haiku/src/system/kernel/debug/gdb.c

/* Contains the code to interface with a remote GDB */

/*
** Copyright 2002, Manuel J. Petit. All rights reserved.
** Distributed under the terms of the NewOS License.
*/
#include <string.h>
#include <stdarg.h>
#include <stdio.h>
#include <vm.h>
#include <smp.h>
#include <debug.h>
#include <gdb.h>
#include <arch/dbg_console.h>


enum { INIT= 0, CMDREAD, CKSUM1, CKSUM2, WAITACK, QUIT, GDBSTATES };


static char cmd[512];
static int  cmd_ptr;
static int  checksum;

static char reply[512];

static char safe_mem[512];


/*
 * utility functions
 */

static int
parse_nibble(int input)
{
	int nibble = 0xff;

	if (input >= '0' && input <= '9')
		nibble = input - '0';

	if (input >= 'A' && input <= 'F')
		nibble = 0x0a + input - 'A';

	if (input >= 'a' && input <= 'f')
		nibble = 0x0a + input - 'a';

	return nibble;
}



/*
 * GDB protocol ACK & NAK & Reply
 *
 */

static void
gdb_ack(void)
{
	dbg_putch('+');
}


static void
gdb_nak(void)
{
	dbg_putch('-');
}


static void
gdb_resend_reply(void)
{
	dbg_puts(reply);
}


static void
gdb_reply(char const *fmt, ...)
{
	int i;
	int len;
	int sum;
	va_list args;

	va_start(args, fmt);
	reply[0] = '$';
	vsprintf(reply + 1, fmt, args);
	va_end(args);

	len = strlen(reply);
	sum = 0;
	for (i = 1; i < len; i++) {
		sum += reply[i];
	}
	sum %= 256;

	sprintf(reply + len, "#%02x", sum);

	gdb_resend_reply();
}


static void
gdb_regreply(int const *regs, int numregs)
{
	int i;
	int len;
	int sum;

	reply[0] = '$';
	for (i = 0; i < numregs; i++) {
		sprintf(reply+1+8*i, "%08lx", B_HOST_TO_BENDIAN_INT32(regs[i]));
	}

	len = strlen(reply);
	sum = 0;
	for (i = 1; i < len; i++) {
		sum += reply[i];
	}
	sum %= 256;

	sprintf(reply + len, "#%02x", sum);

	gdb_resend_reply();
}


static void
gdb_memreply(char const *bytes, int numbytes)
{
	int i;
	int len;
	int sum;

	reply[0] = '$';
	for (i = 0; i < numbytes; i++) {
		sprintf(reply+1+2*i, "%02x", (uint8)bytes[i]);
	}

	len = strlen(reply);
	sum = 0;
	for (i = 1; i < len; i++) {
		sum += reply[i];
	}
	sum %= 256;

	sprintf(reply + len, "#%02x", sum);

	gdb_resend_reply();
}



/*
 * checksum verification
 */

static int
gdb_verify_checksum(void)
{
	int i;
	int len;
	int sum;

	len = strlen(cmd);
	sum = 0;
	for (i = 0; i < len; i++) {
		sum += cmd[i];
	}
	sum %= 256;

	return (sum == checksum) ? 1 : 0;
}


/*
 * command parsing an dispatching
 */

static int
gdb_parse_command(void)
{
	if (!gdb_verify_checksum()) {
		gdb_nak();
		return INIT;
	} else
		gdb_ack();

	switch (cmd[0]) {
		case 'H':
			/*
			 * Command H (actually Hct) is used to select
			 * the current thread (-1 meaning all threads)
			 * We just fake we recognize the the command
			 * and send an 'OK' response.
			 */
			gdb_reply("OK");
			break;

		case 'q':
			{
				extern unsigned __data_start;
				extern unsigned __bss_start;

				/*
				 * There are several q commands:
				 *
				 *     qXXXX        Request info about XXXX.
				 *     QXXXX=yyyy   Set value of XXXX to yyyy.
				 *     qOffsets     Get segment offsets
				 *
				 * Currently we only support the 'qOffsets'
				 * form.
				 *
				 * *Note* that we actually have to lie,
				 * At first thought looks like we should
				 * return '_start', '__data_start' &
				 * '__bss_start', however gdb gets
				 * confused because the kernel link script
				 * pre-links at 0x80000000. To keep gdb
				 * gdb happy we just substract that amount.
				 */
				if (strcmp(cmd+1, "Offsets") == 0) {
					gdb_reply("Text=%x;Data=%x;Bss=%x", 0,
						((unsigned)(&__data_start))-0x80000000,
						((unsigned)(&__bss_start))-0x80000000);
				} else
					gdb_reply("ENS");
			}
			break;

		case '?':
			/*
			 * command '?' is used for retrieving the signal
			 * that stopped the program. Fully implemeting
			 * this command requires help from the debugger,
			 * by now we just fake a SIGKILL
			 */
			gdb_reply("S09");	/* SIGKILL = 9 */
			break;

		case 'g':
			{
				int cpu;

				/*
				 * command 'g' is used for reading the register
				 * file. Faked by now.
				 *
				 * For x86 the register order is:
				 *
				 *    eax, ebx, ecx, edx,
				 *    esp, ebp, esi, edi,
				 *    eip, eflags,
				 *    cs, ss, ds, es
				 *
				 * Note that even thought the segment descriptors
				 * are actually 16 bits wide, gdb requires them
				 * as 32 bit integers. Note also that for some
				 * reason (unknown to me) gdb wants the register
				 * dump in *big endian* format.
				 */
				cpu = smp_get_current_cpu();
				gdb_regreply(dbg_register_file[cpu], 14);
			}
			break;

		case 'm':
			{
				char *ptr;
				unsigned address;
				unsigned len;

				/*
				 * The 'm' command has the form mAAA,LLL
				 * where AAA is the address and LLL is the
				 * number of bytes.
				 */
				ptr = cmd+1;
				address = 0;
				len = 0;
				while (ptr && *ptr && (*ptr != ',')) {
					address <<= 4;
					address += parse_nibble(*ptr);
					ptr += 1;
				}
				if (*ptr == ',')
					ptr+= 1;

				while (ptr && *ptr) {
					len <<= 4;
					len += parse_nibble(*ptr);
					ptr += 1;
				}

				if (len> 128)
					len = 128;

				/*
				 * We cannot directly access the requested memory
				 * for gdb may be trying to access an stray pointer
				 * We copy the memory to a safe buffer using
				 * the bulletproof user_memcpy().
				 */
				if (user_memcpy(safe_mem, (char *)address, len) < 0)
					gdb_reply("E02");
				else
					gdb_memreply(safe_mem, len);
			}
			break;

		case 'k':
			/*
			 * Command 'k' actual semantics is 'kill the damn thing'.
			 * However gdb sends that command when you disconnect
			 * from a debug session. I guess that 'kill' for the
			 * kernel would map to reboot... however that's a
			 * a very mean thing to do, instead we just quit
			 * the gdb state machine and fallback to the regular
			 * kernel debugger command prompt.
			 */
			return QUIT;

		default:
			gdb_reply("E01");
			break;
	}

	return WAITACK;
}



/*
 * GDB protocol state machine
 */

static int
gdb_init_handler(int input)
{
	switch (input) {
		case '$':
			memset(cmd, 0, sizeof(cmd));
			cmd_ptr = 0;
			return CMDREAD;

		default:
#if 0
			gdb_nak();
#else
			/*
			 * looks to me like we should send
			 * a NAK here but it kinda works
			 * better if we just gobble all
			 * junk chars silently
			 */
#endif
			return INIT;
	}
}


static int
gdb_cmdread_handler(int input)
{
	switch (input) {
		case '#':
			return CKSUM1;

		default:
			cmd[cmd_ptr] = input;
			cmd_ptr += 1;
			return CMDREAD;
	}
}


static int
gdb_cksum1_handler(int input)
{
	int nibble = parse_nibble(input);

	if (nibble == 0xff) {
#if 0
		gdb_nak();
		return INIT;
#else
		/*
		 * looks to me like we should send
		 * a NAK here but it kinda works
		 * better if we just gobble all
		 * junk chars silently
		 */
#endif
	}

	checksum = nibble << 4;

	return CKSUM2;
}


static int
gdb_cksum2_handler(int input)
{
	int nibble = parse_nibble(input);

	if (nibble == 0xff) {
#if 0
		gdb_nak();
		return INIT;
#else
		/*
		 * looks to me like we should send
		 * a NAK here but it kinda works
		 * better if we just gobble all
		 * junk chars silently
		 */
#endif
	}

	checksum += nibble;

	return gdb_parse_command();
}


static int
gdb_waitack_handler(int input)
{
	switch (input) {
		case '+':
			return INIT;
		case '-':
			gdb_resend_reply();
			return WAITACK;

		default:
			/*
			 * looks like gdb and us are out of synch,
			 * send a NAK and retry from INIT state.
			 */
			gdb_nak();
			return INIT;
	}
}


static int
gdb_quit_handler(int input)
{
	(void)(input);

	/*
	 * actually we should never be here
	 */
	return QUIT;
}


static int (*dispatch_table[GDBSTATES])(int) = {
	&gdb_init_handler,
	&gdb_cmdread_handler,
	&gdb_cksum1_handler,
	&gdb_cksum2_handler,
	&gdb_waitack_handler,
	&gdb_quit_handler
};


static int
gdb_state_dispatch(int curr, int input)
{
	if (curr < INIT || curr >= GDBSTATES)
		return QUIT;

	return dispatch_table[curr](input);
}


static int
gdb_state_machine(void)
{
	int state = INIT;
	int c;

	while (state != QUIT) {
		c = arch_dbg_con_read();
		state = gdb_state_dispatch(state, c);
	}

	return 0;
}


int
cmd_gdb(int argc, char **argv)
{
	(void)(argc);
	(void)(argv);

	return gdb_state_machine();
}