gdbstub.c

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/*
 * 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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

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

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <byteswap.h>
#include <gpxe/gdbstub.h>
#include "gdbmach.h"

enum {
        POSIX_EINVAL = 0x1c,  /* used to report bad arguments to GDB */
        SIZEOF_PAYLOAD = 256, /* 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;
        if ( !gdbstub_get_packet_args ( stub, args, sizeof args / sizeof args [ 0 ], NULL ) ) {
                gdbstub_send_errno ( stub, POSIX_EINVAL );
                return;
        }
        if ( gdbmach_set_breakpoint ( args [ 0 ], args [ 1 ], args [ 2 ], enable ) ) {
                gdbstub_send_ok ( stub );
        } else {
                /* Not supported */
                stub->len = 0;
                gdbstub_tx_packet ( 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_breakpoint();
}