| wdenk | 591dda5 | 2002-11-18 00:14:45 +0000 | [diff] [blame] | 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 | |
| 25 | /* 32bit -> 16bit -> 32bit mode switch code */ |
| 26 | |
| 27 | /* |
| 28 | * Stack frame at 0xe00 |
| 29 | * e00 ebx; |
| 30 | * e04 ecx; |
| 31 | * e08 edx; |
| 32 | * e0c esi; |
| 33 | * e10 edi; |
| 34 | * e14 ebp; |
| 35 | * e18 eax; |
| 36 | * e1c ds; |
| 37 | * e20 es; |
| 38 | * e24 fs; |
| 39 | * e28 gs; |
| 40 | * e2c orig_eax; |
| 41 | * e30 eip; |
| 42 | * e34 cs; |
| 43 | * e38 eflags; |
| 44 | * e3c esp; |
| 45 | * e40 ss; |
| 46 | */ |
| 47 | |
| 48 | #define a32 .byte 0x67; /* address size prefix 32 */ |
| 49 | #define o32 .byte 0x66; /* operand size prefix 32 */ |
| 50 | |
| 51 | .section .realmode, "ax" |
| 52 | .code16 |
| 53 | |
| 54 | /* 16bit protected mode code here */ |
| 55 | .globl realmode_enter |
| 56 | realmode_enter: |
| 57 | o32 pusha |
| 58 | o32 pushf |
| 59 | cli |
| 60 | sidt saved_idt |
| 61 | sgdt saved_gdt |
| 62 | movl %esp, %eax |
| 63 | movl %eax, saved_protected_mode_esp |
| 64 | |
| 65 | movl $0x10, %eax |
| 66 | movl %eax, %esp |
| 67 | movw $0x28, %ax |
| 68 | movw %ax, %ds |
| 69 | movw %ax, %es |
| 70 | movw %ax, %fs |
| 71 | movw %ax, %gs |
| 72 | |
| 73 | lidt realmode_idt_ptr |
| 74 | movl %cr0, %eax /* Go back into real mode by */ |
| 75 | andl $0x7ffffffe, %eax /* clearing PE to 0 */ |
| 76 | movl %eax, %cr0 |
| 77 | ljmp $0x0,$do_realmode /* switch to real mode */ |
| 78 | |
| 79 | do_realmode: /* realmode code from here */ |
| 80 | movw %cs,%ax |
| 81 | movw %ax,%ds |
| 82 | movw %ax,%es |
| 83 | movw %ax,%fs |
| 84 | movw %ax,%gs |
| 85 | |
| 86 | /* create a temporary stack */ |
| 87 | |
| 88 | movw $0xc0, %ax |
| 89 | movw %ax, %ss |
| 90 | movw $0x200, %ax |
| 91 | movw %ax, %sp |
| 92 | |
| 93 | popl %ebx |
| 94 | popl %ecx |
| 95 | popl %edx |
| 96 | popl %esi |
| 97 | popl %edi |
| 98 | popl %ebp |
| 99 | popl %eax |
| 100 | movl %eax, temp_eax |
| 101 | popl %eax |
| 102 | movw %ax, %ds |
| 103 | popl %eax |
| 104 | movw %ax, %es |
| 105 | popl %eax |
| 106 | movw %ax, %fs |
| 107 | popl %eax |
| 108 | movw %ax, %gs |
| 109 | popl %eax /* orig_eax */ |
| 110 | popl %eax |
| 111 | cs movw %ax, temp_ip |
| 112 | popl %eax |
| 113 | cs movw %ax, temp_cs |
| 114 | o32 popf |
| 115 | popl %eax |
| 116 | popw %ss |
| 117 | movl %eax, %esp |
| 118 | cs movl temp_eax, %eax |
| 119 | wbinvd /* self-modifying code, |
| 120 | * better flush the cache */ |
| 121 | |
| 122 | .byte 0x9a /* lcall */ |
| 123 | temp_ip: |
| 124 | .word 0 /* new ip */ |
| 125 | temp_cs: |
| 126 | .word 0 /* new cs */ |
| 127 | realmode_ret: |
| 128 | /* save eax, esp and ss */ |
| 129 | cs movl %eax, saved_eax |
| 130 | movl %esp, %eax |
| 131 | cs movl %eax, saved_esp |
| 132 | movw %ss, %ax |
| 133 | cs movw %ax, saved_ss |
| 134 | |
| 135 | /* restore the stack, note that we set sp to 0x244; |
| 136 | * pt_regs is 0x44 bytes long and we push the structure |
| 137 | * backwards on to the stack, bottom first */ |
| 138 | |
| 139 | movw $0xc0, %ax |
| 140 | movw %ax, %ss |
| 141 | movw $0x244, %ax |
| 142 | movw %ax, %sp |
| 143 | |
| 144 | xorl %eax,%eax |
| 145 | cs movw saved_ss, %ax |
| 146 | pushl %eax |
| 147 | cs movl saved_esp, %eax |
| 148 | pushl %eax |
| 149 | o32 pushf |
| 150 | xorl %eax,%eax |
| 151 | cs movw temp_cs, %ax |
| 152 | pushl %eax |
| 153 | cs movw temp_ip, %ax |
| 154 | pushl %eax |
| 155 | pushl $0 |
| 156 | movw %gs, %ax |
| 157 | pushl %eax |
| 158 | movw %fs, %ax |
| 159 | pushl %eax |
| 160 | movw %es, %ax |
| 161 | pushl %eax |
| 162 | movw %ds, %ax |
| 163 | pushl %eax |
| 164 | movl saved_eax, %eax |
| 165 | pushl %eax |
| 166 | pushl %ebp |
| 167 | pushl %edi |
| 168 | pushl %esi |
| 169 | pushl %edx |
| 170 | pushl %ecx |
| 171 | pushl %ebx |
| 172 | |
| 173 | o32 cs lidt saved_idt |
| 174 | o32 cs lgdt saved_gdt /* Set GDTR */ |
| 175 | |
| 176 | movl %cr0, %eax /* Go back into protected mode */ |
| 177 | orl $1,%eax /* reset PE to 1 */ |
| 178 | movl %eax, %cr0 |
| 179 | jmp next_line /* flush prefetch queue */ |
| 180 | next_line: |
| 181 | movw $return_ptr, %ax |
| 182 | movw %ax,%bp |
| 183 | o32 cs ljmp *(%bp) |
| 184 | |
| 185 | .code32 |
| 186 | protected_mode: |
| 187 | movl $0x18,%eax /* reload GDT[3] */ |
| 188 | movw %ax,%fs /* reset FS */ |
| 189 | movw %ax,%ds /* reset DS */ |
| 190 | movw %ax,%gs /* reset GS */ |
| 191 | movw %ax,%es /* reset ES */ |
| 192 | movw %ax,%ss /* reset SS */ |
| 193 | movl saved_protected_mode_esp, %eax |
| 194 | movl %eax, %esp |
| 195 | popf |
| 196 | popa |
| 197 | ret |
| 198 | |
| 199 | temp_eax: |
| 200 | .long 0 |
| 201 | |
| 202 | saved_ss: |
| 203 | .word 0 |
| 204 | saved_esp: |
| 205 | .long 0 |
| 206 | saved_eax: |
| 207 | .long 0 |
| 208 | |
| 209 | realmode_idt_ptr: |
| 210 | .word 0x400 |
| 211 | .word 0x0, 0x0 |
| 212 | |
| 213 | saved_gdt: |
| 214 | .word 0, 0, 0, 0 |
| 215 | saved_idt: |
| 216 | .word 0, 0, 0, 0 |
| 217 | |
| 218 | saved_protected_mode_esp: |
| 219 | .long 0 |
| 220 | |
| 221 | return_ptr: |
| 222 | .long protected_mode |
| 223 | .word 0x10 |