How to define local string in MASM?

[alaphate]

Just like C

function MyProc()

{

char szTemp[] = "Hello World!"

}

In MASM:

MyProc PROC

local szTemp:byte

MyProc ENDP

The problem is how to transfer "Hello World!" to szTemp, WITHOUT defining global variable in .DATA segment.

I figured out one way, but it will not be the best way.

MyProc PROC

local szTemp[128]:byte

mov al, 48h ;ASCII of 'H'

mov szTemp, al

mov al,65h ;ASCII of 'e'

mov szTemp+1, al

;etc...

MyProc ENDP

Could any buddy suggest me better solutions?

Thanks in advance.

Edited April 22, 2009 by alaphate

[diablo2oo2]

myproc proc local sztemp[128]:byte;---method 1----
 fn lstrcpy,addr sztemp,"hello world" ;helloworld will be copied from .data section to sztemp;---method 2---
 jmp @F
 hello_world db "hello world",0 ;string is in .code section here
 @@:
 fn lstrcpy,addr sztemp,addr hello_world
;---method 3---
 mov sztemp[0],"h"	;chars are stored as constant in .code section , same as method 2, but stupid
 mov sztemp[1],"e"
 mov sztemp[2],"l"
;---method 4 (without api function)---
 lea edi,sztemp
 mov esi,offset hello_world
 mov ecx,sizeof hello_world
 rep movsb
 ...
  ret
myproc endp

Edited April 22, 2009 by diablo2oo2

[MACH4]

;---method 2---

jmp @F

hello_world db "hello world",0 ;string is in .code section here

@@:

fn lstrcpy,addr sztemp,addr hello_world

If the intention is to hide the string in a procedure then this one is not too good, it will be seen as hard coded text in a dissembly.

MACH4

[alaphate]

diablo2oo2,

Thank you for reply.

Using method 1, I got compiling error:

error A2084: struction or register not accepted in current CPU mode

.386
.model flat, stdcall
include user32.inc
include kernel32.inc.data
szCaption  db "WIN32 ASM",0.code
main proc
  local szTemp[128]:byte
  invoke lstrcpy, addr szTemp, "Hello World!"
  invoke MessageBoxA, 0, ADDR szTemp, ADDR szCaption, 0
  invoke ExitProcess, 0
main endp
end main

In Method 4, Need I add:

move ax,ds

mov es,ds

;before

lea edi,szTemp

because the dest String address should be ES:EDI

I'm not sure whether ES is same to DS or not in FLAT model.

Edited April 22, 2009 by alaphate

[diablo2oo2]

diablo2oo2,

Thank you for reply.

Using method 1, I got compiling error:

error A2084: struction or register not accepted in current CPU mode

.386
.model flat, stdcall
include user32.inc
include kernel32.inc.data
szCaption  db "WIN32 ASM",0.code
main proc
  local szTemp[128]:byte
  invoke lstrcpy, addr szTemp, "Hello World!"
  invoke MessageBoxA, 0, ADDR szTemp, ADDR szCaption, 0
  invoke ExitProcess, 0
main endp
end main

use latest MASM version. MASM is so powerfull because of its macros. use them! one of this macros is the "fn"macro. Use the "fn" command instead "invoke". the "fn" instruction will allow you to use strings like in c. so you don not need to put them to .data section! there is also a macro called "fnc", its used for c-style escape characters like "hello\nworld". \n is nextline. see masm helpfiles for more information.

Also you don't need to add an "A" to apinames.masm uses ansi api functions by default. but if you want to use the unicodeformat you must add an "W" to the name.

here is my file:

.586p
.mmx			
.model flat, stdcall
option casemap :noneinclude				\masm32\include\windows.inc
include				\masm32\include\user32.inc
include				\masm32\include\kernel32.inc
include				\masm32\include\masm32.inc
include				\masm32\macros\macros.asmincludelib			\masm32\lib\user32.lib
includelib			\masm32\lib\kernel32.lib
includelib			\masm32\lib\masm32.lib.data.code
main proc
  local szTemp[128]:byte  fn lstrcpy, addr szTemp, "Hello World!"
  fn MessageBox, 0, addr szTemp, "WIN32 ASM", MB_ICONINFORMATION  fn ExitProcess, 0
main endpend main

Edited April 22, 2009 by diablo2oo2

[alaphate]

diablo2oo2,

The fnc macro is so useful, thank you.

Here's another question.

In Method 4, Need I add:

move ax,ds

mov es,ax

;before

lea edi,szTemp

because the dest String address should be ES:EDI

I'm not sure whether ES is same to DS or not in FLAT model.

Edited April 22, 2009 by alaphate

[diablo2oo2]

diablo2oo2,

The fnc macro is so useful, thank you.

Here's another question.

In Method 4, Need I add:

move ax,ds

mov es,ax

;before

lea edi,szTemp

because the dest String address should be ES:EDI

I'm not sure whether ES is same to DS or not in FLAT model.

i dont understand this "old" assembler stuff with "ds,es,int..." i code only win32 assembly with highlevel language syntax (.if .else..). and it's ok, its all i need.

[alaphate]

I used debug to check the register's value.

DS == ES

You are right, no need transfer DS to ES.

Thank you for your 4 methods. I learned a lot. Thx!

Edited April 22, 2009 by alaphate

[D1N]

use latest MASM version. MASM is so powerfull because of its macros. use them! one of this macros is the "fn"macro. Use the "fn" command instead "invoke". the "fn" instruction will allow you to use strings like in c. so you don not need to put them to .data section! there is also a macro called "fnc", its used for c-style escape characters like "hello\nworld". \n is nextline. see masm helpfiles for more information.

@diablo2oo2

I think this was one of the coolest things they did with MASM adding the fn macro. fnc is good as well ive used it for new lines\n.

Nice methods.

[EvOlUtIoN]

to solve this problem, just use functions provided by masm lib...you'll do anithing you want.

[Ksbunker]

Similiar to method 2, but a bit more difficult to step with Olly;

To figure out why this MACRO works you must know how the CALL instruction works. CALLs changes EIP to new destination address and pushes return EIP after the CALL instruction into ESP. So this MACRO pushes the return instruction (i.e. OFFSET "string") into ESP. If you try to step through the code, you will cease execution at the szCALL "string" or "00401004 . E8 07000000 CALL gamespy.00401010".

	szCALL MACRO sz
		CALL @F
		BYTE sz, NULL
		@@:
 	ENDM
.CODE
start:	push 0
	push 0
	szCALL "string"
	push 0
	call MessageBox
	ret
end start

00401000 > $ 6A 00		  PUSH 0
00401002   . 6A 00		  PUSH 0
00401004   . E8 07000000	CALL gamespy.00401010				   ; stepping fails here
00401009   . 73 74		  JNB SHORT gamespy.0040107F
0040100B   . 72 69		  JB SHORT gamespy.00401076
0040100D   . 6E			 OUTS DX,BYTE PTR ES:[EDI]				
0040100E	 67			 DB 67								   
0040100F	 00			 DB 00
00401010   . 6A 00		  PUSH 0								   
00401012   . E8 01000000	CALL <JMP.&user32.MessageBoxA>			
00401017   . C3			 RETN
00401018   $-FF25 00204000  JMP DWORD PTR DS:[<&user32.MessageBoxA>];  user32.MessageBoxA

Similiar to method 3, but a bit more non-sequitor;

OPTION PROLOGUE:NONE		
OPTION EPILOGUE:NONE	StackSZ PROTO		  
		push ebp		  
		mov ebp, esp		  
		sub esp, 4		  
		mov dword ptr [ebp-4], "321"; MOV DWORD PTR SS:[EBP-4],796548		  
		mov eax, ebp		  
		sub eax, 4		  
		INVOKE MessageBox, 0, eax, 0, 0; eax = "123", NULL   
		add esp, 4		  
		leave		  
		ret		
	StackSZ ENDPOPTION PROLOGUE:PrologueDef		
OPTION EPILOGUE:EpilogueDef

[SunBeam]

Pretty cool info. That damn "fn" macro is what I've been looking for all along - I always had stupid errors with INVOKE regarding PERFECTLY written params for some APIs or functions. FN helps a lot! Good show everyone!