Towards adding sys_clone()

Stopped working on self_spawn() - going to finish clone() syscall first.
Arch-specific clone() library call that does ipc() and cloned child setup.
- Need to finish thread_create() that satisfy clone() necessities. i.e. setting up its stack.
  Question: Does the pager (and thus the microkernel) have to explicitly set SP_USR?
  Once the call is known to be successful, the library could set it.

tasks/libl4/include/l4lib/ipcdefs.h

@@ -46,6 +46,7 @@
 #define L4_IPC_TAG_STAT			23
 #define L4_IPC_TAG_FSTAT		24
 #define L4_IPC_TAG_FSYNC		25	/* Pager notifies vfs of file close */
+#define L4_IPC_TAG_CLONE		26	/* Pager notifies vfs of file close */
 
 
 /* Tags for ipc between fs0 and mm0 */

tasks/libl4/src/arm/syscalls.S

@@ -39,6 +39,48 @@ BEGIN_PROC(l4_kread)
 		 */
 END_PROC(l4_kread)
 
+/*
+ * For clone() we need special assembler handling
+ * Same signature as ipc(): @r0 = to, @r1 = from
+ *
+ * NOTE: MR_RETURN register is hardcoded here.
+ * It must be updated if MR_RETURN offset is changed!
+ */
+BEGIN_PROC(clone_asm)
+	stmfd	sp!, {r4-r8,lr}		@ Save context.
+	utcb_address r12		@ Get utcb address.
+	ldmia	r12!, {r3-r8}		@ Load 6 Message registers from utcb. MR0-MR5
+	ldr	r12, =__l4_ipc
+	mov	lr, pc
+	ldr	pc, [r12]		@ Perform the ipc()
+
+	/*
+	 * At this moment:
+	 * - MR_RETURN tells us whether we are parent or child (or have failed).
+	 * - Child has new SP set, with |func_ptr|arg1|{End of stack}SP<-| on stack.
+	 * - Child needs exit logic when its function is finished.
+	 */
+	cmp	r0, #0			@ Check ipc success
+	blt	ipc_failed
+	cmp	r2, #0			@ Check ipc return register MR_RETURN.
+	blt	clone_failed		@ Ipc was ok but clone() failed.
+	bgt	parent_return		@ It has child pid, goto parent return.
+child:
+	ldr	r0, [sp, #-4]!		@ Load child's first argument.
+	mov	lr, pc			@ Save return address
+	ldr	pc, [sp, #-4]!		@ Load function pointer from stack
+child_exit:
+	b	child_exit		@ We infinitely loop for now.
+
+	@ Return with normal ipc return sequence
+parent_return:
+clone_failed:
+ipc_failed:
+	utcb_address r12		@ Get utcb
+	stmia	r12, {r3-r8}		@ Store mrs.
+	ldmfd	sp!, {r4-r8,pc}		@ Return restoring pc and context.
+END_PROC(clone_asm)
+
 /*
  * Inter-process communication. Loads message registers as arguments before the call,
  * and stores them as results after the call. @r0 = to, @r1 = from.

tasks/libposix/fork.c

@@ -47,3 +47,39 @@ int fork(void)
 	return ret;
 }
 
+extern int arch_clone(int, int);
+
+int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
+{
+	/* Set up the child stack */
+	unsigned int *stack = child_stack;
+	int ret;
+
+	/* First word of new stack is arg */
+	stack[-1] = (unsigned long)arg;
+
+	/* Second word of new stack is function address */
+	stack[-2] = (unsigned long)fn;
+
+	/* Write the tag */
+	l4_set_tag(L4_IPC_TAG_CLONE);
+
+	/* Write the args as in usual ipc */
+	write_mr(L4SYS_ARG0, flags);
+	write_mr(L4SYS_ARG1, (unsigned long)child_stack);
+
+	/* Perform an ipc but with different return logic. See implementation. */
+	if ((ret = arch_clone(PAGER_TID, PAGER_TID)) < 0) {
+		printf("%s: L4 IPC Error: %d.\n", __FUNCTION__, ret);
+		return ret;
+	}
+
+	if ((ret = l4_get_retval()) < 0) {
+		printf("%s: CLONE Error: %d.\n", __FUNCTION__, ret);
+		return ret;
+	}
+	return ret;
+}
+
+
+

tasks/mm0/main.c

@@ -150,11 +150,16 @@ void handle_requests(void)
 	}
 }
 
+#if 0
+/*
+ * Executes the given function in a new thread in the current
+ * address space but on a brand new stack.
+ */
 int self_spawn(void)
 {
 	struct task_ids ids;
 	struct tcb *self, *self_child;
-	// void *stack;
+	unsigned long stack, stack_size;
 
 	BUG_ON(!(self = find_task(self_tid())));
 
@@ -166,6 +171,10 @@ int self_spawn(void)
 	self_child = task_create(self, &ids, THREAD_CREATE_SAMESPC,
 				 TCB_SHARED_VM | TCB_SHARED_FILES);
 
+	if (IS_ERR(self_child = tcb_alloc_init(TCB_SHARED_VM
+					       | TCB_SHARED_FILES)))
+		BUG();
+
 	/*
 	 * Create a new utcb. Every pager thread will
 	 * need its own utcb to answer calls.
@@ -176,24 +185,44 @@ int self_spawn(void)
 	task_map_prefault_utcb(self_child, self_child);
 
 	/*
-	 * TODO: Set up a child stack by mmapping an anonymous
-	 * region of mmap's choice. TODO: Time to add MAP_GROWSDOWN ???
+	 * Set up a child stack by mmapping an anonymous region.
 	 */
-	if (do_mmap(0, 0, self, 0,
-		    VM_READ | VM_WRITE | VMA_ANONYMOUS | VMA_PRIVATE, 1) < 0)
+	stack_size = self->stack_end - self->stack_start;
+	if (IS_ERR(stack = do_mmap(0, 0, self, 0,
+				   VM_READ | VM_WRITE | VMA_ANONYMOUS
+				   | VMA_PRIVATE | VMA_GROWSDOWN,
+				   __pfn(stack_size)))) {
+		printf("%s: Error spawning %s, Error code: %d\n",
+		       __FUNCTION__, __TASKNAME__, (int)stack);
 		BUG();
+	}
 
-	/* TODO: Notify vfs ??? */
+	/* Modify stack marker of child tcb */
+	self_child->stack_end = stack;
+	self_child->stack_start = stack - stack_size;
+
+	/* Prefault child stack */
+	for (int i = 0; i < __pfn(stack_size); i++)
+		prefault_page(self_child,
+			      self_child->stack_start + __pfn_to_addr(i),
+		      	      VM_READ | VM_WRITE);
+
+	/* Copy current stack to child */
+	memcpy((void *)self_child->stack_start,
+	       (void *)self->stack_start, stack_size);
 
 	/* TODO: Modify registers ???, it depends on what state is copied in C0 */
 
+	/* TODO: Notify vfs ??? */
+
 	task_add_global(self_child);
 
+	if (l4_thread_control(THREAD_CREATE | THREAD_CREATE_SAMESPC, ids)
 	l4_thread_control(THREAD_RUN, &ids);
 
 	return 0;
 }
-
+#endif
 
 void main(void)
 {

tasks/mm0/src/clone.c

@@ -63,8 +63,11 @@ int do_fork(struct tcb *parent)
 	 * Create a new L4 thread with parent's page tables
 	 * kernel stack and kernel-side tcb copied
 	 */
-	child = task_create(parent, &ids, THREAD_CREATE_COPYSPC,
-			    TCB_NO_SHARING);
+	if (IS_ERR(child = task_create(parent, &ids, THREAD_CREATE_COPYSPC,
+			    	       TCB_NO_SHARING))) {
+		l4_ipc_return((int)child);
+		return 0;
+	}
 
 	/* Create new utcb for child since it can't use its parent's */
 	child->utcb = utcb_vaddr_new();
@@ -110,3 +113,66 @@ int sys_fork(l4id_t sender)
 
 	return do_fork(parent);
 }
+
+
+int sys_clone(l4id_t sender, void *child_stack, unsigned int flags)
+{
+	struct task_ids ids;
+	struct vm_file *utcb_shm;
+	struct tcb *parent, *child;
+	unsigned long stack, stack_size;
+
+	BUG_ON(!(parent = find_task(sender)));
+
+	ids.tid = TASK_ID_INVALID;
+	ids.spid = parent->spid;
+	ids.tgid = parent->tgid;
+
+	if (IS_ERR(child = task_create(parent, &ids, THREAD_CREATE_SAMESPC,
+			    	       TCB_SHARED_VM | TCB_SHARED_FILES))) {
+		l4_ipc_return((int)child);
+		return 0;
+	}
+
+	/* Allocate a unique utcb address for child */
+	child->utcb = utcb_vaddr_new();
+
+	/*
+	 * Create the utcb shared memory segment
+	 * available for child to shmat()
+	 */
+	if (IS_ERR(utcb_shm = shm_new((key_t)child->utcb,
+				      __pfn(DEFAULT_UTCB_SIZE)))) {
+		l4_ipc_return((int)utcb_shm);
+		return 0;
+	}
+
+	/* Map and prefault child's utcb to vfs task */
+	task_map_prefault_utcb(find_task(VFS_TID), child);
+
+	/* Set up child stack marks with given stack argument */
+	child->stack_end = (unsigned long)child_stack;
+	child->stack_start = 0;
+
+	/* We can now notify vfs about forked process */
+	vfs_notify_fork(child, parent);
+
+	/* Add child to global task list */
+	task_add_global(child);
+
+	printf("%s/%s: Starting forked child.\n", __TASKNAME__, __FUNCTION__);
+	/* Start forked child. */
+	l4_thread_control(THREAD_RUN, &ids);
+
+	/* Return back to parent */
+	l4_ipc_return(child->tid);
+
+	return 0;
+}
+
+
+
+
+
+
+