| 1 | ; $Id: bs3-mode-SwitchToLM16.asm 98103 2023-01-17 14:15:46Z vboxsync $
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| 2 | ;; @file
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| 3 | ; BS3Kit - Bs3SwitchToLM16
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| 4 | ;
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| 5 |
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| 6 | ;
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| 7 | ; Copyright (C) 2007-2023 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 | ; 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 | %include "bs3kit-template-header.mac"
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| 38 |
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| 39 |
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| 40 | ;;
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| 41 | ; Switch to 16-bit long mode from any other mode.
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| 42 | ;
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| 43 | ; @cproto BS3_DECL(void) Bs3SwitchToLM16(void);
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| 44 | ;
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| 45 | ; @uses Nothing (except possibly high 32-bit and/or upper 64-bit register parts).
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| 46 | ;
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| 47 | ; @remarks Obviously returns to 16-bit mode, even if the caller was in 32-bit
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| 48 | ; or 64-bit mode. It doesn't not preserve the callers ring, but
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| 49 | ; instead changes to ring-0.
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| 50 | ;
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| 51 | ; @remarks Does not require 20h of parameter scratch space in 64-bit mode.
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| 52 | ;
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| 53 | %if TMPL_BITS == 16
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| 54 | BS3_GLOBAL_NAME_EX TMPL_NM(Bs3SwitchToLM16_Safe), function , 0
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| 55 | %endif
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| 56 | BS3_PROC_BEGIN_MODE Bs3SwitchToLM16, BS3_PBC_NEAR
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| 57 | %ifdef TMPL_LM16
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| 58 | extern BS3_CMN_NM(Bs3SwitchToRing0)
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| 59 | call BS3_CMN_NM(Bs3SwitchToRing0)
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| 60 | push ax
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| 61 | mov ax, BS3_SEL_R0_DS16
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| 62 | mov ds, ax
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| 63 | mov es, ax
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| 64 | pop ax
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| 65 | ret
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| 66 |
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| 67 | %elifdef TMPL_CMN_LM
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| 68 | ;
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| 69 | ; Already in long mode, just switch to 16-bit.
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| 70 | ;
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| 71 | extern BS3_CMN_NM(Bs3SwitchTo16Bit)
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| 72 | jmp BS3_CMN_NM(Bs3SwitchTo16Bit)
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| 73 |
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| 74 | %else
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| 75 | ;
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| 76 | ; Switch to LM32 and then switch to 64-bits (IDT & TSS are the same for
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| 77 | ; LM16, LM32 and LM64, unlike the rest).
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| 78 | ;
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| 79 | ; (The long mode switching code is going via 32-bit protected mode, so
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| 80 | ; Bs3SwitchToLM32 contains the actual code for switching to avoid
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| 81 | ; unnecessary 32-bit -> 64-bit -> 32-bit trips.)
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| 82 | ;
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| 83 | extern TMPL_NM(Bs3SwitchToLM32)
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| 84 | call TMPL_NM(Bs3SwitchToLM32)
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| 85 | BS3_SET_BITS 32
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| 86 |
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| 87 | extern _Bs3SwitchTo16Bit_c32
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| 88 | %if TMPL_BITS == 16
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| 89 | sub esp, 2
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| 90 | shr dword [esp], 16
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| 91 | %elif TMPL_BITS == 64
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| 92 | pop dword [esp + 4]
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| 93 | %endif
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| 94 | jmp _Bs3SwitchTo16Bit_c32
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| 95 | %endif
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| 96 | BS3_PROC_END_MODE Bs3SwitchToLM16
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| 97 |
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| 98 |
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| 99 | %if TMPL_BITS == 16
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| 100 | ;;
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| 101 | ; Custom far stub.
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| 102 | BS3_BEGIN_TEXT16_FARSTUBS
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| 103 | BS3_PROC_BEGIN_MODE Bs3SwitchToLM16, BS3_PBC_FAR
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| 104 | inc bp
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| 105 | push bp
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| 106 | mov bp, sp
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| 107 |
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| 108 | ; Call the real thing.
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| 109 | call TMPL_NM(Bs3SwitchToLM16)
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| 110 |
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| 111 | %if BS3_MODE_IS_RM_OR_V86(TMPL_MODE)
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| 112 | ; Jmp to common code for the tedious conversion.
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| 113 | BS3_EXTERN_CMN Bs3SwitchHlpConvRealModeRetfPopBpDecBpAndReturn
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| 114 | jmp Bs3SwitchHlpConvRealModeRetfPopBpDecBpAndReturn
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| 115 | %else
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| 116 | pop bp
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| 117 | dec bp
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| 118 | retf
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| 119 | %endif
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| 120 | BS3_PROC_END_MODE Bs3SwitchToLM16
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| 121 |
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| 122 | %else
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| 123 | ;;
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| 124 | ; Safe far return to non-BS3TEXT16 code.
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| 125 | BS3_EXTERN_CMN Bs3SwitchHlpConvFlatRetToRetfProtMode
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| 126 | BS3_BEGIN_TEXT16
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| 127 | BS3_SET_BITS TMPL_BITS
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| 128 | BS3_PROC_BEGIN_MODE Bs3SwitchToLM16_Safe, BS3_PBC_NEAR
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| 129 | call Bs3SwitchHlpConvFlatRetToRetfProtMode ; Special internal function. Uses nothing, but modifies the stack.
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| 130 | call TMPL_NM(Bs3SwitchToLM16)
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| 131 | BS3_SET_BITS 16
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| 132 | retf
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| 133 | BS3_PROC_END_MODE Bs3SwitchToLM16_Safe
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| 134 |
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| 135 | %endif
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| 136 |
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