Article ID: 172393
Article Last Modified on 9/23/2003
APPLIES TO
- The Linker (LINK.EXE), when used with:
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 4.1 Subscription
- Microsoft Visual C++ 4.2 Professional Edition
- Microsoft Visual C++ 4.2 Enterprise Edition
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 4.2 Professional Edition
- Microsoft Visual C++ 5.0 Professional Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition
- Microsoft Visual C++ .NET 2002 Standard Edition
- Microsoft Visual C++ .NET 2003 Standard Edition
This article was previously published under Q172393
SYMPTOMS
When you are using the linker supplied with the Visual C++ compiler versions mentioned above to build a DLL and the following applies:
- You export multiple symbols from a DLL.
- The symbols differ only by the number of leading underscores or by the number of leading question marks.
- The first letter in the symbol is uppercase.
- The symbols are located in an assembly source file.
Then, the Visual C++ linker incorrectly matches some of the symbol names.
RESOLUTION
There are several workarounds:
- Do not use leading underscores or leading question marks to differentiate between different symbols. -or-
- Use Visual C or Visual C++ instead of assembly. -or-
- Use aliases in the EXPORTS section of the .def file as shown below. The left-hand side of the "=" symbol is the name of the function that is exported by the DLL and an external application/DLL can call. The right- hand side is the symbol the linker will use to match during the link phase. Note the missing underscore on the right hand side symbol.
EXPORTS_symbol1=symbol1
Use the following link command to build the DLL:
link -dll -out:MYDLL.LIB -def:MYDLL.DEF MYDLL.OBJ
STATUS
This behavior is by design.
MORE INFORMATION
The following sample code is used to demonstrate the third (last listed) workaround. The "-noentry" option is used for the linker in this sample because no entry point function is defined for the DLL. The "-map" option is used for comparison with the DUMPBIN output of exported symbols.
Assembler options needed: /nologo /coff /Cx /c
Linker options: -dll -noentry -map -out:MYDLL.LIB -def:MYDLL.DEF \ MYDLL.OBJ
TITLE mydll.asm
.386
.MODEL flat, SYSCALL
.CODE
Nosymbol PROC
ret
Nosymbol ENDP
_symbol PROC
ret
_symbol ENDP
__symbol PROC
ret
__symbol ENDP
___symbol PROC
ret
___symbol ENDP
____symbol PROC
ret
____symbol ENDP
_symbol1 PROC
ret
_symbol1 ENDP
__symbol2 PROC
ret
__symbol2 ENDP
___symbol3 PROC
ret
___symbol3 ENDP
____symbol4 PROC
ret
____symbol4 ENDP
END
Use the following module definition file to build the DLL:
; The module definition file MYDLL.DEF
EXPORTS
Nosymbol
_symbol=symbol
__symbol=_symbol
___symbol=__symbol
____symbol=___symbol
_symbol1=symbol1
__symbol2=_symbol2
___symbol3=__symbol3
____symbol4=___symbol4
Following are the contents of the mydll.map file:
mydll
Timestamp is 33e12fbb (Thu Jul 31 17:37:15 1997)
Preferred load address is 10000000
Start Length Name Class
0001:00000000 00000009H .text CODE
0002:00000000 000000e5H .edata DATA
Address Publics by Value Rva+Base Lib:Object
0001:00000000 Nosymbol 10001000 f mydll.obj
0001:00000001 _symbol 10001001 f mydll.obj
0001:00000002 __symbol 10001002 f mydll.obj
0001:00000003 ___symbol 10001003 f mydll.obj
0001:00000004 ____symbol 10001004 f mydll.obj
0001:00000005 _symbol1 10001005 f mydll.obj
0001:00000006 __symbol2 10001006 f mydll.obj
0001:00000007 ___symbol3 10001007 f mydll.obj
0001:00000008 ____symbol4 10001008 f mydll.obj
entry point at 0000:00000000
Static symbols
Compare the symbols of the above map file output with that of the "DUMPBIN /exports mydll.dll" output below.
Microsoft (R) COFF Binary File Dumper Version 5.00.7022
Copyright (C) Microsoft Corp 1992-1997. All rights reserved.
<BR/><BR/>
Dump of file mydll.dll
<BR/><BR/>
File Type: DLL
Section contains the following Exports for mydll.dll
0 characteristics
33E12FBA time date stamp Thu Jul 31 17:37:14 1997
0.00 version
1 ordinal base
9 number of functions
9 number of names
ordinal hint name
1 0 Nosymbol (00001000)
2 1 ____symbol (00001004)
3 2 ____symbol4 (00001008)
4 3 ___symbol (00001003)
5 4 ___symbol3 (00001007)
6 5 __symbol (00001002)
7 6 __symbol2 (00001006)
8 7 _symbol (00001001)
9 8 _symbol1 (00001005)
Summary
1000 .rdata
1000 .reloc
1000 .text
Keywords: kbprb KB172393
