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Zhuma How do I cheat?
Reputation: 0
Joined: 11 Feb 2023 Posts: 5
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Posted: Sat Feb 11, 2023 11:19 am Post subject: Trying to compare XMM0 is greater than value |
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I tried to do it myself, but it didn't end well, also I found pretty much the same question (Can't post URL to this question `cause of the new account), but every thing recommended there didn't help me. What I want to do, is to compare the value in XMM register (XMM0), with float [rcx+30], if [rcx+30] is bigger, I want to run original code, otherwise, I want to jump to exit.
Original code:
Code: | originalcode:
movss [rcx+30],xmm0
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Hope you can help me!
Last edited by Zhuma on Sat Feb 11, 2023 1:06 pm; edited 2 times in total |
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LeFiXER Grandmaster Cheater Supreme
Reputation: 20
Joined: 02 Sep 2011 Posts: 1069 Location: 0x90
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Posted: Sat Feb 11, 2023 12:36 pm Post subject: |
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You could try this:
Code: |
...
alloc(number,4)
number:
dd (float) 0
newmem:
movss [number],xmm0
cmp [number],0
je exit
movss [rcx+30],xmm0
...
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Zhuma How do I cheat?
Reputation: 0
Joined: 11 Feb 2023 Posts: 5
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Posted: Sat Feb 11, 2023 1:04 pm Post subject: |
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LeFiXER wrote: | You could try this:
Code: |
...
alloc(number,4)
number:
dd (float) 0
newmem:
movss [number],xmm0
cmp [number],0
je exit
movss [rcx+30],xmm0
...
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Actually, I wrote topic wrong, I need to check, which of values [rcx+30] or XMM0 is greater, and if [rcx+30], then I need to skip running original code (To not set lower value to my money address). I tried your code, for some reason, it always returns only one result.
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ParkourPenguin I post too much
Reputation: 152
Joined: 06 Jul 2014 Posts: 4695
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Posted: Sat Feb 11, 2023 3:04 pm Post subject: |
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Zhuma wrote: | if [rcx+30] is bigger, I want to run original code |
Zhuma wrote: | I need to check, which of values [rcx+30] or XMM0 is greater, and if [rcx+30], then I need to skip running original code | What?
Use `ucomiss`
Code: | newmem:
ucomiss xmm0,[rcx+30]
jae exit // jump if (float) xmm0 >= [rcx+30]
// original code:
movss [rcx+30],xmm0
exit:
jmp return | Maybe `jbe` is what you're looking for instead?
_________________
I don't know where I'm going, but I'll figure it out when I get there. |
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Zhuma How do I cheat?
Reputation: 0
Joined: 11 Feb 2023 Posts: 5
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Posted: Sun Feb 12, 2023 7:35 am Post subject: |
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Actualy, it was so easy to make..
Code that works perfectly:
Code: | newmem:
movss xmm15,xmm0
cmpss xmm0,[rcx+30],4
jl exit
originalcode:
movss [rcx+30],xmm15
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Thanks for help!
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ParkourPenguin I post too much
Reputation: 152
Joined: 06 Jul 2014 Posts: 4695
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Posted: Sun Feb 12, 2023 2:19 pm Post subject: |
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For other people reading this: `cmpss` doesn't work that way. Use `ucomiss` instead.
`cmpss` compares the first value against the second value using the comparison operation defined by the third 8-bit immediate value. If the comparison is true, the first dword in the first parameter has all bits set to 1 (0xFFFFFFFF); if false, the bits are unset (0).
`cmpss` doesn't modify the eflags register. Instructions that use eflags (e.g. `jl`) don't work with cmpss.
Even if it did, the 8-bit immediate "4" means "not equal to". It has nothing to do with greater than or less than like OP presumably wanted.
Zhuma wrote: | Code: | newmem:
movss xmm15,xmm0
cmpss xmm0,[rcx+30],4
jl exit
originalcode:
movss [rcx+30],xmm15 |
| All this does is write 0xFFFFFFFF to xmm0 if (float)xmm0 != [rcx+30] and 0x00000000 otherwise. The `jl` instruction is meaningless in this context.
As for why this might work for OP, I'd guess the original code has some instruction that sets eflags before the injection point, and it just so happens to behave like OP wants.
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I don't know where I'm going, but I'll figure it out when I get there. |
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