summaryrefslogtreecommitdiffstats
path: root/tools/lib/bpf/usdt.bpf.h
blob: f6763300b26a48b3204f83b27b0ed54b8047c384 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
#ifndef __USDT_BPF_H__
#define __USDT_BPF_H__

#include <linux/errno.h>
#include "bpf_helpers.h"
#include "bpf_tracing.h"

/* Below types and maps are internal implementation details of libbpf's USDT
 * support and are subjects to change. Also, bpf_usdt_xxx() API helpers should
 * be considered an unstable API as well and might be adjusted based on user
 * feedback from using libbpf's USDT support in production.
 */

/* User can override BPF_USDT_MAX_SPEC_CNT to change default size of internal
 * map that keeps track of USDT argument specifications. This might be
 * necessary if there are a lot of USDT attachments.
 */
#ifndef BPF_USDT_MAX_SPEC_CNT
#define BPF_USDT_MAX_SPEC_CNT 256
#endif
/* User can override BPF_USDT_MAX_IP_CNT to change default size of internal
 * map that keeps track of IP (memory address) mapping to USDT argument
 * specification.
 * Note, if kernel supports BPF cookies, this map is not used and could be
 * resized all the way to 1 to save a bit of memory.
 */
#ifndef BPF_USDT_MAX_IP_CNT
#define BPF_USDT_MAX_IP_CNT (4 * BPF_USDT_MAX_SPEC_CNT)
#endif

enum __bpf_usdt_arg_type {
	BPF_USDT_ARG_CONST,
	BPF_USDT_ARG_REG,
	BPF_USDT_ARG_REG_DEREF,
};

struct __bpf_usdt_arg_spec {
	/* u64 scalar interpreted depending on arg_type, see below */
	__u64 val_off;
	/* arg location case, see bpf_udst_arg() for details */
	enum __bpf_usdt_arg_type arg_type;
	/* offset of referenced register within struct pt_regs */
	short reg_off;
	/* whether arg should be interpreted as signed value */
	bool arg_signed;
	/* number of bits that need to be cleared and, optionally,
	 * sign-extended to cast arguments that are 1, 2, or 4 bytes
	 * long into final 8-byte u64/s64 value returned to user
	 */
	char arg_bitshift;
};

/* should match USDT_MAX_ARG_CNT in usdt.c exactly */
#define BPF_USDT_MAX_ARG_CNT 12
struct __bpf_usdt_spec {
	struct __bpf_usdt_arg_spec args[BPF_USDT_MAX_ARG_CNT];
	__u64 usdt_cookie;
	short arg_cnt;
};

struct {
	__uint(type, BPF_MAP_TYPE_ARRAY);
	__uint(max_entries, BPF_USDT_MAX_SPEC_CNT);
	__type(key, int);
	__type(value, struct __bpf_usdt_spec);
} __bpf_usdt_specs SEC(".maps") __weak;

struct {
	__uint(type, BPF_MAP_TYPE_HASH);
	__uint(max_entries, BPF_USDT_MAX_IP_CNT);
	__type(key, long);
	__type(value, __u32);
} __bpf_usdt_ip_to_spec_id SEC(".maps") __weak;

extern const _Bool LINUX_HAS_BPF_COOKIE __kconfig;

static __always_inline
int __bpf_usdt_spec_id(struct pt_regs *ctx)
{
	if (!LINUX_HAS_BPF_COOKIE) {
		long ip = PT_REGS_IP(ctx);
		int *spec_id_ptr;

		spec_id_ptr = bpf_map_lookup_elem(&__bpf_usdt_ip_to_spec_id, &ip);
		return spec_id_ptr ? *spec_id_ptr : -ESRCH;
	}

	return bpf_get_attach_cookie(ctx);
}

/* Return number of USDT arguments defined for currently traced USDT. */
__weak __hidden
int bpf_usdt_arg_cnt(struct pt_regs *ctx)
{
	struct __bpf_usdt_spec *spec;
	int spec_id;

	spec_id = __bpf_usdt_spec_id(ctx);
	if (spec_id < 0)
		return -ESRCH;

	spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id);
	if (!spec)
		return -ESRCH;

	return spec->arg_cnt;
}

/* Fetch USDT argument #*arg_num* (zero-indexed) and put its value into *res.
 * Returns 0 on success; negative error, otherwise.
 * On error *res is guaranteed to be set to zero.
 */
__weak __hidden
int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res)
{
	struct __bpf_usdt_spec *spec;
	struct __bpf_usdt_arg_spec *arg_spec;
	unsigned long val;
	int err, spec_id;

	*res = 0;

	spec_id = __bpf_usdt_spec_id(ctx);
	if (spec_id < 0)
		return -ESRCH;

	spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id);
	if (!spec)
		return -ESRCH;

	if (arg_num >= BPF_USDT_MAX_ARG_CNT)
		return -ENOENT;
	barrier_var(arg_num);
	if (arg_num >= spec->arg_cnt)
		return -ENOENT;

	arg_spec = &spec->args[arg_num];
	switch (arg_spec->arg_type) {
	case BPF_USDT_ARG_CONST:
		/* Arg is just a constant ("-4@$-9" in USDT arg spec).
		 * value is recorded in arg_spec->val_off directly.
		 */
		val = arg_spec->val_off;
		break;
	case BPF_USDT_ARG_REG:
		/* Arg is in a register (e.g, "8@%rax" in USDT arg spec),
		 * so we read the contents of that register directly from
		 * struct pt_regs. To keep things simple user-space parts
		 * record offsetof(struct pt_regs, <regname>) in arg_spec->reg_off.
		 */
		err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off);
		if (err)
			return err;
		break;
	case BPF_USDT_ARG_REG_DEREF:
		/* Arg is in memory addressed by register, plus some offset
		 * (e.g., "-4@-1204(%rbp)" in USDT arg spec). Register is
		 * identified like with BPF_USDT_ARG_REG case, and the offset
		 * is in arg_spec->val_off. We first fetch register contents
		 * from pt_regs, then do another user-space probe read to
		 * fetch argument value itself.
		 */
		err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off);
		if (err)
			return err;
		err = bpf_probe_read_user(&val, sizeof(val), (void *)val + arg_spec->val_off);
		if (err)
			return err;
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
		val >>= arg_spec->arg_bitshift;
#endif
		break;
	default:
		return -EINVAL;
	}

	/* cast arg from 1, 2, or 4 bytes to final 8 byte size clearing
	 * necessary upper arg_bitshift bits, with sign extension if argument
	 * is signed
	 */
	val <<= arg_spec->arg_bitshift;
	if (arg_spec->arg_signed)
		val = ((long)val) >> arg_spec->arg_bitshift;
	else
		val = val >> arg_spec->arg_bitshift;
	*res = val;
	return 0;
}

/* Retrieve user-specified cookie value provided during attach as
 * bpf_usdt_opts.usdt_cookie. This serves the same purpose as BPF cookie
 * returned by bpf_get_attach_cookie(). Libbpf's support for USDT is itself
 * utilizing BPF cookies internally, so user can't use BPF cookie directly
 * for USDT programs and has to use bpf_usdt_cookie() API instead.
 */
__weak __hidden
long bpf_usdt_cookie(struct pt_regs *ctx)
{
	struct __bpf_usdt_spec *spec;
	int spec_id;

	spec_id = __bpf_usdt_spec_id(ctx);
	if (spec_id < 0)
		return 0;

	spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id);
	if (!spec)
		return 0;

	return spec->usdt_cookie;
}

/* we rely on ___bpf_apply() and ___bpf_narg() macros already defined in bpf_tracing.h */
#define ___bpf_usdt_args0() ctx
#define ___bpf_usdt_args1(x) ___bpf_usdt_args0(), ({ long _x; bpf_usdt_arg(ctx, 0, &_x); (void *)_x; })
#define ___bpf_usdt_args2(x, args...) ___bpf_usdt_args1(args), ({ long _x; bpf_usdt_arg(ctx, 1, &_x); (void *)_x; })
#define ___bpf_usdt_args3(x, args...) ___bpf_usdt_args2(args), ({ long _x; bpf_usdt_arg(ctx, 2, &_x); (void *)_x; })
#define ___bpf_usdt_args4(x, args...) ___bpf_usdt_args3(args), ({ long _x; bpf_usdt_arg(ctx, 3, &_x); (void *)_x; })
#define ___bpf_usdt_args5(x, args...) ___bpf_usdt_args4(args), ({ long _x; bpf_usdt_arg(ctx, 4, &_x); (void *)_x; })
#define ___bpf_usdt_args6(x, args...) ___bpf_usdt_args5(args), ({ long _x; bpf_usdt_arg(ctx, 5, &_x); (void *)_x; })
#define ___bpf_usdt_args7(x, args...) ___bpf_usdt_args6(args), ({ long _x; bpf_usdt_arg(ctx, 6, &_x); (void *)_x; })
#define ___bpf_usdt_args8(x, args...) ___bpf_usdt_args7(args), ({ long _x; bpf_usdt_arg(ctx, 7, &_x); (void *)_x; })
#define ___bpf_usdt_args9(x, args...) ___bpf_usdt_args8(args), ({ long _x; bpf_usdt_arg(ctx, 8, &_x); (void *)_x; })
#define ___bpf_usdt_args10(x, args...) ___bpf_usdt_args9(args), ({ long _x; bpf_usdt_arg(ctx, 9, &_x); (void *)_x; })
#define ___bpf_usdt_args11(x, args...) ___bpf_usdt_args10(args), ({ long _x; bpf_usdt_arg(ctx, 10, &_x); (void *)_x; })
#define ___bpf_usdt_args12(x, args...) ___bpf_usdt_args11(args), ({ long _x; bpf_usdt_arg(ctx, 11, &_x); (void *)_x; })
#define ___bpf_usdt_args(args...) ___bpf_apply(___bpf_usdt_args, ___bpf_narg(args))(args)

/*
 * BPF_USDT serves the same purpose for USDT handlers as BPF_PROG for
 * tp_btf/fentry/fexit BPF programs and BPF_KPROBE for kprobes.
 * Original struct pt_regs * context is preserved as 'ctx' argument.
 */
#define BPF_USDT(name, args...)						    \
name(struct pt_regs *ctx);						    \
static __always_inline typeof(name(0))					    \
____##name(struct pt_regs *ctx, ##args);				    \
typeof(name(0)) name(struct pt_regs *ctx)				    \
{									    \
        _Pragma("GCC diagnostic push")					    \
        _Pragma("GCC diagnostic ignored \"-Wint-conversion\"")		    \
        return ____##name(___bpf_usdt_args(args));			    \
        _Pragma("GCC diagnostic pop")					    \
}									    \
static __always_inline typeof(name(0))					    \
____##name(struct pt_regs *ctx, ##args)

#endif /* __USDT_BPF_H__ */