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fstp qword ptr [esi]?

 
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Gwinx
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Posts: 65

PostPosted: Tue Jun 26, 2012 4:48 pm    Post subject: fstp qword ptr [esi]? Reply with quote

What is this opcode doing? fstp qword ptr [esi]


How can I read the value of esi and write to it?
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Fresco
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Joined: 07 Nov 2010
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PostPosted: Wed Jun 27, 2012 4:07 am    Post subject: Reply with quote

is writes the register st0 (fpu) to the value of address esi and pops st0

if esi = 0009ABCD
then it writes double (because of the QWORD) to the value of address 0009ABCD
and then pops out of the fpu stack the st0 register.

you can trace the value of esi like that:
go in the debugger, one line above the code ( fstp qword ptr [esi] ) right click on it and hit > trace > now insert a number 3, play the game, the tracer should show you all the registers at that point, before, during and after the execution, remember ? you traced 3 instruction Smile

as for how to modify it, just go in the debugger, select the code fstp qword ptr [esi] and hit ctrl+a now search in the menus for auto assemble, there you go, you can modify it there Smile
for more info, you should complete cheat engine tutorial, in ce 6.2 hit help and ce tut

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Gwinx
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PostPosted: Sat Jun 30, 2012 2:00 am    Post subject: Reply with quote

Thanks Fresco for replying (:
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Fresco
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PostPosted: Sat Jun 30, 2012 3:27 am    Post subject: Reply with quote

i totally forgot, if you just want temporarily changes to the register, just do this:

open the debugger, go to the instruction you would like to modify any register, right click on it and hit > change register at this location, there you can modify anything you want temporarily.

to undo the changes, right click the highlighted instruction, and hit > toggle breakpoint. and everything should be back to normal.

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