lib_i386/realmode.c

   1 /*
   2  * (C) Copyright 2002
   3  * Daniel Engström, Omicron Ceti AB, daniel@omicron.se
   4  *
   5  * See file CREDITS for list of people who contributed to this
   6  * project.
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License as
  10  * published by the Free Software Foundation; either version 2 of
  11  * the License, or (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  21  * MA 02111-1307 USA
  22  */
  23
  24 #include <common.h>
  25 #include <asm/io.h>
  26 #include <asm/ptrace.h>
  27 #include <asm/realmode.h>
  28
  29
  30 #define REALMODE_BASE    ((char*)0x7c0)
  31 #define REALMODE_MAILBOX ((char*)0xe00)
  32
  33
  34 extern char realmode_enter;
  35
  36 int realmode_setup(void)
  37 {
  38         /* copy the realmode switch code */
  39         if (i386boot_realmode_size > (REALMODE_MAILBOX-REALMODE_BASE)) {
  40                 printf("realmode switch too large (%ld bytes, max is %d)\n",
  41                        i386boot_realmode_size, (REALMODE_MAILBOX-REALMODE_BASE));
  42                 return -1;
  43         }
  44
  45         memcpy(REALMODE_BASE, (void*)i386boot_realmode, i386boot_realmode_size);
  46         asm("wbinvd\n");
  47
  48         return 0;
  49 }
  50
  51 int enter_realmode(u16 seg, u16 off, struct pt_regs *in, struct pt_regs *out)
  52 {
  53
  54         /* setup out thin bios emulation */
  55         if (bios_setup()) {
  56                 return -1;
  57         }
  58
  59         if (realmode_setup()) {
  60                 return -1;
  61         }
  62
  63         in->eip = off;
  64         in->xcs = seg;
  65         if (3>(in->esp & 0xffff)) {
  66                 printf("Warning: entering realmode with sp < 4 will fail\n");
  67         }
  68
  69         memcpy(REALMODE_MAILBOX, in, sizeof(struct pt_regs));
  70         asm("wbinvd\n");
  71
  72         __asm__ volatile (
  73                  "lcall $0x20,%0\n"  : :  "i" (&realmode_enter) );
  74
  75         asm("wbinvd\n");
  76         memcpy(out, REALMODE_MAILBOX, sizeof(struct pt_regs));
  77
  78         return out->eax;
  79 }
  80
  81
  82 /* This code is supposed to access a realmode interrupt
  83  * it does currently not work for me */
  84 int enter_realmode_int(u8 lvl, struct pt_regs *in, struct pt_regs *out)
  85 {
  86         /* place two instructions at 0x700 */
  87         writeb(0xcd, 0x700);  /* int $lvl */
  88         writeb(lvl, 0x701);
  89         writeb(0xcb, 0x702);  /* lret */
  90         asm("wbinvd\n");
  91
  92         enter_realmode(0x00, 0x700, in, out);
  93
  94         return out->eflags&1;
  95 }