diff --git a/arch/um/Kconfig.i386 b/arch/um/Kconfig.i386
index d6cffb2..9876d80 100644
--- a/arch/um/Kconfig.i386
+++ b/arch/um/Kconfig.i386
@@ -65,20 +65,6 @@
 	However, this it experimental on 32-bit architectures, so if unsure say
 	N (on x86-64 it's automatically enabled, instead, as it's safe there).
 
-config STUB_CODE
-	hex
-	default 0xbfffe000 if !HOST_VMSPLIT_2G
-	default 0x7fffe000 if HOST_VMSPLIT_2G
-
-config STUB_DATA
-	hex
-	default 0xbffff000 if !HOST_VMSPLIT_2G
-	default 0x7ffff000 if HOST_VMSPLIT_2G
-
-config STUB_START
-	hex
-	default STUB_CODE
-
 config ARCH_HAS_SC_SIGNALS
 	bool
 	default y
diff --git a/arch/um/Kconfig.x86_64 b/arch/um/Kconfig.x86_64
index f60e9e5..d632e9a 100644
--- a/arch/um/Kconfig.x86_64
+++ b/arch/um/Kconfig.x86_64
@@ -17,24 +17,12 @@
 
 config TOP_ADDR
  	hex
-	default 0x80000000
+	default 0x7fc0000000
 
 config 3_LEVEL_PGTABLES
        bool
        default y
 
-config STUB_CODE
-	hex
-	default 0x7fbfffe000
-
-config STUB_DATA
-	hex
-	default 0x7fbffff000
-
-config STUB_START
-	hex
-	default STUB_CODE
-
 config ARCH_HAS_SC_SIGNALS
 	bool
 	default n
diff --git a/arch/um/defconfig b/arch/um/defconfig
index 1cbbe98..f609ede 100644
--- a/arch/um/defconfig
+++ b/arch/um/defconfig
@@ -59,9 +59,6 @@
 # CONFIG_HOST_2G_2G is not set
 CONFIG_TOP_ADDR=0xc0000000
 # CONFIG_3_LEVEL_PGTABLES is not set
-CONFIG_STUB_CODE=0xbfffe000
-CONFIG_STUB_DATA=0xbffff000
-CONFIG_STUB_START=0xbfffe000
 CONFIG_ARCH_HAS_SC_SIGNALS=y
 CONFIG_ARCH_REUSE_HOST_VSYSCALL_AREA=y
 CONFIG_GENERIC_HWEIGHT=y
diff --git a/arch/um/include/as-layout.h b/arch/um/include/as-layout.h
index 2f16a1c..a5cdf95 100644
--- a/arch/um/include/as-layout.h
+++ b/arch/um/include/as-layout.h
@@ -6,6 +6,28 @@
 #ifndef __START_H__
 #define __START_H__
 
+#include "uml-config.h"
+#include "kern_constants.h"
+
+/*
+ * Assembly doesn't want any casting, but C does, so define these
+ * without casts here, and define new symbols with casts inside the C
+ * section.
+ */
+#define ASM_STUB_CODE (UML_CONFIG_TOP_ADDR - 2 * UM_KERN_PAGE_SIZE)
+#define ASM_STUB_DATA (UML_CONFIG_TOP_ADDR - UM_KERN_PAGE_SIZE)
+#define ASM_STUB_START ASM_STUB_CODE
+
+/*
+ * This file is included by the assembly stubs, which just want the
+ * definitions above.
+ */
+#ifndef __ASSEMBLY__
+
+#define STUB_CODE ((unsigned long) ASM_STUB_CODE)
+#define STUB_DATA ((unsigned long) ASM_STUB_DATA)
+#define STUB_START ((unsigned long) ASM_STUB_START)
+
 #include "sysdep/ptrace.h"
 
 struct cpu_task {
@@ -32,3 +54,5 @@
 extern void (*sig_info[])(int, struct uml_pt_regs *);
 
 #endif
+
+#endif
diff --git a/arch/um/include/sysdep-i386/stub.h b/arch/um/include/sysdep-i386/stub.h
index 19c85f3..8c097b8 100644
--- a/arch/um/include/sysdep-i386/stub.h
+++ b/arch/um/include/sysdep-i386/stub.h
@@ -9,6 +9,7 @@
 #include <sys/mman.h>
 #include <asm/ptrace.h>
 #include <asm/unistd.h>
+#include "as-layout.h"
 #include "stub-data.h"
 #include "kern_constants.h"
 #include "uml-config.h"
@@ -89,12 +90,12 @@
 {
 	__asm__ volatile ("movl %%eax,%%ebp ; movl %0,%%eax ; int $0x80 ;"
 			  "movl %7, %%ebx ; movl %%eax, (%%ebx)"
-			  : : "g" (STUB_MMAP_NR), "b" (UML_CONFIG_STUB_DATA), 
-			    "c" (UM_KERN_PAGE_SIZE), 
+			  : : "g" (STUB_MMAP_NR), "b" (STUB_DATA),
+			    "c" (UM_KERN_PAGE_SIZE),
 			    "d" (PROT_READ | PROT_WRITE),
-			    "S" (MAP_FIXED | MAP_SHARED), "D" (fd), 
-			    "a" (offset), 
-			    "i" (&((struct stub_data *) UML_CONFIG_STUB_DATA)->err) 
+			    "S" (MAP_FIXED | MAP_SHARED), "D" (fd),
+			    "a" (offset),
+			    "i" (&((struct stub_data *) STUB_DATA)->err)
 			  : "memory");
 }
 
diff --git a/arch/um/include/sysdep-x86_64/stub.h b/arch/um/include/sysdep-x86_64/stub.h
index 92e989f..655f9c2 100644
--- a/arch/um/include/sysdep-x86_64/stub.h
+++ b/arch/um/include/sysdep-x86_64/stub.h
@@ -9,6 +9,7 @@
 #include <sys/mman.h>
 #include <asm/unistd.h>
 #include <sysdep/ptrace_user.h>
+#include "as-layout.h"
 #include "stub-data.h"
 #include "kern_constants.h"
 #include "uml-config.h"
@@ -94,13 +95,13 @@
 {
 	__asm__ volatile ("movq %4,%%r10 ; movq %5,%%r8 ; "
 			  "movq %6, %%r9; " __syscall "; movq %7, %%rbx ; "
-			  "movq %%rax, (%%rbx)": 
-			  : "a" (STUB_MMAP_NR), "D" (UML_CONFIG_STUB_DATA), 
-			    "S" (UM_KERN_PAGE_SIZE), 
-			    "d" (PROT_READ | PROT_WRITE), 
-                            "g" (MAP_FIXED | MAP_SHARED), "g" (fd), 
+			  "movq %%rax, (%%rbx)":
+			  : "a" (STUB_MMAP_NR), "D" (STUB_DATA),
+			    "S" (UM_KERN_PAGE_SIZE),
+			    "d" (PROT_READ | PROT_WRITE),
+                            "g" (MAP_FIXED | MAP_SHARED), "g" (fd),
 			    "g" (offset),
-			    "i" (&((struct stub_data *) UML_CONFIG_STUB_DATA)->err)
+			    "i" (&((struct stub_data *) STUB_DATA)->err)
 			  : __syscall_clobber, "r10", "r8", "r9" );
 }
 
diff --git a/arch/um/kernel/exec.c b/arch/um/kernel/exec.c
index 7c77ade..8196450 100644
--- a/arch/um/kernel/exec.c
+++ b/arch/um/kernel/exec.c
@@ -11,6 +11,7 @@
 #include "asm/current.h"
 #include "asm/processor.h"
 #include "asm/uaccess.h"
+#include "as-layout.h"
 #include "mem_user.h"
 #include "skas.h"
 #include "os.h"
@@ -18,7 +19,7 @@
 void flush_thread(void)
 {
 	void *data = NULL;
-	unsigned long end = proc_mm ? task_size : CONFIG_STUB_START;
+	unsigned long end = proc_mm ? task_size : STUB_START;
 	int ret;
 
 	arch_flush_thread(&current->thread.arch);
diff --git a/arch/um/kernel/skas/clone.c b/arch/um/kernel/skas/clone.c
index 47b812b..d119f4f 100644
--- a/arch/um/kernel/skas/clone.c
+++ b/arch/um/kernel/skas/clone.c
@@ -4,6 +4,7 @@
 #include <sys/time.h>
 #include <asm/unistd.h>
 #include <asm/page.h>
+#include "as-layout.h"
 #include "ptrace_user.h"
 #include "skas.h"
 #include "stub-data.h"
@@ -21,12 +22,11 @@
 void __attribute__ ((__section__ (".__syscall_stub")))
 stub_clone_handler(void)
 {
-	struct stub_data *data = (struct stub_data *) UML_CONFIG_STUB_DATA;
+	struct stub_data *data = (struct stub_data *) STUB_DATA;
 	long err;
 
 	err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
-			    UML_CONFIG_STUB_DATA + UM_KERN_PAGE_SIZE / 2 -
-			    sizeof(void *));
+			    STUB_DATA + UM_KERN_PAGE_SIZE / 2 - sizeof(void *));
 	if(err != 0)
 		goto out;
 
diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index ae79888..f859ec3 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -7,6 +7,7 @@
 #include "linux/sched.h"
 #include "asm/pgalloc.h"
 #include "asm/pgtable.h"
+#include "as-layout.h"
 #include "os.h"
 #include "skas.h"
 
@@ -83,12 +84,12 @@
 		 */
 		mm->pgd[USER_PTRS_PER_PGD] = __pgd(0);
 
-		ret = init_stub_pte(mm, CONFIG_STUB_CODE,
+		ret = init_stub_pte(mm, STUB_CODE,
 				    (unsigned long) &__syscall_stub_start);
 		if (ret)
 			goto out_free;
 
-		ret = init_stub_pte(mm, CONFIG_STUB_DATA, stack);
+		ret = init_stub_pte(mm, STUB_DATA, stack);
 		if (ret)
 			goto out_free;
 
diff --git a/arch/um/kernel/skas/process.c b/arch/um/kernel/skas/process.c
index 0297e63..fce389c 100644
--- a/arch/um/kernel/skas/process.c
+++ b/arch/um/kernel/skas/process.c
@@ -18,7 +18,7 @@
 		return fd;
 
 	if (skas_needs_stub)
-		map_stub_pages(fd, CONFIG_STUB_CODE, CONFIG_STUB_DATA, stack);
+		map_stub_pages(fd, STUB_CODE, STUB_DATA, stack);
 
 	return fd;
 }
diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c
index 942f20e..f4a0e40 100644
--- a/arch/um/kernel/tlb.c
+++ b/arch/um/kernel/tlb.c
@@ -485,8 +485,8 @@
 static void fix_range(struct mm_struct *mm, unsigned long start_addr,
 		      unsigned long end_addr, int force)
 {
-	if (!proc_mm && (end_addr > CONFIG_STUB_START))
-		end_addr = CONFIG_STUB_START;
+	if (!proc_mm && (end_addr > STUB_START))
+		end_addr = STUB_START;
 
 	fix_range_common(mm, start_addr, end_addr, force);
 }
@@ -510,7 +510,7 @@
 	if (atomic_read(&mm->mm_users) == 0)
 		return;
 
-	end = proc_mm ? task_size : CONFIG_STUB_START;
+	end = proc_mm ? task_size : STUB_START;
 	fix_range(mm, 0, end, 0);
 }
 
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 1993e5e1..f1c7139 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -242,7 +242,8 @@
 
 	if (!skas_needs_stub)
 		*task_size_out = host_task_size;
-	else *task_size_out = CONFIG_STUB_START & PGDIR_MASK;
+	else
+		*task_size_out = STUB_START & PGDIR_MASK;
 
 	return host_task_size;
 }
diff --git a/arch/um/os-Linux/skas/mem.c b/arch/um/os-Linux/skas/mem.c
index d58d111..484e68f 100644
--- a/arch/um/os-Linux/skas/mem.c
+++ b/arch/um/os-Linux/skas/mem.c
@@ -10,6 +10,7 @@
 #include <sys/mman.h>
 #include "init.h"
 #include "kern_constants.h"
+#include "as-layout.h"
 #include "mm_id.h"
 #include "os.h"
 #include "proc_mm.h"
@@ -40,7 +41,7 @@
 static int __init init_syscall_regs(void)
 {
 	get_safe_registers(syscall_regs);
-	syscall_regs[REGS_IP_INDEX] = UML_CONFIG_STUB_CODE +
+	syscall_regs[REGS_IP_INDEX] = STUB_CODE +
 		((unsigned long) &batch_syscall_stub -
 		 (unsigned long) &__syscall_stub_start);
 	return 0;
@@ -93,8 +94,7 @@
 	ret = *((unsigned long *) mm_idp->stack);
 	offset = *((unsigned long *) mm_idp->stack + 1);
 	if (offset) {
-		data = (unsigned long *)(mm_idp->stack +
-					 offset - UML_CONFIG_STUB_DATA);
+		data = (unsigned long *)(mm_idp->stack + offset - STUB_DATA);
 		printk(UM_KERN_ERR "do_syscall_stub : ret = %ld, offset = %ld, "
 		       "data = %p\n", ret, offset, data);
 		syscall = (unsigned long *)((unsigned long)data + data[0]);
@@ -182,7 +182,7 @@
 	memcpy(stack + 1, data, data_count * sizeof(long));
 
 	*stub_addr = (void *)(((unsigned long)(stack + 1) &
-			       ~UM_KERN_PAGE_MASK) + UML_CONFIG_STUB_DATA);
+			       ~UM_KERN_PAGE_MASK) + STUB_DATA);
 
 	return 0;
 }
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index 8548f12..e60d6e6 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -191,22 +191,23 @@
 		int fd;
 		unsigned long long offset;
 		fd = phys_mapping(to_phys(&__syscall_stub_start), &offset);
-		addr = mmap64((void *) UML_CONFIG_STUB_CODE, UM_KERN_PAGE_SIZE,
+		addr = mmap64((void *) STUB_CODE, UM_KERN_PAGE_SIZE,
 			      PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
 		if (addr == MAP_FAILED) {
-			printk(UM_KERN_ERR "mapping mmap stub failed, "
-			       "errno = %d\n", errno);
+			printk(UM_KERN_ERR "mapping mmap stub at 0x%lx failed, "
+			       "errno = %d\n", STUB_CODE, errno);
 			exit(1);
 		}
 
 		if (stack != NULL) {
 			fd = phys_mapping(to_phys(stack), &offset);
-			addr = mmap((void *) UML_CONFIG_STUB_DATA,
+			addr = mmap((void *) STUB_DATA,
 				    UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
 				    MAP_FIXED | MAP_SHARED, fd, offset);
 			if (addr == MAP_FAILED) {
 				printk(UM_KERN_ERR "mapping segfault stack "
-				       "failed, errno = %d\n", errno);
+				       "at 0x%lx failed, errno = %d\n",
+				       STUB_DATA, errno);
 				exit(1);
 			}
 		}
@@ -214,11 +215,11 @@
 	if (!ptrace_faultinfo && (stack != NULL)) {
 		struct sigaction sa;
 
-		unsigned long v = UML_CONFIG_STUB_CODE +
+		unsigned long v = STUB_CODE +
 				  (unsigned long) stub_segv_handler -
 				  (unsigned long) &__syscall_stub_start;
 
-		set_sigstack((void *) UML_CONFIG_STUB_DATA, UM_KERN_PAGE_SIZE);
+		set_sigstack((void *) STUB_DATA, UM_KERN_PAGE_SIZE);
 		sigemptyset(&sa.sa_mask);
 		sigaddset(&sa.sa_mask, SIGIO);
 		sigaddset(&sa.sa_mask, SIGWINCH);
@@ -382,10 +383,10 @@
 {
 	get_safe_registers(thread_regs);
 	/* Set parent's instruction pointer to start of clone-stub */
-	thread_regs[REGS_IP_INDEX] = UML_CONFIG_STUB_CODE +
+	thread_regs[REGS_IP_INDEX] = STUB_CODE +
 				(unsigned long) stub_clone_handler -
 				(unsigned long) &__syscall_stub_start;
-	thread_regs[REGS_SP_INDEX] = UML_CONFIG_STUB_DATA + UM_KERN_PAGE_SIZE -
+	thread_regs[REGS_SP_INDEX] = STUB_DATA + UM_KERN_PAGE_SIZE -
 		sizeof(void *);
 #ifdef __SIGNAL_FRAMESIZE
 	thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
@@ -443,7 +444,7 @@
 	 * child's stack and check it.
 	 */
 	wait_stub_done(pid);
-	if (child_data->err != UML_CONFIG_STUB_DATA)
+	if (child_data->err != STUB_DATA)
 		panic("copy_context_skas0 - stub-child reports error %ld\n",
 		      child_data->err);
 
diff --git a/arch/um/sys-i386/stub.S b/arch/um/sys-i386/stub.S
index 6a70d9a..e730772 100644
--- a/arch/um/sys-i386/stub.S
+++ b/arch/um/sys-i386/stub.S
@@ -1,4 +1,5 @@
 #include "uml-config.h"
+#include "as-layout.h"
 
 	.globl syscall_stub
 .section .__syscall_stub, "x"
@@ -6,7 +7,7 @@
 	.globl batch_syscall_stub
 batch_syscall_stub:
 	/* load pointer to first operation */
-	mov	$(UML_CONFIG_STUB_DATA+8), %esp
+	mov	$(ASM_STUB_DATA+8), %esp
 
 again:
 	/* load length of additional data */
@@ -14,12 +15,12 @@
 
 	/* if(length == 0) : end of list */
 	/* write possible 0 to header */
-	mov	%eax, UML_CONFIG_STUB_DATA+4
+	mov	%eax, ASM_STUB_DATA+4
 	cmpl	$0, %eax
 	jz	done
 
 	/* save current pointer */
-	mov	%esp, UML_CONFIG_STUB_DATA+4
+	mov	%esp, ASM_STUB_DATA+4
 
 	/* skip additional data */
 	add	%eax, %esp
@@ -45,7 +46,7 @@
 
 done:
 	/* save return value */
-	mov	%eax, UML_CONFIG_STUB_DATA
+	mov	%eax, ASM_STUB_DATA
 
 	/* stop */
 	int3
diff --git a/arch/um/sys-i386/stub_segv.c b/arch/um/sys-i386/stub_segv.c
index 2355dc1..b3999cb 100644
--- a/arch/um/sys-i386/stub_segv.c
+++ b/arch/um/sys-i386/stub_segv.c
@@ -6,6 +6,7 @@
 #include <signal.h>
 #include <sys/select.h> /* The only way I can see to get sigset_t */
 #include <asm/unistd.h>
+#include "as-layout.h"
 #include "uml-config.h"
 #include "sysdep/stub.h"
 #include "sysdep/sigcontext.h"
@@ -17,8 +18,7 @@
 	struct sigcontext *sc = (struct sigcontext *) (&sig + 1);
 	int pid;
 
-	GET_FAULTINFO_FROM_SC(*((struct faultinfo *) UML_CONFIG_STUB_DATA),
-			      sc);
+	GET_FAULTINFO_FROM_SC(*((struct faultinfo *) STUB_DATA), sc);
 
 	pid = stub_syscall0(__NR_getpid);
 	stub_syscall2(__NR_kill, pid, SIGUSR1);
diff --git a/arch/um/sys-x86_64/stub.S b/arch/um/sys-x86_64/stub.S
index 03c2797..4afe204 100644
--- a/arch/um/sys-x86_64/stub.S
+++ b/arch/um/sys-x86_64/stub.S
@@ -1,4 +1,5 @@
 #include "uml-config.h"
+#include "as-layout.h"
 
 	.globl syscall_stub
 .section .__syscall_stub, "x"
@@ -7,18 +8,18 @@
 	/* We don't have 64-bit constants, so this constructs the address
 	 * we need.
 	 */
-	movq	$(UML_CONFIG_STUB_DATA >> 32), %rbx
+	movq	$(ASM_STUB_DATA >> 32), %rbx
 	salq	$32, %rbx
-	movq	$(UML_CONFIG_STUB_DATA & 0xffffffff), %rcx
+	movq	$(ASM_STUB_DATA & 0xffffffff), %rcx
 	or	%rcx, %rbx
 	movq	%rax, (%rbx)
 	int3
 
 	.globl batch_syscall_stub
 batch_syscall_stub:
-	mov	$(UML_CONFIG_STUB_DATA >> 32), %rbx
+	mov	$(ASM_STUB_DATA >> 32), %rbx
 	sal	$32, %rbx
-	mov	$(UML_CONFIG_STUB_DATA & 0xffffffff), %rax
+	mov	$(ASM_STUB_DATA & 0xffffffff), %rax
 	or	%rax, %rbx
 	/* load pointer to first operation */
 	mov	%rbx, %rsp
diff --git a/arch/um/sys-x86_64/stub_segv.c b/arch/um/sys-x86_64/stub_segv.c
index 652fa34..3afb590 100644
--- a/arch/um/sys-x86_64/stub_segv.c
+++ b/arch/um/sys-x86_64/stub_segv.c
@@ -6,6 +6,7 @@
 #include <stddef.h>
 #include <signal.h>
 #include <asm/unistd.h>
+#include "as-layout.h"
 #include "uml-config.h"
 #include "sysdep/sigcontext.h"
 #include "sysdep/faultinfo.h"
@@ -33,7 +34,7 @@
         int pid;
 
 	__asm__ __volatile__("movq %%rdx, %0" : "=g" (uc) :);
-	GET_FAULTINFO_FROM_SC(*((struct faultinfo *) UML_CONFIG_STUB_DATA),
+	GET_FAULTINFO_FROM_SC(*((struct faultinfo *) STUB_DATA),
 			      &uc->uc_mcontext);
 
 	pid = stub_syscall0(__NR_getpid);