[apple/xnu.git] / osfmk / i386 / db_interface.c

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_OSREFERENCE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code 
 * as defined in and that are subject to the Apple Public Source License 
 * Version 2.0 (the 'License'). You may not use this file except in 
 * compliance with the License.  The rights granted to you under the 
 * License may not be used to create, or enable the creation or 
 * redistribution of, unlawful or unlicensed copies of an Apple operating 
 * system, or to circumvent, violate, or enable the circumvention or 
 * violation of, any terms of an Apple operating system software license 
 * agreement.
 *
 * Please obtain a copy of the License at 
 * http://www.opensource.apple.com/apsl/ and read it before using this 
 * file.
 *
 * The 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, QUIET ENJOYMENT OR NON-INFRINGEMENT. 
 * Please see the License for the specific language governing rights and 
 * limitations under the License.
 *
 * @APPLE_LICENSE_OSREFERENCE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */
/* 
 * Mach Operating System
 * Copyright (c) 1991,1990 Carnegie Mellon University
 * All Rights Reserved.
 * 
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 * 
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 * 
 * Carnegie Mellon requests users of this software to return to
 * 
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 * 
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 */

/*
 * Interface to new debugger.
 */
#include <platforms.h>
#include <time_stamp.h>
#include <mach_mp_debug.h>
#include <mach_ldebug.h>
#include <kern/spl.h>
#include <kern/cpu_number.h>
#include <kern/kern_types.h>
#include <kern/misc_protos.h>
#include <vm/pmap.h>

#include <i386/thread.h>
#include <i386/db_machdep.h>
#include <i386/seg.h>
#include <i386/trap.h>
#include <i386/setjmp.h>
#include <i386/pmap.h>
#include <i386/misc_protos.h>

#include <mach/vm_param.h>
#include <vm/vm_map.h>
#include <kern/thread.h>
#include <kern/task.h>

#include <ddb/db_command.h>
#include <ddb/db_task_thread.h>
#include <ddb/db_run.h>
#include <ddb/db_trap.h>
#include <ddb/db_output.h>
#include <ddb/db_access.h>
#include <ddb/db_sym.h>
#include <ddb/db_break.h>
#include <ddb/db_watch.h>

int      db_active = 0;
struct   i386_saved_state *i386_last_saved_statep;
struct   i386_saved_state i386_nested_saved_state;
unsigned i386_last_kdb_sp;

extern  thread_t db_default_act;
extern pt_entry_t *DMAP1;
extern caddr_t DADDR1;

#if     MACH_MP_DEBUG
extern int masked_state_cnt[];
#endif  /* MACH_MP_DEBUG */

/*
 *      Enter KDB through a keyboard trap.
 *      We show the registers as of the keyboard interrupt
 *      instead of those at its call to KDB.
 */
struct int_regs {
        int     gs;
        int     fs;
        int     edi;
        int     esi;
        int     ebp;
        int     ebx;
        struct i386_interrupt_state *is;
};

extern char *   trap_type[];
extern int      TRAP_TYPES;

/* Forward */

extern void     kdbprinttrap(
                        int                     type,
                        int                     code,
                        int                     *pc,
                        int                     sp);
extern void     kdb_kentry(
                        struct int_regs         *int_regs);
extern int      db_user_to_kernel_address(
                        task_t                  task,
                        vm_offset_t             addr,
                        unsigned                *kaddr,
                        int                     flag);
extern void     db_write_bytes_user_space(
                        vm_offset_t             addr,
                        int                     size,
                        char                    *data,
                        task_t                  task);
extern int      db_search_null(
                        task_t                  task,
                        unsigned                *svaddr,
                        unsigned                evaddr,
                        unsigned                *skaddr,
                        int                     flag);
extern int      kdb_enter(int);
extern void     kdb_leave(void);
extern void     lock_kdb(void);
extern void     unlock_kdb(void);

/*
 *  kdb_trap - field a TRACE or BPT trap
 */


extern jmp_buf_t *db_recover;

/*
 * Translate the state saved in a task state segment into an
 * exception frame.  Since we "know" we always want the state
 * in a ktss, we hard-wire that in, rather than indexing the gdt
 * with tss_sel to derive a pointer to the desired tss.
 */
void
db_tss_to_frame(
        int tss_sel,
        struct i386_saved_state *regs)
{
        extern struct i386_tss ktss;
        int mycpu = cpu_number();
        struct i386_tss *tss;

        tss = cpu_datap(mycpu)->cpu_desc_index.cdi_ktss;        /* XXX */

        /*
         * ddb will overwrite whatever's in esp, so put esp0 elsewhere, too.
         */
        regs->esp = tss->esp0;
        regs->efl = tss->eflags;
        regs->eip = tss->eip;
        regs->trapno = tss->ss0;        /* XXX */
        regs->err = tss->esp0;  /* XXX */
        regs->eax = tss->eax;
        regs->ecx = tss->ecx;
        regs->edx = tss->edx;
        regs->ebx = tss->ebx;
        regs->uesp = tss->esp;
        regs->ebp = tss->ebp;
        regs->esi = tss->esi;
        regs->edi = tss->edi;
        regs->es = tss->es;
        regs->ss = tss->ss;
        regs->cs = tss->cs;
        regs->ds = tss->ds;
        regs->fs = tss->fs;
        regs->gs = tss->gs;
}

/*
 * Compose a call to the debugger from the saved state in regs.  (No
 * reason not to do this in C.)
 */
boolean_t
db_trap_from_asm(
        struct i386_saved_state *regs)
{
        int     code;
        int     type;

        type = regs->trapno;
        code = regs->err;
        return (kdb_trap(type, code, regs));
}

int
kdb_trap(
        int                     type,
        int                     code,
        struct i386_saved_state *regs)
{
        extern char             etext;
        boolean_t               trap_from_user;
        spl_t                   s = splhigh();

        switch (type) {
            case T_DEBUG:       /* single_step */
            {
                extern int dr_addr[];
                int addr;
                int status = dr6();

                if (status & 0xf) {     /* hmm hdw break */
                        addr =  status & 0x8 ? dr_addr[3] :
                                status & 0x4 ? dr_addr[2] :
                                status & 0x2 ? dr_addr[1] :
                                               dr_addr[0];
                        regs->efl |= EFL_RF;
                        db_single_step_cmd(addr, 0, 1, "p");
                }
            }
            case T_INT3:        /* breakpoint */
            case T_WATCHPOINT:  /* watchpoint */
            case -1:    /* keyboard interrupt */
                break;

            default:
                if (db_recover) {
                    i386_nested_saved_state = *regs;
                    db_printf("Caught ");
                    if (type < 0 || type > TRAP_TYPES)
                        db_printf("type %d", type);
                    else
                        db_printf("%s", trap_type[type]);
                    db_printf(" trap, code = %x, pc = %x\n",
                              code, regs->eip);
                        splx(s);
                    db_error("");
                    /*NOTREACHED*/
                }
                kdbprinttrap(type, code, (int *)&regs->eip, regs->uesp);
        }

        disable_preemption();

        current_cpu_datap()->cpu_kdb_saved_ipl = s;
        current_cpu_datap()->cpu_kdb_saved_state = regs;

        i386_last_saved_statep = regs;
        i386_last_kdb_sp = (unsigned) &type;

        if (!kdb_enter(regs->eip))
                goto kdb_exit;

        /*  Should switch to kdb's own stack here. */

        if (!IS_USER_TRAP(regs, &etext)) {
                bzero((char *)&ddb_regs, sizeof (ddb_regs));
                *(struct i386_saved_state_from_kernel *)&ddb_regs =
                        *(struct i386_saved_state_from_kernel *)regs;
                trap_from_user = FALSE;
        }
        else {
                ddb_regs = *regs;
                trap_from_user = TRUE;
        }
        if (!trap_from_user) {
            /*
             * Kernel mode - esp and ss not saved
             */
            ddb_regs.uesp = (int)&regs->uesp;   /* kernel stack pointer */
            ddb_regs.ss   = KERNEL_DS;
        }

        db_active++;
        db_task_trap(type, code, trap_from_user);
        db_active--;

        regs->eip    = ddb_regs.eip;
        regs->efl    = ddb_regs.efl;
        regs->eax    = ddb_regs.eax;
        regs->ecx    = ddb_regs.ecx;
        regs->edx    = ddb_regs.edx;
        regs->ebx    = ddb_regs.ebx;
        if (trap_from_user) {
            /*
             * user mode - saved esp and ss valid
             */
            regs->uesp = ddb_regs.uesp;         /* user stack pointer */
            regs->ss   = ddb_regs.ss & 0xffff;  /* user stack segment */
        }
        regs->ebp    = ddb_regs.ebp;
        regs->esi    = ddb_regs.esi;
        regs->edi    = ddb_regs.edi;
        regs->es     = ddb_regs.es & 0xffff;
        regs->cs     = ddb_regs.cs & 0xffff;
        regs->ds     = ddb_regs.ds & 0xffff;
        regs->fs     = ddb_regs.fs & 0xffff;
        regs->gs     = ddb_regs.gs & 0xffff;

        if ((type == T_INT3) &&
            (db_get_task_value(regs->eip,
                               BKPT_SIZE,
                               FALSE,
                               db_target_space(current_thread(),
                                               trap_from_user))
                              == BKPT_INST))
            regs->eip += BKPT_SIZE;

kdb_exit:
        kdb_leave();

        current_cpu_datap()->cpu_kdb_saved_state = 0;

#if     MACH_MP_DEBUG
        current_cpu_datap()->cpu_masked_state_cnt = 0;
#endif  /* MACH_MP_DEBUG */

        enable_preemption();

        splx(s);

        /* Allow continue to upper layers of exception handling if
         * trap was not a debugging trap.
         */

        if (trap_from_user && type != T_DEBUG && type != T_INT3 
                && type != T_WATCHPOINT)
                return 0;
        else
                return (1);
}

/*
 *      Enter KDB through a keyboard trap.
 *      We show the registers as of the keyboard interrupt
 *      instead of those at its call to KDB.
 */

spl_t kdb_oldspl;

void
kdb_kentry(
        struct int_regs *int_regs)
{
        extern char etext;
        boolean_t trap_from_user;
        struct i386_interrupt_state *is = int_regs->is;
        struct i386_saved_state regs;
        spl_t s;

        s = splhigh();
        kdb_oldspl = s;

        if (IS_USER_TRAP(is, &etext))
        {
            regs.uesp = ((int *)(is+1))[0];
            regs.ss   = ((int *)(is+1))[1];
        }
        else {
            regs.ss  = KERNEL_DS;
            regs.uesp= (int)(is+1);
        }
        regs.efl = is->efl;
        regs.cs  = is->cs;
        regs.eip = is->eip;
        regs.eax = is->eax;
        regs.ecx = is->ecx;
        regs.edx = is->edx;
        regs.ebx = int_regs->ebx;
        regs.ebp = int_regs->ebp;
        regs.esi = int_regs->esi;
        regs.edi = int_regs->edi;
        regs.ds  = is->ds;
        regs.es  = is->es;
        regs.fs  = int_regs->fs;
        regs.gs  = int_regs->gs;

        disable_preemption();

        current_cpu_datap()->cpu_kdb_saved_state = &regs;

        if (!kdb_enter(regs.eip))
                goto kdb_exit;

        bcopy((char *)&regs, (char *)&ddb_regs, sizeof (ddb_regs));
        trap_from_user = IS_USER_TRAP(&ddb_regs, &etext);

        db_active++;
        db_task_trap(-1, 0, trap_from_user);
        db_active--;

        if (trap_from_user) {
            ((int *)(is+1))[0] = ddb_regs.uesp;
            ((int *)(is+1))[1] = ddb_regs.ss & 0xffff;
        }
        is->efl = ddb_regs.efl;
        is->cs  = ddb_regs.cs & 0xffff;
        is->eip = ddb_regs.eip;
        is->eax = ddb_regs.eax;
        is->ecx = ddb_regs.ecx;
        is->edx = ddb_regs.edx;
        int_regs->ebx = ddb_regs.ebx;
        int_regs->ebp = ddb_regs.ebp;
        int_regs->esi = ddb_regs.esi;
        int_regs->edi = ddb_regs.edi;
        is->ds  = ddb_regs.ds & 0xffff;
        is->es  = ddb_regs.es & 0xffff;
        int_regs->fs = ddb_regs.fs & 0xffff;
        int_regs->gs = ddb_regs.gs & 0xffff;

kdb_exit:
        kdb_leave();
        current_cpu_datap()->cpu_kdb_saved_state = 0;

        enable_preemption();

        splx(s);
}

/*
 * Print trap reason.
 */

void
kdbprinttrap(
        int     type,
        int     code,
        int     *pc,
        int     sp)
{
        printf("kernel: ");
        if (type < 0 || type > TRAP_TYPES)
            db_printf("type %d", type);
        else
            db_printf("%s", trap_type[type]);
        db_printf(" trap, code=%x eip@%x = %x esp=%x\n",
                  code, pc, *(int *)pc, sp);
        db_run_mode = STEP_CONTINUE;
}

int
db_user_to_kernel_address(
        task_t          task,
        vm_offset_t     addr,
        unsigned        *kaddr,
        int             flag)
{
        register pt_entry_t *ptp;
        
        ptp = pmap_pte(task->map->pmap, addr);
        if (ptp == PT_ENTRY_NULL || (*ptp & INTEL_PTE_VALID) == 0) {
            if (flag) {
                db_printf("\nno memory is assigned to address %08x\n", addr);
                db_error(0);
                /* NOTREACHED */
            }
            return(-1);
        }

        src = (vm_offset_t)pte_to_pa(*ptp);
        *(int *) DMAP1 = INTEL_PTE_VALID | INTEL_PTE_RW | (src & PG_FRAME) | 
          INTEL_PTE_REF | INTEL_PTE_MOD;
#if defined(I386_CPU)
        if (cpu_class == CPUCLASS_386) {
                invltlb();
        } else
#endif
        {
                invlpg((u_int)DADDR1);
        }

        *kaddr = (unsigned)DADDR1 + (addr & PAGE_MASK);

        return(0);
}
        
/*
 * Read bytes from kernel address space for debugger.
 */

void
db_read_bytes(
        vm_offset_t     addr,
        int             size,
        char            *data,
        task_t          task)
{
        register char   *src;
        register int    n;
        unsigned        kern_addr;

        src = (char *)addr;
        if (task == kernel_task || task == TASK_NULL) {
            while (--size >= 0) {
                if (addr++ > VM_MAX_KERNEL_ADDRESS) {
                    db_printf("\nbad address %x\n", addr);
                    db_error(0);
                    /* NOTREACHED */
                }
                *data++ = *src++;
            }
            return;
        }
        while (size > 0) {
            if (db_user_to_kernel_address(task, addr, &kern_addr, 1) < 0)
                return;
            src = (char *)kern_addr;
            n = intel_trunc_page(addr+INTEL_PGBYTES) - addr;
            if (n > size)
                n = size;
            size -= n;
            addr += n;
            while (--n >= 0)
                *data++ = *src++;
        }
}

/*
 * Write bytes to kernel address space for debugger.
 */

void
db_write_bytes(
        vm_offset_t     addr,
        int             size,
        char            *data,
        task_t          task)
{
        register char   *dst;

        register pt_entry_t *ptep0 = 0;
        pt_entry_t      oldmap0 = 0;
        vm_offset_t     addr1;
        register pt_entry_t *ptep1 = 0;
        pt_entry_t      oldmap1 = 0;
        extern char     etext;

        if (task && task != kernel_task) {
            db_write_bytes_user_space(addr, size, data, task);
            return;
        }

            
        if (addr >= VM_MIN_KERNEL_LOADED_ADDRESS) {
                db_write_bytes_user_space(addr, size, data, kernel_task);
                return;
        }

        if (addr >= VM_MIN_KERNEL_ADDRESS &&
            addr <= (vm_offset_t)&etext)
        {
            ptep0 = pmap_pte(kernel_pmap, addr);
            oldmap0 = *ptep0;
            *ptep0 |= INTEL_PTE_WRITE;

            addr1 = i386_trunc_page(addr + size - 1);
            if (i386_trunc_page(addr) != addr1) {
                /* data crosses a page boundary */

                ptep1 = pmap_pte(kernel_pmap, addr1);
                oldmap1 = *ptep1;
                *ptep1 |= INTEL_PTE_WRITE;
            }
            flush_tlb();
        } 

        dst = (char *)addr;

        while (--size >= 0) {
            if (addr++ > VM_MAX_KERNEL_ADDRESS) {
                db_printf("\nbad address %x\n", addr);
                db_error(0);
                /* NOTREACHED */
            }
            *dst++ = *data++;
        }

        if (ptep0) {
            *ptep0 = oldmap0;
            if (ptep1) {
                *ptep1 = oldmap1;
            }
            flush_tlb();
        }
}
        
void
db_write_bytes_user_space(
        vm_offset_t     addr,
        int             size,
        char            *data,
        task_t          task)
{
        register char   *dst;
        register int    n;
        unsigned        kern_addr;

        while (size > 0) {
            if (db_user_to_kernel_address(task, addr, &kern_addr, 1) < 0)
                return;
            dst = (char *)kern_addr;
            n = intel_trunc_page(addr+INTEL_PGBYTES) - addr;
            if (n > size)
                n = size;
            size -= n;
            addr += n;
            while (--n >= 0)
                *dst++ = *data++;
        }
}

boolean_t
db_check_access(
        vm_offset_t     addr,
        int             size,
        task_t          task)
{
        register        n;
        unsigned        kern_addr;

        if (task == kernel_task || task == TASK_NULL) {
            if (kernel_task == TASK_NULL)
                return(TRUE);
            task = kernel_task;
        } else if (task == TASK_NULL) {
            if (current_thread() == THREAD_NULL)
                return(FALSE);
            task = current_thread()->task;
        }
        while (size > 0) {
            if (db_user_to_kernel_address(task, addr, &kern_addr, 0) < 0)
                return(FALSE);
            n = intel_trunc_page(addr+INTEL_PGBYTES) - addr;
            if (n > size)
                n = size;
            size -= n;
            addr += n;
        }
        return(TRUE);
}

boolean_t
db_phys_eq(
        task_t          task1,
        vm_offset_t     addr1,
        task_t          task2,
        vm_offset_t     addr2)
{
        unsigned        kern_addr1, kern_addr2;

        if ((addr1 & (INTEL_PGBYTES-1)) != (addr2 & (INTEL_PGBYTES-1)))
            return(FALSE);
        if (task1 == TASK_NULL) {
            if (current_thread() == THREAD_NULL)
                return(FALSE);
            task1 = current_thread()->task;
        }
        if (db_user_to_kernel_address(task1, addr1, &kern_addr1, 0) < 0 ||
                db_user_to_kernel_address(task2, addr2, &kern_addr2, 0) < 0)
            return(FALSE);
        return(kern_addr1 == kern_addr2);
}

#define DB_USER_STACK_ADDR              (VM_MIN_KERNEL_ADDRESS)
#define DB_NAME_SEARCH_LIMIT            (DB_USER_STACK_ADDR-(INTEL_PGBYTES*3))

int
db_search_null(
        task_t          task,
        unsigned        *svaddr,
        unsigned        evaddr,
        unsigned        *skaddr,
        int             flag)
{
        register unsigned vaddr;
        register unsigned *kaddr;

        kaddr = (unsigned *)*skaddr;
        for (vaddr = *svaddr; vaddr > evaddr; vaddr -= sizeof(unsigned)) {
            if (vaddr % INTEL_PGBYTES == 0) {
                vaddr -= sizeof(unsigned);
                if (db_user_to_kernel_address(task, vaddr, skaddr, 0) < 0)
                    return(-1);
                kaddr = (unsigned *)*skaddr;
            } else {
                vaddr -= sizeof(unsigned);
                kaddr--;
            }
            if ((*kaddr == 0) ^ (flag  == 0)) {
                *svaddr = vaddr;
                *skaddr = (unsigned)kaddr;
                return(0);
            }
        }
        return(-1);
}

void
db_task_name(
        task_t          task)
{
        register char *p;
        register n;
        unsigned vaddr, kaddr;

        vaddr = DB_USER_STACK_ADDR;
        kaddr = 0;

        /*
         * skip nulls at the end
         */
        if (db_search_null(task, &vaddr, DB_NAME_SEARCH_LIMIT, &kaddr, 0) < 0) {
            db_printf(DB_NULL_TASK_NAME);
            return;
        }
        /*
         * search start of args
         */
        if (db_search_null(task, &vaddr, DB_NAME_SEARCH_LIMIT, &kaddr, 1) < 0) {
            db_printf(DB_NULL_TASK_NAME);
            return;
        }

        n = DB_TASK_NAME_LEN-1;
        p = (char *)kaddr + sizeof(unsigned);
        for (vaddr += sizeof(int); vaddr < DB_USER_STACK_ADDR && n > 0; 
                                                        vaddr++, p++, n--) {
            if (vaddr % INTEL_PGBYTES == 0) {
                (void)db_user_to_kernel_address(task, vaddr, &kaddr, 0);
                p = (char*)kaddr;
            }
            db_printf("%c", (*p < ' ' || *p > '~')? ' ': *p);
        }
        while (n-- >= 0)        /* compare with >= 0 for one more space */
            db_printf(" ");
}

/*
 * Code used to synchronize kdb among all cpus, one active at a time, switch
 * from on to another using kdb_on! #cpu or cpu #cpu
 */

decl_simple_lock_data(, kdb_lock)       /* kdb lock                     */

#define db_simple_lock_init(l, e)       hw_lock_init(&((l)->interlock))
#define db_simple_lock_try(l)           hw_lock_try(&((l)->interlock))
#define db_simple_unlock(l)             hw_lock_unlock(&((l)->interlock))

int                     kdb_cpu = -1;   /* current cpu running kdb      */
int                     kdb_debug = 0;
volatile unsigned int   cpus_holding_bkpts;     /* counter for number of cpus holding
                                                   breakpoints (ie: cpus that did not
                                                   insert back breakpoints) */
extern boolean_t        db_breakpoints_inserted;

void
db_machdep_init(void)
{
        int c;

        db_simple_lock_init(&kdb_lock, 0);
        for (c = 0; c < real_ncpus; ++c) {
                db_stacks[c] = (vm_offset_t) (db_stack_store +
                        (INTSTACK_SIZE * (c + 1)) - sizeof (natural_t));
                if (c == master_cpu) {
                        dbtss.esp0 = (int)(db_task_stack_store +
                                (INTSTACK_SIZE * (c + 1)) - sizeof (natural_t));
                        dbtss.esp = dbtss.esp0;
                        dbtss.eip = (int)&db_task_start;
                        /*
                         * The TSS for the debugging task on each slave CPU
                         * is set up in mp_desc_init().
                         */
                }
        }
}

/*
 * Called when entering kdb:
 * Takes kdb lock. If if we were called remotely (slave state) we just
 * wait for kdb_cpu to be equal to cpu_number(). Otherwise enter kdb if
 * not active on another cpu.
 * If db_pass_thru[cpu_number()] > 0, then kdb can't stop now.
 */

int
kdb_enter(int pc)
{
        int mycpu;
        int retval;

        disable_preemption();

        mycpu = cpu_number();

        if (current_cpu_datap()->cpu_db_pass_thru) {
                retval = 0;
                goto kdb_exit;
        }

        current_cpu_datap()->cpu_kdb_active++;
        lock_kdb();

        if (kdb_debug)
                db_printf("kdb_enter: cpu %d, is_slave %d, kdb_cpu %d, run mode %d pc %x (%x) holds %d\n",
                          my_cpu, current_cpu_datap()->cpu_kdb_is_slave, kdb_cpu,
                          db_run_mode, pc, *(int *)pc, cpus_holding_bkpts);
        if (db_breakpoints_inserted)
                cpus_holding_bkpts++;
        if (kdb_cpu == -1 && !current_cpu_datap()->cpu_kdb_is_slave) {
                kdb_cpu = my_cpu;
                remote_kdb();   /* stop other cpus */
                retval = 1;
        } else if (kdb_cpu == my_cpu) 
                retval = 1;
        else
                retval = 0;

kdb_exit:
        enable_preemption();

        return (retval);
}

void
kdb_leave(void)
{
        int my_cpu;
        boolean_t       wait = FALSE;

        disable_preemption();

        my_cpu = cpu_number();

        if (db_run_mode == STEP_CONTINUE) {
                wait = TRUE;
                kdb_cpu = -1;
        }
        if (db_breakpoints_inserted)
                cpus_holding_bkpts--;
        if (current_cpu_datap()->cpu_kdb_is_slave)
                current_cpu_datap()->cpu_kdb_is_slave--;
        if (kdb_debug)
                db_printf("kdb_leave: cpu %d, kdb_cpu %d, run_mode %d pc %x (%x) holds %d\n",
                          my_cpu, kdb_cpu, db_run_mode,
                          ddb_regs.eip, *(int *)ddb_regs.eip,
                          cpus_holding_bkpts);
        clear_kdb_intr();
        unlock_kdb();
        current_cpu_datap()->cpu_kdb_active--;

        enable_preemption();

        if (wait) {
                while(cpus_holding_bkpts);
        }
}

void
lock_kdb(void)
{
        int             my_cpu;
        register        i;
        extern void     kdb_console(void);

        disable_preemption();

        my_cpu = cpu_number();

        for(;;) {
                kdb_console();
                if (kdb_cpu != -1 && kdb_cpu != my_cpu) {
                        continue;
                }
                if (db_simple_lock_try(&kdb_lock)) {
                        if (kdb_cpu == -1 || kdb_cpu == my_cpu)
                                break;
                        db_simple_unlock(&kdb_lock);
                }
        } 

        enable_preemption();
}

#if     TIME_STAMP
extern unsigned old_time_stamp;
#endif  /* TIME_STAMP */

void
unlock_kdb(void)
{
        db_simple_unlock(&kdb_lock);
#if     TIME_STAMP
        old_time_stamp = 0;
#endif  /* TIME_STAMP */
}


#ifdef  __STDC__
#define KDB_SAVE(type, name) extern type name; type name##_save = name
#define KDB_RESTORE(name) name = name##_save
#else   /* __STDC__ */
#define KDB_SAVE(type, name) extern type name; type name/**/_save = name
#define KDB_RESTORE(name) name = name/**/_save
#endif  /* __STDC__ */

#define KDB_SAVE_CTXT() \
        KDB_SAVE(int, db_run_mode); \
        KDB_SAVE(boolean_t, db_sstep_print); \
        KDB_SAVE(int, db_loop_count); \
        KDB_SAVE(int, db_call_depth); \
        KDB_SAVE(int, db_inst_count); \
        KDB_SAVE(int, db_last_inst_count); \
        KDB_SAVE(int, db_load_count); \
        KDB_SAVE(int, db_store_count); \
        KDB_SAVE(boolean_t, db_cmd_loop_done); \
        KDB_SAVE(jmp_buf_t *, db_recover); \
        KDB_SAVE(db_addr_t, db_dot); \
        KDB_SAVE(db_addr_t, db_last_addr); \
        KDB_SAVE(db_addr_t, db_prev); \
        KDB_SAVE(db_addr_t, db_next); \
        KDB_SAVE(db_regs_t, ddb_regs); 

#define KDB_RESTORE_CTXT() \
        KDB_RESTORE(db_run_mode); \
        KDB_RESTORE(db_sstep_print); \
        KDB_RESTORE(db_loop_count); \
        KDB_RESTORE(db_call_depth); \
        KDB_RESTORE(db_inst_count); \
        KDB_RESTORE(db_last_inst_count); \
        KDB_RESTORE(db_load_count); \
        KDB_RESTORE(db_store_count); \
        KDB_RESTORE(db_cmd_loop_done); \
        KDB_RESTORE(db_recover); \
        KDB_RESTORE(db_dot); \
        KDB_RESTORE(db_last_addr); \
        KDB_RESTORE(db_prev); \
        KDB_RESTORE(db_next); \
        KDB_RESTORE(ddb_regs); 

/*
 * switch to another cpu
 */

void
kdb_on(
        int             cpu)
{
        KDB_SAVE_CTXT();
        if (cpu < 0 || cpu >= real_ncpus || !cpu_datap(cpu)->cpu_kdb_active)
                return;
        db_set_breakpoints();
        db_set_watchpoints();
        kdb_cpu = cpu;
        unlock_kdb();
        lock_kdb();
        db_clear_breakpoints();
        db_clear_watchpoints();
        KDB_RESTORE_CTXT();
        if (kdb_cpu == -1)  {/* someone continued */
                kdb_cpu = cpu_number();
                db_continue_cmd(0, 0, 0, "");
        }
}

void db_reboot(
        db_expr_t       addr,
        boolean_t       have_addr,
        db_expr_t       count,
        char            *modif)
{
        boolean_t       reboot = TRUE;
        char            *cp, c;
        
        cp = modif;
        while ((c = *cp++) != 0) {
                if (c == 'r')   /* reboot */
                        reboot = TRUE;
                if (c == 'h')   /* halt */
                        reboot = FALSE;
        }
        halt_all_cpus(reboot);
}