feat: terminal, start app by ID

src/aarch64/mmu.rs

@@ -273,7 +273,7 @@ pub fn map_page(
     let table = unsafe { &mut *table_ptr };
 
     if !table.0[l3_off].is_invalid() {
-        return Err(NovaError::Paging);
+        return Err(NovaError::Paging("Page already occupied."));
     }
 
     table.0[l3_off] = TableEntry::page_descriptor(physical_address, additional_flags);
@@ -315,7 +315,7 @@ pub fn map_l2_block(
 
     // Verify virtual address is available.
     if !table.0[l2_off].is_invalid() {
-        return Err(NovaError::Paging);
+        return Err(NovaError::Paging("Block already occupied."));
     }
 
     let new_entry = TableEntry::block_descriptor(physical_address, additional_flags);
@@ -392,7 +392,7 @@ fn next_table(
     match table.0[offset].value & 0b11 {
         0 => {
             if !create_missing {
-                return Err(NovaError::Paging);
+                return Err(NovaError::Paging("No table defined."));
             }
             let new_phys_page_table_address = reserve_page();
 
@@ -406,7 +406,9 @@ fn next_table(
 
             Ok(resolve_table_addr(table.0[offset].address()) as *mut PageTable)
         }
-        1 => Err(NovaError::Paging),
+        1 => Err(NovaError::Paging(
+            "Can't navigate table due to block mapping.",
+        )),
         3 => Ok(resolve_table_addr(table.0[offset].address()) as *mut PageTable),
         _ => unreachable!(),
     }

src/aarch64/mmu/physical_mapping.rs

@@ -24,7 +24,7 @@ pub fn reserve_page_explicit(physical_address: usize) -> Result<PhysAddr, NovaEr
     let word_index = page / 64;
 
     if unsafe { PAGING_BITMAP.bitmap[word_index] } & (1 << (page % 64)) > 0 {
-        return Err(NovaError::Paging);
+        return Err(NovaError::Paging("Page PA already taken."));
     }
 
     unsafe { PAGING_BITMAP.bitmap[word_index] |= 1 << (page % 64) };
@@ -47,7 +47,7 @@ pub fn reserve_block_explicit(physical_address: usize) -> Result<(), NovaError>
     for i in 0..L2_BLOCK_BITMAP_WORDS {
         unsafe {
             if PAGING_BITMAP.bitmap[(page / 64) + i] != 0 {
-                return Err(NovaError::Paging);
+                return Err(NovaError::Paging("Block PA already taken."));
             }
         };
     }

src/application_manager.rs

@@ -7,6 +7,8 @@ use crate::{
 };
 use alloc::vec::Vec;
 use core::arch::asm;
+use log::error;
+use nova_error::NovaError;
 use spin::Mutex;
 
 pub struct Application {
@@ -28,7 +30,7 @@ impl Application {
         )
         .unwrap();
 
-        // TODO: Temporary fix, while kernel and app share some memory regions
+        // TODO: Temporary solution, while kernel and app share some memory regions
         #[allow(static_mut_refs)]
         unsafe {
             let table = &mut *(virtual_address as *mut PageTable);
@@ -40,6 +42,13 @@ impl Application {
             start_addr,
         }
     }
+
+    /// Starts an application.
+    ///
+    /// `ELR_EL1` ->  Exception Link Register (starting virtual address)
+    /// `SPSR_EL1` -> Saved Program State Register (settings for `eret` behaviour)
+    /// `SP_EL0` -> Stack Pointer Register (virtual_address of stack Pointer)
+    /// `TTBR0_EL1` -> Translation Table base Register Register
     pub fn start(&self) {
         unsafe {
             asm!("msr ELR_EL1, {}", in(reg) self.start_addr);
@@ -69,14 +78,27 @@ pub fn initialize_app_manager() {
     let mut guard = APP_MANAGER.lock();
     guard.apps = Some(Vec::new());
 }
-pub fn add_app(app: Application) {
+
+pub fn add_app(app: Application) -> Result<(), NovaError> {
     if let Some(app_list) = APP_MANAGER.lock().apps.as_mut() {
         app_list.push(app);
+        Ok(())
+    } else {
+        Err(NovaError::General("AppManager not initalized."))
     }
 }
 
-pub fn start_app(index: usize) {
-    if let Some(app_list) = APP_MANAGER.lock().apps.as_mut() {
-        app_list[index].start();
+pub fn start_app(index: usize) -> Result<(), NovaError> {
+    if let Some(app) = APP_MANAGER
+        .lock()
+        .apps
+        .as_mut()
+        .and_then(|am| am.get(index))
+    {
+        app.start();
+        unreachable!()
+    } else {
+        error!("Unable to start app due to invalid App ID.");
+        Err(NovaError::General("Invalid app id."))
     }
 }

src/interrupt_handlers/synchronous.rs

@@ -20,12 +20,15 @@ unsafe extern "C" fn rust_synchronous_interrupt_imm_lower_aarch64(frame: &mut Tr
     log_sync_exception();
     match esr.ec {
         0b100100 => {
-            warn!("Cause: Data Abort from a lower Exception level");
+            error!("Cause: Data Abort from a lower Exception level");
         }
         0b010101 => {
             debug!("Cause: SVC instruction execution in AArch64");
             return handle_svc(frame);
         }
+        0b100010 => {
+            error!("Cause: PC alignment fault.");
+        }
         _ => {
             error!("Synchronous interrupt: Unknown Error Code: {:b}", esr.ec);
         }

src/main.rs

@@ -105,7 +105,7 @@ pub extern "C" fn kernel_main() {
     enable_irq_source(IRQSource::UartInt);
 
     let app = Application::new(el0 as *const () as usize);
-    add_app(app);
+    add_app(app).unwrap();
 
     kernel_loop();
 }

src/terminal.rs

@@ -38,14 +38,20 @@ impl Terminal {
         let val = self.input.clone();
         self.input.clear();
 
-        match val.as_str() {
+        let mut parts = val.split(" ");
+
+        match parts.next().unwrap() {
             "temp" => {
                 println!("{}", read_soc_temp([0]).unwrap()[1]);
             }
-            "el0" => unsafe {
-                let i = 69;
-                asm!("", in("x0") i);
-                start_app(0);
+            "app" => unsafe {
+                if let Some(app_id) = parts.next().and_then(|a| a.parse::<usize>().ok()) {
+                    let i = 69;
+                    asm!("", in("x0") i);
+                    let _ = start_app(app_id);
+                } else {
+                    println!("App ID not set.");
+                }
             },
             _ => {
                 println!("Unknown command: \"{}\"", self.input);

workspace/nova_error/src/lib.rs

@@ -5,11 +5,12 @@ use core::prelude::rust_2024::derive;
 
 #[derive(Debug)]
 pub enum NovaError {
+    General(&'static str),
     Mailbox,
     HeapFull,
     EmptyHeapSegmentNotAllowed,
     Misalignment,
     InvalidGranularity,
-    Paging,
+    Paging(&'static str),
     OutOfMeomory,
 }