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9
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1 ;#!/usr/bin/nasm
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2
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3 ;
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4 ; See http://wiki.osdev.org/User:Stephanvanschaik/Setting_Up_Long_Mode
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5 ; Loader assembly to load the 64 bits kernel just after this file.
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6
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7 ; Assume that we are loaded at 1M (0x100000)
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8 ;org 0x100000 ; this only works with flat bin output, not with elf64 output.
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9
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10 bits 32 ; Start in 32 bits mode.
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11 ; Multiboot header:
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12 ; Settings for multiboot header
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13 PAGE_ALIGN equ 1 << 0
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14 MEM_INFO equ 1 << 1
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15 KLUDGE equ 1 << 16
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16 MAGIC equ 0x1BADB002
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17 FLAGS equ PAGE_ALIGN | MEM_INFO | KLUDGE ; align and provide memory map
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18 CHECKSUM equ -(MAGIC+FLAGS)
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19
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20 ; actual multiboot header:
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21 align 4
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22 MultiBootHeader:
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23 dd MAGIC
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24 dd FLAGS
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25 dd CHECKSUM
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26 ; item below are present if bit 16 is set in flags
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27 dd MultiBootHeader ; physical address in file of header (will be 0x100000 if put at start)
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28 dd 0x100000 ; load_addr: load address, the address to start loading
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29 dd 0x0 ; load_end_addr: zero indicates to load whole file
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30 dd 0x0 ; bss_end_addr: zero indicates no bss segment present
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31 dd loader ; entry_addr: jump to here
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32
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33 ; GDT, three entries: one for code, one for data
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34 GDT64:
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35 .Null: equ $ - GDT64
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36 dw 0
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37 dw 0
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38 db 0
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39 db 0
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40 db 0
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41 db 0
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42 .Code: equ $ - GDT64
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43 dw 0
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44 dw 0
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45 db 0
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46 db 10011000b ; access
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47 db 00100000b ; granularity
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48 db 0
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49 .Data: equ $ - GDT64
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50 dw 0
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51 dw 0
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52 db 0
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53 db 10010000b ; access
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54 db 00000000b ; granularity
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55 db 0
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56 .Pointer: ; GDT pointer
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57 dw $ - GDT64 - 1 ; Limit
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58 dq GDT64 ; Base
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59
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60 ; Start of loader code:
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61 global loader
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62 loader:
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63
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64 ; Prepare paging:
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65 ; PML4T - 0x1000
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66 ; PDPT - 0x2000
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67 ; PDT - 0x3000
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68 ; PT - 0x4000
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69
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70 ; Clear the tables:
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71 mov edi, 0x1000
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72 mov cr3, edi ; CR3 is the page table address!
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73 xor eax, eax
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74 mov ecx, 4096
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75 rep stosd
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76 mov edi, cr3 ; restore edi
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77
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78 mov DWORD [edi], 0x2003 ; present and readwrite, points to first PDPT
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79 add edi, 0x1000
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80 mov DWORD [edi], 0x3003 ; present and readwrite, points to first PDT
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81 add edi, 0x1000
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82 mov DWORD [edi], 0x4003 ; present and readwrite, points to first PT
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83 add edi, 0x1000
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84
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85 ; identity map the first two megabytes:
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86 mov ebx, 0x00000003
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87 mov ecx, 512
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88 ; Fill all PT entries at 0x4000
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89 SetEntry:
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90 mov DWORD [edi], ebx
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91 add ebx, 0x1000
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92 add edi, 8
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93 loop SetEntry
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94
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95 ; Enable paging:
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96 mov eax, cr4
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97 or eax, 1 << 5 ; PAE-bit is bit 5
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98 mov cr4, eax
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99
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100 ; Set LM-bit (Long Mode bit):
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101 mov ecx, 0xC0000080
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102 rdmsr
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103 or eax, 0x100 ; Set bit 8 (LM-bit)
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104 wrmsr
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105
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106 ; Enable paging:
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107 mov eax, cr0
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108 or eax, 0x80000000 ; Set bit 31 (PG-bit)
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109 mov cr0, eax
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110
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111 ; Load the GDT:
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112 lgdt [GDT64.Pointer]
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113
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114 ; Jump to 64 bits kernel:
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115 jmp GDT64.Code:Realm64
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116
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117 bits 64
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118
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119 ; realm64
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120 Realm64:
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121
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122 cli
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123 mov ax, GDT64.Data
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124 mov ds, ax
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125 mov es, ax
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126 mov fs, ax
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127 mov gs, ax
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128
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129 ; Done!
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130
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131 ; Setup stack pointer:
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132 mov rsp, stackEnd
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133 ; Put a B upper left corner
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134 mov al, 66 ; 'B'
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135 mov [0xb8000], al
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136
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137 ; Jump to code that is glued after this file
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138 jmp einde
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139
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140 align 16
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141 dataEnd:
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142 ; reserve bytes for stack:
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143 stackBegin:
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144 resb 1024
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145 stackEnd:
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146
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147 einde:
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148 XCHG BX, BX ; bochs breakpoint
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149
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150 # Call kernel:
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151 extern kmain
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152 call kmain
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153 # Should we ever return, remain in endless loop:
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154 cli
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155 hang:
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156 hlt
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157 jmp hang
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158
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