LXR linux/tools/lib/bpf/bpf_core

   1/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
   2#ifndef __BPF_CORE_READ_H__
   3#define __BPF_CORE_READ_H__
   4
   5/*
   6 * enum bpf_field_info_kind is passed as a second argument into
   7 * __builtin_preserve_field_info() built-in to get a specific aspect of
   8 * a field, captured as a first argument. __builtin_preserve_field_info(field,
   9 * info_kind) returns __u32 integer and produces BTF field relocation, which
  10 * is understood and processed by libbpf during BPF object loading. See
  11 * selftests/bpf for examples.
  12 */
  13enum bpf_field_info_kind {
  14        BPF_FIELD_BYTE_OFFSET = 0,      /* field byte offset */
  15        BPF_FIELD_BYTE_SIZE = 1,
  16        BPF_FIELD_EXISTS = 2,           /* field existence in target kernel */
  17        BPF_FIELD_SIGNED = 3,
  18        BPF_FIELD_LSHIFT_U64 = 4,
  19        BPF_FIELD_RSHIFT_U64 = 5,
  20};
  21
  22#define __CORE_RELO(src, field, info)                                         \
  23        __builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
  24
  25#if __BYTE_ORDER == __LITTLE_ENDIAN
  26#define __CORE_BITFIELD_PROBE_READ(dst, src, fld)                             \
  27        bpf_probe_read((void *)dst,                                           \
  28                       __CORE_RELO(src, fld, BYTE_SIZE),                      \
  29                       (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
  30#else
  31/* semantics of LSHIFT_64 assumes loading values into low-ordered bytes, so
  32 * for big-endian we need to adjust destination pointer accordingly, based on
  33 * field byte size
  34 */
  35#define __CORE_BITFIELD_PROBE_READ(dst, src, fld)                             \
  36        bpf_probe_read((void *)dst + (8 - __CORE_RELO(src, fld, BYTE_SIZE)),  \
  37                       __CORE_RELO(src, fld, BYTE_SIZE),                      \
  38                       (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
  39#endif
  40
  41/*
  42 * Extract bitfield, identified by s->field, and return its value as u64.
  43 * All this is done in relocatable manner, so bitfield changes such as
  44 * signedness, bit size, offset changes, this will be handled automatically.
  45 * This version of macro is using bpf_probe_read() to read underlying integer
  46 * storage. Macro functions as an expression and its return type is
  47 * bpf_probe_read()'s return value: 0, on success, <0 on error.
  48 */
  49#define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({                            \
  50        unsigned long long val = 0;                                           \
  51                                                                              \
  52        __CORE_BITFIELD_PROBE_READ(&val, s, field);                           \
  53        val <<= __CORE_RELO(s, field, LSHIFT_U64);                            \
  54        if (__CORE_RELO(s, field, SIGNED))                                    \
  55                val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64);  \
  56        else                                                                  \
  57                val = val >> __CORE_RELO(s, field, RSHIFT_U64);               \
  58        val;                                                                  \
  59})
  60
  61/*
  62 * Extract bitfield, identified by s->field, and return its value as u64.
  63 * This version of macro is using direct memory reads and should be used from
  64 * BPF program types that support such functionality (e.g., typed raw
  65 * tracepoints).
  66 */
  67#define BPF_CORE_READ_BITFIELD(s, field) ({                                   \
  68        const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
  69        unsigned long long val;                                               \
  70                                                                              \
  71        switch (__CORE_RELO(s, field, BYTE_SIZE)) {                           \
  72        case 1: val = *(const unsigned char *)p;                              \
  73        case 2: val = *(const unsigned short *)p;                             \
  74        case 4: val = *(const unsigned int *)p;                               \
  75        case 8: val = *(const unsigned long long *)p;                         \
  76        }                                                                     \
  77        val <<= __CORE_RELO(s, field, LSHIFT_U64);                            \
  78        if (__CORE_RELO(s, field, SIGNED))                                    \
  79                val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64);  \
  80        else                                                                  \
  81                val = val >> __CORE_RELO(s, field, RSHIFT_U64);               \
  82        val;                                                                  \
  83})
  84
  85/*
  86 * Convenience macro to check that field actually exists in target kernel's.
  87 * Returns:
  88 *    1, if matching field is present in target kernel;
  89 *    0, if no matching field found.
  90 */
  91#define bpf_core_field_exists(field)                                        \
  92        __builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
  93
  94/*
  95 * Convenience macro to get byte size of a field. Works for integers,
  96 * struct/unions, pointers, arrays, and enums.
  97 */
  98#define bpf_core_field_size(field)                                          \
  99        __builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)
 100
 101/*
 102 * bpf_core_read() abstracts away bpf_probe_read() call and captures offset
 103 * relocation for source address using __builtin_preserve_access_index()
 104 * built-in, provided by Clang.
 105 *
 106 * __builtin_preserve_access_index() takes as an argument an expression of
 107 * taking an address of a field within struct/union. It makes compiler emit
 108 * a relocation, which records BTF type ID describing root struct/union and an
 109 * accessor string which describes exact embedded field that was used to take
 110 * an address. See detailed description of this relocation format and
 111 * semantics in comments to struct bpf_field_reloc in libbpf_internal.h.
 112 *
 113 * This relocation allows libbpf to adjust BPF instruction to use correct
 114 * actual field offset, based on target kernel BTF type that matches original
 115 * (local) BTF, used to record relocation.
 116 */
 117#define bpf_core_read(dst, sz, src)                                         \
 118        bpf_probe_read(dst, sz,                                             \
 119                       (const void *)__builtin_preserve_access_index(src))
 120
 121/*
 122 * bpf_core_read_str() is a thin wrapper around bpf_probe_read_str()
 123 * additionally emitting BPF CO-RE field relocation for specified source
 124 * argument.
 125 */
 126#define bpf_core_read_str(dst, sz, src)                                     \
 127        bpf_probe_read_str(dst, sz,                                         \
 128                           (const void *)__builtin_preserve_access_index(src))
 129
 130#define ___concat(a, b) a ## b
 131#define ___apply(fn, n) ___concat(fn, n)
 132#define ___nth(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __11, N, ...) N
 133
 134/*
 135 * return number of provided arguments; used for switch-based variadic macro
 136 * definitions (see ___last, ___arrow, etc below)
 137 */
 138#define ___narg(...) ___nth(_, ##__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
 139/*
 140 * return 0 if no arguments are passed, N - otherwise; used for
 141 * recursively-defined macros to specify termination (0) case, and generic
 142 * (N) case (e.g., ___read_ptrs, ___core_read)
 143 */
 144#define ___empty(...) ___nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)
 145
 146#define ___last1(x) x
 147#define ___last2(a, x) x
 148#define ___last3(a, b, x) x
 149#define ___last4(a, b, c, x) x
 150#define ___last5(a, b, c, d, x) x
 151#define ___last6(a, b, c, d, e, x) x
 152#define ___last7(a, b, c, d, e, f, x) x
 153#define ___last8(a, b, c, d, e, f, g, x) x
 154#define ___last9(a, b, c, d, e, f, g, h, x) x
 155#define ___last10(a, b, c, d, e, f, g, h, i, x) x
 156#define ___last(...) ___apply(___last, ___narg(__VA_ARGS__))(__VA_ARGS__)
 157
 158#define ___nolast2(a, _) a
 159#define ___nolast3(a, b, _) a, b
 160#define ___nolast4(a, b, c, _) a, b, c
 161#define ___nolast5(a, b, c, d, _) a, b, c, d
 162#define ___nolast6(a, b, c, d, e, _) a, b, c, d, e
 163#define ___nolast7(a, b, c, d, e, f, _) a, b, c, d, e, f
 164#define ___nolast8(a, b, c, d, e, f, g, _) a, b, c, d, e, f, g
 165#define ___nolast9(a, b, c, d, e, f, g, h, _) a, b, c, d, e, f, g, h
 166#define ___nolast10(a, b, c, d, e, f, g, h, i, _) a, b, c, d, e, f, g, h, i
 167#define ___nolast(...) ___apply(___nolast, ___narg(__VA_ARGS__))(__VA_ARGS__)
 168
 169#define ___arrow1(a) a
 170#define ___arrow2(a, b) a->b
 171#define ___arrow3(a, b, c) a->b->c
 172#define ___arrow4(a, b, c, d) a->b->c->d
 173#define ___arrow5(a, b, c, d, e) a->b->c->d->e
 174#define ___arrow6(a, b, c, d, e, f) a->b->c->d->e->f
 175#define ___arrow7(a, b, c, d, e, f, g) a->b->c->d->e->f->g
 176#define ___arrow8(a, b, c, d, e, f, g, h) a->b->c->d->e->f->g->h
 177#define ___arrow9(a, b, c, d, e, f, g, h, i) a->b->c->d->e->f->g->h->i
 178#define ___arrow10(a, b, c, d, e, f, g, h, i, j) a->b->c->d->e->f->g->h->i->j
 179#define ___arrow(...) ___apply(___arrow, ___narg(__VA_ARGS__))(__VA_ARGS__)
 180
 181#define ___type(...) typeof(___arrow(__VA_ARGS__))
 182
 183#define ___read(read_fn, dst, src_type, src, accessor)                      \
 184        read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)
 185
 186/* "recursively" read a sequence of inner pointers using local __t var */
 187#define ___rd_first(src, a) ___read(bpf_core_read, &__t, ___type(src), src, a);
 188#define ___rd_last(...)                                                     \
 189        ___read(bpf_core_read, &__t,                                        \
 190                ___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__));
 191#define ___rd_p1(...) const void *__t; ___rd_first(__VA_ARGS__)
 192#define ___rd_p2(...) ___rd_p1(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 193#define ___rd_p3(...) ___rd_p2(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 194#define ___rd_p4(...) ___rd_p3(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 195#define ___rd_p5(...) ___rd_p4(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 196#define ___rd_p6(...) ___rd_p5(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 197#define ___rd_p7(...) ___rd_p6(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 198#define ___rd_p8(...) ___rd_p7(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 199#define ___rd_p9(...) ___rd_p8(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 200#define ___read_ptrs(src, ...)                                              \
 201        ___apply(___rd_p, ___narg(__VA_ARGS__))(src, __VA_ARGS__)
 202
 203#define ___core_read0(fn, dst, src, a)                                      \
 204        ___read(fn, dst, ___type(src), src, a);
 205#define ___core_readN(fn, dst, src, ...)                                    \
 206        ___read_ptrs(src, ___nolast(__VA_ARGS__))                           \
 207        ___read(fn, dst, ___type(src, ___nolast(__VA_ARGS__)), __t,         \
 208                ___last(__VA_ARGS__));
 209#define ___core_read(fn, dst, src, a, ...)                                  \
 210        ___apply(___core_read, ___empty(__VA_ARGS__))(fn, dst,              \
 211                                                      src, a, ##__VA_ARGS__)
 212
 213/*
 214 * BPF_CORE_READ_INTO() is a more performance-conscious variant of
 215 * BPF_CORE_READ(), in which final field is read into user-provided storage.
 216 * See BPF_CORE_READ() below for more details on general usage.
 217 */
 218#define BPF_CORE_READ_INTO(dst, src, a, ...)                                \
 219        ({                                                                  \
 220                ___core_read(bpf_core_read, dst, src, a, ##__VA_ARGS__)     \
 221        })
 222
 223/*
 224 * BPF_CORE_READ_STR_INTO() does same "pointer chasing" as
 225 * BPF_CORE_READ() for intermediate pointers, but then executes (and returns
 226 * corresponding error code) bpf_core_read_str() for final string read.
 227 */
 228#define BPF_CORE_READ_STR_INTO(dst, src, a, ...)                            \
 229        ({                                                                  \
 230                ___core_read(bpf_core_read_str, dst, src, a, ##__VA_ARGS__) \
 231        })
 232
 233/*
 234 * BPF_CORE_READ() is used to simplify BPF CO-RE relocatable read, especially
 235 * when there are few pointer chasing steps.
 236 * E.g., what in non-BPF world (or in BPF w/ BCC) would be something like:
 237 *      int x = s->a.b.c->d.e->f->g;
 238 * can be succinctly achieved using BPF_CORE_READ as:
 239 *      int x = BPF_CORE_READ(s, a.b.c, d.e, f, g);
 240 *
 241 * BPF_CORE_READ will decompose above statement into 4 bpf_core_read (BPF
 242 * CO-RE relocatable bpf_probe_read() wrapper) calls, logically equivalent to:
 243 * 1. const void *__t = s->a.b.c;
 244 * 2. __t = __t->d.e;
 245 * 3. __t = __t->f;
 246 * 4. return __t->g;
 247 *
 248 * Equivalence is logical, because there is a heavy type casting/preservation
 249 * involved, as well as all the reads are happening through bpf_probe_read()
 250 * calls using __builtin_preserve_access_index() to emit CO-RE relocations.
 251 *
 252 * N.B. Only up to 9 "field accessors" are supported, which should be more
 253 * than enough for any practical purpose.
 254 */
 255#define BPF_CORE_READ(src, a, ...)                                          \
 256        ({                                                                  \
 257                ___type(src, a, ##__VA_ARGS__) __r;                         \
 258                BPF_CORE_READ_INTO(&__r, src, a, ##__VA_ARGS__);            \
 259                __r;                                                        \
 260        })
 261
 262#endif
 263
 264