I have the following assembly line and I have my problems to understand it, because until now I have always seen lines like this: mov eax, 0 and so on. But now, I have the following (I use IDA PRO):

 mov ds:dword_4870058 , offset loc_4048E0

When I click on offset loc_4048E0, I see:

 mov al, 10h
 jmp sub_402774

when I interpret dword_4870058 as a global variable, can I assume that dword_4870058 gets the value 10h (if I regard al as a return value register) . This is the only thing that I can imagine.

Is it a right or wrong assumption ?

  • No. loc_4048E0 SEEMS to be a function. if so dword_4870058 is a function pointer (and a global variable as you already found out), if not it is a pointer to data that for some reason IDA seems to think of as a function (No idea how likely IDA mislabels that)
    – user45891
    Sep 11, 2014 at 23:45
  • I thought that the mov-instruction is for storing data/content. Is it different when it is a function pointer, or ? I mean, is there a reason why the compiler pick mov instead of lea ? Sep 12, 2014 at 0:43
  • lea / mov difference is covered pretty well here.. stackoverflow.com/questions/1658294/…
    – evlncrn8
    Sep 12, 2014 at 2:55

1 Answer 1


The cleaner version would be:

mov [dword_4870058] , offset loc_4048E0

Then, a variant:

mov [address], value

Where, the [ ] signifies its a memory address contained within the [] and the value put in it for this case is another memory address (in the code section).

To move it to a register it would be:

mov register, value ; eg : mov eax, 12345678h

The value portion can be a value, a pointer, a constant... They're all the same ... just numbers.

Little thing to pay in mind, in x86 you cant do memory to memory moves. So, the "can I assume that dword_4870058 gets the value 10h" is completely wrong, the function at that address has NOT been called has it ? So, it cant get the value 10h...

Its simply storing one value (the address of a function) into another memory block.

  • And presumably, the OP would find something like call ds:[dword_4870058] somewhere else in the code. Whether or not that will call this particular function needs a full flow trace to find out if it's a constant (once written, never modified), or only can be determined during run-time.
    – Jongware
    Sep 13, 2014 at 10:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.