/*
 * 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 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#include <sys/fasttrap_isa.h>
#include <sys/fasttrap_impl.h>
#include <sys/dtrace.h>
#include <sys/dtrace_impl.h>
#include <sys/cmn_err.h>
#include <sys/regset.h>
#include <sys/privregs.h>
#include <sys/segments.h>
#include <sys/x86_archext.h>
#include <sys/sysmacros.h>
#include <sys/trap.h>
#include <sys/archsystm.h>

/*
 * Lossless User-Land Tracing on x86
 * ---------------------------------
 *
 * The execution of most instructions is not dependent on the address; for
 * these instructions it is sufficient to copy them into the user process's
 * address space and execute them. To effectively single-step an instruction
 * in user-land, we copy out the following sequence of instructions to scratch
 * space in the user thread's ulwp_t structure.
 *
 * We then set the program counter (%eip or %rip) to point to this scratch
 * space. Once execution resumes, the original instruction is executed and
 * then control flow is redirected to what was originally the subsequent
 * instruction. If the kernel attemps to deliver a signal while single-
 * stepping, the signal is deferred and the program counter is moved into the
 * second sequence of instructions. The second sequence ends in a trap into
 * the kernel where the deferred signal is then properly handled and delivered.
 *
 * For instructions whose execute is position dependent, we perform simple
 * emulation. These instructions are limited to control transfer
 * instructions in 32-bit mode, but in 64-bit mode there's the added wrinkle
 * of %rip-relative addressing that means that almost any instruction can be
 * position dependent. For all the details on how we emulate generic
 * instructions included %rip-relative instructions, see the code in
 * fasttrap_pid_probe() below where we handle instructions of type
 * FASTTRAP_T_COMMON (under the header: Generic Instruction Tracing).
 */

#define FASTTRAP_MODRM_MOD(modrm)       (((modrm) >> 6) & 0x3)
#define FASTTRAP_MODRM_REG(modrm)       (((modrm) >> 3) & 0x7)
#define FASTTRAP_MODRM_RM(modrm)        ((modrm) & 0x7)
#define FASTTRAP_MODRM(mod, reg, rm)    (((mod) << 6) | ((reg) << 3) | (rm))

#define FASTTRAP_SIB_SCALE(sib)         (((sib) >> 6) & 0x3)
#define FASTTRAP_SIB_INDEX(sib)         (((sib) >> 3) & 0x7)
#define FASTTRAP_SIB_BASE(sib)          ((sib) & 0x7)

#define FASTTRAP_REX_W(rex)             (((rex) >> 3) & 1)
#define FASTTRAP_REX_R(rex)             (((rex) >> 2) & 1)
#define FASTTRAP_REX_X(rex)             (((rex) >> 1) & 1)
#define FASTTRAP_REX_B(rex)             ((rex) & 1)
#define FASTTRAP_REX(w, r, x, b)        \
        (0x40 | ((w) << 3) | ((r) << 2) | ((x) << 1) | (b))

/*
 * Single-byte op-codes.
 */
#define FASTTRAP_PUSHL_EBP      0x55

#define FASTTRAP_JO             0x70
#define FASTTRAP_JNO            0x71
#define FASTTRAP_JB             0x72
#define FASTTRAP_JAE            0x73
#define FASTTRAP_JE             0x74
#define FASTTRAP_JNE            0x75
#define FASTTRAP_JBE            0x76
#define FASTTRAP_JA             0x77
#define FASTTRAP_JS             0x78
#define FASTTRAP_JNS            0x79
#define FASTTRAP_JP             0x7a
#define FASTTRAP_JNP            0x7b
#define FASTTRAP_JL             0x7c
#define FASTTRAP_JGE            0x7d
#define FASTTRAP_JLE            0x7e
#define FASTTRAP_JG             0x7f

#define FASTTRAP_NOP            0x90

#define FASTTRAP_MOV_EAX        0xb8
#define FASTTRAP_MOV_ECX        0xb9

#define FASTTRAP_RET16          0xc2
#define FASTTRAP_RET            0xc3

#define FASTTRAP_LOOPNZ         0xe0
#define FASTTRAP_LOOPZ          0xe1
#define FASTTRAP_LOOP           0xe2
#define FASTTRAP_JCXZ           0xe3

#define FASTTRAP_CALL           0xe8
#define FASTTRAP_JMP32          0xe9
#define FASTTRAP_JMP8           0xeb

#define FASTTRAP_INT3           0xcc
#define FASTTRAP_INT            0xcd

#define FASTTRAP_2_BYTE_OP      0x0f
#define FASTTRAP_GROUP5_OP      0xff

/*
 * Two-byte op-codes (second byte only).
 */
#define FASTTRAP_0F_JO          0x80
#define FASTTRAP_0F_JNO         0x81
#define FASTTRAP_0F_JB          0x82
#define FASTTRAP_0F_JAE         0x83
#define FASTTRAP_0F_JE          0x84
#define FASTTRAP_0F_JNE         0x85
#define FASTTRAP_0F_JBE         0x86
#define FASTTRAP_0F_JA          0x87
#define FASTTRAP_0F_JS          0x88
#define FASTTRAP_0F_JNS         0x89
#define FASTTRAP_0F_JP          0x8a
#define FASTTRAP_0F_JNP         0x8b
#define FASTTRAP_0F_JL          0x8c
#define FASTTRAP_0F_JGE         0x8d
#define FASTTRAP_0F_JLE         0x8e
#define FASTTRAP_0F_JG          0x8f

#define FASTTRAP_EFLAGS_OF      0x800
#define FASTTRAP_EFLAGS_DF      0x400
#define FASTTRAP_EFLAGS_SF      0x080
#define FASTTRAP_EFLAGS_ZF      0x040
#define FASTTRAP_EFLAGS_AF      0x010
#define FASTTRAP_EFLAGS_PF      0x004
#define FASTTRAP_EFLAGS_CF      0x001

/*
 * Instruction prefixes.
 */
#define FASTTRAP_PREFIX_OPERAND 0x66
#define FASTTRAP_PREFIX_ADDRESS 0x67
#define FASTTRAP_PREFIX_CS      0x2E
#define FASTTRAP_PREFIX_DS      0x3E
#define FASTTRAP_PREFIX_ES      0x26
#define FASTTRAP_PREFIX_FS      0x64
#define FASTTRAP_PREFIX_GS      0x65
#define FASTTRAP_PREFIX_SS      0x36
#define FASTTRAP_PREFIX_LOCK    0xF0
#define FASTTRAP_PREFIX_REP     0xF3
#define FASTTRAP_PREFIX_REPNE   0xF2

#define FASTTRAP_NOREG  0xff

/*
 * Map between instruction register encodings and the kernel constants which
 * correspond to indicies into struct regs.
 */
static const uint8_t regmap[16] = {
        REG_RAX, REG_RCX, REG_RDX, REG_RBX, REG_RSP, REG_RBP, REG_RSI, REG_RDI,
        REG_R8, REG_R9, REG_R10, REG_R11, REG_R12, REG_R13, REG_R14, REG_R15,
};

static ulong_t fasttrap_getreg(struct regs *, uint_t);

static uint64_t
fasttrap_anarg(struct regs *rp, int function_entry, int argno)
{
        uint64_t value;
        int shift = function_entry ? 1 : 0;

        if (curproc->p_model == DATAMODEL_LP64) {
                uintptr_t *stack;

                /*
                 * In 64-bit mode, the first six arguments are stored in
                 * registers.
                 */
                if (argno < 6)
                        return ((&rp->r_rdi)[argno]);

                stack = (uintptr_t *)rp->r_sp;
                DTRACE_CPUFLAG_SET(CPU_DTRACE_NOFAULT);
                value = dtrace_fulword(&stack[argno - 6 + shift]);
                DTRACE_CPUFLAG_CLEAR(CPU_DTRACE_NOFAULT | CPU_DTRACE_BADADDR);
        } else {
                uint32_t *stack = (uint32_t *)rp->r_sp;
                DTRACE_CPUFLAG_SET(CPU_DTRACE_NOFAULT);
                value = dtrace_fuword32(&stack[argno + shift]);
                DTRACE_CPUFLAG_CLEAR(CPU_DTRACE_NOFAULT | CPU_DTRACE_BADADDR);
        }

        return (value);
}

/*ARGSUSED*/
int
fasttrap_tracepoint_init(proc_t *p, fasttrap_tracepoint_t *tp, uintptr_t pc,
    fasttrap_probe_type_t type)
{
        uint8_t instr[FASTTRAP_MAX_INSTR_SIZE + 10];
        size_t len = FASTTRAP_MAX_INSTR_SIZE;
        size_t first = MIN(len, PAGESIZE - (pc & PAGEOFFSET));
        uint_t start = 0;
        int rmindex, size;
        uint8_t seg, rex = 0;

        /*
         * Read the instruction at the given address out of the process's
         * address space. We don't have to worry about a debugger
         * changing this instruction before we overwrite it with our trap
         * instruction since P_PR_LOCK is set. Since instructions can span
         * pages, we potentially read the instruction in two parts. If the
         * second part fails, we just zero out that part of the instruction.
         */
        if (uread(p, &instr[0], first, pc) != 0)
                return (-1);
        if (len > first &&
            uread(p, &instr[first], len - first, pc + first) != 0) {
                bzero(&instr[first], len - first);
                len = first;
        }

        /*
         * If the disassembly fails, then we have a malformed instruction.
         */
        if ((size = dtrace_instr_size_isa(instr, p->p_model, &rmindex)) <= 0)
                return (-1);

        /*
         * Make sure the disassembler isn't completely broken.
         */
        ASSERT(-1 <= rmindex && rmindex < size);

        /*
         * If the computed size is greater than the number of bytes read,
         * then it was a malformed instruction possibly because it fell on a
         * page boundary and the subsequent page was missing or because of
         * some malicious user.
         */
        if (size > len)
                return (-1);

        tp->ftt_size = (uint8_t)size;
        tp->ftt_segment = FASTTRAP_SEG_NONE;

        /*
         * Find the start of the instruction's opcode by processing any
         * legacy prefixes.
         */
        for (;;) {
                seg = 0;
                switch (instr[start]) {
                case FASTTRAP_PREFIX_SS:
                        seg++;
                        /*FALLTHRU*/
                case FASTTRAP_PREFIX_GS:
                        seg++;
                        /*FALLTHRU*/
                case FASTTRAP_PREFIX_FS:
                        seg++;
                        /*FALLTHRU*/
                case FASTTRAP_PREFIX_ES:
                        seg++;
                        /*FALLTHRU*/
                case FASTTRAP_PREFIX_DS:
                        seg++;
                        /*FALLTHRU*/
                case FASTTRAP_PREFIX_CS:
                        seg++;
                        /*FALLTHRU*/
                case FASTTRAP_PREFIX_OPERAND:
                case FASTTRAP_PREFIX_ADDRESS:
                case FASTTRAP_PREFIX_LOCK:
                case FASTTRAP_PREFIX_REP:
                case FASTTRAP_PREFIX_REPNE:
                        if (seg != 0) {
                                /*
                                 * It's illegal for an instruction to specify
                                 * two segment prefixes -- give up on this
                                 * illegal instruction.
                                 */
                                if (tp->ftt_segment != FASTTRAP_SEG_NONE)
                                        return (-1);

                                tp->ftt_segment = seg;
                        }
                        start++;
                        continue;
                }
                break;
        }

        /*
         * Identify the REX prefix on 64-bit processes.
         */
        if (p->p_model == DATAMODEL_LP64 && (instr[start] & 0xf0) == 0x40)
                rex = instr[start++];

        /*
         * Now that we're pretty sure that the instruction is okay, copy the
         * valid part to the tracepoint.
         */
        bcopy(instr, tp->ftt_instr, FASTTRAP_MAX_INSTR_SIZE);

        tp->ftt_type = FASTTRAP_T_COMMON;
        if (instr[start] == FASTTRAP_2_BYTE_OP) {
                switch (instr[start + 1]) {
                case FASTTRAP_0F_JO:
                case FASTTRAP_0F_JNO:
                case FASTTRAP_0F_JB:
                case FASTTRAP_0F_JAE:
                case FASTTRAP_0F_JE:
                case FASTTRAP_0F_JNE:
                case FASTTRAP_0F_JBE:
                case FASTTRAP_0F_JA:
                case FASTTRAP_0F_JS:
                case FASTTRAP_0F_JNS:
                case FASTTRAP_0F_JP:
                case FASTTRAP_0F_JNP:
                case FASTTRAP_0F_JL:
                case FASTTRAP_0F_JGE:
                case FASTTRAP_0F_JLE:
                case FASTTRAP_0F_JG:
                        tp->ftt_type = FASTTRAP_T_JCC;
                        tp->ftt_code = (instr[start + 1] & 0x0f) | FASTTRAP_JO;
                        tp->ftt_dest = pc + tp->ftt_size +
                            /* LINTED - alignment */
                            *(int32_t *)&instr[start + 2];
                        break;
                }
        } else if (instr[start] == FASTTRAP_GROUP5_OP) {
                uint_t mod = FASTTRAP_MODRM_MOD(instr[start + 1]);
                uint_t reg = FASTTRAP_MODRM_REG(instr[start + 1]);
                uint_t rm = FASTTRAP_MODRM_RM(instr[start + 1]);

                if (reg == 2 || reg == 4) {
                        uint_t i, sz;

                        if (reg == 2)
                                tp->ftt_type = FASTTRAP_T_CALL;
                        else
                                tp->ftt_type = FASTTRAP_T_JMP;

                        if (mod == 3)
                                tp->ftt_code = 2;
                        else
                                tp->ftt_code = 1;

                        ASSERT(p->p_model == DATAMODEL_LP64 || rex == 0);

                        /*
                         * See AMD x86-64 Architecture Programmer's Manual
                         * Volume 3, Section 1.2.7, Table 1-12, and
                         * Appendix A.3.1, Table A-15.
                         */
                        if (mod != 3 && rm == 4) {
                                uint8_t sib = instr[start + 2];
                                uint_t index = FASTTRAP_SIB_INDEX(sib);
                                uint_t base = FASTTRAP_SIB_BASE(sib);

                                tp->ftt_scale = FASTTRAP_SIB_SCALE(sib);

                                tp->ftt_index = (index == 4) ?
                                    FASTTRAP_NOREG :
                                    regmap[index | (FASTTRAP_REX_X(rex) << 3)];
                                tp->ftt_base = (mod == 0 && base == 5) ?
                                    FASTTRAP_NOREG :
                                    regmap[base | (FASTTRAP_REX_B(rex) << 3)];

                                i = 3;
                                sz = mod == 1 ? 1 : 4;
                        } else {
                                /*
                                 * In 64-bit mode, mod == 0 and r/m == 5
                                 * denotes %rip-relative addressing; in 32-bit
                                 * mode, the base register isn't used. In both
                                 * modes, there is a 32-bit operand.
                                 */
                                if (mod == 0 && rm == 5) {
                                        if (p->p_model == DATAMODEL_LP64)
                                                tp->ftt_base = REG_RIP;
                                        else
                                                tp->ftt_base = FASTTRAP_NOREG;
                                        sz = 4;
                                } else  {
                                        uint8_t base = rm |
                                            (FASTTRAP_REX_B(rex) << 3);

                                        tp->ftt_base = regmap[base];
                                        sz = mod == 1 ? 1 : mod == 2 ? 4 : 0;
                                }
                                tp->ftt_index = FASTTRAP_NOREG;
                                i = 2;
                        }

                        if (sz == 1) {
                                tp->ftt_dest = *(int8_t *)&instr[start + i];
                        } else if (sz == 4) {
                                /* LINTED - alignment */
                                tp->ftt_dest = *(int32_t *)&instr[start + i];
                        } else {
                                tp->ftt_dest = 0;
                        }
                }
        } else {
                switch (instr[start]) {
                case FASTTRAP_RET:
                        tp->ftt_type = FASTTRAP_T_RET;
                        break;

                case FASTTRAP_RET16:
                        tp->ftt_type = FASTTRAP_T_RET16;
                        /* LINTED - alignment */
                        tp->ftt_dest = *(uint16_t *)&instr[start + 1];
                        break;

                case FASTTRAP_JO:
                case FASTTRAP_JNO:
                case FASTTRAP_JB:
                case FASTTRAP_JAE:
                case FASTTRAP_JE:
                case FASTTRAP_JNE:
                case FASTTRAP_JBE:
                case FASTTRAP_JA:
                case FASTTRAP_JS:
                case FASTTRAP_JNS:
                case FASTTRAP_JP:
                case FASTTRAP_JNP:
                case FASTTRAP_JL:
                case FASTTRAP_JGE:
                case FASTTRAP_JLE:
                case FASTTRAP_JG:
                        tp->ftt_type = FASTTRAP_T_JCC;
                        tp->ftt_code = instr[start];
                        tp->ftt_dest = pc + tp->ftt_size +
                            (int8_t)instr[start + 1];
                        break;

                case FASTTRAP_LOOPNZ:
                case FASTTRAP_LOOPZ:
                case FASTTRAP_LOOP:
                        tp->ftt_type = FASTTRAP_T_LOOP;
                        tp->ftt_code = instr[start];
                        tp->ftt_dest = pc + tp->ftt_size +
                            (int8_t)instr[start + 1];
                        break;

                case FASTTRAP_JCXZ:
                        tp->ftt_type = FASTTRAP_T_JCXZ;
                        tp->ftt_dest = pc + tp->ftt_size +
                            (int8_t)instr[start + 1];
                        break;

                case FASTTRAP_CALL:
                        tp->ftt_type = FASTTRAP_T_CALL;
                        tp->ftt_dest = pc + tp->ftt_size +
                            /* LINTED - alignment */
                            *(int32_t *)&instr[start + 1];
                        tp->ftt_code = 0;
                        break;

                case FASTTRAP_JMP32:
                        tp->ftt_type = FASTTRAP_T_JMP;
                        tp->ftt_dest = pc + tp->ftt_size +
                            /* LINTED - alignment */
                            *(int32_t *)&instr[start + 1];
                        break;
                case FASTTRAP_JMP8:
                        tp->ftt_type = FASTTRAP_T_JMP;
                        tp->ftt_dest = pc + tp->ftt_size +
                            (int8_t)instr[start + 1];
                        break;

                case FASTTRAP_PUSHL_EBP:
                        if (start == 0)
                                tp->ftt_type = FASTTRAP_T_PUSHL_EBP;
                        break;

                case FASTTRAP_NOP:
                        ASSERT(p->p_model == DATAMODEL_LP64 || rex == 0);

                        /*
                         * On amd64 we have to be careful not to confuse a nop
                         * (actually xchgl %eax, %eax) with an instruction using
                         * the same opcode, but that does something different
                         * (e.g. xchgl %r8d, %eax or xcghq %r8, %rax).
                         */
                        if (FASTTRAP_REX_B(rex) == 0)
                                tp->ftt_type = FASTTRAP_T_NOP;
                        break;

                case FASTTRAP_INT3:
                        /*
                         * The pid provider shares the int3 trap with debugger
                         * breakpoints so we can't instrument them.
                         */
                        ASSERT(instr[start] == FASTTRAP_INSTR);
                        return (-1);

                case FASTTRAP_INT:
                        /*
                         * Interrupts seem like they could be traced with
                         * no negative implications, but it's possible that
                         * a thread could be redirected by the trap handling
                         * code which would eventually return to the
                         * instruction after the interrupt. If the interrupt
                         * were in our scratch space, the subsequent
                         * instruction might be overwritten before we return.
                         * Accordingly we refuse to instrument any interrupt.
                         */
                        return (-1);
                }
        }

        if (p->p_model == DATAMODEL_LP64 && tp->ftt_type == FASTTRAP_T_COMMON) {
                /*
                 * If the process is 64-bit and the instruction type is still
                 * FASTTRAP_T_COMMON -- meaning we're going to copy it out an
                 * execute it -- we need to watch for %rip-relative
                 * addressing mode. See the portion of fasttrap_pid_probe()
                 * below where we handle tracepoints with type
                 * FASTTRAP_T_COMMON for how we emulate instructions that
                 * employ %rip-relative addressing.
                 */
                if (rmindex != -1) {
                        uint_t mod = FASTTRAP_MODRM_MOD(instr[rmindex]);
                        uint_t reg = FASTTRAP_MODRM_REG(instr[rmindex]);
                        uint_t rm = FASTTRAP_MODRM_RM(instr[rmindex]);

                        ASSERT(rmindex > start);

                        if (mod == 0 && rm == 5) {
                                /*
                                 * We need to be sure to avoid other
                                 * registers used by this instruction. While
                                 * the reg field may determine the op code
                                 * rather than denoting a register, assuming
                                 * that it denotes a register is always safe.
                                 * We leave the REX field intact and use
                                 * whatever value's there for simplicity.
                                 */
                                if (reg != 0) {
                                        tp->ftt_ripmode = FASTTRAP_RIP_1 |
                                            (FASTTRAP_RIP_X *
                                            FASTTRAP_REX_B(rex));
                                        rm = 0;
                                } else {
                                        tp->ftt_ripmode = FASTTRAP_RIP_2 |
                                            (FASTTRAP_RIP_X *
                                            FASTTRAP_REX_B(rex));
                                        rm = 1;
                                }

                                tp->ftt_modrm = tp->ftt_instr[rmindex];
                                tp->ftt_instr[rmindex] =
                                    FASTTRAP_MODRM(2, reg, rm);
                        }
                }
        }

        return (0);
}

int
fasttrap_tracepoint_install(proc_t *p, fasttrap_tracepoint_t *tp)
{
        fasttrap_instr_t instr = FASTTRAP_INSTR;

        if (uwrite(p, &instr, 1, tp->ftt_pc) != 0)
                return (-1);

        return (0);
}

int
fasttrap_tracepoint_remove(proc_t *p, fasttrap_tracepoint_t *tp)
{
        uint8_t instr;

        /*
         * Distinguish between read or write failures and a changed
         * instruction.
         */
        if (uread(p, &instr, 1, tp->ftt_pc) != 0)
                return (0);
        if (instr != FASTTRAP_INSTR)
                return (0);
        if (uwrite(p, &tp->ftt_instr[0], 1, tp->ftt_pc) != 0)
                return (-1);

        return (0);
}

static uintptr_t
fasttrap_fulword_noerr(const void *uaddr)
{
        uintptr_t ret;

        if (fasttrap_fulword(uaddr, &ret) == 0)
                return (ret);

        return (0);
}

static uint32_t
fasttrap_fuword32_noerr(const void *uaddr)
{
        uint32_t ret;

        if (fasttrap_fuword32(uaddr, &ret) == 0)
                return (ret);

        return (0);
}

static void
fasttrap_return_common(struct regs *rp, uintptr_t pc, pid_t pid,
    uintptr_t new_pc)
{
        fasttrap_tracepoint_t *tp;
        fasttrap_bucket_t *bucket;
        fasttrap_id_t *id;
        kmutex_t *pid_mtx;

        pid_mtx = &cpu_core[CPU->cpu_id].cpuc_pid_lock;
        mutex_enter(pid_mtx);
        bucket = &fasttrap_tpoints.fth_table[FASTTRAP_TPOINTS_INDEX(pid, pc)];

        for (tp = bucket->ftb_data; tp != NULL; tp = tp->ftt_next) {
                if (pid == tp->ftt_pid && pc == tp->ftt_pc &&
                    tp->ftt_proc->ftpc_acount != 0)
                        break;
        }

        /*
         * Don't sweat it if we can't find the tracepoint again; unlike
         * when we're in fasttrap_pid_probe(), finding the tracepoint here
         * is not essential to the correct execution of the process.
         */
        if (tp == NULL) {
                mutex_exit(pid_mtx);
                return;
        }

        for (id = tp->ftt_retids; id != NULL; id = id->fti_next) {
                /*
                 * If there's a branch that could act as a return site, we
                 * need to trace it, and check here if the program counter is
                 * external to the function.
                 */
                if (tp->ftt_type != FASTTRAP_T_RET &&
                    tp->ftt_type != FASTTRAP_T_RET16 &&
                    new_pc - id->fti_probe->ftp_faddr <
                    id->fti_probe->ftp_fsize)
                        continue;

                dtrace_probe(id->fti_probe->ftp_id,
                    pc - id->fti_probe->ftp_faddr,
                    rp->r_r0, rp->r_r1, 0, 0);
        }

        mutex_exit(pid_mtx);
}

static void
fasttrap_sigsegv(proc_t *p, kthread_t *t, uintptr_t addr)
{
        sigqueue_t *sqp = kmem_zalloc(sizeof (sigqueue_t), KM_SLEEP);

        sqp->sq_info.si_signo = SIGSEGV;
        sqp->sq_info.si_code = SEGV_MAPERR;
        sqp->sq_info.si_addr = (caddr_t)addr;

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

        if (t != NULL)
                aston(t);
}

static void
fasttrap_usdt_args64(fasttrap_probe_t *probe, struct regs *rp, int argc,
    uintptr_t *argv)
{
        int i, x, cap = MIN(argc, probe->ftp_nargs);
        uintptr_t *stack = (uintptr_t *)rp->r_sp;

        for (i = 0; i < cap; i++) {
                x = probe->ftp_argmap[i];

                if (x < 6)
                        argv[i] = (&rp->r_rdi)[x];
                else
                        argv[i] = fasttrap_fulword_noerr(&stack[x]);
        }

        for (; i < argc; i++) {
                argv[i] = 0;
        }
}

static void
fasttrap_usdt_args32(fasttrap_probe_t *probe, struct regs *rp, int argc,
    uint32_t *argv)
{
        int i, x, cap = MIN(argc, probe->ftp_nargs);
        uint32_t *stack = (uint32_t *)rp->r_sp;

        for (i = 0; i < cap; i++) {
                x = probe->ftp_argmap[i];

                argv[i] = fasttrap_fuword32_noerr(&stack[x]);
        }

        for (; i < argc; i++) {
                argv[i] = 0;
        }
}

static int
fasttrap_do_seg(fasttrap_tracepoint_t *tp, struct regs *rp, uintptr_t *addr)
{
        proc_t *p = curproc;
        user_desc_t *desc;
        uint16_t sel, ndx, type;
        uintptr_t limit;

        switch (tp->ftt_segment) {
        case FASTTRAP_SEG_CS:
                sel = rp->r_cs;
                break;
        case FASTTRAP_SEG_DS:
                sel = rp->r_ds;
                break;
        case FASTTRAP_SEG_ES:
                sel = rp->r_es;
                break;
        case FASTTRAP_SEG_FS:
                sel = rp->r_fs;
                break;
        case FASTTRAP_SEG_GS:
                sel = rp->r_gs;
                break;
        case FASTTRAP_SEG_SS:
                sel = rp->r_ss;
                break;
        }

        /*
         * Make sure the given segment register specifies a user priority
         * selector rather than a kernel selector.
         */
        if (!SELISUPL(sel))
                return (-1);

        ndx = SELTOIDX(sel);

        /*
         * Check the bounds and grab the descriptor out of the specified
         * descriptor table.
         */
        if (SELISLDT(sel)) {
                if (ndx > p->p_ldtlimit)
                        return (-1);

                desc = p->p_ldt + ndx;

        } else {
                if (ndx >= NGDT)
                        return (-1);

                desc = cpu_get_gdt() + ndx;
        }

        /*
         * The descriptor must have user privilege level and it must be
         * present in memory.
         */
        if (desc->usd_dpl != SEL_UPL || desc->usd_p != 1)
                return (-1);

        type = desc->usd_type;

        /*
         * If the S bit in the type field is not set, this descriptor can
         * only be used in system context.
         */
        if ((type & 0x10) != 0x10)
                return (-1);

        limit = USEGD_GETLIMIT(desc) * (desc->usd_gran ? PAGESIZE : 1);

        if (tp->ftt_segment == FASTTRAP_SEG_CS) {
                /*
                 * The code/data bit and readable bit must both be set.
                 */
                if ((type & 0xa) != 0xa)
                        return (-1);

                if (*addr > limit)
                        return (-1);
        } else {
                /*
                 * The code/data bit must be clear.
                 */
                if ((type & 0x8) != 0)
                        return (-1);

                /*
                 * If the expand-down bit is clear, we just check the limit as
                 * it would naturally be applied. Otherwise, we need to check
                 * that the address is the range [limit + 1 .. 0xffff] or
                 * [limit + 1 ... 0xffffffff] depending on if the default
                 * operand size bit is set.
                 */
                if ((type & 0x4) == 0) {
                        if (*addr > limit)
                                return (-1);
                } else if (desc->usd_def32) {
                        if (*addr < limit + 1 || 0xffff < *addr)
                                return (-1);
                } else {
                        if (*addr < limit + 1 || 0xffffffff < *addr)
                                return (-1);
                }
        }

        *addr += USEGD_GETBASE(desc);

        return (0);
}

int
fasttrap_pid_probe(struct regs *rp)
{
        proc_t *p = curproc;
        uintptr_t pc = rp->r_pc - 1, new_pc = 0;
        fasttrap_bucket_t *bucket;
        kmutex_t *pid_mtx;
        fasttrap_tracepoint_t *tp, tp_local;
        pid_t pid;
        dtrace_icookie_t cookie;
        uint_t is_enabled = 0;

        /*
         * It's possible that a user (in a veritable orgy of bad planning)
         * could redirect this thread's flow of control before it reached the
         * return probe fasttrap. In this case we need to kill the process
         * since it's in a unrecoverable state.
         */
        if (curthread->t_dtrace_step) {
                ASSERT(curthread->t_dtrace_on);
                fasttrap_sigtrap(p, curthread, pc);
                return (0);
        }

        /*
         * Clear all user tracing flags.
         */
        curthread->t_dtrace_ft = 0;
        curthread->t_dtrace_pc = 0;
        curthread->t_dtrace_npc = 0;
        curthread->t_dtrace_scrpc = 0;
        curthread->t_dtrace_astpc = 0;
        curthread->t_dtrace_regv = 0;

        /*
         * Treat a child created by a call to vfork(2) as if it were its
         * parent. We know that there's only one thread of control in such a
         * process: this one.
         */
        while (p->p_flag & SVFORK) {
                p = p->p_parent;
        }

        pid = p->p_pid;
        pid_mtx = &cpu_core[CPU->cpu_id].cpuc_pid_lock;
        mutex_enter(pid_mtx);
        bucket = &fasttrap_tpoints.fth_table[FASTTRAP_TPOINTS_INDEX(pid, pc)];

        /*
         * Lookup the tracepoint that the process just hit.
         */
        for (tp = bucket->ftb_data; tp != NULL; tp = tp->ftt_next) {
                if (pid == tp->ftt_pid && pc == tp->ftt_pc &&
                    tp->ftt_proc->ftpc_acount != 0)
                        break;
        }

        /*
         * If we couldn't find a matching tracepoint, either a tracepoint has
         * been inserted without using the pid<pid> ioctl interface (see
         * fasttrap_ioctl), or somehow we have mislaid this tracepoint.
         */
        if (tp == NULL) {
                mutex_exit(pid_mtx);
                return (-1);
        }

        /*
         * Set the program counter to the address of the traced instruction
         * so that it looks right in ustack() output.
         */
        rp->r_pc = pc;

        if (tp->ftt_ids != NULL) {
                fasttrap_id_t *id;

                if (p->p_model == DATAMODEL_LP64) {
                        for (id = tp->ftt_ids; id != NULL; id = id->fti_next) {
                                fasttrap_probe_t *probe = id->fti_probe;

                                if (id->fti_ptype == DTFTP_ENTRY) {
                                        /*
                                         * We note that this was an entry
                                         * probe to help ustack() find the
                                         * first caller.
                                         */
                                        cookie = dtrace_interrupt_disable();
                                        DTRACE_CPUFLAG_SET(CPU_DTRACE_ENTRY);
                                        dtrace_probe(probe->ftp_id, rp->r_rdi,
                                            rp->r_rsi, rp->r_rdx, rp->r_rcx,
                                            rp->r_r8);
                                        DTRACE_CPUFLAG_CLEAR(CPU_DTRACE_ENTRY);
                                        dtrace_interrupt_enable(cookie);
                                } else if (id->fti_ptype == DTFTP_IS_ENABLED) {
                                        /*
                                         * Note that in this case, we don't
                                         * call dtrace_probe() since it's only
                                         * an artificial probe meant to change
                                         * the flow of control so that it
                                         * encounters the true probe.
                                         */
                                        is_enabled = 1;
                                } else if (probe->ftp_argmap == NULL) {
                                        dtrace_probe(probe->ftp_id, rp->r_rdi,
                                            rp->r_rsi, rp->r_rdx, rp->r_rcx,
                                            rp->r_r8);
                                } else {
                                        uintptr_t t[5];

                                        fasttrap_usdt_args64(probe, rp,
                                            sizeof (t) / sizeof (t[0]), t);

                                        dtrace_probe(probe->ftp_id, t[0], t[1],
                                            t[2], t[3], t[4]);
                                }
                        }
                } else {
                        uintptr_t s0, s1, s2, s3, s4, s5;
                        uint32_t *stack = (uint32_t *)rp->r_sp;

                        /*
                         * In 32-bit mode, all arguments are passed on the
                         * stack. If this is a function entry probe, we need
                         * to skip the first entry on the stack as it
                         * represents the return address rather than a
                         * parameter to the function.
                         */
                        s0 = fasttrap_fuword32_noerr(&stack[0]);
                        s1 = fasttrap_fuword32_noerr(&stack[1]);
                        s2 = fasttrap_fuword32_noerr(&stack[2]);
                        s3 = fasttrap_fuword32_noerr(&stack[3]);
                        s4 = fasttrap_fuword32_noerr(&stack[4]);
                        s5 = fasttrap_fuword32_noerr(&stack[5]);

                        for (id = tp->ftt_ids; id != NULL; id = id->fti_next) {
                                fasttrap_probe_t *probe = id->fti_probe;

                                if (id->fti_ptype == DTFTP_ENTRY) {
                                        /*
                                         * We note that this was an entry
                                         * probe to help ustack() find the
                                         * first caller.
                                         */
                                        cookie = dtrace_interrupt_disable();
                                        DTRACE_CPUFLAG_SET(CPU_DTRACE_ENTRY);
                                        dtrace_probe(probe->ftp_id, s1, s2,
                                            s3, s4, s5);
                                        DTRACE_CPUFLAG_CLEAR(CPU_DTRACE_ENTRY);
                                        dtrace_interrupt_enable(cookie);
                                } else if (id->fti_ptype == DTFTP_IS_ENABLED) {
                                        /*
                                         * Note that in this case, we don't
                                         * call dtrace_probe() since it's only
                                         * an artificial probe meant to change
                                         * the flow of control so that it
                                         * encounters the true probe.
                                         */
                                        is_enabled = 1;
                                } else if (probe->ftp_argmap == NULL) {
                                        dtrace_probe(probe->ftp_id, s0, s1,
                                            s2, s3, s4);
                                } else {
                                        uint32_t t[5];

                                        fasttrap_usdt_args32(probe, rp,
                                            sizeof (t) / sizeof (t[0]), t);

                                        dtrace_probe(probe->ftp_id, t[0], t[1],
                                            t[2], t[3], t[4]);
                                }
                        }
                }
        }

        /*
         * We're about to do a bunch of work so we cache a local copy of
         * the tracepoint to emulate the instruction, and then find the
         * tracepoint again later if we need to light up any return probes.
         */
        tp_local = *tp;
        mutex_exit(pid_mtx);
        tp = &tp_local;

        /*
         * Set the program counter to appear as though the traced instruction
         * had completely executed. This ensures that fasttrap_getreg() will
         * report the expected value for REG_RIP.
         */
        rp->r_pc = pc + tp->ftt_size;

        /*
         * If there's an is-enabled probe connected to this tracepoint it
         * means that there was a 'xorl %eax, %eax' or 'xorq %rax, %rax'
         * instruction that was placed there by DTrace when the binary was
         * linked. As this probe is, in fact, enabled, we need to stuff 1
         * into %eax or %rax. Accordingly, we can bypass all the instruction
         * emulation logic since we know the inevitable result. It's possible
         * that a user could construct a scenario where the 'is-enabled'
         * probe was on some other instruction, but that would be a rather
         * exotic way to shoot oneself in the foot.
         */
        if (is_enabled) {
                rp->r_r0 = 1;
                new_pc = rp->r_pc;
                goto done;
        }

        /*
         * We emulate certain types of instructions to ensure correctness
         * (in the case of position dependent instructions) or optimize
         * common cases. The rest we have the thread execute back in user-
         * land.
         */
        switch (tp->ftt_type) {
        case FASTTRAP_T_RET:
        case FASTTRAP_T_RET16:
        {
                uintptr_t dst;
                uintptr_t addr;
                int ret;

                /*
                 * We have to emulate _every_ facet of the behavior of a ret
                 * instruction including what happens if the load from %esp
                 * fails; in that case, we send a SIGSEGV.
                 */
                if (p->p_model == DATAMODEL_NATIVE) {
                        ret = fasttrap_fulword((void *)rp->r_sp, &dst);
                        addr = rp->r_sp + sizeof (uintptr_t);
                } else {
                        uint32_t dst32;
                        ret = fasttrap_fuword32((void *)rp->r_sp, &dst32);
                        dst = dst32;
                        addr = rp->r_sp + sizeof (uint32_t);
                }

                if (ret == -1) {
                        fasttrap_sigsegv(p, curthread, rp->r_sp);
                        new_pc = pc;
                        break;
                }

                if (tp->ftt_type == FASTTRAP_T_RET16)
                        addr += tp->ftt_dest;

                rp->r_sp = addr;
                new_pc = dst;
                break;
        }

        case FASTTRAP_T_JCC:
        {
                uint_t taken;

                switch (tp->ftt_code) {
                case FASTTRAP_JO:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_OF) != 0;
                        break;
                case FASTTRAP_JNO:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_OF) == 0;
                        break;
                case FASTTRAP_JB:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_CF) != 0;
                        break;
                case FASTTRAP_JAE:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_CF) == 0;
                        break;
                case FASTTRAP_JE:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_ZF) != 0;
                        break;
                case FASTTRAP_JNE:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_ZF) == 0;
                        break;
                case FASTTRAP_JBE:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_CF) != 0 ||
                            (rp->r_ps & FASTTRAP_EFLAGS_ZF) != 0;
                        break;
                case FASTTRAP_JA:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_CF) == 0 &&
                            (rp->r_ps & FASTTRAP_EFLAGS_ZF) == 0;
                        break;
                case FASTTRAP_JS:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_SF) != 0;
                        break;
                case FASTTRAP_JNS:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_SF) == 0;
                        break;
                case FASTTRAP_JP:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_PF) != 0;
                        break;
                case FASTTRAP_JNP:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_PF) == 0;
                        break;
                case FASTTRAP_JL:
                        taken = ((rp->r_ps & FASTTRAP_EFLAGS_SF) == 0) !=
                            ((rp->r_ps & FASTTRAP_EFLAGS_OF) == 0);
                        break;
                case FASTTRAP_JGE:
                        taken = ((rp->r_ps & FASTTRAP_EFLAGS_SF) == 0) ==
                            ((rp->r_ps & FASTTRAP_EFLAGS_OF) == 0);
                        break;
                case FASTTRAP_JLE:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_ZF) != 0 ||
                            ((rp->r_ps & FASTTRAP_EFLAGS_SF) == 0) !=
                            ((rp->r_ps & FASTTRAP_EFLAGS_OF) == 0);
                        break;
                case FASTTRAP_JG:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_ZF) == 0 &&
                            ((rp->r_ps & FASTTRAP_EFLAGS_SF) == 0) ==
                            ((rp->r_ps & FASTTRAP_EFLAGS_OF) == 0);
                        break;

                }

                if (taken)
                        new_pc = tp->ftt_dest;
                else
                        new_pc = pc + tp->ftt_size;
                break;
        }

        case FASTTRAP_T_LOOP:
        {
                uint_t taken;
                greg_t cx = rp->r_rcx--;

                switch (tp->ftt_code) {
                case FASTTRAP_LOOPNZ:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_ZF) == 0 &&
                            cx != 0;
                        break;
                case FASTTRAP_LOOPZ:
                        taken = (rp->r_ps & FASTTRAP_EFLAGS_ZF) != 0 &&
                            cx != 0;
                        break;
                case FASTTRAP_LOOP:
                        taken = (cx != 0);
                        break;
                }

                if (taken)
                        new_pc = tp->ftt_dest;
                else
                        new_pc = pc + tp->ftt_size;
                break;
        }

        case FASTTRAP_T_JCXZ:
        {
                greg_t cx = rp->r_rcx;

                if (cx == 0)
                        new_pc = tp->ftt_dest;
                else
                        new_pc = pc + tp->ftt_size;
                break;
        }

        case FASTTRAP_T_PUSHL_EBP:
        {
                int ret;
                uintptr_t addr;
                if (p->p_model == DATAMODEL_NATIVE) {
                        addr = rp->r_sp - sizeof (uintptr_t);
                        ret = fasttrap_sulword((void *)addr, rp->r_fp);
                } else {
                        addr = rp->r_sp - sizeof (uint32_t);
                        ret = fasttrap_suword32((void *)addr,
                            (uint32_t)rp->r_fp);
                }

                if (ret == -1) {
                        fasttrap_sigsegv(p, curthread, addr);
                        new_pc = pc;
                        break;
                }

                rp->r_sp = addr;
                new_pc = pc + tp->ftt_size;
                break;
        }

        case FASTTRAP_T_NOP:
                new_pc = pc + tp->ftt_size;
                break;

        case FASTTRAP_T_JMP:
        case FASTTRAP_T_CALL:
                if (tp->ftt_code == 0) {
                        new_pc = tp->ftt_dest;
                } else {
                        uintptr_t value, addr = tp->ftt_dest;

                        if (tp->ftt_base != FASTTRAP_NOREG)
                                addr += fasttrap_getreg(rp, tp->ftt_base);
                        if (tp->ftt_index != FASTTRAP_NOREG)
                                addr += fasttrap_getreg(rp, tp->ftt_index) <<
                                    tp->ftt_scale;

                        if (tp->ftt_code == 1) {
                                /*
                                 * If there's a segment prefix for this
                                 * instruction, we'll need to check permissions
                                 * and bounds on the given selector, and adjust
                                 * the address accordingly.
                                 */
                                if (tp->ftt_segment != FASTTRAP_SEG_NONE &&
                                    fasttrap_do_seg(tp, rp, &addr) != 0) {
                                        fasttrap_sigsegv(p, curthread, addr);
                                        new_pc = pc;
                                        break;
                                }

                                if (p->p_model == DATAMODEL_NATIVE) {
                                        if (fasttrap_fulword((void *)addr,
                                            &value) == -1) {
                                                fasttrap_sigsegv(p, curthread,
                                                    addr);
                                                new_pc = pc;
                                                break;
                                        }
                                        new_pc = value;
                                } else {
                                        uint32_t value32;
                                        addr = (uintptr_t)(uint32_t)addr;
                                        if (fasttrap_fuword32((void *)addr,
                                            &value32) == -1) {
                                                fasttrap_sigsegv(p, curthread,
                                                    addr);
                                                new_pc = pc;
                                                break;
                                        }
                                        new_pc = value32;
                                }
                        } else {
                                new_pc = addr;
                        }
                }

                /*
                 * If this is a call instruction, we need to push the return
                 * address onto the stack. If this fails, we send the process
                 * a SIGSEGV and reset the pc to emulate what would happen if
                 * this instruction weren't traced.
                 */
                if (tp->ftt_type == FASTTRAP_T_CALL) {
                        int ret;
                        uintptr_t addr;
                        if (p->p_model == DATAMODEL_NATIVE) {
                                addr = rp->r_sp - sizeof (uintptr_t);
                                ret = fasttrap_sulword((void *)addr,
                                    pc + tp->ftt_size);
                        } else {
                                addr = rp->r_sp - sizeof (uint32_t);
                                ret = fasttrap_suword32((void *)addr,
                                    (uint32_t)(pc + tp->ftt_size));
                        }

                        if (ret == -1) {
                                fasttrap_sigsegv(p, curthread, addr);
                                new_pc = pc;
                                break;
                        }

                        rp->r_sp = addr;
                }

                break;

        case FASTTRAP_T_COMMON:
        {
                uintptr_t addr;
                uint8_t scratch[2 * FASTTRAP_MAX_INSTR_SIZE + 22];
                uint_t i = 0;
                klwp_t *lwp = ttolwp(curthread);

                /*
                 * Compute the address of the ulwp_t and step over the
                 * ul_self pointer. The method used to store the user-land
                 * thread pointer is very different on 32- and 64-bit
                 * kernels.
                 */
                if (p->p_model == DATAMODEL_LP64) {
                        addr = lwp->lwp_pcb.pcb_fsbase;
                        addr += sizeof (void *);
                } else {
                        addr = lwp->lwp_pcb.pcb_gsbase;
                        addr += sizeof (caddr32_t);
                }

                /*
                 * Generic Instruction Tracing
                 * ---------------------------
                 *
                 * This is the layout of the scratch space in the user-land
                 * thread structure for our generated instructions.
                 *
                 *      32-bit mode                     bytes
                 *      ------------------------        -----
                 * a:   <original instruction>          <= 15
                 *      jmp     <pc + tp->ftt_size>         5
                 * b:   <original instrction>           <= 15
                 *      int     T_DTRACE_RET                2
                 *                                      -----
                 *                                      <= 37
                 *
                 *      64-bit mode                     bytes
                 *      ------------------------        -----
                 * a:   <original instruction>          <= 15
                 *      jmp     0(%rip)                     6
                 *      <pc + tp->ftt_size>                 8
                 * b:   <original instruction>          <= 15
                 *      int     T_DTRACE_RET                2
                 *                                      -----
                 *                                      <= 46
                 *
                 * The %pc is set to a, and curthread->t_dtrace_astpc is set
                 * to b. If we encounter a signal on the way out of the
                 * kernel, trap() will set %pc to curthread->t_dtrace_astpc
                 * so that we execute the original instruction and re-enter
                 * the kernel rather than redirecting to the next instruction.
                 *
                 * If there are return probes (so we know that we're going to
                 * need to reenter the kernel after executing the original
                 * instruction), the scratch space will just contain the
                 * original instruction followed by an interrupt -- the same
                 * data as at b.
                 *
                 * %rip-relative Addressing
                 * ------------------------
                 *
                 * There's a further complication in 64-bit mode due to %rip-
                 * relative addressing. While this is clearly a beneficial
                 * architectural decision for position independent code, it's
                 * hard not to see it as a personal attack against the pid
                 * provider since before there was a relatively small set of
                 * instructions to emulate; with %rip-relative addressing,
                 * almost every instruction can potentially depend on the
                 * address at which it's executed. Rather than emulating
                 * the broad spectrum of instructions that can now be
                 * position dependent, we emulate jumps and others as in
                 * 32-bit mode, and take a different tack for instructions
                 * using %rip-relative addressing.
                 *
                 * For every instruction that uses the ModRM byte, the
                 * in-kernel disassembler reports its location. We use the
                 * ModRM byte to identify that an instruction uses
                 * %rip-relative addressing and to see what other registers
                 * the instruction uses. To emulate those instructions,
                 * we modify the instruction to be %rax-relative rather than
                 * %rip-relative (or %rcx-relative if the instruction uses
                 * %rax; or %r8- or %r9-relative if the REX.B is present so
                 * we don't have to rewrite the REX prefix). We then load
                 * the value that %rip would have been into the scratch
                 * register and generate an instruction to reset the scratch
                 * register back to its original value. The instruction
                 * sequence looks like this:
                 *
                 *      64-mode %rip-relative           bytes
                 *      ------------------------        -----
                 * a:   <modified instruction>          <= 15
                 *      movq    $<value>, %<scratch>        6
                 *      jmp     0(%rip)                     6
                 *      <pc + tp->ftt_size>                 8
                 * b:   <modified instruction>          <= 15
                 *      int     T_DTRACE_RET                2
                 *                                      -----
                 *                                         52
                 *
                 * We set curthread->t_dtrace_regv so that upon receiving
                 * a signal we can reset the value of the scratch register.
                 */

                ASSERT(tp->ftt_size < FASTTRAP_MAX_INSTR_SIZE);

                curthread->t_dtrace_scrpc = addr;
                bcopy(tp->ftt_instr, &scratch[i], tp->ftt_size);
                i += tp->ftt_size;

                if (tp->ftt_ripmode != 0) {
                        greg_t *reg;

                        ASSERT(p->p_model == DATAMODEL_LP64);
                        ASSERT(tp->ftt_ripmode &
                            (FASTTRAP_RIP_1 | FASTTRAP_RIP_2));

                        /*
                         * If this was a %rip-relative instruction, we change
                         * it to be either a %rax- or %rcx-relative
                         * instruction (depending on whether those registers
                         * are used as another operand; or %r8- or %r9-
                         * relative depending on the value of REX.B). We then
                         * set that register and generate a movq instruction
                         * to reset the value.
                         */
                        if (tp->ftt_ripmode & FASTTRAP_RIP_X)
                                scratch[i++] = FASTTRAP_REX(1, 0, 0, 1);
                        else
                                scratch[i++] = FASTTRAP_REX(1, 0, 0, 0);

                        if (tp->ftt_ripmode & FASTTRAP_RIP_1)
                                scratch[i++] = FASTTRAP_MOV_EAX;
                        else
                                scratch[i++] = FASTTRAP_MOV_ECX;

                        switch (tp->ftt_ripmode) {
                        case FASTTRAP_RIP_1:
                                reg = &rp->r_rax;
                                curthread->t_dtrace_reg = REG_RAX;
                                break;
                        case FASTTRAP_RIP_2:
                                reg = &rp->r_rcx;
                                curthread->t_dtrace_reg = REG_RCX;
                                break;
                        case FASTTRAP_RIP_1 | FASTTRAP_RIP_X:
                                reg = &rp->r_r8;
                                curthread->t_dtrace_reg = REG_R8;
                                break;
                        case FASTTRAP_RIP_2 | FASTTRAP_RIP_X:
                                reg = &rp->r_r9;
                                curthread->t_dtrace_reg = REG_R9;
                                break;
                        }

                        /* LINTED - alignment */
                        *(uint64_t *)&scratch[i] = *reg;
                        curthread->t_dtrace_regv = *reg;
                        *reg = pc + tp->ftt_size;
                        i += sizeof (uint64_t);
                }

                /*
                 * Generate the branch instruction to what would have
                 * normally been the subsequent instruction. In 32-bit mode,
                 * this is just a relative branch; in 64-bit mode this is a
                 * %rip-relative branch that loads the 64-bit pc value
                 * immediately after the jmp instruction.
                 */
                if (p->p_model == DATAMODEL_LP64) {
                        scratch[i++] = FASTTRAP_GROUP5_OP;
                        scratch[i++] = FASTTRAP_MODRM(0, 4, 5);
                        /* LINTED - alignment */
                        *(uint32_t *)&scratch[i] = 0;
                        i += sizeof (uint32_t);
                        /* LINTED - alignment */
                        *(uint64_t *)&scratch[i] = pc + tp->ftt_size;
                        i += sizeof (uint64_t);
                } else {
                        /*
                         * Set up the jmp to the next instruction; note that
                         * the size of the traced instruction cancels out.
                         */
                        scratch[i++] = FASTTRAP_JMP32;
                        /* LINTED - alignment */
                        *(uint32_t *)&scratch[i] = pc - addr - 5;
                        i += sizeof (uint32_t);
                }

                curthread->t_dtrace_astpc = addr + i;
                bcopy(tp->ftt_instr, &scratch[i], tp->ftt_size);
                i += tp->ftt_size;
                scratch[i++] = FASTTRAP_INT;
                scratch[i++] = T_DTRACE_RET;

                ASSERT(i <= sizeof (scratch));

                if (fasttrap_copyout(scratch, (char *)addr, i)) {
                        fasttrap_sigtrap(p, curthread, pc);
                        new_pc = pc;
                        break;
                }

                if (tp->ftt_retids != NULL) {
                        curthread->t_dtrace_step = 1;
                        curthread->t_dtrace_ret = 1;
                        new_pc = curthread->t_dtrace_astpc;
                } else {
                        new_pc = curthread->t_dtrace_scrpc;
                }

                curthread->t_dtrace_pc = pc;
                curthread->t_dtrace_npc = pc + tp->ftt_size;
                curthread->t_dtrace_on = 1;
                break;
        }

        default:
                panic("fasttrap: mishandled an instruction");
        }

done:
        /*
         * If there were no return probes when we first found the tracepoint,
         * we should feel no obligation to honor any return probes that were
         * subsequently enabled -- they'll just have to wait until the next
         * time around.
         */
        if (tp->ftt_retids != NULL) {
                /*
                 * We need to wait until the results of the instruction are
                 * apparent before invoking any return probes. If this
                 * instruction was emulated we can just call
                 * fasttrap_return_common(); if it needs to be executed, we
                 * need to wait until the user thread returns to the kernel.
                 */
                if (tp->ftt_type != FASTTRAP_T_COMMON) {
                        /*
                         * Set the program counter to the address of the traced
                         * instruction so that it looks right in ustack()
                         * output. We had previously set it to the end of the
                         * instruction to simplify %rip-relative addressing.
                         */
                        rp->r_pc = pc;

                        fasttrap_return_common(rp, pc, pid, new_pc);
                } else {
                        ASSERT(curthread->t_dtrace_ret != 0);
                        ASSERT(curthread->t_dtrace_pc == pc);
                        ASSERT(curthread->t_dtrace_scrpc != 0);
                        ASSERT(new_pc == curthread->t_dtrace_astpc);
                }
        }

        rp->r_pc = new_pc;

        return (0);
}

int
fasttrap_return_probe(struct regs *rp)
{
        proc_t *p = curproc;
        uintptr_t pc = curthread->t_dtrace_pc;
        uintptr_t npc = curthread->t_dtrace_npc;

        curthread->t_dtrace_pc = 0;
        curthread->t_dtrace_npc = 0;
        curthread->t_dtrace_scrpc = 0;
        curthread->t_dtrace_astpc = 0;

        /*
         * Treat a child created by a call to vfork(2) as if it were its
         * parent. We know that there's only one thread of control in such a
         * process: this one.
         */
        while (p->p_flag & SVFORK) {
                p = p->p_parent;
        }

        /*
         * We set rp->r_pc to the address of the traced instruction so
         * that it appears to dtrace_probe() that we're on the original
         * instruction, and so that the user can't easily detect our
         * complex web of lies. dtrace_return_probe() (our caller)
         * will correctly set %pc after we return.
         */
        rp->r_pc = pc;

        fasttrap_return_common(rp, pc, p->p_pid, npc);

        return (0);
}

/*ARGSUSED*/
uint64_t
fasttrap_pid_getarg(void *arg, dtrace_id_t id, void *parg, int argno,
    int aframes)
{
        return (fasttrap_anarg(ttolwp(curthread)->lwp_regs, 1, argno));
}

/*ARGSUSED*/
uint64_t
fasttrap_usdt_getarg(void *arg, dtrace_id_t id, void *parg, int argno,
    int aframes)
{
        return (fasttrap_anarg(ttolwp(curthread)->lwp_regs, 0, argno));
}

static ulong_t
fasttrap_getreg(struct regs *rp, uint_t reg)
{
        switch (reg) {
        case REG_R15:           return (rp->r_r15);
        case REG_R14:           return (rp->r_r14);
        case REG_R13:           return (rp->r_r13);
        case REG_R12:           return (rp->r_r12);
        case REG_R11:           return (rp->r_r11);
        case REG_R10:           return (rp->r_r10);
        case REG_R9:            return (rp->r_r9);
        case REG_R8:            return (rp->r_r8);
        case REG_RDI:           return (rp->r_rdi);
        case REG_RSI:           return (rp->r_rsi);
        case REG_RBP:           return (rp->r_rbp);
        case REG_RBX:           return (rp->r_rbx);
        case REG_RDX:           return (rp->r_rdx);
        case REG_RCX:           return (rp->r_rcx);
        case REG_RAX:           return (rp->r_rax);
        case REG_TRAPNO:        return (rp->r_trapno);
        case REG_ERR:           return (rp->r_err);
        case REG_RIP:           return (rp->r_rip);
        case REG_CS:            return (rp->r_cs);
        case REG_RFL:           return (rp->r_rfl);
        case REG_RSP:           return (rp->r_rsp);
        case REG_SS:            return (rp->r_ss);
        case REG_FS:            return (rp->r_fs);
        case REG_GS:            return (rp->r_gs);
        case REG_DS:            return (rp->r_ds);
        case REG_ES:            return (rp->r_es);
        case REG_FSBASE:        return (rdmsr(MSR_AMD_FSBASE));
        case REG_GSBASE:        return (rdmsr(MSR_AMD_GSBASE));
        }

        panic("dtrace: illegal register constant");
        /*NOTREACHED*/
}