Re: windows static archive, missing symbols

[Howard Chu]

Bob Rossi wrote:
> Hi,
>
> I've got a quick question hopefully. I'm building pcre on windows. I've
> been able to build it into a dll and link against it with a small
> program. However, when I build a static library, and link it with a
> small program, I get the missing symbols error. 
>
> I know the symbols are in the library because nm tells me so,
>   $ nm -g /home/bobbybrasko/download/pcre/pcre/install/lib/libpcre.a|grep compile                         
>   libpcre_la-pcre_compile.o:                                                                              
>   00005550 T _pcre_compile                                                                                
>
> Here is the link line of the small program,
>   $ gcc-4.1 -g -Wall -o test test.c 
> -L/home/bobbybrasko/download/pcre/pcre/install/lib \
>     -lpcreposix -lpcre 
>   -I/home/bobbybrasko/download/pcre/pcre/install/include                                                  
>   C:/WINDOWS/TEMP/ccgGAsIC.o(.text+0x2e): In function `main':                                             
>   C:/msys/1.0/home/bobbybrasko/download/pcre/pcre/build/tmp/test.c:13: 
>     undefined reference to `_imp__pcre_compile'                                                                                                collect2: ld returned 1 exit status                                                                     
>
> Does anyone understand why I'd be getting these errors? Are .def files
> important for static windows libraries or only for dll's? Any advice?
>   
First of all, obviously "_imp__pcre_compile" is not the same as 
"_pcre_compile" so the error message is legitimate - the symbol that 
it's actually looking for is not there.

The next question is, why is it looking for an import symbol instead of 
using the real symbol. The answer to that must lie in your header files; 
they probably declare the function to be a DLL export, which causes the 
compiler to generate references to an import symbol. Have a look at your 
header files. Remove any DLL declspec's on any function declarations you 
find there; modern linkers don't need them. I.e., the GNU linker is 
smart enough to use an import symbol in place of a reference to a real 
symbol. Apparently it won't do the opposite.

Unfortunately if a library exports variables as well, you need to 
preserve the export declspecs there. This means for any Windows library 
that you use, you have to know whether you will be using a static or a 
dynamic version, whenever compiling an app that uses the library. Very 
braindead, and there's no solution to that problem. The workaround is to 
never export variables from your libraries, only functions/accessor methods.

--
 -- Howard Chu
 Chief Architect, Symas Corp.  http://www.symas.com
 Director, Highland Sun        http://highlandsun.com/hyc
 OpenLDAP Core Team            http://www.openldap.org/project/