Reverse Engineering for Beginners

CHAPTER 12. CONDITIONAL JUMPS CHAPTER 12. CONDITIONAL JUMPS

Now let’s review thef_signed()function, which works with signed values, in OllyDbg.

Flags are set in the same way: C=1, P=1, A=1, Z=0, S=1, T=0, D=0, O=0.

The first conditional jumpJLEis to be triggered:

Figure 12.4:OllyDbg:f_signed(): first conditional jump

In [Int13] we find that this instruction is triggered if ZF=1 or SF≠OF. SF≠OF in our case, so the jump triggers.