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mgostIH
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 Posted: Mon Apr 18, 2016 8:10 am Post subject: Multiplying a double register |
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I want to make this short.
Basically, I want to multiply the xmm1 register by a constant value, without messing up any of the other registers.
This is the code I want to intercept:
| Code: | | movsd [esi+00000540],xmm1 |
I want to modify the xmm1 register before it actually stores its value in memory, how could I do that, since mulsd doesn't accept fixed values?
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hhhuut
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| Posted: Mon Apr 18, 2016 8:13 am Post subject: |
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I don't think there's a way to let xmm registers and fixed values interact in any way ...
But what's the problem with taking another register to hold your multiplication value?
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mgostIH
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| Posted: Mon Apr 18, 2016 8:18 am Post subject: |
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| hhhuut wrote: | I don't think there's a way to let xmm registers and fixed values interact in any way ...
But what's the problem with taking another register to hold your multiplication value? |
It's not a problem to use other registers, I just want all of them to keep the same value as before the code injection.
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ParkourPenguin
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| Posted: Mon Apr 18, 2016 8:52 am Post subject: |
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You can push/pop the registers if you want. But you don't even need to do that:
| Code: | alloc(newmem,2048)
label(value)
newmem:
mulsd xmm1,[value]
movsd [esi+00000540],xmm1
value:
dq (double)5.0 |
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mgostIH
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| Posted: Mon Apr 18, 2016 9:19 am Post subject: |
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| ParkourPenguin wrote: | You can push/pop the registers if you want. But you don't even need to do that:
| Code: | alloc(newmem,2048)
label(value)
newmem:
mulsd xmm1,[value]
movsd [esi+00000540],xmm1
value:
dq (double)5.0 |
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Nice method, but is there one that can be used without needing of allocating any memory space (except for the code cave itself)?
Basically, an "only code" method.
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ParkourPenguin
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mgostIH
Expert Cheater
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Joined: 01 Jan 2016
Posts: 159
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| Posted: Mon Apr 18, 2016 10:32 am Post subject: |
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| ParkourPenguin wrote: | This takes up more memory than my previous example and is less dynamic, but...
| Code: | alloc(newmem,2048)
newmem:
push 40140000
push 0
mulsd xmm1,[esp]
add esp,8
movsd [esi+00000540],xmm1 |
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Excellent, +1 reputation deserved
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