Fix shared module support on Windows

Unlike Linux and OS X, when a library is loaded, all the symbols aren't
loaded into a single namespace. You must fetch the symbol by iterating over
all loaded modules.

So, we shouldn't use /FORCE:UNRESOLVED since that is not what modules do
on Windows. Instead, we now do exactly what GModule does on Windows.

Also use `void` for functions that take no arguments.

mesonbuild/compilers.py

@@ -1926,9 +1926,6 @@ class VisualStudioCCompiler(CCompiler):
         pdbarr += ['pdb']
         return ['/DEBUG', '/PDB:' + '.'.join(pdbarr)]
 
-    def get_std_shared_module_link_args(self):
-        return ['/DLL', '/FORCE:UNRESOLVED']
-
 class VisualStudioCPPCompiler(VisualStudioCCompiler, CPPCompiler):
     def __init__(self, exelist, version, is_cross, exe_wrap):
         self.language = 'cpp'

test cases/common/125 shared module/module.c

@@ -9,6 +9,54 @@
   #endif
 #endif
 
+#ifdef _WIN32
+
+#include <stdio.h>
+#include <windows.h>
+#include <tlhelp32.h>
+
+typedef int (*fptr) (void);
+
+/* Unlike Linux and OS X, when a library is loaded, all the symbols aren't
+ * loaded into a single namespace. You must fetch the symbol by iterating over
+ * all loaded modules. Code for finding the function from any of the loaded
+ * modules is taken from gmodule.c in glib */
+fptr find_any_f (const char *name) {
+    fptr f;
+    HANDLE snapshot;
+    MODULEENTRY32 me32;
+
+    snapshot = CreateToolhelp32Snapshot (TH32CS_SNAPMODULE, 0);
+    if (snapshot == (HANDLE) -1) {
+        printf("Could not get snapshot\n");
+        return 0;
+    }
+
+    me32.dwSize = sizeof (me32);
+
+    f = NULL;
+    if (Module32First (snapshot, &me32)) {
+        do {
+            if ((f = (fptr) GetProcAddress (me32.hModule, name)) != NULL)
+                break;
+        } while (Module32Next (snapshot, &me32));
+    }
+
+    CloseHandle (snapshot);
+    return f;
+}
+
+int DLL_PUBLIC func() {
+    fptr f;
+
+    f = find_any_f ("func_from_language_runtime");
+    if (f != NULL)
+        return f();
+    printf ("Could not find function\n");
+    return 1;
+}
+
+#else
 /*
  * Shared modules often have references to symbols that are not defined
  * at link time, but which will be provided from deps of the executable that
@@ -17,6 +65,7 @@
  */
 int func_from_language_runtime();
 
-int DLL_PUBLIC func() {
+int DLL_PUBLIC func(void) {
     return func_from_language_runtime();
 }
+#endif

test cases/common/125 shared module/prog.c

@@ -1,38 +1,102 @@
+
+#include <stdio.h>
+
+int func_from_language_runtime(void);
+typedef int (*fptr) (void);
+
 #ifdef _WIN32
-// FIXME: add implementation using Winapi functions for dlopen.
 
-int main(int argc, char **argv) {
-    return 0;
+#include <windows.h>
+
+wchar_t*
+win32_get_last_error (void)
+{
+    wchar_t *msg = NULL;
+
+    FormatMessageW (FORMAT_MESSAGE_ALLOCATE_BUFFER
+                    | FORMAT_MESSAGE_IGNORE_INSERTS
+                    | FORMAT_MESSAGE_FROM_SYSTEM,
+                    NULL, GetLastError (), 0,
+                    (LPWSTR) &msg, 0, NULL);
+    return msg;
+}
+
+int
+main (int argc, char **argv)
+{
+    HINSTANCE handle;
+    fptr importedfunc;
+    int expected, actual;
+    int ret = 1;
+
+    handle = LoadLibraryA (argv[1]);
+    if (!handle) {
+        wchar_t *msg = win32_get_last_error ();
+        printf ("Could not open %s: %S\n", argv[1], msg);
+        goto nohandle;
+    }
+
+    importedfunc = (fptr) GetProcAddress (handle, "func");
+    if (importedfunc == NULL) {
+        wchar_t *msg = win32_get_last_error ();
+        printf ("Could not find 'func': %S\n", msg);
+        goto out;
+    }
+
+    actual = importedfunc ();
+    expected = func_from_language_runtime ();
+    if (actual != expected) {
+        printf ("Got %i instead of %i\n", actual, expected);
+        goto out;
+    }
+
+    ret = 0;
+out:
+    FreeLibrary (handle);
+nohandle:
+    return ret;
 }
 
 #else
 
 #include<dlfcn.h>
 #include<assert.h>
-#include<stdio.h>
-
-int func();
-int func_from_language_runtime();
 
 int main(int argc, char **argv) {
     void *dl;
-    int (*importedfunc)();
-    int success;
+    fptr importedfunc;
+    int expected, actual;
     char *error;
+    int ret = 1;
 
     dlerror();
     dl = dlopen(argv[1], RTLD_LAZY);
     error = dlerror();
     if(error) {
         printf("Could not open %s: %s\n", argv[1], error);
-        return 1;
+        goto nodl;
     }
-    importedfunc = (int (*)()) dlsym(dl, "func");
-    assert(importedfunc);
+
+    importedfunc = (fptr) dlsym(dl, "func");
+    if (importedfunc == NULL) {
+        printf ("Could not find 'func'\n");
+        goto out;
+    }
+
     assert(importedfunc != func_from_language_runtime);
-    success = (*importedfunc)() == func_from_language_runtime();
+
+    actual = (*importedfunc)();
+    expected = func_from_language_runtime ();
+    if (actual != expected) {
+        printf ("Got %i instead of %i\n", actual, expected);
+        goto out;
+    }
+
+    ret = 0;
+out:
     dlclose(dl);
-    return !success;
+nodl:
+    return ret;
 }
 
 #endif

test cases/common/125 shared module/runtime.c

@@ -14,6 +14,6 @@
  * modules.
  */
 
-int DLL_PUBLIC func_from_language_runtime() {
+int DLL_PUBLIC func_from_language_runtime(void) {
     return 86;
 }