feat: implement process control system calls (exit, getpid, gettid, sched_yield, wait4)

1 files changed, 143 insertions, 0 deletions

diff --git a/na/kernel/sys_process.cc b/na/kernel/sys_process.cc
new file mode 100644
index 0000000..1759a81
--- /dev/null
+++ b/na/kernel/sys_process.cc
@@ -0,0 +1,143 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * Process Control System Calls
+ *
+ * Implements: exit, exit_group, getpid, gettid, getppid,
+ *             sched_yield, clone (stub), wait4 (stub),
+ *             set_tid_address, getuid, getgid.
+ *
+ * Reference: docs/specs/syscall.md §7.1
+ */
+
+#include <lume/types.h>
+#include <lume/task.h>
+#include <lume/sched.h>
+#include <lume/errno.h>
+#include <lume/uaccess.h>
+#include <lume/wait.h>
+
+/* External: task lifecycle (kernel/task.cc) */
+extern void task_exit(int code);
+extern void task_destroy(TaskControlBlock* task);
+extern int32 task_wait(int32* exit_code);
+extern int32 task_fork(arch::TrapFrame* tf);
+
+/* ======================================================================
+ * sys_exit / sys_exit_group
+ * ====================================================================== */
+
+int64 sys_exit(uint64 code, uint64, uint64, uint64, uint64, uint64)
+{
+    task_exit(static_cast<int>(code & 0xFF));
+    __builtin_unreachable();
+}
+
+int64 sys_exit_group(uint64 code, uint64, uint64, uint64, uint64, uint64)
+{
+    /* Phase 2: single-threaded, equivalent to sys_exit.
+     * Phase 3: kill all threads in tgid then exit. */
+    task_exit(static_cast<int>(code & 0xFF));
+    __builtin_unreachable();
+}
+
+/* ======================================================================
+ * sys_getpid / sys_gettid / sys_getppid
+ * ====================================================================== */
+
+int64 sys_getpid(uint64, uint64, uint64, uint64, uint64, uint64)
+{
+    return current_task()->tgid;  /* Linux: getpid() returns tgid */
+}
+
+int64 sys_gettid(uint64, uint64, uint64, uint64, uint64, uint64)
+{
+    return current_task()->pid;   /* Linux: gettid() returns real tid */
+}
+
+int64 sys_getppid(uint64, uint64, uint64, uint64, uint64, uint64)
+{
+    TaskControlBlock* parent = current_task()->parent;
+    return parent ? parent->tgid : 0;
+}
+
+/* ======================================================================
+ * sys_sched_yield
+ * ====================================================================== */
+
+int64 sys_sched_yield_wrapper(uint64, uint64, uint64, uint64, uint64, uint64)
+{
+    sched_yield();
+    return 0;
+}
+
+int64 sys_clone_wrapper(uint64 flags, uint64 child_stack,
+                        uint64 ptid, uint64 ctid, uint64 tls, uint64)
+{
+    /* Phase A: Simple fork() support.
+     * Ignore flags/stack for now and just clone the current task. */
+    (void)flags; (void)child_stack; (void)ptid; (void)ctid; (void)tls;
+
+    arch::TrapFrame* tf = current_task()->trapframe;
+    if (!tf) return -EINVAL;
+
+    return task_fork(tf);
+}
+
+/* ========================================================================
+ * sys_wait4 — Wait for child to exit
+ * ======================================================================== */
+
+int64 sys_wait4_wrapper(uint64 pid, uint64 wstatus_ptr,
+                        uint64 options, uint64, uint64, uint64)
+{
+    /* Phase A: Basic wait() support.
+     * TODO: Implement pid-specific wait and WNOHANG in task_wait. */
+    (void)pid; (void)options;
+
+    int32 exit_code = 0;
+    int32 child_pid = task_wait(&exit_code);
+
+    if (child_pid < 0) return child_pid;
+
+    if (wstatus_ptr != 0) {
+        int wstatus = 0;
+        if (exit_code & kExitCodeSignalFlag) {
+            wstatus = exit_code & 0x7F;
+        } else {
+            wstatus = W_EXITCODE(exit_code);
+        }
+        if (copy_to_user(wstatus_ptr, &wstatus, sizeof(int)) < 0)
+            return -EFAULT;
+    }
+
+    return child_pid;
+}
+
+/* ======================================================================
+ * sys_set_tid_address — musl libc calls this very early
+ * ====================================================================== */
+
+int64 sys_set_tid_address(uint64 tidptr, uint64, uint64,
+                          uint64, uint64, uint64)
+{
+    /* Phase 2: store the clear_child_tid pointer (needed for futex wakeup).
+     * For now just return current tid. */
+    (void)tidptr;
+    return current_task()->pid;
+}
+
+/* ======================================================================
+ * sys_getuid / sys_getgid — Phase 2: always root
+ * ====================================================================== */
+
+int64 sys_getuid(uint64, uint64, uint64, uint64, uint64, uint64)
+{
+    return 0; /* root */
+}
+
+int64 sys_getgid(uint64, uint64, uint64, uint64, uint64, uint64)
+{
+    return 0; /* root */
+}