// SPDX-License-Identifier: GPL-2.0-only
/*
 * Kernel Debug Core
 *
 * 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@ucw.cz>
 * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
 * 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 <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>
 */

#include <linux/kernel.h>
#include <linux/sched/signal.h>
#include <linux/hex.h>
#include <linux/kgdb.h>
#include <linux/kdb.h>
#include <linux/serial_core.h>
#include <linux/string.h>
#include <linux/reboot.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <linux/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 = copy_from_kernel_nofault(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 copy_to_kernel_nofault(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 overwritten 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 copy_to_kernel_nofault(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);
                strscpy(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
                strscpy(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 register 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 register 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);
        strscpy(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
                strscpy(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 {
                        strscpy(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");
                strscpy(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++;
                        }
                }

                for_each_process_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++;
                }

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

        case 'C':
                /* Current thread id */
                strscpy(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) {
                                strscpy(remcom_out_buffer, "E01");
                                break;
                        }
                        kgdb_hex2mem(remcom_in_buffer + 6,
                                     remcom_out_buffer, len);
                        len = len / 2;
                        remcom_out_buffer[len++] = 0;

                        kdb_common_init_state(ks);
                        kdb_parse(remcom_out_buffer);
                        kdb_common_deinit_state();

                        strscpy(remcom_out_buffer, "OK");
                }
                break;
#endif
#ifdef CONFIG_HAVE_ARCH_KGDB_QXFER_PKT
        case 'S':
                if (!strncmp(remcom_in_buffer, "qSupported:", 11))
                        strscpy(remcom_out_buffer, kgdb_arch_gdb_stub_feature);
                break;
        case 'X':
                if (!strncmp(remcom_in_buffer, "qXfer:", 6))
                        kgdb_arch_handle_qxfer_pkt(remcom_in_buffer,
                                                   remcom_out_buffer);
                break;
#endif
        default:
                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;
                strscpy(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;
                }
                strscpy(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)
                strscpy(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)
                strscpy(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 processing
 */
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;
                        }
                        fallthrough;
#endif
                case 'C': /* Exception passing */
                        tmp = gdb_cmd_exception_pass(ks);
                        if (tmp > 0)
                                goto default_handle;
                        if (tmp == 0)
                                break;
                        fallthrough;    /* 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;
                        }
                        fallthrough;    /* 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':
                strscpy(remcom_in_buffer, cmd, sizeof(remcom_in_buffer));
                return 0;
        case '$':
                strscpy(remcom_in_buffer, cmd, sizeof(remcom_in_buffer));
                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;
}

/**
 * gdbstub_exit - Send an exit message to GDB
 * @status: The exit code to report.
 */
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();
}