summaryrefslogtreecommitdiff
path: root/tools/testing/selftests/bpf/progs/strobemeta.h
blob: 40df2cc26eaf9d83005756fa8c67fd2e20171847 (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
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2019 Facebook

#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>
#include <linux/bpf.h>
#include <linux/ptrace.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <bpf/bpf_helpers.h>

typedef uint32_t pid_t;
struct task_struct {};

#define TASK_COMM_LEN 16
#define PERF_MAX_STACK_DEPTH 127

#define STROBE_TYPE_INVALID 0
#define STROBE_TYPE_INT 1
#define STROBE_TYPE_STR 2
#define STROBE_TYPE_MAP 3

#define STACK_TABLE_EPOCH_SHIFT 20
#define STROBE_MAX_STR_LEN 1
#define STROBE_MAX_CFGS 32
#define READ_MAP_VAR_PAYLOAD_CAP					\
	((1 + STROBE_MAX_MAP_ENTRIES * 2) * STROBE_MAX_STR_LEN)
#define STROBE_MAX_PAYLOAD						\
	(STROBE_MAX_STRS * STROBE_MAX_STR_LEN +				\
	 STROBE_MAX_MAPS * READ_MAP_VAR_PAYLOAD_CAP)

struct strobe_value_header {
	/*
	 * meaning depends on type:
	 * 1. int: 0, if value not set, 1 otherwise
	 * 2. str: 1 always, whether value is set or not is determined by ptr
	 * 3. map: 1 always, pointer points to additional struct with number
	 *    of entries (up to STROBE_MAX_MAP_ENTRIES)
	 */
	uint16_t len;
	/*
	 * _reserved might be used for some future fields/flags, but we always
	 * want to keep strobe_value_header to be 8 bytes, so BPF can read 16
	 * bytes in one go and get both header and value
	 */
	uint8_t _reserved[6];
};

/*
 * strobe_value_generic is used from BPF probe only, but needs to be a union
 * of strobe_value_int/strobe_value_str/strobe_value_map
 */
struct strobe_value_generic {
	struct strobe_value_header header;
	union {
		int64_t val;
		void *ptr;
	};
};

struct strobe_value_int {
	struct strobe_value_header header;
	int64_t value;
};

struct strobe_value_str {
	struct strobe_value_header header;
	const char* value;
};

struct strobe_value_map {
	struct strobe_value_header header;
	const struct strobe_map_raw* value;
};

struct strobe_map_entry {
	const char* key;
	const char* val;
};

/*
 * Map of C-string key/value pairs with fixed maximum capacity. Each map has
 * corresponding int64 ID, which application can use (or ignore) in whatever
 * way appropriate. Map is "write-only", there is no way to get data out of
 * map. Map is intended to be used to provide metadata for profilers and is
 * not to be used for internal in-app communication. All methods are
 * thread-safe.
 */
struct strobe_map_raw {
	/*
	 * general purpose unique ID that's up to application to decide
	 * whether and how to use; for request metadata use case id is unique
	 * request ID that's used to match metadata with stack traces on
	 * Strobelight backend side
	 */
	int64_t id;
	/* number of used entries in map */
	int64_t cnt;
	/*
	 * having volatile doesn't change anything on BPF side, but clang
	 * emits warnings for passing `volatile const char *` into
	 * bpf_probe_read_user_str that expects just `const char *`
	 */
	const char* tag;
	/*
	 * key/value entries, each consisting of 2 pointers to key and value
	 * C strings
	 */
	struct strobe_map_entry entries[STROBE_MAX_MAP_ENTRIES];
};

/* Following values define supported values of TLS mode */
#define TLS_NOT_SET -1
#define TLS_LOCAL_EXEC 0
#define TLS_IMM_EXEC 1
#define TLS_GENERAL_DYN 2

/*
 * structure that universally represents TLS location (both for static
 * executables and shared libraries)
 */
struct strobe_value_loc {
	/*
	 * tls_mode defines what TLS mode was used for particular metavariable:
	 * - -1 (TLS_NOT_SET) - no metavariable;
	 * - 0 (TLS_LOCAL_EXEC) - Local Executable mode;
	 * - 1 (TLS_IMM_EXEC) - Immediate Executable mode;
	 * - 2 (TLS_GENERAL_DYN) - General Dynamic mode;
	 * Local Dynamic mode is not yet supported, because never seen in
	 * practice.  Mode defines how offset field is interpreted. See
	 * calc_location() in below for details.
	 */
	int64_t tls_mode;
	/*
	 * TLS_LOCAL_EXEC: offset from thread pointer (fs:0 for x86-64,
	 * tpidr_el0 for aarch64).
	 * TLS_IMM_EXEC: absolute address of GOT entry containing offset
	 * from thread pointer;
	 * TLS_GENERAL_DYN: absolute address of double GOT entry
	 * containing tls_index_t struct;
	 */
	int64_t offset;
};

struct strobemeta_cfg {
	int64_t req_meta_idx;
	struct strobe_value_loc int_locs[STROBE_MAX_INTS];
	struct strobe_value_loc str_locs[STROBE_MAX_STRS];
	struct strobe_value_loc map_locs[STROBE_MAX_MAPS];
};

struct strobe_map_descr {
	uint64_t id;
	int16_t tag_len;
	/*
	 * cnt <0 - map value isn't set;
	 * 0 - map has id set, but no key/value entries
	 */
	int16_t cnt;
	/*
	 * both key_lens[i] and val_lens[i] should be >0 for present key/value
	 * entry
	 */
	uint16_t key_lens[STROBE_MAX_MAP_ENTRIES];
	uint16_t val_lens[STROBE_MAX_MAP_ENTRIES];
};

struct strobemeta_payload {
	/* req_id has valid request ID, if req_meta_valid == 1 */
	int64_t req_id;
	uint8_t req_meta_valid;
	/*
	 * mask has Nth bit set to 1, if Nth metavar was present and
	 * successfully read
	 */
	uint64_t int_vals_set_mask;
	int64_t int_vals[STROBE_MAX_INTS];
	/* len is >0 for present values */
	uint16_t str_lens[STROBE_MAX_STRS];
	/* if map_descrs[i].cnt == -1, metavar is not present/set */
	struct strobe_map_descr map_descrs[STROBE_MAX_MAPS];
	/*
	 * payload has compactly packed values of str and map variables in the
	 * form: strval1\0strval2\0map1key1\0map1val1\0map2key1\0map2val1\0
	 * (and so on); str_lens[i], key_lens[i] and val_lens[i] determines
	 * value length
	 */
	char payload[STROBE_MAX_PAYLOAD];
};

struct strobelight_bpf_sample {
	uint64_t ktime;
	char comm[TASK_COMM_LEN];
	pid_t pid;
	int user_stack_id;
	int kernel_stack_id;
	int has_meta;
	struct strobemeta_payload metadata;
	/*
	 * makes it possible to pass (<real payload size> + 1) as data size to
	 * perf_submit() to avoid perf_submit's paranoia about passing zero as
	 * size, as it deduces that <real payload size> might be
	 * **theoretically** zero
	 */
	char dummy_safeguard;
};

struct {
	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
	__uint(max_entries, 32);
	__uint(key_size, sizeof(int));
	__uint(value_size, sizeof(int));
} samples SEC(".maps");

struct {
	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
	__uint(max_entries, 16);
	__uint(key_size, sizeof(uint32_t));
	__uint(value_size, sizeof(uint64_t) * PERF_MAX_STACK_DEPTH);
} stacks_0 SEC(".maps");

struct {
	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
	__uint(max_entries, 16);
	__uint(key_size, sizeof(uint32_t));
	__uint(value_size, sizeof(uint64_t) * PERF_MAX_STACK_DEPTH);
} stacks_1 SEC(".maps");

struct {
	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
	__uint(max_entries, 1);
	__type(key, uint32_t);
	__type(value, struct strobelight_bpf_sample);
} sample_heap SEC(".maps");

struct {
	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
	__uint(max_entries, STROBE_MAX_CFGS);
	__type(key, pid_t);
	__type(value, struct strobemeta_cfg);
} strobemeta_cfgs SEC(".maps");

/* Type for the dtv.  */
/* https://github.com/lattera/glibc/blob/master/nptl/sysdeps/x86_64/tls.h#L34 */
typedef union dtv {
	size_t counter;
	struct {
		void* val;
		bool is_static;
	} pointer;
} dtv_t;

/* Partial definition for tcbhead_t */
/* https://github.com/bminor/glibc/blob/master/sysdeps/x86_64/nptl/tls.h#L42 */
struct tcbhead {
	void* tcb;
	dtv_t* dtv;
};

/*
 * TLS module/offset information for shared library case.
 * For x86-64, this is mapped onto two entries in GOT.
 * For aarch64, this is pointed to by second GOT entry.
 */
struct tls_index {
	uint64_t module;
	uint64_t offset;
};

#ifdef SUBPROGS
__noinline
#else
__always_inline
#endif
static void *calc_location(struct strobe_value_loc *loc, void *tls_base)
{
	/*
	 * tls_mode value is:
	 * - -1 (TLS_NOT_SET), if no metavar is present;
	 * - 0 (TLS_LOCAL_EXEC), if metavar uses Local Executable mode of TLS
	 * (offset from fs:0 for x86-64 or tpidr_el0 for aarch64);
	 * - 1 (TLS_IMM_EXEC), if metavar uses Immediate Executable mode of TLS;
	 * - 2 (TLS_GENERAL_DYN), if metavar uses General Dynamic mode of TLS;
	 * This schema allows to use something like:
	 * (tls_mode + 1) * (tls_base + offset)
	 * to get NULL for "no metavar" location, or correct pointer for local
	 * executable mode without doing extra ifs.
	 */
	if (loc->tls_mode <= TLS_LOCAL_EXEC) {
		/* static executable is simple, we just have offset from
		 * tls_base */
		void *addr = tls_base + loc->offset;
		/* multiply by (tls_mode + 1) to get NULL, if we have no
		 * metavar in this slot */
		return (void *)((loc->tls_mode + 1) * (int64_t)addr);
	}
	/*
	 * Other modes are more complicated, we need to jump through few hoops.
	 *
	 * For immediate executable mode (currently supported only for aarch64):
	 *  - loc->offset is pointing to a GOT entry containing fixed offset
	 *  relative to tls_base;
	 *
	 * For general dynamic mode:
	 *  - loc->offset is pointing to a beginning of double GOT entries;
	 *  - (for aarch64 only) second entry points to tls_index_t struct;
	 *  - (for x86-64 only) two GOT entries are already tls_index_t;
	 *  - tls_index_t->module is used to find start of TLS section in
	 *  which variable resides;
	 *  - tls_index_t->offset provides offset within that TLS section,
	 *  pointing to value of variable.
	 */
	struct tls_index tls_index;
	dtv_t *dtv;
	void *tls_ptr;

	bpf_probe_read_user(&tls_index, sizeof(struct tls_index),
			    (void *)loc->offset);
	/* valid module index is always positive */
	if (tls_index.module > 0) {
		/* dtv = ((struct tcbhead *)tls_base)->dtv[tls_index.module] */
		bpf_probe_read_user(&dtv, sizeof(dtv),
				    &((struct tcbhead *)tls_base)->dtv);
		dtv += tls_index.module;
	} else {
		dtv = NULL;
	}
	bpf_probe_read_user(&tls_ptr, sizeof(void *), dtv);
	/* if pointer has (void *)-1 value, then TLS wasn't initialized yet */
	return tls_ptr && tls_ptr != (void *)-1
		? tls_ptr + tls_index.offset
		: NULL;
}

#ifdef SUBPROGS
__noinline
#else
__always_inline
#endif
static void read_int_var(struct strobemeta_cfg *cfg,
			 size_t idx, void *tls_base,
			 struct strobe_value_generic *value,
			 struct strobemeta_payload *data)
{
	void *location = calc_location(&cfg->int_locs[idx], tls_base);
	if (!location)
		return;

	bpf_probe_read_user(value, sizeof(struct strobe_value_generic), location);
	data->int_vals[idx] = value->val;
	if (value->header.len)
		data->int_vals_set_mask |= (1 << idx);
}

static __always_inline uint64_t read_str_var(struct strobemeta_cfg *cfg,
					     size_t idx, void *tls_base,
					     struct strobe_value_generic *value,
					     struct strobemeta_payload *data,
					     size_t off)
{
	void *location;
	uint64_t len;

	data->str_lens[idx] = 0;
	location = calc_location(&cfg->str_locs[idx], tls_base);
	if (!location)
		return 0;

	bpf_probe_read_user(value, sizeof(struct strobe_value_generic), location);
	len = bpf_probe_read_user_str(&data->payload[off], STROBE_MAX_STR_LEN, value->ptr);
	/*
	 * if bpf_probe_read_user_str returns error (<0), due to casting to
	 * unsinged int, it will become big number, so next check is
	 * sufficient to check for errors AND prove to BPF verifier, that
	 * bpf_probe_read_user_str won't return anything bigger than
	 * STROBE_MAX_STR_LEN
	 */
	if (len > STROBE_MAX_STR_LEN)
		return 0;

	data->str_lens[idx] = len;
	return off + len;
}

static __always_inline uint64_t read_map_var(struct strobemeta_cfg *cfg,
					     size_t idx, void *tls_base,
					     struct strobe_value_generic *value,
					     struct strobemeta_payload *data,
					     size_t off)
{
	struct strobe_map_descr* descr = &data->map_descrs[idx];
	struct strobe_map_raw map;
	void *location;
	uint64_t len;

	descr->tag_len = 0; /* presume no tag is set */
	descr->cnt = -1; /* presume no value is set */

	location = calc_location(&cfg->map_locs[idx], tls_base);
	if (!location)
		return off;

	bpf_probe_read_user(value, sizeof(struct strobe_value_generic), location);
	if (bpf_probe_read_user(&map, sizeof(struct strobe_map_raw), value->ptr))
		return off;

	descr->id = map.id;
	descr->cnt = map.cnt;
	if (cfg->req_meta_idx == idx) {
		data->req_id = map.id;
		data->req_meta_valid = 1;
	}

	len = bpf_probe_read_user_str(&data->payload[off], STROBE_MAX_STR_LEN, map.tag);
	if (len <= STROBE_MAX_STR_LEN) {
		descr->tag_len = len;
		off += len;
	}

#ifdef NO_UNROLL
#pragma clang loop unroll(disable)
#else
#pragma unroll
#endif
	for (int i = 0; i < STROBE_MAX_MAP_ENTRIES; ++i) {
		if (i >= map.cnt)
			break;

		descr->key_lens[i] = 0;
		len = bpf_probe_read_user_str(&data->payload[off], STROBE_MAX_STR_LEN,
					      map.entries[i].key);
		if (len <= STROBE_MAX_STR_LEN) {
			descr->key_lens[i] = len;
			off += len;
		}
		descr->val_lens[i] = 0;
		len = bpf_probe_read_user_str(&data->payload[off], STROBE_MAX_STR_LEN,
					      map.entries[i].val);
		if (len <= STROBE_MAX_STR_LEN) {
			descr->val_lens[i] = len;
			off += len;
		}
	}

	return off;
}

#ifdef USE_BPF_LOOP
enum read_type {
	READ_INT_VAR,
	READ_MAP_VAR,
	READ_STR_VAR,
};

struct read_var_ctx {
	struct strobemeta_payload *data;
	void *tls_base;
	struct strobemeta_cfg *cfg;
	size_t payload_off;
	/* value gets mutated */
	struct strobe_value_generic *value;
	enum read_type type;
};

static int read_var_callback(__u64 index, struct read_var_ctx *ctx)
{
	/* lose precision info for ctx->payload_off, verifier won't track
	 * double xor, barrier_var() is needed to force clang keep both xors.
	 */
	ctx->payload_off ^= index;
	barrier_var(ctx->payload_off);
	ctx->payload_off ^= index;
	switch (ctx->type) {
	case READ_INT_VAR:
		if (index >= STROBE_MAX_INTS)
			return 1;
		read_int_var(ctx->cfg, index, ctx->tls_base, ctx->value, ctx->data);
		break;
	case READ_MAP_VAR:
		if (index >= STROBE_MAX_MAPS)
			return 1;
		if (ctx->payload_off > sizeof(ctx->data->payload) - READ_MAP_VAR_PAYLOAD_CAP)
			return 1;
		ctx->payload_off = read_map_var(ctx->cfg, index, ctx->tls_base,
						ctx->value, ctx->data, ctx->payload_off);
		break;
	case READ_STR_VAR:
		if (index >= STROBE_MAX_STRS)
			return 1;
		if (ctx->payload_off > sizeof(ctx->data->payload) - STROBE_MAX_STR_LEN)
			return 1;
		ctx->payload_off = read_str_var(ctx->cfg, index, ctx->tls_base,
						ctx->value, ctx->data, ctx->payload_off);
		break;
	}
	return 0;
}
#endif /* USE_BPF_LOOP */

/*
 * read_strobe_meta returns NULL, if no metadata was read; otherwise returns
 * pointer to *right after* payload ends
 */
#ifdef SUBPROGS
__noinline
#else
__always_inline
#endif
static void *read_strobe_meta(struct task_struct *task,
			      struct strobemeta_payload *data)
{
	pid_t pid = bpf_get_current_pid_tgid() >> 32;
	struct strobe_value_generic value = {0};
	struct strobemeta_cfg *cfg;
	size_t payload_off;
	void *tls_base;

	cfg = bpf_map_lookup_elem(&strobemeta_cfgs, &pid);
	if (!cfg)
		return NULL;

	data->int_vals_set_mask = 0;
	data->req_meta_valid = 0;
	payload_off = 0;
	/*
	 * we don't have struct task_struct definition, it should be:
	 * tls_base = (void *)task->thread.fsbase;
	 */
	tls_base = (void *)task;

#ifdef USE_BPF_LOOP
	struct read_var_ctx ctx = {
		.cfg = cfg,
		.tls_base = tls_base,
		.value = &value,
		.data = data,
		.payload_off = 0,
	};
	int err;

	ctx.type = READ_INT_VAR;
	err = bpf_loop(STROBE_MAX_INTS, read_var_callback, &ctx, 0);
	if (err != STROBE_MAX_INTS)
		return NULL;

	ctx.type = READ_STR_VAR;
	err = bpf_loop(STROBE_MAX_STRS, read_var_callback, &ctx, 0);
	if (err != STROBE_MAX_STRS)
		return NULL;

	ctx.type = READ_MAP_VAR;
	err = bpf_loop(STROBE_MAX_MAPS, read_var_callback, &ctx, 0);
	if (err != STROBE_MAX_MAPS)
		return NULL;

	payload_off = ctx.payload_off;
	/* this should not really happen, here only to satisfy verifer */
	if (payload_off > sizeof(data->payload))
		payload_off = sizeof(data->payload);
#else
#ifdef NO_UNROLL
#pragma clang loop unroll(disable)
#else
#pragma unroll
#endif /* NO_UNROLL */
	for (int i = 0; i < STROBE_MAX_INTS; ++i) {
		read_int_var(cfg, i, tls_base, &value, data);
	}
#ifdef NO_UNROLL
#pragma clang loop unroll(disable)
#else
#pragma unroll
#endif /* NO_UNROLL */
	for (int i = 0; i < STROBE_MAX_STRS; ++i) {
		payload_off = read_str_var(cfg, i, tls_base, &value, data, payload_off);
	}
#ifdef NO_UNROLL
#pragma clang loop unroll(disable)
#else
#pragma unroll
#endif /* NO_UNROLL */
	for (int i = 0; i < STROBE_MAX_MAPS; ++i) {
		payload_off = read_map_var(cfg, i, tls_base, &value, data, payload_off);
	}
#endif /* USE_BPF_LOOP */

	/*
	 * return pointer right after end of payload, so it's possible to
	 * calculate exact amount of useful data that needs to be sent
	 */
	return &data->payload[payload_off];
}

SEC("raw_tracepoint/kfree_skb")
int on_event(struct pt_regs *ctx) {
	pid_t pid =  bpf_get_current_pid_tgid() >> 32;
	struct strobelight_bpf_sample* sample;
	struct task_struct *task;
	uint32_t zero = 0;
	uint64_t ktime_ns;
	void *sample_end;

	sample = bpf_map_lookup_elem(&sample_heap, &zero);
	if (!sample)
		return 0; /* this will never happen */

	sample->pid = pid;
	bpf_get_current_comm(&sample->comm, TASK_COMM_LEN);
	ktime_ns = bpf_ktime_get_ns();
	sample->ktime = ktime_ns;

	task = (struct task_struct *)bpf_get_current_task();
	sample_end = read_strobe_meta(task, &sample->metadata);
	sample->has_meta = sample_end != NULL;
	sample_end = sample_end ? : &sample->metadata;

	if ((ktime_ns >> STACK_TABLE_EPOCH_SHIFT) & 1) {
		sample->kernel_stack_id = bpf_get_stackid(ctx, &stacks_1, 0);
		sample->user_stack_id = bpf_get_stackid(ctx, &stacks_1, BPF_F_USER_STACK);
	} else {
		sample->kernel_stack_id = bpf_get_stackid(ctx, &stacks_0, 0);
		sample->user_stack_id = bpf_get_stackid(ctx, &stacks_0, BPF_F_USER_STACK);
	}

	uint64_t sample_size = sample_end - (void *)sample;
	/* should always be true */
	if (sample_size < sizeof(struct strobelight_bpf_sample))
		bpf_perf_event_output(ctx, &samples, 0, sample, 1 + sample_size);
	return 0;
}

char _license[] SEC("license") = "GPL";