1 /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
2 #ifndef __BPF_CORE_READ_H__
3 #define __BPF_CORE_READ_H__
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.
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 */
18 BPF_FIELD_LSHIFT_U64 = 4,
19 BPF_FIELD_RSHIFT_U64 = 5,
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 */
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 */
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 */
40 #define __CORE_RELO(src, field, info) \
41 __builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
43 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
44 #define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
45 bpf_probe_read_kernel( \
47 __CORE_RELO(src, fld, BYTE_SIZE), \
48 (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
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
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))
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.
69 #define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({ \
70 unsigned long long val = 0; \
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); \
77 val = val >> __CORE_RELO(s, field, RSHIFT_U64); \
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
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; \
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. \
97 asm volatile("" : "=r"(p) : "0"(p)); \
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; \
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); \
109 val = val >> __CORE_RELO(s, field, RSHIFT_U64); \
114 * Convenience macro to check that field actually exists in target kernel's.
116 * 1, if matching field is present in target kernel;
117 * 0, if no matching field found.
119 #define bpf_core_field_exists(field) \
120 __builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
123 * Convenience macro to get the byte size of a field. Works for integers,
124 * struct/unions, pointers, arrays, and enums.
126 #define bpf_core_field_size(field) \
127 __builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)
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.
134 #define bpf_core_type_id_local(type) \
135 __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_LOCAL)
138 * Convenience macro to get BTF type ID of a target kernel's type that matches
139 * specified local type.
141 * - valid 32-bit unsigned type ID in kernel BTF;
142 * - 0, if no matching type was found in a target kernel BTF.
144 #define bpf_core_type_id_kernel(type) \
145 __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_TARGET)
148 * Convenience macro to check that provided named type
149 * (struct/union/enum/typedef) exists in a target kernel.
151 * 1, if such type is present in target kernel's BTF;
152 * 0, if no matching type is found.
154 #define bpf_core_type_exists(type) \
155 __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_EXISTS)
158 * Convenience macro to get the byte size of a provided named type
159 * (struct/union/enum/typedef) in a target kernel.
161 * >= 0 size (in bytes), if type is present in target kernel's BTF;
162 * 0, if no matching type is found.
164 #define bpf_core_type_size(type) \
165 __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_SIZE)
168 * Convenience macro to check that provided enumerator value is defined in
171 * 1, if specified enum type and its enumerator value are present in target
173 * 0, if no matching enum and/or enum value within that enum is found.
175 #define bpf_core_enum_value_exists(enum_type, enum_value) \
176 __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_EXISTS)
179 * Convenience macro to get the integer value of an enumerator value in
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.
186 #define bpf_core_enum_value(enum_type, enum_value) \
187 __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_VALUE)
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.
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.
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.
205 #define bpf_core_read(dst, sz, src) \
206 bpf_probe_read_kernel(dst, sz, \
207 (const void *)__builtin_preserve_access_index(src))
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
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))
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
223 * return number of provided arguments; used for switch-based variadic macro
224 * definitions (see ___last, ___arrow, etc below)
226 #define ___narg(...) ___nth(_, ##__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
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)
232 #define ___empty(...) ___nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)
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__)
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__)
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__)
269 #define ___type(...) typeof(___arrow(__VA_ARGS__))
271 #define ___read(read_fn, dst, src_type, src, accessor) \
272 read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)
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__)
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__)
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.
306 #define BPF_CORE_READ_INTO(dst, src, a, ...) \
308 ___core_read(bpf_core_read, dst, (src), a, ##__VA_ARGS__) \
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.
316 #define BPF_CORE_READ_STR_INTO(dst, src, a, ...) \
318 ___core_read(bpf_core_read_str, dst, (src), a, ##__VA_ARGS__)\
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);
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
332 * 1. const void *__t = s->a.b.c;
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.
342 * N.B. Only up to 9 "field accessors" are supported, which should be more
343 * than enough for any practical purpose.
345 #define BPF_CORE_READ(src, a, ...) \
347 ___type((src), a, ##__VA_ARGS__) __r; \
348 BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \