test-runner: Check that logging keeps working right up until EBS

We've had a few bugs where logging stopped working at some point during the
tests. It's easy to miss that if you aren't paying careful attention to the log
output, so add a test for it.

uefi-test-runner/src/main.rs

@@ -186,13 +186,18 @@ fn shutdown(mut st: SystemTable<Boot>) -> ! {
     // Get our text output back.
     st.stdout().reset(false).unwrap();
 
-    info!("Testing complete, shutting down...");
-
     // Tell the host that tests are done. We are about to exit boot
     // services, so we can't easily communicate with the host any later
     // than this.
     send_request_to_host(st.boot_services(), HostRequest::TestsComplete);
 
+    // Send a special log to the host so that we can verify that logging works
+    // up until exiting boot services. See `reconnect_serial_to_console` for the
+    // type of regression this prevents.
+    info!("LOGGING_STILL_WORKING_RIGHT_BEFORE_EBS");
+
+    info!("Testing complete, shutting down...");
+
     // Exit boot services as a proof that it works :)
     let (st, _iter) = st.exit_boot_services(MemoryType::LOADER_DATA);
 

xtask/src/qemu.rs

@@ -311,6 +311,7 @@ impl Io {
 
 fn process_qemu_io(mut monitor_io: Io, mut serial_io: Io, tmp_dir: &Path) -> Result<()> {
     let mut tests_complete = false;
+    let mut logging_still_working_right_before_ebs = false;
 
     // This regex is used to detect and strip ANSI escape codes. These
     // escapes are added by the console output protocol when writing to
@@ -371,6 +372,11 @@ fn process_qemu_io(mut monitor_io: Io, mut serial_io: Io, tmp_dir: &Path) -> Res
             tests_complete = true;
 
             reply_ok()?;
+        } else if line.ends_with("LOGGING_STILL_WORKING_RIGHT_BEFORE_EBS") {
+            // The app sends this right before calling
+            // `exit_boot_services`. This serves as a test that we didn't break
+            // logging by opening the serial device in exclusive mode.
+            logging_still_working_right_before_ebs = true;
         } else {
             println!("{line}");
         }
@@ -380,6 +386,10 @@ fn process_qemu_io(mut monitor_io: Io, mut serial_io: Io, tmp_dir: &Path) -> Res
         bail!("tests did not complete successfully");
     }
 
+    if !logging_still_working_right_before_ebs {
+        bail!("logging stopped working sometime before exiting boot services");
+    }
+
     Ok(())
 }