보호 모드 프로그래밍에서 IDT 설정

처음 부팅돼고 보호 모드로 들어가기 전에

IDT를 NULL로 설정하려고 합니다.

리눅스 소스 arch/i386/boot/setup.S 에 나온대로

offsetIDT
.word 0
.word 0, 0

이렇게 idtr 에 저장할 값을 만들고

역시 소스그대로

lidt offsetIDT

이렇게 했더니 재부팅이 돼버립니다.

제가 뭘 잘못한걸까요?

전체 소스도 올립니다.

----------------------------------------------------------------

.equ SETUPSEG, 0x9020
.equ STACKSEG, 0x9000
.equ STACKOFF, 0x8000

.equ OSCODE, 0x8
.equ OSDATA, 0x10

.code16
.text

.global _start
_start
#movb $'3', %al
#call PRINT_CHAR
call PRINT_NL

#call PRINT_REGISTERS
jmp START_SETUP

nBytesPerSect
.word 0x200
nSectPerTrack
.word 0x12
nHeads
.word 0x2
bBootDrive
.byte 0x00

stGDT
.word 0, 0, 0, 0 # NULL descriptor
.word 0xffff, 0, 0x9a00, 0xcf # OS code descriptor
.word 0xffff, 0, 0x9200, 0xcf # OS data descriptor
.word 0, 0, 0, 0 # dummy

offsetGDT
.word 0x800
.word 0, 0

offsetIDT
.word 0
.word 0, 0

START_SETUP
# set data segment
movw %cs, %ax
movw %ax, %ds
movw %ax, %es
#call PRINT_REGISTERS

# print setup message
movw $SETUP_MSG, %si
call PRINT_STRING

cli

call ACTIVATE_A20

# set IDT to null
lidt offsetIDT #=============>> 여기서 재부팅이 됍니다.
call PRINT_REGISTERS

# set GDT
xorl %eax, %eax # compute address of stGDT
movw %ds, %ax
shll $4, %eax
addl $stGDT, %eax
movl %eax, (offsetGDT+2) # save address in pIDT
lgdt offsetGDT # set gdtr

sti

call PRINT_REGISTERS
movw $PMODE_MSG, %si
call PRINT_STRING

movl %cr0, %eax
orl $0x1, %eax
movl %eax, %cr0

ljmp $OSCODE, $OK_PMODE

# activate A20 line
ACTIVATE_A20
pushw %ax

ACTIVATE_A20_UPPER
inb $0x64, %al
testb $0x2, %al
jnz ACTIVATE_A20_UPPER
movb $0xd1, %al
outb %al, $0x64

ACTIVATE_A20_BOTTOM
inb $0x64, %al
testb $2, %al
jnz ACTIVATE_A20_BOTTOM
movb $0xdf, %al
outb %al, $0x60

popw %ax
ret

# print registers
PRINT_REGISTERS
pusha

movb $'a', %al # print ax
call PRINT_CHAR
call PRINT_WORD
call PRINT_NL

movb $'b', %al # print bx
call PRINT_CHAR
movw %bx, %ax
call PRINT_WORD
call PRINT_NL

movb $'c', %al # print cx
call PRINT_CHAR
movw %cx, %ax
call PRINT_WORD
call PRINT_NL

movb $'d', %al # print dx
call PRINT_CHAR
movw %dx, %ax
call PRINT_WORD
call PRINT_NL

movb $'c', %al # print cs
call PRINT_CHAR
movw %cs, %ax
call PRINT_WORD
call PRINT_NL

movb $'d', %al # print ds
call PRINT_CHAR
movw %ds, %ax
call PRINT_WORD
call PRINT_NL

movb $'s', %al # print ss
call PRINT_CHAR
movw %ss, %ax
call PRINT_WORD
call PRINT_NL

movb $'p', %al # print sp
call PRINT_CHAR
movw %sp, %ax
call PRINT_WORD
call PRINT_NL

popa
ret

# print one character
# argument al
PRINT_CHAR
pushw bx
# int 0x10 - 0xe service
movb $0xe, %ah
movw $0x7, %bx
int $0x10
popw bx
ret

# print new-line
PRINT_NL
pushw %ax
movb $0xd, %al
call PRINT_CHAR
movb $0xa, %al
call PRINT_CHAR
popw %ax
ret

# print ascii-zero string
# argument si (pointer of string)
PRINT_STRING
pushw ax
PRINT_STRING_LOOP
movb (%si), %al
cmpb $0, %al
je PRINT_STRING_END
call PRINT_CHAR
incw %si
jmp PRINT_STRING_LOOP
PRINT_STRING_END
popw ax
ret

# print one word
# argument ax
PRINT_WORD
pushw %dx
movw %ax, %dx # save original value
movb %dh, %al # print upper byte
call PRINT_BYTE
movb %dl, %al # print bottom byte
call PRINT_BYTE
popw %dx
ret

# print one byte number
# argument al (number to print)
PRINT_BYTE
pushw %dx
pushw %bx
movw $0x7, %bx
movb $0xe, %ah

movb %al, %dl # save original value

shrb $4, %al # print upper nibble
addb $0x30, %al
cmp $0x39, %al
jle PRINT_BYTE_UPPER
addb $7, %al
PRINT_BYTE_UPPER
int $0x10

movb %dl, %al # restore al
andb $0xf, %al # print bottom nibble
addb $0x30, %al
cmp $0x39, %al
jle PRINT_BYTE_LOWER
addb $7, %al
PRINT_BYTE_LOWER
int $0x10

popw %bx
popw %dx
ret

SETUP_MSG
.ascii "start setup"
.byte 0xd, 0xa, 0x0

PMODE_MSG
.ascii "turn to protected mode"
.byte 0xd, 0xa, 0x0

.code32
OK_PMODE
movw $0x10, %ax
movw %ax, %ds
movl $0xb8000, %esi
movl $'O', (%esi)

END_SETUP
jmp END_SETUP

.org 1024