kgdb: use atomic_inc and atomic_dec instead of atomic_set

[safe/jmp/linux-2.6] / kernel / kgdb.c

/*
 * KGDB stub.
 *
 * Maintainer: Jason Wessel <jason.wessel@windriver.com>
 *
 * Copyright (C) 2000-2001 VERITAS Software Corporation.
 * Copyright (C) 2002-2004 Timesys Corporation
 * Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
 * Copyright (C) 2004 Pavel Machek <pavel@suse.cz>
 * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
 * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
 * Copyright (C) 2005-2008 Wind River Systems, Inc.
 * Copyright (C) 2007 MontaVista Software, Inc.
 * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 * Contributors at various stages not listed above:
 *  Jason Wessel ( jason.wessel@windriver.com )
 *  George Anzinger <george@mvista.com>
 *  Anurekh Saxena (anurekh.saxena@timesys.com)
 *  Lake Stevens Instrument Division (Glenn Engel)
 *  Jim Kingdon, Cygnus Support.
 *
 * Original KGDB stub: David Grothe <dave@gcom.com>,
 * Tigran Aivazian <tigran@sco.com>
 *
 * This file is licensed under the terms of the GNU General Public License
 * version 2. This program is licensed "as is" without any warranty of any
 * kind, whether express or implied.
 */
#include <linux/pid_namespace.h>
#include <linux/clocksource.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/console.h>
#include <linux/threads.h>
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/reboot.h>
#include <linux/string.h>
#include <linux/delay.h>
#include <linux/sched.h>
#include <linux/sysrq.h>
#include <linux/init.h>
#include <linux/kgdb.h>
#include <linux/pid.h>
#include <linux/smp.h>
#include <linux/mm.h>

#include <asm/cacheflush.h>
#include <asm/byteorder.h>
#include <asm/atomic.h>
#include <asm/system.h>
#include <asm/unaligned.h>

static int kgdb_break_asap;

#define KGDB_MAX_THREAD_QUERY 17
struct kgdb_state {
        int                     ex_vector;
        int                     signo;
        int                     err_code;
        int                     cpu;
        int                     pass_exception;
        unsigned long           thr_query;
        unsigned long           threadid;
        long                    kgdb_usethreadid;
        struct pt_regs          *linux_regs;
};

/* Exception state values */
#define DCPU_WANT_MASTER 0x1 /* Waiting to become a master kgdb cpu */
#define DCPU_NEXT_MASTER 0x2 /* Transition from one master cpu to another */
#define DCPU_IS_SLAVE    0x4 /* Slave cpu enter exception */
#define DCPU_SSTEP       0x8 /* CPU is single stepping */

static struct debuggerinfo_struct {
        void                    *debuggerinfo;
        struct task_struct      *task;
        int                     exception_state;
} kgdb_info[NR_CPUS];

/**
 * kgdb_connected - Is a host GDB connected to us?
 */
int                             kgdb_connected;
EXPORT_SYMBOL_GPL(kgdb_connected);

/* All the KGDB handlers are installed */
static int                      kgdb_io_module_registered;

/* Guard for recursive entry */
static int                      exception_level;

static struct kgdb_io           *kgdb_io_ops;
static DEFINE_SPINLOCK(kgdb_registration_lock);

/* kgdb console driver is loaded */
static int kgdb_con_registered;
/* determine if kgdb console output should be used */
static int kgdb_use_con;

static int __init opt_kgdb_con(char *str)
{
        kgdb_use_con = 1;
        return 0;
}

early_param("kgdbcon", opt_kgdb_con);

module_param(kgdb_use_con, int, 0644);

/*
 * Holds information about breakpoints in a kernel. These breakpoints are
 * added and removed by gdb.
 */
static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
        [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
};

/*
 * The CPU# of the active CPU, or -1 if none:
 */
atomic_t                        kgdb_active = ATOMIC_INIT(-1);

/*
 * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 * bootup code (which might not have percpu set up yet):
 */
static atomic_t                 passive_cpu_wait[NR_CPUS];
static atomic_t                 cpu_in_kgdb[NR_CPUS];
atomic_t                        kgdb_setting_breakpoint;

struct task_struct              *kgdb_usethread;
struct task_struct              *kgdb_contthread;

int                             kgdb_single_step;
pid_t                           kgdb_sstep_pid;

/* Our I/O buffers. */
static char                     remcom_in_buffer[BUFMAX];
static char                     remcom_out_buffer[BUFMAX];

/* Storage for the registers, in GDB format. */
static unsigned long            gdb_regs[(NUMREGBYTES +
                                        sizeof(unsigned long) - 1) /
                                        sizeof(unsigned long)];

/* to keep track of the CPU which is doing the single stepping*/
atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);

/*
 * If you are debugging a problem where roundup (the collection of
 * all other CPUs) is a problem [this should be extremely rare],
 * then use the nokgdbroundup option to avoid roundup. In that case
 * the other CPUs might interfere with your debugging context, so
 * use this with care:
 */
static int kgdb_do_roundup = 1;

static int __init opt_nokgdbroundup(char *str)
{
        kgdb_do_roundup = 0;

        return 0;
}

early_param("nokgdbroundup", opt_nokgdbroundup);

/*
 * Finally, some KGDB code :-)
 */

/*
 * Weak aliases for breakpoint management,
 * can be overriden by architectures when needed:
 */
int __weak kgdb_arch_set_breakpoint(unsigned long addr, char *saved_instr)
{
        int err;

        err = probe_kernel_read(saved_instr, (char *)addr, BREAK_INSTR_SIZE);
        if (err)
                return err;

        return probe_kernel_write((char *)addr, arch_kgdb_ops.gdb_bpt_instr,
                                  BREAK_INSTR_SIZE);
}

int __weak kgdb_arch_remove_breakpoint(unsigned long addr, char *bundle)
{
        return probe_kernel_write((char *)addr,
                                  (char *)bundle, BREAK_INSTR_SIZE);
}

int __weak kgdb_validate_break_address(unsigned long addr)
{
        char tmp_variable[BREAK_INSTR_SIZE];
        int err;
        /* Validate setting the breakpoint and then removing it.  In the
         * remove fails, the kernel needs to emit a bad message because we
         * are deep trouble not being able to put things back the way we
         * found them.
         */
        err = kgdb_arch_set_breakpoint(addr, tmp_variable);
        if (err)
                return err;
        err = kgdb_arch_remove_breakpoint(addr, tmp_variable);
        if (err)
                printk(KERN_ERR "KGDB: Critical breakpoint error, kernel "
                   "memory destroyed at: %lx", addr);
        return err;
}

unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
{
        return instruction_pointer(regs);
}

int __weak kgdb_arch_init(void)
{
        return 0;
}

int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
{
        return 0;
}

void __weak
kgdb_post_primary_code(struct pt_regs *regs, int e_vector, int err_code)
{
        return;
}

/**
 *      kgdb_disable_hw_debug - Disable hardware debugging while we in kgdb.
 *      @regs: Current &struct pt_regs.
 *
 *      This function will be called if the particular architecture must
 *      disable hardware debugging while it is processing gdb packets or
 *      handling exception.
 */
void __weak kgdb_disable_hw_debug(struct pt_regs *regs)
{
}

/*
 * GDB remote protocol parser:
 */

static int hex(char ch)
{
        if ((ch >= 'a') && (ch <= 'f'))
                return ch - 'a' + 10;
        if ((ch >= '0') && (ch <= '9'))
                return ch - '0';
        if ((ch >= 'A') && (ch <= 'F'))
                return ch - 'A' + 10;
        return -1;
}

/* scan for the sequence $<data>#<checksum> */
static void get_packet(char *buffer)
{
        unsigned char checksum;
        unsigned char xmitcsum;
        int count;
        char ch;

        do {
                /*
                 * Spin and wait around for the start character, ignore all
                 * other characters:
                 */
                while ((ch = (kgdb_io_ops->read_char())) != '$')
                        /* nothing */;

                kgdb_connected = 1;
                checksum = 0;
                xmitcsum = -1;

                count = 0;

                /*
                 * now, read until a # or end of buffer is found:
                 */
                while (count < (BUFMAX - 1)) {
                        ch = kgdb_io_ops->read_char();
                        if (ch == '#')
                                break;
                        checksum = checksum + ch;
                        buffer[count] = ch;
                        count = count + 1;
                }
                buffer[count] = 0;

                if (ch == '#') {
                        xmitcsum = hex(kgdb_io_ops->read_char()) << 4;
                        xmitcsum += hex(kgdb_io_ops->read_char());

                        if (checksum != xmitcsum)
                                /* failed checksum */
                                kgdb_io_ops->write_char('-');
                        else
                                /* successful transfer */
                                kgdb_io_ops->write_char('+');
                        if (kgdb_io_ops->flush)
                                kgdb_io_ops->flush();
                }
        } while (checksum != xmitcsum);
}

/*
 * Send the packet in buffer.
 * Check for gdb connection if asked for.
 */
static void put_packet(char *buffer)
{
        unsigned char checksum;
        int count;
        char ch;

        /*
         * $<packet info>#<checksum>.
         */
        while (1) {
                kgdb_io_ops->write_char('$');
                checksum = 0;
                count = 0;

                while ((ch = buffer[count])) {
                        kgdb_io_ops->write_char(ch);
                        checksum += ch;
                        count++;
                }

                kgdb_io_ops->write_char('#');
                kgdb_io_ops->write_char(hex_asc_hi(checksum));
                kgdb_io_ops->write_char(hex_asc_lo(checksum));
                if (kgdb_io_ops->flush)
                        kgdb_io_ops->flush();

                /* Now see what we get in reply. */
                ch = kgdb_io_ops->read_char();

                if (ch == 3)
                        ch = kgdb_io_ops->read_char();

                /* If we get an ACK, we are done. */
                if (ch == '+')
                        return;

                /*
                 * If we get the start of another packet, this means
                 * that GDB is attempting to reconnect.  We will NAK
                 * the packet being sent, and stop trying to send this
                 * packet.
                 */
                if (ch == '$') {
                        kgdb_io_ops->write_char('-');
                        if (kgdb_io_ops->flush)
                                kgdb_io_ops->flush();
                        return;
                }
        }
}

/*
 * Convert the memory pointed to by mem into hex, placing result in buf.
 * Return a pointer to the last char put in buf (null). May return an error.
 */
int kgdb_mem2hex(char *mem, char *buf, int count)
{
        char *tmp;
        int err;

        /*
         * We use the upper half of buf as an intermediate buffer for the
         * raw memory copy.  Hex conversion will work against this one.
         */
        tmp = buf + count;

        err = probe_kernel_read(tmp, mem, count);
        if (!err) {
                while (count > 0) {
                        buf = pack_hex_byte(buf, *tmp);
                        tmp++;
                        count--;
                }

                *buf = 0;
        }

        return err;
}

/*
 * Copy the binary array pointed to by buf into mem.  Fix $, #, and
 * 0x7d escaped with 0x7d. Return -EFAULT on failure or 0 on success.
 * The input buf is overwitten with the result to write to mem.
 */
static int kgdb_ebin2mem(char *buf, char *mem, int count)
{
        int size = 0;
        char *c = buf;

        while (count-- > 0) {
                c[size] = *buf++;
                if (c[size] == 0x7d)
                        c[size] = *buf++ ^ 0x20;
                size++;
        }

        return probe_kernel_write(mem, c, size);
}

/*
 * Convert the hex array pointed to by buf into binary to be placed in mem.
 * Return a pointer to the character AFTER the last byte written.
 * May return an error.
 */
int kgdb_hex2mem(char *buf, char *mem, int count)
{
        char *tmp_raw;
        char *tmp_hex;

        /*
         * We use the upper half of buf as an intermediate buffer for the
         * raw memory that is converted from hex.
         */
        tmp_raw = buf + count * 2;

        tmp_hex = tmp_raw - 1;
        while (tmp_hex >= buf) {
                tmp_raw--;
                *tmp_raw = hex(*tmp_hex--);
                *tmp_raw |= hex(*tmp_hex--) << 4;
        }

        return probe_kernel_write(mem, tmp_raw, count);
}

/*
 * While we find nice hex chars, build a long_val.
 * Return number of chars processed.
 */
int kgdb_hex2long(char **ptr, unsigned long *long_val)
{
        int hex_val;
        int num = 0;
        int negate = 0;

        *long_val = 0;

        if (**ptr == '-') {
                negate = 1;
                (*ptr)++;
        }
        while (**ptr) {
                hex_val = hex(**ptr);
                if (hex_val < 0)
                        break;

                *long_val = (*long_val << 4) | hex_val;
                num++;
                (*ptr)++;
        }

        if (negate)
                *long_val = -*long_val;

        return num;
}

/* Write memory due to an 'M' or 'X' packet. */
static int write_mem_msg(int binary)
{
        char *ptr = &remcom_in_buffer[1];
        unsigned long addr;
        unsigned long length;
        int err;

        if (kgdb_hex2long(&ptr, &addr) > 0 && *(ptr++) == ',' &&
            kgdb_hex2long(&ptr, &length) > 0 && *(ptr++) == ':') {
                if (binary)
                        err = kgdb_ebin2mem(ptr, (char *)addr, length);
                else
                        err = kgdb_hex2mem(ptr, (char *)addr, length);
                if (err)
                        return err;
                if (CACHE_FLUSH_IS_SAFE)
                        flush_icache_range(addr, addr + length);
                return 0;
        }

        return -EINVAL;
}

static void error_packet(char *pkt, int error)
{
        error = -error;
        pkt[0] = 'E';
        pkt[1] = hex_asc[(error / 10)];
        pkt[2] = hex_asc[(error % 10)];
        pkt[3] = '\0';
}

/*
 * Thread ID accessors. We represent a flat TID space to GDB, where
 * the per CPU idle threads (which under Linux all have PID 0) are
 * remapped to negative TIDs.
 */

#define BUF_THREAD_ID_SIZE      16

static char *pack_threadid(char *pkt, unsigned char *id)
{
        char *limit;

        limit = pkt + BUF_THREAD_ID_SIZE;
        while (pkt < limit)
                pkt = pack_hex_byte(pkt, *id++);

        return pkt;
}

static void int_to_threadref(unsigned char *id, int value)
{
        unsigned char *scan;
        int i = 4;

        scan = (unsigned char *)id;
        while (i--)
                *scan++ = 0;
        put_unaligned_be32(value, scan);
}

static struct task_struct *getthread(struct pt_regs *regs, int tid)
{
        /*
         * Non-positive TIDs are remapped to the cpu shadow information
         */
        if (tid == 0 || tid == -1)
                tid = -atomic_read(&kgdb_active) - 2;
        if (tid < -1 && tid > -NR_CPUS - 2) {
                if (kgdb_info[-tid - 2].task)
                        return kgdb_info[-tid - 2].task;
                else
                        return idle_task(-tid - 2);
        }
        if (tid <= 0) {
                printk(KERN_ERR "KGDB: Internal thread select error\n");
                dump_stack();
                return NULL;
        }

        /*
         * find_task_by_pid_ns() does not take the tasklist lock anymore
         * but is nicely RCU locked - hence is a pretty resilient
         * thing to use:
         */
        return find_task_by_pid_ns(tid, &init_pid_ns);
}

/*
 * Some architectures need cache flushes when we set/clear a
 * breakpoint:
 */
static void kgdb_flush_swbreak_addr(unsigned long addr)
{
        if (!CACHE_FLUSH_IS_SAFE)
                return;

        if (current->mm && current->mm->mmap_cache) {
                flush_cache_range(current->mm->mmap_cache,
                                  addr, addr + BREAK_INSTR_SIZE);
        }
        /* Force flush instruction cache if it was outside the mm */
        flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
}

/*
 * SW breakpoint management:
 */
static int kgdb_activate_sw_breakpoints(void)
{
        unsigned long addr;
        int error;
        int ret = 0;
        int i;

        for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
                if (kgdb_break[i].state != BP_SET)
                        continue;

                addr = kgdb_break[i].bpt_addr;
                error = kgdb_arch_set_breakpoint(addr,
                                kgdb_break[i].saved_instr);
                if (error) {
                        ret = error;
                        printk(KERN_INFO "KGDB: BP install failed: %lx", addr);
                        continue;
                }

                kgdb_flush_swbreak_addr(addr);
                kgdb_break[i].state = BP_ACTIVE;
        }
        return ret;
}

static int kgdb_set_sw_break(unsigned long addr)
{
        int err = kgdb_validate_break_address(addr);
        int breakno = -1;
        int i;

        if (err)
                return err;

        for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
                if ((kgdb_break[i].state == BP_SET) &&
                                        (kgdb_break[i].bpt_addr == addr))
                        return -EEXIST;
        }
        for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
                if (kgdb_break[i].state == BP_REMOVED &&
                                        kgdb_break[i].bpt_addr == addr) {
                        breakno = i;
                        break;
                }
        }

        if (breakno == -1) {
                for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
                        if (kgdb_break[i].state == BP_UNDEFINED) {
                                breakno = i;
                                break;
                        }
                }
        }

        if (breakno == -1)
                return -E2BIG;

        kgdb_break[breakno].state = BP_SET;
        kgdb_break[breakno].type = BP_BREAKPOINT;
        kgdb_break[breakno].bpt_addr = addr;

        return 0;
}

static int kgdb_deactivate_sw_breakpoints(void)
{
        unsigned long addr;
        int error;
        int ret = 0;
        int i;

        for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
                if (kgdb_break[i].state != BP_ACTIVE)
                        continue;
                addr = kgdb_break[i].bpt_addr;
                error = kgdb_arch_remove_breakpoint(addr,
                                        kgdb_break[i].saved_instr);
                if (error) {
                        printk(KERN_INFO "KGDB: BP remove failed: %lx\n", addr);
                        ret = error;
                }

                kgdb_flush_swbreak_addr(addr);
                kgdb_break[i].state = BP_SET;
        }
        return ret;
}

static int kgdb_remove_sw_break(unsigned long addr)
{
        int i;

        for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
                if ((kgdb_break[i].state == BP_SET) &&
                                (kgdb_break[i].bpt_addr == addr)) {
                        kgdb_break[i].state = BP_REMOVED;
                        return 0;
                }
        }
        return -ENOENT;
}

int kgdb_isremovedbreak(unsigned long addr)
{
        int i;

        for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
                if ((kgdb_break[i].state == BP_REMOVED) &&
                                        (kgdb_break[i].bpt_addr == addr))
                        return 1;
        }
        return 0;
}

static int remove_all_break(void)
{
        unsigned long addr;
        int error;
        int i;

        /* Clear memory breakpoints. */
        for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
                if (kgdb_break[i].state != BP_ACTIVE)
                        goto setundefined;
                addr = kgdb_break[i].bpt_addr;
                error = kgdb_arch_remove_breakpoint(addr,
                                kgdb_break[i].saved_instr);
                if (error)
                        printk(KERN_ERR "KGDB: breakpoint remove failed: %lx\n",
                           addr);
setundefined:
                kgdb_break[i].state = BP_UNDEFINED;
        }

        /* Clear hardware breakpoints. */
        if (arch_kgdb_ops.remove_all_hw_break)
                arch_kgdb_ops.remove_all_hw_break();

        return 0;
}

/*
 * Remap normal tasks to their real PID,
 * CPU shadow threads are mapped to -CPU - 2
 */
static inline int shadow_pid(int realpid)
{
        if (realpid)
                return realpid;

        return -raw_smp_processor_id() - 2;
}

static char gdbmsgbuf[BUFMAX + 1];

static void kgdb_msg_write(const char *s, int len)
{
        char *bufptr;
        int wcount;
        int i;

        /* 'O'utput */
        gdbmsgbuf[0] = 'O';

        /* Fill and send buffers... */
        while (len > 0) {
                bufptr = gdbmsgbuf + 1;

                /* Calculate how many this time */
                if ((len << 1) > (BUFMAX - 2))
                        wcount = (BUFMAX - 2) >> 1;
                else
                        wcount = len;

                /* Pack in hex chars */
                for (i = 0; i < wcount; i++)
                        bufptr = pack_hex_byte(bufptr, s[i]);
                *bufptr = '\0';

                /* Move up */
                s += wcount;
                len -= wcount;

                /* Write packet */
                put_packet(gdbmsgbuf);
        }
}

/*
 * Return true if there is a valid kgdb I/O module.  Also if no
 * debugger is attached a message can be printed to the console about
 * waiting for the debugger to attach.
 *
 * The print_wait argument is only to be true when called from inside
 * the core kgdb_handle_exception, because it will wait for the
 * debugger to attach.
 */
static int kgdb_io_ready(int print_wait)
{
        if (!kgdb_io_ops)
                return 0;
        if (kgdb_connected)
                return 1;
        if (atomic_read(&kgdb_setting_breakpoint))
                return 1;
        if (print_wait)
                printk(KERN_CRIT "KGDB: Waiting for remote debugger\n");
        return 1;
}

/*
 * All the functions that start with gdb_cmd are the various
 * operations to implement the handlers for the gdbserial protocol
 * where KGDB is communicating with an external debugger
 */

/* Handle the '?' status packets */
static void gdb_cmd_status(struct kgdb_state *ks)
{
        /*
         * We know that this packet is only sent
         * during initial connect.  So to be safe,
         * we clear out our breakpoints now in case
         * GDB is reconnecting.
         */
        remove_all_break();

        remcom_out_buffer[0] = 'S';
        pack_hex_byte(&remcom_out_buffer[1], ks->signo);
}

/* Handle the 'g' get registers request */
static void gdb_cmd_getregs(struct kgdb_state *ks)
{
        struct task_struct *thread;
        void *local_debuggerinfo;
        int i;

        thread = kgdb_usethread;
        if (!thread) {
                thread = kgdb_info[ks->cpu].task;
                local_debuggerinfo = kgdb_info[ks->cpu].debuggerinfo;
        } else {
                local_debuggerinfo = NULL;
                for_each_online_cpu(i) {
                        /*
                         * Try to find the task on some other
                         * or possibly this node if we do not
                         * find the matching task then we try
                         * to approximate the results.
                         */
                        if (thread == kgdb_info[i].task)
                                local_debuggerinfo = kgdb_info[i].debuggerinfo;
                }
        }

        /*
         * All threads that don't have debuggerinfo should be
         * in schedule() sleeping, since all other CPUs
         * are in kgdb_wait, and thus have debuggerinfo.
         */
        if (local_debuggerinfo) {
                pt_regs_to_gdb_regs(gdb_regs, local_debuggerinfo);
        } else {
                /*
                 * Pull stuff saved during switch_to; nothing
                 * else is accessible (or even particularly
                 * relevant).
                 *
                 * This should be enough for a stack trace.
                 */
                sleeping_thread_to_gdb_regs(gdb_regs, thread);
        }
        kgdb_mem2hex((char *)gdb_regs, remcom_out_buffer, NUMREGBYTES);
}

/* Handle the 'G' set registers request */
static void gdb_cmd_setregs(struct kgdb_state *ks)
{
        kgdb_hex2mem(&remcom_in_buffer[1], (char *)gdb_regs, NUMREGBYTES);

        if (kgdb_usethread && kgdb_usethread != current) {
                error_packet(remcom_out_buffer, -EINVAL);
        } else {
                gdb_regs_to_pt_regs(gdb_regs, ks->linux_regs);
                strcpy(remcom_out_buffer, "OK");
        }
}

/* Handle the 'm' memory read bytes */
static void gdb_cmd_memread(struct kgdb_state *ks)
{
        char *ptr = &remcom_in_buffer[1];
        unsigned long length;
        unsigned long addr;
        int err;

        if (kgdb_hex2long(&ptr, &addr) > 0 && *ptr++ == ',' &&
                                        kgdb_hex2long(&ptr, &length) > 0) {
                err = kgdb_mem2hex((char *)addr, remcom_out_buffer, length);
                if (err)
                        error_packet(remcom_out_buffer, err);
        } else {
                error_packet(remcom_out_buffer, -EINVAL);
        }
}

/* Handle the 'M' memory write bytes */
static void gdb_cmd_memwrite(struct kgdb_state *ks)
{
        int err = write_mem_msg(0);

        if (err)
                error_packet(remcom_out_buffer, err);
        else
                strcpy(remcom_out_buffer, "OK");
}

/* Handle the 'X' memory binary write bytes */
static void gdb_cmd_binwrite(struct kgdb_state *ks)
{
        int err = write_mem_msg(1);

        if (err)
                error_packet(remcom_out_buffer, err);
        else
                strcpy(remcom_out_buffer, "OK");
}

/* Handle the 'D' or 'k', detach or kill packets */
static void gdb_cmd_detachkill(struct kgdb_state *ks)
{
        int error;

        /* The detach case */
        if (remcom_in_buffer[0] == 'D') {
                error = remove_all_break();
                if (error < 0) {
                        error_packet(remcom_out_buffer, error);
                } else {
                        strcpy(remcom_out_buffer, "OK");
                        kgdb_connected = 0;
                }
                put_packet(remcom_out_buffer);
        } else {
                /*
                 * Assume the kill case, with no exit code checking,
                 * trying to force detach the debugger:
                 */
                remove_all_break();
                kgdb_connected = 0;
        }
}

/* Handle the 'R' reboot packets */
static int gdb_cmd_reboot(struct kgdb_state *ks)
{
        /* For now, only honor R0 */
        if (strcmp(remcom_in_buffer, "R0") == 0) {
                printk(KERN_CRIT "Executing emergency reboot\n");
                strcpy(remcom_out_buffer, "OK");
                put_packet(remcom_out_buffer);

                /*
                 * Execution should not return from
                 * machine_emergency_restart()
                 */
                machine_emergency_restart();
                kgdb_connected = 0;

                return 1;
        }
        return 0;
}

/* Handle the 'q' query packets */
static void gdb_cmd_query(struct kgdb_state *ks)
{
        struct task_struct *g;
        struct task_struct *p;
        unsigned char thref[8];
        char *ptr;
        int i;
        int cpu;
        int finished = 0;

        switch (remcom_in_buffer[1]) {
        case 's':
        case 'f':
                if (memcmp(remcom_in_buffer + 2, "ThreadInfo", 10)) {
                        error_packet(remcom_out_buffer, -EINVAL);
                        break;
                }

                i = 0;
                remcom_out_buffer[0] = 'm';
                ptr = remcom_out_buffer + 1;
                if (remcom_in_buffer[1] == 'f') {
                        /* Each cpu is a shadow thread */
                        for_each_online_cpu(cpu) {
                                ks->thr_query = 0;
                                int_to_threadref(thref, -cpu - 2);
                                pack_threadid(ptr, thref);
                                ptr += BUF_THREAD_ID_SIZE;
                                *(ptr++) = ',';
                                i++;
                        }
                }

                do_each_thread(g, p) {
                        if (i >= ks->thr_query && !finished) {
                                int_to_threadref(thref, p->pid);
                                pack_threadid(ptr, thref);
                                ptr += BUF_THREAD_ID_SIZE;
                                *(ptr++) = ',';
                                ks->thr_query++;
                                if (ks->thr_query % KGDB_MAX_THREAD_QUERY == 0)
                                        finished = 1;
                        }
                        i++;
                } while_each_thread(g, p);

                *(--ptr) = '\0';
                break;

        case 'C':
                /* Current thread id */
                strcpy(remcom_out_buffer, "QC");
                ks->threadid = shadow_pid(current->pid);
                int_to_threadref(thref, ks->threadid);
                pack_threadid(remcom_out_buffer + 2, thref);
                break;
        case 'T':
                if (memcmp(remcom_in_buffer + 1, "ThreadExtraInfo,", 16)) {
                        error_packet(remcom_out_buffer, -EINVAL);
                        break;
                }
                ks->threadid = 0;
                ptr = remcom_in_buffer + 17;
                kgdb_hex2long(&ptr, &ks->threadid);
                if (!getthread(ks->linux_regs, ks->threadid)) {
                        error_packet(remcom_out_buffer, -EINVAL);
                        break;
                }
                if ((int)ks->threadid > 0) {
                        kgdb_mem2hex(getthread(ks->linux_regs,
                                        ks->threadid)->comm,
                                        remcom_out_buffer, 16);
                } else {
                        static char tmpstr[23 + BUF_THREAD_ID_SIZE];

                        sprintf(tmpstr, "shadowCPU%d",
                                        (int)(-ks->threadid - 2));
                        kgdb_mem2hex(tmpstr, remcom_out_buffer, strlen(tmpstr));
                }
                break;
        }
}

/* Handle the 'H' task query packets */
static void gdb_cmd_task(struct kgdb_state *ks)
{
        struct task_struct *thread;
        char *ptr;

        switch (remcom_in_buffer[1]) {
        case 'g':
                ptr = &remcom_in_buffer[2];
                kgdb_hex2long(&ptr, &ks->threadid);
                thread = getthread(ks->linux_regs, ks->threadid);
                if (!thread && ks->threadid > 0) {
                        error_packet(remcom_out_buffer, -EINVAL);
                        break;
                }
                kgdb_usethread = thread;
                ks->kgdb_usethreadid = ks->threadid;
                strcpy(remcom_out_buffer, "OK");
                break;
        case 'c':
                ptr = &remcom_in_buffer[2];
                kgdb_hex2long(&ptr, &ks->threadid);
                if (!ks->threadid) {
                        kgdb_contthread = NULL;
                } else {
                        thread = getthread(ks->linux_regs, ks->threadid);
                        if (!thread && ks->threadid > 0) {
                                error_packet(remcom_out_buffer, -EINVAL);
                                break;
                        }
                        kgdb_contthread = thread;
                }
                strcpy(remcom_out_buffer, "OK");
                break;
        }
}

/* Handle the 'T' thread query packets */
static void gdb_cmd_thread(struct kgdb_state *ks)
{
        char *ptr = &remcom_in_buffer[1];
        struct task_struct *thread;

        kgdb_hex2long(&ptr, &ks->threadid);
        thread = getthread(ks->linux_regs, ks->threadid);
        if (thread)
                strcpy(remcom_out_buffer, "OK");
        else
                error_packet(remcom_out_buffer, -EINVAL);
}

/* Handle the 'z' or 'Z' breakpoint remove or set packets */
static void gdb_cmd_break(struct kgdb_state *ks)
{
        /*
         * Since GDB-5.3, it's been drafted that '0' is a software
         * breakpoint, '1' is a hardware breakpoint, so let's do that.
         */
        char *bpt_type = &remcom_in_buffer[1];
        char *ptr = &remcom_in_buffer[2];
        unsigned long addr;
        unsigned long length;
        int error = 0;

        if (arch_kgdb_ops.set_hw_breakpoint && *bpt_type >= '1') {
                /* Unsupported */
                if (*bpt_type > '4')
                        return;
        } else {
                if (*bpt_type != '0' && *bpt_type != '1')
                        /* Unsupported. */
                        return;
        }

        /*
         * Test if this is a hardware breakpoint, and
         * if we support it:
         */
        if (*bpt_type == '1' && !(arch_kgdb_ops.flags & KGDB_HW_BREAKPOINT))
                /* Unsupported. */
                return;

        if (*(ptr++) != ',') {
                error_packet(remcom_out_buffer, -EINVAL);
                return;
        }
        if (!kgdb_hex2long(&ptr, &addr)) {
                error_packet(remcom_out_buffer, -EINVAL);
                return;
        }
        if (*(ptr++) != ',' ||
                !kgdb_hex2long(&ptr, &length)) {
                error_packet(remcom_out_buffer, -EINVAL);
                return;
        }

        if (remcom_in_buffer[0] == 'Z' && *bpt_type == '0')
                error = kgdb_set_sw_break(addr);
        else if (remcom_in_buffer[0] == 'z' && *bpt_type == '0')
                error = kgdb_remove_sw_break(addr);
        else if (remcom_in_buffer[0] == 'Z')
                error = arch_kgdb_ops.set_hw_breakpoint(addr,
                        (int)length, *bpt_type - '0');
        else if (remcom_in_buffer[0] == 'z')
                error = arch_kgdb_ops.remove_hw_breakpoint(addr,
                        (int) length, *bpt_type - '0');

        if (error == 0)
                strcpy(remcom_out_buffer, "OK");
        else
                error_packet(remcom_out_buffer, error);
}

/* Handle the 'C' signal / exception passing packets */
static int gdb_cmd_exception_pass(struct kgdb_state *ks)
{
        /* C09 == pass exception
         * C15 == detach kgdb, pass exception
         */
        if (remcom_in_buffer[1] == '0' && remcom_in_buffer[2] == '9') {

                ks->pass_exception = 1;
                remcom_in_buffer[0] = 'c';

        } else if (remcom_in_buffer[1] == '1' && remcom_in_buffer[2] == '5') {

                ks->pass_exception = 1;
                remcom_in_buffer[0] = 'D';
                remove_all_break();
                kgdb_connected = 0;
                return 1;

        } else {
                kgdb_msg_write("KGDB only knows signal 9 (pass)"
                        " and 15 (pass and disconnect)\n"
                        "Executing a continue without signal passing\n", 0);
                remcom_in_buffer[0] = 'c';
        }

        /* Indicate fall through */
        return -1;
}

/*
 * This function performs all gdbserial command procesing
 */
static int gdb_serial_stub(struct kgdb_state *ks)
{
        int error = 0;
        int tmp;

        /* Clear the out buffer. */
        memset(remcom_out_buffer, 0, sizeof(remcom_out_buffer));

        if (kgdb_connected) {
                unsigned char thref[8];
                char *ptr;

                /* Reply to host that an exception has occurred */
                ptr = remcom_out_buffer;
                *ptr++ = 'T';
                ptr = pack_hex_byte(ptr, ks->signo);
                ptr += strlen(strcpy(ptr, "thread:"));
                int_to_threadref(thref, shadow_pid(current->pid));
                ptr = pack_threadid(ptr, thref);
                *ptr++ = ';';
                put_packet(remcom_out_buffer);
        }

        kgdb_usethread = kgdb_info[ks->cpu].task;
        ks->kgdb_usethreadid = shadow_pid(kgdb_info[ks->cpu].task->pid);
        ks->pass_exception = 0;

        while (1) {
                error = 0;

                /* Clear the out buffer. */
                memset(remcom_out_buffer, 0, sizeof(remcom_out_buffer));

                get_packet(remcom_in_buffer);

                switch (remcom_in_buffer[0]) {
                case '?': /* gdbserial status */
                        gdb_cmd_status(ks);
                        break;
                case 'g': /* return the value of the CPU registers */
                        gdb_cmd_getregs(ks);
                        break;
                case 'G': /* set the value of the CPU registers - return OK */
                        gdb_cmd_setregs(ks);
                        break;
                case 'm': /* mAA..AA,LLLL  Read LLLL bytes at address AA..AA */
                        gdb_cmd_memread(ks);
                        break;
                case 'M': /* MAA..AA,LLLL: Write LLLL bytes at address AA..AA */
                        gdb_cmd_memwrite(ks);
                        break;
                case 'X': /* XAA..AA,LLLL: Write LLLL bytes at address AA..AA */
                        gdb_cmd_binwrite(ks);
                        break;
                        /* kill or detach. KGDB should treat this like a
                         * continue.
                         */
                case 'D': /* Debugger detach */
                case 'k': /* Debugger detach via kill */
                        gdb_cmd_detachkill(ks);
                        goto default_handle;
                case 'R': /* Reboot */
                        if (gdb_cmd_reboot(ks))
                                goto default_handle;
                        break;
                case 'q': /* query command */
                        gdb_cmd_query(ks);
                        break;
                case 'H': /* task related */
                        gdb_cmd_task(ks);
                        break;
                case 'T': /* Query thread status */
                        gdb_cmd_thread(ks);
                        break;
                case 'z': /* Break point remove */
                case 'Z': /* Break point set */
                        gdb_cmd_break(ks);
                        break;
                case 'C': /* Exception passing */
                        tmp = gdb_cmd_exception_pass(ks);
                        if (tmp > 0)
                                goto default_handle;
                        if (tmp == 0)
                                break;
                        /* Fall through on tmp < 0 */
                case 'c': /* Continue packet */
                case 's': /* Single step packet */
                        if (kgdb_contthread && kgdb_contthread != current) {
                                /* Can't switch threads in kgdb */
                                error_packet(remcom_out_buffer, -EINVAL);
                                break;
                        }
                        kgdb_activate_sw_breakpoints();
                        /* Fall through to default processing */
                default:
default_handle:
                        error = kgdb_arch_handle_exception(ks->ex_vector,
                                                ks->signo,
                                                ks->err_code,
                                                remcom_in_buffer,
                                                remcom_out_buffer,
                                                ks->linux_regs);
                        /*
                         * Leave cmd processing on error, detach,
                         * kill, continue, or single step.
                         */
                        if (error >= 0 || remcom_in_buffer[0] == 'D' ||
                            remcom_in_buffer[0] == 'k') {
                                error = 0;
                                goto kgdb_exit;
                        }

                }

                /* reply to the request */
                put_packet(remcom_out_buffer);
        }

kgdb_exit:
        if (ks->pass_exception)
                error = 1;
        return error;
}

static int kgdb_reenter_check(struct kgdb_state *ks)
{
        unsigned long addr;

        if (atomic_read(&kgdb_active) != raw_smp_processor_id())
                return 0;

        /* Panic on recursive debugger calls: */
        exception_level++;
        addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
        kgdb_deactivate_sw_breakpoints();

        /*
         * If the break point removed ok at the place exception
         * occurred, try to recover and print a warning to the end
         * user because the user planted a breakpoint in a place that
         * KGDB needs in order to function.
         */
        if (kgdb_remove_sw_break(addr) == 0) {
                exception_level = 0;
                kgdb_skipexception(ks->ex_vector, ks->linux_regs);
                kgdb_activate_sw_breakpoints();
                printk(KERN_CRIT "KGDB: re-enter error: breakpoint removed %lx\n",
                        addr);
                WARN_ON_ONCE(1);

                return 1;
        }
        remove_all_break();
        kgdb_skipexception(ks->ex_vector, ks->linux_regs);

        if (exception_level > 1) {
                dump_stack();
                panic("Recursive entry to debugger");
        }

        printk(KERN_CRIT "KGDB: re-enter exception: ALL breakpoints killed\n");
        dump_stack();
        panic("Recursive entry to debugger");

        return 1;
}

static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs)
{
        unsigned long flags;
        int sstep_tries = 100;
        int error = 0;
        int i, cpu;
acquirelock:
        /*
         * Interrupts will be restored by the 'trap return' code, except when
         * single stepping.
         */
        local_irq_save(flags);

        cpu = ks->cpu;
        kgdb_info[cpu].debuggerinfo = regs;
        kgdb_info[cpu].task = current;
        /*
         * Make sure the above info reaches the primary CPU before
         * our cpu_in_kgdb[] flag setting does:
         */
        atomic_inc(&cpu_in_kgdb[cpu]);

        /*
         * CPU will loop if it is a slave or request to become a kgdb
         * master cpu and acquire the kgdb_active lock:
         */
        while (1) {
                if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
                        if (atomic_cmpxchg(&kgdb_active, -1, cpu) == cpu)
                                break;
                } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
                        if (!atomic_read(&passive_cpu_wait[cpu]))
                                goto return_normal;
                } else {
return_normal:
                        /* Return to normal operation by executing any
                         * hw breakpoint fixup.
                         */
                        if (arch_kgdb_ops.correct_hw_break)
                                arch_kgdb_ops.correct_hw_break();
                        atomic_dec(&cpu_in_kgdb[cpu]);
                        touch_softlockup_watchdog_sync();
                        clocksource_touch_watchdog();
                        local_irq_restore(flags);
                        return 0;
                }
                cpu_relax();
        }

        /*
         * For single stepping, try to only enter on the processor
         * that was single stepping.  To gaurd against a deadlock, the
         * kernel will only try for the value of sstep_tries before
         * giving up and continuing on.
         */
        if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
            (kgdb_info[cpu].task &&
             kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
                atomic_set(&kgdb_active, -1);
                touch_softlockup_watchdog_sync();
                clocksource_touch_watchdog();
                local_irq_restore(flags);

                goto acquirelock;
        }

        if (!kgdb_io_ready(1)) {
                error = 1;
                goto kgdb_restore; /* No I/O connection, so resume the system */
        }

        /*
         * Don't enter if we have hit a removed breakpoint.
         */
        if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
                goto kgdb_restore;

        /* Call the I/O driver's pre_exception routine */
        if (kgdb_io_ops->pre_exception)
                kgdb_io_ops->pre_exception();

        kgdb_disable_hw_debug(ks->linux_regs);

        /*
         * Get the passive CPU lock which will hold all the non-primary
         * CPU in a spin state while the debugger is active
         */
        if (!kgdb_single_step) {
                for (i = 0; i < NR_CPUS; i++)
                        atomic_inc(&passive_cpu_wait[i]);
        }

#ifdef CONFIG_SMP
        /* Signal the other CPUs to enter kgdb_wait() */
        if ((!kgdb_single_step) && kgdb_do_roundup)
                kgdb_roundup_cpus(flags);
#endif

        /*
         * Wait for the other CPUs to be notified and be waiting for us:
         */
        for_each_online_cpu(i) {
                while (!atomic_read(&cpu_in_kgdb[i]))
                        cpu_relax();
        }

        /*
         * At this point the primary processor is completely
         * in the debugger and all secondary CPUs are quiescent
         */
        kgdb_post_primary_code(ks->linux_regs, ks->ex_vector, ks->err_code);
        kgdb_deactivate_sw_breakpoints();
        kgdb_single_step = 0;
        kgdb_contthread = current;
        exception_level = 0;

        /* Talk to debugger with gdbserial protocol */
        error = gdb_serial_stub(ks);

        /* Call the I/O driver's post_exception routine */
        if (kgdb_io_ops->post_exception)
                kgdb_io_ops->post_exception();

        atomic_dec(&cpu_in_kgdb[ks->cpu]);

        if (!kgdb_single_step) {
                for (i = NR_CPUS-1; i >= 0; i--)
                        atomic_dec(&passive_cpu_wait[i]);
                /*
                 * Wait till all the CPUs have quit
                 * from the debugger.
                 */
                for_each_online_cpu(i) {
                        while (atomic_read(&cpu_in_kgdb[i]))
                                cpu_relax();
                }
        }

kgdb_restore:
        if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
                int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
                if (kgdb_info[sstep_cpu].task)
                        kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
                else
                        kgdb_sstep_pid = 0;
        }
        /* Free kgdb_active */
        atomic_set(&kgdb_active, -1);
        touch_softlockup_watchdog_sync();
        clocksource_touch_watchdog();
        local_irq_restore(flags);

        return error;
}

/*
 * kgdb_handle_exception() - main entry point from a kernel exception
 *
 * Locking hierarchy:
 *      interface locks, if any (begin_session)
 *      kgdb lock (kgdb_active)
 */
int
kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
{
        struct kgdb_state kgdb_var;
        struct kgdb_state *ks = &kgdb_var;
        int ret;

        ks->cpu                 = raw_smp_processor_id();
        ks->ex_vector           = evector;
        ks->signo               = signo;
        ks->ex_vector           = evector;
        ks->err_code            = ecode;
        ks->kgdb_usethreadid    = 0;
        ks->linux_regs          = regs;

        if (kgdb_reenter_check(ks))
                return 0; /* Ouch, double exception ! */
        kgdb_info[ks->cpu].exception_state |= DCPU_WANT_MASTER;
        ret = kgdb_cpu_enter(ks, regs);
        kgdb_info[ks->cpu].exception_state &= ~DCPU_WANT_MASTER;
        return ret;
}

int kgdb_nmicallback(int cpu, void *regs)
{
#ifdef CONFIG_SMP
        struct kgdb_state kgdb_var;
        struct kgdb_state *ks = &kgdb_var;

        memset(ks, 0, sizeof(struct kgdb_state));
        ks->cpu                 = cpu;
        ks->linux_regs          = regs;

        if (!atomic_read(&cpu_in_kgdb[cpu]) &&
            atomic_read(&kgdb_active) != -1 &&
            atomic_read(&kgdb_active) != cpu) {
                kgdb_info[cpu].exception_state |= DCPU_IS_SLAVE;
                kgdb_cpu_enter(ks, regs);
                kgdb_info[cpu].exception_state &= ~DCPU_IS_SLAVE;
                return 0;
        }
#endif
        return 1;
}

static void kgdb_console_write(struct console *co, const char *s,
   unsigned count)
{
        unsigned long flags;

        /* If we're debugging, or KGDB has not connected, don't try
         * and print. */
        if (!kgdb_connected || atomic_read(&kgdb_active) != -1)
                return;

        local_irq_save(flags);
        kgdb_msg_write(s, count);
        local_irq_restore(flags);
}

static struct console kgdbcons = {
        .name           = "kgdb",
        .write          = kgdb_console_write,
        .flags          = CON_PRINTBUFFER | CON_ENABLED,
        .index          = -1,
};

#ifdef CONFIG_MAGIC_SYSRQ
static void sysrq_handle_gdb(int key, struct tty_struct *tty)
{
        if (!kgdb_io_ops) {
                printk(KERN_CRIT "ERROR: No KGDB I/O module available\n");
                return;
        }
        if (!kgdb_connected)
                printk(KERN_CRIT "Entering KGDB\n");

        kgdb_breakpoint();
}

static struct sysrq_key_op sysrq_gdb_op = {
        .handler        = sysrq_handle_gdb,
        .help_msg       = "debug(G)",
        .action_msg     = "DEBUG",
};
#endif

static void kgdb_register_callbacks(void)
{
        if (!kgdb_io_module_registered) {
                kgdb_io_module_registered = 1;
                kgdb_arch_init();
#ifdef CONFIG_MAGIC_SYSRQ
                register_sysrq_key('g', &sysrq_gdb_op);
#endif
                if (kgdb_use_con && !kgdb_con_registered) {
                        register_console(&kgdbcons);
                        kgdb_con_registered = 1;
                }
        }
}

static void kgdb_unregister_callbacks(void)
{
        /*
         * When this routine is called KGDB should unregister from the
         * panic handler and clean up, making sure it is not handling any
         * break exceptions at the time.
         */
        if (kgdb_io_module_registered) {
                kgdb_io_module_registered = 0;
                kgdb_arch_exit();
#ifdef CONFIG_MAGIC_SYSRQ
                unregister_sysrq_key('g', &sysrq_gdb_op);
#endif
                if (kgdb_con_registered) {
                        unregister_console(&kgdbcons);
                        kgdb_con_registered = 0;
                }
        }
}

static void kgdb_initial_breakpoint(void)
{
        kgdb_break_asap = 0;

        printk(KERN_CRIT "kgdb: Waiting for connection from remote gdb...\n");
        kgdb_breakpoint();
}

/**
 *      kgdb_register_io_module - register KGDB IO module
 *      @new_kgdb_io_ops: the io ops vector
 *
 *      Register it with the KGDB core.
 */
int kgdb_register_io_module(struct kgdb_io *new_kgdb_io_ops)
{
        int err;

        spin_lock(&kgdb_registration_lock);

        if (kgdb_io_ops) {
                spin_unlock(&kgdb_registration_lock);

                printk(KERN_ERR "kgdb: Another I/O driver is already "
                                "registered with KGDB.\n");
                return -EBUSY;
        }

        if (new_kgdb_io_ops->init) {
                err = new_kgdb_io_ops->init();
                if (err) {
                        spin_unlock(&kgdb_registration_lock);
                        return err;
                }
        }

        kgdb_io_ops = new_kgdb_io_ops;

        spin_unlock(&kgdb_registration_lock);

        printk(KERN_INFO "kgdb: Registered I/O driver %s.\n",
               new_kgdb_io_ops->name);

        /* Arm KGDB now. */
        kgdb_register_callbacks();

        if (kgdb_break_asap)
                kgdb_initial_breakpoint();

        return 0;
}
EXPORT_SYMBOL_GPL(kgdb_register_io_module);

/**
 *      kkgdb_unregister_io_module - unregister KGDB IO module
 *      @old_kgdb_io_ops: the io ops vector
 *
 *      Unregister it with the KGDB core.
 */
void kgdb_unregister_io_module(struct kgdb_io *old_kgdb_io_ops)
{
        BUG_ON(kgdb_connected);

        /*
         * KGDB is no longer able to communicate out, so
         * unregister our callbacks and reset state.
         */
        kgdb_unregister_callbacks();

        spin_lock(&kgdb_registration_lock);

        WARN_ON_ONCE(kgdb_io_ops != old_kgdb_io_ops);
        kgdb_io_ops = NULL;

        spin_unlock(&kgdb_registration_lock);

        printk(KERN_INFO
                "kgdb: Unregistered I/O driver %s, debugger disabled.\n",
                old_kgdb_io_ops->name);
}
EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);

/**
 * kgdb_breakpoint - generate breakpoint exception
 *
 * This function will generate a breakpoint exception.  It is used at the
 * beginning of a program to sync up with a debugger and can be used
 * otherwise as a quick means to stop program execution and "break" into
 * the debugger.
 */
void kgdb_breakpoint(void)
{
        atomic_inc(&kgdb_setting_breakpoint);
        wmb(); /* Sync point before breakpoint */
        arch_kgdb_breakpoint();
        wmb(); /* Sync point after breakpoint */
        atomic_dec(&kgdb_setting_breakpoint);
}
EXPORT_SYMBOL_GPL(kgdb_breakpoint);

static int __init opt_kgdb_wait(char *str)
{
        kgdb_break_asap = 1;

        if (kgdb_io_module_registered)
                kgdb_initial_breakpoint();

        return 0;
}

early_param("kgdbwait", opt_kgdb_wait);