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:

Quote:

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

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

Code:

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#define        DWORD        unsigned int

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

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and in main:

Code:

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dwDataLen = Base64_Decode(cpInputBuffer, dwFileSize, cpOutputBuffer);

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my .asm file:

Code:

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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

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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?

Quote:

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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?

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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.

Quote:

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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.

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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?????