[apple/xnu.git] / osfmk / ppc / pcb.c

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */
/* 
 * Copyright (c) 1990,1991,1992 The University of Utah and
 * the Center for Software Science (CSS).  All rights reserved.
 *
 * Permission to use, copy, modify and distribute this software is hereby
 * granted provided that (1) source code retains these copyright, permission,
 * and disclaimer notices, and (2) redistributions including binaries
 * reproduce the notices in supporting documentation, and (3) all advertising
 * materials mentioning features or use of this software display the following
 * acknowledgement: ``This product includes software developed by the Center
 * for Software Science at the University of Utah.''
 *
 * THE UNIVERSITY OF UTAH AND CSS ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS
 * IS" CONDITION.  THE UNIVERSITY OF UTAH AND CSS DISCLAIM ANY LIABILITY OF
 * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * CSS requests users of this software to return to css-dist@cs.utah.edu any
 * improvements that they make and grant CSS redistribution rights.
 *
 *      Utah $Hdr: pcb.c 1.23 92/06/27$
 */

#include <cpus.h>
#include <debug.h>

#include <types.h>
#include <kern/task.h>
#include <kern/thread.h>
#include <kern/thread_act.h>
#include <kern/thread_swap.h>
#include <mach/thread_status.h>
#include <vm/vm_kern.h>
#include <kern/mach_param.h>

#include <kern/misc_protos.h>
#include <ppc/misc_protos.h>
#include <ppc/fpu_protos.h>
#include <ppc/exception.h>
#include <ppc/proc_reg.h>
#include <kern/spl.h>
#include <ppc/pmap.h>
#include <ppc/trap.h>
#include <ppc/mappings.h>
#include <ppc/savearea.h>
#include <ppc/Firmware.h>
#include <ppc/asm.h>
#include <ppc/thread_act.h>
#include <ppc/vmachmon.h>
#include <ppc/low_trace.h>

#include <sys/kdebug.h>

extern int              real_ncpus;                                             /* Number of actual CPUs */
extern struct   Saveanchor saveanchor;                  /* Aliged savearea anchor */

/*
 * These constants are dumb. They should not be in asm.h!
 */

#define KF_SIZE         (FM_SIZE+ARG_SIZE+FM_REDZONE)

#if DEBUG
int   fpu_trap_count = 0;
int   fpu_switch_count = 0;
int   vec_trap_count = 0;
int   vec_switch_count = 0;
#endif

extern struct thread_shuttle    *Switch_context(
                                        struct thread_shuttle   *old,
                                        void                    (*cont)(void),
                                        struct thread_shuttle   *new);


#if     MACH_LDEBUG || MACH_KDB
void            log_thread_action (char *, long, long, long);
#endif


/*
 * consider_machine_collect: try to collect machine-dependent pages
 */
void
consider_machine_collect()
{
    /*
     * none currently available
     */
        return;
}

void
consider_machine_adjust()
{
        consider_mapping_adjust();
}


/*
 * stack_attach: Attach a kernel stack to a thread.
 */
void
machine_kernel_stack_init(
        struct thread_shuttle *thread,
        void            (*start_pos)(thread_t))
{
    vm_offset_t stack;
    unsigned int                        *kss;
        struct savearea                 *sv;

    assert(thread->top_act->mact.pcb);
    assert(thread->kernel_stack);
    stack = thread->kernel_stack;

#if     MACH_ASSERT
    if (watchacts & WA_PCB)
                printf("machine_kernel_stack_init(thr=%x,stk=%x,start_pos=%x)\n", thread,stack,start_pos);
#endif  /* MACH_ASSERT */
        
        kss = (unsigned int *)STACK_IKS(stack);
        sv=(savearea *)(thread->top_act->mact.pcb);                     /* This for the sake of C */

        sv->save_lr = (unsigned int) start_pos;                 /* Set up the execution address */
        sv->save_srr0 = (unsigned int) start_pos;               /* Here too */
        sv->save_srr1 = MSR_SUPERVISOR_INT_OFF;                         /* Set the normal running MSR */
        sv->save_r1 = (vm_offset_t) ((int)kss - KF_SIZE);       /* Point to the top frame on the stack */
        sv->save_xfpscrpad = 0;                                                         /* Start with a clear fpscr */
        sv->save_xfpscr = 0;                                                            /* Start with a clear fpscr */

        *((int *)sv->save_r1) = 0;                                                      /* Zero the frame backpointer */
        thread->top_act->mact.ksp = 0;                                          /* Show that the kernel stack is in use already */

}

/*
 * switch_context: Switch from one thread to another, needed for
 *                 switching of space
 * 
 */
struct thread_shuttle*
switch_context(
        struct thread_shuttle *old,
        void (*continuation)(void),
        struct thread_shuttle *new)
{
        register thread_act_t old_act = old->top_act, new_act = new->top_act;
        register struct thread_shuttle* retval;
        pmap_t  new_pmap;
#if     MACH_LDEBUG || MACH_KDB
        log_thread_action("switch", 
                          (long)old, 
                          (long)new, 
                          (long)__builtin_return_address(0));
#endif
        per_proc_info[cpu_number()].old_thread = old;
        per_proc_info[cpu_number()].cpu_flags &= ~traceBE;  /* disable branch tracing if on */
        assert(old_act->kernel_loaded ||
               active_stacks[cpu_number()] == old_act->thread->kernel_stack);
               
        check_simple_locks();

        /* Our context might wake up on another processor, so we must
         * not keep hot state in our FPU, it must go back to the pcb
         * so that it can be found by the other if needed
         */
        if(real_ncpus > 1) {    /* This is potentially slow, so only do when actually SMP */
                fpu_save(old_act);      /* Save floating point if used */
                vec_save(old_act);      /* Save vector if used */
        }

#if DEBUG
        if (watchacts & WA_PCB) {
                printf("switch_context(0x%08x, 0x%x, 0x%08x)\n",
                       old,continuation,new);
        }
#endif /* DEBUG */

        /*
         * We do not have to worry about the PMAP module, so switch.
         *
         * We must not use top_act->map since this may not be the actual
         * task map, but the map being used for a klcopyin/out.
         */

        if(new_act->mact.specFlags & runningVM) {                       /* Is the new guy running a VM? */
                pmap_switch(new_act->mact.vmmCEntry->vmmPmap);  /* Switch to the VM's pmap */
        }
        else {                                                                                          /* otherwise, we use the task's pmap */
                new_pmap = new_act->task->map->pmap;
                if ((old_act->task->map->pmap != new_pmap) || (old_act->mact.specFlags & runningVM)) {
                        pmap_switch(new_pmap);                                          /* Switch if there is a change */
                }
        }

        /* Sanity check - is the stack pointer inside the stack that
         * we're about to switch to? Is the execution address within
         * the kernel's VM space??
         */
#if 0
        printf("************* stack=%08X; R1=%08X; LR=%08X; old=%08X; cont=%08X; new=%08X\n",
                new->kernel_stack, new_act->mact.pcb->ss.r1,
                new_act->mact.pcb->ss.lr, old, continuation, new);      /* (TEST/DEBUG) */
        assert((new->kernel_stack < new_act->mact.pcb->ss.r1) &&
               ((unsigned int)STACK_IKS(new->kernel_stack) >
                new_act->mact.pcb->ss.r1));
        assert(new_act->mact.pcb->ss.lr < VM_MAX_KERNEL_ADDRESS);
#endif


        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SCHED,MACH_SCHED) | DBG_FUNC_NONE,
                     (int)old, (int)new, old->sched_pri, new->sched_pri, 0);


        retval = Switch_context(old, continuation, new);
        assert(retval != (struct thread_shuttle*)NULL);

        if (branch_tracing_enabled())
          per_proc_info[cpu_number()].cpu_flags |= traceBE;  /* restore branch tracing */

        /* We've returned from having switched context, so we should be
         * back in the original context.
         */

        return retval;
}

/*
 * Alter the thread's state so that a following thread_exception_return
 * will make the thread return 'retval' from a syscall.
 */
void
thread_set_syscall_return(
        struct thread_shuttle *thread,
        kern_return_t   retval)
{
        struct ppc_saved_state *ssp = &thread->top_act->mact.pcb->ss;

#if     MACH_ASSERT
        if (watchacts & WA_PCB)
                printf("thread_set_syscall_return(thr=%x,retval=%d)\n", thread,retval);
#endif  /* MACH_ASSERT */

        ssp->r3 = retval;
}

/*
 * Initialize the machine-dependent state for a new thread.
 */
kern_return_t
thread_machine_create(
                      struct thread_shuttle *thread,
                      thread_act_t thr_act,
                      void (*start_pos)(thread_t))
{

        savearea                *sv;                                                                    /* Pointer to newly allocated savearea */
        unsigned int    *CIsTooLimited, i;


#if     MACH_ASSERT
    if (watchacts & WA_PCB)
        printf("thread_machine_create(thr=%x,thr_act=%x,st=%x)\n", thread, thr_act, start_pos);
#endif  /* MACH_ASSERT */

        hw_atomic_add(&saveanchor.saveneed, 4);                                 /* Account for the number of saveareas we think we "need"
                                                                                                                           for this activation */
        assert(thr_act->mact.pcb == (pcb_t)0);                                  /* Make sure there was no previous savearea */
        
        sv = save_alloc();                                                                              /* Go get us a savearea */
                
        bzero((char *) sv, sizeof(struct pcb));                                 /* Clear out the whole shebang */
        
        sv->save_act = thr_act;                                                                 /* Set who owns it */
        sv->save_vrsave = 0;
        thr_act->mact.pcb = (pcb_t)sv;                                                  /* Point to the save area */

#if     MACH_ASSERT
        if (watchacts & WA_PCB)
                printf("pcb_init(%x) pcb=%x\n", thr_act, sv);
#endif  /* MACH_ASSERT */
        /*
         * User threads will pull their context from the pcb when first
         * returning to user mode, so fill in all the necessary values.
         * Kernel threads are initialized from the save state structure 
         * at the base of the kernel stack (see stack_attach()).
         */

        sv->save_srr1 = MSR_EXPORT_MASK_SET;                                    /* Set the default user MSR */
        
        CIsTooLimited = (unsigned int *)(&sv->save_sr0);                        /* Make a pointer 'cause C can't cast on the left */
        for(i=0; i<16; i++) {                                                                   /* Initialize all SRs */
                CIsTooLimited[i] = SEG_REG_PROT | (i << 20) | thr_act->task->map->pmap->space;  /* Set the SR value */
        }
        sv->save_sr_copyin = SEG_REG_PROT | (SR_COPYIN_NUM<<20) | thr_act->task->map->pmap->space;      /* Default the copyin */

    return(KERN_SUCCESS);
}

/*
 * Machine-dependent cleanup prior to destroying a thread
 */
void
thread_machine_destroy( thread_t thread )
{
        spl_t s;

        if (thread->kernel_stack) {
                s = splsched();
                stack_free(thread);
                splx(s);
        }
}

/*
 * flush out any lazily evaluated HW state in the
 * owning thread's context, before termination.
 */
void
thread_machine_flush( thread_act_t cur_act )
{
}

/*
 * Number of times we needed to swap an activation back in before
 * switching to it.
 */
int switch_act_swapins = 0;

/*
 * machine_switch_act
 *
 * Machine-dependent details of activation switching.  Called with
 * RPC locks held and preemption disabled.
 */
void
machine_switch_act( 
        thread_t        thread,
        thread_act_t    old,
        thread_act_t    new,
        int                             cpu)
{
        pmap_t          new_pmap;

        /* Our context might wake up on another processor, so we must
         * not keep hot state in our FPU, it must go back to the pcb
         * so that it can be found by the other if needed
         */
        if(real_ncpus > 1) {    /* This is potentially slow, so only do when actually SMP */
                fpu_save(old);          /* Save floating point if used */
                vec_save(old);          /* Save vector if used */
        }

        active_stacks[cpu] = thread->kernel_stack;

        ast_context(new, cpu);

        /* Activations might have different pmaps 
         * (process->kernel->server, for example).
         * Change space if needed
         */

        if(new->mact.specFlags & runningVM) {                   /* Is the new guy running a VM? */
                pmap_switch(new->mact.vmmCEntry->vmmPmap);      /* Switch to the VM's pmap */
        }
        else {                                                                                          /* otherwise, we use the task's pmap */
                new_pmap = new->task->map->pmap;
                if ((old->task->map->pmap != new_pmap)  || (old->mact.specFlags & runningVM)) {
                        pmap_switch(new_pmap);
                }
        }

}

void
pcb_user_to_kernel(thread_act_t act)
{

        return;                                                                                                 /* Not needed, I hope... */
}


/*
 * act_machine_sv_free
 * release saveareas associated with an act. if flag is true, release
 * user level savearea(s) too, else don't
 *
 * this code cannot block so we call the proper save area free routine
 */
void
act_machine_sv_free(thread_act_t act)
{
        register pcb_t pcb,userpcb,npcb;
        register savearea *svp;
        register int i;

/*
 *      This next bit insures that any live facility context for this thread is discarded on every processor
 *      that may have it.  We go through all per-processor blocks and zero the facility owner if
 *      it is the thread being destroyed. This needs to be done via a compare-and-swap because
 *      some other processor could change the owner while we are clearing it. It turns out that 
 *      this is the only place where we need the interlock, normal use of the owner field is cpu-local
 *      and doesn't need the interlock. Because we are called during termintation, and a thread
 *      terminates itself, the context on other processors has been saved (because we save it as
 *      part of the context switch), even if it is still considered live. Since the dead thread is 
 *      not running elsewhere, and the context is saved, any other processor looking at the owner
 *      field will not attempt to save context again, meaning that it doesn't matter if the owner
 *      changes out from under it.
 */
 
        /* 
         * free VMX and FPU saveareas.  do not free user save areas.
     * user VMX and FPU saveareas, if any, i'm told are last in
     * the chain so we just stop if we find them
         * we identify user VMX and FPU saveareas when we find a pcb
         * with a save level of 0.  we identify user regular save
         * areas when we find one with MSR_PR set
         */

        pcb = act->mact.VMX_pcb;                                                                /* Get the top vector savearea */
        while(pcb) {                                                                                    /* Any VMX saved state? */
                svp = (savearea *)pcb;                                                          /* save lots of casting later */
                if (svp->save_level_vec == 0) break;   /* done when hit user if any */
                pcb = (pcb_t)svp->save_prev_vector;                             /* Get one underneath our's */          
                svp->save_flags &= ~SAVvmxvalid;                                                /* Clear the VMX flag */
                if(!(svp->save_flags & SAVinuse)) {                                     /* Anyone left with this one? */                        

                                save_ret(svp);                          /* release it */
                }
        }
        act->mact.VMX_pcb = pcb;
        if (act->mact.VMX_lvl != 0) {
          for(i=0; i < real_ncpus; i++) {                                                       /* Cycle through processors */
                (void)hw_compare_and_store((unsigned int)act, 0, &per_proc_info[i].VMX_thread); /* Clear if ours */
          }
        }

        pcb = act->mact.FPU_pcb;                                                                /* Get the top floating point savearea */
        while(pcb) {                                                                                    /* Any floating point saved state? */
                svp = (savearea *)pcb;
                if (svp->save_level_fp == 0) break;     /* done when hit user if any */
                pcb = (pcb_t)svp->save_prev_float;                                      /* Get one underneath our's */          
                svp->save_flags &= ~SAVfpuvalid;                                                /* Clear the floating point flag */
                if(!(svp->save_flags & SAVinuse)) {                                     /* Anyone left with this one? */                        
                                save_ret(svp);                                                  /* Nope, release it */
                }
        }
        act->mact.FPU_pcb = pcb;
        if (act->mact.FPU_lvl != 0) {
          for(i=0; i < real_ncpus; i++) {                                                       /* Cycle through processors */
                (void)hw_compare_and_store((unsigned int)act, 0, &per_proc_info[i].FPU_thread); /* Clear if ours */
          }
        }

        /*
         * free all regular saveareas except a user savearea, if any
         */

        pcb = act->mact.pcb;
        userpcb = (pcb_t)0;
        while(pcb) {
          svp = (savearea *)pcb;
          if ((svp->save_srr1 & MASK(MSR_PR))) {
                assert(userpcb == (pcb_t)0);
                userpcb = pcb;
                svp = (savearea *)userpcb;
                npcb = (pcb_t)svp->save_prev;
                svp->save_prev = (struct savearea *)0;
          } else {
                svp->save_flags &= ~SAVattach;          /* Clear the attached flag */
                npcb = (pcb_t)svp->save_prev;
                if(!(svp->save_flags & SAVinuse))       /* Anyone left with this one? */
                        save_ret(svp);
          }
          pcb = npcb;
        }
        act->mact.pcb = userpcb;

}


/*
 * act_virtual_machine_destroy:
 * Shutdown any virtual machines associated with a thread
 */
void
act_virtual_machine_destroy(thread_act_t act)
{
        if(act->mact.bbDescAddr) {                                                              /* Check if the Blue box assist is active */
                disable_bluebox_internal(act);                                          /* Kill off bluebox */
        }
        
        if(act->mact.vmmControl) {                                                              /* Check if VMM is active */
                vmm_tear_down_all(act);                                                         /* Kill off all VMM contexts */
        }
}

/*
 * act_machine_destroy: Shutdown any state associated with a thread pcb.
 */
void
act_machine_destroy(thread_act_t act)
{
        register pcb_t  pcb, opcb;
        int i;

#if     MACH_ASSERT
        if (watchacts & WA_PCB)
                printf("act_machine_destroy(0x%x)\n", act);
#endif  /* MACH_ASSERT */

        act_virtual_machine_destroy(act);

/*
 *      This next bit insures that any live facility context for this thread is discarded on every processor
 *      that may have it.  We go through all per-processor blocks and zero the facility owner if
 *      it is the thread being destroyed. This needs to be done via a compare-and-swap because
 *      some other processor could change the owner while we are clearing it. It turns out that 
 *      this is the only place where we need the interlock, normal use of the owner field is cpu-local
 *      and doesn't need the interlock. Because we are called during termintation, and a thread
 *      terminates itself, the context on other processors has been saved (because we save it as
 *      part of the context switch), even if it is still considered live. Since the dead thread is 
 *      not running elsewhere, and the context is saved, any other processor looking at the owner
 *      field will not attempt to save context again, meaning that it doesn't matter if the owner
 *      changes out from under it.
 */
 
        for(i=0; i < real_ncpus; i++) {                                                 /* Cycle through processors */
                (void)hw_compare_and_store((unsigned int)act, 0, &per_proc_info[i].FPU_thread); /* Clear if ours */
                (void)hw_compare_and_store((unsigned int)act, 0, &per_proc_info[i].VMX_thread); /* Clear if ours */
        }
        
        pcb = act->mact.VMX_pcb;                                                                /* Get the top vector savearea */
        while(pcb) {                                                                                    /* Any VMX saved state? */
                opcb = pcb;                                                                                     /* Save current savearea address */
                pcb = (pcb_t)(((savearea *)pcb)->save_prev_vector);     /* Get one underneath our's */          
                ((savearea *)opcb)->save_flags &= ~SAVvmxvalid;         /* Clear the VMX flag */
                
                if(!(((savearea *)opcb)->save_flags & SAVinuse)) {      /* Anyone left with this one? */                        
                        save_release((savearea *)opcb);                                 /* Nope, release it */
                }
        }
        act->mact.VMX_pcb = (pcb_t)0;                                                   /* Clear pointer */     

        pcb = act->mact.FPU_pcb;                                                                /* Get the top floating point savearea */
        while(pcb) {                                                                                    /* Any floating point saved state? */
                opcb = pcb;                                                                                     /* Save current savearea address */
                pcb = (pcb_t)(((savearea *)pcb)->save_prev_float);      /* Get one underneath our's */          
                ((savearea *)opcb)->save_flags &= ~SAVfpuvalid;         /* Clear the floating point flag */
                
                if(!(((savearea *)opcb)->save_flags & SAVinuse)) {      /* Anyone left with this one? */                        
                        save_release((savearea *)opcb);                                 /* Nope, release it */
                }
        }
        act->mact.FPU_pcb = (pcb_t)0;                                                   /* Clear pointer */     

        pcb = act->mact.pcb;                                                                    /* Get the top normal savearea */
        act->mact.pcb = (pcb_t)0;                                                               /* Clear pointer */     
        
        while(pcb) {                                                                                    /* Any normal saved state left? */
                opcb = pcb;                                                                                     /* Keep track of what we're working on */
                pcb = (pcb_t)(((savearea *)pcb)->save_prev);            /* Get one underneath our's */
                
                ((savearea *)opcb)->save_flags = 0;                                     /* Clear all flags since we release this in any case */
                save_release((savearea *)opcb);                                         /* Release this one */
        }

        hw_atomic_sub(&saveanchor.saveneed, 4);                                 /* Unaccount for the number of saveareas we think we "need"
                                                                                                                           for this activation */
}

kern_return_t
act_machine_create(task_t task, thread_act_t thr_act)
{
        /*
         * Clear & Init the pcb  (sets up user-mode s regs)
         * We don't use this anymore.
         */

        register pcb_t pcb;
        register int i;
        unsigned int *CIsTooLimited;
        pmap_t pmap;
        
        return KERN_SUCCESS;
}

void act_machine_init()
{
#if     MACH_ASSERT
    if (watchacts & WA_PCB)
        printf("act_machine_init()\n");
#endif  /* MACH_ASSERT */

    /* Good to verify these once */
    assert( THREAD_MACHINE_STATE_MAX <= THREAD_STATE_MAX );

    assert( THREAD_STATE_MAX >= PPC_THREAD_STATE_COUNT );
    assert( THREAD_STATE_MAX >= PPC_EXCEPTION_STATE_COUNT );
    assert( THREAD_STATE_MAX >= PPC_FLOAT_STATE_COUNT );
    assert( THREAD_STATE_MAX >= sizeof(struct ppc_saved_state)/sizeof(int));

    /*
     * If we start using kernel activations,
     * would normally create kernel_thread_pool here,
     * populating it from the act_zone
     */
}

void
act_machine_return(int code)
{
    thread_act_t thr_act = current_act();

#if     MACH_ASSERT
    if (watchacts & WA_EXIT)
        printf("act_machine_return(0x%x) cur_act=%x(%d) thr=%x(%d)\n",
               code, thr_act, thr_act->ref_count,
               thr_act->thread, thr_act->thread->ref_count);
#endif  /* MACH_ASSERT */


        /*
         * This code is called with nothing locked.
         * It also returns with nothing locked, if it returns.
         *
         * This routine terminates the current thread activation.
         * If this is the only activation associated with its
         * thread shuttle, then the entire thread (shuttle plus
         * activation) is terminated.
         */
        assert( code == KERN_TERMINATED );
        assert( thr_act );

        act_lock_thread(thr_act);

#ifdef CALLOUT_RPC_MODEL
        /*
         * JMM - This needs to get cleaned up to work under the much simpler
         * return (instead of callout model).
         */
        if (thr_act->thread->top_act != thr_act) {
                /*
                 * this is not the top activation;
                 * if possible, we should clone the shuttle so that
                 * both the root RPC-chain and the soon-to-be-orphaned
                 * RPC-chain have shuttles
                 *
                 * JMM - Cloning is a horrible idea!  Instead we should alert
                 * the pieces upstream to return the shuttle.  We will use
                 * alerts for this.
                 */
                act_unlock_thread(thr_act);
                panic("act_machine_return: ORPHAN CASE NOT YET IMPLEMENTED");
        }

        if (thr_act->lower != THR_ACT_NULL) {
                thread_t        cur_thread = current_thread();
                thread_act_t    cur_act;
                struct ipc_port *iplock;

                /* terminate the entire thread (shuttle plus activation) */
                /* terminate only this activation, send an appropriate   */
                /* return code back to the activation that invoked us.   */
                iplock = thr_act->pool_port;    /* remember for unlock call */
                thr_act->lower->alerts |= SERVER_TERMINATED;
                install_special_handler(thr_act->lower);
                
                /* Return to previous act with error code */

                act_locked_act_reference(thr_act);      /* keep it around */
                act_switch_swapcheck(cur_thread, (ipc_port_t)0);

                (void) switch_act(THR_ACT_NULL);
                /* assert(thr_act->ref_count == 0); */          /* XXX */
                cur_act = cur_thread->top_act;
                MACH_RPC_RET(cur_act) = KERN_RPC_SERVER_TERMINATED;         
                machine_kernel_stack_init(cur_thread, mach_rpc_return_error);
                /*
                 * The following unlocks must be done separately since fields 
                 * used by `act_unlock_thread()' have been cleared, meaning
                 * that it would not release all of the appropriate locks.
                 */
                rpc_unlock(cur_thread);
                if (iplock) ip_unlock(iplock);  /* must be done separately */
                act_unlock(thr_act);
                act_deallocate(thr_act);                /* free it */
                Load_context(cur_thread);
                /*NOTREACHED*/
                
                panic("act_machine_return: TALKING ZOMBIE! (2)");
        }

#endif /* CALLOUT_RPC_MODEL */

        /* This is the only activation attached to the shuttle... */

        assert(thr_act->thread->top_act == thr_act);
        act_unlock_thread(thr_act);
        thread_terminate_self();

        /*NOTREACHED*/
        panic("act_machine_return: TALKING ZOMBIE! (1)");
}

void
thread_machine_set_current(struct thread_shuttle *thread)
{
    register int        my_cpu = cpu_number();

    cpu_data[my_cpu].active_thread = thread;
        
    active_kloaded[my_cpu] = thread->top_act->kernel_loaded ? thread->top_act : THR_ACT_NULL;
}

void
thread_machine_init(void)
{
#ifdef  MACHINE_STACK
#if KERNEL_STACK_SIZE > PPC_PGBYTES
        panic("KERNEL_STACK_SIZE can't be greater than PPC_PGBYTES\n");
#endif
#endif
}

#if MACH_ASSERT
void
dump_pcb(pcb_t pcb)
{
        printf("pcb @ %8.8x:\n", pcb);
#if DEBUG
        regDump(&pcb->ss);
#endif /* DEBUG */
}

void
dump_thread(thread_t th)
{
        printf(" thread @ 0x%x:\n", th);
}

int
    dump_act(thread_act_t thr_act)
{
    if (!thr_act)
        return(0);

    printf("thr_act(0x%x)(%d): thread=%x(%d) task=%x(%d)\n",
           thr_act, thr_act->ref_count,
           thr_act->thread, thr_act->thread ? thr_act->thread->ref_count:0,
           thr_act->task,   thr_act->task   ? thr_act->task->ref_count : 0);

    printf("\talerts=%x mask=%x susp=%x active=%x hi=%x lo=%x\n",
           thr_act->alerts, thr_act->alert_mask,
           thr_act->suspend_count, thr_act->active,
           thr_act->higher, thr_act->lower);

    return((int)thr_act);
}

#endif

unsigned int 
get_useraddr()
{

        thread_act_t thr_act = current_act();

        return(thr_act->mact.pcb->ss.srr0);
}

/*
 * detach and return a kernel stack from a thread
 */

vm_offset_t
stack_detach(thread_t thread)
{
  vm_offset_t stack;

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_SCHED,MACH_STACK_DETACH),
                        thread, thread->priority,
                        thread->sched_pri, 0,
                        0);

  stack = thread->kernel_stack;
  thread->kernel_stack = 0;
  return(stack);
}

/*
 * attach a kernel stack to a thread and initialize it
 *
 * attaches a stack to a thread. if there is no save
 * area we allocate one.  the top save area is then
 * loaded with the pc (continuation address), the initial
 * stack pointer, and a std kernel MSR. if the top
 * save area is the user save area bad things will 
 * happen
 *
 */

void
stack_attach(struct thread_shuttle *thread,
             vm_offset_t stack,
             void (*start_pos)(thread_t))
{
  thread_act_t thr_act;
  unsigned int *kss;
  struct savearea *sv;

        KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_SCHED,MACH_STACK_ATTACH),
            thread, thread->priority,
            thread->sched_pri, start_pos,
            0);

  assert(stack);
  kss = (unsigned int *)STACK_IKS(stack);
  thread->kernel_stack = stack;

  /* during initialization we sometimes do not have an
     activation. in that case do not do anything */
  if ((thr_act = thread->top_act) != 0) {
    sv = save_get();  /* cannot block */
    //    bzero((char *) sv, sizeof(struct pcb));
    sv->save_act = thr_act;
        sv->save_prev = (struct savearea *)thr_act->mact.pcb;
    thr_act->mact.pcb = (pcb_t)sv;

    sv->save_srr0 = (unsigned int) start_pos;
    /* sv->save_r3 = ARG ? */
    sv->save_r1 = (vm_offset_t)((int)kss - KF_SIZE);
        sv->save_srr1 = MSR_SUPERVISOR_INT_OFF;
        sv->save_xfpscrpad = 0;                                         /* Start with a clear fpscr */
        sv->save_xfpscr = 0;                                            /* Start with a clear fpscr */
    *((int *)sv->save_r1) = 0;
    thr_act->mact.ksp = 0;                            
  }

  return;
}

/*
 * move a stack from old to new thread
 */

void
stack_handoff(thread_t old,
              thread_t new)
{

  vm_offset_t stack;
  pmap_t new_pmap;

  assert(new->top_act);
  assert(old->top_act);

  stack = stack_detach(old);
  new->kernel_stack = stack;

  per_proc_info[cpu_number()].cpu_flags &= ~traceBE;

#if NCPUS > 1
  if (real_ncpus > 1) {
        fpu_save(old->top_act);
        vec_save(old->top_act);
  }
#endif

  KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SCHED,MACH_STACK_HANDOFF) | DBG_FUNC_NONE,
                     (int)old, (int)new, old->sched_pri, new->sched_pri, 0);


        if(new->top_act->mact.specFlags & runningVM) {  /* Is the new guy running a VM? */
                pmap_switch(new->top_act->mact.vmmCEntry->vmmPmap);     /* Switch to the VM's pmap */
        }
        else {                                                                                  /* otherwise, we use the task's pmap */
                new_pmap = new->top_act->task->map->pmap;
                if ((old->top_act->task->map->pmap != new_pmap) || (old->top_act->mact.specFlags & runningVM)) {
                        pmap_switch(new_pmap);
                }
        }

  thread_machine_set_current(new);
  active_stacks[cpu_number()] = new->kernel_stack;
  per_proc_info[cpu_number()].Uassist = new->top_act->mact.cthread_self;
#if 1
  per_proc_info[cpu_number()].ppbbTaskEnv = new->top_act->mact.bbTaskEnv;
  per_proc_info[cpu_number()].spcFlags = new->top_act->mact.specFlags;
#endif
  if (branch_tracing_enabled()) 
    per_proc_info[cpu_number()].cpu_flags |= traceBE;
    
  if(trcWork.traceMask) dbgTrace(0x12345678, (unsigned int)old->top_act, (unsigned int)new->top_act);   /* Cut trace entry if tracing */    
    
  return;
}

/*
 * clean and initialize the current kernel stack and go to
 * the given continuation routine
 */

void
call_continuation(void (*continuation)(void) )
{

  unsigned int *kss;
  vm_offset_t tsp;

  assert(current_thread()->kernel_stack);
  kss = (unsigned int *)STACK_IKS(current_thread()->kernel_stack);
  assert(continuation);

  tsp = (vm_offset_t)((int)kss - KF_SIZE);
  assert(tsp);
  *((int *)tsp) = 0;

  Call_continuation(continuation, tsp);
  
  return;
}

void
thread_swapin_mach_alloc(thread_t thread)
{
    struct savearea *sv;

        assert(thread->top_act->mact.pcb == 0);

    sv = save_alloc();
        assert(sv);
        //    bzero((char *) sv, sizeof(struct pcb));
    sv->save_act = thread->top_act;
    thread->top_act->mact.pcb = (pcb_t)sv;

}