For one reason or another you may find yourself with a Linux shared library that you want to use as if it was a Windows Dll. There are various reasons for this including the following: You are porting a large application that uses several third-party libraries. One is available on Linux but you are not yet ready to link to it directly as a Linux shared library. (The ODBC interface in WINE). There is a well-defined interface available and there are several Linux solutions that are available for it. The process for dealing with these situations is actually quite simple. You need to write a spec file that will describe the library's interface in the same format as a Dll (primarily what functions it exports). Also you will want to write a small wrapper around the library. We combine these to form a Wine builtin Dll that links to the Linux library. In this section we will look at two examples. The first example is extremely simple and leads into the subject in "baby steps". The second example is the ODBC interface proxy in Wine. The files to which we will refer for the ODBC example are currently in the dlls/odbc32 directory of the Wine source. The first example is based very closely on a real case (the names of the functions etc. have been changed to protect the innocent). A large Windows application includes a DLL that links to a third-party DLL. For various reasons the third-party DLL does not work too well under Wine. However the third-party DLL is also available for the Linux environment. Conveniently the DLL and Linux shared library export only a small number of functions and the application only uses one of those. Specifically, the application calls a function: signed short WINAPI MyWinFunc (unsigned short a, void *b, void *c, unsigned long *d, void *e, unsigned char f, char g, unsigned char *h); and the linux library exports a corresponding function: signed short MyLinuxFunc (unsigned short a, void *b, void *c, unsigned short *d, void *e, char g, unsigned char *h); Start by writing the spec file. This file will describe the interface as if it was a dll. See elsewhere for the details of the format of a spec file. In the simple example we want a Wine builtin Dll that corresponds to the MyWin Dll. The spec file is libMyWin.spec and looks like this. # # File: libMyWin.spec # # some sort of copyright # # Wine spec file for the libMyWin builtin library (a minimal wrapper around the # linux library libMyLinux) # # For further details of wine spec files see the Winelib documentation at # www.winehq.com name MyWin type win32 mode dll 2 stdcall _MyWinFunc@32 (long ptr ptr ptr ptr long long ptr) MyProxyWinFunc # End of file Notice that the arguments are flagged as long even though they are smaller than that. In the case of the ODBC example you can see this in the file odbc32.spec. names are mangled, how to demangle them, how to call them Firstly we will look at the simple example. The main complication of this case is the slightly different argument lists. The f parameter does not have to be passed to the Linux function and the d parameter (theoretically) has to be converted between unsigned long * and unsigned short *. Doing this ensures that the "high" bits of the returned value are set correctly. /* * File: MyWin.c * * Copyright (c) The copyright holder. * * Basic WINE wrapper for the linux <3rd party library> so that it can be * used by <the application> * * Currently this file makes no attempt to be a full wrapper for the <3rd * party library>; it only exports enough for our own use. * * Note that this is a Unix file; please don't go converting it to DOS format * (e.g. converting line feeds to Carriage return/Line feed). * * This file should be built in a Wine environment as a WineLib library, * linked to the Linux <3rd party> libraries (currently libxxxx.so and * libyyyy.so) */ #include < <3rd party linux header> > #include <windef.h> /* Part of the Wine header files */ signed short WINAPI MyProxyWinFunc (unsigned short a, void *b, void *c, unsigned long *d, void *e, unsigned char f, char g, unsigned char *h) /* This declaration is as defined in the spec file. It is deliberately not * specified in terms of <3rd party> types since we are messing about here * between two operating systems (making it look like a Windows thing when * actually it is a Linux thing). In this way the compiler will point out any * inconsistencies. * For example the fourth argument needs care */ { unsigned short d1; signed short ret; d1 = (unsigned short) *d; ret = <3rd party linux function> (a, b, c, &d1, e, g, h); *d = d1; return ret; } /* End of file */ For a more extensive case we can use the ODBC example. This is implemented as a header file (proxyodbc.h) and the actual C source file (proxyodbc.c). Although the file is quite long it is extremely simple in structure. The MAIN_OdbcInit function is the function that was named in the spec file as the init function. On the process attach event the function dynamically links to the desired Linux ODBC library (since there are several available) and builds a list of function pointers. It unlinks on the process detach event. Then each of the functions simply calls the appropriate Linux function through the function pointer that was set up during initialisation. So how dow we actually build the Wine builtin Dll? The easiest way is to get Winemaker to do the hard work for us. For the simple example we have two source files (the wrapper and the spec file). We also have the 3rd party header and library files of course. Put the two source files in a suitable directory and then use winemaker to create the build framework, including configure script, makefile etc. You will want to use the following options of winemaker: --nosource-fix and --nogenerate-specs (requires winemaker version 0.5.8 or later) to ensure that the two files are not modified. (If using an older version of winemaker then make the two files readonly and ignore the complaints about being unable to modify them). --dll --single-target MyWin --nomfc to specify the target -DMightNeedSomething -I3rd_party_include -L3rd_party_lib -lxxxx -lyyyy where these are the locations of the header files etc. After running winemaker I like to edit the Makefile.in to add the line CEXTRA = -Wall just before the DEFINES =. Then simply run the configure and make as normal (described elsewhere).