feat: add Rust userspace support; fix TLS layout for p_align < 16; kill whole process on sibling-thread faults

programs/rust/montauk-rt/src/thread.rs

@@ -0,0 +1,93 @@
+//! Threads (SYS_THREAD_SPAWN / SYS_THREAD_JOIN).
+//!
+//! The kernel uses the caller's stack verbatim and delivers one argument in
+//! %rdi. A thread cannot free the stack it runs on, so the [`JoinHandle`]
+//! owns it and frees it after a successful join; dropping an unjoined
+//! handle leaks the stack (the thread may still be running on it).
+
+use alloc::alloc::{alloc, dealloc, Layout};
+use alloc::boxed::Box;
+
+use crate::sys::{self, Status};
+
+pub const DEFAULT_STACK_SIZE: usize = 256 * 1024;
+const STACK_ALIGN: usize = 16;
+
+pub struct JoinHandle {
+    tid: u32,
+    stack: *mut u8,
+    stack_layout: Layout,
+}
+
+unsafe impl Send for JoinHandle {}
+
+impl JoinHandle {
+    pub fn id(&self) -> u32 {
+        self.tid
+    }
+
+    /// Wait for the thread to finish and return its exit code.
+    pub fn join(self) -> Result<i32, Status> {
+        let mut code: i32 = 0;
+        let rc = unsafe {
+            sys::syscall2(sys::SYS_THREAD_JOIN, self.tid as u64, &mut code as *mut i32 as u64)
+        };
+        // The kernel reports a bad tid as -1 (GenericFailure).
+        Status::from_result(rc)?;
+        unsafe { dealloc(self.stack, self.stack_layout) };
+        Ok(code)
+    }
+}
+
+/// Spawn a thread running `f`; its return value becomes the exit code.
+pub fn spawn<F>(f: F) -> Result<JoinHandle, Status>
+where
+    F: FnOnce() -> i32 + Send + 'static,
+{
+    spawn_with_stack(DEFAULT_STACK_SIZE, f)
+}
+
+pub fn spawn_with_stack<F>(stack_size: usize, f: F) -> Result<JoinHandle, Status>
+where
+    F: FnOnce() -> i32 + Send + 'static,
+{
+    let stack_layout = Layout::from_size_align(stack_size.max(4096), STACK_ALIGN)
+        .map_err(|_| Status::InvalidArgument)?;
+    let stack = unsafe { alloc(stack_layout) };
+    if stack.is_null() {
+        return Err(Status::OutOfMemory);
+    }
+    let closure = Box::into_raw(Box::new(f));
+    let top = (stack as usize + stack_layout.size()) & !(STACK_ALIGN - 1);
+
+    let rc = unsafe {
+        sys::syscall3(sys::SYS_THREAD_SPAWN, trampoline::<F> as *const () as u64, closure as u64, top as u64)
+    };
+    match Status::from_result(rc) {
+        Ok(tid) => Ok(JoinHandle { tid: tid as u32, stack, stack_layout }),
+        Err(e) => unsafe {
+            drop(Box::from_raw(closure));
+            dealloc(stack, stack_layout);
+            Err(e)
+        },
+    }
+}
+
+extern "C" fn trampoline<F>(arg: *mut F) -> !
+where
+    F: FnOnce() -> i32,
+{
+    let f = unsafe { Box::from_raw(arg) };
+    let code = f();
+    unsafe { sys::syscall1(sys::SYS_THREAD_EXIT, code as u32 as u64) };
+    unreachable!()
+}
+
+/// The calling thread's id (equals the process id on the main thread).
+pub fn current_id() -> u32 {
+    unsafe { sys::syscall0(sys::SYS_THREAD_SELF) as u32 }
+}
+
+pub fn yield_now() {
+    unsafe { sys::syscall0(sys::SYS_YIELD) };
+}