gdbmach.c

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/*
 * Copyright (C) 2008 Stefan Hajnoczi <stefanha@gmail.com>.
 * Copyright (C) 2016 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * 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 );

#include <stddef.h>
#include <stdio.h>
#include <errno.h>
#include <assert.h>
#include <ipxe/uaccess.h>
#include <ipxe/gdbstub.h>
#include <librm.h>

/** @file
 *
 * GDB architecture-specific bits for x86
 *
 */

/** Number of hardware breakpoints */
#define NUM_HWBP 4

/** Debug register 7: Global breakpoint enable */
#define DR7_G( bp ) ( 2 << ( 2 * (bp) ) )

/** Debug register 7: Global exact breakpoint enable */
#define DR7_GE ( 1 << 9 )

/** Debug register 7: Break on data writes */
#define DR7_RWLEN_WRITE 0x11110000

/** Debug register 7: Break on data access */
#define DR7_RWLEN_ACCESS 0x33330000

/** Debug register 7: One-byte length */
#define DR7_RWLEN_1 0x00000000

/** Debug register 7: Two-byte length */
#define DR7_RWLEN_2 0x44440000

/** Debug register 7: Four-byte length */
#define DR7_RWLEN_4 0xcccc0000

/** Debug register 7: Eight-byte length */
#define DR7_RWLEN_8 0x88880000

/** Debug register 7: Breakpoint R/W and length mask */
#define DR7_RWLEN_MASK( bp ) ( 0xf0000 << ( 4 * (bp) ) )

/** Hardware breakpoint addresses (debug registers 0-3) */
static unsigned long dr[NUM_HWBP];

/** Active value of debug register 7 */
static unsigned long dr7 = DR7_GE;

/**
 * Update debug registers
 *
 */
static void gdbmach_update ( void ) {

        /* Set debug registers */
        __asm__ __volatile__ ( "mov %0, %%dr0" : : "r" ( dr[0] ) );
        __asm__ __volatile__ ( "mov %0, %%dr1" : : "r" ( dr[1] ) );
        __asm__ __volatile__ ( "mov %0, %%dr2" : : "r" ( dr[2] ) );
        __asm__ __volatile__ ( "mov %0, %%dr3" : : "r" ( dr[3] ) );
        __asm__ __volatile__ ( "mov %0, %%dr7" : : "r" ( dr7 ) );
}

/**
 * Find reusable or available hardware breakpoint
 *
 * @v addr              Linear address
 * @v rwlen             Control bits
 * @ret bp              Hardware breakpoint, or negative error
 */
static int gdbmach_find ( unsigned long addr, unsigned int rwlen ) {
        unsigned int i;
        int bp = -ENOENT;

        /* Look for a reusable or available breakpoint */
        for ( i = 0 ; i < NUM_HWBP ; i++ ) {

                /* If breakpoint is not enabled, then it is available */
                if ( ! ( dr7 & DR7_G ( i ) ) ) {
                        bp = i;
                        continue;
                }

                /* If breakpoint is enabled and has the same address
                 * and control bits, then reuse it.
                 */
                if ( ( dr[i] == addr ) &&
                     ( ( ( dr7 ^ rwlen ) & DR7_RWLEN_MASK ( i ) ) == 0 ) ) {
                        bp = i;
                        break;
                }
        }

        return bp;
}

/**
 * Set hardware breakpoint
 *
 * @v type              GDB breakpoint type
 * @v addr              Virtual address
 * @v len               Length
 * @v enable            Enable (not disable) breakpoint
 * @ret rc              Return status code
 */
int gdbmach_set_breakpoint ( int type, unsigned long addr, size_t len,
                             int enable ) {
        unsigned int rwlen;
        unsigned long mask;
        int bp;

        /* Parse breakpoint type */
        switch ( type ) {
        case GDBMACH_WATCH:
                rwlen = DR7_RWLEN_WRITE;
                break;
        case GDBMACH_AWATCH:
                rwlen = DR7_RWLEN_ACCESS;
                break;
        default:
                return -ENOTSUP;
        }

        /* Parse breakpoint length */
        switch ( len ) {
        case 1:
                rwlen |= DR7_RWLEN_1;
                break;
        case 2:
                rwlen |= DR7_RWLEN_2;
                break;
        case 4:
                rwlen |= DR7_RWLEN_4;
                break;
        case 8:
                rwlen |= DR7_RWLEN_8;
                break;
        default:
                return -ENOTSUP;
        }

        /* Convert to linear address */
        if ( sizeof ( physaddr_t ) <= sizeof ( uint32_t ) )
                addr = virt_to_phys ( ( void * ) addr );

        /* Find reusable or available hardware breakpoint */
        bp = gdbmach_find ( addr, rwlen );
        if ( bp < 0 )
                return ( enable ? -ENOBUFS : 0 );

        /* Configure this breakpoint */
        DBGC ( &dr[0], "GDB bp %d at %p+%zx type %d (%sabled)\n",
               bp, ( ( void * ) addr ), len, type, ( enable ? "en" : "dis" ) );
        dr[bp] = addr;
        mask = DR7_RWLEN_MASK ( bp );
        dr7 = ( ( dr7 & ~mask ) | ( rwlen & mask ) );
        mask = DR7_G ( bp );
        dr7 &= ~mask;
        if ( enable )
                dr7 |= mask;

        /* Update debug registers */
        gdbmach_update();

        return 0;
}

/**
 * Handle exception
 *
 * @v signo             GDB signal number
 * @v regs              Register dump
 */
__asmcall void gdbmach_handler ( int signo, gdbreg_t *regs ) {
        unsigned long dr7_disabled = DR7_GE;
        unsigned long dr6_clear = 0;

        /* Temporarily disable breakpoints */
        __asm__ __volatile__ ( "mov %0, %%dr7\n" : : "r" ( dr7_disabled ) );

        /* Handle exception */
        DBGC ( &dr[0], "GDB signal %d\n", signo );
        DBGC2_HDA ( &dr[0], 0, regs, ( GDBMACH_NREGS * sizeof ( *regs ) ) );
        gdbstub_handler ( signo, regs );
        DBGC ( &dr[0], "GDB signal %d returning\n", signo );
        DBGC2_HDA ( &dr[0], 0, regs, ( GDBMACH_NREGS * sizeof ( *regs ) ) );

        /* Clear breakpoint status register */
        __asm__ __volatile__ ( "mov %0, %%dr6\n" : : "r" ( dr6_clear ) );

        /* Re-enable breakpoints */
        __asm__ __volatile__ ( "mov %0, %%dr7\n" : : "r" ( dr7 ) );
}

/**
 * CPU exception vectors
 *
 * Note that we cannot intercept anything from INT8 (double fault)
 * upwards, since these overlap by default with IRQ0-7.
 */
static void * gdbmach_vectors[] = {
        gdbmach_sigfpe,         /* Divide by zero */
        gdbmach_sigtrap,        /* Debug trap */
        NULL,                   /* Non-maskable interrupt */
        gdbmach_sigtrap,        /* Breakpoint */
        gdbmach_sigstkflt,      /* Overflow */
        gdbmach_sigstkflt,      /* Bound range exceeded */
        gdbmach_sigill,         /* Invalid opcode */
};

/**
 * Initialise GDB
 */
void gdbmach_init ( void ) {
        unsigned int i;

        /* Hook CPU exception vectors */
        for ( i = 0 ; i < ( sizeof ( gdbmach_vectors ) /
                            sizeof ( gdbmach_vectors[0] ) ) ; i++ ) {
                if ( gdbmach_vectors[i] )
                        set_interrupt_vector ( i, gdbmach_vectors[i] );
        }
}