1 | /*-------------------------------------------------------------------------+ |
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2 | | start.s v1.1 - PC386 BSP - 1997/08/07 |
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3 | +--------------------------------------------------------------------------+ |
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4 | | This file contains the entry point for the application. |
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5 | | The name of this entry point is compiler dependent. |
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6 | | It jumps to the BSP which is responsible for performing all initialization. |
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7 | +--------------------------------------------------------------------------+ |
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8 | | (C) Copyright 1997 - |
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9 | | - NavIST Group - Real-Time Distributed Systems and Industrial Automation |
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10 | | |
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11 | | http://pandora.ist.utl.pt |
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12 | | |
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13 | | Instituto Superior Tecnico * Lisboa * PORTUGAL |
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14 | +--------------------------------------------------------------------------+ |
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15 | | Disclaimer: |
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16 | | |
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17 | | This file is provided "AS IS" without warranty of any kind, either |
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18 | | expressed or implied. |
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19 | +--------------------------------------------------------------------------+ |
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20 | | This code is based on an earlier generation RTEMS i386 start.s and the |
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21 | | following copyright applies: |
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22 | | |
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23 | | ************************************************************************** |
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24 | | * COPYRIGHT (c) 1989-1997. |
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25 | | * On-Line Applications Research Corporation (OAR). |
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26 | | * Copyright assigned to U.S. Government, 1994. |
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27 | | * |
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28 | | * The license and distribution terms for this file may be |
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29 | | * found in the file LICENSE in this distribution or at |
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30 | | * http://www.OARcorp.com/rtems/license.html. |
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31 | | ************************************************************************** |
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32 | | |
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33 | | Also based on (from the Linux source tree): |
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34 | | video.S - Copyright (C) 1995, 1996 Martin Mares <mj@k332.feld.cvut.cz> |
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35 | +--------------------------------------------------------------------------*/ |
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36 | |
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37 | |
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38 | #include "asm.h" |
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39 | |
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40 | /*----------------------------------------------------------------------------+ |
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41 | | Constants |
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42 | +----------------------------------------------------------------------------*/ |
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43 | |
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44 | #ifdef pc386 |
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45 | |
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46 | .set PROT_CODE_SEG, 0x08 # offset of code segment descriptor into GDT |
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47 | .set CR0_PE, 1 # protected mode flag on CR0 register |
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48 | |
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49 | #endif /* pc386 */ |
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50 | |
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51 | /*----------------------------------------------------------------------------+ |
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52 | | A Descriptor table register has the following format: |
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53 | +----------------------------------------------------------------------------*/ |
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54 | |
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55 | .set DTR_LIMIT, 0 # offset of two byte limit |
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56 | .set DTR_BASE, 2 # offset of four byte base address |
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57 | .set DTR_SIZE, 6 # size of DTR register |
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58 | |
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59 | /*----------------------------------------------------------------------------+ |
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60 | | CODE section |
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61 | +----------------------------------------------------------------------------*/ |
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62 | |
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63 | BEGIN_CODE |
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64 | |
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65 | PUBLIC (start) # GNU default entry point |
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66 | |
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67 | EXTERN (main) |
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68 | EXTERN (load_segments) |
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69 | EXTERN (exit) |
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70 | |
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71 | SYM (start): |
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72 | |
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73 | /*----------------------------------------------------------------------------+ |
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74 | | Switch VGA video to 80 lines x 50 columns mode. Has to be done before turning |
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75 | | protected mode on since it uses BIOS int 10h (video) services. |
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76 | +----------------------------------------------------------------------------*/ |
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77 | |
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78 | #if defined(pc386) && defined(RTEMS_VIDEO_80x50) |
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79 | |
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80 | .code16 |
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81 | |
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82 | movw $0x0003, ax # forced set |
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83 | int $0x10 |
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84 | movw $0x1112, ax # use 8x8 font |
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85 | xorb %bl, %bl |
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86 | int $0x10 |
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87 | movw $0x1201, ax # turn off cursor emulation |
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88 | movb $0x34, %bl |
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89 | int $0x10 |
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90 | movb $0x01, ah # define cursor (scan lines 0 to 7) |
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91 | movw $0x0007, cx |
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92 | int $0x10 |
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93 | |
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94 | .code32 |
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95 | |
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96 | #endif /* pc386 && RTEMS_VIDEO_80x50 */ |
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97 | |
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98 | nop |
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99 | cli # DISABLE INTERRUPTS!!! |
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100 | |
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101 | /*----------------------------------------------------------------------------+ |
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102 | | Bare PC machines boot in real mode! We have to turn protected mode on. |
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103 | +----------------------------------------------------------------------------*/ |
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104 | |
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105 | #ifdef pc386 |
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106 | |
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107 | data16 |
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108 | movl $ SYM(gdtptr), eax |
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109 | data16 |
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110 | andl $0x0000ffff, eax # get offset into segment |
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111 | addr16 |
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112 | lgdt cs:(eax) # load Global Descriptor Table |
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113 | data16 |
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114 | movl $ SYM(idtptr), eax |
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115 | data16 |
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116 | andl $0x0000ffff, eax # get offset into segment |
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117 | addr16 |
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118 | lidt cs:(eax) # load Interrupt Descriptor Table |
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119 | |
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120 | movl %cr0, eax |
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121 | data16 |
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122 | orl $CR0_PE, eax |
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123 | movl eax, %cr0 # turn on protected mode |
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124 | |
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125 | data16 |
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126 | ljmp $PROT_CODE_SEG, $ SYM(next) # flush prefetch queue |
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127 | |
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128 | SYM(next): |
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129 | |
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130 | #endif /* pc386 */ |
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131 | |
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132 | /*----------------------------------------------------------------------------+ |
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133 | | Load the segment registers (this is done by the board's BSP) and perform any |
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134 | | other board specific initialization procedures. |
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135 | | |
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136 | | NOTE: Upon return, gs will contain the segment descriptor for a segment which |
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137 | | maps directly to all of physical memory. |
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138 | +----------------------------------------------------------------------------*/ |
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139 | |
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140 | jmp SYM (_load_segments) # load board dependent segments |
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141 | |
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142 | /*----------------------------------------------------------------------------+ |
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143 | | Set up the stack |
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144 | +----------------------------------------------------------------------------*/ |
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145 | |
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146 | PUBLIC (_establish_stack) |
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147 | SYM (_establish_stack): |
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148 | |
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149 | movl $_end, eax # eax = end of bss/start of heap |
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150 | addl $heap_size, eax # eax = end of heap |
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151 | movl eax, stack_start # Save for brk() routine |
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152 | addl $stack_size, eax # make room for stack |
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153 | andl $0xffffffc0, eax # align it on 16 byte boundary |
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154 | movl eax, esp # set stack pointer |
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155 | movl eax, ebp # set base pointer |
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156 | |
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157 | /*----------------------------------------------------------------------------+ |
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158 | | Zero out the BSS segment |
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159 | +----------------------------------------------------------------------------*/ |
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160 | |
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161 | SYM (zero_bss): |
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162 | cld # make direction flag count up |
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163 | movl $ SYM (_end), ecx # find end of .bss |
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164 | movl $ SYM (_bss_start), edi # edi = beginning of .bss |
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165 | subl edi, ecx # ecx = size of .bss in bytes |
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166 | shll ecx # size of .bss in longs |
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167 | xorl eax, eax # value to clear out memory |
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168 | repne # while ecx != 0 |
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169 | stosl # clear a long in the bss |
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170 | |
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171 | /*---------------------------------------------------------------------+ |
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172 | | Copy the Global Descriptor Table to our space |
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173 | +---------------------------------------------------------------------*/ |
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174 | |
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175 | sgdt SYM (_Original_GDTR) # save original GDT |
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176 | movzwl SYM (_Original_GDTR)+DTR_LIMIT, ecx # size of GDT in bytes; |
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177 | # limit is 8192 entries * 8 bytes per |
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178 | |
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179 | /*---------------------------------------------------------------------+ |
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180 | | make ds:esi point to the original GDT |
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181 | +---------------------------------------------------------------------*/ |
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182 | |
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183 | movl SYM (_Original_GDTR)+DTR_BASE, esi |
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184 | push ds # save ds |
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185 | movw gs, ax |
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186 | movw ax, ds |
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187 | |
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188 | /*---------------------------------------------------------------------+ |
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189 | | make es:edi point to the new (our copy) GDT |
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190 | +---------------------------------------------------------------------*/ |
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191 | |
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192 | movl $ SYM (_Global_descriptor_table), edi |
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193 | |
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194 | rep |
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195 | movsb # copy the GDT (ds:esi -> es:edi) |
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196 | |
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197 | pop ds # restore ds |
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198 | |
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199 | /*---------------------------------------------------------------------+ |
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200 | | Build and load new contents of GDTR |
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201 | +---------------------------------------------------------------------*/ |
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202 | |
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203 | movw SYM (_Original_GDTR)+DTR_LIMIT, ecx # set new limit |
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204 | movw cx, SYM (_New_GDTR)+DTR_LIMIT |
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205 | |
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206 | push $ SYM (_Global_descriptor_table) |
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207 | push es |
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208 | call SYM (i386_Logical_to_physical) |
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209 | addl $6, esp |
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210 | movl eax, SYM (_New_GDTR)+DTR_BASE # set new base |
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211 | |
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212 | cmpb $0, SYM (_Do_Load_GDT) # Should the new GDT be loaded? |
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213 | je SYM (no_gdt_load) # NO, then branch |
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214 | lgdt SYM (_New_GDTR) # load the new GDT |
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215 | |
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216 | SYM (no_gdt_load): |
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217 | |
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218 | /*---------------------------------------------------------------------+ |
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219 | | Copy the Interrupt Descriptor Table to our space |
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220 | +---------------------------------------------------------------------*/ |
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221 | |
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222 | sidt SYM (_Original_IDTR) # save original IDT |
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223 | movzwl SYM (_Original_IDTR)+DTR_LIMIT, ecx # size of IDT in bytes; |
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224 | #limit is 256 entries * 8 bytes per |
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225 | |
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226 | /*---------------------------------------------------------------------+ |
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227 | | make ds:esi point to the original IDT |
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228 | +---------------------------------------------------------------------*/ |
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229 | |
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230 | movl SYM (_Original_IDTR)+DTR_BASE, esi |
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231 | |
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232 | push ds # save ds |
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233 | movw gs, ax |
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234 | movw ax, ds |
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235 | |
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236 | /*---------------------------------------------------------------------+ |
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237 | | make es:edi point to the new (our copy) IDT |
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238 | +---------------------------------------------------------------------*/ |
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239 | |
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240 | movl $ SYM (Interrupt_descriptor_table), edi |
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241 | |
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242 | rep |
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243 | movsb # copy the IDT (ds:esi -> es:edi) |
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244 | pop ds # restore ds |
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245 | |
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246 | /*---------------------------------------------------------------------+ |
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247 | | Build and load new contents of IDTR |
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248 | +---------------------------------------------------------------------*/ |
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249 | |
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250 | movw SYM (_Original_IDTR+DTR_LIMIT), ecx # set new limit |
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251 | movw cx, SYM (_New_IDTR)+DTR_LIMIT |
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252 | |
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253 | push $ SYM (Interrupt_descriptor_table) |
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254 | push es |
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255 | call SYM (i386_Logical_to_physical) |
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256 | addl $6, esp |
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257 | movl eax, SYM (_New_IDTR)+DTR_BASE # set new base |
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258 | |
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259 | cmpb $0, SYM (_Do_Load_IDT) # Should the new IDT be loaded? |
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260 | je SYM (no_idt_load) # NO, then branch |
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261 | lidt SYM (_New_IDTR) # load the new IDT |
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262 | SYM (no_idt_load): |
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263 | |
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264 | /*---------------------------------------------------------------------+ |
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265 | | Initialize the i387. |
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266 | | |
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267 | | Using the NO WAIT form of the instruction insures that if it is not |
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268 | | present the board will not lock up or get an exception. |
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269 | +---------------------------------------------------------------------*/ |
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270 | |
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271 | fninit # MUST USE NO-WAIT FORM |
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272 | |
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273 | /*---------------------------------------------------------------------+ |
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274 | | Transfer control to User's Board Support Package |
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275 | +---------------------------------------------------------------------*/ |
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276 | |
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277 | pushl $0 # environp |
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278 | pushl $0 # argv |
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279 | pushl $0 # argc |
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280 | call SYM (main) |
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281 | addl $12, esp |
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282 | |
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283 | /*---------------------------------------------------------------------+ |
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284 | | Clean up |
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285 | +---------------------------------------------------------------------*/ |
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286 | |
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287 | EXTERN (return_to_monitor) |
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288 | |
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289 | PUBLIC (Bsp_cleanup) |
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290 | |
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291 | SYM (Bsp_cleanup): |
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292 | |
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293 | cmpb $0, SYM (_Do_Load_IDT) # Was the new IDT loaded? |
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294 | je SYM (no_idt_restore) # NO, then branch |
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295 | lidt SYM (_Original_IDTR) # restore the new IDT |
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296 | |
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297 | SYM (no_idt_restore): |
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298 | |
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299 | cmpb $0, SYM (_Do_Load_GDT) # Was the new GDT loaded? |
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300 | je SYM (no_gdt_restore) # NO, then branch |
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301 | lgdt SYM (_Original_GDTR) # restore the new GDT |
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302 | |
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303 | SYM (no_gdt_restore): |
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304 | |
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305 | jmp SYM (_return_to_monitor) |
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306 | |
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307 | END_CODE |
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308 | |
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309 | /*----------------------------------------------------------------------------+ |
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310 | | DATA section |
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311 | +----------------------------------------------------------------------------*/ |
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312 | |
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313 | BEGIN_DATA |
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314 | |
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315 | #ifdef pc386 |
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316 | |
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317 | /************************** |
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318 | * GLOBAL DESCRIPTOR TABLE * |
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319 | **************************/ |
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320 | |
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321 | .align 4 |
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322 | SYM(gdtptr): |
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323 | /* we use the NULL descriptor to store the GDT pointer - a trick quite |
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324 | nifty due to: Robert Collins (rcollins@x86.org) */ |
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325 | .word gdtlen - 1 |
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326 | .long gdtptr |
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327 | .word 0x0000 |
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328 | |
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329 | /* code segment */ |
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330 | .word 0xffff, 0 |
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331 | .byte 0, 0x9f, 0xcf, 0 |
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332 | |
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333 | /* data segment */ |
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334 | .word 0xffff, 0 |
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335 | .byte 0, 0x93, 0xcf, 0 |
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336 | |
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337 | .set gdtlen, . - gdtptr # length of GDT |
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338 | |
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339 | /************************************* |
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340 | * INTERRUPT DESCRIPTOR TABLE POINTER * |
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341 | *************************************/ |
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342 | |
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343 | .align 4 |
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344 | SYM(idtptr): |
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345 | .word 0x07ff # limit at maximum (allows all 256 interrupts) |
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346 | .word 0, 0 # base at 0 |
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347 | |
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348 | #endif /* pc386 */ |
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349 | |
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350 | EXTERN (Do_Load_IDT) # defined in the BSP |
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351 | EXTERN (Do_Load_GDT) # defined in the BSP |
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352 | |
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353 | .align 2 |
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354 | PUBLIC (start_frame) |
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355 | SYM (start_frame): |
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356 | .long 0 |
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357 | |
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358 | PUBLIC (stack_start) |
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359 | SYM (stack_start): |
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360 | .long 0 |
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361 | |
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362 | END_DATA |
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363 | |
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364 | /*----------------------------------------------------------------------------+ |
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365 | | BSS section |
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366 | +----------------------------------------------------------------------------*/ |
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367 | |
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368 | BEGIN_BSS |
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369 | |
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370 | PUBLIC (heap_size) |
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371 | .set heap_size, 0x2000 |
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372 | |
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373 | PUBLIC (stack_size) |
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374 | .set stack_size, 0x1000 |
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375 | |
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376 | PUBLIC (Interrupt_descriptor_table) |
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377 | SYM (Interrupt_descriptor_table): |
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378 | .space (256 * 8) # reserve space for all 256 interrupts |
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379 | |
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380 | PUBLIC (_Original_IDTR) |
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381 | SYM (_Original_IDTR): |
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382 | .space DTR_SIZE |
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383 | |
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384 | PUBLIC (_New_IDTR) |
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385 | SYM (_New_IDTR): |
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386 | .space DTR_SIZE |
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387 | |
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388 | PUBLIC (_Global_descriptor_table) |
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389 | SYM (_Global_descriptor_table): |
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390 | #ifdef pc386 |
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391 | |
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392 | .space (3 * 8) # the PC386 bsp only needs 3 segment descriptors: |
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393 | #else # NULL, CODE and DATA |
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394 | .space (8192 * 8) |
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395 | |
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396 | #endif /* pc386 */ |
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397 | |
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398 | PUBLIC (_Original_GDTR) |
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399 | SYM (_Original_GDTR): |
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400 | .space DTR_SIZE |
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401 | |
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402 | PUBLIC (_New_GDTR) |
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403 | SYM (_New_GDTR): |
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404 | .space DTR_SIZE |
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405 | |
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406 | PUBLIC (_Physical_base_of_ds) |
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407 | SYM (_Physical_base_of_ds): |
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408 | .space 4 |
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409 | |
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410 | PUBLIC (_Physical_base_of_cs) |
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411 | SYM (_Physical_base_of_cs): |
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412 | .space 4 |
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413 | |
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414 | END_BSS |
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415 | |
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416 | END |
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