bpo-36085: Enable better DLL resolution on Windows (GH-12302)

Modules/posixmodule.c

@@ -1442,17 +1442,23 @@ win32_error(const char* function, const char* filename)
 }
 
 static PyObject *
-win32_error_object(const char* function, PyObject* filename)
+win32_error_object_err(const char* function, PyObject* filename, DWORD err)
 {
     /* XXX - see win32_error for comments on 'function' */
-    errno = GetLastError();
     if (filename)
         return PyErr_SetExcFromWindowsErrWithFilenameObject(
                     PyExc_OSError,
-                    errno,
+                    err,
                     filename);
     else
-        return PyErr_SetFromWindowsErr(errno);
+        return PyErr_SetFromWindowsErr(err);
+}
+
+static PyObject *
+win32_error_object(const char* function, PyObject* filename)
+{
+    errno = GetLastError();
+    return win32_error_object_err(function, filename, errno);
 }
 
 #endif /* MS_WINDOWS */
@@ -13161,6 +13167,113 @@ error:
 }
 #endif   /* HAVE_GETRANDOM_SYSCALL */
 
+#ifdef MS_WINDOWS
+/* bpo-36085: Helper functions for managing DLL search directories
+ * on win32
+ */
+
+typedef DLL_DIRECTORY_COOKIE (WINAPI *PAddDllDirectory)(PCWSTR newDirectory);
+typedef BOOL (WINAPI *PRemoveDllDirectory)(DLL_DIRECTORY_COOKIE cookie);
+
+/*[clinic input]
+os._add_dll_directory
+
+    path: path_t
+
+Add a path to the DLL search path.
+
+This search path is used when resolving dependencies for imported
+extension modules (the module itself is resolved through sys.path),
+and also by ctypes.
+
+Returns an opaque value that may be passed to os.remove_dll_directory
+to remove this directory from the search path.
+[clinic start generated code]*/
+
+static PyObject *
+os__add_dll_directory_impl(PyObject *module, path_t *path)
+/*[clinic end generated code: output=80b025daebb5d683 input=1de3e6c13a5808c8]*/
+{
+    HMODULE hKernel32;
+    PAddDllDirectory AddDllDirectory;
+    DLL_DIRECTORY_COOKIE cookie = 0;
+    DWORD err = 0;
+
+    /* For Windows 7, we have to load this. As this will be a fairly
+       infrequent operation, just do it each time. Kernel32 is always
+       loaded. */
+    Py_BEGIN_ALLOW_THREADS
+    if (!(hKernel32 = GetModuleHandleW(L"kernel32")) ||
+        !(AddDllDirectory = (PAddDllDirectory)GetProcAddress(
+            hKernel32, "AddDllDirectory")) ||
+        !(cookie = (*AddDllDirectory)(path->wide))) {
+        err = GetLastError();
+    }
+    Py_END_ALLOW_THREADS
+
+    if (err) {
+        return win32_error_object_err("add_dll_directory",
+                                      path->object, err);
+    }
+
+    return PyCapsule_New(cookie, "DLL directory cookie", NULL);
+}
+
+/*[clinic input]
+os._remove_dll_directory
+
+    cookie: object
+
+Removes a path from the DLL search path.
+
+The parameter is an opaque value that was returned from
+os.add_dll_directory. You can only remove directories that you added
+yourself.
+[clinic start generated code]*/
+
+static PyObject *
+os__remove_dll_directory_impl(PyObject *module, PyObject *cookie)
+/*[clinic end generated code: output=594350433ae535bc input=c1d16a7e7d9dc5dc]*/
+{
+    HMODULE hKernel32;
+    PRemoveDllDirectory RemoveDllDirectory;
+    DLL_DIRECTORY_COOKIE cookieValue;
+    DWORD err = 0;
+
+    if (!PyCapsule_IsValid(cookie, "DLL directory cookie")) {
+        PyErr_SetString(PyExc_TypeError,
+            "Provided cookie was not returned from os.add_dll_directory");
+        return NULL;
+    }
+
+    cookieValue = (DLL_DIRECTORY_COOKIE)PyCapsule_GetPointer(
+        cookie, "DLL directory cookie");
+
+    /* For Windows 7, we have to load this. As this will be a fairly
+       infrequent operation, just do it each time. Kernel32 is always
+       loaded. */
+    Py_BEGIN_ALLOW_THREADS
+    if (!(hKernel32 = GetModuleHandleW(L"kernel32")) ||
+        !(RemoveDllDirectory = (PRemoveDllDirectory)GetProcAddress(
+            hKernel32, "RemoveDllDirectory")) ||
+        !(*RemoveDllDirectory)(cookieValue)) {
+        err = GetLastError();
+    }
+    Py_END_ALLOW_THREADS
+
+    if (err) {
+        return win32_error_object_err("remove_dll_directory",
+                                      NULL, err);
+    }
+
+    if (PyCapsule_SetName(cookie, NULL)) {
+        return NULL;
+    }
+
+    Py_RETURN_NONE;
+}
+
+#endif
 
 static PyMethodDef posix_methods[] = {
 
@@ -13349,6 +13462,10 @@ static PyMethodDef posix_methods[] = {
     OS_SCANDIR_METHODDEF
     OS_FSPATH_METHODDEF
     OS_GETRANDOM_METHODDEF
+#ifdef MS_WINDOWS
+    OS__ADD_DLL_DIRECTORY_METHODDEF
+    OS__REMOVE_DLL_DIRECTORY_METHODDEF
+#endif
     {NULL,              NULL}            /* Sentinel */
 };
 
@@ -13826,6 +13943,14 @@ all_ins(PyObject *m)
     if (PyModule_AddIntConstant(m, "_COPYFILE_DATA", COPYFILE_DATA)) return -1;
 #endif
 
+#ifdef MS_WINDOWS
+    if (PyModule_AddIntConstant(m, "_LOAD_LIBRARY_SEARCH_DEFAULT_DIRS", LOAD_LIBRARY_SEARCH_DEFAULT_DIRS)) return -1;
+    if (PyModule_AddIntConstant(m, "_LOAD_LIBRARY_SEARCH_APPLICATION_DIR", LOAD_LIBRARY_SEARCH_APPLICATION_DIR)) return -1;
+    if (PyModule_AddIntConstant(m, "_LOAD_LIBRARY_SEARCH_SYSTEM32", LOAD_LIBRARY_SEARCH_SYSTEM32)) return -1;
+    if (PyModule_AddIntConstant(m, "_LOAD_LIBRARY_SEARCH_USER_DIRS", LOAD_LIBRARY_SEARCH_USER_DIRS)) return -1;
+    if (PyModule_AddIntConstant(m, "_LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR", LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR)) return -1;
+#endif
+
     return 0;
 }