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Why doesn't this compile in AA? lea rdx, [rdx+8+rcx*8]

 
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Merlini
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PostPosted: Wed May 10, 2017 8:07 pm    Post subject: Why doesn't this compile in AA? lea rdx, [rdx+8+rcx*8] Reply with quote

In AA this doesn't compile
lea rdx, [rdx+8+rcx*8]

but this does
lea rdx, [rdx+8+ecx*8]

Is this specific to CE or is that error in general?
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STN
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PostPosted: Thu May 11, 2017 12:02 am    Post subject: Reply with quote

Seems like a size issue.

CE doesn't compile lea rdx, [rdx+8+ecx*8] but rather compiles it as lea edx,[edx+ecx*8+08]

lea rdx, [rdx+8+rcx*8] is fine and should be compiled as such whereas lea rdx, [rdx+8+ecx*8] isn't and shouldn't be compiled or converted.

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SunBeam
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PostPosted: Thu May 11, 2017 2:59 am    Post subject: This post has 1 review(s) Reply with quote

The valid instructions are the x86 and x64 variants (you can't mix-up x64 with x86 like you'd want to):

Code:
00000000FF7A1000 | 48 8D 54 CA 08                                 | LEA RDX,QWORD PTR DS:[RDX+RCX*8+8]                                |
00000000FF7A1005 | 67 8D 54 CA 08                                 | LEA EDX,DWORD PTR DS:[EDX+ECX*8+8]                                |
00000000FF7A100A | 90                                             | NOP                                                               |
00000000FF7A100B | 90                                             | NOP                                                               |
00000000FF7A100C | 90                                             | NOP                                                               |
00000000FF7A100D | 90                                             | NOP                                                               |

BR,
Sun

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Last edited by SunBeam on Fri May 12, 2017 3:42 am; edited 2 times in total
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Merlini
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PostPosted: Thu May 11, 2017 1:57 pm    Post subject: Reply with quote

SunBeam wrote:

Make sure the address you put in RCX/ECX is correctly defined in the script. Example:

Code:

MyAddr:
dd 0

mov rcx,MyAddr
lea rdx,[rdx+rcx*8+8]

This will get compiled as "ecx" not "rcx", because MyAddr is a DWORD, not a QWORD. So "dd 0" should be "dq 0".


SunBeam,
Are you saying that you could get CE's AA to correctly compile
lea rdx,[rdx+rcx*8+8]?

I could not compile this in CE 6.6 AA properly.
And I think STN was pointing out (if I understood him)
that even the
lea rdx,[rdx+ecx*8+8]
which seems to compile in AA isn't doing what we expect it to do.
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ParkourPenguin
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PostPosted: Thu May 11, 2017 2:18 pm    Post subject: Reply with quote

Don't try to use 64-bit registers when working with a 32-bit process.
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Merlini
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PostPosted: Thu May 11, 2017 2:30 pm    Post subject: Reply with quote

ParkourPenguin wrote:
Don't try to use 64-bit registers when working with a 32-bit process.

Using 64bit process.
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ParkourPenguin
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PostPosted: Thu May 11, 2017 2:54 pm    Post subject: Reply with quote

For me, when targeting a 64-bit process, using rcx as the index register works fine and using ecx gives an error. Vise versa for a 32-bit process (what you're experiencing). I don't believe you're targeting a 64-bit process.

Attach CE to the game, go to Table -> Show cheat table Lua script, copy and paste this code in, click "execute", and post what the results are.
Code:
print('CE version:\t',tostring(getCEVersion()))
print('CE is 64-bit:\t',tostring(cheatEngineIs64Bit()))
print('target is 64-bit:\t',tostring(targetIs64Bit()))

assert(autoAssemble('globalalloc(foo,32)'),'globalalloc failed')
print('index reg rcx:\t',tostring(autoAssemble('foo:\r\nlea rdx,[rdx+8+rcx*8]')))
print('index reg ecx:\t',tostring(autoAssemble('foo:\r\nlea rdx,[rdx+8+ecx*8]')))

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Dark Byte
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PostPosted: Thu May 11, 2017 6:39 pm    Post subject: Reply with quote

Code:

CE version:       6.7
CE is 64-bit:     true
target is 64-bit: true
index reg rcx:    true
index reg ecx:    true

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mgr.inz.Player
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PostPosted: Thu May 11, 2017 7:06 pm    Post subject: Reply with quote

In 64bit CE6.7SVN:
Code:
67 8D 54 CA 08        - lea edx,[rdx+ecx*8+08]
8D 54 CA 08           - lea edx,[rdx+rcx*8+08]
67 48 8D 54 CA 08     - lea rdx,[rdx+ecx*8+08]
48 8D 54 CA 08        - lea rdx,[rdx+rcx*8+08]

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ParkourPenguin
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PostPosted: Thu May 11, 2017 8:33 pm    Post subject: Reply with quote

(In my previous post, I was using CE 6.6)

The lea instruction can address a memory location using mod 32 arithmetic instead of mod 64 arithmetic when using the address size override prefix (0x67). The size of the base register should match the index register:
Code:
67 48 8D 54 CA 08 - lea rdx,[edx+ecx*8+08]
48 8D 54 CA 08    - lea rdx,[rdx+rcx*8+08]

CE 6.6 has a couple bugs with regards to the first instruction: CE can't assemble it and doesn't properly disassemble it.

(Source: Intel 64 & 32 Architectures Software Developer's Manual Vol. 2A section 3.2 "LEAŚLoad Effective Address")


I doubt this information helps OP at all since I still think their target is 32-bit.

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Merlini
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PostPosted: Thu May 11, 2017 8:41 pm    Post subject: Reply with quote

ParkourPenguin wrote:
For me, when targeting a 64-bit process, using rcx as the index register works fine and using ecx gives an error. Vise versa for a 32-bit process (what you're experiencing). I don't believe you're targeting a 64-bit process.


Code:
CE version:    6.6
CE is 64-bit:    true
target is 64-bit:    true
index reg rcx:    true
index reg ecx:    false

Works! Shocked

So you were absolutely right and I was wrong. Embarassed

I was at work when I replied last and since the only program I've been using
CE on had been 64bit I automatically assumed it was 64bit.
I must have somehow attached to a 32bit process.

My apologies for creating a hasty and confusing thread without
doing due diligence on my part.
Thank you to all those who chimed in.
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SunBeam
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PostPosted: Fri May 12, 2017 3:41 am    Post subject: Reply with quote

My bad on my previous post.

I gave x64dbg "lea rdx, [rdx+8+ecx*8]" to compile and it worked, but I didn't check the result. What it actually did was to compile the x86 version -> "lea edx, [edx+ecx*8+8]" Very Happy

So, without checking the result, I thought it was some issue with CE Razz

BR,
Sun

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