/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
#ifndef __BPF_CORE_READ_H__
#define __BPF_CORE_READ_H__

#include "bpf_helpers.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 */
        BPF_TYPE_MATCHES = 2,           /* type match 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__ == __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;                  \
        default: val = 0; 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;                                                                  \
})

/*
 * Write to a bitfield, identified by s->field.
 * This is the inverse of BPF_CORE_WRITE_BITFIELD().
 */
#define BPF_CORE_WRITE_BITFIELD(s, field, new_val) ({                   \
        void *p = (void *)s + __CORE_RELO(s, field, BYTE_OFFSET);       \
        unsigned int byte_size = __CORE_RELO(s, field, BYTE_SIZE);      \
        unsigned int lshift = __CORE_RELO(s, field, LSHIFT_U64);        \
        unsigned int rshift = __CORE_RELO(s, field, RSHIFT_U64);        \
        unsigned long long mask, val, nval = new_val;                   \
        unsigned int rpad = rshift - lshift;                            \
                                                                        \
        asm volatile("" : "+r"(p));                                     \
                                                                        \
        switch (byte_size) {                                            \
        case 1: val = *(unsigned char *)p; break;                       \
        case 2: val = *(unsigned short *)p; break;                      \
        case 4: val = *(unsigned int *)p; break;                        \
        case 8: val = *(unsigned long long *)p; break;                  \
        }                                                               \
                                                                        \
        mask = (~0ULL << rshift) >> lshift;                             \
        val = (val & ~mask) | ((nval << rpad) & mask);                  \
                                                                        \
        switch (byte_size) {                                            \
        case 1: *(unsigned char *)p      = val; break;                  \
        case 2: *(unsigned short *)p     = val; break;                  \
        case 4: *(unsigned int *)p       = val; break;                  \
        case 8: *(unsigned long long *)p = val; break;                  \
        }                                                               \
})

/* Differentiator between compilers builtin implementations. This is a
 * requirement due to the compiler parsing differences where GCC optimizes
 * early in parsing those constructs of type pointers to the builtin specific
 * type, resulting in not being possible to collect the required type
 * information in the builtin expansion.
 */
#ifdef __clang__
#define ___bpf_typeof(type) ((typeof(type) *) 0)
#else
#define ___bpf_typeof1(type, NR) ({                                         \
        extern typeof(type) *___concat(bpf_type_tmp_, NR);                  \
        ___concat(bpf_type_tmp_, NR);                                       \
})
#define ___bpf_typeof(type) ___bpf_typeof1(type, __COUNTER__)
#endif

#ifdef __clang__
#define ___bpf_field_ref1(field)        (field)
#define ___bpf_field_ref2(type, field)  (___bpf_typeof(type)->field)
#else
#define ___bpf_field_ref1(field)        (&(field))
#define ___bpf_field_ref2(type, field)  (&(___bpf_typeof(type)->field))
#endif
#define ___bpf_field_ref(args...)                                           \
        ___bpf_apply(___bpf_field_ref, ___bpf_narg(args))(args)

/*
 * 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.
 *
 * Supports two forms:
 *   - field reference through variable access:
 *     bpf_core_field_exists(p->my_field);
 *   - field reference through type and field names:
 *     bpf_core_field_exists(struct my_type, my_field).
 */
#define bpf_core_field_exists(field...)                                     \
        __builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_EXISTS)

/*
 * Convenience macro to get the byte size of a field. Works for integers,
 * struct/unions, pointers, arrays, and enums.
 *
 * Supports two forms:
 *   - field reference through variable access:
 *     bpf_core_field_size(p->my_field);
 *   - field reference through type and field names:
 *     bpf_core_field_size(struct my_type, my_field).
 */
#define bpf_core_field_size(field...)                                       \
        __builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_BYTE_SIZE)

/*
 * Convenience macro to get field's byte offset.
 *
 * Supports two forms:
 *   - field reference through variable access:
 *     bpf_core_field_offset(p->my_field);
 *   - field reference through type and field names:
 *     bpf_core_field_offset(struct my_type, my_field).
 */
#define bpf_core_field_offset(field...)                                     \
        __builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_BYTE_OFFSET)

/*
 * 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(*___bpf_typeof(type), 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(*___bpf_typeof(type), 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(*___bpf_typeof(type), BPF_TYPE_EXISTS)

/*
 * Convenience macro to check that provided named type
 * (struct/union/enum/typedef) "matches" that in a target kernel.
 * Returns:
 *    1, if the type matches in the target kernel's BTF;
 *    0, if the type does not match any in the target kernel
 */
#define bpf_core_type_matches(type)                                         \
        __builtin_preserve_type_info(*___bpf_typeof(type), BPF_TYPE_MATCHES)

/*
 * 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(*___bpf_typeof(type), 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.
 */
#ifdef __clang__
#define bpf_core_enum_value_exists(enum_type, enum_value)                   \
        __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_EXISTS)
#else
#define bpf_core_enum_value_exists(enum_type, enum_value)                   \
        __builtin_preserve_enum_value(___bpf_typeof(enum_type), enum_value, BPF_ENUMVAL_EXISTS)
#endif

/*
 * 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.
 */
#ifdef __clang__
#define bpf_core_enum_value(enum_type, enum_value)                          \
        __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_VALUE)
#else
#define bpf_core_enum_value(enum_type, enum_value)                          \
        __builtin_preserve_enum_value(___bpf_typeof(enum_type), enum_value, BPF_ENUMVAL_VALUE)
#endif

/*
 * 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_core_relo in include/uapi/linux/bpf.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))

extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak;

/*
 * Cast provided pointer *ptr* into a pointer to a specified *type* in such
 * a way that BPF verifier will become aware of associated kernel-side BTF
 * type. This allows to access members of kernel types directly without the
 * need to use BPF_CORE_READ() macros.
 */
#define bpf_core_cast(ptr, type)                                            \
        ((typeof(type) *)bpf_rdonly_cast((ptr), bpf_core_type_id_kernel(type)))

#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__)

#if defined(__clang__) && (__clang_major__ >= 19)
#define ___type(...) __typeof_unqual__(___arrow(__VA_ARGS__))
#elif defined(__GNUC__) && (__GNUC__ >= 14)
#define ___type(...) __typeof_unqual__(___arrow(__VA_ARGS__))
#else
#define ___type(...) typeof(___arrow(__VA_ARGS__))
#endif

#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_kernel, bpf_probe_read_kernel,          \
                     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_kernel_str, bpf_probe_read_kernel,      \
                     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