1 | ; $Id: bs3-mode-SwitchToPE16.asm 60686 2016-04-25 12:51:41Z vboxsync $
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2 | ;; @file
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3 | ; BS3Kit - Bs3SwitchToPE16
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4 | ;
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5 |
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6 | ;
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7 | ; Copyright (C) 2007-2015 Oracle Corporation
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8 | ;
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9 | ; This file is part of VirtualBox Open Source Edition (OSE), as
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10 | ; available from http://www.virtualbox.org. This file is free software;
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11 | ; you can redistribute it and/or modify it under the terms of the GNU
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12 | ; General Public License (GPL) as published by the Free Software
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13 | ; Foundation, in version 2 as it comes in the "COPYING" file of the
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14 | ; VirtualBox OSE distribution. VirtualBox OSE is distributed in the
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15 | ; hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
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16 | ;
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17 | ; The contents of this file may alternatively be used under the terms
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18 | ; of the Common Development and Distribution License Version 1.0
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19 | ; (CDDL) only, as it comes in the "COPYING.CDDL" file of the
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20 | ; VirtualBox OSE distribution, in which case the provisions of the
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21 | ; CDDL are applicable instead of those of the GPL.
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22 | ;
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23 | ; You may elect to license modified versions of this file under the
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24 | ; terms and conditions of either the GPL or the CDDL or both.
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25 | ;
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26 |
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27 | %include "bs3kit-template-header.mac"
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28 |
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29 |
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30 | ;;
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31 | ; Switch to 16-bit unpaged protected mode from any other mode.
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32 | ;
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33 | ; @cproto BS3_DECL(void) Bs3SwitchToPE16(void);
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34 | ;
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35 | ; @uses Nothing (except high 32-bit register parts).
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36 | ;
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37 | ; @remarks Obviously returns to 16-bit mode, even if the caller was
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38 | ; in 32-bit or 64-bit mode.
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39 | ;
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40 | ; @remarks Does not require 20h of parameter scratch space in 64-bit mode.
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41 | ;
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42 | %if TMPL_BITS == 16
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43 | BS3_GLOBAL_NAME_EX TMPL_NM(Bs3SwitchToPE16_Safe), function , 0
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44 | %endif
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45 | BS3_PROC_BEGIN_MODE Bs3SwitchToPE16, BS3_PBC_NEAR
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46 | %ifdef TMPL_PE16
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47 | extern BS3_CMN_NM(Bs3SwitchToRing0)
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48 | call BS3_CMN_NM(Bs3SwitchToRing0)
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49 | push ax
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50 | mov ax, BS3_SEL_R0_DS16
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51 | mov ds, ax
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52 | mov es, ax
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53 | pop ax
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54 | ret
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55 |
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56 | %elif BS3_MODE_IS_V86(TMPL_MODE)
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57 | ;
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58 | ; V8086 - Switch to 16-bit ring-0 and call worker for that mode.
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59 | ;
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60 | extern BS3_CMN_NM(Bs3SwitchToRing0)
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61 | call BS3_CMN_NM(Bs3SwitchToRing0)
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62 | extern %[BS3_MODE_R0_NM_ %+ TMPL_MODE](Bs3SwitchToPE16)
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63 | jmp %[BS3_MODE_R0_NM_ %+ TMPL_MODE](Bs3SwitchToPE16)
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64 |
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65 | %else
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66 | ;
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67 | ; Switch to 16-bit mode and prepare for returning in 16-bit mode.
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68 | ;
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69 | %if TMPL_BITS != 16
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70 | shl xPRE [xSP + xCB], TMPL_BITS - 16 ; Adjust the return address.
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71 | add xSP, xCB - 2
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72 |
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73 | ; Must be in 16-bit segment when calling Bs3SwitchTo16Bit.
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74 | jmp .sixteen_bit_segment
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75 | BS3_BEGIN_TEXT16
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76 | BS3_SET_BITS TMPL_BITS
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77 | .sixteen_bit_segment:
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78 | %endif
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79 |
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80 | ;
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81 | ; Switch to real mode.
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82 | ;
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83 | extern TMPL_NM(Bs3SwitchToRM)
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84 | call TMPL_NM(Bs3SwitchToRM)
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85 | BS3_SET_BITS 16
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86 |
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87 | push ax
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88 | push cx
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89 | pushf
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90 | cli
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91 |
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92 | ;
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93 | ; Load the GDT and enable PE16.
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94 | ;
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95 | BS3_EXTERN_SYSTEM16 Bs3Lgdt_Gdt
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96 | BS3_EXTERN_SYSTEM16 Bs3LgdtDef_Gdt
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97 | BS3_BEGIN_TEXT16
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98 | mov ax, BS3SYSTEM16
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99 | mov ds, ax
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100 | lgdt [Bs3LgdtDef_Gdt] ; Will only load 24-bit base!
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101 |
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102 | smsw ax
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103 | or ax, X86_CR0_PE
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104 | lmsw ax
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105 |
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106 | ;
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107 | ; Convert from real mode stack to protected mode stack.
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108 | ;
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109 | mov ax, .p16_stack
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110 | extern NAME(Bs3ConvertRMStackToP16UsingCxReturnToAx_c16)
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111 | jmp NAME(Bs3ConvertRMStackToP16UsingCxReturnToAx_c16)
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112 | .p16_stack:
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113 |
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114 | ;
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115 | ; Call routine for doing mode specific setups.
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116 | ;
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117 | extern NAME(Bs3EnteredMode_pe16)
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118 | call NAME(Bs3EnteredMode_pe16)
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119 |
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120 | ;
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121 | ; Load full 32-bit GDT base address from 32-bit segment, if 386+ CPU.
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122 | ;
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123 | BS3_EXTERN_DATA16 g_uBs3CpuDetected
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124 | BS3_BEGIN_TEXT16
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125 | cmp byte [g_uBs3CpuDetected], BS3CPU_80386
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126 | jb .old_cpu_skip_32bit_lgdt
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127 | push ds
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128 | mov ax, BS3_SEL_SYSTEM16
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129 | mov ds, ax
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130 | jmp dword BS3_SEL_R0_CS32:.load_full_gdt_base wrt FLAT
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131 | .load_full_gdt_base:
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132 | BS3_SET_BITS 32
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133 | lgdt [Bs3Lgdt_Gdt wrt BS3SYSTEM16]
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134 | jmp BS3_SEL_R0_CS16:.back_to_16bit
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135 | .back_to_16bit:
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136 | BS3_SET_BITS 16
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137 | pop ds
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138 | .old_cpu_skip_32bit_lgdt:
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139 |
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140 | popf
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141 | pop cx
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142 | pop ax
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143 | ret
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144 |
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145 | %if TMPL_BITS != 16
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146 | TMPL_BEGIN_TEXT
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147 | %endif
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148 | %endif
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149 | BS3_PROC_END_MODE Bs3SwitchToPE16
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150 |
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151 |
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152 | %if TMPL_BITS == 16
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153 | ;;
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154 | ; Custom far stub.
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155 | BS3_BEGIN_TEXT16_FARSTUBS
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156 | BS3_PROC_BEGIN_MODE Bs3SwitchToPE16, BS3_PBC_FAR
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157 | inc bp
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158 | push bp
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159 | mov bp, sp
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160 |
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161 | ; Call the real thing.
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162 | call TMPL_NM(Bs3SwitchToPE16)
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163 |
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164 | %if BS3_MODE_IS_RM_OR_V86(TMPL_MODE)
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165 | ; Jmp to common code for the tedious conversion.
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166 | BS3_EXTERN_CMN Bs3SwitchHlpConvRealModeRetfPopBpDecBpAndReturn
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167 | jmp Bs3SwitchHlpConvRealModeRetfPopBpDecBpAndReturn
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168 | %else
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169 | pop bp
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170 | dec bp
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171 | retf
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172 | %endif
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173 | BS3_PROC_END_MODE Bs3SwitchToPE16
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174 |
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175 | %else
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176 | ;;
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177 | ; Safe far return to non-BS3TEXT16 code.
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178 | BS3_EXTERN_CMN Bs3SwitchHlpConvFlatRetToRetfProtMode
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179 | BS3_BEGIN_TEXT16
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180 | BS3_SET_BITS TMPL_BITS
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181 | BS3_PROC_BEGIN_MODE Bs3SwitchToPE16_Safe, BS3_PBC_NEAR
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182 | call Bs3SwitchHlpConvFlatRetToRetfProtMode ; Special internal function. Uses nothing, but modifies the stack.
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183 | call TMPL_NM(Bs3SwitchToPE16)
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184 | BS3_SET_BITS 16
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185 | retf
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186 | BS3_PROC_END_MODE Bs3SwitchToPE16_Safe
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187 | %endif
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188 |
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