id;
     v->offset = offset;
     v->size = byte_sz;
 
     /* update parent type's vlen */
     t = btf_last_type(btf);
     btf_type_inc_vlen(t);
 
     btf->hdr->type_len += sz;
     btf->hdr->str_off += sz;
     return 0;
 }
 
 /*
  * Append new BTF_KIND_DECL_TAG type with:
  *   - *value* - non-empty/non-NULL string;
  *   - *ref_type_id* - referenced type ID, it might not exist yet;
  *   - *component_idx* - -1 for tagging reference type, otherwise struct/union
  *     member or function argument index;
  * Returns:
  *   - >0, type ID of newly added BTF type;
  *   - <0, on error.
  */
 int btf__add_decl_tag(struct btf *btf, const char *value, int ref_type_id,
          int component_idx)
 {
     struct btf_type *t;
     int sz, value_off;
 
     if (!value || !value[0] || component_idx < -1)
         return libbpf_err(-EINVAL);
 
     if (validate_type_id(ref_type_id))
         return libbpf_err(-EINVAL);
 
     if (btf_ensure_modifiable(btf))
         return libbpf_err(-ENOMEM);
 
     sz = sizeof(struct btf_type) + sizeof(struct btf_decl_tag);
     t = btf_add_type_mem(btf, sz);
     if (!t)
         return libbpf_err(-ENOMEM);
 
     value_off = btf__add_str(btf, value);
     if (value_off < 0)
         return value_off;
 
     t->name_off = value_off;
     t->info = btf_type_info(BTF_KIND_DECL_TAG, 0, false);
     t->type = ref_type_id;
     btf_decl_tag(t)->component_idx = component_idx;
 
     return btf_commit_type(btf, sz);
 }
 
 struct btf_ext_sec_setup_param {
     __u32 off;
     __u32 len;
     __u32 min_rec_size;
     struct btf_ext_info *ext_info;
     const char *desc;
 };
 
 static int btf_ext_setup_info(struct btf_ext *btf_ext,
                   struct btf_ext_sec_setup_param *ext_sec)
 {
     const struct btf_ext_info_sec *sinfo;
     struct btf_ext_info *ext_info;
     __u32 info_left, record_size;
     size_t sec_cnt = 0;
     /* 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;
         sec_cnt++;
     }
 
     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);
     ext_info->sec_cnt = sec_cnt;
 
     return 0;
 }
 
 static int btf_ext_setup_func_info(struct btf_ext *btf_ext)
 {
     struct btf_ext_sec_setup_param param = {
         .off = btf_ext->hdr->func_info_off,
         .len = btf_ext->hdr->func_info_len,
         .min_rec_size = sizeof(struct bpf_func_info_min),
         .ext_info = &btf_ext->func_info,
         .desc = "func_info"
     };
 
     return btf_ext_setup_info(btf_ext, &param);
 }
 
 static int btf_ext_setup_line_info(struct btf_ext *btf_ext)
 {
     struct btf_ext_sec_setup_param param = {
         .off = btf_ext->hdr->line_info_off,
         .len = btf_ext->hdr->line_info_len,
         .min_rec_size = sizeof(struct bpf_line_info_min),
         .ext_info = &btf_ext->line_info,
         .desc = "line_info",
     };
 
     return btf_ext_setup_info(btf_ext, &param);
 }
 
 static int btf_ext_setup_core_relos(struct btf_ext *btf_ext)
 {
     struct btf_ext_sec_setup_param param = {
         .off = btf_ext->hdr->core_relo_off,
         .len = btf_ext->hdr->core_relo_len,
         .min_rec_size = sizeof(struct bpf_core_relo),
         .ext_info = &btf_ext->core_relo_info,
         .desc = "core_relo",
     };
 
     return btf_ext_setup_info(btf_ext, &param);
 }
 
 static int btf_ext_parse_hdr(__u8 *data, __u32 data_size)
 {
     const struct btf_ext_header *hdr = (struct btf_ext_header *)data;
 
     if (data_size < offsetofend(struct btf_ext_header, hdr_len) ||
         data_size < hdr->hdr_len) {
         pr_debug("BTF.ext header not found");
         return -EINVAL;
     }
 
     if (hdr->magic == bswap_16(BTF_MAGIC)) {
         pr_warn("BTF.ext in non-native endianness is not supported\n");
         return -ENOTSUP;
     } else if (hdr->magic != BTF_MAGIC) {
         pr_debug("Invalid BTF.ext magic:%x\n", hdr->magic);
         return -EINVAL;
     }
 
     if (hdr->version != BTF_VERSION) {
         pr_debug("Unsupported BTF.ext version:%u\n", hdr->version);
         return -ENOTSUP;
     }
 
     if (hdr->flags) {
         pr_debug("Unsupported BTF.ext flags:%x\n", hdr->flags);
         return -ENOTSUP;
     }
 
     if (data_size == hdr->hdr_len) {
         pr_debug("BTF.ext has no data\n");
         return -EINVAL;
     }
 
     return 0;
 }
 
 void btf_ext__free(struct btf_ext *btf_ext)
 {
     if (IS_ERR_OR_NULL(btf_ext))
         return;
     free(btf_ext->func_info.sec_idxs);
     free(btf_ext->line_info.sec_idxs);
     free(btf_ext->core_relo_info.sec_idxs);
     free(btf_ext->data);
     free(btf_ext);
 }
 
 struct btf_ext *btf_ext__new(const __u8 *data, __u32 size)
 {
     struct btf_ext *btf_ext;
     int err;
 
     btf_ext = calloc(1, sizeof(struct btf_ext));
     if (!btf_ext)
         return libbpf_err_ptr(-ENOMEM);
 
     btf_ext->data_size = size;
     btf_ext->data = malloc(size);
     if (!btf_ext->data) {
         err = -ENOMEM;
         goto done;
     }
     memcpy(btf_ext->data, data, size);
 
     err = btf_ext_parse_hdr(btf_ext->data, size);
     if (err)
         goto done;
 
     if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, line_info_len)) {
         err = -EINVAL;
         goto done;
     }
 
     err = btf_ext_setup_func_info(btf_ext);
     if (err)
         goto done;
 
     err = btf_ext_setup_line_info(btf_ext);
     if (err)
         goto done;
 
     if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len))
         goto done; /* skip core relos parsing */
 
     err = btf_ext_setup_core_relos(btf_ext);
     if (err)
         goto done;
 
 done:
     if (err) {
         btf_ext__free(btf_ext);
         return libbpf_err_ptr(err);
     }
 
     return btf_ext;
 }
 
 const void *btf_ext__get_raw_data(const struct btf_ext *btf_ext, __u32 *size)
 {
     *size = btf_ext->data_size;
     return btf_ext->data;
 }
 
 struct btf_dedup;
 
 static struct btf_dedup *btf_dedup_new(struct btf *btf, const struct btf_dedup_opts *opts);
 static void btf_dedup_free(struct btf_dedup *d);
 static int btf_dedup_prep(struct btf_dedup *d);
 static int btf_dedup_strings(struct btf_dedup *d);
 static int btf_dedup_prim_types(struct btf_dedup *d);
 static int btf_dedup_struct_types(struct btf_dedup *d);
 static int btf_dedup_ref_types(struct btf_dedup *d);
 static int btf_dedup_compact_types(struct btf_dedup *d);
 static int btf_dedup_remap_types(struct btf_dedup *d);
 
 /*
  * Deduplicate BTF types and strings.
  *
  * BTF dedup algorithm takes as an input `struct btf` representing `.BTF` ELF
  * section with all BTF type descriptors and string data. It overwrites that
  * memory in-place with deduplicated types and strings without any loss of
  * information. If optional `struct btf_ext` representing '.BTF.ext' ELF section
  * is provided, all the strings referenced from .BTF.ext section are honored
  * and updated to point to the right offsets after deduplication.
  *
  * If function returns with error, type/string data might be garbled and should
  * be discarded.
  *
  * More verbose and detailed description of both problem btf_dedup is solving,
  * as well as solution could be found at:
  * https://facebookmicrosites.github.io/bpf/blog/2018/11/14/btf-enhancement.html
  *
  * Problem description and justification
  * =====================================
  *
  * BTF type information is typically emitted either as a result of conversion
  * from DWARF to BTF or directly by compiler. In both cases, each compilation
  * unit contains information about a subset of all the types that are used
  * in an application. These subsets are frequently overlapping and contain a lot
  * of duplicated information when later concatenated together into a single
  * binary. This algorithm ensures that each unique type is represented by single
  * BTF type descriptor, greatly reducing resulting size of BTF data.
  *
  * Compilation unit isolation and subsequent duplication of data is not the only
  * problem. The same type hierarchy (e.g., struct and all the type that struct
  * references) in different compilation units can be represented in BTF to
  * various degrees of completeness (or, rather, incompleteness) due to
  * struct/union forward declarations.
  *
  * Let's take a look at an example, that we'll use to better understand the
  * problem (and solution). Suppose we have two compilation units, each using
  * same `struct S`, but each of them having incomplete type information about
  * struct's fields:
  *
  * // CU #1:
  * struct S;
  * struct A {
  *  int a;
  *  struct A* self;
  *  struct S* parent;
  * };
  * struct B;
  * struct S {
  *  struct A* a_ptr;
  *  struct B* b_ptr;
  * };
  *
  * // CU #2:
  * struct S;
  * struct A;
  * struct B {
  *  int b;
  *  struct B* self;
  *  struct S* parent;
  * };
  * struct S {
  *  struct A* a_ptr;
  *  struct B* b_ptr;
  * };
  *
  * In case of CU #1, BTF data will know only that `struct B` exist (but no
  * more), but will know the complete type information about `struct A`. While
  * for CU #2, it will know full type information about `struct B`, but will
  * only know about forward declaration of `struct A` (in BTF terms, it will
  * have `BTF_KIND_FWD` type descriptor with name `B`).
  *
  * This compilation unit isolation means that it's possible that there is no
  * single CU with complete type information describing structs `S`, `A`, and
  * `B`. Also, we might get tons of duplicated and redundant type information.
  *
  * Additional complication we need to keep in mind comes from the fact that
  * types, in general, can form graphs containing cycles, not just DAGs.
  *
  * While algorithm does deduplication, it also merges and resolves type
  * information (unless disabled throught `struct btf_opts`), whenever possible.
  * E.g., in the example above with two compilation units having partial type
  * information for structs `A` and `B`, the output of algorithm will emit
  * a single copy of each BTF type that describes structs `A`, `B`, and `S`
  * (as well as type information for `int` and pointers), as if they were defined
  * in a single compilation unit as:
  *
  * struct A {
  *  int a;
  *  struct A* self;
  *  struct S* parent;
  * };
  * 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, const struct btf_dedup_opts *opts)
 {
     struct btf_dedup *d;
     int err;
 
     if (!OPTS_VALID(opts, btf_dedup_opts))
         return libbpf_err(-EINVAL);
 
     d = btf_dedup_new(btf, opts);
     if (IS_ERR(d)) {
         pr_debug("btf_dedup_new failed: %ld", PTR_ERR(d));
         return libbpf_err(-EINVAL);
     }
 
     if (btf_ensure_modifiable(btf)) {
         err = -ENOMEM;
         goto done;
     }
 
     err = btf_dedup_prep(d);
     if (err) {
         pr_debug("btf_dedup_prep failed:%d\n", err);
         goto done;
     }
     err = btf_dedup_strings(d);
     if (err < 0) {
         pr_debug("btf_dedup_strings failed:%d\n", err);
         goto done;
     }
     err = btf_dedup_prim_types(d);
     if (err < 0) {
         pr_debug("btf_dedup_prim_types failed:%d\n", err);
         goto done;
     }
     err = btf_dedup_struct_types(d);
     if (err < 0) {
         pr_debug("btf_dedup_struct_types failed:%d\n", err);
         goto done;
     }
     err = btf_dedup_ref_types(d);
     if (err < 0) {
         pr_debug("btf_dedup_ref_types failed:%d\n", err);
         goto done;
     }
     err = btf_dedup_compact_types(d);
     if (err < 0) {
         pr_debug("btf_dedup_compact_types failed:%d\n", err);
         goto done;
     }
     err = btf_dedup_remap_types(d);
     if (err < 0) {
         pr_debug("btf_dedup_remap_types failed:%d\n", err);
         goto done;
     }
 
 done:
     btf_dedup_free(d);
     return libbpf_err(err);
 }
 
 #define BTF_UNPROCESSED_ID ((__u32)-1)
 #define BTF_IN_PROGRESS_ID ((__u32)-2)
 
 struct btf_dedup {
     /* .BTF section to be deduped in-place */
     struct btf *btf;
     /*
      * Optional .BTF.ext section. When provided, any strings referenced
      * from it will be taken into account when deduping strings
      */
     struct btf_ext *btf_ext;
     /*
      * This is a map from any type's signature hash to a list of possible
      * canonical representative type candidates. Hash collisions are
      * ignored, so even types of various kinds can share same list of
      * candidates, which is fine because we rely on subsequent
      * btf_xxx_equal() checks to authoritatively verify type equality.
      */
     struct hashmap *dedup_table;
     /* Canonical types map */
     __u32 *map;
     /* Hypothetical mapping, used during type graph equivalence checks */
     __u32 *hypot_map;
     __u32 *hypot_list;
     size_t hypot_cnt;
     size_t hypot_cap;
     /* Whether hypothetical mapping, if successful, would need to adjust
      * already canonicalized types (due to a new forward declaration to
      * concrete type resolution). In such case, during split BTF dedup
      * candidate type would still be considered as different, because base
      * BTF is considered to be immutable.
      */
     bool hypot_adjust_canon;
     /* Various option modifying behavior of algorithm */
     struct btf_dedup_opts opts;
     /* temporary strings deduplication state */
     struct strset *strs_set;
 };
 
 static long hash_combine(long h, long value)
 {
     return h * 31 + value;
 }
 
 #define for_each_dedup_cand(d, node, hash) \
     hashmap__for_each_key_entry(d->dedup_table, node, (void *)hash)
 
 static int btf_dedup_table_add(struct btf_dedup *d, long hash, __u32 type_id)
 {
     return hashmap__append(d->dedup_table,
                    (void *)hash, (void *)(long)type_id);
 }
 
 static int btf_dedup_hypot_map_add(struct btf_dedup *d,
                    __u32 from_id, __u32 to_id)
 {
     if (d->hypot_cnt == d->hypot_cap) {
         __u32 *new_list;
 
         d->hypot_cap += max((size_t)16, d->hypot_cap / 2);
         new_list = libbpf_reallocarray(d->hypot_list, d->hypot_cap, sizeof(__u32));
         if (!new_list)
             return -ENOMEM;
         d->hypot_list = new_list;
     }
     d->hypot_list[d->hypot_cnt++] = from_id;
     d->hypot_map[from_id] = to_id;
     return 0;
 }
 
 static void btf_dedup_clear_hypot_map(struct btf_dedup *d)
 {
     int i;
 
     for (i = 0; i < d->hypot_cnt; i++)
         d->hypot_map[d->hypot_list[i]] = BTF_UNPROCESSED_ID;
     d->hypot_cnt = 0;
     d->hypot_adjust_canon = false;
 }
 
 static void btf_dedup_free(struct btf_dedup *d)
 {
     hashmap__free(d->dedup_table);
     d->dedup_table = NULL;
 
     free(d->map);
     d->map = NULL;
 
     free(d->hypot_map);
     d->hypot_map = NULL;
 
     free(d->hypot_list);
     d->hypot_list = NULL;
 
     free(d);
 }
 
 static size_t btf_dedup_identity_hash_fn(const void *key, void *ctx)
 {
     return (size_t)key;
 }
 
 static size_t btf_dedup_collision_hash_fn(const void *key, void *ctx)
 {
     return 0;
 }
 
 static bool btf_dedup_equal_fn(const void *k1, const void *k2, void *ctx)
 {
     return k1 == k2;
 }
 
 static struct btf_dedup *btf_dedup_new(struct btf *btf, const struct btf_dedup_opts *opts)
 {
     struct btf_dedup *d = calloc(1, sizeof(struct btf_dedup));
     hashmap_hash_fn hash_fn = btf_dedup_identity_hash_fn;
     int i, err = 0, type_cnt;
 
     if (!d)
         return ERR_PTR(-ENOMEM);
 
     if (OPTS_GET(opts, force_collisions, false))
         hash_fn = btf_dedup_collision_hash_fn;
 
     d->btf = btf;
     d->btf_ext = OPTS_GET(opts, btf_ext, NULL);
 
     d->dedup_table = hashmap__new(hash_fn, btf_dedup_equal_fn, NULL);
     if (IS_ERR(d->dedup_table)) {
         err = PTR_ERR(d->dedup_table);
         d->dedup_table = NULL;
         goto done;
     }
 
     type_cnt = btf__type_cnt(btf);
     d->map = malloc(sizeof(__u32) * type_cnt);
     if (!d->map) {
         err = -ENOMEM;
         goto done;
     }
     /* special BTF "void" type is made canonical immediately */
     d->map[0] = 0;
     for (i = 1; i < type_cnt; i++) {
         struct btf_type *t = btf_type_by_id(d->btf, i);
 
         /* VAR and DATASEC are never deduped and are self-canonical */
         if (btf_is_var(t) || btf_is_datasec(t))
             d->map[i] = i;
         else
             d->map[i] = BTF_UNPROCESSED_ID;
     }
 
     d->hypot_map = malloc(sizeof(__u32) * type_cnt);
     if (!d->hypot_map) {
         err = -ENOMEM;
         goto done;
     }
     for (i = 0; i < type_cnt; i++)
         d->hypot_map[i] = BTF_UNPROCESSED_ID;
 
 done:
     if (err) {
         btf_dedup_free(d);
         return ERR_PTR(err);
     }
 
     return d;
 }
 
 /*
  * Iterate over all possible places in .BTF and .BTF.ext that can reference
  * string and pass pointer to it to a provided callback `fn`.
  */
 static int btf_for_each_str_off(struct btf_dedup *d, str_off_visit_fn fn, void *ctx)
 {
     int i, r;
 
     for (i = 0; i < d->btf->nr_types; i++) {
         struct btf_type *t = btf_type_by_id(d->btf, d->btf->start_id + i);
 
         r = btf_type_visit_str_offs(t, fn, ctx);
         if (r)
             return r;
     }
 
     if (!d->btf_ext)
         return 0;
 
     r = btf_ext_visit_str_offs(d->btf_ext, fn, ctx);
     if (r)
         return r;
 
     return 0;
 }
 
 static int strs_dedup_remap_str_off(__u32 *str_off_ptr, void *ctx)
 {
     struct btf_dedup *d = ctx;
     __u32 str_off = *str_off_ptr;
     const char *s;
     int off, err;
 
     /* don't touch empty string or string in main BTF */
     if (str_off == 0 || str_off < d->btf->start_str_off)
         return 0;
 
     s = btf__str_by_offset(d->btf, str_off);
     if (d->btf->base_btf) {
         err = btf__find_str(d->btf->base_btf, s);
         if (err >= 0) {
             *str_off_ptr = err;
             return 0;
         }
         if (err != -ENOENT)
             return err;
     }
 
     off = strset__add_str(d->strs_set, s);
     if (off < 0)
         return off;
 
     *str_off_ptr = d->btf->start_str_off + off;
     return 0;
 }
 
 /*
  * Dedup string and filter out those that are not referenced from either .BTF
  * or .BTF.ext (if provided) sections.
  *
  * This is done by building index of all strings in BTF's string section,
  * then iterating over all entities that can reference strings (e.g., type
  * names, struct field names, .BTF.ext line info, etc) and marking corresponding
  * strings as used. After that all used strings are deduped and compacted into
  * sequential blob of memory and new offsets are calculated. Then all the string
  * references are iterated again and rewritten using new offsets.
  */
 static int btf_dedup_strings(struct btf_dedup *d)
 {
     int err;
 
     if (d->btf->strs_deduped)
         return 0;
 
     d->strs_set = strset__new(BTF_MAX_STR_OFFSET, NULL, 0);
     if (IS_ERR(d->strs_set)) {
         err = PTR_ERR(d->strs_set);
         goto err_out;
     }
 
     if (!d->btf->base_btf) {
         /* insert empty string; we won't be looking it up during strings
          * dedup, but it's good to have it for generic BTF string lookups
          */
         err = strset__add_str(d->strs_set, "");
         if (err < 0)
             goto err_out;
     }
 
     /* remap string offsets */
     err = btf_for_each_str_off(d, strs_dedup_remap_str_off, d);
     if (err)
         goto err_out;
 
     /* replace BTF string data and hash with deduped ones */
     strset__free(d->btf->strs_set);
     d->btf->hdr->str_len = strset__data_size(d->strs_set);
     d->btf->strs_set = d->strs_set;
     d->strs_set = NULL;
     d->btf->strs_deduped = true;
     return 0;
 
 err_out:
     strset__free(d->strs_set);
     d->strs_set = NULL;
 
     return err;
 }
 
 static long btf_hash_common(struct btf_type *t)
 {
     long h;
 
     h = hash_combine(0, t->name_off);
     h = hash_combine(h, t->info);
     h = hash_combine(h, t->size);
     return h;
 }
 
 static bool btf_equal_common(struct btf_type *t1, struct btf_type *t2)
 {
     return t1->name_off == t2->name_off &&
            t1->info == t2->info &&
            t1->size == t2->size;
 }
 
 /* Calculate type signature hash of INT or TAG. */
 static long btf_hash_int_decl_tag(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 or TAGs. */
 static bool btf_equal_int_tag(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/ENUM64. */
 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 bool btf_equal_enum64(struct btf_type *t1, struct btf_type *t2)
 {
     const struct btf_enum64 *m1, *m2;
     __u16 vlen;
     int i;
 
     if (!btf_equal_common(t1, t2))
         return false;
 
     vlen = btf_vlen(t1);
     m1 = btf_enum64(t1);
     m2 = btf_enum64(t2);
     for (i = 0; i < vlen; i++) {
         if (m1->name_off != m2->name_off || m1->val_lo32 != m2->val_lo32 ||
             m1->val_hi32 != m2->val_hi32)
             return false;
         m1++;
         m2++;
     }
     return true;
 }
 
 static inline bool btf_is_enum_fwd(struct btf_type *t)
 {
     return btf_is_any_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;
 }
 
 static bool btf_compat_enum64(struct btf_type *t1, struct btf_type *t2)
 {
     if (!btf_is_enum_fwd(t1) && !btf_is_enum_fwd(t2))
         return btf_equal_enum64(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 STRUCTs/UNIONs, ignoring referenced
  * type IDs. This check is performed during type graph equivalence check and
  * referenced types equivalence is checked separately.
  */
 static bool btf_shallow_equal_struct(struct btf_type *t1, struct btf_type *t2)
 {
     const struct btf_member *m1, *m2;
     __u16 vlen;
     int i;
 
     if (!btf_equal_common(t1, t2))
         return false;
 
     vlen = btf_vlen(t1);
     m1 = btf_members(t1);
     m2 = btf_members(t2);
     for (i = 0; i < vlen; i++) {
         if (m1->name_off != m2->name_off || m1->offset != m2->offset)
             return false;
         m1++;
         m2++;
     }
     return true;
 }
 
 /*
  * Calculate type signature hash of ARRAY, including referenced type IDs,
  * under assumption that they were already resolved to canonical type IDs and
  * are not going to change.
  */
 static long btf_hash_array(struct btf_type *t)
 {
     const struct btf_array *info = btf_array(t);
     long h = btf_hash_common(t);
 
     h = hash_combine(h, info->type);
     h = hash_combine(h, info->index_type);
     h = hash_combine(h, info->nelems);
     return h;
 }
 
 /*
  * Check exact equality of two ARRAYs, taking into account referenced
  * type IDs, under assumption that they were already resolved to canonical
  * type IDs and are not going to change.
  * This function is called during reference types deduplication to compare
  * ARRAY to potential canonical representative.
  */
 static bool btf_equal_array(struct btf_type *t1, struct btf_type *t2)
 {
     const struct btf_array *info1, *info2;
 
     if (!btf_equal_common(t1, t2))
         return false;
 
     info1 = btf_array(t1);
     info2 = btf_array(t2);
     return info1->type == info2->type &&
            info1->index_type == info2->index_type &&
            info1->nelems == info2->nelems;
 }
 
 /*
  * Check structural compatibility of two ARRAYs, ignoring referenced type
  * IDs. This check is performed during type graph equivalence check and
  * referenced types equivalence is checked separately.
  */
 static bool btf_compat_array(struct btf_type *t1, struct btf_type *t2)
 {
     if (!btf_equal_common(t1, t2))
         return false;
 
     return btf_array(t1)->nelems == btf_array(t2)->nelems;
 }
 
 /*
  * Calculate type signature hash of FUNC_PROTO, including referenced type IDs,
  * under assumption that they were already resolved to canonical type IDs and
  * are not going to change.
  */
 static long btf_hash_fnproto(struct btf_type *t)
 {
     const struct btf_param *member = btf_params(t);
     __u16 vlen = btf_vlen(t);
     long h = btf_hash_common(t);
     int i;
 
     for (i = 0; i < vlen; i++) {
         h = hash_combine(h, member->name_off);
         h = hash_combine(h, member->type);
         member++;
     }
     return h;
 }
 
 /*
  * Check exact equality of two FUNC_PROTOs, taking into account referenced
  * type IDs, under assumption that they were already resolved to canonical
  * type IDs and are not going to change.
  * This function is called during reference types deduplication to compare
  * FUNC_PROTO to potential canonical representative.
  */
 static bool btf_equal_fnproto(struct btf_type *t1, struct btf_type *t2)
 {
     const struct btf_param *m1, *m2;
     __u16 vlen;
     int i;
 
     if (!btf_equal_common(t1, t2))
         return false;
 
     vlen = btf_vlen(t1);
     m1 = btf_params(t1);
     m2 = btf_params(t2);
     for (i = 0; i < vlen; i++) {
         if (m1->name_off != m2->name_off || m1->type != m2->type)
             return false;
         m1++;
         m2++;
     }
     return true;
 }
 
 /*
  * Check structural compatibility of two FUNC_PROTOs, ignoring referenced type
  * IDs. This check is performed during type graph equivalence check and
  * referenced types equivalence is checked separately.
  */
 static bool btf_compat_fnproto(struct btf_type *t1, struct btf_type *t2)
 {
     const struct btf_param *m1, *m2;
     __u16 vlen;
     int i;
 
     /* skip return type ID */
     if (t1->name_off != t2->name_off || t1->info != t2->info)
         return false;
 
     vlen = btf_vlen(t1);
     m1 = btf_params(t1);
     m2 = btf_params(t2);
     for (i = 0; i < vlen; i++) {
         if (m1->name_off != m2->name_off)
             return false;
         m1++;
         m2++;
     }
     return true;
 }
 
 /* Prepare split BTF for deduplication by calculating hashes of base BTF's
  * types and initializing the rest of the state (canonical type mapping) for
  * the fixed base BTF part.
  */
 static int btf_dedup_prep(struct btf_dedup *d)
 {
     struct btf_type *t;
     int type_id;
     long h;
 
     if (!d->btf->base_btf)
         return 0;
 
     for (type_id = 1; type_id < d->btf->start_id; type_id++) {
         t = btf_type_by_id(d->btf, type_id);
 
         /* all base BTF types are self-canonical by definition */
         d->map[type_id] = type_id;
 
         switch (btf_kind(t)) {
         case BTF_KIND_VAR:
         case BTF_KIND_DATASEC:
             /* VAR and DATASEC are never hash/deduplicated */
             continue;
         case BTF_KIND_CONST:
         case BTF_KIND_VOLATILE:
         case BTF_KIND_RESTRICT:
         case BTF_KIND_PTR:
         case BTF_KIND_FWD:
         case BTF_KIND_TYPEDEF:
         case BTF_KIND_FUNC:
         case BTF_KIND_FLOAT:
         case BTF_KIND_TYPE_TAG:
             h = btf_hash_common(t);
             break;
         case BTF_KIND_INT:
         case BTF_KIND_DECL_TAG:
             h = btf_hash_int_decl_tag(t);
             break;
         case BTF_KIND_ENUM:
         case BTF_KIND_ENUM64:
             h = btf_hash_enum(t);
             break;
         case BTF_KIND_STRUCT:
         case BTF_KIND_UNION:
             h = btf_hash_struct(t);
             break;
         case BTF_KIND_ARRAY:
             h = btf_hash_array(t);
             break;
         case BTF_KIND_FUNC_PROTO:
             h = btf_hash_fnproto(t);
             break;
         default:
             pr_debug("unknown kind %d for type [%d]\n", btf_kind(t), type_id);
             return -EINVAL;
         }
         if (btf_dedup_table_add(d, h, type_id))
             return -ENOMEM;
     }
 
     return 0;
 }
 
 /*
  * Deduplicate primitive types, that can't reference other types, by calculating
  * their type signature hash and comparing them with any possible canonical
  * candidate. If no canonical candidate matches, type itself is marked as
  * canonical and is added into `btf_dedup->dedup_table` as another candidate.
  */
 static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
 {
     struct btf_type *t = btf_type_by_id(d->btf, type_id);
     struct hashmap_entry *hash_entry;
     struct btf_type *cand;
     /* if we don't find equivalent type, then we are canonical */
     __u32 new_id = type_id;
     __u32 cand_id;
     long h;
 
     switch (btf_kind(t)) {
     case BTF_KIND_CONST:
     case BTF_KIND_VOLATILE:
     case BTF_KIND_RESTRICT:
     case BTF_KIND_PTR:
     case BTF_KIND_TYPEDEF:
     case BTF_KIND_ARRAY:
     case BTF_KIND_STRUCT:
     case BTF_KIND_UNION:
     case BTF_KIND_FUNC:
     case BTF_KIND_FUNC_PROTO:
     case BTF_KIND_VAR:
     case BTF_KIND_DATASEC:
     case BTF_KIND_DECL_TAG:
     case BTF_KIND_TYPE_TAG:
         return 0;
 
     case BTF_KIND_INT:
         h = btf_hash_int_decl_tag(t);
         for_each_dedup_cand(d, hash_entry, h) {
             cand_id = (__u32)(long)hash_entry->value;
             cand = btf_type_by_id(d->btf, cand_id);
             if (btf_equal_int_tag(t, cand)) {
                 new_id = cand_id;
                 break;
             }
         }
         break;
 
     case BTF_KIND_ENUM:
         h = btf_hash_enum(t);
         for_each_dedup_cand(d, hash_entry, h) {
             cand_id = (__u32)(long)hash_entry->value;
             cand = btf_type_by_id(d->btf, cand_id);
             if (btf_equal_enum(t, cand)) {
                 new_id = cand_id;
                 break;
             }
             if (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_ENUM64:
         h = btf_hash_enum(t);
         for_each_dedup_cand(d, hash_entry, h) {
             cand_id = (__u32)(long)hash_entry->value;
             cand = btf_type_by_id(d->btf, cand_id);
             if (btf_equal_enum64(t, cand)) {
                 new_id = cand_id;
                 break;
             }
             if (btf_compat_enum64(t, cand)) {
                 if (btf_is_enum_fwd(t)) {
                     /* resolve fwd to full enum */
                     new_id = cand_id;
                     break;
                 }
                 /* resolve canonical enum fwd to full enum */
                 d->map[cand_id] = type_id;
             }
         }
         break;
 
     case BTF_KIND_FWD:
     case BTF_KIND_FLOAT:
         h = btf_hash_common(t);
         for_each_dedup_cand(d, hash_entry, h) {
             cand_id = (__u32)(long)hash_entry->value;
             cand = btf_type_by_id(d->btf, cand_id);
             if (btf_equal_common(t, cand)) {
                 new_id = cand_id;
                 break;
             }
         }
         break;
 
     default:
         return -EINVAL;
     }
 
     d->map[type_id] = new_id;
     if (type_id == new_id && btf_dedup_table_add(d, h, type_id))
         return -ENOMEM;
 
     return 0;
 }
 
 static int btf_dedup_prim_types(struct btf_dedup *d)
 {
     int i, err;
 
     for (i = 0; i < d->btf->nr_types; i++) {
         err = btf_dedup_prim_type(d, d->btf->start_id + i);
         if (err)
             return err;
     }
     return 0;
 }
 
 /*
  * Check whether type is already mapped into canonical one (could be to itself).
  */
 static inline bool is_type_mapped(struct btf_dedup *d, uint32_t type_id)
 {
     return d->map[type_id] <= BTF_MAX_NR_TYPES;
 }
 
 /*
  * Resolve type ID into its canonical type ID, if any; otherwise return original
  * type ID. If type is FWD and is resolved into STRUCT/UNION already, follow
  * STRUCT/UNION link and resolve it into canonical type ID as well.
  */
 static inline __u32 resolve_type_id(struct btf_dedup *d, __u32 type_id)
 {
     while (is_type_mapped(d, type_id) && d->map[type_id] != type_id)
         type_id = d->map[type_id];
     return type_id;
 }
 
 /*
  * Resolve FWD to underlying STRUCT/UNION, if any; otherwise return original
  * type ID.
  */
 static uint32_t resolve_fwd_id(struct btf_dedup *d, uint32_t type_id)
 {
     __u32 orig_type_id = type_id;
 
     if (!btf_is_fwd(btf__type_by_id(d->btf, type_id)))
         return type_id;
 
     while (is_type_mapped(d, type_id) && d->map[type_id] != type_id)
         type_id = d->map[type_id];
 
     if (!btf_is_fwd(btf__type_by_id(d->btf, type_id)))
         return type_id;
 
     return orig_type_id;
 }
 
 
 static inline __u16 btf_fwd_kind(struct btf_type *t)
 {
     return btf_kflag(t) ? BTF_KIND_UNION : BTF_KIND_STRUCT;
 }
 
 /* Check if given two types are identical ARRAY definitions */
 static int btf_dedup_identical_arrays(struct btf_dedup *d, __u32 id1, __u32 id2)
 {
     struct btf_type *t1, *t2;
 
     t1 = btf_type_by_id(d->btf, id1);
     t2 = btf_type_by_id(d->btf, id2);
     if (!btf_is_array(t1) || !btf_is_array(t2))
         return 0;
 
     return btf_equal_array(t1, t2);
 }
 
 /* Check if given two types are identical STRUCT/UNION definitions */
 static bool btf_dedup_identical_structs(struct btf_dedup *d, __u32 id1, __u32 id2)
 {
     const struct btf_member *m1, *m2;
     struct btf_type *t1, *t2;
     int n, i;
 
     t1 = btf_type_by_id(d->btf, id1);
     t2 = btf_type_by_id(d->btf, id2);
 
     if (!btf_is_composite(t1) || btf_kind(t1) != btf_kind(t2))
         return false;
 
     if (!btf_shallow_equal_struct(t1, t2))
         return false;
 
     m1 = btf_members(t1);
     m2 = btf_members(t2);
     for (i = 0, n = btf_vlen(t1); i < n; i++, m1++, m2++) {
         if (m1->type != m2->type)
             return false;
     }
     return true;
 }
 
 /*
  * 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) {
         if (hypot_type_id == cand_id)
             return 1;
         /* In some cases compiler will generate different DWARF types
          * for *identical* array type definitions and use them for
          * different fields within the *same* struct. This breaks type
          * equivalence check, which makes an assumption that candidate
          * types sub-graph has a consistent and deduped-by-compiler
          * types within a single CU. So work around that by explicitly
          * allowing identical array types here.
          */
         if (btf_dedup_identical_arrays(d, hypot_type_id, cand_id))
             return 1;
         /* It turns out that similar situation can happen with
          * struct/union sometimes, sigh... Handle the case where
          * structs/unions are exactly the same, down to the referenced
          * type IDs. Anything more complicated (e.g., if referenced
          * types are different, but equivalent) is *way more*
          * complicated and requires a many-to-many equivalence mapping.
          */
         if (btf_dedup_identical_structs(d, hypot_type_id, cand_id))
             return 1;
         return 0;
     }
 
     if (btf_dedup_hypot_map_add(d, canon_id, cand_id))
         return -ENOMEM;
 
     cand_type = btf_type_by_id(d->btf, cand_id);
     canon_type = btf_type_by_id(d->btf, canon_id);
     cand_kind = btf_kind(cand_type);
     canon_kind = btf_kind(canon_type);
 
     if (cand_type->name_off != canon_type->name_off)
         return 0;
 
     /* FWD <--> STRUCT/UNION equivalence check, if enabled */
     if ((cand_kind == BTF_KIND_FWD || canon_kind == BTF_KIND_FWD)
         && cand_kind != canon_kind) {
         __u16 real_kind;
         __u16 fwd_kind;
 
         if (cand_kind == BTF_KIND_FWD) {
             real_kind = canon_kind;
             fwd_kind = btf_fwd_kind(cand_type);
         } else {
             real_kind = cand_kind;
             fwd_kind = btf_fwd_kind(canon_type);
             /* we'd need to resolve base FWD to STRUCT/UNION */
             if (fwd_kind == real_kind && canon_id < d->btf->start_id)
                 d->hypot_adjust_canon = true;
         }
         return fwd_kind == real_kind;
     }
 
     if (cand_kind != canon_kind)
         return 0;
 
     switch (cand_kind) {
     case BTF_KIND_INT:
         return btf_equal_int_tag(cand_type, canon_type);
 
     case BTF_KIND_ENUM:
         return btf_compat_enum(cand_type, canon_type);
 
     case BTF_KIND_ENUM64:
         return btf_compat_enum64(cand_type, canon_type);
 
     case BTF_KIND_FWD:
     case BTF_KIND_FLOAT:
         return btf_equal_common(cand_type, canon_type);
 
     case BTF_KIND_CONST:
     case BTF_KIND_VOLATILE:
     case BTF_KIND_RESTRICT:
     case BTF_KIND_PTR:
     case BTF_KIND_TYPEDEF:
     case BTF_KIND_FUNC:
     case BTF_KIND_TYPE_TAG:
         if (cand_type->info != canon_type->info)
             return 0;
         return btf_dedup_is_equiv(d, cand_type->type, canon_type->type);
 
     case BTF_KIND_ARRAY: {
         const struct btf_array *cand_arr, *canon_arr;
 
         if (!btf_compat_array(cand_type, canon_type))
             return 0;
         cand_arr = btf_array(cand_type);
         canon_arr = btf_array(canon_type);
         eq = btf_dedup_is_equiv(d, cand_arr->index_type, canon_arr->index_type);
         if (eq <= 0)
             return eq;
         return btf_dedup_is_equiv(d, cand_arr->type, canon_arr->type);
     }
 
     case BTF_KIND_STRUCT:
     case BTF_KIND_UNION: {
         const struct btf_member *cand_m, *canon_m;
         __u16 vlen;
 
         if (!btf_shallow_equal_struct(cand_type, canon_type))
             return 0;
         vlen = btf_vlen(cand_type);
         cand_m = btf_members(cand_type);
         canon_m = btf_members(canon_type);
         for (i = 0; i < vlen; i++) {
             eq = btf_dedup_is_equiv(d, cand_m->type, canon_m->type);
             if (eq <= 0)
                 return eq;
             cand_m++;
             canon_m++;
         }
 
         return 1;
     }
 
     case BTF_KIND_FUNC_PROTO: {
         const struct btf_param *cand_p, *canon_p;
         __u16 vlen;
 
         if (!btf_compat_fnproto(cand_type, canon_type))
             return 0;
         eq = btf_dedup_is_equiv(d, cand_type->type, canon_type->type);
         if (eq <= 0)
             return eq;
         vlen = btf_vlen(cand_type);
         cand_p = btf_params(cand_type);
         canon_p = btf_params(canon_type);
         for (i = 0; i < vlen; i++) {
             eq = btf_dedup_is_equiv(d, cand_p->type, canon_p->type);
             if (eq <= 0)
                 return eq;
             cand_p++;
             canon_p++;
         }
         return 1;
     }
 
     default:
         return -EINVAL;
     }
     return 0;
 }
 
 /*
  * Use hypothetical mapping, produced by successful type graph equivalence
  * check, to augment existing struct/union canonical mapping, where possible.
  *
  * If BTF_KIND_FWD resolution is allowed, this mapping is also used to record
  * FWD -> STRUCT/UNION correspondence as well. FWD resolution is bidirectional:
  * it doesn't matter if FWD type was part of canonical graph or candidate one,
  * we are recording the mapping anyway. As opposed to carefulness required
  * for struct/union correspondence mapping (described below), for FWD resolution
  * it's not important, as by the time that FWD type (reference type) will be
  * deduplicated all structs/unions will be deduped already anyway.
  *
  * Recording STRUCT/UNION mapping is purely a performance optimization and is
  * not required for correctness. It needs to be done carefully to ensure that
  * struct/union from candidate's type graph is not mapped into corresponding
  * struct/union from canonical type graph that itself hasn't been resolved into
  * canonical representative. The only guarantee we have is that canonical
  * struct/union was determined as canonical and that won't change. But any
  * types referenced through that struct/union fields could have been not yet
  * resolved, so in case like that it's too early to establish any kind of
  * correspondence between structs/unions.
  *
  * No canonical correspondence is derived for primitive types (they are already
  * deduplicated completely already anyway) or reference types (they rely on
  * stability of struct/union canonical relationship for equivalence checks).
  */
 static void btf_dedup_merge_hypot_map(struct btf_dedup *d)
 {
     __u32 canon_type_id, targ_type_id;
     __u16 t_kind, c_kind;
     __u32 t_id, c_id;
     int i;
 
     for (i = 0; i < d->hypot_cnt; i++) {
         canon_type_id = d->hypot_list[i];
         targ_type_id = d->hypot_map[canon_type_id];
         t_id = resolve_type_id(d, targ_type_id);
         c_id = resolve_type_id(d, canon_type_id);
         t_kind = btf_kind(btf__type_by_id(d->btf, t_id));
         c_kind = btf_kind(btf__type_by_id(d->btf, 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 it's the split BTF case, we still need to point base FWD
          * to STRUCT/UNION in a split BTF, because FWDs from split BTF
          * will be resolved against base FWD. If we don't point base
          * canonical FWD to the resolved STRUCT/UNION, then all the
          * FWDs in split BTF won't be correctly resolved to a proper
          * STRUCT/UNION.
          */
         if (t_kind != BTF_KIND_FWD && c_kind == BTF_KIND_FWD)
             d->map[c_id] = t_id;
 
         /* if graph equivalence determined that we'd need to adjust
          * base canonical types, then we need to only point base FWDs
          * to STRUCTs/UNIONs and do no more modifications. For all
          * other purposes the type graphs were not equivalent.
          */
         if (d->hypot_adjust_canon)
             continue;
 
         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 = btf_type_by_id(d->btf, 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 = btf_type_by_id(d->btf, 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;
         btf_dedup_merge_hypot_map(d);
         if (d->hypot_adjust_canon) /* not really equivalent */
             continue;
         new_id = cand_id;
         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 = 0; i < d->btf->nr_types; i++) {
         err = btf_dedup_struct_type(d, d->btf->start_id + 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 = btf_type_by_id(d->btf, 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:
     case BTF_KIND_TYPE_TAG:
         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 = btf_type_by_id(d->btf, cand_id);
             if (btf_equal_common(t, cand)) {
                 new_id = cand_id;
                 break;
             }
         }
         break;
 
     case BTF_KIND_DECL_TAG:
         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_int_decl_tag(t);
         for_each_dedup_cand(d, hash_entry, h) {
             cand_id = (__u32)(long)hash_entry->value;
             cand = btf_type_by_id(d->btf, cand_id);
             if (btf_equal_int_tag(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 = btf_type_by_id(d->btf, 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 = btf_type_by_id(d->btf, 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 = 0; i < d->btf->nr_types; i++) {
         err = btf_dedup_ref_type(d, d->btf->start_id + 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)
 {
     __u32 *new_offs;
     __u32 next_type_id = d->btf->start_id;
     const struct btf_type *t;
     void *p;
     int i, id, len;
 
     /* we are going to reuse hypot_map to store compaction remapping */
     d->hypot_map[0] = 0;
     /* base BTF types are not renumbered */
     for (id = 1; id < d->btf->start_id; id++)
         d->hypot_map[id] = id;
     for (i = 0, id = d->btf->start_id; i < d->btf->nr_types; i++, id++)
         d->hypot_map[id] = BTF_UNPROCESSED_ID;
 
     p = d->btf->types_data;
 
     for (i = 0, id = d->btf->start_id; i < d->btf->nr_types; i++, id++) {
         if (d->map[id] != id)
             continue;
 
         t = btf__type_by_id(d->btf, id);
         len = btf_type_size(t);
         if (len < 0)
             return len;
 
         memmove(p, t, len);
         d->hypot_map[id] = next_type_id;
         d->btf->type_offs[next_type_id - d->btf->start_id] = p - d->btf->types_data;
         p += len;
         next_type_id++;
     }
 
     /* shrink struct btf's internal types index and update btf_header */
     d->btf->nr_types = next_type_id - d->btf->start_id;
     d->btf->type_offs_cap = d->btf->nr_types;
     d->btf->hdr->type_len = p - d->btf->types_data;
     new_offs = libbpf_reallocarray(d->btf->type_offs, d->btf->type_offs_cap,
                        sizeof(*new_offs));
     if (d->btf->type_offs_cap && !new_offs)
         return -ENOMEM;
     d->btf->type_offs = new_offs;
     d->btf->hdr->str_off = d->btf->hdr->type_len;
     d->btf->raw_size = d->btf->hdr->hdr_len + d->btf->hdr->type_len + d->btf->hdr->str_len;
     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(__u32 *type_id, void *ctx)
 {
     struct btf_dedup *d = ctx;
     __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;
 
     *type_id = new_type_id;
     return 0;
 }
 
 /*
  * 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_types(struct btf_dedup *d)
 {
     int i, r;
 
     for (i = 0; i < d->btf->nr_types; i++) {
         struct btf_type *t = btf_type_by_id(d->btf, d->btf->start_id + i);
 
         r = btf_type_visit_type_ids(t, btf_dedup_remap_type_id, d);
         if (r)
             return r;
     }
 
     if (!d->btf_ext)
         return 0;
 
     r = btf_ext_visit_type_ids(d->btf_ext, btf_dedup_remap_type_id, d);
     if (r)
         return r;
 
     return 0;
 }
 
 /*
  * Probe few well-known locations for vmlinux kernel image and try to load BTF
  * data out of it to use for target BTF.
  */
 struct btf *btf__load_vmlinux_btf(void)
 {
     struct {
         const char *path_fmt;
         bool raw_btf;
     } locations[] = {
         /* try canonical vmlinux BTF through sysfs first */
         { "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
         /* fall back to trying to find vmlinux ELF on disk otherwise */
         { "/boot/vmlinux-%1$s" },
         { "/lib/modules/%1$s/vmlinux-%1$s" },
         { "/lib/modules/%1$s/build/vmlinux" },
         { "/usr/lib/modules/%1$s/kernel/vmlinux" },
         { "/usr/lib/debug/boot/vmlinux-%1$s" },
         { "/usr/lib/debug/boot/vmlinux-%1$s.debug" },
         { "/usr/lib/debug/lib/modules/%1$s/vmlinux" },
     };
     char path[PATH_MAX + 1];
     struct utsname buf;
     struct btf *btf;
     int i, err;
 
     uname(&buf);
 
     for (i = 0; i < ARRAY_SIZE(locations); i++) {
         snprintf(path, PATH_MAX, locations[i].path_fmt, buf.release);
 
         if (access(path, R_OK))
             continue;
 
         if (locations[i].raw_btf)
             btf = btf__parse_raw(path);
         else
             btf = btf__parse_elf(path, NULL);
         err = libbpf_get_error(btf);
         pr_debug("loading kernel BTF '%s': %d\n", path, err);
         if (err)
             continue;
 
         return btf;
     }
 
     pr_warn("failed to find valid kernel BTF\n");
     return libbpf_err_ptr(-ESRCH);
 }
 
 struct btf *libbpf_find_kernel_btf(void) __attribute__((alias("btf__load_vmlinux_btf")));
 
 struct btf *btf__load_module_btf(const char *module_name, struct btf *vmlinux_btf)
 {
     char path[80];
 
     snprintf(path, sizeof(path), "/sys/kernel/btf/%s", module_name);
     return btf__parse_split(path, vmlinux_btf);
 }
 
 int btf_type_visit_type_ids(struct btf_type *t, type_id_visit_fn visit, void *ctx)
 {
     int i, n, err;
 
     switch (btf_kind(t)) {
     case BTF_KIND_INT:
     case BTF_KIND_FLOAT:
     case BTF_KIND_ENUM:
     case BTF_KIND_ENUM64:
         return 0;
 
     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:
     case BTF_KIND_DECL_TAG:
     case BTF_KIND_TYPE_TAG:
         return visit(&t->type, ctx);
 
     case BTF_KIND_ARRAY: {
         struct btf_array *a = btf_array(t);
 
         err = visit(&a->type, ctx);
         err = err ?: visit(&a->index_type, ctx);
         return err;
     }
 
     case BTF_KIND_STRUCT:
     case BTF_KIND_UNION: {
         struct btf_member *m = btf_members(t);
 
         for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
             err = visit(&m->type, ctx);
             if (err)
                 return err;
         }
         return 0;
     }
 
     case BTF_KIND_FUNC_PROTO: {
         struct btf_param *m = btf_params(t);
 
         err = visit(&t->type, ctx);
         if (err)
             return err;
         for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
             err = visit(&m->type, ctx);
             if (err)
                 return err;
         }
         return 0;
     }
 
     case BTF_KIND_DATASEC: {
         struct btf_var_secinfo *m = btf_var_secinfos(t);
 
         for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
             err = visit(&m->type, ctx);
             if (err)
                 return err;
         }
         return 0;
     }
 
     default:
         return -EINVAL;
     }
 }
 
 int btf_type_visit_str_offs(struct btf_type *t, str_off_visit_fn visit, void *ctx)
 {
     int i, n, err;
 
     err = visit(&t->name_off, ctx);
     if (err)
         return err;
 
     switch (btf_kind(t)) {
     case BTF_KIND_STRUCT:
     case BTF_KIND_UNION: {
         struct btf_member *m = btf_members(t);
 
         for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
             err = visit(&m->name_off, ctx);
             if (err)
                 return err;
         }
         break;
     }
     case BTF_KIND_ENUM: {
         struct btf_enum *m = btf_enum(t);
 
         for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
             err = visit(&m->name_off, ctx);
             if (err)
                 return err;
         }
         break;
     }
     case BTF_KIND_ENUM64: {
         struct btf_enum64 *m = btf_enum64(t);
 
         for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
             err = visit(&m->name_off, ctx);
             if (err)
                 return err;
         }
         break;
     }
     case BTF_KIND_FUNC_PROTO: {
         struct btf_param *m = btf_params(t);
 
         for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
             err = visit(&m->name_off, ctx);
             if (err)
                 return err;
         }
         break;
     }
     default:
         break;
     }
 
     return 0;
 }
 
 int btf_ext_visit_type_ids(struct btf_ext *btf_ext, type_id_visit_fn visit, void *ctx)
 {
     const struct btf_ext_info *seg;
     struct btf_ext_info_sec *sec;
     int i, err;
 
     seg = &btf_ext->func_info;
     for_each_btf_ext_sec(seg, sec) {
         struct bpf_func_info_min *rec;
 
         for_each_btf_ext_rec(seg, sec, i, rec) {
             err = visit(&rec->type_id, ctx);
             if (err < 0)
                 return err;
         }
     }
 
     seg = &btf_ext->core_relo_info;
     for_each_btf_ext_sec(seg, sec) {
         struct bpf_core_relo *rec;
 
         for_each_btf_ext_rec(seg, sec, i, rec) {
             err = visit(&rec->type_id, ctx);
             if (err < 0)
                 return err;
         }
     }
 
     return 0;
 }
 
 int btf_ext_visit_str_offs(struct btf_ext *btf_ext, str_off_visit_fn visit, void *ctx)
 {
     const struct btf_ext_info *seg;
     struct btf_ext_info_sec *sec;
     int i, err;
 
     seg = &btf_ext->func_info;
     for_each_btf_ext_sec(seg, sec) {
         err = visit(&sec->sec_name_off, ctx);
         if (err)
             return err;
     }
 
     seg = &btf_ext->line_info;
     for_each_btf_ext_sec(seg, sec) {
         struct bpf_line_info_min *rec;
 
         err = visit(&sec->sec_name_off, ctx);
         if (err)
             return err;
 
         for_each_btf_ext_rec(seg, sec, i, rec) {
             err = visit(&rec->file_name_off, ctx);
             if (err)
                 return err;
             err = visit(&rec->line_off, ctx);
             if (err)
                 return err;
         }
     }
 
     seg = &btf_ext->core_relo_info;
     for_each_btf_ext_sec(seg, sec) {
         struct bpf_core_relo *rec;
 
         err = visit(&sec->sec_name_off, ctx);
         if (err)
             return err;
 
         for_each_btf_ext_rec(seg, sec, i, rec) {
             err = visit(&rec->access_str_off, ctx);
             if (err)
                 return err;
         }
     }
 
     return 0;
 }