1 /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
2 /* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
6 #include <linux/errno.h>
7 #include <bpf/bpf_helpers.h>
8 #include <bpf/bpf_tracing.h>
9 #include <bpf/bpf_core_read.h>
11 /* Below types and maps are internal implementation details of libbpf's USDT
12 * support and are subjects to change. Also, bpf_usdt_xxx() API helpers should
13 * be considered an unstable API as well and might be adjusted based on user
14 * feedback from using libbpf's USDT support in production.
17 /* User can override BPF_USDT_MAX_SPEC_CNT to change default size of internal
18 * map that keeps track of USDT argument specifications. This might be
19 * necessary if there are a lot of USDT attachments.
21 #ifndef BPF_USDT_MAX_SPEC_CNT
22 #define BPF_USDT_MAX_SPEC_CNT 256
24 /* User can override BPF_USDT_MAX_IP_CNT to change default size of internal
25 * map that keeps track of IP (memory address) mapping to USDT argument
27 * Note, if kernel supports BPF cookies, this map is not used and could be
28 * resized all the way to 1 to save a bit of memory.
30 #ifndef BPF_USDT_MAX_IP_CNT
31 #define BPF_USDT_MAX_IP_CNT (4 * BPF_USDT_MAX_SPEC_CNT)
33 /* We use BPF CO-RE to detect support for BPF cookie from BPF side. This is
34 * the only dependency on CO-RE, so if it's undesirable, user can override
35 * BPF_USDT_HAS_BPF_COOKIE to specify whether to BPF cookie is supported or not.
37 #ifndef BPF_USDT_HAS_BPF_COOKIE
38 #define BPF_USDT_HAS_BPF_COOKIE \
39 bpf_core_enum_value_exists(enum bpf_func_id___usdt, BPF_FUNC_get_attach_cookie___usdt)
42 enum __bpf_usdt_arg_type {
45 BPF_USDT_ARG_REG_DEREF,
48 struct __bpf_usdt_arg_spec {
49 /* u64 scalar interpreted depending on arg_type, see below */
51 /* arg location case, see bpf_udst_arg() for details */
52 enum __bpf_usdt_arg_type arg_type;
53 /* offset of referenced register within struct pt_regs */
55 /* whether arg should be interpreted as signed value */
57 /* number of bits that need to be cleared and, optionally,
58 * sign-extended to cast arguments that are 1, 2, or 4 bytes
59 * long into final 8-byte u64/s64 value returned to user
64 /* should match USDT_MAX_ARG_CNT in usdt.c exactly */
65 #define BPF_USDT_MAX_ARG_CNT 12
66 struct __bpf_usdt_spec {
67 struct __bpf_usdt_arg_spec args[BPF_USDT_MAX_ARG_CNT];
73 __uint(type, BPF_MAP_TYPE_ARRAY);
74 __uint(max_entries, BPF_USDT_MAX_SPEC_CNT);
76 __type(value, struct __bpf_usdt_spec);
77 } __bpf_usdt_specs SEC(".maps") __weak;
80 __uint(type, BPF_MAP_TYPE_HASH);
81 __uint(max_entries, BPF_USDT_MAX_IP_CNT);
84 } __bpf_usdt_ip_to_spec_id SEC(".maps") __weak;
86 /* don't rely on user's BPF code to have latest definition of bpf_func_id */
87 enum bpf_func_id___usdt {
88 BPF_FUNC_get_attach_cookie___usdt = 0xBAD, /* value doesn't matter */
91 static __always_inline
92 int __bpf_usdt_spec_id(struct pt_regs *ctx)
94 if (!BPF_USDT_HAS_BPF_COOKIE) {
95 long ip = PT_REGS_IP(ctx);
98 spec_id_ptr = bpf_map_lookup_elem(&__bpf_usdt_ip_to_spec_id, &ip);
99 return spec_id_ptr ? *spec_id_ptr : -ESRCH;
102 return bpf_get_attach_cookie(ctx);
105 /* Return number of USDT arguments defined for currently traced USDT. */
107 int bpf_usdt_arg_cnt(struct pt_regs *ctx)
109 struct __bpf_usdt_spec *spec;
112 spec_id = __bpf_usdt_spec_id(ctx);
116 spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id);
120 return spec->arg_cnt;
123 /* Fetch USDT argument #*arg_num* (zero-indexed) and put its value into *res.
124 * Returns 0 on success; negative error, otherwise.
125 * On error *res is guaranteed to be set to zero.
128 int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res)
130 struct __bpf_usdt_spec *spec;
131 struct __bpf_usdt_arg_spec *arg_spec;
137 spec_id = __bpf_usdt_spec_id(ctx);
141 spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id);
145 if (arg_num >= BPF_USDT_MAX_ARG_CNT || arg_num >= spec->arg_cnt)
148 arg_spec = &spec->args[arg_num];
149 switch (arg_spec->arg_type) {
150 case BPF_USDT_ARG_CONST:
151 /* Arg is just a constant ("-4@$-9" in USDT arg spec).
152 * value is recorded in arg_spec->val_off directly.
154 val = arg_spec->val_off;
156 case BPF_USDT_ARG_REG:
157 /* Arg is in a register (e.g, "8@%rax" in USDT arg spec),
158 * so we read the contents of that register directly from
159 * struct pt_regs. To keep things simple user-space parts
160 * record offsetof(struct pt_regs, <regname>) in arg_spec->reg_off.
162 err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off);
166 case BPF_USDT_ARG_REG_DEREF:
167 /* Arg is in memory addressed by register, plus some offset
168 * (e.g., "-4@-1204(%rbp)" in USDT arg spec). Register is
169 * identified like with BPF_USDT_ARG_REG case, and the offset
170 * is in arg_spec->val_off. We first fetch register contents
171 * from pt_regs, then do another user-space probe read to
172 * fetch argument value itself.
174 err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off);
177 err = bpf_probe_read_user(&val, sizeof(val), (void *)val + arg_spec->val_off);
180 #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
181 val >>= arg_spec->arg_bitshift;
188 /* cast arg from 1, 2, or 4 bytes to final 8 byte size clearing
189 * necessary upper arg_bitshift bits, with sign extension if argument
192 val <<= arg_spec->arg_bitshift;
193 if (arg_spec->arg_signed)
194 val = ((long)val) >> arg_spec->arg_bitshift;
196 val = val >> arg_spec->arg_bitshift;
201 /* Retrieve user-specified cookie value provided during attach as
202 * bpf_usdt_opts.usdt_cookie. This serves the same purpose as BPF cookie
203 * returned by bpf_get_attach_cookie(). Libbpf's support for USDT is itself
204 * utilizing BPF cookies internally, so user can't use BPF cookie directly
205 * for USDT programs and has to use bpf_usdt_cookie() API instead.
208 long bpf_usdt_cookie(struct pt_regs *ctx)
210 struct __bpf_usdt_spec *spec;
213 spec_id = __bpf_usdt_spec_id(ctx);
217 spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id);
221 return spec->usdt_cookie;
224 /* we rely on ___bpf_apply() and ___bpf_narg() macros already defined in bpf_tracing.h */
225 #define ___bpf_usdt_args0() ctx
226 #define ___bpf_usdt_args1(x) ___bpf_usdt_args0(), ({ long _x; bpf_usdt_arg(ctx, 0, &_x); (void *)_x; })
227 #define ___bpf_usdt_args2(x, args...) ___bpf_usdt_args1(args), ({ long _x; bpf_usdt_arg(ctx, 1, &_x); (void *)_x; })
228 #define ___bpf_usdt_args3(x, args...) ___bpf_usdt_args2(args), ({ long _x; bpf_usdt_arg(ctx, 2, &_x); (void *)_x; })
229 #define ___bpf_usdt_args4(x, args...) ___bpf_usdt_args3(args), ({ long _x; bpf_usdt_arg(ctx, 3, &_x); (void *)_x; })
230 #define ___bpf_usdt_args5(x, args...) ___bpf_usdt_args4(args), ({ long _x; bpf_usdt_arg(ctx, 4, &_x); (void *)_x; })
231 #define ___bpf_usdt_args6(x, args...) ___bpf_usdt_args5(args), ({ long _x; bpf_usdt_arg(ctx, 5, &_x); (void *)_x; })
232 #define ___bpf_usdt_args7(x, args...) ___bpf_usdt_args6(args), ({ long _x; bpf_usdt_arg(ctx, 6, &_x); (void *)_x; })
233 #define ___bpf_usdt_args8(x, args...) ___bpf_usdt_args7(args), ({ long _x; bpf_usdt_arg(ctx, 7, &_x); (void *)_x; })
234 #define ___bpf_usdt_args9(x, args...) ___bpf_usdt_args8(args), ({ long _x; bpf_usdt_arg(ctx, 8, &_x); (void *)_x; })
235 #define ___bpf_usdt_args10(x, args...) ___bpf_usdt_args9(args), ({ long _x; bpf_usdt_arg(ctx, 9, &_x); (void *)_x; })
236 #define ___bpf_usdt_args11(x, args...) ___bpf_usdt_args10(args), ({ long _x; bpf_usdt_arg(ctx, 10, &_x); (void *)_x; })
237 #define ___bpf_usdt_args12(x, args...) ___bpf_usdt_args11(args), ({ long _x; bpf_usdt_arg(ctx, 11, &_x); (void *)_x; })
238 #define ___bpf_usdt_args(args...) ___bpf_apply(___bpf_usdt_args, ___bpf_narg(args))(args)
241 * BPF_USDT serves the same purpose for USDT handlers as BPF_PROG for
242 * tp_btf/fentry/fexit BPF programs and BPF_KPROBE for kprobes.
243 * Original struct pt_regs * context is preserved as 'ctx' argument.
245 #define BPF_USDT(name, args...) \
246 name(struct pt_regs *ctx); \
247 static __attribute__((always_inline)) typeof(name(0)) \
248 ____##name(struct pt_regs *ctx, ##args); \
249 typeof(name(0)) name(struct pt_regs *ctx) \
251 _Pragma("GCC diagnostic push") \
252 _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
253 return ____##name(___bpf_usdt_args(args)); \
254 _Pragma("GCC diagnostic pop") \
256 static __attribute__((always_inline)) typeof(name(0)) \
257 ____##name(struct pt_regs *ctx, ##args)
259 #endif /* __USDT_BPF_H__ */