gdbmach.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.
 */

#include <stddef.h>
#include <stdio.h>
#include <assert.h>
#include <gpxe/uaccess.h>
#include <gpxe/gdbstub.h>
#include <gdbmach.h>

/** @file
 *
 * GDB architecture-specific bits for i386
 *
 */

enum {
        DR7_CLEAR = 0x00000400,    /* disable hardware breakpoints */
        DR6_CLEAR = 0xffff0ff0,    /* clear breakpoint status */
};

/** Hardware breakpoint, fields stored in x86 bit pattern form */
struct hwbp {
        int type;           /* type (1=write watchpoint, 3=access watchpoint) */
        unsigned long addr; /* linear address */
        size_t len;         /* length (0=1-byte, 1=2-byte, 3=4-byte) */
        int enabled;
};

static struct hwbp hwbps [ 4 ];
static gdbreg_t dr7 = DR7_CLEAR;

static struct hwbp *gdbmach_find_hwbp ( int type, unsigned long addr, size_t len ) {
        struct hwbp *available = NULL;
        unsigned int i;
        for ( i = 0; i < sizeof hwbps / sizeof hwbps [ 0 ]; i++ ) {
                if ( hwbps [ i ].type == type && hwbps [ i ].addr == addr && hwbps [ i ].len == len ) {
                        return &hwbps [ i ];
                }
                if ( !hwbps [ i ].enabled ) {
                        available = &hwbps [ i ];
                }
        }
        return available;
}

static void gdbmach_commit_hwbp ( struct hwbp *bp ) {
        unsigned int regnum = bp - hwbps;

        /* Set breakpoint address */
        assert ( regnum < ( sizeof hwbps / sizeof hwbps [ 0 ] ) );
        switch ( regnum ) {
                case 0:
                        __asm__ __volatile__ ( "movl %0, %%dr0\n" : : "r" ( bp->addr ) );
                        break;
                case 1:
                        __asm__ __volatile__ ( "movl %0, %%dr1\n" : : "r" ( bp->addr ) );
                        break;
                case 2:
                        __asm__ __volatile__ ( "movl %0, %%dr2\n" : : "r" ( bp->addr ) );
                        break;
                case 3:
                        __asm__ __volatile__ ( "movl %0, %%dr3\n" : : "r" ( bp->addr ) );
                        break;
        }

        /* Set type */
        dr7 &= ~( 0x3 << ( 16 + 4 * regnum ) );
        dr7 |= bp->type << ( 16 + 4 * regnum );

        /* Set length */
        dr7 &= ~( 0x3 << ( 18 + 4 * regnum ) );
        dr7 |= bp->len << ( 18 + 4 * regnum );

        /* Set/clear local enable bit */
        dr7 &= ~( 0x3 << 2 * regnum );
        dr7 |= bp->enabled << 2 * regnum;
}

int gdbmach_set_breakpoint ( int type, unsigned long addr, size_t len, int enable ) {
        struct hwbp *bp;
        
        /* Check and convert breakpoint type to x86 type */
        switch ( type ) {
                case GDBMACH_WATCH:
                        type = 0x1;
                        break;
                case GDBMACH_AWATCH:
                        type = 0x3;
                        break;
                default:
                        return 0; /* unsupported breakpoint type */
        }

        /* Only lengths 1, 2, and 4 are supported */
        if ( len != 2 && len != 4 ) {
                len = 1;
        }
        len--; /* convert to x86 breakpoint length bit pattern */

        /* Calculate linear address by adding segment base */
        addr += virt_offset;

        /* Set up the breakpoint */
        bp = gdbmach_find_hwbp ( type, addr, len );
        if ( !bp ) {
                return 0; /* ran out of hardware breakpoints */
        }
        bp->type = type;
        bp->addr = addr;
        bp->len = len;
        bp->enabled = enable;
        gdbmach_commit_hwbp ( bp );
        return 1;
}

static void gdbmach_disable_hwbps ( void ) {
        /* Store and clear hardware breakpoints */
        __asm__ __volatile__ ( "movl %0, %%dr7\n" : : "r" ( DR7_CLEAR ) );
}

static void gdbmach_enable_hwbps ( void ) {
        /* Clear breakpoint status register */
        __asm__ __volatile__ ( "movl %0, %%dr6\n" : : "r" ( DR6_CLEAR ) );

        /* Restore hardware breakpoints */
        __asm__ __volatile__ ( "movl %0, %%dr7\n" : : "r" ( dr7 ) );
}

__asmcall void gdbmach_handler ( int signo, gdbreg_t *regs ) {
        gdbmach_disable_hwbps();
        gdbstub_handler ( signo, regs );
        gdbmach_enable_hwbps();
}