[kernel] Stop creating user stacks in the kernel

Stop creating stacks in user space for user threads, that should be done
by the thread's creator. This change adds process and stack_top
arguments to the thread_create syscall, so that threads can be created
in other processes, and given a stack address.

Also included is a fix in add_thunk_user due to the r11/flags change.

THIS COMMIT BREAKS USERSPACE. See subsequent commits for the user side
changes related to this change.

definitions/objects/thread.def

@@ -2,6 +2,8 @@ object thread : kobject {
     uid 11f23e593d5761bd
 
     method create [constructor] {
+        param process object process
+        param stack_top address
         param entrypoint address
     }
 

src/kernel/objects/process.cpp

@@ -86,7 +86,7 @@ process::update()
 }
 
 thread *
-process::create_thread(uint8_t priority, bool user)
+process::create_thread(uintptr_t rsp3, uint8_t priority)
 {
     if (priority == default_priority)
         priority = scheduler::default_priority;
@@ -94,17 +94,8 @@ process::create_thread(uint8_t priority, bool user)
     thread *th = new thread(*this, priority);
     kassert(th, "Failed to create thread!");
 
-    if (user) {
+    if (rsp3)
-        uintptr_t stack_top = stacks_top - (m_threads.count() * stack_size);
+        th->tcb()->rsp3 = rsp3;
-
-        vm_flags flags = vm_flags::zero|vm_flags::write;
-        vm_area *vma = new vm_area_open(stack_size, flags);
-        m_space.add(stack_top - stack_size, vma);
-
-        // Space for null frame - because the page gets zeroed on
-        // allocation, just pointing rsp here does the trick
-        th->tcb()->rsp3 = stack_top - 2 * sizeof(uint64_t);
-    }
 
     m_threads.append(th);
     scheduler::get().add_thread(th->tcb());

src/kernel/objects/process.h

@@ -43,10 +43,10 @@ public:
     vm_space & space() { return m_space; }
 
     /// Create a new thread in this process
+    /// \args rsp3      If non-zero, sets the ring3 stack pointer to this value
     /// \args priority  The new thread's scheduling priority
-    /// \args user      If true, create a userspace stack for this thread
     /// \returns        The newly created thread object
-    thread * create_thread(uint8_t priorty = default_priority, bool user = true);
+    thread * create_thread(uintptr_t rsp3 = 0, uint8_t priorty = default_priority);
 
     /// Start tracking an object with a handle.
     /// \args obj  The object this handle refers to

src/kernel/objects/thread.cpp

@@ -172,14 +172,15 @@ thread::add_thunk_user(uintptr_t rip3, uintptr_t rip0, uint64_t flags)
     // b) come out of the kernel/user trampoline and start executing
     //    in user mode at rip
 
-    m_tcb.rsp -= sizeof(uintptr_t) * 8;
-    uintptr_t *stack = reinterpret_cast<uintptr_t*>(m_tcb.rsp);
     flags |= 0x200;
+    m_tcb.rflags3 = flags;
 
-    stack[7] = rip3;       // return rip in rcx
+    m_tcb.rsp -= sizeof(uintptr_t) * 7;
-    stack[6] = m_tcb.rsp3; // rbp
+    uintptr_t *stack = reinterpret_cast<uintptr_t*>(m_tcb.rsp);
-    stack[5] = 0xbbbbbbbb; // rbx
+
-    stack[4] = flags;      // r11 sets RFLAGS
+    stack[6] = rip3;       // return rip in rcx
+    stack[5] = m_tcb.rsp3; // rbp
+    stack[4] = 0xbbbbbbbb; // rbx
     stack[3] = 0x12121212; // r12
     stack[2] = 0x13131313; // r13
     stack[1] = 0x14141414; // r14

src/kernel/scheduler.cpp

@@ -70,7 +70,7 @@ inline T * push(uintptr_t &rsp, size_t size = sizeof(T)) {
 void
 scheduler::create_kernel_task(void (*task)(), uint8_t priority, bool constant)
 {
-    thread *th = process::kernel_process().create_thread(priority, false);
+    thread *th = process::kernel_process().create_thread(0, priority);
     auto *tcb = th->tcb();
 
     th->add_thunk_kernel(reinterpret_cast<uintptr_t>(task));

src/kernel/syscalls/thread.cpp

@@ -9,19 +9,22 @@
 namespace syscalls {
 
 j6_status_t
-thread_create(j6_handle_t *handle, uintptr_t entrypoint)
+thread_create(j6_handle_t *handle, j6_handle_t proc, uintptr_t stack_top, uintptr_t entrypoint)
 {
-    thread &parent = thread::current();
+    thread &parent_th = thread::current();
-    process &p = parent.parent();
+    process &parent_pr = parent_th.parent();
 
-    thread *child = p.create_thread();
+    process *owner = get_handle<process>(proc);
+    if (!owner) return j6_err_invalid_arg;
+
+    thread *child = owner->create_thread(stack_top);
     child->add_thunk_user(entrypoint);
     *handle = child->self_handle();
     child->clear_state(thread::state::loading);
     child->set_state(thread::state::ready);
 
-    log::debug(logs::task, "Thread %llx spawned new thread %llx, handle %d",
+    log::debug(logs::task, "Thread %llx:%llx spawned new thread %llx:%llx",
-        parent.koid(), child->koid(), *handle);
+        parent_pr.koid(), parent_th.koid(), owner->koid(), child->koid());
 
     return j6_status_ok;
 }