| 1 | ; $Id: bs3-cmn-SelProtModeCodeToRealMode.asm 106061 2024-09-16 14:03:52Z vboxsync $
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| 2 | ;; @file
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| 3 | ; BS3Kit - Bs3SelProtModeCodeToRealMode.
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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 | %include "bs3kit-template-header.mac"
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| 38 |
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| 39 | ;
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| 40 | ; Make sure we can get at all the segments.
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| 41 | ;
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| 42 | BS3_BEGIN_TEXT16
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| 43 | BS3_BEGIN_RMTEXT16
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| 44 | BS3_BEGIN_X0TEXT16
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| 45 | BS3_BEGIN_X1TEXT16
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| 46 | TMPL_BEGIN_TEXT
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| 47 |
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| 48 |
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| 49 | ;;
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| 50 | ; @cproto BS3_CMN_PROTO(uint16_t, Bs3SelProtModeCodeToRealMode,(uint16_t uRealSel), false);
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| 51 | ; @uses ax (return register)
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| 52 | ;
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| 53 | BS3_PROC_BEGIN_CMN Bs3SelProtModeCodeToRealMode, BS3_PBC_NEAR
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| 54 | BS3_CALL_CONV_PROLOG 1
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| 55 | push xBP
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| 56 | mov xBP, xSP
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| 57 |
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| 58 | ; Load it and mask off the RPL.
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| 59 | mov ax, [xBP + xCB + cbCurRetAddr]
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| 60 | and ax, X86_SEL_MASK_OFF_RPL
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| 61 |
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| 62 | ; We're allowed to use the real-mode segment value.
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| 63 | cmp ax, CGROUP16
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| 64 | je .bs3text16
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| 65 |
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| 66 | ; Check for typical code segments.
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| 67 | cmp ax, BS3_SEL_R0_CS16
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| 68 | je .bs3text16
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| 69 | cmp ax, BS3_SEL_RMTEXT16_CS
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| 70 | je .bs3rmtext16
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| 71 | cmp ax, BS3_SEL_X0TEXT16_CS
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| 72 | je .bs3x0text16
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| 73 | cmp ax, BS3_SEL_X1TEXT16_CS
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| 74 | je .bs3x1text16
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| 75 |
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| 76 | ; Check for less common BS3_SEL_R*_CS16_* values.
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| 77 | cmp ax, BS3_SEL_R0_FIRST
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| 78 | jb .panic
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| 79 | cmp ax, BS3_SEL_R3_FIRST + (1 << BS3_SEL_RING_SHIFT)
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| 80 | jae .panic
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| 81 |
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| 82 | ; Since the relevant bits now are the lower 8 ones, we skip the
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| 83 | ; AND AX, BS3_SEL_RING_SHIFT
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| 84 | ; ADD AX, BS3_SEL_R0_FIRST
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| 85 | ; bits and compare AL with lower 8-bit of the BS3_SEL_R0_CS16* values.
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| 86 | AssertCompile(BS3_SEL_RING_SHIFT == 8)
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| 87 | cmp al, BS3_SEL_R0_CS16 & 0xff
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| 88 | je .bs3text16
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| 89 | cmp al, BS3_SEL_R0_CS16_EO & 0xff
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| 90 | je .bs3text16
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| 91 | cmp ax, BS3_SEL_R0_CS16_CNF & 0xff
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| 92 | je .bs3text16
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| 93 | cmp ax, BS3_SEL_R0_CS16_CNF_EO & 0xff
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| 94 | je .bs3text16
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| 95 | .panic:
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| 96 | extern BS3_CMN_NM(Bs3Panic)
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| 97 | call BS3_CMN_NM(Bs3Panic)
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| 98 | jmp .return
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| 99 |
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| 100 | .bs3x1text16:
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| 101 | mov ax, BS3GROUPX1TEXT16
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| 102 | jmp .return
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| 103 | .bs3x0text16:
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| 104 | mov ax, BS3GROUPX0TEXT16
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| 105 | jmp .return
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| 106 | .bs3rmtext16:
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| 107 | mov ax, BS3GROUPRMTEXT16
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| 108 | jmp .return
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| 109 | .bs3text16:
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| 110 | mov ax, CGROUP16
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| 111 | .return:
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| 112 | pop xBP
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| 113 | BS3_CALL_CONV_EPILOG 1
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| 114 | BS3_HYBRID_RET
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| 115 | BS3_PROC_END_CMN Bs3SelProtModeCodeToRealMode
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| 116 |
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| 117 | ;
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| 118 | ; We may be using the near code in some critical code paths, so don't
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| 119 | ; penalize it.
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| 120 | ;
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| 121 | BS3_CMN_FAR_STUB Bs3SelProtModeCodeToRealMode, 2
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| 122 |
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