| 1 | ; $Id: bs3-mode-SwitchToPP16.asm 106061 2024-09-16 14:03:52Z vboxsync $
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| 2 | ;; @file
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| 3 | ; BS3Kit - Bs3SwitchToPP16
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| 4 | ;
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| 5 |
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| 6 | ;
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| 7 | ; Copyright (C) 2007-2024 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 | ; The contents of this file may alternatively be used under the terms
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| 26 | ; of the Common Development and Distribution License Version 1.0
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| 27 | ; (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
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| 28 | ; in the VirtualBox distribution, in which case the provisions of the
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| 29 | ; CDDL are applicable instead of those of the GPL.
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| 30 | ;
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| 31 | ; You may elect to license modified versions of this file under the
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| 32 | ; terms and conditions of either the GPL or the CDDL or both.
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| 33 | ;
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| 34 | ; SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
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| 35 | ;
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| 36 |
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| 37 | ;*********************************************************************************************************************************
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| 38 | ;* Header Files *
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| 39 | ;*********************************************************************************************************************************
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| 40 | %include "bs3kit-template-header.mac"
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| 41 |
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| 42 | ;*********************************************************************************************************************************
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| 43 | ;* External Symbols *
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| 44 | ;*********************************************************************************************************************************
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| 45 | %ifndef TMPL_PP16
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| 46 | BS3_BEGIN_TEXT16
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| 47 | extern NAME(Bs3EnteredMode_pp16)
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| 48 | %ifdef TMPL_PP32
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| 49 | BS3_EXTERN_CMN Bs3SwitchTo16Bit
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| 50 | %endif
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| 51 | TMPL_BEGIN_TEXT
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| 52 | %endif
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| 53 |
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| 54 |
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| 55 | ;;
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| 56 | ; Switch to 16-bit paged protected mode from any other mode.
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| 57 | ;
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| 58 | ; @cproto BS3_DECL(void) Bs3SwitchToPP16(void);
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| 59 | ;
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| 60 | ; @uses Nothing (except high 32-bit register parts).
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| 61 | ;
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| 62 | ; @remarks Obviously returns to 16-bit mode, even if the caller was
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| 63 | ; in 32-bit or 64-bit mode.
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| 64 | ;
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| 65 | ; @remarks Does not require 20h of parameter scratch space in 64-bit mode.
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| 66 | ;
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| 67 | %if TMPL_BITS == 16
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| 68 | BS3_GLOBAL_NAME_EX TMPL_NM(Bs3SwitchToPP16_Safe), function , 0
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| 69 | %endif
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| 70 | BS3_PROC_BEGIN_MODE Bs3SwitchToPP16, BS3_PBC_NEAR
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| 71 | %ifdef TMPL_PP16
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| 72 | extern BS3_CMN_NM(Bs3SwitchToRing0)
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| 73 | call BS3_CMN_NM(Bs3SwitchToRing0)
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| 74 | push ax
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| 75 | mov ax, BS3_SEL_R0_DS16
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| 76 | mov ds, ax
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| 77 | mov es, ax
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| 78 | pop ax
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| 79 | ret
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| 80 |
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| 81 | %elif BS3_MODE_IS_V86(TMPL_MODE)
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| 82 | ;
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| 83 | ; V8086 - Switch to 16-bit ring-0 and call worker for that mode.
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| 84 | ;
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| 85 | extern BS3_CMN_NM(Bs3SwitchToRing0)
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| 86 | call BS3_CMN_NM(Bs3SwitchToRing0)
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| 87 | extern %[BS3_MODE_R0_NM_ %+ TMPL_MODE](Bs3SwitchToPP16)
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| 88 | jmp %[BS3_MODE_R0_NM_ %+ TMPL_MODE](Bs3SwitchToPP16)
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| 89 |
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| 90 | %else
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| 91 |
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| 92 | ;
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| 93 | ; Switch to 16-bit text segment and prepare for returning in 16-bit mode.
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| 94 | ;
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| 95 | %if TMPL_BITS != 16
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| 96 | shl xPRE [xSP], TMPL_BITS - 16 ; Adjust the return address.
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| 97 | add xSP, xCB - 2
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| 98 |
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| 99 | ; Must be in 16-bit segment when calling Bs3SwitchToRM and Bs3SwitchTo16Bit.
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| 100 | jmp .sixteen_bit_segment
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| 101 | BS3_BEGIN_TEXT16
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| 102 | BS3_SET_BITS TMPL_BITS
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| 103 | BS3_GLOBAL_LOCAL_LABEL .sixteen_bit_segment
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| 104 | %endif
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| 105 |
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| 106 | %ifdef TMPL_PP32
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| 107 | ;
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| 108 | ; No need to go to real-mode here, we use the same CR3 and stuff.
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| 109 | ; Just switch to 32-bit mode and call the Bs3EnteredMode routine to
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| 110 | ; load the right descriptor tables.
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| 111 | ;
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| 112 | call Bs3SwitchTo16Bit
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| 113 | BS3_SET_BITS 16
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| 114 | call NAME(Bs3EnteredMode_pp16)
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| 115 | ret
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| 116 | %else
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| 117 |
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| 118 | ;
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| 119 | ; Switch to real mode.
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| 120 | ;
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| 121 | extern TMPL_NM(Bs3SwitchToRM)
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| 122 | call TMPL_NM(Bs3SwitchToRM)
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| 123 | BS3_SET_BITS 16
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| 124 |
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| 125 | push eax
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| 126 | push ecx
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| 127 | pushfd
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| 128 | %ifdef BS3_STRICT
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| 129 | mov ax, ds
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| 130 | cmp ax, BS3_ADDR_BS3DATA16 >> 4
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| 131 | je .real_mode_ds_ok
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| 132 | hlt
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| 133 | .real_mode_ds_ok:
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| 134 | %endif
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| 135 |
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| 136 | ;
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| 137 | ; Get the page directory (returned in eax).
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| 138 | ; Will lazy init page tables (in 16-bit prot mode).
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| 139 | ;
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| 140 | extern NAME(Bs3PagingGetRootForPP16_rm)
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| 141 | call NAME(Bs3PagingGetRootForPP16_rm)
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| 142 |
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| 143 | cli
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| 144 | mov cr3, eax
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| 145 |
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| 146 | ;
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| 147 | ; Make sure PAE is really off and that PSE is enabled when supported.
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| 148 | ;
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| 149 | BS3_EXTERN_DATA16 g_uBs3CpuDetected
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| 150 | BS3_BEGIN_TEXT16
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| 151 | test byte [1 + BS3_DATA16_WRT(g_uBs3CpuDetected)], (BS3CPU_F_CPUID >> 8)
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| 152 | jz .cr4_is_fine
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| 153 | mov eax, cr4
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| 154 | mov ecx, eax
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| 155 | and eax, ~(X86_CR4_PAE | X86_CR4_PSE)
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| 156 | test byte [1 + BS3_DATA16_WRT(g_uBs3CpuDetected)], (BS3CPU_F_PSE >> 8)
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| 157 | jz .no_pse
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| 158 | or eax, X86_CR4_PSE
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| 159 | .no_pse:
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| 160 | cmp eax, ecx
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| 161 | je .cr4_is_fine
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| 162 | mov cr4, eax
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| 163 | .cr4_is_fine:
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| 164 |
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| 165 | ;
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| 166 | ; Load the GDT and enable PP16.
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| 167 | ;
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| 168 | BS3_EXTERN_SYSTEM16 Bs3LgdtDef_Gdt
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| 169 | BS3_EXTERN_SYSTEM16 Bs3Lgdt_Gdt
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| 170 | BS3_BEGIN_TEXT16
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| 171 | mov ax, BS3SYSTEM16
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| 172 | mov ds, ax
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| 173 | lgdt [Bs3LgdtDef_Gdt] ; Will only load 24-bit base!
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| 174 |
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| 175 | mov eax, cr0
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| 176 | or eax, X86_CR0_PE | X86_CR0_PG
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| 177 | mov cr0, eax
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| 178 | jmp BS3_SEL_R0_CS16:.reload_cs_and_stuff
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| 179 | .reload_cs_and_stuff:
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| 180 |
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| 181 | ;
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| 182 | ; Convert the (now) real mode stack to 16-bit.
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| 183 | ;
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| 184 | mov ax, .stack_fix_return
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| 185 | extern NAME(Bs3ConvertRMStackToP16UsingCxReturnToAx_c16)
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| 186 | jmp NAME(Bs3ConvertRMStackToP16UsingCxReturnToAx_c16)
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| 187 | .stack_fix_return:
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| 188 |
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| 189 | ;
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| 190 | ; Call rountine for doing mode specific setups.
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| 191 | ;
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| 192 | call NAME(Bs3EnteredMode_pp16)
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| 193 |
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| 194 | ;
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| 195 | ; Load full 32-bit GDT base address from 32-bit segment.
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| 196 | ;
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| 197 | push ds
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| 198 | mov ax, BS3_SEL_SYSTEM16
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| 199 | mov ds, ax
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| 200 | jmp dword BS3_SEL_R0_CS32:.load_full_gdt_base wrt FLAT
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| 201 | .load_full_gdt_base:
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| 202 | BS3_SET_BITS 32
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| 203 | lgdt [Bs3Lgdt_Gdt wrt BS3SYSTEM16]
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| 204 | jmp BS3_SEL_R0_CS16:.back_to_16bit
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| 205 | .back_to_16bit:
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| 206 | BS3_SET_BITS 16
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| 207 | pop ds
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| 208 |
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| 209 | popfd
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| 210 | pop ecx
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| 211 | pop eax
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| 212 | ret
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| 213 |
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| 214 | %endif ; !TMPL_PP32
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| 215 | %if TMPL_BITS != 16
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| 216 | TMPL_BEGIN_TEXT
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| 217 | %endif
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| 218 | %endif
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| 219 | BS3_PROC_END_MODE Bs3SwitchToPP16
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| 220 |
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| 221 |
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| 222 | %if TMPL_BITS == 16
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| 223 | ;;
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| 224 | ; Custom far stub.
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| 225 | BS3_BEGIN_TEXT16_FARSTUBS
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| 226 | BS3_PROC_BEGIN_MODE Bs3SwitchToPP16, BS3_PBC_FAR
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| 227 | inc bp
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| 228 | push bp
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| 229 | mov bp, sp
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| 230 |
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| 231 | ; Call the real thing.
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| 232 | call TMPL_NM(Bs3SwitchToPP16)
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| 233 |
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| 234 | %if BS3_MODE_IS_RM_OR_V86(TMPL_MODE)
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| 235 | ; Jmp to common code for the tedious conversion.
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| 236 | BS3_EXTERN_CMN Bs3SwitchHlpConvRealModeRetfPopBpDecBpAndReturn
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| 237 | jmp Bs3SwitchHlpConvRealModeRetfPopBpDecBpAndReturn
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| 238 | %else
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| 239 | pop bp
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| 240 | dec bp
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| 241 | retf
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| 242 | %endif
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| 243 | BS3_PROC_END_MODE Bs3SwitchToPP16
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| 244 |
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| 245 | %else
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| 246 | ;;
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| 247 | ; Safe far return to non-BS3TEXT16 code.
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| 248 | BS3_EXTERN_CMN Bs3SwitchHlpConvFlatRetToRetfProtMode
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| 249 | BS3_BEGIN_TEXT16
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| 250 | BS3_SET_BITS TMPL_BITS
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| 251 | BS3_PROC_BEGIN_MODE Bs3SwitchToPP16_Safe, BS3_PBC_NEAR
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| 252 | call Bs3SwitchHlpConvFlatRetToRetfProtMode ; Special internal function. Uses nothing, but modifies the stack.
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| 253 | call TMPL_NM(Bs3SwitchToPP16)
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| 254 | BS3_SET_BITS 16
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| 255 | retf
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| 256 | BS3_PROC_END_MODE Bs3SwitchToPP16_Safe
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| 257 | %endif
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| 258 |
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