Clean up emergency console and use panic for unexpected exceptions.

This removes `eprintln`, which was easy to misuse and not really sound.
Instead, use `emergency_uart`, which has been made unsafe with a clearly
documented safety requirement that it can only be called when the normal
UART instance will never be used again, e.g. just before rebooting.
Also changed `emergency_uart` to return an error rather than panicking,
so panic handler can ignore the error.

Test: atest vmbase_example.integration_test
Change-Id: I76ac1911cf905fde0010054cfd8bc239699298f6
diff --git a/guest/pvmfw/src/arch/aarch64/exceptions.rs b/guest/pvmfw/src/arch/aarch64/exceptions.rs
index 4c867fb..c8c0156 100644
--- a/guest/pvmfw/src/arch/aarch64/exceptions.rs
+++ b/guest/pvmfw/src/arch/aarch64/exceptions.rs
@@ -18,9 +18,7 @@
     arch::aarch64::exceptions::{
         handle_permission_fault, handle_translation_fault, ArmException, Esr, HandleExceptionError,
     },
-    eprintln, logger,
-    power::reboot,
-    read_sysreg,
+    logger, read_sysreg,
 };
 
 fn handle_exception(exception: &ArmException) -> Result<(), HandleExceptionError> {
@@ -41,55 +39,44 @@
 
     let exception = ArmException::from_el1_regs();
     if let Err(e) = handle_exception(&exception) {
-        exception.print("sync_exception_current", e, elr);
-        reboot()
+        exception.print_and_reboot("sync_exception_current", e, elr);
     }
 }
 
 #[no_mangle]
 extern "C" fn irq_current(_elr: u64, _spsr: u64) {
-    eprintln!("irq_current");
-    reboot();
+    panic!("irq_current");
 }
 
 #[no_mangle]
 extern "C" fn fiq_current(_elr: u64, _spsr: u64) {
-    eprintln!("fiq_current");
-    reboot();
+    panic!("fiq_current");
 }
 
 #[no_mangle]
 extern "C" fn serr_current(_elr: u64, _spsr: u64) {
     let esr = read_sysreg!("esr_el1");
-    eprintln!("serr_current");
-    eprintln!("esr={esr:#08x}");
-    reboot();
+    panic!("serr_current, esr={esr:#08x}");
 }
 
 #[no_mangle]
 extern "C" fn sync_lower(_elr: u64, _spsr: u64) {
     let esr = read_sysreg!("esr_el1");
-    eprintln!("sync_lower");
-    eprintln!("esr={esr:#08x}");
-    reboot();
+    panic!("sync_lower, esr={esr:#08x}");
 }
 
 #[no_mangle]
 extern "C" fn irq_lower(_elr: u64, _spsr: u64) {
-    eprintln!("irq_lower");
-    reboot();
+    panic!("irq_lower");
 }
 
 #[no_mangle]
 extern "C" fn fiq_lower(_elr: u64, _spsr: u64) {
-    eprintln!("fiq_lower");
-    reboot();
+    panic!("fiq_lower");
 }
 
 #[no_mangle]
 extern "C" fn serr_lower(_elr: u64, _spsr: u64) {
     let esr = read_sysreg!("esr_el1");
-    eprintln!("serr_lower");
-    eprintln!("esr={esr:#08x}");
-    reboot();
+    panic!("serr_lower, esr={esr:#08x}");
 }
diff --git a/guest/pvmfw/src/entry.rs b/guest/pvmfw/src/entry.rs
index 8ada6a1..cde4cfe 100644
--- a/guest/pvmfw/src/entry.rs
+++ b/guest/pvmfw/src/entry.rs
@@ -98,7 +98,7 @@
     };
 
     const REBOOT_REASON_CONSOLE: usize = 1;
-    console_writeln!(REBOOT_REASON_CONSOLE, "{}", reboot_reason.as_avf_reboot_string());
+    console_writeln!(REBOOT_REASON_CONSOLE, "{}", reboot_reason.as_avf_reboot_string()).unwrap();
     reboot()
 
     // if we reach this point and return, vmbase::entry::rust_entry() will call power::shutdown().