diff --git a/conts/libl4thread/include/l4thread/addr.h b/conts/libl4thread/include/l4thread/addr.h
index e7b4519..8182ec0 100644
--- a/conts/libl4thread/include/l4thread/addr.h
+++ b/conts/libl4thread/include/l4thread/addr.h
@@ -1,5 +1,5 @@
 /*
- * Address allocation pool
+ * Address allocation pool.
  *
  * Copyright (C) 2007 Bahadir Balban
  */
@@ -21,7 +21,7 @@ int address_pool_init_with_idpool(struct address_pool *pool,
 int address_pool_init(struct address_pool *pool,
 			unsigned long start, unsigned long end,
 			int size);
-void *address_new(struct address_pool *pool, int npages);
-int address_del(struct address_pool *, void *addr, int npages);
+void *address_new(struct address_pool *pool, int nitems, int size);
+int address_del(struct address_pool *, void *addr, int nitems, int size);
 
 #endif /* __ADDR_H__ */
diff --git a/conts/libl4thread/include/l4thread/stack.h b/conts/libl4thread/include/l4thread/stack.h
new file mode 100644
index 0000000..d0e5f09
--- /dev/null
+++ b/conts/libl4thread/include/l4thread/stack.h
@@ -0,0 +1,19 @@
+/*
+ * Stack space helper routines.
+ *
+ * Copyright (C) 2009 B Labs Ltd.
+ */
+#ifndef __LIB_STACK_H__
+#define __LIB_STACK_H__
+
+/* Checks if l4_set_stack_params is called. */
+#define IS_STACK_SETUP()	(lib_stack_size)
+
+int stack_pool_init(unsigned long stack_start,
+			unsigned long stack_end,
+			unsigned long stack_size);
+
+void *get_stack_space(void);
+int delete_stack_space(void *stack_address);
+
+#endif /* __LIB_STACK_H__ */
diff --git a/conts/libl4thread/include/l4thread/tcb.h b/conts/libl4thread/include/l4thread/tcb.h
index 1c81111..da332e0 100644
--- a/conts/libl4thread/include/l4thread/tcb.h
+++ b/conts/libl4thread/include/l4thread/tcb.h
@@ -14,22 +14,30 @@ struct utcb_head {
 };
 
 /* A simple thread control block for the thread library. */
-struct l4t_tcb {
+struct tcb {
+	/* Task list */
 	struct link list;
+
+	/* Task id */
 	int tid;
+
+	/* Chain of utcb descriptors */
 	struct utcb_head *utcb_head;
+
+	/* Stack and utcb address */
 	unsigned long utcb_addr;
+	unsigned long stack_addr;
 };
 
-/* This struct keeps track of all the threads handled by the thread lib. */
-struct l4t_global_list {
+/* All the threads handled by the thread lib are kept in this list. */
+struct global_list {
 	int total;
 	struct link list;
 };
 
-struct l4t_tcb *l4t_find_task(int tid);
-struct l4t_tcb *l4t_tcb_alloc_init(struct l4t_tcb *parent, unsigned int flags);
-void l4t_global_add_task(struct l4t_tcb *task);
-void l4t_global_remove_task(struct l4t_tcb *task);
+struct tcb *find_task(int tid);
+struct tcb *tcb_alloc_init(struct tcb *parent, unsigned int flags);
+void global_add_task(struct tcb *task);
+void global_remove_task(struct tcb *task);
 
 #endif /* __LIB_TCB_H__ */
diff --git a/conts/libl4thread/include/l4thread/thread.h b/conts/libl4thread/include/l4thread/thread.h
index 319233e..8cd3125 100644
--- a/conts/libl4thread/include/l4thread/thread.h
+++ b/conts/libl4thread/include/l4thread/thread.h
@@ -6,13 +6,13 @@
 #ifndef __LIB_THREAD_H__
 #define __LIB_THREAD_H__
 
-int set_stack_params(unsigned long stack_top,
+int l4_set_stack_params(unsigned long stack_top,
 			unsigned long stack_bottom,
 			unsigned long stack_size);
-int set_utcb_params(unsigned long utcb_start, unsigned long utcb_end);
+int l4_set_utcb_params(unsigned long utcb_start, unsigned long utcb_end);
 
-int l4thread_create(struct task_ids *ids, unsigned int flags,
+int l4_thread_create(struct task_ids *ids, unsigned int flags,
 			int (*func)(void *), void *arg);
-void l4thread_kill(struct task_ids *ids);
+void l4_thread_exit(int retval);
 
 #endif /* __LIB_THREAD_H__ */
diff --git a/conts/libl4thread/include/l4thread/utcb-common.h b/conts/libl4thread/include/l4thread/utcb-common.h
index e5f5fef..47d71f8 100644
--- a/conts/libl4thread/include/l4thread/utcb-common.h
+++ b/conts/libl4thread/include/l4thread/utcb-common.h
@@ -1,5 +1,5 @@
 /*
- * UTCB handling common helper routines
+ * UTCB handling common helper routines.
  *
  * Copyright (C) 2009 B Labs Ltd.
  */
diff --git a/conts/libl4thread/include/l4thread/utcb.h b/conts/libl4thread/include/l4thread/utcb.h
index f16f310..086aa93 100644
--- a/conts/libl4thread/include/l4thread/utcb.h
+++ b/conts/libl4thread/include/l4thread/utcb.h
@@ -1,5 +1,5 @@
 /*
- * UTCB handling helper routines
+ * UTCB handling helper routines.
  *
  * Copyright (C) 2009 B Labs Ltd.
  */
@@ -8,7 +8,10 @@
 
 #include <tcb.h>
 
-unsigned long get_utcb_addr(struct l4t_tcb *task);
-int delete_utcb_addr(struct l4t_tcb *task);
+/* Checks if l4_set_stack_params is called. */
+#define IS_UTCB_SETUP()	(lib_utcb_range_size)
+
+unsigned long get_utcb_addr(struct tcb *task);
+int delete_utcb_addr(struct tcb *task);
 
 #endif /* __LIB_UTCB_H__ */
diff --git a/conts/libl4thread/src/addr.c b/conts/libl4thread/src/addr.c
index 90c67dd..7318aca 100644
--- a/conts/libl4thread/src/addr.c
+++ b/conts/libl4thread/src/addr.c
@@ -33,21 +33,21 @@ int address_pool_init(struct address_pool *pool,
 	return 0;
 }
 
-void *address_new(struct address_pool *pool, int npages)
+void *address_new(struct address_pool *pool, int nitems, int size)
 {
-	unsigned int pfn;
+	unsigned int idx;
 
-	if ((int)(pfn = ids_new_contiguous(pool->idpool, npages)) < 0)
+	if ((int)(idx = ids_new_contiguous(pool->idpool, nitems)) < 0)
 		return 0;
 
-	return (void *)__pfn_to_addr(pfn) + pool->start;
+	return (void *)(idx * size) + pool->start;
 }
 
-int address_del(struct address_pool *pool, void *addr, int npages)
+int address_del(struct address_pool *pool, void *addr, int nitems, int size)
 {
-	unsigned long pfn = __pfn(page_align(addr) - pool->start);
+	unsigned long idx = (addr - (void *)pool->start) / size;
 
-	if (ids_del_contiguous(pool->idpool, pfn, npages) < 0) {
+	if (ids_del_contiguous(pool->idpool, idx, nitems) < 0) {
 		printf("%s: Invalid address range returned to "
 		       "virtual address pool.\n", __FUNCTION__);
 		return -1;
diff --git a/conts/libl4thread/src/arch-arm/new_thread.S b/conts/libl4thread/src/arch-arm/new_thread.S
new file mode 100644
index 0000000..1014817
--- /dev/null
+++ b/conts/libl4thread/src/arch-arm/new_thread.S
@@ -0,0 +1,12 @@
+#include <l4lib/arch/asm.h>
+
+
+BEGIN_PROC(setup_new_thread)
+	ldr	r0, [sp], #-4		@ Load first argument
+	mov	lr, pc			@ Save return address
+	ldr	pc, [sp], #-4		@ Load function pointer from stack
+	b	l4_thread_exit		@ Call l4_thread_exit for cleanup
+new_thread_exit:
+	b	new_thread_exit		@ Never reaches here
+END_PROC(setup_new_thread)
+
diff --git a/conts/libl4thread/src/idpool.c b/conts/libl4thread/src/idpool.c
new file mode 100644
index 0000000..17fd450
--- /dev/null
+++ b/conts/libl4thread/src/idpool.c
@@ -0,0 +1,87 @@
+/*
+ * Used for thread and space ids, and also for
+ * utcb tracking in page-sized-chunks.
+ *
+ * Copyright (C) 2009 B Labs Ltd.
+ */
+#include <idpool.h>
+#include <stdio.h>
+#include <l4/api/errno.h>
+#include <malloc/malloc.h>
+
+struct id_pool *id_pool_new_init(int totalbits)
+{
+	int nwords = BITWISE_GETWORD(totalbits) + 1;
+	struct id_pool *new = kzalloc((nwords * SZ_WORD)
+				      + sizeof(struct id_pool));
+	if (!new)
+		return PTR_ERR(-ENOMEM);
+
+	new->nwords = nwords;
+	new->bitlimit = totalbits;
+
+	return new;
+}
+
+/* Search for a free slot up to the limit given */
+int id_new(struct id_pool *pool)
+{
+	return find_and_set_first_free_bit(pool->bitmap, pool->bitlimit);
+}
+
+/* This finds n contiguous free ids, allocates and returns the first one */
+int ids_new_contiguous(struct id_pool *pool, int numids)
+{
+	int id = find_and_set_first_free_contig_bits(pool->bitmap,
+						     pool->bitlimit,
+						     numids);
+	if (id < 0)
+		printf("%s: Warning! New id alloc failed\n", __FUNCTION__);
+	return id;
+}
+
+/* This deletes a list of contiguous ids given the first one and number of ids */
+int ids_del_contiguous(struct id_pool *pool, int first, int numids)
+{
+	int ret;
+
+	if (pool->nwords * WORD_BITS < first + numids)
+		return -1;
+	if ((ret = check_and_clear_contig_bits(pool->bitmap, first, numids)))
+		printf("%s: Error: Invalid argument range.\n", __FUNCTION__);
+	return ret;
+}
+
+int id_del(struct id_pool *pool, int id)
+{
+	int ret;
+
+	if (pool->nwords * WORD_BITS < id)
+		return -1;
+
+	if ((ret = check_and_clear_bit(pool->bitmap, id) < 0))
+		printf("%s: Error: Could not delete id.\n", __FUNCTION__);
+	return ret;
+}
+
+/* Return a specific id, if available */
+int id_get(struct id_pool *pool, int id)
+{
+	int ret;
+
+	ret = check_and_set_bit(pool->bitmap, id);
+
+	if (ret < 0)
+		return ret;
+	else
+		return id;
+}
+
+int id_is_empty(struct id_pool *pool)
+{
+	for (int i = 0; i < pool->nwords; i++)
+		if (pool->bitmap[i])
+			return 0;
+	return 1;
+}
+
diff --git a/conts/libl4thread/src/stack.c b/conts/libl4thread/src/stack.c
new file mode 100644
index 0000000..5fedcba
--- /dev/null
+++ b/conts/libl4thread/src/stack.c
@@ -0,0 +1,97 @@
+/*
+ * Stack management in libl4thread.
+ *
+ * Copyright © 2009 B Labs Ltd.
+ */
+#include <stdio.h>
+#include <addr.h>
+#include <l4/api/errno.h>
+#include <l4lib/mutex.h>
+#include <stack.h>
+
+/* Extern declarations */
+extern struct l4_mutex lib_mutex;
+
+/* Global variables */
+unsigned long lib_stack_size;
+
+/* Stack virtual region pool */
+static struct address_pool stack_region_pool;
+
+int stack_pool_init(unsigned long stack_start,
+			unsigned long stack_end,
+			unsigned long stack_size)
+{
+	int err;
+
+	/* Initialise the global stack virtual address pool. */
+	if ((err = address_pool_init(&stack_region_pool,
+					stack_start, stack_end,
+					stack_size) < 0)) {
+		printf("Stack address pool initialisation failed.\n");
+		return err;
+	}
+
+	return 0;
+}
+
+void *get_stack_space(void)
+{
+	return address_new(&stack_region_pool, 1, lib_stack_size);
+}
+
+int delete_stack_space(void *stack_address)
+{
+	return address_del(&stack_region_pool, stack_address, 1, lib_stack_size);
+}
+
+int l4_set_stack_params(unsigned long stack_top,
+			unsigned long stack_bottom,
+			unsigned long stack_size)
+{
+	/* Ensure that arguments are valid. */
+	if (IS_STACK_SETUP()) {
+		printf("libl4thread: You have already called: %s.\n",
+			__FUNCTION__);
+		return -EPERM;
+	}
+	if (!stack_top || !stack_bottom) {
+		printf("libl4thread: Stack address range cannot contain "
+			"0x0 as a start and/or end address(es).\n");
+		return -EINVAL;
+	}
+	// FIXME: Aligning should be taken into account.
+        /*
+	 * Stack grows downward so the top of the stack will have
+	 * the lowest numbered address.
+         */
+	if (stack_top >= stack_bottom) {
+		printf("libl4thread: Stack bottom address must be bigger "
+			"than stack top address.\n");
+		return -EINVAL;
+	}
+	if (!stack_size) {
+		printf("libl4thread: Stack size cannot be zero.\n");
+		return -EINVAL;
+	}
+	/* stack_size at least must be equal to the difference. */
+	if ((stack_bottom - stack_top) < stack_size) {
+		printf("libl4thread: The given range size is lesser than "
+			"the stack size(0x%x).\n", stack_size);
+		return -EINVAL;
+	}
+	/* Arguments passed the validity tests. */
+
+	/* Initialize internal variables. */
+	lib_stack_size = stack_size;
+
+	/* Initialize stack virtual address pool. */
+	if (stack_pool_init(stack_top, stack_bottom, stack_size) < 0)
+		BUG();
+
+	/* Initialize the global mutex. */
+	l4_mutex_init(&lib_mutex);
+
+	return 0;
+}
+
diff --git a/conts/libl4thread/src/tcb.c b/conts/libl4thread/src/tcb.c
index d0125bb..dec4918 100644
--- a/conts/libl4thread/src/tcb.c
+++ b/conts/libl4thread/src/tcb.c
@@ -1,3 +1,8 @@
+/*
+ * Thread management in libl4thread.
+ *
+ * Copyright (C) 2009 B Labs Ltd.
+ */
 #include <stdio.h>
 #include <malloc/malloc.h>
 #include <l4/api/errno.h>
@@ -5,50 +10,53 @@
 #include <tcb.h>
 
 /* Global task list. */
-struct l4t_global_list l4t_global_tasks = {
-	.list = { &l4t_global_tasks.list, &l4t_global_tasks.list },
+struct global_list global_tasks = {
+	.list = { &global_tasks.list, &global_tasks.list },
 	.total = 0,
 };
 
 /* Function definitions */
-void l4t_global_add_task(struct l4t_tcb *task)
+void global_add_task(struct tcb *task)
 {
 	BUG_ON(!list_empty(&task->list));
-	list_insert_tail(&task->list, &l4t_global_tasks.list);
-	l4t_global_tasks.total++;
+	list_insert_tail(&task->list, &global_tasks.list);
+	global_tasks.total++;
 }
 
-void l4t_global_remove_task(struct l4t_tcb *task)
+void global_remove_task(struct tcb *task)
 {
 	BUG_ON(list_empty(&task->list));
 	list_remove_init(&task->list);
-	BUG_ON(--l4t_global_tasks.total < 0);
+	BUG_ON(--global_tasks.total < 0);
 }
 
-struct l4t_tcb *l4t_find_task(int tid)
+struct tcb *find_task(int tid)
 {
-	struct l4t_tcb *t;
+	struct tcb *t;
 
-	list_foreach_struct(t, &l4t_global_tasks.list, list)
+	list_foreach_struct(t, &global_tasks.list, list)
 		if (t->tid == tid)
 			return t;
 	return 0;
 }
 
-struct l4t_tcb *l4t_tcb_alloc_init(struct l4t_tcb *parent, unsigned int flags)
+struct tcb *tcb_alloc_init(struct tcb *parent, unsigned int flags)
 {
-	struct l4t_tcb *task;
+	struct tcb *task;
 
-	if (!(task = kzalloc(sizeof(struct l4t_tcb))))
+	if (!(task = kzalloc(sizeof(struct tcb))))
 		return PTR_ERR(-ENOMEM);
 
 	link_init(&task->list);
 
-	if ((parent) && (flags & TC_SHARE_SPACE))
+	if (flags & TC_SHARE_SPACE)
 		task->utcb_head = parent->utcb_head;
 	else {
-		if (!(task->utcb_head = kzalloc(sizeof(struct utcb_head))))
+		/* COPY or NEW space */
+		if (!(task->utcb_head = kzalloc(sizeof(struct utcb_head)))) {
+			kfree(task);
 			return PTR_ERR(-ENOMEM);
+		}
 		link_init(&task->utcb_head->list);
 	}
 
diff --git a/conts/libl4thread/src/thread.c b/conts/libl4thread/src/thread.c
index 87e84b4..61b0f53 100644
--- a/conts/libl4thread/src/thread.c
+++ b/conts/libl4thread/src/thread.c
@@ -5,181 +5,206 @@
  */
 #include <stdio.h>
 #include <l4lib/arch/syscalls.h>
+#include <l4lib/arch/syslib.h>
 #include <l4lib/exregs.h>
+#include <l4lib/mutex.h>
 #include <l4/api/thread.h>
 #include <l4/api/errno.h>
 #include <malloc/malloc.h>
 #include <utcb.h>
-
-/* Symbolic constants and macros */
-#define IS_STACK_SETUP()	(lib_stack_size)
+#include <stack.h>
 
 /* Extern declarations */
 extern void setup_new_thread(void);
+extern unsigned long lib_stack_size;
+extern unsigned long lib_utcb_range_size;
 
 /* Static variable definitions */
-static unsigned long lib_stack_top_addr;
-static unsigned long lib_stack_bot_addr;
-static unsigned long lib_stack_size;
+struct l4_mutex lib_mutex;
 
 /* Function definitions */
-int set_stack_params(unsigned long stack_top,
-			unsigned long stack_bottom,
-			unsigned long stack_size)
-{
-	/* Ensure that arguments are valid. */
-	if (IS_STACK_SETUP()) {
-		printf("libl4thread: You have already called: %s.\n",
-				__FUNCTION__);
-		return -EPERM;
-	}
-	if (!stack_top || !stack_bottom) {
-		printf("libl4thread: Stack address range cannot contain "
-			"0x0 as a start and/or end address(es).\n");
-		return -EINVAL;
-	}
-	// FIXME: Aligning should be taken into account.
-        /*
-	 * Stack grows downward so the top of the stack will have
-	 * the lowest numbered address.
-         */
-	if (stack_top >= stack_bottom) {
-		printf("libl4thread: Stack bottom address must be bigger "
-			"than stack top address.\n");
-		return -EINVAL;
-	}
-	if (!stack_size) {
-		printf("libl4thread: Stack size cannot be zero.\n");
-		return -EINVAL;
-	}
-	/* stack_size at least must be equal to the difference. */
-	if ((stack_bottom - stack_top) < stack_size) {
-		printf("libl4thread: The given range size is lesser than "
-			"the stack size(0x%x).\n", stack_size);
-		return -EINVAL;
-	}
-	/* Arguments passed the validity tests. */
-
-	/* Initialize internal variables */
-	lib_stack_bot_addr = stack_bottom;
-	lib_stack_top_addr = stack_top;
-	lib_stack_size = stack_size;
-
-	return 0;
-}
-
-int l4thread_create(struct task_ids *ids, unsigned int flags,
+int l4_thread_create(struct task_ids *ids, unsigned int flags,
 			int (*func)(void *), void *arg)
 {
 	struct exregs_data exregs;
 	unsigned long utcb_addr;
-	struct l4t_tcb *parent, *child;
-	int err;
+	struct tcb *parent, *child;
+	unsigned long stack_top_addr, stack_bot_addr;
+	int err = 0;
 
 	/* A few controls before granting access to thread creation */
-	// FIXME: check if utcb region is setup
-	if (!IS_STACK_SETUP()) {
+	if (!IS_STACK_SETUP() || !IS_UTCB_SETUP()) {
 		printf("libl4thread: Stack and/or utcb have not been "
-				"set up.\n");
+			"set up.\n");
 		return -EPERM;
 	}
 
-	/* Is there enough stack space for the new thread? */
-	if (lib_stack_top_addr >= lib_stack_bot_addr) {
-		printf("libl4thread: No stack space left.\n");
-		return -ENOMEM;
-	}
-
-	// FIXME: Check if there is enough utcb space
-
-	if (!(TC_SHARE_SPACE & flags)) {
-		printf("libl4thread: Only allows shared space thread "
-				"creation.\n");
-
-		return -EINVAL;
-	}
+	/* Before doing any operation get the global mutex. */
+	l4_mutex_lock(&lib_mutex);
 
 	/* Get parent's ids and find the tcb belonging to it. */
 	l4_getid(ids);
-	if (!(parent = l4t_find_task(ids->tid)))
-		return-ESRCH;
+	if (!(parent = find_task(ids->tid))) {
+		err = -ESRCH;
+		goto out_err1;
+	}
 
 	/* Allocate tcb for the child. */
-	if (!(child = l4t_tcb_alloc_init(parent, flags))) {
+	if (!(child = tcb_alloc_init(parent, flags))) {
+		// FIXME: What happens to utcb_head
 		printf("libl4thread: No heap space left.\n");
-		return -ENOMEM;
+		err = -ENOMEM;
+		goto out_err1;
 	}
 
-	/* Get a utcb addr for this thread */
+	/* Get a utcb addr. */
 	if (!(utcb_addr = get_utcb_addr(child))) {
-		printf("libl4thread: No utcb address left.\n");
-		// FIXME: Check if there is any memory leak
-		kfree(child);
-		return -ENOMEM;
+		printf("libl4thread: No utcb space left.\n");
+		err = -ENOMEM;
+		goto out_err2;
 	}
 
+	/* Get a stack space and calculate the bottom addr of the stack. */
+	stack_top_addr = (unsigned long)get_stack_space();
+	if (!stack_top_addr) {
+		printf("libl4thread: No stack space left.\n");
+		err = -ENOMEM;
+		goto out_err3;
+	}
+	stack_bot_addr = stack_top_addr + lib_stack_size;
+	child->stack_addr = stack_top_addr;
+
 	/* Create thread */
 	if ((err = l4_thread_control(THREAD_CREATE | flags, ids)) < 0) {
 		printf("libl4thread: l4_thread_control(THREAD_CREATE) "
-				"failed with (%d).\n", err);
-		// FIXME: Check if there is any memory leak
-		kfree(child);
-		delete_utcb_addr(child);
-		return err;
+			"failed with (%d).\n", err);
+		goto out_err4;
 	}
 
 	/* Setup new thread pc, sp, utcb */
 	memset(&exregs, 0, sizeof(exregs));
-	exregs_set_stack(&exregs, align((lib_stack_bot_addr - 1), 8));
+	exregs_set_stack(&exregs, align((stack_bot_addr - 1), 8));
 	exregs_set_pc(&exregs, (unsigned long)setup_new_thread);
 	exregs_set_utcb(&exregs, (unsigned long)utcb_addr);
 
 	if ((err = l4_exchange_registers(&exregs, ids->tid)) < 0) {
 		printf("libl4thread: l4_exchange_registers failed with "
-				"(%d).\n", err);
-		// FIXME: Check if there is any memory leak
-		return err;
+			"(%d).\n", err);
+		goto out_err5;
 	}
 
 	/* First word of new stack is arg */
-	((unsigned long *)align((lib_stack_bot_addr - 1), 8))[0] =
-					(unsigned long)arg;
+	((unsigned long *)align((stack_bot_addr - 1), 8))[0] =
+						(unsigned long)arg;
 	/* Second word of new stack is function address */
-	((unsigned long *)align((lib_stack_bot_addr - 1), 8))[-1] =
-					(unsigned long)func;
-	/* Update the stack address */
-	lib_stack_bot_addr -= lib_stack_size;
+	((unsigned long *)align((stack_bot_addr - 1), 8))[-1] =
+						(unsigned long)func;
 
 	/* Add child to the global task list */
 	child->tid = ids->tid;
-	l4t_global_add_task(child);
+	global_add_task(child);
 
 	/* Start the new thread */
 	if ((err = l4_thread_control(THREAD_RUN, ids)) < 0) {
 		printf("libl4thread: l4_thread_control(THREAD_RUN) "
-				"failed with (%d).\n", err);
-		return err;
+			"failed with (%d).\n", err);
+		goto out_err6;
 	}
 
+	/* Release the global mutex. */
+	l4_mutex_unlock(&lib_mutex);
+
 	return 0;
+
+	/* Error handling. */
+out_err6:
+	global_remove_task(child);
+out_err5:
+	l4_thread_control(THREAD_DESTROY, ids);
+out_err4:
+	delete_stack_space((void *)child->stack_addr);
+out_err3:
+	delete_utcb_addr(child);
+out_err2:
+	if ((flags & TC_COPY_SPACE) || (flags & TC_NEW_SPACE))
+		kfree(child->utcb_head);
+	kfree(child);
+out_err1:
+	l4_mutex_unlock(&lib_mutex);
+
+	return err;
 }
 
-void l4thread_kill(struct task_ids *ids)
+void l4_thread_exit(int retval)
 {
-	struct l4t_tcb *task;
+	struct tcb *task;
+	struct task_ids ids;
 
-	/* Find the task to be killed. */
-	task = l4t_find_task(ids->tid);
+	/* Before doing any operation get the global mutex. */
+	l4_mutex_lock(&lib_mutex);
+
+	/* Find the task. */
+	l4_getid(&ids);
+	/* Cant find the thread means it wasnt added to the list. */
+	if (!(task = find_task(ids.tid)))
+		BUG();
+
+	/* Remove child from the global task list. */
+	global_remove_task(task);
+
+	/* Delete the stack space. */
+	if (delete_stack_space((void *)task->stack_addr) < 0)
+		BUG();
 
 	/* Delete the utcb address. */
 	delete_utcb_addr(task);
 
+	// FIXME: We assume that main thread never leaves the scene
+	// FIXME: What happens to task->utcb_head?
+	kfree(task);
+
+	/* Release the global mutex. */
+	l4_mutex_unlock(&lib_mutex);
+
+	/* Relinquish the control. */
+	l4_exit(retval);
+
+	/* Should never reach here. */
+	BUG();
+}
+
+int l4_thread_kill(struct task_ids *ids)
+{
+	struct tcb *task;
+
+	/* Before doing any operation get the global mutex. */
+	l4_mutex_lock(&lib_mutex);
+
+	/* Find the task to be killed. */
+	if (!(task = find_task(ids->tid))) {
+		l4_mutex_unlock(&lib_mutex);
+		return -ESRCH;
+	}
+
 	/* Remove child from the global task list. */
-	l4t_global_remove_task(task);
+	global_remove_task(task);
+
+	/* Delete the stack space. */
+	if (delete_stack_space((void *)task->stack_addr) < 0)
+		BUG();
+
+	/* Delete the utcb address. */
+	delete_utcb_addr(task);
 
 	// FIXME: We assume that main thread never leaves the scene
+	// FIXME: What happens to task->utcb_head?
 	kfree(task);
 
+	/* Release the global mutex. */
+	l4_mutex_unlock(&lib_mutex);
+
 	/* Finally, destroy the thread. */
 	l4_thread_control(THREAD_DESTROY, ids);
+
+	return 0;
 }
diff --git a/conts/libl4thread/src/utcb-common.c b/conts/libl4thread/src/utcb-common.c
index 38df843..5ad511a 100644
--- a/conts/libl4thread/src/utcb-common.c
+++ b/conts/libl4thread/src/utcb-common.c
@@ -1,7 +1,7 @@
 /*
- * UTCB management in Codezero
+ * UTCB management in libl4thread.
  *
- * Copyright © 2009 B Labs Ltd
+ * Copyright © 2009 B Labs Ltd.
  */
 #include <stdio.h>
 #include <addr.h>
@@ -18,7 +18,7 @@ int utcb_pool_init(unsigned long utcb_start, unsigned long utcb_end)
 	/* Initialise the global utcb virtual address pool */
 	if ((err = address_pool_init(&utcb_region_pool,
 					utcb_start, utcb_end,
-					UTCB_SIZE) < 0)) {
+					PAGE_SIZE) < 0)) {
 		printf("UTCB address pool initialisation failed.\n");
 		return err;
 	}
@@ -26,14 +26,14 @@ int utcb_pool_init(unsigned long utcb_start, unsigned long utcb_end)
 	return 0;
 }
 
-static inline void *utcb_new_address(int npages)
+static inline void *utcb_new_address(int nitems)
 {
-	return address_new(&utcb_region_pool, npages);
+	return address_new(&utcb_region_pool, nitems, PAGE_SIZE);
 }
 
-static inline int utcb_delete_address(void *utcb_address, int npages)
+static inline int utcb_delete_address(void *utcb_address, int nitems)
 {
-	return address_del(&utcb_region_pool, utcb_address, npages);
+	return address_del(&utcb_region_pool, utcb_address, nitems, PAGE_SIZE);
 }
 
 /* Return an empty utcb slot in this descriptor */
@@ -72,7 +72,11 @@ struct utcb_desc *utcb_new_desc(void)
 
 	/* Obtain a new and unique utcb base */
 	/* FIXME: Use variable size than a page */
-	d->utcb_base = (unsigned long)utcb_new_address(1);
+	if (!(d->utcb_base = (unsigned long)utcb_new_address(1))) {
+		kfree(d->slots);
+		kfree(d);
+		return 0;
+	}
 
 	return d;
 }
diff --git a/conts/libl4thread/src/utcb.c b/conts/libl4thread/src/utcb.c
index 4dd7fef..5bed78c 100644
--- a/conts/libl4thread/src/utcb.c
+++ b/conts/libl4thread/src/utcb.c
@@ -1,5 +1,5 @@
 /*
- * UTCB handling helper routines
+ * UTCB handling helper routines.
  *
  * Copyright (C) 2009 B Labs Ltd.
  */
@@ -13,10 +13,13 @@
 #include <utcb.h>
 
 /* Extern declarations */
-extern struct l4t_global_list l4t_global_tasks;
+extern struct global_list global_tasks;
+
+/* Global variables */
+unsigned long lib_utcb_range_size;
 
 /* Function definitions */
-unsigned long get_utcb_addr(struct l4t_tcb *task)
+unsigned long get_utcb_addr(struct tcb *task)
 {
 	struct utcb_desc *udesc;
 	unsigned long slot;
@@ -30,7 +33,8 @@ unsigned long get_utcb_addr(struct l4t_tcb *task)
 			goto found;
 
 	/* Allocate a new utcb memory region and return its base. */
-	udesc = utcb_new_desc();
+	if (!(udesc = utcb_new_desc()))
+		return 0;
 	slot = utcb_new_slot(udesc);
 	list_insert(&udesc->list, &task->utcb_head->list);
 found:
@@ -39,7 +43,7 @@ found:
 	return slot;
 }
 
-int delete_utcb_addr(struct l4t_tcb *task)
+int delete_utcb_addr(struct tcb *task)
 {
 	struct utcb_desc *udesc;
 
@@ -68,55 +72,56 @@ static int set_utcb_addr(void)
 {
 	struct exregs_data exregs;
 	struct task_ids ids;
-	struct l4t_tcb *task;
+	struct tcb *task;
 	struct utcb_desc *udesc;
 	int err;
 
 	/* Create a task. */
-	if (IS_ERR(task = l4t_tcb_alloc_init(0, 0)))
+	if (IS_ERR(task = tcb_alloc_init(0, 0)))
 		return -ENOMEM;
 
 	/* Add child to the global task list. */
-	list_insert_tail(&task->list, &l4t_global_tasks.list);
-	l4t_global_tasks.total++;
+	list_insert_tail(&task->list, &global_tasks.list);
+	global_tasks.total++;
 
-	udesc = utcb_new_desc();
+	if (!(udesc = utcb_new_desc()))
+		return -ENOMEM;
 	task->utcb_addr = utcb_new_slot(udesc);
 	list_insert(&udesc->list, &task->utcb_head->list);
 
 	memset(&exregs, 0, sizeof(exregs));
-	exregs_set_utcb(&exregs, (unsigned long)task->utcb_addr);
+	exregs_set_utcb(&exregs, task->utcb_addr);
 
 	l4_getid(&ids);
+	task->tid = ids.tid;
 	if ((err = l4_exchange_registers(&exregs, ids.tid)) < 0) {
 		printf("libl4thread: l4_exchange_registers failed with "
-				"(%d).\n", err);
+			"(%d).\n", err);
 		return err;
 	}
 
 	return 0;
 }
 
-int set_utcb_params(unsigned long utcb_start, unsigned long utcb_end)
+int l4_set_utcb_params(unsigned long utcb_start, unsigned long utcb_end)
 {
 	int err;
 
 	/* Ensure that arguments are valid. */
-	// FIXME: Check if set_utcb_params is called
-	/*if (IS_UTCB_SETUP()) {*/
-		/*printf("libl4thread: You have already called: %s.\n",*/
-				/*__FUNCTION__);*/
-		/*return -EPERM;*/
-	/*}*/
+	if (IS_UTCB_SETUP()) {
+		printf("libl4thread: You have already called: %s.\n",
+			__FUNCTION__);
+		return -EPERM;
+	}
 	if (!utcb_start || !utcb_end) {
 		printf("libl4thread: Utcb address range cannot contain "
 			"0x0 as a start and/or end address(es).\n");
 		return -EINVAL;
 	}
-	/* Check if the start address is aligned on UTCB_SIZE. */
-	if (utcb_start & !UTCB_SIZE) {
+	/* Check if the start address is aligned on PAGE_SIZE. */
+	if (utcb_start & PAGE_MASK) {
 		printf("libl4thread: Utcb start address must be aligned "
-			"on UTCB_SIZE(0x%x).\n", UTCB_SIZE);
+			"on PAGE_SIZE(0x%x).\n", PAGE_SIZE);
 		return -EINVAL;
 	}
 	/* The range must be a valid one. */
@@ -128,7 +133,7 @@ int set_utcb_params(unsigned long utcb_start, unsigned long utcb_end)
 	/*
 	 * This check guarantees two things:
 	 *	1. The range must be multiple of UTCB_SIZE, at least one item.
-	 *	2. utcb_end is aligned on UTCB_SIZE
+	 *	2. utcb_end is aligned on UTCB_SIZE.
 	 */
 	if ((utcb_end - utcb_start) % UTCB_SIZE) {
 		printf("libl4thread: The given range size must be multiple "
@@ -137,12 +142,19 @@ int set_utcb_params(unsigned long utcb_start, unsigned long utcb_end)
 	}
 	/* Arguments passed the validity tests. */
 
-	/* Init utcb virtual address pool */
-	utcb_pool_init(utcb_start, utcb_end);
+	/* Init utcb virtual address pool. */
+	if (utcb_pool_init(utcb_start, utcb_end) < 0)
+		BUG();
 
-	/* The very first thread's utcb address is assigned. */
+	/*
+	 * The very first thread's utcb address is assigned.
+	 * It should not return an error value.
+	 */
 	if ((err = set_utcb_addr()) < 0)
-		return err;
+		BUG();
+
+	/* Initialize internal variables. */
+	lib_utcb_range_size = utcb_end - utcb_start;
 
 	return 0;
 }