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

/*
 * Copyright (c) 1992, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright 2019 Joyent, Inc.
 */

#include <sys/param.h>
#include <sys/vmparam.h>
#include <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/systm.h>
#include <sys/signal.h>
#include <sys/stack.h>
#include <sys/cred.h>
#include <sys/cmn_err.h>
#include <sys/user.h>
#include <sys/privregs.h>
#include <sys/psw.h>
#include <sys/debug.h>
#include <sys/errno.h>
#include <sys/proc.h>
#include <sys/modctl.h>
#include <sys/var.h>
#include <sys/inline.h>
#include <sys/syscall.h>
#include <sys/ucontext.h>
#include <sys/cpuvar.h>
#include <sys/siginfo.h>
#include <sys/trap.h>
#include <sys/vtrace.h>
#include <sys/sysinfo.h>
#include <sys/procfs.h>
#include <sys/prsystm.h>
#include <c2/audit.h>
#include <sys/modctl.h>
#include <sys/aio_impl.h>
#include <sys/copyops.h>
#include <sys/priv.h>
#include <sys/msacct.h>

int syscalltrace = 0;
#ifdef SYSCALLTRACE
static kmutex_t systrace_lock;          /* syscall tracing lock */
#else
#define syscalltrace 0
#endif /* SYSCALLTRACE */

typedef int64_t (*llfcn_t)();   /* function returning long long */

int pre_syscall(void);
void post_syscall(long rval1, long rval2);
static krwlock_t *lock_syscall(struct sysent *, uint_t);
void deferred_singlestep_trap(caddr_t);

#ifdef _SYSCALL32_IMPL
#define LWP_GETSYSENT(lwp)      \
        (lwp_getdatamodel(lwp) == DATAMODEL_NATIVE ? sysent : sysent32)
#else
#define LWP_GETSYSENT(lwp)      (sysent)
#endif

/*
 * If watchpoints are active, don't make copying in of
 * system call arguments take a read watchpoint trap.
 */
static int
copyin_args(struct regs *rp, long *ap, uint_t nargs)
{
        greg_t *sp = 1 + (greg_t *)rp->r_sp;            /* skip ret addr */

        ASSERT(nargs <= MAXSYSARGS);

        return (copyin_nowatch(sp, ap, nargs * sizeof (*sp)));
}

#if defined(_SYSCALL32_IMPL)
static int
copyin_args32(struct regs *rp, long *ap, uint_t nargs)
{
        greg32_t *sp = 1 + (greg32_t *)rp->r_sp;        /* skip ret addr */
        uint32_t a32[MAXSYSARGS];
        int rc;

        ASSERT(nargs <= MAXSYSARGS);

        if ((rc = copyin_nowatch(sp, a32, nargs * sizeof (*sp))) == 0) {
                uint32_t *a32p = &a32[0];

                while (nargs--)
                        *ap++ = (ulong_t)*a32p++;
        }
        return (rc);
}
#define COPYIN_ARGS32   copyin_args32
#else
#define COPYIN_ARGS32   copyin_args
#endif

/*
 * Error handler for system calls where arg copy gets fault.
 */
static longlong_t
syscall_err()
{
        return (0);
}

/*
 * Corresponding sysent entry to allow syscall_entry caller
 * to invoke syscall_err.
 */
static struct sysent sysent_err =  {
        0, SE_32RVAL1, NULL, NULL, (llfcn_t)syscall_err
};

/*
 * Called from syscall() when a non-trivial 32-bit system call occurs.
 *      Sets up the args and returns a pointer to the handler.
 */
struct sysent *
syscall_entry(kthread_t *t, long *argp)
{
        klwp_t *lwp = ttolwp(t);
        struct regs *rp = lwptoregs(lwp);
        unsigned int code;
        struct sysent *callp;
        struct sysent *se = LWP_GETSYSENT(lwp);
        int error = 0;
        uint_t nargs;

        ASSERT(t == curthread && curthread->t_schedflag & TS_DONT_SWAP);

        lwp->lwp_ru.sysc++;
        lwp->lwp_eosys = NORMALRETURN;  /* assume this will be normal */

        /*
         * Set lwp_ap to point to the args, even if none are needed for this
         * system call.  This is for the loadable-syscall case where the
         * number of args won't be known until the system call is loaded, and
         * also maintains a non-NULL lwp_ap setup for get_syscall_args(). Note
         * that lwp_ap MUST be set to a non-NULL value _BEFORE_ t_sysnum is
         * set to non-zero; otherwise get_syscall_args(), seeing a non-zero
         * t_sysnum for this thread, will charge ahead and dereference lwp_ap.
         */
        lwp->lwp_ap = argp;             /* for get_syscall_args */

        code = rp->r_r0;
        t->t_sysnum = (short)code;
        callp = code >= NSYSCALL ? &nosys_ent : se + code;

        if ((t->t_pre_sys | syscalltrace) != 0) {
                error = pre_syscall();

                /*
                 * pre_syscall() has taken care so that lwp_ap is current;
                 * it either points to syscall-entry-saved amd64 regs,
                 * or it points to lwp_arg[], which has been re-copied from
                 * the ia32 ustack, but either way, it's a current copy after
                 * /proc has possibly mucked with the syscall args.
                 */

                if (error)
                        return (&sysent_err);   /* use dummy handler */
        }

        /*
         * Fetch the system call arguments to the kernel stack copy used
         * for syscall handling.
         * Note: for loadable system calls the number of arguments required
         * may not be known at this point, and will be zero if the system call
         * was never loaded.  Once the system call has been loaded, the number
         * of args is not allowed to be changed.
         */
        if ((nargs = (uint_t)callp->sy_narg) != 0 &&
            COPYIN_ARGS32(rp, argp, nargs)) {
                (void) set_errno(EFAULT);
                return (&sysent_err);   /* use dummy handler */
        }

        return (callp);         /* return sysent entry for caller */
}

void
syscall_exit(kthread_t *t, long rval1, long rval2)
{
        /*
         * Handle signals and other post-call events if necessary.
         */
        if ((t->t_post_sys_ast | syscalltrace) == 0) {
                klwp_t *lwp = ttolwp(t);
                struct regs *rp = lwptoregs(lwp);

                /*
                 * Normal return.
                 * Clear error indication and set return values.
                 */
                rp->r_ps &= ~PS_C;      /* reset carry bit */
                rp->r_r0 = rval1;
                rp->r_r1 = rval2;
                lwp->lwp_state = LWP_USER;
        } else {
                post_syscall(rval1, rval2);
        }
        t->t_sysnum = 0;                /* invalidate args */
}

/*
 * Perform pre-system-call processing, including stopping for tracing,
 * auditing, etc.
 *
 * This routine is called only if the t_pre_sys flag is set. Any condition
 * requiring pre-syscall handling must set the t_pre_sys flag. If the
 * condition is persistent, this routine will repost t_pre_sys.
 */
int
pre_syscall()
{
        kthread_t *t = curthread;
        unsigned code = t->t_sysnum;
        klwp_t *lwp = ttolwp(t);
        proc_t *p = ttoproc(t);
        int     repost;

        t->t_pre_sys = repost = 0;      /* clear pre-syscall processing flag */

        ASSERT(t->t_schedflag & TS_DONT_SWAP);

#if defined(DEBUG)
        /*
         * On the i386 kernel, lwp_ap points at the piece of the thread
         * stack that we copy the users arguments into.
         *
         * On the amd64 kernel, the syscall arguments in the rdi..r9
         * registers should be pointed at by lwp_ap.  If the args need to
         * be copied so that those registers can be changed without losing
         * the ability to get the args for /proc, they can be saved by
         * save_syscall_args(), and lwp_ap will be restored by post_syscall().
         */
        if (lwp_getdatamodel(lwp) == DATAMODEL_NATIVE) {
#if defined(_LP64)
                ASSERT(lwp->lwp_ap == (long *)&lwptoregs(lwp)->r_rdi);
        } else {
#endif
                ASSERT((caddr_t)lwp->lwp_ap > t->t_stkbase &&
                    (caddr_t)lwp->lwp_ap < t->t_stk);
        }
#endif  /* DEBUG */

        /*
         * Make sure the thread is holding the latest credentials for the
         * process.  The credentials in the process right now apply to this
         * thread for the entire system call.
         */
        if (t->t_cred != p->p_cred) {
                cred_t *oldcred = t->t_cred;
                /*
                 * DTrace accesses t_cred in probe context.  t_cred must
                 * always be either NULL, or point to a valid, allocated cred
                 * structure.
                 */
                t->t_cred = crgetcred();
                crfree(oldcred);
        }

        /*
         * From the proc(5) manual page:
         * When entry to a system call is being traced, the traced process
         * stops after having begun the call to the system but before the
         * system call arguments have been fetched from the process.
         */
        if (PTOU(p)->u_systrap) {
                if (prismember(&PTOU(p)->u_entrymask, code)) {
                        mutex_enter(&p->p_lock);
                        /*
                         * Recheck stop condition, now that lock is held.
                         */
                        if (PTOU(p)->u_systrap &&
                            prismember(&PTOU(p)->u_entrymask, code)) {
                                stop(PR_SYSENTRY, code);

                                /*
                                 * /proc may have modified syscall args,
                                 * either in regs for amd64 or on ustack
                                 * for ia32.  Either way, arrange to
                                 * copy them again, both for the syscall
                                 * handler and for other consumers in
                                 * post_syscall (like audit).  Here, we
                                 * only do amd64, and just set lwp_ap
                                 * back to the kernel-entry stack copy;
                                 * the syscall ml code redoes
                                 * move-from-regs to set up for the
                                 * syscall handler after we return.  For
                                 * ia32, save_syscall_args() below makes
                                 * an lwp_ap-accessible copy.
                                 */
#if defined(_LP64)
                                if (lwp_getdatamodel(lwp) == DATAMODEL_NATIVE) {
                                        lwp->lwp_argsaved = 0;
                                        lwp->lwp_ap =
                                            (long *)&lwptoregs(lwp)->r_rdi;
                                }
#endif
                        }
                        mutex_exit(&p->p_lock);
                }
                repost = 1;
        }

        /*
         * ia32 kernel, or ia32 proc on amd64 kernel: keep args in
         * lwp_arg for post-syscall processing, regardless of whether
         * they might have been changed in /proc above.
         */
#if defined(_LP64)
        if (lwp_getdatamodel(lwp) != DATAMODEL_NATIVE)
#endif
                (void) save_syscall_args();

        if (lwp->lwp_sysabort) {
                /*
                 * lwp_sysabort may have been set via /proc while the process
                 * was stopped on PR_SYSENTRY.  If so, abort the system call.
                 * Override any error from the copyin() of the arguments.
                 */
                lwp->lwp_sysabort = 0;
                (void) set_errno(EINTR);        /* forces post_sys */
                t->t_pre_sys = 1;       /* repost anyway */
                return (1);             /* don't do system call, return EINTR */
        }

        /*
         * begin auditing for this syscall if the c2audit module is loaded
         * and auditing is enabled
         */
        if (audit_active == C2AUDIT_LOADED) {
                uint32_t auditing = au_zone_getstate(NULL);

                if (auditing & AU_AUDIT_MASK) {
                        int error;
                        if (error = audit_start(T_SYSCALL, code, auditing, \
                            0, lwp)) {
                                t->t_pre_sys = 1;       /* repost anyway */
                                (void) set_errno(error);
                                return (1);
                        }
                        repost = 1;
                }
        }

#ifdef SYSCALLTRACE
        if (syscalltrace) {
                int i;
                long *ap;
                char *cp;
                char *sysname;
                struct sysent *callp;

                if (code >= NSYSCALL)
                        callp = &nosys_ent;     /* nosys has no args */
                else
                        callp = LWP_GETSYSENT(lwp) + code;
                (void) save_syscall_args();
                mutex_enter(&systrace_lock);
                printf("%d: ", p->p_pid);
                if (code >= NSYSCALL) {
                        printf("0x%x", code);
                } else {
                        sysname = mod_getsysname(code);
                        printf("%s[0x%x/0x%p]", sysname == NULL ? "NULL" :
                            sysname, code, callp->sy_callc);
                }
                cp = "(";
                for (i = 0, ap = lwp->lwp_ap; i < callp->sy_narg; i++, ap++) {
                        printf("%s%lx", cp, *ap);
                        cp = ", ";
                }
                if (i)
                        printf(")");
                printf(" %s id=0x%p\n", PTOU(p)->u_comm, curthread);
                mutex_exit(&systrace_lock);
        }
#endif /* SYSCALLTRACE */

        /*
         * If there was a continuing reason for pre-syscall processing,
         * set the t_pre_sys flag for the next system call.
         */
        if (repost)
                t->t_pre_sys = 1;
        lwp->lwp_error = 0;     /* for old drivers */
        lwp->lwp_badpriv = PRIV_NONE;
        return (0);
}


/*
 * Post-syscall processing.  Perform abnormal system call completion
 * actions such as /proc tracing, profiling, signals, preemption, etc.
 *
 * This routine is called only if t_post_sys, t_sig_check, or t_astflag is set.
 * Any condition requiring pre-syscall handling must set one of these.
 * If the condition is persistent, this routine will repost t_post_sys.
 */
void
post_syscall(long rval1, long rval2)
{
        kthread_t *t = curthread;
        klwp_t *lwp = ttolwp(t);
        proc_t *p = ttoproc(t);
        struct regs *rp = lwptoregs(lwp);
        uint_t  error;
        uint_t  code = t->t_sysnum;
        int     repost = 0;
        int     proc_stop = 0;          /* non-zero if stopping */
        int     sigprof = 0;            /* non-zero if sending SIGPROF */

        t->t_post_sys = 0;

        error = lwp->lwp_errno;

        /*
         * Code can be zero if this is a new LWP returning after a forkall(),
         * other than the one which matches the one in the parent which called
         * forkall().  In these LWPs, skip most of post-syscall activity.
         */
        if (code == 0)
                goto sig_check;
        /*
         * If the trace flag is set, mark the lwp to take a single-step trap
         * on return to user level (below). The x86 lcall interface and
         * sysenter has already done this, and turned off the flag, but
         * amd64 syscall interface has not.
         */
        if (rp->r_ps & PS_T) {
                lwp->lwp_pcb.pcb_flags |= DEBUG_PENDING;
                rp->r_ps &= ~PS_T;
                aston(curthread);
        }

        /* put out audit record for this syscall */
        if (AU_AUDITING()) {
                rval_t  rval;

                /* XX64 -- truncation of 64-bit return values? */
                rval.r_val1 = (int)rval1;
                rval.r_val2 = (int)rval2;
                audit_finish(T_SYSCALL, code, error, &rval);
                repost = 1;
        }

        if (curthread->t_pdmsg != NULL) {
                char *m = curthread->t_pdmsg;

                uprintf("%s", m);
                kmem_free(m, strlen(m) + 1);
                curthread->t_pdmsg = NULL;
        }

        /*
         * If we're going to stop for /proc tracing, set the flag and
         * save the arguments so that the return values don't smash them.
         */
        if (PTOU(p)->u_systrap) {
                if (prismember(&PTOU(p)->u_exitmask, code)) {
                        if (lwp_getdatamodel(lwp) == DATAMODEL_LP64)
                                (void) save_syscall_args();
                        proc_stop = 1;
                }
                repost = 1;
        }

        /*
         * Similarly check to see if SIGPROF might be sent.
         */
        if (curthread->t_rprof != NULL &&
            curthread->t_rprof->rp_anystate != 0) {
                if (lwp_getdatamodel(lwp) == DATAMODEL_LP64)
                        (void) save_syscall_args();
                sigprof = 1;
        }

        if (lwp->lwp_eosys == NORMALRETURN) {
                if (error == 0) {
#ifdef SYSCALLTRACE
                        if (syscalltrace) {
                                mutex_enter(&systrace_lock);
                                printf(
                                    "%d: r_val1=0x%lx, r_val2=0x%lx, id 0x%p\n",
                                    p->p_pid, rval1, rval2, curthread);
                                mutex_exit(&systrace_lock);
                        }
#endif /* SYSCALLTRACE */
                        rp->r_ps &= ~PS_C;
                        rp->r_r0 = rval1;
                        rp->r_r1 = rval2;
                } else {
                        int sig;
#ifdef SYSCALLTRACE
                        if (syscalltrace) {
                                mutex_enter(&systrace_lock);
                                printf("%d: error=%d, id 0x%p\n",
                                    p->p_pid, error, curthread);
                                mutex_exit(&systrace_lock);
                        }
#endif /* SYSCALLTRACE */
                        if (error == EINTR && t->t_activefd.a_stale)
                                error = EBADF;
                        if (error == EINTR &&
                            (sig = lwp->lwp_cursig) != 0 &&
                            sigismember(&PTOU(p)->u_sigrestart, sig) &&
                            PTOU(p)->u_signal[sig - 1] != SIG_DFL &&
                            PTOU(p)->u_signal[sig - 1] != SIG_IGN)
                                error = ERESTART;
                        rp->r_r0 = error;
                        rp->r_ps |= PS_C;
                }
        }

        /*
         * From the proc(5) manual page:
         * When exit from a system call is being traced, the traced process
         * stops on completion of the system call just prior to checking for
         * signals and returning to user level.  At this point all return
         * values have been stored into the traced process's saved registers.
         */
        if (proc_stop) {
                mutex_enter(&p->p_lock);
                if (PTOU(p)->u_systrap &&
                    prismember(&PTOU(p)->u_exitmask, code))
                        stop(PR_SYSEXIT, code);
                mutex_exit(&p->p_lock);
        }

        /*
         * If we are the parent returning from a successful
         * vfork, wait for the child to exec or exit.
         * This code must be here and not in the bowels of the system
         * so that /proc can intercept exit from vfork in a timely way.
         */
        if (t->t_flag & T_VFPARENT) {
                ASSERT(code == SYS_vfork || code == SYS_forksys);
                ASSERT(rp->r_r1 == 0 && error == 0);
                vfwait((pid_t)rval1);
                t->t_flag &= ~T_VFPARENT;
        }

        /*
         * If profiling is active, bill the current PC in user-land
         * and keep reposting until profiling is disabled.
         */
        if (p->p_prof.pr_scale) {
                if (lwp->lwp_oweupc)
                        profil_tick(rp->r_pc);
                repost = 1;
        }

sig_check:
        /*
         * Reset flag for next time.
         * We must do this after stopping on PR_SYSEXIT
         * because /proc uses the information in lwp_eosys.
         */
        lwp->lwp_eosys = NORMALRETURN;
        clear_stale_fd();
        t->t_flag &= ~T_FORKALL;

        if (t->t_astflag | t->t_sig_check) {
                /*
                 * Turn off the AST flag before checking all the conditions that
                 * may have caused an AST.  This flag is on whenever a signal or
                 * unusual condition should be handled after the next trap or
                 * syscall.
                 */
                astoff(t);
                /*
                 * If a single-step trap occurred on a syscall (see trap())
                 * recognize it now.  Do this before checking for signals
                 * because deferred_singlestep_trap() may generate a SIGTRAP to
                 * the LWP or may otherwise mark the LWP to call issig(FORREAL).
                 */
                if (lwp->lwp_pcb.pcb_flags & DEBUG_PENDING)
                        deferred_singlestep_trap((caddr_t)rp->r_pc);

                t->t_sig_check = 0;

                /*
                 * The following check is legal for the following reasons:
                 *      1) The thread we are checking, is ourselves, so there is
                 *         no way the proc can go away.
                 *      2) The only time we need to be protected by the
                 *         lock is if the binding is changed.
                 *
                 *      Note we will still take the lock and check the binding
                 *      if the condition was true without the lock held.  This
                 *      prevents lock contention among threads owned by the
                 *      same proc.
                 */

                if (curthread->t_proc_flag & TP_CHANGEBIND) {
                        mutex_enter(&p->p_lock);
                        if (curthread->t_proc_flag & TP_CHANGEBIND) {
                                timer_lwpbind();
                                curthread->t_proc_flag &= ~TP_CHANGEBIND;
                        }
                        mutex_exit(&p->p_lock);
                }

                /*
                 * for kaio requests on the special kaio poll queue,
                 * copyout their results to user memory.
                 */
                if (p->p_aio)
                        aio_cleanup(0);
                /*
                 * If this LWP was asked to hold, call holdlwp(), which will
                 * stop.  holdlwps() sets this up and calls pokelwps() which
                 * sets the AST flag.
                 *
                 * Also check TP_EXITLWP, since this is used by fresh new LWPs
                 * through lwp_rtt().  That flag is set if the lwp_create(2)
                 * syscall failed after creating the LWP.
                 */
                if (ISHOLD(p) || (t->t_proc_flag & TP_EXITLWP))
                        holdlwp();

                /*
                 * All code that sets signals and makes ISSIG_PENDING
                 * evaluate true must set t_sig_check afterwards.
                 */
                if (ISSIG_PENDING(t, lwp, p)) {
                        if (issig(FORREAL))
                                psig();
                        t->t_sig_check = 1;     /* recheck next time */
                }

                if (sigprof) {
                        int nargs = (code > 0 && code < NSYSCALL)?
                            LWP_GETSYSENT(lwp)[code].sy_narg : 0;
                        realsigprof(code, nargs, error);
                        t->t_sig_check = 1;     /* recheck next time */
                }

                /*
                 * If a performance counter overflow interrupt was
                 * delivered *during* the syscall, then re-enable the
                 * AST so that we take a trip through trap() to cause
                 * the SIGEMT to be delivered.
                 */
                if (lwp->lwp_pcb.pcb_flags & CPC_OVERFLOW)
                        aston(t);

                /*
                 * /proc can't enable/disable the trace bit itself
                 * because that could race with the call gate used by
                 * system calls via "lcall". If that happened, an
                 * invalid EFLAGS would result. prstep()/prnostep()
                 * therefore schedule an AST for the purpose.
                 */
                if (lwp->lwp_pcb.pcb_flags & REQUEST_STEP) {
                        lwp->lwp_pcb.pcb_flags &= ~REQUEST_STEP;
                        rp->r_ps |= PS_T;
                }
                if (lwp->lwp_pcb.pcb_flags & REQUEST_NOSTEP) {
                        lwp->lwp_pcb.pcb_flags &= ~REQUEST_NOSTEP;
                        rp->r_ps &= ~PS_T;
                }
        }

        lwp->lwp_errno = 0;             /* clear error for next time */

        /*
         * Set state to LWP_USER here so preempt won't give us a kernel
         * priority if it occurs after this point.  Call CL_TRAPRET() to
         * restore the user-level priority.
         *
         * It is important that no locks (other than spinlocks) be entered
         * after this point before returning to user mode (unless lwp_state
         * is set back to LWP_SYS).
         *
         * XXX Sampled times past this point are charged to the user.
         */
        lwp->lwp_state = LWP_USER;

        if (t->t_trapret) {
                t->t_trapret = 0;
                thread_lock(t);
                CL_TRAPRET(t);
                thread_unlock(t);
        }
        if (CPU->cpu_runrun || t->t_schedflag & TS_ANYWAITQ)
                preempt();
        prunstop();

        lwp->lwp_errno = 0;             /* clear error for next time */

        /*
         * The thread lock must be held in order to clear sysnum and reset
         * lwp_ap atomically with respect to other threads in the system that
         * may be looking at the args via lwp_ap from get_syscall_args().
         */

        thread_lock(t);
        t->t_sysnum = 0;                /* no longer in a system call */

        if (lwp_getdatamodel(lwp) == DATAMODEL_NATIVE) {
#if defined(_LP64)
                /*
                 * In case the args were copied to the lwp, reset the
                 * pointer so the next syscall will have the right
                 * lwp_ap pointer.
                 */
                lwp->lwp_ap = (long *)&rp->r_rdi;
        } else {
#endif
                lwp->lwp_ap = NULL;     /* reset on every syscall entry */
        }
        thread_unlock(t);

        lwp->lwp_argsaved = 0;

        /*
         * If there was a continuing reason for post-syscall processing,
         * set the t_post_sys flag for the next system call.
         */
        if (repost)
                t->t_post_sys = 1;

        /*
         * If there is a ustack registered for this lwp, and the stack rlimit
         * has been altered, read in the ustack. If the saved stack rlimit
         * matches the bounds of the ustack, update the ustack to reflect
         * the new rlimit. If the new stack rlimit is RLIM_INFINITY, disable
         * stack checking by setting the size to 0.
         */
        if (lwp->lwp_ustack != 0 && lwp->lwp_old_stk_ctl != 0) {
                rlim64_t new_size;
                caddr_t top;
                stack_t stk;
                struct rlimit64 rl;

                mutex_enter(&p->p_lock);
                new_size = p->p_stk_ctl;
                top = p->p_usrstack;
                (void) rctl_rlimit_get(rctlproc_legacy[RLIMIT_STACK], p, &rl);
                mutex_exit(&p->p_lock);

                if (rl.rlim_cur == RLIM64_INFINITY)
                        new_size = 0;

                if (copyin((stack_t *)lwp->lwp_ustack, &stk,
                    sizeof (stack_t)) == 0 &&
                    (stk.ss_size == lwp->lwp_old_stk_ctl ||
                    stk.ss_size == 0) &&
                    stk.ss_sp == top - stk.ss_size) {
                        stk.ss_sp = (void *)((uintptr_t)stk.ss_sp +
                            stk.ss_size - (uintptr_t)new_size);
                        stk.ss_size = new_size;

                        (void) copyout(&stk, (stack_t *)lwp->lwp_ustack,
                            sizeof (stack_t));
                }

                lwp->lwp_old_stk_ctl = 0;
        }
}

/*
 * Called from post_syscall() when a deferred singlestep is to be taken.
 */
void
deferred_singlestep_trap(caddr_t pc)
{
        proc_t *p = ttoproc(curthread);
        klwp_t *lwp = ttolwp(curthread);
        pcb_t *pcb = &lwp->lwp_pcb;
        uint_t fault = 0;
        k_siginfo_t siginfo;

        bzero(&siginfo, sizeof (siginfo));

        /*
         * If both NORMAL_STEP and WATCH_STEP are in
         * effect, give precedence to WATCH_STEP.
         * If neither is set, user must have set the
         * PS_T bit in %efl; treat this as NORMAL_STEP.
         */
        if ((fault = undo_watch_step(&siginfo)) == 0 &&
            ((pcb->pcb_flags & NORMAL_STEP) ||
            !(pcb->pcb_flags & WATCH_STEP))) {
                siginfo.si_signo = SIGTRAP;
                siginfo.si_code = TRAP_TRACE;
                siginfo.si_addr  = pc;
                fault = FLTTRACE;
        }
        pcb->pcb_flags &= ~(DEBUG_PENDING|NORMAL_STEP|WATCH_STEP);

        if (fault) {
                /*
                 * Remember the fault and fault adddress
                 * for real-time (SIGPROF) profiling.
                 */
                lwp->lwp_lastfault = fault;
                lwp->lwp_lastfaddr = siginfo.si_addr;
                /*
                 * If a debugger has declared this fault to be an
                 * event of interest, stop the lwp.  Otherwise just
                 * deliver the associated signal.
                 */
                if (prismember(&p->p_fltmask, fault) &&
                    stop_on_fault(fault, &siginfo) == 0)
                        siginfo.si_signo = 0;
        }

        if (siginfo.si_signo)
                trapsig(&siginfo, 1);
}

/*
 * nonexistent system call-- signal lwp (may want to handle it)
 * flag error if lwp won't see signal immediately
 */
int64_t
nosys(void)
{
        tsignal(curthread, SIGSYS);
        return (set_errno(ENOSYS));
}

int
nosys32(void)
{
        return (nosys());
}

/*
 * Execute a 32-bit system call on behalf of the current thread.
 */
void
dosyscall(void)
{
        /*
         * Need space on the stack to store syscall arguments.
         */
        long            syscall_args[MAXSYSARGS];
        struct sysent   *se;
        int64_t         ret;

        syscall_mstate(LMS_TRAP, LMS_SYSTEM);

        ASSERT(curproc->p_model == DATAMODEL_ILP32);

        CPU_STATS_ENTER_K();
        CPU_STATS_ADDQ(CPU, sys, syscall, 1);
        CPU_STATS_EXIT_K();

        se = syscall_entry(curthread, syscall_args);

        /*
         * syscall_entry() copied all 8 arguments into syscall_args.
         */
        ret = se->sy_callc(syscall_args[0], syscall_args[1], syscall_args[2],
            syscall_args[3], syscall_args[4], syscall_args[5], syscall_args[6],
            syscall_args[7]);

        syscall_exit(curthread, (int)ret & 0xffffffffu, (int)(ret >> 32));
        syscall_mstate(LMS_SYSTEM, LMS_TRAP);
}

/*
 * Get the arguments to the current system call. See comment atop
 * save_syscall_args() regarding lwp_ap usage.
 */

uint_t
get_syscall_args(klwp_t *lwp, long *argp, int *nargsp)
{
        kthread_t       *t = lwptot(lwp);
        ulong_t mask = 0xfffffffful;
        uint_t  code;
        long    *ap;
        int     nargs;

#if defined(_LP64)
        if (lwp_getdatamodel(lwp) == DATAMODEL_LP64)
                mask = 0xfffffffffffffffful;
#endif

        /*
         * The thread lock must be held while looking at the arguments to ensure
         * they don't go away via post_syscall().
         * get_syscall_args() is the only routine to read them which is callable
         * outside the LWP in question and hence the only one that must be
         * synchronized in this manner.
         */
        thread_lock(t);

        code = t->t_sysnum;
        ap = lwp->lwp_ap;

        thread_unlock(t);

        if (code != 0 && code < NSYSCALL) {
                nargs = LWP_GETSYSENT(lwp)[code].sy_narg;

                ASSERT(nargs <= MAXSYSARGS);

                *nargsp = nargs;
                while (nargs-- > 0)
                        *argp++ = *ap++ & mask;
        } else {
                *nargsp = 0;
        }

        return (code);
}

#ifdef _SYSCALL32_IMPL
/*
 * Get the arguments to the current 32-bit system call.
 */
uint_t
get_syscall32_args(klwp_t *lwp, int *argp, int *nargsp)
{
        long args[MAXSYSARGS];
        uint_t i, code;

        code = get_syscall_args(lwp, args, nargsp);

        for (i = 0; i != *nargsp; i++)
                *argp++ = (int)args[i];
        return (code);
}
#endif

/*
 * Save the system call arguments in a safe place.
 *
 * On the i386 kernel:
 *
 *      Copy the users args prior to changing the stack or stack pointer.
 *      This is so /proc will be able to get a valid copy of the
 *      args from the user stack even after the user stack has been changed.
 *      Note that the kernel stack copy of the args may also have been
 *      changed by a system call handler which takes C-style arguments.
 *
 *      Note that this may be called by stop() from trap().  In that case
 *      t_sysnum will be zero (syscall_exit clears it), so no args will be
 *      copied.
 *
 * On the amd64 kernel:
 *
 *      For 64-bit applications, lwp->lwp_ap normally points to %rdi..%r9
 *      in the reg structure. If the user is going to change the argument
 *      registers, rax, or the stack and might want to get the args (for
 *      /proc tracing), it must copy the args elsewhere via save_syscall_args().
 *
 *      For 32-bit applications, lwp->lwp_ap normally points to a copy of
 *      the system call arguments on the kernel stack made from the user
 *      stack.  Copy the args prior to change the stack or stack pointer.
 *      This is so /proc will be able to get a valid copy of the args
 *      from the user stack even after that stack has been changed.
 *
 *      This may be called from stop() even when we're not in a system call.
 *      Since there's no easy way to tell, this must be safe (not panic).
 *      If the copyins get data faults, return non-zero.
 */
int
save_syscall_args()
{
        kthread_t       *t = curthread;
        klwp_t          *lwp = ttolwp(t);
        uint_t          code = t->t_sysnum;
        uint_t          nargs;

        if (lwp->lwp_argsaved || code == 0)
                return (0);             /* args already saved or not needed */

        if (code >= NSYSCALL) {
                nargs = 0;              /* illegal syscall */
        } else {
                struct sysent *se = LWP_GETSYSENT(lwp);
                struct sysent *callp = se + code;

                nargs = callp->sy_narg;
                if (LOADABLE_SYSCALL(callp) && nargs == 0) {
                        krwlock_t       *module_lock;

                        /*
                         * Find out how many arguments the system
                         * call uses.
                         *
                         * We have the property that loaded syscalls
                         * never change the number of arguments they
                         * use after they've been loaded once.  This
                         * allows us to stop for /proc tracing without
                         * holding the module lock.
                         * /proc is assured that sy_narg is valid.
                         */
                        module_lock = lock_syscall(se, code);
                        nargs = callp->sy_narg;
                        rw_exit(module_lock);
                }
        }

        /*
         * Fetch the system call arguments.
         */
        if (nargs == 0)
                goto out;

        ASSERT(nargs <= MAXSYSARGS);

        if (lwp_getdatamodel(lwp) == DATAMODEL_NATIVE) {
#if defined(_LP64)
                struct regs *rp = lwptoregs(lwp);

                lwp->lwp_arg[0] = rp->r_rdi;
                lwp->lwp_arg[1] = rp->r_rsi;
                lwp->lwp_arg[2] = rp->r_rdx;
                lwp->lwp_arg[3] = rp->r_rcx;
                lwp->lwp_arg[4] = rp->r_r8;
                lwp->lwp_arg[5] = rp->r_r9;
                if (nargs > 6 && copyin_args(rp, &lwp->lwp_arg[6], nargs - 6))
                        return (-1);
        } else {
#endif
                if (COPYIN_ARGS32(lwptoregs(lwp), lwp->lwp_arg, nargs))
                        return (-1);
        }
out:
        lwp->lwp_ap = lwp->lwp_arg;
        lwp->lwp_argsaved = 1;
        t->t_post_sys = 1;      /* so lwp_ap will be reset */
        return (0);
}

void
reset_syscall_args(void)
{
        ttolwp(curthread)->lwp_argsaved = 0;
}

/*
 * Call a system call which takes a pointer to the user args struct and
 * a pointer to the return values.  This is a bit slower than the standard
 * C arg-passing method in some cases.
 */
int64_t
syscall_ap(void)
{
        uint_t  error;
        struct sysent *callp;
        rval_t  rval;
        kthread_t *t = curthread;
        klwp_t  *lwp = ttolwp(t);
        struct regs *rp = lwptoregs(lwp);

        callp = LWP_GETSYSENT(lwp) + t->t_sysnum;

        /*
         * If the arguments don't fit in registers %rdi-%r9, make sure they
         * have been copied to the lwp_arg array.
         */
        if (callp->sy_narg > 6 && save_syscall_args())
                return ((int64_t)set_errno(EFAULT));

        rval.r_val1 = 0;
        rval.r_val2 = rp->r_r1;
        lwp->lwp_error = 0;     /* for old drivers */
        error = (*(callp->sy_call))(lwp->lwp_ap, &rval);
        if (error)
                return ((longlong_t)set_errno(error));
        return (rval.r_vals);
}

/*
 * Load system call module.
 *      Returns with pointer to held read lock for module.
 */
static krwlock_t *
lock_syscall(struct sysent *table, uint_t code)
{
        krwlock_t       *module_lock;
        struct modctl   *modp;
        int             id;
        struct sysent   *callp;

        callp = table + code;
        module_lock = callp->sy_lock;

        /*
         * Optimization to only call modload if we don't have a loaded
         * syscall.
         */
        rw_enter(module_lock, RW_READER);
        if (LOADED_SYSCALL(callp))
                return (module_lock);
        rw_exit(module_lock);

        for (;;) {
                if ((id = modload("sys", syscallnames[code])) == -1)
                        break;

                /*
                 * If we loaded successfully at least once, the modctl
                 * will still be valid, so we try to grab it by filename.
                 * If this call fails, it's because the mod_filename
                 * was changed after the call to modload() (mod_hold_by_name()
                 * is the likely culprit).  We can safely just take
                 * another lap if this is the case;  the modload() will
                 * change the mod_filename back to one by which we can
                 * find the modctl.
                 */
                modp = mod_find_by_filename("sys", syscallnames[code]);

                if (modp == NULL)
                        continue;

                mutex_enter(&mod_lock);

                if (!modp->mod_installed) {
                        mutex_exit(&mod_lock);
                        continue;
                }
                break;
        }
        rw_enter(module_lock, RW_READER);

        if (id != -1)
                mutex_exit(&mod_lock);

        return (module_lock);
}

/*
 * Loadable syscall support.
 *      If needed, load the module, then reserve it by holding a read
 *      lock for the duration of the call.
 *      Later, if the syscall is not unloadable, it could patch the vector.
 */
/*ARGSUSED*/
int64_t
loadable_syscall(
    long a0, long a1, long a2, long a3,
    long a4, long a5, long a6, long a7)
{
        klwp_t *lwp = ttolwp(curthread);
        int64_t rval;
        struct sysent *callp;
        struct sysent *se = LWP_GETSYSENT(lwp);
        krwlock_t *module_lock;
        int code, error = 0;

        code = curthread->t_sysnum;
        callp = se + code;

        /*
         * Try to autoload the system call if necessary
         */
        module_lock = lock_syscall(se, code);

        /*
         * we've locked either the loaded syscall or nosys
         */

        if (lwp_getdatamodel(lwp) == DATAMODEL_NATIVE) {
#if defined(_LP64)
                if (callp->sy_flags & SE_ARGC) {
                        rval = (int64_t)(*callp->sy_call)(a0, a1, a2, a3,
                            a4, a5);
                } else {
                        rval = syscall_ap();
                }
        } else {
#endif
                /*
                 * Now that it's loaded, make sure enough args were copied.
                 */
                if (COPYIN_ARGS32(lwptoregs(lwp), lwp->lwp_ap, callp->sy_narg))
                        error = EFAULT;
                if (error) {
                        rval = set_errno(error);
                } else if (callp->sy_flags & SE_ARGC) {
                        rval = (int64_t)(*callp->sy_call)(lwp->lwp_ap[0],
                            lwp->lwp_ap[1], lwp->lwp_ap[2], lwp->lwp_ap[3],
                            lwp->lwp_ap[4], lwp->lwp_ap[5]);
                } else {
                        rval = syscall_ap();
                }
        }

        rw_exit(module_lock);
        return (rval);
}

/*
 * Indirect syscall handled in libc on x86 architectures
 */
int64_t
indir()
{
        return (nosys());
}

/*
 * set_errno - set an error return from the current system call.
 *      This could be a macro.
 *      This returns the value it is passed, so that the caller can
 *      use tail-recursion-elimination and do return (set_errno(ERRNO));
 */
uint_t
set_errno(uint_t error)
{
        ASSERT(error != 0);             /* must not be used to clear errno */

        curthread->t_post_sys = 1;      /* have post_syscall do error return */
        return (ttolwp(curthread)->lwp_errno = error);
}

/*
 * set_proc_pre_sys - Set pre-syscall processing for entire process.
 */
void
set_proc_pre_sys(proc_t *p)
{
        kthread_t       *t;
        kthread_t       *first;

        ASSERT(MUTEX_HELD(&p->p_lock));

        t = first = p->p_tlist;
        do {
                t->t_pre_sys = 1;
        } while ((t = t->t_forw) != first);
}

/*
 * set_proc_post_sys - Set post-syscall processing for entire process.
 */
void
set_proc_post_sys(proc_t *p)
{
        kthread_t       *t;
        kthread_t       *first;

        ASSERT(MUTEX_HELD(&p->p_lock));

        t = first = p->p_tlist;
        do {
                t->t_post_sys = 1;
        } while ((t = t->t_forw) != first);
}

/*
 * set_proc_sys - Set pre- and post-syscall processing for entire process.
 */
void
set_proc_sys(proc_t *p)
{
        kthread_t       *t;
        kthread_t       *first;

        ASSERT(MUTEX_HELD(&p->p_lock));

        t = first = p->p_tlist;
        do {
                t->t_pre_sys = 1;
                t->t_post_sys = 1;
        } while ((t = t->t_forw) != first);
}

/*
 * set_all_proc_sys - set pre- and post-syscall processing flags for all
 * user processes.
 *
 * This is needed when auditing, tracing, or other facilities which affect
 * all processes are turned on.
 */
void
set_all_proc_sys()
{
        kthread_t       *t;
        kthread_t       *first;

        mutex_enter(&pidlock);
        t = first = curthread;
        do {
                t->t_pre_sys = 1;
                t->t_post_sys = 1;
        } while ((t = t->t_next) != first);
        mutex_exit(&pidlock);
}

/*
 * set_all_zone_usr_proc_sys - set pre- and post-syscall processing flags for
 * all user processes running in the zone of the current process
 *
 * This is needed when auditing, tracing, or other facilities which affect
 * all processes are turned on.
 */
void
set_all_zone_usr_proc_sys(zoneid_t zoneid)
{
        proc_t      *p;
        kthread_t   *t;

        mutex_enter(&pidlock);
        for (p = practive; p != NULL; p = p->p_next) {
                /* skip kernel and incomplete processes */
                if (p->p_exec == NULLVP || p->p_as == &kas ||
                    p->p_stat == SIDL || p->p_stat == SZOMB ||
                    (p->p_flag & (SSYS | SEXITING | SEXITLWPS)))
                        continue;
                /*
                 * Only processes in the given zone (eventually in
                 * all zones) are taken into account
                 */
                if (zoneid == ALL_ZONES || p->p_zone->zone_id == zoneid) {
                        mutex_enter(&p->p_lock);
                        if ((t = p->p_tlist) == NULL) {
                                mutex_exit(&p->p_lock);
                                continue;
                        }
                        /*
                         * Set pre- and post-syscall processing flags
                         * for all threads of the process
                         */
                        do {
                                t->t_pre_sys = 1;
                                t->t_post_sys = 1;
                        } while (p->p_tlist != (t = t->t_forw));
                        mutex_exit(&p->p_lock);
                }
        }
        mutex_exit(&pidlock);
}

/*
 * set_proc_ast - Set asynchronous service trap (AST) flag for all
 * threads in process.
 */
void
set_proc_ast(proc_t *p)
{
        kthread_t       *t;
        kthread_t       *first;

        ASSERT(MUTEX_HELD(&p->p_lock));

        t = first = p->p_tlist;
        do {
                aston(t);
        } while ((t = t->t_forw) != first);
}