get local variable pointer without " lea"?

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celtic88

Joined: 26 Mar 2018
Posts: 6

celtic88 03 Apr 2018, 16:47

hi all,

How can get local variable pointer Without " lea" , thank you

code

Code:

format PE GUI 4.0
entry start

include 'INCLUDE\win32ax.inc'

section '.text' code readable executable

  start:

proc Func
  local pDirectx:DWORD

  ;//lea eax, [pDirectx]

  mov eax, pDirectx       ;// Get  pDirectx Pointer   ??

  ret
endp

03 Apr 2018, 16:47

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 03 Apr 2018, 22:44

celtic88 wrote:

How can get local variable pointer Without " lea" , thank you

LEA is the only way, unless you override MOV with your own macro.

03 Apr 2018, 22:44

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 03 Apr 2018, 22:48

did you mean:

Code:

proc Func
local pDirectx:DWORD
mov eax,pDirectx-ebp       
mov eax,[ebp+eax]
ret
endp

03 Apr 2018, 22:48

ProMiNick

Joined: 24 Mar 2012
Posts: 821
Location: Russian Federation, Sochi

ProMiNick 03 Apr 2018, 22:49

in current example
mov eax, pDirectx equivalent to mov eax,esp or...
... or (only because macro proc used) equivalent to mov eax,ebp
if locals will be more than 1 dword so analog for lea will be 2 instructions instead of one lea, one of them is mov described previously & second is add or sub instruction with value equal to address range from esp (or ebp) to pointer to thour variable

03 Apr 2018, 22:49

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 03 Apr 2018, 22:53

LEA is just an ADD in disguise.

Code:

add eax,ebp,offset ;same as lea eax,[ebp+offset]

But of course is won't assemble because Intel never defined the opcode ADD that way.

03 Apr 2018, 22:53

celtic88

Joined: 26 Mar 2018
Posts: 6

celtic88 04 Apr 2018, 07:40

Currently I use this method!!

Code:

macro LocalPoint localV,localP {LEA eax, [localV]
mov [localP], eax}

proc Func 
  local pDirectx:DWORD,p_pDirectx:DWORD
  LocalPoint pDirectx,p_pDirectx
  ;//lea eax, [pDirectx] 

  mov eax, pDirectx       ;// Get  pDirectx Pointer   ?? 

  ret 
endp

04 Apr 2018, 07:40

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 04 Apr 2018, 08:02

celtic88 wrote:

Currently I use this method!!

Code:

macro LocalPoint localV,localP {LEA eax, [localV]
mov [localP], eax}

proc Func 
  local pDirectx:DWORD,p_pDirectx:DWORD
  LocalPoint pDirectx,p_pDirectx
  ;//lea eax, [pDirectx] 

  mov eax, pDirectx       ;// Get  pDirectx Pointer   ?? 

  ret 
endp

I don't understand why you would prefer to read a memory variable, instead of using the ALU to compute the value directly with lea. To me it looks like more work for the CPU and more work for the programmer. Maybe you have a particular purpose for it?

04 Apr 2018, 08:02

celtic88

Joined: 26 Mar 2018
Posts: 6

celtic88 04 Apr 2018, 19:01

to do this

Code:

proc main
  local testt:DWORD
  
  LEA eax, [testt]
  
  stdcall Set,eax ;; i liked this syntax stdcall Set,test
  
  MOV eax, [testt]
  ret
endp
  
proc Set varbypoint
  MOV eax,[varbypoint]
  MOV dword [eax], 404
  ret
endp

04 Apr 2018, 19:01

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 04 Apr 2018, 22:29

You can use addr

Code:

stdcall Func,addr testt

Less typing for the programmer, and more readable IMO. You just need to be aware that the standard macros will use edx for the temporary holder, whereas you used eax.

04 Apr 2018, 22:29

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