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 Forums >>  IDA Pro  >>  IDAPython: Getting Operand Offset

Topic created on: April 25, 2007 11:35 CDT by stam321 .

Hi,

Is there a way to get the offset and size
of an operand in IDAPython?
The targets are only branch instructions.
For example:
.text:0100296F E8 74 F2 FF FF   call  Name
then i want to get size=4 offset=01002970
(or something similar).
I can use external disas library to do so, or
write a simple one for this perpose only but
I rather not.

Thx,
Stam

  PSUJobu     April 25, 2007 17:19.45 CDT
Though not exactly what you're looking for, you can use the xref stuff to iterate through the "jump" cross-refs at that EA. That would give you the jump target, but not the operand size. Perhaps this is close enough, since I'm not sure what good the operand size does you anyway...

  stam321     April 25, 2007 22:55.29 CDT
> PSUJobu: Though not exactly what you\'re looking for, you can use the xref stuff to iterate through the \"jump\" cross-refs at that EA. That would give you the jump target, but not the operand size. Perhaps this is close enough, since I\'m not sure what good the operand size does you anyway...

I want to auto-patch it to point somewhere else on
certain conditions. So i need to know where to patch
and the size to patch(I know that sometimes I will need
to enlarge the instruction and thats problematic).

  Dyce     April 26, 2007 06:44.57 CDT
Hello,

> stam321: > PSUJobu: Though not exactly what you\\\'re looking for, you can use the xref stuff to iterate through the \\\"jump\\\" cross-refs at that EA. That would give you the jump target, but not the operand size. Perhaps this is close enough, since I\\\'m not sure what good the operand size does you anyway...
>
> I want to auto-patch it to point somewhere else on
> certain conditions. So i need to know where to patch
> and the size to patch(I know that sometimes I will need
> to enlarge the instruction and thats problematic).

For that purpose I would suggest the following:

1,  check op.type, to make sure you have an offset there
2,  op.dtyp gives you the data typeof the operand, which you can translate to size
3,  op.offb and o.offo point you to the actual bytes in the instruction that you can patch

You will need to use ord() on these, see my reply to the op.dtyp problem.


Cheers,

Gergo

  stam321     April 26, 2007 10:55.28 CDT
> Dyce: Hello,
>
> > stam321: > PSUJobu: Though not exactly what you\\\\\\\'re looking for, you can use the xref stuff to iterate through the \\\\\\\"jump\\\\\\\" cross-refs at that EA. That would give you the jump target, but not the operand size. Perhaps this is close enough, since I\\\\\\\'m not sure what good the operand size does you anyway...
> >
> > I want to auto-patch it to point somewhere else on
> > certain conditions. So i need to know where to patch
> > and the size to patch(I know that sometimes I will need
> > to enlarge the instruction and thats problematic).
>
> For that purpose I would suggest the following:
>
> 1,  check op.type, to make sure you have an offset there
> 2,  op.dtyp gives you the data typeof the operand, which you can translate to size
> 3,  op.offb and o.offo point you to the actual bytes in the instruction that you can patch
>
> You will need to use ord() on these, see my reply to the op.dtyp problem.
>
>
> Cheers,
>
> Gergo

Great! Thanks a lot!

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