From 76e31b5e42913f09a1a00bf885a8fdf4282ebd07 Mon Sep 17 00:00:00 2001
From: Mathieu Strypsteen <mathieu@strypsteen.me>
Date: Mon, 23 Dec 2024 21:07:06 +0100
Subject: [PATCH] Add syscall handler

---
 kernel/src/cpu/isr.rs     |  1 +
 kernel/src/cpu/isr.s      |  7 +++++++
 kernel/src/cpu/syscall.s  | 28 +++++++++++++++++++++++++++-
 kernel/src/cpu/usermode.s |  2 ++
 kernel/src/sys/lapic.rs   |  1 +
 kernel/src/sys/mod.rs     |  1 +
 kernel/src/sys/syscall.rs |  2 ++
 kernel/src/sys/task.rs    |  8 +++++++-
 8 files changed, 48 insertions(+), 2 deletions(-)
 create mode 100644 kernel/src/sys/syscall.rs

diff --git a/kernel/src/cpu/isr.rs b/kernel/src/cpu/isr.rs
index dd1d5ca..a5443f3 100644
--- a/kernel/src/cpu/isr.rs
+++ b/kernel/src/cpu/isr.rs
@@ -22,6 +22,7 @@ global_asm!(include_str!("isr.s"), options(att_syntax));
 #[repr(C)]
 #[derive(Clone, Copy)]
 pub struct ISRState {
+    pub ds: u64,
     pub rax: u64,
     pub rbx: u64,
     pub rcx: u64,
diff --git a/kernel/src/cpu/isr.s b/kernel/src/cpu/isr.s
index 3d84804..ded8a3d 100644
--- a/kernel/src/cpu/isr.s
+++ b/kernel/src/cpu/isr.s
@@ -31,10 +31,17 @@ isr_common:
   push %rcx
   push %rbx
   push %rax
+  mov %ds, %rax
+  push %rax
   mov %rsp, %rdi
 
   call isr_handler
 
+  pop %rax
+  mov %ax, %ds
+  mov %ax, %es
+  mov %ax, %fs
+  mov %ax, %gs
   pop %rax
   pop %rbx
   pop %rcx
diff --git a/kernel/src/cpu/syscall.s b/kernel/src/cpu/syscall.s
index 7618096..1cb8aa5 100644
--- a/kernel/src/cpu/syscall.s
+++ b/kernel/src/cpu/syscall.s
@@ -6,4 +6,30 @@ syscall:
   mov %rsp, %gs:8
   mov %gs:0, %rsp
   swapgs
-  jmp .
+  sti
+  push %r11
+  push %r10
+  push %r9
+  push %r8
+  push %rsi
+  push %rdi
+  push %rdx
+  push %rcx
+  push %rax
+
+  call syscall_handler
+
+  pop %rax
+  pop %rcx
+  pop %rdx
+  pop %rdi
+  pop %rsi
+  pop %r8
+  pop %r9
+  pop %r10
+  pop %r11
+  cli
+  swapgs
+  mov %gs:8, %rsp
+  swapgs
+  sysretq
diff --git a/kernel/src/cpu/usermode.s b/kernel/src/cpu/usermode.s
index 5bd79a6..81944ba 100644
--- a/kernel/src/cpu/usermode.s
+++ b/kernel/src/cpu/usermode.s
@@ -2,11 +2,13 @@
 
 .global jump_usermode
 jump_usermode:
+  cli // Ensure consistency in segment registers
   mov $0x1b, %ax
   mov %ax, %ds
   mov %ax, %es
   mov %ax, %fs
   mov %ax, %gs
+  sti
   push $0x1b
   push $0
   pushf
diff --git a/kernel/src/sys/lapic.rs b/kernel/src/sys/lapic.rs
index c0355f9..fd33939 100644
--- a/kernel/src/sys/lapic.rs
+++ b/kernel/src/sys/lapic.rs
@@ -41,6 +41,7 @@ pub fn send_eoi() {
         address.add(REGISTER_EOI).write_volatile(0);
     }
 }
+// It's unsafe to get the LAPIC ID if interrupts are enabled, because the task can have migrated to a different core.
 pub fn get_current_lapic_id() -> usize {
     let address = ADDRESS.load(Ordering::SeqCst);
     let lapic_id = unsafe { address.add(REGISTER_ID).read_volatile() as usize >> 24 };
diff --git a/kernel/src/sys/mod.rs b/kernel/src/sys/mod.rs
index 4edbffd..f72bf59 100644
--- a/kernel/src/sys/mod.rs
+++ b/kernel/src/sys/mod.rs
@@ -10,4 +10,5 @@ pub mod process;
 pub mod scheduler;
 pub mod smp;
 pub mod sync;
+mod syscall;
 pub mod task;
diff --git a/kernel/src/sys/syscall.rs b/kernel/src/sys/syscall.rs
new file mode 100644
index 0000000..4de76fe
--- /dev/null
+++ b/kernel/src/sys/syscall.rs
@@ -0,0 +1,2 @@
+#[no_mangle]
+extern "C" fn syscall_handler() {}
diff --git a/kernel/src/sys/task.rs b/kernel/src/sys/task.rs
index 6ba5687..f18b56a 100644
--- a/kernel/src/sys/task.rs
+++ b/kernel/src/sys/task.rs
@@ -40,6 +40,7 @@ pub struct Task {
     pub sleep_until_us: usize,
     pub block_on_semaphore: Option<Arc<RawSemaphore>>,
     pub semaphore_requested_count: usize,
+    user_stack: u64,
 }
 
 #[repr(C)]
@@ -64,8 +65,10 @@ pub fn allocate_stack() -> u64 {
 pub fn switch_task(current_state: &mut ISRState, new_task: Task) {
     let lapic_id = get_current_lapic_id();
     let mut current_tasks = CURRENT_TASKS.lock();
+    let cpu_data = &mut CPUDATA.lock()[lapic_id];
     if let Some(mut current_task) = current_tasks[lapic_id].take() {
         current_task.state = *current_state;
+        current_task.user_stack = cpu_data.user_stack;
         if current_task.task_state == TaskState::Terminated {
             unsafe {
                 get_kernel_process().lock().address_space.switch();
@@ -90,7 +93,8 @@ pub fn switch_task(current_state: &mut ISRState, new_task: Task) {
         }
     }
     let kernel_stack = new_task.kernel_stack.as_ptr() as u64 + STACK_SIZE as u64;
-    CPUDATA.lock()[lapic_id].kernel_stack = kernel_stack;
+    cpu_data.kernel_stack = kernel_stack;
+    cpu_data.user_stack = new_task.user_stack;
     current_tasks[get_current_lapic_id()] = Some(new_task);
     schedule_timer_interrupt();
 }
@@ -100,6 +104,7 @@ pub fn create_task(process: Arc<Spinlock<Process>>, func: fn()) -> Task {
         id: NEXT_TASK_ID.fetch_add(1, Ordering::SeqCst),
         process,
         state: ISRState {
+            ds: 0x10,
             rax: 0,
             rbx: 0,
             rcx: 0,
@@ -129,6 +134,7 @@ pub fn create_task(process: Arc<Spinlock<Process>>, func: fn()) -> Task {
         sleep_until_us: 0,
         block_on_semaphore: None,
         semaphore_requested_count: 0,
+        user_stack: 0,
     }
 }
 fn create_idle_task() {