Push kernel/user limit to 2GiB, so Mach can address up to close to 2GiB memory.
This makes glibc's local-bigmem.diff patch mandatory.

Index: gnumach/i386/include/mach/i386/vm_param.h
===================================================================
--- gnumach.orig/i386/include/mach/i386/vm_param.h	2012-06-10 23:45:02.000000000 +0200
+++ gnumach/i386/include/mach/i386/vm_param.h	2012-07-14 15:57:26.423861314 +0200
@@ -73,6 +73,6 @@
    with that.
    */
 #define VM_MIN_ADDRESS		(0)
-#define VM_MAX_ADDRESS		(0xc0000000UL)
+#define VM_MAX_ADDRESS		(0x80000000UL)
 
 #endif	/* _MACH_I386_VM_PARAM_H_ */
Index: gnumach/i386/Makefrag.am
===================================================================
--- gnumach.orig/i386/Makefrag.am	2012-06-10 23:45:02.000000000 +0200
+++ gnumach/i386/Makefrag.am	2012-07-14 15:57:26.427861233 +0200
@@ -199,7 +199,7 @@ EXTRA_DIST += \
 	i386/ldscript
 if PLATFORM_at
 gnumach_LINKFLAGS += \
 	--defsym _START_MAP=$(_START_MAP) \
-	--defsym _START=_START_MAP+0xC0000000 \
+	--defsym _START=_START_MAP+0x80000000 \
 	-T '$(srcdir)'/i386/ldscript
 endif
Index: gnumach/i386/i386/vm_param.h
===================================================================
--- gnumach.orig/i386/i386/vm_param.h	2012-06-10 23:45:02.000000000 +0200
+++ gnumach/i386/i386/vm_param.h	2012-07-14 15:57:44.559495669 +0200
@@ -31,7 +31,7 @@
 /* This can be changed freely to separate kernel addresses from user addresses
  * for better trace support in kdb; the _START symbol has to be offset by the
  * same amount. */
-#define VM_MIN_KERNEL_ADDRESS	0xC0000000UL
+#define VM_MIN_KERNEL_ADDRESS	0x80000000UL
 
 #ifdef	MACH_XEN
 /* PV kernels can be loaded directly to the target virtual address */
Index: gnumach/i386/xen/Makefrag.am
===================================================================
--- gnumach.orig/i386/xen/Makefrag.am	2012-07-14 15:58:19.998781083 +0200
+++ gnumach/i386/xen/Makefrag.am	2012-07-14 15:58:30.254574271 +0200
@@ -28,7 +28,7 @@ libkernel_a_SOURCES += \
 
 if PLATFORM_xen
 gnumach_LINKFLAGS += \
-	--defsym _START=0xC0000000 \
-	--defsym _START_MAP=0xC0000000 \
+	--defsym _START=0x80000000 \
+	--defsym _START_MAP=0x80000000 \
 	-T '$(srcdir)'/i386/ldscript
 endif
Index: gnumach/i386/xen/xen_boothdr.S
===================================================================
--- gnumach.orig/i386/xen/xen_boothdr.S	2012-07-14 15:58:13.358914976 +0200
+++ gnumach/i386/xen/xen_boothdr.S	2012-07-14 15:58:39.790381972 +0200
@@ -22,8 +22,8 @@
 	.ascii	"GUEST_OS=GNU Mach"
 	.ascii  ",GUEST_VERSION=1.3"
 	.ascii	",XEN_VER=xen-3.0"
-	.ascii  ",VIRT_BASE=0xC0000000"
-	.ascii  ",ELF_PADDR_OFFSET=0xC0000000"
+	.ascii  ",VIRT_BASE=0x80000000"
+	.ascii  ",ELF_PADDR_OFFSET=0x80000000"
 	.ascii	",HYPERCALL_PAGE=0x2"
 #if PAE
 	.ascii  ",PAE=yes[extended-cr3]"