在保护模式下访问内存步骤:1 获取段选择子2 根据GDTR寄存器获得基地址3 和偏移地址结合获得线性地址 与内存有关的描述符 align 8, db 0 (内存对齐) GDT: ; Descriptor 0 is not used dw 0 dw 0 dw 0 dw 0 ; Descriptor 1: kernel code segment dw 0xFFFF ; bytes 0 and 1 of segment size dw 0x0000 ; bytes 0 and 1 of segment base address db 0x00 ; byte 2 of segment base address db 0x9A ; present, DPL=0, non-system, code, non-conforming, ; readable, not accessed db 0xCF ; granularity=page, 32 bit code, upper nibble of size db 0x00 ; byte 3 of segment base address ; Descriptor 2: kernel data and stack segment ; NOTE: what Intel calls an "expand-up" segment ; actually means that the stack will grow