[apple/xnu.git] / bsd / dev / dtrace / fasttrap.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * #pragma ident        "@(#)fasttrap.c 1.26    08/04/21 SMI"
 */

#include <sys/types.h>
#include <sys/time.h>

#include <sys/errno.h>
#include <sys/stat.h>
#include <sys/conf.h>
#include <sys/systm.h>
#include <sys/kauth.h>
#include <sys/utfconv.h>

#include <sys/fasttrap.h>
#include <sys/fasttrap_impl.h>
#include <sys/fasttrap_isa.h>
#include <sys/dtrace.h>
#include <sys/dtrace_impl.h>
#include <sys/proc.h>

#include <miscfs/devfs/devfs.h>
#include <sys/proc_internal.h>
#include <sys/dtrace_glue.h>
#include <sys/dtrace_ptss.h>

#include <kern/zalloc.h>

/* Solaris proc_t is the struct. Darwin's proc_t is a pointer to it. */
#define proc_t struct proc /* Steer clear of the Darwin typedef for proc_t */

__private_extern__
void
qsort(void *a, size_t n, size_t es, int (*cmp)(const void *, const void *));

/*
 * User-Land Trap-Based Tracing
 * ----------------------------
 *
 * The fasttrap provider allows DTrace consumers to instrument any user-level
 * instruction to gather data; this includes probes with semantic
 * signifigance like entry and return as well as simple offsets into the
 * function. While the specific techniques used are very ISA specific, the
 * methodology is generalizable to any architecture.
 *
 *
 * The General Methodology
 * -----------------------
 *
 * With the primary goal of tracing every user-land instruction and the
 * limitation that we can't trust user space so don't want to rely on much
 * information there, we begin by replacing the instructions we want to trace
 * with trap instructions. Each instruction we overwrite is saved into a hash
 * table keyed by process ID and pc address. When we enter the kernel due to
 * this trap instruction, we need the effects of the replaced instruction to
 * appear to have occurred before we proceed with the user thread's
 * execution.
 *
 * Each user level thread is represented by a ulwp_t structure which is
 * always easily accessible through a register. The most basic way to produce
 * the effects of the instruction we replaced is to copy that instruction out
 * to a bit of scratch space reserved in the user thread's ulwp_t structure
 * (a sort of kernel-private thread local storage), set the PC to that
 * scratch space and single step. When we reenter the kernel after single
 * stepping the instruction we must then adjust the PC to point to what would
 * normally be the next instruction. Of course, special care must be taken
 * for branches and jumps, but these represent such a small fraction of any
 * instruction set that writing the code to emulate these in the kernel is
 * not too difficult.
 *
 * Return probes may require several tracepoints to trace every return site,
 * and, conversely, each tracepoint may activate several probes (the entry
 * and offset 0 probes, for example). To solve this muliplexing problem,
 * tracepoints contain lists of probes to activate and probes contain lists
 * of tracepoints to enable. If a probe is activated, it adds its ID to
 * existing tracepoints or creates new ones as necessary.
 *
 * Most probes are activated _before_ the instruction is executed, but return
 * probes are activated _after_ the effects of the last instruction of the
 * function are visible. Return probes must be fired _after_ we have
 * single-stepped the instruction whereas all other probes are fired
 * beforehand.
 *
 *
 * Lock Ordering
 * -------------
 *
 * The lock ordering below -- both internally and with respect to the DTrace
 * framework -- is a little tricky and bears some explanation. Each provider
 * has a lock (ftp_mtx) that protects its members including reference counts
 * for enabled probes (ftp_rcount), consumers actively creating probes
 * (ftp_ccount) and USDT consumers (ftp_mcount); all three prevent a provider
 * from being freed. A provider is looked up by taking the bucket lock for the
 * provider hash table, and is returned with its lock held. The provider lock
 * may be taken in functions invoked by the DTrace framework, but may not be
 * held while calling functions in the DTrace framework.
 *
 * To ensure consistency over multiple calls to the DTrace framework, the
 * creation lock (ftp_cmtx) should be held. Naturally, the creation lock may
 * not be taken when holding the provider lock as that would create a cyclic
 * lock ordering. In situations where one would naturally take the provider
 * lock and then the creation lock, we instead up a reference count to prevent
 * the provider from disappearing, drop the provider lock, and acquire the
 * creation lock.
 *
 * Briefly:
 *      bucket lock before provider lock
 *      DTrace before provider lock
 *      creation lock before DTrace
 *      never hold the provider lock and creation lock simultaneously
 */

static dev_info_t *fasttrap_devi;
static dtrace_meta_provider_id_t fasttrap_meta_id;

static thread_call_t fasttrap_timeout;
static lck_mtx_t fasttrap_cleanup_mtx;
static uint_t fasttrap_cleanup_work;

/*
 * Generation count on modifications to the global tracepoint lookup table.
 */
static volatile uint64_t fasttrap_mod_gen;

/*
 * APPLE NOTE: When the fasttrap provider is loaded, fasttrap_max is computed
 * base on system memory.  Each time a probe is created, fasttrap_total is
 * incremented by the number of tracepoints that may be associated with that
 * probe; fasttrap_total is capped at fasttrap_max.
 */

static uint32_t fasttrap_max;
static uint32_t fasttrap_total;


#define FASTTRAP_TPOINTS_DEFAULT_SIZE   0x4000
#define FASTTRAP_PROVIDERS_DEFAULT_SIZE 0x100
#define FASTTRAP_PROCS_DEFAULT_SIZE     0x100

fasttrap_hash_t                 fasttrap_tpoints;
static fasttrap_hash_t          fasttrap_provs;
static fasttrap_hash_t          fasttrap_procs;

static uint64_t                 fasttrap_pid_count;     /* pid ref count */
static lck_mtx_t                fasttrap_count_mtx;     /* lock on ref count */

#define FASTTRAP_ENABLE_FAIL    1
#define FASTTRAP_ENABLE_PARTIAL 2

static int fasttrap_tracepoint_enable(proc_t *, fasttrap_probe_t *, uint_t);
static void fasttrap_tracepoint_disable(proc_t *, fasttrap_probe_t *, uint_t);

static fasttrap_provider_t *fasttrap_provider_lookup(pid_t, fasttrap_provider_type_t, const char *,
    const dtrace_pattr_t *);
static void fasttrap_provider_retire(pid_t, const char *, int);
static void fasttrap_provider_free(fasttrap_provider_t *);

static fasttrap_proc_t *fasttrap_proc_lookup(pid_t);
static void fasttrap_proc_release(fasttrap_proc_t *);

#define FASTTRAP_PROVS_INDEX(pid, name) \
        ((fasttrap_hash_str(name) + (pid)) & fasttrap_provs.fth_mask)

#define FASTTRAP_PROCS_INDEX(pid) ((pid) & fasttrap_procs.fth_mask)

/*
 * APPLE NOTE: To save memory, some common memory allocations are given
 * a unique zone. For example, dtrace_probe_t is 72 bytes in size,
 * which means it would fall into the kalloc.128 bucket. With
 * 20k elements allocated, the space saved is substantial.
 */

struct zone *fasttrap_tracepoint_t_zone;

/*
 * APPLE NOTE: fasttrap_probe_t's are variable in size. Some quick profiling has shown
 * that the sweet spot for reducing memory footprint is covering the first
 * three sizes. Everything larger goes into the common pool.
 */
#define FASTTRAP_PROBE_T_ZONE_MAX_TRACEPOINTS 4

struct zone *fasttrap_probe_t_zones[FASTTRAP_PROBE_T_ZONE_MAX_TRACEPOINTS];

static const char *fasttrap_probe_t_zone_names[FASTTRAP_PROBE_T_ZONE_MAX_TRACEPOINTS] = {
        "",
        "dtrace.fasttrap_probe_t[1]",
        "dtrace.fasttrap_probe_t[2]",
        "dtrace.fasttrap_probe_t[3]"
};

/*
 * APPLE NOTE:  We have to manage locks explicitly
 */
lck_grp_t*                      fasttrap_lck_grp;
lck_grp_attr_t*                 fasttrap_lck_grp_attr;
lck_attr_t*                     fasttrap_lck_attr;

static int
fasttrap_highbit(ulong_t i)
{
        int h = 1;

        if (i == 0)
                return (0);
#ifdef _LP64
        if (i & 0xffffffff00000000ul) {
                h += 32; i >>= 32;
        }
#endif
        if (i & 0xffff0000) {
                h += 16; i >>= 16;
        }
        if (i & 0xff00) {
                h += 8; i >>= 8;
        }
        if (i & 0xf0) {
                h += 4; i >>= 4;
        }
        if (i & 0xc) {
                h += 2; i >>= 2;
        }
        if (i & 0x2) {
                h += 1;
        }
        return (h);
}

static uint_t
fasttrap_hash_str(const char *p)
{
        unsigned int g;
        uint_t hval = 0;

        while (*p) {
                hval = (hval << 4) + *p++;
                if ((g = (hval & 0xf0000000)) != 0)
                        hval ^= g >> 24;
                hval &= ~g;
        }
        return (hval);
}

/*
 * APPLE NOTE: fasttrap_sigtrap not implemented
 */
void
fasttrap_sigtrap(proc_t *p, uthread_t t, user_addr_t pc)
{
#pragma unused(p, t, pc)

#if !defined(__APPLE__)
        sigqueue_t *sqp = kmem_zalloc(sizeof (sigqueue_t), KM_SLEEP);

        sqp->sq_info.si_signo = SIGTRAP;
        sqp->sq_info.si_code = TRAP_DTRACE;
        sqp->sq_info.si_addr = (caddr_t)pc;

        mutex_enter(&p->p_lock);
        sigaddqa(p, t, sqp);
        mutex_exit(&p->p_lock);

        if (t != NULL)
                aston(t);
#endif /* __APPLE__ */

        printf("fasttrap_sigtrap called with no implementation.\n");
}

/*
 * This function ensures that no threads are actively using the memory
 * associated with probes that were formerly live.
 */
static void
fasttrap_mod_barrier(uint64_t gen)
{
        unsigned int i;

        if (gen < fasttrap_mod_gen)
                return;

        fasttrap_mod_gen++;

        for (i = 0; i < NCPU; i++) {
                lck_mtx_lock(&cpu_core[i].cpuc_pid_lock);
                lck_mtx_unlock(&cpu_core[i].cpuc_pid_lock);
        }
}

/*
 * This is the timeout's callback for cleaning up the providers and their
 * probes.
 */
/*ARGSUSED*/
static void
fasttrap_pid_cleanup_cb(void *ignored, void* ignored2)
{
#pragma unused(ignored, ignored2)
        fasttrap_provider_t **fpp, *fp;
        fasttrap_bucket_t *bucket;
        dtrace_provider_id_t provid;
        unsigned int i, later = 0;

        static volatile int in = 0;
        ASSERT(in == 0);
        in = 1;

        lck_mtx_lock(&fasttrap_cleanup_mtx);
        while (fasttrap_cleanup_work) {
                fasttrap_cleanup_work = 0;
                lck_mtx_unlock(&fasttrap_cleanup_mtx);

                later = 0;

                /*
                 * Iterate over all the providers trying to remove the marked
                 * ones. If a provider is marked but not retired, we just
                 * have to take a crack at removing it -- it's no big deal if
                 * we can't.
                 */
                for (i = 0; i < fasttrap_provs.fth_nent; i++) {
                        bucket = &fasttrap_provs.fth_table[i];
                        lck_mtx_lock(&bucket->ftb_mtx);
                        fpp = (fasttrap_provider_t **)&bucket->ftb_data;

                        while ((fp = *fpp) != NULL) {
                                if (!fp->ftp_marked) {
                                        fpp = &fp->ftp_next;
                                        continue;
                                }

                                lck_mtx_lock(&fp->ftp_mtx);

                                /*
                                 * If this provider has consumers actively
                                 * creating probes (ftp_ccount) or is a USDT
                                 * provider (ftp_mcount), we can't unregister
                                 * or even condense.
                                 */
                                if (fp->ftp_ccount != 0 ||
                                    fp->ftp_mcount != 0) {
                                        fp->ftp_marked = 0;
                                        lck_mtx_unlock(&fp->ftp_mtx);
                                        continue;
                                }

                                if (!fp->ftp_retired || fp->ftp_rcount != 0)
                                        fp->ftp_marked = 0;

                                lck_mtx_unlock(&fp->ftp_mtx);

                                /*
                                 * If we successfully unregister this
                                 * provider we can remove it from the hash
                                 * chain and free the memory. If our attempt
                                 * to unregister fails and this is a retired
                                 * provider, increment our flag to try again
                                 * pretty soon. If we've consumed more than
                                 * half of our total permitted number of
                                 * probes call dtrace_condense() to try to
                                 * clean out the unenabled probes.
                                 */
                                provid = fp->ftp_provid;
                                if (dtrace_unregister(provid) != 0) {
                                        if (fasttrap_total > fasttrap_max / 2)
                                                (void) dtrace_condense(provid);
                                        later += fp->ftp_marked;
                                        fpp = &fp->ftp_next;
                                } else {
                                        *fpp = fp->ftp_next;
                                        fasttrap_provider_free(fp);
                                }
                        }
                        lck_mtx_unlock(&bucket->ftb_mtx);
                }

                lck_mtx_lock(&fasttrap_cleanup_mtx);
        }

        ASSERT(fasttrap_timeout != 0);

        /*
         * APPLE NOTE: You must hold the fasttrap_cleanup_mtx to do this!
         */
        if (fasttrap_timeout != (thread_call_t)1)
                thread_call_free(fasttrap_timeout);

        /*
         * If we were unable to remove a retired provider, try again after
         * a second. This situation can occur in certain circumstances where
         * providers cannot be unregistered even though they have no probes
         * enabled because of an execution of dtrace -l or something similar.
         * If the timeout has been disabled (set to 1 because we're trying
         * to detach), we set fasttrap_cleanup_work to ensure that we'll
         * get a chance to do that work if and when the timeout is reenabled
         * (if detach fails).
         */
        if (later > 0 && fasttrap_timeout != (thread_call_t)1)
                /* The time value passed to dtrace_timeout is in nanos */
                fasttrap_timeout = dtrace_timeout(&fasttrap_pid_cleanup_cb, NULL, NANOSEC / SEC);
        else if (later > 0)
                fasttrap_cleanup_work = 1;
        else
                fasttrap_timeout = 0;

        lck_mtx_unlock(&fasttrap_cleanup_mtx);
        in = 0;
}

/*
 * Activates the asynchronous cleanup mechanism.
 */
static void
fasttrap_pid_cleanup(void)
{
        lck_mtx_lock(&fasttrap_cleanup_mtx);
        fasttrap_cleanup_work = 1;
        if (fasttrap_timeout == 0)
                fasttrap_timeout = dtrace_timeout(&fasttrap_pid_cleanup_cb, NULL, NANOSEC / MILLISEC);
        lck_mtx_unlock(&fasttrap_cleanup_mtx);
}

/*
 * This is called from cfork() via dtrace_fasttrap_fork(). The child
 * process's address space is a (roughly) a copy of the parent process's so
 * we have to remove all the instrumentation we had previously enabled in the
 * parent.
 */
static void
fasttrap_fork(proc_t *p, proc_t *cp)
{
        pid_t ppid = p->p_pid;
        unsigned int i;

        ASSERT(current_proc() == p);
        lck_mtx_assert(&p->p_dtrace_sprlock, LCK_MTX_ASSERT_OWNED);
        ASSERT(p->p_dtrace_count > 0);
        ASSERT(cp->p_dtrace_count == 0);

        /*
         * This would be simpler and faster if we maintained per-process
         * hash tables of enabled tracepoints. It could, however, potentially
         * slow down execution of a tracepoint since we'd need to go
         * through two levels of indirection. In the future, we should
         * consider either maintaining per-process ancillary lists of
         * enabled tracepoints or hanging a pointer to a per-process hash
         * table of enabled tracepoints off the proc structure.
         */

        /*
         * We don't have to worry about the child process disappearing
         * because we're in fork().
         */
        if (cp != sprlock(cp->p_pid)) {
                printf("fasttrap_fork: sprlock(%d) returned a differt proc\n", cp->p_pid);
                return;
        }
        proc_unlock(cp);

        /*
         * Iterate over every tracepoint looking for ones that belong to the
         * parent process, and remove each from the child process.
         */
        for (i = 0; i < fasttrap_tpoints.fth_nent; i++) {
                fasttrap_tracepoint_t *tp;
                fasttrap_bucket_t *bucket = &fasttrap_tpoints.fth_table[i];

                lck_mtx_lock(&bucket->ftb_mtx);
                for (tp = bucket->ftb_data; tp != NULL; tp = tp->ftt_next) {
                        if (tp->ftt_pid == ppid &&
                            tp->ftt_proc->ftpc_acount != 0) {
                                fasttrap_tracepoint_remove(cp, tp);

                                /*
                                 * The count of active providers can only be
                                 * decremented (i.e. to zero) during exec,
                                 * exit, and removal of a meta provider so it
                                 * should be impossible to drop the count
                                 * mid-fork.
                                 */
                                 ASSERT(tp->ftt_proc->ftpc_acount != 0);
                        }
                }
                lck_mtx_unlock(&bucket->ftb_mtx);
        }

        /*
         * Free any ptss pages/entries in the child.
         */
        dtrace_ptss_fork(p, cp);

        proc_lock(cp);
        sprunlock(cp);
}

/*
 * This is called from proc_exit() or from exec_common() if p_dtrace_probes
 * is set on the proc structure to indicate that there is a pid provider
 * associated with this process.
 */
static void
fasttrap_exec_exit(proc_t *p)
{
        ASSERT(p == current_proc());
        lck_mtx_assert(&p->p_mlock, LCK_MTX_ASSERT_OWNED);
        lck_mtx_assert(&p->p_dtrace_sprlock, LCK_MTX_ASSERT_NOTOWNED);


        /* APPLE NOTE: Okay, the locking here is really odd and needs some
         * explaining. This method is always called with the proc_lock held.
         * We must drop the proc_lock before calling fasttrap_provider_retire
         * to avoid a deadlock when it takes the bucket lock.
         * 
         * Next, the dtrace_ptss_exec_exit function requires the sprlock
         * be held, but not the proc_lock. 
         *
         * Finally, we must re-acquire the proc_lock
         */
        proc_unlock(p);

        /*
         * We clean up the pid provider for this process here; user-land
         * static probes are handled by the meta-provider remove entry point.
         */
        fasttrap_provider_retire(p->p_pid, FASTTRAP_PID_NAME, 0);

        /*
         * APPLE NOTE: We also need to remove any aliased providers.
         * XXX optimization: track which provider types are instantiated
         * and only retire as needed.
         */
        fasttrap_provider_retire(p->p_pid, FASTTRAP_OBJC_NAME, 0);
        fasttrap_provider_retire(p->p_pid, FASTTRAP_ONESHOT_NAME, 0);

        /*
         * This should be called after it is no longer possible for a user
         * thread to execute (potentially dtrace instrumented) instructions.
         */
        lck_mtx_lock(&p->p_dtrace_sprlock);
        dtrace_ptss_exec_exit(p);
        lck_mtx_unlock(&p->p_dtrace_sprlock);

        proc_lock(p);
}


/*ARGSUSED*/
static void
fasttrap_pid_provide(void *arg, const dtrace_probedesc_t *desc)
{
#pragma unused(arg, desc)
        /*
         * There are no "default" pid probes.
         */
}

static int
fasttrap_tracepoint_enable(proc_t *p, fasttrap_probe_t *probe, uint_t index)
{
        fasttrap_tracepoint_t *tp, *new_tp = NULL;
        fasttrap_bucket_t *bucket;
        fasttrap_id_t *id;
        pid_t pid;
        user_addr_t pc;

        ASSERT(index < probe->ftp_ntps);

        pid = probe->ftp_pid;
        pc = probe->ftp_tps[index].fit_tp->ftt_pc;
        id = &probe->ftp_tps[index].fit_id;

        ASSERT(probe->ftp_tps[index].fit_tp->ftt_pid == pid);

        //ASSERT(!(p->p_flag & SVFORK));

        /*
         * Before we make any modifications, make sure we've imposed a barrier
         * on the generation in which this probe was last modified.
         */
        fasttrap_mod_barrier(probe->ftp_gen);

        bucket = &fasttrap_tpoints.fth_table[FASTTRAP_TPOINTS_INDEX(pid, pc)];

        /*
         * If the tracepoint has already been enabled, just add our id to the
         * list of interested probes. This may be our second time through
         * this path in which case we'll have constructed the tracepoint we'd
         * like to install. If we can't find a match, and have an allocated
         * tracepoint ready to go, enable that one now.
         *
         * A tracepoint whose process is defunct is also considered defunct.
         */
again:
        lck_mtx_lock(&bucket->ftb_mtx);
        for (tp = bucket->ftb_data; tp != NULL; tp = tp->ftt_next) {
                /*
                 * Note that it's safe to access the active count on the
                 * associated proc structure because we know that at least one
                 * provider (this one) will still be around throughout this
                 * operation.
                 */
                if (tp->ftt_pid != pid || tp->ftt_pc != pc ||
                    tp->ftt_proc->ftpc_acount == 0)
                        continue;

                /*
                 * Now that we've found a matching tracepoint, it would be
                 * a decent idea to confirm that the tracepoint is still
                 * enabled and the trap instruction hasn't been overwritten.
                 * Since this is a little hairy, we'll punt for now.
                 */

                /*
                 * This can't be the first interested probe. We don't have
                 * to worry about another thread being in the midst of
                 * deleting this tracepoint (which would be the only valid
                 * reason for a tracepoint to have no interested probes)
                 * since we're holding P_PR_LOCK for this process.
                 */
                ASSERT(tp->ftt_ids != NULL || tp->ftt_retids != NULL);

                switch (id->fti_ptype) {
                case DTFTP_ENTRY:
                case DTFTP_OFFSETS:
                case DTFTP_IS_ENABLED:
                        id->fti_next = tp->ftt_ids;
                        dtrace_membar_producer();
                        tp->ftt_ids = id;
                        dtrace_membar_producer();
                        break;

                case DTFTP_RETURN:
                case DTFTP_POST_OFFSETS:
                        id->fti_next = tp->ftt_retids;
                        dtrace_membar_producer();
                        tp->ftt_retids = id;
                        dtrace_membar_producer();
                        break;

                default:
                        ASSERT(0);
                }

                lck_mtx_unlock(&bucket->ftb_mtx);

                if (new_tp != NULL) {
                        new_tp->ftt_ids = NULL;
                        new_tp->ftt_retids = NULL;
                }

                return (0);
        }

        /*
         * If we have a good tracepoint ready to go, install it now while
         * we have the lock held and no one can screw with us.
         */
        if (new_tp != NULL) {
                int rc = 0;

                new_tp->ftt_next = bucket->ftb_data;
                dtrace_membar_producer();
                bucket->ftb_data = new_tp;
                dtrace_membar_producer();
                lck_mtx_unlock(&bucket->ftb_mtx);

                /*
                 * Activate the tracepoint in the ISA-specific manner.
                 * If this fails, we need to report the failure, but
                 * indicate that this tracepoint must still be disabled
                 * by calling fasttrap_tracepoint_disable().
                 */
                if (fasttrap_tracepoint_install(p, new_tp) != 0)
                        rc = FASTTRAP_ENABLE_PARTIAL;

                /*
                 * Increment the count of the number of tracepoints active in
                 * the victim process.
                 */
                //ASSERT(p->p_proc_flag & P_PR_LOCK);
                p->p_dtrace_count++;

                return (rc);
        }

        lck_mtx_unlock(&bucket->ftb_mtx);

        /*
         * Initialize the tracepoint that's been preallocated with the probe.
         */
        new_tp = probe->ftp_tps[index].fit_tp;

        ASSERT(new_tp->ftt_pid == pid);
        ASSERT(new_tp->ftt_pc == pc);
        ASSERT(new_tp->ftt_proc == probe->ftp_prov->ftp_proc);
        ASSERT(new_tp->ftt_ids == NULL);
        ASSERT(new_tp->ftt_retids == NULL);

        switch (id->fti_ptype) {
        case DTFTP_ENTRY:
        case DTFTP_OFFSETS:
        case DTFTP_IS_ENABLED:
                id->fti_next = NULL;
                new_tp->ftt_ids = id;
                break;

        case DTFTP_RETURN:
        case DTFTP_POST_OFFSETS:
                id->fti_next = NULL;
                new_tp->ftt_retids = id;
                break;

        default:
                ASSERT(0);
        }

        /*
         * If the ISA-dependent initialization goes to plan, go back to the
         * beginning and try to install this freshly made tracepoint.
         */
        if (fasttrap_tracepoint_init(p, new_tp, pc, id->fti_ptype) == 0)
                goto again;

        new_tp->ftt_ids = NULL;
        new_tp->ftt_retids = NULL;

        return (FASTTRAP_ENABLE_FAIL);
}

static void
fasttrap_tracepoint_disable(proc_t *p, fasttrap_probe_t *probe, uint_t index)
{
        fasttrap_bucket_t *bucket;
        fasttrap_provider_t *provider = probe->ftp_prov;
        fasttrap_tracepoint_t **pp, *tp;
        fasttrap_id_t *id, **idp;
        pid_t pid;
        user_addr_t pc;

        ASSERT(index < probe->ftp_ntps);

        pid = probe->ftp_pid;
        pc = probe->ftp_tps[index].fit_tp->ftt_pc;
        id = &probe->ftp_tps[index].fit_id;

        ASSERT(probe->ftp_tps[index].fit_tp->ftt_pid == pid);

        /*
         * Find the tracepoint and make sure that our id is one of the
         * ones registered with it.
         */
        bucket = &fasttrap_tpoints.fth_table[FASTTRAP_TPOINTS_INDEX(pid, pc)];
        lck_mtx_lock(&bucket->ftb_mtx);
        for (tp = bucket->ftb_data; tp != NULL; tp = tp->ftt_next) {
                if (tp->ftt_pid == pid && tp->ftt_pc == pc &&
                    tp->ftt_proc == provider->ftp_proc)
                        break;
        }

        /*
         * If we somehow lost this tracepoint, we're in a world of hurt.
         */
        ASSERT(tp != NULL);

        switch (id->fti_ptype) {
                case DTFTP_ENTRY:
                case DTFTP_OFFSETS:
                case DTFTP_IS_ENABLED:
                        ASSERT(tp->ftt_ids != NULL);
                        idp = &tp->ftt_ids;
                        break;
                        
                case DTFTP_RETURN:
                case DTFTP_POST_OFFSETS:
                        ASSERT(tp->ftt_retids != NULL);
                        idp = &tp->ftt_retids;
                        break;
                        
                default:
                        /* Fix compiler warning... */
                        idp = NULL;
                        ASSERT(0);
        }

        while ((*idp)->fti_probe != probe) {
                idp = &(*idp)->fti_next;
                ASSERT(*idp != NULL);
        }

        id = *idp;
        *idp = id->fti_next;
        dtrace_membar_producer();

        ASSERT(id->fti_probe == probe);

        /*
         * If there are other registered enablings of this tracepoint, we're
         * all done, but if this was the last probe assocated with this
         * this tracepoint, we need to remove and free it.
         */
        if (tp->ftt_ids != NULL || tp->ftt_retids != NULL) {

                /*
                 * If the current probe's tracepoint is in use, swap it
                 * for an unused tracepoint.
                 */
                if (tp == probe->ftp_tps[index].fit_tp) {
                        fasttrap_probe_t *tmp_probe;
                        fasttrap_tracepoint_t **tmp_tp;
                        uint_t tmp_index;

                        if (tp->ftt_ids != NULL) {
                                tmp_probe = tp->ftt_ids->fti_probe;
                                /* LINTED - alignment */
                                tmp_index = FASTTRAP_ID_INDEX(tp->ftt_ids);
                                tmp_tp = &tmp_probe->ftp_tps[tmp_index].fit_tp;
                        } else {
                                tmp_probe = tp->ftt_retids->fti_probe;
                                /* LINTED - alignment */
                                tmp_index = FASTTRAP_ID_INDEX(tp->ftt_retids);
                                tmp_tp = &tmp_probe->ftp_tps[tmp_index].fit_tp;
                        }

                        ASSERT(*tmp_tp != NULL);
                        ASSERT(*tmp_tp != probe->ftp_tps[index].fit_tp);
                        ASSERT((*tmp_tp)->ftt_ids == NULL);
                        ASSERT((*tmp_tp)->ftt_retids == NULL);

                        probe->ftp_tps[index].fit_tp = *tmp_tp;
                        *tmp_tp = tp;

                }

                lck_mtx_unlock(&bucket->ftb_mtx);

                /*
                 * Tag the modified probe with the generation in which it was
                 * changed.
                 */
                probe->ftp_gen = fasttrap_mod_gen;
                return;
        }

        lck_mtx_unlock(&bucket->ftb_mtx);

        /*
         * We can't safely remove the tracepoint from the set of active
         * tracepoints until we've actually removed the fasttrap instruction
         * from the process's text. We can, however, operate on this
         * tracepoint secure in the knowledge that no other thread is going to
         * be looking at it since we hold P_PR_LOCK on the process if it's
         * live or we hold the provider lock on the process if it's dead and
         * gone.
         */

        /*
         * We only need to remove the actual instruction if we're looking
         * at an existing process
         */
        if (p != NULL) {
                /*
                 * If we fail to restore the instruction we need to kill
                 * this process since it's in a completely unrecoverable
                 * state.
                 */
                if (fasttrap_tracepoint_remove(p, tp) != 0)
                        fasttrap_sigtrap(p, NULL, pc);

                /*
                 * Decrement the count of the number of tracepoints active
                 * in the victim process.
                 */
                //ASSERT(p->p_proc_flag & P_PR_LOCK);
                p->p_dtrace_count--;
        }

        /*
         * Remove the probe from the hash table of active tracepoints.
         */
        lck_mtx_lock(&bucket->ftb_mtx);
        pp = (fasttrap_tracepoint_t **)&bucket->ftb_data;
        ASSERT(*pp != NULL);
        while (*pp != tp) {
                pp = &(*pp)->ftt_next;
                ASSERT(*pp != NULL);
        }

        *pp = tp->ftt_next;
        dtrace_membar_producer();

        lck_mtx_unlock(&bucket->ftb_mtx);

        /*
         * Tag the modified probe with the generation in which it was changed.
         */
        probe->ftp_gen = fasttrap_mod_gen;
}

static void
fasttrap_enable_callbacks(void)
{
        /*
         * We don't have to play the rw lock game here because we're
         * providing something rather than taking something away --
         * we can be sure that no threads have tried to follow this
         * function pointer yet.
         */
        lck_mtx_lock(&fasttrap_count_mtx);
        if (fasttrap_pid_count == 0) {
                ASSERT(dtrace_pid_probe_ptr == NULL);
                ASSERT(dtrace_return_probe_ptr == NULL);
                dtrace_pid_probe_ptr = &fasttrap_pid_probe;
                dtrace_return_probe_ptr = &fasttrap_return_probe;
        }
        ASSERT(dtrace_pid_probe_ptr == &fasttrap_pid_probe);
        ASSERT(dtrace_return_probe_ptr == &fasttrap_return_probe);
        fasttrap_pid_count++;
        lck_mtx_unlock(&fasttrap_count_mtx);
}

static void
fasttrap_disable_callbacks(void)
{
        //ASSERT(MUTEX_HELD(&cpu_lock));

        lck_mtx_lock(&fasttrap_count_mtx);
        ASSERT(fasttrap_pid_count > 0);
        fasttrap_pid_count--;
        if (fasttrap_pid_count == 0) {
                dtrace_cpu_t *cur, *cpu = CPU;

                /*
                 * APPLE NOTE: This loop seems broken, it touches every CPU
                 * but the one we're actually running on. Need to ask Sun folks
                 * if that is safe. Scenario is this: We're running on CPU A,
                 * and lock all but A. Then we get preempted, and start running
                 * on CPU B. A probe fires on A, and is allowed to enter. BOOM!
                 */
                for (cur = cpu->cpu_next; cur != cpu; cur = cur->cpu_next) {
                        lck_rw_lock_exclusive(&cur->cpu_ft_lock);
                        // rw_enter(&cur->cpu_ft_lock, RW_WRITER);
                }

                dtrace_pid_probe_ptr = NULL;
                dtrace_return_probe_ptr = NULL;

                for (cur = cpu->cpu_next; cur != cpu; cur = cur->cpu_next) {
                        lck_rw_unlock_exclusive(&cur->cpu_ft_lock);
                        // rw_exit(&cur->cpu_ft_lock);
                }
        }
        lck_mtx_unlock(&fasttrap_count_mtx);
}

/*ARGSUSED*/
static int
fasttrap_pid_enable(void *arg, dtrace_id_t id, void *parg)
{
#pragma unused(arg, id)
        fasttrap_probe_t *probe = parg;
        proc_t *p;
        int i, rc;

        ASSERT(probe != NULL);
        ASSERT(!probe->ftp_enabled);
        ASSERT(id == probe->ftp_id);
        // ASSERT(MUTEX_HELD(&cpu_lock));

        /*
         * Increment the count of enabled probes on this probe's provider;
         * the provider can't go away while the probe still exists. We
         * must increment this even if we aren't able to properly enable
         * this probe.
         */
        lck_mtx_lock(&probe->ftp_prov->ftp_mtx);
        probe->ftp_prov->ftp_rcount++;
        lck_mtx_unlock(&probe->ftp_prov->ftp_mtx);

        /*
         * If this probe's provider is retired (meaning it was valid in a
         * previously exec'ed incarnation of this address space), bail out. The
         * provider can't go away while we're in this code path.
         */
        if (probe->ftp_prov->ftp_retired)
            return(0);

        /*
         * If we can't find the process, it may be that we're in the context of
         * a fork in which the traced process is being born and we're copying
         * USDT probes. Otherwise, the process is gone so bail.
         */
        if ((p = sprlock(probe->ftp_pid)) == PROC_NULL) {
                /*
                 * APPLE NOTE: We should never end up here. The Solaris sprlock()
                 * does not return process's with SIDL set, but we always return
                 * the child process.
                 */
            return(0);
        }

        /*
         * APPLE NOTE: We do not have an equivalent thread structure to Solaris.
         * Solaris uses its ulwp_t struct for scratch space to support the pid provider.
         * To mimic this, we allocate on demand scratch space. If this is the first
         * time a probe has been enabled in this process, we need to allocate scratch
         * space for each already existing thread. Now is a good time to do this, as
         * the target process is suspended and the proc_lock is held.
         */
        if (p->p_dtrace_ptss_pages == NULL) {
                dtrace_ptss_enable(p);
        }

        // ASSERT(!(p->p_flag & SVFORK));
        proc_unlock(p);

        /*
         * We have to enable the trap entry point before any user threads have
         * the chance to execute the trap instruction we're about to place
         * in their process's text.
         */
        fasttrap_enable_callbacks();

        /*
         * Enable all the tracepoints and add this probe's id to each
         * tracepoint's list of active probes.
         */
        for (i = 0; i < (int)probe->ftp_ntps; i++) {
                if ((rc = fasttrap_tracepoint_enable(p, probe, i)) != 0) {
                        /*
                         * If enabling the tracepoint failed completely,
                         * we don't have to disable it; if the failure
                         * was only partial we must disable it.
                         */
                        if (rc == FASTTRAP_ENABLE_FAIL)
                                i--;
                        else
                                ASSERT(rc == FASTTRAP_ENABLE_PARTIAL);

                        /*
                         * Back up and pull out all the tracepoints we've
                         * created so far for this probe.
                         */
                        while (i >= 0) {
                                fasttrap_tracepoint_disable(p, probe, i);
                                i--;
                        }

                        proc_lock(p);
                        sprunlock(p);

                        /*
                         * Since we're not actually enabling this probe,
                         * drop our reference on the trap table entry.
                         */
                        fasttrap_disable_callbacks();
                        return(0);
                }
        }

        proc_lock(p);
        sprunlock(p);

        probe->ftp_enabled = 1;
        return (0);
}

/*ARGSUSED*/
static void
fasttrap_pid_disable(void *arg, dtrace_id_t id, void *parg)
{
#pragma unused(arg, id)
        fasttrap_probe_t *probe = parg;
        fasttrap_provider_t *provider = probe->ftp_prov;
        proc_t *p;
        int i, whack = 0;

        ASSERT(id == probe->ftp_id);

        /*
         * We won't be able to acquire a /proc-esque lock on the process
         * iff the process is dead and gone. In this case, we rely on the
         * provider lock as a point of mutual exclusion to prevent other
         * DTrace consumers from disabling this probe.
         */
        if ((p = sprlock(probe->ftp_pid)) != PROC_NULL) {
                // ASSERT(!(p->p_flag & SVFORK));
                proc_unlock(p);
        }

        lck_mtx_lock(&provider->ftp_mtx);

        /*
         * Disable all the associated tracepoints (for fully enabled probes).
         */
        if (probe->ftp_enabled) {
                for (i = 0; i < (int)probe->ftp_ntps; i++) {
                        fasttrap_tracepoint_disable(p, probe, i);
                }
        }

        ASSERT(provider->ftp_rcount > 0);
        provider->ftp_rcount--;

        if (p != NULL) {
                /*
                 * Even though we may not be able to remove it entirely, we
                 * mark this retired provider to get a chance to remove some
                 * of the associated probes.
                 */
                if (provider->ftp_retired && !provider->ftp_marked)
                        whack = provider->ftp_marked = 1;
                lck_mtx_unlock(&provider->ftp_mtx);

                proc_lock(p);
                sprunlock(p);
        } else {
                /*
                 * If the process is dead, we're just waiting for the
                 * last probe to be disabled to be able to free it.
                 */
                if (provider->ftp_rcount == 0 && !provider->ftp_marked)
                        whack = provider->ftp_marked = 1;
                lck_mtx_unlock(&provider->ftp_mtx);
        }

        if (whack)
                fasttrap_pid_cleanup();

        if (!probe->ftp_enabled)
                return;

        probe->ftp_enabled = 0;

        // ASSERT(MUTEX_HELD(&cpu_lock));
        fasttrap_disable_callbacks();
}

/*ARGSUSED*/
static void
fasttrap_pid_getargdesc(void *arg, dtrace_id_t id, void *parg,
    dtrace_argdesc_t *desc)
{
#pragma unused(arg, id)
        fasttrap_probe_t *probe = parg;
        char *str;
        int i, ndx;

        desc->dtargd_native[0] = '\0';
        desc->dtargd_xlate[0] = '\0';

        if (probe->ftp_prov->ftp_retired != 0 ||
            desc->dtargd_ndx >= probe->ftp_nargs) {
                desc->dtargd_ndx = DTRACE_ARGNONE;
                return;
        }

        ndx = (probe->ftp_argmap != NULL) ?
                probe->ftp_argmap[desc->dtargd_ndx] : desc->dtargd_ndx;

        str = probe->ftp_ntypes;
        for (i = 0; i < ndx; i++) {
                str += strlen(str) + 1;
        }

        (void) strlcpy(desc->dtargd_native, str, sizeof(desc->dtargd_native));

        if (probe->ftp_xtypes == NULL)
                return;

        str = probe->ftp_xtypes;
        for (i = 0; i < desc->dtargd_ndx; i++) {
                str += strlen(str) + 1;
        }

        (void) strlcpy(desc->dtargd_xlate, str, sizeof(desc->dtargd_xlate));
}

/*ARGSUSED*/
static void
fasttrap_pid_destroy(void *arg, dtrace_id_t id, void *parg)
{
#pragma unused(arg, id)
        fasttrap_probe_t *probe = parg;
        unsigned int i;

        ASSERT(probe != NULL);
        ASSERT(!probe->ftp_enabled);
        ASSERT(fasttrap_total >= probe->ftp_ntps);

        atomic_add_32(&fasttrap_total, -probe->ftp_ntps);

        if (probe->ftp_gen + 1 >= fasttrap_mod_gen)
                fasttrap_mod_barrier(probe->ftp_gen);

        for (i = 0; i < probe->ftp_ntps; i++) {
                zfree(fasttrap_tracepoint_t_zone, probe->ftp_tps[i].fit_tp);
        }

        if (probe->ftp_ntps < FASTTRAP_PROBE_T_ZONE_MAX_TRACEPOINTS) {
                zfree(fasttrap_probe_t_zones[probe->ftp_ntps], probe);
        } else {
                size_t size = offsetof(fasttrap_probe_t, ftp_tps[probe->ftp_ntps]);
                kmem_free(probe, size);
        }
}


static const dtrace_pattr_t pid_attr = {
{ DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_ISA },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
{ DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_ISA },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
};

static dtrace_pops_t pid_pops = {
        fasttrap_pid_provide,
        NULL,
        fasttrap_pid_enable,
        fasttrap_pid_disable,
        NULL,
        NULL,
        fasttrap_pid_getargdesc,
        fasttrap_pid_getarg,
        NULL,
        fasttrap_pid_destroy
};

static dtrace_pops_t usdt_pops = {
        fasttrap_pid_provide,
        NULL,
        fasttrap_pid_enable,
        fasttrap_pid_disable,
        NULL,
        NULL,
        fasttrap_pid_getargdesc,
        fasttrap_usdt_getarg,
        NULL,
        fasttrap_pid_destroy
};

static fasttrap_proc_t *
fasttrap_proc_lookup(pid_t pid)
{
        fasttrap_bucket_t *bucket;
        fasttrap_proc_t *fprc, *new_fprc;

        bucket = &fasttrap_procs.fth_table[FASTTRAP_PROCS_INDEX(pid)];
        lck_mtx_lock(&bucket->ftb_mtx);

        for (fprc = bucket->ftb_data; fprc != NULL; fprc = fprc->ftpc_next) {
                if (fprc->ftpc_pid == pid && fprc->ftpc_acount != 0) {
                        lck_mtx_lock(&fprc->ftpc_mtx);
                        lck_mtx_unlock(&bucket->ftb_mtx);
                        fprc->ftpc_rcount++;
                        atomic_add_64(&fprc->ftpc_acount, 1);
                        ASSERT(fprc->ftpc_acount <= fprc->ftpc_rcount);
                        lck_mtx_unlock(&fprc->ftpc_mtx);

                        return (fprc);
                }
        }

        /*
         * Drop the bucket lock so we don't try to perform a sleeping
         * allocation under it.
         */
        lck_mtx_unlock(&bucket->ftb_mtx);

        new_fprc = kmem_zalloc(sizeof (fasttrap_proc_t), KM_SLEEP);
        ASSERT(new_fprc != NULL);
        new_fprc->ftpc_pid = pid;
        new_fprc->ftpc_rcount = 1;
        new_fprc->ftpc_acount = 1;

        lck_mtx_lock(&bucket->ftb_mtx);

        /*
         * Take another lap through the list to make sure a proc hasn't
         * been created for this pid while we weren't under the bucket lock.
         */
        for (fprc = bucket->ftb_data; fprc != NULL; fprc = fprc->ftpc_next) {
                if (fprc->ftpc_pid == pid && fprc->ftpc_acount != 0) {
                        lck_mtx_lock(&fprc->ftpc_mtx);
                        lck_mtx_unlock(&bucket->ftb_mtx);
                        fprc->ftpc_rcount++;
                        atomic_add_64(&fprc->ftpc_acount, 1);
                        ASSERT(fprc->ftpc_acount <= fprc->ftpc_rcount);
                        lck_mtx_unlock(&fprc->ftpc_mtx);

                        kmem_free(new_fprc, sizeof (fasttrap_proc_t));

                        return (fprc);
                }
        }

        /*
         * APPLE NOTE: We have to initialize all locks explicitly
         */
        lck_mtx_init(&new_fprc->ftpc_mtx, fasttrap_lck_grp, fasttrap_lck_attr);

        new_fprc->ftpc_next = bucket->ftb_data;
        bucket->ftb_data = new_fprc;

        lck_mtx_unlock(&bucket->ftb_mtx);

        return (new_fprc);
}

static void
fasttrap_proc_release(fasttrap_proc_t *proc)
{
        fasttrap_bucket_t *bucket;
        fasttrap_proc_t *fprc, **fprcp;
        pid_t pid = proc->ftpc_pid;

        lck_mtx_lock(&proc->ftpc_mtx);

        ASSERT(proc->ftpc_rcount != 0);
        ASSERT(proc->ftpc_acount <= proc->ftpc_rcount);

        if (--proc->ftpc_rcount != 0) {
                lck_mtx_unlock(&proc->ftpc_mtx);
                return;
        }

        lck_mtx_unlock(&proc->ftpc_mtx);

        /*
         * There should definitely be no live providers associated with this
         * process at this point.
         */
         ASSERT(proc->ftpc_acount == 0);

        bucket = &fasttrap_procs.fth_table[FASTTRAP_PROCS_INDEX(pid)];
        lck_mtx_lock(&bucket->ftb_mtx);

        fprcp = (fasttrap_proc_t **)&bucket->ftb_data;
        while ((fprc = *fprcp) != NULL) {
                if (fprc == proc)
                        break;

                fprcp = &fprc->ftpc_next;
        }

        /*
         * Something strange has happened if we can't find the proc.
         */
        ASSERT(fprc != NULL);

        *fprcp = fprc->ftpc_next;

        lck_mtx_unlock(&bucket->ftb_mtx);

        /*
         * APPLE NOTE: explicit lock management. Not 100% certain we need this, the
         * memory is freed even without the destroy. Maybe accounting cleanup?
         */
        lck_mtx_destroy(&fprc->ftpc_mtx, fasttrap_lck_grp);

        kmem_free(fprc, sizeof (fasttrap_proc_t));
}

/*
 * Lookup a fasttrap-managed provider based on its name and associated pid.
 * If the pattr argument is non-NULL, this function instantiates the provider
 * if it doesn't exist otherwise it returns NULL. The provider is returned
 * with its lock held.
 */
static fasttrap_provider_t *
fasttrap_provider_lookup(pid_t pid, fasttrap_provider_type_t provider_type, const char *name,
    const dtrace_pattr_t *pattr)
{
        fasttrap_provider_t *fp, *new_fp = NULL;
        fasttrap_bucket_t *bucket;
        char provname[DTRACE_PROVNAMELEN];
        proc_t *p;
        cred_t *cred;

        ASSERT(strlen(name) < sizeof (fp->ftp_name));
        ASSERT(pattr != NULL);

        bucket = &fasttrap_provs.fth_table[FASTTRAP_PROVS_INDEX(pid, name)];
        lck_mtx_lock(&bucket->ftb_mtx);

        /*
         * Take a lap through the list and return the match if we find it.
         */
        for (fp = bucket->ftb_data; fp != NULL; fp = fp->ftp_next) {
                if (fp->ftp_pid == pid &&
                    fp->ftp_provider_type == provider_type &&
                    strncmp(fp->ftp_name, name, sizeof(fp->ftp_name)) == 0 &&
                    !fp->ftp_retired) {
                        lck_mtx_lock(&fp->ftp_mtx);
                        lck_mtx_unlock(&bucket->ftb_mtx);
                        return (fp);
                }
        }

        /*
         * Drop the bucket lock so we don't try to perform a sleeping
         * allocation under it.
         */
        lck_mtx_unlock(&bucket->ftb_mtx);

        /*
         * Make sure the process exists, isn't a child created as the result
         * of a vfork(2), and isn't a zombie (but may be in fork).
         */
        if ((p = proc_find(pid)) == NULL) {
                return NULL;
        }
        proc_lock(p);
        if (p->p_lflag & (P_LINVFORK | P_LEXIT)) {
                proc_unlock(p);
                proc_rele(p);
                return (NULL);
        }

        /*
         * Increment p_dtrace_probes so that the process knows to inform us
         * when it exits or execs. fasttrap_provider_free() decrements this
         * when we're done with this provider.
         */
        p->p_dtrace_probes++;

        /*
         * Grab the credentials for this process so we have
         * something to pass to dtrace_register().
         * APPLE NOTE:  We have no equivalent to crhold,
         * even though there is a cr_ref filed in ucred.
         */
        // lck_mtx_lock(&p->p_crlock;
        crhold(p->p_ucred);
        cred = p->p_ucred;
        // lck_mtx_unlock(&p->p_crlock);
        proc_unlock(p);
        proc_rele(p);

        new_fp = kmem_zalloc(sizeof (fasttrap_provider_t), KM_SLEEP);
        ASSERT(new_fp != NULL);
        new_fp->ftp_pid = pid;
        new_fp->ftp_proc = fasttrap_proc_lookup(pid);
        new_fp->ftp_provider_type = provider_type;

        /*
         * APPLE NOTE:  locks require explicit init
         */
        lck_mtx_init(&new_fp->ftp_mtx, fasttrap_lck_grp, fasttrap_lck_attr);
        lck_mtx_init(&new_fp->ftp_cmtx, fasttrap_lck_grp, fasttrap_lck_attr);

        ASSERT(new_fp->ftp_proc != NULL);

        lck_mtx_lock(&bucket->ftb_mtx);

        /*
         * Take another lap through the list to make sure a provider hasn't
         * been created for this pid while we weren't under the bucket lock.
         */
        for (fp = bucket->ftb_data; fp != NULL; fp = fp->ftp_next) {
                if (fp->ftp_pid == pid && strncmp(fp->ftp_name, name, sizeof(fp->ftp_name)) == 0 &&
                    !fp->ftp_retired) {
                        lck_mtx_lock(&fp->ftp_mtx);
                        lck_mtx_unlock(&bucket->ftb_mtx);
                        fasttrap_provider_free(new_fp);
                        crfree(cred);
                        return (fp);
                }
        }

        (void) strlcpy(new_fp->ftp_name, name, sizeof(new_fp->ftp_name));

        /*
         * Fail and return NULL if either the provider name is too long
         * or we fail to register this new provider with the DTrace
         * framework. Note that this is the only place we ever construct
         * the full provider name -- we keep it in pieces in the provider
         * structure.
         */
        if (snprintf(provname, sizeof (provname), "%s%u", name, (uint_t)pid) >=
            (int)sizeof (provname) ||
            dtrace_register(provname, pattr,
            DTRACE_PRIV_PROC | DTRACE_PRIV_OWNER | DTRACE_PRIV_ZONEOWNER, cred,
            pattr == &pid_attr ? &pid_pops : &usdt_pops, new_fp,
            &new_fp->ftp_provid) != 0) {
                lck_mtx_unlock(&bucket->ftb_mtx);
                fasttrap_provider_free(new_fp);
                crfree(cred);
                return (NULL);
        }

        new_fp->ftp_next = bucket->ftb_data;
        bucket->ftb_data = new_fp;

        lck_mtx_lock(&new_fp->ftp_mtx);
        lck_mtx_unlock(&bucket->ftb_mtx);

        crfree(cred);
        return (new_fp);
}

static void
fasttrap_provider_free(fasttrap_provider_t *provider)
{
        pid_t pid = provider->ftp_pid;
        proc_t *p;

        /*
         * There need to be no associated enabled probes, no consumers
         * creating probes, and no meta providers referencing this provider.
         */
        ASSERT(provider->ftp_rcount == 0);
        ASSERT(provider->ftp_ccount == 0);
        ASSERT(provider->ftp_mcount == 0);

        /*
         * If this provider hasn't been retired, we need to explicitly drop the
         * count of active providers on the associated process structure.
         */
        if (!provider->ftp_retired) {
                atomic_add_64(&provider->ftp_proc->ftpc_acount, -1);
                ASSERT(provider->ftp_proc->ftpc_acount <
                provider->ftp_proc->ftpc_rcount);
        }

        fasttrap_proc_release(provider->ftp_proc);

        /*
         * APPLE NOTE:  explicit lock management. Not 100% certain we need this, the
         * memory is freed even without the destroy. Maybe accounting cleanup?
         */
        lck_mtx_destroy(&provider->ftp_mtx, fasttrap_lck_grp);
        lck_mtx_destroy(&provider->ftp_cmtx, fasttrap_lck_grp);

        kmem_free(provider, sizeof (fasttrap_provider_t));

        /*
         * Decrement p_dtrace_probes on the process whose provider we're
         * freeing. We don't have to worry about clobbering somone else's
         * modifications to it because we have locked the bucket that
         * corresponds to this process's hash chain in the provider hash
         * table. Don't sweat it if we can't find the process.
         */
        if ((p = proc_find(pid)) == NULL) {
                return;
        }

        proc_lock(p);
        p->p_dtrace_probes--;
        proc_unlock(p);
        
        proc_rele(p);
}

static void
fasttrap_provider_retire(pid_t pid, const char *name, int mprov)
{
        fasttrap_provider_t *fp;
        fasttrap_bucket_t *bucket;
        dtrace_provider_id_t provid;

        ASSERT(strlen(name) < sizeof (fp->ftp_name));

        bucket = &fasttrap_provs.fth_table[FASTTRAP_PROVS_INDEX(pid, name)];
        lck_mtx_lock(&bucket->ftb_mtx);

        for (fp = bucket->ftb_data; fp != NULL; fp = fp->ftp_next) {
                if (fp->ftp_pid == pid && strncmp(fp->ftp_name, name, sizeof(fp->ftp_name)) == 0 &&
                    !fp->ftp_retired)
                        break;
        }

        if (fp == NULL) {
                lck_mtx_unlock(&bucket->ftb_mtx);
                return;
        }

        lck_mtx_lock(&fp->ftp_mtx);
        ASSERT(!mprov || fp->ftp_mcount > 0);
        if (mprov && --fp->ftp_mcount != 0)  {
                lck_mtx_unlock(&fp->ftp_mtx);
                lck_mtx_unlock(&bucket->ftb_mtx);
                return;
        }

        /*
         * Mark the provider to be removed in our post-processing step, mark it
         * retired, and drop the active count on its proc. Marking it indicates
         * that we should try to remove it; setting the retired flag indicates
         * that we're done with this provider; dropping the active the proc
         * releases our hold, and when this reaches zero (as it will during
         * exit or exec) the proc and associated providers become defunct.
         *
         * We obviously need to take the bucket lock before the provider lock
         * to perform the lookup, but we need to drop the provider lock
         * before calling into the DTrace framework since we acquire the
         * provider lock in callbacks invoked from the DTrace framework. The
         * bucket lock therefore protects the integrity of the provider hash
         * table.
         */
        atomic_add_64(&fp->ftp_proc->ftpc_acount, -1);
        ASSERT(fp->ftp_proc->ftpc_acount < fp->ftp_proc->ftpc_rcount);

        fp->ftp_retired = 1;
        fp->ftp_marked = 1;
        provid = fp->ftp_provid;
        lck_mtx_unlock(&fp->ftp_mtx);

        /*
         * We don't have to worry about invalidating the same provider twice
         * since fasttrap_provider_lookup() will ignore provider that have
         * been marked as retired.
         */
        dtrace_invalidate(provid);

        lck_mtx_unlock(&bucket->ftb_mtx);

        fasttrap_pid_cleanup();
}

static int
fasttrap_uint32_cmp(const void *ap, const void *bp)
{
        return (*(const uint32_t *)ap - *(const uint32_t *)bp);
}

static int
fasttrap_uint64_cmp(const void *ap, const void *bp)
{
        return (*(const uint64_t *)ap - *(const uint64_t *)bp);
}

static int
fasttrap_add_probe(fasttrap_probe_spec_t *pdata)
{
        fasttrap_provider_t *provider;
        fasttrap_probe_t *pp;
        fasttrap_tracepoint_t *tp;
        const char *name;
        unsigned int i, aframes, whack;

        /*
         * There needs to be at least one desired trace point.
         */
         if (pdata->ftps_noffs == 0)
                return (EINVAL);

        switch (pdata->ftps_probe_type) {
        case DTFTP_ENTRY:
                name = "entry";
                aframes = FASTTRAP_ENTRY_AFRAMES;
                break;
        case DTFTP_RETURN:
                name = "return";
                aframes = FASTTRAP_RETURN_AFRAMES;
                break;
        case DTFTP_OFFSETS:
                aframes = 0;
                name = NULL;
                break;
        default:
                return (EINVAL);
        }

        const char* provider_name;
        switch (pdata->ftps_provider_type) {
                case DTFTP_PROVIDER_PID:
                        provider_name = FASTTRAP_PID_NAME;
                        break;
                case DTFTP_PROVIDER_OBJC:
                        provider_name = FASTTRAP_OBJC_NAME;
                        break;
                case DTFTP_PROVIDER_ONESHOT:
                        provider_name = FASTTRAP_ONESHOT_NAME;
                        break;
                default:
                        return (EINVAL);
        }

        if ((provider = fasttrap_provider_lookup(pdata->ftps_pid, pdata->ftps_provider_type,
                                                 provider_name, &pid_attr)) == NULL)
                return (ESRCH);

        /*
         * Increment this reference count to indicate that a consumer is
         * actively adding a new probe associated with this provider. This
         * prevents the provider from being deleted -- we'll need to check
         * for pending deletions when we drop this reference count.
         */
        provider->ftp_ccount++;
        lck_mtx_unlock(&provider->ftp_mtx);

        /*
         * Grab the creation lock to ensure consistency between calls to
         * dtrace_probe_lookup() and dtrace_probe_create() in the face of
         * other threads creating probes. We must drop the provider lock
         * before taking this lock to avoid a three-way deadlock with the
         * DTrace framework.
         */
        lck_mtx_lock(&provider->ftp_cmtx);

        if (name == NULL) {
                for (i = 0; i < pdata->ftps_noffs; i++) {
                        char name_str[17];

                        (void) snprintf(name_str, sizeof(name_str), "%llx",
                            (uint64_t)pdata->ftps_offs[i]);

                        if (dtrace_probe_lookup(provider->ftp_provid,
                            pdata->ftps_mod, pdata->ftps_func, name_str) != 0)
                                continue;

                        atomic_add_32(&fasttrap_total, 1);

                        if (fasttrap_total > fasttrap_max) {
                                atomic_add_32(&fasttrap_total, -1);
                                goto no_mem;
                        }

                        pp = zalloc(fasttrap_probe_t_zones[1]);
                        bzero(pp, sizeof (fasttrap_probe_t));

                        pp->ftp_prov = provider;
                        pp->ftp_faddr = pdata->ftps_pc;
                        pp->ftp_fsize = pdata->ftps_size;
                        pp->ftp_pid = pdata->ftps_pid;
                        pp->ftp_ntps = 1;

                        tp = zalloc(fasttrap_tracepoint_t_zone);                        
                        bzero(tp, sizeof (fasttrap_tracepoint_t));

                        tp->ftt_proc = provider->ftp_proc;
                        tp->ftt_pc = pdata->ftps_offs[i] + pdata->ftps_pc;
                        tp->ftt_pid = pdata->ftps_pid;


                        pp->ftp_tps[0].fit_tp = tp;
                        pp->ftp_tps[0].fit_id.fti_probe = pp;
                        pp->ftp_tps[0].fit_id.fti_ptype = pdata->ftps_probe_type;
                        pp->ftp_id = dtrace_probe_create(provider->ftp_provid,
                            pdata->ftps_mod, pdata->ftps_func, name_str,
                            FASTTRAP_OFFSET_AFRAMES, pp);
                }

        } else if (dtrace_probe_lookup(provider->ftp_provid, pdata->ftps_mod,
            pdata->ftps_func, name) == 0) {
                atomic_add_32(&fasttrap_total, pdata->ftps_noffs);

                if (fasttrap_total > fasttrap_max) {
                        atomic_add_32(&fasttrap_total, -pdata->ftps_noffs);
                        goto no_mem;
                }

                /*
                 * Make sure all tracepoint program counter values are unique.
                 * We later assume that each probe has exactly one tracepoint
                 * for a given pc.
                 */
                qsort(pdata->ftps_offs, pdata->ftps_noffs,
                        sizeof (uint64_t), fasttrap_uint64_cmp);
                for (i = 1; i < pdata->ftps_noffs; i++) {
                        if (pdata->ftps_offs[i] > pdata->ftps_offs[i - 1])
                                continue;

                        atomic_add_32(&fasttrap_total, -pdata->ftps_noffs);
                        goto no_mem;
                }

                ASSERT(pdata->ftps_noffs > 0);
                if (pdata->ftps_noffs < FASTTRAP_PROBE_T_ZONE_MAX_TRACEPOINTS) {
                        pp = zalloc(fasttrap_probe_t_zones[pdata->ftps_noffs]);
                        bzero(pp, offsetof(fasttrap_probe_t, ftp_tps[pdata->ftps_noffs]));
                } else {
                        pp = kmem_zalloc(offsetof(fasttrap_probe_t, ftp_tps[pdata->ftps_noffs]), KM_SLEEP);
                }

                pp->ftp_prov = provider;
                pp->ftp_faddr = pdata->ftps_pc;
                pp->ftp_fsize = pdata->ftps_size;
                pp->ftp_pid = pdata->ftps_pid;
                pp->ftp_ntps = pdata->ftps_noffs;

                for (i = 0; i < pdata->ftps_noffs; i++) {
                        tp = zalloc(fasttrap_tracepoint_t_zone);
                        bzero(tp, sizeof (fasttrap_tracepoint_t));
                        tp->ftt_proc = provider->ftp_proc;
                        tp->ftt_pc = pdata->ftps_offs[i] + pdata->ftps_pc;
                        tp->ftt_pid = pdata->ftps_pid;

                        pp->ftp_tps[i].fit_tp = tp;
                        pp->ftp_tps[i].fit_id.fti_probe = pp;
                        pp->ftp_tps[i].fit_id.fti_ptype = pdata->ftps_probe_type;
                }

                pp->ftp_id = dtrace_probe_create(provider->ftp_provid,
                    pdata->ftps_mod, pdata->ftps_func, name, aframes, pp);
        }

        lck_mtx_unlock(&provider->ftp_cmtx);

        /*
         * We know that the provider is still valid since we incremented the
         * creation reference count. If someone tried to clean up this provider
         * while we were using it (e.g. because the process called exec(2) or
         * exit(2)), take note of that and try to clean it up now.
         */
        lck_mtx_lock(&provider->ftp_mtx);
        provider->ftp_ccount--;
        whack = provider->ftp_retired;
        lck_mtx_unlock(&provider->ftp_mtx);

        if (whack)
                fasttrap_pid_cleanup();

        return (0);

no_mem:
        /*
         * If we've exhausted the allowable resources, we'll try to remove
         * this provider to free some up. This is to cover the case where
         * the user has accidentally created many more probes than was
         * intended (e.g. pid123:::).
         */
        lck_mtx_unlock(&provider->ftp_cmtx);
        lck_mtx_lock(&provider->ftp_mtx);
        provider->ftp_ccount--;
        provider->ftp_marked = 1;
        lck_mtx_unlock(&provider->ftp_mtx);

        fasttrap_pid_cleanup();

        return (ENOMEM);
}

/*ARGSUSED*/
static void *
fasttrap_meta_provide(void *arg, dtrace_helper_provdesc_t *dhpv, pid_t pid)
{
#pragma unused(arg)
        fasttrap_provider_t *provider;

        /*
         * A 32-bit unsigned integer (like a pid for example) can be
         * expressed in 10 or fewer decimal digits. Make sure that we'll
         * have enough space for the provider name.
         */
        if (strlen(dhpv->dthpv_provname) + 10 >=
            sizeof (provider->ftp_name)) {
                cmn_err(CE_WARN, "failed to instantiate provider %s: "
                    "name too long to accomodate pid", dhpv->dthpv_provname);
                return (NULL);
        }

        /*
         * Don't let folks spoof the true pid provider.
         */
        if (strncmp(dhpv->dthpv_provname, FASTTRAP_PID_NAME, sizeof(FASTTRAP_PID_NAME)) == 0) {
                cmn_err(CE_WARN, "failed to instantiate provider %s: "
                    "%s is an invalid name", dhpv->dthpv_provname,
                    FASTTRAP_PID_NAME);
                return (NULL);
        }

        /*
         * APPLE NOTE: We also need to check the objc and oneshot pid provider types
         */
        if (strncmp(dhpv->dthpv_provname, FASTTRAP_OBJC_NAME, sizeof(FASTTRAP_OBJC_NAME)) == 0) {
                cmn_err(CE_WARN, "failed to instantiate provider %s: "
                    "%s is an invalid name", dhpv->dthpv_provname,
                    FASTTRAP_OBJC_NAME);
                return (NULL);
        }
        if (strncmp(dhpv->dthpv_provname, FASTTRAP_ONESHOT_NAME, sizeof(FASTTRAP_ONESHOT_NAME)) == 0) {
                cmn_err(CE_WARN, "failed to instantiate provider %s: "
                    "%s is an invalid name", dhpv->dthpv_provname,
                    FASTTRAP_ONESHOT_NAME);
                return (NULL);
        }

        /*
         * The highest stability class that fasttrap supports is ISA; cap
         * the stability of the new provider accordingly.
         */
        if (dhpv->dthpv_pattr.dtpa_provider.dtat_class > DTRACE_CLASS_ISA)
                dhpv->dthpv_pattr.dtpa_provider.dtat_class = DTRACE_CLASS_ISA;
        if (dhpv->dthpv_pattr.dtpa_mod.dtat_class > DTRACE_CLASS_ISA)
                dhpv->dthpv_pattr.dtpa_mod.dtat_class = DTRACE_CLASS_ISA;
        if (dhpv->dthpv_pattr.dtpa_func.dtat_class > DTRACE_CLASS_ISA)
                dhpv->dthpv_pattr.dtpa_func.dtat_class = DTRACE_CLASS_ISA;
        if (dhpv->dthpv_pattr.dtpa_name.dtat_class > DTRACE_CLASS_ISA)
                dhpv->dthpv_pattr.dtpa_name.dtat_class = DTRACE_CLASS_ISA;
        if (dhpv->dthpv_pattr.dtpa_args.dtat_class > DTRACE_CLASS_ISA)
                dhpv->dthpv_pattr.dtpa_args.dtat_class = DTRACE_CLASS_ISA;

        if ((provider = fasttrap_provider_lookup(pid, DTFTP_PROVIDER_USDT, dhpv->dthpv_provname,
            &dhpv->dthpv_pattr)) == NULL) {
                cmn_err(CE_WARN, "failed to instantiate provider %s for "
                    "process %u",  dhpv->dthpv_provname, (uint_t)pid);
                return (NULL);
        }

        /*
         * APPLE NOTE!
         *
         * USDT probes (fasttrap meta probes) are very expensive to create.
         * Profiling has shown that the largest single cost is verifying that
         * dtrace hasn't already created a given meta_probe. The reason for
         * this is dtrace_match() often has to strcmp ~100 hashed entries for
         * each static probe being created. We want to get rid of that check.
         * The simplest way of eliminating it is to deny the ability to add
         * probes to an existing provider. If the provider already exists, BZZT!
         * This still leaves the possibility of intentionally malformed DOF
         * having duplicate probes. However, duplicate probes are not fatal,
         * and there is no way to get that by accident, so we will not check
         * for that case.
         *
         * UPDATE: It turns out there are several use cases that require adding
         * probes to existing providers. Disabling the dtrace_probe_lookup()
         * optimization for now. See APPLE NOTE in fasttrap_meta_create_probe.
         */

        /*
         * Up the meta provider count so this provider isn't removed until
         * the meta provider has been told to remove it.
         */
        provider->ftp_mcount++;

        lck_mtx_unlock(&provider->ftp_mtx);

        return (provider);
}

/*ARGSUSED*/
static void
fasttrap_meta_create_probe(void *arg, void *parg,
    dtrace_helper_probedesc_t *dhpb)
{
#pragma unused(arg)
        fasttrap_provider_t *provider = parg;
        fasttrap_probe_t *pp;
        fasttrap_tracepoint_t *tp;
        unsigned int i, j;
        uint32_t ntps;

        /*
         * Since the meta provider count is non-zero we don't have to worry
         * about this provider disappearing.
         */
        ASSERT(provider->ftp_mcount > 0);

        /*
         * The offsets must be unique.
         */
        qsort(dhpb->dthpb_offs, dhpb->dthpb_noffs, sizeof (uint32_t),
                fasttrap_uint32_cmp);
        for (i = 1; i < dhpb->dthpb_noffs; i++) {
                if (dhpb->dthpb_base + dhpb->dthpb_offs[i] <=
                        dhpb->dthpb_base + dhpb->dthpb_offs[i - 1])
                                return;
        }

        qsort(dhpb->dthpb_enoffs, dhpb->dthpb_nenoffs, sizeof (uint32_t),
                fasttrap_uint32_cmp);
        for (i = 1; i < dhpb->dthpb_nenoffs; i++) {
                if (dhpb->dthpb_base + dhpb->dthpb_enoffs[i] <=
                        dhpb->dthpb_base + dhpb->dthpb_enoffs[i - 1])
                                return;
        }

        /*
         * Grab the creation lock to ensure consistency between calls to
         * dtrace_probe_lookup() and dtrace_probe_create() in the face of
         * other threads creating probes.
         */
        lck_mtx_lock(&provider->ftp_cmtx);

#if 0
        /*
         * APPLE NOTE: This is hideously expensive. See note in 
         * fasttrap_meta_provide() for why we can get away without
         * checking here.
         */
        if (dtrace_probe_lookup(provider->ftp_provid, dhpb->dthpb_mod,
            dhpb->dthpb_func, dhpb->dthpb_name) != 0) {
                lck_mtx_unlock(&provider->ftp_cmtx);
                return;
        }
#endif

        ntps = dhpb->dthpb_noffs + dhpb->dthpb_nenoffs;
        ASSERT(ntps > 0);

        atomic_add_32(&fasttrap_total, ntps);

        if (fasttrap_total > fasttrap_max) {
                atomic_add_32(&fasttrap_total, -ntps);
                lck_mtx_unlock(&provider->ftp_cmtx);
                return;
        }

        if (ntps < FASTTRAP_PROBE_T_ZONE_MAX_TRACEPOINTS) {
                pp = zalloc(fasttrap_probe_t_zones[ntps]);
                bzero(pp, offsetof(fasttrap_probe_t, ftp_tps[ntps]));
        } else {
                pp = kmem_zalloc(offsetof(fasttrap_probe_t, ftp_tps[ntps]), KM_SLEEP);
        }

        pp->ftp_prov = provider;
        pp->ftp_pid = provider->ftp_pid;
        pp->ftp_ntps = ntps;
        pp->ftp_nargs = dhpb->dthpb_xargc;
        pp->ftp_xtypes = dhpb->dthpb_xtypes;
        pp->ftp_ntypes = dhpb->dthpb_ntypes;

        /*
         * First create a tracepoint for each actual point of interest.
         */
        for (i = 0; i < dhpb->dthpb_noffs; i++) {
                tp = zalloc(fasttrap_tracepoint_t_zone);
                bzero(tp, sizeof (fasttrap_tracepoint_t));

                tp->ftt_proc = provider->ftp_proc;

                /*
                 * APPLE NOTE: We have linker support when creating DOF to handle all relocations for us.
                 * Unfortunately, a side effect of this is that the relocations do not point at exactly
                 * the location we want. We need to fix up the addresses here. The fixups vary by arch and type.
                 */
#if defined(__x86_64__)
                /*
                 * Both 32 & 64 bit want to go back one byte, to point at the first NOP
                 */
                tp->ftt_pc = dhpb->dthpb_base + (int64_t)dhpb->dthpb_offs[i] - 1;
#else
#error "Architecture not supported"
#endif

                tp->ftt_pid = provider->ftp_pid;

                pp->ftp_tps[i].fit_tp = tp;
                pp->ftp_tps[i].fit_id.fti_probe = pp;
                pp->ftp_tps[i].fit_id.fti_ptype = DTFTP_OFFSETS;
        }

        /*
         * Then create a tracepoint for each is-enabled point.
         */
        for (j = 0; i < ntps; i++, j++) {
                tp = zalloc(fasttrap_tracepoint_t_zone);
                bzero(tp, sizeof (fasttrap_tracepoint_t));

                tp->ftt_proc = provider->ftp_proc;

                /*
                 * APPLE NOTE: We have linker support when creating DOF to handle all relocations for us.
                 * Unfortunately, a side effect of this is that the relocations do not point at exactly
                 * the location we want. We need to fix up the addresses here. The fixups vary by arch and type.
                 */
#if defined(__x86_64__)
                /*
                 * Both 32 & 64 bit want to go forward two bytes, to point at a single byte nop.
                 */
                tp->ftt_pc = dhpb->dthpb_base + (int64_t)dhpb->dthpb_enoffs[j] + 2;
#else
#error "Architecture not supported"
#endif

                tp->ftt_pid = provider->ftp_pid;

                pp->ftp_tps[i].fit_tp = tp;
                pp->ftp_tps[i].fit_id.fti_probe = pp;
                pp->ftp_tps[i].fit_id.fti_ptype = DTFTP_IS_ENABLED;
        }

        /*
         * If the arguments are shuffled around we set the argument remapping
         * table. Later, when the probe fires, we only remap the arguments
         * if the table is non-NULL.
         */
        for (i = 0; i < dhpb->dthpb_xargc; i++) {
                if (dhpb->dthpb_args[i] != i) {
                        pp->ftp_argmap = dhpb->dthpb_args;
                        break;
                }
        }

        /*
         * The probe is fully constructed -- register it with DTrace.
         */
        pp->ftp_id = dtrace_probe_create(provider->ftp_provid, dhpb->dthpb_mod,
            dhpb->dthpb_func, dhpb->dthpb_name, FASTTRAP_OFFSET_AFRAMES, pp);

        lck_mtx_unlock(&provider->ftp_cmtx);
}

/*ARGSUSED*/
static void
fasttrap_meta_remove(void *arg, dtrace_helper_provdesc_t *dhpv, pid_t pid)
{
#pragma unused(arg)
        /*
         * Clean up the USDT provider. There may be active consumers of the
         * provider busy adding probes, no damage will actually befall the
         * provider until that count has dropped to zero. This just puts
         * the provider on death row.
         */
        fasttrap_provider_retire(pid, dhpv->dthpv_provname, 1);
}

static dtrace_mops_t fasttrap_mops = {
        fasttrap_meta_create_probe,
        fasttrap_meta_provide,
        fasttrap_meta_remove
};

/*
 * Validate a null-terminated string. If str is not null-terminated,
 * or not a UTF8 valid string, the function returns -1. Otherwise, 0 is
 * returned.
 *
 * str: string to validate.
 * maxlen: maximal length of the string, null-terminated byte included.
 */
static int
fasttrap_validatestr(char const* str, size_t maxlen) {
        size_t len;

        assert(str);
        assert(maxlen != 0);

        /* Check if the string is null-terminated. */
        len = strnlen(str, maxlen);
        if (len >= maxlen)
                return -1;

        /* Finally, check for UTF8 validity. */
        return utf8_validatestr((unsigned const char*) str, len);
}

/*ARGSUSED*/
static int
fasttrap_ioctl(dev_t dev, u_long cmd, user_addr_t arg, int md, cred_t *cr, int *rv)
{
#pragma unused(dev, md, rv)
        if (!dtrace_attached())
                return (EAGAIN);

        if (cmd == FASTTRAPIOC_MAKEPROBE) {
                fasttrap_probe_spec_t *probe;
                uint64_t noffs;
                size_t size;
                int ret;

                if (copyin(arg + __offsetof(fasttrap_probe_spec_t, ftps_noffs), &noffs,
                    sizeof (probe->ftps_noffs)))
                        return (EFAULT);

                /*
                 * Probes must have at least one tracepoint.
                 */
                if (noffs == 0)
                        return (EINVAL);

                /*
                 * We want to check the number of noffs before doing
                 * sizing math, to prevent potential buffer overflows.
                 */
                if (noffs > ((1024 * 1024) - sizeof(fasttrap_probe_spec_t)) / sizeof(probe->ftps_offs[0]))
                        return (ENOMEM);

                size = sizeof (fasttrap_probe_spec_t) +
                    sizeof (probe->ftps_offs[0]) * (noffs - 1);

                probe = kmem_alloc(size, KM_SLEEP);

                if (copyin(arg, probe, size) != 0 ||
                    probe->ftps_noffs != noffs) {
                        kmem_free(probe, size);
                        return (EFAULT);
                }

                /*
                 * Verify that the function and module strings contain no
                 * funny characters.
                 */

                if (fasttrap_validatestr(probe->ftps_func, sizeof(probe->ftps_func)) != 0) {
                        ret = EINVAL;
                        goto err;
                }

                if (fasttrap_validatestr(probe->ftps_mod, sizeof(probe->ftps_mod)) != 0) {
                        ret = EINVAL;
                        goto err;
                }

                if (!PRIV_POLICY_CHOICE(cr, PRIV_ALL, B_FALSE)) {
                        proc_t *p;
                        pid_t pid = probe->ftps_pid;

                        /*
                         * Report an error if the process doesn't exist
                         * or is actively being birthed.
                         */
                        if ((p = proc_find(pid)) == PROC_NULL || p->p_stat == SIDL) {
                                if (p != PROC_NULL)
                                        proc_rele(p);
                                ret = ESRCH;
                                goto err;
                        }
                        // proc_lock(p);
                        // FIXME! How is this done on OS X?
                        // if ((ret = priv_proc_cred_perm(cr, p, NULL,
                        //     VREAD | VWRITE)) != 0) {
                        //      mutex_exit(&p->p_lock);
                        //      return (ret);
                        // }
                        // proc_unlock(p);
                        proc_rele(p);
                }

                ret = fasttrap_add_probe(probe);

err:
                kmem_free(probe, size);

                return (ret);

        } else if (cmd == FASTTRAPIOC_GETINSTR) {
                fasttrap_instr_query_t instr;
                fasttrap_tracepoint_t *tp;
                uint_t index;
                // int ret;

                if (copyin(arg, &instr, sizeof (instr)) != 0)
                        return (EFAULT);

                if (!PRIV_POLICY_CHOICE(cr, PRIV_ALL, B_FALSE)) {
                        proc_t *p;
                        pid_t pid = instr.ftiq_pid;

                        /*
                         * Report an error if the process doesn't exist
                         * or is actively being birthed.
                         */
                        if ((p = proc_find(pid)) == NULL || p->p_stat == SIDL) {
                                if (p != PROC_NULL)
                                        proc_rele(p);
                                return (ESRCH);
                        }
                        //proc_lock(p);
                        // FIXME! How is this done on OS X?
                        // if ((ret = priv_proc_cred_perm(cr, p, NULL,
                        //     VREAD)) != 0) {
                        //      mutex_exit(&p->p_lock);
                        //      return (ret);
                        // }
                        // proc_unlock(p);
                        proc_rele(p);
                }

                index = FASTTRAP_TPOINTS_INDEX(instr.ftiq_pid, instr.ftiq_pc);

                lck_mtx_lock(&fasttrap_tpoints.fth_table[index].ftb_mtx);
                tp = fasttrap_tpoints.fth_table[index].ftb_data;
                while (tp != NULL) {
                        if (instr.ftiq_pid == tp->ftt_pid &&
                            instr.ftiq_pc == tp->ftt_pc &&
                            tp->ftt_proc->ftpc_acount != 0)
                                break;

                        tp = tp->ftt_next;
                }

                if (tp == NULL) {
                        lck_mtx_unlock(&fasttrap_tpoints.fth_table[index].ftb_mtx);
                        return (ENOENT);
                }

                bcopy(&tp->ftt_instr, &instr.ftiq_instr,
                    sizeof (instr.ftiq_instr));
                lck_mtx_unlock(&fasttrap_tpoints.fth_table[index].ftb_mtx);

                if (copyout(&instr, arg, sizeof (instr)) != 0)
                        return (EFAULT);

                return (0);
        }

        return (EINVAL);
}

static int
fasttrap_attach(dev_info_t *devi, ddi_attach_cmd_t cmd)
{
        ulong_t nent;

        switch (cmd) {
        case DDI_ATTACH:
                break;
        case DDI_RESUME:
                return (DDI_SUCCESS);
        default:
                return (DDI_FAILURE);
        }

        ddi_report_dev(devi);
        fasttrap_devi = devi;

        /*
         * Install our hooks into fork(2), exec(2), and exit(2).
         */
        dtrace_fasttrap_fork_ptr = &fasttrap_fork;
        dtrace_fasttrap_exit_ptr = &fasttrap_exec_exit;
        dtrace_fasttrap_exec_ptr = &fasttrap_exec_exit;

        /*
         * APPLE NOTE:  We size the maximum number of fasttrap probes
         * based on system memory. 100k probes per 256M of system memory.
         * Yes, this is a WAG.
         */
        fasttrap_max = (sane_size >> 28) * 100000;
        if (fasttrap_max == 0)
                fasttrap_max = 50000;

        fasttrap_total = 0;

        /*
         * Conjure up the tracepoints hashtable...
         */
        nent = ddi_getprop(DDI_DEV_T_ANY, devi, DDI_PROP_DONTPASS,
            "fasttrap-hash-size", FASTTRAP_TPOINTS_DEFAULT_SIZE);

        if (nent <= 0 || nent > 0x1000000)
                nent = FASTTRAP_TPOINTS_DEFAULT_SIZE;

        if ((nent & (nent - 1)) == 0)
                fasttrap_tpoints.fth_nent = nent;
        else
                fasttrap_tpoints.fth_nent = 1 << fasttrap_highbit(nent);
        ASSERT(fasttrap_tpoints.fth_nent > 0);
        fasttrap_tpoints.fth_mask = fasttrap_tpoints.fth_nent - 1;
        fasttrap_tpoints.fth_table = kmem_zalloc(fasttrap_tpoints.fth_nent *
            sizeof (fasttrap_bucket_t), KM_SLEEP);
        ASSERT(fasttrap_tpoints.fth_table != NULL);

        /*
         * APPLE NOTE:  explicitly initialize all locks...
         */
        unsigned int i;
        for (i=0; i<fasttrap_tpoints.fth_nent; i++) {
                lck_mtx_init(&fasttrap_tpoints.fth_table[i].ftb_mtx, fasttrap_lck_grp, fasttrap_lck_attr);
        }

        /*
         * ... and the providers hash table...
         */
        nent = FASTTRAP_PROVIDERS_DEFAULT_SIZE;
        if ((nent & (nent - 1)) == 0)
                fasttrap_provs.fth_nent = nent;
        else
                fasttrap_provs.fth_nent = 1 << fasttrap_highbit(nent);
        ASSERT(fasttrap_provs.fth_nent > 0);
        fasttrap_provs.fth_mask = fasttrap_provs.fth_nent - 1;
        fasttrap_provs.fth_table = kmem_zalloc(fasttrap_provs.fth_nent *
            sizeof (fasttrap_bucket_t), KM_SLEEP);
        ASSERT(fasttrap_provs.fth_table != NULL);

        /*
         * APPLE NOTE: explicitly initialize all locks...
         */
        for (i=0; i<fasttrap_provs.fth_nent; i++) {
                lck_mtx_init(&fasttrap_provs.fth_table[i].ftb_mtx, fasttrap_lck_grp, fasttrap_lck_attr);
        }

        /*
         * ... and the procs hash table.
         */
        nent = FASTTRAP_PROCS_DEFAULT_SIZE;
        if ((nent & (nent - 1)) == 0)
                fasttrap_procs.fth_nent = nent;
        else
                fasttrap_procs.fth_nent = 1 << fasttrap_highbit(nent);
        ASSERT(fasttrap_procs.fth_nent > 0);
        fasttrap_procs.fth_mask = fasttrap_procs.fth_nent - 1;
        fasttrap_procs.fth_table = kmem_zalloc(fasttrap_procs.fth_nent *
            sizeof (fasttrap_bucket_t), KM_SLEEP);
        ASSERT(fasttrap_procs.fth_table != NULL);

        /*
         * APPLE NOTE: explicitly initialize all locks...
         */
        for (i=0; i<fasttrap_procs.fth_nent; i++) {
                lck_mtx_init(&fasttrap_procs.fth_table[i].ftb_mtx, fasttrap_lck_grp, fasttrap_lck_attr);
        }

        (void) dtrace_meta_register("fasttrap", &fasttrap_mops, NULL,
            &fasttrap_meta_id);

        return (DDI_SUCCESS);
}

static int 
_fasttrap_open(dev_t dev, int flags, int devtype, struct proc *p)
{
#pragma unused(dev, flags, devtype, p)
        return  0;
}

static int
_fasttrap_ioctl(dev_t dev, u_long cmd, caddr_t data, int fflag, struct proc *p)
{
        int err, rv = 0;
    user_addr_t uaddrp;

    if (proc_is64bit(p))
        uaddrp = *(user_addr_t *)data;
    else
        uaddrp = (user_addr_t) *(uint32_t *)data;

        err = fasttrap_ioctl(dev, cmd, uaddrp, fflag, CRED(), &rv);

        /* XXX Darwin's BSD ioctls only return -1 or zero. Overload errno to mimic Solaris. 20 bits suffice. */
        if (err != 0) {
                ASSERT( (err & 0xfffff000) == 0 );
                return (err & 0xfff); /* ioctl returns -1 and errno set to an error code < 4096 */
        } else if (rv != 0) {
                ASSERT( (rv & 0xfff00000) == 0 );
                return (((rv & 0xfffff) << 12)); /* ioctl returns -1 and errno set to a return value >= 4096 */
        } else 
                return 0;
}

static int gFasttrapInited = 0;

#define FASTTRAP_MAJOR  -24 /* let the kernel pick the device number */

/*
 * A struct describing which functions will get invoked for certain
 * actions.
 */

static struct cdevsw fasttrap_cdevsw =
{
        _fasttrap_open,         /* open */
        eno_opcl,               /* close */
        eno_rdwrt,              /* read */
        eno_rdwrt,              /* write */
        _fasttrap_ioctl,        /* ioctl */
        (stop_fcn_t *)nulldev,  /* stop */
        (reset_fcn_t *)nulldev, /* reset */
        NULL,                   /* tty's */
        eno_select,             /* select */
        eno_mmap,               /* mmap */
        eno_strat,              /* strategy */
        eno_getc,               /* getc */
        eno_putc,               /* putc */
        0                       /* type */
};

void fasttrap_init(void);

void
fasttrap_init( void )
{
        /*
         * This method is now invoked from multiple places. Any open of /dev/dtrace,
         * also dtrace_init if the dtrace_dof_mode is DTRACE_DOF_MODE_NON_LAZY.
         *
         * The reason is to delay allocating the (rather large) resources as late as possible.
         */
        if (0 == gFasttrapInited) {
                int majdevno = cdevsw_add(FASTTRAP_MAJOR, &fasttrap_cdevsw);

                if (majdevno < 0) {
                        // FIX ME! What kind of error reporting to do here?
                        printf("fasttrap_init: failed to allocate a major number!\n");
                        return;
                }

                dev_t device = makedev( (uint32_t)majdevno, 0 );
                if (NULL == devfs_make_node( device, DEVFS_CHAR, UID_ROOT, GID_WHEEL, 0666, "fasttrap", 0 )) {
                        return;
                }

                /*
                 * Allocate the fasttrap_tracepoint_t zone
                 */
                fasttrap_tracepoint_t_zone = zinit(sizeof(fasttrap_tracepoint_t),
                                                   1024 * sizeof(fasttrap_tracepoint_t),
                                                   sizeof(fasttrap_tracepoint_t),
                                                   "dtrace.fasttrap_tracepoint_t");

                /*
                 * fasttrap_probe_t's are variable in size. We use an array of zones to
                 * cover the most common sizes.
                 */
                int i;
                for (i=1; i<FASTTRAP_PROBE_T_ZONE_MAX_TRACEPOINTS; i++) {
                        size_t zone_element_size = offsetof(fasttrap_probe_t, ftp_tps[i]);
                        fasttrap_probe_t_zones[i] = zinit(zone_element_size,
                                                          1024 * zone_element_size,
                                                          zone_element_size,
                                                          fasttrap_probe_t_zone_names[i]);
                }

                
                /*
                 * Create the fasttrap lock group. Must be done before fasttrap_attach()!
                 */
                fasttrap_lck_attr = lck_attr_alloc_init();
                fasttrap_lck_grp_attr= lck_grp_attr_alloc_init();               
                fasttrap_lck_grp = lck_grp_alloc_init("fasttrap",  fasttrap_lck_grp_attr);

                /*
                 * Initialize global locks
                 */
                lck_mtx_init(&fasttrap_cleanup_mtx, fasttrap_lck_grp, fasttrap_lck_attr);
                lck_mtx_init(&fasttrap_count_mtx, fasttrap_lck_grp, fasttrap_lck_attr);

                if (DDI_FAILURE == fasttrap_attach((dev_info_t *)(uintptr_t)device, 0 )) {
                        // FIX ME! Do we remove the devfs node here?
                        // What kind of error reporting?
                        printf("fasttrap_init: Call to fasttrap_attach failed.\n");
                        return;
                }

                gFasttrapInited = 1;            
        }
}

#undef FASTTRAP_MAJOR