hello to all! :)
i've a trouble in completing the very very very last code for my thesis in computer science. I'm playing with interrupt hooking in 16 bit DOS mode, but my code acts strange:
-------------------------
ORG 0x100
; old int21h
mov ax, 0x3521
int 0x21
; save it
mov [OLDINT], bx
mov [OLDINT+2], es
lea di, [OLDINT]
; simulate 'exit to dos' int21h service using a far call
mov ax, 0x4C00
pushf
call far dword [cs:di]
OLDINT dd 0x00
-----------------------
well it crashes at location 011E. Debugging it i can see:
2048:011D 9C pushf
2048:011E 2E CS:
2048:011F 66 DB 66
2048:0120 .... call far [DI+0]
..........
from NASM manual i read:
"When NASM is in BITS 16 mode, instructions which use 32-bit data are prefixed with an 0x66 byte, and those referring to 32-bit addresses have an 0x67 prefix. In BITS 32 mode, the reverse is true: 32-bit instructions require no prefixes, whereas instructions using 16-bit data need an 0x66 and those working on 16-bit addresses need an 0x67."
but why does the program crash?