path: root/arch/sh/kernel/kgdb_stub.c

/*
 * May be copied or modified under the terms of the GNU General Public
 * License.  See linux/COPYING for more information.
 *
 * Contains extracts from code by Glenn Engel, Jim Kingdon,
 * David Grothe <dave@gcom.com>, Tigran Aivazian <tigran@sco.com>,
 * Amit S. Kale <akale@veritas.com>,  William Gatliff <bgat@open-widgets.com>,
 * Ben Lee, Steve Chamberlain and Benoit Miller <fulg@iname.com>.
 *
 * This version by Henry Bell <henry.bell@st.com>
 * Minor modifications by Jeremy Siegel <jsiegel@mvista.com>
 *
 * Contains low-level support for remote debug using GDB.
 *
 * To enable debugger support, two things need to happen. A call to
 * set_debug_traps() is necessary in order to allow any breakpoints
 * or error conditions to be properly intercepted and reported to gdb.
 * A breakpoint also needs to be generated to begin communication.  This
 * is most easily accomplished by a call to breakpoint() which does
 * a trapa if the initialisation phase has been successfully completed.
 *
 * In this case, set_debug_traps() is not used to "take over" exceptions;
 * other kernel code is modified instead to enter the kgdb functions here
 * when appropriate (see entry.S for breakpoint traps and NMI interrupts,
 * see traps.c for kernel error exceptions).
 *
 * The following gdb commands are supported:
 *
 *    Command       Function                               Return value
 *
 *    g             return the value of the CPU registers  hex data or ENN
 *    G             set the value of the CPU registers     OK or ENN
 *
 *    mAA..AA,LLLL  Read LLLL bytes at address AA..AA      hex data or ENN
 *    MAA..AA,LLLL: Write LLLL bytes at address AA.AA      OK or ENN
 *    XAA..AA,LLLL: Same, but data is binary (not hex)     OK or ENN
 *
 *    c             Resume at current address              SNN   ( signal NN)
 *    cAA..AA       Continue at address AA..AA             SNN
 *    CNN;          Resume at current address with signal  SNN
 *    CNN;AA..AA    Resume at address AA..AA with signal   SNN
 *
 *    s             Step one instruction                   SNN
 *    sAA..AA       Step one instruction from AA..AA       SNN
 *    SNN;          Step one instruction with signal       SNN
 *    SNNAA..AA     Step one instruction from AA..AA w/NN  SNN
 *
 *    k             kill (Detach GDB)
 *
 *    d             Toggle debug flag
 *    D             Detach GDB
 *
 *    Hct           Set thread t for operations,           OK or ENN
 *                  c = 'c' (step, cont), c = 'g' (other
 *                  operations)
 *
 *    qC            Query current thread ID                QCpid
 *    qfThreadInfo  Get list of current threads (first)    m<id>
 *    qsThreadInfo   "    "  "     "      "   (subsequent)
 *    qOffsets      Get section offsets                  Text=x;Data=y;Bss=z
 *
 *    TXX           Find if thread XX is alive             OK or ENN
 *    ?             What was the last sigval ?             SNN   (signal NN)
 *    O             Output to GDB console
 *
 * Remote communication protocol.
 *
 *    A debug packet whose contents are <data> is encapsulated for
 *    transmission in the form:
 *
 *       $ <data> # CSUM1 CSUM2
 *
 *       <data> must be ASCII alphanumeric and cannot include characters
 *       '$' or '#'.  If <data> starts with two characters followed by
 *       ':', then the existing stubs interpret this as a sequence number.
 *
 *       CSUM1 and CSUM2 are ascii hex representation of an 8-bit
 *       checksum of <data>, the most significant nibble is sent first.
 *       the hex digits 0-9,a-f are used.
 *
 *    Receiver responds with:
 *
 *       +       - if CSUM is correct and ready for next packet
 *       -       - if CSUM is incorrect
 *
 * Responses can be run-length encoded to save space.  A '*' means that
 * the next character is an ASCII encoding giving a repeat count which
 * stands for that many repetitions of the character preceding the '*'.
 * The encoding is n+29, yielding a printable character where n >=3
 * (which is where RLE starts to win).  Don't use an n > 126.
 *
 * So "0* " means the same as "0000".
 */

#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/spinlock.h>
#include <linux/delay.h>
#include <linux/linkage.h>
#include <linux/init.h>
#include <linux/console.h>
#include <linux/sysrq.h>
#include <asm/system.h>
#include <asm/cacheflush.h>
#include <asm/current.h>
#include <asm/signal.h>
#include <asm/pgtable.h>
#include <asm/ptrace.h>
#include <asm/kgdb.h>
#include <asm/io.h>

/* Function pointers for linkage */
kgdb_debug_hook_t *kgdb_debug_hook;
kgdb_bus_error_hook_t *kgdb_bus_err_hook;

int (*kgdb_getchar)(void);
void (*kgdb_putchar)(int);

static void put_debug_char(int c)
{
	if (!kgdb_putchar)
		return;
	(*kgdb_putchar)(c);
}
static int get_debug_char(void)
{
	if (!kgdb_getchar)
		return -1;
	return (*kgdb_getchar)();
}

/* Num chars in in/out bound buffers, register packets need NUMREGBYTES * 2 */
#define BUFMAX 1024
#define NUMREGBYTES (MAXREG*4)
#define OUTBUFMAX (NUMREGBYTES*2+512)

enum regs {
	R0 = 0, R1,  R2,  R3,   R4,   R5,  R6, R7,
	R8, R9, R10, R11, R12,  R13,  R14, R15,
	PC, PR, GBR, VBR, MACH, MACL, SR,
	/*  */
	MAXREG
};

static unsigned int registers[MAXREG];
struct kgdb_regs trap_registers;

char kgdb_in_gdb_mode;
char in_nmi;			/* Set during NMI to prevent reentry */
int kgdb_nofault;		/* Boolean to ignore bus errs (i.e. in GDB) */

/* Default values for SCI (can override via kernel args in setup.c) */
#ifndef CONFIG_KGDB_DEFPORT
#define CONFIG_KGDB_DEFPORT 1
#endif

#ifndef CONFIG_KGDB_DEFBAUD
#define CONFIG_KGDB_DEFBAUD 115200
#endif

#if defined(CONFIG_KGDB_DEFPARITY_E)
#define CONFIG_KGDB_DEFPARITY 'E'
#elif defined(CONFIG_KGDB_DEFPARITY_O)
#define CONFIG_KGDB_DEFPARITY 'O'
#else /* CONFIG_KGDB_DEFPARITY_N */
#define CONFIG_KGDB_DEFPARITY 'N'
#endif

#ifdef CONFIG_KGDB_DEFBITS_7
#define CONFIG_KGDB_DEFBITS '7'
#else /* CONFIG_KGDB_DEFBITS_8 */
#define CONFIG_KGDB_DEFBITS '8'
#endif

/* SCI/UART settings, used in kgdb_console_setup() */
int  kgdb_portnum = CONFIG_KGDB_DEFPORT;
int  kgdb_baud = CONFIG_KGDB_DEFBAUD;
char kgdb_parity = CONFIG_KGDB_DEFPARITY;
char kgdb_bits = CONFIG_KGDB_DEFBITS;

/* Jump buffer for setjmp/longjmp */
static jmp_buf rem_com_env;

/* TRA differs sh3/4 */
#if defined(CONFIG_CPU_SH3)
#define TRA 0xffffffd0
#elif defined(CONFIG_CPU_SH4)
#define TRA 0xff000020
#endif

/* Macros for single step instruction identification */
#define OPCODE_BT(op)         (((op) & 0xff00) == 0x8900)
#define OPCODE_BF(op)         (((op) & 0xff00) == 0x8b00)
#define OPCODE_BTF_DISP(op)   (((op) & 0x80) ? (((op) | 0xffffff80) << 1) : \
			      (((op) & 0x7f ) << 1))
#define OPCODE_BFS(op)        (((op) & 0xff00) == 0x8f00)
#define OPCODE_BTS(op)        (((op) & 0xff00) == 0x8d00)
#define OPCODE_BRA(op)        (((op) & 0xf000) == 0xa000)
#define OPCODE_BRA_DISP(op)   (((op) & 0x800) ? (((op) | 0xfffff800) << 1) : \
			      (((op) & 0x7ff) << 1))
#define OPCODE_BRAF(op)       (((op) & 0xf0ff) == 0x0023)
#define OPCODE_BRAF_REG(op)   (((op) & 0x0f00) >> 8)
#define OPCODE_BSR(op)        (((op) & 0xf000) == 0xb000)
#define OPCODE_BSR_DISP(op)   (((op) & 0x800) ? (((op) | 0xfffff800) << 1) : \
			      (((op) & 0x7ff) << 1))
#define OPCODE_BSRF(op)       (((op) & 0xf0ff) == 0x0003)
#define OPCODE_BSRF_REG(op)   (((op) >> 8) & 0xf)
#define OPCODE_JMP(op)        (((op) & 0xf0ff) == 0x402b)
#define OPCODE_JMP_REG(op)    (((op) >> 8) & 0xf)
#define OPCODE_JSR(op)        (((op) & 0xf0ff) == 0x400b)
#define OPCODE_JSR_REG(op)    (((op) >> 8) & 0xf)
#define OPCODE_RTS(op)        ((op) == 0xb)
#define OPCODE_RTE(op)        ((op) == 0x2b)

#define SR_T_BIT_MASK           0x1
#define STEP_OPCODE             0xc320
#define BIOS_CALL_TRAP          0x3f

/* Exception codes as per SH-4 core manual */
#define ADDRESS_ERROR_LOAD_VEC   7
#define ADDRESS_ERROR_STORE_VEC  8
#define TRAP_VEC                 11
#define INVALID_INSN_VEC         12
#define INVALID_SLOT_VEC         13
#define NMI_VEC                  14
#define USER_BREAK_VEC           15
#define SERIAL_BREAK_VEC         58

/* Misc static */
static int stepped_address;
static short stepped_opcode;
static char in_buffer[BUFMAX];
static char out_buffer[OUTBUFMAX];

static void kgdb_to_gdb(const char *s);

/* Convert ch to hex */
static int hex(const 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);
}

/* Convert the memory pointed to by mem into hex, placing result in buf.
   Returns a pointer to the last char put in buf (null) */
static char *mem_to_hex(const char *mem, char *buf, const int count)
{
	int i;
	int ch;
	unsigned short s_val;
	unsigned long l_val;

	/* Check for 16 or 32 */
	if (count == 2 && ((long) mem & 1) == 0) {
		s_val = *(unsigned short *) mem;
		mem = (char *) &s_val;
	} else if (count == 4 && ((long) mem & 3) == 0) {
		l_val = *(unsigned long *) mem;
		mem = (char *) &l_val;
	}
	for (i = 0; i < count; i++) {
		ch = *mem++;
		*buf++ = highhex(ch);
		*buf++ = lowhex(ch);
	}
	*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 */
static char *hex_to_mem(const char *buf, char *mem, const int count)
{
	int i;
	unsigned char ch;

	for (i = 0; i < count; i++) {
		ch = hex(*buf++) << 4;
		ch = ch + hex(*buf++);
		*mem++ = ch;
	}
	return (mem);
}

/* While finding valid hex chars, convert to an integer, then return it */
static int hex_to_int(char **ptr, int *int_value)
{
	int num_chars = 0;
	int hex_value;

	*int_value = 0;

	while (**ptr) {
		hex_value = hex(**ptr);
		if (hex_value >= 0) {
			*int_value = (*int_value << 4) | hex_value;
			num_chars++;
		} else
			break;
		(*ptr)++;
	}
	return num_chars;
}

/*  Copy the binary array pointed to by buf into mem.  Fix $, #,
    and 0x7d escaped with 0x7d.  Return a pointer to the character
    after the last byte written. */
static char *ebin_to_mem(const char *buf, char *mem, int count)
{
	for (; count > 0; count--, buf++) {
		if (*buf == 0x7d)
			*mem++ = *(++buf) ^ 0x20;
		else
			*mem++ = *buf;
	}
	return mem;
}

/* Pack a hex byte */
static char *pack_hex_byte(char *pkt, int byte)
{
	*pkt++ = hexchars[(byte >> 4) & 0xf];
	*pkt++ = hexchars[(byte & 0xf)];
	return pkt;
}

/* Scan for the start char '$', read the packet and check the checksum */
static void get_packet(char *buffer, int buflen)
{
	unsigned char checksum;
	unsigned char xmitcsum;
	int i;
	int count;
	char ch;

	do {
		/* Ignore everything until the start character */
		while ((ch = get_debug_char()) != '$');

		checksum = 0;
		xmitcsum = -1;
		count = 0;

		/* Now, read until a # or end of buffer is found */
		while (count < (buflen - 1)) {
			ch = get_debug_char();

			if (ch == '#')
				break;

			checksum = checksum + ch;
			buffer[count] = ch;
			count = count + 1;
		}

		buffer[count] = 0;

		/* Continue to read checksum following # */
		if (ch == '#') {
			xmitcsum = hex(get_debug_char()) << 4;
			xmitcsum += hex(get_debug_char());

			/* Checksum */
			if (checksum != xmitcsum)
				put_debug_char('-');	/* Failed checksum */
			else {
				/* Ack successful transfer */
				put_debug_char('+');

				/* If a sequence char is present, reply
				   the sequence ID */
				if (buffer[2] == ':') {
					put_debug_char(buffer[0]);
					put_debug_char(buffer[1]);

					/* Remove sequence chars from buffer */
					count = strlen(buffer);
					for (i = 3; i <= count; i++)
						buffer[i - 3] = buffer[i];
				}
			}
		}
	}
	while (checksum != xmitcsum);	/* Keep trying while we fail */
}

/* Send the packet in the buffer with run-length encoding */
static void put_packet(char *buffer)
{
	int checksum;
	char *src;
	int runlen;
	int encode;

	do {
		src = buffer;
		put_debug_char('$');
		checksum = 0;

		/* Continue while we still have chars left */
		while (*src) {
			/* Check for runs up to 99 chars long */
			for (runlen = 1; runlen < 99; runlen++) {
				if (src[0] != src[runlen])
					break;
			}

			if (runlen > 3) {
				/* Got a useful amount, send encoding */
				encode = runlen + ' ' - 4;
				put_debug_char(*src);   checksum += *src;
				put_debug_char('*');    checksum += '*';
				put_debug_char(encode); checksum += encode;
				src += runlen;
			} else {
				/* Otherwise just send the current char */
				put_debug_char(*src);   checksum += *src;
				src += 1;
			}
		}

		/* '#' Separator, put high and low components of checksum */
		put_debug_char('#');
		put_debug_char(highhex(checksum));
		put_debug_char(lowhex(checksum));
	}
	while ((get_debug_char()) != '+');	/* While no ack */
}

/* A bus error has occurred - perform a longjmp to return execution and
   allow handling of the error */
static void kgdb_handle_bus_error(void)
{
	longjmp(rem_com_env, 1);
}

/* Translate SH-3/4 exception numbers to unix-like signal values */
static int compute_signal(const int excep_code)
{
	int sigval;

	switch (excep_code) {

	case INVALID_INSN_VEC:
	case INVALID_SLOT_VEC:
		sigval = SIGILL;
		break;
	case ADDRESS_ERROR_LOAD_VEC:
	case ADDRESS_ERROR_STORE_VEC:
		sigval = SIGSEGV;
		break;

	case SERIAL_BREAK_VEC:
	case NMI_VEC:
		sigval = SIGINT;
		break;

	case USER_BREAK_VEC:
	case TRAP_VEC:
		sigval = SIGTRAP;
		break;

	default:
		sigval = SIGBUS;	/* "software generated" */
		break;
	}

	return (sigval);
}

/* Make a local copy of the registers passed into the handler (bletch) */
static void kgdb_regs_to_gdb_regs(const struct kgdb_regs *regs,
				  int *gdb_regs)
{
	gdb_regs[R0] = regs->regs[R0];
	gdb_regs[R1] = regs->regs[R1];
	gdb_regs[R2] = regs->regs[R2];
	gdb_regs[R3] = regs->regs[R3];
	gdb_regs[R4] = regs->regs[R4];
	gdb_regs[R5] = regs->regs[R5];
	gdb_regs[R6] = regs->regs[R6];
	gdb_regs[R7] = regs->regs[R7];
	gdb_regs[R8] = regs->regs[R8];
	gdb_regs[R9] = regs->regs[R9];
	gdb_regs[R10] = regs->regs[R10];
	gdb_regs[R11] = regs->regs[R11];
	gdb_regs[R12] = regs->regs[R12];
	gdb_regs[R13] = regs->regs[R13];
	gdb_regs[R14] = regs->regs[R14];
	gdb_regs[R15] = regs->regs[R15];
	gdb_regs[PC] = regs->pc;
	gdb_regs[PR] = regs->pr;
	gdb_regs[GBR] = regs->gbr;
	gdb_regs[MACH] = regs->mach;
	gdb_regs[MACL] = regs->macl;
	gdb_regs[SR] = regs->sr;
	gdb_regs[VBR] = regs->vbr;
}

/* Copy local gdb registers back to kgdb regs, for later copy to kernel */
static void gdb_regs_to_kgdb_regs(const int *gdb_regs,
				  struct kgdb_regs *regs)
{
	regs->regs[R0] = gdb_regs[R0];
	regs->regs[R1] = gdb_regs[R1];
	regs->regs[R2] = gdb_regs[R2];
	regs->regs[R3] = gdb_regs[R3];
	regs->regs[R4] = gdb_regs[R4];
	regs->regs[R5] = gdb_regs[R5];
	regs->regs[R6] = gdb_regs[R6];
	regs->regs[R7] = gdb_regs[R7];
	regs->regs[R8] = gdb_regs[R8];
	regs->regs[R9] = gdb_regs[R9];
	regs->regs[R10] = gdb_regs[R10];
	regs->regs[R11] = gdb_regs[R11];
	regs->regs[R12] = gdb_regs[R12];
	regs->regs[R13] = gdb_regs[R13];
	regs->regs[R14] = gdb_regs[R14];
	regs->regs[R15] = gdb_regs[R15];
	regs->pc = gdb_regs[PC];
	regs->pr = gdb_regs[PR];
	regs->gbr = gdb_regs[GBR];
	regs->mach = gdb_regs[MACH];
	regs->macl = gdb_regs[MACL];
	regs->sr = gdb_regs[SR];
	regs->vbr = gdb_regs[VBR];
}

/* Calculate the new address for after a step */
static short *get_step_address(void)
{
	short op = *(short *) trap_registers.pc;
	long addr;

	/* BT */
	if (OPCODE_BT(op)) {
		if (trap_registers.sr & SR_T_BIT_MASK)
			addr = trap_registers.pc + 4 + OPCODE_BTF_DISP(op);
		else
			addr = trap_registers.pc + 2;
	}

	/* BTS */
	else if (OPCODE_BTS(op)) {
		if (trap_registers.sr & SR_T_BIT_MASK)
			addr = trap_registers.pc + 4 + OPCODE_BTF_DISP(op);
		else
			addr = trap_registers.pc + 4;	/* Not in delay slot */
	}

	/* BF */
	else if (OPCODE_BF(op)) {
		if (!(trap_registers.sr & SR_T_BIT_MASK))
			addr = trap_registers.pc + 4 + OPCODE_BTF_DISP(op);
		else
			addr = trap_registers.pc + 2;
	}

	/* BFS */
	else if (OPCODE_BFS(op)) {
		if (!(trap_registers.sr & SR_T_BIT_MASK))
			addr = trap_registers.pc + 4 + OPCODE_BTF_DISP(op);
		else
			addr = trap_registers.pc + 4;	/* Not in delay slot */
	}

	/* BRA */
	else if (OPCODE_BRA(op))
		addr = trap_registers.pc + 4 + OPCODE_BRA_DISP(op);

	/* BRAF */
	else if (OPCODE_BRAF(op))
		addr = trap_registers.pc + 4
		    + trap_registers.regs[OPCODE_BRAF_REG(op)];

	/* BSR */
	else if (OPCODE_BSR(op))
		addr = trap_registers.pc + 4 + OPCODE_BSR_DISP(op);

	/* BSRF */
	else if (OPCODE_BSRF(op))
		addr = trap_registers.pc + 4
		    + trap_registers.regs[OPCODE_BSRF_REG(op)];

	/* JMP */
	else if (OPCODE_JMP(op))
		addr = trap_registers.regs[OPCODE_JMP_REG(op)];

	/* JSR */
	else if (OPCODE_JSR(op))
		addr = trap_registers.regs[OPCODE_JSR_REG(op)];

	/* RTS */
	else if (OPCODE_RTS(op))
		addr = trap_registers.pr;

	/* RTE */
	else if (OPCODE_RTE(op))
		addr = trap_registers.regs[15];

	/* Other */
	else
		addr = trap_registers.pc + 2;

	kgdb_flush_icache_range(addr, addr + 2);
	return (short *) addr;
}

/* Set up a single-step.  Replace the instruction immediately after the
   current instruction (i.e. next in the expected flow of control) with a
   trap instruction, so that returning will cause only a single instruction
   to be executed. Note that this model is slightly broken for instructions
   with delay slots (e.g. B[TF]S, BSR, BRA etc), where both the branch
   and the instruction in the delay slot will be executed. */
static void do_single_step(void)
{
	unsigned short *addr = 0;

	/* Determine where the target instruction will send us to */
	addr = get_step_address();
	stepped_address = (int)addr;

	/* Replace it */
	stepped_opcode = *(short *)addr;
	*addr = STEP_OPCODE;

	/* Flush and return */
	kgdb_flush_icache_range((long) addr, (long) addr + 2);
}

/* Undo a single step */
static void undo_single_step(void)
{
	/* If we have stepped, put back the old instruction */
	/* Use stepped_address in case we stopped elsewhere */
	if (stepped_opcode != 0) {
		*(short*)stepped_address = stepped_opcode;
		kgdb_flush_icache_range(stepped_address, stepped_address + 2);
	}
	stepped_opcode = 0;
}

/* Send a signal message */
static void send_signal_msg(const int signum)
{
	out_buffer[0] = 'S';
	out_buffer[1] = highhex(signum);
	out_buffer[2] = lowhex(signum);
	out_buffer[3] = 0;
	put_packet(out_buffer);
}

/* Reply that all was well */
static void send_ok_msg(void)
{
	strcpy(out_buffer, "OK");
	put_packet(out_buffer);
}

/* Reply that an error occurred */
static void send_err_msg(void)
{
	strcpy(out_buffer, "E01");
	put_packet(out_buffer);
}

/* Empty message indicates unrecognised command */
static void send_empty_msg(void)
{
	put_packet("");
}

/* Read memory due to 'm' message */
static void read_mem_msg(void)
{
	char *ptr;
	int addr;
	int length;

	/* Jmp, disable bus error handler */
	if (setjmp(rem_com_env) == 0) {

		kgdb_nofault = 1;

		/* Walk through, have m<addr>,<length> */
		ptr = &in_buffer[1];
		if (hex_to_int(&ptr, &addr) && (*ptr++ == ','))
			if (hex_to_int(&ptr, &length)) {
				ptr = 0;
				if (length * 2 > OUTBUFMAX)
					length = OUTBUFMAX / 2;
				mem_to_hex((char *) addr, out_buffer, length);
			}
		if (ptr)
			send_err_msg();
		else
			put_packet(out_buffer);
	} else
		send_err_msg();

	/* Restore bus error handler */
	kgdb_nofault = 0;
}

/* Write memory due to 'M' or 'X' message */
static void write_mem_msg(int binary)
{
	char *ptr;
	int addr;
	int length;

	if (setjmp(rem_com_env) == 0) {

		kgdb_nofault = 1;

		/* Walk through, have M<addr>,<length>:<data> */
		ptr = &in_buffer[1];
		if (hex_to_int(&ptr, &addr) && (*ptr++ == ','))
			if (hex_to_int(&ptr, &length) && (*ptr++ == ':')) {
				if (binary)
					ebin_to_mem(ptr, (char*)addr, length);
				else
					hex_to_mem(ptr, (char*)addr, length);
				kgdb_flush_icache_range(addr, addr + length);
				ptr = 0;
				send_ok_msg();
			}
		if (ptr)
			send_err_msg();
	} else
		send_err_msg();

	/* Restore bus error handler */
	kgdb_nofault = 0;
}

/* Continue message  */
static void continue_msg(void)
{
	/* Try to read optional parameter, PC unchanged if none */
	char *ptr = &in_buffer[1];
	int addr;

	if (hex_to_int(&ptr, &addr))
		trap_registers.pc = addr;
}

/* Continue message with signal */
static void continue_with_sig_msg(void)
{
	int signal;
	char *ptr = &in_buffer[1];
	int addr;

	/* Report limitation */
	kgdb_to_gdb("Cannot force signal in kgdb, continuing anyway.\n");

	/* Signal */
	hex_to_int(&ptr, &signal);
	if (*ptr == ';')
		ptr++;

	/* Optional address */
	if (hex_to_int(&ptr, &addr))
		trap_registers.pc = addr;
}

/* Step message */
static void step_msg(void)
{
	continue_msg();
	do_single_step();
}

/* Step message with signal */
static void step_with_sig_msg(void)
{
	continue_with_sig_msg();
	do_single_step();
}

/* Send register contents */
static void send_regs_msg(void)
{
	kgdb_regs_to_gdb_regs(&trap_registers, registers);
	mem_to_hex((char *) registers, out_buffer, NUMREGBYTES);
	put_packet(out_buffer);
}

/* Set register contents - currently can't set other thread's registers */
static void set_regs_msg(void)
{
	kgdb_regs_to_gdb_regs(&trap_registers, registers);
	hex_to_mem(&in_buffer[1], (char *) registers, NUMREGBYTES);
	gdb_regs_to_kgdb_regs(registers, &trap_registers);
	send_ok_msg();
}

#ifdef CONFIG_SH_KGDB_CONSOLE
/*
 * Bring up the ports..
 */
static int __init kgdb_serial_setup(void)
{
	struct console dummy;
	return kgdb_console_setup(&dummy, 0);
}
#else
#define kgdb_serial_setup()	0
#endif

/* The command loop, read and act on requests */
static void kgdb_command_loop(const int excep_code, const int trapa_value)
{
	int sigval;

	/* Enter GDB mode (e.g. after detach) */
	if (!kgdb_in_gdb_mode) {
		/* Do serial setup, notify user, issue preemptive ack */
		printk(KERN_NOTICE "KGDB: Waiting for GDB\n");
		kgdb_in_gdb_mode = 1;
		put_debug_char('+');
	}

	/* Reply to host that an exception has occurred */
	sigval = compute_signal(excep_code);
	send_signal_msg(sigval);

	/* TRAP_VEC exception indicates a software trap inserted in place of
	   code by GDB so back up PC by one instruction, as this instruction
	   will later be replaced by its original one.  Do NOT do this for
	   trap 0xff, since that indicates a compiled-in breakpoint which
	   will not be replaced (and we would retake the trap forever) */
	if ((excep_code == TRAP_VEC) && (trapa_value != (0x3c << 2)))
		trap_registers.pc -= 2;

	/* Undo any stepping we may have done */
	undo_single_step();

	while (1) {
		out_buffer[0] = 0;
		get_packet(in_buffer, BUFMAX);

		/* Examine first char of buffer to see what we need to do */
		switch (in_buffer[0]) {
		case '?':	/* Send which signal we've received */
			send_signal_msg(sigval);
			break;

		case 'g':	/* Return the values of the CPU registers */
			send_regs_msg();
			break;

		case 'G':	/* Set the value of the CPU registers */
			set_regs_msg();
			break;

		case 'm':	/* Read LLLL bytes address AA..AA */
			read_mem_msg();
			break;

		case 'M':	/* Write LLLL bytes address AA..AA, ret OK */
			write_mem_msg(0);	/* 0 = data in hex */
			break;

		case 'X':	/* Write LLLL bytes esc bin address AA..AA */
			if (kgdb_bits == '8')
				write_mem_msg(1); /* 1 = data in binary */
			else
				send_empty_msg();
			break;

		case 'C':	/* Continue, signum included, we ignore it */
			continue_with_sig_msg();
			return;

		case 'c':	/* Continue at address AA..AA (optional) */
			continue_msg();
			return;

		case 'S':	/* Step, signum included, we ignore it */
			step_with_sig_msg();
			return;

		case 's':	/* Step one instruction from AA..AA */
			step_msg();
			return;

		case 'k':	/* 'Kill the program' with a kernel ? */
			break;

		case 'D':	/* Detach from program, send reply OK */
			kgdb_in_gdb_mode = 0;
			send_ok_msg();
			get_debug_char();
			return;

		default:
			send_empty_msg();
			break;
		}
	}
}

/* There has been an exception, most likely a breakpoint. */
static void handle_exception(struct pt_regs *regs)
{
	int excep_code, vbr_val;
	int count;
	int trapa_value = ctrl_inl(TRA);

	/* Copy kernel regs (from stack) */
	for (count = 0; count < 16; count++)
		trap_registers.regs[count] = regs->regs[count];
	trap_registers.pc = regs->pc;
	trap_registers.pr = regs->pr;
	trap_registers.sr = regs->sr;
	trap_registers.gbr = regs->gbr;
	trap_registers.mach = regs->mach;
	trap_registers.macl = regs->macl;

	asm("stc vbr, %0":"=r"(vbr_val));
	trap_registers.vbr = vbr_val;

	/* Get excode for command loop call, user access */
	asm("stc r2_bank, %0":"=r"(excep_code));

	/* Act on the exception */
	kgdb_command_loop(excep_code, trapa_value);

	/* Copy back the (maybe modified) registers */
	for (count = 0; count < 16; count++)
		regs->regs[count] = trap_registers.regs[count];
	regs->pc = trap_registers.pc;
	regs->pr = trap_registers.pr;
	regs->sr = trap_registers.sr;
	regs->gbr = trap_registers.gbr;
	regs->mach = trap_registers.mach;
	regs->macl = trap_registers.macl;

	vbr_val = trap_registers.vbr;
	asm("ldc %0, vbr": :"r"(vbr_val));
}

asmlinkage void kgdb_handle_exception(unsigned long r4, unsigned long r5,
				      unsigned long r6, unsigned long r7,
				      struct pt_regs __regs)
{
	struct pt_regs *regs = RELOC_HIDE(&__regs, 0);
	handle_exception(regs);
}

/* Initialise the KGDB data structures and serial configuration */
int __init kgdb_init(void)
{
	in_nmi = 0;
	kgdb_nofault = 0;
	stepped_opcode = 0;
	kgdb_in_gdb_mode = 0;

	if (kgdb_serial_setup() != 0) {
		printk(KERN_NOTICE "KGDB: serial setup error\n");
		return -1;
	}

	/* Init ptr to exception handler */
	kgdb_debug_hook = handle_exception;
	kgdb_bus_err_hook = kgdb_handle_bus_error;

	/* Enter kgdb now if requested, or just report init done */
	printk(KERN_NOTICE "KGDB: stub is initialized.\n");

	return 0;
}

/* Make function available for "user messages"; console will use it too. */

char gdbmsgbuf[BUFMAX];
#define MAXOUT ((BUFMAX-2)/2)

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

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

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

		/* Calculate how many this time */
		wcount = (count > MAXOUT) ? MAXOUT : count;

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

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

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

static void kgdb_to_gdb(const char *s)
{
	kgdb_msg_write(s, strlen(s));
}

#ifdef CONFIG_SH_KGDB_CONSOLE
void kgdb_console_write(struct console *co, const char *s, unsigned count)
{
	/* Bail if we're not talking to GDB */
	if (!kgdb_in_gdb_mode)
		return;

	kgdb_msg_write(s, count);
}
#endif

#ifdef CONFIG_KGDB_SYSRQ
static void sysrq_handle_gdb(int key, struct tty_struct *tty)
{
	printk("Entering GDB stub\n");
	breakpoint();
}

static struct sysrq_key_op sysrq_gdb_op = {
        .handler        = sysrq_handle_gdb,
        .help_msg       = "Gdb",
        .action_msg     = "GDB",
};

static int gdb_register_sysrq(void)
{
	printk("Registering GDB sysrq handler\n");
	register_sysrq_key('g', &sysrq_gdb_op);
	return 0;
}
module_init(gdb_register_sysrq);
#endif