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gdbstub.h
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gdbstub.h
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/*
* Copyright (c) 2016-2022 Matt Borgerson
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#ifndef GDBSTUB_H
#define GDBSTUB_H
/* Enable debug statements (printf) */
#ifndef DEBUG
#define DEBUG 0
#endif
/*****************************************************************************
*
* Mock
*
****************************************************************************/
#ifdef GDBSTUB_ARCH_MOCK
/*****************************************************************************
* Types
****************************************************************************/
typedef unsigned int address;
typedef unsigned int reg;
enum GDB_REGISTER {
GDB_CPU_NUM_REGISTERS = 4
};
struct gdb_state {
int signum;
reg registers[GDB_CPU_NUM_REGISTERS];
};
/*****************************************************************************
* Prototypes
****************************************************************************/
struct gdb_buffer;
extern struct gdb_buffer gdb_input, gdb_output;
void gdb_buf_write(struct gdb_buffer *buf, int ch);
int gdb_buf_read(struct gdb_buffer *buf);
#endif /* GDBSTUB_ARCH_MOCK */
/*****************************************************************************
*
* x86
*
****************************************************************************/
#ifdef GDBSTUB_ARCH_X86
/*****************************************************************************
* Types
****************************************************************************/
#ifndef GDBSTUB_DONT_DEFINE_STDINT_TYPES
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned long uint32_t;
#endif
typedef unsigned int address;
typedef unsigned int reg;
enum GDB_REGISTER {
GDB_CPU_I386_REG_EAX = 0,
GDB_CPU_I386_REG_ECX = 1,
GDB_CPU_I386_REG_EDX = 2,
GDB_CPU_I386_REG_EBX = 3,
GDB_CPU_I386_REG_ESP = 4,
GDB_CPU_I386_REG_EBP = 5,
GDB_CPU_I386_REG_ESI = 6,
GDB_CPU_I386_REG_EDI = 7,
GDB_CPU_I386_REG_PC = 8,
GDB_CPU_I386_REG_PS = 9,
GDB_CPU_I386_REG_CS = 10,
GDB_CPU_I386_REG_SS = 11,
GDB_CPU_I386_REG_DS = 12,
GDB_CPU_I386_REG_ES = 13,
GDB_CPU_I386_REG_FS = 14,
GDB_CPU_I386_REG_GS = 15,
GDB_CPU_NUM_REGISTERS = 16
};
struct gdb_state {
int signum;
reg registers[GDB_CPU_NUM_REGISTERS];
};
#endif /* GDBSTUB_ARCH_X86 */
/*****************************************************************************
*
* GDB Remote Serial Protocol
*
****************************************************************************/
/*****************************************************************************
* Macros
****************************************************************************/
#if DEBUG
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#define GDB_PRINT(...) fprintf(stderr, __VA_ARGS__)
#else
#define GDB_PRINT(...)
#endif
#define GDB_EOF (-1)
#ifndef NULL
#define NULL ((void*)0)
#endif
#ifndef GDB_ASSERT
#if DEBUG
#define GDB_ASSERT(x) { \
if (!(x)) { \
fprintf(stderr, "ASSERTION FAILED\n"); \
fprintf(stderr, " Assertion: %s\n", #x); \
fprintf(stderr, " Location: %s @ %s:%d\n", __func__, \
__FILE__, __LINE__); \
exit(1); \
} \
}
#else
#define GDB_ASSERT(x) \
do {} while (0)
#endif
#endif
/*****************************************************************************
* Prototypes
****************************************************************************/
int gdb_main(struct gdb_state *state);
/* System functions, supported by all stubs */
void gdb_sys_init(void);
int gdb_sys_getc(struct gdb_state *state);
int gdb_sys_putchar(struct gdb_state *state, int ch);
int gdb_sys_mem_readb(struct gdb_state *state, address addr, char *val);
int gdb_sys_mem_writeb(struct gdb_state *state, address addr, char val);
int gdb_sys_continue(struct gdb_state *state);
int gdb_sys_step(struct gdb_state *state);
#ifdef GDBSTUB_IMPLEMENTATION
/*****************************************************************************
* Types
****************************************************************************/
typedef int (*gdb_enc_func)(char *buf, unsigned int buf_len, const char *data,
unsigned int data_len);
typedef int (*gdb_dec_func)(const char *buf, unsigned int buf_len, char *data,
unsigned int data_len);
/*****************************************************************************
* Const Data
****************************************************************************/
static const char digits[] = "0123456789abcdef";
/*****************************************************************************
* Prototypes
****************************************************************************/
/* Communication functions */
static int gdb_write(struct gdb_state *state, const char *buf,
unsigned int len);
static int gdb_read(struct gdb_state *state, char *buf, unsigned int buf_len,
unsigned int len);
/* String processing helper functions */
static int gdb_strlen(const char *ch);
#if DEBUG
static int gdb_is_printable_char(char ch);
#endif
static char gdb_get_digit(int val);
static int gdb_get_val(char digit, int base);
static int gdb_strtol(const char *str, unsigned int len, int base,
const char **endptr);
/* Packet functions */
static int gdb_send_packet(struct gdb_state *state, const char *pkt,
unsigned int pkt_len);
static int gdb_recv_packet(struct gdb_state *state, char *pkt_buf,
unsigned int pkt_buf_len, unsigned int *pkt_len);
static int gdb_checksum(const char *buf, unsigned int len);
static int gdb_recv_ack(struct gdb_state *state);
/* Data encoding/decoding */
static int gdb_enc_hex(char *buf, unsigned int buf_len, const char *data,
unsigned int data_len);
static int gdb_dec_hex(const char *buf, unsigned int buf_len, char *data,
unsigned int data_len);
static int gdb_enc_bin(char *buf, unsigned int buf_len, const char *data,
unsigned int data_len);
static int gdb_dec_bin(const char *buf, unsigned int buf_len, char *data,
unsigned int data_len);
/* Packet creation helpers */
static int gdb_send_ok_packet(struct gdb_state *state, char *buf,
unsigned int buf_len);
static int gdb_send_conmsg_packet(struct gdb_state *state, char *buf,
unsigned int buf_len, const char *msg);
static int gdb_send_signal_packet(struct gdb_state *state, char *buf,
unsigned int buf_len, char signal);
static int gdb_send_error_packet(struct gdb_state *state, char *buf,
unsigned int buf_len, char error);
/* Command functions */
static int gdb_mem_read(struct gdb_state *state, char *buf,
unsigned int buf_len, address addr, unsigned int len,
gdb_enc_func enc);
static int gdb_mem_write(struct gdb_state *state, const char *buf,
unsigned int buf_len, address addr, unsigned int len,
gdb_dec_func dec);
static int gdb_continue(struct gdb_state *state);
static int gdb_step(struct gdb_state *state);
/*****************************************************************************
* String Processing Helper Functions
****************************************************************************/
/*
* Get null-terminated string length.
*/
static int gdb_strlen(const char *ch)
{
int len;
len = 0;
while (*ch++) {
len += 1;
}
return len;
}
/*
* Get integer value for a string representation.
*
* If the string starts with + or -, it will be signed accordingly.
*
* If base == 0, the base will be determined:
* base 16 if the string starts with 0x or 0X,
* base 10 otherwise
*
* If endptr is specified, it will point to the last non-digit in the
* string. If there are no digits in the string, it will be set to NULL.
*/
static int gdb_strtol(const char *str, unsigned int len, int base,
const char **endptr)
{
unsigned int pos;
int sign, tmp, value, valid;
value = 0;
pos = 0;
sign = 1;
valid = 0;
if (endptr) {
*endptr = NULL;
}
if (len < 1) {
return 0;
}
/* Detect negative numbers */
if (str[pos] == '-') {
sign = -1;
pos += 1;
} else if (str[pos] == '+') {
sign = 1;
pos += 1;
}
/* Detect '0x' hex prefix */
if ((pos + 2 < len) && (str[pos] == '0') &&
((str[pos+1] == 'x') || (str[pos+1] == 'X'))) {
base = 16;
pos += 2;
}
if (base == 0) {
base = 10;
}
for (; (pos < len) && (str[pos] != '\x00'); pos++) {
tmp = gdb_get_val(str[pos], base);
if (tmp == GDB_EOF) {
break;
}
value = value*base + tmp;
valid = 1; /* At least one digit is valid */
}
if (!valid) {
return 0;
}
if (endptr) {
*endptr = str+pos;
}
value *= sign;
return value;
}
/*
* Get the corresponding ASCII hex digit character for a value.
*/
static char gdb_get_digit(int val)
{
if ((val >= 0) && (val <= 0xf)) {
return digits[val];
} else {
return GDB_EOF;
}
}
/*
* Get the corresponding value for a ASCII digit character.
*
* Supports bases 2-16.
*/
static int gdb_get_val(char digit, int base)
{
int value;
if ((digit >= '0') && (digit <= '9')) {
value = digit-'0';
} else if ((digit >= 'a') && (digit <= 'f')) {
value = digit-'a'+0xa;
} else if ((digit >= 'A') && (digit <= 'F')) {
value = digit-'A'+0xa;
} else {
return GDB_EOF;
}
return (value < base) ? value : GDB_EOF;
}
#if DEBUG
/*
* Determine if this is a printable ASCII character.
*/
static int gdb_is_printable_char(char ch)
{
return (ch >= 0x20 && ch <= 0x7e);
}
#endif
/*****************************************************************************
* Packet Functions
****************************************************************************/
/*
* Receive a packet acknowledgment
*
* Returns:
* 0 if an ACK (+) was received
* 1 if a NACK (-) was received
* GDB_EOF otherwise
*/
static int gdb_recv_ack(struct gdb_state *state)
{
int response;
/* Wait for packet ack */
switch (response = gdb_sys_getc(state)) {
case '+':
/* Packet acknowledged */
return 0;
case '-':
/* Packet negative acknowledged */
return 1;
default:
/* Bad response! */
GDB_PRINT("received bad packet response: 0x%2x\n", response);
return GDB_EOF;
}
}
/*
* Calculate 8-bit checksum of a buffer.
*
* Returns:
* 8-bit checksum.
*/
static int gdb_checksum(const char *buf, unsigned int len)
{
unsigned char csum;
csum = 0;
while (len--) {
csum += *buf++;
}
return csum;
}
/*
* Transmits a packet of data.
* Packets are of the form: $<packet-data>#<checksum>
*
* Returns:
* 0 if the packet was transmitted and acknowledged
* 1 if the packet was transmitted but not acknowledged
* GDB_EOF otherwise
*/
static int gdb_send_packet(struct gdb_state *state, const char *pkt_data,
unsigned int pkt_len)
{
char buf[3];
char csum;
/* Send packet start */
if (gdb_sys_putchar(state, '$') == GDB_EOF) {
return GDB_EOF;
}
#if DEBUG
{
unsigned int p;
GDB_PRINT("-> ");
for (p = 0; p < pkt_len; p++) {
if (gdb_is_printable_char(pkt_data[p])) {
GDB_PRINT("%c", pkt_data[p]);
} else {
GDB_PRINT("\\x%02x", pkt_data[p]&0xff);
}
}
GDB_PRINT("\n");
}
#endif
/* Send packet data */
if (gdb_write(state, pkt_data, pkt_len) == GDB_EOF) {
return GDB_EOF;
}
/* Send the checksum */
buf[0] = '#';
csum = gdb_checksum(pkt_data, pkt_len);
if ((gdb_enc_hex(buf+1, sizeof(buf)-1, &csum, 1) == GDB_EOF) ||
(gdb_write(state, buf, sizeof(buf)) == GDB_EOF)) {
return GDB_EOF;
}
return gdb_recv_ack(state);
}
/*
* Receives a packet of data, assuming a 7-bit clean connection.
*
* Returns:
* 0 if the packet was received
* GDB_EOF otherwise
*/
static int gdb_recv_packet(struct gdb_state *state, char *pkt_buf,
unsigned int pkt_buf_len, unsigned int *pkt_len)
{
int data;
char expected_csum, actual_csum;
char buf[2];
/* Wait for packet start */
actual_csum = 0;
while (1) {
data = gdb_sys_getc(state);
if (data == GDB_EOF) {
return GDB_EOF;
} else if (data == '$') {
/* Detected start of packet. */
break;
}
}
/* Read until checksum */
*pkt_len = 0;
while (1) {
data = gdb_sys_getc(state);
if (data == GDB_EOF) {
/* Error receiving character */
return GDB_EOF;
} else if (data == '#') {
/* End of packet */
break;
} else {
/* Check for space */
if (*pkt_len >= pkt_buf_len) {
GDB_PRINT("packet buffer overflow\n");
return GDB_EOF;
}
/* Store character and update checksum */
pkt_buf[(*pkt_len)++] = (char) data;
}
}
#if DEBUG
{
unsigned int p;
GDB_PRINT("<- ");
for (p = 0; p < *pkt_len; p++) {
if (gdb_is_printable_char(pkt_buf[p])) {
GDB_PRINT("%c", pkt_buf[p]);
} else {
GDB_PRINT("\\x%02x", pkt_buf[p] & 0xff);
}
}
GDB_PRINT("\n");
}
#endif
/* Receive the checksum */
if ((gdb_read(state, buf, sizeof(buf), 2) == GDB_EOF) ||
(gdb_dec_hex(buf, 2, &expected_csum, 1) == GDB_EOF)) {
return GDB_EOF;
}
/* Verify checksum */
actual_csum = gdb_checksum(pkt_buf, *pkt_len);
if (actual_csum != expected_csum) {
/* Send packet nack */
GDB_PRINT("received packet with bad checksum\n");
gdb_sys_putchar(state, '-');
return GDB_EOF;
}
/* Send packet ack */
gdb_sys_putchar(state, '+');
return 0;
}
/*****************************************************************************
* Data Encoding/Decoding
****************************************************************************/
/*
* Encode data to its hex-value representation in a buffer.
*
* Returns:
* 0+ number of bytes written to buf
* GDB_EOF if the buffer is too small
*/
static int gdb_enc_hex(char *buf, unsigned int buf_len, const char *data,
unsigned int data_len)
{
unsigned int pos;
if (buf_len < data_len*2) {
/* Buffer too small */
return GDB_EOF;
}
for (pos = 0; pos < data_len; pos++) {
*buf++ = gdb_get_digit((data[pos] >> 4) & 0xf);
*buf++ = gdb_get_digit((data[pos] ) & 0xf);
}
return data_len*2;
}
/*
* Decode data from its hex-value representation to a buffer.
*
* Returns:
* 0 if successful
* GDB_EOF if the buffer is too small
*/
static int gdb_dec_hex(const char *buf, unsigned int buf_len, char *data,
unsigned int data_len)
{
unsigned int pos;
int tmp;
if (buf_len != data_len*2) {
/* Buffer too small */
return GDB_EOF;
}
for (pos = 0; pos < data_len; pos++) {
/* Decode high nibble */
tmp = gdb_get_val(*buf++, 16);
if (tmp == GDB_EOF) {
/* Buffer contained junk. */
GDB_ASSERT(0);
return GDB_EOF;
}
data[pos] = tmp << 4;
/* Decode low nibble */
tmp = gdb_get_val(*buf++, 16);
if (tmp == GDB_EOF) {
/* Buffer contained junk. */
GDB_ASSERT(0);
return GDB_EOF;
}
data[pos] |= tmp;
}
return 0;
}
/*
* Encode data to its binary representation in a buffer.
*
* Returns:
* 0+ number of bytes written to buf
* GDB_EOF if the buffer is too small
*/
static int gdb_enc_bin(char *buf, unsigned int buf_len, const char *data,
unsigned int data_len)
{
unsigned int buf_pos, data_pos;
for (buf_pos = 0, data_pos = 0; data_pos < data_len; data_pos++) {
if (data[data_pos] == '$' ||
data[data_pos] == '#' ||
data[data_pos] == '}' ||
data[data_pos] == '*') {
if (buf_pos+1 >= buf_len) {
GDB_ASSERT(0);
return GDB_EOF;
}
buf[buf_pos++] = '}';
buf[buf_pos++] = data[data_pos] ^ 0x20;
} else {
if (buf_pos >= buf_len) {
GDB_ASSERT(0);
return GDB_EOF;
}
buf[buf_pos++] = data[data_pos];
}
}
return buf_pos;
}
/*
* Decode data from its bin-value representation to a buffer.
*
* Returns:
* 0+ if successful, number of bytes decoded
* GDB_EOF if the buffer is too small
*/
static int gdb_dec_bin(const char *buf, unsigned int buf_len, char *data,
unsigned int data_len)
{
unsigned int buf_pos, data_pos;
for (buf_pos = 0, data_pos = 0; buf_pos < buf_len; buf_pos++) {
if (data_pos >= data_len) {
/* Output buffer overflow */
GDB_ASSERT(0);
return GDB_EOF;
}
if (buf[buf_pos] == '}') {
/* The next byte is escaped! */
if (buf_pos+1 >= buf_len) {
/* There's an escape character, but no escaped character
* following the escape character. */
GDB_ASSERT(0);
return GDB_EOF;
}
buf_pos += 1;
data[data_pos++] = buf[buf_pos] ^ 0x20;
} else {
data[data_pos++] = buf[buf_pos];
}
}
return data_pos;
}
/*****************************************************************************
* Command Functions
****************************************************************************/
/*
* Read from memory and encode into buf.
*
* Returns:
* 0+ number of bytes written to buf
* GDB_EOF if the buffer is too small
*/
static int gdb_mem_read(struct gdb_state *state, char *buf,
unsigned int buf_len, address addr, unsigned int len,
gdb_enc_func enc)
{
char data[64];
unsigned int pos;
if (len > sizeof(data)) {
return GDB_EOF;
}
/* Read from system memory */
for (pos = 0; pos < len; pos++) {
if (gdb_sys_mem_readb(state, addr+pos, &data[pos])) {
/* Failed to read */
return GDB_EOF;
}
}
/* Encode data */
return enc(buf, buf_len, data, len);
}
/*
* Write to memory from encoded buf.
*/
static int gdb_mem_write(struct gdb_state *state, const char *buf,
unsigned int buf_len, address addr, unsigned int len,
gdb_dec_func dec)
{
char data[64];
unsigned int pos;
if (len > sizeof(data)) {
return GDB_EOF;
}
/* Decode data */
if (dec(buf, buf_len, data, len) == GDB_EOF) {
return GDB_EOF;
}
/* Write to system memory */
for (pos = 0; pos < len; pos++) {
if (gdb_sys_mem_writeb(state, addr+pos, data[pos])) {
/* Failed to write */
return GDB_EOF;
}
}
return 0;
}
/*
* Continue program execution at PC.
*/
int gdb_continue(struct gdb_state *state)
{
gdb_sys_continue(state);
return 0;
}
/*
* Step one instruction.
*/
int gdb_step(struct gdb_state *state)
{
gdb_sys_step(state);
return 0;
}
/*****************************************************************************
* Packet Creation Helpers
****************************************************************************/
/*
* Send OK packet
*/
static int gdb_send_ok_packet(struct gdb_state *state, char *buf,
unsigned int buf_len)
{
return gdb_send_packet(state, "OK", 2);
}
/*
* Send a message to the debugging console (via O XX... packet)
*/
static int gdb_send_conmsg_packet(struct gdb_state *state, char *buf,
unsigned int buf_len, const char *msg)
{
unsigned int size;
int status;
if (buf_len < 2) {
/* Buffer too small */
return GDB_EOF;
}
buf[0] = 'O';
status = gdb_enc_hex(&buf[1], buf_len-1, msg, gdb_strlen(msg));
if (status == GDB_EOF) {
return GDB_EOF;
}
size = 1 + status;
return gdb_send_packet(state, buf, size);
}
/*
* Send a signal packet (S AA).
*/
static int gdb_send_signal_packet(struct gdb_state *state, char *buf,
unsigned int buf_len, char signal)
{
unsigned int size;
int status;
if (buf_len < 4) {
/* Buffer too small */
return GDB_EOF;
}
buf[0] = 'S';
status = gdb_enc_hex(&buf[1], buf_len-1, &signal, 1);
if (status == GDB_EOF) {
return GDB_EOF;
}
size = 1 + status;
return gdb_send_packet(state, buf, size);
}
/*
* Send a error packet (E AA).
*/
static int gdb_send_error_packet(struct gdb_state *state, char *buf,
unsigned int buf_len, char error)
{
unsigned int size;
int status;
if (buf_len < 4) {
/* Buffer too small */
return GDB_EOF;
}
buf[0] = 'E';
status = gdb_enc_hex(&buf[1], buf_len-1, &error, 1);
if (status == GDB_EOF) {
return GDB_EOF;
}
size = 1 + status;
return gdb_send_packet(state, buf, size);
}
/*****************************************************************************
* Communication Functions
****************************************************************************/
/*
* Write a sequence of bytes.
*
* Returns:
* 0 if successful
* GDB_EOF if failed to write all bytes
*/
static int gdb_write(struct gdb_state *state, const char *buf, unsigned int len)
{
while (len--) {
if (gdb_sys_putchar(state, *buf++) == GDB_EOF) {
return GDB_EOF;
}
}
return 0;
}
/*
* Read a sequence of bytes.
*
* Returns:
* 0 if successfully read len bytes
* GDB_EOF if failed to read all bytes
*/
static int gdb_read(struct gdb_state *state, char *buf, unsigned int buf_len,
unsigned int len)
{
char c;
if (buf_len < len) {
/* Buffer too small */
return GDB_EOF;
}
while (len--) {
if ((c = gdb_sys_getc(state)) == GDB_EOF) {
return GDB_EOF;
}
*buf++ = c;
}
return 0;
}
/*****************************************************************************
* Main Loop
****************************************************************************/
/*
* Main debug loop. Handles commands.
*/
int gdb_main(struct gdb_state *state)
{
address addr;
char pkt_buf[256];
int status;
unsigned int length;
unsigned int pkt_len;
const char *ptr_next;
gdb_send_signal_packet(state, pkt_buf, sizeof(pkt_buf), state->signum);
while (1) {
/* Receive the next packet */
status = gdb_recv_packet(state, pkt_buf, sizeof(pkt_buf), &pkt_len);
if (status == GDB_EOF) {
break;
}
if (pkt_len == 0) {
/* Received empty packet.. */
continue;
}
ptr_next = pkt_buf;
/*
* Handle one letter commands
*/
switch (pkt_buf[0]) {
/* Calculate remaining space in packet from ptr_next position. */
#define token_remaining_buf (pkt_len-(ptr_next-pkt_buf))
/* Expecting a seperator. If not present, go to error */
#define token_expect_seperator(c) \
{ \
if (!ptr_next || *ptr_next != c) { \
goto error; \
} else { \
ptr_next += 1; \
} \
}
/* Expecting an integer argument. If not present, go to error */
#define token_expect_integer_arg(arg) \
{ \
arg = gdb_strtol(ptr_next, token_remaining_buf, \
16, &ptr_next); \
if (!ptr_next) { \
goto error; \
} \
}
/*
* Read Registers
* Command Format: g
*/
case 'g':
/* Encode registers */
status = gdb_enc_hex(pkt_buf, sizeof(pkt_buf),
(char *)&(state->registers),
sizeof(state->registers));
if (status == GDB_EOF) {
goto error;
}
pkt_len = status;
gdb_send_packet(state, pkt_buf, pkt_len);
break;