initial commit with v3.6.7

[linux-3.6.7-moxart.git] / arch / arm / kernel / perf_event.c

#undef DEBUG

/*
 * ARM performance counter support.
 *
 * Copyright (C) 2009 picoChip Designs, Ltd., Jamie Iles
 * Copyright (C) 2010 ARM Ltd., Will Deacon <will.deacon@arm.com>
 *
 * This code is based on the sparc64 perf event code, which is in turn based
 * on the x86 code. Callchain code is based on the ARM OProfile backtrace
 * code.
 */
#define pr_fmt(fmt) "hw perfevents: " fmt

#include <linux/bitmap.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/perf_event.h>
#include <linux/platform_device.h>
#include <linux/spinlock.h>
#include <linux/uaccess.h>

#include <asm/cputype.h>
#include <asm/irq.h>
#include <asm/irq_regs.h>
#include <asm/pmu.h>
#include <asm/stacktrace.h>

/*
 * ARMv6 supports a maximum of 3 events, starting from index 0. If we add
 * another platform that supports more, we need to increase this to be the
 * largest of all platforms.
 *
 * ARMv7 supports up to 32 events:
 *  cycle counter CCNT + 31 events counters CNT0..30.
 *  Cortex-A8 has 1+4 counters, Cortex-A9 has 1+6 counters.
 */
#define ARMPMU_MAX_HWEVENTS             32

static DEFINE_PER_CPU(struct perf_event * [ARMPMU_MAX_HWEVENTS], hw_events);
static DEFINE_PER_CPU(unsigned long [BITS_TO_LONGS(ARMPMU_MAX_HWEVENTS)], used_mask);
static DEFINE_PER_CPU(struct pmu_hw_events, cpu_hw_events);

#define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))

/* Set at runtime when we know what CPU type we are. */
static struct arm_pmu *cpu_pmu;

const char *perf_pmu_name(void)
{
        if (!cpu_pmu)
                return NULL;

        return cpu_pmu->pmu.name;
}
EXPORT_SYMBOL_GPL(perf_pmu_name);

int perf_num_counters(void)
{
        int max_events = 0;

        if (cpu_pmu != NULL)
                max_events = cpu_pmu->num_events;

        return max_events;
}
EXPORT_SYMBOL_GPL(perf_num_counters);

#define HW_OP_UNSUPPORTED               0xFFFF

#define C(_x) \
        PERF_COUNT_HW_CACHE_##_x

#define CACHE_OP_UNSUPPORTED            0xFFFF

static int
armpmu_map_cache_event(const unsigned (*cache_map)
                                      [PERF_COUNT_HW_CACHE_MAX]
                                      [PERF_COUNT_HW_CACHE_OP_MAX]
                                      [PERF_COUNT_HW_CACHE_RESULT_MAX],
                       u64 config)
{
        unsigned int cache_type, cache_op, cache_result, ret;

        cache_type = (config >>  0) & 0xff;
        if (cache_type >= PERF_COUNT_HW_CACHE_MAX)
                return -EINVAL;

        cache_op = (config >>  8) & 0xff;
        if (cache_op >= PERF_COUNT_HW_CACHE_OP_MAX)
                return -EINVAL;

        cache_result = (config >> 16) & 0xff;
        if (cache_result >= PERF_COUNT_HW_CACHE_RESULT_MAX)
                return -EINVAL;

        ret = (int)(*cache_map)[cache_type][cache_op][cache_result];

        if (ret == CACHE_OP_UNSUPPORTED)
                return -ENOENT;

        return ret;
}

static int
armpmu_map_event(const unsigned (*event_map)[PERF_COUNT_HW_MAX], u64 config)
{
        int mapping = (*event_map)[config];
        return mapping == HW_OP_UNSUPPORTED ? -ENOENT : mapping;
}

static int
armpmu_map_raw_event(u32 raw_event_mask, u64 config)
{
        return (int)(config & raw_event_mask);
}

static int map_cpu_event(struct perf_event *event,
                         const unsigned (*event_map)[PERF_COUNT_HW_MAX],
                         const unsigned (*cache_map)
                                        [PERF_COUNT_HW_CACHE_MAX]
                                        [PERF_COUNT_HW_CACHE_OP_MAX]
                                        [PERF_COUNT_HW_CACHE_RESULT_MAX],
                         u32 raw_event_mask)
{
        u64 config = event->attr.config;

        switch (event->attr.type) {
        case PERF_TYPE_HARDWARE:
                return armpmu_map_event(event_map, config);
        case PERF_TYPE_HW_CACHE:
                return armpmu_map_cache_event(cache_map, config);
        case PERF_TYPE_RAW:
                return armpmu_map_raw_event(raw_event_mask, config);
        }

        return -ENOENT;
}

int
armpmu_event_set_period(struct perf_event *event,
                        struct hw_perf_event *hwc,
                        int idx)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        s64 left = local64_read(&hwc->period_left);
        s64 period = hwc->sample_period;
        int ret = 0;

        if (unlikely(left <= -period)) {
                left = period;
                local64_set(&hwc->period_left, left);
                hwc->last_period = period;
                ret = 1;
        }

        if (unlikely(left <= 0)) {
                left += period;
                local64_set(&hwc->period_left, left);
                hwc->last_period = period;
                ret = 1;
        }

        if (left > (s64)armpmu->max_period)
                left = armpmu->max_period;

        local64_set(&hwc->prev_count, (u64)-left);

        armpmu->write_counter(idx, (u64)(-left) & 0xffffffff);

        perf_event_update_userpage(event);

        return ret;
}

u64
armpmu_event_update(struct perf_event *event,
                    struct hw_perf_event *hwc,
                    int idx)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        u64 delta, prev_raw_count, new_raw_count;

again:
        prev_raw_count = local64_read(&hwc->prev_count);
        new_raw_count = armpmu->read_counter(idx);

        if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
                             new_raw_count) != prev_raw_count)
                goto again;

        delta = (new_raw_count - prev_raw_count) & armpmu->max_period;

        local64_add(delta, &event->count);
        local64_sub(delta, &hwc->period_left);

        return new_raw_count;
}

static void
armpmu_read(struct perf_event *event)
{
        struct hw_perf_event *hwc = &event->hw;

        /* Don't read disabled counters! */
        if (hwc->idx < 0)
                return;

        armpmu_event_update(event, hwc, hwc->idx);
}

static void
armpmu_stop(struct perf_event *event, int flags)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        struct hw_perf_event *hwc = &event->hw;

        /*
         * ARM pmu always has to update the counter, so ignore
         * PERF_EF_UPDATE, see comments in armpmu_start().
         */
        if (!(hwc->state & PERF_HES_STOPPED)) {
                armpmu->disable(hwc, hwc->idx);
                barrier(); /* why? */
                armpmu_event_update(event, hwc, hwc->idx);
                hwc->state |= PERF_HES_STOPPED | PERF_HES_UPTODATE;
        }
}

static void
armpmu_start(struct perf_event *event, int flags)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        struct hw_perf_event *hwc = &event->hw;

        /*
         * ARM pmu always has to reprogram the period, so ignore
         * PERF_EF_RELOAD, see the comment below.
         */
        if (flags & PERF_EF_RELOAD)
                WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));

        hwc->state = 0;
        /*
         * Set the period again. Some counters can't be stopped, so when we
         * were stopped we simply disabled the IRQ source and the counter
         * may have been left counting. If we don't do this step then we may
         * get an interrupt too soon or *way* too late if the overflow has
         * happened since disabling.
         */
        armpmu_event_set_period(event, hwc, hwc->idx);
        armpmu->enable(hwc, hwc->idx);
}

static void
armpmu_del(struct perf_event *event, int flags)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        struct pmu_hw_events *hw_events = armpmu->get_hw_events();
        struct hw_perf_event *hwc = &event->hw;
        int idx = hwc->idx;

        WARN_ON(idx < 0);

        armpmu_stop(event, PERF_EF_UPDATE);
        hw_events->events[idx] = NULL;
        clear_bit(idx, hw_events->used_mask);

        perf_event_update_userpage(event);
}

static int
armpmu_add(struct perf_event *event, int flags)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        struct pmu_hw_events *hw_events = armpmu->get_hw_events();
        struct hw_perf_event *hwc = &event->hw;
        int idx;
        int err = 0;

        perf_pmu_disable(event->pmu);

        /* If we don't have a space for the counter then finish early. */
        idx = armpmu->get_event_idx(hw_events, hwc);
        if (idx < 0) {
                err = idx;
                goto out;
        }

        /*
         * If there is an event in the counter we are going to use then make
         * sure it is disabled.
         */
        event->hw.idx = idx;
        armpmu->disable(hwc, idx);
        hw_events->events[idx] = event;

        hwc->state = PERF_HES_STOPPED | PERF_HES_UPTODATE;
        if (flags & PERF_EF_START)
                armpmu_start(event, PERF_EF_RELOAD);

        /* Propagate our changes to the userspace mapping. */
        perf_event_update_userpage(event);

out:
        perf_pmu_enable(event->pmu);
        return err;
}

static int
validate_event(struct pmu_hw_events *hw_events,
               struct perf_event *event)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        struct hw_perf_event fake_event = event->hw;
        struct pmu *leader_pmu = event->group_leader->pmu;

        if (event->pmu != leader_pmu || event->state <= PERF_EVENT_STATE_OFF)
                return 1;

        return armpmu->get_event_idx(hw_events, &fake_event) >= 0;
}

static int
validate_group(struct perf_event *event)
{
        struct perf_event *sibling, *leader = event->group_leader;
        struct pmu_hw_events fake_pmu;
        DECLARE_BITMAP(fake_used_mask, ARMPMU_MAX_HWEVENTS);

        /*
         * Initialise the fake PMU. We only need to populate the
         * used_mask for the purposes of validation.
         */
        memset(fake_used_mask, 0, sizeof(fake_used_mask));
        fake_pmu.used_mask = fake_used_mask;

        if (!validate_event(&fake_pmu, leader))
                return -EINVAL;

        list_for_each_entry(sibling, &leader->sibling_list, group_entry) {
                if (!validate_event(&fake_pmu, sibling))
                        return -EINVAL;
        }

        if (!validate_event(&fake_pmu, event))
                return -EINVAL;

        return 0;
}

static irqreturn_t armpmu_platform_irq(int irq, void *dev)
{
        struct arm_pmu *armpmu = (struct arm_pmu *) dev;
        struct platform_device *plat_device = armpmu->plat_device;
        struct arm_pmu_platdata *plat = dev_get_platdata(&plat_device->dev);

        return plat->handle_irq(irq, dev, armpmu->handle_irq);
}

static void
armpmu_release_hardware(struct arm_pmu *armpmu)
{
        int i, irq, irqs;
        struct platform_device *pmu_device = armpmu->plat_device;
        struct arm_pmu_platdata *plat =
                dev_get_platdata(&pmu_device->dev);

        irqs = min(pmu_device->num_resources, num_possible_cpus());

        for (i = 0; i < irqs; ++i) {
                if (!cpumask_test_and_clear_cpu(i, &armpmu->active_irqs))
                        continue;
                irq = platform_get_irq(pmu_device, i);
                if (irq >= 0) {
                        if (plat && plat->disable_irq)
                                plat->disable_irq(irq);
                        free_irq(irq, armpmu);
                }
        }

        release_pmu(armpmu->type);
}

static int
armpmu_reserve_hardware(struct arm_pmu *armpmu)
{
        struct arm_pmu_platdata *plat;
        irq_handler_t handle_irq;
        int i, err, irq, irqs;
        struct platform_device *pmu_device = armpmu->plat_device;

        if (!pmu_device)
                return -ENODEV;

        err = reserve_pmu(armpmu->type);
        if (err) {
                pr_warning("unable to reserve pmu\n");
                return err;
        }

        plat = dev_get_platdata(&pmu_device->dev);
        if (plat && plat->handle_irq)
                handle_irq = armpmu_platform_irq;
        else
                handle_irq = armpmu->handle_irq;

        irqs = min(pmu_device->num_resources, num_possible_cpus());
        if (irqs < 1) {
                pr_err("no irqs for PMUs defined\n");
                return -ENODEV;
        }

        for (i = 0; i < irqs; ++i) {
                err = 0;
                irq = platform_get_irq(pmu_device, i);
                if (irq < 0)
                        continue;

                /*
                 * If we have a single PMU interrupt that we can't shift,
                 * assume that we're running on a uniprocessor machine and
                 * continue. Otherwise, continue without this interrupt.
                 */
                if (irq_set_affinity(irq, cpumask_of(i)) && irqs > 1) {
                        pr_warning("unable to set irq affinity (irq=%d, cpu=%u)\n",
                                    irq, i);
                        continue;
                }

                err = request_irq(irq, handle_irq,
                                  IRQF_DISABLED | IRQF_NOBALANCING,
                                  "arm-pmu", armpmu);
                if (err) {
                        pr_err("unable to request IRQ%d for ARM PMU counters\n",
                                irq);
                        armpmu_release_hardware(armpmu);
                        return err;
                } else if (plat && plat->enable_irq)
                        plat->enable_irq(irq);

                cpumask_set_cpu(i, &armpmu->active_irqs);
        }

        return 0;
}

static void
hw_perf_event_destroy(struct perf_event *event)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        atomic_t *active_events  = &armpmu->active_events;
        struct mutex *pmu_reserve_mutex = &armpmu->reserve_mutex;

        if (atomic_dec_and_mutex_lock(active_events, pmu_reserve_mutex)) {
                armpmu_release_hardware(armpmu);
                mutex_unlock(pmu_reserve_mutex);
        }
}

static int
event_requires_mode_exclusion(struct perf_event_attr *attr)
{
        return attr->exclude_idle || attr->exclude_user ||
               attr->exclude_kernel || attr->exclude_hv;
}

static int
__hw_perf_event_init(struct perf_event *event)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        struct hw_perf_event *hwc = &event->hw;
        int mapping, err;

        mapping = armpmu->map_event(event);

        if (mapping < 0) {
                pr_debug("event %x:%llx not supported\n", event->attr.type,
                         event->attr.config);
                return mapping;
        }

        /*
         * We don't assign an index until we actually place the event onto
         * hardware. Use -1 to signify that we haven't decided where to put it
         * yet. For SMP systems, each core has it's own PMU so we can't do any
         * clever allocation or constraints checking at this point.
         */
        hwc->idx                = -1;
        hwc->config_base        = 0;
        hwc->config             = 0;
        hwc->event_base         = 0;

        /*
         * Check whether we need to exclude the counter from certain modes.
         */
        if ((!armpmu->set_event_filter ||
             armpmu->set_event_filter(hwc, &event->attr)) &&
             event_requires_mode_exclusion(&event->attr)) {
                pr_debug("ARM performance counters do not support "
                         "mode exclusion\n");
                return -EOPNOTSUPP;
        }

        /*
         * Store the event encoding into the config_base field.
         */
        hwc->config_base            |= (unsigned long)mapping;

        if (!hwc->sample_period) {
                /*
                 * For non-sampling runs, limit the sample_period to half
                 * of the counter width. That way, the new counter value
                 * is far less likely to overtake the previous one unless
                 * you have some serious IRQ latency issues.
                 */
                hwc->sample_period  = armpmu->max_period >> 1;
                hwc->last_period    = hwc->sample_period;
                local64_set(&hwc->period_left, hwc->sample_period);
        }

        err = 0;
        if (event->group_leader != event) {
                err = validate_group(event);
                if (err)
                        return -EINVAL;
        }

        return err;
}

static int armpmu_event_init(struct perf_event *event)
{
        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
        int err = 0;
        atomic_t *active_events = &armpmu->active_events;

        /* does not support taken branch sampling */
        if (has_branch_stack(event))
                return -EOPNOTSUPP;

        if (armpmu->map_event(event) == -ENOENT)
                return -ENOENT;

        event->destroy = hw_perf_event_destroy;

        if (!atomic_inc_not_zero(active_events)) {
                mutex_lock(&armpmu->reserve_mutex);
                if (atomic_read(active_events) == 0)
                        err = armpmu_reserve_hardware(armpmu);

                if (!err)
                        atomic_inc(active_events);
                mutex_unlock(&armpmu->reserve_mutex);
        }

        if (err)
                return err;

        err = __hw_perf_event_init(event);
        if (err)
                hw_perf_event_destroy(event);

        return err;
}

static void armpmu_enable(struct pmu *pmu)
{
        struct arm_pmu *armpmu = to_arm_pmu(pmu);
        struct pmu_hw_events *hw_events = armpmu->get_hw_events();
        int enabled = bitmap_weight(hw_events->used_mask, armpmu->num_events);

        if (enabled)
                armpmu->start();
}

static void armpmu_disable(struct pmu *pmu)
{
        struct arm_pmu *armpmu = to_arm_pmu(pmu);
        armpmu->stop();
}

static void __init armpmu_init(struct arm_pmu *armpmu)
{
        atomic_set(&armpmu->active_events, 0);
        mutex_init(&armpmu->reserve_mutex);

        armpmu->pmu = (struct pmu) {
                .pmu_enable     = armpmu_enable,
                .pmu_disable    = armpmu_disable,
                .event_init     = armpmu_event_init,
                .add            = armpmu_add,
                .del            = armpmu_del,
                .start          = armpmu_start,
                .stop           = armpmu_stop,
                .read           = armpmu_read,
        };
}

int __init armpmu_register(struct arm_pmu *armpmu, char *name, int type)
{
        armpmu_init(armpmu);
        return perf_pmu_register(&armpmu->pmu, name, type);
}

/* Include the PMU-specific implementations. */
#include "perf_event_xscale.c"
#include "perf_event_v6.c"
#include "perf_event_v7.c"

/*
 * Ensure the PMU has sane values out of reset.
 * This requires SMP to be available, so exists as a separate initcall.
 */
static int __init
cpu_pmu_reset(void)
{
        if (cpu_pmu && cpu_pmu->reset)
                return on_each_cpu(cpu_pmu->reset, NULL, 1);
        return 0;
}
arch_initcall(cpu_pmu_reset);

/*
 * PMU platform driver and devicetree bindings.
 */
static struct of_device_id armpmu_of_device_ids[] = {
        {.compatible = "arm,cortex-a9-pmu"},
        {.compatible = "arm,cortex-a8-pmu"},
        {.compatible = "arm,arm1136-pmu"},
        {.compatible = "arm,arm1176-pmu"},
        {},
};

static struct platform_device_id armpmu_plat_device_ids[] = {
        {.name = "arm-pmu"},
        {},
};

static int __devinit armpmu_device_probe(struct platform_device *pdev)
{
        if (!cpu_pmu)
                return -ENODEV;

        cpu_pmu->plat_device = pdev;
        return 0;
}

static struct platform_driver armpmu_driver = {
        .driver         = {
                .name   = "arm-pmu",
                .of_match_table = armpmu_of_device_ids,
        },
        .probe          = armpmu_device_probe,
        .id_table       = armpmu_plat_device_ids,
};

static int __init register_pmu_driver(void)
{
        return platform_driver_register(&armpmu_driver);
}
device_initcall(register_pmu_driver);

static struct pmu_hw_events *armpmu_get_cpu_events(void)
{
        return &__get_cpu_var(cpu_hw_events);
}

static void __init cpu_pmu_init(struct arm_pmu *armpmu)
{
        int cpu;
        for_each_possible_cpu(cpu) {
                struct pmu_hw_events *events = &per_cpu(cpu_hw_events, cpu);
                events->events = per_cpu(hw_events, cpu);
                events->used_mask = per_cpu(used_mask, cpu);
                raw_spin_lock_init(&events->pmu_lock);
        }
        armpmu->get_hw_events = armpmu_get_cpu_events;
        armpmu->type = ARM_PMU_DEVICE_CPU;
}

/*
 * PMU hardware loses all context when a CPU goes offline.
 * When a CPU is hotplugged back in, since some hardware registers are
 * UNKNOWN at reset, the PMU must be explicitly reset to avoid reading
 * junk values out of them.
 */
static int __cpuinit pmu_cpu_notify(struct notifier_block *b,
                                        unsigned long action, void *hcpu)
{
        if ((action & ~CPU_TASKS_FROZEN) != CPU_STARTING)
                return NOTIFY_DONE;

        if (cpu_pmu && cpu_pmu->reset)
                cpu_pmu->reset(NULL);

        return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata pmu_cpu_notifier = {
        .notifier_call = pmu_cpu_notify,
};

/*
 * CPU PMU identification and registration.
 */
static int __init
init_hw_perf_events(void)
{
        unsigned long cpuid = read_cpuid_id();
        unsigned long implementor = (cpuid & 0xFF000000) >> 24;
        unsigned long part_number = (cpuid & 0xFFF0);

        /* ARM Ltd CPUs. */
        if (0x41 == implementor) {
                switch (part_number) {
                case 0xB360:    /* ARM1136 */
                case 0xB560:    /* ARM1156 */
                case 0xB760:    /* ARM1176 */
                        cpu_pmu = armv6pmu_init();
                        break;
                case 0xB020:    /* ARM11mpcore */
                        cpu_pmu = armv6mpcore_pmu_init();
                        break;
                case 0xC080:    /* Cortex-A8 */
                        cpu_pmu = armv7_a8_pmu_init();
                        break;
                case 0xC090:    /* Cortex-A9 */
                        cpu_pmu = armv7_a9_pmu_init();
                        break;
                case 0xC050:    /* Cortex-A5 */
                        cpu_pmu = armv7_a5_pmu_init();
                        break;
                case 0xC0F0:    /* Cortex-A15 */
                        cpu_pmu = armv7_a15_pmu_init();
                        break;
                case 0xC070:    /* Cortex-A7 */
                        cpu_pmu = armv7_a7_pmu_init();
                        break;
                }
        /* Intel CPUs [xscale]. */
        } else if (0x69 == implementor) {
                part_number = (cpuid >> 13) & 0x7;
                switch (part_number) {
                case 1:
                        cpu_pmu = xscale1pmu_init();
                        break;
                case 2:
                        cpu_pmu = xscale2pmu_init();
                        break;
                }
        }

        if (cpu_pmu) {
                pr_info("enabled with %s PMU driver, %d counters available\n",
                        cpu_pmu->name, cpu_pmu->num_events);
                cpu_pmu_init(cpu_pmu);
                register_cpu_notifier(&pmu_cpu_notifier);
                armpmu_register(cpu_pmu, cpu_pmu->name, PERF_TYPE_RAW);
        } else {
                pr_info("no hardware support available\n");
        }

        return 0;
}
early_initcall(init_hw_perf_events);

/*
 * Callchain handling code.
 */

/*
 * The registers we're interested in are at the end of the variable
 * length saved register structure. The fp points at the end of this
 * structure so the address of this struct is:
 * (struct frame_tail *)(xxx->fp)-1
 *
 * This code has been adapted from the ARM OProfile support.
 */
struct frame_tail {
        struct frame_tail __user *fp;
        unsigned long sp;
        unsigned long lr;
} __attribute__((packed));

/*
 * Get the return address for a single stackframe and return a pointer to the
 * next frame tail.
 */
static struct frame_tail __user *
user_backtrace(struct frame_tail __user *tail,
               struct perf_callchain_entry *entry)
{
        struct frame_tail buftail;

        /* Also check accessibility of one struct frame_tail beyond */
        if (!access_ok(VERIFY_READ, tail, sizeof(buftail)))
                return NULL;
        if (__copy_from_user_inatomic(&buftail, tail, sizeof(buftail)))
                return NULL;

        perf_callchain_store(entry, buftail.lr);

        /*
         * Frame pointers should strictly progress back up the stack
         * (towards higher addresses).
         */
        if (tail + 1 >= buftail.fp)
                return NULL;

        return buftail.fp - 1;
}

void
perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
{
        struct frame_tail __user *tail;


        tail = (struct frame_tail __user *)regs->ARM_fp - 1;

        while ((entry->nr < PERF_MAX_STACK_DEPTH) &&
               tail && !((unsigned long)tail & 0x3))
                tail = user_backtrace(tail, entry);
}

/*
 * Gets called by walk_stackframe() for every stackframe. This will be called
 * whist unwinding the stackframe and is like a subroutine return so we use
 * the PC.
 */
static int
callchain_trace(struct stackframe *fr,
                void *data)
{
        struct perf_callchain_entry *entry = data;
        perf_callchain_store(entry, fr->pc);
        return 0;
}

void
perf_callchain_kernel(struct perf_callchain_entry *entry, struct pt_regs *regs)
{
        struct stackframe fr;

        fr.fp = regs->ARM_fp;
        fr.sp = regs->ARM_sp;
        fr.lr = regs->ARM_lr;
        fr.pc = regs->ARM_pc;
        walk_stackframe(&fr, callchain_trace, entry);
}