xnu-792.13.8.tar.gz

[apple/xnu.git] / bsd / kern / kdebug.c

/*
 * Copyright (c) 2000-2005 Apple Computer, Inc. All rights reserved.
 *
 * @Apple_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This 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 OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */

#include <machine/spl.h>

#include <sys/errno.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc_internal.h>
#include <sys/vm.h>
#include <sys/sysctl.h>
#include <sys/kdebug.h>
#include <sys/sysproto.h>

#define HZ      100
#include <mach/clock_types.h>
#include <mach/mach_types.h>
#include <mach/mach_time.h>
#include <machine/machine_routines.h>

#include <kern/thread.h>
#include <kern/task.h>
#include <vm/vm_kern.h>
#include <sys/lock.h>

#include <sys/malloc.h>
#include <sys/kauth.h>

#include <mach/mach_host.h>             /* for host_info() */
#include <libkern/OSAtomic.h>

/* XXX should have prototypes, but Mach does not provide one */
void task_act_iterate_wth_args(task_t, void(*)(thread_t, void *), void *);
int cpu_number(void);   /* XXX <machine/...> include path broken */

/* XXX should probably be static, but it's debugging code... */
int kdbg_read(user_addr_t, size_t *);
void kdbg_control_chud(int, void *);
int kdbg_control(int *, u_int, user_addr_t, size_t *);
int kdbg_getentropy (user_addr_t, size_t *, int);
int kdbg_readmap(user_addr_t, size_t *);
int kdbg_getreg(kd_regtype *);
int kdbg_setreg(kd_regtype *);
int kdbg_setrtcdec(kd_regtype *);
int kdbg_setpidex(kd_regtype *);
int kdbg_setpid(kd_regtype *);
void kdbg_mapinit(void);
int kdbg_reinit(void);
int kdbg_bootstrap(void);

static int  create_buffers(void);
static void delete_buffers(void);

#ifdef ppc
extern uint32_t maxDec;
#endif

/* trace enable status */
unsigned int kdebug_enable = 0;

/* track timestamps for security server's entropy needs */
uint64_t *                kd_entropy_buffer = 0;
unsigned int      kd_entropy_bufsize = 0;
unsigned int      kd_entropy_count  = 0;
unsigned int      kd_entropy_indx   = 0;
unsigned int      kd_entropy_buftomem = 0;


#define SLOW_NOLOG      0x01
#define SLOW_CHECKS     0x02
#define SLOW_ENTROPY    0x04

unsigned int kdebug_slowcheck=SLOW_NOLOG;

unsigned int kd_cpus;

struct kd_bufinfo {
        kd_buf * kd_stop;
        kd_buf * kd_bufptr;
        kd_buf * kd_buffer;
        kd_buf * kd_buflast;
        kd_buf * kd_readlast;
        int      kd_wrapped;    /* plus, the global flag KDBG_WRAPPED is set if one of the buffers has wrapped */
        uint64_t kd_prev_timebase;
        int      kd_pad[24];    /* pad out to 128 bytes so that no cache line is shared between CPUs */

};

struct kd_bufinfo *kdbip = NULL;

#define KDCOPYBUF_COUNT 1024
#define KDCOPYBUF_SIZE  (KDCOPYBUF_COUNT * sizeof(kd_buf))
kd_buf *kdcopybuf = NULL;


unsigned int nkdbufs = 8192;
unsigned int kd_bufsize = 0;
unsigned int kdebug_flags = 0;
unsigned int kdlog_beg=0;
unsigned int kdlog_end=0;
unsigned int kdlog_value1=0;
unsigned int kdlog_value2=0;
unsigned int kdlog_value3=0;
unsigned int kdlog_value4=0;

static lck_mtx_t  * kd_trace_mtx_sysctl;
static lck_grp_t  * kd_trace_mtx_sysctl_grp;
static lck_attr_t * kd_trace_mtx_sysctl_attr;
static lck_grp_attr_t   *kd_trace_mtx_sysctl_grp_attr;

static lck_grp_t       *stackshot_subsys_lck_grp;
static lck_grp_attr_t  *stackshot_subsys_lck_grp_attr;
static lck_attr_t      *stackshot_subsys_lck_attr;
static lck_mtx_t        stackshot_subsys_mutex;

void *stackshot_snapbuf = NULL;

int
stack_snapshot2(pid_t pid, user_addr_t tracebuf, uint32_t tracebuf_size, uint32_t options, register_t *retval);

extern void
kdp_snapshot_preflight(int pid, void  *tracebuf, uint32_t tracebuf_size, uint32_t options);

extern int
kdp_stack_snapshot_geterror(void);
extern unsigned int
kdp_stack_snapshot_bytes_traced(void);

kd_threadmap *kd_mapptr = 0;
unsigned int kd_mapsize = 0;
unsigned int kd_mapcount = 0;
unsigned int kd_maptomem = 0;

pid_t global_state_pid = -1;       /* Used to control exclusive use of kd_buffer */

#define DBG_FUNC_MASK 0xfffffffc

/* task to string structure */
struct tts
{
  task_t    task;            /* from procs task */
  pid_t     pid;             /* from procs p_pid  */
  char      task_comm[20];   /* from procs p_comm */
};

typedef struct tts tts_t;

struct krt
{
  kd_threadmap *map;    /* pointer to the map buffer */
  int count;
  int maxcount;
  struct tts *atts;
};

typedef struct krt krt_t;

/* This is for the CHUD toolkit call */
typedef void (*kd_chudhook_fn) (unsigned int debugid, unsigned int arg1,
                                unsigned int arg2, unsigned int arg3,
                                unsigned int arg4, unsigned int arg5);

kd_chudhook_fn kdebug_chudhook = 0;   /* pointer to CHUD toolkit function */

__private_extern__ void stackshot_lock_init( void );

/* Support syscall SYS_kdebug_trace */
int
kdebug_trace(__unused struct proc *p, struct kdebug_trace_args *uap, __unused register_t *retval)
{
    if ( (kdebug_enable == 0) )
        return(EINVAL);
  
    kernel_debug(uap->code, uap->arg1, uap->arg2, uap->arg3, uap->arg4, 0);
    return(0);
}



static int
create_buffers(void)
{
        unsigned int    cpu, i;
        int     nentries;

        nentries = nkdbufs / kd_cpus;
        kd_bufsize = nentries * sizeof(kd_buf);

        bzero((char *)kdbip, sizeof(struct kd_bufinfo) * kd_cpus);

        if (kdcopybuf == 0) {
                if (kmem_alloc(kernel_map, (unsigned int *)&kdcopybuf, (vm_size_t)KDCOPYBUF_SIZE) != KERN_SUCCESS)
                        return ENOMEM;
        }
        for (cpu = 0; cpu < kd_cpus; cpu++) {
                if (kmem_alloc(kernel_map, (unsigned int *)&kdbip[cpu].kd_buffer, kd_bufsize) != KERN_SUCCESS)
                        break;
        }
        if (cpu < kd_cpus) {
                for (i = 0; i < cpu; i++)
                        kmem_free(kernel_map, (vm_offset_t)kdbip[i].kd_buffer, kd_bufsize);
                kd_bufsize = 0;

                kmem_free(kernel_map, (vm_offset_t)kdcopybuf, KDCOPYBUF_SIZE);
                kdcopybuf = NULL;
                
                return(ENOMEM);
        }
        for (cpu = 0; cpu < kd_cpus; cpu++) {
                kdbip[cpu].kd_bufptr = kdbip[cpu].kd_buffer;
                kdbip[cpu].kd_buflast = &kdbip[cpu].kd_bufptr[nentries];
                kdbip[cpu].kd_readlast = kdbip[cpu].kd_bufptr;
        }
        kdebug_flags |= KDBG_BUFINIT;

        return(0);
}


static void
delete_buffers(void)
{
        unsigned int    cpu;

        if (kd_bufsize && (kdebug_flags & KDBG_BUFINIT)) {
                for (cpu = 0; cpu < kd_cpus; cpu++)
                        kmem_free(kernel_map, (vm_offset_t)kdbip[cpu].kd_buffer, kd_bufsize);
                kd_bufsize = 0;
        }
        if (kdcopybuf) {
                kmem_free(kernel_map, (vm_offset_t)kdcopybuf, KDCOPYBUF_SIZE);
                kdcopybuf = NULL;
        }
        kdebug_flags &= ~KDBG_BUFINIT;
}


static void
kernel_debug_internal(unsigned int debugid, unsigned int arg1, unsigned int arg2, unsigned int arg3,
                      unsigned int arg4, unsigned int arg5, int entropy_flag)
{
        int s;
        kd_buf * kd;
        struct proc *curproc;
        unsigned long long now;
        int cpu;
        
        s = ml_set_interrupts_enabled(FALSE);

        now = mach_absolute_time() & KDBG_TIMESTAMP_MASK;
        cpu = cpu_number();

        if (kdebug_enable & KDEBUG_ENABLE_CHUD) {
            if (kdebug_chudhook)
                kdebug_chudhook(debugid, arg1, arg2, arg3, arg4, arg5);

            if ( !(kdebug_enable & (KDEBUG_ENABLE_ENTROPY | KDEBUG_ENABLE_TRACE)))
                goto out;
        }

        if (kdebug_slowcheck == 0)
            goto record_trace;

        if (entropy_flag && (kdebug_enable & KDEBUG_ENABLE_ENTROPY))
          {
            if (kd_entropy_indx < kd_entropy_count)
              {
                kd_entropy_buffer [ kd_entropy_indx] = mach_absolute_time();
                kd_entropy_indx++;
              }
            
            if (kd_entropy_indx == kd_entropy_count)
              {
                /* Disable entropy collection */
                kdebug_enable &= ~KDEBUG_ENABLE_ENTROPY;
                kdebug_slowcheck &= ~SLOW_ENTROPY;
              }
          }

        if ( (kdebug_slowcheck & SLOW_NOLOG) )
            goto out;
        
        if (kdebug_flags & KDBG_PIDCHECK)
          {
            /* If kdebug flag is not set for current proc, return  */
            curproc = current_proc();
            if ((curproc && !(curproc->p_flag & P_KDEBUG)) &&
                ((debugid&0xffff0000) != (MACHDBG_CODE(DBG_MACH_SCHED, 0) | DBG_FUNC_NONE)))
                goto out;
          }
        else if (kdebug_flags & KDBG_PIDEXCLUDE)
          {
            /* If kdebug flag is set for current proc, return  */
            curproc = current_proc();
            if ((curproc && (curproc->p_flag & P_KDEBUG)) &&
                ((debugid&0xffff0000) != (MACHDBG_CODE(DBG_MACH_SCHED, 0) | DBG_FUNC_NONE)))
                goto out;
          }

        if (kdebug_flags & KDBG_RANGECHECK)
          {
            if ((debugid < kdlog_beg)
                || ((debugid >= kdlog_end) && (debugid >> 24 != DBG_TRACE)))
                goto out;
          }
        else if (kdebug_flags & KDBG_VALCHECK)
          {
            if ((debugid & DBG_FUNC_MASK) != kdlog_value1 &&
                (debugid & DBG_FUNC_MASK) != kdlog_value2 &&
                (debugid & DBG_FUNC_MASK) != kdlog_value3 &&
                (debugid & DBG_FUNC_MASK) != kdlog_value4 &&
                (debugid >> 24 != DBG_TRACE))
                goto out;
          }

record_trace:
        kd = kdbip[cpu].kd_bufptr;
        kd->debugid = debugid;
        kd->arg1 = arg1;
        kd->arg2 = arg2;
        kd->arg3 = arg3;
        kd->arg4 = arg4;
        kd->arg5 = arg5;
                  
        /*
         * Watch for out of order timestamps
         */     
        if (now < kdbip[cpu].kd_prev_timebase)
          {
            /*
             * if so, just store the previous timestamp + a cycle
             */
            now = ++kdbip[cpu].kd_prev_timebase & KDBG_TIMESTAMP_MASK;
          }
        else
          {
            kdbip[cpu].kd_prev_timebase = now;
          }
        kd->timestamp = now | (((uint64_t)cpu) << KDBG_CPU_SHIFT);

        kdbip[cpu].kd_bufptr++;

        if (kdbip[cpu].kd_bufptr >= kdbip[cpu].kd_buflast)
                kdbip[cpu].kd_bufptr = kdbip[cpu].kd_buffer;

        if (kdbip[cpu].kd_bufptr == kdbip[cpu].kd_readlast) {
                if (kdebug_flags & KDBG_NOWRAP)
                        kdebug_slowcheck |= SLOW_NOLOG;
                kdbip[cpu].kd_wrapped = 1;
                kdebug_flags |= KDBG_WRAPPED;
        }

out:
        ml_set_interrupts_enabled(s);
}

void
kernel_debug(unsigned int debugid, unsigned int arg1, unsigned int arg2, unsigned int arg3,
                      unsigned int arg4, __unused unsigned int arg5)
{
        kernel_debug_internal(debugid, arg1, arg2, arg3, arg4, (int)current_thread(), 1);
}

void
kernel_debug1(unsigned int debugid, unsigned int arg1, unsigned int arg2, unsigned int arg3,
                      unsigned int arg4, unsigned int arg5)
{
        kernel_debug_internal(debugid, arg1, arg2, arg3, arg4, arg5, 0);
}

static void
kdbg_lock_init(void)
{
        host_basic_info_data_t hinfo;
        mach_msg_type_number_t count = HOST_BASIC_INFO_COUNT;


        if (kdebug_flags & KDBG_LOCKINIT)
                return;

        /* get the number of cpus and cache it */
#define BSD_HOST 1
        host_info((host_t)BSD_HOST, HOST_BASIC_INFO, (host_info_t)&hinfo, &count);
        kd_cpus = hinfo.physical_cpu_max;

        if (kmem_alloc(kernel_map, (unsigned int *)&kdbip, sizeof(struct kd_bufinfo) * kd_cpus) != KERN_SUCCESS)
                return;

        /*
         * allocate lock group attribute and group
         */
        kd_trace_mtx_sysctl_grp_attr = lck_grp_attr_alloc_init();
        kd_trace_mtx_sysctl_grp = lck_grp_alloc_init("kdebug", kd_trace_mtx_sysctl_grp_attr);
                
        /*
         * allocate the lock attribute
         */
        kd_trace_mtx_sysctl_attr = lck_attr_alloc_init();


        /*
         * allocate and initialize spin lock and mutex
         */
        kd_trace_mtx_sysctl = lck_mtx_alloc_init(kd_trace_mtx_sysctl_grp, kd_trace_mtx_sysctl_attr);

        kdebug_flags |= KDBG_LOCKINIT;
}


int
kdbg_bootstrap(void)
{
        kdebug_flags &= ~KDBG_WRAPPED;

        return (create_buffers());
}

int
kdbg_reinit(void)
{
    int ret=0;

    /*
     * Disable trace collecting
     * First make sure we're not in
     * the middle of cutting a trace
     */

    kdebug_enable &= ~KDEBUG_ENABLE_TRACE;
    kdebug_slowcheck |= SLOW_NOLOG;

    /*
     * make sure the SLOW_NOLOG is seen
     * by everyone that might be trying
     * to cut a trace..
     */
    IOSleep(100);

    delete_buffers();

    if ((kdebug_flags & KDBG_MAPINIT) && kd_mapsize && kd_mapptr)
      {
        kmem_free(kernel_map, (vm_offset_t)kd_mapptr, kd_mapsize);
        kdebug_flags &= ~KDBG_MAPINIT;
        kd_mapsize = 0;
        kd_mapptr = (kd_threadmap *) 0;
        kd_mapcount = 0;
      }  

    ret = kdbg_bootstrap();

    return(ret);
}

void
kdbg_trace_data(struct proc *proc, long *arg_pid)
{
    if (!proc)
        *arg_pid = 0;
    else
        *arg_pid = proc->p_pid;
    
    return;
}


void
kdbg_trace_string(struct proc *proc, long *arg1, long *arg2, long *arg3, long *arg4)
{
    int i;
    char *dbg_nameptr; 
    int dbg_namelen;
    long dbg_parms[4];

    if (!proc)
      {
        *arg1 = 0;
        *arg2 = 0;
        *arg3 = 0;
        *arg4 = 0;
        return;
      }

    /* Collect the pathname for tracing */
    dbg_nameptr = proc->p_comm;
    dbg_namelen = strlen(proc->p_comm);
    dbg_parms[0]=0L;
    dbg_parms[1]=0L;
    dbg_parms[2]=0L;
    dbg_parms[3]=0L;
  
    if(dbg_namelen > (int)sizeof(dbg_parms))
      dbg_namelen = sizeof(dbg_parms);
    
    for(i=0;dbg_namelen > 0; i++)
      {
        dbg_parms[i]=*(long*)dbg_nameptr;
        dbg_nameptr += sizeof(long);
        dbg_namelen -= sizeof(long);
      }

    *arg1=dbg_parms[0];
    *arg2=dbg_parms[1];
    *arg3=dbg_parms[2];
    *arg4=dbg_parms[3];
}

static void
kdbg_resolve_map(thread_t th_act, void *opaque)
{
  kd_threadmap *mapptr;
  krt_t *t = (krt_t *)opaque;

  if(t->count < t->maxcount)
    {
      mapptr=&t->map[t->count];
      mapptr->thread  = (unsigned int)th_act;
      (void) strncpy (mapptr->command, t->atts->task_comm,
                      sizeof(t->atts->task_comm)-1);
      mapptr->command[sizeof(t->atts->task_comm)-1] = '\0';

      /*
        Some kernel threads have no associated pid.
        We still need to mark the entry as valid.
      */
      if (t->atts->pid)
          mapptr->valid = t->atts->pid;
      else
          mapptr->valid = 1;

      t->count++;
    }
}

void
kdbg_mapinit(void)
{
        struct proc *p;
        struct krt akrt;
        int tts_count;    /* number of task-to-string structures */
        struct tts *tts_mapptr;
        unsigned int tts_mapsize = 0;
        unsigned int tts_maptomem=0;
        int i;


        if (kdebug_flags & KDBG_MAPINIT)
          return;

        /* Calculate the sizes of map buffers*/
        for (p = allproc.lh_first, kd_mapcount=0, tts_count=0; p; 
             p = p->p_list.le_next)
          {
            kd_mapcount += get_task_numacts((task_t)p->task);
            tts_count++;
          }

        /*
         * The proc count could change during buffer allocation,
         * so introduce a small fudge factor to bump up the
         * buffer sizes. This gives new tasks some chance of 
         * making into the tables.  Bump up by 10%.
         */
        kd_mapcount += kd_mapcount/10;
        tts_count += tts_count/10;

        kd_mapsize = kd_mapcount * sizeof(kd_threadmap);
        if((kmem_alloc(kernel_map, & kd_maptomem,
                       (vm_size_t)kd_mapsize) == KERN_SUCCESS))
        {
            kd_mapptr = (kd_threadmap *) kd_maptomem;
            bzero(kd_mapptr, kd_mapsize);
        }
        else
            kd_mapptr = (kd_threadmap *) 0;

        tts_mapsize = tts_count * sizeof(struct tts);
        if((kmem_alloc(kernel_map, & tts_maptomem,
                       (vm_size_t)tts_mapsize) == KERN_SUCCESS))
        {
            tts_mapptr = (struct tts *) tts_maptomem;
            bzero(tts_mapptr, tts_mapsize);
        }
        else
            tts_mapptr = (struct tts *) 0;


        /* 
         * We need to save the procs command string
         * and take a reference for each task associated
         * with a valid process
         */

        if (tts_mapptr) {
                for (p = allproc.lh_first, i=0; p && i < tts_count; 
                     p = p->p_list.le_next) {
                        if (p->p_flag & P_WEXIT)
                                continue;

                        if (p->task) {
                                task_reference(p->task);
                                tts_mapptr[i].task = p->task;
                                tts_mapptr[i].pid  = p->p_pid;
                                (void)strncpy(tts_mapptr[i].task_comm, p->p_comm, sizeof(tts_mapptr[i].task_comm) - 1);
                                i++;
                        }
                }
                tts_count = i;
        }


        if (kd_mapptr && tts_mapptr)
          {
            kdebug_flags |= KDBG_MAPINIT;
            /* Initialize thread map data */
            akrt.map = kd_mapptr;
            akrt.count = 0;
            akrt.maxcount = kd_mapcount;
            
            for (i=0; i < tts_count; i++)
              {
                akrt.atts = &tts_mapptr[i];
                task_act_iterate_wth_args(tts_mapptr[i].task, kdbg_resolve_map, &akrt);
                task_deallocate((task_t) tts_mapptr[i].task);
              }
            kmem_free(kernel_map, (vm_offset_t)tts_mapptr, tts_mapsize);
          }
}

static void
kdbg_clear(void)
{
        /*
         * Clean up the trace buffer
         * First make sure we're not in
         * the middle of cutting a trace
         */

        kdebug_enable &= ~KDEBUG_ENABLE_TRACE;
        kdebug_slowcheck = SLOW_NOLOG;

        /*
         * make sure the SLOW_NOLOG is seen
         * by everyone that might be trying
         * to cut a trace..
         */
        IOSleep(100);

        if (kdebug_enable & KDEBUG_ENABLE_ENTROPY)
                kdebug_slowcheck |= SLOW_ENTROPY;

        global_state_pid = -1;
        kdebug_flags &= (unsigned int)~KDBG_CKTYPES;
        kdebug_flags &= ~(KDBG_NOWRAP | KDBG_RANGECHECK | KDBG_VALCHECK);
        kdebug_flags &= ~(KDBG_PIDCHECK | KDBG_PIDEXCLUDE);

        delete_buffers();

        /* Clean up the thread map buffer */
        kdebug_flags &= ~KDBG_MAPINIT;
        kmem_free(kernel_map, (vm_offset_t)kd_mapptr, kd_mapsize);
        kd_mapptr = (kd_threadmap *) 0;
        kd_mapsize = 0;
        kd_mapcount = 0;
}

int
kdbg_setpid(kd_regtype *kdr)
{
  pid_t pid;
  int flag, ret=0;
  struct proc *p;

  pid = (pid_t)kdr->value1;
  flag = (int)kdr->value2;

  if (pid > 0)
    {
      if ((p = pfind(pid)) == NULL)
        ret = ESRCH;
      else
        {
          if (flag == 1)  /* turn on pid check for this and all pids */
            {
              kdebug_flags |= KDBG_PIDCHECK;
              kdebug_flags &= ~KDBG_PIDEXCLUDE;
              kdebug_slowcheck |= SLOW_CHECKS;

              p->p_flag |= P_KDEBUG;
            }
          else  /* turn off pid check for this pid value */
            {
              /* Don't turn off all pid checking though */
              /* kdebug_flags &= ~KDBG_PIDCHECK;*/   
              p->p_flag &= ~P_KDEBUG;
            }
        }
    }
  else
    ret = EINVAL;
  return(ret);
}

/* This is for pid exclusion in the trace buffer */
int
kdbg_setpidex(kd_regtype *kdr)
{
  pid_t pid;
  int flag, ret=0;
  struct proc *p;

  pid = (pid_t)kdr->value1;
  flag = (int)kdr->value2;

  if (pid > 0)
    {
      if ((p = pfind(pid)) == NULL)
        ret = ESRCH;
      else
        {
          if (flag == 1)  /* turn on pid exclusion */
            {
              kdebug_flags |= KDBG_PIDEXCLUDE;
              kdebug_flags &= ~KDBG_PIDCHECK;
              kdebug_slowcheck |= SLOW_CHECKS;

              p->p_flag |= P_KDEBUG;
            }
          else  /* turn off pid exclusion for this pid value */
            {
              /* Don't turn off all pid exclusion though */
              /* kdebug_flags &= ~KDBG_PIDEXCLUDE;*/   
              p->p_flag &= ~P_KDEBUG;
            }
        }
    }
  else
    ret = EINVAL;
  return(ret);
}

/* This is for setting a maximum decrementer value */
int
kdbg_setrtcdec(kd_regtype *kdr)
{
  int ret=0;
  natural_t decval;

  decval = (natural_t)kdr->value1;

  if (decval && decval < KDBG_MINRTCDEC)
        ret = EINVAL;
#ifdef ppc
        else {
                maxDec = decval ? decval : 0x7FFFFFFF;  /* Set or reset the max decrementer */
        }
#else
        else
                ret = ENOTSUP;
#endif /* ppc */

  return(ret);
}

int
kdbg_setreg(kd_regtype * kdr)
{
        int ret=0;
        unsigned int val_1, val_2, val;
        switch (kdr->type) {
        
        case KDBG_CLASSTYPE :
                val_1 = (kdr->value1 & 0xff);
                val_2 = (kdr->value2 & 0xff);
                kdlog_beg = (val_1<<24);
                kdlog_end = (val_2<<24);
                kdebug_flags &= (unsigned int)~KDBG_CKTYPES;
                kdebug_flags &= ~KDBG_VALCHECK;       /* Turn off specific value check  */
                kdebug_flags |= (KDBG_RANGECHECK | KDBG_CLASSTYPE);
                kdebug_slowcheck |= SLOW_CHECKS;
                break;
        case KDBG_SUBCLSTYPE :
                val_1 = (kdr->value1 & 0xff);
                val_2 = (kdr->value2 & 0xff);
                val = val_2 + 1;
                kdlog_beg = ((val_1<<24) | (val_2 << 16));
                kdlog_end = ((val_1<<24) | (val << 16));
                kdebug_flags &= (unsigned int)~KDBG_CKTYPES;
                kdebug_flags &= ~KDBG_VALCHECK;       /* Turn off specific value check  */
                kdebug_flags |= (KDBG_RANGECHECK | KDBG_SUBCLSTYPE);
                kdebug_slowcheck |= SLOW_CHECKS;
                break;
        case KDBG_RANGETYPE :
                kdlog_beg = (kdr->value1);
                kdlog_end = (kdr->value2);
                kdebug_flags &= (unsigned int)~KDBG_CKTYPES;
                kdebug_flags &= ~KDBG_VALCHECK;       /* Turn off specific value check  */
                kdebug_flags |= (KDBG_RANGECHECK | KDBG_RANGETYPE);
                kdebug_slowcheck |= SLOW_CHECKS;
                break;
        case KDBG_VALCHECK:
                kdlog_value1 = (kdr->value1);
                kdlog_value2 = (kdr->value2);
                kdlog_value3 = (kdr->value3);
                kdlog_value4 = (kdr->value4);
                kdebug_flags &= (unsigned int)~KDBG_CKTYPES;
                kdebug_flags &= ~KDBG_RANGECHECK;    /* Turn off range check */
                kdebug_flags |= KDBG_VALCHECK;       /* Turn on specific value check  */
                kdebug_slowcheck |= SLOW_CHECKS;
                break;
        case KDBG_TYPENONE :
                kdebug_flags &= (unsigned int)~KDBG_CKTYPES;

                if ( (kdebug_flags & (KDBG_RANGECHECK | KDBG_VALCHECK | KDBG_PIDCHECK | KDBG_PIDEXCLUDE)) )
                        kdebug_slowcheck |= SLOW_CHECKS;
                else
                        kdebug_slowcheck &= ~SLOW_CHECKS;

                kdlog_beg = 0;
                kdlog_end = 0;
                break;
        default :
                ret = EINVAL;
                break;
        }
        return(ret);
}

int
kdbg_getreg(__unused kd_regtype * kdr)
{
#if 0   
        int i,j, ret=0;
        unsigned int val_1, val_2, val;

        switch (kdr->type) {
        case KDBG_CLASSTYPE :
                val_1 = (kdr->value1 & 0xff);
                val_2 = val_1 + 1;
                kdlog_beg = (val_1<<24);
                kdlog_end = (val_2<<24);
                kdebug_flags &= (unsigned int)~KDBG_CKTYPES;
                kdebug_flags |= (KDBG_RANGECHECK | KDBG_CLASSTYPE);
                break;
        case KDBG_SUBCLSTYPE :
                val_1 = (kdr->value1 & 0xff);
                val_2 = (kdr->value2 & 0xff);
                val = val_2 + 1;
                kdlog_beg = ((val_1<<24) | (val_2 << 16));
                kdlog_end = ((val_1<<24) | (val << 16));
                kdebug_flags &= (unsigned int)~KDBG_CKTYPES;
                kdebug_flags |= (KDBG_RANGECHECK | KDBG_SUBCLSTYPE);
                break;
        case KDBG_RANGETYPE :
                kdlog_beg = (kdr->value1);
                kdlog_end = (kdr->value2);
                kdebug_flags &= (unsigned int)~KDBG_CKTYPES;
                kdebug_flags |= (KDBG_RANGECHECK | KDBG_RANGETYPE);
                break;
        case KDBG_TYPENONE :
                kdebug_flags &= (unsigned int)~KDBG_CKTYPES;
                kdlog_beg = 0;
                kdlog_end = 0;
                break;
        default :
                ret = EINVAL;
                break;
        }
#endif /* 0 */
        return(EINVAL);
}


int
kdbg_readmap(user_addr_t buffer, size_t *number)
{
  int avail = *number;
  int ret = 0;
  unsigned int count = 0;

  count = avail/sizeof (kd_threadmap);

  if (count && (count <= kd_mapcount))
    {
      if((kdebug_flags & KDBG_MAPINIT) && kd_mapsize && kd_mapptr)
        {
          if (*number < kd_mapsize)
            ret=EINVAL;
          else
            {
              if (copyout(kd_mapptr, buffer, kd_mapsize))
                ret=EINVAL;
            }
        }
      else
        ret=EINVAL;
    }
  else
    ret=EINVAL;

  if ((kdebug_flags & KDBG_MAPINIT) && kd_mapsize && kd_mapptr)
    {
      kmem_free(kernel_map, (vm_offset_t)kd_mapptr, kd_mapsize);
      kdebug_flags &= ~KDBG_MAPINIT;
      kd_mapsize = 0;
      kd_mapptr = (kd_threadmap *) 0;
      kd_mapcount = 0;
    }  

  return(ret);
}

int
kdbg_getentropy (user_addr_t buffer, size_t *number, int ms_timeout)
{
  int avail = *number;
  int ret = 0;

  if (kd_entropy_buffer)
    return(EBUSY);

  kd_entropy_count = avail/sizeof(mach_timespec_t);
  kd_entropy_bufsize = kd_entropy_count * sizeof(mach_timespec_t);
  kd_entropy_indx = 0;

  /* Enforce maximum entropy entries here if needed */

  /* allocate entropy buffer */
  if (kmem_alloc(kernel_map, &kd_entropy_buftomem,
                 (vm_size_t)kd_entropy_bufsize) == KERN_SUCCESS)
    {
      kd_entropy_buffer = (uint64_t *) kd_entropy_buftomem;
    }
  else
    {
      kd_entropy_buffer = (uint64_t *) 0;
      kd_entropy_count = 0;
      kd_entropy_indx = 0;
      return (EINVAL);
    }

  if (ms_timeout < 10)
    ms_timeout = 10;

  /* Enable entropy sampling */
  kdebug_enable |= KDEBUG_ENABLE_ENTROPY;
  kdebug_slowcheck |= SLOW_ENTROPY;

  ret = tsleep (kdbg_getentropy, PRIBIO | PCATCH, "kd_entropy", (ms_timeout/(1000/HZ)));

  /* Disable entropy sampling */
  kdebug_enable &= ~KDEBUG_ENABLE_ENTROPY;
  kdebug_slowcheck &= ~SLOW_ENTROPY;

  *number = 0;
  ret = 0;

  if (kd_entropy_indx > 0)
    {
      /* copyout the buffer */
      if (copyout(kd_entropy_buffer, buffer, kd_entropy_indx * sizeof(mach_timespec_t)))
          ret = EINVAL;
      else
          *number = kd_entropy_indx;
    }

  /* Always cleanup */
  kd_entropy_count = 0;
  kd_entropy_indx = 0;
  kd_entropy_buftomem = 0;
  kmem_free(kernel_map, (vm_offset_t)kd_entropy_buffer, kd_entropy_bufsize);
  kd_entropy_buffer = (uint64_t *) 0;
  return(ret);
}


/*
 * This function is provided for the CHUD toolkit only.
 *    int val:
 *        zero disables kdebug_chudhook function call
 *        non-zero enables kdebug_chudhook function call
 *    char *fn:
 *        address of the enabled kdebug_chudhook function
*/

void
kdbg_control_chud(int val, void *fn)
{
        if (val) {
                /* enable chudhook */
                kdebug_chudhook = fn;
                kdebug_enable |= KDEBUG_ENABLE_CHUD;
        }
        else {
                /* disable chudhook */
                kdebug_enable &= ~KDEBUG_ENABLE_CHUD;
                kdebug_chudhook = 0;
        }
}

        
int
kdbg_control(int *name, __unused u_int namelen, user_addr_t where, size_t *sizep)
{
    int ret=0;
        size_t size=*sizep;
        unsigned int max_entries;
        unsigned int value = name[1];
        kd_regtype kd_Reg;
        kbufinfo_t kd_bufinfo;
        pid_t curpid;
        struct proc *p, *curproc;


        kdbg_lock_init();

        if ( !(kdebug_flags & KDBG_LOCKINIT))
                return(ENOMEM);

        lck_mtx_lock(kd_trace_mtx_sysctl);

        if (name[0] == KERN_KDGETBUF) {
            /* 
             * Does not alter the global_state_pid
             * This is a passive request.
             */
            if (size < sizeof(kd_bufinfo.nkdbufs)) {
                /* 
                 * There is not enough room to return even
                 * the first element of the info structure.
                 */
                lck_mtx_unlock(kd_trace_mtx_sysctl);

                return(EINVAL);
            }
            kd_bufinfo.nkdbufs = nkdbufs;
            kd_bufinfo.nkdthreads = kd_mapsize / sizeof(kd_threadmap);

            if ( (kdebug_slowcheck & SLOW_NOLOG) )
                kd_bufinfo.nolog = 1;
            else
                kd_bufinfo.nolog = 0;
            kd_bufinfo.flags = kdebug_flags;
            kd_bufinfo.bufid = global_state_pid;
           
            if (size >= sizeof(kd_bufinfo)) {
            /*
                     * Provide all the info we have
                    */
                if (copyout (&kd_bufinfo, where, sizeof(kd_bufinfo))) {
                        lck_mtx_unlock(kd_trace_mtx_sysctl);

                return(EINVAL);
                    }
            }
            else {
                /* 
                         * For backwards compatibility, only provide
                         * as much info as there is room for.
                         */
                if (copyout (&kd_bufinfo, where, size)) {
                        lck_mtx_unlock(kd_trace_mtx_sysctl);

                        return(EINVAL);
                    }
            }
            lck_mtx_unlock(kd_trace_mtx_sysctl);

            return(0);
        } else if (name[0] == KERN_KDGETENTROPY) {
            if (kd_entropy_buffer)
                ret = EBUSY;
            else
                ret = kdbg_getentropy(where, sizep, value);
            lck_mtx_unlock(kd_trace_mtx_sysctl);

            return (ret);
        }
        
        if ((curproc = current_proc()) != NULL)
            curpid = curproc->p_pid;
        else {
            lck_mtx_unlock(kd_trace_mtx_sysctl);

            return (ESRCH);
        }
        if (global_state_pid == -1)
            global_state_pid = curpid;
        else if (global_state_pid != curpid) {
            if ((p = pfind(global_state_pid)) == NULL) {
                /*
                 * The global pid no longer exists
                 */
                global_state_pid = curpid;
            } else {
                /*
                 * The global pid exists, deny this request
                 */
                lck_mtx_unlock(kd_trace_mtx_sysctl);

                return(EBUSY);
            }
        }

        switch(name[0]) {
                case KERN_KDEFLAGS:
                        value &= KDBG_USERFLAGS;
                        kdebug_flags |= value;
                        break;
                case KERN_KDDFLAGS:
                        value &= KDBG_USERFLAGS;
                        kdebug_flags &= ~value;
                        break;
                case KERN_KDENABLE:    /* used to enable or disable */
                  if (value)
                    {
                      /* enable only if buffer is initialized */
                      if (!(kdebug_flags & KDBG_BUFINIT))
                        {
                          ret=EINVAL;
                          break;
                        }
                      kdbg_mapinit();

                      kdebug_enable |= KDEBUG_ENABLE_TRACE;
                      kdebug_slowcheck &= ~SLOW_NOLOG;
                    }
                  else
                    {
                      kdebug_enable &= ~KDEBUG_ENABLE_TRACE;
                      kdebug_slowcheck |= SLOW_NOLOG;
                    }
                  break;
                case KERN_KDSETBUF:
                  /* We allow a maximum buffer size of 25% of either ram or max mapped address, whichever is smaller */
                  /* 'value' is the desired number of trace entries */
                        max_entries = (sane_size/4) / sizeof(kd_buf);
                        if (value <= max_entries)
                                nkdbufs = value;
                        else
                          nkdbufs = max_entries;
                        break;
                case KERN_KDSETUP:
                        ret=kdbg_reinit();
                        break;
                case KERN_KDREMOVE:
                        kdbg_clear();
                        break;
                case KERN_KDSETREG:
                        if(size < sizeof(kd_regtype)) {
                                ret=EINVAL;
                                break;
                        }
                        if (copyin(where, &kd_Reg, sizeof(kd_regtype))) {
                                ret= EINVAL;
                                break;
                        }
                        ret = kdbg_setreg(&kd_Reg);
                        break;
                case KERN_KDGETREG:
                        if(size < sizeof(kd_regtype)) {
                                ret = EINVAL;
                                break;
                        }
                        ret = kdbg_getreg(&kd_Reg);
                        if (copyout(&kd_Reg, where, sizeof(kd_regtype))){
                                ret=EINVAL;
                        }
                        break;
                case KERN_KDREADTR:
                        ret = kdbg_read(where, sizep);
                        break;
                case KERN_KDPIDTR:
                        if (size < sizeof(kd_regtype)) {
                                ret = EINVAL;
                                break;
                        }
                        if (copyin(where, &kd_Reg, sizeof(kd_regtype))) {
                                ret= EINVAL;
                                break;
                        }
                        ret = kdbg_setpid(&kd_Reg);
                        break;
                case KERN_KDPIDEX:
                        if (size < sizeof(kd_regtype)) {
                                ret = EINVAL;
                                break;
                        }
                        if (copyin(where, &kd_Reg, sizeof(kd_regtype))) {
                                ret= EINVAL;
                                break;
                        }
                        ret = kdbg_setpidex(&kd_Reg);
                        break;
                case KERN_KDTHRMAP:
                        ret = kdbg_readmap(where, sizep);
                        break;
                case KERN_KDSETRTCDEC:
                        if (size < sizeof(kd_regtype)) {
                                ret = EINVAL;
                                break;
                        }
                        if (copyin(where, &kd_Reg, sizeof(kd_regtype))) {
                                ret= EINVAL;
                                break;
                        }
                        ret = kdbg_setrtcdec(&kd_Reg);
                        break;
                       
                default:
                        ret= EINVAL;
        }
        lck_mtx_unlock(kd_trace_mtx_sysctl);

        return(ret);
}


/*
 * This code can run concurrently with kernel_debug_internal()
 * without the need of any locks, because all reads of kd_bufptr[i],
 * which get modified by kernel_debug_internal(), are safe.
 */
int
kdbg_read(user_addr_t buffer, size_t *number)
{
        unsigned int count;
        unsigned int cpu;
        int mincpu;
        uint64_t  mintime, t, last_wrap_time;
        int last_wrap_cpu;
        int error = 0;
        kd_buf *tempbuf;
        uint32_t tempbuf_count;
        uint32_t tempbuf_number;
        unsigned int old_kdebug_flags, new_kdebug_flags;
        unsigned int old_kdebug_slowcheck, new_kdebug_slowcheck;
        count = *number/sizeof(kd_buf);
        *number = 0;

        if (count == 0 || !(kdebug_flags & KDBG_BUFINIT) || kdcopybuf == 0)
                return EINVAL;

        /*
         * because we hold kd_trace_mtx_sysctl, no other control threads can 
         * be playing with kdebug_flags... the code that cuts new events could
         * be running, but it only reads kdebug_flags, it doesn't write it..
         * use an OSCompareAndSwap to make sure the other processors see the 
         * change of state immediately, not to protect against 2 threads racing to update it
         */
        old_kdebug_slowcheck = kdebug_slowcheck;
        do {
                old_kdebug_flags = kdebug_flags;
                new_kdebug_flags = old_kdebug_flags & ~KDBG_WRAPPED;
                new_kdebug_flags |= KDBG_NOWRAP;
        } while ( !OSCompareAndSwap((UInt32)old_kdebug_flags, (UInt32)new_kdebug_flags, (UInt32 *)&kdebug_flags));

        last_wrap_time = 0;
        last_wrap_cpu  = -1;

        for (cpu = 0; cpu < kd_cpus; cpu++) {
                kd_buf *cur_bufptr;
                
                if ((cur_bufptr = kdbip[cpu].kd_bufptr) >= kdbip[cpu].kd_buflast)
                        cur_bufptr = kdbip[cpu].kd_buffer;

                if (kdbip[cpu].kd_wrapped) {
                        kdbip[cpu].kd_wrapped = 0;
                        kdbip[cpu].kd_readlast = cur_bufptr;
                        kdbip[cpu].kd_stop = cur_bufptr;

                        if (kd_cpus > 1 && ((cur_bufptr->timestamp & KDBG_TIMESTAMP_MASK) > last_wrap_time)) {
                                last_wrap_time = cur_bufptr->timestamp & KDBG_TIMESTAMP_MASK;
                                last_wrap_cpu = cpu;
                        }
                } else {
                        if (kdbip[cpu].kd_readlast == cur_bufptr)
                                kdbip[cpu].kd_stop = 0;
                        else
                                kdbip[cpu].kd_stop = cur_bufptr;
                }
        }
        if (count > nkdbufs)
                count = nkdbufs;

        if ((tempbuf_count = count) > KDCOPYBUF_COUNT)
                tempbuf_count = KDCOPYBUF_COUNT;

        while (count) {
                tempbuf = kdcopybuf;
                tempbuf_number = 0;

                while (tempbuf_count) {
                        mintime = 0xffffffffffffffffULL; /* all actual timestamps are below */
                        mincpu = -1;

                        for (cpu = 0; cpu < kd_cpus; cpu++) {
                                if (kdbip[cpu].kd_stop == 0)     /* empty buffer */
                                        continue;
                                t = kdbip[cpu].kd_readlast[0].timestamp & KDBG_TIMESTAMP_MASK;

                                if (t < mintime) {
                                        mintime = t;
                                        mincpu = cpu;
                                }
                        }
                        if (mincpu < 0)
                                /*
                                 * all buffers ran empty early
                                 */
                                break;

                        if (last_wrap_cpu == mincpu) {
                                tempbuf->debugid = MISCDBG_CODE(DBG_BUFFER, 0) | DBG_FUNC_NONE;
                                tempbuf->arg1 = 0;
                                tempbuf->arg2 = 0;
                                tempbuf->arg3 = 0;
                                tempbuf->arg4 = 0;
                                tempbuf->arg5 = (int)current_thread();
                  
                                tempbuf->timestamp = last_wrap_time | (((uint64_t)last_wrap_cpu) << KDBG_CPU_SHIFT);

                                tempbuf++;

                                last_wrap_cpu = -1;

                        } else {
                                *(tempbuf++) = kdbip[mincpu].kd_readlast[0];

                                kdbip[mincpu].kd_readlast++;

                                if (kdbip[mincpu].kd_readlast == kdbip[mincpu].kd_buflast)
                                        kdbip[mincpu].kd_readlast = kdbip[mincpu].kd_buffer;
                                if (kdbip[mincpu].kd_readlast == kdbip[mincpu].kd_stop)
                                        kdbip[mincpu].kd_stop = 0;
                        }
                        tempbuf_count--;
                        tempbuf_number++;
                }
                if (tempbuf_number) {
                        if ((error = copyout(kdcopybuf, buffer, tempbuf_number * sizeof(kd_buf)))) {
                                *number = 0;
                                error = EINVAL;
                                break;
                        }
                        count   -= tempbuf_number;
                        *number += tempbuf_number;
                        buffer  += (tempbuf_number * sizeof(kd_buf));
                }
                if (tempbuf_count)
                       /*
                        * all trace buffers are empty
                        */
                        break;

                if ((tempbuf_count = count) > KDCOPYBUF_COUNT)
                        tempbuf_count = KDCOPYBUF_COUNT;
        }
        if ( !(old_kdebug_flags & KDBG_NOWRAP)) {
                do {
                        old_kdebug_flags = kdebug_flags;
                        new_kdebug_flags = old_kdebug_flags & ~KDBG_NOWRAP;
                } while ( !OSCompareAndSwap((UInt32)old_kdebug_flags, (UInt32)new_kdebug_flags, (UInt32 *)&kdebug_flags));

                if ( !(old_kdebug_slowcheck & SLOW_NOLOG)) {
                        do {
                                old_kdebug_slowcheck = kdebug_slowcheck;
                                new_kdebug_slowcheck = old_kdebug_slowcheck & ~SLOW_NOLOG;
                        } while ( !OSCompareAndSwap((UInt32)old_kdebug_slowcheck, (UInt32)new_kdebug_slowcheck, (UInt32 *)&kdebug_slowcheck));
                }
        }
        return (error);
}


unsigned char *getProcName(struct proc *proc);
unsigned char *getProcName(struct proc *proc) {

        return (unsigned char *) &proc->p_comm; /* Return pointer to the proc name */

}

#define STACKSHOT_SUBSYS_LOCK() lck_mtx_lock(&stackshot_subsys_mutex)
#define STACKSHOT_SUBSYS_UNLOCK() lck_mtx_unlock(&stackshot_subsys_mutex)
#ifdef __i386__
#define TRAP_DEBUGGER __asm__ volatile("int3");
#endif
#ifdef __ppc__
#define TRAP_DEBUGGER   __asm__ volatile("tw 4,r3,r3");
#endif

#define SANE_TRACEBUF_SIZE 2*1024*1024

/* Initialize the mutex governing access to the stack snapshot subsystem */
__private_extern__ void
stackshot_lock_init( void )
{
        stackshot_subsys_lck_grp_attr = lck_grp_attr_alloc_init();

        stackshot_subsys_lck_grp = lck_grp_alloc_init("stackshot_subsys_lock", stackshot_subsys_lck_grp_attr);

        stackshot_subsys_lck_attr = lck_attr_alloc_init();

        lck_mtx_init(&stackshot_subsys_mutex, stackshot_subsys_lck_grp, stackshot_subsys_lck_attr);
}

/*
 * stack_snapshot:   Obtains a coherent set of stack traces for all threads
 *                   on the system, tracing both kernel and user stacks
 *                   where available. Uses machine specific trace routines
 *                   for ppc, ppc64 and x86.
 * Inputs:           uap->pid - process id of process to be traced, or -1
 *                   for the entire system
 *                   uap->tracebuf - address of the user space destination
 *                   buffer 
 *                   uap->tracebuf_size - size of the user space trace buffer
 *                   uap->options - various options, including the maximum
 *                   number of frames to trace.
 * Outputs:          EPERM if the caller is not privileged
 *                   EINVAL if the supplied trace buffer isn't sanely sized
 *                   ENOMEM if we don't have enough memory to satisfy the
 *                   request
 *                   ENOENT if the target pid isn't found
 *                   ENOSPC if the supplied buffer is insufficient
 *                   *retval contains the number of bytes traced, if successful
 *                   and -1 otherwise. If the request failed due to
 *                   tracebuffer exhaustion, we copyout as much as possible.
 */
int
stack_snapshot(struct proc *p, register struct stack_snapshot_args *uap, register_t *retval) {
        int error = 0;

        if ((error = suser(kauth_cred_get(), &p->p_acflag)))
                return(error);

        return stack_snapshot2(uap->pid, uap->tracebuf, uap->tracebuf_size,
            uap->options, retval);
}

int
stack_snapshot2(pid_t pid, user_addr_t tracebuf, uint32_t tracebuf_size, uint32_t options, register_t *retval)
{
        int error = 0;
        unsigned bytesTraced = 0;

        *retval = -1;
/* Serialize tracing */ 
        STACKSHOT_SUBSYS_LOCK();
        
        if ((tracebuf_size <= 0) || (tracebuf_size > SANE_TRACEBUF_SIZE)) {
                error = EINVAL;
                goto error_exit;
        }

        MALLOC(stackshot_snapbuf, void *, tracebuf_size, M_TEMP, M_WAITOK);

        if (stackshot_snapbuf == NULL) {
                error = ENOMEM;
                goto error_exit;
        }
/* Preload trace parameters*/   
        kdp_snapshot_preflight(pid, stackshot_snapbuf, tracebuf_size, options);

/* Trap to the debugger to obtain a coherent stack snapshot; this populates
 * the trace buffer
 */
        TRAP_DEBUGGER;

        bytesTraced = kdp_stack_snapshot_bytes_traced();
                        
        if (bytesTraced > 0) {
                if ((error = copyout(stackshot_snapbuf, tracebuf,
                        ((bytesTraced < tracebuf_size) ?
                            bytesTraced : tracebuf_size))))
                        goto error_exit;
                *retval = bytesTraced;
        }
        else {
                error = ENOENT;
                goto error_exit;
        }

        error = kdp_stack_snapshot_geterror();
        if (error == -1) {
                error = ENOSPC;
                *retval = -1;
                goto error_exit;
        }

error_exit:
        if (stackshot_snapbuf != NULL)
                FREE(stackshot_snapbuf, M_TEMP);
        stackshot_snapbuf = NULL;
        STACKSHOT_SUBSYS_UNLOCK();
        return error;
}