- Copy stable/10 (r259064) to releng/10.0 as part of the

[FreeBSD/releng/10.0.git] / cddl / contrib / opensolaris / lib / libdtrace / common / dt_proc.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 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * DTrace Process Control
 *
 * This file provides a set of routines that permit libdtrace and its clients
 * to create and grab process handles using libproc, and to share these handles
 * between library mechanisms that need libproc access, such as ustack(), and
 * client mechanisms that need libproc access, such as dtrace(1M) -c and -p.
 * The library provides several mechanisms in the libproc control layer:
 *
 * Reference Counting: The library code and client code can independently grab
 * the same process handles without interfering with one another.  Only when
 * the reference count drops to zero and the handle is not being cached (see
 * below for more information on caching) will Prelease() be called on it.
 *
 * Handle Caching: If a handle is grabbed PGRAB_RDONLY (e.g. by ustack()) and
 * the reference count drops to zero, the handle is not immediately released.
 * Instead, libproc handles are maintained on dph_lrulist in order from most-
 * recently accessed to least-recently accessed.  Idle handles are maintained
 * until a pre-defined LRU cache limit is exceeded, permitting repeated calls
 * to ustack() to avoid the overhead of releasing and re-grabbing processes.
 *
 * Process Control: For processes that are grabbed for control (~PGRAB_RDONLY)
 * or created by dt_proc_create(), a control thread is created to provide
 * callbacks on process exit and symbol table caching on dlopen()s.
 *
 * MT-Safety: Libproc is not MT-Safe, so dt_proc_lock() and dt_proc_unlock()
 * are provided to synchronize access to the libproc handle between libdtrace
 * code and client code and the control thread's use of the ps_prochandle.
 *
 * NOTE: MT-Safety is NOT provided for libdtrace itself, or for use of the
 * dtrace_proc_grab/dtrace_proc_create mechanisms.  Like all exported libdtrace
 * calls, these are assumed to be MT-Unsafe.  MT-Safety is ONLY provided for
 * synchronization between libdtrace control threads and the client thread.
 *
 * The ps_prochandles themselves are maintained along with a dt_proc_t struct
 * in a hash table indexed by PID.  This provides basic locking and reference
 * counting.  The dt_proc_t is also maintained in LRU order on dph_lrulist.
 * The dph_lrucnt and dph_lrulim count the number of cacheable processes and
 * the current limit on the number of actively cached entries.
 *
 * The control thread for a process establishes breakpoints at the rtld_db
 * locations of interest, updates mappings and symbol tables at these points,
 * and handles exec and fork (by always following the parent).  The control
 * thread automatically exits when the process dies or control is lost.
 *
 * A simple notification mechanism is provided for libdtrace clients using
 * dtrace_handle_proc() for notification of PS_UNDEAD or PS_LOST events.  If
 * such an event occurs, the dt_proc_t itself is enqueued on a notification
 * list and the control thread broadcasts to dph_cv.  dtrace_sleep() will wake
 * up using this condition and will then call the client handler as necessary.
 */

#include <sys/wait.h>
#if defined(sun)
#include <sys/lwp.h>
#endif
#include <strings.h>
#include <signal.h>
#include <assert.h>
#include <errno.h>

#include <dt_proc.h>
#include <dt_pid.h>
#include <dt_impl.h>

#if !defined(sun)
#include <sys/syscall.h>
#include <libproc_compat.h>
#define SYS_forksys SYS_fork
#endif

#define IS_SYS_EXEC(w)  (w == SYS_execve)
#define IS_SYS_FORK(w)  (w == SYS_vfork || w == SYS_forksys)

static dt_bkpt_t *
dt_proc_bpcreate(dt_proc_t *dpr, uintptr_t addr, dt_bkpt_f *func, void *data)
{
        struct ps_prochandle *P = dpr->dpr_proc;
        dt_bkpt_t *dbp;

        assert(DT_MUTEX_HELD(&dpr->dpr_lock));

        if ((dbp = dt_zalloc(dpr->dpr_hdl, sizeof (dt_bkpt_t))) != NULL) {
                dbp->dbp_func = func;
                dbp->dbp_data = data;
                dbp->dbp_addr = addr;

                if (Psetbkpt(P, dbp->dbp_addr, &dbp->dbp_instr) == 0)
                        dbp->dbp_active = B_TRUE;

                dt_list_append(&dpr->dpr_bps, dbp);
        }

        return (dbp);
}

static void
dt_proc_bpdestroy(dt_proc_t *dpr, int delbkpts)
{
        int state = Pstate(dpr->dpr_proc);
        dt_bkpt_t *dbp, *nbp;

        assert(DT_MUTEX_HELD(&dpr->dpr_lock));

        for (dbp = dt_list_next(&dpr->dpr_bps); dbp != NULL; dbp = nbp) {
                if (delbkpts && dbp->dbp_active &&
                    state != PS_LOST && state != PS_UNDEAD) {
                        (void) Pdelbkpt(dpr->dpr_proc,
                            dbp->dbp_addr, dbp->dbp_instr);
                }
                nbp = dt_list_next(dbp);
                dt_list_delete(&dpr->dpr_bps, dbp);
                dt_free(dpr->dpr_hdl, dbp);
        }
}

static void
dt_proc_bpmatch(dtrace_hdl_t *dtp, dt_proc_t *dpr)
{
#if defined(sun)
        const lwpstatus_t *psp = &Pstatus(dpr->dpr_proc)->pr_lwp;
#else
        unsigned long pc;
#endif
        dt_bkpt_t *dbp;

        assert(DT_MUTEX_HELD(&dpr->dpr_lock));

#if !defined(sun)
        proc_regget(dpr->dpr_proc, REG_PC, &pc);
        proc_bkptregadj(&pc);
#endif

        for (dbp = dt_list_next(&dpr->dpr_bps);
            dbp != NULL; dbp = dt_list_next(dbp)) {
#if defined(sun)
                if (psp->pr_reg[R_PC] == dbp->dbp_addr)
                        break;
#else
                if (pc == dbp->dbp_addr)
                        break;
#endif
        }

        if (dbp == NULL) {
                dt_dprintf("pid %d: spurious breakpoint wakeup for %lx\n",
#if defined(sun)
                    (int)dpr->dpr_pid, (ulong_t)psp->pr_reg[R_PC]);
#else
                    (int)dpr->dpr_pid, pc);
#endif
                return;
        }

        dt_dprintf("pid %d: hit breakpoint at %lx (%lu)\n",
            (int)dpr->dpr_pid, (ulong_t)dbp->dbp_addr, ++dbp->dbp_hits);

        dbp->dbp_func(dtp, dpr, dbp->dbp_data);
        (void) Pxecbkpt(dpr->dpr_proc, dbp->dbp_instr);
}

static void
dt_proc_bpenable(dt_proc_t *dpr)
{
        dt_bkpt_t *dbp;

        assert(DT_MUTEX_HELD(&dpr->dpr_lock));

        for (dbp = dt_list_next(&dpr->dpr_bps);
            dbp != NULL; dbp = dt_list_next(dbp)) {
                if (!dbp->dbp_active && Psetbkpt(dpr->dpr_proc,
                    dbp->dbp_addr, &dbp->dbp_instr) == 0)
                        dbp->dbp_active = B_TRUE;
        }

        dt_dprintf("breakpoints enabled\n");
}

static void
dt_proc_bpdisable(dt_proc_t *dpr)
{
        dt_bkpt_t *dbp;

        assert(DT_MUTEX_HELD(&dpr->dpr_lock));

        for (dbp = dt_list_next(&dpr->dpr_bps);
            dbp != NULL; dbp = dt_list_next(dbp)) {
                if (dbp->dbp_active && Pdelbkpt(dpr->dpr_proc,
                    dbp->dbp_addr, dbp->dbp_instr) == 0)
                        dbp->dbp_active = B_FALSE;
        }

        dt_dprintf("breakpoints disabled\n");
}

static void
dt_proc_notify(dtrace_hdl_t *dtp, dt_proc_hash_t *dph, dt_proc_t *dpr,
    const char *msg)
{
        dt_proc_notify_t *dprn = dt_alloc(dtp, sizeof (dt_proc_notify_t));

        if (dprn == NULL) {
                dt_dprintf("failed to allocate notification for %d %s\n",
                    (int)dpr->dpr_pid, msg);
        } else {
                dprn->dprn_dpr = dpr;
                if (msg == NULL)
                        dprn->dprn_errmsg[0] = '\0';
                else
                        (void) strlcpy(dprn->dprn_errmsg, msg,
                            sizeof (dprn->dprn_errmsg));

                (void) pthread_mutex_lock(&dph->dph_lock);

                dprn->dprn_next = dph->dph_notify;
                dph->dph_notify = dprn;

                (void) pthread_cond_broadcast(&dph->dph_cv);
                (void) pthread_mutex_unlock(&dph->dph_lock);
        }
}

/*
 * Check to see if the control thread was requested to stop when the victim
 * process reached a particular event (why) rather than continuing the victim.
 * If 'why' is set in the stop mask, we wait on dpr_cv for dt_proc_continue().
 * If 'why' is not set, this function returns immediately and does nothing.
 */
static void
dt_proc_stop(dt_proc_t *dpr, uint8_t why)
{
        assert(DT_MUTEX_HELD(&dpr->dpr_lock));
        assert(why != DT_PROC_STOP_IDLE);

        if (dpr->dpr_stop & why) {
                dpr->dpr_stop |= DT_PROC_STOP_IDLE;
                dpr->dpr_stop &= ~why;

                (void) pthread_cond_broadcast(&dpr->dpr_cv);

                /*
                 * We disable breakpoints while stopped to preserve the
                 * integrity of the program text for both our own disassembly
                 * and that of the kernel.
                 */
                dt_proc_bpdisable(dpr);

                while (dpr->dpr_stop & DT_PROC_STOP_IDLE)
                        (void) pthread_cond_wait(&dpr->dpr_cv, &dpr->dpr_lock);

                dt_proc_bpenable(dpr);
        }
}

/*ARGSUSED*/
static void
dt_proc_bpmain(dtrace_hdl_t *dtp, dt_proc_t *dpr, const char *fname)
{
        dt_dprintf("pid %d: breakpoint at %s()\n", (int)dpr->dpr_pid, fname);
        dt_proc_stop(dpr, DT_PROC_STOP_MAIN);
}

static void
dt_proc_rdevent(dtrace_hdl_t *dtp, dt_proc_t *dpr, const char *evname)
{
        rd_event_msg_t rdm;
        rd_err_e err;

        if ((err = rd_event_getmsg(dpr->dpr_rtld, &rdm)) != RD_OK) {
                dt_dprintf("pid %d: failed to get %s event message: %s\n",
                    (int)dpr->dpr_pid, evname, rd_errstr(err));
                return;
        }

        dt_dprintf("pid %d: rtld event %s type=%d state %d\n",
            (int)dpr->dpr_pid, evname, rdm.type, rdm.u.state);

        switch (rdm.type) {
        case RD_DLACTIVITY:
                if (rdm.u.state != RD_CONSISTENT)
                        break;

                Pupdate_syms(dpr->dpr_proc);
                if (dt_pid_create_probes_module(dtp, dpr) != 0)
                        dt_proc_notify(dtp, dtp->dt_procs, dpr,
                            dpr->dpr_errmsg);

                break;
        case RD_PREINIT:
                Pupdate_syms(dpr->dpr_proc);
                dt_proc_stop(dpr, DT_PROC_STOP_PREINIT);
                break;
        case RD_POSTINIT:
                Pupdate_syms(dpr->dpr_proc);
                dt_proc_stop(dpr, DT_PROC_STOP_POSTINIT);
                break;
        }
}

static void
dt_proc_rdwatch(dt_proc_t *dpr, rd_event_e event, const char *evname)
{
        rd_notify_t rdn;
        rd_err_e err;

        if ((err = rd_event_addr(dpr->dpr_rtld, event, &rdn)) != RD_OK) {
                dt_dprintf("pid %d: failed to get event address for %s: %s\n",
                    (int)dpr->dpr_pid, evname, rd_errstr(err));
                return;
        }

        if (rdn.type != RD_NOTIFY_BPT) {
                dt_dprintf("pid %d: event %s has unexpected type %d\n",
                    (int)dpr->dpr_pid, evname, rdn.type);
                return;
        }

        (void) dt_proc_bpcreate(dpr, rdn.u.bptaddr,
#if defined(sun)
            (dt_bkpt_f *)dt_proc_rdevent, (void *)evname);
#else
            /* XXX ugly */
            (dt_bkpt_f *)dt_proc_rdevent, __DECONST(void *, evname));
#endif
}

/*
 * Common code for enabling events associated with the run-time linker after
 * attaching to a process or after a victim process completes an exec(2).
 */
static void
dt_proc_attach(dt_proc_t *dpr, int exec)
{
#if defined(sun)
        const pstatus_t *psp = Pstatus(dpr->dpr_proc);
#endif
        rd_err_e err;
        GElf_Sym sym;

        assert(DT_MUTEX_HELD(&dpr->dpr_lock));

        if (exec) {
#if defined(sun)
                if (psp->pr_lwp.pr_errno != 0)
                        return; /* exec failed: nothing needs to be done */
#endif

                dt_proc_bpdestroy(dpr, B_FALSE);
#if defined(sun)
                Preset_maps(dpr->dpr_proc);
#endif
        }
        if ((dpr->dpr_rtld = Prd_agent(dpr->dpr_proc)) != NULL &&
            (err = rd_event_enable(dpr->dpr_rtld, B_TRUE)) == RD_OK) {
#if defined(sun)
                dt_proc_rdwatch(dpr, RD_PREINIT, "RD_PREINIT");
#endif
                dt_proc_rdwatch(dpr, RD_POSTINIT, "RD_POSTINIT");
#if defined(sun)
                dt_proc_rdwatch(dpr, RD_DLACTIVITY, "RD_DLACTIVITY");
#endif
        } else {
                dt_dprintf("pid %d: failed to enable rtld events: %s\n",
                    (int)dpr->dpr_pid, dpr->dpr_rtld ? rd_errstr(err) :
                    "rtld_db agent initialization failed");
        }

        Pupdate_maps(dpr->dpr_proc);

        if (Pxlookup_by_name(dpr->dpr_proc, LM_ID_BASE,
            "a.out", "main", &sym, NULL) == 0) {
                (void) dt_proc_bpcreate(dpr, (uintptr_t)sym.st_value,
                    (dt_bkpt_f *)dt_proc_bpmain, "a.out`main");
        } else {
                dt_dprintf("pid %d: failed to find a.out`main: %s\n",
                    (int)dpr->dpr_pid, strerror(errno));
        }
}

/*
 * Wait for a stopped process to be set running again by some other debugger.
 * This is typically not required by /proc-based debuggers, since the usual
 * model is that one debugger controls one victim.  But DTrace, as usual, has
 * its own needs: the stop() action assumes that prun(1) or some other tool
 * will be applied to resume the victim process.  This could be solved by
 * adding a PCWRUN directive to /proc, but that seems like overkill unless
 * other debuggers end up needing this functionality, so we implement a cheap
 * equivalent to PCWRUN using the set of existing kernel mechanisms.
 *
 * Our intent is really not just to wait for the victim to run, but rather to
 * wait for it to run and then stop again for a reason other than the current
 * PR_REQUESTED stop.  Since PCWSTOP/Pstopstatus() can be applied repeatedly
 * to a stopped process and will return the same result without affecting the
 * victim, we can just perform these operations repeatedly until Pstate()
 * changes, the representative LWP ID changes, or the stop timestamp advances.
 * dt_proc_control() will then rediscover the new state and continue as usual.
 * When the process is still stopped in the same exact state, we sleep for a
 * brief interval before waiting again so as not to spin consuming CPU cycles.
 */
static void
dt_proc_waitrun(dt_proc_t *dpr)
{
printf("%s:%s(%d): DOODAD\n",__FUNCTION__,__FILE__,__LINE__);
#ifdef DOODAD
        struct ps_prochandle *P = dpr->dpr_proc;
        const lwpstatus_t *psp = &Pstatus(P)->pr_lwp;

        int krflag = psp->pr_flags & (PR_KLC | PR_RLC);
        timestruc_t tstamp = psp->pr_tstamp;
        lwpid_t lwpid = psp->pr_lwpid;

        const long wstop = PCWSTOP;
        int pfd = Pctlfd(P);

        assert(DT_MUTEX_HELD(&dpr->dpr_lock));
        assert(psp->pr_flags & PR_STOPPED);
        assert(Pstate(P) == PS_STOP);

        /*
         * While we are waiting for the victim to run, clear PR_KLC and PR_RLC
         * so that if the libdtrace client is killed, the victim stays stopped.
         * dt_proc_destroy() will also observe this and perform PRELEASE_HANG.
         */
        (void) Punsetflags(P, krflag);
        Psync(P);

        (void) pthread_mutex_unlock(&dpr->dpr_lock);

        while (!dpr->dpr_quit) {
                if (write(pfd, &wstop, sizeof (wstop)) == -1 && errno == EINTR)
                        continue; /* check dpr_quit and continue waiting */

                (void) pthread_mutex_lock(&dpr->dpr_lock);
                (void) Pstopstatus(P, PCNULL, 0);
                psp = &Pstatus(P)->pr_lwp;

                /*
                 * If we've reached a new state, found a new representative, or
                 * the stop timestamp has changed, restore PR_KLC/PR_RLC to its
                 * original setting and then return with dpr_lock held.
                 */
                if (Pstate(P) != PS_STOP || psp->pr_lwpid != lwpid ||
                    bcmp(&psp->pr_tstamp, &tstamp, sizeof (tstamp)) != 0) {
                        (void) Psetflags(P, krflag);
                        Psync(P);
                        return;
                }

                (void) pthread_mutex_unlock(&dpr->dpr_lock);
                (void) poll(NULL, 0, MILLISEC / 2);
        }

        (void) pthread_mutex_lock(&dpr->dpr_lock);
#endif
}

typedef struct dt_proc_control_data {
        dtrace_hdl_t *dpcd_hdl;                 /* DTrace handle */
        dt_proc_t *dpcd_proc;                   /* proccess to control */
} dt_proc_control_data_t;

/*
 * Main loop for all victim process control threads.  We initialize all the
 * appropriate /proc control mechanisms, and then enter a loop waiting for
 * the process to stop on an event or die.  We process any events by calling
 * appropriate subroutines, and exit when the victim dies or we lose control.
 *
 * The control thread synchronizes the use of dpr_proc with other libdtrace
 * threads using dpr_lock.  We hold the lock for all of our operations except
 * waiting while the process is running: this is accomplished by writing a
 * PCWSTOP directive directly to the underlying /proc/<pid>/ctl file.  If the
 * libdtrace client wishes to exit or abort our wait, SIGCANCEL can be used.
 */
static void *
dt_proc_control(void *arg)
{
        dt_proc_control_data_t *datap = arg;
        dtrace_hdl_t *dtp = datap->dpcd_hdl;
        dt_proc_t *dpr = datap->dpcd_proc;
        dt_proc_hash_t *dph = dpr->dpr_hdl->dt_procs;
        struct ps_prochandle *P = dpr->dpr_proc;
        int pid = dpr->dpr_pid;

#if defined(sun)
        int pfd = Pctlfd(P);

        const long wstop = PCWSTOP;
#endif
        int notify = B_FALSE;

        /*
         * We disable the POSIX thread cancellation mechanism so that the
         * client program using libdtrace can't accidentally cancel our thread.
         * dt_proc_destroy() uses SIGCANCEL explicitly to simply poke us out
         * of PCWSTOP with EINTR, at which point we will see dpr_quit and exit.
         */
        (void) pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);

        /*
         * Set up the corresponding process for tracing by libdtrace.  We want
         * to be able to catch breakpoints and efficiently single-step over
         * them, and we need to enable librtld_db to watch libdl activity.
         */
        (void) pthread_mutex_lock(&dpr->dpr_lock);

#if defined(sun)
        (void) Punsetflags(P, PR_ASYNC);        /* require synchronous mode */
        (void) Psetflags(P, PR_BPTADJ);         /* always adjust eip on x86 */
        (void) Punsetflags(P, PR_FORK);         /* do not inherit on fork */

        (void) Pfault(P, FLTBPT, B_TRUE);       /* always trace breakpoints */
        (void) Pfault(P, FLTTRACE, B_TRUE);     /* always trace single-step */

        /*
         * We must trace exit from exec() system calls so that if the exec is
         * successful, we can reset our breakpoints and re-initialize libproc.
         */
        (void) Psysexit(P, SYS_execve, B_TRUE);

        /*
         * We must trace entry and exit for fork() system calls in order to
         * disable our breakpoints temporarily during the fork.  We do not set
         * the PR_FORK flag, so if fork succeeds the child begins executing and
         * does not inherit any other tracing behaviors or a control thread.
         */
        (void) Psysentry(P, SYS_vfork, B_TRUE);
        (void) Psysexit(P, SYS_vfork, B_TRUE);
        (void) Psysentry(P, SYS_forksys, B_TRUE);
        (void) Psysexit(P, SYS_forksys, B_TRUE);

        Psync(P);                               /* enable all /proc changes */
#endif
        dt_proc_attach(dpr, B_FALSE);           /* enable rtld breakpoints */

        /*
         * If PR_KLC is set, we created the process; otherwise we grabbed it.
         * Check for an appropriate stop request and wait for dt_proc_continue.
         */
#if defined(sun)
        if (Pstatus(P)->pr_flags & PR_KLC)
#else
        if (proc_getflags(P) & PR_KLC)
#endif
                dt_proc_stop(dpr, DT_PROC_STOP_CREATE);
        else
                dt_proc_stop(dpr, DT_PROC_STOP_GRAB);

        if (Psetrun(P, 0, 0) == -1) {
                dt_dprintf("pid %d: failed to set running: %s\n",
                    (int)dpr->dpr_pid, strerror(errno));
        }

        (void) pthread_mutex_unlock(&dpr->dpr_lock);

        /*
         * Wait for the process corresponding to this control thread to stop,
         * process the event, and then set it running again.  We want to sleep
         * with dpr_lock *unheld* so that other parts of libdtrace can use the
         * ps_prochandle in the meantime (e.g. ustack()).  To do this, we write
         * a PCWSTOP directive directly to the underlying /proc/<pid>/ctl file.
         * Once the process stops, we wake up, grab dpr_lock, and then call
         * Pwait() (which will return immediately) and do our processing.
         */
        while (!dpr->dpr_quit) {
                const lwpstatus_t *psp;

#if defined(sun)
                if (write(pfd, &wstop, sizeof (wstop)) == -1 && errno == EINTR)
                        continue; /* check dpr_quit and continue waiting */
#else
                /* Wait for the process to report status. */
                proc_wstatus(P);
                if (errno == EINTR)
                        continue; /* check dpr_quit and continue waiting */
#endif

                (void) pthread_mutex_lock(&dpr->dpr_lock);

#if defined(sun)
pwait_locked:
                if (Pstopstatus(P, PCNULL, 0) == -1 && errno == EINTR) {
                        (void) pthread_mutex_unlock(&dpr->dpr_lock);
                        continue; /* check dpr_quit and continue waiting */
                }
#endif

                switch (Pstate(P)) {
                case PS_STOP:
#if defined(sun)
                        psp = &Pstatus(P)->pr_lwp;
#else
                        psp = proc_getlwpstatus(P);
#endif

                        dt_dprintf("pid %d: proc stopped showing %d/%d\n",
                            pid, psp->pr_why, psp->pr_what);

                        /*
                         * If the process stops showing PR_REQUESTED, then the
                         * DTrace stop() action was applied to it or another
                         * debugging utility (e.g. pstop(1)) asked it to stop.
                         * In either case, the user's intention is for the
                         * process to remain stopped until another external
                         * mechanism (e.g. prun(1)) is applied.  So instead of
                         * setting the process running ourself, we wait for
                         * someone else to do so.  Once that happens, we return
                         * to our normal loop waiting for an event of interest.
                         */
                        if (psp->pr_why == PR_REQUESTED) {
                                dt_proc_waitrun(dpr);
                                (void) pthread_mutex_unlock(&dpr->dpr_lock);
                                continue;
                        }

                        /*
                         * If the process stops showing one of the events that
                         * we are tracing, perform the appropriate response.
                         * Note that we ignore PR_SUSPENDED, PR_CHECKPOINT, and
                         * PR_JOBCONTROL by design: if one of these conditions
                         * occurs, we will fall through to Psetrun() but the
                         * process will remain stopped in the kernel by the
                         * corresponding mechanism (e.g. job control stop).
                         */
                        if (psp->pr_why == PR_FAULTED && psp->pr_what == FLTBPT)
                                dt_proc_bpmatch(dtp, dpr);
                        else if (psp->pr_why == PR_SYSENTRY &&
                            IS_SYS_FORK(psp->pr_what))
                                dt_proc_bpdisable(dpr);
                        else if (psp->pr_why == PR_SYSEXIT &&
                            IS_SYS_FORK(psp->pr_what))
                                dt_proc_bpenable(dpr);
                        else if (psp->pr_why == PR_SYSEXIT &&
                            IS_SYS_EXEC(psp->pr_what))
                                dt_proc_attach(dpr, B_TRUE);
                        break;

                case PS_LOST:
#if defined(sun)
                        if (Preopen(P) == 0)
                                goto pwait_locked;
#endif

                        dt_dprintf("pid %d: proc lost: %s\n",
                            pid, strerror(errno));

                        dpr->dpr_quit = B_TRUE;
                        notify = B_TRUE;
                        break;

                case PS_UNDEAD:
                        dt_dprintf("pid %d: proc died\n", pid);
                        dpr->dpr_quit = B_TRUE;
                        notify = B_TRUE;
                        break;
                }

                if (Pstate(P) != PS_UNDEAD && Psetrun(P, 0, 0) == -1) {
                        dt_dprintf("pid %d: failed to set running: %s\n",
                            (int)dpr->dpr_pid, strerror(errno));
                }

                (void) pthread_mutex_unlock(&dpr->dpr_lock);
        }

        /*
         * If the control thread detected PS_UNDEAD or PS_LOST, then enqueue
         * the dt_proc_t structure on the dt_proc_hash_t notification list.
         */
        if (notify)
                dt_proc_notify(dtp, dph, dpr, NULL);

        /*
         * Destroy and remove any remaining breakpoints, set dpr_done and clear
         * dpr_tid to indicate the control thread has exited, and notify any
         * waiting thread in dt_proc_destroy() that we have succesfully exited.
         */
        (void) pthread_mutex_lock(&dpr->dpr_lock);

        dt_proc_bpdestroy(dpr, B_TRUE);
        dpr->dpr_done = B_TRUE;
        dpr->dpr_tid = 0;

        (void) pthread_cond_broadcast(&dpr->dpr_cv);
        (void) pthread_mutex_unlock(&dpr->dpr_lock);

        return (NULL);
}

/*PRINTFLIKE3*/
static struct ps_prochandle *
dt_proc_error(dtrace_hdl_t *dtp, dt_proc_t *dpr, const char *format, ...)
{
        va_list ap;

        va_start(ap, format);
        dt_set_errmsg(dtp, NULL, NULL, NULL, 0, format, ap);
        va_end(ap);

        if (dpr->dpr_proc != NULL)
                Prelease(dpr->dpr_proc, 0);

        dt_free(dtp, dpr);
        (void) dt_set_errno(dtp, EDT_COMPILER);
        return (NULL);
}

dt_proc_t *
dt_proc_lookup(dtrace_hdl_t *dtp, struct ps_prochandle *P, int remove)
{
        dt_proc_hash_t *dph = dtp->dt_procs;
#if defined(sun)
        pid_t pid = Pstatus(P)->pr_pid;
#else
        pid_t pid = proc_getpid(P);
#endif
        dt_proc_t *dpr, **dpp = &dph->dph_hash[pid & (dph->dph_hashlen - 1)];

        for (dpr = *dpp; dpr != NULL; dpr = dpr->dpr_hash) {
                if (dpr->dpr_pid == pid)
                        break;
                else
                        dpp = &dpr->dpr_hash;
        }

        assert(dpr != NULL);
        assert(dpr->dpr_proc == P);

        if (remove)
                *dpp = dpr->dpr_hash; /* remove from pid hash chain */

        return (dpr);
}

static void
dt_proc_destroy(dtrace_hdl_t *dtp, struct ps_prochandle *P)
{
        dt_proc_t *dpr = dt_proc_lookup(dtp, P, B_FALSE);
        dt_proc_hash_t *dph = dtp->dt_procs;
        dt_proc_notify_t *npr, **npp;
        int rflag;

        assert(dpr != NULL);

        /*
         * If neither PR_KLC nor PR_RLC is set, then the process is stopped by
         * an external debugger and we were waiting in dt_proc_waitrun().
         * Leave the process in this condition using PRELEASE_HANG.
         */
#if defined(sun)
        if (!(Pstatus(dpr->dpr_proc)->pr_flags & (PR_KLC | PR_RLC))) {
#else
        if (!(proc_getflags(dpr->dpr_proc) & (PR_KLC | PR_RLC))) {
#endif
                dt_dprintf("abandoning pid %d\n", (int)dpr->dpr_pid);
                rflag = PRELEASE_HANG;
#if defined(sun)
        } else if (Pstatus(dpr->dpr_proc)->pr_flags & PR_KLC) {
#else
        } else if (proc_getflags(dpr->dpr_proc) & PR_KLC) {
#endif
                dt_dprintf("killing pid %d\n", (int)dpr->dpr_pid);
                rflag = PRELEASE_KILL; /* apply kill-on-last-close */
        } else {
                dt_dprintf("releasing pid %d\n", (int)dpr->dpr_pid);
                rflag = 0; /* apply run-on-last-close */
        }

        if (dpr->dpr_tid) {
                /*
                 * Set the dpr_quit flag to tell the daemon thread to exit.  We
                 * send it a SIGCANCEL to poke it out of PCWSTOP or any other
                 * long-term /proc system call.  Our daemon threads have POSIX
                 * cancellation disabled, so EINTR will be the only effect.  We
                 * then wait for dpr_done to indicate the thread has exited.
                 *
                 * We can't use pthread_kill() to send SIGCANCEL because the
                 * interface forbids it and we can't use pthread_cancel()
                 * because with cancellation disabled it won't actually
                 * send SIGCANCEL to the target thread, so we use _lwp_kill()
                 * to do the job.  This is all built on evil knowledge of
                 * the details of the cancellation mechanism in libc.
                 */
                (void) pthread_mutex_lock(&dpr->dpr_lock);
                dpr->dpr_quit = B_TRUE;
#if defined(sun)
                (void) _lwp_kill(dpr->dpr_tid, SIGCANCEL);
#else
                pthread_kill(dpr->dpr_tid, SIGTHR);
#endif

                /*
                 * If the process is currently idling in dt_proc_stop(), re-
                 * enable breakpoints and poke it into running again.
                 */
                if (dpr->dpr_stop & DT_PROC_STOP_IDLE) {
                        dt_proc_bpenable(dpr);
                        dpr->dpr_stop &= ~DT_PROC_STOP_IDLE;
                        (void) pthread_cond_broadcast(&dpr->dpr_cv);
                }

                while (!dpr->dpr_done)
                        (void) pthread_cond_wait(&dpr->dpr_cv, &dpr->dpr_lock);

                (void) pthread_mutex_unlock(&dpr->dpr_lock);
        }

        /*
         * Before we free the process structure, remove this dt_proc_t from the
         * lookup hash, and then walk the dt_proc_hash_t's notification list
         * and remove this dt_proc_t if it is enqueued.
         */
        (void) pthread_mutex_lock(&dph->dph_lock);
        (void) dt_proc_lookup(dtp, P, B_TRUE);
        npp = &dph->dph_notify;

        while ((npr = *npp) != NULL) {
                if (npr->dprn_dpr == dpr) {
                        *npp = npr->dprn_next;
                        dt_free(dtp, npr);
                } else {
                        npp = &npr->dprn_next;
                }
        }

        (void) pthread_mutex_unlock(&dph->dph_lock);

        /*
         * Remove the dt_proc_list from the LRU list, release the underlying
         * libproc handle, and free our dt_proc_t data structure.
         */
        if (dpr->dpr_cacheable) {
                assert(dph->dph_lrucnt != 0);
                dph->dph_lrucnt--;
        }

        dt_list_delete(&dph->dph_lrulist, dpr);
        Prelease(dpr->dpr_proc, rflag);
        dt_free(dtp, dpr);
}

static int
dt_proc_create_thread(dtrace_hdl_t *dtp, dt_proc_t *dpr, uint_t stop)
{
        dt_proc_control_data_t data;
        sigset_t nset, oset;
        pthread_attr_t a;
        int err;

        (void) pthread_mutex_lock(&dpr->dpr_lock);
        dpr->dpr_stop |= stop; /* set bit for initial rendezvous */

        (void) pthread_attr_init(&a);
        (void) pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);

        (void) sigfillset(&nset);
        (void) sigdelset(&nset, SIGABRT);       /* unblocked for assert() */
#if defined(sun)
        (void) sigdelset(&nset, SIGCANCEL);     /* see dt_proc_destroy() */
#else
        (void) sigdelset(&nset, SIGUSR1);       /* see dt_proc_destroy() */
#endif

        data.dpcd_hdl = dtp;
        data.dpcd_proc = dpr;

        (void) pthread_sigmask(SIG_SETMASK, &nset, &oset);
        err = pthread_create(&dpr->dpr_tid, &a, dt_proc_control, &data);
        (void) pthread_sigmask(SIG_SETMASK, &oset, NULL);

        /*
         * If the control thread was created, then wait on dpr_cv for either
         * dpr_done to be set (the victim died or the control thread failed)
         * or DT_PROC_STOP_IDLE to be set, indicating that the victim is now
         * stopped by /proc and the control thread is at the rendezvous event.
         * On success, we return with the process and control thread stopped:
         * the caller can then apply dt_proc_continue() to resume both.
         */
        if (err == 0) {
                while (!dpr->dpr_done && !(dpr->dpr_stop & DT_PROC_STOP_IDLE))
                        (void) pthread_cond_wait(&dpr->dpr_cv, &dpr->dpr_lock);

                /*
                 * If dpr_done is set, the control thread aborted before it
                 * reached the rendezvous event.  This is either due to PS_LOST
                 * or PS_UNDEAD (i.e. the process died).  We try to provide a
                 * small amount of useful information to help figure it out.
                 */
                if (dpr->dpr_done) {
#if defined(sun)
                        const psinfo_t *prp = Ppsinfo(dpr->dpr_proc);
                        int stat = prp ? prp->pr_wstat : 0;
                        int pid = dpr->dpr_pid;
#else
                        int stat = proc_getwstat(dpr->dpr_proc);
                        int pid = proc_getpid(dpr->dpr_proc);
#endif
                        if (proc_state(dpr->dpr_proc) == PS_LOST) {
                                (void) dt_proc_error(dpr->dpr_hdl, dpr,
                                    "failed to control pid %d: process exec'd "
                                    "set-id or unobservable program\n", pid);
                        } else if (WIFSIGNALED(stat)) {
                                (void) dt_proc_error(dpr->dpr_hdl, dpr,
                                    "failed to control pid %d: process died "
                                    "from signal %d\n", pid, WTERMSIG(stat));
                        } else {
                                (void) dt_proc_error(dpr->dpr_hdl, dpr,
                                    "failed to control pid %d: process exited "
                                    "with status %d\n", pid, WEXITSTATUS(stat));
                        }

                        err = ESRCH; /* cause grab() or create() to fail */
                }
        } else {
                (void) dt_proc_error(dpr->dpr_hdl, dpr,
                    "failed to create control thread for process-id %d: %s\n",
                    (int)dpr->dpr_pid, strerror(err));
        }

        if (err == 0)
                (void) pthread_mutex_unlock(&dpr->dpr_lock);
        (void) pthread_attr_destroy(&a);

        return (err);
}

struct ps_prochandle *
dt_proc_create(dtrace_hdl_t *dtp, const char *file, char *const *argv,
    proc_child_func *pcf, void *child_arg)
{
        dt_proc_hash_t *dph = dtp->dt_procs;
        dt_proc_t *dpr;
        int err;

        if ((dpr = dt_zalloc(dtp, sizeof (dt_proc_t))) == NULL)
                return (NULL); /* errno is set for us */

        (void) pthread_mutex_init(&dpr->dpr_lock, NULL);
        (void) pthread_cond_init(&dpr->dpr_cv, NULL);

#if defined(sun)
        if ((dpr->dpr_proc = Pcreate(file, argv, &err, NULL, 0)) == NULL) {
#else
        if ((err = proc_create(file, argv, pcf, child_arg,
            &dpr->dpr_proc)) != 0) {
#endif
                return (dt_proc_error(dtp, dpr,
                    "failed to execute %s: %s\n", file, Pcreate_error(err)));
        }

        dpr->dpr_hdl = dtp;
#if defined(sun)
        dpr->dpr_pid = Pstatus(dpr->dpr_proc)->pr_pid;
#else
        dpr->dpr_pid = proc_getpid(dpr->dpr_proc);
#endif

        (void) Punsetflags(dpr->dpr_proc, PR_RLC);
        (void) Psetflags(dpr->dpr_proc, PR_KLC);

        if (dt_proc_create_thread(dtp, dpr, dtp->dt_prcmode) != 0)
                return (NULL); /* dt_proc_error() has been called for us */

        dpr->dpr_hash = dph->dph_hash[dpr->dpr_pid & (dph->dph_hashlen - 1)];
        dph->dph_hash[dpr->dpr_pid & (dph->dph_hashlen - 1)] = dpr;
        dt_list_prepend(&dph->dph_lrulist, dpr);

        dt_dprintf("created pid %d\n", (int)dpr->dpr_pid);
        dpr->dpr_refs++;

        return (dpr->dpr_proc);
}

struct ps_prochandle *
dt_proc_grab(dtrace_hdl_t *dtp, pid_t pid, int flags, int nomonitor)
{
        dt_proc_hash_t *dph = dtp->dt_procs;
        uint_t h = pid & (dph->dph_hashlen - 1);
        dt_proc_t *dpr, *opr;
        int err;

        /*
         * Search the hash table for the pid.  If it is already grabbed or
         * created, move the handle to the front of the lrulist, increment
         * the reference count, and return the existing ps_prochandle.
         */
        for (dpr = dph->dph_hash[h]; dpr != NULL; dpr = dpr->dpr_hash) {
                if (dpr->dpr_pid == pid && !dpr->dpr_stale) {
                        /*
                         * If the cached handle was opened read-only and
                         * this request is for a writeable handle, mark
                         * the cached handle as stale and open a new handle.
                         * Since it's stale, unmark it as cacheable.
                         */
                        if (dpr->dpr_rdonly && !(flags & PGRAB_RDONLY)) {
                                dt_dprintf("upgrading pid %d\n", (int)pid);
                                dpr->dpr_stale = B_TRUE;
                                dpr->dpr_cacheable = B_FALSE;
                                dph->dph_lrucnt--;
                                break;
                        }

                        dt_dprintf("grabbed pid %d (cached)\n", (int)pid);
                        dt_list_delete(&dph->dph_lrulist, dpr);
                        dt_list_prepend(&dph->dph_lrulist, dpr);
                        dpr->dpr_refs++;
                        return (dpr->dpr_proc);
                }
        }

        if ((dpr = dt_zalloc(dtp, sizeof (dt_proc_t))) == NULL)
                return (NULL); /* errno is set for us */

        (void) pthread_mutex_init(&dpr->dpr_lock, NULL);
        (void) pthread_cond_init(&dpr->dpr_cv, NULL);

#if defined(sun)
        if ((dpr->dpr_proc = Pgrab(pid, flags, &err)) == NULL) {
#else
        if ((err = proc_attach(pid, flags, &dpr->dpr_proc)) != 0) {
#endif
                return (dt_proc_error(dtp, dpr,
                    "failed to grab pid %d: %s\n", (int)pid, Pgrab_error(err)));
        }

        dpr->dpr_hdl = dtp;
        dpr->dpr_pid = pid;

        (void) Punsetflags(dpr->dpr_proc, PR_KLC);
        (void) Psetflags(dpr->dpr_proc, PR_RLC);

        /*
         * If we are attempting to grab the process without a monitor
         * thread, then mark the process cacheable only if it's being
         * grabbed read-only.  If we're currently caching more process
         * handles than dph_lrulim permits, attempt to find the
         * least-recently-used handle that is currently unreferenced and
         * release it from the cache.  Otherwise we are grabbing the process
         * for control: create a control thread for this process and store
         * its ID in dpr->dpr_tid.
         */
        if (nomonitor || (flags & PGRAB_RDONLY)) {
                if (dph->dph_lrucnt >= dph->dph_lrulim) {
                        for (opr = dt_list_prev(&dph->dph_lrulist);
                            opr != NULL; opr = dt_list_prev(opr)) {
                                if (opr->dpr_cacheable && opr->dpr_refs == 0) {
                                        dt_proc_destroy(dtp, opr->dpr_proc);
                                        break;
                                }
                        }
                }

                if (flags & PGRAB_RDONLY) {
                        dpr->dpr_cacheable = B_TRUE;
                        dpr->dpr_rdonly = B_TRUE;
                        dph->dph_lrucnt++;
                }

        } else if (dt_proc_create_thread(dtp, dpr, DT_PROC_STOP_GRAB) != 0)
                return (NULL); /* dt_proc_error() has been called for us */

        dpr->dpr_hash = dph->dph_hash[h];
        dph->dph_hash[h] = dpr;
        dt_list_prepend(&dph->dph_lrulist, dpr);

        dt_dprintf("grabbed pid %d\n", (int)pid);
        dpr->dpr_refs++;

        return (dpr->dpr_proc);
}

void
dt_proc_release(dtrace_hdl_t *dtp, struct ps_prochandle *P)
{
        dt_proc_t *dpr = dt_proc_lookup(dtp, P, B_FALSE);
        dt_proc_hash_t *dph = dtp->dt_procs;

        assert(dpr != NULL);
        assert(dpr->dpr_refs != 0);

        if (--dpr->dpr_refs == 0 &&
            (!dpr->dpr_cacheable || dph->dph_lrucnt > dph->dph_lrulim))
                dt_proc_destroy(dtp, P);
}

void
dt_proc_continue(dtrace_hdl_t *dtp, struct ps_prochandle *P)
{
        dt_proc_t *dpr = dt_proc_lookup(dtp, P, B_FALSE);

        (void) pthread_mutex_lock(&dpr->dpr_lock);

        if (dpr->dpr_stop & DT_PROC_STOP_IDLE) {
                dpr->dpr_stop &= ~DT_PROC_STOP_IDLE;
                (void) pthread_cond_broadcast(&dpr->dpr_cv);
        }

        (void) pthread_mutex_unlock(&dpr->dpr_lock);
}

void
dt_proc_lock(dtrace_hdl_t *dtp, struct ps_prochandle *P)
{
        dt_proc_t *dpr = dt_proc_lookup(dtp, P, B_FALSE);
        int err = pthread_mutex_lock(&dpr->dpr_lock);
        assert(err == 0); /* check for recursion */
}

void
dt_proc_unlock(dtrace_hdl_t *dtp, struct ps_prochandle *P)
{
        dt_proc_t *dpr = dt_proc_lookup(dtp, P, B_FALSE);
        int err = pthread_mutex_unlock(&dpr->dpr_lock);
        assert(err == 0); /* check for unheld lock */
}

void
dt_proc_hash_create(dtrace_hdl_t *dtp)
{
        if ((dtp->dt_procs = dt_zalloc(dtp, sizeof (dt_proc_hash_t) +
            sizeof (dt_proc_t *) * _dtrace_pidbuckets - 1)) != NULL) {

                (void) pthread_mutex_init(&dtp->dt_procs->dph_lock, NULL);
                (void) pthread_cond_init(&dtp->dt_procs->dph_cv, NULL);

                dtp->dt_procs->dph_hashlen = _dtrace_pidbuckets;
                dtp->dt_procs->dph_lrulim = _dtrace_pidlrulim;
        }
}

void
dt_proc_hash_destroy(dtrace_hdl_t *dtp)
{
        dt_proc_hash_t *dph = dtp->dt_procs;
        dt_proc_t *dpr;

        while ((dpr = dt_list_next(&dph->dph_lrulist)) != NULL)
                dt_proc_destroy(dtp, dpr->dpr_proc);

        dtp->dt_procs = NULL;
        dt_free(dtp, dph);
}

struct ps_prochandle *
dtrace_proc_create(dtrace_hdl_t *dtp, const char *file, char *const *argv,
    proc_child_func *pcf, void *child_arg)
{
        dt_ident_t *idp = dt_idhash_lookup(dtp->dt_macros, "target");
        struct ps_prochandle *P = dt_proc_create(dtp, file, argv, pcf, child_arg);

        if (P != NULL && idp != NULL && idp->di_id == 0) {
#if defined(sun)
                idp->di_id = Pstatus(P)->pr_pid; /* $target = created pid */
#else
                idp->di_id = proc_getpid(P); /* $target = created pid */
#endif
        }

        return (P);
}

struct ps_prochandle *
dtrace_proc_grab(dtrace_hdl_t *dtp, pid_t pid, int flags)
{
        dt_ident_t *idp = dt_idhash_lookup(dtp->dt_macros, "target");
        struct ps_prochandle *P = dt_proc_grab(dtp, pid, flags, 0);

        if (P != NULL && idp != NULL && idp->di_id == 0)
                idp->di_id = pid; /* $target = grabbed pid */

        return (P);
}

void
dtrace_proc_release(dtrace_hdl_t *dtp, struct ps_prochandle *P)
{
        dt_proc_release(dtp, P);
}

void
dtrace_proc_continue(dtrace_hdl_t *dtp, struct ps_prochandle *P)
{
        dt_proc_continue(dtp, P);
}