feat: implement context switching, SavedContext with pc/status fields, wire all syscall outcomes and timer preemption

crates/domain/src/thread/mod.rs

@@ -29,14 +29,17 @@ pub enum ThreadState {
 
 pub struct SavedContext {
     registers: [usize; 32],
+    pc: usize,
+    status: usize,
 }
 
-pub const PC_REGISTER: usize = 0;
-pub const SP_REGISTER: usize = 1;
-
 impl SavedContext {
     pub fn empty() -> Self {
-        Self { registers: [0; 32] }
+        Self {
+            registers: [0; 32],
+            pc: 0,
+            status: 0,
+        }
     }
 
     pub fn with_entry_and_stack(
@@ -44,17 +47,33 @@ impl SavedContext {
         stack: types::address::StackPointer,
     ) -> Self {
         let mut ctx = Self::empty();
-        ctx.registers[PC_REGISTER] = entry.raw();
-        ctx.registers[SP_REGISTER] = stack.raw();
+        ctx.pc = entry.raw();
+        ctx.registers[2] = stack.raw();
         ctx
     }
 
     pub fn program_counter(&self) -> usize {
-        self.registers[PC_REGISTER]
+        self.pc
     }
 
-    pub fn stack_pointer(&self) -> usize {
-        self.registers[SP_REGISTER]
+    pub fn set_pc(&mut self, pc: usize) {
+        self.pc = pc;
+    }
+
+    pub fn status(&self) -> usize {
+        self.status
+    }
+
+    pub fn set_status(&mut self, status: usize) {
+        self.status = status;
+    }
+
+    pub fn registers(&self) -> &[usize; 32] {
+        &self.registers
+    }
+
+    pub fn registers_mut(&mut self) -> &mut [usize; 32] {
+        &mut self.registers
     }
 }
 
@@ -107,6 +126,10 @@ impl Thread {
         &self.saved_context
     }
 
+    pub fn saved_context_mut(&mut self) -> &mut SavedContext {
+        &mut self.saved_context
+    }
+
     pub fn id(&self) -> ThreadId {
         self.id
     }