Is this possible? - Forums

Home » Forums » MAIN » Is this possible?

Basically, if I had a load of variables which I specifically knew what they did but were lets say spread out over memory at irregular intervals, the best way I can think to do acces them is to create an array of pointers to the various variables and then I could access them mathamatically. Ok thats going off the point, but I'm just giving an example of how this applies to variables, is the same possible of lables. After all they are memory address just like variables.

Posted on 2001-03-05 15:08:00 by Zadkiel

Is this possible?

Yes, one example is a jump/call table:

; Copyright 2000 Wayne J. Radburn
;;
;;	MAIN WINDOW MESSAGES
;;
       	.CONST
MainMsg	DWORD	WM_COMMAND,
		WM_WINDOWPOSCHANGED,
		WM_PAINT,
		WM_CREATE, WM_CLOSE, WM_DESTROY
	DWORD	MainWM_COMMAND,
		MainWM_WINDOWPOSCHANGED,
		MainWM_PAINT,
		MainWM_CREATE, MainWM_CLOSE, MainWM_DESTROY

;Equates used to simplify references to window procedure parameters
lParam 	TEXTEQU	
wParam 	TEXTEQU	
uMsg   	TEXTEQU	
hWnd   	TEXTEQU	

	.CODE
MainWND	PROC
	push	ebp
	mov	ebp,esp	;hWnd=EBP+08h, uMsg=EBP+0Ch, wParam=EBP+10h, lParam=EBP+14h

	push	ebx
	push	esi
	push	edi

;IF message is not found
	mov	eax,
	mov	edi,OFFSET MainMsg
	mov	ecx,LENGTHOF MainMsg
	repne scasd
	je	Process

;THEN let DefWindowProc handle this message
Default:
	push			;lParam
	push			;wParam
	push				;Msg
	push				;hWnd
	call			;USER

	jmp	Return

;ELSE process this message possibly setting carry flag for default processing
	ALIGN 4
Process:
	call	DWORD PTR 
	jc	Default
Return:
	pop	edi
	pop	esi
	pop	ebx

	mov	esp,ebp
	pop	ebp
	ret	10h
MainWND	ENDP

Thanks to Wayne for the example :) bitRAKE

Posted on 2001-03-05 16:02:00 by bitRAKE

Is this possible?

Hrmmmm, a table of procedure lables. Kinda like a table of function pointers like a COM interface uses? Sure, very possible. In fact, you may wish to stuff em all into a structure to make accessing them easier.


; define the members
; default values set here to the procedures
FunctionTable_  STRUCT
  FunctionA    proto2 FunctionA_Impl 
  FunctionB    proto3 FunctionB_Impl
  FunctionC    proto8 FunctionC_Impl
FunctionTable_  ENDS

;make an instance of this struct
FunctionTable FunctionTable_ { }

Then, later in your code you can invoke these functions:


invoke FunctionTable.FunctionA, p1, p2
...
invoke FunctionTable.FunctionB, p1, p2, p3
...
invoke FunctionTable.FunctionC, p1, p2, p3, p4, p5, p6, p7, p8

Now, I left a kinda importaint set-up detail out. You need to prototype the functions. Since we do loose type checking in masm32, the protos will only do a count of parameters. Since they are also all pointers, they need be defined in two steps:


Proto2Impl      typedef proto :DWORD, :DWORD
Proto3Impl      typedef proto :DWORD, :DWORD, :DWORD

Proto8Impl      typedef proto :DWORD, :DWORD, :DWORD, :DWORD, :DWORD, :DWORD, :DWORD, :DWORD


proto2           typedef ptr Proto2Impl
proto3           typedef ptr Proto3Impl

proto8           typedef ptr Proto8Impl

When I defined such a table, I did it once, for 1 to 15 parameters, stuck it into an .inc file, and re-use it all the time. Finally, you need to somehow change the function names, one name for the table member, 2nd for the actual proc. I'll preface the proc name with the table name (which in COM means it preface with the interface name). So the stubs for these procs look like this:


FunctionA_Impl PROC  p1, p2
	ret
FunctionA_Impl ENDP


FunctionB_Impl PROC   p1, p2, p3
	ret
FunctionB_Impl ENDP


FunctionC_Impl PROC  p1, p2, p3, p4, p5, p6, p7, p8
	ret
FunctionC_Impl ENDP

Posted on 2001-03-05 19:24:00 by Ernie

Is this possible?

Here is my example of message crackers (plus a few other things) Please comment. While I did a bit of asm work in the past I'm real rusty. James www.jcfuller.com/RTDASM.ZIP This message was edited by jcfuller, on 3/6/2001 9:42:31 AM This message was edited by jcfuller, on 3/6/2001 9:45:06 AM This message was edited by jcfuller, on 3/6/2001 9:45:58 AM

Posted on 2001-03-06 09:40:00 by jcfuller

Is this possible?

Thanks everyone who replied, that should work perfectly.

Posted on 2001-03-06 16:34:00 by Zadkiel

ASM Community