perf tools: Add Intel PT support

Add support for Intel Processor Trace.

Intel PT support fits within the new auxtrace infrastructure.  Recording
is supporting by identifying the Intel PT PMU, parsing options and
setting up events.

Decoding is supported by queuing up trace data by cpu or thread and then
decoding synchronously delivering synthesized event samples into the
session processing for tools to consume.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1437150840-31811-7-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 754 insertions, 0 deletions

diff --git a/tools/perf/arch/x86/util/Build b/tools/perf/arch/x86/util/Build
index cfbccc4e3187..139608878888 100644
--- a/tools/perf/arch/x86/util/Build
+++ b/tools/perf/arch/x86/util/Build
@@ -6,3 +6,5 @@ libperf-$(CONFIG_DWARF) += dwarf-regs.o
 
 libperf-$(CONFIG_LIBUNWIND)          += unwind-libunwind.o
 libperf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
+
+libperf-$(CONFIG_AUXTRACE) += intel-pt.o
diff --git a/tools/perf/arch/x86/util/intel-pt.c b/tools/perf/arch/x86/util/intel-pt.c
new file mode 100644
index 000000000000..da7d2c15e611
--- /dev/null
+++ b/tools/perf/arch/x86/util/intel-pt.c
@@ -0,0 +1,752 @@
+/*
+ * intel_pt.c: Intel Processor 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 <stdbool.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/bitops.h>
+#include <linux/log2.h>
+
+#include "../../perf.h"
+#include "../../util/session.h"
+#include "../../util/event.h"
+#include "../../util/evlist.h"
+#include "../../util/evsel.h"
+#include "../../util/cpumap.h"
+#include "../../util/parse-options.h"
+#include "../../util/parse-events.h"
+#include "../../util/pmu.h"
+#include "../../util/debug.h"
+#include "../../util/auxtrace.h"
+#include "../../util/tsc.h"
+#include "../../util/intel-pt.h"
+
+#define KiB(x) ((x) * 1024)
+#define MiB(x) ((x) * 1024 * 1024)
+#define KiB_MASK(x) (KiB(x) - 1)
+#define MiB_MASK(x) (MiB(x) - 1)
+
+#define INTEL_PT_DEFAULT_SAMPLE_SIZE	KiB(4)
+
+#define INTEL_PT_MAX_SAMPLE_SIZE	KiB(60)
+
+#define INTEL_PT_PSB_PERIOD_NEAR	256
+
+struct intel_pt_snapshot_ref {
+	void *ref_buf;
+	size_t ref_offset;
+	bool wrapped;
+};
+
+struct intel_pt_recording {
+	struct auxtrace_record		itr;
+	struct perf_pmu			*intel_pt_pmu;
+	int				have_sched_switch;
+	struct perf_evlist		*evlist;
+	bool				snapshot_mode;
+	bool				snapshot_init_done;
+	size_t				snapshot_size;
+	size_t				snapshot_ref_buf_size;
+	int				snapshot_ref_cnt;
+	struct intel_pt_snapshot_ref	*snapshot_refs;
+};
+
+static int intel_pt_parse_terms_with_default(struct list_head *formats,
+					     const char *str,
+					     u64 *config)
+{
+	struct list_head *terms;
+	struct perf_event_attr attr = { .size = 0, };
+	int err;
+
+	terms = malloc(sizeof(struct list_head));
+	if (!terms)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(terms);
+
+	err = parse_events_terms(terms, str);
+	if (err)
+		goto out_free;
+
+	attr.config = *config;
+	err = perf_pmu__config_terms(formats, &attr, terms, true, NULL);
+	if (err)
+		goto out_free;
+
+	*config = attr.config;
+out_free:
+	parse_events__free_terms(terms);
+	return err;
+}
+
+static int intel_pt_parse_terms(struct list_head *formats, const char *str,
+				u64 *config)
+{
+	*config = 0;
+	return intel_pt_parse_terms_with_default(formats, str, config);
+}
+
+static size_t intel_pt_psb_period(struct perf_pmu *intel_pt_pmu __maybe_unused,
+				  struct perf_evlist *evlist __maybe_unused)
+{
+	return 256;
+}
+
+static u64 intel_pt_default_config(struct perf_pmu *intel_pt_pmu)
+{
+	u64 config;
+
+	intel_pt_parse_terms(&intel_pt_pmu->format, "tsc", &config);
+	return config;
+}
+
+static int intel_pt_parse_snapshot_options(struct auxtrace_record *itr,
+					   struct record_opts *opts,
+					   const char *str)
+{
+	struct intel_pt_recording *ptr =
+			container_of(itr, struct intel_pt_recording, itr);
+	unsigned long long snapshot_size = 0;
+	char *endptr;
+
+	if (str) {
+		snapshot_size = strtoull(str, &endptr, 0);
+		if (*endptr || snapshot_size > SIZE_MAX)
+			return -1;
+	}
+
+	opts->auxtrace_snapshot_mode = true;
+	opts->auxtrace_snapshot_size = snapshot_size;
+
+	ptr->snapshot_size = snapshot_size;
+
+	return 0;
+}
+
+struct perf_event_attr *
+intel_pt_pmu_default_config(struct perf_pmu *intel_pt_pmu)
+{
+	struct perf_event_attr *attr;
+
+	attr = zalloc(sizeof(struct perf_event_attr));
+	if (!attr)
+		return NULL;
+
+	attr->config = intel_pt_default_config(intel_pt_pmu);
+
+	intel_pt_pmu->selectable = true;
+
+	return attr;
+}
+
+static size_t intel_pt_info_priv_size(struct auxtrace_record *itr __maybe_unused)
+{
+	return INTEL_PT_AUXTRACE_PRIV_SIZE;
+}
+
+static int intel_pt_info_fill(struct auxtrace_record *itr,
+			      struct perf_session *session,
+			      struct auxtrace_info_event *auxtrace_info,
+			      size_t priv_size)
+{
+	struct intel_pt_recording *ptr =
+			container_of(itr, struct intel_pt_recording, itr);
+	struct perf_pmu *intel_pt_pmu = ptr->intel_pt_pmu;
+	struct perf_event_mmap_page *pc;
+	struct perf_tsc_conversion tc = { .time_mult = 0, };
+	bool cap_user_time_zero = false, per_cpu_mmaps;
+	u64 tsc_bit, noretcomp_bit;
+	int err;
+
+	if (priv_size != INTEL_PT_AUXTRACE_PRIV_SIZE)
+		return -EINVAL;
+
+	intel_pt_parse_terms(&intel_pt_pmu->format, "tsc", &tsc_bit);
+	intel_pt_parse_terms(&intel_pt_pmu->format, "noretcomp",
+			     &noretcomp_bit);
+
+	if (!session->evlist->nr_mmaps)
+		return -EINVAL;
+
+	pc = session->evlist->mmap[0].base;
+	if (pc) {
+		err = perf_read_tsc_conversion(pc, &tc);
+		if (err) {
+			if (err != -EOPNOTSUPP)
+				return err;
+		} else {
+			cap_user_time_zero = tc.time_mult != 0;
+		}
+		if (!cap_user_time_zero)
+			ui__warning("Intel Processor Trace: TSC not available\n");
+	}
+
+	per_cpu_mmaps = !cpu_map__empty(session->evlist->cpus);
+
+	auxtrace_info->type = PERF_AUXTRACE_INTEL_PT;
+	auxtrace_info->priv[INTEL_PT_PMU_TYPE] = intel_pt_pmu->type;
+	auxtrace_info->priv[INTEL_PT_TIME_SHIFT] = tc.time_shift;
+	auxtrace_info->priv[INTEL_PT_TIME_MULT] = tc.time_mult;
+	auxtrace_info->priv[INTEL_PT_TIME_ZERO] = tc.time_zero;
+	auxtrace_info->priv[INTEL_PT_CAP_USER_TIME_ZERO] = cap_user_time_zero;
+	auxtrace_info->priv[INTEL_PT_TSC_BIT] = tsc_bit;
+	auxtrace_info->priv[INTEL_PT_NORETCOMP_BIT] = noretcomp_bit;
+	auxtrace_info->priv[INTEL_PT_HAVE_SCHED_SWITCH] = ptr->have_sched_switch;
+	auxtrace_info->priv[INTEL_PT_SNAPSHOT_MODE] = ptr->snapshot_mode;
+	auxtrace_info->priv[INTEL_PT_PER_CPU_MMAPS] = per_cpu_mmaps;
+
+	return 0;
+}
+
+static int intel_pt_track_switches(struct perf_evlist *evlist)
+{
+	const char *sched_switch = "sched:sched_switch";
+	struct perf_evsel *evsel;
+	int err;
+
+	if (!perf_evlist__can_select_event(evlist, sched_switch))
+		return -EPERM;
+
+	err = parse_events(evlist, sched_switch, NULL);
+	if (err) {
+		pr_debug2("%s: failed to parse %s, error %d\n",
+			  __func__, sched_switch, err);
+		return err;
+	}
+
+	evsel = perf_evlist__last(evlist);
+
+	perf_evsel__set_sample_bit(evsel, CPU);
+	perf_evsel__set_sample_bit(evsel, TIME);
+
+	evsel->system_wide = true;
+	evsel->no_aux_samples = true;
+	evsel->immediate = true;
+
+	return 0;
+}
+
+static int intel_pt_recording_options(struct auxtrace_record *itr,
+				      struct perf_evlist *evlist,
+				      struct record_opts *opts)
+{
+	struct intel_pt_recording *ptr =
+			container_of(itr, struct intel_pt_recording, itr);
+	struct perf_pmu *intel_pt_pmu = ptr->intel_pt_pmu;
+	bool have_timing_info;
+	struct perf_evsel *evsel, *intel_pt_evsel = NULL;
+	const struct cpu_map *cpus = evlist->cpus;
+	bool privileged = geteuid() == 0 || perf_event_paranoid() < 0;
+	u64 tsc_bit;
+
+	ptr->evlist = evlist;
+	ptr->snapshot_mode = opts->auxtrace_snapshot_mode;
+
+	evlist__for_each(evlist, evsel) {
+		if (evsel->attr.type == intel_pt_pmu->type) {
+			if (intel_pt_evsel) {
+				pr_err("There may be only one " INTEL_PT_PMU_NAME " event\n");
+				return -EINVAL;
+			}
+			evsel->attr.freq = 0;
+			evsel->attr.sample_period = 1;
+			intel_pt_evsel = evsel;
+			opts->full_auxtrace = true;
+		}
+	}
+
+	if (opts->auxtrace_snapshot_mode && !opts->full_auxtrace) {
+		pr_err("Snapshot mode (-S option) requires " INTEL_PT_PMU_NAME " PMU event (-e " INTEL_PT_PMU_NAME ")\n");
+		return -EINVAL;
+	}
+
+	if (opts->use_clockid) {
+		pr_err("Cannot use clockid (-k option) with " INTEL_PT_PMU_NAME "\n");
+		return -EINVAL;
+	}
+
+	if (!opts->full_auxtrace)
+		return 0;
+
+	/* Set default sizes for snapshot mode */
+	if (opts->auxtrace_snapshot_mode) {
+		size_t psb_period = intel_pt_psb_period(intel_pt_pmu, evlist);
+
+		if (!opts->auxtrace_snapshot_size && !opts->auxtrace_mmap_pages) {
+			if (privileged) {
+				opts->auxtrace_mmap_pages = MiB(4) / page_size;
+			} else {
+				opts->auxtrace_mmap_pages = KiB(128) / page_size;
+				if (opts->mmap_pages == UINT_MAX)
+					opts->mmap_pages = KiB(256) / page_size;
+			}
+		} else if (!opts->auxtrace_mmap_pages && !privileged &&
+			   opts->mmap_pages == UINT_MAX) {
+			opts->mmap_pages = KiB(256) / page_size;
+		}
+		if (!opts->auxtrace_snapshot_size)
+			opts->auxtrace_snapshot_size =
+				opts->auxtrace_mmap_pages * (size_t)page_size;
+		if (!opts->auxtrace_mmap_pages) {
+			size_t sz = opts->auxtrace_snapshot_size;
+
+			sz = round_up(sz, page_size) / page_size;
+			opts->auxtrace_mmap_pages = roundup_pow_of_two(sz);
+		}
+		if (opts->auxtrace_snapshot_size >
+				opts->auxtrace_mmap_pages * (size_t)page_size) {
+			pr_err("Snapshot size %zu must not be greater than AUX area tracing mmap size %zu\n",
+			       opts->auxtrace_snapshot_size,
+			       opts->auxtrace_mmap_pages * (size_t)page_size);
+			return -EINVAL;
+		}
+		if (!opts->auxtrace_snapshot_size || !opts->auxtrace_mmap_pages) {
+			pr_err("Failed to calculate default snapshot size and/or AUX area tracing mmap pages\n");
+			return -EINVAL;
+		}
+		pr_debug2("Intel PT snapshot size: %zu\n",
+			  opts->auxtrace_snapshot_size);
+		if (psb_period &&
+		    opts->auxtrace_snapshot_size <= psb_period +
+						  INTEL_PT_PSB_PERIOD_NEAR)
+			ui__warning("Intel PT snapshot size (%zu) may be too small for PSB period (%zu)\n",
+				    opts->auxtrace_snapshot_size, psb_period);
+	}
+
+	/* Set default sizes for full trace mode */
+	if (opts->full_auxtrace && !opts->auxtrace_mmap_pages) {
+		if (privileged) {
+			opts->auxtrace_mmap_pages = MiB(4) / page_size;
+		} else {
+			opts->auxtrace_mmap_pages = KiB(128) / page_size;
+			if (opts->mmap_pages == UINT_MAX)
+				opts->mmap_pages = KiB(256) / page_size;
+		}
+	}
+
+	/* Validate auxtrace_mmap_pages */
+	if (opts->auxtrace_mmap_pages) {
+		size_t sz = opts->auxtrace_mmap_pages * (size_t)page_size;
+		size_t min_sz;
+
+		if (opts->auxtrace_snapshot_mode)
+			min_sz = KiB(4);
+		else
+			min_sz = KiB(8);
+
+		if (sz < min_sz || !is_power_of_2(sz)) {
+			pr_err("Invalid mmap size for Intel Processor Trace: must be at least %zuKiB and a power of 2\n",
+			       min_sz / 1024);
+			return -EINVAL;
+		}
+	}
+
+	intel_pt_parse_terms(&intel_pt_pmu->format, "tsc", &tsc_bit);
+
+	if (opts->full_auxtrace && (intel_pt_evsel->attr.config & tsc_bit))
+		have_timing_info = true;
+	else
+		have_timing_info = false;
+
+	/*
+	 * Per-cpu recording needs sched_switch events to distinguish different
+	 * threads.
+	 */
+	if (have_timing_info && !cpu_map__empty(cpus)) {
+		int err;
+
+		err = intel_pt_track_switches(evlist);
+		if (err == -EPERM)
+			pr_debug2("Unable to select sched:sched_switch\n");
+		else if (err)
+			return err;
+		else
+			ptr->have_sched_switch = 1;
+	}
+
+	if (intel_pt_evsel) {
+		/*
+		 * To obtain the auxtrace buffer file descriptor, the auxtrace
+		 * event must come first.
+		 */
+		perf_evlist__to_front(evlist, intel_pt_evsel);
+		/*
+		 * In the case of per-cpu mmaps, we need the CPU on the
+		 * AUX event.
+		 */
+		if (!cpu_map__empty(cpus))
+			perf_evsel__set_sample_bit(intel_pt_evsel, CPU);
+	}
+
+	/* Add dummy event to keep tracking */
+	if (opts->full_auxtrace) {
+		struct perf_evsel *tracking_evsel;
+		int err;
+
+		err = parse_events(evlist, "dummy:u", NULL);
+		if (err)
+			return err;
+
+		tracking_evsel = perf_evlist__last(evlist);
+
+		perf_evlist__set_tracking_event(evlist, tracking_evsel);
+
+		tracking_evsel->attr.freq = 0;
+		tracking_evsel->attr.sample_period = 1;
+
+		/* In per-cpu case, always need the time of mmap events etc */
+		if (!cpu_map__empty(cpus))
+			perf_evsel__set_sample_bit(tracking_evsel, TIME);
+	}
+
+	/*
+	 * Warn the user when we do not have enough information to decode i.e.
+	 * per-cpu with no sched_switch (except workload-only).
+	 */
+	if (!ptr->have_sched_switch && !cpu_map__empty(cpus) &&
+	    !target__none(&opts->target))
+		ui__warning("Intel Processor Trace decoding will not be possible except for kernel tracing!\n");
+
+	return 0;
+}
+
+static int intel_pt_snapshot_start(struct auxtrace_record *itr)
+{
+	struct intel_pt_recording *ptr =
+			container_of(itr, struct intel_pt_recording, itr);
+	struct perf_evsel *evsel;
+
+	evlist__for_each(ptr->evlist, evsel) {
+		if (evsel->attr.type == ptr->intel_pt_pmu->type)
+			return perf_evlist__disable_event(ptr->evlist, evsel);
+	}
+	return -EINVAL;
+}
+
+static int intel_pt_snapshot_finish(struct auxtrace_record *itr)
+{
+	struct intel_pt_recording *ptr =
+			container_of(itr, struct intel_pt_recording, itr);
+	struct perf_evsel *evsel;
+
+	evlist__for_each(ptr->evlist, evsel) {
+		if (evsel->attr.type == ptr->intel_pt_pmu->type)
+			return perf_evlist__enable_event(ptr->evlist, evsel);
+	}
+	return -EINVAL;
+}
+
+static int intel_pt_alloc_snapshot_refs(struct intel_pt_recording *ptr, int idx)
+{
+	const size_t sz = sizeof(struct intel_pt_snapshot_ref);
+	int cnt = ptr->snapshot_ref_cnt, new_cnt = cnt * 2;
+	struct intel_pt_snapshot_ref *refs;
+
+	if (!new_cnt)
+		new_cnt = 16;
+
+	while (new_cnt <= idx)
+		new_cnt *= 2;
+
+	refs = calloc(new_cnt, sz);
+	if (!refs)
+		return -ENOMEM;
+
+	memcpy(refs, ptr->snapshot_refs, cnt * sz);
+
+	ptr->snapshot_refs = refs;
+	ptr->snapshot_ref_cnt = new_cnt;
+
+	return 0;
+}
+
+static void intel_pt_free_snapshot_refs(struct intel_pt_recording *ptr)
+{
+	int i;
+
+	for (i = 0; i < ptr->snapshot_ref_cnt; i++)
+		zfree(&ptr->snapshot_refs[i].ref_buf);
+	zfree(&ptr->snapshot_refs);
+}
+
+static void intel_pt_recording_free(struct auxtrace_record *itr)
+{
+	struct intel_pt_recording *ptr =
+			container_of(itr, struct intel_pt_recording, itr);
+
+	intel_pt_free_snapshot_refs(ptr);
+	free(ptr);
+}
+
+static int intel_pt_alloc_snapshot_ref(struct intel_pt_recording *ptr, int idx,
+				       size_t snapshot_buf_size)
+{
+	size_t ref_buf_size = ptr->snapshot_ref_buf_size;
+	void *ref_buf;
+
+	ref_buf = zalloc(ref_buf_size);
+	if (!ref_buf)
+		return -ENOMEM;
+
+	ptr->snapshot_refs[idx].ref_buf = ref_buf;
+	ptr->snapshot_refs[idx].ref_offset = snapshot_buf_size - ref_buf_size;
+
+	return 0;
+}
+
+static size_t intel_pt_snapshot_ref_buf_size(struct intel_pt_recording *ptr,
+					     size_t snapshot_buf_size)
+{
+	const size_t max_size = 256 * 1024;
+	size_t buf_size = 0, psb_period;
+
+	if (ptr->snapshot_size <= 64 * 1024)
+		return 0;
+
+	psb_period = intel_pt_psb_period(ptr->intel_pt_pmu, ptr->evlist);
+	if (psb_period)
+		buf_size = psb_period * 2;
+
+	if (!buf_size || buf_size > max_size)
+		buf_size = max_size;
+
+	if (buf_size >= snapshot_buf_size)
+		return 0;
+
+	if (buf_size >= ptr->snapshot_size / 2)
+		return 0;
+
+	return buf_size;
+}
+
+static int intel_pt_snapshot_init(struct intel_pt_recording *ptr,
+				  size_t snapshot_buf_size)
+{
+	if (ptr->snapshot_init_done)
+		return 0;
+
+	ptr->snapshot_init_done = true;
+
+	ptr->snapshot_ref_buf_size = intel_pt_snapshot_ref_buf_size(ptr,
+							snapshot_buf_size);
+
+	return 0;
+}
+
+/**
+ * intel_pt_compare_buffers - compare bytes in a buffer to a circular buffer.
+ * @buf1: first buffer
+ * @compare_size: number of bytes to compare
+ * @buf2: second buffer (a circular buffer)
+ * @offs2: offset in second buffer
+ * @buf2_size: size of second buffer
+ *
+ * The comparison allows for the possibility that the bytes to compare in the
+ * circular buffer are not contiguous.  It is assumed that @compare_size <=
+ * @buf2_size.  This function returns %false if the bytes are identical, %true
+ * otherwise.
+ */
+static bool intel_pt_compare_buffers(void *buf1, size_t compare_size,
+				     void *buf2, size_t offs2, size_t buf2_size)
+{
+	size_t end2 = offs2 + compare_size, part_size;
+
+	if (end2 <= buf2_size)
+		return memcmp(buf1, buf2 + offs2, compare_size);
+
+	part_size = end2 - buf2_size;
+	if (memcmp(buf1, buf2 + offs2, part_size))
+		return true;
+
+	compare_size -= part_size;
+
+	return memcmp(buf1 + part_size, buf2, compare_size);
+}
+
+static bool intel_pt_compare_ref(void *ref_buf, size_t ref_offset,
+				 size_t ref_size, size_t buf_size,
+				 void *data, size_t head)
+{
+	size_t ref_end = ref_offset + ref_size;
+
+	if (ref_end > buf_size) {
+		if (head > ref_offset || head < ref_end - buf_size)
+			return true;
+	} else if (head > ref_offset && head < ref_end) {
+		return true;
+	}
+
+	return intel_pt_compare_buffers(ref_buf, ref_size, data, ref_offset,
+					buf_size);
+}
+
+static void intel_pt_copy_ref(void *ref_buf, size_t ref_size, size_t buf_size,
+			      void *data, size_t head)
+{
+	if (head >= ref_size) {
+		memcpy(ref_buf, data + head - ref_size, ref_size);
+	} else {
+		memcpy(ref_buf, data, head);
+		ref_size -= head;
+		memcpy(ref_buf + head, data + buf_size - ref_size, ref_size);
+	}
+}
+
+static bool intel_pt_wrapped(struct intel_pt_recording *ptr, int idx,
+			     struct auxtrace_mmap *mm, unsigned char *data,
+			     u64 head)
+{
+	struct intel_pt_snapshot_ref *ref = &ptr->snapshot_refs[idx];
+	bool wrapped;
+
+	wrapped = intel_pt_compare_ref(ref->ref_buf, ref->ref_offset,
+				       ptr->snapshot_ref_buf_size, mm->len,
+				       data, head);
+
+	intel_pt_copy_ref(ref->ref_buf, ptr->snapshot_ref_buf_size, mm->len,
+			  data, head);
+
+	return wrapped;
+}
+
+static bool intel_pt_first_wrap(u64 *data, size_t buf_size)
+{
+	int i, a, b;
+
+	b = buf_size >> 3;
+	a = b - 512;
+	if (a < 0)
+		a = 0;
+
+	for (i = a; i < b; i++) {
+		if (data[i])
+			return true;
+	}
+
+	return false;
+}
+
+static int intel_pt_find_snapshot(struct auxtrace_record *itr, int idx,
+				  struct auxtrace_mmap *mm, unsigned char *data,
+				  u64 *head, u64 *old)
+{
+	struct intel_pt_recording *ptr =
+			container_of(itr, struct intel_pt_recording, itr);
+	bool wrapped;
+	int err;
+
+	pr_debug3("%s: mmap index %d old head %zu new head %zu\n",
+		  __func__, idx, (size_t)*old, (size_t)*head);
+
+	err = intel_pt_snapshot_init(ptr, mm->len);
+	if (err)
+		goto out_err;
+
+	if (idx >= ptr->snapshot_ref_cnt) {
+		err = intel_pt_alloc_snapshot_refs(ptr, idx);
+		if (err)
+			goto out_err;
+	}
+
+	if (ptr->snapshot_ref_buf_size) {
+		if (!ptr->snapshot_refs[idx].ref_buf) {
+			err = intel_pt_alloc_snapshot_ref(ptr, idx, mm->len);
+			if (err)
+				goto out_err;
+		}
+		wrapped = intel_pt_wrapped(ptr, idx, mm, data, *head);
+	} else {
+		wrapped = ptr->snapshot_refs[idx].wrapped;
+		if (!wrapped && intel_pt_first_wrap((u64 *)data, mm->len)) {
+			ptr->snapshot_refs[idx].wrapped = true;
+			wrapped = true;
+		}
+	}
+
+	/*
+	 * In full trace mode 'head' continually increases.  However in snapshot
+	 * mode 'head' is an offset within the buffer.  Here 'old' and 'head'
+	 * are adjusted to match the full trace case which expects that 'old' is
+	 * always less than 'head'.
+	 */
+	if (wrapped) {
+		*old = *head;
+		*head += mm->len;
+	} else {
+		if (mm->mask)
+			*old &= mm->mask;
+		else
+			*old %= mm->len;
+		if (*old > *head)
+			*head += mm->len;
+	}
+
+	pr_debug3("%s: wrap-around %sdetected, adjusted old head %zu adjusted new head %zu\n",
+		  __func__, wrapped ? "" : "not ", (size_t)*old, (size_t)*head);
+
+	return 0;
+
+out_err:
+	pr_err("%s: failed, error %d\n", __func__, err);
+	return err;
+}
+
+static u64 intel_pt_reference(struct auxtrace_record *itr __maybe_unused)
+{
+	return rdtsc();
+}
+
+static int intel_pt_read_finish(struct auxtrace_record *itr, int idx)
+{
+	struct intel_pt_recording *ptr =
+			container_of(itr, struct intel_pt_recording, itr);
+	struct perf_evsel *evsel;
+
+	evlist__for_each(ptr->evlist, evsel) {
+		if (evsel->attr.type == ptr->intel_pt_pmu->type)
+			return perf_evlist__enable_event_idx(ptr->evlist, evsel,
+							     idx);
+	}
+	return -EINVAL;
+}
+
+struct auxtrace_record *intel_pt_recording_init(int *err)
+{
+	struct perf_pmu *intel_pt_pmu = perf_pmu__find(INTEL_PT_PMU_NAME);
+	struct intel_pt_recording *ptr;
+
+	if (!intel_pt_pmu)
+		return NULL;
+
+	ptr = zalloc(sizeof(struct intel_pt_recording));
+	if (!ptr) {
+		*err = -ENOMEM;
+		return NULL;
+	}
+
+	ptr->intel_pt_pmu = intel_pt_pmu;
+	ptr->itr.recording_options = intel_pt_recording_options;
+	ptr->itr.info_priv_size = intel_pt_info_priv_size;
+	ptr->itr.info_fill = intel_pt_info_fill;
+	ptr->itr.free = intel_pt_recording_free;
+	ptr->itr.snapshot_start = intel_pt_snapshot_start;
+	ptr->itr.snapshot_finish = intel_pt_snapshot_finish;
+	ptr->itr.find_snapshot = intel_pt_find_snapshot;
+	ptr->itr.parse_snapshot_options = intel_pt_parse_snapshot_options;
+	ptr->itr.reference = intel_pt_reference;
+	ptr->itr.read_finish = intel_pt_read_finish;
+	return &ptr->itr;
+}