2

I am reading through the 'Practical Malware Analysis' book and got to page 74 which says:

lea ebx, [eax*4+4] is the functional equivalent of ebx = (eax+1)* 5 where eax is a number.

As of my understanding, lea ebx, [eax*4 + 4] should multiply eax value by 4, add 4 to it and then store it back in ebx, which is different than (eax+1) * 5.

Is that a typo? Or I got things wrong?

I think it should be: ebx = (eax+1) * 4

  • Yes, this is probably a typo. – NirIzr Jun 13 '17 at 4:27
  • most probably ... – Ahmad Kouraiem Jun 13 '17 at 4:29
5

This is a typo. The instruction lea ebx,[eax*4+4] will set ebx to 4*eax+4 or 4*(eax+1).

I believe I found a revision online of that book which has:

For example, it is common to see an instruction such as lea ebx, [eax*5+5], where eax is a number, rather than a memory address. This instruction is the functional equivalent of ebx = (eax+1)*5, ...

so it seems as though it was corrected at some point. Note that, technically, lea ebx, [eax*5+5] is really implemented as lea ebx, [eax*4+eax+5].

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  • The question is: lea ebx, [eax*4+4] is the same as ebx = (eax+1)*5 – Ahmad Kouraiem Jun 13 '17 at 4:26

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