xnu-3248.30.4.tar.gz

[apple/xnu.git] / osfmk / kern / telemetry.c

/*
 * Copyright (c) 2012-2013 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
#include <mach/host_priv.h>
#include <mach/host_special_ports.h>
#include <mach/mach_types.h>
#include <mach/telemetry_notification_server.h>

#include <kern/assert.h>
#include <kern/clock.h>
#include <kern/debug.h>
#include <kern/host.h>
#include <kern/kalloc.h>
#include <kern/kern_types.h> 
#include <kern/locks.h> 
#include <kern/misc_protos.h> 
#include <kern/sched.h>
#include <kern/sched_prim.h>
#include <kern/telemetry.h>
#include <kern/timer_call.h>

#include <pexpert/pexpert.h>

#include <vm/vm_kern.h>
#include <vm/vm_shared_region.h>

#include <kperf/kperf.h>
#include <kperf/context.h>
#include <kperf/callstack.h>

#include <sys/kdebug.h>
#include <uuid/uuid.h>
#include <kdp/kdp_dyld.h>

#define TELEMETRY_DEBUG 0

extern int      proc_pid(void *);
extern char     *proc_name_address(void *p);
extern uint64_t proc_uniqueid(void *p);
extern uint64_t proc_was_throttled(void *p);
extern uint64_t proc_did_throttle(void *p);
extern uint64_t get_dispatchqueue_serialno_offset_from_proc(void *p);
extern int      proc_selfpid(void);

struct micro_snapshot_buffer {
        vm_offset_t             buffer;
        uint32_t                size;
        uint32_t                current_position;
        uint32_t                end_point;
};

void telemetry_take_sample(thread_t thread, uint8_t microsnapshot_flags, struct micro_snapshot_buffer * current_buffer);
int telemetry_buffer_gather(user_addr_t buffer, uint32_t *length, boolean_t mark, struct micro_snapshot_buffer * current_buffer);

#define TELEMETRY_DEFAULT_SAMPLE_RATE (1) /* 1 sample every 1 second */
#define TELEMETRY_DEFAULT_WINDOW_BUFFER_SIZE (512*1024) /* Should hopefully provide 10 seconds worth of samples */
#define TELEMETRY_DEFAULT_BUFFER_SIZE (16*1024)
#define TELEMETRY_MAX_BUFFER_SIZE (64*1024)

#define TELEMETRY_DEFAULT_NOTIFY_LEEWAY (4*1024) // Userland gets 4k of leeway to collect data after notification
#define TELEMETRY_MAX_UUID_COUNT (128) // Max of 128 non-shared-cache UUIDs to log for symbolication

uint32_t                        telemetry_sample_rate = 0;
volatile boolean_t      telemetry_needs_record = FALSE;
volatile boolean_t      telemetry_windowed_record = FALSE;
volatile boolean_t      telemetry_needs_timer_arming_record = FALSE;

/*
 * Tells the scheduler that we want it to invoke
 * compute_telemetry_windowed(); it is still our responsibility
 * to ensure that we do not panic if someone disables the window
 * buffer immediately after the scheduler does so.
 */
volatile boolean_t      telemetry_window_enabled = FALSE;

/*
 * If TRUE, record micro-stackshot samples for all tasks.
 * If FALSE, only sample tasks which are marked for telemetry.
 */
boolean_t                       telemetry_sample_all_tasks = FALSE;
uint32_t                        telemetry_active_tasks = 0; // Number of tasks opted into telemetry

uint32_t                        telemetry_timestamp = 0;

/*
 * We have two buffers.  The telemetry_buffer is responsible
 * for timer samples and interrupt samples that are driven by
 * compute_averages().  It will notify its client (if one
 * exists) when it has enough data to be worth flushing.
 *
 * The window_buffer contains only interrupt_samples that are
 * driven by the scheduler.  Its intent is to provide a
 * window of recent activity on the cpu(s).
 */
struct micro_snapshot_buffer telemetry_buffer = {0, 0, 0, 0};
struct micro_snapshot_buffer window_buffer = {0, 0, 0, 0};

int                                     telemetry_bytes_since_last_mark = -1; // How much data since buf was last marked?
int                                     telemetry_buffer_notify_at = 0;

lck_grp_t               telemetry_lck_grp;
lck_mtx_t               telemetry_mtx;

#define TELEMETRY_LOCK() do { lck_mtx_lock(&telemetry_mtx); } while(0)
#define TELEMETRY_TRY_SPIN_LOCK() lck_mtx_try_lock_spin(&telemetry_mtx)
#define TELEMETRY_UNLOCK() do { lck_mtx_unlock(&telemetry_mtx); } while(0)

void telemetry_init(void)
{
        kern_return_t ret;
        uint32_t          telemetry_notification_leeway;

        lck_grp_init(&telemetry_lck_grp, "telemetry group", LCK_GRP_ATTR_NULL);
        lck_mtx_init(&telemetry_mtx, &telemetry_lck_grp, LCK_ATTR_NULL);

        if (!PE_parse_boot_argn("telemetry_buffer_size", &telemetry_buffer.size, sizeof(telemetry_buffer.size))) {
                telemetry_buffer.size = TELEMETRY_DEFAULT_BUFFER_SIZE;
        }

        if (telemetry_buffer.size > TELEMETRY_MAX_BUFFER_SIZE)
                telemetry_buffer.size = TELEMETRY_MAX_BUFFER_SIZE;

        ret = kmem_alloc(kernel_map, &telemetry_buffer.buffer, telemetry_buffer.size, VM_KERN_MEMORY_DIAG);
        if (ret != KERN_SUCCESS) {
                kprintf("Telemetry: Allocation failed: %d\n", ret);
                return;
        }
        bzero((void *) telemetry_buffer.buffer, telemetry_buffer.size);

        if (!PE_parse_boot_argn("telemetry_notification_leeway", &telemetry_notification_leeway, sizeof(telemetry_notification_leeway))) {
                /*
                 * By default, notify the user to collect the buffer when there is this much space left in the buffer.
                 */
                telemetry_notification_leeway = TELEMETRY_DEFAULT_NOTIFY_LEEWAY;
        }
        if (telemetry_notification_leeway >= telemetry_buffer.size) {
                printf("telemetry: nonsensical telemetry_notification_leeway boot-arg %d changed to %d\n",
                       telemetry_notification_leeway, TELEMETRY_DEFAULT_NOTIFY_LEEWAY);
                telemetry_notification_leeway = TELEMETRY_DEFAULT_NOTIFY_LEEWAY;
        }
        telemetry_buffer_notify_at = telemetry_buffer.size - telemetry_notification_leeway;

        if (!PE_parse_boot_argn("telemetry_sample_rate", &telemetry_sample_rate, sizeof(telemetry_sample_rate))) {
                telemetry_sample_rate = TELEMETRY_DEFAULT_SAMPLE_RATE;
        }

        /*
         * To enable telemetry for all tasks, include "telemetry_sample_all_tasks=1" in boot-args.
         */
        if (!PE_parse_boot_argn("telemetry_sample_all_tasks", &telemetry_sample_all_tasks, sizeof(telemetry_sample_all_tasks))) {

                telemetry_sample_all_tasks = TRUE;

        }

        kprintf("Telemetry: Sampling %stasks once per %u second%s\n",
                (telemetry_sample_all_tasks) ? "all " : "",
                telemetry_sample_rate, telemetry_sample_rate == 1 ? "" : "s");
}

/*
 * Enable or disable global microstackshots (ie telemetry_sample_all_tasks).
 *
 * enable_disable == 1: turn it on
 * enable_disable == 0: turn it off
 */
void
telemetry_global_ctl(int enable_disable) 
{
        if (enable_disable == 1) {
                telemetry_sample_all_tasks = TRUE;
        } else {
                telemetry_sample_all_tasks = FALSE;
        }
}

/*
 * Opt the given task into or out of the telemetry stream.
 *
 * Supported reasons (callers may use any or all of):
 *     TF_CPUMON_WARNING
 *     TF_WAKEMON_WARNING
 *
 * enable_disable == 1: turn it on
 * enable_disable == 0: turn it off
 */
void
telemetry_task_ctl(task_t task, uint32_t reasons, int enable_disable)
{
        task_lock(task);
        telemetry_task_ctl_locked(task, reasons, enable_disable);
        task_unlock(task);
}

void
telemetry_task_ctl_locked(task_t task, uint32_t reasons, int enable_disable)
{
        uint32_t origflags;

        assert((reasons != 0) && ((reasons | TF_TELEMETRY) == TF_TELEMETRY));

        task_lock_assert_owned(task);

        origflags = task->t_flags;

        if (enable_disable == 1) {
                task->t_flags |= reasons;
                if ((origflags & TF_TELEMETRY) == 0) {
                        OSIncrementAtomic(&telemetry_active_tasks);
#if TELEMETRY_DEBUG                     
                        printf("%s: telemetry OFF -> ON (%d active)\n", proc_name_address(task->bsd_info), telemetry_active_tasks);
#endif                  
                }
        } else {
                task->t_flags &= ~reasons;
                if (((origflags & TF_TELEMETRY) != 0) && ((task->t_flags & TF_TELEMETRY) == 0)) {
                        /*
                         * If this task went from having at least one telemetry bit to having none,
                         * the net change was to disable telemetry for the task.
                         */
                        OSDecrementAtomic(&telemetry_active_tasks);
#if TELEMETRY_DEBUG
                        printf("%s: telemetry ON -> OFF (%d active)\n", proc_name_address(task->bsd_info), telemetry_active_tasks);
#endif
                }
        }
}

/*
 * Enable the window_buffer, and do any associated setup.
 */
kern_return_t
telemetry_enable_window(void)
{
        kern_return_t ret = KERN_SUCCESS;
        vm_offset_t kern_buffer = 0;
        vm_size_t kern_buffer_size = TELEMETRY_DEFAULT_WINDOW_BUFFER_SIZE;

        /*
         * We have no guarantee we won't allocate the buffer, take
         * the lock, and then discover someone beat us to the punch,
         * but we would prefer to avoid blocking while holding the
         * lock.
         */
        ret = kmem_alloc(kernel_map, &kern_buffer, kern_buffer_size, VM_KERN_MEMORY_DIAG);

        TELEMETRY_LOCK();

        if (!window_buffer.buffer) {
                if (ret == KERN_SUCCESS) {
                        /* No existing buffer was found, so... */
                        window_buffer.end_point = 0;
                        window_buffer.current_position = 0;
        
                        /* Hand off the buffer, and... */
                        window_buffer.size = (uint32_t) kern_buffer_size;
                        window_buffer.buffer = kern_buffer;
                        kern_buffer = 0;
                        kern_buffer_size = 0;
                        bzero((void *) window_buffer.buffer, window_buffer.size);
        
                        /* Let the scheduler know it should drive windowed samples */
                        telemetry_window_enabled = TRUE;
                }
        } else {
                /* We already have a buffer, so we have "succeeded" */
                ret = KERN_SUCCESS;
        }

        TELEMETRY_UNLOCK();

        if (kern_buffer)
                kmem_free(kernel_map, kern_buffer, kern_buffer_size);

        return ret;
}

/*
 * Disable the window_buffer, and do any associated teardown.
 */
void
telemetry_disable_window(void)
{
        vm_offset_t kern_buffer = 0;
        vm_size_t kern_buffer_size = 0;

        TELEMETRY_LOCK();

        if (window_buffer.buffer) {
                /* We have a window buffer, so tear it down */
                telemetry_window_enabled = FALSE;
                kern_buffer = window_buffer.buffer;
                kern_buffer_size = window_buffer.size;
                window_buffer.buffer = 0;
                window_buffer.size = 0;
                window_buffer.current_position = 0;
                window_buffer.end_point = 0;
        }

        TELEMETRY_UNLOCK();

        if (kern_buffer)
                kmem_free(kernel_map, kern_buffer, kern_buffer_size);
}

/*
 * Determine if the current thread is eligible for telemetry:
 *
 * telemetry_sample_all_tasks: All threads are eligible. This takes precedence.
 * telemetry_active_tasks: Count of tasks opted in.
 * task->t_flags & TF_TELEMETRY: This task is opted in.
 */
static boolean_t
telemetry_is_active(thread_t thread)
{
        task_t task = thread->task;

        if (task == kernel_task) {
                /* Kernel threads never return to an AST boundary, and are ineligible */
                return FALSE;
        }

        if (telemetry_sample_all_tasks == TRUE) {
                return (TRUE);
        }

        if ((telemetry_active_tasks > 0) && ((thread->task->t_flags & TF_TELEMETRY) != 0)) {
                return (TRUE);
        }
 
        return (FALSE);
}

/*
 * Userland is arming a timer. If we are eligible for such a record,
 * sample now. No need to do this one at the AST because we're already at
 * a safe place in this system call.
 */
int telemetry_timer_event(__unused uint64_t deadline, __unused uint64_t interval, __unused uint64_t leeway)
{
        if (telemetry_needs_timer_arming_record == TRUE) {
                telemetry_needs_timer_arming_record = FALSE;
                telemetry_take_sample(current_thread(), kTimerArmingRecord | kUserMode, &telemetry_buffer);
        }

        return (0);
}

/*
 * Mark the current thread for an interrupt-based
 * telemetry record, to be sampled at the next AST boundary.
 */
void telemetry_mark_curthread(boolean_t interrupted_userspace)
{
        uint32_t ast_bits = 0;
        thread_t thread = current_thread();

        /*
         * If telemetry isn't active for this thread, return and try
         * again next time.
         */
        if (telemetry_is_active(thread) == FALSE) {
                return;
        }

        ast_bits |= (interrupted_userspace ? AST_TELEMETRY_USER : AST_TELEMETRY_KERNEL);

        if (telemetry_windowed_record) {
                ast_bits |= AST_TELEMETRY_WINDOWED;
        }

        telemetry_windowed_record = FALSE;
        telemetry_needs_record = FALSE;
        thread_ast_set(thread, ast_bits);
        ast_propagate(thread->ast);
}

void compute_telemetry(void *arg __unused)
{
        if (telemetry_sample_all_tasks || (telemetry_active_tasks > 0)) {
                if ((++telemetry_timestamp) % telemetry_sample_rate == 0) {
                        telemetry_needs_record = TRUE;
                        telemetry_needs_timer_arming_record = TRUE;
                }
        }
}

void compute_telemetry_windowed(void)
{
        if (telemetry_sample_all_tasks || (telemetry_active_tasks > 0)) {
                /*
                 * Due to the relationship between the two fields here,
                 * a request for a windowed record will "squash" a
                 * request for a regular interrupt record.  We hedge
                 * against this by doing a quick check for an existing
                 * request.  compute_telemetry doesn't hedge because
                 * a regular request cannot squash a windowed request
                 * (due to the implementation).
                 *
                 * If we really want to do this properly, we could make
                 * telemetry_needs_record a bitfield, and process one
                 * request per telemetry_mark_curthread... but that
                 * would be more expensive (atomics).  This should be
                 * robust enough for now (although it biases in favor
                 * of the regular records).
                 */
                if (!telemetry_needs_record) {
                        telemetry_needs_record = TRUE;
                        telemetry_windowed_record = TRUE;
                }
        }
}

/*
 * If userland has registered a port for telemetry notifications, send one now.
 */
static void
telemetry_notify_user(void)
{
        mach_port_t user_port;
        uint32_t        flags = 0;
        int                     error;

        error = host_get_telemetry_port(host_priv_self(), &user_port);
        if ((error != KERN_SUCCESS) || !IPC_PORT_VALID(user_port)) {
                return;
        }

        telemetry_notification(user_port, flags);
}

void telemetry_ast(thread_t thread, boolean_t interrupted_userspace, boolean_t is_windowed)
{
        uint8_t microsnapshot_flags = kInterruptRecord;

        if (interrupted_userspace)
                microsnapshot_flags |= kUserMode;

        if (is_windowed) {
                telemetry_take_sample(thread, microsnapshot_flags, &window_buffer);
        } else {
                telemetry_take_sample(thread, microsnapshot_flags, &telemetry_buffer);
        }
}

void telemetry_take_sample(thread_t thread, uint8_t microsnapshot_flags, struct micro_snapshot_buffer * current_buffer)
{
        task_t task;
        void *p;
        struct kperf_context ctx;
        struct callstack cs;
        uint32_t btcount, bti;
        struct micro_snapshot *msnap;
        struct task_snapshot *tsnap;
        struct thread_snapshot *thsnap;
        clock_sec_t secs;
        clock_usec_t usecs;
        vm_size_t framesize;
        uint32_t current_record_start;
        uint32_t tmp = 0;
        boolean_t notify = FALSE;

        if (thread == THREAD_NULL)
                return;

        task = thread->task;
        if ((task == TASK_NULL) || (task == kernel_task))
                return;

        /*
         * To avoid overloading the system with telemetry requests, make
         * sure we don't add more requests while existing ones are
         * in-flight.  Attempt this by checking if we can grab the lock.
         *
         * This concerns me a little; this working as intended is
         * contingent on the workload being done in the context of the
         * telemetry lock being the expensive part of telemetry.  This
         * includes populating the buffer and the client gathering it,
         * but excludes the copyin overhead.
         */
        if (!TELEMETRY_TRY_SPIN_LOCK())
                return;

        TELEMETRY_UNLOCK();

        /* telemetry_XXX accessed outside of lock for instrumentation only */
        /* TODO */
        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_STACKSHOT, MICROSTACKSHOT_RECORD) | DBG_FUNC_START, microsnapshot_flags, telemetry_bytes_since_last_mark, 0, 0, (&telemetry_buffer != current_buffer));

        p = get_bsdtask_info(task);

        ctx.cur_thread = thread;
        ctx.cur_pid = proc_pid(p);

        /*
         * Gather up the data we'll need for this sample. The sample is written into the kernel
         * buffer with the global telemetry lock held -- so we must do our (possibly faulting)
         * copies from userland here, before taking the lock.
         */
        kperf_ucallstack_sample(&cs, &ctx);
        if (!(cs.flags & CALLSTACK_VALID))
                return;

        /*
         * Find the actual [slid] address of the shared cache's UUID, and copy it in from userland.
         */
        int                                                     shared_cache_uuid_valid = 0;
        uint64_t                                        shared_cache_base_address;
        struct _dyld_cache_header       shared_cache_header;
        uint64_t                                        shared_cache_slide;

        /*
         * Don't copy in the entire shared cache header; we only need the UUID. Calculate the
         * offset of that one field.
         */
        int sc_header_uuid_offset = (char *)&shared_cache_header.uuid - (char *)&shared_cache_header;
        vm_shared_region_t sr = vm_shared_region_get(task);
        if (sr != NULL) {
                if ((vm_shared_region_start_address(sr, &shared_cache_base_address) == KERN_SUCCESS) &&
                        (copyin(shared_cache_base_address + sc_header_uuid_offset, (char *)&shared_cache_header.uuid,
                    sizeof (shared_cache_header.uuid)) == 0)) {
                        shared_cache_uuid_valid = 1;
                        shared_cache_slide = vm_shared_region_get_slide(sr);
                }
                // vm_shared_region_get() gave us a reference on the shared region.
                vm_shared_region_deallocate(sr);
        }

        /*
         * Retrieve the array of UUID's for binaries used by this task.
         * We reach down into DYLD's data structures to find the array.
         *
         * XXX - make this common with kdp?
         */
        uint32_t                        uuid_info_count = 0;
        mach_vm_address_t       uuid_info_addr = 0;
        if (task_has_64BitAddr(task)) {
                struct user64_dyld_all_image_infos task_image_infos;
                if (copyin(task->all_image_info_addr, (char *)&task_image_infos, sizeof(task_image_infos)) == 0) {
                        uuid_info_count = (uint32_t)task_image_infos.uuidArrayCount;
                        uuid_info_addr = task_image_infos.uuidArray;
                }
        } else {
                struct user32_dyld_all_image_infos task_image_infos;
                if (copyin(task->all_image_info_addr, (char *)&task_image_infos, sizeof(task_image_infos)) == 0) {
                        uuid_info_count = task_image_infos.uuidArrayCount;
                        uuid_info_addr = task_image_infos.uuidArray;
                }
        }

        /*
         * If we get a NULL uuid_info_addr (which can happen when we catch dyld in the middle of updating
         * this data structure), we zero the uuid_info_count so that we won't even try to save load info
         * for this task.
         */
        if (!uuid_info_addr) {
                uuid_info_count = 0;
        }

        /*
         * Don't copy in an unbounded amount of memory. The main binary and interesting
         * non-shared-cache libraries should be in the first few images.
         */
        if (uuid_info_count > TELEMETRY_MAX_UUID_COUNT) {
                uuid_info_count = TELEMETRY_MAX_UUID_COUNT;
        }

        uint32_t uuid_info_size = (uint32_t)(task_has_64BitAddr(thread->task) ? sizeof(struct user64_dyld_uuid_info) : sizeof(struct user32_dyld_uuid_info));
        uint32_t uuid_info_array_size = uuid_info_count * uuid_info_size;
        char     *uuid_info_array = NULL;

        if (uuid_info_count > 0) {
                if ((uuid_info_array = (char *)kalloc(uuid_info_array_size)) == NULL) {
                        return;
                }

                /*
                 * Copy in the UUID info array.
                 * It may be nonresident, in which case just fix up nloadinfos to 0 in the task snapshot.
                 */
                if (copyin(uuid_info_addr, uuid_info_array, uuid_info_array_size) != 0) {
                        kfree(uuid_info_array, uuid_info_array_size);
                        uuid_info_array = NULL;
                        uuid_info_array_size = 0;
                }
        }

        /*
         * Look for a dispatch queue serial number, and copy it in from userland if present.
         */
        uint64_t dqserialnum = 0;
        int              dqserialnum_valid = 0;

        uint64_t dqkeyaddr = thread_dispatchqaddr(thread);
        if (dqkeyaddr != 0) {
                uint64_t dqaddr = 0;
                uint64_t dq_serialno_offset = get_dispatchqueue_serialno_offset_from_proc(task->bsd_info);
                if ((copyin(dqkeyaddr, (char *)&dqaddr, (task_has_64BitAddr(task) ? 8 : 4)) == 0) &&
                    (dqaddr != 0) && (dq_serialno_offset != 0)) {
                        uint64_t dqserialnumaddr = dqaddr + dq_serialno_offset;
                        if (copyin(dqserialnumaddr, (char *)&dqserialnum, (task_has_64BitAddr(task) ? 8 : 4)) == 0) {
                                dqserialnum_valid = 1;
                        }
                }
        }

        clock_get_calendar_microtime(&secs, &usecs);

        TELEMETRY_LOCK();

        /*
         * For the benefit of the window buffer; if our buffer is not backed by anything,
         * then we cannot take the sample.  Meant to allow us to deallocate the window
         * buffer if it is disabled.
         */
        if (!current_buffer->buffer)
                goto cancel_sample;

        /*
         * We do the bulk of the operation under the telemetry lock, on assumption that
         * any page faults during execution will not cause another AST_TELEMETRY_ALL
         * to deadlock; they will just block until we finish. This makes it easier
         * to copy into the buffer directly. As soon as we unlock, userspace can copy
         * out of our buffer.
         */

copytobuffer:

        current_record_start = current_buffer->current_position;

        if ((current_buffer->size - current_buffer->current_position) < sizeof(struct micro_snapshot)) {
                /*
                 * We can't fit a record in the space available, so wrap around to the beginning.
                 * Save the current position as the known end point of valid data.
                 */
                current_buffer->end_point = current_record_start;
                current_buffer->current_position = 0;
                if (current_record_start == 0) {
                        /* This sample is too large to fit in the buffer even when we started at 0, so skip it */
                        goto cancel_sample;
                }
                goto copytobuffer;
        }

        msnap = (struct micro_snapshot *)(uintptr_t)(current_buffer->buffer + current_buffer->current_position);
        msnap->snapshot_magic = STACKSHOT_MICRO_SNAPSHOT_MAGIC;
        msnap->ms_flags = microsnapshot_flags;
        msnap->ms_opaque_flags = 0; /* namespace managed by userspace */
        msnap->ms_cpu = 0; /* XXX - does this field make sense for a micro-stackshot? */
        msnap->ms_time = secs;
        msnap->ms_time_microsecs = usecs;

        current_buffer->current_position += sizeof(struct micro_snapshot);

        if ((current_buffer->size - current_buffer->current_position) < sizeof(struct task_snapshot)) {
                current_buffer->end_point = current_record_start;
                current_buffer->current_position = 0;
                if (current_record_start == 0) {
                        /* This sample is too large to fit in the buffer even when we started at 0, so skip it */
                        goto cancel_sample;
                }
                goto copytobuffer;
        }

        tsnap = (struct task_snapshot *)(uintptr_t)(current_buffer->buffer + current_buffer->current_position);
        bzero(tsnap, sizeof(*tsnap));
        tsnap->snapshot_magic = STACKSHOT_TASK_SNAPSHOT_MAGIC;
        tsnap->pid = proc_pid(p);
        tsnap->uniqueid = proc_uniqueid(p);
        tsnap->user_time_in_terminated_threads = task->total_user_time;
        tsnap->system_time_in_terminated_threads = task->total_system_time;
        tsnap->suspend_count = task->suspend_count;
        tsnap->task_size = pmap_resident_count(task->map->pmap);
        tsnap->faults = task->faults;
        tsnap->pageins = task->pageins;
        tsnap->cow_faults = task->cow_faults;
        /*
         * The throttling counters are maintained as 64-bit counters in the proc
         * structure. However, we reserve 32-bits (each) for them in the task_snapshot
         * struct to save space and since we do not expect them to overflow 32-bits. If we
         * find these values overflowing in the future, the fix would be to simply 
         * upgrade these counters to 64-bit in the task_snapshot struct
         */
        tsnap->was_throttled = (uint32_t) proc_was_throttled(p);
        tsnap->did_throttle = (uint32_t) proc_did_throttle(p);
        
        if (task->t_flags & TF_TELEMETRY) {
                tsnap->ss_flags |= kTaskRsrcFlagged;
        }

        if (task->effective_policy.darwinbg == 1) {
                tsnap->ss_flags |= kTaskDarwinBG;
        }

        proc_get_darwinbgstate(task, &tmp);

        if (task->requested_policy.t_role == TASK_FOREGROUND_APPLICATION) {
                tsnap->ss_flags |= kTaskIsForeground;
        }

        if (tmp & PROC_FLAG_ADAPTIVE_IMPORTANT) {
                tsnap->ss_flags |= kTaskIsBoosted;
        }

        if (tmp & PROC_FLAG_SUPPRESSED) {
                tsnap->ss_flags |= kTaskIsSuppressed;
        }

        tsnap->latency_qos = task_grab_latency_qos(task);

        strlcpy(tsnap->p_comm, proc_name_address(p), sizeof(tsnap->p_comm));
        if (task_has_64BitAddr(thread->task)) {
                tsnap->ss_flags |= kUser64_p;
        }

        if (shared_cache_uuid_valid) {
                tsnap->shared_cache_slide = shared_cache_slide;
                bcopy(shared_cache_header.uuid, tsnap->shared_cache_identifier, sizeof (shared_cache_header.uuid));
        }

        current_buffer->current_position += sizeof(struct task_snapshot);

        /*
         * Directly after the task snapshot, place the array of UUID's corresponding to the binaries
         * used by this task.
         */
        if ((current_buffer->size - current_buffer->current_position) < uuid_info_array_size) {
                current_buffer->end_point = current_record_start;
                current_buffer->current_position = 0;
                if (current_record_start == 0) {
                        /* This sample is too large to fit in the buffer even when we started at 0, so skip it */
                        goto cancel_sample;
                }
                goto copytobuffer;
        }

        /*
         * Copy the UUID info array into our sample.
         */
        if (uuid_info_array_size > 0) {
                bcopy(uuid_info_array, (char *)(current_buffer->buffer + current_buffer->current_position), uuid_info_array_size);
                tsnap->nloadinfos = uuid_info_count;
        }

        current_buffer->current_position += uuid_info_array_size;

        /*
         * After the task snapshot & list of binary UUIDs, we place a thread snapshot.
         */

        if ((current_buffer->size - current_buffer->current_position) < sizeof(struct thread_snapshot)) {
                /* wrap and overwrite */
                current_buffer->end_point = current_record_start;               
                current_buffer->current_position = 0;
                if (current_record_start == 0) {
                        /* This sample is too large to fit in the buffer even when we started at 0, so skip it */
                        goto cancel_sample;
                }
                goto copytobuffer;
        }

        thsnap = (struct thread_snapshot *)(uintptr_t)(current_buffer->buffer + current_buffer->current_position);
        bzero(thsnap, sizeof(*thsnap));

        thsnap->snapshot_magic = STACKSHOT_THREAD_SNAPSHOT_MAGIC;
        thsnap->thread_id = thread_tid(thread);
        thsnap->state = thread->state;
        thsnap->priority = thread->base_pri;
        thsnap->sched_pri = thread->sched_pri;
        thsnap->sched_flags = thread->sched_flags;
        thsnap->ss_flags |= kStacksPCOnly;
        thsnap->ts_qos = thread->effective_policy.thep_qos;
        thsnap->ts_rqos = thread->requested_policy.thrp_qos;
        thsnap->ts_rqos_override = thread->requested_policy.thrp_qos_override;

        if (thread->effective_policy.darwinbg) {
                thsnap->ss_flags |= kThreadDarwinBG;
        }

        thsnap->user_time = timer_grab(&thread->user_timer);

        uint64_t tval = timer_grab(&thread->system_timer);

        if (thread->precise_user_kernel_time) {
                thsnap->system_time = tval;
        } else {
                thsnap->user_time += tval;
                thsnap->system_time = 0;
        }

        current_buffer->current_position += sizeof(struct thread_snapshot);

        /*
         * If this thread has a dispatch queue serial number, include it here.
         */
        if (dqserialnum_valid) {
                if ((current_buffer->size - current_buffer->current_position) < sizeof(dqserialnum)) {
                        /* wrap and overwrite */
                        current_buffer->end_point = current_record_start;               
                        current_buffer->current_position = 0;
                        if (current_record_start == 0) {
                                /* This sample is too large to fit in the buffer even when we started at 0, so skip it */
                                goto cancel_sample;
                        }
                        goto copytobuffer;
                }

                thsnap->ss_flags |= kHasDispatchSerial;
                bcopy(&dqserialnum, (char *)current_buffer->buffer + current_buffer->current_position, sizeof (dqserialnum));
                current_buffer->current_position += sizeof (dqserialnum);
        }

        if (task_has_64BitAddr(task)) {
                framesize = 8;
                thsnap->ss_flags |= kUser64_p;
        } else {
                framesize = 4;
        }

        btcount = cs.nframes;

        /*
         * If we can't fit this entire stacktrace then cancel this record, wrap to the beginning,
         * and start again there so that we always store a full record.
         */
        if ((current_buffer->size - current_buffer->current_position)/framesize < btcount) {
                current_buffer->end_point = current_record_start;
                current_buffer->current_position = 0;
                if (current_record_start == 0) {
                        /* This sample is too large to fit in the buffer even when we started at 0, so skip it */
                        goto cancel_sample;
                }
                goto copytobuffer;
        }

        for (bti=0; bti < btcount; bti++, current_buffer->current_position += framesize) {
                if (framesize == 8) {
                        *(uint64_t *)(uintptr_t)(current_buffer->buffer + current_buffer->current_position) = cs.frames[bti];
                } else {
                        *(uint32_t *)(uintptr_t)(current_buffer->buffer + current_buffer->current_position) = (uint32_t)cs.frames[bti];
                }
        }

        if (current_buffer->end_point < current_buffer->current_position) {
                /*
                 * Each time the cursor wraps around to the beginning, we leave a
                 * differing amount of unused space at the end of the buffer. Make
                 * sure the cursor pushes the end point in case we're making use of
                 * more of the buffer than we did the last time we wrapped.
                 */
                current_buffer->end_point = current_buffer->current_position;
        }

        thsnap->nuser_frames = btcount;

        /*
         * Now THIS is a hack.
         */
        if (current_buffer == &telemetry_buffer) {
                telemetry_bytes_since_last_mark += (current_buffer->current_position - current_record_start);
                if (telemetry_bytes_since_last_mark > telemetry_buffer_notify_at) {
                        notify = TRUE;
                }
        }

cancel_sample:

        TELEMETRY_UNLOCK();

        /* TODO */
        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_STACKSHOT, MICROSTACKSHOT_RECORD) | DBG_FUNC_END, notify, telemetry_bytes_since_last_mark, current_buffer->current_position, current_buffer->end_point, (&telemetry_buffer != current_buffer));

        if (notify) {
                telemetry_notify_user();
        }

        if (uuid_info_array != NULL) {
                kfree(uuid_info_array, uuid_info_array_size);
        }
}

#if TELEMETRY_DEBUG
static void
log_telemetry_output(vm_offset_t buf, uint32_t pos, uint32_t sz)
{
        struct micro_snapshot *p;
        uint32_t offset;
        
        printf("Copying out %d bytes of telemetry at offset %d\n", sz, pos);

        buf += pos;

        /*
         * Find and log each timestamp in this chunk of buffer.
         */
        for (offset = 0; offset < sz; offset++) {
                p = (struct micro_snapshot *)(buf + offset);
                if (p->snapshot_magic == STACKSHOT_MICRO_SNAPSHOT_MAGIC) {
                        printf("telemetry timestamp: %lld\n", p->ms_time);
                }
        }
}
#endif

int telemetry_gather(user_addr_t buffer, uint32_t *length, boolean_t mark)
{
        return telemetry_buffer_gather(buffer, length, mark, &telemetry_buffer);
}

int telemetry_gather_windowed(user_addr_t buffer, uint32_t *length)
{
        return telemetry_buffer_gather(buffer, length, 0, &window_buffer);
}

int telemetry_buffer_gather(user_addr_t buffer, uint32_t *length, boolean_t mark, struct micro_snapshot_buffer * current_buffer)
{
        int result = 0;
        uint32_t oldest_record_offset;

        /* TODO */
        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_STACKSHOT, MICROSTACKSHOT_GATHER) | DBG_FUNC_START, mark, telemetry_bytes_since_last_mark, 0, 0, (&telemetry_buffer != current_buffer));

        TELEMETRY_LOCK();

        if (current_buffer->buffer == 0) {
                *length = 0;            
                goto out;
        }

        if (*length < current_buffer->size) {
                result = KERN_NO_SPACE;
                goto out;
        }

        /*
         * Copy the ring buffer out to userland in order sorted by time: least recent to most recent.
         * First, we need to search forward from the cursor to find the oldest record in our buffer.
         */
        oldest_record_offset = current_buffer->current_position;
        do {
                if (((oldest_record_offset + sizeof(uint32_t)) > current_buffer->size) ||
                    ((oldest_record_offset + sizeof(uint32_t)) > current_buffer->end_point)) {

                        if (*(uint32_t *)(uintptr_t)(current_buffer->buffer) == 0) {
                                /*
                                 * There is no magic number at the start of the buffer, which means
                                 * it's empty; nothing to see here yet.
                                 */
                                *length = 0;
                                goto out;
                        }
                        /*
                         * We've looked through the end of the active buffer without finding a valid
                         * record; that means all valid records are in a single chunk, beginning at
                         * the very start of the buffer.
                         */

                        oldest_record_offset = 0;
                        assert(*(uint32_t *)(uintptr_t)(current_buffer->buffer) == STACKSHOT_MICRO_SNAPSHOT_MAGIC);
                        break;
                }

                if (*(uint32_t *)(uintptr_t)(current_buffer->buffer + oldest_record_offset) == STACKSHOT_MICRO_SNAPSHOT_MAGIC)
                        break;

                /*
                 * There are no alignment guarantees for micro-stackshot records, so we must search at each
                 * byte offset.
                 */
                oldest_record_offset++;
        } while (oldest_record_offset != current_buffer->current_position);

        /*
         * If needed, copyout in two chunks: from the oldest record to the end of the buffer, and then
         * from the beginning of the buffer up to the current position.
         */
        if (oldest_record_offset != 0) {
#if TELEMETRY_DEBUG
                log_telemetry_output(current_buffer->buffer, oldest_record_offset,
                                     current_buffer->end_point - oldest_record_offset);
#endif
                if ((result = copyout((void *)(current_buffer->buffer + oldest_record_offset), buffer,
                    current_buffer->end_point - oldest_record_offset)) != 0) {
                        *length = 0;
                        goto out;
                }
                *length = current_buffer->end_point - oldest_record_offset;
        } else {
                *length = 0;
        }

#if TELEMETRY_DEBUG
        log_telemetry_output(current_buffer->buffer, 0, current_buffer->current_position);
#endif
        if ((result = copyout((void *)current_buffer->buffer, buffer + *length,
            current_buffer->current_position)) != 0) {
                *length = 0;
                goto out;
        }
        *length += (uint32_t)current_buffer->current_position;

out:

        if (mark && (*length > 0)) {
                telemetry_bytes_since_last_mark = 0;
        }

        TELEMETRY_UNLOCK();

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_STACKSHOT, MICROSTACKSHOT_GATHER) | DBG_FUNC_END, current_buffer->current_position, *length, current_buffer->end_point, 0, (&telemetry_buffer != current_buffer));

        return (result);
}

/************************/
/* BOOT PROFILE SUPPORT */
/************************/
/*
 * Boot Profiling
 *
 * The boot-profiling support is a mechanism to sample activity happening on the
 * system during boot. This mechanism sets up a periodic timer and on every timer fire,
 * captures a full backtrace into the boot profiling buffer. This buffer can be pulled
 * out and analyzed from user-space. It is turned on using the following boot-args:
 * "bootprofile_buffer_size" specifies the size of the boot profile buffer
 * "bootprofile_interval_ms" specifies the interval for the profiling timer
 *
 * Process Specific Boot Profiling
 *
 * The boot-arg "bootprofile_proc_name" can be used to specify a certain
 * process that needs to profiled during boot. Setting this boot-arg changes
 * the way stackshots are captured. At every timer fire, the code looks at the
 * currently running process and takes a stackshot only if the requested process
 * is on-core (which makes it unsuitable for MP systems).
 *
 * Trigger Events
 *
 * The boot-arg "bootprofile_type=boot" starts the timer during early boot. Using
 * "wake" starts the timer at AP wake from suspend-to-RAM.
 */

#define BOOTPROFILE_MAX_BUFFER_SIZE (64*1024*1024) /* see also COPYSIZELIMIT_PANIC */

vm_offset_t                     bootprofile_buffer = 0;
uint32_t                        bootprofile_buffer_size = 0;
uint32_t                        bootprofile_buffer_current_position = 0;
uint32_t                        bootprofile_interval_ms = 0;
uint64_t                        bootprofile_interval_abs = 0;
uint64_t                        bootprofile_next_deadline = 0;
uint32_t                        bootprofile_all_procs = 0;
char                            bootprofile_proc_name[17];

lck_grp_t               bootprofile_lck_grp;
lck_mtx_t               bootprofile_mtx;

enum {
        kBootProfileDisabled = 0,
        kBootProfileStartTimerAtBoot,
        kBootProfileStartTimerAtWake
} bootprofile_type = kBootProfileDisabled;


static timer_call_data_t        bootprofile_timer_call_entry;

#define BOOTPROFILE_LOCK() do { lck_mtx_lock(&bootprofile_mtx); } while(0)
#define BOOTPROFILE_TRY_SPIN_LOCK() lck_mtx_try_lock_spin(&bootprofile_mtx)
#define BOOTPROFILE_UNLOCK() do { lck_mtx_unlock(&bootprofile_mtx); } while(0)

static void bootprofile_timer_call(
        timer_call_param_t      param0,
        timer_call_param_t      param1);

extern int  
stack_snapshot_from_kernel(int pid, void *buf, uint32_t size, uint32_t flags, unsigned *retbytes);

void bootprofile_init(void)
{
        kern_return_t ret;
        char type[32];

        lck_grp_init(&bootprofile_lck_grp, "bootprofile group", LCK_GRP_ATTR_NULL);
        lck_mtx_init(&bootprofile_mtx, &bootprofile_lck_grp, LCK_ATTR_NULL);

        if (!PE_parse_boot_argn("bootprofile_buffer_size", &bootprofile_buffer_size, sizeof(bootprofile_buffer_size))) {
                bootprofile_buffer_size = 0;
        }

        if (bootprofile_buffer_size > BOOTPROFILE_MAX_BUFFER_SIZE)
                bootprofile_buffer_size = BOOTPROFILE_MAX_BUFFER_SIZE;

        if (!PE_parse_boot_argn("bootprofile_interval_ms", &bootprofile_interval_ms, sizeof(bootprofile_interval_ms))) {
                bootprofile_interval_ms = 0;
        }

        if (!PE_parse_boot_argn("bootprofile_proc_name", &bootprofile_proc_name, sizeof(bootprofile_proc_name))) {
                bootprofile_all_procs = 1;
                bootprofile_proc_name[0] = '\0';
        }

        if (PE_parse_boot_argn("bootprofile_type", type, sizeof(type))) {
                if (0 == strcmp(type, "boot")) {
                        bootprofile_type = kBootProfileStartTimerAtBoot;
                } else if (0 == strcmp(type, "wake")) {
                        bootprofile_type = kBootProfileStartTimerAtWake;                        
                } else {
                        bootprofile_type = kBootProfileDisabled;
                }
        } else {
                bootprofile_type = kBootProfileDisabled;
        }

        clock_interval_to_absolutetime_interval(bootprofile_interval_ms, NSEC_PER_MSEC, &bootprofile_interval_abs);

        /* Both boot args must be set to enable */
        if ((bootprofile_type == kBootProfileDisabled) || (bootprofile_buffer_size == 0) || (bootprofile_interval_abs == 0)) {
                return;
        }

        ret = kmem_alloc(kernel_map, &bootprofile_buffer, bootprofile_buffer_size, VM_KERN_MEMORY_DIAG);
        if (ret != KERN_SUCCESS) {
                kprintf("Boot profile: Allocation failed: %d\n", ret);
                return;
        }
        bzero((void *) bootprofile_buffer, bootprofile_buffer_size);

        kprintf("Boot profile: Sampling %s once per %u ms at %s\n", bootprofile_all_procs ? "all procs" : bootprofile_proc_name,  bootprofile_interval_ms,
                        bootprofile_type == kBootProfileStartTimerAtBoot ? "boot" : (bootprofile_type == kBootProfileStartTimerAtWake ? "wake" : "unknown"));

        timer_call_setup(&bootprofile_timer_call_entry,
                                         bootprofile_timer_call,
                                         NULL);

        if (bootprofile_type == kBootProfileStartTimerAtBoot) {
                bootprofile_next_deadline = mach_absolute_time() + bootprofile_interval_abs;
                timer_call_enter_with_leeway(&bootprofile_timer_call_entry,
                                                                         NULL,
                                                                         bootprofile_next_deadline,
                                                                         0,
                                                                         TIMER_CALL_SYS_NORMAL,
                                                                         FALSE);
        }
}

void
bootprofile_wake_from_sleep(void)
{
        if (bootprofile_type == kBootProfileStartTimerAtWake) {
                bootprofile_next_deadline = mach_absolute_time() + bootprofile_interval_abs;
                timer_call_enter_with_leeway(&bootprofile_timer_call_entry,
                                                                         NULL,
                                                                         bootprofile_next_deadline,
                                                                         0,
                                                                         TIMER_CALL_SYS_NORMAL,
                                                                         FALSE);
        }
}


static void bootprofile_timer_call(
        timer_call_param_t      param0 __unused,
        timer_call_param_t      param1 __unused)
{
        unsigned retbytes = 0;
        int pid_to_profile = -1;

        if (!BOOTPROFILE_TRY_SPIN_LOCK()) {
                goto reprogram;
        }

        /* Check if process-specific boot profiling is turned on */
        if (!bootprofile_all_procs) {
                /*
                 * Since boot profiling initializes really early in boot, it is
                 * possible that at this point, the task/proc is not initialized.
                 * Nothing to do in that case.
                 */

                if ((current_task() != NULL) && (current_task()->bsd_info != NULL) &&
                    (0 == strncmp(bootprofile_proc_name, proc_name_address(current_task()->bsd_info), 17))) {
                        pid_to_profile = proc_selfpid();
                }
                else {
                        /*
                         * Process-specific boot profiling requested but the on-core process is
                         * something else. Nothing to do here.
                         */
                        BOOTPROFILE_UNLOCK();
                        goto reprogram;
                }
        }

        /* initiate a stackshot with whatever portion of the buffer is left */
        if (bootprofile_buffer_current_position < bootprofile_buffer_size) {
                stack_snapshot_from_kernel(
                        pid_to_profile,
                        (void *)(bootprofile_buffer + bootprofile_buffer_current_position),
                        bootprofile_buffer_size - bootprofile_buffer_current_position,
                        STACKSHOT_SAVE_LOADINFO | STACKSHOT_SAVE_KEXT_LOADINFO | STACKSHOT_GET_GLOBAL_MEM_STATS,
            &retbytes
                        );

                bootprofile_buffer_current_position += retbytes;
        }

        BOOTPROFILE_UNLOCK();

        /* If we didn't get any data or have run out of buffer space, stop profiling */
        if ((retbytes == 0) || (bootprofile_buffer_current_position == bootprofile_buffer_size)) {
                return;
        }


reprogram:
        /* If the user gathered the buffer, no need to keep profiling */
        if (bootprofile_interval_abs == 0) {
                return;
        }

        clock_deadline_for_periodic_event(bootprofile_interval_abs,
                                                                          mach_absolute_time(),
                                                                          &bootprofile_next_deadline);
        timer_call_enter_with_leeway(&bootprofile_timer_call_entry,
                                                                 NULL,
                                                                 bootprofile_next_deadline,
                                                                 0,
                                                                 TIMER_CALL_SYS_NORMAL,
                                                                 FALSE);
}

int bootprofile_gather(user_addr_t buffer, uint32_t *length)
{
        int result = 0;

        BOOTPROFILE_LOCK();

        if (bootprofile_buffer == 0) {
                *length = 0;            
                goto out;
        }

        if (*length < bootprofile_buffer_current_position) {
                result = KERN_NO_SPACE;
                goto out;
        }

        if ((result = copyout((void *)bootprofile_buffer, buffer,
            bootprofile_buffer_current_position)) != 0) {
                *length = 0;
                goto out;
        }
        *length = bootprofile_buffer_current_position;

        /* cancel future timers */
        bootprofile_interval_abs = 0;

out:

        BOOTPROFILE_UNLOCK();

        return (result);
}