1 /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */ 2 /* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */ 3 #ifndef __USDT_BPF_H__ 4 #define __USDT_BPF_H__ 5 6 #include <linux/errno.h> 7 #include "bpf_helpers.h" 8 #include "bpf_tracing.h" 9 10 /* Below types and maps are internal implementation details of libbpf's USDT 11 * support and are subjects to change. Also, bpf_usdt_xxx() API helpers should 12 * be considered an unstable API as well and might be adjusted based on user 13 * feedback from using libbpf's USDT support in production. 14 */ 15 16 /* User can override BPF_USDT_MAX_SPEC_CNT to change default size of internal 17 * map that keeps track of USDT argument specifications. This might be 18 * necessary if there are a lot of USDT attachments. 19 */ 20 #ifndef BPF_USDT_MAX_SPEC_CNT 21 #define BPF_USDT_MAX_SPEC_CNT 256 22 #endif 23 /* User can override BPF_USDT_MAX_IP_CNT to change default size of internal 24 * map that keeps track of IP (memory address) mapping to USDT argument 25 * specification. 26 * Note, if kernel supports BPF cookies, this map is not used and could be 27 * resized all the way to 1 to save a bit of memory. 28 */ 29 #ifndef BPF_USDT_MAX_IP_CNT 30 #define BPF_USDT_MAX_IP_CNT (4 * BPF_USDT_MAX_SPEC_CNT) 31 #endif 32 33 enum __bpf_usdt_arg_type { 34 BPF_USDT_ARG_CONST, 35 BPF_USDT_ARG_REG, 36 BPF_USDT_ARG_REG_DEREF, 37 }; 38 39 struct __bpf_usdt_arg_spec { 40 /* u64 scalar interpreted depending on arg_type, see below */ 41 __u64 val_off; 42 /* arg location case, see bpf_udst_arg() for details */ 43 enum __bpf_usdt_arg_type arg_type; 44 /* offset of referenced register within struct pt_regs */ 45 short reg_off; 46 /* whether arg should be interpreted as signed value */ 47 bool arg_signed; 48 /* number of bits that need to be cleared and, optionally, 49 * sign-extended to cast arguments that are 1, 2, or 4 bytes 50 * long into final 8-byte u64/s64 value returned to user 51 */ 52 char arg_bitshift; 53 }; 54 55 /* should match USDT_MAX_ARG_CNT in usdt.c exactly */ 56 #define BPF_USDT_MAX_ARG_CNT 12 57 struct __bpf_usdt_spec { 58 struct __bpf_usdt_arg_spec args[BPF_USDT_MAX_ARG_CNT]; 59 __u64 usdt_cookie; 60 short arg_cnt; 61 }; 62 63 struct { 64 __uint(type, BPF_MAP_TYPE_ARRAY); 65 __uint(max_entries, BPF_USDT_MAX_SPEC_CNT); 66 __type(key, int); 67 __type(value, struct __bpf_usdt_spec); 68 } __bpf_usdt_specs SEC(".maps") __weak; 69 70 struct { 71 __uint(type, BPF_MAP_TYPE_HASH); 72 __uint(max_entries, BPF_USDT_MAX_IP_CNT); 73 __type(key, long); 74 __type(value, __u32); 75 } __bpf_usdt_ip_to_spec_id SEC(".maps") __weak; 76 77 extern const _Bool LINUX_HAS_BPF_COOKIE __kconfig; 78 79 static __always_inline 80 int __bpf_usdt_spec_id(struct pt_regs *ctx) 81 { 82 if (!LINUX_HAS_BPF_COOKIE) { 83 long ip = PT_REGS_IP(ctx); 84 int *spec_id_ptr; 85 86 spec_id_ptr = bpf_map_lookup_elem(&__bpf_usdt_ip_to_spec_id, &ip); 87 return spec_id_ptr ? *spec_id_ptr : -ESRCH; 88 } 89 90 return bpf_get_attach_cookie(ctx); 91 } 92 93 /* Return number of USDT arguments defined for currently traced USDT. */ 94 __weak __hidden 95 int bpf_usdt_arg_cnt(struct pt_regs *ctx) 96 { 97 struct __bpf_usdt_spec *spec; 98 int spec_id; 99 100 spec_id = __bpf_usdt_spec_id(ctx); 101 if (spec_id < 0) 102 return -ESRCH; 103 104 spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id); 105 if (!spec) 106 return -ESRCH; 107 108 return spec->arg_cnt; 109 } 110 111 /* Fetch USDT argument #*arg_num* (zero-indexed) and put its value into *res. 112 * Returns 0 on success; negative error, otherwise. 113 * On error *res is guaranteed to be set to zero. 114 */ 115 __weak __hidden 116 int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res) 117 { 118 struct __bpf_usdt_spec *spec; 119 struct __bpf_usdt_arg_spec *arg_spec; 120 unsigned long val; 121 int err, spec_id; 122 123 *res = 0; 124 125 spec_id = __bpf_usdt_spec_id(ctx); 126 if (spec_id < 0) 127 return -ESRCH; 128 129 spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id); 130 if (!spec) 131 return -ESRCH; 132 133 if (arg_num >= BPF_USDT_MAX_ARG_CNT) 134 return -ENOENT; 135 barrier_var(arg_num); 136 if (arg_num >= spec->arg_cnt) 137 return -ENOENT; 138 139 arg_spec = &spec->args[arg_num]; 140 switch (arg_spec->arg_type) { 141 case BPF_USDT_ARG_CONST: 142 /* Arg is just a constant ("-4@$-9" in USDT arg spec). 143 * value is recorded in arg_spec->val_off directly. 144 */ 145 val = arg_spec->val_off; 146 break; 147 case BPF_USDT_ARG_REG: 148 /* Arg is in a register (e.g, "8@%rax" in USDT arg spec), 149 * so we read the contents of that register directly from 150 * struct pt_regs. To keep things simple user-space parts 151 * record offsetof(struct pt_regs, <regname>) in arg_spec->reg_off. 152 */ 153 err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off); 154 if (err) 155 return err; 156 break; 157 case BPF_USDT_ARG_REG_DEREF: 158 /* Arg is in memory addressed by register, plus some offset 159 * (e.g., "-4@-1204(%rbp)" in USDT arg spec). Register is 160 * identified like with BPF_USDT_ARG_REG case, and the offset 161 * is in arg_spec->val_off. We first fetch register contents 162 * from pt_regs, then do another user-space probe read to 163 * fetch argument value itself. 164 */ 165 err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off); 166 if (err) 167 return err; 168 err = bpf_probe_read_user(&val, sizeof(val), (void *)val + arg_spec->val_off); 169 if (err) 170 return err; 171 #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ 172 val >>= arg_spec->arg_bitshift; 173 #endif 174 break; 175 default: 176 return -EINVAL; 177 } 178 179 /* cast arg from 1, 2, or 4 bytes to final 8 byte size clearing 180 * necessary upper arg_bitshift bits, with sign extension if argument 181 * is signed 182 */ 183 val <<= arg_spec->arg_bitshift; 184 if (arg_spec->arg_signed) 185 val = ((long)val) >> arg_spec->arg_bitshift; 186 else 187 val = val >> arg_spec->arg_bitshift; 188 *res = val; 189 return 0; 190 } 191 192 /* Retrieve user-specified cookie value provided during attach as 193 * bpf_usdt_opts.usdt_cookie. This serves the same purpose as BPF cookie 194 * returned by bpf_get_attach_cookie(). Libbpf's support for USDT is itself 195 * utilizing BPF cookies internally, so user can't use BPF cookie directly 196 * for USDT programs and has to use bpf_usdt_cookie() API instead. 197 */ 198 __weak __hidden 199 long bpf_usdt_cookie(struct pt_regs *ctx) 200 { 201 struct __bpf_usdt_spec *spec; 202 int spec_id; 203 204 spec_id = __bpf_usdt_spec_id(ctx); 205 if (spec_id < 0) 206 return 0; 207 208 spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id); 209 if (!spec) 210 return 0; 211 212 return spec->usdt_cookie; 213 } 214 215 /* we rely on ___bpf_apply() and ___bpf_narg() macros already defined in bpf_tracing.h */ 216 #define ___bpf_usdt_args0() ctx 217 #define ___bpf_usdt_args1(x) ___bpf_usdt_args0(), ({ long _x; bpf_usdt_arg(ctx, 0, &_x); (void *)_x; }) 218 #define ___bpf_usdt_args2(x, args...) ___bpf_usdt_args1(args), ({ long _x; bpf_usdt_arg(ctx, 1, &_x); (void *)_x; }) 219 #define ___bpf_usdt_args3(x, args...) ___bpf_usdt_args2(args), ({ long _x; bpf_usdt_arg(ctx, 2, &_x); (void *)_x; }) 220 #define ___bpf_usdt_args4(x, args...) ___bpf_usdt_args3(args), ({ long _x; bpf_usdt_arg(ctx, 3, &_x); (void *)_x; }) 221 #define ___bpf_usdt_args5(x, args...) ___bpf_usdt_args4(args), ({ long _x; bpf_usdt_arg(ctx, 4, &_x); (void *)_x; }) 222 #define ___bpf_usdt_args6(x, args...) ___bpf_usdt_args5(args), ({ long _x; bpf_usdt_arg(ctx, 5, &_x); (void *)_x; }) 223 #define ___bpf_usdt_args7(x, args...) ___bpf_usdt_args6(args), ({ long _x; bpf_usdt_arg(ctx, 6, &_x); (void *)_x; }) 224 #define ___bpf_usdt_args8(x, args...) ___bpf_usdt_args7(args), ({ long _x; bpf_usdt_arg(ctx, 7, &_x); (void *)_x; }) 225 #define ___bpf_usdt_args9(x, args...) ___bpf_usdt_args8(args), ({ long _x; bpf_usdt_arg(ctx, 8, &_x); (void *)_x; }) 226 #define ___bpf_usdt_args10(x, args...) ___bpf_usdt_args9(args), ({ long _x; bpf_usdt_arg(ctx, 9, &_x); (void *)_x; }) 227 #define ___bpf_usdt_args11(x, args...) ___bpf_usdt_args10(args), ({ long _x; bpf_usdt_arg(ctx, 10, &_x); (void *)_x; }) 228 #define ___bpf_usdt_args12(x, args...) ___bpf_usdt_args11(args), ({ long _x; bpf_usdt_arg(ctx, 11, &_x); (void *)_x; }) 229 #define ___bpf_usdt_args(args...) ___bpf_apply(___bpf_usdt_args, ___bpf_narg(args))(args) 230 231 /* 232 * BPF_USDT serves the same purpose for USDT handlers as BPF_PROG for 233 * tp_btf/fentry/fexit BPF programs and BPF_KPROBE for kprobes. 234 * Original struct pt_regs * context is preserved as 'ctx' argument. 235 */ 236 #define BPF_USDT(name, args...) \ 237 name(struct pt_regs *ctx); \ 238 static __always_inline typeof(name(0)) \ 239 ____##name(struct pt_regs *ctx, ##args); \ 240 typeof(name(0)) name(struct pt_regs *ctx) \ 241 { \ 242 _Pragma("GCC diagnostic push") \ 243 _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \ 244 return ____##name(___bpf_usdt_args(args)); \ 245 _Pragma("GCC diagnostic pop") \ 246 } \ 247 static __always_inline typeof(name(0)) \ 248 ____##name(struct pt_regs *ctx, ##args) 249 250 #endif /* __USDT_BPF_H__ */ 251