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assemblyx86att

What exactly is this lea supposed to do?

I'm solving a school assignment and so far everything has been quite simple. However, I encountered the following piece of code:

mov 0x8(%ebp), %eax    ;load pointer function argument into eax
mov (%eax), %eax       ;dereference the pointer
test %eax, %eax        ;
sete %dl               ;test if it was 0
lea 0x1(%eax), %ecx    ;???
mov 0x8(%ebp), %eax    ;load the argument again
mov %ecx, (%eax)       ;store whatever is in ecx on the pointed-to address
...

I'm really at my wit's end here, does the register have an address? Way I see it, the lea would store the address of eax (offset by 1) into ecx, but that doesn't make sense, does it?

Solution

  • lea 0x1(%eax), %ecx loads the register %ecx with %eax + 1. The lea instruction is commonly used for arithmetic computations, thanks to the relatively sophisticated addressing modes of this instruction set.

    If you do not identify %eax as an address, this is likely what is happening here (as Oli says, we don't have enough context to tell).