gdbstub.c

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/*
 * Kernel Debug Core
 *
 * Maintainer: Jason Wessel <[email protected]>
 *
 * Copyright (C) 2000-2001 VERITAS Software Corporation.
 * Copyright (C) 2002-2004 Timesys Corporation
 * Copyright (C) 2003-2004 Amit S. Kale <[email protected]>
 * Copyright (C) 2004 Pavel Machek <[email protected]>
 * Copyright (C) 2004-2006 Tom Rini <[email protected]>
 * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
 * Copyright (C) 2005-2009 Wind River Systems, Inc.
 * Copyright (C) 2007 MontaVista Software, Inc.
 * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <[email protected]>
 *
 * Contributors at various stages not listed above:
 *  Jason Wessel ( [email protected] )
 *  George Anzinger <[email protected]>
 *  Anurekh Saxena ([email protected])
 *  Lake Stevens Instrument Division (Glenn Engel)
 *  Jim Kingdon, Cygnus Support.
 *
 * Original KGDB stub: David Grothe <[email protected]>,
 * Tigran Aivazian <[email protected]>
 *
 * 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/kernel.h>
#include <linux/kgdb.h>
#include <linux/kdb.h>
#include <linux/reboot.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/unaligned.h>
#include "debug_core.h"

#define KGDB_MAX_THREAD_QUERY 17

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

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

/*
 * GDB remote protocol parser:
 */

#ifdef CONFIG_KGDB_KDB
static int gdbstub_read_wait(void)
{
    int ret = -1;
    int i;

    if (unlikely(gdbstub_use_prev_in_buf)) {
        if (gdbstub_prev_in_buf_pos < gdbstub_use_prev_in_buf)
            return remcom_in_buffer[gdbstub_prev_in_buf_pos++];
        else
            gdbstub_use_prev_in_buf = 0;
    }

    /* poll any additional I/O interfaces that are defined */
    while (ret < 0)
        for (i = 0; kdb_poll_funcs[i] != NULL; i++) {
            ret = kdb_poll_funcs[i]();
            if (ret > 0)
                break;
        }
    return ret;
}
#else
static int gdbstub_read_wait(void)
{
    int ret = dbg_io_ops->read_char();
    while (ret == NO_POLL_CHAR)
        ret = dbg_io_ops->read_char();
    return ret;
}
#endif
/* 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 = (gdbstub_read_wait())) != '$')
            /* 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 = gdbstub_read_wait();
            if (ch == '#')
                break;
            checksum = checksum + ch;
            buffer[count] = ch;
            count = count + 1;
        }

        if (ch == '#') {
            xmitcsum = hex_to_bin(gdbstub_read_wait()) << 4;
            xmitcsum += hex_to_bin(gdbstub_read_wait());

            if (checksum != xmitcsum)
                /* failed checksum */
                dbg_io_ops->write_char('-');
            else
                /* successful transfer */
                dbg_io_ops->write_char('+');
            if (dbg_io_ops->flush)
                dbg_io_ops->flush();
        }
        buffer[count] = 0;
    } 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;

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

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

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

        /* Now see what we get in reply. */
        ch = gdbstub_read_wait();

        if (ch == 3)
            ch = gdbstub_read_wait();

        /* 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 == '$') {
            dbg_io_ops->write_char('-');
            if (dbg_io_ops->flush)
                dbg_io_ops->flush();
            return;
        }
    }
}

static char gdbmsgbuf[BUFMAX + 1];

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

    if (len == 0)
        len = strlen(s);

    /* '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 = hex_byte_pack(bufptr, s[i]);
        *bufptr = '\0';

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

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

/*
 * 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.
 */
char *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)
        return NULL;
    while (count > 0) {
        buf = hex_byte_pack(buf, *tmp);
        tmp++;
        count--;
    }
    *buf = 0;

    return buf;
}

/*
 * 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_to_bin(*tmp_hex--);
        *tmp_raw |= hex_to_bin(*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_to_bin(**ptr);
        if (hex_val < 0)
            break;

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

    if (negate)
        *long_val = -*long_val;

    return num;
}

/*
 * 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);
}

#if DBG_MAX_REG_NUM > 0
void pt_regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *regs)
{
    int i;
    int idx = 0;
    char *ptr = (char *)gdb_regs;

    for (i = 0; i < DBG_MAX_REG_NUM; i++) {
        dbg_get_reg(i, ptr + idx, regs);
        idx += dbg_reg_def[i].size;
    }
}

void gdb_regs_to_pt_regs(unsigned long *gdb_regs, struct pt_regs *regs)
{
    int i;
    int idx = 0;
    char *ptr = (char *)gdb_regs;

    for (i = 0; i < DBG_MAX_REG_NUM; i++) {
        dbg_set_reg(i, ptr + idx, regs);
        idx += dbg_reg_def[i].size;
    }
}
#endif /* DBG_MAX_REG_NUM > 0 */

/* 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  8

static char *pack_threadid(char *pkt, unsigned char *id)
{
    unsigned char *limit;
    int lzero = 1;

    limit = id + (BUF_THREAD_ID_SIZE / 2);
    while (id < limit) {
        if (!lzero || *id != 0) {
            pkt = hex_byte_pack(pkt, *id);
            lzero = 0;
        }
        id++;
    }

    if (lzero)
        pkt = hex_byte_pack(pkt, 0);

    return pkt;
}

static void int_to_threadref(unsigned char *id, int value)
{
    put_unaligned_be32(value, id);
}

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);
}


/*
 * 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;
}

/*
 * 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.
     */
    dbg_remove_all_break();

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

static void gdb_get_regs_helper(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);
    }
}

/* Handle the 'g' get registers request */
static void gdb_cmd_getregs(struct kgdb_state *ks)
{
    gdb_get_regs_helper(ks);
    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;
    char *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, -EINVAL);
    } 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");
}

#if DBG_MAX_REG_NUM > 0
static char *gdb_hex_reg_helper(int regnum, char *out)
{
    int i;
    int offset = 0;

    for (i = 0; i < regnum; i++)
        offset += dbg_reg_def[i].size;
    return kgdb_mem2hex((char *)gdb_regs + offset, out,
                dbg_reg_def[i].size);
}

/* Handle the 'p' individual regster get */
static void gdb_cmd_reg_get(struct kgdb_state *ks)
{
    unsigned long regnum;
    char *ptr = &remcom_in_buffer[1];

    kgdb_hex2long(&ptr, &regnum);
    if (regnum >= DBG_MAX_REG_NUM) {
        error_packet(remcom_out_buffer, -EINVAL);
        return;
    }
    gdb_get_regs_helper(ks);
    gdb_hex_reg_helper(regnum, remcom_out_buffer);
}

/* Handle the 'P' individual regster set */
static void gdb_cmd_reg_set(struct kgdb_state *ks)
{
    unsigned long regnum;
    char *ptr = &remcom_in_buffer[1];
    int i = 0;

    kgdb_hex2long(&ptr, &regnum);
    if (*ptr++ != '=' ||
        !(!kgdb_usethread || kgdb_usethread == current) ||
        !dbg_get_reg(regnum, gdb_regs, ks->linux_regs)) {
        error_packet(remcom_out_buffer, -EINVAL);
        return;
    }
    memset(gdb_regs, 0, sizeof(gdb_regs));
    while (i < sizeof(gdb_regs) * 2)
        if (hex_to_bin(ptr[i]) >= 0)
            i++;
        else
            break;
    i = i / 2;
    kgdb_hex2mem(ptr, (char *)gdb_regs, i);
    dbg_set_reg(regnum, gdb_regs, ks->linux_regs);
    strcpy(remcom_out_buffer, "OK");
}
#endif /* DBG_MAX_REG_NUM > 0 */

/* 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 = dbg_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:
         */
        dbg_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[BUF_THREAD_ID_SIZE];
    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))
            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);
                ptr = pack_threadid(ptr, thref);
                *(ptr++) = ',';
                i++;
            }
        }

        do_each_thread(g, p) {
            if (i >= ks->thr_query && !finished) {
                int_to_threadref(thref, p->pid);
                ptr = pack_threadid(ptr, thref);
                *(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))
            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;
#ifdef CONFIG_KGDB_KDB
    case 'R':
        if (strncmp(remcom_in_buffer, "qRcmd,", 6) == 0) {
            int len = strlen(remcom_in_buffer + 6);

            if ((len % 2) != 0) {
                strcpy(remcom_out_buffer, "E01");
                break;
            }
            kgdb_hex2mem(remcom_in_buffer + 6,
                     remcom_out_buffer, len);
            len = len / 2;
            remcom_out_buffer[len++] = 0;

            kdb_parse(remcom_out_buffer);
            strcpy(remcom_out_buffer, "OK");
        }
        break;
#endif
    }
}

/* 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 = dbg_set_sw_break(addr);
    else if (remcom_in_buffer[0] == 'z' && *bpt_type == '0')
        error = dbg_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';
        dbg_remove_all_break();
        kgdb_connected = 0;
        return 1;

    } else {
        gdbstub_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
 */
int gdb_serial_stub(struct kgdb_state *ks)
{
    int error = 0;
    int tmp;

    /* Initialize comm buffer and globals. */
    memset(remcom_out_buffer, 0, sizeof(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;

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

        /* Reply to host that an exception has occurred */
        ptr = remcom_out_buffer;
        *ptr++ = 'T';
        ptr = hex_byte_pack(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);
    }

    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;
#if DBG_MAX_REG_NUM > 0
        case 'p': /* pXX Return gdb register XX (in hex) */
            gdb_cmd_reg_get(ks);
            break;
        case 'P': /* PXX=aaaa Set gdb register XX to aaaa (in hex) */
            gdb_cmd_reg_set(ks);
            break;
#endif /* DBG_MAX_REG_NUM > 0 */
        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;
#ifdef CONFIG_KGDB_KDB
        case '3': /* Escape into back into kdb */
            if (remcom_in_buffer[1] == '\0') {
                gdb_cmd_detachkill(ks);
                return DBG_PASS_EVENT;
            }
#endif
        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;
            }
            dbg_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;
}

int gdbstub_state(struct kgdb_state *ks, char *cmd)
{
    int error;

    switch (cmd[0]) {
    case 'e':
        error = kgdb_arch_handle_exception(ks->ex_vector,
                           ks->signo,
                           ks->err_code,
                           remcom_in_buffer,
                           remcom_out_buffer,
                           ks->linux_regs);
        return error;
    case 's':
    case 'c':
        strcpy(remcom_in_buffer, cmd);
        return 0;
    case '$':
        strcpy(remcom_in_buffer, cmd);
        gdbstub_use_prev_in_buf = strlen(remcom_in_buffer);
        gdbstub_prev_in_buf_pos = 0;
        return 0;
    }
    dbg_io_ops->write_char('+');
    put_packet(remcom_out_buffer);
    return 0;
}

void gdbstub_exit(int status)
{
    unsigned char checksum, ch, buffer[3];
    int loop;

    if (!kgdb_connected)
        return;
    kgdb_connected = 0;

    if (!dbg_io_ops || dbg_kdb_mode)
        return;

    buffer[0] = 'W';
    buffer[1] = hex_asc_hi(status);
    buffer[2] = hex_asc_lo(status);

    dbg_io_ops->write_char('$');
    checksum = 0;

    for (loop = 0; loop < 3; loop++) {
        ch = buffer[loop];
        checksum += ch;
        dbg_io_ops->write_char(ch);
    }

    dbg_io_ops->write_char('#');
    dbg_io_ops->write_char(hex_asc_hi(checksum));
    dbg_io_ops->write_char(hex_asc_lo(checksum));

    /* make sure the output is flushed, lest the bootloader clobber it */
    if (dbg_io_ops->flush)
        dbg_io_ops->flush();
}