From 142505d8a47aa0cf9641b90870787890585abffd Mon Sep 17 00:00:00 2001
From: Gabriel Kaszewski <gabrielkaszewski@gmail.com>
Date: Sun, 18 Oct 2026 01:24:56 +0200
Subject: [PATCH] feat: add SavedContext::with_entry_and_stack, wire
 SpawnThread to preserve entry point and stack

---
 crates/domain/src/thread/mod.rs        | 63 ++++++++++++++++++++++++++
 crates/kernel/src/syscall/lifecycle.rs |  8 ++--
 crates/kernel/src/tests/helpers.rs     |  4 ++
 crates/kernel/src/tests/lifecycle.rs   | 16 +++++++
 4 files changed, 88 insertions(+), 3 deletions(-)

diff --git a/crates/domain/src/thread/mod.rs b/crates/domain/src/thread/mod.rs
index 77a125e..3f2c665 100644
--- a/crates/domain/src/thread/mod.rs
+++ b/crates/domain/src/thread/mod.rs
@@ -31,10 +31,31 @@ pub struct SavedContext {
     registers: [usize; 32],
 }
 
+pub const PC_REGISTER: usize = 0;
+pub const SP_REGISTER: usize = 1;
+
 impl SavedContext {
     pub fn empty() -> Self {
         Self { registers: [0; 32] }
     }
+
+    pub fn with_entry_and_stack(
+        entry: types::address::EntryPoint,
+        stack: types::address::StackPointer,
+    ) -> Self {
+        let mut ctx = Self::empty();
+        ctx.registers[PC_REGISTER] = entry.raw();
+        ctx.registers[SP_REGISTER] = stack.raw();
+        ctx
+    }
+
+    pub fn program_counter(&self) -> usize {
+        self.registers[PC_REGISTER]
+    }
+
+    pub fn stack_pointer(&self) -> usize {
+        self.registers[SP_REGISTER]
+    }
 }
 
 pub enum BlockReason {
@@ -63,6 +84,29 @@ impl Thread {
         }
     }
 
+    pub fn with_context(
+        id: ThreadId,
+        process: ProcessId,
+        priority: Priority,
+        time_slice: TimeSlice,
+        core_affinity: Option<CoreId>,
+        context: SavedContext,
+    ) -> Self {
+        Self {
+            id,
+            process,
+            state: ThreadState::Ready,
+            saved_context: context,
+            priority,
+            time_slice,
+            core_affinity,
+        }
+    }
+
+    pub fn saved_context(&self) -> &SavedContext {
+        &self.saved_context
+    }
+
     pub fn id(&self) -> ThreadId {
         self.id
     }
@@ -173,6 +217,25 @@ impl ThreadTable {
         Ok(id)
     }
 
+    pub fn spawn_with_context(
+        &mut self,
+        process: ProcessId,
+        priority: Priority,
+        time_slice: TimeSlice,
+        core_affinity: Option<CoreId>,
+        context: SavedContext,
+    ) -> Result<ThreadId, KernelError> {
+        let idx = self
+            .threads
+            .iter()
+            .position(|s| s.is_none())
+            .ok_or(KernelError::TooManyThreads)?;
+
+        let id = ThreadId::from_raw(idx as u16);
+        self.threads[idx] = Some(Thread::with_context(id, process, priority, time_slice, core_affinity, context));
+        Ok(id)
+    }
+
     pub fn get(&self, id: ThreadId) -> Result<&Thread, KernelError> {
         let idx = id.raw() as usize;
         self.threads
diff --git a/crates/kernel/src/syscall/lifecycle.rs b/crates/kernel/src/syscall/lifecycle.rs
index 11d2da9..128940a 100644
--- a/crates/kernel/src/syscall/lifecycle.rs
+++ b/crates/kernel/src/syscall/lifecycle.rs
@@ -7,16 +7,18 @@ impl<P: Platform> Kernel<P> {
     pub(crate) fn handle_spawn_thread(
         &mut self,
         pid: types::id::ProcessId,
-        _entry: types::address::EntryPoint,
-        _stack: types::address::StackPointer,
+        entry: types::address::EntryPoint,
+        stack: types::address::StackPointer,
     ) -> SyscallOutcome {
         use domain::scheduler::Scheduler;
+        use domain::thread::SavedContext;
 
         let priority = types::bounded::Priority::new(16)
             .unwrap_or_else(|| unreachable!());
         let time_slice = types::time::TimeSlice::new(100);
+        let context = SavedContext::with_entry_and_stack(entry, stack);
 
-        let tid = match self.threads.spawn(pid, priority, time_slice, None) {
+        let tid = match self.threads.spawn_with_context(pid, priority, time_slice, None, context) {
             Ok(t) => t,
             Err(e) => return SyscallOutcome::Complete(SyscallResult::Error(e)),
         };
diff --git a/crates/kernel/src/tests/helpers.rs b/crates/kernel/src/tests/helpers.rs
index b106fbf..ab22fb3 100644
--- a/crates/kernel/src/tests/helpers.rs
+++ b/crates/kernel/src/tests/helpers.rs
@@ -97,4 +97,8 @@ impl Kernel<MockPlatform> {
     ) -> CapSlot {
         self.grant_cap(pid, resource, permissions).expect("grant cap")
     }
+
+    pub fn thread_context(&self, tid: ThreadId) -> &domain::thread::SavedContext {
+        self.threads.get(tid).expect("thread").saved_context()
+    }
 }
diff --git a/crates/kernel/src/tests/lifecycle.rs b/crates/kernel/src/tests/lifecycle.rs
index ad83368..c766596 100644
--- a/crates/kernel/src/tests/lifecycle.rs
+++ b/crates/kernel/src/tests/lifecycle.rs
@@ -3,6 +3,7 @@ use crate::{SyscallOutcome, SyscallResult};
 use domain::syscall::Syscall;
 use types::address::{DataRef, EntryPoint, StackPointer};
 use types::bounded::CapSlot;
+use types::id::ThreadId;
 
 #[test]
 fn spawn_thread_creates_ready_thread() {
@@ -17,6 +18,21 @@ fn spawn_thread_creates_ready_thread() {
     ));
 }
 
+#[test]
+fn spawn_thread_preserves_entry_and_stack() {
+    let (mut k, _) = kernel_with_process();
+    let tid = match k.handle_syscall(Syscall::SpawnThread {
+        entry: EntryPoint::from_raw(0xDEAD),
+        stack: StackPointer::from_raw(0xBEEF),
+    }) {
+        SyscallOutcome::Complete(SyscallResult::Value(v)) => ThreadId::from_raw(v as u16),
+        _ => panic!("expected Value"),
+    };
+    let ctx = k.thread_context(tid);
+    assert_eq!(ctx.program_counter(), 0xDEAD);
+    assert_eq!(ctx.stack_pointer(), 0xBEEF);
+}
+
 #[test]
 fn create_process_with_cap_succeeds() {
     let (mut k, _) = kernel_with_process();