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section .text
org 8000h
;
; 32-bit bcopy routine for real mode
;
; We enter protected mode, set up a flat 32-bit environment, run rep movsd
; and then exit. IMPORTANT: This code assumes cs == ss == 0.
;
; This code is probably excessively anal-retentive in its handling of
; segments.
;
bcopy_main: jmp short bcopy
bcopy_gdt_ptr: dw bcopy_gdt_size-1
dd bcopy_gdt
align 4
bcopy_gdt: dd 0 ; Null descriptor
dd 0
dd 0000ffffh ; Code segment, use16, readable,
dd 00009b00h ; present, dpl 0, cover 64K
dd 0000ffffh ; Data segment, use16, read/write,
dd 008f9300h ; present, dpl 0, cover all 4G
dd 0000ffffh ; Data segment, use16, read/write,
dd 00009300h ; present, dpl 0, cover 64K
bcopy_gdt_size: equ $-bcopy_gdt
bcopy:
push eax
push gs
push fs
push ds
push es
lgdt [bcopy_gdt_ptr]
mov eax,cr0
or eax,byte 1
cli
mov cr0,eax ; Enter protected mode
jmp 8:.in_pm
.in_pm: xor ax,ax ; Null selector
mov fs,ax
mov gs,ax
mov al,16 ; Data segment selector
mov es,ax
mov ds,ax
mov al,24 ; "Real-mode-like" data segment
mov ss,ax
a32 rep movsd ; Do our business
mov es,ax ; Set to "real-mode-like"
mov ds,ax
mov fs,ax
mov gs,ax
mov eax,cr0
and eax,0fffffffeh
mov cr0,eax ; Disable protected mode
jmp 0:.in_rm
.in_rm: xor ax,ax ; Back in real mode
mov ss,ax
sti
pop es
pop ds
pop fs
pop gs
pop eax
ret
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