40 lines
1.1 KiB
ArmAsm
40 lines
1.1 KiB
ArmAsm
.section .data
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gdt_start: # don't remove the labels, they're needed to compute sizes and jumps
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# the GDT starts with a null 8-byte
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.long 0x0 # 4 byte
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.long 0x0 # 4 byte
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# GDT for code segment. base = 0x00000000, length = 0xfffff
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# for flags, refer to os-dev.pdf document, page 36
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gdt_code:
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.word 0xffff # segment length, bits 0-15
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.word 0x0 # segment base, bits 0-15
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.byte 0x0 # segment base, bits 16-23
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.byte 0b10011010 # flags (8 bits)
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.byte 0b11001111 # flags (4 bits) + segment length, bits 16-19
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.byte 0x0 # segment base, bits 24-31
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# GDT for data segment. base and length identical to code segment
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# some flags changed, again, refer to os-dev.pdf
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gdt_data:
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.word 0xffff
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.word 0x0
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.byte 0x0
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.byte 0b10010010
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.byte 0b11001111
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.byte 0x0
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gdt_end:
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# GDT descriptor
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gdt_descriptor:
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.long gdt_end-gdt_start-1
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.long gdt_start
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//MISMATCH: " dw gdt_end - gdt_start - 1 "
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//MISMATCH: " dd gdt_start "
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# define some constants for later use
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code_seg: .long gdt_code - gdt_start
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data_seg: .long gdt_data - gdt_start
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