71 lines
1.4 KiB
ArmAsm
71 lines
1.4 KiB
ArmAsm
#include "cpu/gdt.h"
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.code16
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.global _start
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_start:
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mov $banner, %si
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call print_string
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call switch_to_32bit
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hlt
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jmp . // loop forever
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switch_to_32bit:
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mov $2, %al
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out %al, $0x92 // enable A20
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cli // 1. disable interrupts
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lgdt gdt_descriptor // 2. load GDT descriptor
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mov %cr0, %eax
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or $1, %eax // 3. enable protected mode
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mov %eax, %cr0
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ljmp $SEG_KCODE << 3, $init_32bit // 4. far jump
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.code32
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init_32bit:
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mov $SEG_KDATA << 3, %ax // 5. update segment registers
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mov %ax, %ds
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mov %ax, %ss
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mov %ax, %es
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mov %ax, %fs
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mov %ax, %gs
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mov $KERN_STACK_BASE, %ebp // 6. setup stack
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mov %ebp, %esp
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call bootmain // 7. load and run kernel
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jmp . // 8. loop forever
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.code16
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print_string:
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mov $0x0e, %ah // "teletype output"
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repeat:
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lodsb // equivalent to mov (%si), %al; inc %si
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test %al, %al
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je done
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int $0x10 // bios interrupt
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jmp repeat
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done:
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ret
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banner:
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.asciz "Loader \n"
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.balign 4
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gdt_start:
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.quad 0x0 // null descriptor
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SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg
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SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg
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gdt_end:
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// GDT descriptor
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gdt_descriptor:
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.word gdt_end - gdt_start - 1 // size (16 bit)
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.int gdt_start // address (32 bit)
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