warning: `extern` block uses type `std::boxed::Box<module::PamDataT>`, which is not FFI-safe
  --> /home/user/pam-rs/pam/src/module.rs:32:27
   |
32 |                     data: Box<PamDataT>,
   |                           ^^^^^^^^^^^^^ not FFI-safe
   |
   = note: `#[warn(improper_ctypes)]` on by default
   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
   = note: this struct has unspecified layout

warning: `extern` block uses type `std::boxed::Box<module::PamDataT>`, which is not FFI-safe
  --> /home/user/pam-rs/pam/src/module.rs:33:30
   |
33 |                       cleanup: extern "C" fn(pamh: *const PamHandle,
   |  ______________________________^
34 | |                                            data: Box<PamDataT>,
35 | |                                            error_status: PamResultCode))
   | |_______________________________________________________________________^ not FFI-safe
   |
   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
   = note: this struct has unspecified layout

warning: functions generic over types or consts must be mangled
  --> /home/user/pam-rs/pam/src/module.rs:55:1
   |
54 |   #[no_mangle]
   |   ------------ help: remove this attribute
55 | / pub extern "C" fn cleanup<T>(_: *const PamHandle, c_data: Box<PamDataT>, _: PamResultCode) {
56 | |     unsafe {
57 | |         let data: Box<T> = mem::transmute(c_data);
58 | |         mem::drop(data);
59 | |     }
60 | | }
   | |_^
   |
   = note: `#[warn(no_mangle_generic_items)]` on by default