Simplify event callback with context test

Rather than opening the Output protocol, which isn't important for this
test, just write through the context pointer and assert that the
expected data was written.

Author: nicholasbishop

uefi-test-runner/src/boot/misc.rs

@@ -1,7 +1,6 @@
 use core::ffi::c_void;
 use core::ptr::NonNull;
 
-use uefi::proto::console::text::Output;
 use uefi::table::boot::{BootServices, EventType, TimerTrigger, Tpl};
 use uefi::Event;
 
@@ -37,28 +36,35 @@ fn test_event_callback(bt: &BootServices) {
 }
 
 fn test_callback_with_ctx(bt: &BootServices) {
+    let mut data = 123u32;
+
     extern "efiapi" fn callback(_event: Event, ctx: Option<NonNull<c_void>>) {
         info!("Inside the event callback with context");
+        // Safety: this callback is run within the parent function's
+        // scope, so the context pointer is still valid.
         unsafe {
-            let ctx = &mut *(ctx.unwrap().as_ptr() as *mut Output);
-            // Clear the screen as a quick test that we successfully passed context
-            ctx.clear().expect("Failed to clear screen");
+            let ctx = ctx.unwrap().as_ptr().cast::<u32>();
+            *ctx = 456;
         }
     }
 
-    let ctx = unsafe { &mut *(bt.locate_protocol::<Output>().unwrap().get()) };
+    let ctx: *mut u32 = &mut data;
+    let ctx = NonNull::new(ctx.cast::<c_void>()).unwrap();
 
     let event = unsafe {
         bt.create_event(
             EventType::NOTIFY_WAIT,
             Tpl::CALLBACK,
             Some(callback),
-            Some(NonNull::new_unchecked(ctx as *mut _ as *mut c_void)),
+            Some(ctx),
         )
         .expect("Failed to create event with context")
     };
 
     bt.check_event(event).expect("Failed to check event");
+
+    // Check that `data` was updated inside the event callback.
+    assert_eq!(data, 456);
 }
 
 fn test_watchdog(bt: &BootServices) {