ASM Community

Hi,

the following small prog compiles and linkes without errors:

        .386

        .Model flat,stdcall

		option casemap:none



	.nolist

	.nocref

	include \masm32\include\windows.inc

	include \masm32\include\kernel32.inc

	include \masm32\include\user32.inc

	.list

	.cref



CStr macro y:req

local sym

CONST segment dword public 'DATA'

ifidni <y>,<"">

sym db 0

else

sym db y,0

endif

CONST ends

	exitm <offset sym>

	endm



	.data



szDef db "default",0



    .code



DisplayLine proto :ptr byte



WinMain proc hInst:HINSTANCE,hPrevInst:HINSTANCE,lpszCmdLine:ptr byte,iCmdShow:sdword



	local var1:dword



;	nop						; program executes ok if activated

    mov eax,CStr("Hello")

	invoke DisplayLine,eax

	xor eax,eax

	ret



WinMain	endp



DisplayLine PROC pString:ptr byte



	local var1:dword



	mov 	eax,pString

	.IF (eax == 0)

		mov eax,offset szDef

	.ENDIF

	invoke MessageBox,0,eax,0,MB_OK

	ret

DisplayLine ENDP



WinMainCRTStartup proc



		invoke GetModuleHandle,0

		invoke WinMain,eax,0,0,0

		invoke ExitProcess,eax

        ret



WinMainCRTStartup endp



        end

but the generated code crashes. If the "nop" line in proc WinMain is activated, the prog runs ok.


the generated listing file is very interesting. Heres an excerpt:

 00000000			WinMain proc hInst:HINSTANCE,hPrevInst:HINSTANCE,lpszCmdLine:ptr byte,iCmdShow:sdword



					local var1:dword



				;	nop						; program executes ok if activated

 00000000  55		   *	    push   ebp

 00000001  8B EC	   *	    mov    ebp, esp

 00000003  83 C4 FC	   *	    add    esp, 0FFFFFFFCh

 00000000		     1	CONST segment dword public 'DATA'

 00000000 48 65 6C 6C 6F     1	??0019 db "Hello",0

	   00

 00000006		     1	CONST ends

 00000006  B8 00000000 R	    mov eax,CStr("Hello")

					invoke DisplayLine,eax

 0000000B  50		   *	    push   eax

 0000000C  E8 00000000	   *	    call   DisplayLine

 00000011  33 C0			xor eax,eax

					ret

 00000013  C9		   *	    leave  

 00000014  C2 0010	   *	    ret    00010h



 00000017			WinMain	endp



 00000017			DisplayLine PROC pString:ptr byte



					local var1:dword



 00000017  55		   *	    push   ebp

 00000018  8B EC	   *	    mov    ebp, esp

 0000001A  83 C4 FC	   *	    add    esp, 0FFFFFFFCh

 0000001D  8B 45 08			mov 	eax,pString

					.IF (eax == 0)

 00000020  0B C0	   *	    or	eax, eax

 00000022  75 FF	   *	    jne    @C0001

 00000024  B8 00000000 R			mov eax,offset szDef

					.ENDIF

 00000023		   *@C0001:

					invoke MessageBox,0,eax,0,MB_OK

 00000023  6A 00	   *	    push   +000000000h

 00000025  6A 00	   *	    push   +000000000h

 00000027  50		   *	    push   eax

 00000028  6A 00	   *	    push   +000000000h

 0000002A  FF 15 00000000 E *	    call   _imp__MessageBoxA@16

					ret

Have a look at eip 00000024. Here masm calculates wrong as eip of next line is 00000023.

Problem seems to be the use of macro CStr, but only if it is used in the first line of a proc (and the error becomes visible only in the next proc?!?)

Has anyone had a similar problem? Or could anyone explain what is wrong?

japheth

Correct me if I am wrong but there is no indicator to the assembler where the program starts and stops.

Would it work if you used "Start:" and "End Start" ?

Regards,

hutch@movsd.com

This sounds like a MASM bug. Any instruction that you put after "local var1:DWORD" makes the program works perfectly. Replace nop with anything you want and it will work

Naaaa...

Its just his funny code. :)


I comment out and replaced these two lines and all works well...

;CONST segment dword public 'DATA'

.data



...



;CONST ends

.code

I cant say i know where one learns that form (seen others use simular stuff), but .data and .code always worked for me... and seems to be winning the race at this point :)

Hope this helps..
:alright:
NaN

to define string pointers in the any section you can use this macro.

$TO MACRO sText

; $TO defines text both in .data or .code sections and returns its offset

local szText, SegName

	SegName TEXTEQU @CurSeg

	.data

	IF @SizeStr(<sText>) NE 0

		szText db sText, 0

	ELSE

		szText db 0

	ENDIF

	@CurSeg ENDS

	SegName SEGMENT

	EXITM <offset szText>

ENDM

Works fine in your code.