/*-
 * SPDX-License-Identifier: BSD-4-Clause
 *
 * Copyright (C) 1994, David Greenman
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * 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.
 */

#include <sys/cdefs.h>
/*
 * 386 Trap and System call handling
 */

#include "opt_clock.h"
#include "opt_cpu.h"
#include "opt_hwpmc_hooks.h"
#include "opt_isa.h"
#include "opt_kdb.h"
#include "opt_trap.h"

#include <sys/param.h>
#include <sys/bus.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/ptrace.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/syscall.h>
#include <sys/sysctl.h>
#include <sys/sysent.h>
#include <sys/uio.h>
#include <sys/vmmeter.h>
#ifdef HWPMC_HOOKS
#include <sys/pmckern.h>
PMC_SOFT_DEFINE( , , page_fault, all);
PMC_SOFT_DEFINE( , , page_fault, read);
PMC_SOFT_DEFINE( , , page_fault, write);
#endif
#include <security/audit/audit.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#include <vm/vm_kern.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>
#include <vm/vm_extern.h>

#include <machine/cpu.h>
#include <machine/intr_machdep.h>
#include <x86/mca.h>
#include <machine/md_var.h>
#include <machine/pcb.h>
#ifdef SMP
#include <machine/smp.h>
#endif
#include <machine/stack.h>
#include <machine/trap.h>
#include <machine/tss.h>
#include <machine/vm86.h>

#ifdef POWERFAIL_NMI
#include <sys/syslog.h>
#include <machine/clock.h>
#endif

#ifdef KDTRACE_HOOKS
#include <sys/dtrace_bsd.h>
#endif

void trap(struct trapframe *frame);
void syscall(struct trapframe *frame);

static int trap_pfault(struct trapframe *, bool, vm_offset_t, int *, int *);
static void trap_fatal(struct trapframe *, vm_offset_t);
#ifdef KDTRACE_HOOKS
static bool trap_user_dtrace(struct trapframe *,
    int (**hook)(struct trapframe *));
#endif
void dblfault_handler(void);

extern inthand_t IDTVEC(bpt), IDTVEC(dbg), IDTVEC(int0x80_syscall);
extern uint64_t pg_nx;

struct trap_data {
        bool            ei;
        const char      *msg;
};

static const struct trap_data trap_data[] = {
        [T_PRIVINFLT] = { .ei = true,   .msg = "privileged instruction fault" },
        [T_BPTFLT] =    { .ei = false,  .msg = "breakpoint instruction fault" },
        [T_ARITHTRAP] = { .ei = true,   .msg = "arithmetic trap" },
        [T_PROTFLT] =   { .ei = true,   .msg = "general protection fault" },
        [T_TRCTRAP] =   { .ei = false,  .msg = "debug exception" },
        [T_PAGEFLT] =   { .ei = true,   .msg = "page fault" },
        [T_ALIGNFLT] =  { .ei = true,   .msg = "alignment fault" },
        [T_DIVIDE] =    { .ei = true,   .msg = "integer divide fault" },
        [T_NMI] =       { .ei = false,  .msg = "non-maskable interrupt trap" },
        [T_OFLOW] =     { .ei = true,   .msg = "overflow trap" },
        [T_BOUND] =     { .ei = true,   .msg = "FPU bounds check fault" },
        [T_DNA] =       { .ei = true,   .msg = "FPU device not available" },
        [T_DOUBLEFLT] = { .ei = false,  .msg = "double fault" },
        [T_FPOPFLT] =   { .ei = true,   .msg = "FPU operand fetch fault" },
        [T_TSSFLT] =    { .ei = true,   .msg = "invalid TSS fault" },
        [T_SEGNPFLT] =  { .ei = true,   .msg = "segment not present fault" },
        [T_STKFLT] =    { .ei = true,   .msg = "stack fault" },
        [T_MCHK] =      { .ei = true,   .msg = "machine check trap" },
        [T_XMMFLT] =    { .ei = true,   .msg = "SIMD floating-point exception" },
        [T_DTRACE_RET] ={ .ei = true,   .msg = "DTrace pid return trap" },
};

static bool
trap_enable_intr(int trapno)
{

        MPASS(trapno > 0);
        if (trapno < nitems(trap_data) && trap_data[trapno].msg != NULL)
                return (trap_data[trapno].ei);
        return (false);
}

static const char *
trap_msg(int trapno)
{
        const char *res;
        static const char unkn[] = "UNKNOWN";

        res = NULL;
        if (trapno < nitems(trap_data))
                res = trap_data[trapno].msg;
        if (res == NULL)
                res = unkn;
        return (res);
}

#if defined(I586_CPU) && !defined(NO_F00F_HACK)
int has_f00f_bug = 0;           /* Initialized so that it can be patched. */
#endif

static int uprintf_signal;
SYSCTL_INT(_machdep, OID_AUTO, uprintf_signal, CTLFLAG_RW,
    &uprintf_signal, 0,
    "Print debugging information on trap signal to ctty");


#ifdef INVARIANTS
static __inline register_t
read_esp(void)
{
        register_t res;

        __asm __volatile("movl\t%%esp,%0" : "=r" (res));
        return (res);
}

void
trap_check_kstack(void)
{
        struct thread *td;
        vm_offset_t stk;

        td = curthread;
        stk = read_esp();
        if (stk >= PMAP_TRM_MIN_ADDRESS)
                panic("td %p stack %#x in trampoline", td, stk);
        if (!kstack_contains(td, stk, 0))
                panic("td %p stack %#x not in kstack VA %#x %d",
                    td, stk, td->td_kstack, td->td_kstack_pages);
}
#endif

/*
 * Exception, fault, and trap interface to the FreeBSD 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.
 */

void
trap(struct trapframe *frame)
{
        ksiginfo_t ksi;
        struct thread *td;
        struct proc *p;
        int pf, signo, ucode;
        u_int type;
        register_t addr, dr6;
        vm_offset_t eva;
#ifdef POWERFAIL_NMI
        static int lastalert = 0;
#endif

        td = curthread;
        p = td->td_proc;
        dr6 = 0;

        VM_CNT_INC(v_trap);
        type = frame->tf_trapno;

        KASSERT((read_eflags() & PSL_I) == 0,
            ("trap: interrupts enabled, type %d frame %p", type, frame));

#ifdef KDB
        if (kdb_active) {
                kdb_reenter();
                return;
        }
#endif
        trap_check_kstack();

        if (type == T_NMI) {
                nmi_handle_intr(frame);
                return;
        }

        if (type == T_RESERVED) {
                trap_fatal(frame, 0);
                return;
        }

        if (type == T_MCHK) {
                mca_intr();
                return;
        }

#ifdef KDTRACE_HOOKS
        /*
         * A trap can occur while DTrace executes a probe. Before
         * executing the probe, DTrace blocks re-scheduling and sets
         * a flag in its per-cpu flags to indicate that it doesn't
         * want to fault. On returning from the probe, the no-fault
         * flag is cleared and finally re-scheduling is enabled.
         */
        if ((type == T_PROTFLT || type == T_PAGEFLT) &&
            dtrace_trap_func != NULL && (*dtrace_trap_func)(frame, type))
                return;
#endif

        /*
         * We must not allow context switches until %cr2 is read.
         * Also, for some Cyrix CPUs, %cr2 is clobbered by interrupts.
         * All faults use interrupt gates, so %cr2 can be safely read
         * now, before optional enable of the interrupts below.
         */
        if (type == T_PAGEFLT)
                eva = rcr2();

        /*
         * 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.
         */
        if ((frame->tf_eflags & PSL_I) == 0 && TRAPF_USERMODE(frame) &&
            (curpcb->pcb_flags & PCB_VM86CALL) == 0)
                uprintf("pid %ld (%s): usermode trap %d (%s) with "
                    "interrupts disabled\n",
                    (long)curproc->p_pid, curthread->td_name, type,
                    trap_data[type].msg);

        /*
         * Conditionally reenable interrupts.  If we hold a spin lock,
         * then we must not reenable interrupts.  This might be a
         * spurious page fault.
         */
        if (trap_enable_intr(type) && td->td_md.md_spinlock_count == 0 &&
            frame->tf_eip != (int)cpu_switch_load_gs)
                enable_intr();

        if (TRAPF_USERMODE(frame) && (curpcb->pcb_flags & PCB_VM86CALL) == 0) {
                /* user trap */

                td->td_pticks = 0;
                td->td_frame = frame;
                addr = frame->tf_eip;
                if (td->td_cowgen != atomic_load_int(&p->p_cowgen))
                        thread_cow_update(td);

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

                case T_BPTFLT:          /* bpt instruction fault */
#ifdef KDTRACE_HOOKS
                        if (trap_user_dtrace(frame, &dtrace_pid_probe_ptr))
                                return;
#else
                        enable_intr();
#endif
                        signo = SIGTRAP;
                        ucode = TRAP_BRKPT;
                        break;

                case T_TRCTRAP:         /* debug exception */
                        enable_intr();
user_trctrap_out:
                        signo = SIGTRAP;
                        ucode = TRAP_TRACE;
                        dr6 = rdr6();
                        if ((dr6 & DBREG_DR6_BS) != 0) {
                                PROC_LOCK(td->td_proc);
                                if ((td->td_dbgflags & TDB_STEP) != 0) {
                                        td->td_frame->tf_eflags &= ~PSL_T;
                                        td->td_dbgflags &= ~TDB_STEP;
                                }
                                PROC_UNLOCK(td->td_proc);
                        }
                        break;

                case T_ARITHTRAP:       /* arithmetic trap */
                        ucode = npxtrap_x87();
                        if (ucode == -1)
                                return;
                        signo = SIGFPE;
                        break;

                /*
                 * The following two traps can happen in vm86 mode,
                 * and, if so, we want to handle them specially.
                 */
                case T_PROTFLT:         /* general protection fault */
                case T_STKFLT:          /* stack fault */
                        if (frame->tf_eflags & PSL_VM) {
                                signo = vm86_emulate((struct vm86frame *)frame);
                                ucode = 0;      /* XXXKIB: better code ? */
                                if (signo == SIGTRAP) {
                                        load_dr6(rdr6() | 0x4000);
                                        goto user_trctrap_out;
                                }
                                if (signo == 0)
                                        goto user;
                                break;
                        }
                        signo = SIGBUS;
                        ucode = (type == T_PROTFLT) ? BUS_OBJERR : BUS_ADRERR;
                        break;
                case T_SEGNPFLT:        /* segment not present fault */
                        signo = SIGBUS;
                        ucode = BUS_ADRERR;
                        break;
                case T_TSSFLT:          /* invalid TSS fault */
                        signo = SIGBUS;
                        ucode = BUS_OBJERR;
                        break;
                case T_ALIGNFLT:
                        signo = SIGBUS;
                        ucode = BUS_ADRALN;
                        break;
                case T_DOUBLEFLT:       /* double fault */
                default:
                        signo = SIGBUS;
                        ucode = BUS_OBJERR;
                        break;

                case T_PAGEFLT:         /* page fault */
                        addr = eva;
                        pf = trap_pfault(frame, true, eva, &signo, &ucode);
#if defined(I586_CPU) && !defined(NO_F00F_HACK)
                        if (pf == -2) {
                                /*
                                 * The f00f hack workaround has triggered, so
                                 * treat the fault as an illegal instruction 
                                 * (T_PRIVINFLT) instead of a page fault.
                                 */
                                type = frame->tf_trapno = T_PRIVINFLT;
                                break;
                        }
#endif
                        if (pf == -1)
                                return;
                        if (pf == 0)
                                goto user;
                        break;

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

                case T_NMI:
#ifdef POWERFAIL_NMI
#ifndef TIMER_FREQ
#  define TIMER_FREQ 1193182
#endif
                        if (time_second - lastalert > 10) {
                                log(LOG_WARNING, "NMI: power fail\n");
                                sysbeep(880, SBT_1S);
                                lastalert = time_second;
                        }
                        return;
#else /* !POWERFAIL_NMI */
                        nmi_handle_intr(frame);
                        return;
#endif /* POWERFAIL_NMI */

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

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

                case T_DNA:
                        KASSERT(PCB_USER_FPU(td->td_pcb),
                            ("kernel FPU ctx has leaked"));
                        /* transparent fault (due to context switch "late") */
                        if (npxdna())
                                return;
                        uprintf("pid %d killed due to lack of floating point\n",
                                p->p_pid);
                        signo = SIGKILL;
                        ucode = 0;
                        break;

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

                case T_XMMFLT:          /* SIMD floating-point exception */
                        ucode = npxtrap_sse();
                        if (ucode == -1)
                                return;
                        signo = SIGFPE;
                        break;
#ifdef KDTRACE_HOOKS
                case T_DTRACE_RET:
                        (void)trap_user_dtrace(frame, &dtrace_return_probe_ptr);
                        return;
#endif
                }
        } else {
                /* kernel trap */

                KASSERT(cold || td->td_ucred != NULL,
                    ("kernel trap doesn't have ucred"));
                switch (type) {
                case T_PAGEFLT:                 /* page fault */
                        (void)trap_pfault(frame, false, eva, NULL, NULL);
                        return;

                case T_DNA:
                        if (PCB_USER_FPU(td->td_pcb))
                                panic("Unregistered use of FPU in kernel");
                        if (npxdna())
                                return;
                        break;

                case T_ARITHTRAP:       /* arithmetic trap */
                case T_XMMFLT:          /* SIMD floating-point exception */
                case T_FPOPFLT:         /* FPU operand fetch fault */
                        /*
                         * XXXKIB for now disable any FPU traps in kernel
                         * handler registration seems to be overkill
                         */
                        trap_fatal(frame, 0);
                        return;

                        /*
                         * The following two traps can happen in
                         * vm86 mode, and, if so, we want to handle
                         * them specially.
                         */
                case T_PROTFLT:         /* general protection fault */
                case T_STKFLT:          /* stack fault */
                        if (frame->tf_eflags & PSL_VM) {
                                signo = vm86_emulate((struct vm86frame *)frame);
                                if (signo == SIGTRAP) {
                                        type = T_TRCTRAP;
                                        load_dr6(rdr6() | 0x4000);
                                        goto kernel_trctrap;
                                }
                                if (signo != 0)
                                        /*
                                         * returns to original process
                                         */
                                        vm86_trap((struct vm86frame *)frame);
                                return;
                        }
                        /* FALL THROUGH */
                case T_SEGNPFLT:        /* segment not present fault */
                        if (curpcb->pcb_flags & PCB_VM86CALL)
                                break;

                        /*
                         * Invalid %fs's and %gs's can be created using
                         * procfs or PT_SETREGS or by invalidating the
                         * underlying LDT entry.  This causes a fault
                         * in kernel mode when the kernel attempts to
                         * switch contexts.  Lose the bad context
                         * (XXX) so that we can continue, and generate
                         * a signal.
                         */
                        if (frame->tf_eip == (int)cpu_switch_load_gs) {
                                curpcb->pcb_gs = 0;
#if 0                           
                                PROC_LOCK(p);
                                kern_psignal(p, SIGBUS);
                                PROC_UNLOCK(p);
#endif                          
                                return;
                        }

                        if (td->td_intr_nesting_level != 0)
                                break;

                        /*
                         * Invalid segment selectors and out of bounds
                         * %eip's and %esp'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.
                         *
                         * N.B. Comparing to long mode, 32-bit mode
                         * does not push %esp on the trap frame,
                         * because iretl faulted while in ring 0.  As
                         * the consequence, there is no need to fixup
                         * the stack pointer for doreti_iret_fault,
                         * the fixup and the complimentary trap() call
                         * are executed on the main thread stack, not
                         * on the trampoline stack.
                         */
                        if (frame->tf_eip == (int)doreti_iret + setidt_disp) {
                                frame->tf_eip = (int)doreti_iret_fault +
                                    setidt_disp;
                                return;
                        }
                        if (type == T_STKFLT)
                                break;

                        if (frame->tf_eip == (int)doreti_popl_ds +
                            setidt_disp) {
                                frame->tf_eip = (int)doreti_popl_ds_fault +
                                    setidt_disp;
                                return;
                        }
                        if (frame->tf_eip == (int)doreti_popl_es +
                            setidt_disp) {
                                frame->tf_eip = (int)doreti_popl_es_fault +
                                    setidt_disp;
                                return;
                        }
                        if (frame->tf_eip == (int)doreti_popl_fs +
                            setidt_disp) {
                                frame->tf_eip = (int)doreti_popl_fs_fault +
                                    setidt_disp;
                                return;
                        }
                        if (curpcb->pcb_onfault != NULL) {
                                frame->tf_eip = (int)curpcb->pcb_onfault;
                                return;
                        }
                        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_eflags & PSL_NT) {
                                frame->tf_eflags &= ~PSL_NT;
                                return;
                        }
                        break;

                case T_TRCTRAP:  /* debug exception */
kernel_trctrap:
                        /* Clear any pending debug events. */
                        dr6 = rdr6();
                        load_dr6(0);

                        /*
                         * Ignore debug register exceptions 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(dr6) &&
                           !(curpcb->pcb_flags & PCB_VM86CALL))
                                return;

                        /*
                         * Malicious user code can configure a debug
                         * register watchpoint to trap on data access
                         * to the top of stack and then execute 'pop
                         * %ss; int 3'.  Due to exception deferral for
                         * 'pop %ss', the CPU will not interrupt 'int
                         * 3' to raise the DB# exception for the debug
                         * register but will postpone the DB# until
                         * execution of the first instruction of the
                         * BP# handler (in kernel mode).  Normally the
                         * previous check would ignore DB# exceptions
                         * for watchpoints on user addresses raised in
                         * kernel mode.  However, some CPU errata
                         * include cases where DB# exceptions do not
                         * properly set bits in %dr6, e.g. Haswell
                         * HSD23 and Skylake-X SKZ24.
                         *
                         * A deferred DB# can also be raised on the
                         * first instructions of system call entry
                         * points or single-step traps via similar use
                         * of 'pop %ss' or 'mov xxx, %ss'.
                         */
                        if (frame->tf_eip ==
                            (uintptr_t)IDTVEC(int0x80_syscall) + setidt_disp ||
                            frame->tf_eip == (uintptr_t)IDTVEC(bpt) +
                            setidt_disp ||
                            frame->tf_eip == (uintptr_t)IDTVEC(dbg) +
                            setidt_disp)
                                return;
                        /*
                         * FALLTHROUGH (TRCTRAP kernel mode, kernel address)
                         */
                case T_BPTFLT:
                        /*
                         * If KDB is enabled, let it handle the debugger trap.
                         * Otherwise, debugger traps "can't happen".
                         */
#ifdef KDB
                        if (kdb_trap(type, dr6, frame))
                                return;
#endif
                        break;

                case T_NMI:
#ifdef POWERFAIL_NMI
                        if (time_second - lastalert > 10) {
                                log(LOG_WARNING, "NMI: power fail\n");
                                sysbeep(880, SBT_1S);
                                lastalert = time_second;
                        }
                        return;
#else /* !POWERFAIL_NMI */
                        nmi_handle_intr(frame);
                        return;
#endif /* POWERFAIL_NMI */
                }

                trap_fatal(frame, eva);
                return;
        }

        ksiginfo_init_trap(&ksi);
        ksi.ksi_signo = signo;
        ksi.ksi_code = ucode;
        ksi.ksi_addr = (void *)addr;
        ksi.ksi_trapno = type;
        if (uprintf_signal) {
                uprintf("pid %d comm %s: signal %d err %#x code %d type %d "
                    "addr %#x ss %#04x esp %#08x cs %#04x eip %#08x eax %#08x"
                    "<%02x %02x %02x %02x %02x %02x %02x %02x>\n",
                    p->p_pid, p->p_comm, signo, frame->tf_err, ucode, type,
                    addr, frame->tf_ss, frame->tf_esp, frame->tf_cs,
                    frame->tf_eip, frame->tf_eax,
                    fubyte((void *)(frame->tf_eip + 0)),
                    fubyte((void *)(frame->tf_eip + 1)),
                    fubyte((void *)(frame->tf_eip + 2)),
                    fubyte((void *)(frame->tf_eip + 3)),
                    fubyte((void *)(frame->tf_eip + 4)),
                    fubyte((void *)(frame->tf_eip + 5)),
                    fubyte((void *)(frame->tf_eip + 6)),
                    fubyte((void *)(frame->tf_eip + 7)));
        }
        KASSERT((read_eflags() & PSL_I) != 0, ("interrupts disabled"));
        trapsignal(td, &ksi);

user:
        userret(td, frame);
        KASSERT(PCB_USER_FPU(td->td_pcb),
            ("Return from trap with kernel FPU ctx leaked"));
}

/*
 * Handle all details of a page fault.
 * Returns:
 * -2 if the fault was caused by triggered workaround for Intel Pentium
 *    0xf00f bug.
 * -1 if this fault was fatal, typically from kernel mode
 *    (cannot happen, but we need to return something).
 * 0  if this fault was handled by updating either the user or kernel
 *    page table, execution can continue.
 * 1  if this fault was from usermode and it was not handled, a synchronous
 *    signal should be delivered to the thread.  *signo returns the signal
 *    number, *ucode gives si_code.
 */
static int
trap_pfault(struct trapframe *frame, bool usermode, vm_offset_t eva,
    int *signo, int *ucode)
{
        struct thread *td;
        struct proc *p;
        vm_map_t map;
        int rv;
        vm_prot_t ftype;

        MPASS(!usermode || (signo != NULL && ucode != NULL));

        td = curthread;
        p = td->td_proc;

        if (__predict_false((td->td_pflags & TDP_NOFAULTING) != 0)) {
                /*
                 * Due to both processor errata and lazy TLB invalidation when
                 * access restrictions are removed from virtual pages, memory
                 * accesses that are allowed by the physical mapping layer may
                 * nonetheless cause one spurious page fault per virtual page. 
                 * When the thread is executing a "no faulting" section that
                 * is bracketed by vm_fault_{disable,enable}_pagefaults(),
                 * every page fault is treated as a spurious page fault,
                 * unless it accesses the same virtual address as the most
                 * recent page fault within the same "no faulting" section.
                 */
                if (td->td_md.md_spurflt_addr != eva ||
                    (td->td_pflags & TDP_RESETSPUR) != 0) {
                        /*
                         * Do nothing to the TLB.  A stale TLB entry is
                         * flushed automatically by a page fault.
                         */
                        td->td_md.md_spurflt_addr = eva;
                        td->td_pflags &= ~TDP_RESETSPUR;
                        return (0);
                }
        } else {
                /*
                 * If we get a page fault while in a critical section, then
                 * it is most likely a fatal kernel page fault.  The kernel
                 * is already going to panic trying to get a sleep lock to
                 * do the VM lookup, so just consider it a fatal trap so the
                 * kernel can print out a useful trap message and even get
                 * to the debugger.
                 *
                 * If we get a page fault while holding a non-sleepable
                 * lock, then it is most likely a fatal kernel page fault.
                 * If WITNESS is enabled, then it's going to whine about
                 * bogus LORs with various VM locks, so just skip to the
                 * fatal trap handling directly.
                 */
                if (td->td_critnest != 0 ||
                    WITNESS_CHECK(WARN_SLEEPOK | WARN_GIANTOK, NULL,
                    "Kernel page fault") != 0) {
                        trap_fatal(frame, eva);
                        return (-1);
                }
        }
        if (eva >= PMAP_TRM_MIN_ADDRESS) {
                /*
                 * Don't allow user-mode faults in kernel address space.
                 * An exception:  if the faulting address is the invalid
                 * instruction entry in the IDT, then the Intel Pentium
                 * F00F bug workaround was triggered, and we need to
                 * treat it is as an illegal instruction, and not a page
                 * fault.
                 */
#if defined(I586_CPU) && !defined(NO_F00F_HACK)
                if ((eva == (unsigned int)&idt[6]) && has_f00f_bug) {
                        *ucode = ILL_PRVOPC;
                        *signo = SIGILL;
                        return (-2);
                }
#endif
                if (usermode) {
                        *signo = SIGSEGV;
                        *ucode = SEGV_MAPERR;
                        return (1);
                }
                trap_fatal(frame, eva);
                return (-1);
        } else {
                map = usermode ? &p->p_vmspace->vm_map : kernel_map;

                /*
                 * Kernel cannot access a user-space address directly
                 * because user pages are not mapped.  Also, page
                 * faults must not be caused during the interrupts.
                 */
                if (!usermode && td->td_intr_nesting_level != 0) {
                        trap_fatal(frame, eva);
                        return (-1);
                }
        }

        /*
         * If the trap was caused by errant bits in the PTE then panic.
         */
        if (frame->tf_err & PGEX_RSV) {
                trap_fatal(frame, eva);
                return (-1);
        }

        /*
         * 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) && pg_nx != 0)
                ftype = VM_PROT_EXECUTE;
        else
                ftype = VM_PROT_READ;

        /* Fault in the page. */
        rv = vm_fault_trap(map, eva, ftype, VM_FAULT_NORMAL, signo, ucode);
        if (rv == KERN_SUCCESS) {
#ifdef HWPMC_HOOKS
                if (ftype == VM_PROT_READ || ftype == VM_PROT_WRITE) {
                        PMC_SOFT_CALL_TF( , , page_fault, all, frame);
                        if (ftype == VM_PROT_READ)
                                PMC_SOFT_CALL_TF( , , page_fault, read,
                                    frame);
                        else
                                PMC_SOFT_CALL_TF( , , page_fault, write,
                                    frame);
                }
#endif
                return (0);
        }
        if (usermode)
                return (1);
        if (td->td_intr_nesting_level == 0 &&
            curpcb->pcb_onfault != NULL) {
                frame->tf_eip = (int)curpcb->pcb_onfault;
                return (0);
        }
        trap_fatal(frame, eva);
        return (-1);
}

static void
trap_fatal(struct trapframe *frame, vm_offset_t eva)
{
        int code, ss, esp;
        u_int type;
        struct soft_segment_descriptor softseg;
#ifdef KDB
        bool handled;
#endif

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

        printf("\n\nFatal trap %d: %s while in %s mode\n", type, trap_msg(type),
            frame->tf_eflags & PSL_VM ? "vm86" :
            ISPL(frame->tf_cs) == SEL_UPL ? "user" : "kernel");
#ifdef SMP
        /* two separate prints in case of a trap on an unmapped page */
        printf("cpuid = %d; ", PCPU_GET(cpuid));
        printf("apic id = %02x\n", PCPU_GET(apic_id));
#endif
        if (type == T_PAGEFLT) {
                printf("fault virtual address   = 0x%x\n", eva);
                printf("fault code              = %s %s%s, %s\n",
                        code & PGEX_U ? "user" : "supervisor",
                        code & PGEX_W ? "write" : "read",
                        pg_nx != 0 ?
                        (code & PGEX_I ? " instruction" : " data") :
                        "",
                        code & PGEX_RSV ? "reserved bits in PTE" :
                        code & PGEX_P ? "protection violation" : "page not present");
        } else {
                printf("error code              = %#x\n", code);
        }
        printf("instruction pointer     = 0x%x:0x%x\n",
               frame->tf_cs & 0xffff, frame->tf_eip);
        if (TF_HAS_STACKREGS(frame)) {
                ss = frame->tf_ss & 0xffff;
                esp = frame->tf_esp;
        } else {
                ss = GSEL(GDATA_SEL, SEL_KPL);
                esp = (int)&frame->tf_esp;
        }
        printf("stack pointer           = 0x%x:0x%x\n", ss, esp);
        printf("frame pointer           = 0x%x:0x%x\n", ss, frame->tf_ebp);
        printf("code segment            = base 0x%x, limit 0x%x, type 0x%x\n",
               softseg.ssd_base, softseg.ssd_limit, softseg.ssd_type);
        printf("                        = DPL %d, pres %d, def32 %d, gran %d\n",
               softseg.ssd_dpl, softseg.ssd_p, softseg.ssd_def32,
               softseg.ssd_gran);
        printf("processor eflags        = ");
        if (frame->tf_eflags & PSL_T)
                printf("trace trap, ");
        if (frame->tf_eflags & PSL_I)
                printf("interrupt enabled, ");
        if (frame->tf_eflags & PSL_NT)
                printf("nested task, ");
        if (frame->tf_eflags & PSL_RF)
                printf("resume, ");
        if (frame->tf_eflags & PSL_VM)
                printf("vm86, ");
        printf("IOPL = %d\n", (frame->tf_eflags & PSL_IOPL) >> 12);
        printf("current process         = %d (%s)\n",
            curproc->p_pid, curthread->td_name);

#ifdef KDB
        if (debugger_on_trap) {
                kdb_why = KDB_WHY_TRAP;
                frame->tf_err = eva;    /* smuggle fault address to ddb */
                handled = kdb_trap(type, 0, frame);
                frame->tf_err = code;   /* restore error code */
                kdb_why = KDB_WHY_UNSET;
                if (handled)
                        return;
        }
#endif
        printf("trap number             = %d\n", type);
        if (trap_msg(type) != NULL)
                panic("%s", trap_msg(type));
        else
                panic("unknown/reserved trap");
}

#ifdef KDTRACE_HOOKS
/*
 * Invoke a userspace DTrace hook.  The hook pointer is cleared when no
 * userspace probes are enabled, so we must synchronize with DTrace to ensure
 * that a trapping thread is able to call the hook before it is cleared.
 */
static bool
trap_user_dtrace(struct trapframe *frame, int (**hookp)(struct trapframe *))
{
        int (*hook)(struct trapframe *);

        hook = atomic_load_ptr(hookp);
        enable_intr();
        if (hook != NULL)
                return ((hook)(frame) == 0);
        return (false);
}
#endif

/*
 * 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).
 *
 * XXX Note that the current PTD gets replaced by IdlePTD when the
 * task switch occurs. This means that the stack that was active at
 * the time of the double fault is not available at <kstack> unless
 * the machine was idle when the double fault occurred. The downside
 * of this is that "trace <ebp>" in ddb won't work.
 */
void
dblfault_handler(void)
{
        struct i386tss *t;

#ifdef KDTRACE_HOOKS
        if (dtrace_doubletrap_func != NULL)
                (*dtrace_doubletrap_func)();
#endif
        printf("\nFatal double fault:\n");
        t = PCPU_GET(common_tssp);
        printf(
            "eip = %#08x esp = %#08x ebp = %#08x eax = %#08x\n"
            "edx = %#08x ecx = %#08x edi = %#08x esi = %#08x\n"
            "ebx = %#08x\n"
            "psl = %#08x cs  = %#08x ss  = %#08x ds  = %#08x\n"
            "es  = %#08x fs  = %#08x gs  = %#08x cr3 = %#08x\n",
            t->tss_eip, t->tss_esp, t->tss_ebp, t->tss_eax,
            t->tss_edx, t->tss_ecx, t->tss_edi, t->tss_esi,
            t->tss_ebx,
            t->tss_eflags, t->tss_cs, t->tss_ss, t->tss_ds,
            t->tss_es, t->tss_fs, t->tss_gs, t->tss_cr3);
#ifdef SMP
        printf("cpuid = %d; apic id = %02x\n", PCPU_GET(cpuid),
            PCPU_GET(apic_id));
#endif
        panic("double fault");
}

int
cpu_fetch_syscall_args(struct thread *td)
{
        struct proc *p;
        struct trapframe *frame;
        struct syscall_args *sa;
        caddr_t params;
        long tmp;
        int error;
#ifdef COMPAT_43
        u_int32_t eip;
        int cs;
#endif

        p = td->td_proc;
        frame = td->td_frame;
        sa = &td->td_sa;

#ifdef COMPAT_43
        if (__predict_false(frame->tf_cs == 7 && frame->tf_eip == 2)) {
                /*
                 * In lcall $7,$0 after int $0x80.  Convert the user
                 * frame to what it would be for a direct int 0x80 instead
                 * of lcall $7,$0, by popping the lcall return address.
                 */
                error = fueword32((void *)frame->tf_esp, &eip);
                if (error == -1)
                        return (EFAULT);
                cs = fuword16((void *)(frame->tf_esp + sizeof(u_int32_t)));
                if (cs == -1)
                        return (EFAULT);

                /*
                 * Unwind in-kernel frame after all stack frame pieces
                 * were successfully read.
                 */
                frame->tf_eip = eip;
                frame->tf_cs = cs;
                frame->tf_esp += 2 * sizeof(u_int32_t);
                frame->tf_err = 7;      /* size of lcall $7,$0 */
        }
#endif

        sa->code = frame->tf_eax;
        sa->original_code = sa->code;
        params = (caddr_t)frame->tf_esp + sizeof(uint32_t);

        /*
         * Need to check if this is a 32 bit or 64 bit syscall.
         */
        if (sa->code == SYS_syscall) {
                /*
                 * Code is first argument, followed by actual args.
                 */
                error = fueword(params, &tmp);
                if (error == -1)
                        return (EFAULT);
                sa->code = tmp;
                params += sizeof(uint32_t);
        } else if (sa->code == SYS___syscall) {
                /*
                 * Like syscall, but code is a quad, so as to maintain
                 * quad alignment for the rest of the arguments.
                 */
                error = fueword(params, &tmp);
                if (error == -1)
                        return (EFAULT);
                sa->code = tmp;
                params += sizeof(quad_t);
        }

        if (sa->code >= p->p_sysent->sv_size)
                sa->callp = &nosys_sysent;
        else
                sa->callp = &p->p_sysent->sv_table[sa->code];

        if (params != NULL && sa->callp->sy_narg != 0)
                error = copyin(params, (caddr_t)sa->args,
                    (u_int)(sa->callp->sy_narg * sizeof(uint32_t)));
        else
                error = 0;

        if (error == 0) {
                td->td_retval[0] = 0;
                td->td_retval[1] = frame->tf_edx;
        }
                
        return (error);
}

#include "../../kern/subr_syscall.c"

/*
 * syscall - system call request C handler.  A system call is
 * essentially treated as a trap by reusing the frame layout.
 */
void
syscall(struct trapframe *frame)
{
        struct thread *td;
        register_t orig_tf_eflags;
        ksiginfo_t ksi;

#ifdef DIAGNOSTIC
        if (!(TRAPF_USERMODE(frame) &&
            (curpcb->pcb_flags & PCB_VM86CALL) == 0)) {
                panic("syscall");
                /* NOT REACHED */
        }
#endif
        trap_check_kstack();
        orig_tf_eflags = frame->tf_eflags;

        td = curthread;
        td->td_frame = frame;

        syscallenter(td);

        /*
         * Traced syscall.
         */
        if ((orig_tf_eflags & PSL_T) && !(orig_tf_eflags & PSL_VM)) {
                frame->tf_eflags &= ~PSL_T;
                ksiginfo_init_trap(&ksi);
                ksi.ksi_signo = SIGTRAP;
                ksi.ksi_code = TRAP_TRACE;
                ksi.ksi_addr = (void *)frame->tf_eip;
                trapsignal(td, &ksi);
        }

        KASSERT(PCB_USER_FPU(td->td_pcb),
            ("System call %s returning with kernel FPU ctx leaked",
             syscallname(td->td_proc, td->td_sa.code)));
        KASSERT(td->td_pcb->pcb_save == get_pcb_user_save_td(td),
            ("System call %s returning with mangled pcb_save",
             syscallname(td->td_proc, td->td_sa.code)));

        syscallret(td);
}