diff --git a/arch/ia64/Makefile b/arch/ia64/Makefile
index 88f1a55c6c94..3b9c8cadfd34 100644
--- a/arch/ia64/Makefile
+++ b/arch/ia64/Makefile
@@ -99,3 +99,9 @@ define archhelp
   echo '  boot		- Build vmlinux and bootloader for Ski simulator'
   echo '* unwcheck	- Check vmlinux for invalid unwind info'
 endef
+
+archprepare: make_nr_irqs_h FORCE
+PHONY += make_nr_irqs_h FORCE
+
+make_nr_irqs_h: FORCE
+	$(Q)$(MAKE) $(build)=arch/ia64/kernel include/asm-ia64/nr-irqs.h
diff --git a/arch/ia64/kernel/Makefile b/arch/ia64/kernel/Makefile
index cea91f17d44b..87fea11aecb7 100644
--- a/arch/ia64/kernel/Makefile
+++ b/arch/ia64/kernel/Makefile
@@ -73,6 +73,39 @@ $(obj)/gate-syms.o: $(obj)/gate.lds $(obj)/gate.o FORCE
 # Note: kbuild does not track this dependency due to usage of .incbin
 $(obj)/gate-data.o: $(obj)/gate.so
 
+# Calculate NR_IRQ = max(IA64_NATIVE_NR_IRQS, XEN_NR_IRQS, ...) based on config
+define sed-y
+	"/^->/{s:^->\([^ ]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:; s:->::; p;}"
+endef
+quiet_cmd_nr_irqs = GEN     $@
+define cmd_nr_irqs
+	(set -e; \
+	 echo "#ifndef __ASM_NR_IRQS_H__"; \
+	 echo "#define __ASM_NR_IRQS_H__"; \
+	 echo "/*"; \
+	 echo " * DO NOT MODIFY."; \
+	 echo " *"; \
+	 echo " * This file was generated by Kbuild"; \
+	 echo " *"; \
+	 echo " */"; \
+	 echo ""; \
+	 sed -ne $(sed-y) $<; \
+	 echo ""; \
+	 echo "#endif" ) > $@
+endef
+
+# We use internal kbuild rules to avoid the "is up to date" message from make
+arch/$(SRCARCH)/kernel/nr-irqs.s: $(srctree)/arch/$(SRCARCH)/kernel/nr-irqs.c \
+				$(wildcard $(srctree)/include/asm-ia64/*/irq.h)
+	$(Q)mkdir -p $(dir $@)
+	$(call if_changed_dep,cc_s_c)
+
+include/asm-ia64/nr-irqs.h: arch/$(SRCARCH)/kernel/nr-irqs.s
+	$(Q)mkdir -p $(dir $@)
+	$(call cmd,nr_irqs)
+
+clean-files += $(objtree)/include/asm-ia64/nr-irqs.h
+
 #
 # native ivt.S and entry.S
 #
diff --git a/arch/ia64/kernel/nr-irqs.c b/arch/ia64/kernel/nr-irqs.c
new file mode 100644
index 000000000000..1ae049181e83
--- /dev/null
+++ b/arch/ia64/kernel/nr-irqs.c
@@ -0,0 +1,24 @@
+/*
+ * calculate
+ * NR_IRQS = max(IA64_NATIVE_NR_IRQS, XEN_NR_IRQS, FOO_NR_IRQS...)
+ * depending on config.
+ * This must be calculated before processing asm-offset.c.
+ */
+
+#define ASM_OFFSETS_C 1
+
+#include <linux/kbuild.h>
+#include <linux/threads.h>
+#include <asm-ia64/native/irq.h>
+
+void foo(void)
+{
+	union paravirt_nr_irqs_max {
+		char ia64_native_nr_irqs[IA64_NATIVE_NR_IRQS];
+#ifdef CONFIG_XEN
+		char xen_nr_irqs[XEN_NR_IRQS];
+#endif
+	};
+
+	DEFINE(NR_IRQS, sizeof (union paravirt_nr_irqs_max));
+}
diff --git a/include/asm-ia64/irq.h b/include/asm-ia64/irq.h
index a66d26827cbb..3627116fb0e2 100644
--- a/include/asm-ia64/irq.h
+++ b/include/asm-ia64/irq.h
@@ -13,14 +13,7 @@
 
 #include <linux/types.h>
 #include <linux/cpumask.h>
-
-#define NR_VECTORS	256
-
-#if (NR_VECTORS + 32 * NR_CPUS) < 1024
-#define NR_IRQS (NR_VECTORS + 32 * NR_CPUS)
-#else
-#define NR_IRQS 1024
-#endif
+#include <asm-ia64/nr-irqs.h>
 
 static __inline__ int
 irq_canonicalize (int irq)
diff --git a/include/asm-ia64/native/irq.h b/include/asm-ia64/native/irq.h
new file mode 100644
index 000000000000..efe9ff74a3c4
--- /dev/null
+++ b/include/asm-ia64/native/irq.h
@@ -0,0 +1,35 @@
+/******************************************************************************
+ * include/asm-ia64/native/irq.h
+ *
+ * Copyright (c) 2008 Isaku Yamahata <yamahata at valinux co jp>
+ *                    VA Linux Systems Japan K.K.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * moved from linux/include/asm-ia64/irq.h.
+ */
+
+#ifndef _ASM_IA64_NATIVE_IRQ_H
+#define _ASM_IA64_NATIVE_IRQ_H
+
+#define NR_VECTORS	256
+
+#if (NR_VECTORS + 32 * NR_CPUS) < 1024
+#define IA64_NATIVE_NR_IRQS (NR_VECTORS + 32 * NR_CPUS)
+#else
+#define IA64_NATIVE_NR_IRQS 1024
+#endif
+
+#endif /* _ASM_IA64_NATIVE_IRQ_H */