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__ == __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 /* This is a so-called barrier_var() operation that makes specified \ 92 * variable "a black box" for optimizing compiler. \ 93 * It forces compiler to perform BYTE_OFFSET relocation on p and use \ 94 * its calculated value in the switch below, instead of applying \ 95 * the same relocation 4 times for each individual memory load. \ 96 */ \ 97 asm volatile("" : "=r"(p) : "0"(p)); \ 98 \ 99 switch (__CORE_RELO(s, field, BYTE_SIZE)) { \ 100 case 1: val = *(const unsigned char *)p; break; \ 101 case 2: val = *(const unsigned short *)p; break; \ 102 case 4: val = *(const unsigned int *)p; break; \ 103 case 8: val = *(const unsigned long long *)p; break; \ 104 } \ 105 val <<= __CORE_RELO(s, field, LSHIFT_U64); \ 106 if (__CORE_RELO(s, field, SIGNED)) \ 107 val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64); \ 108 else \ 109 val = val >> __CORE_RELO(s, field, RSHIFT_U64); \ 110 val; \ 111 }) 112 113 /* 114 * Convenience macro to check that field actually exists in target kernel's. 115 * Returns: 116 * 1, if matching field is present in target kernel; 117 * 0, if no matching field found. 118 */ 119 #define bpf_core_field_exists(field) \ 120 __builtin_preserve_field_info(field, BPF_FIELD_EXISTS) 121 122 /* 123 * Convenience macro to get the byte size of a field. Works for integers, 124 * struct/unions, pointers, arrays, and enums. 125 */ 126 #define bpf_core_field_size(field) \ 127 __builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE) 128 129 /* 130 * Convenience macro to get BTF type ID of a specified type, using a local BTF 131 * information. Return 32-bit unsigned integer with type ID from program's own 132 * BTF. Always succeeds. 133 */ 134 #define bpf_core_type_id_local(type) \ 135 __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_LOCAL) 136 137 /* 138 * Convenience macro to get BTF type ID of a target kernel's type that matches 139 * specified local type. 140 * Returns: 141 * - valid 32-bit unsigned type ID in kernel BTF; 142 * - 0, if no matching type was found in a target kernel BTF. 143 */ 144 #define bpf_core_type_id_kernel(type) \ 145 __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_TARGET) 146 147 /* 148 * Convenience macro to check that provided named type 149 * (struct/union/enum/typedef) exists in a target kernel. 150 * Returns: 151 * 1, if such type is present in target kernel's BTF; 152 * 0, if no matching type is found. 153 */ 154 #define bpf_core_type_exists(type) \ 155 __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_EXISTS) 156 157 /* 158 * Convenience macro to get the byte size of a provided named type 159 * (struct/union/enum/typedef) in a target kernel. 160 * Returns: 161 * >= 0 size (in bytes), if type is present in target kernel's BTF; 162 * 0, if no matching type is found. 163 */ 164 #define bpf_core_type_size(type) \ 165 __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_SIZE) 166 167 /* 168 * Convenience macro to check that provided enumerator value is defined in 169 * a target kernel. 170 * Returns: 171 * 1, if specified enum type and its enumerator value are present in target 172 * kernel's BTF; 173 * 0, if no matching enum and/or enum value within that enum is found. 174 */ 175 #define bpf_core_enum_value_exists(enum_type, enum_value) \ 176 __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_EXISTS) 177 178 /* 179 * Convenience macro to get the integer value of an enumerator value in 180 * a target kernel. 181 * Returns: 182 * 64-bit value, if specified enum type and its enumerator value are 183 * present in target kernel's BTF; 184 * 0, if no matching enum and/or enum value within that enum is found. 185 */ 186 #define bpf_core_enum_value(enum_type, enum_value) \ 187 __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_VALUE) 188 189 /* 190 * bpf_core_read() abstracts away bpf_probe_read_kernel() call and captures 191 * offset relocation for source address using __builtin_preserve_access_index() 192 * built-in, provided by Clang. 193 * 194 * __builtin_preserve_access_index() takes as an argument an expression of 195 * taking an address of a field within struct/union. It makes compiler emit 196 * a relocation, which records BTF type ID describing root struct/union and an 197 * accessor string which describes exact embedded field that was used to take 198 * an address. See detailed description of this relocation format and 199 * semantics in comments to struct bpf_field_reloc in libbpf_internal.h. 200 * 201 * This relocation allows libbpf to adjust BPF instruction to use correct 202 * actual field offset, based on target kernel BTF type that matches original 203 * (local) BTF, used to record relocation. 204 */ 205 #define bpf_core_read(dst, sz, src) \ 206 bpf_probe_read_kernel(dst, sz, \ 207 (const void *)__builtin_preserve_access_index(src)) 208 209 /* 210 * bpf_core_read_str() is a thin wrapper around bpf_probe_read_str() 211 * additionally emitting BPF CO-RE field relocation for specified source 212 * argument. 213 */ 214 #define bpf_core_read_str(dst, sz, src) \ 215 bpf_probe_read_kernel_str(dst, sz, \ 216 (const void *)__builtin_preserve_access_index(src)) 217 218 #define ___concat(a, b) a ## b 219 #define ___apply(fn, n) ___concat(fn, n) 220 #define ___nth(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __11, N, ...) N 221 222 /* 223 * return number of provided arguments; used for switch-based variadic macro 224 * definitions (see ___last, ___arrow, etc below) 225 */ 226 #define ___narg(...) ___nth(_, ##__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0) 227 /* 228 * return 0 if no arguments are passed, N - otherwise; used for 229 * recursively-defined macros to specify termination (0) case, and generic 230 * (N) case (e.g., ___read_ptrs, ___core_read) 231 */ 232 #define ___empty(...) ___nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0) 233 234 #define ___last1(x) x 235 #define ___last2(a, x) x 236 #define ___last3(a, b, x) x 237 #define ___last4(a, b, c, x) x 238 #define ___last5(a, b, c, d, x) x 239 #define ___last6(a, b, c, d, e, x) x 240 #define ___last7(a, b, c, d, e, f, x) x 241 #define ___last8(a, b, c, d, e, f, g, x) x 242 #define ___last9(a, b, c, d, e, f, g, h, x) x 243 #define ___last10(a, b, c, d, e, f, g, h, i, x) x 244 #define ___last(...) ___apply(___last, ___narg(__VA_ARGS__))(__VA_ARGS__) 245 246 #define ___nolast2(a, _) a 247 #define ___nolast3(a, b, _) a, b 248 #define ___nolast4(a, b, c, _) a, b, c 249 #define ___nolast5(a, b, c, d, _) a, b, c, d 250 #define ___nolast6(a, b, c, d, e, _) a, b, c, d, e 251 #define ___nolast7(a, b, c, d, e, f, _) a, b, c, d, e, f 252 #define ___nolast8(a, b, c, d, e, f, g, _) a, b, c, d, e, f, g 253 #define ___nolast9(a, b, c, d, e, f, g, h, _) a, b, c, d, e, f, g, h 254 #define ___nolast10(a, b, c, d, e, f, g, h, i, _) a, b, c, d, e, f, g, h, i 255 #define ___nolast(...) ___apply(___nolast, ___narg(__VA_ARGS__))(__VA_ARGS__) 256 257 #define ___arrow1(a) a 258 #define ___arrow2(a, b) a->b 259 #define ___arrow3(a, b, c) a->b->c 260 #define ___arrow4(a, b, c, d) a->b->c->d 261 #define ___arrow5(a, b, c, d, e) a->b->c->d->e 262 #define ___arrow6(a, b, c, d, e, f) a->b->c->d->e->f 263 #define ___arrow7(a, b, c, d, e, f, g) a->b->c->d->e->f->g 264 #define ___arrow8(a, b, c, d, e, f, g, h) a->b->c->d->e->f->g->h 265 #define ___arrow9(a, b, c, d, e, f, g, h, i) a->b->c->d->e->f->g->h->i 266 #define ___arrow10(a, b, c, d, e, f, g, h, i, j) a->b->c->d->e->f->g->h->i->j 267 #define ___arrow(...) ___apply(___arrow, ___narg(__VA_ARGS__))(__VA_ARGS__) 268 269 #define ___type(...) typeof(___arrow(__VA_ARGS__)) 270 271 #define ___read(read_fn, dst, src_type, src, accessor) \ 272 read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor) 273 274 /* "recursively" read a sequence of inner pointers using local __t var */ 275 #define ___rd_first(src, a) ___read(bpf_core_read, &__t, ___type(src), src, a); 276 #define ___rd_last(...) \ 277 ___read(bpf_core_read, &__t, \ 278 ___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__)); 279 #define ___rd_p1(...) const void *__t; ___rd_first(__VA_ARGS__) 280 #define ___rd_p2(...) ___rd_p1(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__) 281 #define ___rd_p3(...) ___rd_p2(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__) 282 #define ___rd_p4(...) ___rd_p3(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__) 283 #define ___rd_p5(...) ___rd_p4(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__) 284 #define ___rd_p6(...) ___rd_p5(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__) 285 #define ___rd_p7(...) ___rd_p6(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__) 286 #define ___rd_p8(...) ___rd_p7(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__) 287 #define ___rd_p9(...) ___rd_p8(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__) 288 #define ___read_ptrs(src, ...) \ 289 ___apply(___rd_p, ___narg(__VA_ARGS__))(src, __VA_ARGS__) 290 291 #define ___core_read0(fn, dst, src, a) \ 292 ___read(fn, dst, ___type(src), src, a); 293 #define ___core_readN(fn, dst, src, ...) \ 294 ___read_ptrs(src, ___nolast(__VA_ARGS__)) \ 295 ___read(fn, dst, ___type(src, ___nolast(__VA_ARGS__)), __t, \ 296 ___last(__VA_ARGS__)); 297 #define ___core_read(fn, dst, src, a, ...) \ 298 ___apply(___core_read, ___empty(__VA_ARGS__))(fn, dst, \ 299 src, a, ##__VA_ARGS__) 300 301 /* 302 * BPF_CORE_READ_INTO() is a more performance-conscious variant of 303 * BPF_CORE_READ(), in which final field is read into user-provided storage. 304 * See BPF_CORE_READ() below for more details on general usage. 305 */ 306 #define BPF_CORE_READ_INTO(dst, src, a, ...) \ 307 ({ \ 308 ___core_read(bpf_core_read, dst, (src), a, ##__VA_ARGS__) \ 309 }) 310 311 /* 312 * BPF_CORE_READ_STR_INTO() does same "pointer chasing" as 313 * BPF_CORE_READ() for intermediate pointers, but then executes (and returns 314 * corresponding error code) bpf_core_read_str() for final string read. 315 */ 316 #define BPF_CORE_READ_STR_INTO(dst, src, a, ...) \ 317 ({ \ 318 ___core_read(bpf_core_read_str, dst, (src), a, ##__VA_ARGS__)\ 319 }) 320 321 /* 322 * BPF_CORE_READ() is used to simplify BPF CO-RE relocatable read, especially 323 * when there are few pointer chasing steps. 324 * E.g., what in non-BPF world (or in BPF w/ BCC) would be something like: 325 * int x = s->a.b.c->d.e->f->g; 326 * can be succinctly achieved using BPF_CORE_READ as: 327 * int x = BPF_CORE_READ(s, a.b.c, d.e, f, g); 328 * 329 * BPF_CORE_READ will decompose above statement into 4 bpf_core_read (BPF 330 * CO-RE relocatable bpf_probe_read_kernel() wrapper) calls, logically 331 * equivalent to: 332 * 1. const void *__t = s->a.b.c; 333 * 2. __t = __t->d.e; 334 * 3. __t = __t->f; 335 * 4. return __t->g; 336 * 337 * Equivalence is logical, because there is a heavy type casting/preservation 338 * involved, as well as all the reads are happening through 339 * bpf_probe_read_kernel() calls using __builtin_preserve_access_index() to 340 * emit CO-RE relocations. 341 * 342 * N.B. Only up to 9 "field accessors" are supported, which should be more 343 * than enough for any practical purpose. 344 */ 345 #define BPF_CORE_READ(src, a, ...) \ 346 ({ \ 347 ___type((src), a, ##__VA_ARGS__) __r; \ 348 BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \ 349 __r; \ 350 }) 351 352 #endif 353 354