modules/genunix/thread.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */
/*
 * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
 */


#include <mdb/mdb_modapi.h>
#include <mdb/mdb_ks.h>
#include <sys/types.h>
#include <sys/thread.h>
#include <sys/lwp.h>
#include <sys/proc.h>
#include <sys/cpuvar.h>
#include <sys/cpupart.h>
#include <sys/disp.h>
#include <sys/taskq_impl.h>
#include <sys/stack.h>

#ifndef STACK_BIAS
#define STACK_BIAS  0
#endif

typedef struct thread_walk {
    kthread_t *tw_thread;
    uintptr_t tw_last;
    uint_t tw_inproc;
    uint_t tw_step;
} thread_walk_t;

int
thread_walk_init(mdb_walk_state_t *wsp)
{
    thread_walk_t *twp = mdb_alloc(sizeof (thread_walk_t), UM_SLEEP);

    if (wsp->walk_addr == NULL) {
        if (mdb_readvar(&wsp->walk_addr, "allthreads") == -1) {
            mdb_warn("failed to read 'allthreads'");
            mdb_free(twp, sizeof (thread_walk_t));
            return (WALK_ERR);
        }

        twp->tw_inproc = FALSE;

    } else {
        proc_t pr;

        if (mdb_vread(&pr, sizeof (proc_t), wsp->walk_addr) == -1) {
            mdb_warn("failed to read proc at %p", wsp->walk_addr);
            mdb_free(twp, sizeof (thread_walk_t));
            return (WALK_ERR);
        }

        wsp->walk_addr = (uintptr_t)pr.p_tlist;
        twp->tw_inproc = TRUE;
    }

    twp->tw_thread = mdb_alloc(sizeof (kthread_t), UM_SLEEP);
    twp->tw_last = wsp->walk_addr;
    twp->tw_step = FALSE;

    wsp->walk_data = twp;
    return (WALK_NEXT);
}

int
thread_walk_step(mdb_walk_state_t *wsp)
{
    thread_walk_t *twp = (thread_walk_t *)wsp->walk_data;
    int status;

    if (wsp->walk_addr == NULL)
        return (WALK_DONE); /* Proc has 0 threads or allthreads = 0 */

    if (twp->tw_step && wsp->walk_addr == twp->tw_last)
        return (WALK_DONE); /* We've wrapped around */

    if (mdb_vread(twp->tw_thread, sizeof (kthread_t),
        wsp->walk_addr) == -1) {
        mdb_warn("failed to read thread at %p", wsp->walk_addr);
        return (WALK_DONE);
    }

    status = wsp->walk_callback(wsp->walk_addr, twp->tw_thread,
        wsp->walk_cbdata);

    if (twp->tw_inproc)
        wsp->walk_addr = (uintptr_t)twp->tw_thread->t_forw;
    else
        wsp->walk_addr = (uintptr_t)twp->tw_thread->t_next;

    twp->tw_step = TRUE;
    return (status);
}

void
thread_walk_fini(mdb_walk_state_t *wsp)
{
    thread_walk_t *twp = (thread_walk_t *)wsp->walk_data;

    mdb_free(twp->tw_thread, sizeof (kthread_t));
    mdb_free(twp, sizeof (thread_walk_t));
}

int
deathrow_walk_init(mdb_walk_state_t *wsp)
{
    if (mdb_layered_walk("thread_deathrow", wsp) == -1) {
        mdb_warn("couldn't walk 'thread_deathrow'");
        return (WALK_ERR);
    }

    if (mdb_layered_walk("lwp_deathrow", wsp) == -1) {
        mdb_warn("couldn't walk 'lwp_deathrow'");
        return (WALK_ERR);
    }

    return (WALK_NEXT);
}

int
deathrow_walk_step(mdb_walk_state_t *wsp)
{
    kthread_t t;
    uintptr_t addr = wsp->walk_addr;

    if (addr == NULL)
        return (WALK_DONE);

    if (mdb_vread(&t, sizeof (t), addr) == -1) {
        mdb_warn("couldn't read deathrow thread at %p", addr);
        return (WALK_ERR);
    }

    wsp->walk_addr = (uintptr_t)t.t_forw;

    return (wsp->walk_callback(addr, &t, wsp->walk_cbdata));
}

int
thread_deathrow_walk_init(mdb_walk_state_t *wsp)
{
    if (mdb_readvar(&wsp->walk_addr, "thread_deathrow") == -1) {
        mdb_warn("couldn't read symbol 'thread_deathrow'");
        return (WALK_ERR);
    }

    return (WALK_NEXT);
}

int
lwp_deathrow_walk_init(mdb_walk_state_t *wsp)
{
    if (mdb_readvar(&wsp->walk_addr, "lwp_deathrow") == -1) {
        mdb_warn("couldn't read symbol 'lwp_deathrow'");
        return (WALK_ERR);
    }

    return (WALK_NEXT);
}


typedef struct dispq_walk {
    int dw_npri;
    uintptr_t dw_dispq;
    uintptr_t dw_last;
} dispq_walk_t;

int
cpu_dispq_walk_init(mdb_walk_state_t *wsp)
{
    uintptr_t addr = wsp->walk_addr;
    dispq_walk_t *dw;
    cpu_t cpu;
    dispq_t dispq;
    disp_t disp;

    if (addr == NULL) {
        mdb_warn("cpu_dispq walk needs a cpu_t address\n");
        return (WALK_ERR);
    }

    if (mdb_vread(&cpu, sizeof (cpu_t), addr) == -1) {
        mdb_warn("failed to read cpu_t at %p", addr);
        return (WALK_ERR);
    }

    if (mdb_vread(&disp, sizeof (disp_t), (uintptr_t)cpu.cpu_disp) == -1) {
        mdb_warn("failed to read disp_t at %p", cpu.cpu_disp);
        return (WALK_ERR);
    }

    if (mdb_vread(&dispq, sizeof (dispq_t),
        (uintptr_t)disp.disp_q) == -1) {
        mdb_warn("failed to read dispq_t at %p", disp.disp_q);
        return (WALK_ERR);
    }

    dw = mdb_alloc(sizeof (dispq_walk_t), UM_SLEEP);

    dw->dw_npri = disp.disp_npri;
    dw->dw_dispq = (uintptr_t)disp.disp_q;
    dw->dw_last = (uintptr_t)dispq.dq_last;

    wsp->walk_addr = (uintptr_t)dispq.dq_first;
    wsp->walk_data = dw;

    return (WALK_NEXT);
}

int
cpupart_dispq_walk_init(mdb_walk_state_t *wsp)
{
    uintptr_t addr = wsp->walk_addr;
    dispq_walk_t *dw;
    cpupart_t cpupart;
    dispq_t dispq;

    if (addr == NULL) {
        mdb_warn("cpupart_dispq walk needs a cpupart_t address\n");
        return (WALK_ERR);
    }

    if (mdb_vread(&cpupart, sizeof (cpupart_t), addr) == -1) {
        mdb_warn("failed to read cpupart_t at %p", addr);
        return (WALK_ERR);
    }

    if (mdb_vread(&dispq, sizeof (dispq_t),
        (uintptr_t)cpupart.cp_kp_queue.disp_q) == -1) {
        mdb_warn("failed to read dispq_t at %p",
            cpupart.cp_kp_queue.disp_q);
        return (WALK_ERR);
    }

    dw = mdb_alloc(sizeof (dispq_walk_t), UM_SLEEP);

    dw->dw_npri = cpupart.cp_kp_queue.disp_npri;
    dw->dw_dispq = (uintptr_t)cpupart.cp_kp_queue.disp_q;
    dw->dw_last = (uintptr_t)dispq.dq_last;

    wsp->walk_addr = (uintptr_t)dispq.dq_first;
    wsp->walk_data = dw;

    return (WALK_NEXT);
}

int
dispq_walk_step(mdb_walk_state_t *wsp)
{
    uintptr_t addr = wsp->walk_addr;
    dispq_walk_t *dw = wsp->walk_data;
    dispq_t dispq;
    kthread_t t;

    while (addr == NULL) {
        if (--dw->dw_npri == 0)
            return (WALK_DONE);

        dw->dw_dispq += sizeof (dispq_t);

        if (mdb_vread(&dispq, sizeof (dispq_t), dw->dw_dispq) == -1) {
            mdb_warn("failed to read dispq_t at %p", dw->dw_dispq);
            return (WALK_ERR);
        }

        dw->dw_last = (uintptr_t)dispq.dq_last;
        addr = (uintptr_t)dispq.dq_first;
    }

    if (mdb_vread(&t, sizeof (kthread_t), addr) == -1) {
        mdb_warn("failed to read kthread_t at %p", addr);
        return (WALK_ERR);
    }

    if (addr == dw->dw_last)
        wsp->walk_addr = NULL;
    else
        wsp->walk_addr = (uintptr_t)t.t_link;

    return (wsp->walk_callback(addr, &t, wsp->walk_cbdata));
}

void
dispq_walk_fini(mdb_walk_state_t *wsp)
{
    mdb_free(wsp->walk_data, sizeof (dispq_walk_t));
}

struct thread_state {
    uint_t ts_state;
    const char *ts_name;
} thread_states[] = {
    { TS_FREE,  "free" },
    { TS_SLEEP, "sleep" },
    { TS_RUN,   "run" },
    { TS_ONPROC,    "onproc" },
    { TS_ZOMB,  "zomb" },
    { TS_STOPPED,   "stopped" },
    { TS_WAIT,  "wait" }
};
#define NUM_THREAD_STATES (sizeof (thread_states) / sizeof (*thread_states))

void
thread_state_to_text(uint_t state, char *out, size_t out_sz)
{
    int idx;

    for (idx = 0; idx < NUM_THREAD_STATES; idx++) {
        struct thread_state *tsp = &thread_states[idx];
        if (tsp->ts_state == state) {
            mdb_snprintf(out, out_sz, "%s", tsp->ts_name);
            return;
        }
    }
    mdb_snprintf(out, out_sz, "inval/%02x", state);
}

int
thread_text_to_state(const char *state, uint_t *out)
{
    int idx;

    for (idx = 0; idx < NUM_THREAD_STATES; idx++) {
        struct thread_state *tsp = &thread_states[idx];
        if (strcasecmp(tsp->ts_name, state) == 0) {
            *out = tsp->ts_state;
            return (0);
        }
    }
    return (-1);
}

void
thread_walk_states(void (*cbfunc)(uint_t, const char *, void *), void *cbarg)
{
    int idx;

    for (idx = 0; idx < NUM_THREAD_STATES; idx++) {
        struct thread_state *tsp = &thread_states[idx];
        cbfunc(tsp->ts_state, tsp->ts_name, cbarg);
    }
}

#define TF_INTR     0x01
#define TF_PROC     0x02
#define TF_BLOCK    0x04
#define TF_SIG      0x08
#define TF_DISP     0x10
#define TF_MERGE    0x20

/*
 * Display a kthread_t.
 * This is a little complicated, as there is a lot of information that
 * the user could be interested in.  The flags "ipbsd" are used to
 * indicate which subset of the thread's members are to be displayed
 * ('i' is the default).  If multiple options are specified, multiple
 * sets of data will be displayed in a vaguely readable format.  If the
 * 'm' option is specified, all the selected sets will be merged onto a
 * single line for the benefit of those using wider-than-normal
 * terminals.  Having a generic mechanism for doing this would be
 * really useful, but is a project best left to another day.
 */

int
thread(uintptr_t addr, uint_t flags, int argc, const mdb_arg_t *argv)
{
    kthread_t   t;
    uint_t      oflags = 0;
    uint_t      fflag = FALSE;
    int     first;
    char        stbuf[20];

    /*
     * "Gracefully" handle printing a boatload of stuff to the
     * screen.  If we are not printing our first set of data, and
     * we haven't been instructed to merge sets together, output a
     * newline and indent such that the thread addresses form a
     * column of their own.
     */
#define SPACER()                \
    if (first) {                \
        first = FALSE;          \
    } else if (!(oflags & TF_MERGE)) {  \
        mdb_printf("\n%?s", "");    \
    }

    if (!(flags & DCMD_ADDRSPEC)) {
        if (mdb_walk_dcmd("thread", "thread", argc, argv) == -1) {
            mdb_warn("can't walk threads");
            return (DCMD_ERR);
        }
        return (DCMD_OK);
    }

    if (mdb_getopts(argc, argv,
        'f', MDB_OPT_SETBITS, TRUE, &fflag,
        'i', MDB_OPT_SETBITS, TF_INTR, &oflags,
        'p', MDB_OPT_SETBITS, TF_PROC, &oflags,
        'b', MDB_OPT_SETBITS, TF_BLOCK, &oflags,
        's', MDB_OPT_SETBITS, TF_SIG, &oflags,
        'd', MDB_OPT_SETBITS, TF_DISP, &oflags,
        'm', MDB_OPT_SETBITS, TF_MERGE, &oflags, NULL) != argc)
        return (DCMD_USAGE);

    /*
     * If no sets were specified, choose the 'i' set.
     */
    if (!(oflags & ~TF_MERGE))
#ifdef  _LP64
        oflags = TF_INTR;
#else
        oflags = TF_INTR | TF_DISP | TF_MERGE;
#endif

    /*
     * Print the relevant headers; note use of SPACER().
     */
    if (DCMD_HDRSPEC(flags)) {
        first = TRUE;
        mdb_printf("%<u>%?s%</u>", "ADDR");
        mdb_flush();

        if (oflags & TF_PROC) {
            SPACER();
            mdb_printf("%<u> %?s %?s %?s%</u>",
                "PROC", "LWP", "CRED");
        }

        if (oflags & TF_INTR) {
            SPACER();
            mdb_printf("%<u> %8s %4s %4s %4s %5s %5s %3s %?s%</u>",
                "STATE", "FLG", "PFLG",
                "SFLG", "PRI", "EPRI", "PIL", "INTR");
        }

        if (oflags & TF_BLOCK) {
            SPACER();
            mdb_printf("%<u> %?s %?s %?s %11s%</u>",
                "WCHAN", "TS", "PITS", "SOBJ OPS");
        }

        if (oflags & TF_SIG) {
            SPACER();
            mdb_printf("%<u> %?s %16s %16s%</u>",
                "SIGQUEUE", "SIG PEND", "SIG HELD");
        }

        if (oflags & TF_DISP) {
            SPACER();
            mdb_printf("%<u> %?s %5s %2s %-6s%</u>",
                "DISPTIME", "BOUND", "PR", "SWITCH");
        }
        mdb_printf("\n");
    }

    if (mdb_vread(&t, sizeof (kthread_t), addr) == -1) {
        mdb_warn("can't read kthread_t at %#lx", addr);
        return (DCMD_ERR);
    }

    if (fflag && (t.t_state == TS_FREE))
        return (DCMD_OK);

    first = TRUE;
    mdb_printf("%0?lx", addr);

    /* process information */
    if (oflags & TF_PROC) {
        SPACER();
        mdb_printf(" %?p %?p %?p", t.t_procp, t.t_lwp, t.t_cred);
    }

    /* priority/interrupt information */
    if (oflags & TF_INTR) {
        SPACER();
        thread_state_to_text(t.t_state, stbuf, sizeof (stbuf));
        if (t.t_intr == NULL) {
            mdb_printf(" %-8s %4x %4x %4x %5d %5d %3d %?s",
                stbuf, t.t_flag, t.t_proc_flag, t.t_schedflag,
                t.t_pri, t.t_epri, t.t_pil, "n/a");
        } else {
            mdb_printf(" %-8s %4x %4x %4x %5d %5d %3d %?p",
                stbuf, t.t_flag, t.t_proc_flag, t.t_schedflag,
                t.t_pri, t.t_epri, t.t_pil, t.t_intr);
        }
    }

    /* blocking information */
    if (oflags & TF_BLOCK) {
        SPACER();
        (void) mdb_snprintf(stbuf, 20, "%a", t.t_sobj_ops);
        stbuf[11] = '\0';
        mdb_printf(" %?p %?p %?p %11s",
            t.t_wchan, t.t_ts, t.t_prioinv, stbuf);
    }

    /* signal information */
    if (oflags & TF_SIG) {
        SPACER();
        mdb_printf(" %?p %016llx %016llx",
            t.t_sigqueue, t.t_sig, t.t_hold);
    }

    /* dispatcher stuff */
    if (oflags & TF_DISP) {
        SPACER();
        mdb_printf(" %?lx %5d %2d ",
            t.t_disp_time, t.t_bind_cpu, t.t_preempt);
        if (t.t_disp_time != 0)
            mdb_printf("t-%-4d",
                (clock_t)mdb_get_lbolt() - t.t_disp_time);
        else
            mdb_printf("%-6s", "-");
    }

    mdb_printf("\n");

#undef SPACER

    return (DCMD_OK);
}

void
thread_help(void)
{
    mdb_printf(
        "The flags -ipbsd control which information is displayed.  When\n"
        "combined, the fields are displayed on separate lines unless the\n"
        "-m option is given.\n"
        "\n"
        "\t-b\tprint blocked thread state\n"
        "\t-d\tprint dispatcher state\n"
        "\t-f\tignore freed threads\n"
        "\t-i\tprint basic thread state (default)\n"
        "\t-m\tdisplay results on a single line\n"
        "\t-p\tprint process and lwp state\n"
        "\t-s\tprint signal state\n");
}

/*
 * List a combination of kthread_t and proc_t. Add stack traces in verbose mode.
 */
int
threadlist(uintptr_t addr, uint_t flags, int argc, const mdb_arg_t *argv)
{
    int i;
    uint_t count =  0;
    uint_t verbose = FALSE;
    uint_t notaskq = FALSE;
    kthread_t t;
    taskq_t tq;
    proc_t p;
    char cmd[80];
    mdb_arg_t cmdarg;

    if (!(flags & DCMD_ADDRSPEC)) {
        if (mdb_walk_dcmd("thread", "threadlist", argc, argv) == -1) {
            mdb_warn("can't walk threads");
            return (DCMD_ERR);
        }
        return (DCMD_OK);
    }

    i = mdb_getopts(argc, argv,
        't', MDB_OPT_SETBITS, TRUE, &notaskq,
        'v', MDB_OPT_SETBITS, TRUE, &verbose, NULL);

    if (i != argc) {
        if (i != argc - 1 || !verbose)
            return (DCMD_USAGE);

        if (argv[i].a_type == MDB_TYPE_IMMEDIATE)
            count = (uint_t)argv[i].a_un.a_val;
        else
            count = (uint_t)mdb_strtoull(argv[i].a_un.a_str);
    }

    if (DCMD_HDRSPEC(flags)) {
        if (verbose)
            mdb_printf("%<u>%?s %?s %?s %3s %3s %?s%</u>\n",
                "ADDR", "PROC", "LWP", "CLS", "PRI", "WCHAN");
        else
            mdb_printf("%<u>%?s %?s %?s %s/%s%</u>\n",
                "ADDR", "PROC", "LWP", "CMD", "LWPID");
    }

    if (mdb_vread(&t, sizeof (kthread_t), addr) == -1) {
        mdb_warn("failed to read kthread_t at %p", addr);
        return (DCMD_ERR);
    }

    if (notaskq && t.t_taskq != NULL)
        return (DCMD_OK);

    if (t.t_state == TS_FREE)
        return (DCMD_OK);

    if (mdb_vread(&p, sizeof (proc_t), (uintptr_t)t.t_procp) == -1) {
        mdb_warn("failed to read proc at %p", t.t_procp);
        return (DCMD_ERR);
    }

    if (mdb_vread(&tq, sizeof (taskq_t), (uintptr_t)t.t_taskq) == -1)
        tq.tq_name[0] = '\0';

    if (verbose) {
        mdb_printf("%0?p %?p %?p %3u %3d %?p\n",
            addr, t.t_procp, t.t_lwp, t.t_cid, t.t_pri, t.t_wchan);

        mdb_inc_indent(2);

        mdb_printf("PC: %a", t.t_pc);
        if (t.t_tid == 0) {
            if (tq.tq_name[0] != '\0')
                mdb_printf("    TASKQ: %s\n", tq.tq_name);
            else
                mdb_printf("    THREAD: %a()\n", t.t_startpc);
        } else {
            mdb_printf("    CMD: %s\n", p.p_user.u_psargs);
        }

        mdb_snprintf(cmd, sizeof (cmd), "<.$c%d", count);
        cmdarg.a_type = MDB_TYPE_STRING;
        cmdarg.a_un.a_str = cmd;

        (void) mdb_call_dcmd("findstack", addr, flags, 1, &cmdarg);

        mdb_dec_indent(2);

        mdb_printf("\n");
    } else {
        mdb_printf("%0?p %?p %?p", addr, t.t_procp, t.t_lwp);
        if (t.t_tid == 0) {
            if (tq.tq_name[0] != '\0')
                mdb_printf(" tq:%s\n", tq.tq_name);
            else
                mdb_printf(" %a()\n", t.t_startpc);
        } else {
            mdb_printf(" %s/%u\n", p.p_user.u_comm, t.t_tid);
        }
    }

    return (DCMD_OK);
}

void
threadlist_help(void)
{
    mdb_printf(
        "   -v         print verbose output including C stack trace\n"
        "   -t         skip threads belonging to a taskq\n"
        "   count      print no more than count arguments (default 0)\n");
}

static size_t
stk_compute_percent(caddr_t t_stk, caddr_t t_stkbase, caddr_t sp)
{
    size_t percent;
    size_t s;

    if (t_stk > t_stkbase) {
        /* stack grows down */
        if (sp > t_stk) {
            return (0);
        }
        if (sp < t_stkbase) {
            return (100);
        }
        percent = t_stk - sp + 1;
        s = t_stk - t_stkbase + 1;
    } else {
        /* stack grows up */
        if (sp < t_stk) {
            return (0);
        }
        if (sp > t_stkbase) {
            return (100);
        }
        percent = sp - t_stk + 1;
        s = t_stkbase - t_stk + 1;
    }
    percent = ((100 * percent) / s) + 1;
    if (percent > 100) {
        percent = 100;
    }
    return (percent);
}

/*
 * Display kthread stack infos.
 */
int
stackinfo(uintptr_t addr, uint_t flags, int argc, const mdb_arg_t *argv)
{
    kthread_t t;
    proc_t p;
    uint64_t *ptr;  /* pattern pointer */
    caddr_t start;  /* kernel stack start */
    caddr_t end;    /* kernel stack end */
    caddr_t ustack; /* userland copy of kernel stack */
    size_t usize;   /* userland copy of kernel stack size */
    caddr_t ustart; /* userland copy of kernel stack, aligned start */
    caddr_t uend;   /* userland copy of kernel stack, aligned end */
    size_t percent = 0;
    uint_t all = FALSE; /* don't show TS_FREE kthread by default */
    uint_t history = FALSE;
    int i = 0;
    unsigned int ukmem_stackinfo;
    uintptr_t allthreads;

    /* handle options */
    if (mdb_getopts(argc, argv,
        'a', MDB_OPT_SETBITS, TRUE, &all,
        'h', MDB_OPT_SETBITS, TRUE, &history, NULL) != argc) {
        return (DCMD_USAGE);
    }

    /* walk all kthread if needed */
    if ((history == FALSE) && !(flags & DCMD_ADDRSPEC)) {
        if (mdb_walk_dcmd("thread", "stackinfo", argc, argv) == -1) {
            mdb_warn("can't walk threads");
            return (DCMD_ERR);
        }
        return (DCMD_OK);
    }

    /* read 'kmem_stackinfo' */
    if (mdb_readsym(&ukmem_stackinfo, sizeof (ukmem_stackinfo),
        "kmem_stackinfo") == -1) {
        mdb_warn("failed to read 'kmem_stackinfo'\n");
        ukmem_stackinfo = 0;
    }

    /* read 'allthreads' */
    if (mdb_readsym(&allthreads, sizeof (kthread_t *),
        "allthreads") == -1) {
        mdb_warn("failed to read 'allthreads'\n");
        allthreads = NULL;
    }

    if (history == TRUE) {
        kmem_stkinfo_t *log;
        uintptr_t kaddr;

        mdb_printf("Dead kthreads stack usage history:\n");
        if (ukmem_stackinfo == 0) {
            mdb_printf("Tunable kmem_stackinfo is unset, history ");
            mdb_printf("feature is off.\nUse ::help stackinfo ");
            mdb_printf("for more details.\n");
            return (DCMD_OK);
        }

        mdb_printf("%<u>%?s%</u>", "THREAD");
        mdb_printf(" %<u>%?s%</u>", "STACK");
        mdb_printf("%<u>%s%</u>", "   SIZE  MAX CMD/LWPID or STARTPC");
        mdb_printf("\n");
        usize = KMEM_STKINFO_LOG_SIZE * sizeof (kmem_stkinfo_t);
        log = (kmem_stkinfo_t *)mdb_alloc(usize, UM_SLEEP);
        if (mdb_readsym(&kaddr, sizeof (kaddr),
            "kmem_stkinfo_log") == -1) {
            mdb_free((void *)log, usize);
            mdb_warn("failed to read 'kmem_stkinfo_log'\n");
            return (DCMD_ERR);
        }
        if (kaddr == NULL) {
            mdb_free((void *)log, usize);
            return (DCMD_OK);
        }
        if (mdb_vread(log, usize, kaddr) == -1) {
            mdb_free((void *)log, usize);
            mdb_warn("failed to read %p\n", kaddr);
            return (DCMD_ERR);
        }
        for (i = 0; i < KMEM_STKINFO_LOG_SIZE; i++) {
            if (log[i].kthread == NULL) {
                continue;
            }
            mdb_printf("%0?p %0?p %6x %3d%%",
                log[i].kthread,
                log[i].start,
                (uint_t)log[i].stksz,
                (int)log[i].percent);
            if (log[i].t_tid != 0) {
                mdb_printf(" %s/%u\n",
                    log[i].cmd, log[i].t_tid);
            } else {
                mdb_printf(" %p (%a)\n", log[i].t_startpc,
                    log[i].t_startpc);
            }
        }
        mdb_free((void *)log, usize);
        return (DCMD_OK);
    }

    /* display header */
    if (DCMD_HDRSPEC(flags)) {
        if (ukmem_stackinfo == 0) {
            mdb_printf("Tunable kmem_stackinfo is unset, ");
            mdb_printf("MAX value is not available.\n");
            mdb_printf("Use ::help stackinfo for more details.\n");
        }
        mdb_printf("%<u>%?s%</u>", "THREAD");
        mdb_printf(" %<u>%?s%</u>", "STACK");
        mdb_printf("%<u>%s%</u>", "   SIZE  CUR  MAX CMD/LWPID");
        mdb_printf("\n");
    }

    /* read kthread */
    if (mdb_vread(&t, sizeof (kthread_t), addr) == -1) {
        mdb_warn("can't read kthread_t at %#lx\n", addr);
        return (DCMD_ERR);
    }

    if (t.t_state == TS_FREE && all == FALSE) {
        return (DCMD_OK);
    }

    /* read proc */
    if (mdb_vread(&p, sizeof (proc_t), (uintptr_t)t.t_procp) == -1) {
        mdb_warn("failed to read proc at %p\n", t.t_procp);
        return (DCMD_ERR);
    }

    /*
     * Stack grows up or down, see thread_create(),
     * compute stack memory aera start and end (start < end).
     */
    if (t.t_stk > t.t_stkbase) {
        /* stack grows down */
        start = t.t_stkbase;
        end = t.t_stk;
    } else {
        /* stack grows up */
        start = t.t_stk;
        end = t.t_stkbase;
    }

    /* display stack info */
    mdb_printf("%0?p %0?p", addr, start);

    /* (end - start), kernel stack size as found in kthread_t */
    if ((end <= start) || ((end - start) > (1024 * 1024))) {
        /* negative or stack size > 1 meg, assume bogus */
        mdb_warn(" t_stk/t_stkbase problem\n");
        return (DCMD_ERR);
    }

    /* display stack size */
    mdb_printf(" %6x", end - start);

    /* display current stack usage */
    percent = stk_compute_percent(t.t_stk, t.t_stkbase,
        (caddr_t)t.t_sp + STACK_BIAS);

    mdb_printf(" %3d%%", percent);
    percent = 0;

    if (ukmem_stackinfo == 0) {
        mdb_printf("  n/a");
        if (t.t_tid == 0) {
            mdb_printf(" %a()", t.t_startpc);
        } else {
            mdb_printf(" %s/%u", p.p_user.u_comm, t.t_tid);
        }
        mdb_printf("\n");
        return (DCMD_OK);
    }

    if ((((uintptr_t)start) & 0x7) != 0) {
        start = (caddr_t)((((uintptr_t)start) & (~0x7)) + 8);
    }
    end = (caddr_t)(((uintptr_t)end) & (~0x7));
    /* size to scan in userland copy of kernel stack */
    usize = end - start; /* is a multiple of 8 bytes */

    /*
     * Stackinfo pattern size is 8 bytes. Ensure proper 8 bytes
     * alignement for ustart and uend, in boundaries.
     */
    ustart = ustack = (caddr_t)mdb_alloc(usize + 8, UM_SLEEP);
    if ((((uintptr_t)ustart) & 0x7) != 0) {
        ustart = (caddr_t)((((uintptr_t)ustart) & (~0x7)) + 8);
    }
    uend = ustart + usize;

    /* read the kernel stack */
    if (mdb_vread(ustart, usize, (uintptr_t)start) != usize) {
        mdb_free((void *)ustack, usize + 8);
        mdb_printf("\n");
        mdb_warn("couldn't read entire stack\n");
        return (DCMD_ERR);
    }

    /* scan the stack */
    if (t.t_stk > t.t_stkbase) {
        /* stack grows down */
#if defined(__i386) || defined(__amd64)
        /*
         * 6 longs are pushed on stack, see thread_load(). Skip
         * them, so if kthread has never run, percent is zero.
         * 8 bytes alignement is preserved for a 32 bit kernel,
         * 6 x 4 = 24, 24 is a multiple of 8.
         */
        uend -= (6 * sizeof (long));
#endif
        ptr = (uint64_t *)((void *)ustart);
        while (ptr < (uint64_t *)((void *)uend)) {
            if (*ptr != KMEM_STKINFO_PATTERN) {
                percent = stk_compute_percent(uend,
                    ustart, (caddr_t)ptr);
                break;
            }
            ptr++;
        }
    } else {
        /* stack grows up */
        ptr = (uint64_t *)((void *)uend);
        ptr--;
        while (ptr >= (uint64_t *)((void *)ustart)) {
            if (*ptr != KMEM_STKINFO_PATTERN) {
                percent = stk_compute_percent(ustart,
                    uend, (caddr_t)ptr);
                break;
            }
            ptr--;
        }
    }

    /* thread 't0' stack is not created by thread_create() */
    if (addr == allthreads) {
        percent = 0;
    }
    if (percent != 0) {
        mdb_printf(" %3d%%", percent);
    } else {
        mdb_printf("  n/a");
    }
    if (t.t_tid == 0) {
        mdb_printf(" %a()", t.t_startpc);
    } else {
        mdb_printf(" %s/%u", p.p_user.u_comm, t.t_tid);
    }
    mdb_printf("\n");
    mdb_free((void *)ustack, usize + 8);
    return (DCMD_OK);
}

void
stackinfo_help(void)
{
    mdb_printf(
        "Shows kernel stacks real utilization, if /etc/system "
        "kmem_stackinfo tunable\n");
    mdb_printf(
        "(an unsigned integer) is non zero at kthread creation time. ");
    mdb_printf("For example:\n");
    mdb_printf(
        "          THREAD            STACK   SIZE  CUR  MAX CMD/LWPID\n");
    mdb_printf(
        "ffffff014f5f2c20 ffffff0004153000   4f00   4%%  43%% init/1\n");
    mdb_printf(
        "The stack size utilization for this kthread is at 4%%"
        " of its maximum size,\n");
    mdb_printf(
        "but has already used up to 43%%, stack size is 4f00 bytes.\n");
    mdb_printf(
        "MAX value can be shown as n/a (not available):\n");
    mdb_printf(
        "  - for the very first kthread (sched/1)\n");
    mdb_printf(
        "  - kmem_stackinfo was zero at kthread creation time\n");
    mdb_printf(
        "  - kthread has not yet run\n");
    mdb_printf("\n");
    mdb_printf("Options:\n");
    mdb_printf(
        "-a shows also TS_FREE kthreads (interrupt kthreads)\n");
    mdb_printf(
        "-h shows history, dead kthreads that used their "
        "kernel stack the most\n");
    mdb_printf(
        "\nSee Solaris Modular Debugger Guide for detailed usage.\n");
    mdb_flush();
}