compat/win32/lazyload.h

   1 #ifndef LAZYLOAD_H
   2 #define LAZYLOAD_H
   3
   4 /*
   5  * A pair of macros to simplify loading of DLL functions. Example:
   6  *
   7  *   DECLARE_PROC_ADDR(kernel32.dll, BOOL, CreateHardLinkW,
   8  *                     LPCWSTR, LPCWSTR, LPSECURITY_ATTRIBUTES);
   9  *
  10  *   if (!INIT_PROC_ADDR(CreateHardLinkW))
  11  *           return error("Could not find CreateHardLinkW() function";
  12  *
  13  *   if (!CreateHardLinkW(source, target, NULL))
  14  *           return error("could not create hardlink from %S to %S",
  15  *                        source, target);
  16  */
  17
  18 struct proc_addr {
  19         const char *const dll;
  20         const char *const function;
  21         FARPROC pfunction;
  22         unsigned initialized : 1;
  23 };
  24
  25 /* Declares a function to be loaded dynamically from a DLL. */
  26 #define DECLARE_PROC_ADDR(dll, rettype, function, ...) \
  27         static struct proc_addr proc_addr_##function = \
  28         { #dll, #function, NULL, 0 }; \
  29         typedef rettype (WINAPI *proc_type_##function)(__VA_ARGS__); \
  30         static proc_type_##function function
  31
  32 /*
  33  * Loads a function from a DLL (once-only).
  34  * Returns non-NULL function pointer on success.
  35  * Returns NULL + errno == ENOSYS on failure.
  36  * This function is not thread-safe.
  37  */
  38 #define INIT_PROC_ADDR(function) \
  39         (function = (proc_type_##function)get_proc_addr(&proc_addr_##function))
  40
  41 static inline FARPROC get_proc_addr(struct proc_addr *proc)
  42 {
  43         /* only do this once */
  44         if (!proc->initialized) {
  45                 HANDLE hnd;
  46                 proc->initialized = 1;
  47                 hnd = LoadLibraryExA(proc->dll, NULL,
  48                                      LOAD_LIBRARY_SEARCH_SYSTEM32);
  49                 if (hnd)
  50                         proc->pfunction = GetProcAddress(hnd, proc->function);
  51         }
  52         /* set ENOSYS if DLL or function was not found */
  53         if (!proc->pfunction)
  54                 errno = ENOSYS;
  55         return proc->pfunction;
  56 }
  57
  58 #endif