text: // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
  /* Copyright (c) 2018 Facebook */
  
  #include <endian.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <fcntl.h>
  #include <unistd.h>
  #include <errno.h>
  #include <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"
  
  #define BTF_MAX_NR_TYPES 0x7fffffffU
  #define BTF_MAX_STR_OFFSET 0x7fffffffU
  
  static struct btf_type btf_void;
  
  struct btf {
  	union {
  		struct btf_header *hdr;
  		void *data;
  	};
  	struct btf_type **types;
  	const char *strings;
  	void *nohdr_data;
  	__u32 nr_types;
  	__u32 types_size;
  	__u32 data_size;
  	int fd;
  	int ptr_sz;
  };
  
  static inline __u64 ptr_to_u64(const void *ptr)
  {
  	return (__u64) (unsigned long) ptr;
  }
  
  static int btf_add_type(struct btf *btf, struct btf_type *t)
  {
  	if (btf->types_size - btf->nr_types < 2) {
  		struct btf_type **new_types;
  		__u32 expand_by, new_size;
  
  		if (btf->types_size == BTF_MAX_NR_TYPES)
  			return -E2BIG;
  
  		expand_by = max(btf->types_size >> 2, 16U);
  		new_size = min(BTF_MAX_NR_TYPES, btf->types_size + expand_by);
  
  		new_types = libbpf_reallocarray(btf->types, new_size, sizeof(*new_types));
  		if (!new_types)
  			return -ENOMEM;
  
  		if (btf->nr_types == 0)
  			new_types[0] = &btf_void;
  
  		btf->types = new_types;
  		btf->types_size = new_size;
  	}
  
  	btf->types[++(btf->nr_types)] = t;
  
  	return 0;
  }
  
  static int btf_parse_hdr(struct btf *btf)
  {
  	const struct btf_header *hdr = btf->hdr;
  	__u32 meta_left;
  
  	if (btf->data_size < sizeof(struct btf_header)) {
  		pr_debug("BTF header not found\n");
  		return -EINVAL;
  	}
  
  	if (hdr->magic != BTF_MAGIC) {
  		pr_debug("Invalid BTF magic:%x\n", hdr->magic);
  		return -EINVAL;
  	}
  
  	if (hdr->version != BTF_VERSION) {
  		pr_debug("Unsupported BTF version:%u\n", hdr->version);
  		return -ENOTSUP;
  	}
  
  	if (hdr->flags) {
  		pr_debug("Unsupported BTF flags:%x\n", hdr->flags);
  		return -ENOTSUP;
  	}
  
  	meta_left = btf->data_size - sizeof(*hdr);
  	if (!meta_left) {
  		pr_debug("BTF has no data\n");
  		return -EINVAL;
  	}
  
  	if (meta_left < hdr->type_off) {
  		pr_debug("Invalid BTF type section offset:%u\n", hdr->type_off);
  		return -EINVAL;
  	}
  
  	if (meta_left < hdr->str_off) {
  		pr_debug("Invalid BTF string section offset:%u\n", hdr->str_off);
  		return -EINVAL;
  	}
  
  	if (hdr->type_off >= hdr->str_off) {
  		pr_debug("BTF type section offset >= string section offset. No type?\n");
  		return -EINVAL;
  	}
  
  	if (hdr->type_off & 0x02) {
  		pr_debug("BTF type section is not aligned to 4 bytes\n");
  		return -EINVAL;
  	}
  
  	btf->nohdr_data = btf->hdr + 1;
  
  	return 0;
  }
  
  static int btf_parse_str_sec(struct btf *btf)
  {
  	const struct btf_header *hdr = btf->hdr;
  	const char *start = btf->nohdr_data + hdr->str_off;
  	const char *end = start + btf->hdr->str_len;
  
  	if (!hdr->str_len || hdr->str_len - 1 > BTF_MAX_STR_OFFSET ||
  	    start[0] || end[-1]) {
  		pr_debug("Invalid BTF string section\n");
  		return -EINVAL;
  	}
  
  	btf->strings = start;
  
  	return 0;
  }
  
  static int btf_type_size(struct btf_type *t)
  {
  	int base_size = sizeof(struct btf_type);
  	__u16 vlen = btf_vlen(t);
  
  	switch (btf_kind(t)) {
  	case BTF_KIND_FWD:
  	case BTF_KIND_CONST:
  	case BTF_KIND_VOLATILE:
  	case BTF_KIND_RESTRICT:
  	case BTF_KIND_PTR:
  	case BTF_KIND_TYPEDEF:
  	case BTF_KIND_FUNC:
  		return base_size;
  	case BTF_KIND_INT:
  		return base_size + sizeof(__u32);
  	case BTF_KIND_ENUM:
  		return base_size + vlen * sizeof(struct btf_enum);
  	case BTF_KIND_ARRAY:
  		return base_size + sizeof(struct btf_array);
  	case BTF_KIND_STRUCT:
  	case BTF_KIND_UNION:
  		return base_size + vlen * sizeof(struct btf_member);
  	case BTF_KIND_FUNC_PROTO:
  		return base_size + vlen * sizeof(struct btf_param);
  	case BTF_KIND_VAR:
  		return base_size + sizeof(struct btf_var);
  	case BTF_KIND_DATASEC:
  		return base_size + vlen * sizeof(struct btf_var_secinfo);
  	default:
  		pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
  		return -EINVAL;
  	}
  }
  
  static int btf_parse_type_sec(struct btf *btf)
  {
  	struct btf_header *hdr = btf->hdr;
  	void *nohdr_data = btf->nohdr_data;
  	void *next_type = nohdr_data + hdr->type_off;
  	void *end_type = nohdr_data + hdr->str_off;
  
  	while (next_type < end_type) {
  		struct btf_type *t = next_type;
  		int type_size;
  		int err;
  
  		type_size = btf_type_size(t);
  		if (type_size < 0)
  			return type_size;
  		next_type += type_size;
  		err = btf_add_type(btf, t);
  		if (err)
  			return err;
  	}
  
  	return 0;
  }
  
  __u32 btf__get_nr_types(const struct btf *btf)
  {
  	return btf->nr_types;
  }
  
  const struct btf_type *btf__type_by_id(const struct btf *btf, __u32 type_id)
  {
  	if (type_id > btf->nr_types)
  		return NULL;
  
  	return btf->types[type_id];
  }
  
  static int determine_ptr_size(const struct btf *btf)
  {
  	const struct btf_type *t;
  	const char *name;
  	int i;
  
  	for (i = 1; i <= btf->nr_types; i++) {
  		t = btf__type_by_id(btf, i);
  		if (!btf_is_int(t))
  			continue;
  
  		name = btf__name_by_offset(btf, t->name_off);
  		if (!name)
  			continue;
  
  		if (strcmp(name, "long int") == 0 ||
  		    strcmp(name, "long unsigned int") == 0) {
  			if (t->size != 4 && t->size != 8)
  				continue;
  			return t->size;
  		}
  	}
  
  	return -1;
  }
  
  static size_t btf_ptr_sz(const struct btf *btf)
  {
  	if (!btf->ptr_sz)
  		((struct btf *)btf)->ptr_sz = determine_ptr_size(btf);
  	return btf->ptr_sz < 0 ? sizeof(void *) : btf->ptr_sz;
  }
  
  /* Return pointer size this BTF instance assumes. The size is heuristically
   * determined by looking for 'long' or 'unsigned long' integer type and
   * recording its size in bytes. If BTF type information doesn't have any such
   * type, this function returns 0. In the latter case, native architecture's
   * pointer size is assumed, so will be either 4 or 8, depending on
   * architecture that libbpf was compiled for. It's possible to override
   * guessed value by using btf__set_pointer_size() API.
   */
  size_t btf__pointer_size(const struct btf *btf)
  {
  	if (!btf->ptr_sz)
  		((struct btf *)btf)->ptr_sz = determine_ptr_size(btf);
  
  	if (btf->ptr_sz < 0)
  		/* not enough BTF type info to guess */
  		return 0;
  
  	return btf->ptr_sz;
  }
  
  /* Override or set pointer size in bytes. Only values of 4 and 8 are
   * supported.
   */
  int btf__set_pointer_size(struct btf *btf, size_t ptr_sz)
  {
  	if (ptr_sz != 4 && ptr_sz != 8)
  		return -EINVAL;
  	btf->ptr_sz = ptr_sz;
  	return 0;
  }
  
  static bool btf_type_is_void(const struct btf_type *t)
  {
  	return t == &btf_void || btf_is_fwd(t);
  }
  
  static bool btf_type_is_void_or_null(const struct btf_type *t)
  {
  	return !t || btf_type_is_void(t);
  }
  
  #define MAX_RESOLVE_DEPTH 32
  
  __s64 btf__resolve_size(const struct btf *btf, __u32 type_id)
  {
  	const struct btf_array *array;
  	const struct btf_type *t;
  	__u32 nelems = 1;
  	__s64 size = -1;
  	int i;
  
  	t = btf__type_by_id(btf, type_id);
  	for (i = 0; i < MAX_RESOLVE_DEPTH && !btf_type_is_void_or_null(t);
  	     i++) {
  		switch (btf_kind(t)) {
  		case BTF_KIND_INT:
  		case BTF_KIND_STRUCT:
  		case BTF_KIND_UNION:
  		case BTF_KIND_ENUM:
  		case BTF_KIND_DATASEC:
  			size = t->size;
  			goto done;
  		case BTF_KIND_PTR:
  			size = btf_ptr_sz(btf);
  			goto done;
  		case BTF_KIND_TYPEDEF:
  		case BTF_KIND_VOLATILE:
  		case BTF_KIND_CONST:
  		case BTF_KIND_RESTRICT:
  		case BTF_KIND_VAR:
  			type_id = t->type;
  			break;
  		case BTF_KIND_ARRAY:
  			array = btf_array(t);
  			if (nelems && array->nelems > UINT32_MAX / nelems)
  				return -E2BIG;
  			nelems *= array->nelems;
  			type_id = array->type;
  			break;
  		default:
  			return -EINVAL;
  		}
  
  		t = btf__type_by_id(btf, type_id);
  	}
  
  done:
  	if (size < 0)
  		return -EINVAL;
  	if (nelems && size > UINT32_MAX / nelems)
  		return -E2BIG;
  
  	return nelems * size;
  }
  
  int btf__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:
  		return min(btf_ptr_sz(btf), (size_t)t->size);
  	case BTF_KIND_PTR:
  		return btf_ptr_sz(btf);
  	case BTF_KIND_TYPEDEF:
  	case BTF_KIND_VOLATILE:
  	case BTF_KIND_CONST:
  	case BTF_KIND_RESTRICT:
  		return btf__align_of(btf, t->type);
  	case BTF_KIND_ARRAY:
  		return btf__align_of(btf, btf_array(t)->type);
  	case BTF_KIND_STRUCT:
  	case BTF_KIND_UNION: {
  		const struct btf_member *m = btf_members(t);
  		__u16 vlen = btf_vlen(t);
  		int i, max_align = 1, align;
  
  		for (i = 0; i < vlen; i++, m++) {
  			align = btf__align_of(btf, m->type);
  			if (align <= 0)
  				return align;
  			max_align = max(max_align, align);
  		}
  
  		return max_align;
  	}
  	default:
  		pr_warn("unsupported BTF_KIND:%u\n", btf_kind(t));
  		return 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 -EINVAL;
  
  	return type_id;
  }
  
  __s32 btf__find_by_name(const struct btf *btf, const char *type_name)
  {
  	__u32 i;
  
  	if (!strcmp(type_name, "void"))
  		return 0;
  
  	for (i = 1; i <= btf->nr_types; i++) {
  		const struct btf_type *t = btf->types[i];
  		const char *name = btf__name_by_offset(btf, t->name_off);
  
  		if (name && !strcmp(type_name, name))
  			return i;
  	}
  
  	return -ENOENT;
  }
  
  __s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
  			     __u32 kind)
  {
  	__u32 i;
  
  	if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
  		return 0;
  
  	for (i = 1; i <= btf->nr_types; i++) {
  		const struct btf_type *t = btf->types[i];
  		const char *name;
  
  		if (btf_kind(t) != kind)
  			continue;
  		name = btf__name_by_offset(btf, t->name_off);
  		if (name && !strcmp(type_name, name))
  			return i;
  	}
  
  	return -ENOENT;
  }
  
  void btf__free(struct btf *btf)
  {
  	if (IS_ERR_OR_NULL(btf))
  		return;
  
  	if (btf->fd >= 0)
  		close(btf->fd);
  
  	free(btf->data);
  	free(btf->types);
  	free(btf);
  }
  
  struct btf *btf__new(const void *data, __u32 size)
  {
  	struct btf *btf;
  	int err;
  
  	btf = calloc(1, sizeof(struct btf));
  	if (!btf)
  		return ERR_PTR(-ENOMEM);
  
  	btf->fd = -1;
  
  	btf->data = malloc(size);
  	if (!btf->data) {
  		err = -ENOMEM;
  		goto done;
  	}
  
  	memcpy(btf->data, data, size);
  	btf->data_size = size;
  
  	err = btf_parse_hdr(btf);
  	if (err)
  		goto done;
  
  	err = btf_parse_str_sec(btf);
  	if (err)
  		goto done;
  
  	err = btf_parse_type_sec(btf);
  
  done:
  	if (err) {
  		btf__free(btf);
  		return ERR_PTR(err);
  	}
  
  	return btf;
  }
  
  static bool btf_check_endianness(const GElf_Ehdr *ehdr)
  {
  #if __BYTE_ORDER == __LITTLE_ENDIAN
  	return ehdr->e_ident[EI_DATA] == ELFDATA2LSB;
  #elif __BYTE_ORDER == __BIG_ENDIAN
  	return ehdr->e_ident[EI_DATA] == ELFDATA2MSB;
  #else
  # error "Unrecognized __BYTE_ORDER__"
  #endif
  }
  
  struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)
  {
  	Elf_Data *btf_data = NULL, *btf_ext_data = NULL;
  	int err = 0, fd = -1, idx = 0;
  	struct btf *btf = NULL;
  	Elf_Scn *scn = NULL;
  	Elf *elf = NULL;
  	GElf_Ehdr ehdr;
  
  	if (elf_version(EV_CURRENT) == EV_NONE) {
  		pr_warn("failed to init libelf for %s\n", path);
  		return ERR_PTR(-LIBBPF_ERRNO__LIBELF);
  	}
  
  	fd = open(path, O_RDONLY);
  	if (fd < 0) {
  		err = -errno;
  		pr_warn("failed to open %s: %s\n", path, strerror(errno));
  		return ERR_PTR(err);
  	}
  
  	err = -LIBBPF_ERRNO__FORMAT;
  
  	elf = elf_begin(fd, ELF_C_READ, NULL);
  	if (!elf) {
  		pr_warn("failed to open %s as ELF file\n", path);
  		goto done;
  	}
  	if (!gelf_getehdr(elf, &ehdr)) {
  		pr_warn("failed to get EHDR from %s\n", path);
  		goto done;
  	}
  	if (!btf_check_endianness(&ehdr)) {
  		pr_warn("non-native ELF endianness is not supported\n");
  		goto done;
  	}
  	if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) {
  		pr_warn("failed to get e_shstrndx from %s\n", path);
  		goto done;
  	}
  
  	while ((scn = elf_nextscn(elf, scn)) != NULL) {
  		GElf_Shdr sh;
  		char *name;
  
  		idx++;
  		if (gelf_getshdr(scn, &sh) != &sh) {
  			pr_warn("failed to get section(%d) header from %s\n",
  				idx, path);
  			goto done;
  		}
  		name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name);
  		if (!name) {
  			pr_warn("failed to get section(%d) name from %s\n",
  				idx, path);
  			goto done;
  		}
  		if (strcmp(name, BTF_ELF_SEC) == 0) {
  			btf_data = elf_getdata(scn, 0);
  			if (!btf_data) {
  				pr_warn("failed to get section(%d, %s) data from %s\n",
  					idx, name, path);
  				goto done;
  			}
  			continue;
  		} else if (btf_ext && strcmp(name, BTF_EXT_ELF_SEC) == 0) {
  			btf_ext_data = elf_getdata(scn, 0);
  			if (!btf_ext_data) {
  				pr_warn("failed to get section(%d, %s) data from %s\n",
  					idx, name, path);
  				goto done;
  			}
  			continue;
  		}
  	}
  
  	err = 0;
  
  	if (!btf_data) {
  		err = -ENOENT;
  		goto done;
  	}
  	btf = btf__new(btf_data->d_buf, btf_data->d_size);
  	if (IS_ERR(btf))
  		goto done;
  
  	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);
  		if (IS_ERR(*btf_ext))
  			goto done;
  	} else if (btf_ext) {
  		*btf_ext = NULL;
  	}
  done:
  	if (elf)
  		elf_end(elf);
  	close(fd);
  
  	if (err)
  		return ERR_PTR(err);
  	/*
  	 * btf is always parsed before btf_ext, so no need to clean up
  	 * btf_ext, if btf loading failed
  	 */
  	if (IS_ERR(btf))
  		return btf;
  	if (btf_ext && IS_ERR(*btf_ext)) {
  		btf__free(btf);
  		err = PTR_ERR(*btf_ext);
  		return ERR_PTR(err);
  	}
  	return btf;
  }
  
  struct btf *btf__parse_raw(const char *path)
  {
  	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 == __bswap_16(BTF_MAGIC)) {
  		/* non-native endian raw BTF */
  		pr_warn("non-native BTF endianness is not supported\n");
  		err = -LIBBPF_ERRNO__ENDIAN;
  		goto err_out;
  	}
  	if (magic != 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);
  
  err_out:
  	free(data);
  	if (f)
  		fclose(f);
  	return err ? ERR_PTR(err) : btf;
  }
  
  struct btf *btf__parse(const char *path, struct btf_ext **btf_ext)
  {
  	struct btf *btf;
  
  	if (btf_ext)
  		*btf_ext = NULL;
  
  	btf = btf__parse_raw(path);
  	if (!IS_ERR(btf) || PTR_ERR(btf) != -EPROTO)
  		return btf;
  
  	return btf__parse_elf(path, btf_ext);
  }
  
  static int compare_vsi_off(const void *_a, const void *_b)
  {
  	const struct btf_var_secinfo *a = _a;
  	const struct btf_var_secinfo *b = _b;
  
  	return a->offset - b->offset;
  }
  
  static int btf_fixup_datasec(struct bpf_object *obj, struct btf *btf,
  			     struct btf_type *t)
  {
  	__u32 size = 0, off = 0, i, vars = btf_vlen(t);
  	const char *name = btf__name_by_offset(btf, t->name_off);
  	const struct btf_type *t_var;
  	struct btf_var_secinfo *vsi;
  	const struct btf_var *var;
  	int ret;
  
  	if (!name) {
  		pr_debug("No name found in string section for DATASEC kind.\n");
  		return -ENOENT;
  	}
  
  	/* .extern datasec size and var offsets were set correctly during
  	 * extern collection step, so just skip straight to sorting variables
  	 */
  	if (t->size)
  		goto sort_vars;
  
  	ret = bpf_object__section_size(obj, name, &size);
  	if (ret || !size || (t->size && t->size != size)) {
  		pr_debug("Invalid size for section %s: %u bytes\n", name, size);
  		return -ENOENT;
  	}
  
  	t->size = size;
  
  	for (i = 0, vsi = btf_var_secinfos(t); i < vars; i++, vsi++) {
  		t_var = btf__type_by_id(btf, vsi->type);
  		var = btf_var(t_var);
  
  		if (!btf_is_var(t_var)) {
  			pr_debug("Non-VAR type seen in section %s\n", name);
  			return -EINVAL;
  		}
  
  		if (var->linkage == BTF_VAR_STATIC)
  			continue;
  
  		name = btf__name_by_offset(btf, t_var->name_off);
  		if (!name) {
  			pr_debug("No name found in string section for VAR kind\n");
  			return -ENOENT;
  		}
  
  		ret = bpf_object__variable_offset(obj, name, &off);
  		if (ret) {
  			pr_debug("No offset found in symbol table for VAR %s\n",
  				 name);
  			return -ENOENT;
  		}
  
  		vsi->offset = off;
  	}
  
  sort_vars:
  	qsort(btf_var_secinfos(t), vars, sizeof(*vsi), compare_vsi_off);
  	return 0;
  }
  
  int btf__finalize_data(struct bpf_object *obj, struct btf *btf)
  {
  	int err = 0;
  	__u32 i;
  
  	for (i = 1; i <= btf->nr_types; i++) {
  		struct btf_type *t = btf->types[i];
  
  		/* Loader needs to fix up some of the things compiler
  		 * couldn't get its hands on while emitting BTF. This
  		 * is section size and global variable offset. We use
  		 * the info from the ELF itself for this purpose.
  		 */
  		if (btf_is_datasec(t)) {
  			err = btf_fixup_datasec(obj, btf, t);
  			if (err)
  				break;
  		}
  	}
  
  	return err;
  }
  
  int btf__load(struct btf *btf)
  {
  	__u32 log_buf_size = 0;
  	char *log_buf = NULL;
  	int err = 0;
  
  	if (btf->fd >= 0)
  		return -EEXIST;
  
  retry_load:
  	if (log_buf_size) {
  		log_buf = malloc(log_buf_size);
  		if (!log_buf)
  			return -ENOMEM;
  
  		*log_buf = 0;
  	}
  
  	btf->fd = bpf_load_btf(btf->data, btf->data_size,
  			       log_buf, log_buf_size, false);
  	if (btf->fd < 0) {
  		if (!log_buf || errno == ENOSPC) {
  			log_buf_size = max((__u32)BPF_LOG_BUF_SIZE,
  					   log_buf_size << 1);
  			free(log_buf);
  			goto retry_load;
  		}
  
  		err = -errno;
  		pr_warn("Error loading BTF: %s(%d)\n", strerror(errno), errno);
  		if (*log_buf)
  			pr_warn("%s\n", log_buf);
  		goto done;
  	}
  
  done:
  	free(log_buf);
  	return err;
  }
  
  int btf__fd(const struct btf *btf)
  {
  	return btf->fd;
  }
  
  void btf__set_fd(struct btf *btf, int fd)
  {
  	btf->fd = fd;
  }
  
  const void *btf__get_raw_data(const struct btf *btf, __u32 *size)
  {
  	*size = btf->data_size;
  	return btf->data;
  }
  
  const char *btf__name_by_offset(const struct btf *btf, __u32 offset)
  {
  	if (offset < btf->hdr->str_len)
  		return &btf->strings[offset];
  	else
  		return NULL;
  }
  
  int btf__get_from_id(__u32 id, struct btf **btf)
  {
  	struct bpf_btf_info btf_info = { 0 };
  	__u32 len = sizeof(btf_info);
  	__u32 last_size;
  	int btf_fd;
  	void *ptr;
  	int err;
  
  	err = 0;
  	*btf = NULL;
  	btf_fd = bpf_btf_get_fd_by_id(id);
  	if (btf_fd < 0)
  		return 0;
  
  	/* we won't know btf_size until we call bpf_obj_get_info_by_fd(). so
  	 * let's start with a sane default - 4KiB here - and resize it only if
  	 * bpf_obj_get_info_by_fd() needs a bigger buffer.
  	 */
  	btf_info.btf_size = 4096;
  	last_size = btf_info.btf_size;
  	ptr = malloc(last_size);
  	if (!ptr) {
  		err = -ENOMEM;
  		goto exit_free;
  	}
  
  	memset(ptr, 0, last_size);
  	btf_info.btf = ptr_to_u64(ptr);
  	err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
  
  	if (!err && btf_info.btf_size > last_size) {
  		void *temp_ptr;
  
  		last_size = btf_info.btf_size;
  		temp_ptr = realloc(ptr, last_size);
  		if (!temp_ptr) {
  			err = -ENOMEM;
  			goto exit_free;
  		}
  		ptr = temp_ptr;
  		memset(ptr, 0, last_size);
  		btf_info.btf = ptr_to_u64(ptr);
  		err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
  	}
  
  	if (err || btf_info.btf_size > last_size) {
  		err = errno;
  		goto exit_free;
  	}
  
  	*btf = btf__new((__u8 *)(long)btf_info.btf, btf_info.btf_size);
  	if (IS_ERR(*btf)) {
  		err = PTR_ERR(*btf);
  		*btf = NULL;
  	}
  
  exit_free:
  	close(btf_fd);
  	free(ptr);
  
  	return err;
  }
  
  int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
  			 __u32 expected_key_size, __u32 expected_value_size,
  			 __u32 *key_type_id, __u32 *value_type_id)
  {
  	const struct btf_type *container_type;
  	const struct btf_member *key, *value;
  	const size_t max_name = 256;
  	char container_name[max_name];
  	__s64 key_size, value_size;
  	__s32 container_id;
  
  	if (snprintf(container_name, max_name, "____btf_map_%s", map_name) ==
  	    max_name) {
  		pr_warn("map:%s length of '____btf_map_%s' is too long\n",
  			map_name, map_name);
  		return -EINVAL;
  	}
  
  	container_id = btf__find_by_name(btf, container_name);
  	if (container_id < 0) {
  		pr_debug("map:%s container_name:%s cannot be found in BTF. Missing BPF_ANNOTATE_KV_PAIR?\n",
  			 map_name, container_name);
  		return container_id;
  	}
  
  	container_type = btf__type_by_id(btf, container_id);
  	if (!container_type) {
  		pr_warn("map:%s cannot find BTF type for container_id:%u\n",
  			map_name, container_id);
  		return -EINVAL;
  	}
  
  	if (!btf_is_struct(container_type) || btf_vlen(container_type) < 2) {
  		pr_warn("map:%s container_name:%s is an invalid container struct\n",
  			map_name, container_name);
  		return -EINVAL;
  	}
  
  	key = btf_members(container_type);
  	value = key + 1;
  
  	key_size = btf__resolve_size(btf, key->type);
  	if (key_size < 0) {
  		pr_warn("map:%s invalid BTF key_type_size\n", map_name);
  		return key_size;
  	}
  
  	if (expected_key_size != key_size) {
  		pr_warn("map:%s btf_key_type_size:%u != map_def_key_size:%u\n",
  			map_name, (__u32)key_size, expected_key_size);
  		return -EINVAL;
  	}
  
  	value_size = btf__resolve_size(btf, value->type);
  	if (value_size < 0) {
  		pr_warn("map:%s invalid BTF value_type_size\n", map_name);
  		return value_size;
  	}
  
  	if (expected_value_size != value_size) {
  		pr_warn("map:%s btf_value_type_size:%u != map_def_value_size:%u\n",
  			map_name, (__u32)value_size, expected_value_size);
  		return -EINVAL;
  	}
  
  	*key_type_id = key->type;
  	*value_type_id = value->type;
  
  	return 0;
  }
  
  struct btf_ext_sec_setup_param {
  	__u32 off;
  	__u32 len;
  	__u32 min_rec_size;
  	struct btf_ext_info *ext_info;
  	const char *desc;
  };
  
  static int btf_ext_setup_info(struct btf_ext *btf_ext,
  			      struct btf_ext_sec_setup_param *ext_sec)
  {
  	const struct btf_ext_info_sec *sinfo;
  	struct btf_ext_info *ext_info;
  	__u32 info_left, record_size;
  	/* The start of the info sec (including the __u32 record_size). */
  	void *info;
  
  	if (ext_sec->len == 0)
  		return 0;
  
  	if (ext_sec->off & 0x03) {
  		pr_debug(".BTF.ext %s section is not aligned to 4 bytes\n",
  		     ext_sec->desc);
  		return -EINVAL;
  	}
  
  	info = btf_ext->data + btf_ext->hdr->hdr_len + ext_sec->off;
  	info_left = ext_sec->len;
  
  	if (btf_ext->data + btf_ext->data_size < info + ext_sec->len) {
  		pr_debug("%s section (off:%u len:%u) is beyond the end of the ELF section .BTF.ext\n",
  			 ext_sec->desc, ext_sec->off, ext_sec->len);
  		return -EINVAL;
  	}
  
  	/* At least a record size */
  	if (info_left < sizeof(__u32)) {
  		pr_debug(".BTF.ext %s record size not found\n", ext_sec->desc);
  		return -EINVAL;
  	}
  
  	/* The record size needs to meet the minimum standard */
  	record_size = *(__u32 *)info;
  	if (record_size < ext_sec->min_rec_size ||
  	    record_size & 0x03) {
  		pr_debug("%s section in .BTF.ext has invalid record size %u\n",
  			 ext_sec->desc, record_size);
  		return -EINVAL;
  	}
  
  	sinfo = info + sizeof(__u32);
  	info_left -= sizeof(__u32);
  
  	/* If no records, return failure now so .BTF.ext won't be used. */
  	if (!info_left) {
  		pr_debug("%s section in .BTF.ext has no records", ext_sec->desc);
  		return -EINVAL;
  	}
  
  	while (info_left) {
  		unsigned int sec_hdrlen = sizeof(struct btf_ext_info_sec);
  		__u64 total_record_size;
  		__u32 num_records;
  
  		if (info_left < sec_hdrlen) {
  			pr_debug("%s section header is not found in .BTF.ext\n",
  			     ext_sec->desc);
  			return -EINVAL;
  		}
  
  		num_records = sinfo->num_info;
  		if (num_records == 0) {
  			pr_debug("%s section has incorrect num_records in .BTF.ext\n",
  			     ext_sec->desc);
  			return -EINVAL;
  		}
  
  		total_record_size = sec_hdrlen +
  				    (__u64)num_records * record_size;
  		if (info_left < total_record_size) {
  			pr_debug("%s section has incorrect num_records in .BTF.ext\n",
  			     ext_sec->desc);
  			return -EINVAL;
  		}
  
  		info_left -= total_record_size;
  		sinfo = (void *)sinfo + total_record_size;
  	}
  
  	ext_info = ext_sec->ext_info;
  	ext_info->len = ext_sec->len - sizeof(__u32);
  	ext_info->rec_size = record_size;
  	ext_info->info = info + sizeof(__u32);
  
  	return 0;
  }
  
  static int btf_ext_setup_func_info(struct btf_ext *btf_ext)
  {
  	struct btf_ext_sec_setup_param param = {
  		.off = btf_ext->hdr->func_info_off,
  		.len = btf_ext->hdr->func_info_len,
  		.min_rec_size = sizeof(struct bpf_func_info_min),
  		.ext_info = &btf_ext->func_info,
  		.desc = "func_info"
  	};
  
  	return btf_ext_setup_info(btf_ext, &param);
  }
  
  static int btf_ext_setup_line_info(struct btf_ext *btf_ext)
  {
  	struct btf_ext_sec_setup_param param = {
  		.off = btf_ext->hdr->line_info_off,
  		.len = btf_ext->hdr->line_info_len,
  		.min_rec_size = sizeof(struct bpf_line_info_min),
  		.ext_info = &btf_ext->line_info,
  		.desc = "line_info",
  	};
  
  	return btf_ext_setup_info(btf_ext, &param);
  }
  
  static int btf_ext_setup_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 != BTF_MAGIC) {
  		pr_debug("Invalid BTF.ext magic:%x\n", hdr->magic);
  		return -EINVAL;
  	}
  
  	if (hdr->version != BTF_VERSION) {
  		pr_debug("Unsupported BTF.ext version:%u\n", hdr->version);
  		return -ENOTSUP;
  	}
  
  	if (hdr->flags) {
  		pr_debug("Unsupported BTF.ext flags:%x\n", hdr->flags);
  		return -ENOTSUP;
  	}
  
  	if (data_size == hdr->hdr_len) {
  		pr_debug("BTF.ext has no data\n");
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  void btf_ext__free(struct btf_ext *btf_ext)
  {
  	if (IS_ERR_OR_NULL(btf_ext))
  		return;
  	free(btf_ext->data);
  	free(btf_ext);
  }
  
  struct btf_ext *btf_ext__new(__u8 *data, __u32 size)
  {
  	struct btf_ext *btf_ext;
  	int err;
  
  	err = btf_ext_parse_hdr(data, size);
  	if (err)
  		return ERR_PTR(err);
  
  	btf_ext = calloc(1, sizeof(struct btf_ext));
  	if (!btf_ext)
  		return ERR_PTR(-ENOMEM);
  
  	btf_ext->data_size = size;
  	btf_ext->data = malloc(size);
  	if (!btf_ext->data) {
  		err = -ENOMEM;
  		goto done;
  	}
  	memcpy(btf_ext->data, data, size);
  
  	if (btf_ext->hdr->hdr_len <
  	    offsetofend(struct btf_ext_header, line_info_len))
  		goto done;
  	err = btf_ext_setup_func_info(btf_ext);
  	if (err)
  		goto done;
  
  	err = btf_ext_setup_line_info(btf_ext);
  	if (err)
  		goto done;
  
  	if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len))
  		goto done;
  	err = btf_ext_setup_core_relos(btf_ext);
  	if (err)
  		goto done;
  
  done:
  	if (err) {
  		btf_ext__free(btf_ext);
  		return ERR_PTR(err);
  	}
  
  	return btf_ext;
  }
  
  const void *btf_ext__get_raw_data(const struct btf_ext *btf_ext, __u32 *size)
  {
  	*size = btf_ext->data_size;
  	return btf_ext->data;
  }
  
  static int btf_ext_reloc_info(const struct btf *btf,
  			      const struct btf_ext_info *ext_info,
  			      const char *sec_name, __u32 insns_cnt,
  			      void **info, __u32 *cnt)
  {
  	__u32 sec_hdrlen = sizeof(struct btf_ext_info_sec);
  	__u32 i, record_size, existing_len, records_len;
  	struct btf_ext_info_sec *sinfo;
  	const char *info_sec_name;
  	__u64 remain_len;
  	void *data;
  
  	record_size = ext_info->rec_size;
  	sinfo = ext_info->info;
  	remain_len = ext_info->len;
  	while (remain_len > 0) {
  		records_len = sinfo->num_info * record_size;
  		info_sec_name = btf__name_by_offset(btf, sinfo->sec_name_off);
  		if (strcmp(info_sec_name, sec_name)) {
  			remain_len -= sec_hdrlen + records_len;
  			sinfo = (void *)sinfo + sec_hdrlen + records_len;
  			continue;
  		}
  
  		existing_len = (*cnt) * record_size;
  		data = realloc(*info, existing_len + records_len);
  		if (!data)
  			return -ENOMEM;
  
  		memcpy(data + existing_len, sinfo->data, records_len);
  		/* adjust insn_off only, the rest data will be passed
  		 * to the kernel.
  		 */
  		for (i = 0; i < sinfo->num_info; i++) {
  			__u32 *insn_off;
  
  			insn_off = data + existing_len + (i * record_size);
  			*insn_off = *insn_off / sizeof(struct bpf_insn) +
  				insns_cnt;
  		}
  		*info = data;
  		*cnt += sinfo->num_info;
  		return 0;
  	}
  
  	return -ENOENT;
  }
  
  int btf_ext__reloc_func_info(const struct btf *btf,
  			     const struct btf_ext *btf_ext,
  			     const char *sec_name, __u32 insns_cnt,
  			     void **func_info, __u32 *cnt)
  {
  	return btf_ext_reloc_info(btf, &btf_ext->func_info, sec_name,
  				  insns_cnt, func_info, cnt);
  }
  
  int btf_ext__reloc_line_info(const struct btf *btf,
  			     const struct btf_ext *btf_ext,
  			     const char *sec_name, __u32 insns_cnt,
  			     void **line_info, __u32 *cnt)
  {
  	return btf_ext_reloc_info(btf, &btf_ext->line_info, sec_name,
  				  insns_cnt, line_info, cnt);
  }
  
  __u32 btf_ext__func_info_rec_size(const struct btf_ext *btf_ext)
  {
  	return btf_ext->func_info.rec_size;
  }
  
  __u32 btf_ext__line_info_rec_size(const struct btf_ext *btf_ext)
  {
  	return btf_ext->line_info.rec_size;
  }
  
  struct btf_dedup;
  
  static struct btf_dedup *btf_dedup_new(struct btf *btf, struct btf_ext *btf_ext,
  				       const struct btf_dedup_opts *opts);
  static void btf_dedup_free(struct btf_dedup *d);
  static int btf_dedup_strings(struct btf_dedup *d);
  static int btf_dedup_prim_types(struct btf_dedup *d);
  static int btf_dedup_struct_types(struct btf_dedup *d);
  static int btf_dedup_ref_types(struct btf_dedup *d);
  static int btf_dedup_compact_types(struct btf_dedup *d);
  static int btf_dedup_remap_types(struct btf_dedup *d);
  
  /*
   * Deduplicate BTF types and strings.
   *
   * BTF dedup algorithm takes as an input `struct btf` representing `.BTF` ELF
   * section with all BTF type descriptors and string data. It overwrites that
   * memory in-place with deduplicated types and strings without any loss of
   * information. If optional `struct btf_ext` representing '.BTF.ext' ELF section
   * is provided, all the strings referenced from .BTF.ext section are honored
   * and updated to point to the right offsets after deduplication.
   *
   * If function returns with error, type/string data might be garbled and should
   * be discarded.
   *
   * More verbose and detailed description of both problem btf_dedup is solving,
   * as well as solution could be found at:
   * https://facebookmicrosites.github.io/bpf/blog/2018/11/14/btf-enhancement.html
   *
   * Problem description and justification
   * =====================================
   *
   * BTF type information is typically emitted either as a result of conversion
   * from DWARF to BTF or directly by compiler. In both cases, each compilation
   * unit contains information about a subset of all the types that are used
   * in an application. These subsets are frequently overlapping and contain a lot
   * of duplicated information when later concatenated together into a single
   * binary. This algorithm ensures that each unique type is represented by single
   * BTF type descriptor, greatly reducing resulting size of BTF data.
   *
   * Compilation unit isolation and subsequent duplication of data is not the only
   * problem. The same type hierarchy (e.g., struct and all the type that struct
   * references) in different compilation units can be represented in BTF to
   * various degrees of completeness (or, rather, incompleteness) due to
   * struct/union forward declarations.
   *
   * Let's take a look at an example, that we'll use to better understand the
   * problem (and solution). Suppose we have two compilation units, each using
   * same `struct S`, but each of them having incomplete type information about
   * struct's fields:
   *
   * // CU #1:
   * struct S;
   * struct A {
   *	int a;
   *	struct A* self;
   *	struct S* parent;
   * };
   * struct B;
   * struct S {
   *	struct A* a_ptr;
   *	struct B* b_ptr;
   * };
   *
   * // CU #2:
   * struct S;
   * struct A;
   * struct B {
   *	int b;
   *	struct B* self;
   *	struct S* parent;
   * };
   * struct S {
   *	struct A* a_ptr;
   *	struct B* b_ptr;
   * };
   *
   * In case of CU #1, BTF data will know only that `struct B` exist (but no
   * more), but will know the complete type information about `struct A`. While
   * for CU #2, it will know full type information about `struct B`, but will
   * only know about forward declaration of `struct A` (in BTF terms, it will
   * have `BTF_KIND_FWD` type descriptor with name `B`).
   *
   * This compilation unit isolation means that it's possible that there is no
   * single CU with complete type information describing structs `S`, `A`, and
   * `B`. Also, we might get tons of duplicated and redundant type information.
   *
   * Additional complication we need to keep in mind comes from the fact that
   * types, in general, can form graphs containing cycles, not just DAGs.
   *
   * While algorithm does deduplication, it also merges and resolves type
   * information (unless disabled throught `struct btf_opts`), whenever possible.
   * E.g., in the example above with two compilation units having partial type
   * information for structs `A` and `B`, the output of algorithm will emit
   * a single copy of each BTF type that describes structs `A`, `B`, and `S`
   * (as well as type information for `int` and pointers), as if they were defined
   * in a single compilation unit as:
   *
   * struct A {
   *	int a;
   *	struct A* self;
   *	struct S* parent;
   * };
   * struct B {
   *	int b;
   *	struct B* self;
   *	struct S* parent;
   * };
   * struct S {
   *	struct A* a_ptr;
   *	struct B* b_ptr;
   * };
   *
   * Algorithm summary
   * =================
   *
   * Algorithm completes its work in 6 separate passes:
   *
   * 1. Strings deduplication.
   * 2. Primitive types deduplication (int, enum, fwd).
   * 3. Struct/union types deduplication.
   * 4. Reference types deduplication (pointers, typedefs, arrays, funcs, func
   *    protos, and const/volatile/restrict modifiers).
   * 5. Types compaction.
   * 6. Types remapping.
   *
   * Algorithm determines canonical type descriptor, which is a single
   * representative type for each truly unique type. This canonical type is the
   * one that will go into final deduplicated BTF type information. For
   * struct/unions, it is also the type that algorithm will merge additional type
   * information into (while resolving FWDs), as it discovers it from data in
   * other CUs. Each input BTF type eventually gets either mapped to itself, if
   * that type is canonical, or to some other type, if that type is equivalent
   * and was chosen as canonical representative. This mapping is stored in
   * `btf_dedup->map` array. This map is also used to record STRUCT/UNION that
   * FWD type got resolved to.
   *
   * To facilitate fast discovery of canonical types, we also maintain canonical
   * index (`btf_dedup->dedup_table`), which maps type descriptor's signature hash
   * (i.e., hashed kind, name, size, fields, etc) into a list of canonical types
   * that match that signature. With sufficiently good choice of type signature
   * hashing function, we can limit number of canonical types for each unique type
   * signature to a very small number, allowing to find canonical type for any
   * duplicated type very quickly.
   *
   * Struct/union deduplication is the most critical part and algorithm for
   * deduplicating structs/unions is described in greater details in comments for
   * `btf_dedup_is_equiv` function.
   */
  int btf__dedup(struct btf *btf, struct btf_ext *btf_ext,
  	       const struct btf_dedup_opts *opts)
  {
  	struct btf_dedup *d = btf_dedup_new(btf, btf_ext, opts);
  	int err;
  
  	if (IS_ERR(d)) {
  		pr_debug("btf_dedup_new failed: %ld", PTR_ERR(d));
  		return -EINVAL;
  	}
  
  	err = btf_dedup_strings(d);
  	if (err < 0) {
  		pr_debug("btf_dedup_strings failed:%d\n", err);
  		goto done;
  	}
  	err = btf_dedup_prim_types(d);
  	if (err < 0) {
  		pr_debug("btf_dedup_prim_types failed:%d\n", err);
  		goto done;
  	}
  	err = btf_dedup_struct_types(d);
  	if (err < 0) {
  		pr_debug("btf_dedup_struct_types failed:%d\n", err);
  		goto done;
  	}
  	err = btf_dedup_ref_types(d);
  	if (err < 0) {
  		pr_debug("btf_dedup_ref_types failed:%d\n", err);
  		goto done;
  	}
  	err = btf_dedup_compact_types(d);
  	if (err < 0) {
  		pr_debug("btf_dedup_compact_types failed:%d\n", err);
  		goto done;
  	}
  	err = btf_dedup_remap_types(d);
  	if (err < 0) {
  		pr_debug("btf_dedup_remap_types failed:%d\n", err);
  		goto done;
  	}
  
  done:
  	btf_dedup_free(d);
  	return err;
  }
  
  #define BTF_UNPROCESSED_ID ((__u32)-1)
  #define BTF_IN_PROGRESS_ID ((__u32)-2)
  
  struct btf_dedup {
  	/* .BTF section to be deduped in-place */
  	struct btf *btf;
  	/*
  	 * Optional .BTF.ext section. When provided, any strings referenced
  	 * from it will be taken into account when deduping strings
  	 */
  	struct btf_ext *btf_ext;
  	/*
  	 * This is a map from any type's signature hash to a list of possible
  	 * canonical representative type candidates. Hash collisions are
  	 * ignored, so even types of various kinds can share same list of
  	 * candidates, which is fine because we rely on subsequent
  	 * btf_xxx_equal() checks to authoritatively verify type equality.
  	 */
  	struct hashmap *dedup_table;
  	/* Canonical types map */
  	__u32 *map;
  	/* Hypothetical mapping, used during type graph equivalence checks */
  	__u32 *hypot_map;
  	__u32 *hypot_list;
  	size_t hypot_cnt;
  	size_t hypot_cap;
  	/* Various option modifying behavior of algorithm */
  	struct btf_dedup_opts opts;
  };
  
  struct btf_str_ptr {
  	const char *str;
  	__u32 new_off;
  	bool used;
  };
  
  struct btf_str_ptrs {
  	struct btf_str_ptr *ptrs;
  	const char *data;
  	__u32 cnt;
  	__u32 cap;
  };
  
  static long hash_combine(long h, long value)
  {
  	return h * 31 + value;
  }
  
  #define for_each_dedup_cand(d, node, hash) \
  	hashmap__for_each_key_entry(d->dedup_table, node, (void *)hash)
  
  static int btf_dedup_table_add(struct btf_dedup *d, long hash, __u32 type_id)
  {
  	return hashmap__append(d->dedup_table,
  			       (void *)hash, (void *)(long)type_id);
  }
  
  static int btf_dedup_hypot_map_add(struct btf_dedup *d,
  				   __u32 from_id, __u32 to_id)
  {
  	if (d->hypot_cnt == d->hypot_cap) {
  		__u32 *new_list;
  
  		d->hypot_cap += max((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;
  }
  
  static void btf_dedup_free(struct btf_dedup *d)
  {
  	hashmap__free(d->dedup_table);
  	d->dedup_table = NULL;
  
  	free(d->map);
  	d->map = NULL;
  
  	free(d->hypot_map);
  	d->hypot_map = NULL;
  
  	free(d->hypot_list);
  	d->hypot_list = NULL;
  
  	free(d);
  }
  
  static size_t btf_dedup_identity_hash_fn(const void *key, void *ctx)
  {
  	return (size_t)key;
  }
  
  static size_t btf_dedup_collision_hash_fn(const void *key, void *ctx)
  {
  	return 0;
  }
  
  static bool btf_dedup_equal_fn(const void *k1, const void *k2, void *ctx)
  {
  	return k1 == k2;
  }
  
  static struct btf_dedup *btf_dedup_new(struct btf *btf, struct btf_ext *btf_ext,
  				       const struct btf_dedup_opts *opts)
  {
  	struct btf_dedup *d = calloc(1, sizeof(struct btf_dedup));
  	hashmap_hash_fn hash_fn = btf_dedup_identity_hash_fn;
  	int i, err = 0;
  
  	if (!d)
  		return ERR_PTR(-ENOMEM);
  
  	d->opts.dont_resolve_fwds = opts && opts->dont_resolve_fwds;
  	/* dedup_table_size is now used only to force collisions in tests */
  	if (opts && opts->dedup_table_size == 1)
  		hash_fn = btf_dedup_collision_hash_fn;
  
  	d->btf = btf;
  	d->btf_ext = btf_ext;
  
  	d->dedup_table = hashmap__new(hash_fn, btf_dedup_equal_fn, NULL);
  	if (IS_ERR(d->dedup_table)) {
  		err = PTR_ERR(d->dedup_table);
  		d->dedup_table = NULL;
  		goto done;
  	}
  
  	d->map = malloc(sizeof(__u32) * (1 + btf->nr_types));
  	if (!d->map) {
  		err = -ENOMEM;
  		goto done;
  	}
  	/* special BTF "void" type is made canonical immediately */
  	d->map[0] = 0;
  	for (i = 1; i <= btf->nr_types; i++) {
  		struct btf_type *t = d->btf->types[i];
  
  		/* VAR and DATASEC are never deduped and are self-canonical */
  		if (btf_is_var(t) || btf_is_datasec(t))
  			d->map[i] = i;
  		else
  			d->map[i] = BTF_UNPROCESSED_ID;
  	}
  
  	d->hypot_map = malloc(sizeof(__u32) * (1 + btf->nr_types));
  	if (!d->hypot_map) {
  		err = -ENOMEM;
  		goto done;
  	}
  	for (i = 0; i <= btf->nr_types; i++)
  		d->hypot_map[i] = BTF_UNPROCESSED_ID;
  
  done:
  	if (err) {
  		btf_dedup_free(d);
  		return ERR_PTR(err);
  	}
  
  	return d;
  }
  
  typedef int (*str_off_fn_t)(__u32 *str_off_ptr, void *ctx);
  
  /*
   * Iterate over all possible places in .BTF and .BTF.ext that can reference
   * string and pass pointer to it to a provided callback `fn`.
   */
  static int btf_for_each_str_off(struct btf_dedup *d, str_off_fn_t fn, void *ctx)
  {
  	void *line_data_cur, *line_data_end;
  	int i, j, r, rec_size;
  	struct btf_type *t;
  
  	for (i = 1; i <= d->btf->nr_types; i++) {
  		t = d->btf->types[i];
  		r = fn(&t->name_off, ctx);
  		if (r)
  			return r;
  
  		switch (btf_kind(t)) {
  		case BTF_KIND_STRUCT:
  		case BTF_KIND_UNION: {
  			struct btf_member *m = btf_members(t);
  			__u16 vlen = btf_vlen(t);
  
  			for (j = 0; j < vlen; j++) {
  				r = fn(&m->name_off, ctx);
  				if (r)
  					return r;
  				m++;
  			}
  			break;
  		}
  		case BTF_KIND_ENUM: {
  			struct btf_enum *m = btf_enum(t);
  			__u16 vlen = btf_vlen(t);
  
  			for (j = 0; j < vlen; j++) {
  				r = fn(&m->name_off, ctx);
  				if (r)
  					return r;
  				m++;
  			}
  			break;
  		}
  		case BTF_KIND_FUNC_PROTO: {
  			struct btf_param *m = btf_params(t);
  			__u16 vlen = btf_vlen(t);
  
  			for (j = 0; j < vlen; j++) {
  				r = fn(&m->name_off, ctx);
  				if (r)
  					return r;
  				m++;
  			}
  			break;
  		}
  		default:
  			break;
  		}
  	}
  
  	if (!d->btf_ext)
  		return 0;
  
  	line_data_cur = d->btf_ext->line_info.info;
  	line_data_end = d->btf_ext->line_info.info + d->btf_ext->line_info.len;
  	rec_size = d->btf_ext->line_info.rec_size;
  
  	while (line_data_cur < line_data_end) {
  		struct btf_ext_info_sec *sec = line_data_cur;
  		struct bpf_line_info_min *line_info;
  		__u32 num_info = sec->num_info;
  
  		r = fn(&sec->sec_name_off, ctx);
  		if (r)
  			return r;
  
  		line_data_cur += sizeof(struct btf_ext_info_sec);
  		for (i = 0; i < num_info; i++) {
  			line_info = line_data_cur;
  			r = fn(&line_info->file_name_off, ctx);
  			if (r)
  				return r;
  			r = fn(&line_info->line_off, ctx);
  			if (r)
  				return r;
  			line_data_cur += rec_size;
  		}
  	}
  
  	return 0;
  }
  
  static int str_sort_by_content(const void *a1, const void *a2)
  {
  	const struct btf_str_ptr *p1 = a1;
  	const struct btf_str_ptr *p2 = a2;
  
  	return strcmp(p1->str, p2->str);
  }
  
  static int str_sort_by_offset(const void *a1, const void *a2)
  {
  	const struct btf_str_ptr *p1 = a1;
  	const struct btf_str_ptr *p2 = a2;
  
  	if (p1->str != p2->str)
  		return p1->str < p2->str ? -1 : 1;
  	return 0;
  }
  
  static int btf_dedup_str_ptr_cmp(const void *str_ptr, const void *pelem)
  {
  	const struct btf_str_ptr *p = pelem;
  
  	if (str_ptr != p->str)
  		return (const char *)str_ptr < p->str ? -1 : 1;
  	return 0;
  }
  
  static int btf_str_mark_as_used(__u32 *str_off_ptr, void *ctx)
  {
  	struct btf_str_ptrs *strs;
  	struct btf_str_ptr *s;
  
  	if (*str_off_ptr == 0)
  		return 0;
  
  	strs = ctx;
  	s = bsearch(strs->data + *str_off_ptr, strs->ptrs, strs->cnt,
  		    sizeof(struct btf_str_ptr), btf_dedup_str_ptr_cmp);
  	if (!s)
  		return -EINVAL;
  	s->used = true;
  	return 0;
  }
  
  static int btf_str_remap_offset(__u32 *str_off_ptr, void *ctx)
  {
  	struct btf_str_ptrs *strs;
  	struct btf_str_ptr *s;
  
  	if (*str_off_ptr == 0)
  		return 0;
  
  	strs = ctx;
  	s = bsearch(strs->data + *str_off_ptr, strs->ptrs, strs->cnt,
  		    sizeof(struct btf_str_ptr), btf_dedup_str_ptr_cmp);
  	if (!s)
  		return -EINVAL;
  	*str_off_ptr = s->new_off;
  	return 0;
  }
  
  /*
   * Dedup string and filter out those that are not referenced from either .BTF
   * or .BTF.ext (if provided) sections.
   *
   * This is done by building index of all strings in BTF's string section,
   * then iterating over all entities that can reference strings (e.g., type
   * names, struct field names, .BTF.ext line info, etc) and marking corresponding
   * strings as used. After that all used strings are deduped and compacted into
   * sequential blob of memory and new offsets are calculated. Then all the string
   * references are iterated again and rewritten using new offsets.
   */
  static int btf_dedup_strings(struct btf_dedup *d)
  {
  	const struct btf_header *hdr = d->btf->hdr;
  	char *start = (char *)d->btf->nohdr_data + hdr->str_off;
  	char *end = start + d->btf->hdr->str_len;
  	char *p = start, *tmp_strs = NULL;
  	struct btf_str_ptrs strs = {
  		.cnt = 0,
  		.cap = 0,
  		.ptrs = NULL,
  		.data = start,
  	};
  	int i, j, err = 0, grp_idx;
  	bool grp_used;
  
  	/* build index of all strings */
  	while (p < end) {
  		if (strs.cnt + 1 > strs.cap) {
  			struct btf_str_ptr *new_ptrs;
  
  			strs.cap += max(strs.cnt / 2, 16U);
  			new_ptrs = libbpf_reallocarray(strs.ptrs, strs.cap, sizeof(strs.ptrs[0]));
  			if (!new_ptrs) {
  				err = -ENOMEM;
  				goto done;
  			}
  			strs.ptrs = new_ptrs;
  		}
  
  		strs.ptrs[strs.cnt].str = p;
  		strs.ptrs[strs.cnt].used = false;
  
  		p += strlen(p) + 1;
  		strs.cnt++;
  	}
  
  	/* temporary storage for deduplicated strings */
  	tmp_strs = malloc(d->btf->hdr->str_len);
  	if (!tmp_strs) {
  		err = -ENOMEM;
  		goto done;
  	}
  
  	/* mark all used strings */
  	strs.ptrs[0].used = true;
  	err = btf_for_each_str_off(d, btf_str_mark_as_used, &strs);
  	if (err)
  		goto done;
  
  	/* sort strings by context, so that we can identify duplicates */
  	qsort(strs.ptrs, strs.cnt, sizeof(strs.ptrs[0]), str_sort_by_content);
  
  	/*
  	 * iterate groups of equal strings and if any instance in a group was
  	 * referenced, emit single instance and remember new offset
  	 */
  	p = tmp_strs;
  	grp_idx = 0;
  	grp_used = strs.ptrs[0].used;
  	/* iterate past end to avoid code duplication after loop */
  	for (i = 1; i <= strs.cnt; i++) {
  		/*
  		 * when i == strs.cnt, we want to skip string comparison and go
  		 * straight to handling last group of strings (otherwise we'd
  		 * need to handle last group after the loop w/ duplicated code)
  		 */
  		if (i < strs.cnt &&
  		    !strcmp(strs.ptrs[i].str, strs.ptrs[grp_idx].str)) {
  			grp_used = grp_used || strs.ptrs[i].used;
  			continue;
  		}
  
  		/*
  		 * this check would have been required after the loop to handle
  		 * last group of strings, but due to <= condition in a loop
  		 * we avoid that duplication
  		 */
  		if (grp_used) {
  			int new_off = p - tmp_strs;
  			__u32 len = strlen(strs.ptrs[grp_idx].str);
  
  			memmove(p, strs.ptrs[grp_idx].str, len + 1);
  			for (j = grp_idx; j < i; j++)
  				strs.ptrs[j].new_off = new_off;
  			p += len + 1;
  		}
  
  		if (i < strs.cnt) {
  			grp_idx = i;
  			grp_used = strs.ptrs[i].used;
  		}
  	}
  
  	/* replace original strings with deduped ones */
  	d->btf->hdr->str_len = p - tmp_strs;
  	memmove(start, tmp_strs, d->btf->hdr->str_len);
  	end = start + d->btf->hdr->str_len;
  
  	/* restore original order for further binary search lookups */
  	qsort(strs.ptrs, strs.cnt, sizeof(strs.ptrs[0]), str_sort_by_offset);
  
  	/* remap string offsets */
  	err = btf_for_each_str_off(d, btf_str_remap_offset, &strs);
  	if (err)
  		goto done;
  
  	d->btf->hdr->str_len = end - start;
  
  done:
  	free(tmp_strs);
  	free(strs.ptrs);
  	return err;
  }
  
  static long btf_hash_common(struct btf_type *t)
  {
  	long h;
  
  	h = hash_combine(0, t->name_off);
  	h = hash_combine(h, t->info);
  	h = hash_combine(h, t->size);
  	return h;
  }
  
  static bool btf_equal_common(struct btf_type *t1, struct btf_type *t2)
  {
  	return t1->name_off == t2->name_off &&
  	       t1->info == t2->info &&
  	       t1->size == t2->size;
  }
  
  /* Calculate type signature hash of INT. */
  static long btf_hash_int(struct btf_type *t)
  {
  	__u32 info = *(__u32 *)(t + 1);
  	long h;
  
  	h = btf_hash_common(t);
  	h = hash_combine(h, info);
  	return h;
  }
  
  /* Check structural equality of two INTs. */
  static bool btf_equal_int(struct btf_type *t1, struct btf_type *t2)
  {
  	__u32 info1, info2;
  
  	if (!btf_equal_common(t1, t2))
  		return false;
  	info1 = *(__u32 *)(t1 + 1);
  	info2 = *(__u32 *)(t2 + 1);
  	return info1 == info2;
  }
  
  /* Calculate type signature hash of ENUM. */
  static long btf_hash_enum(struct btf_type *t)
  {
  	long h;
  
  	/* don't hash vlen and enum members to support enum fwd resolving */
  	h = hash_combine(0, t->name_off);
  	h = hash_combine(h, t->info & ~0xffff);
  	h = hash_combine(h, t->size);
  	return h;
  }
  
  /* Check structural equality of two ENUMs. */
  static bool btf_equal_enum(struct btf_type *t1, struct btf_type *t2)
  {
  	const struct btf_enum *m1, *m2;
  	__u16 vlen;
  	int i;
  
  	if (!btf_equal_common(t1, t2))
  		return false;
  
  	vlen = btf_vlen(t1);
  	m1 = btf_enum(t1);
  	m2 = btf_enum(t2);
  	for (i = 0; i < vlen; i++) {
  		if (m1->name_off != m2->name_off || m1->val != m2->val)
  			return false;
  		m1++;
  		m2++;
  	}
  	return true;
  }
  
  static inline bool btf_is_enum_fwd(struct btf_type *t)
  {
  	return btf_is_enum(t) && btf_vlen(t) == 0;
  }
  
  static bool btf_compat_enum(struct btf_type *t1, struct btf_type *t2)
  {
  	if (!btf_is_enum_fwd(t1) && !btf_is_enum_fwd(t2))
  		return btf_equal_enum(t1, t2);
  	/* ignore vlen when comparing */
  	return t1->name_off == t2->name_off &&
  	       (t1->info & ~0xffff) == (t2->info & ~0xffff) &&
  	       t1->size == t2->size;
  }
  
  /*
   * Calculate type signature hash of STRUCT/UNION, ignoring referenced type IDs,
   * as referenced type IDs equivalence is established separately during type
   * graph equivalence check algorithm.
   */
  static long btf_hash_struct(struct btf_type *t)
  {
  	const struct btf_member *member = btf_members(t);
  	__u32 vlen = btf_vlen(t);
  	long h = btf_hash_common(t);
  	int i;
  
  	for (i = 0; i < vlen; i++) {
  		h = hash_combine(h, member->name_off);
  		h = hash_combine(h, member->offset);
  		/* no hashing of referenced type ID, it can be unresolved yet */
  		member++;
  	}
  	return h;
  }
  
  /*
   * Check structural compatibility of two FUNC_PROTOs, ignoring referenced type
   * IDs. This check is performed during type graph equivalence check and
   * referenced types equivalence is checked separately.
   */
  static bool btf_shallow_equal_struct(struct btf_type *t1, struct btf_type *t2)
  {
  	const struct btf_member *m1, *m2;
  	__u16 vlen;
  	int i;
  
  	if (!btf_equal_common(t1, t2))
  		return false;
  
  	vlen = btf_vlen(t1);
  	m1 = btf_members(t1);
  	m2 = btf_members(t2);
  	for (i = 0; i < vlen; i++) {
  		if (m1->name_off != m2->name_off || m1->offset != m2->offset)
  			return false;
  		m1++;
  		m2++;
  	}
  	return true;
  }
  
  /*
   * Calculate type signature hash of ARRAY, including referenced type IDs,
   * under assumption that they were already resolved to canonical type IDs and
   * are not going to change.
   */
  static long btf_hash_array(struct btf_type *t)
  {
  	const struct btf_array *info = btf_array(t);
  	long h = btf_hash_common(t);
  
  	h = hash_combine(h, info->type);
  	h = hash_combine(h, info->index_type);
  	h = hash_combine(h, info->nelems);
  	return h;
  }
  
  /*
   * Check exact equality of two ARRAYs, taking into account referenced
   * type IDs, under assumption that they were already resolved to canonical
   * type IDs and are not going to change.
   * This function is called during reference types deduplication to compare
   * ARRAY to potential canonical representative.
   */
  static bool btf_equal_array(struct btf_type *t1, struct btf_type *t2)
  {
  	const struct btf_array *info1, *info2;
  
  	if (!btf_equal_common(t1, t2))
  		return false;
  
  	info1 = btf_array(t1);
  	info2 = btf_array(t2);
  	return info1->type == info2->type &&
  	       info1->index_type == info2->index_type &&
  	       info1->nelems == info2->nelems;
  }
  
  /*
   * Check structural compatibility of two ARRAYs, ignoring referenced type
   * IDs. This check is performed during type graph equivalence check and
   * referenced types equivalence is checked separately.
   */
  static bool btf_compat_array(struct btf_type *t1, struct btf_type *t2)
  {
  	if (!btf_equal_common(t1, t2))
  		return false;
  
  	return btf_array(t1)->nelems == btf_array(t2)->nelems;
  }
  
  /*
   * Calculate type signature hash of FUNC_PROTO, including referenced type IDs,
   * under assumption that they were already resolved to canonical type IDs and
   * are not going to change.
   */
  static long btf_hash_fnproto(struct btf_type *t)
  {
  	const struct btf_param *member = btf_params(t);
  	__u16 vlen = btf_vlen(t);
  	long h = btf_hash_common(t);
  	int i;
  
  	for (i = 0; i < vlen; i++) {
  		h = hash_combine(h, member->name_off);
  		h = hash_combine(h, member->type);
  		member++;
  	}
  	return h;
  }
  
  /*
   * Check exact equality of two FUNC_PROTOs, taking into account referenced
   * type IDs, under assumption that they were already resolved to canonical
   * type IDs and are not going to change.
   * This function is called during reference types deduplication to compare
   * FUNC_PROTO to potential canonical representative.
   */
  static bool btf_equal_fnproto(struct btf_type *t1, struct btf_type *t2)
  {
  	const struct btf_param *m1, *m2;
  	__u16 vlen;
  	int i;
  
  	if (!btf_equal_common(t1, t2))
  		return false;
  
  	vlen = btf_vlen(t1);
  	m1 = btf_params(t1);
  	m2 = btf_params(t2);
  	for (i = 0; i < vlen; i++) {
  		if (m1->name_off != m2->name_off || m1->type != m2->type)
  			return false;
  		m1++;
  		m2++;
  	}
  	return true;
  }
  
  /*
   * Check structural compatibility of two FUNC_PROTOs, ignoring referenced type
   * IDs. This check is performed during type graph equivalence check and
   * referenced types equivalence is checked separately.
   */
  static bool btf_compat_fnproto(struct btf_type *t1, struct btf_type *t2)
  {
  	const struct btf_param *m1, *m2;
  	__u16 vlen;
  	int i;
  
  	/* skip return type ID */
  	if (t1->name_off != t2->name_off || t1->info != t2->info)
  		return false;
  
  	vlen = btf_vlen(t1);
  	m1 = btf_params(t1);
  	m2 = btf_params(t2);
  	for (i = 0; i < vlen; i++) {
  		if (m1->name_off != m2->name_off)
  			return false;
  		m1++;
  		m2++;
  	}
  	return true;
  }
  
  /*
   * Deduplicate primitive types, that can't reference other types, by calculating
   * their type signature hash and comparing them with any possible canonical
   * candidate. If no canonical candidate matches, type itself is marked as
   * canonical and is added into `btf_dedup->dedup_table` as another candidate.
   */
  static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
  {
  	struct btf_type *t = d->btf->types[type_id];
  	struct hashmap_entry *hash_entry;
  	struct btf_type *cand;
  	/* if we don't find equivalent type, then we are canonical */
  	__u32 new_id = type_id;
  	__u32 cand_id;
  	long h;
  
  	switch (btf_kind(t)) {
  	case BTF_KIND_CONST:
  	case BTF_KIND_VOLATILE:
  	case BTF_KIND_RESTRICT:
  	case BTF_KIND_PTR:
  	case BTF_KIND_TYPEDEF:
  	case BTF_KIND_ARRAY:
  	case BTF_KIND_STRUCT:
  	case BTF_KIND_UNION:
  	case BTF_KIND_FUNC:
  	case BTF_KIND_FUNC_PROTO:
  	case BTF_KIND_VAR:
  	case BTF_KIND_DATASEC:
  		return 0;
  
  	case BTF_KIND_INT:
  		h = btf_hash_int(t);
  		for_each_dedup_cand(d, hash_entry, h) {
  			cand_id = (__u32)(long)hash_entry->value;
  			cand = d->btf->types[cand_id];
  			if (btf_equal_int(t, cand)) {
  				new_id = cand_id;
  				break;
  			}
  		}
  		break;
  
  	case BTF_KIND_ENUM:
  		h = btf_hash_enum(t);
  		for_each_dedup_cand(d, hash_entry, h) {
  			cand_id = (__u32)(long)hash_entry->value;
  			cand = d->btf->types[cand_id];
  			if (btf_equal_enum(t, cand)) {
  				new_id = cand_id;
  				break;
  			}
  			if (d->opts.dont_resolve_fwds)
  				continue;
  			if (btf_compat_enum(t, cand)) {
  				if (btf_is_enum_fwd(t)) {
  					/* resolve fwd to full enum */
  					new_id = cand_id;
  					break;
  				}
  				/* resolve canonical enum fwd to full enum */
  				d->map[cand_id] = type_id;
  			}
  		}
  		break;
  
  	case BTF_KIND_FWD:
  		h = btf_hash_common(t);
  		for_each_dedup_cand(d, hash_entry, h) {
  			cand_id = (__u32)(long)hash_entry->value;
  			cand = d->btf->types[cand_id];
  			if (btf_equal_common(t, cand)) {
  				new_id = cand_id;
  				break;
  			}
  		}
  		break;
  
  	default:
  		return -EINVAL;
  	}
  
  	d->map[type_id] = new_id;
  	if (type_id == new_id && btf_dedup_table_add(d, h, type_id))
  		return -ENOMEM;
  
  	return 0;
  }
  
  static int btf_dedup_prim_types(struct btf_dedup *d)
  {
  	int i, err;
  
  	for (i = 1; i <= d->btf->nr_types; i++) {
  		err = btf_dedup_prim_type(d, i);
  		if (err)
  			return err;
  	}
  	return 0;
  }
  
  /*
   * Check whether type is already mapped into canonical one (could be to itself).
   */
  static inline bool is_type_mapped(struct btf_dedup *d, uint32_t type_id)
  {
  	return d->map[type_id] <= BTF_MAX_NR_TYPES;
  }
  
  /*
   * Resolve type ID into its canonical type ID, if any; otherwise return original
   * type ID. If type is FWD and is resolved into STRUCT/UNION already, follow
   * STRUCT/UNION link and resolve it into canonical type ID as well.
   */
  static inline __u32 resolve_type_id(struct btf_dedup *d, __u32 type_id)
  {
  	while (is_type_mapped(d, type_id) && d->map[type_id] != type_id)
  		type_id = d->map[type_id];
  	return type_id;
  }
  
  /*
   * Resolve FWD to underlying STRUCT/UNION, if any; otherwise return original
   * type ID.
   */
  static uint32_t resolve_fwd_id(struct btf_dedup *d, uint32_t type_id)
  {
  	__u32 orig_type_id = type_id;
  
  	if (!btf_is_fwd(d->btf->types[type_id]))
  		return type_id;
  
  	while (is_type_mapped(d, type_id) && d->map[type_id] != type_id)
  		type_id = d->map[type_id];
  
  	if (!btf_is_fwd(d->btf->types[type_id]))
  		return type_id;
  
  	return orig_type_id;
  }
  
  
  static inline __u16 btf_fwd_kind(struct btf_type *t)
  {
  	return btf_kflag(t) ? BTF_KIND_UNION : BTF_KIND_STRUCT;
  }
  
  /*
   * Check equivalence of BTF type graph formed by candidate struct/union (we'll
   * call it "candidate graph" in this description for brevity) to a type graph
   * formed by (potential) canonical struct/union ("canonical graph" for brevity
   * here, though keep in mind that not all types in canonical graph are
   * necessarily canonical representatives themselves, some of them might be
   * duplicates or its uniqueness might not have been established yet).
   * Returns:
   *  - >0, if type graphs are equivalent;
   *  -  0, if not equivalent;
   *  - <0, on error.
   *
   * Algorithm performs side-by-side DFS traversal of both type graphs and checks
   * equivalence of BTF types at each step. If at any point BTF types in candidate
   * and canonical graphs are not compatible structurally, whole graphs are
   * incompatible. If types are structurally equivalent (i.e., all information
   * except referenced type IDs is exactly the same), a mapping from `canon_id` to
   * a `cand_id` is recored in hypothetical mapping (`btf_dedup->hypot_map`).
   * If a type references other types, then those referenced types are checked
   * for equivalence recursively.
   *
   * During DFS traversal, if we find that for current `canon_id` type we
   * already have some mapping in hypothetical map, we check for two possible
   * situations:
   *   - `canon_id` is mapped to exactly the same type as `cand_id`. This will
   *     happen when type graphs have cycles. In this case we assume those two
   *     types are equivalent.
   *   - `canon_id` is mapped to different type. This is contradiction in our
   *     hypothetical mapping, because same graph in canonical graph corresponds
   *     to two different types in candidate graph, which for equivalent type
   *     graphs shouldn't happen. This condition terminates equivalence check
   *     with negative result.
   *
   * If type graphs traversal exhausts types to check and find no contradiction,
   * then type graphs are equivalent.
   *
   * When checking types for equivalence, there is one special case: FWD types.
   * If FWD type resolution is allowed and one of the types (either from canonical
   * or candidate graph) is FWD and other is STRUCT/UNION (depending on FWD's kind
   * flag) and their names match, hypothetical mapping is updated to point from
   * FWD to STRUCT/UNION. If graphs will be determined as equivalent successfully,
   * this mapping will be used to record FWD -> STRUCT/UNION mapping permanently.
   *
   * Technically, this could lead to incorrect FWD to STRUCT/UNION resolution,
   * if there are two exactly named (or anonymous) structs/unions that are
   * compatible structurally, one of which has FWD field, while other is concrete
   * STRUCT/UNION, but according to C sources they are different structs/unions
   * that are referencing different types with the same name. This is extremely
   * unlikely to happen, but btf_dedup API allows to disable FWD resolution if
   * this logic is causing problems.
   *
   * Doing FWD resolution means that both candidate and/or canonical graphs can
   * consists of portions of the graph that come from multiple compilation units.
   * This is due to the fact that types within single compilation unit are always
   * deduplicated and FWDs are already resolved, if referenced struct/union
   * definiton is available. So, if we had unresolved FWD and found corresponding
   * STRUCT/UNION, they will be from different compilation units. This
   * consequently means that when we "link" FWD to corresponding STRUCT/UNION,
   * type graph will likely have at least two different BTF types that describe
   * same type (e.g., most probably there will be two different BTF types for the
   * same 'int' primitive type) and could even have "overlapping" parts of type
   * graph that describe same subset of types.
   *
   * This in turn means that our assumption that each type in canonical graph
   * must correspond to exactly one type in candidate graph might not hold
   * anymore and will make it harder to detect contradictions using hypothetical
   * map. To handle this problem, we allow to follow FWD -> STRUCT/UNION
   * resolution only in canonical graph. FWDs in candidate graphs are never
   * resolved. To see why it's OK, let's check all possible situations w.r.t. FWDs
   * that can occur:
   *   - Both types in canonical and candidate graphs are FWDs. If they are
   *     structurally equivalent, then they can either be both resolved to the
   *     same STRUCT/UNION or not resolved at all. In both cases they are
   *     equivalent and there is no need to resolve FWD on candidate side.
   *   - Both types in canonical and candidate graphs are concrete STRUCT/UNION,
   *     so nothing to resolve as well, algorithm will check equivalence anyway.
   *   - Type in canonical graph is FWD, while type in candidate is concrete
   *     STRUCT/UNION. In this case candidate graph comes from single compilation
   *     unit, so there is exactly one BTF type for each unique C type. After
   *     resolving FWD into STRUCT/UNION, there might be more than one BTF type
   *     in canonical graph mapping to single BTF type in candidate graph, but
   *     because hypothetical mapping maps from canonical to candidate types, it's
   *     alright, and we still maintain the property of having single `canon_id`
   *     mapping to single `cand_id` (there could be two different `canon_id`
   *     mapped to the same `cand_id`, but it's not contradictory).
   *   - Type in canonical graph is concrete STRUCT/UNION, while type in candidate
   *     graph is FWD. In this case we are just going to check compatibility of
   *     STRUCT/UNION and corresponding FWD, and if they are compatible, we'll
   *     assume that whatever STRUCT/UNION FWD resolves to must be equivalent to
   *     a concrete STRUCT/UNION from canonical graph. If the rest of type graphs
   *     turn out equivalent, we'll re-resolve FWD to concrete STRUCT/UNION from
   *     canonical graph.
   */
  static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
  			      __u32 canon_id)
  {
  	struct btf_type *cand_type;
  	struct btf_type *canon_type;
  	__u32 hypot_type_id;
  	__u16 cand_kind;
  	__u16 canon_kind;
  	int i, eq;
  
  	/* if both resolve to the same canonical, they must be equivalent */
  	if (resolve_type_id(d, cand_id) == resolve_type_id(d, canon_id))
  		return 1;
  
  	canon_id = resolve_fwd_id(d, canon_id);
  
  	hypot_type_id = d->hypot_map[canon_id];
  	if (hypot_type_id <= BTF_MAX_NR_TYPES)
  		return hypot_type_id == cand_id;
  
  	if (btf_dedup_hypot_map_add(d, canon_id, cand_id))
  		return -ENOMEM;
  
  	cand_type = d->btf->types[cand_id];
  	canon_type = d->btf->types[canon_id];
  	cand_kind = btf_kind(cand_type);
  	canon_kind = btf_kind(canon_type);
  
  	if (cand_type->name_off != canon_type->name_off)
  		return 0;
  
  	/* FWD <--> STRUCT/UNION equivalence check, if enabled */
  	if (!d->opts.dont_resolve_fwds
  	    && (cand_kind == BTF_KIND_FWD || canon_kind == BTF_KIND_FWD)
  	    && cand_kind != canon_kind) {
  		__u16 real_kind;
  		__u16 fwd_kind;
  
  		if (cand_kind == BTF_KIND_FWD) {
  			real_kind = canon_kind;
  			fwd_kind = btf_fwd_kind(cand_type);
  		} else {
  			real_kind = cand_kind;
  			fwd_kind = btf_fwd_kind(canon_type);
  		}
  		return fwd_kind == real_kind;
  	}
  
  	if (cand_kind != canon_kind)
  		return 0;
  
  	switch (cand_kind) {
  	case BTF_KIND_INT:
  		return btf_equal_int(cand_type, canon_type);
  
  	case BTF_KIND_ENUM:
  		if (d->opts.dont_resolve_fwds)
  			return btf_equal_enum(cand_type, canon_type);
  		else
  			return btf_compat_enum(cand_type, canon_type);
  
  	case BTF_KIND_FWD:
  		return btf_equal_common(cand_type, canon_type);
  
  	case BTF_KIND_CONST:
  	case BTF_KIND_VOLATILE:
  	case BTF_KIND_RESTRICT:
  	case BTF_KIND_PTR:
  	case BTF_KIND_TYPEDEF:
  	case BTF_KIND_FUNC:
  		if (cand_type->info != canon_type->info)
  			return 0;
  		return btf_dedup_is_equiv(d, cand_type->type, canon_type->type);
  
  	case BTF_KIND_ARRAY: {
  		const struct btf_array *cand_arr, *canon_arr;
  
  		if (!btf_compat_array(cand_type, canon_type))
  			return 0;
  		cand_arr = btf_array(cand_type);
  		canon_arr = btf_array(canon_type);
  		eq = btf_dedup_is_equiv(d,
  			cand_arr->index_type, canon_arr->index_type);
  		if (eq <= 0)
  			return eq;
  		return btf_dedup_is_equiv(d, cand_arr->type, canon_arr->type);
  	}
  
  	case BTF_KIND_STRUCT:
  	case BTF_KIND_UNION: {
  		const struct btf_member *cand_m, *canon_m;
  		__u16 vlen;
  
  		if (!btf_shallow_equal_struct(cand_type, canon_type))
  			return 0;
  		vlen = btf_vlen(cand_type);
  		cand_m = btf_members(cand_type);
  		canon_m = btf_members(canon_type);
  		for (i = 0; i < vlen; i++) {
  			eq = btf_dedup_is_equiv(d, cand_m->type, canon_m->type);
  			if (eq <= 0)
  				return eq;
  			cand_m++;
  			canon_m++;
  		}
  
  		return 1;
  	}
  
  	case BTF_KIND_FUNC_PROTO: {
  		const struct btf_param *cand_p, *canon_p;
  		__u16 vlen;
  
  		if (!btf_compat_fnproto(cand_type, canon_type))
  			return 0;
  		eq = btf_dedup_is_equiv(d, cand_type->type, canon_type->type);
  		if (eq <= 0)
  			return eq;
  		vlen = btf_vlen(cand_type);
  		cand_p = btf_params(cand_type);
  		canon_p = btf_params(canon_type);
  		for (i = 0; i < vlen; i++) {
  			eq = btf_dedup_is_equiv(d, cand_p->type, canon_p->type);
  			if (eq <= 0)
  				return eq;
  			cand_p++;
  			canon_p++;
  		}
  		return 1;
  	}
  
  	default:
  		return -EINVAL;
  	}
  	return 0;
  }
  
  /*
   * Use hypothetical mapping, produced by successful type graph equivalence
   * check, to augment existing struct/union canonical mapping, where possible.
   *
   * If BTF_KIND_FWD resolution is allowed, this mapping is also used to record
   * FWD -> STRUCT/UNION correspondence as well. FWD resolution is bidirectional:
   * it doesn't matter if FWD type was part of canonical graph or candidate one,
   * we are recording the mapping anyway. As opposed to carefulness required
   * for struct/union correspondence mapping (described below), for FWD resolution
   * it's not important, as by the time that FWD type (reference type) will be
   * deduplicated all structs/unions will be deduped already anyway.
   *
   * Recording STRUCT/UNION mapping is purely a performance optimization and is
   * not required for correctness. It needs to be done carefully to ensure that
   * struct/union from candidate's type graph is not mapped into corresponding
   * struct/union from canonical type graph that itself hasn't been resolved into
   * canonical representative. The only guarantee we have is that canonical
   * struct/union was determined as canonical and that won't change. But any
   * types referenced through that struct/union fields could have been not yet
   * resolved, so in case like that it's too early to establish any kind of
   * correspondence between structs/unions.
   *
   * No canonical correspondence is derived for primitive types (they are already
   * deduplicated completely already anyway) or reference types (they rely on
   * stability of struct/union canonical relationship for equivalence checks).
   */
  static void btf_dedup_merge_hypot_map(struct btf_dedup *d)
  {
  	__u32 cand_type_id, targ_type_id;
  	__u16 t_kind, c_kind;
  	__u32 t_id, c_id;
  	int i;
  
  	for (i = 0; i < d->hypot_cnt; i++) {
  		cand_type_id = d->hypot_list[i];
  		targ_type_id = d->hypot_map[cand_type_id];
  		t_id = resolve_type_id(d, targ_type_id);
  		c_id = resolve_type_id(d, cand_type_id);
  		t_kind = btf_kind(d->btf->types[t_id]);
  		c_kind = btf_kind(d->btf->types[c_id]);
  		/*
  		 * Resolve FWD into STRUCT/UNION.
  		 * It's ok to resolve FWD into STRUCT/UNION that's not yet
  		 * mapped to canonical representative (as opposed to
  		 * STRUCT/UNION <--> STRUCT/UNION mapping logic below), because
  		 * eventually that struct is going to be mapped and all resolved
  		 * FWDs will automatically resolve to correct canonical
  		 * representative. This will happen before ref type deduping,
  		 * which critically depends on stability of these mapping. This
  		 * stability is not a requirement for STRUCT/UNION equivalence
  		 * checks, though.
  		 */
  		if (t_kind != BTF_KIND_FWD && c_kind == BTF_KIND_FWD)
  			d->map[c_id] = t_id;
  		else if (t_kind == BTF_KIND_FWD && c_kind != BTF_KIND_FWD)
  			d->map[t_id] = c_id;
  
  		if ((t_kind == BTF_KIND_STRUCT || t_kind == BTF_KIND_UNION) &&
  		    c_kind != BTF_KIND_FWD &&
  		    is_type_mapped(d, c_id) &&
  		    !is_type_mapped(d, t_id)) {
  			/*
  			 * as a perf optimization, we can map struct/union
  			 * that's part of type graph we just verified for
  			 * equivalence. We can do that for struct/union that has
  			 * canonical representative only, though.
  			 */
  			d->map[t_id] = c_id;
  		}
  	}
  }
  
  /*
   * Deduplicate struct/union types.
   *
   * For each struct/union type its type signature hash is calculated, taking
   * into account type's name, size, number, order and names of fields, but
   * ignoring type ID's referenced from fields, because they might not be deduped
   * completely until after reference types deduplication phase. This type hash
   * is used to iterate over all potential canonical types, sharing same hash.
   * For each canonical candidate we check whether type graphs that they form
   * (through referenced types in fields and so on) are equivalent using algorithm
   * implemented in `btf_dedup_is_equiv`. If such equivalence is found and
   * BTF_KIND_FWD resolution is allowed, then hypothetical mapping
   * (btf_dedup->hypot_map) produced by aforementioned type graph equivalence
   * algorithm is used to record FWD -> STRUCT/UNION mapping. It's also used to
   * potentially map other structs/unions to their canonical representatives,
   * if such relationship hasn't yet been established. This speeds up algorithm
   * by eliminating some of the duplicate work.
   *
   * If no matching canonical representative was found, struct/union is marked
   * as canonical for itself and is added into btf_dedup->dedup_table hash map
   * for further look ups.
   */
  static int btf_dedup_struct_type(struct btf_dedup *d, __u32 type_id)
  {
  	struct btf_type *cand_type, *t;
  	struct hashmap_entry *hash_entry;
  	/* if we don't find equivalent type, then we are canonical */
  	__u32 new_id = type_id;
  	__u16 kind;
  	long h;
  
  	/* already deduped or is in process of deduping (loop detected) */
  	if (d->map[type_id] <= BTF_MAX_NR_TYPES)
  		return 0;
  
  	t = d->btf->types[type_id];
  	kind = btf_kind(t);
  
  	if (kind != BTF_KIND_STRUCT && kind != BTF_KIND_UNION)
  		return 0;
  
  	h = btf_hash_struct(t);
  	for_each_dedup_cand(d, hash_entry, h) {
  		__u32 cand_id = (__u32)(long)hash_entry->value;
  		int eq;
  
  		/*
  		 * Even though btf_dedup_is_equiv() checks for
  		 * btf_shallow_equal_struct() internally when checking two
  		 * structs (unions) for equivalence, we need to guard here
  		 * from picking matching FWD type as a dedup candidate.
  		 * This can happen due to hash collision. In such case just
  		 * relying on btf_dedup_is_equiv() would lead to potentially
  		 * creating a loop (FWD -> STRUCT and STRUCT -> FWD), because
  		 * FWD and compatible STRUCT/UNION are considered equivalent.
  		 */
  		cand_type = d->btf->types[cand_id];
  		if (!btf_shallow_equal_struct(t, cand_type))
  			continue;
  
  		btf_dedup_clear_hypot_map(d);
  		eq = btf_dedup_is_equiv(d, type_id, cand_id);
  		if (eq < 0)
  			return eq;
  		if (!eq)
  			continue;
  		new_id = cand_id;
  		btf_dedup_merge_hypot_map(d);
  		break;
  	}
  
  	d->map[type_id] = new_id;
  	if (type_id == new_id && btf_dedup_table_add(d, h, type_id))
  		return -ENOMEM;
  
  	return 0;
  }
  
  static int btf_dedup_struct_types(struct btf_dedup *d)
  {
  	int i, err;
  
  	for (i = 1; i <= d->btf->nr_types; i++) {
  		err = btf_dedup_struct_type(d, i);
  		if (err)
  			return err;
  	}
  	return 0;
  }
  
  /*
   * Deduplicate reference type.
   *
   * Once all primitive and struct/union types got deduplicated, we can easily
   * deduplicate all other (reference) BTF types. This is done in two steps:
   *
   * 1. Resolve all referenced type IDs into their canonical type IDs. This
   * resolution can be done either immediately for primitive or struct/union types
   * (because they were deduped in previous two phases) or recursively for
   * reference types. Recursion will always terminate at either primitive or
   * struct/union type, at which point we can "unwind" chain of reference types
   * one by one. There is no danger of encountering cycles because in C type
   * system the only way to form type cycle is through struct/union, so any chain
   * of reference types, even those taking part in a type cycle, will inevitably
   * reach struct/union at some point.
   *
   * 2. Once all referenced type IDs are resolved into canonical ones, BTF type
   * becomes "stable", in the sense that no further deduplication will cause
   * any changes to it. With that, it's now possible to calculate type's signature
   * hash (this time taking into account referenced type IDs) and loop over all
   * potential canonical representatives. If no match was found, current type
   * will become canonical representative of itself and will be added into
   * btf_dedup->dedup_table as another possible canonical representative.
   */
  static int btf_dedup_ref_type(struct btf_dedup *d, __u32 type_id)
  {
  	struct hashmap_entry *hash_entry;
  	__u32 new_id = type_id, cand_id;
  	struct btf_type *t, *cand;
  	/* if we don't find equivalent type, then we are representative type */
  	int ref_type_id;
  	long h;
  
  	if (d->map[type_id] == BTF_IN_PROGRESS_ID)
  		return -ELOOP;
  	if (d->map[type_id] <= BTF_MAX_NR_TYPES)
  		return resolve_type_id(d, type_id);
  
  	t = d->btf->types[type_id];
  	d->map[type_id] = BTF_IN_PROGRESS_ID;
  
  	switch (btf_kind(t)) {
  	case BTF_KIND_CONST:
  	case BTF_KIND_VOLATILE:
  	case BTF_KIND_RESTRICT:
  	case BTF_KIND_PTR:
  	case BTF_KIND_TYPEDEF:
  	case BTF_KIND_FUNC:
  		ref_type_id = btf_dedup_ref_type(d, t->type);
  		if (ref_type_id < 0)
  			return ref_type_id;
  		t->type = ref_type_id;
  
  		h = btf_hash_common(t);
  		for_each_dedup_cand(d, hash_entry, h) {
  			cand_id = (__u32)(long)hash_entry->value;
  			cand = d->btf->types[cand_id];
  			if (btf_equal_common(t, cand)) {
  				new_id = cand_id;
  				break;
  			}
  		}
  		break;
  
  	case BTF_KIND_ARRAY: {
  		struct btf_array *info = btf_array(t);
  
  		ref_type_id = btf_dedup_ref_type(d, info->type);
  		if (ref_type_id < 0)
  			return ref_type_id;
  		info->type = ref_type_id;
  
  		ref_type_id = btf_dedup_ref_type(d, info->index_type);
  		if (ref_type_id < 0)
  			return ref_type_id;
  		info->index_type = ref_type_id;
  
  		h = btf_hash_array(t);
  		for_each_dedup_cand(d, hash_entry, h) {
  			cand_id = (__u32)(long)hash_entry->value;
  			cand = d->btf->types[cand_id];
  			if (btf_equal_array(t, cand)) {
  				new_id = cand_id;
  				break;
  			}
  		}
  		break;
  	}
  
  	case BTF_KIND_FUNC_PROTO: {
  		struct btf_param *param;
  		__u16 vlen;
  		int i;
  
  		ref_type_id = btf_dedup_ref_type(d, t->type);
  		if (ref_type_id < 0)
  			return ref_type_id;
  		t->type = ref_type_id;
  
  		vlen = btf_vlen(t);
  		param = btf_params(t);
  		for (i = 0; i < vlen; i++) {
  			ref_type_id = btf_dedup_ref_type(d, param->type);
  			if (ref_type_id < 0)
  				return ref_type_id;
  			param->type = ref_type_id;
  			param++;
  		}
  
  		h = btf_hash_fnproto(t);
  		for_each_dedup_cand(d, hash_entry, h) {
  			cand_id = (__u32)(long)hash_entry->value;
  			cand = d->btf->types[cand_id];
  			if (btf_equal_fnproto(t, cand)) {
  				new_id = cand_id;
  				break;
  			}
  		}
  		break;
  	}
  
  	default:
  		return -EINVAL;
  	}
  
  	d->map[type_id] = new_id;
  	if (type_id == new_id && btf_dedup_table_add(d, h, type_id))
  		return -ENOMEM;
  
  	return new_id;
  }
  
  static int btf_dedup_ref_types(struct btf_dedup *d)
  {
  	int i, err;
  
  	for (i = 1; i <= d->btf->nr_types; i++) {
  		err = btf_dedup_ref_type(d, i);
  		if (err < 0)
  			return err;
  	}
  	/* we won't need d->dedup_table anymore */
  	hashmap__free(d->dedup_table);
  	d->dedup_table = NULL;
  	return 0;
  }
  
  /*
   * Compact types.
   *
   * After we established for each type its corresponding canonical representative
   * type, we now can eliminate types that are not canonical and leave only
   * canonical ones layed out sequentially in memory by copying them over
   * duplicates. During compaction btf_dedup->hypot_map array is reused to store
   * a map from original type ID to a new compacted type ID, which will be used
   * during next phase to "fix up" type IDs, referenced from struct/union and
   * reference types.
   */
  static int btf_dedup_compact_types(struct btf_dedup *d)
  {
  	struct btf_type **new_types;
  	__u32 next_type_id = 1;
  	char *types_start, *p;
  	int i, len;
  
  	/* we are going to reuse hypot_map to store compaction remapping */
  	d->hypot_map[0] = 0;
  	for (i = 1; i <= d->btf->nr_types; i++)
  		d->hypot_map[i] = BTF_UNPROCESSED_ID;
  
  	types_start = d->btf->nohdr_data + d->btf->hdr->type_off;
  	p = types_start;
  
  	for (i = 1; i <= d->btf->nr_types; i++) {
  		if (d->map[i] != i)
  			continue;
  
  		len = btf_type_size(d->btf->types[i]);
  		if (len < 0)
  			return len;
  
  		memmove(p, d->btf->types[i], len);
  		d->hypot_map[i] = next_type_id;
  		d->btf->types[next_type_id] = (struct btf_type *)p;
  		p += len;
  		next_type_id++;
  	}
  
  	/* shrink struct btf's internal types index and update btf_header */
  	d->btf->nr_types = next_type_id - 1;
  	d->btf->types_size = d->btf->nr_types;
  	d->btf->hdr->type_len = p - types_start;
  	new_types = libbpf_reallocarray(d->btf->types, (1 + d->btf->nr_types),
  					sizeof(struct btf_type *));
  	if (!new_types)
  		return -ENOMEM;
  	d->btf->types = new_types;
  
  	/* make sure string section follows type information without gaps */
  	d->btf->hdr->str_off = p - (char *)d->btf->nohdr_data;
  	memmove(p, d->btf->strings, d->btf->hdr->str_len);
  	d->btf->strings = p;
  	p += d->btf->hdr->str_len;
  
  	d->btf->data_size = p - (char *)d->btf->data;
  	return 0;
  }
  
  /*
   * Figure out final (deduplicated and compacted) type ID for provided original
   * `type_id` by first resolving it into corresponding canonical type ID and
   * then mapping it to a deduplicated type ID, stored in btf_dedup->hypot_map,
   * which is populated during compaction phase.
   */
  static int btf_dedup_remap_type_id(struct btf_dedup *d, __u32 type_id)
  {
  	__u32 resolved_type_id, new_type_id;
  
  	resolved_type_id = resolve_type_id(d, type_id);
  	new_type_id = d->hypot_map[resolved_type_id];
  	if (new_type_id > BTF_MAX_NR_TYPES)
  		return -EINVAL;
  	return new_type_id;
  }
  
  /*
   * Remap referenced type IDs into deduped type IDs.
   *
   * After BTF types are deduplicated and compacted, their final type IDs may
   * differ from original ones. The map from original to a corresponding
   * deduped type ID is stored in btf_dedup->hypot_map and is populated during
   * compaction phase. During remapping phase we are rewriting all type IDs
   * referenced from any BTF type (e.g., struct fields, func proto args, etc) to
   * their final deduped type IDs.
   */
  static int btf_dedup_remap_type(struct btf_dedup *d, __u32 type_id)
  {
  	struct btf_type *t = d->btf->types[type_id];
  	int i, r;
  
  	switch (btf_kind(t)) {
  	case BTF_KIND_INT:
  	case BTF_KIND_ENUM:
  		break;
  
  	case BTF_KIND_FWD:
  	case BTF_KIND_CONST:
  	case BTF_KIND_VOLATILE:
  	case BTF_KIND_RESTRICT:
  	case BTF_KIND_PTR:
  	case BTF_KIND_TYPEDEF:
  	case BTF_KIND_FUNC:
  	case BTF_KIND_VAR:
  		r = btf_dedup_remap_type_id(d, t->type);
  		if (r < 0)
  			return r;
  		t->type = r;
  		break;
  
  	case BTF_KIND_ARRAY: {
  		struct btf_array *arr_info = btf_array(t);
  
  		r = btf_dedup_remap_type_id(d, arr_info->type);
  		if (r < 0)
  			return r;
  		arr_info->type = r;
  		r = btf_dedup_remap_type_id(d, arr_info->index_type);
  		if (r < 0)
  			return r;
  		arr_info->index_type = r;
  		break;
  	}
  
  	case BTF_KIND_STRUCT:
  	case BTF_KIND_UNION: {
  		struct btf_member *member = btf_members(t);
  		__u16 vlen = btf_vlen(t);
  
  		for (i = 0; i < vlen; i++) {
  			r = btf_dedup_remap_type_id(d, member->type);
  			if (r < 0)
  				return r;
  			member->type = r;
  			member++;
  		}
  		break;
  	}
  
  	case BTF_KIND_FUNC_PROTO: {
  		struct btf_param *param = btf_params(t);
  		__u16 vlen = btf_vlen(t);
  
  		r = btf_dedup_remap_type_id(d, t->type);
  		if (r < 0)
  			return r;
  		t->type = r;
  
  		for (i = 0; i < vlen; i++) {
  			r = btf_dedup_remap_type_id(d, param->type);
  			if (r < 0)
  				return r;
  			param->type = r;
  			param++;
  		}
  		break;
  	}
  
  	case BTF_KIND_DATASEC: {
  		struct btf_var_secinfo *var = btf_var_secinfos(t);
  		__u16 vlen = btf_vlen(t);
  
  		for (i = 0; i < vlen; i++) {
  			r = btf_dedup_remap_type_id(d, var->type);
  			if (r < 0)
  				return r;
  			var->type = r;
  			var++;
  		}
  		break;
  	}
  
  	default:
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static int btf_dedup_remap_types(struct btf_dedup *d)
  {
  	int i, r;
  
  	for (i = 1; i <= d->btf->nr_types; i++) {
  		r = btf_dedup_remap_type(d, i);
  		if (r < 0)
  			return r;
  	}
  	return 0;
  }
  
  /*
   * 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 *libbpf_find_kernel_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;
  
  	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);
  
  		pr_debug("loading kernel BTF '%s': %ld\n",
  			 path, IS_ERR(btf) ? PTR_ERR(btf) : 0);
  		if (IS_ERR(btf))
  			continue;
  
  		return btf;
  	}
  
  	pr_warn("failed to find valid kernel BTF\n");
  	return ERR_PTR(-ESRCH);
  }
  