diff --git a/arch/um/sys-i386/ldt.c b/arch/um/sys-i386/ldt.c
index 36b5c2c..6360f1c 100644
--- a/arch/um/sys-i386/ldt.c
+++ b/arch/um/sys-i386/ldt.c
@@ -3,53 +3,26 @@
  * Licensed under the GPL
  */
 
+#include "linux/stddef.h"
 #include "linux/config.h"
 #include "linux/sched.h"
 #include "linux/slab.h"
 #include "linux/types.h"
+#include "linux/errno.h"
 #include "asm/uaccess.h"
-#include "asm/ptrace.h"
 #include "asm/smp.h"
 #include "asm/ldt.h"
+#include "asm/unistd.h"
 #include "choose-mode.h"
 #include "kern.h"
 #include "mode_kern.h"
 
-#ifdef CONFIG_MODE_TT
-
 extern int modify_ldt(int func, void *ptr, unsigned long bytecount);
 
-static int do_modify_ldt_tt(int func, void *ptr, unsigned long bytecount)
-{
-	return modify_ldt(func, ptr, bytecount);
-}
+#ifdef CONFIG_MODE_TT
 
-#endif
-
-#ifdef CONFIG_MODE_SKAS
-
-#include "skas.h"
-#include "skas_ptrace.h"
-
-static int do_modify_ldt_skas(int func, void *ptr, unsigned long bytecount)
-{
-	struct ptrace_ldt ldt;
-	u32 cpu;
-	int res;
-
-	ldt = ((struct ptrace_ldt) { .func	= func,
-				     .ptr	= ptr,
-				     .bytecount = bytecount });
-
-	cpu = get_cpu();
-	res = ptrace(PTRACE_LDT, userspace_pid[cpu], 0, (unsigned long) &ldt);
-	put_cpu();
-
-	return res;
-}
-#endif
-
-int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
+static long do_modify_ldt_tt(int func, void __user *ptr,
+			      unsigned long bytecount)
 {
 	struct user_desc info;
 	int res = 0;
@@ -89,8 +62,7 @@
 		goto out;
 	}
 
-	res = CHOOSE_MODE_PROC(do_modify_ldt_tt, do_modify_ldt_skas, func,
-				p, bytecount);
+	res = modify_ldt(func, p, bytecount);
 	if(res < 0)
 		goto out;
 
@@ -108,3 +80,467 @@
 	kfree(buf);
 	return res;
 }
+
+#endif
+
+#ifdef CONFIG_MODE_SKAS
+
+#include "skas.h"
+#include "skas_ptrace.h"
+#include "asm/mmu_context.h"
+
+long write_ldt_entry(struct mm_id * mm_idp, int func, struct user_desc * desc,
+		     void **addr, int done)
+{
+	long res;
+
+	if(proc_mm){
+		/* This is a special handling for the case, that the mm to
+		 * modify isn't current->active_mm.
+		 * If this is called directly by modify_ldt,
+		 *     (current->active_mm->context.skas.u == mm_idp)
+		 * will be true. So no call to switch_mm_skas(mm_idp) is done.
+		 * If this is called in case of init_new_ldt or PTRACE_LDT,
+		 * mm_idp won't belong to current->active_mm, but child->mm.
+		 * So we need to switch child's mm into our userspace, then
+		 * later switch back.
+		 *
+		 * Note: I'm unshure: should interrupts be disabled here?
+		 */
+		if(!current->active_mm || current->active_mm == &init_mm ||
+		   mm_idp != &current->active_mm->context.skas.id)
+			switch_mm_skas(mm_idp);
+	}
+
+	if(ptrace_ldt) {
+		struct ptrace_ldt ldt_op = (struct ptrace_ldt) {
+			.func = func,
+			.ptr = desc,
+			.bytecount = sizeof(*desc)};
+		u32 cpu;
+		int pid;
+
+		if(!proc_mm)
+			pid = mm_idp->u.pid;
+		else {
+			cpu = get_cpu();
+			pid = userspace_pid[cpu];
+		}
+
+		res = ptrace(PTRACE_LDT, pid, 0, (unsigned long) &ldt_op);
+		if(res)
+			res = errno;
+
+		if(proc_mm)
+			put_cpu();
+	}
+	else {
+		void *stub_addr;
+		res = syscall_stub_data(mm_idp, (unsigned long *)desc,
+					(sizeof(*desc) + sizeof(long) - 1) &
+					    ~(sizeof(long) - 1),
+					addr, &stub_addr);
+		if(!res){
+			unsigned long args[] = { func,
+						 (unsigned long)stub_addr,
+						 sizeof(*desc),
+						 0, 0, 0 };
+			res = run_syscall_stub(mm_idp, __NR_modify_ldt, args,
+					       0, addr, done);
+		}
+	}
+
+	if(proc_mm){
+		/* This is the second part of special handling, that makes
+		 * PTRACE_LDT possible to implement.
+		 */
+		if(current->active_mm && current->active_mm != &init_mm &&
+		   mm_idp != &current->active_mm->context.skas.id)
+			switch_mm_skas(&current->active_mm->context.skas.id);
+	}
+
+	return res;
+}
+
+static long read_ldt_from_host(void __user * ptr, unsigned long bytecount)
+{
+	int res, n;
+	struct ptrace_ldt ptrace_ldt = (struct ptrace_ldt) {
+			.func = 0,
+			.bytecount = bytecount,
+			.ptr = (void *)kmalloc(bytecount, GFP_KERNEL)};
+	u32 cpu;
+
+	if(ptrace_ldt.ptr == NULL)
+		return -ENOMEM;
+
+	/* This is called from sys_modify_ldt only, so userspace_pid gives
+	 * us the right number
+	 */
+
+	cpu = get_cpu();
+	res = ptrace(PTRACE_LDT, userspace_pid[cpu], 0,
+		     (unsigned long) &ptrace_ldt);
+	put_cpu();
+	if(res < 0)
+		goto out;
+
+	n = copy_to_user(ptr, ptrace_ldt.ptr, res);
+	if(n != 0)
+		res = -EFAULT;
+
+  out:
+	kfree(ptrace_ldt.ptr);
+
+	return res;
+}
+
+/*
+ * In skas mode, we hold our own ldt data in UML.
+ * Thus, the code implementing sys_modify_ldt_skas
+ * is very similar to (and mostly stolen from) sys_modify_ldt
+ * for arch/i386/kernel/ldt.c
+ * The routines copied and modified in part are:
+ * - read_ldt
+ * - read_default_ldt
+ * - write_ldt
+ * - sys_modify_ldt_skas
+ */
+
+static int read_ldt(void __user * ptr, unsigned long bytecount)
+{
+	int i, err = 0;
+	unsigned long size;
+	uml_ldt_t * ldt = &current->mm->context.skas.ldt;
+
+	if(!ldt->entry_count)
+		goto out;
+	if(bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
+		bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
+	err = bytecount;
+
+	if(ptrace_ldt){
+		return read_ldt_from_host(ptr, bytecount);
+	}
+
+	down(&ldt->semaphore);
+	if(ldt->entry_count <= LDT_DIRECT_ENTRIES){
+		size = LDT_ENTRY_SIZE*LDT_DIRECT_ENTRIES;
+		if(size > bytecount)
+			size = bytecount;
+		if(copy_to_user(ptr, ldt->entries, size))
+			err = -EFAULT;
+		bytecount -= size;
+		ptr += size;
+	}
+	else {
+		for(i=0; i<ldt->entry_count/LDT_ENTRIES_PER_PAGE && bytecount;
+			 i++){
+			size = PAGE_SIZE;
+			if(size > bytecount)
+				size = bytecount;
+			if(copy_to_user(ptr, ldt->pages[i], size)){
+				err = -EFAULT;
+				break;
+			}
+			bytecount -= size;
+			ptr += size;
+		}
+	}
+	up(&ldt->semaphore);
+
+	if(bytecount == 0 || err == -EFAULT)
+		goto out;
+
+	if(clear_user(ptr, bytecount))
+		err = -EFAULT;
+
+out:
+	return err;
+}
+
+static int read_default_ldt(void __user * ptr, unsigned long bytecount)
+{
+	int err;
+
+	if(bytecount > 5*LDT_ENTRY_SIZE)
+		bytecount = 5*LDT_ENTRY_SIZE;
+
+	err = bytecount;
+	/* UML doesn't support lcall7 and lcall27.
+	 * So, we don't really have a default ldt, but emulate
+	 * an empty ldt of common host default ldt size.
+	 */
+	if(clear_user(ptr, bytecount))
+		err = -EFAULT;
+
+	return err;
+}
+
+static int write_ldt(void __user * ptr, unsigned long bytecount, int func)
+{
+	uml_ldt_t * ldt = &current->mm->context.skas.ldt;
+	struct mm_id * mm_idp = &current->mm->context.skas.id;
+	int i, err;
+	struct user_desc ldt_info;
+	struct ldt_entry entry0, *ldt_p;
+	void *addr = NULL;
+
+	err = -EINVAL;
+	if(bytecount != sizeof(ldt_info))
+		goto out;
+	err = -EFAULT;
+	if(copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
+		goto out;
+
+	err = -EINVAL;
+	if(ldt_info.entry_number >= LDT_ENTRIES)
+		goto out;
+	if(ldt_info.contents == 3){
+		if (func == 1)
+			goto out;
+		if (ldt_info.seg_not_present == 0)
+			goto out;
+	}
+
+        if(!ptrace_ldt)
+                down(&ldt->semaphore);
+
+	err = write_ldt_entry(mm_idp, func, &ldt_info, &addr, 1);
+	if(err)
+		goto out_unlock;
+        else if(ptrace_ldt) {
+	/* With PTRACE_LDT available, this is used as a flag only */
+                ldt->entry_count = 1;
+                goto out;
+        }
+
+	if(ldt_info.entry_number >= ldt->entry_count &&
+	   ldt_info.entry_number >= LDT_DIRECT_ENTRIES){
+		for(i=ldt->entry_count/LDT_ENTRIES_PER_PAGE;
+		    i*LDT_ENTRIES_PER_PAGE <= ldt_info.entry_number;
+		    i++){
+			if(i == 0)
+				memcpy(&entry0, ldt->entries, sizeof(entry0));
+			ldt->pages[i] = (struct ldt_entry *)
+					__get_free_page(GFP_KERNEL|__GFP_ZERO);
+			if(!ldt->pages[i]){
+				err = -ENOMEM;
+				/* Undo the change in host */
+				memset(&ldt_info, 0, sizeof(ldt_info));
+				write_ldt_entry(mm_idp, 1, &ldt_info, &addr, 1);
+				goto out_unlock;
+			}
+			if(i == 0) {
+				memcpy(ldt->pages[0], &entry0, sizeof(entry0));
+				memcpy(ldt->pages[0]+1, ldt->entries+1,
+				       sizeof(entry0)*(LDT_DIRECT_ENTRIES-1));
+			}
+			ldt->entry_count = (i + 1) * LDT_ENTRIES_PER_PAGE;
+		}
+	}
+	if(ldt->entry_count <= ldt_info.entry_number)
+		ldt->entry_count = ldt_info.entry_number + 1;
+
+	if(ldt->entry_count <= LDT_DIRECT_ENTRIES)
+		ldt_p = ldt->entries + ldt_info.entry_number;
+	else
+		ldt_p = ldt->pages[ldt_info.entry_number/LDT_ENTRIES_PER_PAGE] +
+			ldt_info.entry_number%LDT_ENTRIES_PER_PAGE;
+
+	if(ldt_info.base_addr == 0 && ldt_info.limit == 0 &&
+	   (func == 1 || LDT_empty(&ldt_info))){
+		ldt_p->a = 0;
+		ldt_p->b = 0;
+	}
+	else{
+		if (func == 1)
+			ldt_info.useable = 0;
+		ldt_p->a = LDT_entry_a(&ldt_info);
+		ldt_p->b = LDT_entry_b(&ldt_info);
+	}
+	err = 0;
+
+out_unlock:
+	up(&ldt->semaphore);
+out:
+	return err;
+}
+
+static long do_modify_ldt_skas(int func, void __user *ptr,
+			       unsigned long bytecount)
+{
+	int ret = -ENOSYS;
+
+	switch (func) {
+		case 0:
+			ret = read_ldt(ptr, bytecount);
+			break;
+		case 1:
+		case 0x11:
+			ret = write_ldt(ptr, bytecount, func);
+			break;
+		case 2:
+			ret = read_default_ldt(ptr, bytecount);
+			break;
+	}
+	return ret;
+}
+
+short dummy_list[9] = {0, -1};
+short * host_ldt_entries = NULL;
+
+void ldt_get_host_info(void)
+{
+	long ret;
+	struct ldt_entry * ldt;
+	int i, size, k, order;
+
+	host_ldt_entries = dummy_list+1;
+
+	for(i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++);
+
+	ldt = (struct ldt_entry *)
+	      __get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
+	if(ldt == NULL) {
+		printk("ldt_get_host_info: couldn't allocate buffer for host ldt\n");
+		return;
+	}
+
+	ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
+	if(ret < 0) {
+		printk("ldt_get_host_info: couldn't read host ldt\n");
+		goto out_free;
+	}
+	if(ret == 0) {
+		/* default_ldt is active, simply write an empty entry 0 */
+		host_ldt_entries = dummy_list;
+		goto out_free;
+	}
+
+	for(i=0, size=0; i<ret/LDT_ENTRY_SIZE; i++){
+		if(ldt[i].a != 0 || ldt[i].b != 0)
+			size++;
+	}
+
+	if(size < sizeof(dummy_list)/sizeof(dummy_list[0])) {
+		host_ldt_entries = dummy_list;
+	}
+	else {
+		size = (size + 1) * sizeof(dummy_list[0]);
+		host_ldt_entries = (short *)kmalloc(size, GFP_KERNEL);
+		if(host_ldt_entries == NULL) {
+			printk("ldt_get_host_info: couldn't allocate host ldt list\n");
+			goto out_free;
+		}
+	}
+
+	for(i=0, k=0; i<ret/LDT_ENTRY_SIZE; i++){
+		if(ldt[i].a != 0 || ldt[i].b != 0) {
+			host_ldt_entries[k++] = i;
+		}
+	}
+	host_ldt_entries[k] = -1;
+
+out_free:
+	free_pages((unsigned long)ldt, order);
+}
+
+long init_new_ldt(struct mmu_context_skas * new_mm,
+		  struct mmu_context_skas * from_mm)
+{
+	struct user_desc desc;
+	short * num_p;
+	int i;
+	long page, err=0;
+	void *addr = NULL;
+
+	memset(&desc, 0, sizeof(desc));
+
+	if(!ptrace_ldt)
+		init_MUTEX(&new_mm->ldt.semaphore);
+
+	if(!from_mm){
+		/*
+		 * We have to initialize a clean ldt.
+		 */
+		if(proc_mm) {
+			/*
+			 * If the new mm was created using proc_mm, host's
+			 * default-ldt currently is assigned, which normally
+			 * contains the call-gates for lcall7 and lcall27.
+			 * To remove these gates, we simply write an empty
+			 * entry as number 0 to the host.
+			 */
+			err = write_ldt_entry(&new_mm->id, 1, &desc,
+					      &addr, 1);
+		}
+		else{
+			/*
+			 * Now we try to retrieve info about the ldt, we
+			 * inherited from the host. All ldt-entries found
+			 * will be reset in the following loop
+			 */
+			if(host_ldt_entries == NULL)
+				ldt_get_host_info();
+			for(num_p=host_ldt_entries; *num_p != -1; num_p++){
+				desc.entry_number = *num_p;
+				err = write_ldt_entry(&new_mm->id, 1, &desc,
+						      &addr, *(num_p + 1) == -1);
+				if(err)
+					break;
+			}
+		}
+		new_mm->ldt.entry_count = 0;
+	}
+	else if (!ptrace_ldt) {
+		/* Our local LDT is used to supply the data for
+		 * modify_ldt(READLDT), if PTRACE_LDT isn't available,
+		 * i.e., we have to use the stub for modify_ldt, which
+		 * can't handle the big read buffer of up to 64kB.
+		 */
+		down(&from_mm->ldt.semaphore);
+		if(from_mm->ldt.entry_count <= LDT_DIRECT_ENTRIES){
+			memcpy(new_mm->ldt.entries, from_mm->ldt.entries,
+			       sizeof(new_mm->ldt.entries));
+		}
+		else{
+			i = from_mm->ldt.entry_count / LDT_ENTRIES_PER_PAGE;
+			while(i-->0){
+				page = __get_free_page(GFP_KERNEL|__GFP_ZERO);
+				if (!page){
+					err = -ENOMEM;
+					break;
+				}
+				new_mm->ldt.pages[i] = (struct ldt_entry*)page;
+				memcpy(new_mm->ldt.pages[i],
+				       from_mm->ldt.pages[i], PAGE_SIZE);
+			}
+		}
+		new_mm->ldt.entry_count = from_mm->ldt.entry_count;
+		up(&from_mm->ldt.semaphore);
+	}
+
+	return err;
+}
+
+
+void free_ldt(struct mmu_context_skas * mm)
+{
+	int i;
+
+	if(!ptrace_ldt && mm->ldt.entry_count > LDT_DIRECT_ENTRIES){
+		i = mm->ldt.entry_count / LDT_ENTRIES_PER_PAGE;
+		while(i-- > 0){
+			free_page((long )mm->ldt.pages[i]);
+		}
+	}
+	mm->ldt.entry_count = 0;
+}
+#endif
+
+int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
+{
+	return(CHOOSE_MODE_PROC(do_modify_ldt_tt, do_modify_ldt_skas, func,
+	                        ptr, bytecount));
+}