intel/dtrace/fbt.c

	fbt.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (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 2005 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

#include <sys/modctl.h>
#include <sys/dtrace.h>
#include <sys/kobj.h>
#include <sys/stat.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
#include <sys/conf.h>

#define FBT_PUSHL_EBP       0x55
#define FBT_MOVL_ESP_EBP0_V0    0x8b
#define FBT_MOVL_ESP_EBP1_V0    0xec
#define FBT_MOVL_ESP_EBP0_V1    0x89
#define FBT_MOVL_ESP_EBP1_V1    0xe5
#define FBT_REX_RSP_RBP     0x48

#define FBT_POPL_EBP        0x5d
#define FBT_RET         0xc3
#define FBT_RET_IMM16       0xc2
#define FBT_LEAVE       0xc9

#ifdef __amd64
#define FBT_PATCHVAL        0xcc
#else
#define FBT_PATCHVAL        0xf0
#endif

#define FBT_ENTRY   "entry"
#define FBT_RETURN  "return"
#define FBT_ADDR2NDX(addr)  ((((uintptr_t)(addr)) >> 4) & fbt_probetab_mask)
#define FBT_PROBETAB_SIZE   0x8000      /* 32k entries -- 128K total */

typedef struct fbt_probe {
    struct fbt_probe *fbtp_hashnext;
    uint8_t     *fbtp_patchpoint;
    int8_t      fbtp_rval;
    uint8_t     fbtp_patchval;
    uint8_t     fbtp_savedval;
    uintptr_t   fbtp_roffset;
    dtrace_id_t fbtp_id;
    char        *fbtp_name;
    struct modctl   *fbtp_ctl;
    int     fbtp_loadcnt;
    int     fbtp_symndx;
    int     fbtp_primary;
    struct fbt_probe *fbtp_next;
} fbt_probe_t;

static dev_info_t       *fbt_devi;
static dtrace_provider_id_t fbt_id;
static fbt_probe_t      **fbt_probetab;
static int          fbt_probetab_size;
static int          fbt_probetab_mask;
static int          fbt_verbose = 0;

static int
fbt_invop(uintptr_t addr, uintptr_t *stack, uintptr_t rval)
{
    uintptr_t stack0, stack1, stack2, stack3, stack4;
    fbt_probe_t *fbt = fbt_probetab[FBT_ADDR2NDX(addr)];

    for (; fbt != NULL; fbt = fbt->fbtp_hashnext) {
        if ((uintptr_t)fbt->fbtp_patchpoint == addr) {
            if (fbt->fbtp_roffset == 0) {
                int i = 0;
                /*
                 * When accessing the arguments on the stack,
                 * we must protect against accessing beyond
                 * the stack.  We can safely set NOFAULT here
                 * -- we know that interrupts are already
                 * disabled.
                 */
                DTRACE_CPUFLAG_SET(CPU_DTRACE_NOFAULT);
                CPU->cpu_dtrace_caller = stack[i++];
#ifdef __amd64
                /*
                 * On amd64, stack[0] contains the dereferenced
                 * stack pointer, stack[1] contains savfp,
                 * stack[2] contains savpc.  We want to step
                 * over these entries.
                 */
                i += 2;
#endif
                stack0 = stack[i++];
                stack1 = stack[i++];
                stack2 = stack[i++];
                stack3 = stack[i++];
                stack4 = stack[i++];
                DTRACE_CPUFLAG_CLEAR(CPU_DTRACE_NOFAULT |
                    CPU_DTRACE_BADADDR);

                dtrace_probe(fbt->fbtp_id, stack0, stack1,
                    stack2, stack3, stack4);

                CPU->cpu_dtrace_caller = NULL;
            } else {
#ifdef __amd64
                /*
                 * On amd64, we instrument the ret, not the
                 * leave.  We therefore need to set the caller
                 * to assure that the top frame of a stack()
                 * action is correct.
                 */
                DTRACE_CPUFLAG_SET(CPU_DTRACE_NOFAULT);
                CPU->cpu_dtrace_caller = stack[0];
                DTRACE_CPUFLAG_CLEAR(CPU_DTRACE_NOFAULT |
                    CPU_DTRACE_BADADDR);
#endif

                dtrace_probe(fbt->fbtp_id, fbt->fbtp_roffset,
                    rval, 0, 0, 0);
                CPU->cpu_dtrace_caller = NULL;
            }

            return (fbt->fbtp_rval);
        }
    }

    return (0);
}

/*ARGSUSED*/
static void
fbt_provide_module(void *arg, struct modctl *ctl)
{
    struct module *mp = ctl->mod_mp;
    char *str = mp->strings;
    int nsyms = mp->nsyms;
    Shdr *symhdr = mp->symhdr;
    char *modname = ctl->mod_modname;
    char *name;
    fbt_probe_t *fbt, *retfbt;
    size_t symsize;
    int i, size;

    /*
     * Employees of dtrace and their families are ineligible.  Void
     * where prohibited.
     */
    if (strcmp(modname, "dtrace") == 0)
        return;

    if (ctl->mod_requisites != NULL) {
        struct modctl_list *list;

        list = (struct modctl_list *)ctl->mod_requisites;

        for (; list != NULL; list = list->modl_next) {
            if (strcmp(list->modl_modp->mod_modname, "dtrace") == 0)
                return;
        }
    }

    /*
     * KMDB is ineligible for instrumentation -- it may execute in
     * any context, including probe context.
     */
    if (strcmp(modname, "kmdbmod") == 0)
        return;

    if (str == NULL || symhdr == NULL || symhdr->sh_addr == NULL) {
        /*
         * If this module doesn't (yet) have its string or symbol
         * table allocated, clear out.
         */
        return;
    }

    symsize = symhdr->sh_entsize;

    if (mp->fbt_nentries) {
        /*
         * This module has some FBT entries allocated; we're afraid
         * to screw with it.
         */
        return;
    }

    for (i = 1; i < nsyms; i++) {
        uint8_t *instr, *limit;
        Sym *sym = (Sym *)(symhdr->sh_addr + i * symsize);

        if (ELF_ST_TYPE(sym->st_info) != STT_FUNC)
            continue;

        /*
         * Weak symbols are not candidates.  This could be made to
         * work (where weak functions and their underlying function
         * appear as two disjoint probes), but it's not simple.
         */
        if (ELF_ST_BIND(sym->st_info) == STB_WEAK)
            continue;

        name = str + sym->st_name;

        if (strstr(name, "dtrace_") == name &&
            strstr(name, "dtrace_safe_") != name) {
            /*
             * Anything beginning with "dtrace_" may be called
             * from probe context unless it explitly indicates
             * that it won't be called from probe context by
             * using the prefix "dtrace_safe_".
             */
            continue;
        }

        if (strstr(name, "kdi_") == name) {
            /*
             * Anything beginning with "kdi_" is a part of the
             * kernel debugger interface and may be called in
             * arbitrary context -- including probe context.
             */
            continue;
        }

        /*
         * Due to 4524008, _init and _fini may have a bloated st_size.
         * While this bug was fixed quite some time ago, old drivers
         * may be lurking.  We need to develop a better solution to
         * this problem, such that correct _init and _fini functions
         * (the vast majority) may be correctly traced.  One solution
         * may be to scan through the entire symbol table to see if
         * any symbol overlaps with _init.  If none does, set a bit in
         * the module structure that this module has correct _init and
         * _fini sizes.  This will cause some pain the first time a
         * module is scanned, but at least it would be O(N) instead of
         * O(N log N)...
         */
        if (strcmp(name, "_init") == 0)
            continue;

        if (strcmp(name, "_fini") == 0)
            continue;

        /*
         * In order to be eligible, the function must begin with the
         * following sequence:
         *
         *  pushl   %esp
         *  movl    %esp, %ebp
         *
         * Note that there are two variants of encodings that generate
         * the movl; we must check for both.  For 64-bit, we would
         * normally insist that a function begin with the following
         * sequence:
         *
         *  pushq   %rbp
         *  movq    %rsp, %rbp
         *
         * However, the compiler for 64-bit often splits these two
         * instructions -- and the first instruction in the function
         * is often not the pushq.  As a result, on 64-bit we look
         * for any "pushq %rbp" in the function and we instrument
         * this with a breakpoint instruction.
         */
        instr = (uint8_t *)sym->st_value;
        limit = (uint8_t *)(sym->st_value + sym->st_size);

#ifdef __amd64
        while (instr < limit) {
            if (*instr == FBT_PUSHL_EBP)
                break;

            if ((size = dtrace_instr_size(instr)) <= 0)
                break;

            instr += size;
        }

        if (instr >= limit || *instr != FBT_PUSHL_EBP) {
            /*
             * We either don't save the frame pointer in this
             * function, or we ran into some disassembly
             * screw-up.  Either way, we bail.
             */
            continue;
        }
#else
        if (instr[0] != FBT_PUSHL_EBP)
            continue;

        if (!(instr[1] == FBT_MOVL_ESP_EBP0_V0 &&
            instr[2] == FBT_MOVL_ESP_EBP1_V0) &&
            !(instr[1] == FBT_MOVL_ESP_EBP0_V1 &&
            instr[2] == FBT_MOVL_ESP_EBP1_V1))
            continue;
#endif

        fbt = kmem_zalloc(sizeof (fbt_probe_t), KM_SLEEP);
        fbt->fbtp_name = name;
        fbt->fbtp_id = dtrace_probe_create(fbt_id, modname,
            name, FBT_ENTRY, 3, fbt);
        fbt->fbtp_patchpoint = instr;
        fbt->fbtp_ctl = ctl;
        fbt->fbtp_loadcnt = ctl->mod_loadcnt;
        fbt->fbtp_rval = DTRACE_INVOP_PUSHL_EBP;
        fbt->fbtp_savedval = *instr;
        fbt->fbtp_patchval = FBT_PATCHVAL;

        fbt->fbtp_hashnext = fbt_probetab[FBT_ADDR2NDX(instr)];
        fbt->fbtp_symndx = i;
        fbt_probetab[FBT_ADDR2NDX(instr)] = fbt;

        mp->fbt_nentries++;

        retfbt = NULL;
again:
        if (instr >= limit)
            continue;

        /*
         * If this disassembly fails, then we've likely walked off into
         * a jump table or some other unsuitable area.  Bail out of the
         * disassembly now.
         */
        if ((size = dtrace_instr_size(instr)) <= 0)
            continue;

#ifdef __amd64
        /*
         * We only instrument "ret" on amd64 -- we don't yet instrument
         * ret imm16, largely because the compiler doesn't seem to
         * (yet) emit them in the kernel...
         */
        if (*instr != FBT_RET) {
            instr += size;
            goto again;
        }
#else
        if (!(size == 1 &&
            (*instr == FBT_POPL_EBP || *instr == FBT_LEAVE) &&
            (*(instr + 1) == FBT_RET ||
            *(instr + 1) == FBT_RET_IMM16))) {
            instr += size;
            goto again;
        }
#endif

        /*
         * We have a winner!
         */
        fbt = kmem_zalloc(sizeof (fbt_probe_t), KM_SLEEP);
        fbt->fbtp_name = name;

        if (retfbt == NULL) {
            fbt->fbtp_id = dtrace_probe_create(fbt_id, modname,
                name, FBT_RETURN, 3, fbt);
        } else {
            retfbt->fbtp_next = fbt;
            fbt->fbtp_id = retfbt->fbtp_id;
        }

        retfbt = fbt;
        fbt->fbtp_patchpoint = instr;
        fbt->fbtp_ctl = ctl;
        fbt->fbtp_loadcnt = ctl->mod_loadcnt;

#ifndef __amd64
        if (*instr == FBT_POPL_EBP) {
            fbt->fbtp_rval = DTRACE_INVOP_POPL_EBP;
        } else {
            ASSERT(*instr == FBT_LEAVE);
            fbt->fbtp_rval = DTRACE_INVOP_LEAVE;
        }
        fbt->fbtp_roffset =
            (uintptr_t)(instr - (uint8_t *)sym->st_value) + 1;

#else
        ASSERT(*instr == FBT_RET);
        fbt->fbtp_rval = DTRACE_INVOP_RET;
        fbt->fbtp_roffset =
            (uintptr_t)(instr - (uint8_t *)sym->st_value);
#endif

        fbt->fbtp_savedval = *instr;
        fbt->fbtp_patchval = FBT_PATCHVAL;
        fbt->fbtp_hashnext = fbt_probetab[FBT_ADDR2NDX(instr)];
        fbt->fbtp_symndx = i;
        fbt_probetab[FBT_ADDR2NDX(instr)] = fbt;

        mp->fbt_nentries++;

        instr += size;
        goto again;
    }
}

/*ARGSUSED*/
static void
fbt_destroy(void *arg, dtrace_id_t id, void *parg)
{
    fbt_probe_t *fbt = parg, *next, *hash, *last;
    struct modctl *ctl = fbt->fbtp_ctl;
    int ndx;

    do {
        if (ctl != NULL && ctl->mod_loadcnt == fbt->fbtp_loadcnt) {
            if ((ctl->mod_loadcnt == fbt->fbtp_loadcnt &&
                ctl->mod_loaded)) {
                ((struct module *)
                    (ctl->mod_mp))->fbt_nentries--;
            }
        }

        /*
         * Now we need to remove this probe from the fbt_probetab.
         */
        ndx = FBT_ADDR2NDX(fbt->fbtp_patchpoint);
        last = NULL;
        hash = fbt_probetab[ndx];

        while (hash != fbt) {
            ASSERT(hash != NULL);
            last = hash;
            hash = hash->fbtp_hashnext;
        }

        if (last != NULL) {
            last->fbtp_hashnext = fbt->fbtp_hashnext;
        } else {
            fbt_probetab[ndx] = fbt->fbtp_hashnext;
        }

        next = fbt->fbtp_next;
        kmem_free(fbt, sizeof (fbt_probe_t));

        fbt = next;
    } while (fbt != NULL);
}

/*ARGSUSED*/
static void
fbt_enable(void *arg, dtrace_id_t id, void *parg)
{
    fbt_probe_t *fbt = parg;
    struct modctl *ctl = fbt->fbtp_ctl;

    ctl->mod_nenabled++;

    if (!ctl->mod_loaded) {
        if (fbt_verbose) {
            cmn_err(CE_NOTE, "fbt is failing for probe %s "
                "(module %s unloaded)",
                fbt->fbtp_name, ctl->mod_modname);
        }

        return;
    }

    /*
     * Now check that our modctl has the expected load count.  If it
     * doesn't, this module must have been unloaded and reloaded -- and
     * we're not going to touch it.
     */
    if (ctl->mod_loadcnt != fbt->fbtp_loadcnt) {
        if (fbt_verbose) {
            cmn_err(CE_NOTE, "fbt is failing for probe %s "
                "(module %s reloaded)",
                fbt->fbtp_name, ctl->mod_modname);
        }

        return;
    }

    for (; fbt != NULL; fbt = fbt->fbtp_next)
        *fbt->fbtp_patchpoint = fbt->fbtp_patchval;
}

/*ARGSUSED*/
static void
fbt_disable(void *arg, dtrace_id_t id, void *parg)
{
    fbt_probe_t *fbt = parg;
    struct modctl *ctl = fbt->fbtp_ctl;

    ASSERT(ctl->mod_nenabled > 0);
    ctl->mod_nenabled--;

    if (!ctl->mod_loaded || (ctl->mod_loadcnt != fbt->fbtp_loadcnt))
        return;

    for (; fbt != NULL; fbt = fbt->fbtp_next)
        *fbt->fbtp_patchpoint = fbt->fbtp_savedval;
}

/*ARGSUSED*/
static void
fbt_suspend(void *arg, dtrace_id_t id, void *parg)
{
    fbt_probe_t *fbt = parg;
    struct modctl *ctl = fbt->fbtp_ctl;

    ASSERT(ctl->mod_nenabled > 0);

    if (!ctl->mod_loaded || (ctl->mod_loadcnt != fbt->fbtp_loadcnt))
        return;

    for (; fbt != NULL; fbt = fbt->fbtp_next)
        *fbt->fbtp_patchpoint = fbt->fbtp_savedval;
}

/*ARGSUSED*/
static void
fbt_resume(void *arg, dtrace_id_t id, void *parg)
{
    fbt_probe_t *fbt = parg;
    struct modctl *ctl = fbt->fbtp_ctl;

    ASSERT(ctl->mod_nenabled > 0);

    if (!ctl->mod_loaded || (ctl->mod_loadcnt != fbt->fbtp_loadcnt))
        return;

    for (; fbt != NULL; fbt = fbt->fbtp_next)
        *fbt->fbtp_patchpoint = fbt->fbtp_patchval;
}

/*ARGSUSED*/
static void
fbt_getargdesc(void *arg, dtrace_id_t id, void *parg, dtrace_argdesc_t *desc)
{
    fbt_probe_t *fbt = parg;
    struct modctl *ctl = fbt->fbtp_ctl;
    struct module *mp = ctl->mod_mp;
    ctf_file_t *fp = NULL, *pfp;
    ctf_funcinfo_t f;
    int error;
    ctf_id_t argv[32], type;
    int argc = sizeof (argv) / sizeof (ctf_id_t);
    const char *parent;

    if (!ctl->mod_loaded || (ctl->mod_loadcnt != fbt->fbtp_loadcnt))
        goto err;

    if (fbt->fbtp_roffset != 0 && desc->dtargd_ndx == 0) {
        (void) strcpy(desc->dtargd_native, "int");
        return;
    }

    if ((fp = ctf_modopen(mp, &error)) == NULL) {
        /*
         * We have no CTF information for this module -- and therefore
         * no args[] information.
         */
        goto err;
    }

    /*
     * If we have a parent container, we must manually import it.
     */
    if ((parent = ctf_parent_name(fp)) != NULL) {
        struct modctl *mod;

        /*
         * We must iterate over all modules to find the module that
         * is our parent.
         */
        for (mod = &modules; mod != NULL; mod = mod->mod_next) {
            if (strcmp(mod->mod_filename, parent) == 0)
                break;
        }

        if (mod == NULL)
            goto err;

        if ((pfp = ctf_modopen(mod->mod_mp, &error)) == NULL)
            goto err;

        if (ctf_import(fp, pfp) != 0) {
            ctf_close(pfp);
            goto err;
        }

        ctf_close(pfp);
    }

    if (ctf_func_info(fp, fbt->fbtp_symndx, &f) == CTF_ERR)
        goto err;

    if (fbt->fbtp_roffset != 0) {
        if (desc->dtargd_ndx > 1)
            goto err;

        ASSERT(desc->dtargd_ndx == 1);
        type = f.ctc_return;
    } else {
        if (desc->dtargd_ndx + 1 > f.ctc_argc)
            goto err;

        if (ctf_func_args(fp, fbt->fbtp_symndx, argc, argv) == CTF_ERR)
            goto err;

        type = argv[desc->dtargd_ndx];
    }

    if (ctf_type_name(fp, type, desc->dtargd_native,
        DTRACE_ARGTYPELEN) != NULL) {
        ctf_close(fp);
        return;
    }
err:
    if (fp != NULL)
        ctf_close(fp);

    desc->dtargd_ndx = DTRACE_ARGNONE;
}

static dtrace_pattr_t fbt_attr = {
{ DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_ISA },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
{ DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_ISA },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_ISA },
};

static dtrace_pops_t fbt_pops = {
    NULL,
    fbt_provide_module,
    fbt_enable,
    fbt_disable,
    fbt_suspend,
    fbt_resume,
    fbt_getargdesc,
    NULL,
    NULL,
    fbt_destroy
};

static void
fbt_cleanup(dev_info_t *devi)
{
    dtrace_invop_remove(fbt_invop);
    ddi_remove_minor_node(devi, NULL);
    kmem_free(fbt_probetab, fbt_probetab_size * sizeof (fbt_probe_t *));
    fbt_probetab = NULL;
    fbt_probetab_mask = 0;
}

static int
fbt_attach(dev_info_t *devi, ddi_attach_cmd_t cmd)
{
    switch (cmd) {
    case DDI_ATTACH:
        break;
    case DDI_RESUME:
        return (DDI_SUCCESS);
    default:
        return (DDI_FAILURE);
    }

    if (fbt_probetab_size == 0)
        fbt_probetab_size = FBT_PROBETAB_SIZE;

    fbt_probetab_mask = fbt_probetab_size - 1;
    fbt_probetab =
        kmem_zalloc(fbt_probetab_size * sizeof (fbt_probe_t *), KM_SLEEP);

    dtrace_invop_add(fbt_invop);

    if (ddi_create_minor_node(devi, "fbt", S_IFCHR, 0,
        DDI_PSEUDO, NULL) == DDI_FAILURE ||
        dtrace_register("fbt", &fbt_attr, DTRACE_PRIV_KERNEL, 0,
        &fbt_pops, NULL, &fbt_id) != 0) {
        fbt_cleanup(devi);
        return (DDI_FAILURE);
    }

    ddi_report_dev(devi);
    fbt_devi = devi;

    return (DDI_SUCCESS);
}

static int
fbt_detach(dev_info_t *devi, ddi_detach_cmd_t cmd)
{
    switch (cmd) {
    case DDI_DETACH:
        break;
    case DDI_SUSPEND:
        return (DDI_SUCCESS);
    default:
        return (DDI_FAILURE);
    }

    if (dtrace_unregister(fbt_id) != 0)
        return (DDI_FAILURE);

    fbt_cleanup(devi);

    return (DDI_SUCCESS);
}

/*ARGSUSED*/
static int
fbt_info(dev_info_t *dip, ddi_info_cmd_t infocmd, void *arg, void **result)
{
    int error;

    switch (infocmd) {
    case DDI_INFO_DEVT2DEVINFO:
        *result = (void *)fbt_devi;
        error = DDI_SUCCESS;
        break;
    case DDI_INFO_DEVT2INSTANCE:
        *result = (void *)0;
        error = DDI_SUCCESS;
        break;
    default:
        error = DDI_FAILURE;
    }
    return (error);
}

/*ARGSUSED*/
static int
fbt_open(dev_t *devp, int flag, int otyp, cred_t *cred_p)
{
    return (0);
}

static struct cb_ops fbt_cb_ops = {
    fbt_open,       /* open */
    nodev,          /* close */
    nulldev,        /* strategy */
    nulldev,        /* print */
    nodev,          /* dump */
    nodev,          /* read */
    nodev,          /* write */
    nodev,          /* ioctl */
    nodev,          /* devmap */
    nodev,          /* mmap */
    nodev,          /* segmap */
    nochpoll,       /* poll */
    ddi_prop_op,        /* cb_prop_op */
    0,          /* streamtab  */
    D_NEW | D_MP        /* Driver compatibility flag */
};

static struct dev_ops fbt_ops = {
    DEVO_REV,       /* devo_rev */
    0,          /* refcnt */
    fbt_info,       /* get_dev_info */
    nulldev,        /* identify */
    nulldev,        /* probe */
    fbt_attach,     /* attach */
    fbt_detach,     /* detach */
    nodev,          /* reset */
    &fbt_cb_ops,        /* driver operations */
    NULL,           /* bus operations */
    nodev           /* dev power */
};

/*
 * Module linkage information for the kernel.
 */
static struct modldrv modldrv = {
    &mod_driverops,     /* module type (this is a pseudo driver) */
    "Function Boundary Tracing",    /* name of module */
    &fbt_ops,       /* driver ops */
};

static struct modlinkage modlinkage = {
    MODREV_1,
    (void *)&modldrv,
    NULL
};

int
_init(void)
{
    return (mod_install(&modlinkage));
}

int
_info(struct modinfo *modinfop)
{
    return (mod_info(&modlinkage, modinfop));
}

int
_fini(void)
{
    return (mod_remove(&modlinkage));
}