text: /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
  #ifndef __BPF_CORE_READ_H__
  #define __BPF_CORE_READ_H__
  
  /*
   * enum bpf_field_info_kind is passed as a second argument into
   * __builtin_preserve_field_info() built-in to get a specific aspect of
   * a field, captured as a first argument. __builtin_preserve_field_info(field,
   * info_kind) returns __u32 integer and produces BTF field relocation, which
   * is understood and processed by libbpf during BPF object loading. See
   * selftests/bpf for examples.
   */
  enum bpf_field_info_kind {
      BPF_FIELD_BYTE_OFFSET = 0, /* field byte offset */
      BPF_FIELD_BYTE_SIZE = 1,
      BPF_FIELD_EXISTS = 2, /* field existence in target kernel */
      BPF_FIELD_SIGNED = 3,
      BPF_FIELD_LSHIFT_U64 = 4,
      BPF_FIELD_RSHIFT_U64 = 5,
  };
  
  /* second argument to __builtin_btf_type_id() built-in */
  enum bpf_type_id_kind {
      BPF_TYPE_ID_LOCAL = 0,  /* BTF type ID in local program */
      BPF_TYPE_ID_TARGET = 1, /* BTF type ID in target kernel */
  };
  
  /* second argument to __builtin_preserve_type_info() built-in */
  enum bpf_type_info_kind {
      BPF_TYPE_EXISTS = 0, /* type existence in target kernel */
      BPF_TYPE_SIZE = 1,   /* type size in target kernel */
  };
  
  /* second argument to __builtin_preserve_enum_value() built-in */
  enum bpf_enum_value_kind {
      BPF_ENUMVAL_EXISTS = 0, /* enum value existence in kernel */
      BPF_ENUMVAL_VALUE = 1,  /* enum value value relocation */
  };
  
  #define __CORE_RELO(src, field, info) \
      __builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
  
  #if __BYTE_ORDER == __LITTLE_ENDIAN
  #define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
      bpf_probe_read_kernel(                        \
          (void *)dst,                              \
          __CORE_RELO(src, fld, BYTE_SIZE),         \
          (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
  #else
  /* semantics of LSHIFT_64 assumes loading values into low-ordered bytes, so
   * for big-endian we need to adjust destination pointer accordingly, based on
   * field byte size
   */
  #define __CORE_BITFIELD_PROBE_READ(dst, src, fld)             \
      bpf_probe_read_kernel(                                    \
          (void *)dst + (8 - __CORE_RELO(src, fld, BYTE_SIZE)), \
          __CORE_RELO(src, fld, BYTE_SIZE),                     \
          (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
  #endif
  
  /*
   * Extract bitfield, identified by s->field, and return its value as u64.
   * All this is done in relocatable manner, so bitfield changes such as
   * signedness, bit size, offset changes, this will be handled automatically.
   * This version of macro is using bpf_probe_read_kernel() to read underlying
   * integer storage. Macro functions as an expression and its return type is
   * bpf_probe_read_kernel()'s return value: 0, on success, <0 on error.
   */
  #define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({                   \
      unsigned long long val = 0;                                      \
                                                                       \
      __CORE_BITFIELD_PROBE_READ(&val, s, field);                      \
      val <<= __CORE_RELO(s, field, LSHIFT_U64);                       \
      if (__CORE_RELO(s, field, SIGNED))                               \
          val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64); \
      else                                                             \
          val = val >> __CORE_RELO(s, field, RSHIFT_U64);              \
      val;                                                             \
  })
  
  /*
   * Extract bitfield, identified by s->field, and return its value as u64.
   * This version of macro is using direct memory reads and should be used from
   * BPF program types that support such functionality (e.g., typed raw
   * tracepoints).
   */
  #define BPF_CORE_READ_BITFIELD(s, field) ({                               \
      const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
      unsigned long long val;                                               \
                                                                            \
      /* This is a so-called barrier_var() operation that makes specified   \
       * variable "a black box" for optimizing compiler.                    \
       * It forces compiler to perform BYTE_OFFSET relocation on p and use  \
       * its calculated value in the switch below, instead of applying      \
       * the same relocation 4 times for each individual memory load.       \
       */                                                                   \
      asm volatile(""                                                       \
                   : "=r"(p)                                                \
                   : "0"(p));                                               \
                                                                            \
      switch (__CORE_RELO(s, field, BYTE_SIZE)) {                           \
      case 1: val = *(const unsigned char *)p; break;                       \
      case 2: val = *(const unsigned short *)p; break;                      \
      case 4: val = *(const unsigned int *)p; break;                        \
      case 8: val = *(const unsigned long long *)p; break;                  \
      }                                                                     \
      val <<= __CORE_RELO(s, field, LSHIFT_U64);                            \
      if (__CORE_RELO(s, field, SIGNED))                                    \
          val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64);      \
      else                                                                  \
          val = val >> __CORE_RELO(s, field, RSHIFT_U64);                   \
      val;                                                                  \
  })
  
  /*
   * Convenience macro to check that field actually exists in target kernel's.
   * Returns:
   *    1, if matching field is present in target kernel;
   *    0, if no matching field found.
   */
  #define bpf_core_field_exists(field) \
      __builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
  
  /*
   * Convenience macro to get the byte size of a field. Works for integers,
   * struct/unions, pointers, arrays, and enums.
   */
  #define bpf_core_field_size(field) \
      __builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)
  
  /*
   * Convenience macro to get BTF type ID of a specified type, using a local BTF
   * information. Return 32-bit unsigned integer with type ID from program's own
   * BTF. Always succeeds.
   */
  #define bpf_core_type_id_local(type) \
      __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_LOCAL)
  
  /*
   * Convenience macro to get BTF type ID of a target kernel's type that matches
   * specified local type.
   * Returns:
   *    - valid 32-bit unsigned type ID in kernel BTF;
   *    - 0, if no matching type was found in a target kernel BTF.
   */
  #define bpf_core_type_id_kernel(type) \
      __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_TARGET)
  
  /*
   * Convenience macro to check that provided named type
   * (struct/union/enum/typedef) exists in a target kernel.
   * Returns:
   *    1, if such type is present in target kernel's BTF;
   *    0, if no matching type is found.
   */
  #define bpf_core_type_exists(type) \
      __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_EXISTS)
  
  /*
   * Convenience macro to get the byte size of a provided named type
   * (struct/union/enum/typedef) in a target kernel.
   * Returns:
   *    >= 0 size (in bytes), if type is present in target kernel's BTF;
   *    0, if no matching type is found.
   */
  #define bpf_core_type_size(type) \
      __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_SIZE)
  
  /*
   * Convenience macro to check that provided enumerator value is defined in
   * a target kernel.
   * Returns:
   *    1, if specified enum type and its enumerator value are present in target
   *    kernel's BTF;
   *    0, if no matching enum and/or enum value within that enum is found.
   */
  #define bpf_core_enum_value_exists(enum_type, enum_value) \
      __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_EXISTS)
  
  /*
   * Convenience macro to get the integer value of an enumerator value in
   * a target kernel.
   * Returns:
   *    64-bit value, if specified enum type and its enumerator value are
   *    present in target kernel's BTF;
   *    0, if no matching enum and/or enum value within that enum is found.
   */
  #define bpf_core_enum_value(enum_type, enum_value) \
      __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_VALUE)
  
  /*
   * bpf_core_read() abstracts away bpf_probe_read_kernel() call and captures
   * offset relocation for source address using __builtin_preserve_access_index()
   * built-in, provided by Clang.
   *
   * __builtin_preserve_access_index() takes as an argument an expression of
   * taking an address of a field within struct/union. It makes compiler emit
   * a relocation, which records BTF type ID describing root struct/union and an
   * accessor string which describes exact embedded field that was used to take
   * an address. See detailed description of this relocation format and
   * semantics in comments to struct bpf_field_reloc in libbpf_internal.h.
   *
   * This relocation allows libbpf to adjust BPF instruction to use correct
   * actual field offset, based on target kernel BTF type that matches original
   * (local) BTF, used to record relocation.
   */
  #define bpf_core_read(dst, sz, src) \
      bpf_probe_read_kernel(dst, sz, (const void *)__builtin_preserve_access_index(src))
  
  /* NOTE: see comments for BPF_CORE_READ_USER() about the proper types use. */
  #define bpf_core_read_user(dst, sz, src) \
      bpf_probe_read_user(dst, sz, (const void *)__builtin_preserve_access_index(src))
  /*
   * bpf_core_read_str() is a thin wrapper around bpf_probe_read_str()
   * additionally emitting BPF CO-RE field relocation for specified source
   * argument.
   */
  #define bpf_core_read_str(dst, sz, src) \
      bpf_probe_read_kernel_str(dst, sz, (const void *)__builtin_preserve_access_index(src))
  
  /* NOTE: see comments for BPF_CORE_READ_USER() about the proper types use. */
  #define bpf_core_read_user_str(dst, sz, src) \
      bpf_probe_read_user_str(dst, sz, (const void *)__builtin_preserve_access_index(src))
  
  #define ___concat(a, b) a##b
  #define ___apply(fn, n) ___concat(fn, n)
  #define ___nth(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __11, N, ...) N
  
  /*
   * return number of provided arguments; used for switch-based variadic macro
   * definitions (see ___last, ___arrow, etc below)
   */
  #define ___narg(...) ___nth(_, ##__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
  /*
   * return 0 if no arguments are passed, N - otherwise; used for
   * recursively-defined macros to specify termination (0) case, and generic
   * (N) case (e.g., ___read_ptrs, ___core_read)
   */
  #define ___empty(...) ___nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)
  
  #define ___last1(x) x
  #define ___last2(a, x) x
  #define ___last3(a, b, x) x
  #define ___last4(a, b, c, x) x
  #define ___last5(a, b, c, d, x) x
  #define ___last6(a, b, c, d, e, x) x
  #define ___last7(a, b, c, d, e, f, x) x
  #define ___last8(a, b, c, d, e, f, g, x) x
  #define ___last9(a, b, c, d, e, f, g, h, x) x
  #define ___last10(a, b, c, d, e, f, g, h, i, x) x
  #define ___last(...) ___apply(___last, ___narg(__VA_ARGS__))(__VA_ARGS__)
  
  #define ___nolast2(a, _) a
  #define ___nolast3(a, b, _) a, b
  #define ___nolast4(a, b, c, _) a, b, c
  #define ___nolast5(a, b, c, d, _) a, b, c, d
  #define ___nolast6(a, b, c, d, e, _) a, b, c, d, e
  #define ___nolast7(a, b, c, d, e, f, _) a, b, c, d, e, f
  #define ___nolast8(a, b, c, d, e, f, g, _) a, b, c, d, e, f, g
  #define ___nolast9(a, b, c, d, e, f, g, h, _) a, b, c, d, e, f, g, h
  #define ___nolast10(a, b, c, d, e, f, g, h, i, _) a, b, c, d, e, f, g, h, i
  #define ___nolast(...) ___apply(___nolast, ___narg(__VA_ARGS__))(__VA_ARGS__)
  
  #define ___arrow1(a) a
  #define ___arrow2(a, b) a->b
  #define ___arrow3(a, b, c) a->b->c
  #define ___arrow4(a, b, c, d) a->b->c->d
  #define ___arrow5(a, b, c, d, e) a->b->c->d->e
  #define ___arrow6(a, b, c, d, e, f) a->b->c->d->e->f
  #define ___arrow7(a, b, c, d, e, f, g) a->b->c->d->e->f->g
  #define ___arrow8(a, b, c, d, e, f, g, h) a->b->c->d->e->f->g->h
  #define ___arrow9(a, b, c, d, e, f, g, h, i) a->b->c->d->e->f->g->h->i
  #define ___arrow10(a, b, c, d, e, f, g, h, i, j) a->b->c->d->e->f->g->h->i->j
  #define ___arrow(...) ___apply(___arrow, ___narg(__VA_ARGS__))(__VA_ARGS__)
  
  #define ___type(...) typeof(___arrow(__VA_ARGS__))
  
  #define ___read(read_fn, dst, src_type, src, accessor) \
      read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)
  
  /* "recursively" read a sequence of inner pointers using local __t var */
  #define ___rd_first(fn, src, a) ___read(fn, &__t, ___type(src), src, a);
  #define ___rd_last(fn, ...) \
      ___read(fn, &__t, ___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__));
  #define ___rd_p1(fn, ...) \
      const void *__t;      \
      ___rd_first(fn, __VA_ARGS__)
  #define ___rd_p2(fn, ...) ___rd_p1(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
  #define ___rd_p3(fn, ...) ___rd_p2(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
  #define ___rd_p4(fn, ...) ___rd_p3(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
  #define ___rd_p5(fn, ...) ___rd_p4(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
  #define ___rd_p6(fn, ...) ___rd_p5(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
  #define ___rd_p7(fn, ...) ___rd_p6(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
  #define ___rd_p8(fn, ...) ___rd_p7(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
  #define ___rd_p9(fn, ...) ___rd_p8(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
  #define ___read_ptrs(fn, src, ...) \
      ___apply(___rd_p, ___narg(__VA_ARGS__))(fn, src, __VA_ARGS__)
  
  #define ___core_read0(fn, fn_ptr, dst, src, a) \
      ___read(fn, dst, ___type(src), src, a);
  #define ___core_readN(fn, fn_ptr, dst, src, ...)                    \
      ___read_ptrs(fn_ptr, src, ___nolast(__VA_ARGS__))               \
          ___read(fn, dst, ___type(src, ___nolast(__VA_ARGS__)), __t, \
                  ___last(__VA_ARGS__));
  #define ___core_read(fn, fn_ptr, dst, src, a, ...)                 \
      ___apply(___core_read, ___empty(__VA_ARGS__))(fn, fn_ptr, dst, \
                                                    src, a, ##__VA_ARGS__)
  
  /*
   * BPF_CORE_READ_INTO() is a more performance-conscious variant of
   * BPF_CORE_READ(), in which final field is read into user-provided storage.
   * See BPF_CORE_READ() below for more details on general usage.
   */
  #define BPF_CORE_READ_INTO(dst, src, a, ...) ({___core_read(bpf_core_read, bpf_core_read, \
                                                              dst, (src), a, ##__VA_ARGS__)})
  
  /*
   * Variant of BPF_CORE_READ_INTO() for reading from user-space memory.
   *
   * NOTE: see comments for BPF_CORE_READ_USER() about the proper types use.
   */
  #define BPF_CORE_READ_USER_INTO(dst, src, a, ...) ({___core_read(bpf_core_read_user, bpf_core_read_user, \
                                                                   dst, (src), a, ##__VA_ARGS__)})
  
  /* Non-CO-RE variant of BPF_CORE_READ_INTO() */
  #define BPF_PROBE_READ_INTO(dst, src, a, ...) ({___core_read(bpf_probe_read, bpf_probe_read, \
                                                               dst, (src), a, ##__VA_ARGS__)})
  
  /* Non-CO-RE variant of BPF_CORE_READ_USER_INTO().
   *
   * As no CO-RE relocations are emitted, source types can be arbitrary and are
   * not restricted to kernel types only.
   */
  #define BPF_PROBE_READ_USER_INTO(dst, src, a, ...) ({___core_read(bpf_probe_read_user, bpf_probe_read_user, \
                                                                    dst, (src), a, ##__VA_ARGS__)})
  
  /*
   * BPF_CORE_READ_STR_INTO() does same "pointer chasing" as
   * BPF_CORE_READ() for intermediate pointers, but then executes (and returns
   * corresponding error code) bpf_core_read_str() for final string read.
   */
  #define BPF_CORE_READ_STR_INTO(dst, src, a, ...) ({___core_read(bpf_core_read_str, bpf_core_read, \
                                                                  dst, (src), a, ##__VA_ARGS__)})
  
  /*
   * Variant of BPF_CORE_READ_STR_INTO() for reading from user-space memory.
   *
   * NOTE: see comments for BPF_CORE_READ_USER() about the proper types use.
   */
  #define BPF_CORE_READ_USER_STR_INTO(dst, src, a, ...) ({___core_read(bpf_core_read_user_str, bpf_core_read_user, \
                                                                       dst, (src), a, ##__VA_ARGS__)})
  
  /* Non-CO-RE variant of BPF_CORE_READ_STR_INTO() */
  #define BPF_PROBE_READ_STR_INTO(dst, src, a, ...) ({___core_read(bpf_probe_read_str, bpf_probe_read, \
                                                                   dst, (src), a, ##__VA_ARGS__)})
  
  /*
   * Non-CO-RE variant of BPF_CORE_READ_USER_STR_INTO().
   *
   * As no CO-RE relocations are emitted, source types can be arbitrary and are
   * not restricted to kernel types only.
   */
  #define BPF_PROBE_READ_USER_STR_INTO(dst, src, a, ...) ({___core_read(bpf_probe_read_user_str, bpf_probe_read_user, \
                                                                        dst, (src), a, ##__VA_ARGS__)})
  
  /*
   * BPF_CORE_READ() is used to simplify BPF CO-RE relocatable read, especially
   * when there are few pointer chasing steps.
   * E.g., what in non-BPF world (or in BPF w/ BCC) would be something like:
   *	int x = s->a.b.c->d.e->f->g;
   * can be succinctly achieved using BPF_CORE_READ as:
   *	int x = BPF_CORE_READ(s, a.b.c, d.e, f, g);
   *
   * BPF_CORE_READ will decompose above statement into 4 bpf_core_read (BPF
   * CO-RE relocatable bpf_probe_read_kernel() wrapper) calls, logically
   * equivalent to:
   * 1. const void *__t = s->a.b.c;
   * 2. __t = __t->d.e;
   * 3. __t = __t->f;
   * 4. return __t->g;
   *
   * Equivalence is logical, because there is a heavy type casting/preservation
   * involved, as well as all the reads are happening through
   * bpf_probe_read_kernel() calls using __builtin_preserve_access_index() to
   * emit CO-RE relocations.
   *
   * N.B. Only up to 9 "field accessors" are supported, which should be more
   * than enough for any practical purpose.
   */
  #define BPF_CORE_READ(src, a, ...) ({                  \
      ___type((src), a, ##__VA_ARGS__) __r;              \
      BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \
      __r;                                               \
  })
  
  /*
   * Variant of BPF_CORE_READ() for reading from user-space memory.
   *
   * NOTE: all the source types involved are still *kernel types* and need to
   * exist in kernel (or kernel module) BTF, otherwise CO-RE relocation will
   * fail. Custom user types are not relocatable with CO-RE.
   * The typical situation in which BPF_CORE_READ_USER() might be used is to
   * read kernel UAPI types from the user-space memory passed in as a syscall
   * input argument.
   */
  #define BPF_CORE_READ_USER(src, a, ...) ({                  \
      ___type((src), a, ##__VA_ARGS__) __r;                   \
      BPF_CORE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \
      __r;                                                    \
  })
  
  /* Non-CO-RE variant of BPF_CORE_READ() */
  #define BPF_PROBE_READ(src, a, ...) ({                  \
      ___type((src), a, ##__VA_ARGS__) __r;               \
      BPF_PROBE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \
      __r;                                                \
  })
  
  /*
   * Non-CO-RE variant of BPF_CORE_READ_USER().
   *
   * As no CO-RE relocations are emitted, source types can be arbitrary and are
   * not restricted to kernel types only.
   */
  #define BPF_PROBE_READ_USER(src, a, ...) ({                  \
      ___type((src), a, ##__VA_ARGS__) __r;                    \
      BPF_PROBE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \
      __r;                                                     \
  })
  
  #endif
  