feat(11): Adapt exception demo for Raspberry Pi 5 memory layout

Adjusts the tutorial's exception-triggering demonstration to ensure it produces the intended translation fault on the Raspberry Pi 5.

The Pi 5 port uses a 128 GiB virtual address space to accommodate the RP1 peripheral map. The original tutorial's faulting address of 8 GiB falls within this space, which would lead to an identity mapping and a bus error instead of the desired translation fault.

This commit changes the faulting addresses to 129 GiB and 130 GiB, placing them outside the defined virtual address space. The exception handler is updated accordingly to catch the new 129 GiB address for the recoverable fault demonstration.

Author: devansh-lodha

11_exceptions_part1_groundwork/src/_arch/aarch64/exception.rs

@@ -90,9 +90,10 @@ extern "C" fn current_elx_synchronous(e: &mut ExceptionContext) {
     if e.fault_address_valid() {
         let far_el1 = FAR_EL1.get();
 
-        // This catches the demo case for this tutorial. If the fault address happens to be 8 GiB,
-        // advance the exception link register for one instruction, so that execution can continue.
-        if far_el1 == 8 * 1024 * 1024 * 1024 {
+        // This catches the demo case for this tutorial. If the fault address happens to be
+        // 129 GiB, advance the exception link register for one instruction, so that execution
+        // can continue.
+        if far_el1 == 129 * 1024 * 1024 * 1024 {
             e.elr_el1 += 4;
 
             return;

11_exceptions_part1_groundwork/src/main.rs

@@ -195,14 +195,13 @@ fn kernel_main() -> ! {
     info!("Timer test, spinning for 1 second");
     time::time_manager().spin_for(Duration::from_secs(1));
 
-    // Cause an exception by accessing a virtual address for which no translation was set up. This
-    // code accesses the address 8 GiB, which is outside the mapped address space.
+    // Cause an exception by accessing a virtual address for which no translation was set up.
     //
-    // For demo purposes, the exception handler will catch the faulting 8 GiB address and allow
-    // execution to continue.
+    // For RPi5, the address space is 128 GiB. We must pick an address outside this range
+    // to guarantee a translation fault. Let's use 129 GiB.
     info!("");
-    info!("Trying to read from address 8 GiB...");
-    let mut big_addr: u64 = 8 * 1024 * 1024 * 1024;
+    info!("Trying to read from address 129 GiB...");
+    let mut big_addr: u64 = 129 * 1024 * 1024 * 1024;
     unsafe { core::ptr::read_volatile(big_addr as *mut u64) };
 
     info!("************************************************");
@@ -211,9 +210,9 @@ fn kernel_main() -> ! {
     info!("");
     info!("Let's try again");
 
-    // Now use address 9 GiB. The exception handler won't forgive us this time.
-    info!("Trying to read from address 9 GiB...");
-    big_addr = 9 * 1024 * 1024 * 1024;
+    // Now use address 130 GiB. The exception handler won't forgive us this time.
+    info!("Trying to read from address 130 GiB...");
+    big_addr = 130 * 1024 * 1024 * 1024;
     unsafe { core::ptr::read_volatile(big_addr as *mut u64) };
 
     // Will never reach here in this tutorial.
@@ -226,3 +225,4 @@ fn kernel_main() -> ! {
         console().write_char(c);
     }
 }
+