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What are all the ways a program can jump to an opcode?

 
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mStorm
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PostPosted: Tue Jul 21, 2009 2:36 pm    Post subject: What are all the ways a program can jump to an opcode? Reply with quote

I've been tracing the code to jump in a game by using breakpoints and seeing if the jump triggers it. I've followed it back from a function and through tons of assembly code but I've hit a spot where it has "int 3"s above it and I cannot find what line of code calls it.

How would I trace what Opcode "jmp"'ed to it. I've looked for all the variations of jmps and the opcodes.

je 10328383
jna 10328383
jnge 10328383

etc...

I've, of course, already tried to see if it was a function "call 10328383"

anyone have any clues? Very Happy
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Dark Byte
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PostPosted: Tue Jul 21, 2009 4:48 pm    Post subject: Reply with quote

If you use ce you could try the code dissector, it'll then write the code that jumps to there

Other jumps/calls:

Code:

call register


Code:

call [0xxxxxxxxx] (0xxxxxxxxx=10328382)


Code:

push xxxx
ret


Code:

jmp [0xxxxxxxxx]  (0xxxxxxxxx=10328383)


Code:

int xxxx


Anyhow, have you made sure it's not a call function. (Set a breakpoint at the start and look at the location of esp)

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mStorm
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PostPosted: Tue Jul 21, 2009 6:26 pm    Post subject: Reply with quote

Never used the code dissector

I tried it and it finished but didn't output anything.
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Dark Byte
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PostPosted: Tue Jul 21, 2009 7:56 pm    Post subject: Reply with quote

it doesn't 'output' anything directly, but it does adjust the disassembler view by adding some data above lines that get jumped to
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mStorm
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PostPosted: Wed Jul 22, 2009 12:06 am    Post subject: Reply with quote

All it does is highlight the instructions above it. Where is the extra information at? :[
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&Vage
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PostPosted: Wed Jul 22, 2009 2:31 pm    Post subject: Reply with quote

Try looking at the EDI or EDP register. Maybe the address is in the stack Neutral
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Slugsnack
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PostPosted: Wed Jul 22, 2009 2:54 pm    Post subject: Reply with quote

; wrote:
Try looking at the EDI or EDP register. Maybe the address is in the stack Neutral

what's EDP ? yeah i think edi is along the stack somewhere.. that's what i heard
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&Vage
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PostPosted: Wed Jul 22, 2009 3:31 pm    Post subject: Reply with quote

Slugsnack wrote:
; wrote:
Try looking at the EDI or EDP register. Maybe the address is in the stack Neutral

what's EDP ? yeah i think edi is along the stack somewhere.. that's what i heard

EBP I mean, oh yeah, PTRZ PZ.
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Sean1337
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PostPosted: Thu Jul 23, 2009 7:19 am    Post subject: Re: What are all the ways a program can jump to an opcode? Reply with quote

mStorm wrote:
I've been tracing the code to jump in a game by using breakpoints and seeing if the jump triggers it. I've followed it back from a function and through tons of assembly code but I've hit a spot where it has "int 3"s above it and I cannot find what line of code calls it.

How would I trace what Opcode "jmp"'ed to it. I've looked for all the variations of jmps and the opcodes.

je 10328383
jna 10328383
jnge 10328383

etc...

I've, of course, already tried to see if it was a function "call 10328383"

anyone have any clues? Very Happy


Select the entire function and copy paste it here.

Indicate which address you are looking at.

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