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0x07.asm
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0x07.asm
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;
; $Id: 0x07.asm,v 1.1.1.1 2016/03/27 08:40:12 raptor Exp $
;
; 0x07 explanation - from xchg rax,rax by xorpd@xorpd.net
; Copyright (c) 2016 Marco Ivaldi <raptor@0xdeadbeef.info>
;
; This snippet sets rax with its initial value, in a way
; similar to the previous snippet 0x06. The following C
; code performs the same calculations:
;
; #include <stdio.h>
; main()
; {
; int rax = 5;
; printf("in: %d\n", rax);
; rax = ~((~(rax + 1) + 1) + 1) + 1;
; printf("out: %d\n", rax);
; }
;
; I guess the main takeway here (as in the previous snippet)
; is that "not rax" can be rewritten as:
;
; inc rax
; neg rax
;
; Similarly, "neg rax" can be rewritten as:
;
; not rax
; inc rax
;
; This analysis was facilitated by the assembly REPL rappel
; by yrp604@yahoo.com:
;
; https://github.com/yrp604/rappel/
;
BITS 64
SECTION .text
global main
main:
inc rax ; rax = rax + 1
neg rax ; rax = ~rax + 1
inc rax ; rax = rax + 1
neg rax ; rax = ~rax + 1