| 1 | ; $Id: pmode.inc 98103 2023-01-17 14:15:46Z vboxsync $
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| 2 | ;; @file
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| 3 | ; Enter and exit a minimal protected-mode environment.
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| 4 | ;
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| 5 |
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| 6 | ;
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| 7 | ; Copyright (C) 2004-2023 Oracle and/or its affiliates.
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| 8 | ;
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| 9 | ; This file is part of VirtualBox base platform packages, as
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| 10 | ; available from https://www.virtualbox.org.
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| 11 | ;
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| 12 | ; This program is free software; you can redistribute it and/or
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| 13 | ; modify it under the terms of the GNU General Public License
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| 14 | ; as published by the Free Software Foundation, in version 3 of the
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| 15 | ; License.
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| 16 | ;
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| 17 | ; This program is distributed in the hope that it will be useful, but
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| 18 | ; WITHOUT ANY WARRANTY; without even the implied warranty of
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| 19 | ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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| 20 | ; General Public License for more details.
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| 21 | ;
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| 22 | ; You should have received a copy of the GNU General Public License
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| 23 | ; along with this program; if not, see <https://www.gnu.org/licenses>.
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| 24 | ;
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| 25 | ; SPDX-License-Identifier: GPL-3.0-only
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| 26 | ;
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| 27 |
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| 28 | ;; Caveats: May only be called from the F000 segment (16-bit). Does not
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| 29 | ;; switch stacks. Must be run with disabled interrupts(!), any exceptions
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| 30 | ;; will cause a crash. On return from pmode_enter, DS contains a selector
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| 31 | ;; which can address the entire 4GB address space.
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| 32 |
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| 33 | public pmode_enter
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| 34 | public pmode_exit
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| 35 | public pmbios_gdt_desc
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| 36 | public pmbios_gdt
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| 37 |
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| 38 | pmode_enter proc near
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| 39 |
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| 40 | push cs
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| 41 | pop ds
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| 42 | .386p
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| 43 | lgdt fword ptr [pmbios_gdt_desc]
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| 44 | mov eax, cr0
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| 45 | or al, 1
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| 46 | mov cr0, eax
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| 47 | ; jmp far ptr 20h:really_enter_pm
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| 48 | db 0EAh
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| 49 | dw really_enter_pm
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| 50 | dw 20h
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| 51 | really_enter_pm:
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| 52 | mov ax, 18h
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| 53 | mov ds, ax
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| 54 | ret
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| 55 |
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| 56 | pmode_enter endp
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| 57 |
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| 58 |
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| 59 | pmode_exit proc near
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| 60 |
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| 61 | mov ax, 40h ; Ensure RM limit/attributes
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| 62 | mov ds, ax ; (where base = selector << 4)
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| 63 |
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| 64 | mov eax, cr0
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| 65 | and al, 0FEh
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| 66 | mov cr0, eax
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| 67 | SET_DEFAULT_CPU_286
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| 68 | jmp far ptr really_exit_pm
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| 69 | really_exit_pm:
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| 70 | ret
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| 71 |
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| 72 | pmode_exit endp
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| 73 |
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| 74 |
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| 75 |
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| 76 | pmbios_gdt_desc:
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| 77 | dw 40h + 7 ; last selector plus 8 - 1
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| 78 | dw pmbios_gdt
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| 79 | dw 000Fh
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| 80 |
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| 81 | pmbios_gdt:
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| 82 | dw 0, 0, 0, 0
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| 83 | dw 0, 0, 0, 0
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| 84 | dw 0ffffh, 0, 9b00h, 00cfh ; 32-bit code (0x10)
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| 85 | dw 0ffffh, 0, 9300h, 00cfh ; 32-bit data (0x18)
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| 86 | dw 0ffffh, 0, 9b0fh, 0000h ; 16-bit code, base=0xf0000
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| 87 | dw 0ffffh, 0, 9300h, 0000h ; 16-bit data, base=0x0
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| 88 | dw 0, 0, 0, 0
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| 89 | dw 0, 0, 0, 0
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| 90 | dw 0ffffh, 400h, 9300h, 0000h ; 16-bit data, base=0x40
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| 91 |
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