src/core/gdbstub.c

/*
 * Copyright (C) 2008 Stefan Hajnoczi <stefanha@gmail.com>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
FILE_SECBOOT ( FORBIDDEN );

/**
 * @file
 *
 * GDB stub for remote debugging
 *
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <byteswap.h>
#include <ipxe/gdbstub.h>

enum {
	POSIX_EINVAL = 0x1c,  /* used to report bad arguments to GDB */
	SIZEOF_PAYLOAD = 512, /* buffer size of GDB payload data */
};

struct gdbstub {
	struct gdb_transport *trans;
	int exit_handler; /* leave interrupt handler */

	int signo;
	gdbreg_t *regs;

	void ( * parse ) ( struct gdbstub *stub, char ch );
	uint8_t cksum1;

	/* Buffer for payload data when parsing a packet.  Once the
	 * packet has been received, this buffer is used to hold
	 * the reply payload. */
	char buf [ SIZEOF_PAYLOAD + 4 ]; /* $...PAYLOAD...#XX */
	char *payload;                   /* start of payload */
	int len;                         /* length of payload */
};

/* Packet parser states */
static void gdbstub_state_new ( struct gdbstub *stub, char ch );
static void gdbstub_state_data ( struct gdbstub *stub, char ch );
static void gdbstub_state_cksum1 ( struct gdbstub *stub, char ch );
static void gdbstub_state_cksum2 ( struct gdbstub *stub, char ch );
static void gdbstub_state_wait_ack ( struct gdbstub *stub, char ch );

static uint8_t gdbstub_from_hex_digit ( char ch ) {
	return ( isdigit ( ch ) ? ch - '0' : tolower ( ch ) - 'a' + 0xa ) & 0xf;
}

static uint8_t gdbstub_to_hex_digit ( uint8_t b ) {
	b &= 0xf;
	return ( b < 0xa ? '0' : 'a' - 0xa ) + b;
}

/*
 * To make reading/writing device memory atomic, we check for
 * 2- or 4-byte aligned operations and handle them specially.
 */

static void gdbstub_from_hex_buf ( char *dst, char *src, int lenbytes ) {
	if ( lenbytes == 2 && ( ( unsigned long ) dst & 0x1 ) == 0 ) {
		uint16_t i = gdbstub_from_hex_digit ( src [ 2 ] ) << 12 |
			gdbstub_from_hex_digit ( src [ 3 ] ) << 8 |
			gdbstub_from_hex_digit ( src [ 0 ] ) << 4 |
			gdbstub_from_hex_digit ( src [ 1 ] );
		* ( uint16_t * ) dst = cpu_to_le16 ( i );
	} else if ( lenbytes == 4 && ( ( unsigned long ) dst & 0x3 ) == 0 ) {
		uint32_t i = gdbstub_from_hex_digit ( src [ 6 ] ) << 28 |
			gdbstub_from_hex_digit ( src [ 7 ] ) << 24 |
			gdbstub_from_hex_digit ( src [ 4 ] ) << 20 |
			gdbstub_from_hex_digit ( src [ 5 ] ) << 16 |
			gdbstub_from_hex_digit ( src [ 2 ] ) << 12 |
			gdbstub_from_hex_digit ( src [ 3 ] ) << 8 |
			gdbstub_from_hex_digit ( src [ 0 ] ) << 4 |
			gdbstub_from_hex_digit ( src [ 1 ] );
		* ( uint32_t * ) dst = cpu_to_le32 ( i );
	} else {
		while ( lenbytes-- > 0 ) {
			*dst++ = gdbstub_from_hex_digit ( src [ 0 ] ) << 4 |
				gdbstub_from_hex_digit ( src [ 1 ] );
			src += 2;
		}
	}
}

static void gdbstub_to_hex_buf ( char *dst, char *src, int lenbytes ) {
	if ( lenbytes == 2 && ( ( unsigned long ) src & 0x1 ) == 0 ) {
		uint16_t i = cpu_to_le16 ( * ( uint16_t * ) src );
		dst [ 0 ] = gdbstub_to_hex_digit ( i >> 4 );
		dst [ 1 ] = gdbstub_to_hex_digit ( i );
		dst [ 2 ] = gdbstub_to_hex_digit ( i >> 12 );
		dst [ 3 ] = gdbstub_to_hex_digit ( i >> 8 );
	} else if ( lenbytes == 4 && ( ( unsigned long ) src & 0x3 ) == 0 ) {
		uint32_t i = cpu_to_le32 ( * ( uint32_t * ) src );
		dst [ 0 ] = gdbstub_to_hex_digit ( i >> 4 );
		dst [ 1 ] = gdbstub_to_hex_digit ( i );
		dst [ 2 ] = gdbstub_to_hex_digit ( i >> 12 );
		dst [ 3 ] = gdbstub_to_hex_digit ( i >> 8 );
		dst [ 4 ] = gdbstub_to_hex_digit ( i >> 20 );
		dst [ 5 ] = gdbstub_to_hex_digit ( i >> 16);
		dst [ 6 ] = gdbstub_to_hex_digit ( i >> 28 );
		dst [ 7 ] = gdbstub_to_hex_digit ( i >> 24 );
	} else {
		while ( lenbytes-- > 0 ) {
			*dst++ = gdbstub_to_hex_digit ( *src >> 4 );
			*dst++ = gdbstub_to_hex_digit ( *src );
			src++;
		}
	}
}

static uint8_t gdbstub_cksum ( char *data, int len ) {
	uint8_t cksum = 0;
	while ( len-- > 0 ) {
		cksum += ( uint8_t ) *data++;
	}
	return cksum;
}

static void gdbstub_tx_packet ( struct gdbstub *stub ) {
	uint8_t cksum = gdbstub_cksum ( stub->payload, stub->len );
	stub->buf [ 0 ] = '$';
	stub->buf [ stub->len + 1 ] = '#';
	stub->buf [ stub->len + 2 ] = gdbstub_to_hex_digit ( cksum >> 4 );
	stub->buf [ stub->len + 3 ] = gdbstub_to_hex_digit ( cksum );
	stub->trans->send ( stub->buf, stub->len + 4 );
	stub->parse = gdbstub_state_wait_ack;
}

/* GDB commands */
static void gdbstub_send_ok ( struct gdbstub *stub ) {
	stub->payload [ 0 ] = 'O';
	stub->payload [ 1 ] = 'K';
	stub->len = 2;
	gdbstub_tx_packet ( stub );
}

static void gdbstub_send_num_packet ( struct gdbstub *stub, char reply, int num ) {
	stub->payload [ 0 ] = reply;
	stub->payload [ 1 ] = gdbstub_to_hex_digit ( ( char ) num >> 4 );
	stub->payload [ 2 ] = gdbstub_to_hex_digit ( ( char ) num );
	stub->len = 3;
	gdbstub_tx_packet ( stub );
}

/* Format is arg1,arg2,...,argn:data where argn are hex integers and data is not an argument */
static int gdbstub_get_packet_args ( struct gdbstub *stub, unsigned long *args, int nargs, int *stop_idx ) {
	int i;
	char ch = 0;
	int argc = 0;
	unsigned long val = 0;
	for ( i = 1; i < stub->len && argc < nargs; i++ ) {
		ch = stub->payload [ i ];
		if ( ch == ':' ) {
			break;
		} else if ( ch == ',' ) {
			args [ argc++ ] = val;
			val = 0;
		} else {
			val = ( val << 4 ) | gdbstub_from_hex_digit ( ch );
		}
	}
	if ( stop_idx ) {
		*stop_idx = i;
	}
	if ( argc < nargs ) {
		args [ argc++ ] = val;
	}
	return ( ( i == stub->len || ch == ':' ) && argc == nargs );
}

static void gdbstub_send_errno ( struct gdbstub *stub, int errno ) {
	gdbstub_send_num_packet ( stub, 'E', errno );
}

static void gdbstub_report_signal ( struct gdbstub *stub ) {
	gdbstub_send_num_packet ( stub, 'S', stub->signo );
}

static void gdbstub_read_regs ( struct gdbstub *stub ) {
	gdbstub_to_hex_buf ( stub->payload, ( char * ) stub->regs, GDBMACH_SIZEOF_REGS );
	stub->len = GDBMACH_SIZEOF_REGS * 2;
	gdbstub_tx_packet ( stub );
}

static void gdbstub_write_regs ( struct gdbstub *stub ) {
	if ( stub->len != 1 + GDBMACH_SIZEOF_REGS * 2 ) {
		gdbstub_send_errno ( stub, POSIX_EINVAL );
		return;
	}
	gdbstub_from_hex_buf ( ( char * ) stub->regs, &stub->payload [ 1 ], GDBMACH_SIZEOF_REGS );
	gdbstub_send_ok ( stub );
}

static void gdbstub_read_mem ( struct gdbstub *stub ) {
	unsigned long args [ 2 ];
	if ( !gdbstub_get_packet_args ( stub, args, sizeof args / sizeof args [ 0 ], NULL ) ) {
		gdbstub_send_errno ( stub, POSIX_EINVAL );
		return;
	}
	args [ 1 ] = ( args [ 1 ] < SIZEOF_PAYLOAD / 2 ) ? args [ 1 ] : SIZEOF_PAYLOAD / 2;
	gdbstub_to_hex_buf ( stub->payload, ( char * ) args [ 0 ], args [ 1 ] );
	stub->len = args [ 1 ] * 2;
	gdbstub_tx_packet ( stub );
}

static void gdbstub_write_mem ( struct gdbstub *stub ) {
	unsigned long args [ 2 ];
	int colon;
	if ( !gdbstub_get_packet_args ( stub, args, sizeof args / sizeof args [ 0 ], &colon ) ||
			colon >= stub->len || stub->payload [ colon ] != ':' ||
			( stub->len - colon - 1 ) % 2 != 0 ) {
		gdbstub_send_errno ( stub, POSIX_EINVAL );
		return;
	}
	gdbstub_from_hex_buf ( ( char * ) args [ 0 ], &stub->payload [ colon + 1 ], ( stub->len - colon - 1 ) / 2 );
	gdbstub_send_ok ( stub );
}

static void gdbstub_continue ( struct gdbstub *stub, int single_step ) {
	gdbreg_t pc;
	if ( stub->len > 1 && gdbstub_get_packet_args ( stub, &pc, 1, NULL ) ) {
		gdbmach_set_pc ( stub->regs, pc );
	}
	gdbmach_set_single_step ( stub->regs, single_step );
	stub->exit_handler = 1;
	/* Reply will be sent when we hit the next breakpoint or interrupt */
}

static void gdbstub_breakpoint ( struct gdbstub *stub ) {
	unsigned long args [ 3 ];
	int enable = stub->payload [ 0 ] == 'Z' ? 1 : 0;
	int rc;

	if ( !gdbstub_get_packet_args ( stub, args, sizeof args / sizeof args [ 0 ], NULL ) ) {
		gdbstub_send_errno ( stub, POSIX_EINVAL );
		return;
	}
	if ( ( rc = gdbmach_set_breakpoint ( args [ 0 ], args [ 1 ],
					     args [ 2 ], enable ) ) != 0 ) {
		/* Not supported */
		stub->len = 0;
		gdbstub_tx_packet ( stub );
		return;
	}
	gdbstub_send_ok ( stub );
}

static void gdbstub_rx_packet ( struct gdbstub *stub ) {
	switch ( stub->payload [ 0 ] ) {
		case '?':
			gdbstub_report_signal ( stub );
			break;
		case 'g':
			gdbstub_read_regs ( stub );
			break;
		case 'G':
			gdbstub_write_regs ( stub );
			break;
		case 'm':
			gdbstub_read_mem ( stub );
			break;
		case 'M':
			gdbstub_write_mem ( stub );
			break;
		case 'c': /* Continue */
		case 'k': /* Kill */
		case 's': /* Step */
		case 'D': /* Detach */
			gdbstub_continue ( stub, stub->payload [ 0 ] == 's' );
			if ( stub->payload [ 0 ] == 'D' ) {
				gdbstub_send_ok ( stub );
			}
			break;
		case 'Z': /* Insert breakpoint */
		case 'z': /* Remove breakpoint */
			gdbstub_breakpoint ( stub );
			break;
		default:
			stub->len = 0;
			gdbstub_tx_packet ( stub );
			break;
	}
}

/* GDB packet parser */
static void gdbstub_state_new ( struct gdbstub *stub, char ch ) {
	if ( ch == '$' ) {
		stub->len = 0;
		stub->parse = gdbstub_state_data;
	}
}

static void gdbstub_state_data ( struct gdbstub *stub, char ch ) {
	if ( ch == '#' ) {
		stub->parse = gdbstub_state_cksum1;
	} else if ( ch == '$' ) {
		stub->len = 0; /* retry new packet */
	} else {
		/* If the length exceeds our buffer, let the checksum fail */
		if ( stub->len < SIZEOF_PAYLOAD ) {
			stub->payload [ stub->len++ ] = ch;
		}
	}
}

static void gdbstub_state_cksum1 ( struct gdbstub *stub, char ch ) {
	stub->cksum1 = gdbstub_from_hex_digit ( ch ) << 4;
	stub->parse = gdbstub_state_cksum2;
}

static void gdbstub_state_cksum2 ( struct gdbstub *stub, char ch ) {
	uint8_t their_cksum;
	uint8_t our_cksum;

	stub->parse = gdbstub_state_new;
	their_cksum = stub->cksum1 + gdbstub_from_hex_digit ( ch );
	our_cksum = gdbstub_cksum ( stub->payload, stub->len );
	if ( their_cksum == our_cksum ) {
		stub->trans->send ( "+", 1 );
		if ( stub->len > 0 ) {
			gdbstub_rx_packet ( stub );
		}
	} else {
		stub->trans->send ( "-", 1 );
	}
}

static void gdbstub_state_wait_ack ( struct gdbstub *stub, char ch ) {
	if ( ch == '+' ) {
		stub->parse = gdbstub_state_new;
	} else {
		/* This retransmit is very aggressive but necessary to keep
		 * in sync with GDB. */
		gdbstub_tx_packet ( stub );
	}
}

static void gdbstub_parse ( struct gdbstub *stub, char ch ) {
	stub->parse ( stub, ch );
}

static struct gdbstub stub = {
	.parse = gdbstub_state_new
};

void gdbstub_handler ( int signo, gdbreg_t *regs ) {
	char packet [ SIZEOF_PAYLOAD + 4 ];
	size_t len, i;

	/* A transport must be set up */
	if ( !stub.trans ) {
		return;
	}

	stub.signo = signo;
	stub.regs = regs;
	stub.exit_handler = 0;
	gdbstub_report_signal ( &stub );
	while ( !stub.exit_handler && ( len = stub.trans->recv ( packet, sizeof ( packet ) ) ) > 0 ) {
		for ( i = 0; i < len; i++ ) {
			gdbstub_parse ( &stub, packet [ i ] );
		}
	}
}

struct gdb_transport *find_gdb_transport ( const char *name ) {
	struct gdb_transport *trans;

	for_each_table_entry ( trans, GDB_TRANSPORTS ) {
		if ( strcmp ( trans->name, name ) == 0 ) {
			return trans;
		}
	}
	return NULL;
}

void gdbstub_start ( struct gdb_transport *trans ) {
	stub.trans = trans;
	stub.payload = &stub.buf [ 1 ];
	gdbmach_init();
	gdbmach_breakpoint();
}