Nasm syntax problem

[Prochamber]

You should clear interrupt before changing the stack pointer and segment then restore them afterwards.

It's not necessary to disable interrupts if the SS is loaded first. The processor does it for you automatically.

Not on really old processors. This won't be relevant for the OP anyway because the OP loaded the stack pointer two instructions before the stack segment.

[gerryg400]

You're correct of course. Some 8088 processors have this bug.

However, it doesn't change the fact that the correct way to modify the SS, (E)SP pair is to modify the SS first and then the (E)SP. That's the way Intel recommends it, presumably because CLI by itself doesn't prevent an NMI or a debug trap.

[qw]

If possible, LSS is even more recommended:

To prevent this situation, the 80386, after both a MOV to SS and a POP to SS instruction, inhibits NMI, INTR, debug exceptions, and single-step traps at the instruction boundary following the instruction that changes SS. Some exceptions may still occur; namely, page fault and general protection fault. Always use the 80386 LSS instruction, and the problem will not occur.

[Griwes]

That's the exact same quote as in post #15...

[Antti]

Is this a true uninterruptible loop? Except an SMM...

Code: Select all

; Uninterruptible Busy Loop Program (loop.asm)
; Written by Antti

; Compile: nasm -f bin -o loop.img loop.asm

[BITS 16]

start:
	cli
	xor ax, ax
	mov ss, ax
	mov sp, ax
	mov ax, 0x1000
	mov es, ax

	cld
	mov ax, 0xD08E         ; Opcodes:  "mov ss, ax"
	mov cx, 0x8000
	xor di, di
	rep stosw              ; Fill 0x10000-0x1FFFF with "mov ss, ax"

	xor ax, ax
	jmp 0x1000:0x0000

times 510 - ($ - $$) db 0
dw 0xAA55

times 1474560 - ($ - $$) db 0  ; "Standard floppy size"

EDIT: It seems that IP does not wrap around...