.section .data
gdt_start:  # don't remove the labels, they're needed to compute sizes and jumps
    # the GDT starts with a null 8-byte
    .long 0x0 # 4 byte
    .long 0x0 # 4 byte

# GDT for code segment. base = 0x00000000, length = 0xfffff
# for flags, refer to os-dev.pdf document, page 36
gdt_code: 
    .word 0xffff # segment length, bits 0-15
    .word 0x0    # segment base, bits 0-15
    .byte 0x0    # segment base, bits 16-23
    .byte 0b10011010 # flags (8 bits)
    .byte 0b11001111 # flags (4 bits) + segment length, bits 16-19
    .byte 0x0    # segment base, bits 24-31

# GDT for data segment. base and length identical to code segment
# some flags changed, again, refer to os-dev.pdf
gdt_data: 
    .word 0xffff
    .word 0x0
    .byte 0x0
    .byte 0b10010010
    .byte 0b11001111
    .byte 0x0

gdt_end: 

# GDT descriptor
gdt_descriptor:
.long gdt_end-gdt_start-1
.long gdt_start
//MISMATCH: "    dw gdt_end - gdt_start - 1 "
//MISMATCH: "    dd gdt_start "

# define some constants for later use
code_seg: .long gdt_code - gdt_start
data_seg: .long gdt_data - gdt_start