/src/libbpf/src/relo_core.c

Source (jump to first uncovered line)
// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/* Copyright (c) 2019 Facebook */

#ifdef __KERNEL__
#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/string.h>
#include <linux/bpf_verifier.h>
#include "relo_core.h"

static const char *btf_kind_str(const struct btf_type *t)
{
  return btf_type_str(t);
}

static bool is_ldimm64_insn(struct bpf_insn *insn)
{
  return insn->code == (BPF_LD | BPF_IMM | BPF_DW);
}

static const struct btf_type *
skip_mods_and_typedefs(const struct btf *btf, u32 id, u32 *res_id)
{
  return btf_type_skip_modifiers(btf, id, res_id);
}

static const char *btf__name_by_offset(const struct btf *btf, u32 offset)
{
  return btf_name_by_offset(btf, offset);
}

static s64 btf__resolve_size(const struct btf *btf, u32 type_id)
{
  const struct btf_type *t;
  int size;

  t = btf_type_by_id(btf, type_id);
  t = btf_resolve_size(btf, t, &size);
  if (IS_ERR(t))
    return PTR_ERR(t);
  return size;
}

enum libbpf_print_level {
  LIBBPF_WARN,
  LIBBPF_INFO,
  LIBBPF_DEBUG,
};

#undef pr_warn
#undef pr_info
#undef pr_debug
#define pr_warn(fmt, log, ...)  bpf_log((void *)log, fmt, "", ##__VA_ARGS__)
#define pr_info(fmt, log, ...)  bpf_log((void *)log, fmt, "", ##__VA_ARGS__)
#define pr_debug(fmt, log, ...) bpf_log((void *)log, fmt, "", ##__VA_ARGS__)
#define libbpf_print(level, fmt, ...) bpf_log((void *)prog_name, fmt, ##__VA_ARGS__)
#else
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include <linux/err.h>

#include "libbpf.h"
#include "bpf.h"
#include "btf.h"
#include "str_error.h"
#include "libbpf_internal.h"
#endif

static bool is_flex_arr(const struct btf *btf,
      const struct bpf_core_accessor *acc,
      const struct btf_array *arr)
{
  const struct btf_type *t;

  /* not a flexible array, if not inside a struct or has non-zero size */
  if (!acc->name || arr->nelems > 0)
    return false;

  /* has to be the last member of enclosing struct */
  t = btf_type_by_id(btf, acc->type_id);
  return acc->idx == btf_vlen(t) - 1;
}

static const char *core_relo_kind_str(enum bpf_core_relo_kind kind)
{
  switch (kind) {
  case BPF_CORE_FIELD_BYTE_OFFSET: return "byte_off";
  case BPF_CORE_FIELD_BYTE_SIZE: return "byte_sz";
  case BPF_CORE_FIELD_EXISTS: return "field_exists";
  case BPF_CORE_FIELD_SIGNED: return "signed";
  case BPF_CORE_FIELD_LSHIFT_U64: return "lshift_u64";
  case BPF_CORE_FIELD_RSHIFT_U64: return "rshift_u64";
  case BPF_CORE_TYPE_ID_LOCAL: return "local_type_id";
  case BPF_CORE_TYPE_ID_TARGET: return "target_type_id";
  case BPF_CORE_TYPE_EXISTS: return "type_exists";
  case BPF_CORE_TYPE_MATCHES: return "type_matches";
  case BPF_CORE_TYPE_SIZE: return "type_size";
  case BPF_CORE_ENUMVAL_EXISTS: return "enumval_exists";
  case BPF_CORE_ENUMVAL_VALUE: return "enumval_value";
  default: return "unknown";
  }
}

static bool core_relo_is_field_based(enum bpf_core_relo_kind kind)
{
  switch (kind) {
  case BPF_CORE_FIELD_BYTE_OFFSET:
  case BPF_CORE_FIELD_BYTE_SIZE:
  case BPF_CORE_FIELD_EXISTS:
  case BPF_CORE_FIELD_SIGNED:
  case BPF_CORE_FIELD_LSHIFT_U64:
  case BPF_CORE_FIELD_RSHIFT_U64:
    return true;
  default:
    return false;
  }
}

static bool core_relo_is_type_based(enum bpf_core_relo_kind kind)
{
  switch (kind) {
  case BPF_CORE_TYPE_ID_LOCAL:
  case BPF_CORE_TYPE_ID_TARGET:
  case BPF_CORE_TYPE_EXISTS:
  case BPF_CORE_TYPE_MATCHES:
  case BPF_CORE_TYPE_SIZE:
    return true;
  default:
    return false;
  }
}

static bool core_relo_is_enumval_based(enum bpf_core_relo_kind kind)
{
  switch (kind) {
  case BPF_CORE_ENUMVAL_EXISTS:
  case BPF_CORE_ENUMVAL_VALUE:
    return true;
  default:
    return false;
  }
}

int __bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id,
        const struct btf *targ_btf, __u32 targ_id, int level)
{
  const struct btf_type *local_type, *targ_type;
  int depth = 32; /* max recursion depth */

  /* caller made sure that names match (ignoring flavor suffix) */
  local_type = btf_type_by_id(local_btf, local_id);
  targ_type = btf_type_by_id(targ_btf, targ_id);
  if (!btf_kind_core_compat(local_type, targ_type))
    return 0;

recur:
  depth--;
  if (depth < 0)
    return -EINVAL;

  local_type = skip_mods_and_typedefs(local_btf, local_id, &local_id);
  targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
  if (!local_type || !targ_type)
    return -EINVAL;

  if (!btf_kind_core_compat(local_type, targ_type))
    return 0;

  switch (btf_kind(local_type)) {
  case BTF_KIND_UNKN:
  case BTF_KIND_STRUCT:
  case BTF_KIND_UNION:
  case BTF_KIND_ENUM:
  case BTF_KIND_FWD:
  case BTF_KIND_ENUM64:
    return 1;
  case BTF_KIND_INT:
    /* just reject deprecated bitfield-like integers; all other
     * integers are by default compatible between each other
     */
    return btf_int_offset(local_type) == 0 && btf_int_offset(targ_type) == 0;
  case BTF_KIND_PTR:
    local_id = local_type->type;
    targ_id = targ_type->type;
    goto recur;
  case BTF_KIND_ARRAY:
    local_id = btf_array(local_type)->type;
    targ_id = btf_array(targ_type)->type;
    goto recur;
  case BTF_KIND_FUNC_PROTO: {
    struct btf_param *local_p = btf_params(local_type);
    struct btf_param *targ_p = btf_params(targ_type);
    __u16 local_vlen = btf_vlen(local_type);
    __u16 targ_vlen = btf_vlen(targ_type);
    int i, err;

    if (local_vlen != targ_vlen)
      return 0;

    for (i = 0; i < local_vlen; i++, local_p++, targ_p++) {
      if (level <= 0)
        return -EINVAL;

      skip_mods_and_typedefs(local_btf, local_p->type, &local_id);
      skip_mods_and_typedefs(targ_btf, targ_p->type, &targ_id);
      err = __bpf_core_types_are_compat(local_btf, local_id, targ_btf, targ_id,
                level - 1);
      if (err <= 0)
        return err;
    }

    /* tail recurse for return type check */
    skip_mods_and_typedefs(local_btf, local_type->type, &local_id);
    skip_mods_and_typedefs(targ_btf, targ_type->type, &targ_id);
    goto recur;
  }
  default:
    pr_warn("unexpected kind %s relocated, local [%d], target [%d]\n",
      btf_kind_str(local_type), local_id, targ_id);
    return 0;
  }
}

/*
 * Turn bpf_core_relo into a low- and high-level spec representation,
 * validating correctness along the way, as well as calculating resulting
 * field bit offset, specified by accessor string. Low-level spec captures
 * every single level of nestedness, including traversing anonymous
 * struct/union members. High-level one only captures semantically meaningful
 * "turning points": named fields and array indicies.
 * E.g., for this case:
 *
 *   struct sample {
 *       int __unimportant;
 *       struct {
 *           int __1;
 *           int __2;
 *           int a[7];
 *       };
 *   };
 *
 *   struct sample *s = ...;
 *
 *   int x = &s->a[3]; // access string = '0:1:2:3'
 *
 * Low-level spec has 1:1 mapping with each element of access string (it's
 * just a parsed access string representation): [0, 1, 2, 3].
 *
 * High-level spec will capture only 3 points:
 *   - initial zero-index access by pointer (&s->... is the same as &s[0]...);
 *   - field 'a' access (corresponds to '2' in low-level spec);
 *   - array element #3 access (corresponds to '3' in low-level spec).
 *
 * Type-based relocations (TYPE_EXISTS/TYPE_MATCHES/TYPE_SIZE,
 * TYPE_ID_LOCAL/TYPE_ID_TARGET) don't capture any field information. Their
 * spec and raw_spec are kept empty.
 *
 * Enum value-based relocations (ENUMVAL_EXISTS/ENUMVAL_VALUE) use access
 * string to specify enumerator's value index that need to be relocated.
 */
int bpf_core_parse_spec(const char *prog_name, const struct btf *btf,
      const struct bpf_core_relo *relo,
      struct bpf_core_spec *spec)
{
  int access_idx, parsed_len, i;
  struct bpf_core_accessor *acc;
  const struct btf_type *t;
  const char *name, *spec_str;
  __u32 id, name_off;
  __s64 sz;

  spec_str = btf__name_by_offset(btf, relo->access_str_off);
  if (str_is_empty(spec_str) || *spec_str == ':')
    return -EINVAL;

  memset(spec, 0, sizeof(*spec));
  spec->btf = btf;
  spec->root_type_id = relo->type_id;
  spec->relo_kind = relo->kind;

  /* type-based relocations don't have a field access string */
  if (core_relo_is_type_based(relo->kind)) {
    if (strcmp(spec_str, "0"))
      return -EINVAL;
    return 0;
  }

  /* parse spec_str="0:1:2:3:4" into array raw_spec=[0, 1, 2, 3, 4] */
  while (*spec_str) {
    if (*spec_str == ':')
      ++spec_str;
    if (sscanf(spec_str, "%d%n", &access_idx, &parsed_len) != 1)
      return -EINVAL;
    if (spec->raw_len == BPF_CORE_SPEC_MAX_LEN)
      return -E2BIG;
    spec_str += parsed_len;
    spec->raw_spec[spec->raw_len++] = access_idx;
  }

  if (spec->raw_len == 0)
    return -EINVAL;

  t = skip_mods_and_typedefs(btf, relo->type_id, &id);
  if (!t)
    return -EINVAL;

  access_idx = spec->raw_spec[0];
  acc = &spec->spec[0];
  acc->type_id = id;
  acc->idx = access_idx;
  spec->len++;

  if (core_relo_is_enumval_based(relo->kind)) {
    if (!btf_is_any_enum(t) || spec->raw_len > 1 || access_idx >= btf_vlen(t))
      return -EINVAL;

    /* record enumerator name in a first accessor */
    name_off = btf_is_enum(t) ? btf_enum(t)[access_idx].name_off
            : btf_enum64(t)[access_idx].name_off;
    acc->name = btf__name_by_offset(btf, name_off);
    return 0;
  }

  if (!core_relo_is_field_based(relo->kind))
    return -EINVAL;

  sz = btf__resolve_size(btf, id);
  if (sz < 0)
    return sz;
  spec->bit_offset = access_idx * sz * 8;

  for (i = 1; i < spec->raw_len; i++) {
    t = skip_mods_and_typedefs(btf, id, &id);
    if (!t)
      return -EINVAL;

    access_idx = spec->raw_spec[i];
    acc = &spec->spec[spec->len];

    if (btf_is_composite(t)) {
      const struct btf_member *m;
      __u32 bit_offset;

      if (access_idx >= btf_vlen(t))
        return -EINVAL;

      bit_offset = btf_member_bit_offset(t, access_idx);
      spec->bit_offset += bit_offset;

      m = btf_members(t) + access_idx;
      if (m->name_off) {
        name = btf__name_by_offset(btf, m->name_off);
        if (str_is_empty(name))
          return -EINVAL;

        acc->type_id = id;
        acc->idx = access_idx;
        acc->name = name;
        spec->len++;
      }

      id = m->type;
    } else if (btf_is_array(t)) {
      const struct btf_array *a = btf_array(t);
      bool flex;

      t = skip_mods_and_typedefs(btf, a->type, &id);
      if (!t)
        return -EINVAL;

      flex = is_flex_arr(btf, acc - 1, a);
      if (!flex && access_idx >= a->nelems)
        return -EINVAL;

      spec->spec[spec->len].type_id = id;
      spec->spec[spec->len].idx = access_idx;
      spec->len++;

      sz = btf__resolve_size(btf, id);
      if (sz < 0)
        return sz;
      spec->bit_offset += access_idx * sz * 8;
    } else {
      pr_warn("prog '%s': relo for [%u] %s (at idx %d) captures type [%d] of unexpected kind %s\n",
        prog_name, relo->type_id, spec_str, i, id, btf_kind_str(t));
      return -EINVAL;
    }
  }

  return 0;
}

/* Check two types for compatibility for the purpose of field access
 * relocation. const/volatile/restrict and typedefs are skipped to ensure we
 * are relocating semantically compatible entities:
 *   - any two STRUCTs/UNIONs are compatible and can be mixed;
 *   - any two FWDs are compatible, if their names match (modulo flavor suffix);
 *   - any two PTRs are always compatible;
 *   - for ENUMs, names should be the same (ignoring flavor suffix) or at
 *     least one of enums should be anonymous;
 *   - for ENUMs, check sizes, names are ignored;
 *   - for INT, size and signedness are ignored;
 *   - any two FLOATs are always compatible;
 *   - for ARRAY, dimensionality is ignored, element types are checked for
 *     compatibility recursively;
 *   - everything else shouldn't be ever a target of relocation.
 * These rules are not set in stone and probably will be adjusted as we get
 * more experience with using BPF CO-RE relocations.
 */
static int bpf_core_fields_are_compat(const struct btf *local_btf,
              __u32 local_id,
              const struct btf *targ_btf,
              __u32 targ_id)
{
  const struct btf_type *local_type, *targ_type;

recur:
  local_type = skip_mods_and_typedefs(local_btf, local_id, &local_id);
  targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
  if (!local_type || !targ_type)
    return -EINVAL;

  if (btf_is_composite(local_type) && btf_is_composite(targ_type))
    return 1;
  if (!btf_kind_core_compat(local_type, targ_type))
    return 0;

  switch (btf_kind(local_type)) {
  case BTF_KIND_PTR:
  case BTF_KIND_FLOAT:
    return 1;
  case BTF_KIND_FWD:
  case BTF_KIND_ENUM64:
  case BTF_KIND_ENUM: {
    const char *local_name, *targ_name;
    size_t local_len, targ_len;

    local_name = btf__name_by_offset(local_btf,
             local_type->name_off);
    targ_name = btf__name_by_offset(targ_btf, targ_type->name_off);
    local_len = bpf_core_essential_name_len(local_name);
    targ_len = bpf_core_essential_name_len(targ_name);
    /* one of them is anonymous or both w/ same flavor-less names */
    return local_len == 0 || targ_len == 0 ||
           (local_len == targ_len &&
      strncmp(local_name, targ_name, local_len) == 0);
  }
  case BTF_KIND_INT:
    /* just reject deprecated bitfield-like integers; all other
     * integers are by default compatible between each other
     */
    return btf_int_offset(local_type) == 0 &&
           btf_int_offset(targ_type) == 0;
  case BTF_KIND_ARRAY:
    local_id = btf_array(local_type)->type;
    targ_id = btf_array(targ_type)->type;
    goto recur;
  default:
    return 0;
  }
}

/*
 * Given single high-level named field accessor in local type, find
 * corresponding high-level accessor for a target type. Along the way,
 * maintain low-level spec for target as well. Also keep updating target
 * bit offset.
 *
 * Searching is performed through recursive exhaustive enumeration of all
 * fields of a struct/union. If there are any anonymous (embedded)
 * structs/unions, they are recursively searched as well. If field with
 * desired name is found, check compatibility between local and target types,
 * before returning result.
 *
 * 1 is returned, if field is found.
 * 0 is returned if no compatible field is found.
 * <0 is returned on error.
 */
static int bpf_core_match_member(const struct btf *local_btf,
         const struct bpf_core_accessor *local_acc,
         const struct btf *targ_btf,
         __u32 targ_id,
         struct bpf_core_spec *spec,
         __u32 *next_targ_id)
{
  const struct btf_type *local_type, *targ_type;
  const struct btf_member *local_member, *m;
  const char *local_name, *targ_name;
  __u32 local_id;
  int i, n, found;

  targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
  if (!targ_type)
    return -EINVAL;
  if (!btf_is_composite(targ_type))
    return 0;

  local_id = local_acc->type_id;
  local_type = btf_type_by_id(local_btf, local_id);
  local_member = btf_members(local_type) + local_acc->idx;
  local_name = btf__name_by_offset(local_btf, local_member->name_off);

  n = btf_vlen(targ_type);
  m = btf_members(targ_type);
  for (i = 0; i < n; i++, m++) {
    __u32 bit_offset;

    bit_offset = btf_member_bit_offset(targ_type, i);

    /* too deep struct/union/array nesting */
    if (spec->raw_len == BPF_CORE_SPEC_MAX_LEN)
      return -E2BIG;

    /* speculate this member will be the good one */
    spec->bit_offset += bit_offset;
    spec->raw_spec[spec->raw_len++] = i;

    targ_name = btf__name_by_offset(targ_btf, m->name_off);
    if (str_is_empty(targ_name)) {
      /* embedded struct/union, we need to go deeper */
      found = bpf_core_match_member(local_btf, local_acc,
                  targ_btf, m->type,
                  spec, next_targ_id);
      if (found) /* either found or error */
        return found;
    } else if (strcmp(local_name, targ_name) == 0) {
      /* matching named field */
      struct bpf_core_accessor *targ_acc;

      targ_acc = &spec->spec[spec->len++];
      targ_acc->type_id = targ_id;
      targ_acc->idx = i;
      targ_acc->name = targ_name;

      *next_targ_id = m->type;
      found = bpf_core_fields_are_compat(local_btf,
                 local_member->type,
                 targ_btf, m->type);
      if (!found)
        spec->len--; /* pop accessor */
      return found;
    }
    /* member turned out not to be what we looked for */
    spec->bit_offset -= bit_offset;
    spec->raw_len--;
  }

  return 0;
}

/*
 * Try to match local spec to a target type and, if successful, produce full
 * target spec (high-level, low-level + bit offset).
 */
static int bpf_core_spec_match(struct bpf_core_spec *local_spec,
             const struct btf *targ_btf, __u32 targ_id,
             struct bpf_core_spec *targ_spec)
{
  const struct btf_type *targ_type;
  const struct bpf_core_accessor *local_acc;
  struct bpf_core_accessor *targ_acc;
  int i, sz, matched;
  __u32 name_off;

  memset(targ_spec, 0, sizeof(*targ_spec));
  targ_spec->btf = targ_btf;
  targ_spec->root_type_id = targ_id;
  targ_spec->relo_kind = local_spec->relo_kind;

  if (core_relo_is_type_based(local_spec->relo_kind)) {
    if (local_spec->relo_kind == BPF_CORE_TYPE_MATCHES)
      return bpf_core_types_match(local_spec->btf,
                local_spec->root_type_id,
                targ_btf, targ_id);
    else
      return bpf_core_types_are_compat(local_spec->btf,
               local_spec->root_type_id,
               targ_btf, targ_id);
  }

  local_acc = &local_spec->spec[0];
  targ_acc = &targ_spec->spec[0];

  if (core_relo_is_enumval_based(local_spec->relo_kind)) {
    size_t local_essent_len, targ_essent_len;
    const char *targ_name;

    /* has to resolve to an enum */
    targ_type = skip_mods_and_typedefs(targ_spec->btf, targ_id, &targ_id);
    if (!btf_is_any_enum(targ_type))
      return 0;

    local_essent_len = bpf_core_essential_name_len(local_acc->name);

    for (i = 0; i < btf_vlen(targ_type); i++) {
      if (btf_is_enum(targ_type))
        name_off = btf_enum(targ_type)[i].name_off;
      else
        name_off = btf_enum64(targ_type)[i].name_off;

      targ_name = btf__name_by_offset(targ_spec->btf, name_off);
      targ_essent_len = bpf_core_essential_name_len(targ_name);
      if (targ_essent_len != local_essent_len)
        continue;
      if (strncmp(local_acc->name, targ_name, local_essent_len) == 0) {
        targ_acc->type_id = targ_id;
        targ_acc->idx = i;
        targ_acc->name = targ_name;
        targ_spec->len++;
        targ_spec->raw_spec[targ_spec->raw_len] = targ_acc->idx;
        targ_spec->raw_len++;
        return 1;
      }
    }
    return 0;
  }

  if (!core_relo_is_field_based(local_spec->relo_kind))
    return -EINVAL;

  for (i = 0; i < local_spec->len; i++, local_acc++, targ_acc++) {
    targ_type = skip_mods_and_typedefs(targ_spec->btf, targ_id,
               &targ_id);
    if (!targ_type)
      return -EINVAL;

    if (local_acc->name) {
      matched = bpf_core_match_member(local_spec->btf,
              local_acc,
              targ_btf, targ_id,
              targ_spec, &targ_id);
      if (matched <= 0)
        return matched;
    } else {
      /* for i=0, targ_id is already treated as array element
       * type (because it's the original struct), for others
       * we should find array element type first
       */
      if (i > 0) {
        const struct btf_array *a;
        bool flex;

        if (!btf_is_array(targ_type))
          return 0;

        a = btf_array(targ_type);
        flex = is_flex_arr(targ_btf, targ_acc - 1, a);
        if (!flex && local_acc->idx >= a->nelems)
          return 0;
        if (!skip_mods_and_typedefs(targ_btf, a->type,
                  &targ_id))
          return -EINVAL;
      }

      /* too deep struct/union/array nesting */
      if (targ_spec->raw_len == BPF_CORE_SPEC_MAX_LEN)
        return -E2BIG;

      targ_acc->type_id = targ_id;
      targ_acc->idx = local_acc->idx;
      targ_acc->name = NULL;
      targ_spec->len++;
      targ_spec->raw_spec[targ_spec->raw_len] = targ_acc->idx;
      targ_spec->raw_len++;

      sz = btf__resolve_size(targ_btf, targ_id);
      if (sz < 0)
        return sz;
      targ_spec->bit_offset += local_acc->idx * sz * 8;
    }
  }

  return 1;
}

static int bpf_core_calc_field_relo(const char *prog_name,
            const struct bpf_core_relo *relo,
            const struct bpf_core_spec *spec,
            __u64 *val, __u32 *field_sz, __u32 *type_id,
            bool *validate)
{
  const struct bpf_core_accessor *acc;
  const struct btf_type *t;
  __u32 byte_off, byte_sz, bit_off, bit_sz, field_type_id, elem_id;
  const struct btf_member *m;
  const struct btf_type *mt;
  bool bitfield;
  __s64 sz;

  *field_sz = 0;

  if (relo->kind == BPF_CORE_FIELD_EXISTS) {
    *val = spec ? 1 : 0;
    return 0;
  }

  if (!spec)
    return -EUCLEAN; /* request instruction poisoning */

  acc = &spec->spec[spec->len - 1];
  t = btf_type_by_id(spec->btf, acc->type_id);

  /* a[n] accessor needs special handling */
  if (!acc->name) {
    if (relo->kind == BPF_CORE_FIELD_BYTE_OFFSET) {
      *val = spec->bit_offset / 8;
      /* remember field size for load/store mem size;
       * note, for arrays we care about individual element
       * sizes, not the overall array size
       */
      t = skip_mods_and_typedefs(spec->btf, acc->type_id, &elem_id);
      while (btf_is_array(t))
        t = skip_mods_and_typedefs(spec->btf, btf_array(t)->type, &elem_id);
      sz = btf__resolve_size(spec->btf, elem_id);
      if (sz < 0)
        return -EINVAL;
      *field_sz = sz;
      *type_id = acc->type_id;
    } else if (relo->kind == BPF_CORE_FIELD_BYTE_SIZE) {
      sz = btf__resolve_size(spec->btf, acc->type_id);
      if (sz < 0)
        return -EINVAL;
      *val = sz;
    } else {
      pr_warn("prog '%s': relo %d at insn #%d can't be applied to array access\n",
        prog_name, relo->kind, relo->insn_off / 8);
      return -EINVAL;
    }
    if (validate)
      *validate = true;
    return 0;
  }

  m = btf_members(t) + acc->idx;
  mt = skip_mods_and_typedefs(spec->btf, m->type, &field_type_id);
  bit_off = spec->bit_offset;
  bit_sz = btf_member_bitfield_size(t, acc->idx);

  bitfield = bit_sz > 0;
  if (bitfield) {
    byte_sz = mt->size;
    byte_off = bit_off / 8 / byte_sz * byte_sz;
    /* figure out smallest int size necessary for bitfield load */
    while (bit_off + bit_sz - byte_off * 8 > byte_sz * 8) {
      if (byte_sz >= 8) {
        /* bitfield can't be read with 64-bit read */
        pr_warn("prog '%s': relo %d at insn #%d can't be satisfied for bitfield\n",
          prog_name, relo->kind, relo->insn_off / 8);
        return -E2BIG;
      }
      byte_sz *= 2;
      byte_off = bit_off / 8 / byte_sz * byte_sz;
    }
  } else {
    sz = btf__resolve_size(spec->btf, field_type_id);
    if (sz < 0)
      return -EINVAL;
    byte_sz = sz;
    byte_off = spec->bit_offset / 8;
    bit_sz = byte_sz * 8;
  }

  /* for bitfields, all the relocatable aspects are ambiguous and we
   * might disagree with compiler, so turn off validation of expected
   * value, except for signedness
   */
  if (validate)
    *validate = !bitfield;

  switch (relo->kind) {
  case BPF_CORE_FIELD_BYTE_OFFSET:
    *val = byte_off;
    if (!bitfield) {
      /* remember field size for load/store mem size;
       * note, for arrays we care about individual element
       * sizes, not the overall array size
       */
      t = skip_mods_and_typedefs(spec->btf, field_type_id, &elem_id);
      while (btf_is_array(t))
        t = skip_mods_and_typedefs(spec->btf, btf_array(t)->type, &elem_id);
      sz = btf__resolve_size(spec->btf, elem_id);
      if (sz < 0)
        return -EINVAL;
      *field_sz = sz;
      *type_id = field_type_id;
    }
    break;
  case BPF_CORE_FIELD_BYTE_SIZE:
    *val = byte_sz;
    break;
  case BPF_CORE_FIELD_SIGNED:
    *val = (btf_is_any_enum(mt) && BTF_INFO_KFLAG(mt->info)) ||
           (btf_is_int(mt) && (btf_int_encoding(mt) & BTF_INT_SIGNED));
    if (validate)
      *validate = true; /* signedness is never ambiguous */
    break;
  case BPF_CORE_FIELD_LSHIFT_U64:
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
    *val = 64 - (bit_off + bit_sz - byte_off  * 8);
#else
    *val = (8 - byte_sz) * 8 + (bit_off - byte_off * 8);
#endif
    break;
  case BPF_CORE_FIELD_RSHIFT_U64:
    *val = 64 - bit_sz;
    if (validate)
      *validate = true; /* right shift is never ambiguous */
    break;
  case BPF_CORE_FIELD_EXISTS:
  default:
    return -EOPNOTSUPP;
  }

  return 0;
}

static int bpf_core_calc_type_relo(const struct bpf_core_relo *relo,
           const struct bpf_core_spec *spec,
           __u64 *val, bool *validate)
{
  __s64 sz;

  /* by default, always check expected value in bpf_insn */
  if (validate)
    *validate = true;

  /* type-based relos return zero when target type is not found */
  if (!spec) {
    *val = 0;
    return 0;
  }

  switch (relo->kind) {
  case BPF_CORE_TYPE_ID_TARGET:
    *val = spec->root_type_id;
    /* type ID, embedded in bpf_insn, might change during linking,
     * so enforcing it is pointless
     */
    if (validate)
      *validate = false;
    break;
  case BPF_CORE_TYPE_EXISTS:
  case BPF_CORE_TYPE_MATCHES:
    *val = 1;
    break;
  case BPF_CORE_TYPE_SIZE:
    sz = btf__resolve_size(spec->btf, spec->root_type_id);
    if (sz < 0)
      return -EINVAL;
    *val = sz;
    break;
  case BPF_CORE_TYPE_ID_LOCAL:
  /* BPF_CORE_TYPE_ID_LOCAL is handled specially and shouldn't get here */
  default:
    return -EOPNOTSUPP;
  }

  return 0;
}

static int bpf_core_calc_enumval_relo(const struct bpf_core_relo *relo,
              const struct bpf_core_spec *spec,
              __u64 *val)
{
  const struct btf_type *t;

  switch (relo->kind) {
  case BPF_CORE_ENUMVAL_EXISTS:
    *val = spec ? 1 : 0;
    break;
  case BPF_CORE_ENUMVAL_VALUE:
    if (!spec)
      return -EUCLEAN; /* request instruction poisoning */
    t = btf_type_by_id(spec->btf, spec->spec[0].type_id);
    if (btf_is_enum(t))
      *val = btf_enum(t)[spec->spec[0].idx].val;
    else
      *val = btf_enum64_value(btf_enum64(t) + spec->spec[0].idx);
    break;
  default:
    return -EOPNOTSUPP;
  }

  return 0;
}

/* Calculate original and target relocation values, given local and target
 * specs and relocation kind. These values are calculated for each candidate.
 * If there are multiple candidates, resulting values should all be consistent
 * with each other. Otherwise, libbpf will refuse to proceed due to ambiguity.
 * If instruction has to be poisoned, *poison will be set to true.
 */
static int bpf_core_calc_relo(const char *prog_name,
            const struct bpf_core_relo *relo,
            int relo_idx,
            const struct bpf_core_spec *local_spec,
            const struct bpf_core_spec *targ_spec,
            struct bpf_core_relo_res *res)
{
  int err = -EOPNOTSUPP;

  res->orig_val = 0;
  res->new_val = 0;
  res->poison = false;
  res->validate = true;
  res->fail_memsz_adjust = false;
  res->orig_sz = res->new_sz = 0;
  res->orig_type_id = res->new_type_id = 0;

  if (core_relo_is_field_based(relo->kind)) {
    err = bpf_core_calc_field_relo(prog_name, relo, local_spec,
                 &res->orig_val, &res->orig_sz,
                 &res->orig_type_id, &res->validate);
    err = err ?: bpf_core_calc_field_relo(prog_name, relo, targ_spec,
                  &res->new_val, &res->new_sz,
                  &res->new_type_id, NULL);
    if (err)
      goto done;
    /* Validate if it's safe to adjust load/store memory size.
     * Adjustments are performed only if original and new memory
     * sizes differ.
     */
    res->fail_memsz_adjust = false;
    if (res->orig_sz != res->new_sz) {
      const struct btf_type *orig_t, *new_t;

      orig_t = btf_type_by_id(local_spec->btf, res->orig_type_id);
      new_t = btf_type_by_id(targ_spec->btf, res->new_type_id);

      /* There are two use cases in which it's safe to
       * adjust load/store's mem size:
       *   - reading a 32-bit kernel pointer, while on BPF
       *   size pointers are always 64-bit; in this case
       *   it's safe to "downsize" instruction size due to
       *   pointer being treated as unsigned integer with
       *   zero-extended upper 32-bits;
       *   - reading unsigned integers, again due to
       *   zero-extension is preserving the value correctly.
       *
       * In all other cases it's incorrect to attempt to
       * load/store field because read value will be
       * incorrect, so we poison relocated instruction.
       */
      if (btf_is_ptr(orig_t) && btf_is_ptr(new_t))
        goto done;
      if (btf_is_int(orig_t) && btf_is_int(new_t) &&
          btf_int_encoding(orig_t) != BTF_INT_SIGNED &&
          btf_int_encoding(new_t) != BTF_INT_SIGNED)
        goto done;

      /* mark as invalid mem size adjustment, but this will
       * only be checked for LDX/STX/ST insns
       */
      res->fail_memsz_adjust = true;
    }
  } else if (core_relo_is_type_based(relo->kind)) {
    err = bpf_core_calc_type_relo(relo, local_spec, &res->orig_val, &res->validate);
    err = err ?: bpf_core_calc_type_relo(relo, targ_spec, &res->new_val, NULL);
  } else if (core_relo_is_enumval_based(relo->kind)) {
    err = bpf_core_calc_enumval_relo(relo, local_spec, &res->orig_val);
    err = err ?: bpf_core_calc_enumval_relo(relo, targ_spec, &res->new_val);
  }

done:
  if (err == -EUCLEAN) {
    /* EUCLEAN is used to signal instruction poisoning request */
    res->poison = true;
    err = 0;
  } else if (err == -EOPNOTSUPP) {
    /* EOPNOTSUPP means unknown/unsupported relocation */
    pr_warn("prog '%s': relo #%d: unrecognized CO-RE relocation %s (%d) at insn #%d\n",
      prog_name, relo_idx, core_relo_kind_str(relo->kind),
      relo->kind, relo->insn_off / 8);
  }

  return err;
}

/*
 * Turn instruction for which CO_RE relocation failed into invalid one with
 * distinct signature.
 */
static void bpf_core_poison_insn(const char *prog_name, int relo_idx,
         int insn_idx, struct bpf_insn *insn)
{
  pr_debug("prog '%s': relo #%d: substituting insn #%d w/ invalid insn\n",
     prog_name, relo_idx, insn_idx);
  insn->code = BPF_JMP | BPF_CALL;
  insn->dst_reg = 0;
  insn->src_reg = 0;
  insn->off = 0;
  /* if this instruction is reachable (not a dead code),
   * verifier will complain with the following message:
   * invalid func unknown#195896080
   */
  insn->imm = 195896080; /* => 0xbad2310 => "bad relo" */
}

static int insn_bpf_size_to_bytes(struct bpf_insn *insn)
{
  switch (BPF_SIZE(insn->code)) {
  case BPF_DW: return 8;
  case BPF_W: return 4;
  case BPF_H: return 2;
  case BPF_B: return 1;
  default: return -1;
  }
}

static int insn_bytes_to_bpf_size(__u32 sz)
{
  switch (sz) {
  case 8: return BPF_DW;
  case 4: return BPF_W;
  case 2: return BPF_H;
  case 1: return BPF_B;
  default: return -1;
  }
}

/*
 * Patch relocatable BPF instruction.
 *
 * Patched value is determined by relocation kind and target specification.
 * For existence relocations target spec will be NULL if field/type is not found.
 * Expected insn->imm value is determined using relocation kind and local
 * spec, and is checked before patching instruction. If actual insn->imm value
 * is wrong, bail out with error.
 *
 * Currently supported classes of BPF instruction are:
 * 1. rX = <imm> (assignment with immediate operand);
 * 2. rX += <imm> (arithmetic operations with immediate operand);
 * 3. rX = <imm64> (load with 64-bit immediate value);
 * 4. rX = *(T *)(rY + <off>), where T is one of {u8, u16, u32, u64};
 * 5. *(T *)(rX + <off>) = rY, where T is one of {u8, u16, u32, u64};
 * 6. *(T *)(rX + <off>) = <imm>, where T is one of {u8, u16, u32, u64}.
 */
int bpf_core_patch_insn(const char *prog_name, struct bpf_insn *insn,
      int insn_idx, const struct bpf_core_relo *relo,
      int relo_idx, const struct bpf_core_relo_res *res)
{
  __u64 orig_val, new_val;
  __u8 class;

  class = BPF_CLASS(insn->code);

  if (res->poison) {
poison:
    /* poison second part of ldimm64 to avoid confusing error from
     * verifier about "unknown opcode 00"
     */
    if (is_ldimm64_insn(insn))
      bpf_core_poison_insn(prog_name, relo_idx, insn_idx + 1, insn + 1);
    bpf_core_poison_insn(prog_name, relo_idx, insn_idx, insn);
    return 0;
  }

  orig_val = res->orig_val;
  new_val = res->new_val;

  switch (class) {
  case BPF_ALU:
  case BPF_ALU64:
    if (BPF_SRC(insn->code) != BPF_K)
      return -EINVAL;
    if (res->validate && insn->imm != orig_val) {
      pr_warn("prog '%s': relo #%d: unexpected insn #%d (ALU/ALU64) value: got %u, exp %llu -> %llu\n",
        prog_name, relo_idx,
        insn_idx, insn->imm, (unsigned long long)orig_val,
        (unsigned long long)new_val);
      return -EINVAL;
    }
    orig_val = insn->imm;
    insn->imm = new_val;
    pr_debug("prog '%s': relo #%d: patched insn #%d (ALU/ALU64) imm %llu -> %llu\n",
       prog_name, relo_idx, insn_idx,
       (unsigned long long)orig_val, (unsigned long long)new_val);
    break;
  case BPF_LDX:
  case BPF_ST:
  case BPF_STX:
    if (res->validate && insn->off != orig_val) {
      pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDX/ST/STX) value: got %u, exp %llu -> %llu\n",
        prog_name, relo_idx, insn_idx, insn->off, (unsigned long long)orig_val,
        (unsigned long long)new_val);
      return -EINVAL;
    }
    if (new_val > SHRT_MAX) {
      pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) value too big: %llu\n",
        prog_name, relo_idx, insn_idx, (unsigned long long)new_val);
      return -ERANGE;
    }
    if (res->fail_memsz_adjust) {
      pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) accesses field incorrectly. "
        "Make sure you are accessing pointers, unsigned integers, or fields of matching type and size.\n",
        prog_name, relo_idx, insn_idx);
      goto poison;
    }

    orig_val = insn->off;
    insn->off = new_val;
    pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) off %llu -> %llu\n",
       prog_name, relo_idx, insn_idx, (unsigned long long)orig_val,
       (unsigned long long)new_val);

    if (res->new_sz != res->orig_sz) {
      int insn_bytes_sz, insn_bpf_sz;

      insn_bytes_sz = insn_bpf_size_to_bytes(insn);
      if (insn_bytes_sz != res->orig_sz) {
        pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) unexpected mem size: got %d, exp %u\n",
          prog_name, relo_idx, insn_idx, insn_bytes_sz, res->orig_sz);
        return -EINVAL;
      }

      insn_bpf_sz = insn_bytes_to_bpf_size(res->new_sz);
      if (insn_bpf_sz < 0) {
        pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) invalid new mem size: %u\n",
          prog_name, relo_idx, insn_idx, res->new_sz);
        return -EINVAL;
      }

      insn->code = BPF_MODE(insn->code) | insn_bpf_sz | BPF_CLASS(insn->code);
      pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) mem_sz %u -> %u\n",
         prog_name, relo_idx, insn_idx, res->orig_sz, res->new_sz);
    }
    break;
  case BPF_LD: {
    __u64 imm;

    if (!is_ldimm64_insn(insn) ||
        insn[0].src_reg != 0 || insn[0].off != 0 ||
        insn[1].code != 0 || insn[1].dst_reg != 0 ||
        insn[1].src_reg != 0 || insn[1].off != 0) {
      pr_warn("prog '%s': relo #%d: insn #%d (LDIMM64) has unexpected form\n",
        prog_name, relo_idx, insn_idx);
      return -EINVAL;
    }

    imm = (__u32)insn[0].imm | ((__u64)insn[1].imm << 32);
    if (res->validate && imm != orig_val) {
      pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDIMM64) value: got %llu, exp %llu -> %llu\n",
        prog_name, relo_idx,
        insn_idx, (unsigned long long)imm,
        (unsigned long long)orig_val, (unsigned long long)new_val);
      return -EINVAL;
    }

    insn[0].imm = new_val;
    insn[1].imm = new_val >> 32;
    pr_debug("prog '%s': relo #%d: patched insn #%d (LDIMM64) imm64 %llu -> %llu\n",
       prog_name, relo_idx, insn_idx,
       (unsigned long long)imm, (unsigned long long)new_val);
    break;
  }
  default:
    pr_warn("prog '%s': relo #%d: trying to relocate unrecognized insn #%d, code:0x%x, src:0x%x, dst:0x%x, off:0x%x, imm:0x%x\n",
      prog_name, relo_idx, insn_idx, insn->code,
      insn->src_reg, insn->dst_reg, insn->off, insn->imm);
    return -EINVAL;
  }

  return 0;
}

/* Output spec definition in the format:
 * [<type-id>] (<type-name>) + <raw-spec> => <offset>@<spec>,
 * where <spec> is a C-syntax view of recorded field access, e.g.: x.a[3].b
 */
int bpf_core_format_spec(char *buf, size_t buf_sz, const struct bpf_core_spec *spec)
{
  const struct btf_type *t;
  const char *s;
  __u32 type_id;
  int i, len = 0;

#define append_buf(fmt, args...)        \
  ({              \
    int r;            \
    r = snprintf(buf, buf_sz, fmt, ##args);    \
    len += r;         \
    if (r >= buf_sz)       \
      r = buf_sz;       \
    buf += r;         \
    buf_sz -= r;          \
  })

  type_id = spec->root_type_id;
  t = btf_type_by_id(spec->btf, type_id);
  s = btf__name_by_offset(spec->btf, t->name_off);

  append_buf("<%s> [%u] %s %s",
       core_relo_kind_str(spec->relo_kind),
       type_id, btf_kind_str(t), str_is_empty(s) ? "<anon>" : s);

  if (core_relo_is_type_based(spec->relo_kind))
    return len;

  if (core_relo_is_enumval_based(spec->relo_kind)) {
    t = skip_mods_and_typedefs(spec->btf, type_id, NULL);
    if (btf_is_enum(t)) {
      const struct btf_enum *e;
      const char *fmt_str;

      e = btf_enum(t) + spec->raw_spec[0];
      s = btf__name_by_offset(spec->btf, e->name_off);
      fmt_str = BTF_INFO_KFLAG(t->info) ? "::%s = %d" : "::%s = %u";
      append_buf(fmt_str, s, e->val);
    } else {
      const struct btf_enum64 *e;
      const char *fmt_str;

      e = btf_enum64(t) + spec->raw_spec[0];
      s = btf__name_by_offset(spec->btf, e->name_off);
      fmt_str = BTF_INFO_KFLAG(t->info) ? "::%s = %lld" : "::%s = %llu";
      append_buf(fmt_str, s, (unsigned long long)btf_enum64_value(e));
    }
    return len;
  }

  if (core_relo_is_field_based(spec->relo_kind)) {
    for (i = 0; i < spec->len; i++) {
      if (spec->spec[i].name)
        append_buf(".%s", spec->spec[i].name);
      else if (i > 0 || spec->spec[i].idx > 0)
        append_buf("[%u]", spec->spec[i].idx);
    }

    append_buf(" (");
    for (i = 0; i < spec->raw_len; i++)
      append_buf("%s%d", i == 0 ? "" : ":", spec->raw_spec[i]);

    if (spec->bit_offset % 8)
      append_buf(" @ offset %u.%u)", spec->bit_offset / 8, spec->bit_offset % 8);
    else
      append_buf(" @ offset %u)", spec->bit_offset / 8);
    return len;
  }

  return len;
#undef append_buf
}

/*
 * Calculate CO-RE relocation target result.
 *
 * The outline and important points of the algorithm:
 * 1. For given local type, find corresponding candidate target types.
 *    Candidate type is a type with the same "essential" name, ignoring
 *    everything after last triple underscore (___). E.g., `sample`,
 *    `sample___flavor_one`, `sample___flavor_another_one`, are all candidates
 *    for each other. Names with triple underscore are referred to as
 *    "flavors" and are useful, among other things, to allow to
 *    specify/support incompatible variations of the same kernel struct, which
 *    might differ between different kernel versions and/or build
 *    configurations.
 *
 *    N.B. Struct "flavors" could be generated by bpftool's BTF-to-C
 *    converter, when deduplicated BTF of a kernel still contains more than
 *    one different types with the same name. In that case, ___2, ___3, etc
 *    are appended starting from second name conflict. But start flavors are
 *    also useful to be defined "locally", in BPF program, to extract same
 *    data from incompatible changes between different kernel
 *    versions/configurations. For instance, to handle field renames between
 *    kernel versions, one can use two flavors of the struct name with the
 *    same common name and use conditional relocations to extract that field,
 *    depending on target kernel version.
 * 2. For each candidate type, try to match local specification to this
 *    candidate target type. Matching involves finding corresponding
 *    high-level spec accessors, meaning that all named fields should match,
 *    as well as all array accesses should be within the actual bounds. Also,
 *    types should be compatible (see bpf_core_fields_are_compat for details).
 * 3. It is supported and expected that there might be multiple flavors
 *    matching the spec. As long as all the specs resolve to the same set of
 *    offsets across all candidates, there is no error. If there is any
 *    ambiguity, CO-RE relocation will fail. This is necessary to accommodate
 *    imperfection of BTF deduplication, which can cause slight duplication of
 *    the same BTF type, if some directly or indirectly referenced (by
 *    pointer) type gets resolved to different actual types in different
 *    object files. If such a situation occurs, deduplicated BTF will end up
 *    with two (or more) structurally identical types, which differ only in
 *    types they refer to through pointer. This should be OK in most cases and
 *    is not an error.
 * 4. Candidate types search is performed by linearly scanning through all
 *    types in target BTF. It is anticipated that this is overall more
 *    efficient memory-wise and not significantly worse (if not better)
 *    CPU-wise compared to prebuilding a map from all local type names to
 *    a list of candidate type names. It's also sped up by caching resolved
 *    list of matching candidates per each local "root" type ID, that has at
 *    least one bpf_core_relo associated with it. This list is shared
 *    between multiple relocations for the same type ID and is updated as some
 *    of the candidates are pruned due to structural incompatibility.
 */
int bpf_core_calc_relo_insn(const char *prog_name,
          const struct bpf_core_relo *relo,
          int relo_idx,
          const struct btf *local_btf,
          struct bpf_core_cand_list *cands,
          struct bpf_core_spec *specs_scratch,
          struct bpf_core_relo_res *targ_res)
{
  struct bpf_core_spec *local_spec = &specs_scratch[0];
  struct bpf_core_spec *cand_spec = &specs_scratch[1];
  struct bpf_core_spec *targ_spec = &specs_scratch[2];
  struct bpf_core_relo_res cand_res;
  const struct btf_type *local_type;
  const char *local_name;
  __u32 local_id;
  char spec_buf[256];
  int i, j, err;

  local_id = relo->type_id;
  local_type = btf_type_by_id(local_btf, local_id);
  local_name = btf__name_by_offset(local_btf, local_type->name_off);
  if (!local_name)
    return -EINVAL;

  err = bpf_core_parse_spec(prog_name, local_btf, relo, local_spec);
  if (err) {
    const char *spec_str;

    spec_str = btf__name_by_offset(local_btf, relo->access_str_off);
    pr_warn("prog '%s': relo #%d: parsing [%d] %s %s + %s failed: %d\n",
      prog_name, relo_idx, local_id, btf_kind_str(local_type),
      str_is_empty(local_name) ? "<anon>" : local_name,
      spec_str ?: "<?>", err);
    return -EINVAL;
  }

  bpf_core_format_spec(spec_buf, sizeof(spec_buf), local_spec);
  pr_debug("prog '%s': relo #%d: %s\n", prog_name, relo_idx, spec_buf);

  /* TYPE_ID_LOCAL relo is special and doesn't need candidate search */
  if (relo->kind == BPF_CORE_TYPE_ID_LOCAL) {
    /* bpf_insn's imm value could get out of sync during linking */
    memset(targ_res, 0, sizeof(*targ_res));
    targ_res->validate = false;
    targ_res->poison = false;
    targ_res->orig_val = local_spec->root_type_id;
    targ_res->new_val = local_spec->root_type_id;
    return 0;
  }

  /* libbpf doesn't support candidate search for anonymous types */
  if (str_is_empty(local_name)) {
    pr_warn("prog '%s': relo #%d: <%s> (%d) relocation doesn't support anonymous types\n",
      prog_name, relo_idx, core_relo_kind_str(relo->kind), relo->kind);
    return -EOPNOTSUPP;
  }

  for (i = 0, j = 0; i < cands->len; i++) {
    err = bpf_core_spec_match(local_spec, cands->cands[i].btf,
            cands->cands[i].id, cand_spec);
    if (err < 0) {
      bpf_core_format_spec(spec_buf, sizeof(spec_buf), cand_spec);
      pr_warn("prog '%s': relo #%d: error matching candidate #%d %s: %d\n",
        prog_name, relo_idx, i, spec_buf, err);
      return err;
    }

    bpf_core_format_spec(spec_buf, sizeof(spec_buf), cand_spec);
    pr_debug("prog '%s': relo #%d: %s candidate #%d %s\n", prog_name,
       relo_idx, err == 0 ? "non-matching" : "matching", i, spec_buf);

    if (err == 0)
      continue;

    err = bpf_core_calc_relo(prog_name, relo, relo_idx, local_spec, cand_spec, &cand_res);
    if (err)
      return err;

    if (j == 0) {
      *targ_res = cand_res;
      *targ_spec = *cand_spec;
    } else if (cand_spec->bit_offset != targ_spec->bit_offset) {
      /* if there are many field relo candidates, they
       * should all resolve to the same bit offset
       */
      pr_warn("prog '%s': relo #%d: field offset ambiguity: %u != %u\n",
        prog_name, relo_idx, cand_spec->bit_offset,
        targ_spec->bit_offset);
      return -EINVAL;
    } else if (cand_res.poison != targ_res->poison ||
         cand_res.new_val != targ_res->new_val) {
      /* all candidates should result in the same relocation
       * decision and value, otherwise it's dangerous to
       * proceed due to ambiguity
       */
      pr_warn("prog '%s': relo #%d: relocation decision ambiguity: %s %llu != %s %llu\n",
        prog_name, relo_idx,
        cand_res.poison ? "failure" : "success",
        (unsigned long long)cand_res.new_val,
        targ_res->poison ? "failure" : "success",
        (unsigned long long)targ_res->new_val);
      return -EINVAL;
    }

    cands->cands[j++] = cands->cands[i];
  }

  /*
   * For BPF_CORE_FIELD_EXISTS relo or when used BPF program has field
   * existence checks or kernel version/config checks, it's expected
   * that we might not find any candidates. In this case, if field
   * wasn't found in any candidate, the list of candidates shouldn't
   * change at all, we'll just handle relocating appropriately,
   * depending on relo's kind.
   */
  if (j > 0)
    cands->len = j;

  /*
   * If no candidates were found, it might be both a programmer error,
   * as well as expected case, depending whether instruction w/
   * relocation is guarded in some way that makes it unreachable (dead
   * code) if relocation can't be resolved. This is handled in
   * bpf_core_patch_insn() uniformly by replacing that instruction with
   * BPF helper call insn (using invalid helper ID). If that instruction
   * is indeed unreachable, then it will be ignored and eliminated by
   * verifier. If it was an error, then verifier will complain and point
   * to a specific instruction number in its log.
   */
  if (j == 0) {
    pr_debug("prog '%s': relo #%d: no matching targets found\n",
       prog_name, relo_idx);

    /* calculate single target relo result explicitly */
    err = bpf_core_calc_relo(prog_name, relo, relo_idx, local_spec, NULL, targ_res);
    if (err)
      return err;
  }

  return 0;
}

static bool bpf_core_names_match(const struct btf *local_btf, size_t local_name_off,
         const struct btf *targ_btf, size_t targ_name_off)
{
  const char *local_n, *targ_n;
  size_t local_len, targ_len;

  local_n = btf__name_by_offset(local_btf, local_name_off);
  targ_n = btf__name_by_offset(targ_btf, targ_name_off);

  if (str_is_empty(targ_n))
    return str_is_empty(local_n);

  targ_len = bpf_core_essential_name_len(targ_n);
  local_len = bpf_core_essential_name_len(local_n);

  return targ_len == local_len && strncmp(local_n, targ_n, local_len) == 0;
}

static int bpf_core_enums_match(const struct btf *local_btf, const struct btf_type *local_t,
        const struct btf *targ_btf, const struct btf_type *targ_t)
{
  __u16 local_vlen = btf_vlen(local_t);
  __u16 targ_vlen = btf_vlen(targ_t);
  int i, j;

  if (local_t->size != targ_t->size)
    return 0;

  if (local_vlen > targ_vlen)
    return 0;

  /* iterate over the local enum's variants and make sure each has
   * a symbolic name correspondent in the target
   */
  for (i = 0; i < local_vlen; i++) {
    bool matched = false;
    __u32 local_n_off, targ_n_off;

    local_n_off = btf_is_enum(local_t) ? btf_enum(local_t)[i].name_off :
                 btf_enum64(local_t)[i].name_off;

    for (j = 0; j < targ_vlen; j++) {
      targ_n_off = btf_is_enum(targ_t) ? btf_enum(targ_t)[j].name_off :
                 btf_enum64(targ_t)[j].name_off;

      if (bpf_core_names_match(local_btf, local_n_off, targ_btf, targ_n_off)) {
        matched = true;
        break;
      }
    }

    if (!matched)
      return 0;
  }
  return 1;
}

static int bpf_core_composites_match(const struct btf *local_btf, const struct btf_type *local_t,
             const struct btf *targ_btf, const struct btf_type *targ_t,
             bool behind_ptr, int level)
{
  const struct btf_member *local_m = btf_members(local_t);
  __u16 local_vlen = btf_vlen(local_t);
  __u16 targ_vlen = btf_vlen(targ_t);
  int i, j, err;

  if (local_vlen > targ_vlen)
    return 0;

  /* check that all local members have a match in the target */
  for (i = 0; i < local_vlen; i++, local_m++) {
    const struct btf_member *targ_m = btf_members(targ_t);
    bool matched = false;

    for (j = 0; j < targ_vlen; j++, targ_m++) {
      if (!bpf_core_names_match(local_btf, local_m->name_off,
              targ_btf, targ_m->name_off))
        continue;

      err = __bpf_core_types_match(local_btf, local_m->type, targ_btf,
                 targ_m->type, behind_ptr, level - 1);
      if (err < 0)
        return err;
      if (err > 0) {
        matched = true;
        break;
      }
    }

    if (!matched)
      return 0;
  }
  return 1;
}

/* Check that two types "match". This function assumes that root types were
 * already checked for name match.
 *
 * The matching relation is defined as follows:
 * - modifiers and typedefs are stripped (and, hence, effectively ignored)
 * - generally speaking types need to be of same kind (struct vs. struct, union
 *   vs. union, etc.)
 *   - exceptions are struct/union behind a pointer which could also match a
 *     forward declaration of a struct or union, respectively, and enum vs.
 *     enum64 (see below)
 * Then, depending on type:
 * - integers:
 *   - match if size and signedness match
 * - arrays & pointers:
 *   - target types are recursively matched
 * - structs & unions:
 *   - local members need to exist in target with the same name
 *   - for each member we recursively check match unless it is already behind a
 *     pointer, in which case we only check matching names and compatible kind
 * - enums:
 *   - local variants have to have a match in target by symbolic name (but not
 *     numeric value)
 *   - size has to match (but enum may match enum64 and vice versa)
 * - function pointers:
 *   - number and position of arguments in local type has to match target
 *   - for each argument and the return value we recursively check match
 */
int __bpf_core_types_match(const struct btf *local_btf, __u32 local_id, const struct btf *targ_btf,
         __u32 targ_id, bool behind_ptr, int level)
{
  const struct btf_type *local_t, *targ_t;
  int depth = 32; /* max recursion depth */
  __u16 local_k, targ_k;

  if (level <= 0)
    return -EINVAL;

recur:
  depth--;
  if (depth < 0)
    return -EINVAL;

  local_t = skip_mods_and_typedefs(local_btf, local_id, &local_id);
  targ_t = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
  if (!local_t || !targ_t)
    return -EINVAL;

  /* While the name check happens after typedefs are skipped, root-level
   * typedefs would still be name-matched as that's the contract with
   * callers.
   */
  if (!bpf_core_names_match(local_btf, local_t->name_off, targ_btf, targ_t->name_off))
    return 0;

  local_k = btf_kind(local_t);
  targ_k = btf_kind(targ_t);

  switch (local_k) {
  case BTF_KIND_UNKN:
    return local_k == targ_k;
  case BTF_KIND_FWD: {
    bool local_f = BTF_INFO_KFLAG(local_t->info);

    if (behind_ptr) {
      if (local_k == targ_k)
        return local_f == BTF_INFO_KFLAG(targ_t->info);

      /* for forward declarations kflag dictates whether the
       * target is a struct (0) or union (1)
       */
      return (targ_k == BTF_KIND_STRUCT && !local_f) ||
             (targ_k == BTF_KIND_UNION && local_f);
    } else {
      if (local_k != targ_k)
        return 0;

      /* match if the forward declaration is for the same kind */
      return local_f == BTF_INFO_KFLAG(targ_t->info);
    }
  }
  case BTF_KIND_ENUM:
  case BTF_KIND_ENUM64:
    if (!btf_is_any_enum(targ_t))
      return 0;

    return bpf_core_enums_match(local_btf, local_t, targ_btf, targ_t);
  case BTF_KIND_STRUCT:
  case BTF_KIND_UNION:
    if (behind_ptr) {
      bool targ_f = BTF_INFO_KFLAG(targ_t->info);

      if (local_k == targ_k)
        return 1;

      if (targ_k != BTF_KIND_FWD)
        return 0;

      return (local_k == BTF_KIND_UNION) == targ_f;
    } else {
      if (local_k != targ_k)
        return 0;

      return bpf_core_composites_match(local_btf, local_t, targ_btf, targ_t,
               behind_ptr, level);
    }
  case BTF_KIND_INT: {
    __u8 local_sgn;
    __u8 targ_sgn;

    if (local_k != targ_k)
      return 0;

    local_sgn = btf_int_encoding(local_t) & BTF_INT_SIGNED;
    targ_sgn = btf_int_encoding(targ_t) & BTF_INT_SIGNED;

    return local_t->size == targ_t->size && local_sgn == targ_sgn;
  }
  case BTF_KIND_PTR:
    if (local_k != targ_k)
      return 0;

    behind_ptr = true;

    local_id = local_t->type;
    targ_id = targ_t->type;
    goto recur;
  case BTF_KIND_ARRAY: {
    const struct btf_array *local_array = btf_array(local_t);
    const struct btf_array *targ_array = btf_array(targ_t);

    if (local_k != targ_k)
      return 0;

    if (local_array->nelems != targ_array->nelems)
      return 0;

    local_id = local_array->type;
    targ_id = targ_array->type;
    goto recur;
  }
  case BTF_KIND_FUNC_PROTO: {
    struct btf_param *local_p = btf_params(local_t);
    struct btf_param *targ_p = btf_params(targ_t);
    __u16 local_vlen = btf_vlen(local_t);
    __u16 targ_vlen = btf_vlen(targ_t);
    int i, err;

    if (local_k != targ_k)
      return 0;

    if (local_vlen != targ_vlen)
      return 0;

    for (i = 0; i < local_vlen; i++, local_p++, targ_p++) {
      err = __bpf_core_types_match(local_btf, local_p->type, targ_btf,
                 targ_p->type, behind_ptr, level - 1);
      if (err <= 0)
        return err;
    }

    /* tail recurse for return type check */
    local_id = local_t->type;
    targ_id = targ_t->type;
    goto recur;
  }
  default:
    pr_warn("unexpected kind %s relocated, local [%d], target [%d]\n",
      btf_kind_str(local_t), local_id, targ_id);
    return 0;
  }
}

Coverage Report

Created: 2025-08-29 06:43