tools/perf/util/auxtrace.c

/*
 * auxtrace.c: AUX area trace support
 * Copyright (c) 2013-2015, Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 */

#include <sys/types.h>
#include <sys/mman.h>
#include <stdbool.h>

#include <linux/kernel.h>
#include <linux/perf_event.h>
#include <linux/types.h>
#include <linux/bitops.h>
#include <linux/log2.h>
#include <linux/string.h>

#include <sys/param.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <errno.h>
#include <linux/list.h>

#include "../perf.h"
#include "util.h"
#include "evlist.h"
#include "cpumap.h"
#include "thread_map.h"
#include "asm/bug.h"
#include "auxtrace.h"

#include "event.h"
#include "session.h"
#include "debug.h"
#include "parse-options.h"

int auxtrace_mmap__mmap(struct auxtrace_mmap *mm,
			struct auxtrace_mmap_params *mp,
			void *userpg, int fd)
{
	struct perf_event_mmap_page *pc = userpg;

#if BITS_PER_LONG != 64 && !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT)
	pr_err("Cannot use AUX area tracing mmaps\n");
	return -1;
#endif

	WARN_ONCE(mm->base, "Uninitialized auxtrace_mmap\n");

	mm->userpg = userpg;
	mm->mask = mp->mask;
	mm->len = mp->len;
	mm->prev = 0;
	mm->idx = mp->idx;
	mm->tid = mp->tid;
	mm->cpu = mp->cpu;

	if (!mp->len) {
		mm->base = NULL;
		return 0;
	}

	pc->aux_offset = mp->offset;
	pc->aux_size = mp->len;

	mm->base = mmap(NULL, mp->len, mp->prot, MAP_SHARED, fd, mp->offset);
	if (mm->base == MAP_FAILED) {
		pr_debug2("failed to mmap AUX area\n");
		mm->base = NULL;
		return -1;
	}

	return 0;
}

void auxtrace_mmap__munmap(struct auxtrace_mmap *mm)
{
	if (mm->base) {
		munmap(mm->base, mm->len);
		mm->base = NULL;
	}
}

void auxtrace_mmap_params__init(struct auxtrace_mmap_params *mp,
				off_t auxtrace_offset,
				unsigned int auxtrace_pages,
				bool auxtrace_overwrite)
{
	if (auxtrace_pages) {
		mp->offset = auxtrace_offset;
		mp->len = auxtrace_pages * (size_t)page_size;
		mp->mask = is_power_of_2(mp->len) ? mp->len - 1 : 0;
		mp->prot = PROT_READ | (auxtrace_overwrite ? 0 : PROT_WRITE);
		pr_debug2("AUX area mmap length %zu\n", mp->len);
	} else {
		mp->len = 0;
	}
}

void auxtrace_mmap_params__set_idx(struct auxtrace_mmap_params *mp,
				   struct perf_evlist *evlist, int idx,
				   bool per_cpu)
{
	mp->idx = idx;

	if (per_cpu) {
		mp->cpu = evlist->cpus->map[idx];
		if (evlist->threads)
			mp->tid = evlist->threads->map[0];
		else
			mp->tid = -1;
	} else {
		mp->cpu = -1;
		mp->tid = evlist->threads->map[idx];
	}
}

#define AUXTRACE_INIT_NR_QUEUES	32

static struct auxtrace_queue *auxtrace_alloc_queue_array(unsigned int nr_queues)
{
	struct auxtrace_queue *queue_array;
	unsigned int max_nr_queues, i;

	max_nr_queues = UINT_MAX / sizeof(struct auxtrace_queue);
	if (nr_queues > max_nr_queues)
		return NULL;

	queue_array = calloc(nr_queues, sizeof(struct auxtrace_queue));
	if (!queue_array)
		return NULL;

	for (i = 0; i < nr_queues; i++) {
		INIT_LIST_HEAD(&queue_array[i].head);
		queue_array[i].priv = NULL;
	}

	return queue_array;
}

int auxtrace_queues__init(struct auxtrace_queues *queues)
{
	queues->nr_queues = AUXTRACE_INIT_NR_QUEUES;
	queues->queue_array = auxtrace_alloc_queue_array(queues->nr_queues);
	if (!queues->queue_array)
		return -ENOMEM;
	return 0;
}

static int auxtrace_queues__grow(struct auxtrace_queues *queues,
				 unsigned int new_nr_queues)
{
	unsigned int nr_queues = queues->nr_queues;
	struct auxtrace_queue *queue_array;
	unsigned int i;

	if (!nr_queues)
		nr_queues = AUXTRACE_INIT_NR_QUEUES;

	while (nr_queues && nr_queues < new_nr_queues)
		nr_queues <<= 1;

	if (nr_queues < queues->nr_queues || nr_queues < new_nr_queues)
		return -EINVAL;

	queue_array = auxtrace_alloc_queue_array(nr_queues);
	if (!queue_array)
		return -ENOMEM;

	for (i = 0; i < queues->nr_queues; i++) {
		list_splice_tail(&queues->queue_array[i].head,
				 &queue_array[i].head);
		queue_array[i].priv = queues->queue_array[i].priv;
	}

	queues->nr_queues = nr_queues;
	queues->queue_array = queue_array;

	return 0;
}

static void *auxtrace_copy_data(u64 size, struct perf_session *session)
{
	int fd = perf_data_file__fd(session->file);
	void *p;
	ssize_t ret;

	if (size > SSIZE_MAX)
		return NULL;

	p = malloc(size);
	if (!p)
		return NULL;

	ret = readn(fd, p, size);
	if (ret != (ssize_t)size) {
		free(p);
		return NULL;
	}

	return p;
}

static int auxtrace_queues__add_buffer(struct auxtrace_queues *queues,
				       unsigned int idx,
				       struct auxtrace_buffer *buffer)
{
	struct auxtrace_queue *queue;
	int err;

	if (idx >= queues->nr_queues) {
		err = auxtrace_queues__grow(queues, idx + 1);
		if (err)
			return err;
	}

	queue = &queues->queue_array[idx];

	if (!queue->set) {
		queue->set = true;
		queue->tid = buffer->tid;
		queue->cpu = buffer->cpu;
	} else if (buffer->cpu != queue->cpu || buffer->tid != queue->tid) {
		pr_err("auxtrace queue conflict: cpu %d, tid %d vs cpu %d, tid %d\n",
		       queue->cpu, queue->tid, buffer->cpu, buffer->tid);
		return -EINVAL;
	}

	buffer->buffer_nr = queues->next_buffer_nr++;

	list_add_tail(&buffer->list, &queue->head);

	queues->new_data = true;
	queues->populated = true;

	return 0;
}

/* Limit buffers to 32MiB on 32-bit */
#define BUFFER_LIMIT_FOR_32_BIT (32 * 1024 * 1024)

static int auxtrace_queues__split_buffer(struct auxtrace_queues *queues,
					 unsigned int idx,
					 struct auxtrace_buffer *buffer)
{
	u64 sz = buffer->size;
	bool consecutive = false;
	struct auxtrace_buffer *b;
	int err;

	while (sz > BUFFER_LIMIT_FOR_32_BIT) {
		b = memdup(buffer, sizeof(struct auxtrace_buffer));
		if (!b)
			return -ENOMEM;
		b->size = BUFFER_LIMIT_FOR_32_BIT;
		b->consecutive = consecutive;
		err = auxtrace_queues__add_buffer(queues, idx, b);
		if (err) {
			auxtrace_buffer__free(b);
			return err;
		}
		buffer->data_offset += BUFFER_LIMIT_FOR_32_BIT;
		sz -= BUFFER_LIMIT_FOR_32_BIT;
		consecutive = true;
	}

	buffer->size = sz;
	buffer->consecutive = consecutive;

	return 0;
}

static int auxtrace_queues__add_event_buffer(struct auxtrace_queues *queues,
					     struct perf_session *session,
					     unsigned int idx,
					     struct auxtrace_buffer *buffer)
{
	if (session->one_mmap) {
		buffer->data = buffer->data_offset - session->one_mmap_offset +
			       session->one_mmap_addr;
	} else if (perf_data_file__is_pipe(session->file)) {
		buffer->data = auxtrace_copy_data(buffer->size, session);
		if (!buffer->data)
			return -ENOMEM;
		buffer->data_needs_freeing = true;
	} else if (BITS_PER_LONG == 32 &&
		   buffer->size > BUFFER_LIMIT_FOR_32_BIT) {
		int err;

		err = auxtrace_queues__split_buffer(queues, idx, buffer);
		if (err)
			return err;
	}

	return auxtrace_queues__add_buffer(queues, idx, buffer);
}

int auxtrace_queues__add_event(struct auxtrace_queues *queues,
			       struct perf_session *session,
			       union perf_event *event, off_t data_offset,
			       struct auxtrace_buffer **buffer_ptr)
{
	struct auxtrace_buffer *buffer;
	unsigned int idx;
	int err;

	buffer = zalloc(sizeof(struct auxtrace_buffer));
	if (!buffer)
		return -ENOMEM;

	buffer->pid = -1;
	buffer->tid = event->auxtrace.tid;
	buffer->cpu = event->auxtrace.cpu;
	buffer->data_offset = data_offset;
	buffer->offset = event->auxtrace.offset;
	buffer->reference = event->auxtrace.reference;
	buffer->size = event->auxtrace.size;
	idx = event->auxtrace.idx;

	err = auxtrace_queues__add_event_buffer(queues, session, idx, buffer);
	if (err)
		goto out_err;

	if (buffer_ptr)
		*buffer_ptr = buffer;

	return 0;

out_err:
	auxtrace_buffer__free(buffer);
	return err;
}

void auxtrace_queues__free(struct auxtrace_queues *queues)
{
	unsigned int i;

	for (i = 0; i < queues->nr_queues; i++) {
		while (!list_empty(&queues->queue_array[i].head)) {
			struct auxtrace_buffer *buffer;

			buffer = list_entry(queues->queue_array[i].head.next,
					    struct auxtrace_buffer, list);
			list_del(&buffer->list);
			auxtrace_buffer__free(buffer);
		}
	}

	zfree(&queues->queue_array);
	queues->nr_queues = 0;
}

static void auxtrace_heapify(struct auxtrace_heap_item *heap_array,
			     unsigned int pos, unsigned int queue_nr,
			     u64 ordinal)
{
	unsigned int parent;

	while (pos) {
		parent = (pos - 1) >> 1;
		if (heap_array[parent].ordinal <= ordinal)
			break;
		heap_array[pos] = heap_array[parent];
		pos = parent;
	}
	heap_array[pos].queue_nr = queue_nr;
	heap_array[pos].ordinal = ordinal;
}

int auxtrace_heap__add(struct auxtrace_heap *heap, unsigned int queue_nr,
		       u64 ordinal)
{
	struct auxtrace_heap_item *heap_array;

	if (queue_nr >= heap->heap_sz) {
		unsigned int heap_sz = AUXTRACE_INIT_NR_QUEUES;

		while (heap_sz <= queue_nr)
			heap_sz <<= 1;
		heap_array = realloc(heap->heap_array,
				     heap_sz * sizeof(struct auxtrace_heap_item));
		if (!heap_array)
			return -ENOMEM;
		heap->heap_array = heap_array;
		heap->heap_sz = heap_sz;
	}

	auxtrace_heapify(heap->heap_array, heap->heap_cnt++, queue_nr, ordinal);

	return 0;
}

void auxtrace_heap__free(struct auxtrace_heap *heap)
{
	zfree(&heap->heap_array);
	heap->heap_cnt = 0;
	heap->heap_sz = 0;
}

void auxtrace_heap__pop(struct auxtrace_heap *heap)
{
	unsigned int pos, last, heap_cnt = heap->heap_cnt;
	struct auxtrace_heap_item *heap_array;

	if (!heap_cnt)
		return;

	heap->heap_cnt -= 1;

	heap_array = heap->heap_array;

	pos = 0;
	while (1) {
		unsigned int left, right;

		left = (pos << 1) + 1;
		if (left >= heap_cnt)
			break;
		right = left + 1;
		if (right >= heap_cnt) {
			heap_array[pos] = heap_array[left];
			return;
		}
		if (heap_array[left].ordinal < heap_array[right].ordinal) {
			heap_array[pos] = heap_array[left];
			pos = left;
		} else {
			heap_array[pos] = heap_array[right];
			pos = right;
		}
	}

	last = heap_cnt - 1;
	auxtrace_heapify(heap_array, pos, heap_array[last].queue_nr,
			 heap_array[last].ordinal);
}

size_t auxtrace_record__info_priv_size(struct auxtrace_record *itr)
{
	if (itr)
		return itr->info_priv_size(itr);
	return 0;
}

static int auxtrace_not_supported(void)
{
	pr_err("AUX area tracing is not supported on this architecture\n");
	return -EINVAL;
}

int auxtrace_record__info_fill(struct auxtrace_record *itr,
			       struct perf_session *session,
			       struct auxtrace_info_event *auxtrace_info,
			       size_t priv_size)
{
	if (itr)
		return itr->info_fill(itr, session, auxtrace_info, priv_size);
	return auxtrace_not_supported();
}

void auxtrace_record__free(struct auxtrace_record *itr)
{
	if (itr)
		itr->free(itr);
}

int auxtrace_record__options(struct auxtrace_record *itr,
			     struct perf_evlist *evlist,
			     struct record_opts *opts)
{
	if (itr)
		return itr->recording_options(itr, evlist, opts);
	return 0;
}

u64 auxtrace_record__reference(struct auxtrace_record *itr)
{
	if (itr)
		return itr->reference(itr);
	return 0;
}

struct auxtrace_record *__weak
auxtrace_record__init(struct perf_evlist *evlist __maybe_unused, int *err)
{
	*err = 0;
	return NULL;
}

struct auxtrace_buffer *auxtrace_buffer__next(struct auxtrace_queue *queue,
					      struct auxtrace_buffer *buffer)
{
	if (buffer) {
		if (list_is_last(&buffer->list, &queue->head))
			return NULL;
		return list_entry(buffer->list.next, struct auxtrace_buffer,
				  list);
	} else {
		if (list_empty(&queue->head))
			return NULL;
		return list_entry(queue->head.next, struct auxtrace_buffer,
				  list);
	}
}

void *auxtrace_buffer__get_data(struct auxtrace_buffer *buffer, int fd)
{
	size_t adj = buffer->data_offset & (page_size - 1);
	size_t size = buffer->size + adj;
	off_t file_offset = buffer->data_offset - adj;
	void *addr;

	if (buffer->data)
		return buffer->data;

	addr = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, file_offset);
	if (addr == MAP_FAILED)
		return NULL;

	buffer->mmap_addr = addr;
	buffer->mmap_size = size;

	buffer->data = addr + adj;

	return buffer->data;
}

void auxtrace_buffer__put_data(struct auxtrace_buffer *buffer)
{
	if (!buffer->data || !buffer->mmap_addr)
		return;
	munmap(buffer->mmap_addr, buffer->mmap_size);
	buffer->mmap_addr = NULL;
	buffer->mmap_size = 0;
	buffer->data = NULL;
	buffer->use_data = NULL;
}

void auxtrace_buffer__drop_data(struct auxtrace_buffer *buffer)
{
	auxtrace_buffer__put_data(buffer);
	if (buffer->data_needs_freeing) {
		buffer->data_needs_freeing = false;
		zfree(&buffer->data);
		buffer->use_data = NULL;
		buffer->size = 0;
	}
}

void auxtrace_buffer__free(struct auxtrace_buffer *buffer)
{
	auxtrace_buffer__drop_data(buffer);
	free(buffer);
}

void auxtrace_synth_error(struct auxtrace_error_event *auxtrace_error, int type,
			  int code, int cpu, pid_t pid, pid_t tid, u64 ip,
			  const char *msg)
{
	size_t size;

	memset(auxtrace_error, 0, sizeof(struct auxtrace_error_event));

	auxtrace_error->header.type = PERF_RECORD_AUXTRACE_ERROR;
	auxtrace_error->type = type;
	auxtrace_error->code = code;
	auxtrace_error->cpu = cpu;
	auxtrace_error->pid = pid;
	auxtrace_error->tid = tid;
	auxtrace_error->ip = ip;
	strlcpy(auxtrace_error->msg, msg, MAX_AUXTRACE_ERROR_MSG);

	size = (void *)auxtrace_error->msg - (void *)auxtrace_error +
	       strlen(auxtrace_error->msg) + 1;
	auxtrace_error->header.size = PERF_ALIGN(size, sizeof(u64));
}

int perf_event__synthesize_auxtrace_info(struct auxtrace_record *itr,
					 struct perf_tool *tool,
					 struct perf_session *session,
					 perf_event__handler_t process)
{
	union perf_event *ev;
	size_t priv_size;
	int err;

	pr_debug2("Synthesizing auxtrace information\n");
	priv_size = auxtrace_record__info_priv_size(itr);
	ev = zalloc(sizeof(struct auxtrace_info_event) + priv_size);
	if (!ev)
		return -ENOMEM;

	ev->auxtrace_info.header.type = PERF_RECORD_AUXTRACE_INFO;
	ev->auxtrace_info.header.size = sizeof(struct auxtrace_info_event) +
					priv_size;
	err = auxtrace_record__info_fill(itr, session, &ev->auxtrace_info,
					 priv_size);
	if (err)
		goto out_free;

	err = process(tool, ev, NULL, NULL);
out_free:
	free(ev);
	return err;
}

#define PERF_ITRACE_DEFAULT_PERIOD_TYPE		PERF_ITRACE_PERIOD_NANOSECS
#define PERF_ITRACE_DEFAULT_PERIOD		100000
#define PERF_ITRACE_DEFAULT_CALLCHAIN_SZ	16
#define PERF_ITRACE_MAX_CALLCHAIN_SZ		1024

void itrace_synth_opts__set_default(struct itrace_synth_opts *synth_opts)
{
	synth_opts->instructions = true;
	synth_opts->branches = true;
	synth_opts->errors = true;
	synth_opts->period_type = PERF_ITRACE_DEFAULT_PERIOD_TYPE;
	synth_opts->period = PERF_ITRACE_DEFAULT_PERIOD;
	synth_opts->callchain_sz = PERF_ITRACE_DEFAULT_CALLCHAIN_SZ;
}

/*
 * Please check tools/perf/Documentation/perf-script.txt for information
 * about the options parsed here, which is introduced after this cset,
 * when support in 'perf script' for these options is introduced.
 */
int itrace_parse_synth_opts(const struct option *opt, const char *str,
			    int unset)
{
	struct itrace_synth_opts *synth_opts = opt->value;
	const char *p;
	char *endptr;

	synth_opts->set = true;

	if (unset) {
		synth_opts->dont_decode = true;
		return 0;
	}

	if (!str) {
		itrace_synth_opts__set_default(synth_opts);
		return 0;
	}

	for (p = str; *p;) {
		switch (*p++) {
		case 'i':
			synth_opts->instructions = true;
			while (*p == ' ' || *p == ',')
				p += 1;
			if (isdigit(*p)) {
				synth_opts->period = strtoull(p, &endptr, 10);
				p = endptr;
				while (*p == ' ' || *p == ',')
					p += 1;
				switch (*p++) {
				case 'i':
					synth_opts->period_type =
						PERF_ITRACE_PERIOD_INSTRUCTIONS;
					break;
				case 't':
					synth_opts->period_type =
						PERF_ITRACE_PERIOD_TICKS;
					break;
				case 'm':
					synth_opts->period *= 1000;
					/* Fall through */
				case 'u':
					synth_opts->period *= 1000;
					/* Fall through */
				case 'n':
					if (*p++ != 's')
						goto out_err;
					synth_opts->period_type =
						PERF_ITRACE_PERIOD_NANOSECS;
					break;
				case '\0':
					goto out;
				default:
					goto out_err;
				}
			}
			break;
		case 'b':
			synth_opts->branches = true;
			break;
		case 'e':
			synth_opts->errors = true;
			break;
		case 'd':
			synth_opts->log = true;
			break;
		case 'c':
			synth_opts->branches = true;
			synth_opts->calls = true;
			break;
		case 'r':
			synth_opts->branches = true;
			synth_opts->returns = true;
			break;
		case 'g':
			synth_opts->instructions = true;
			synth_opts->callchain = true;
			synth_opts->callchain_sz =
					PERF_ITRACE_DEFAULT_CALLCHAIN_SZ;
			while (*p == ' ' || *p == ',')
				p += 1;
			if (isdigit(*p)) {
				unsigned int val;

				val = strtoul(p, &endptr, 10);
				p = endptr;
				if (!val || val > PERF_ITRACE_MAX_CALLCHAIN_SZ)
					goto out_err;
				synth_opts->callchain_sz = val;
			}
			break;
		case ' ':
		case ',':
			break;
		default:
			goto out_err;
		}
	}
out:
	if (synth_opts->instructions) {
		if (!synth_opts->period_type)
			synth_opts->period_type =
					PERF_ITRACE_DEFAULT_PERIOD_TYPE;
		if (!synth_opts->period)
			synth_opts->period = PERF_ITRACE_DEFAULT_PERIOD;
	}

	return 0;

out_err:
	pr_err("Bad Instruction Tracing options '%s'\n", str);
	return -EINVAL;
}

static const char * const auxtrace_error_type_name[] = {
	[PERF_AUXTRACE_ERROR_ITRACE] = "instruction trace",
};

static const char *auxtrace_error_name(int type)
{
	const char *error_type_name = NULL;

	if (type < PERF_AUXTRACE_ERROR_MAX)
		error_type_name = auxtrace_error_type_name[type];
	if (!error_type_name)
		error_type_name = "unknown AUX";
	return error_type_name;
}

size_t perf_event__fprintf_auxtrace_error(union perf_event *event, FILE *fp)
{
	struct auxtrace_error_event *e = &event->auxtrace_error;
	int ret;

	ret = fprintf(fp, " %s error type %u",
		      auxtrace_error_name(e->type), e->type);
	ret += fprintf(fp, " cpu %d pid %d tid %d ip %#"PRIx64" code %u: %s\n",
		       e->cpu, e->pid, e->tid, e->ip, e->code, e->msg);
	return ret;
}

void perf_session__auxtrace_error_inc(struct perf_session *session,
				      union perf_event *event)
{
	struct auxtrace_error_event *e = &event->auxtrace_error;

	if (e->type < PERF_AUXTRACE_ERROR_MAX)
		session->evlist->stats.nr_auxtrace_errors[e->type] += 1;
}

void events_stats__auxtrace_error_warn(const struct events_stats *stats)
{
	int i;

	for (i = 0; i < PERF_AUXTRACE_ERROR_MAX; i++) {
		if (!stats->nr_auxtrace_errors[i])
			continue;
		ui__warning("%u %s errors\n",
			    stats->nr_auxtrace_errors[i],
			    auxtrace_error_name(i));
	}
}

int perf_event__process_auxtrace_error(struct perf_tool *tool __maybe_unused,
				       union perf_event *event,
				       struct perf_session *session __maybe_unused)
{
	perf_event__fprintf_auxtrace_error(event, stdout);
	return 0;
}

int auxtrace_mmap__read(struct auxtrace_mmap *mm, struct auxtrace_record *itr,
			struct perf_tool *tool, process_auxtrace_t fn)
{
	u64 head = auxtrace_mmap__read_head(mm);
	u64 old = mm->prev, offset, ref;
	unsigned char *data = mm->base;
	size_t size, head_off, old_off, len1, len2, padding;
	union perf_event ev;
	void *data1, *data2;

	if (old == head)
		return 0;

	pr_debug3("auxtrace idx %d old %#"PRIx64" head %#"PRIx64" diff %#"PRIx64"\n",
		  mm->idx, old, head, head - old);

	if (mm->mask) {
		head_off = head & mm->mask;
		old_off = old & mm->mask;
	} else {
		head_off = head % mm->len;
		old_off = old % mm->len;
	}

	if (head_off > old_off)
		size = head_off - old_off;
	else
		size = mm->len - (old_off - head_off);

	ref = auxtrace_record__reference(itr);

	if (head > old || size <= head || mm->mask) {
		offset = head - size;
	} else {
		/*
		 * When the buffer size is not a power of 2, 'head' wraps at the
		 * highest multiple of the buffer size, so we have to subtract
		 * the remainder here.
		 */
		u64 rem = (0ULL - mm->len) % mm->len;

		offset = head - size - rem;
	}

	if (size > head_off) {
		len1 = size - head_off;
		data1 = &data[mm->len - len1];
		len2 = head_off;
		data2 = &data[0];
	} else {
		len1 = size;
		data1 = &data[head_off - len1];
		len2 = 0;
		data2 = NULL;
	}

	/* padding must be written by fn() e.g. record__process_auxtrace() */
	padding = size & 7;
	if (padding)
		padding = 8 - padding;

	memset(&ev, 0, sizeof(ev));
	ev.auxtrace.header.type = PERF_RECORD_AUXTRACE;
	ev.auxtrace.header.size = sizeof(ev.auxtrace);
	ev.auxtrace.size = size + padding;
	ev.auxtrace.offset = offset;
	ev.auxtrace.reference = ref;
	ev.auxtrace.idx = mm->idx;
	ev.auxtrace.tid = mm->tid;
	ev.auxtrace.cpu = mm->cpu;

	if (fn(tool, &ev, data1, len1, data2, len2))
		return -1;

	mm->prev = head;

	auxtrace_mmap__write_tail(mm, head);
	if (itr->read_finish) {
		int err;

		err = itr->read_finish(itr, mm->idx);
		if (err < 0)
			return err;
	}

	return 1;
}