boot/freeldr/freeldr/arch/i386/drvmap.S

   1 /*
   2  *  FreeLoader
   3  *  Copyright (C) 1998-2002  Brian Palmer  <brianp@sginet.com>
   4  *
   5  *  This program is free software; you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation; either version 2 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  This program is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License along
  16  *  with this program; if not, write to the Free Software Foundation, Inc.,
  17  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18  */
  19
  20 #include <asm.inc>
  21 #include <arch/pc/x86common.h>
  22
  23 .code16
  24
  25 PUBLIC _DriveMapInt13HandlerStart
  26 _DriveMapInt13HandlerStart:
  27
  28 Int13Handler:
  29     push bp
  30     mov bp, sp
  31     push ax
  32     push cx
  33     push si
  34
  35     cld
  36
  37     /* Get callers flags from stack */
  38     mov ax, [bp + 6]
  39     mov word ptr cs:[CallersFlags - Int13Handler], ax
  40
  41     /* Save the drive number they passed in */
  42     mov byte ptr cs:[PassedInDriveNumber - Int13Handler], dl
  43
  44     /* Now we need to perform the mapping */
  45     xor cx, cx
  46     mov si, offset Int13HandlerMapCount - Int13Handler
  47
  48     /* Get the count of drives in the map list */
  49     mov cl, byte ptr cs:[si]
  50     inc si
  51
  52     /* If the map list is empty then just call the old int 13h handler */
  53     cmp cl, 0
  54     jz CallOldInt13Handler
  55
  56 GetMappedDriveNumberLoop:
  57
  58     /* Get the next drive number in the list (store it in AX) */
  59     lods word ptr cs:[si]
  60
  61     /* Check to see if it's the one they are calling int 13h for */
  62     cmp dl, al
  63
  64     /* If not get the next one */
  65     jne GetMappedDriveNumberLoopNext
  66
  67     /* If we get here then we have found a mapped drive */
  68     /* Send new drive number on to the old int 13h handler */
  69     mov dl, ah
  70
  71     /* Call BIOS Int 13 Handler */
  72     jmp CallOldInt13Handler
  73
  74 GetMappedDriveNumberLoopNext:
  75     loop GetMappedDriveNumberLoop
  76
  77 CallOldInt13Handler:
  78     /* Restore the registers we changed off the stack */
  79     pop si
  80     pop cx
  81     pop ax
  82
  83     /* Put flags onto stack */
  84     push word ptr cs:[CallersFlags - Int13Handler]
  85
  86     /* Call old int 13h handler with new drive number */
  87     .byte HEX(9a) /* lcall */
  88 PUBLIC _DriveMapOldInt13HandlerAddress
  89 _DriveMapOldInt13HandlerAddress:
  90     .word   0
  91     .word   0
  92
  93     /* Update the callers flags with the values the BIOS returned */
  94     push ax
  95     pushf
  96     pop ax
  97     mov [bp + 6], ax
  98     pop ax
  99
 100     /* Restore the callers drive number */
 101     mov dl, byte ptr cs:[PassedInDriveNumber - Int13Handler]
 102
 103     pop bp
 104
 105     iret
 106
 107 CallersFlags:
 108     .word   0
 109
 110 PassedInDriveNumber:
 111     .byte   0
 112
 113 /* See the DRIVE_MAP_LIST structure in include/arch/i386/drivemap.h */
 114 PUBLIC _DriveMapInt13HandlerMapList
 115 _DriveMapInt13HandlerMapList:
 116 Int13HandlerMapCount:
 117     .byte   0
 118
 119 Int13HandlerDrive1:
 120     .byte   0
 121 Int13HandlerDriveNew1:
 122     .byte   0
 123
 124 Int13HandlerDrive2:
 125     .byte   0
 126 Int13HandlerDriveNew2:
 127     .byte   0
 128
 129 Int13HandlerDrive3:
 130     .byte   0
 131 Int13HandlerDriveNew3:
 132     .byte   0
 133
 134 Int13HandlerDrive4:
 135     .byte   0
 136 Int13HandlerDriveNew4:
 137     .byte   0
 138
 139 PUBLIC _DriveMapInt13HandlerEnd
 140 _DriveMapInt13HandlerEnd:
 141
 142 .endcode16
 143
 144 END