Question

I use GDB and want to modify an iOS app. (for example: change score in a game)

So, I set breakpoint, for example:

b *0x0032c870

and that in the breakpoint, I enter

info r

after this, gdb shows

r0             0x92717c0    153556928
r1             0x7d47a0 8210336
r2             0x0  0

And now I know what I need is change r2 to 1

set $r2=1

Now the value changes in the game.

OK, there’s a question, how can I edit in hexeditor to set r2=1 instead using gdb everytime?

Thank you

Answer 1

how can I edit in hexeditor to set r2=1 instead using gdb everytime

You can’t: the value of r2 is the value of the register; it doesn’t exist until the program is running.

What you need to do is figure out where that value was loaded into the register, and change the code there to make it load 1 instead of 0.

This could be very easy, or tricky depending on how that value is loaded: easy if it’s loaded as a constant (just change the instruction to load a different constant). But chances are it’s loaded as a return value from some function, in which case you’ll have to change that function to return a different value.