Linking C++ and Assembly

HELP!

Hi, I'm trying to link an assembly procedure to my C++ project, I'm using Visual C++ 2005.

I'm getting an error:

DecodeB64.obj : error LNK2019: unresolved external symbol _Base64_Decode referenced in function _main

I added both the .asm and the .cpp files to my project.
In my cpp file:

Code:

#define	DWORD	unsigned int

extern "C" DWORD Base64_Decode(char *, DWORD, char *);

and in main:

Code:

dwDataLen = Base64_Decode(cpInputBuffer, dwFileSize, cpOutputBuffer);

my .asm file:

Code:

public _Base64_Decode
.386
.MODEL    flat, stdcall

.CODE

_Base64_Decode    proc

	local  InputLen : dword
	local  InputBuf : dword
	local  OutputBuf : dword

	pop    InputBuf
	pop    InputLen
	pop    OutputBuf

	pushad
	
	mov    ecx,InputLen
	mov    esi,InputBuf

	ASCII_TO_B64_LOOP:

		mov    ah,[esi]
		cmp    ah,61h    ;compare to 'a'
		jl     CMP_CAPS
		sub    ah,47h
		jmp    NEXT
	    
		CMP_CAPS:
		cmp    ah,41h    ;compare to 'A'
		jl     CMP_PAD
		sub    ah,41h
		jmp    NEXT
	    
		CMP_PAD:
		cmp    ah,3D     ;compare to '='
		jne    CMP_NUMERAL
		mov    ah,0h
		jmp    NEXT
	    
		CMP_NUMERAL:
		cmp    ah,30h    ;compare to '0'
		jl     SYMBOL
		add    ah,4h
		jmp    NEXT
	    
		SYMBOL:
		cmp    ah,2Fh    ;compare to '/'
		jl     PLUS
		mov    ah,3Fh
		jmp    NEXT
	    
		PLUS:            ;it's '+'     
		mov    ah,3Eh
		jmp    NEXT
	    
		NEXT:
		inc    esi
	                  
	loopw  ASCII_TO_B64_LOOP

	mov    edi,OutputBuf
	mov    esi,InputBuf
	mov    ecx,InputLen
	xor    edx,edx
	mov    eax,4h
	div    ecx
	mov    ecx,eax

	DECODING_LOOP:

		mov    ah,[esi]
		mov    al,[esi+1]
		shl    al,2
		mov    bl,ah
		mov    dh,al
		shld   bx,dx,2
		mov    ah,bl
		mov    [edi],ah
		inc    edi
		inc    esi
	    
		mov    ah,[esi]
		mov    al,[esi+1]
		shl    al,2
		mov    bl,ah
		mov    dh,al
		shld   bx,dx,4
		mov    ah,bl
		mov    [edi],ah
		inc    edi
		inc    esi

		mov    ah,[esi]
		mov    al,[esi+1]
		shl    al,2
		mov    bl,ah
		mov    dh,al
		shld   bx,dx,6
		mov    ah,bl
		mov    [edi],ah
		inc    edi
		inc    esi

		inc    esi

	loopd  DECODING_LOOP

	popad
	
	mov    dx,0h
	mov    ax,sizeof OutputBuf

	ret

_Base64_Decode  endp

end

Hmm. Are you sure the assembler isn't prepending the underscore automatically? I'm not sure, but if you declare a function as "stdcall" it might do that for you. You might try removing the leading underscore from the assembly source file and see if that will link.

I've tried that, should I remove the underscore from all three places where it says _Bit64_Decode? Or just from the first place?

Originally Posted by Warlax

I've tried that, should I remove the underscore from all three places where it says _Bit64_Decode? Or just from the first place?

I'd try removing it everywhere from the .asm file and see if that helps. Failing that, try dumping the contents of the .asm object file and see what symbols are getting put in there.

Originally Posted by brewbuck

I'd try removing it everywhere from the .asm file and see if that helps. Failing that, try dumping the contents of the .asm object file and see what symbols are getting put in there.

Well, I tried removing the underscore in the public statement but not in the procedure name, it failed, I tried the opposite, it failed, it tried without an underscore on all three, it failed and also with an underscore on everything it failed...

What do you mean by dumping?

Use a program called objdump to list the exports of a compiled assembly object file. objdump /EXPORTS blah.o

I found how to use objdump - and it seems the compiler IS adding '_' automatically, but now that I know that, how do I solve the external linking problem?????