加载全局描述符表会导致错误

Question

我的引导加载程序上有一个子例程“ switch32”，应该将过渡到32位保护模式，但是lgdt指令似乎会造成麻烦。这是代码 “ switch32.asm”：

gdt_start:

gdt_null:
    dq 0x0
gdt_code:
    dw 0xFFFF   ;Lower 16 bits of limit
    dw 0x0000   ;Lower 16 bits of base address
    db 0x00     ;Middle 8 bits of base address
    db 10011010b;Access byte: present=1,privilege=00,type=1,exec=1,comform=0,read=1,acc=0
    db 0100111b ;High 4 bits = flags, Low 4 bits = last nibble of limit (20 bits)
    db 0x00     ;Higher 8 bits of base address (32 bits)

gdt_data:
    dw 0xFFFF   ;Lower 16 bits of limit
    dw 0x0000   ;Lower 16 bits of base address
    db 0x00     ;Middle 8 bits of base address
    db 10010010b;Access byte: present=1,privilege=00,type=1,exec=0,dir=0,write=1,acc=0
    db 0100111b ;High 4 bits = flags, Low 4 bits = last nibble of limit (20 bits)
    db 0x00     ;Higher 8 bits of base address (32 bits)

gdt_end:        

gdtr_data:  ;The data to pass to the GDTR register (lower word=size of GDT, higher dword=address of GDT)
    dw gdt_end - gdt_start - 1 ;16 bit size of GDT
    dd gdt_start               ;Address to start of GDT

CODE_SEGMENT equ gdt_code - gdt_start   ;Index of code segment descriptor
DATA_SEGMENT equ gdt_data - gdt_start   ;Index of data segment descriptor

switch32:
    pusha
    cli ;Disable interrupts
    lgdt [gdtr_data]

    ;Set first bit (protected mode enable) in control register 0
    mov eax,cr0
    or eax,0x1
    mov cr0,eax

    jmp CODE_SEGMENT:post_flush       ; 'fake' far jump to trick CPU into flushing pipeline to prevent nasty exceptions
                                      ; according to intel manual, CS register is implicitly set to far JMP's selector
post_flush:
    [bits 32]
    mov eax,DATA_SEGMENT
    mov ds,eax 
    mov ss,eax 
    mov es,eax
    mov fs,eax
    mov gs,eax

    popa
    ret

我正在使用qemu，每当调用子例程时，屏幕开始闪烁，没有任何超过lgdt指令，我很确定这意味着有一个CPU错误。该错误来自lgdt指令，但对于原因，我毫无意义。我是否将正确的数据传递给GDTR寄存器？还是我的整个GDT设置错误？

我正在将Intel I386程序员手册和全球描述符表中的Osdev Wiki文章用作资源，并且根据我阅读的内容设置了GDT。