tools/lib/bpf/bpf_core_read.h

   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  */
  13 enum 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 /* second argument to __builtin_btf_type_id() built-in */
  23 enum bpf_type_id_kind {
  24         BPF_TYPE_ID_LOCAL = 0,          /* BTF type ID in local program */
  25         BPF_TYPE_ID_TARGET = 1,         /* BTF type ID in target kernel */
  26 };
  27
  28 /* second argument to __builtin_preserve_type_info() built-in */
  29 enum bpf_type_info_kind {
  30         BPF_TYPE_EXISTS = 0,            /* type existence in target kernel */
  31         BPF_TYPE_SIZE = 1,              /* type size in target kernel */
  32 };
  33
  34 /* second argument to __builtin_preserve_enum_value() built-in */
  35 enum bpf_enum_value_kind {
  36         BPF_ENUMVAL_EXISTS = 0,         /* enum value existence in kernel */
  37         BPF_ENUMVAL_VALUE = 1,          /* enum value value relocation */
  38 };
  39
  40 #define __CORE_RELO(src, field, info)                                         \
  41         __builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
  42
  43 #if __BYTE_ORDER == __LITTLE_ENDIAN
  44 #define __CORE_BITFIELD_PROBE_READ(dst, src, fld)                             \
  45         bpf_probe_read_kernel(                                                \
  46                         (void *)dst,                                  \
  47                         __CORE_RELO(src, fld, BYTE_SIZE),                     \
  48                         (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
  49 #else
  50 /* semantics of LSHIFT_64 assumes loading values into low-ordered bytes, so
  51  * for big-endian we need to adjust destination pointer accordingly, based on
  52  * field byte size
  53  */
  54 #define __CORE_BITFIELD_PROBE_READ(dst, src, fld)                             \
  55         bpf_probe_read_kernel(                                                \
  56                         (void *)dst + (8 - __CORE_RELO(src, fld, BYTE_SIZE)), \
  57                         __CORE_RELO(src, fld, BYTE_SIZE),                     \
  58                         (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
  59 #endif
  60
  61 /*
  62  * Extract bitfield, identified by s->field, and return its value as u64.
  63  * All this is done in relocatable manner, so bitfield changes such as
  64  * signedness, bit size, offset changes, this will be handled automatically.
  65  * This version of macro is using bpf_probe_read_kernel() to read underlying
  66  * integer storage. Macro functions as an expression and its return type is
  67  * bpf_probe_read_kernel()'s return value: 0, on success, <0 on error.
  68  */
  69 #define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({                            \
  70         unsigned long long val = 0;                                           \
  71                                                                               \
  72         __CORE_BITFIELD_PROBE_READ(&val, s, field);                           \
  73         val <<= __CORE_RELO(s, field, LSHIFT_U64);                            \
  74         if (__CORE_RELO(s, field, SIGNED))                                    \
  75                 val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64);  \
  76         else                                                                  \
  77                 val = val >> __CORE_RELO(s, field, RSHIFT_U64);               \
  78         val;                                                                  \
  79 })
  80
  81 /*
  82  * Extract bitfield, identified by s->field, and return its value as u64.
  83  * This version of macro is using direct memory reads and should be used from
  84  * BPF program types that support such functionality (e.g., typed raw
  85  * tracepoints).
  86  */
  87 #define BPF_CORE_READ_BITFIELD(s, field) ({                                   \
  88         const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
  89         unsigned long long val;                                               \
  90                                                                               \
  91         switch (__CORE_RELO(s, field, BYTE_SIZE)) {                           \
  92         case 1: val = *(const unsigned char *)p;                              \
  93         case 2: val = *(const unsigned short *)p;                             \
  94         case 4: val = *(const unsigned int *)p;                               \
  95         case 8: val = *(const unsigned long long *)p;                         \
  96         }                                                                     \
  97         val <<= __CORE_RELO(s, field, LSHIFT_U64);                            \
  98         if (__CORE_RELO(s, field, SIGNED))                                    \
  99                 val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64);  \
 100         else                                                                  \
 101                 val = val >> __CORE_RELO(s, field, RSHIFT_U64);               \
 102         val;                                                                  \
 103 })
 104
 105 /*
 106  * Convenience macro to check that field actually exists in target kernel's.
 107  * Returns:
 108  *    1, if matching field is present in target kernel;
 109  *    0, if no matching field found.
 110  */
 111 #define bpf_core_field_exists(field)                                        \
 112         __builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
 113
 114 /*
 115  * Convenience macro to get the byte size of a field. Works for integers,
 116  * struct/unions, pointers, arrays, and enums.
 117  */
 118 #define bpf_core_field_size(field)                                          \
 119         __builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)
 120
 121 /*
 122  * Convenience macro to get BTF type ID of a specified type, using a local BTF
 123  * information. Return 32-bit unsigned integer with type ID from program's own
 124  * BTF. Always succeeds.
 125  */
 126 #define bpf_core_type_id_local(type)                                        \
 127         __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_LOCAL)
 128
 129 /*
 130  * Convenience macro to get BTF type ID of a target kernel's type that matches
 131  * specified local type.
 132  * Returns:
 133  *    - valid 32-bit unsigned type ID in kernel BTF;
 134  *    - 0, if no matching type was found in a target kernel BTF.
 135  */
 136 #define bpf_core_type_id_kernel(type)                                       \
 137         __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_TARGET)
 138
 139 /*
 140  * Convenience macro to check that provided named type
 141  * (struct/union/enum/typedef) exists in a target kernel.
 142  * Returns:
 143  *    1, if such type is present in target kernel's BTF;
 144  *    0, if no matching type is found.
 145  */
 146 #define bpf_core_type_exists(type)                                          \
 147         __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_EXISTS)
 148
 149 /*
 150  * Convenience macro to get the byte size of a provided named type
 151  * (struct/union/enum/typedef) in a target kernel.
 152  * Returns:
 153  *    >= 0 size (in bytes), if type is present in target kernel's BTF;
 154  *    0, if no matching type is found.
 155  */
 156 #define bpf_core_type_size(type)                                            \
 157         __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_SIZE)
 158
 159 /*
 160  * Convenience macro to check that provided enumerator value is defined in
 161  * a target kernel.
 162  * Returns:
 163  *    1, if specified enum type and its enumerator value are present in target
 164  *    kernel's BTF;
 165  *    0, if no matching enum and/or enum value within that enum is found.
 166  */
 167 #define bpf_core_enum_value_exists(enum_type, enum_value)                   \
 168         __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_EXISTS)
 169
 170 /*
 171  * Convenience macro to get the integer value of an enumerator value in
 172  * a target kernel.
 173  * Returns:
 174  *    64-bit value, if specified enum type and its enumerator value are
 175  *    present in target kernel's BTF;
 176  *    0, if no matching enum and/or enum value within that enum is found.
 177  */
 178 #define bpf_core_enum_value(enum_type, enum_value)                          \
 179         __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_VALUE)
 180
 181 /*
 182  * bpf_core_read() abstracts away bpf_probe_read_kernel() call and captures
 183  * offset relocation for source address using __builtin_preserve_access_index()
 184  * built-in, provided by Clang.
 185  *
 186  * __builtin_preserve_access_index() takes as an argument an expression of
 187  * taking an address of a field within struct/union. It makes compiler emit
 188  * a relocation, which records BTF type ID describing root struct/union and an
 189  * accessor string which describes exact embedded field that was used to take
 190  * an address. See detailed description of this relocation format and
 191  * semantics in comments to struct bpf_field_reloc in libbpf_internal.h.
 192  *
 193  * This relocation allows libbpf to adjust BPF instruction to use correct
 194  * actual field offset, based on target kernel BTF type that matches original
 195  * (local) BTF, used to record relocation.
 196  */
 197 #define bpf_core_read(dst, sz, src)                                         \
 198         bpf_probe_read_kernel(dst, sz,                                      \
 199                               (const void *)__builtin_preserve_access_index(src))
 200
 201 /*
 202  * bpf_core_read_str() is a thin wrapper around bpf_probe_read_str()
 203  * additionally emitting BPF CO-RE field relocation for specified source
 204  * argument.
 205  */
 206 #define bpf_core_read_str(dst, sz, src)                                     \
 207         bpf_probe_read_kernel_str(dst, sz,                                  \
 208                                   (const void *)__builtin_preserve_access_index(src))
 209
 210 #define ___concat(a, b) a ## b
 211 #define ___apply(fn, n) ___concat(fn, n)
 212 #define ___nth(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __11, N, ...) N
 213
 214 /*
 215  * return number of provided arguments; used for switch-based variadic macro
 216  * definitions (see ___last, ___arrow, etc below)
 217  */
 218 #define ___narg(...) ___nth(_, ##__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
 219 /*
 220  * return 0 if no arguments are passed, N - otherwise; used for
 221  * recursively-defined macros to specify termination (0) case, and generic
 222  * (N) case (e.g., ___read_ptrs, ___core_read)
 223  */
 224 #define ___empty(...) ___nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)
 225
 226 #define ___last1(x) x
 227 #define ___last2(a, x) x
 228 #define ___last3(a, b, x) x
 229 #define ___last4(a, b, c, x) x
 230 #define ___last5(a, b, c, d, x) x
 231 #define ___last6(a, b, c, d, e, x) x
 232 #define ___last7(a, b, c, d, e, f, x) x
 233 #define ___last8(a, b, c, d, e, f, g, x) x
 234 #define ___last9(a, b, c, d, e, f, g, h, x) x
 235 #define ___last10(a, b, c, d, e, f, g, h, i, x) x
 236 #define ___last(...) ___apply(___last, ___narg(__VA_ARGS__))(__VA_ARGS__)
 237
 238 #define ___nolast2(a, _) a
 239 #define ___nolast3(a, b, _) a, b
 240 #define ___nolast4(a, b, c, _) a, b, c
 241 #define ___nolast5(a, b, c, d, _) a, b, c, d
 242 #define ___nolast6(a, b, c, d, e, _) a, b, c, d, e
 243 #define ___nolast7(a, b, c, d, e, f, _) a, b, c, d, e, f
 244 #define ___nolast8(a, b, c, d, e, f, g, _) a, b, c, d, e, f, g
 245 #define ___nolast9(a, b, c, d, e, f, g, h, _) a, b, c, d, e, f, g, h
 246 #define ___nolast10(a, b, c, d, e, f, g, h, i, _) a, b, c, d, e, f, g, h, i
 247 #define ___nolast(...) ___apply(___nolast, ___narg(__VA_ARGS__))(__VA_ARGS__)
 248
 249 #define ___arrow1(a) a
 250 #define ___arrow2(a, b) a->b
 251 #define ___arrow3(a, b, c) a->b->c
 252 #define ___arrow4(a, b, c, d) a->b->c->d
 253 #define ___arrow5(a, b, c, d, e) a->b->c->d->e
 254 #define ___arrow6(a, b, c, d, e, f) a->b->c->d->e->f
 255 #define ___arrow7(a, b, c, d, e, f, g) a->b->c->d->e->f->g
 256 #define ___arrow8(a, b, c, d, e, f, g, h) a->b->c->d->e->f->g->h
 257 #define ___arrow9(a, b, c, d, e, f, g, h, i) a->b->c->d->e->f->g->h->i
 258 #define ___arrow10(a, b, c, d, e, f, g, h, i, j) a->b->c->d->e->f->g->h->i->j
 259 #define ___arrow(...) ___apply(___arrow, ___narg(__VA_ARGS__))(__VA_ARGS__)
 260
 261 #define ___type(...) typeof(___arrow(__VA_ARGS__))
 262
 263 #define ___read(read_fn, dst, src_type, src, accessor)                      \
 264         read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)
 265
 266 /* "recursively" read a sequence of inner pointers using local __t var */
 267 #define ___rd_first(src, a) ___read(bpf_core_read, &__t, ___type(src), src, a);
 268 #define ___rd_last(...)                                                     \
 269         ___read(bpf_core_read, &__t,                                        \
 270                 ___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__));
 271 #define ___rd_p1(...) const void *__t; ___rd_first(__VA_ARGS__)
 272 #define ___rd_p2(...) ___rd_p1(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 273 #define ___rd_p3(...) ___rd_p2(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 274 #define ___rd_p4(...) ___rd_p3(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 275 #define ___rd_p5(...) ___rd_p4(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 276 #define ___rd_p6(...) ___rd_p5(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 277 #define ___rd_p7(...) ___rd_p6(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 278 #define ___rd_p8(...) ___rd_p7(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 279 #define ___rd_p9(...) ___rd_p8(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 280 #define ___read_ptrs(src, ...)                                              \
 281         ___apply(___rd_p, ___narg(__VA_ARGS__))(src, __VA_ARGS__)
 282
 283 #define ___core_read0(fn, dst, src, a)                                      \
 284         ___read(fn, dst, ___type(src), src, a);
 285 #define ___core_readN(fn, dst, src, ...)                                    \
 286         ___read_ptrs(src, ___nolast(__VA_ARGS__))                           \
 287         ___read(fn, dst, ___type(src, ___nolast(__VA_ARGS__)), __t,         \
 288                 ___last(__VA_ARGS__));
 289 #define ___core_read(fn, dst, src, a, ...)                                  \
 290         ___apply(___core_read, ___empty(__VA_ARGS__))(fn, dst,              \
 291                                                       src, a, ##__VA_ARGS__)
 292
 293 /*
 294  * BPF_CORE_READ_INTO() is a more performance-conscious variant of
 295  * BPF_CORE_READ(), in which final field is read into user-provided storage.
 296  * See BPF_CORE_READ() below for more details on general usage.
 297  */
 298 #define BPF_CORE_READ_INTO(dst, src, a, ...)                                \
 299         ({                                                                  \
 300                 ___core_read(bpf_core_read, dst, (src), a, ##__VA_ARGS__)   \
 301         })
 302
 303 /*
 304  * BPF_CORE_READ_STR_INTO() does same "pointer chasing" as
 305  * BPF_CORE_READ() for intermediate pointers, but then executes (and returns
 306  * corresponding error code) bpf_core_read_str() for final string read.
 307  */
 308 #define BPF_CORE_READ_STR_INTO(dst, src, a, ...)                            \
 309         ({                                                                  \
 310                 ___core_read(bpf_core_read_str, dst, (src), a, ##__VA_ARGS__)\
 311         })
 312
 313 /*
 314  * BPF_CORE_READ() is used to simplify BPF CO-RE relocatable read, especially
 315  * when there are few pointer chasing steps.
 316  * E.g., what in non-BPF world (or in BPF w/ BCC) would be something like:
 317  *      int x = s->a.b.c->d.e->f->g;
 318  * can be succinctly achieved using BPF_CORE_READ as:
 319  *      int x = BPF_CORE_READ(s, a.b.c, d.e, f, g);
 320  *
 321  * BPF_CORE_READ will decompose above statement into 4 bpf_core_read (BPF
 322  * CO-RE relocatable bpf_probe_read_kernel() wrapper) calls, logically
 323  * equivalent to:
 324  * 1. const void *__t = s->a.b.c;
 325  * 2. __t = __t->d.e;
 326  * 3. __t = __t->f;
 327  * 4. return __t->g;
 328  *
 329  * Equivalence is logical, because there is a heavy type casting/preservation
 330  * involved, as well as all the reads are happening through
 331  * bpf_probe_read_kernel() calls using __builtin_preserve_access_index() to
 332  * emit CO-RE relocations.
 333  *
 334  * N.B. Only up to 9 "field accessors" are supported, which should be more
 335  * than enough for any practical purpose.
 336  */
 337 #define BPF_CORE_READ(src, a, ...)                                          \
 338         ({                                                                  \
 339                 ___type((src), a, ##__VA_ARGS__) __r;                       \
 340                 BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__);          \
 341                 __r;                                                        \
 342         })
 343
 344 #endif
 345