tools/lib/bpf/usdt.bpf.h

   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_usdt_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); _x; })
 218 #define ___bpf_usdt_args2(x, args...) ___bpf_usdt_args1(args), ({ long _x; bpf_usdt_arg(ctx, 1, &_x); _x; })
 219 #define ___bpf_usdt_args3(x, args...) ___bpf_usdt_args2(args), ({ long _x; bpf_usdt_arg(ctx, 2, &_x); _x; })
 220 #define ___bpf_usdt_args4(x, args...) ___bpf_usdt_args3(args), ({ long _x; bpf_usdt_arg(ctx, 3, &_x); _x; })
 221 #define ___bpf_usdt_args5(x, args...) ___bpf_usdt_args4(args), ({ long _x; bpf_usdt_arg(ctx, 4, &_x); _x; })
 222 #define ___bpf_usdt_args6(x, args...) ___bpf_usdt_args5(args), ({ long _x; bpf_usdt_arg(ctx, 5, &_x); _x; })
 223 #define ___bpf_usdt_args7(x, args...) ___bpf_usdt_args6(args), ({ long _x; bpf_usdt_arg(ctx, 6, &_x); _x; })
 224 #define ___bpf_usdt_args8(x, args...) ___bpf_usdt_args7(args), ({ long _x; bpf_usdt_arg(ctx, 7, &_x); _x; })
 225 #define ___bpf_usdt_args9(x, args...) ___bpf_usdt_args8(args), ({ long _x; bpf_usdt_arg(ctx, 8, &_x); _x; })
 226 #define ___bpf_usdt_args10(x, args...) ___bpf_usdt_args9(args), ({ long _x; bpf_usdt_arg(ctx, 9, &_x); _x; })
 227 #define ___bpf_usdt_args11(x, args...) ___bpf_usdt_args10(args), ({ long _x; bpf_usdt_arg(ctx, 10, &_x); _x; })
 228 #define ___bpf_usdt_args12(x, args...) ___bpf_usdt_args11(args), ({ long _x; bpf_usdt_arg(ctx, 11, &_x); _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__ */