/*-
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 * Copyright (C) 1994, David Greenman
 * Copyright (c) 2008-2018 The DragonFly Project.
 * Copyright (c) 2008 Jordan Gordeev.
 *
 * This code is derived from software contributed to Berkeley by
 * the University of Utah, and William Jolitz.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * from: @(#)trap.c     7.4 (Berkeley) 5/13/91
 * $FreeBSD: src/sys/i386/i386/trap.c,v 1.147.2.11 2003/02/27 19:09:59 luoqi Exp $
 */

/*
 * x86_64 Trap and System call handling
 */

#include "use_isa.h"

#include "opt_ddb.h"
#include "opt_ktrace.h"

#include <machine/frame.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/kerneldump.h>
#include <sys/proc.h>
#include <sys/pioctl.h>
#include <sys/types.h>
#include <sys/signal2.h>
#include <sys/syscall.h>
#include <sys/sysctl.h>
#include <sys/sysent.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif
#include <sys/ktr.h>
#include <sys/sysmsg.h>

#include <vm/pmap.h>
#include <vm/vm.h>
#include <vm/vm_extern.h>
#include <vm/vm_kern.h>
#include <vm/vm_param.h>
#include <machine/cpu.h>
#include <machine/pcb.h>
#include <machine/smp.h>
#include <machine/specialreg.h>
#include <machine/thread.h>
#include <machine/clock.h>
#include <machine/vmparam.h>
#include <machine/md_var.h>
#include <machine_base/isa/isa_intr.h>
#include <machine_base/apic/lapic.h>

#include <ddb/ddb.h>

#include <sys/thread2.h>
#include <sys/spinlock2.h>

/*
 * These %rip's are used to detect a historical CPU artifact on syscall or
 * int $3 entry, if not shortcutted in exception.S via
 * DIRECT_DISALLOW_SS_CPUBUG.
 */
extern void Xbpt(void);
extern void Xfast_syscall(void);
#define IDTVEC(vec)     X##vec

extern void trap(struct trapframe *frame);

static int trap_pfault(struct trapframe *, int);
static void trap_fatal(struct trapframe *, vm_offset_t);
void dblfault_handler(struct trapframe *frame);

#define MAX_TRAP_MSG            30
static char *trap_msg[] = {
        "",                                     /*  0 unused */
        "privileged instruction fault",         /*  1 T_PRIVINFLT */
        "",                                     /*  2 unused */
        "breakpoint instruction fault",         /*  3 T_BPTFLT */
        "",                                     /*  4 unused */
        "",                                     /*  5 unused */
        "arithmetic trap",                      /*  6 T_ARITHTRAP */
        "system forced exception",              /*  7 T_ASTFLT */
        "",                                     /*  8 unused */
        "general protection fault",             /*  9 T_PROTFLT */
        "trace trap",                           /* 10 T_TRCTRAP */
        "",                                     /* 11 unused */
        "page fault",                           /* 12 T_PAGEFLT */
        "",                                     /* 13 unused */
        "alignment fault",                      /* 14 T_ALIGNFLT */
        "",                                     /* 15 unused */
        "",                                     /* 16 unused */
        "",                                     /* 17 unused */
        "integer divide fault",                 /* 18 T_DIVIDE */
        "non-maskable interrupt trap",          /* 19 T_NMI */
        "overflow trap",                        /* 20 T_OFLOW */
        "FPU bounds check fault",               /* 21 T_BOUND */
        "FPU device not available",             /* 22 T_DNA */
        "double fault",                         /* 23 T_DOUBLEFLT */
        "FPU operand fetch fault",              /* 24 T_FPOPFLT */
        "invalid TSS fault",                    /* 25 T_TSSFLT */
        "segment not present fault",            /* 26 T_SEGNPFLT */
        "stack fault",                          /* 27 T_STKFLT */
        "machine check trap",                   /* 28 T_MCHK */
        "SIMD floating-point exception",        /* 29 T_XMMFLT */
        "reserved (unknown) fault",             /* 30 T_RESERVED */
};

#ifdef DDB
static int ddb_on_nmi = 1;
SYSCTL_INT(_machdep, OID_AUTO, ddb_on_nmi, CTLFLAG_RW,
        &ddb_on_nmi, 0, "Go to DDB on NMI");
static int ddb_on_seg_fault = 0;
SYSCTL_INT(_machdep, OID_AUTO, ddb_on_seg_fault, CTLFLAG_RW,
        &ddb_on_seg_fault, 0, "Go to DDB on user seg-fault");
__read_mostly static int freeze_on_seg_fault = 0;
SYSCTL_INT(_machdep, OID_AUTO, freeze_on_seg_fault, CTLFLAG_RW,
        &freeze_on_seg_fault, 0, "Go to DDB on user seg-fault");
#endif
static int panic_on_nmi = 1;
SYSCTL_INT(_machdep, OID_AUTO, panic_on_nmi, CTLFLAG_RW,
        &panic_on_nmi, 0, "Panic on NMI");

/*
 * System call debugging records the worst-case system call
 * overhead (inclusive of blocking), but may be inaccurate.
 */
/*#define SYSCALL_DEBUG*/
#ifdef SYSCALL_DEBUG

#define SCWC_MAXT       30

struct syscallwc {
        uint32_t idx;
        uint32_t dummy;
        uint64_t tot[SYS_MAXSYSCALL];
        uint64_t timings[SYS_MAXSYSCALL][SCWC_MAXT];
} __cachealign;

struct syscallwc SysCallsWorstCase[MAXCPU];

#endif

/*
 * Passively intercepts the thread switch function to increase
 * the thread priority from a user priority to a kernel priority, reducing
 * syscall and trap overhead for the case where no switch occurs.
 *
 * Synchronizes td_ucred with p_ucred.  This is used by system calls,
 * signal handling, faults, AST traps, and anything else that enters the
 * kernel from userland and provides the kernel with a stable read-only
 * copy of the process ucred.
 *
 * To avoid races with another thread updating p_ucred we obtain p_spin.
 * The other thread doing the update will obtain both p_token and p_spin.
 * In the case where the cached cred pointer matches, we will already have
 * the ref and we don't have to do one blessed thing.
 */
static __inline void
userenter(struct thread *curtd, struct proc *curp)
{
        struct ucred *ocred;
        struct ucred *ncred;

        curtd->td_release = lwkt_passive_release;

        if (__predict_false(curtd->td_ucred != curp->p_ucred)) {
                spin_lock(&curp->p_spin);
                ncred = crhold(curp->p_ucred);
                spin_unlock(&curp->p_spin);
                ocred = curtd->td_ucred;
                curtd->td_ucred = ncred;
                if (ocred)
                        crfree(ocred);
        }
}

/*
 * Handle signals, upcalls, profiling, and other AST's and/or tasks that
 * must be completed before we can return to or try to return to userland.
 *
 * Note that td_sticks is a 64 bit quantity, but there's no point doing 64
 * arithmetic on the delta calculation so the absolute tick values are
 * truncated to an integer.
 */
static void
userret(struct lwp *lp, struct trapframe *frame, int sticks)
{
        struct proc *p = lp->lwp_proc;
        int sig;
        int ptok;

        /*
         * Charge system time if profiling.  Note: times are in microseconds.
         * This may do a copyout and block, so do it first even though it
         * means some system time will be charged as user time.
         */
        if (__predict_false(p->p_flags & P_PROFIL)) {
                addupc_task(p, frame->tf_rip,
                        (u_int)((int)lp->lwp_thread->td_sticks - sticks));
        }

recheck:
        /*
         * Specific on-return-to-usermode checks (LWP_MP_WEXIT,
         * LWP_MP_VNLRU, etc).
         */
        if (lp->lwp_mpflags & LWP_MP_URETMASK)
                lwpuserret(lp);

        /*
         * Block here if we are in a stopped state.
         */
        if (__predict_false(STOPLWP(p, lp))) {
                lwkt_gettoken(&p->p_token);
                tstop();
                lwkt_reltoken(&p->p_token);
                goto recheck;
        }
        while (__predict_false(dump_stop_usertds)) {
                tsleep(&dump_stop_usertds, 0, "dumpstp", 0);
        }

        /*
         * Post any pending upcalls.  If running a virtual kernel be sure
         * to restore the virtual kernel's vmspace before posting the upcall.
         */
        if (__predict_false(p->p_flags & (P_SIGVTALRM | P_SIGPROF))) {
                lwkt_gettoken(&p->p_token);
                if (p->p_flags & P_SIGVTALRM) {
                        p->p_flags &= ~P_SIGVTALRM;
                        ksignal(p, SIGVTALRM);
                }
                if (p->p_flags & P_SIGPROF) {
                        p->p_flags &= ~P_SIGPROF;
                        ksignal(p, SIGPROF);
                }
                lwkt_reltoken(&p->p_token);
                goto recheck;
        }

        /*
         * Post any pending signals.  If running a virtual kernel be sure
         * to restore the virtual kernel's vmspace before posting the signal.
         *
         * WARNING!  postsig() can exit and not return.
         */
        if (__predict_false((sig = CURSIG_LCK_TRACE(lp, &ptok)) != 0)) {
                postsig(sig, ptok);
                goto recheck;
        }

        /*
         * In a multi-threaded program it is possible for a thread to change
         * signal state during a system call which temporarily changes the
         * signal mask.  In this case postsig() might not be run and we
         * have to restore the mask ourselves.
         */
        if (__predict_false(lp->lwp_flags & LWP_OLDMASK)) {
                lp->lwp_flags &= ~LWP_OLDMASK;
                lp->lwp_sigmask = lp->lwp_oldsigmask;
                goto recheck;
        }
}

/*
 * Cleanup from userenter and any passive release that might have occured.
 * We must reclaim the current-process designation before we can return
 * to usermode.  We also handle both LWKT and USER reschedule requests.
 */
static __inline void
userexit(struct lwp *lp)
{
        struct thread *td = lp->lwp_thread;
        /* globaldata_t gd = td->td_gd; */

        /*
         * Handle stop requests at kernel priority.  Any requests queued
         * after this loop will generate another AST.
         */
        while (__predict_false(STOPLWP(lp->lwp_proc, lp))) {
                lwkt_gettoken(&lp->lwp_proc->p_token);
                tstop();
                lwkt_reltoken(&lp->lwp_proc->p_token);
        }

        /*
         * Reduce our priority in preparation for a return to userland.  If
         * our passive release function was still in place, our priority was
         * never raised and does not need to be reduced.
         */
        lwkt_passive_recover(td);

        /* WARNING: we may have migrated cpu's */
        /* gd = td->td_gd; */

        /*
         * Become the current user scheduled process if we aren't already,
         * and deal with reschedule requests and other factors.
         *
         * Do a silly hack to avoid RETPOLINE nonsense.
         */
        if (lp->lwp_proc->p_usched == &usched_dfly)
                dfly_acquire_curproc(lp);
        else
                lp->lwp_proc->p_usched->acquire_curproc(lp);
}

/*
 * A page fault on a userspace address is classified as SMAP-induced
 * if:
 *      - SMAP is supported
 *      - kernel mode accessed present data page
 *      - rflags.AC was cleared
 */
static int
trap_is_smap(struct trapframe *frame)
{
        if ((cpu_stdext_feature & CPUID_STDEXT_SMAP) != 0 &&
            (frame->tf_err & (PGEX_P | PGEX_U | PGEX_I | PGEX_RSV)) == PGEX_P &&
            (frame->tf_rflags & PSL_AC) == 0) {
                return 1;
        } else {
                return 0;
        }
}

#if !defined(KTR_KERNENTRY)
#define KTR_KERNENTRY   KTR_ALL
#endif
KTR_INFO_MASTER(kernentry);
KTR_INFO(KTR_KERNENTRY, kernentry, trap, 0,
         "TRAP(pid %d, tid %d, trapno %ld, eva %lu)",
         pid_t pid, lwpid_t tid,  register_t trapno, vm_offset_t eva);
KTR_INFO(KTR_KERNENTRY, kernentry, trap_ret, 0, "TRAP_RET(pid %d, tid %d)",
         pid_t pid, lwpid_t tid);
KTR_INFO(KTR_KERNENTRY, kernentry, syscall, 0, "SYSC(pid %d, tid %d, nr %ld)",
         pid_t pid, lwpid_t tid,  register_t trapno);
KTR_INFO(KTR_KERNENTRY, kernentry, syscall_ret, 0, "SYSRET(pid %d, tid %d, err %d)",
         pid_t pid, lwpid_t tid,  int err);
KTR_INFO(KTR_KERNENTRY, kernentry, fork_ret, 0, "FORKRET(pid %d, tid %d)",
         pid_t pid, lwpid_t tid);

/*
 * Exception, fault, and trap interface to the kernel.
 * This common code is called from assembly language IDT gate entry
 * routines that prepare a suitable stack frame, and restore this
 * frame after the exception has been processed.
 *
 * This function is also called from doreti in an interlock to handle ASTs.
 * For example:  hardwareint->INTROUTINE->(set ast)->doreti->trap
 *
 * NOTE!  We have to retrieve the fault address prior to potentially
 *        blocking, including blocking on any token.
 *
 * NOTE!  NMI and kernel DBG traps remain on their respective pcpu IST
 *        stacks if taken from a kernel RPL. trap() cannot block in this
 *        situation.  DDB entry or a direct report-and-return is ok.
 *
 * XXX gd_trap_nesting_level currently prevents lwkt_switch() from panicing
 * if an attempt is made to switch from a fast interrupt or IPI.
 */
void
trap(struct trapframe *frame)
{
        static struct krate sscpubugrate = { 1 };
        struct globaldata *gd = mycpu;
        struct thread *td = gd->gd_curthread;
        struct lwp *lp = td->td_lwp;
        struct proc *p;
        int sticks = 0;
        int i = 0, ucode = 0, type, code;
#ifdef INVARIANTS
        int crit_count = td->td_critcount;
        lwkt_tokref_t curstop = td->td_toks_stop;
#endif
        vm_offset_t eva;

        p = td->td_proc;
        clear_quickret();

#ifdef DDB
        /*
         * We need to allow T_DNA faults when the debugger is active since
         * some dumping paths do large bcopy() which use the floating
         * point registers for faster copying.
         */
        if (db_active && frame->tf_trapno != T_DNA) {
                eva = (frame->tf_trapno == T_PAGEFLT ? frame->tf_addr : 0);
                ++gd->gd_trap_nesting_level;
                trap_fatal(frame, eva);
                --gd->gd_trap_nesting_level;
                goto out2;
        }
#endif

        eva = 0;

        if ((frame->tf_rflags & PSL_I) == 0) {
                /*
                 * Buggy application or kernel code has disabled interrupts
                 * and then trapped.  Enabling interrupts now is wrong, but
                 * it is better than running with interrupts disabled until
                 * they are accidentally enabled later.
                 */

                type = frame->tf_trapno;
                if (ISPL(frame->tf_cs) == SEL_UPL) {
                        /* JG curproc can be NULL */
                        kprintf(
                            "pid %ld (%s): trap %d with interrupts disabled\n",
                            (long)curproc->p_pid, curproc->p_comm, type);
                } else if ((type == T_STKFLT || type == T_PROTFLT ||
                            type == T_SEGNPFLT) &&
                           frame->tf_rip == (long)doreti_iret) {
                        /*
                         * iretq fault from kernel mode during return to
                         * userland.
                         *
                         * This situation is expected, don't complain.
                         */
                } else if (type != T_NMI && type != T_BPTFLT &&
                           type != T_TRCTRAP) {
                        /*
                         * XXX not quite right, since this may be for a
                         * multiple fault in user mode.
                         */
                        kprintf("kernel trap %d (%s @ 0x%016jx) with "
                                "interrupts disabled\n",
                                type,
                                td->td_comm,
                                frame->tf_rip);
                }
                cpu_enable_intr();
        }

        type = frame->tf_trapno;
        code = frame->tf_err;

        if (ISPL(frame->tf_cs) == SEL_UPL) {
                /* user trap */

                KTR_LOG(kernentry_trap, p->p_pid, lp->lwp_tid,
                        frame->tf_trapno, eva);

                userenter(td, p);

                sticks = (int)td->td_sticks;
                KASSERT(lp->lwp_md.md_regs == frame,
                        ("Frame mismatch %p %p", lp->lwp_md.md_regs, frame));

                switch (type) {
                case T_PRIVINFLT:       /* privileged instruction fault */
                        i = SIGILL;
                        ucode = ILL_PRVOPC;
                        break;

                case T_BPTFLT:          /* bpt instruction fault */
                case T_TRCTRAP:         /* trace trap */
                        frame->tf_rflags &= ~PSL_T;
                        i = SIGTRAP;
                        ucode = (type == T_TRCTRAP ? TRAP_TRACE : TRAP_BRKPT);
                        break;

                case T_ARITHTRAP:       /* arithmetic trap */
                        ucode = code;
                        i = SIGFPE;
                        break;

                case T_ASTFLT:          /* Allow process switch */
                        mycpu->gd_cnt.v_soft++;
                        if (mycpu->gd_reqflags & RQF_AST_OWEUPC) {
                                atomic_clear_int(&mycpu->gd_reqflags,
                                                 RQF_AST_OWEUPC);
                                addupc_task(p, p->p_prof.pr_addr,
                                            p->p_prof.pr_ticks);
                        }
                        goto out;

                case T_PROTFLT:         /* general protection fault */
                        i = SIGBUS;
                        ucode = BUS_OBJERR;
                        break;
                case T_STKFLT:          /* stack fault */
                case T_SEGNPFLT:        /* segment not present fault */
                        i = SIGBUS;
                        ucode = BUS_ADRERR;
                        break;
                case T_TSSFLT:          /* invalid TSS fault */
                case T_DOUBLEFLT:       /* double fault */
                default:
                        i = SIGBUS;
                        ucode = BUS_OBJERR;
                        break;

                case T_PAGEFLT:         /* page fault */
                        i = trap_pfault(frame, TRUE);
#ifdef DDB
                        if (frame->tf_rip == 0) {
                                /* used for kernel debugging only */
                                while (freeze_on_seg_fault)
                                        tsleep(p, 0, "freeze", hz * 20);
                        }
#endif
                        if (i == -1 || i == 0)
                                goto out;
                        if (i == SIGSEGV) {
                                ucode = SEGV_MAPERR;
                        } else {
                                i = SIGSEGV;
                                ucode = SEGV_ACCERR;
                        }
                        break;

                case T_DIVIDE:          /* integer divide fault */
                        ucode = FPE_INTDIV;
                        i = SIGFPE;
                        break;

#if NISA > 0
                case T_NMI:
                        /* machine/parity/power fail/"kitchen sink" faults */
                        if (isa_nmi(code) == 0) {
#ifdef DDB
                                /*
                                 * NMI can be hooked up to a pushbutton
                                 * for debugging.
                                 */
                                if (ddb_on_nmi) {
                                        kprintf ("NMI ... going to debugger\n");
                                        kdb_trap(type, 0, frame);
                                }
#endif /* DDB */
                                goto out2;
                        } else if (panic_on_nmi)
                                panic("NMI indicates hardware failure");
                        break;
#endif /* NISA > 0 */

                case T_OFLOW:           /* integer overflow fault */
                        ucode = FPE_INTOVF;
                        i = SIGFPE;
                        break;

                case T_BOUND:           /* bounds check fault */
                        ucode = FPE_FLTSUB;
                        i = SIGFPE;
                        break;

                case T_DNA:
                        /*
                         * Virtual kernel intercept - pass the DNA exception
                         * to the virtual kernel if it asked to handle it.
                         * This occurs when the virtual kernel is holding
                         * onto the FP context for a different emulated
                         * process then the one currently running.
                         *
                         * We must still call npxdna() since we may have
                         * saved FP state that the virtual kernel needs
                         * to hand over to a different emulated process.
                         */
                        if (lp->lwp_vkernel && lp->lwp_vkernel->ve &&
                            (td->td_pcb->pcb_flags & FP_VIRTFP)
                        ) {
                                npxdna();
                                break;
                        }

                        /*
                         * The kernel may have switched out the FP unit's
                         * state, causing the user process to take a fault
                         * when it tries to use the FP unit.  Restore the
                         * state here
                         */
                        if (npxdna()) {
                                gd->gd_cnt.v_trap++;
                                goto out;
                        }
                        i = SIGFPE;
                        ucode = FPE_FPU_NP_TRAP;
                        break;

                case T_FPOPFLT:         /* FPU operand fetch fault */
                        ucode = ILL_COPROC;
                        i = SIGILL;
                        break;

                case T_XMMFLT:          /* SIMD floating-point exception */
                        ucode = 0; /* XXX */
                        i = SIGFPE;
                        break;
                }
        } else {
                /* kernel trap */

                switch (type) {
                case T_PAGEFLT:                 /* page fault */
                        trap_pfault(frame, FALSE);
                        goto out2;

                case T_DNA:
                        /*
                         * The kernel is apparently using fpu for copying.
                         * XXX this should be fatal unless the kernel has
                         * registered such use.
                         */
                        if (npxdna()) {
                                gd->gd_cnt.v_trap++;
                                goto out2;
                        }
                        break;

                case T_STKFLT:          /* stack fault */
                case T_PROTFLT:         /* general protection fault */
                case T_SEGNPFLT:        /* segment not present fault */
                        /*
                         * Invalid segment selectors and out of bounds
                         * %rip's and %rsp's can be set up in user mode.
                         * This causes a fault in kernel mode when the
                         * kernel tries to return to user mode.  We want
                         * to get this fault so that we can fix the
                         * problem here and not have to check all the
                         * selectors and pointers when the user changes
                         * them.
                         */
                        if (mycpu->gd_intr_nesting_level == 0) {
                                /*
                                 * NOTE: in 64-bit mode traps push rsp/ss
                                 *       even if no ring change occurs.
                                 */
                                if (td->td_pcb->pcb_onfault &&
                                    td->td_pcb->pcb_onfault_sp ==
                                    frame->tf_rsp) {
                                        frame->tf_rip = (register_t)
                                                td->td_pcb->pcb_onfault;
                                        goto out2;
                                }

                                /*
                                 * If the iretq in doreti faults during
                                 * return to user, it will be special-cased
                                 * in IDTVEC(prot) to get here.  We want
                                 * to 'return' to doreti_iret_fault in
                                 * ipl.s in approximately the same state we
                                 * were in at the iretq.
                                 */
                                if (frame->tf_rip == (long)doreti_iret) {
                                        frame->tf_rip = (long)doreti_iret_fault;
                                        goto out2;
                                }
                        }
                        break;

                case T_TSSFLT:
                        /*
                         * PSL_NT can be set in user mode and isn't cleared
                         * automatically when the kernel is entered.  This
                         * causes a TSS fault when the kernel attempts to
                         * `iret' because the TSS link is uninitialized.  We
                         * want to get this fault so that we can fix the
                         * problem here and not every time the kernel is
                         * entered.
                         */
                        if (frame->tf_rflags & PSL_NT) {
                                frame->tf_rflags &= ~PSL_NT;
#if 0
                                /* do we need this? */
                                if (frame->tf_rip == (long)doreti_iret)
                                        frame->tf_rip = (long)doreti_iret_fault;
#endif
                                goto out2;
                        }
                        break;

                case T_TRCTRAP:  /* trace trap */
                        /*
                         * Detect historical CPU artifact on syscall or int $3
                         * entry (if not shortcutted in exception.s via
                         * DIRECT_DISALLOW_SS_CPUBUG).
                         */
                        gd->gd_cnt.v_trap++;
                        if (frame->tf_rip == (register_t)IDTVEC(fast_syscall)) {
                                krateprintf(&sscpubugrate,
                                        "Caught #DB at syscall cpu artifact\n");
                                goto out2;
                        }
                        if (frame->tf_rip == (register_t)IDTVEC(bpt)) {
                                krateprintf(&sscpubugrate,
                                        "Caught #DB at int $N cpu artifact\n");
                                goto out2;
                        }

                        /*
                         * Ignore debug register trace traps due to
                         * accesses in the user's address space, which
                         * can happen under several conditions such as
                         * if a user sets a watchpoint on a buffer and
                         * then passes that buffer to a system call.
                         * We still want to get TRCTRAPS for addresses
                         * in kernel space because that is useful when
                         * debugging the kernel.
                         */
                        if (user_dbreg_trap()) {
                                /*
                                 * Reset breakpoint bits because the
                                 * processor doesn't
                                 */
                                load_dr6(rdr6() & ~0xf);
                                goto out2;
                        }
                        /*
                         * FALLTHROUGH (TRCTRAP kernel mode, kernel address)
                         */
                case T_BPTFLT:
                        /*
                         * If DDB is enabled, let it handle the debugger trap.
                         * Otherwise, debugger traps "can't happen".
                         */
                        ucode = TRAP_BRKPT;
#ifdef DDB
                        if (kdb_trap(type, 0, frame))
                                goto out2;
#endif
                        break;

#if NISA > 0
                case T_NMI:
                        /* machine/parity/power fail/"kitchen sink" faults */
                        if (isa_nmi(code) == 0) {
#ifdef DDB
                                /*
                                 * NMI can be hooked up to a pushbutton
                                 * for debugging.
                                 */
                                if (ddb_on_nmi) {
                                        kprintf ("NMI ... going to debugger\n");
                                        kdb_trap(type, 0, frame);
                                }
#endif /* DDB */
                                goto out2;
                        } else if (panic_on_nmi == 0)
                                goto out2;
#endif /* NISA > 0 */
                        break;
                default:
                        if (type >= T_RESERVED && type < T_RESERVED + 256) {
                                kprintf("Ignoring spurious unknown "
                                        "cpu trap T_RESERVED+%d\n",
                                        type - T_RESERVED);
                                gd->gd_cnt.v_trap++;
                                goto out2;
                        }
                        break;
                }
                trap_fatal(frame, 0);
                goto out2;
        }

        /*
         * Fault from user mode, virtual kernel interecept.
         *
         * If the fault is directly related to a VM context managed by a
         * virtual kernel then let the virtual kernel handle it.
         */
        if (lp->lwp_vkernel && lp->lwp_vkernel->ve) {
                vkernel_trap(lp, frame);
                goto out;
        }

        /* Translate fault for emulators (e.g. Linux) */
        if (*p->p_sysent->sv_transtrap)
                i = (*p->p_sysent->sv_transtrap)(i, type);

        gd->gd_cnt.v_trap++;
        trapsignal(lp, i, ucode);

#ifdef DEBUG
        if (type <= MAX_TRAP_MSG) {
                uprintf("fatal process exception: %s",
                        trap_msg[type]);
                if ((type == T_PAGEFLT) || (type == T_PROTFLT))
                        uprintf(", fault VA = 0x%lx", frame->tf_addr);
                uprintf("\n");
        }
#endif

out:
        userret(lp, frame, sticks);
        userexit(lp);
out2:   ;
        if (p != NULL && lp != NULL)
                KTR_LOG(kernentry_trap_ret, p->p_pid, lp->lwp_tid);
#ifdef INVARIANTS
        KASSERT(crit_count == td->td_critcount,
                ("trap: critical section count mismatch! %d/%d",
                crit_count, td->td_critcount));
        KASSERT(curstop == td->td_toks_stop,
                ("trap: extra tokens held after trap! %ld/%ld (%s)",
                curstop - &td->td_toks_base,
                td->td_toks_stop - &td->td_toks_base,
                td->td_toks_stop[-1].tr_tok->t_desc));
#endif
}

void
trap_handle_userenter(struct thread *td)
{
        userenter(td, td->td_proc);
}

void
trap_handle_userexit(struct trapframe *frame, int sticks)
{
        struct lwp *lp = curthread->td_lwp;

        if (lp) {
                userret(lp, frame, sticks);
                userexit(lp);
        }
}

static int
trap_pfault(struct trapframe *frame, int usermode)
{
        vm_offset_t va;
        struct vmspace *vm = NULL;
        vm_map_t map;
        int rv = 0;
        int fault_flags;
        vm_prot_t ftype;
        thread_t td = curthread;
        struct lwp *lp = td->td_lwp;
        struct proc *p;

        va = trunc_page(frame->tf_addr);
        if (va >= VM_MIN_KERNEL_ADDRESS) {
                /*
                 * Don't allow user-mode faults in kernel address space.
                 */
                if (usermode) {
                        fault_flags = -1;
                        ftype = -1;
                        goto nogo;
                }

                map = kernel_map;
        } else {
                /*
                 * This is a fault on non-kernel virtual memory.
                 * vm is initialized above to NULL. If curproc is NULL
                 * or curproc->p_vmspace is NULL the fault is fatal.
                 */
                if (lp != NULL)
                        vm = lp->lwp_vmspace;

                if (vm == NULL) {
                        fault_flags = -1;
                        ftype = -1;
                        goto nogo;
                }

                if (usermode == 0) {
#ifdef DDB
                        /*
                         * Debugging, catch kernel faults on the user address
                         * space when not inside on onfault (e.g. copyin/
                         * copyout) routine.
                         */
                        if (td->td_pcb == NULL ||
                            td->td_pcb->pcb_onfault == NULL) {
                                if (freeze_on_seg_fault) {
                                        kprintf("trap_pfault: user address "
                                                "fault from kernel mode "
                                                "%016lx\n",
                                                (long)frame->tf_addr);
                                        while (freeze_on_seg_fault) {
                                                    tsleep(&freeze_on_seg_fault,
                                                           0,
                                                           "frzseg",
                                                           hz * 20);
                                        }
                                }
                        }
#endif
                        if (td->td_gd->gd_intr_nesting_level ||
                            trap_is_smap(frame) ||
                            td->td_pcb == NULL ||
                            td->td_pcb->pcb_onfault == NULL) {
                                kprintf("Fatal user address access "
                                        "from kernel mode from %s at %016jx\n",
                                        td->td_comm, frame->tf_rip);
                                trap_fatal(frame, frame->tf_addr);
                                return (-1);
                        }
                }
                map = &vm->vm_map;
        }

        /*
         * PGEX_I is defined only if the execute disable bit capability is
         * supported and enabled.
         */
        if (frame->tf_err & PGEX_W)
                ftype = VM_PROT_WRITE;
        else if (frame->tf_err & PGEX_I)
                ftype = VM_PROT_EXECUTE;
        else
                ftype = VM_PROT_READ;

        lwkt_tokref_t stop = td->td_toks_stop;

        if (map != kernel_map) {
                /*
                 * Keep swapout from messing with us during this
                 *      critical time.
                 */
                PHOLD(lp->lwp_proc);

                /*
                 * Issue fault
                 */
                fault_flags = 0;
                if (usermode)
                        fault_flags |= VM_FAULT_BURST | VM_FAULT_USERMODE;
                if (ftype & VM_PROT_WRITE)
                        fault_flags |= VM_FAULT_DIRTY;
                else
                        fault_flags |= VM_FAULT_NORMAL;
                rv = vm_fault(map, va, ftype, fault_flags);
                if (td->td_toks_stop != stop) {
                        stop = td->td_toks_stop - 1;
                        kprintf("A-HELD TOKENS DURING PFAULT td=%p(%s) map=%p va=%p ftype=%d fault_flags=%d\n", td, td->td_comm, map, (void *)va, ftype, fault_flags);
                        panic("held tokens");
                }

                PRELE(lp->lwp_proc);
        } else {
                /*
                 * Don't have to worry about process locking or stacks in the
                 * kernel.
                 */
                fault_flags = VM_FAULT_NORMAL;
                rv = vm_fault(map, va, ftype, VM_FAULT_NORMAL);
                if (td->td_toks_stop != stop) {
                        stop = td->td_toks_stop - 1;
                        kprintf("B-HELD TOKENS DURING PFAULT td=%p(%s) map=%p va=%p ftype=%d fault_flags=%d\n", td, td->td_comm, map, (void *)va, ftype, VM_FAULT_NORMAL);
                        panic("held tokens");
                }
        }
        if (rv == KERN_SUCCESS)
                return (0);
nogo:
        if (!usermode) {
                /*
                 * NOTE: in 64-bit mode traps push rsp/ss
                 *       even if no ring change occurs.
                 */
                if (td->td_pcb->pcb_onfault &&
                    td->td_pcb->pcb_onfault_sp == frame->tf_rsp &&
                    td->td_gd->gd_intr_nesting_level == 0) {
                        frame->tf_rip = (register_t)td->td_pcb->pcb_onfault;
                        return (0);
                }
                trap_fatal(frame, frame->tf_addr);
                return (-1);
        }

        /*
         * NOTE: on x86_64 we have a tf_addr field in the trapframe, no
         * kludge is needed to pass the fault address to signal handlers.
         */
        p = td->td_proc;
#ifdef DDB
        if (td->td_lwp->lwp_vkernel == NULL) {
                while (freeze_on_seg_fault) {
                        tsleep(p, 0, "freeze", hz * 20);
                }
                if (ddb_on_seg_fault)
                        Debugger("ddb_on_seg_fault");
        }
#endif

        return((rv == KERN_PROTECTION_FAILURE) ? SIGBUS : SIGSEGV);
}

static void
trap_fatal(struct trapframe *frame, vm_offset_t eva)
{
        int code, ss;
        u_int type;
        long rsp;
        struct soft_segment_descriptor softseg;

        code = frame->tf_err;
        type = frame->tf_trapno;
        sdtossd(&mdcpu->gd_gdt[IDXSEL(frame->tf_cs & 0xffff)], &softseg);

        kprintf("\n\nFatal trap %d: ", type);
        if (type <= MAX_TRAP_MSG)
                kprintf("%s ", trap_msg[type]);
        else
                kprintf("rsvd(%d) ", type - T_RESERVED);

        kprintf("while in %s mode\n",
                ISPL(frame->tf_cs) == SEL_UPL ? "user" : "kernel");

        /* three separate prints in case of a trap on an unmapped page */
        kprintf("cpuid = %d; ", mycpu->gd_cpuid);
        if (lapic_usable)
                kprintf("lapic id = %u\n", LAPIC_READID);
        if (type == T_PAGEFLT) {
                kprintf("fault virtual address  = 0x%lx\n", eva);
                kprintf("fault code             = %s %s %s, %s\n",
                        code & PGEX_U ? "user" : "supervisor",
                        code & PGEX_W ? "write" : "read",
                        code & PGEX_I ? "instruction" : "data",
                        code & PGEX_P ? "protection violation" : "page not present");
        }
        kprintf("instruction pointer    = 0x%lx:0x%lx\n",
               frame->tf_cs & 0xffff, frame->tf_rip);
        if (ISPL(frame->tf_cs) == SEL_UPL) {
                ss = frame->tf_ss & 0xffff;
                rsp = frame->tf_rsp;
        } else {
                /*
                 * NOTE: in 64-bit mode traps push rsp/ss even if no ring
                 *       change occurs.
                 */
                ss = GSEL(GDATA_SEL, SEL_KPL);
                rsp = frame->tf_rsp;
        }
        kprintf("stack pointer          = 0x%x:0x%lx\n", ss, rsp);
        kprintf("frame pointer          = 0x%x:0x%lx\n", ss, frame->tf_rbp);
        kprintf("code segment           = base 0x%lx, limit 0x%lx, type 0x%x\n",
               softseg.ssd_base, softseg.ssd_limit, softseg.ssd_type);
        kprintf("                       = DPL %d, pres %d, long %d, def32 %d, gran %d\n",
               softseg.ssd_dpl, softseg.ssd_p, softseg.ssd_long, softseg.ssd_def32,
               softseg.ssd_gran);
        kprintf("processor eflags       = ");
        if (frame->tf_rflags & PSL_T)
                kprintf("trace trap, ");
        if (frame->tf_rflags & PSL_I)
                kprintf("interrupt enabled, ");
        if (frame->tf_rflags & PSL_NT)
                kprintf("nested task, ");
        if (frame->tf_rflags & PSL_RF)
                kprintf("resume, ");
        if (frame->tf_rflags & PSL_AC)
                kprintf("smap_open, ");
        kprintf("IOPL = %ld\n", (frame->tf_rflags & PSL_IOPL) >> 12);
        kprintf("current process                = ");
        if (curproc) {
                kprintf("%lu\n",
                    (u_long)curproc->p_pid);
        } else {
                kprintf("Idle\n");
        }
        kprintf("current thread          = pri %d ", curthread->td_pri);
        if (curthread->td_critcount)
                kprintf("(CRIT)");
        kprintf("\n");

#ifdef DDB
        if ((debugger_on_panic || db_active) && kdb_trap(type, code, frame))
                return;
#endif
        kprintf("trap number            = %d\n", type);
        if (type <= MAX_TRAP_MSG)
                panic("%s", trap_msg[type]);
        else
                panic("unknown/reserved trap");
}

/*
 * Double fault handler. Called when a fault occurs while writing
 * a frame for a trap/exception onto the stack. This usually occurs
 * when the stack overflows (such is the case with infinite recursion,
 * for example).
 */
static __inline
int
in_kstack_guard(register_t rptr)
{
        thread_t td = curthread;

        if ((char *)rptr >= td->td_kstack &&
            (char *)rptr < td->td_kstack + PAGE_SIZE) {
                return 1;
        }
        return 0;
}

void
dblfault_handler(struct trapframe *frame)
{
        thread_t td = curthread;

        if (in_kstack_guard(frame->tf_rsp) || in_kstack_guard(frame->tf_rbp)) {
                kprintf("DOUBLE FAULT - KERNEL STACK GUARD HIT!\n");
                if (in_kstack_guard(frame->tf_rsp))
                        frame->tf_rsp = (register_t)(td->td_kstack + PAGE_SIZE);
                if (in_kstack_guard(frame->tf_rbp))
                        frame->tf_rbp = (register_t)(td->td_kstack + PAGE_SIZE);
        } else {
                kprintf("DOUBLE FAULT\n");
        }
        kprintf("\nFatal double fault\n");
        kprintf("rip = 0x%lx\n", frame->tf_rip);
        kprintf("rsp = 0x%lx\n", frame->tf_rsp);
        kprintf("rbp = 0x%lx\n", frame->tf_rbp);
        /* three separate prints in case of a trap on an unmapped page */
        kprintf("cpuid = %d; ", mycpu->gd_cpuid);
        if (lapic_usable)
                kprintf("lapic id = %u\n", LAPIC_READID);
        panic("double fault");
}

/*
 * syscall2 -   MP aware system call request C handler
 *
 * A system call is essentially treated as a trap except that the
 * MP lock is not held on entry or return.  We are responsible for
 * obtaining the MP lock if necessary and for handling ASTs
 * (e.g. a task switch) prior to return.
 */
void
syscall2(struct trapframe *frame)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct lwp *lp = td->td_lwp;
        struct sysent *callp;
        register_t orig_tf_rflags;
        int sticks;
        int error;
        int narg;
#ifdef INVARIANTS
        int crit_count = td->td_critcount;
#endif
        struct sysmsg sysmsg;
        union sysunion *argp;
        u_int code;
        const int regcnt = 6;   /* number of args passed in registers */

        mycpu->gd_cnt.v_syscall++;

#ifdef DIAGNOSTIC
        if (__predict_false(ISPL(frame->tf_cs) != SEL_UPL)) {
                panic("syscall");
                /* NOT REACHED */
        }
#endif

        KTR_LOG(kernentry_syscall, p->p_pid, lp->lwp_tid,
                frame->tf_rax);

        userenter(td, p);       /* lazy raise our priority */

        /*
         * Misc
         */
        sticks = (int)td->td_sticks;
        orig_tf_rflags = frame->tf_rflags;

        /*
         * Virtual kernel intercept - if a VM context managed by a virtual
         * kernel issues a system call the virtual kernel handles it, not us.
         * Restore the virtual kernel context and return from its system
         * call.  The current frame is copied out to the virtual kernel.
         */
        if (__predict_false(lp->lwp_vkernel && lp->lwp_vkernel->ve)) {
                vkernel_trap(lp, frame);
                error = EJUSTRETURN;
                callp = NULL;
                code = 0;
                goto out;
        }

        /*
         * Get the system call parameters and account for time
         */
#ifdef DIAGNOSTIC
        KASSERT(lp->lwp_md.md_regs == frame,
                ("Frame mismatch %p %p", lp->lwp_md.md_regs, frame));
#endif

        code = (u_int)frame->tf_rax;
        if (code >= p->p_sysent->sv_size)
                code = SYS___nosys;

        argp = (union sysunion *)&frame->tf_rdi;
        callp = &p->p_sysent->sv_table[code];

        /*
         * On x86_64 we get up to six arguments in registers. The rest are
         * on the stack. The first six members of 'struct trapframe' happen
         * to be the registers used to pass arguments, in exactly the right
         * order.
         *
         * Any arguments beyond available argument-passing registers must
         * be copyin()'d from the user stack.
         */
        narg = callp->sy_narg;
        if (__predict_false(narg > regcnt)) {
                register_t *argsdst;
                caddr_t params;

                argsdst = (register_t *)&sysmsg.extargs;
                bcopy(argp, argsdst, sizeof(register_t) * regcnt);
                params = (caddr_t)frame->tf_rsp + sizeof(register_t);
                error = copyin(params, &argsdst[regcnt],
                               (narg - regcnt) * sizeof(register_t));
                argp = (void *)argsdst;
                if (error) {
#ifdef KTRACE
                        if (KTRPOINTP(p, td, KTR_SYSCALL)) {
                                ktrsyscall(lp, code, narg, argp);
                        }
#endif
                        goto bad;
                }
        }

#ifdef KTRACE
        if (KTRPOINTP(p, td, KTR_SYSCALL)) {
                ktrsyscall(lp, code, narg, argp);
        }
#endif

        /*
         * Default return value is 0 (will be copied to %rax).  Double-value
         * returns use %rax and %rdx.  %rdx is left unchanged for system
         * calls which return only one result.
         */
        sysmsg.sysmsg_fds[0] = 0;
        sysmsg.sysmsg_fds[1] = frame->tf_rdx;

        /*
         * The syscall might manipulate the trap frame. If it does it
         * will probably return EJUSTRETURN.
         */
        sysmsg.sysmsg_frame = frame;

        STOPEVENT(p, S_SCE, narg);      /* MP aware */

        /*
         * NOTE: All system calls run MPSAFE now.  The system call itself
         *       is responsible for getting the MP lock.
         */
#ifdef SYSCALL_DEBUG
        tsc_uclock_t tscval = rdtsc();
#endif
        error = (*callp->sy_call)(&sysmsg, argp);
#ifdef SYSCALL_DEBUG
        tscval = rdtsc() - tscval;
        tscval = tscval * 1000000 / (tsc_frequency / 1000);     /* ns */
        {
                struct syscallwc *scwc = &SysCallsWorstCase[mycpu->gd_cpuid];
                int idx = scwc->idx++ % SCWC_MAXT;

                scwc->tot[code] += tscval - scwc->timings[code][idx];
                scwc->timings[code][idx] = tscval;
        }
#endif

out:
        /*
         * MP SAFE (we may or may not have the MP lock at this point)
         */
        //kprintf("SYSMSG %d ", error);
        if (__predict_true(error == 0)) {
                /*
                 * Reinitialize proc pointer `p' as it may be different
                 * if this is a child returning from fork syscall.
                 */
                p = curproc;
                lp = curthread->td_lwp;
                frame->tf_rax = sysmsg.sysmsg_fds[0];
                frame->tf_rdx = sysmsg.sysmsg_fds[1];
                frame->tf_rflags &= ~PSL_C;
        } else if (error == ERESTART) {
                /*
                 * Reconstruct pc, we know that 'syscall' is 2 bytes.
                 * We have to do a full context restore so that %r10
                 * (which was holding the value of %rcx) is restored for
                 * the next iteration.
                 */
                if (frame->tf_err != 0 && frame->tf_err != 2)
                        kprintf("lp %s:%d frame->tf_err is weird %ld\n",
                                td->td_comm, lp->lwp_proc->p_pid, frame->tf_err);
                frame->tf_rip -= frame->tf_err;
                frame->tf_r10 = frame->tf_rcx;
        } else if (error == EJUSTRETURN) {
                /* do nothing */
        } else if (error == EASYNC) {
                panic("Unexpected EASYNC return value (for now)");
        } else {
bad:
                if (p->p_sysent->sv_errsize) {
                        if (error >= p->p_sysent->sv_errsize)
                                error = -1;     /* XXX */
                        else
                                error = p->p_sysent->sv_errtbl[error];
                }
                frame->tf_rax = error;
                frame->tf_rflags |= PSL_C;
        }

        /*
         * Traced syscall.  trapsignal() should now be MP aware
         */
        if (__predict_false(orig_tf_rflags & PSL_T)) {
                frame->tf_rflags &= ~PSL_T;
                trapsignal(lp, SIGTRAP, TRAP_TRACE);
        }

        /*
         * Handle reschedule and other end-of-syscall issues
         */
        userret(lp, frame, sticks);

#ifdef KTRACE
        if (KTRPOINTP(p, td, KTR_SYSRET)) {
                ktrsysret(lp, code, error, sysmsg.sysmsg_result);
        }
#endif

        /*
         * This works because errno is findable through the
         * register set.  If we ever support an emulation where this
         * is not the case, this code will need to be revisited.
         */
        STOPEVENT(p, S_SCX, code);

        userexit(lp);
        KTR_LOG(kernentry_syscall_ret, p->p_pid, lp->lwp_tid, error);
#ifdef INVARIANTS
        KASSERT(crit_count == td->td_critcount,
                ("syscall: critical section count mismatch! "
                 "%d/%d in %s sysno=%d",
                crit_count, td->td_critcount, td->td_comm, code));
        KASSERT(&td->td_toks_base == td->td_toks_stop,
                ("syscall: %ld extra tokens held after trap! syscall %p",
                td->td_toks_stop - &td->td_toks_base,
                callp->sy_call));
#endif
}

/*
 * Handles the syscall() and __syscall() API
 */
void xsyscall(struct sysmsg *sysmsg, struct nosys_args *uap);

int
sys_xsyscall(struct sysmsg *sysmsg, const struct nosys_args *uap)
{
        struct trapframe *frame;
        struct sysent *callp;
        union sysunion *argp;
        struct thread *td;
        struct proc *p;
        const int regcnt = 5;   /* number of args passed in registers */
        u_int code;
        int error;
        int narg;

        td = curthread;
        p = td->td_proc;
        frame = sysmsg->sysmsg_frame;
        code = (u_int)frame->tf_rdi;
        if (code >= p->p_sysent->sv_size)
                code = SYS___nosys;
        argp = (union sysunion *)(&frame->tf_rdi + 1);
        callp = &p->p_sysent->sv_table[code];
        narg = callp->sy_narg;

        /*
         * On x86_64 we get up to six arguments in registers.  The rest are
         * on the stack.  However, for syscall() and __syscall() the syscall
         * number is inserted as the first argument, so the limit is reduced
         * by one to five.
         */
        if (__predict_false(narg > regcnt)) {
                register_t *argsdst;
                caddr_t params;

                argsdst = (register_t *)&sysmsg->extargs;
                bcopy(argp, argsdst, sizeof(register_t) * regcnt);
                params = (caddr_t)frame->tf_rsp + sizeof(register_t);
                error = copyin(params, &argsdst[regcnt],
                               (narg - regcnt) * sizeof(register_t));
                argp = (void *)argsdst;
                if (error) {
#ifdef KTRACE
                        if (KTRPOINTP(p, td, KTR_SYSCALL)) {
                                ktrsyscall(td->td_lwp, code, narg, argp);
                        }
                        if (KTRPOINTP(p, td, KTR_SYSRET)) {
                                ktrsysret(td->td_lwp, code, error,
                                          sysmsg->sysmsg_result);
                        }
#endif
                        return error;
                }
        }

#ifdef KTRACE
        if (KTRPOINTP(p, td, KTR_SYSCALL)) {
                ktrsyscall(td->td_lwp, code, narg, argp);
        }
#endif

        error = (*callp->sy_call)(sysmsg, argp);

#ifdef KTRACE
        if (KTRPOINTP(p, td, KTR_SYSRET)) {
                register_t rval;

                rval = (callp->sy_rsize <= 4) ? sysmsg->sysmsg_result :
                                                sysmsg->sysmsg_lresult;
                ktrsysret(td->td_lwp, code, error, rval);
        }
#endif

        return error;
}

void
fork_return(struct lwp *lp, struct trapframe *frame)
{
        frame->tf_rax = 0;              /* Child returns zero */
        frame->tf_rflags &= ~PSL_C;     /* success */
        frame->tf_rdx = 1;

        generic_lwp_return(lp, frame);
        KTR_LOG(kernentry_fork_ret, lp->lwp_proc->p_pid, lp->lwp_tid);
}

/*
 * Simplified back end of syscall(), used when returning from fork()
 * directly into user mode.
 *
 * This code will return back into the fork trampoline code which then
 * runs doreti.
 */
void
generic_lwp_return(struct lwp *lp, struct trapframe *frame)
{
        struct proc *p = lp->lwp_proc;

        /*
         * Check for exit-race.  If one lwp exits the process concurrent with
         * another lwp creating a new thread, the two operations may cross
         * each other resulting in the newly-created lwp not receiving a
         * KILL signal.
         */
        if (p->p_flags & P_WEXIT) {
                lwpsignal(p, lp, SIGKILL);
        }

        /*
         * Newly forked processes are given a kernel priority.  We have to
         * adjust the priority to a normal user priority and fake entry
         * into the kernel (call userenter()) to install a passive release
         * function just in case userret() decides to stop the process.  This
         * can occur when ^Z races a fork.  If we do not install the passive
         * release function the current process designation will not be
         * released when the thread goes to sleep.
         */
        lwkt_setpri_self(TDPRI_USER_NORM);
        userenter(lp->lwp_thread, p);
        userret(lp, frame, 0);
#ifdef KTRACE
        if (KTRPOINTP(p, lp->lwp_thread, KTR_SYSRET))
                ktrsysret(lp, SYS_fork, 0, 0);
#endif
        lp->lwp_flags |= LWP_PASSIVE_ACQ;
        userexit(lp);
        lp->lwp_flags &= ~LWP_PASSIVE_ACQ;
}

/*
 * If PGEX_FPFAULT is set then set FP_VIRTFP in the PCB to force a T_DNA
 * fault (which is then passed back to the virtual kernel) if an attempt is
 * made to use the FP unit.
 *
 * XXX this is a fairly big hack.
 */
void
set_vkernel_fp(struct trapframe *frame)
{
        struct thread *td = curthread;

        if (frame->tf_xflags & PGEX_FPFAULT) {
                td->td_pcb->pcb_flags |= FP_VIRTFP;
                if (mdcpu->gd_npxthread == td)
                        npxexit();
        } else {
                td->td_pcb->pcb_flags &= ~FP_VIRTFP;
        }
}

/*
 * Called from vkernel_trap() to fixup the vkernel's syscall
 * frame for vmspace_ctl() return.
 */
void
cpu_vkernel_trap(struct trapframe *frame, int error)
{
        frame->tf_rax = error;
        if (error)
                frame->tf_rflags |= PSL_C;
        else
                frame->tf_rflags &= ~PSL_C;
}